DE69615744T2 - Drive arrangement and reverse gear control for a hybrid vehicle - Google Patents

Description

BACKGROUND OF THE INVENTION Technical field of the invention

The present invention relates to a power output device and a method for controlling the same. In particular, the invention relates to a power output device for transmitting or applying the power generated by an internal combustion engine with high efficiency and rotating a drive shaft in the opposite direction to that of the output shaft of the internal combustion engine. The invention further relates to a method for controlling such a power output device.

Description of the state of the art

Torque converters using a fluid are generally used to convert an output torque of an internal combustion engine or the like into power and to transmit the converted power. In the conventional fluid-based torque converters, an input shaft and an output shaft are not completely locked against each other, so that as a result there is an energy loss corresponding to a slip occurring between the input shaft and the output shaft. The energy loss, which is consumed as heat, is expressed as the product of the difference in rotational speed between the input shaft and the output shaft and the torque transmitted at that time. In vehicles in which such a If a torque converter is installed, a high energy loss occurs in a transient state such as starting. The efficiency of the power transmission is not 100% even when driving at a steady speed. Compared to manual transmissions, torque converters lead to lower fuel consumption.

Some proposed power output devices, unlike the conventional torque converters, do not use fluid for torque conversion or power transmission, but transmit power by means of mechanical-electrical-mechanical conversion. For example, a power output device disclosed in JP Laid-Open No. 53-133814 couples an output shaft of an internal combustion engine to a rotary shaft of a DC motor via an electromagnetic clutch to operate the rotary shaft as a drive shaft. The internal combustion engine drives a rotor on the DC field winding side of the electromagnetic clutch, while the other rotor on the AC armature winding side drives the rotary shaft of the DC motor or the drive shaft. Electric power generated by slip between the two rotors of the electromagnetic clutch is supplied from the rotor on the AC armature winding side to the DC motor via a rectifier. The DC motor also receives electrical energy from a battery to rotate the drive shaft. Unlike the conventional fluid-based torque converters, this proposed structure has substantially no energy loss due to slippage. It is therefore possible to keep the energy loss in the power transmission device relatively small by improving the efficiencies of the electromagnetic clutch and the DC motor.

However, in the proposed structure, the drive shaft (rotating shaft of the DC motor) is generally rotated only in the direction of rotation of the output shaft of the internal combustion engine. The requirement to rotate the drive shaft in the opposite direction to the rotation of the output shaft of the internal combustion engine is not specifically taken into account.

GB 1 193 965, which represents the closest prior art for all independent claims except 5 and 16, relates to a torque converter in which an input shaft and an output shaft are connected via a field element and an armature element, which constitutes an alternator. The alternator is designed so that a magnetic lock occurs between the two parts of the alternator when their speeds are equal. The current generated in the alternator can be used to drive the output shaft in reverse.

Document GB-A-2 278 242, which represents the closest prior art for claims 5 and 16, relates to an electromagnetic transmission system in which an input rotor 1 and an output rotor 2 are provided. In one embodiment, rotational energy is transmitted by means of electromagnetic coupling between the rotors and optionally by supplying the energy generated by the input rotor 1 to a coil of a housing 3, so that the output rotor 2 is driven by the field generated in the coil of the housing 3. In a second embodiment, due to the rotation of the input rotor 20 with respect to the output rotor 22, a current is generated in the input rotor 20, which is transmitted to a winding on the housing 3. This winding 3 transmits the energy for rotating the output rotor 22 in reverse to the output rotor 22.

SUMMARY OF THE INVENTION

It is the object of the present invention to transmit or use power from an internal combustion engine with a high efficiency and to enable a drive shaft to rotate opposite to the rotation of the output shaft of the internal combustion engine.

This object is achieved by a first power output device for outputting power to a drive shaft according to claims 1, 3, 5, 8, 12 and by methods according to claims 15, 16, 18, 20, 21, 24.

The first power output device according to the background of the invention comprises: an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, and the first and second rotors being electromagnetically coupled to each other, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; a first motor drive device for exchanging electric currents with the first motor to vary the electromagnetic coupling the first rotor to the second rotor; a second motor having a stator and a third rotor connected to the drive shaft, the stator being electromagnetically coupled to the third rotor; second motor drive means for exchanging electrical currents with the second motor to vary the electromagnetic coupling of the stator to the third rotor; and control means for controlling the second motor drive means to drive the second motor such that the drive shaft is caused to rotate in a second direction opposite to the first direction.

The structure of such a first power output device does not require any special gears to rotate the drive shaft in the opposite direction to the rotation of the output shaft of the internal combustion engine, thereby reducing the overall weight of the power output device, saving time and labor for assembly, and reducing the manufacturing cost.

According to one aspect of the background of the invention, the power output device further comprises: a storage device for storing electric energy; and wherein the control device comprises means for controlling the first motor drive device to set a torque generated by the first motor to at most a predetermined level, and controlling the second motor drive device to supply the electric energy stored in the storage device to the second motor.

In this construction, the control device controls the second motor drive device so that it drives the second motor and thereby drives the drive shaft into the second Direction, ie opposite to the rotation of the output shaft of the internal combustion engine. The electrical energy stored in the storage device is used to rotate the second motor. The control device further controls the first motor drive device so that the torque generated by the first motor becomes equal to or less than a predetermined level. The resulting torque delivered to the drive shaft is thus not greatly reduced by the torque generated by the first motor.

According to another aspect of the background of the invention, the control device comprises means for controlling the first motor drive device to enable the first motor to regenerate electrical energy, and controlling the second motor drive device to supply the regenerated electrical energy to the second motor.

In this structure, the first motor receives the power output from the internal combustion engine to regenerate it as electric energy; the second motor is driven by the regenerated electric power so as to rotate the drive shaft in the opposite direction to the rotation of the output shaft of the internal combustion engine.

This structure can effectively transmit power generated by the internal combustion engine through energy conversion, thereby causing the reverse rotation of the drive shaft.

According to another aspect of the background of the invention, the power output device further comprises: a storage device for storing electrical energy; wherein the control device comprises means for Controlling the first motor drive means to enable the first motor to regenerate electrical energy, and controlling the second motor drive means to supply the regenerated electrical energy and the electrical energy stored in the storage means to the second motor.

In this structure, the second motor is driven not only by the electric energy regenerated by the first motor but also by the electric energy stored in the storage device to rotate the drive shaft in the opposite direction to the rotation of the output shaft of the internal combustion engine. The structure rotates the drive shaft in the reverse direction with the electric energy regenerated by the first motor and the electric energy stored in the storage device, thereby making it possible to output a high torque to the drive shaft.

According to another aspect of the background of the invention, the power output device further comprises: a storage device for storing electric energy; wherein the control device comprises means for controlling the first motor drive device to enable the first motor to regenerate electric energy and controlling the second motor drive device to supply the regenerated electric energy to the second motor and at least partially to the storage device to be stored.

This structure can charge the storage device with the remaining electrical energy while the reverse rotation of the drive shaft is carried out. This structure is particularly advantageous when the storage device has a low residual capacity of electrical energy.

According to another aspect of the background of the invention, a second power output device for outputting power to a drive shaft comprises: an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to each other, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; a motor drive device for exchanging electric currents with the first motor to vary the electromagnetic coupling of the first rotor with the second rotor; a storage device for storing electric energy; and a control device for supplying the electrical energy stored in the storage device to the motor to drive the motor and further enabling the motor to generate a torque acting in a second direction opposite to the first direction and applying the torque to the drive shaft, thereby rotating the drive shaft in the second direction.

In the second power output device of the background of the invention, the control means controls the motor driving means to drive the motor with the electric energy stored in the storage means and further to enable the motor to apply the torque acting in the opposite direction to the rotation of the engine's output shaft to the drive shaft. At the engine's output shaft, the torque generated by the motor essentially balances out the static friction torque of the engine's output shaft (in a steady state). The motor can thus rotate the drive shaft in the opposite direction to the rotation of the engine's output shaft, with the engine's static friction torque as a support.

According to yet another aspect of the background of the invention, a third power output device for outputting power to a drive shaft comprises: an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; a first motor drive device for exchanging electrical currents with the first motor for varying the electromagnetic coupling of the first rotor with the second rotor; a second motor having a stator and a third rotor connected to the drive shaft, the stator being electromagnetically coupled to the third rotor; a second motor drive device for exchanging electrical currents with the second motor for varying the electromagnetic coupling the stator to the third rotor; and a control device for controlling the second motor drive device when the drive shaft rotates in a second direction opposite to the first direction to enable the second motor to regenerate electrical energy, generate a first torque acting in the first direction, and apply the first torque to the drive shaft, the control device simultaneously controlling the first motor drive device to supply the regenerated electrical energy to the first motor to drive the first motor and further enable the first motor to generate a second torque acting in the second direction and apply the second torque to the drive shaft.

In the third power output device of the background of the invention, the control means controls the second motor driving means to enable the second motor to regenerate electric energy while the drive shaft rotates in the opposite direction to the rotation of the internal combustion engine. The control means further controls the first motor driving means to drive the first motor with the electric energy regenerated by the second motor. There is a certain amount of energy loss in the process of transmitting the regenerated power from the second motor to the first motor. The electric energy consumed by the first motor is thus less than the electric energy regenerated by the second motor. The rotational speed of the second motor is lower than the rotational speed of the first motor. The torque generated by the second motor is thus larger in magnitude than the torque generated by the first motor. The torque generated by the first motor acts on the drive shaft. The torque generated by the first motor acts in the opposite direction to the rotation of the engine, while the torque generated by the second motor acts in the direction of rotation of the engine. The resulting torque applied to the drive shaft thus acts in the direction of rotation of the engine. The drive shaft, which rotates in the opposite direction to the rotation of the engine, consequently experiences a deceleration (ie an acceleration in the direction of rotation of the engine) and gradually reduces its speed.

Even when the storage device is in the fully charged state and cannot absorb any more electric energy, the structure of the third power output device can reduce the speed of reverse rotation of the drive shaft while enabling the first motor to consume the regenerated power.

According to another aspect of the background of the invention, a fourth power output device for outputting power to a drive shaft comprises: an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to each other, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; a first motor drive device for exchanging electrical currents with the first motor for varying the electromagnetic coupling of the first rotor with the second rotor; a second motor having a stator and a third rotor connected to the output shaft of the internal combustion engine, the stator being electromagnetically coupled to the third rotor; second motor drive means for exchanging electrical currents with the second motor for varying the electromagnetic coupling of the stator with the third rotor; and control means for controlling the first motor drive means to drive the first motor to cause the drive shaft to rotate in a second direction opposite to the first direction.

The structure of the fourth power output device according to the background of the invention does not require any special gears to rotate the drive shaft in the opposite direction to the rotation of the output shaft of the internal combustion engine, thereby reducing the overall weight of the power output device, saving time and labor for assembly, and reducing the manufacturing cost.

According to another aspect of the background of the invention, the power output device further comprises: a storage device for storing electric energy; wherein the control device comprises means for controlling the second motor drive device to supply the electric energy stored in the storage device to the second motor and enable the second motor to hold the output shaft of the internal combustion engine and prevent the output shaft of the internal combustion engine from rotating, and controlling the first motor drive device to perform the electric energy stored in the storage device to supply electrical energy stored in the first motor.

In this structure, the control means controls the first motor drive means to drive the first motor and rotate the drive shaft in the opposite direction to the rotation of the output shaft of the engine. The electric energy stored in the storage means is used to drive the first motor. The control means further controls the second motor drive means to enable the second motor to hold the output shaft of the engine and to oppose the rotation of the output shaft of the engine. Even if the first motor applies torque to the output shaft of the engine, this structure effectively prevents the output shaft of the engine from rotating. The drive shaft can be sufficiently rotated in the opposite direction with the output shaft of the engine as a support.

According to another aspect of the background of the invention, the control device comprises means for controlling the second motor drive device to enable the second motor to regenerate electrical energy and controlling the first motor drive device to supply the regenerated electrical energy to the first motor.

This structure can effectively transmit the power generated by the internal combustion engine through the energy conversion and accomplish the reverse rotation of the drive shaft.

According to yet another aspect of the background of the invention, the power output device further comprises: storage means for storing electric energy; wherein the control means comprises means for controlling the second motor drive means to enable the second motor to regenerate electric energy and controlling the first motor drive means to supply the regenerated electric energy and the electric energy stored in the storage means to the first motor.

In this structure, the drive shaft is rotated in the opposite direction to the rotation of the output shaft of the internal combustion engine using the electric energy regenerated by the second motor and the electric energy stored in the storage device. This structure enables a high torque to be output to the drive shaft.

According to another aspect of the background of the invention, the power output device further comprises: a storage device for storing electric energy; wherein the control device comprises means for controlling the second motor drive device to enable the second motor to regenerate electric energy and controlling the first motor drive device to supply the regenerated electric energy to the first motor and at least partially to the storage device to be stored.

This structure enables the drive shaft to rotate in the opposite direction to the rotation of the output shaft of the internal combustion engine, while simultaneously charging the storage device with the remaining electrical energy. This structure is particularly preferred when the storage device has a low residual capacity of electrical energy.

According to still another aspect of the background of the invention, a fifth power output device for outputting mechanical energy as power to a drive shaft comprises: an internal combustion engine connected to a rotary shaft; a first motor connected to the rotary shaft; and a second motor connected to the drive shaft; wherein the internal combustion engine generates mechanical energy and transmits the mechanical energy to the rotary shaft; the first motor receives the mechanical energy transmitted via the rotary shaft and mechanical energy transmitted from the second motor, converts all of the mechanical energy into electrical energy, and supplies the converted electrical energy to the second motor; and the second motor converts the electrical energy supplied from the first motor into mechanical energy, transmits a part of the converted mechanical energy to the first motor, and outputs the rest of the converted mechanical energy to the drive shaft.

In the fifth power output device of the background of the invention, the first motor converts the sum of the mechanical energy generated by the internal combustion engine and the mechanical energy transmitted by the second motor into electrical energy, which is converted back into mechanical energy by the second motor. A part of the converted mechanical energy is transmitted to the first motor, while the rest is output to the drive shaft.

The structure of the fifth power output device of the background of the invention can be used by the internal combustion engine efficiently transfer and use the mechanical energy generated. This design is effective when a large amount of electrical energy is required.

According to another aspect of the background of the invention, a sixth power output device for outputting mechanical energy as power to a drive shaft comprises: an internal combustion engine connected to a rotary shaft; a first motor connected to the rotary shaft; a storage device for storing electrical energy; and a second motor connected to the drive shaft; wherein the internal combustion engine generates mechanical energy and transmits the mechanical energy to the rotary shaft; the first motor receives the mechanical energy transmitted via the rotary shaft and the mechanical energy transmitted from the second motor, converts all of the mechanical energy into electrical energy, and supplies the converted electrical energy to the second motor; the storage device supplies the stored electrical energy to the second motor; and the second motor receives the electrical energy supplied by the first motor and the electrical energy supplied by the storage device, converts all of the electrical energy into mechanical energy, transmits a portion of the converted mechanical energy to the first motor, and outputs the remainder of the converted mechanical energy to the drive shaft.

The structure of the sixth power output device according to the background of the invention is suitably applied to those cases where the electric power supplied from the first motor is insufficient.

According to still another aspect of the background of the invention, a seventh power output device for outputting mechanical energy as power to a drive shaft comprises: an internal combustion engine connected to a rotary shaft; a first motor connected to the rotary shaft; a second motor connected to the drive shaft; and a storage device for storing electrical energy; wherein the internal combustion engine generates mechanical energy and transmits the mechanical energy to the rotary shaft; the first motor receives the mechanical energy transmitted via the rotary shaft and the mechanical energy transmitted from the second motor, converts all of the mechanical energy into electrical energy, and supplies the converted electrical energy to the second motor and the storage device; the second motor converts the electrical energy supplied from the first motor into mechanical energy, transmits a part of the converted mechanical energy to the first motor, and outputs the rest of the converted mechanical energy to the drive shaft; and the storage device stores the electrical energy supplied from the first motor.

In the seventh power output device of the background invention, the electric energy supplied from the first motor can be stored in the storage device and taken out as needed.

A first method of controlling a power output device for outputting power to a drive shaft according to the background of the invention comprises the steps of: (a) providing an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft the internal combustion engine, and a second rotor connected to the drive shaft, the second rotor coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; and a second motor having a stator and a third rotor connected to the drive shaft, the stator being electromagnetically coupled to the third rotor; and (b) driving the second motor to cause the drive shaft to rotate in a second direction opposite to the first direction.

A second method for controlling a power output device for outputting power to a drive shaft according to the background of the invention comprises the steps of: (a) providing an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; and a storage device for storing electrical energy; and (b) supplying the electrical energy stored in the storage device to the motor to drive the motor and further enabling the motor to produce a torque acting in a second direction opposite to the first direction and to apply the torque to the drive shaft, thereby rotating the drive shaft in the second direction.

A third method of controlling a power output device to output power to a drive shaft according to the background of the invention comprises the steps of: (a) providing an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to each other, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; and a second motor having a stator and a third rotor connected to the drive shaft, the stator being electromagnetically coupled to the third rotor; (b) enabling the second motor to regenerate electrical energy, produce a first torque acting in the first direction, and apply the first torque to the drive shaft when the drive shaft rotates in a second direction opposite to the first direction; and (c) supplying the regenerated electrical energy to the first motor to drive the first motor and further enabling the first motor to produce a second torque acting in the second direction and apply the second torque to the drive shaft.

A fourth method of controlling a power output device to output power to a drive shaft according to the background of the invention comprises the steps of: (a) providing an internal combustion engine having an output shaft, the internal combustion engine rotating the output shaft in a first direction; a first motor having a first rotor connected to the output shaft of the internal combustion engine and a second rotor connected to the drive shaft, the second rotor being coaxial with and rotatable relative to the first rotor, the first and second rotors being electromagnetically coupled to each other, as a result of which power is transmitted between the output shaft of the internal combustion engine and the drive shaft via the electromagnetic coupling of the first and second rotors; and a second motor having a stator and a third rotor connected to the output shaft of the internal combustion engine, the stator being electromagnetically coupled to the third rotor; and (b) driving the first motor to cause the drive shaft to rotate in a second direction opposite to the first direction.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments together with the accompanying drawings.

SHORT DESCRIPTION OF THE DRAWING

Fig. 1 schematically illustrates the structure of a power output device 20 as a first embodiment according to the present invention;

Fig. 2 is a cross-sectional view for illustrating a detailed structure of a clutch motor 30 and an assist motor 40 included in the power output device 20 of Fig. 1;

Fig. 3 is a schematic view for illustrating the general structure of a vehicle in which the power output device 20 of Fig. 1 is installed;

Fig. 4 is a graph schematically illustrating an amount of energy regenerated by the clutch motor 30 and an amount of energy consumed by the assist motor 40;

Fig. 5 is a graph schematically illustrating an amount of energy consumed by the clutch motor 30 and an amount of energy regenerated by the assist motor 40 in the overdrive state;

Fig. 6 is a flowchart showing a control process of the first embodiment performed by the control CPU 90 to drive the vehicle in the forward direction;

Fig. 7 is a flowchart showing details of the control operation of the clutch motor 30 performed in step S108 in the flowchart of Fig. 6;

Fig. 8 and 9 are flowcharts showing details of the control operation of the assist motor 40, which is performed in step S110 in the flowchart of Fig. 6;

Fig. 10 is a flowchart showing a control process of the first embodiment performed by the control CPU 90 to drive the vehicle in the reverse direction;

Fig. 11 is a graph schematically illustrating an amount of energy regenerated by the clutch motor 30 and an amount of energy consumed by the assist motor 40;

Fig. 12(a) to 12(c) show a power flow between the gasoline engine 50, the clutch motor 30, the assist motor 40 and the battery 94;

Fig. 13 shows torques applied to the respective shafts in the power output device of the second embodiment;

Fig. 14 is a flowchart showing a control process of the second embodiment performed by the control CPU 90 to drive the vehicle in the reverse direction;

Fig. 15 shows torques applied to the respective shafts in the power output device of the third embodiment;

Fig. 16 is a flowchart showing a control process of the third embodiment performed by the control CPU 90 to reduce the speed of the reversing vehicle;

Fig. 17 schematically illustrates an essential part of another power output device 20A as a fourth embodiment of the present invention;

Fig. 18 shows torques applied to the respective shafts of the power output device 20A of Fig. 17;

Fig. 19 also shows torques applied to the respective shafts of the power output device 20A of Fig. 17;

Fig. 20 is a graph schematically illustrating an amount of energy regenerated by the assist motor 40A and an amount of energy consumed by the clutch motor 30A under the condition of Fig. 19;

Fig. 21 shows a power flow between the gasoline engine 50, the clutch motor 30A and the assist motor 40A;

Fig. 22 is a schematic view illustrating an essential part of a power output device 20B as a modification of the invention;

Fig. 23 is a schematic view illustrating an essential part of another power output device 20C as still another modification of the invention; and

Fig. 24 is a schematic view for illustrating an essential part of still another power output device 20D as a further modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 is a schematic view for illustrating the structure of a power output device 20 as a first embodiment according to the present invention; Fig. 2 is a cross-sectional view for illustrating the detailed structure of a clutch motor 30 and an assist motor 40 included in the power output device 20 of Fig. 1; and Fig. 3 is a schematic view for illustrating the general structure of a vehicle in which the power output device 20 of Fig. 1 is installed. The general structure of the vehicle will be described first for simplicity.

Referring to Fig. 3, the vehicle has as a power source or a prime mover a gasoline engine 50 driven by gasoline. The air taken in from an air supply system via a throttle valve 66 is mixed with fuel, i.e., gasoline in this embodiment, injected from a fuel injection valve 51. The air-fuel mixture is supplied to a combustion chamber 52, where it is explosively ignited and burned. The linear motion of a piston 54 pushed down by the explosion of the air-fuel mixture is converted into a rotary motion of a crankshaft 56. The throttle valve 66 is driven by a motor 68 to open and close. A spark plug 62 converts a high voltage applied by an igniter 58 via an ignition distributor 60 into a spark which explosively ignites and burns the air-fuel mixture.

The operation of the gasoline engine 50 is controlled by an electronic control unit (hereinafter referred to as EFIECU) 70. The EFIECU 70 receives information from various sensors that detect operating conditions of the gasoline engine 50. These sensors include a throttle position sensor 67 for detecting the valve movement or position of the throttle valve 66, an intake vacuum sensor 72 for measuring a load applied to the gasoline engine 50, a water temperature sensor 74 for measuring the temperature of cooling water in the gasoline engine 50, and a speed sensor 76 and angle sensor 78 mounted on the ignition distributor 60 for measuring the rotational speed and angle of the crankshaft 56. A starter switch 79 for detecting a start condition 5T of an ignition switch (not shown) is further connected to the EFIECU 70. Other sensors and switches connected to the EFIECU 70 are omitted from the drawing.

The crankshaft 56 of the gasoline engine 50 is coupled to a drive shaft 22 via a clutch motor 30 and an assist motor 40. The drive shaft 22 is further connected to a differential gear 24 which ultimately outputs the torque output from the drive shaft 22 to the left and right drive wheels 26 and 28. The clutch motor 30 and the assist motor 40 are driven and controlled by a controller 80. The controller 80 includes an internal control CPU and receives inputs from a selector lever position sensor 84 attached to a selector lever 82 and an accelerator pedal position sensor 65 attached to an accelerator pedal 64, as described in detail below. The controller 80 sends and receives a variety of data and information to and from the EFIECU 70 by communication. Details of the control process including a communication protocol are described below.

Referring to Fig. 1, the power output device 20 basically includes the gasoline engine 50 for generating power, the clutch motor 30 having an outer rotor 32 and an inner rotor 34, the assist motor 40 having a rotor 42, and the controller 80 for driving and controlling the clutch motor 30 and the assist motor 40. The outer rotor 32 of the clutch motor 30 is mechanically connected to one end of the crankshaft 56 of the gasoline engine 50, while its inner rotor 34 is mechanically coupled to the rotor 42 of the assist motor 40.

As shown in Fig. 1, the clutch motor 30 is constructed as a synchronous motor with permanent magnets 35 attached to an inner surface of the outer rotor 32 and three-phase windings 36 wound on slots formed in the inner rotor 34. Power is supplied to the three-phase windings 36 via a rotary transformer 38. A thin laminar layer of non-directional electromagnetic steel is used to form teeth and slots for the three-phase windings 36 in the inner rotor 34. A resolver 39 for measuring a rotation angle θe of the crankshaft 56 is attached to the crankshaft 56. The resolver 39 may also serve as the angle sensor 78 installed on the ignition distributor 60.

The assist motor 40 is also constructed as a synchronous motor with three-phase windings 44 wound on a stator 43 fixed to a housing 45 for generating a rotating magnetic field. The stator 43 is also made of a thin laminar layer of non-directional electromagnetic steel. A plurality of permanent magnets 46 are attached to an outer surface of the rotor 42. In the assist motor 40, an interaction between a magnetic field formed by the permanent magnets 46 and a rotating magnetic field formed by the three-phase windings 44 causes the rotor 42 to rotate. The rotor 42 is mechanically coupled to the drive shaft 22 serving as a torque output shaft of the power output device 20. A resolver 48 for measuring a rotation angle θd of the drive shaft 22 is attached to the drive shaft 22, which is further supported by a bearing 49 held in the housing 45.

The inner rotor 34 of the clutch motor 30 is mechanically coupled to the rotor 42 of the assist motor 40 and further to the drive shaft 22. When the rotation and axial torque of the crankshaft 56 of the gasoline engine 50 are transmitted to the inner rotor 34 of the clutch motor 30 via the outer rotor 32, the rotation and torque of the assist motor 40 are added to or subtracted from the transmitted rotation and torque.

While the assist motor 40 is constructed as a conventional three-phase synchronous motor of the permanent magnet type, the clutch motor 30 has two rotating elements or rotors, i.e., the outer rotor 32 with the permanent magnets 35 and the inner rotor 34 with the three-phase windings 36. The detailed construction of the clutch motor 30 is described by the cross-sectional view of Fig. 2. The outer rotor 32 of the clutch motor 30 is attached by means of a pressure pin 59a and a screw 59b to a peripheral end of a wheel 57 which is rotated around the crankshaft 56 is attached. A central portion of the gear 57 projects as a shaft-like member to which the inner rotor 34 is rotatably attached through bearings 37A and 37B. One end of the drive shaft 22 is fixed to the inner rotor 34.

A plurality of permanent magnets 35 - four in the present embodiment - are attached to the inner surface of the outer rotor 32 as previously mentioned. The permanent magnets 35 are magnetized in the direction toward the axial center of the clutch motor 30 and have magnetic poles with alternately inverted directions. The three-phase windings 36 of the inner rotor 34, which face the permanent magnets 35 across a small gap, are wound on a total of 24 slots (not shown) formed in the inner rotor 34. The supply of electricity to the respective coils forms magnetic fluxes that run up to the teeth (not shown) separating the slots from each other. The supply of a three-phase alternating current to the respective coils rotates this magnetic field. The three-phase windings 36 are connected to receive electrical energy supplied by the rotary transformer 38. The rotary transformer 38 has primary windings 38a fixed to the housing 45 and secondary windings 38b attached to the drive shaft 22 coupled to the inner rotor 34. Electromagnetic induction enables the transfer of electrical energy from the primary windings 38a to the secondary windings 38b or vice versa. The rotary transformer 38 has windings for three phases, i.e., U, V and W phases, to enable the transfer of three-phase electrical currents.

The interaction between a magnetic field formed by an adjacent pair of permanent magnets 35 and a rotating magnetic field formed by the three-phase windings 36 of the inner rotor 34 results in a variety of behaviors of the outer rotor 32 and the inner rotor 34. The frequency of the three-phase alternating current supplied to the three-phase windings 36 is substantially equal to a difference between the rotational speed (revolutions per second) of the outer rotor 32 directly connected to the crankshaft 56 and the rotational speed of the inner rotor 34. This results in a slip between the rotation of the outer rotor 32 and the inner rotor 34. Details of the control operation of the clutch motor 30 and the assist motor 40 are described below based on the flowcharts.

As mentioned above, the clutch motor 30 and the assist motor 40 are driven and controlled by the controller 80. Referring to Fig. 1, the controller 80 includes a first drive circuit 91 for driving the clutch motor 30, a second drive circuit 92 for driving the assist motor 40, a control CPU 90 for controlling both the first and second drive circuits 91 and 92, and a battery 94 having a number of secondary elements. The control CPU 90 is a single-chip microprocessor including a RAM 90a used as a working memory, a ROM 90b in which various control programs are stored, an input/output port (not shown), and a serial communication port (not shown) through which data is sent to and received from the EFIECU 70. The control CPU 90 receives a variety of data through the input/output port. The input data includes a Rotation angle θe of the crankshaft 56 of the gasoline engine 50 from the resolver 39, a rotation angle θd of the drive shaft 22 from the resolver 48, an accelerator pedal position AP (operating amount of the accelerator pedal 64) from the accelerator pedal position sensor 65, a selector lever position SP from the selector lever position sensor 84, clutch motor currents Iuc and Ivc from two ammeters 95 and 96 in the first drive circuit 91, assist motor currents Iua and Iva from two ammeters 97 and 98 in the second drive circuit 92, and a remaining capacity BRM of the battery 94 from a remaining capacity measuring device 99. The remaining capacity measuring device 99 can determine the remaining capacity BRM of the battery 94 by any known method, for example by measuring the volumetric mass of an electrolyte solution in the battery 94 or the total weight of the battery 94, by Calculating the currents and charging or discharging times, or by creating a momentary short circuit between the terminals of the battery 94 and measuring an internal resistance to the electrical current.

The control CPU 90 outputs a first control signal SW1 for driving six transistors Tr1 to Tr6 acting as switching elements of the first drive circuit 91, and a second control signal SW2 for driving six transistors Tr11 to Tr16 acting as switching elements of the second drive circuit 92. The six transistors Tr1 to Tr6 in the first drive circuit 91 constitute a transistor inverter and are arranged in pairs so as to act as a source and a sink with respect to a pair of power supply lines P1 and P2. The three-phase windings (U, V, W) 36 of the clutch motor 30 are connected to the respective contacts of the paired transistors via the rotary transformer 38. The power supply lines P1 and P2 are connected to a plus and minus terminal of the battery 94, respectively. The first control signal SW1 output from the control CPU 90 sequentially controls the turn-on time of the paired transistors Tr1 to Tr6. The electric current flowing through each coil 36 undergoes PWM (Pulse Width Modulation) and therefore results in a quasi-sine wave, enabling the three-phase windings 36 to form a rotating magnetic field.

The six transistors Tr11 to Tr16 in the second drive circuit 92 also constitute a transistor inverter and are arranged in the same manner as the transistors Tr1 to Tr6 in the first drive circuit 91. The three-phase windings (U, V, W) 44 of the assist motor 40 are connected to the respective contacts of the paired transistors. The second control signal SW2 output from the control CPU 90 sequentially controls the turn-on time of the paired transistors Tr11 to Tr16. The electric current flowing through each coil 44 undergoes PWM and therefore results in a quasi-sine wave, enabling the three-phase windings 44 to form a rotating magnetic field.

The following describes the essential operation of the power output device 20 constructed in this manner. First, a general operation performed to drive the vehicle in the forward direction, that is, to drive the drive shaft 22 in the rotational direction of the crankshaft 56 of the gasoline engine 50, will be described. For example, it is assumed that the gasoline engine 50 controlled by the EFIECU 70 rotates at a predetermined rotational speed Ne. While the transistors Tr1 to Tr6 in the first drive circuit 91 are in the OFF position [OFF], the controller 80 does not supply current through the rotary transformer 38 to the three-phase windings 36 of the clutch motor 30. Absence of supply of electric current results in an interruption of the electromagnetic connection of the outer rotor 32 of the clutch motor 30 from the inner rotor 34. This results in the crankshaft 56 of the gasoline engine 50 being revved up. Under the condition that all transistors Tr1 to Tr6 are in the OFF position, no regeneration of energy from the three-phase windings 36 takes place and the gasoline engine 50 is kept idling.

When the control CPU 90 of the controller 80 outputs the first control signal SW1 to control the transistors Tr1 to Tr6 in the first drive circuit 91 on and off, a constant electric current is passed through the three-phase windings 36 of the clutch motor 30 based on the difference between a rotational speed Ne of the crankshaft 56 of the gasoline engine 50 and a rotational speed Nd of the drive shaft 22 (i.e., the difference Nc (= Ne - Nd) between the rotational speed of the outer rotor 32 and that of the inner rotor 34 in the clutch motor 30). Thus, a certain slip exists between the outer rotor 32 and the inner rotor 34 of the clutch motor 30. At this time, the inner rotor 34 rotates at a rotational speed lower than that of the outer rotor 32. This implies that the rotational speed Nd of the drive shaft 22 is lower than the rotational speed Ne of the crankshaft 56 of the gasoline engine 50 (Nd < Ne). In this state, the clutch motor 30 functions as a generator and performs the regeneration operation for regenerating an electric current via the first drive circuit 91. In order to allow the assist motor 40 to consume energy identical to the electric energy regenerated by the clutch motor 30, the control CPU 90 controls the transistors Tr11 to Tr16 in the second drive circuit 92 on and off. The on/off control of the transistors Tr11 to Tr16 allows an electric current to flow up to the three-phase windings 44 of the assist motor 40, and the assist motor 40 thus performs the power operation so as to generate a torque.

Fig. 4 is a graph schematically illustrating an amount of energy regenerated by the clutch motor 30 and an amount of energy consumed by the assist motor 40. While the crankshaft 56 of the gasoline engine 50 is driven at a rotational speed Ne and a torque Te, energy is regenerated as electric energy in a region Gc by the clutch motor 30. The regenerated power is supplied to the assist motor 40 and converted into energy in a region Ga, which allows the drive shaft 22 to rotate at a rotational speed Nd and a torque Td. The torque conversion is carried out in the manner explained above, and the energy corresponding to the slip in the clutch motor 30 or the rotational speed difference (Ne - Nd) is thus given to the drive shaft 22 as torque.

When the rotational speed Nd of the drive shaft 22 has increased above the rotational speed Ne of the crankshaft 56 of the gasoline engine 50 (Nd > Ne), the vehicle enters the overdrive state. At this time, the inner rotor 34 starts rotating at a rotational speed higher than that of the outer rotor 32 in the clutch motor 30. When the control CPU 90 of the controller 80 outputs the first control signal SW1 to control the transistors Tr1 to Tr6 in the first drive circuit 91 on and off in the overdrive state, the clutch motor 30 as a normal motor. That is, the clutch motor 30 performs the power operation to increase the rotational speed of the inner rotor 34 relative to the outer rotor 32. This further increases the rotational speed Nd of the drive shaft 22 relative to the rotational speed Ne of the gasoline engine 50. While the clutch motor 30 functions as a normal motor, it consumes electric power.

In order to enable the assist motor 40 to regenerate energy identical to the electric energy consumed by the clutch motor 30, the control CPU 90 controls the transistors Tr11 to Tr16 in the second drive circuit 92 on and off. The on/off control of the transistors Tr11 to Tr16 enables the assist motor 40 to perform the regeneration operation. An electric current thus flows up to the three-phase windings 44 of the assist motor 40, as a result of which electric energy is regenerated via the second drive circuit 92. The regenerated power is supplied to the clutch motor 30 to compensate for the electric energy consumed by the clutch motor 30.

Fig. 5 is a graph schematically illustrating an amount of energy consumed by the clutch motor 30 and an amount of energy regenerated by the assist motor 40. For example, it is assumed that the crankshaft 56 of the gasoline engine 50 is driven at a rotational speed Ne and a torque Te, and that the drive shaft 22 is driven at a rotational speed Nd and a torque Td. In this state, energy in a range Ga is regenerated by the assist motor 40 as electric energy. The regenerated power is supplied to the clutch motor 30 and converted into a region Gc into energy which is ultimately consumed by the clutch motor 30. As the torque Td of the drive shaft 22 (ie, the output torque) decreases relative to the torque Te of the gasoline engine 50, the rotational speed Nd of the drive shaft 22 increases relative to the rotational speed Ne of the gasoline engine 50 (ie, the rotational speed of the crankshaft 56).

Apart from the torque conversion and rotational speed conversion explained above, the power output device 20 of the embodiment can charge the battery 94 with a surplus of electric energy or discharge the battery 94 to supplement the electric energy. This is accomplished by controlling the mechanical energy output from the gasoline engine 50 (i.e., the product of the torque Te and the rotational speed Ne), the electric energy regenerated or consumed by the clutch motor 30, and the electric energy regenerated or consumed by the assist motor 40. The energy output from the gasoline engine 50 can therefore be transmitted as power to the drive shaft 22 with a higher efficiency.

Next, a general control operation performed by the controller 80 to drive the vehicle in the forward direction, that is, to rotate the drive shaft 22 in the rotational direction of the crankshaft 56 of the gasoline engine 50, will be described. Fig. 6 is a flowchart showing a control operation of the first embodiment performed by the control CPU 90 to drive the vehicle in the forward direction.

When the program enters the routine, the control CPU 90 first obtains data on the rotational speed Nd of the drive shaft 22 in step S100. The rotational speed Nd of the drive shaft 22 can be calculated from the rotational angle θd of the drive shaft 22 read from the resolver 48. In the following step S101, the control CPU 90 reads the accelerator pedal position AP output from the accelerator pedal position sensor 65. The driver steps on the accelerator pedal 64 when he feels that the output torque is insufficient. The value of the accelerator pedal position AP thus represents the desired output torque (i.e., the desired torque of the drive shaft 22) that the driver requests. The program then proceeds to step S102, in which the control CPU 90 calculates a target output torque Td* (of the drive shaft 22) corresponding to the input accelerator pedal position AP. The target output torque Td* is also referred to as an output torque command value. Output torque command values Td* are set in advance for the respective accelerator pedal positions AP. In response to an input of the accelerator pedal position AP, the output torque command value Td* is derived from the input accelerator pedal position AP.

In step S103, an amount of energy Pd to be output from the drive shaft 22 is calculated according to the expression Pd = Td*x Nd, that is, by multiplying the derived output torque command value Td* (of the drive shaft 22) by the input rotational speed Nd of the drive shaft 22. The program then proceeds to step S104, in which the control CPU 90 sets a target engine torque Te* and a target engine speed Ne* of the gasoline engine 50 based on the output energy Pd thus obtained. It is assumed here that the total amount of energy output from the drive shaft 22 is supplied from the gasoline engine 50. Since the mechanical energy supplied from the gasoline engine 50 is equal to the product of the torque Te and the rotational speed Ne of the gasoline engine 50, the relationship between the output energy Pd, the target engine torque Te*, and the target engine speed Ne* can be expressed as Pd = Te*xNe*. However, there are numerous combinations of the target engine torque Te* and the target engine speed Ne* which satisfy this relationship. In this embodiment, an optimal combination of the target engine torque Te* and the target engine speed Ne* is selected to achieve operation of the gasoline engine 50 with the highest possible efficiency.

In the subsequent step S106, the control CPU 90 determines a torque command value Tc* of the clutch motor 30 based on the engine target torque Te* set in step S104. In order to keep the rotation speed Ne of the gasoline engine 50 at a substantially constant level, it is necessary to balance the torque of the gasoline engine 50 by means of the torque of the clutch motor 30. The processing in step S106 therefore sets the torque command value Tc* of the clutch motor 30 equal to the engine target torque Te*.

After setting the torque command value Tc* of the clutch motor 30 in step S106, the program proceeds to steps S108, 5110, and 5111 to control the clutch motor 30, the assist motor 40, and the gasoline engine 50, respectively. For the sake of simplicity, the operations for controlling the clutch motor 30, the assist motor 40, and the gasoline engine 50 are 50 are shown as separate steps. However, in the actual procedure, these control steps are executed collectively. For example, the control CPU 90 simultaneously controls the clutch motor 30 and the assist motor 40 by interrupt processing while simultaneously transmitting an instruction to the EFIECU 70 for controlling the gasoline engine 50 by communication.

Fig. 7 is a flowchart showing details of the process for controlling the clutch motor 30 executed in step S108 in the flowchart of Fig. 6. When the program enters the clutch motor control routine, the control CPU 90 of the controller 80 first reads the rotation angle Ad of the drive shaft 22 from the resolver 48 in step S112 and the rotation angle θe of the crankshaft 56 of the gasoline engine 50 from the resolver 39 in step S114. The control CPU 90 then calculates a relative angle θc of the drive shaft 22 and the crankshaft 56 using the equation θc = θe - θd in step S116.

The program proceeds to step S118, in which the control CPU 90 obtains from the ammeters 95 and 96 data on the clutch motor currents Iuc and Ivc flowing through the U and V phases, respectively, of the three-phase windings 36 in the clutch motor 30. Although the currents naturally flow through all three phases U, V, and W, measurement is only required for those currents flowing through two phases, since the sum of the currents is zero. In the subsequent step S120, the control CPU 90 performs a coordinate transformation (three-phase to two-phase) using the values of currents flowing through the three phases obtained in step S118. The coordinate transformation lists the values of the currents flowing through the three phases in accordance with the values of the currents flowing through the d and q axes of the permanent type synchronous motor and is carried out according to equation (1) given below:

The coordinate transformation is carried out because the currents flowing through the d and q axes are of critical importance for the torque control in the permanent magnet type synchronous motor. Alternatively, the torque control can be carried out directly with the currents flowing through the three phases. After transformation into the currents of two axes, the control CPU 90 calculates deviations of the currents Idc and Iqc actually flowing through the d and q axes from the current command values Idc* and Iqc* of the respective axes calculated from the torque command value Tc* of the clutch motor 30, and determines voltage command values Vdc and Vqc for the d and q axes in step S122. According to a concrete procedure, the control CPU 90 performs operations following the equations (2) and (3) given below:

ΔIdc = Idc* - Idc

ΔIqc = Iqc* - Iqc (2)

Vdc = Kp1·ΔIdc + ΣKi1·ΔIdc

Vqc = Kp2·ΔIqc + Sigma;Ki2·ΔIqc (3)

where Kp1, Kp2, Ki1 and Ki2 are coefficients that are set to suit the characteristics of the motor used.

The voltage command value Vdc (Vqc) includes a part proportional to the deviation ΔI from the current command value I* (the first term on the right-hand side of equation (3)) and a summation of historical data on the deviations ΔI for 'i' times (the second term on the right-hand side). The control CPU 90 then retransforms the coordinates of the voltage command values thus obtained (transformation from two-phase to three-phase) in step S124. This corresponds to an inverse of the transformation performed in step S120. The inverse transformation determines the voltages Vuc, Vvc and Vwc actually applied to the three-phase windings 36 as follows:

Vwc = -Vuc - Vvc (4)

The actual voltage control is accomplished by means of an on/off operation of the transistors Tr1 to Tr6 in the first drive circuit 91. In step S126, the on and off time of the transistors Tr1 to Tr6 in the first drive circuit 91 is PWM (Pulse Width Modulation) controlled to obtain the voltage command values Vuc, Vvc and Vwc determined by the above equation (4). This operation enables the clutch motor 30 to mechanically transmit the target torque to the drive shaft 22.

8 and 9 are flowcharts showing details of the process for controlling the assist motor 40 executed in step S110 in the flowchart of Fig. 6. Referring to the flowchart of Fig. 8, when the program enters the assist motor control routine, the control CPU 90 first obtains data on the rotational speed Nd of the drive shaft 22 in step S131. The rotational speed Nd of the drive shaft 22 is calculated from the rotational angle θd of the drive shaft 22 read from the resolver 48. The control CPU 90 then obtains data on the rotational speed Ne of the gasoline engine 50 in step S132. The rotational speed Ne of the gasoline engine 50 may be calculated from the rotational angle θe of the crankshaft 56 read from the resolver 39, or directly measured by the rotational speed sensor 76 mounted on the ignition distributor 60. In the latter case, the control CPU 90 obtains data on the rotational speed Ne of the gasoline engine 50 by communicating with the EFIECU 70 connected to the rotational speed sensor 76.

A rotational speed difference Nc between the input rotational speed Nd of the drive shaft 22 and the input rotational speed Ne of the gasoline engine 50 is calculated in step S133 according to the equation Nc = Ne - Nd. In the subsequent step S134, electric power (energy) Pc regenerated by the clutch motor 30 is calculated according to the following expression:

Pc = Ksc · Nc · Tc

where Ksc represents an efficiency of the regeneration operation in the clutch motor 30. The product Ncx Tc defines the energy in the region Gc of Fig. 4, where Nc and Tc denote the rotational speed difference and the actual torque generated by the clutch motor 30, respectively.

In step S135, a torque command value Ta* of the assist motor 40 is determined by the following expression:

Ta* = ksa · Pc/Nd

where ksa represents an efficiency of power operation in the assist motor 40. The torque command value Ta* of the assist motor 40 thus obtained is compared with a maximum torque Tamax that the assist motor 40 can potentially apply in step S136. If the torque command value Ta* exceeds the maximum torque Tamax, the program proceeds to step S138, where the torque command value Ta* is limited to the maximum torque Tamax.

After the torque command value Ta* is set equal to the maximum torque Tamax in step S138, or after it is determined in step S136 that the torque command value Ta* should not exceed the maximum torque Tamax, the control CPU 90 reads the rotation angle θd of the drive shaft 22 from the resolver 48 in step S140, and obtains data on the assist motor currents Iua and Iva flowing through the U-phase and V-phase of the three-phase windings 44 in the assist motor 40 from the ammeters 97 and 98 in step S142. Referring to the flowchart of Fig. 9, the control CPU 90 then performs coordinate transformation for the currents of the three phases in step S144, calculates voltage command values Vda and Vqa in step S146, and performs inverse coordinate transformation for the voltage command values in step S148. In the following step S150, the control CPU 90 determines the on and off times of the transistors Tr11 to Tr16 in the second drive circuit 92 for PWM (Pulse Width Modulation) control. The processing performed in steps S144 to S150 is similar to that performed in steps S120 to S126 of the clutch motor control routine shown in the flowchart of Fig. 7.

The control of the gasoline engine 50 (step S111 in Fig. 6) is performed in the following manner. In order to achieve steady running with the target engine torque Te* and the target engine speed Ne* (set in step S104 in Fig. 6), the control CPU 90 regulates the torque Te and the rotation speed Ne of the gasoline engine 50 so as to approach the target engine torque Te* and the target engine speed Ne*, respectively. According to a concrete operation, the control CPU 90 sends an instruction to the EFIECU 70 to regulate the fuel injection amount or the throttle position through communication. Such regulation results in the torque Te and the rotational speed Ne of the gasoline engine 50 ultimately approaching the target engine torque Te* and the target engine speed Ne*, respectively.

According to the above-described process, the clutch motor 30 converts the torque into electrical energy with the predetermined efficiency Ksc. In other words, the clutch motor 30 regenerates electrical energy in proportion to the difference between the rotational speed of the crankshaft 56 of the gasoline engine 50 and the rotational speed of the inner rotor 34 of the clutch motor 30. The assist motor 40 receives the electrical energy thus regenerated and applies a corresponding torque to the drive shaft 22. The torque generated by The torque applied to the drive shaft 22 by the assist motor 40 coincides with the torque converted into electric energy by the clutch motor 30. In the graph of Fig. 4, the energy in the region Gc is converted into that in the region Ga to perform the torque conversion.

There is, of course, a certain amount of energy loss in the clutch motor 30, the assist motor 40, the first drive circuit 91 and the second drive circuit 92. It is therefore rare that the energy in the region Gc completely coincides with the energy in the region Ga under practical conditions. The energy loss in the clutch motor 30 and the assist motor 40 is relatively small because some recently developed synchronous motors have an efficiency very close to 1. The energy loss in the first drive circuit 91 and the second drive circuit 92 can further be sufficiently small because the ON-state resistance of known transistors such as GTOs usable for Tr1 to Tr16 is extremely small. Most of the rotational speed difference or slip between the rotation of the drive shaft 22 and the crankshaft 56 is thus converted into energy for generation by the three-phase windings 36 and transmitted to the drive shaft 22 as torque by the assist motor 40.

The following describes a general control operation performed by the controller 80 to drive the vehicle in the reverse direction, that is, to rotate the drive shaft 22 in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50. As mentioned above, the prime mover used in the embodiment is the Gasoline engine 50. However, it is impossible to rotate the output shaft of an internal combustion engine such as the gasoline engine 50 in the reverse direction. Based on the reasonable assumption that the reverse travel of the vehicle is generally required only for a short period of time and over a short distance, the power output device 20 is operated in the following manner. Electric power stored in the battery 94 is mainly used as the energy required for the reverse travel of the vehicle. When the battery 94 does not have sufficient remaining capacity, electric energy regenerated by the clutch motor 30 is used to drive the vehicle in the reverse direction.

Fig. 10 is a flowchart showing a control process of the first embodiment performed by the control CPU 90 to drive the vehicle in reverse. When the program enters the routine, the control CPU 90 of the controller 80 first reads the select lever position SP output from the select lever position sensor 84 in step S200 and determines whether the select lever 82 is in the reverse gear position in step S202. If the select lever 82 is in the reverse gear position, the program determines that the driver wants to drive in reverse and proceeds to step S204. On the other hand, if the select lever 82 is not in the reverse gear position, the program determines that the driver does not want to drive in reverse and exits the routine.

In step S204, the control CPU 90 receives data on the rotation speed Nd of the drive shaft 22. Under the condition of this routine, the drive shaft 22 is rotated in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50, ie, rotated in the opposite direction to the rotation detected in step S100 in the flow chart of Fig. 6. The control CPU 90 then reads the accelerator pedal position AP output from the accelerator pedal position sensor 65 in step S206 and calculates the output torque command value Td* (of the drive shaft 22) in accordance with the input accelerator pedal position AP in step S208. In order to move the vehicle in reverse, the output torque Td (of the drive shaft 22) would have to act in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50. The output torque command value Td* calculated in step S208 thus has a negative sign, whereas the output torque command value Td* calculated in step S102 in the flow chart of Fig. 6 has a positive sign.

The control CPU 90 receives the output of the remaining capacity measuring device 99 and compares the remaining capacity BRM of the battery 94 with a reference minimum level Bmin in step S210. If the remaining capacity BRM is above the reference minimum level Bmin, the program determines that the remaining capacity BRM of the battery 94 is sufficient and proceeds to step S212 and subsequent steps to drive the vehicle in reverse using only the electric energy stored in the battery 94. On the other hand, if the remaining capacity BRM is not above the reference minimum level Bmin, the program determines that the remaining capacity BRM of the battery 94 is insufficient and proceeds to step S220 and subsequent steps to enable the clutch motor 30 to regenerate electric energy and drive the vehicle in reverse with the electric energy regenerated by the clutch motor 30.

A concrete procedure of the above control (control of steps S212 to S218) will be described in detail. The control CPU 90 sets the torque command value Tc* of the clutch motor 30 in step S212. The torque command value Tc* of the clutch motor 30 is set equal to zero to disengage the drive shaft 22 from the crankshaft 56.

The control CPU 90 then determines the torque command value Ta* of the assist motor 40 in step S214. The drive shaft 22 generally receives a torque Tc generated by the clutch motor 30 and a torque Ta generated by the assist motor 40. However, since the torque command value Tc* of the clutch motor 30 is set equal to zero in step S212, the drive shaft 22 receives only the torque Ta of the assist motor 40 as the output torque Td. The torque command value Ta* of the assist motor 40 is thus set equal to the output torque command value Td* calculated in step S208. As explained above, the output torque command value Td* should have a negative sign in order to move the vehicle in reverse. Accordingly, the torque command value Ta* of the assist motor 40 set in step S214 has the negative sign, while the torque command value Ta* of the assist motor 40 calculated in step S135 has a positive sign in the flowchart of Fig. 8.

In step S216, the control CPU 90 controls the clutch motor 30 based on the torque command value Tc* of the clutch motor 30 set in step S212. The concrete procedure of the clutch motor control is identical to that described above according to the flowchart of Fig. 7. The clutch motor control makes the torque Tc of the clutch motor 30 equal to zero and substantially cancels the electromagnetic coupling of the outer rotor 32 with the inner rotor 34 in the clutch motor 30. The clutch motor 30 consequently performs neither the regeneration operation nor the power operation. The clutch motor controller further relieves the crankshaft 56 of the gasoline engine 50 of load so that the gasoline engine 50 is kept idling.

In step S218, the control CPU 90 controls the assist motor 40 based on the torque command value Ta* of the assist motor 40 set in step S214. The concrete procedure of the assist motor control is similar to the processing of step S136 and subsequent steps in the flowcharts of Figs. 8 and 9. In the assist motor control of step S218, Tamax in steps S136 and S138 in the flowchart of Fig. 8 represents a maximum torque that the assist motor 40 can apply during the reverse rotation of the assist motor 40. The assist motor control enables the assist motor 40 to perform the reverse power operation and rotate opposite to the rotation of the crankshaft 56 of the gasoline engine 50. The assist motor 40 thus generates the torque Ta which acts in the opposite direction to the rotation of the crankshaft 56 and is communicated to the drive shaft 22 as the output torque Td. Although the torque command value Tc* of the clutch motor 30 is set to zero in the control process described above, the torque command value Tc* may alternatively be set to be equal to or less than a predetermined value to enable the clutch motor 30 to generate a small torque.

A concrete procedure of this control (control of steps S220 to S228) will be described in detail. In step S220, the control CPU 90 calculates the output energy Pd of the drive shaft 22 from the output torque command value Td* (of the drive shaft 22) calculated in step S208 and the rotational speed Nd of the drive shaft 22 read in step S204; Pd = Td*j x Nd. Since the output torque command value Td* has a negative sign in this routine, the absolute value of the output torque command value Td* is used for the calculation of the output energy Pd.

In order to enable the gasoline engine 50 to provide sufficient energy for the output energy Pd calculated in step: S220 of the drive shaft 22, the control CPU 90 increases the rotational speed Ne of the gasoline engine 50 (engine speed). According to a concrete procedure, the control CPU 90 sends an instruction to the EFIECU 70 through communication to increase the fuel injection amount and thereby amplify the energy supplied by the gasoline engine 50 in the rotational speed range of the gasoline engine 50 with a high degree of efficiency. The torque command value Tc* of the clutch motor 30 is set equal to a target value Tmin in step S224 to minimize the torque Tc of the clutch motor 30, that is, the torque Te of the gasoline engine 50 (engine torque).

In step S226, the control CPU 90 controls the clutch motor 30 based on the torque command value Tc* of the clutch motor 30 set in step S224. The concrete procedure of the clutch motor control is identical to that described above according to the flowchart of Fig. 7. The clutch motor control enables the clutch motor 30 to rotate at a low torque and at a high speed and to perform the regeneration operation. While the outer rotor 32 of the clutch motor 30 rotates in the rotational direction of the crankshaft 56, the inner rotor 34 rotates opposite to the rotation of the crankshaft 56. This results in a large rotational speed difference Nc between the outer rotor 32 and the inner rotor 34 (ie, a high rotational speed of the clutch motor 30). The clutch motor 30 performs the regeneration operation to regenerate energy corresponding to the product of the rotational speed difference Nc, the torque Tc, and the efficiency of the regeneration operation Ksc as electric energy.

In the subsequent step S228, the control CPU 90 controls the assist motor 40 according to the assist motor control routine shown in the flowcharts of Figs. 8 and 9. The assist motor control enables the assist motor 40 to perform the reverse power operation with the electric power regenerated by the clutch motor 30 and to rotate in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50. The assist motor 40 thus generates the torque Ta acting in the opposite direction to the rotation of the crankshaft 56. The drive shaft 22 receives the torque Tc generated by the clutch motor 30 in the direction of rotation of the crankshaft 56 and the torque Ta generated by the assist motor 40 in the opposite direction to the rotation of the crankshaft 56. The torque Ta of the assist motor 40 is greater than the torque Tc of the clutch motor 30. The resulting output torque Td has the magnitude Tc - Ta and acts in the opposite direction to the rotation of the crankshaft 56.

In the flowchart of Fig. 10, the operations for controlling the clutch motor 30 and the assist motor 40 are shown as separate steps for simplified illustration. However, in the actual procedure, these control operations are carried out collectively. For example, the control CPU 90 simultaneously controls the clutch motor 30 and the assist motor 40 by interrupt processing.

Fig. 11 is a graph schematically illustrating an amount of energy regenerated by the clutch motor 30 and an amount of energy consumed by the assist motor 40. As clearly shown in Fig. 11, the gasoline engine 50 rotating at an engine speed Ne and an engine torque Te generates energy corresponding to an area Ge. Assuming that the drive shaft 22 rotates at a rotational speed Nd opposite to the rotation of the crankshaft 56 of the gasoline engine 50, the latter control (control of steps S220 to S228) enables the clutch motor 30 to regenerate energy corresponding to the sum of the areas (Ge + Gm) as electric energy. The regenerated energy is supplied to the assist motor 40, which consumes energy corresponding to the sum of the areas (Gd + Gm). This means that the energy in the region Ge is converted into that in the region Gd. The drive shaft 22 therefore outputs the torque difference (Tc - Ta) as the output torque Td, i.e., the drive shaft 22 outputs the energy in the region Ge.

There is a certain amount of energy loss in the process of regenerating electric energy in the clutch motor 30, transmitting the regenerated power to the assist motor 40, and consuming of the transmitted power in the assist motor 40. It is thus rare that the energy in the region Ge completely coincides with the energy in the region Gd in practical operation. However, the energy loss in the clutch motor 30 and in the assist motor 40 is comparatively small, since some recently developed synchronous motors have an efficiency very close to 1.

Fig. 12(a) shows a flow of energy between the gasoline engine 50, the clutch motor 30, the assist motor 40 and the battery 94. In Fig. 12, the solid arrow shows a flow of mechanical energy, and the dashed arrow shows a flow of electrical energy.

As shown in Fig. 12(a), the clutch motor 30 receives mechanical energy Te · Ne generated by the gasoline engine 50 in the region Ge and mechanical energy Tc · Nd transmitted from the assist motor 40 in the region Gm. The clutch motor 30 converts all of the mechanical energy into electrical energy Tc · Nc corresponding to the sum of the regions Gm + Ge. The converted electrical energy is supplied to the assist motor 40. The assist motor 40 then converts the electrical energy supplied from the clutch motor 30 into mechanical energy Ta · Nd corresponding to the sum of the regions Gm + Gd. A part of the mechanical energy Tc · Nd corresponding to the region Gm is transmitted to the clutch motor 30, while the remaining mechanical energy Td · Nd corresponding to the region Gd is output from the drive shaft 22.

The above process allows the drive shaft 22 to rotate opposite to the rotation of the crankshaft 56 of the gasoline engine 50, thereby driving the vehicle in The energy required to drive the vehicle in reverse is primarily supplied by the electric energy stored in the battery 94. When the battery 94 does not have sufficient remaining capacity, the electric energy regenerated by the clutch motor 30 is used to drive the vehicle in reverse. This structure enables the vehicle to be driven in reverse without placing an undesirably high load on the battery 94. The structure does not require any special wheels for moving the vehicle backwards and therefore reduces the overall weight of equipment installed in the vehicle, saves time and labor for assembly, and lowers manufacturing costs.

As explained above, the structure of the first embodiment can effectively transmit or apply the power generated by the gasoline engine 50, thereby improving fuel consumption. The structure also allows the drive shaft 22 to rotate in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50 to move the vehicle in reverse.

According to a possible modification, the rotation speed Ne of the gasoline engine 50 (engine speed) may be further increased to a higher level in step S222 in the flowchart of Fig. 10 when the remaining capacity BRM of the battery 94 is not above the reference minimum level Bmin. This increases the power supplied by the gasoline engine 50 and enables the clutch motor 30 to regenerate more electric energy than the energy consumed by the assist motor 40. Therefore, the battery 94 can be charged with the excess electric energy. In this case, an energy flow between the gasoline engine 5U, the clutch motor 30, the assist motor 40 and the battery 94 as shown in Fig. 12(b).

According to another possible modification, the assist motor 40 can be driven with the electric energy stored in the battery 94 as well as with the electric energy regenerated by the clutch motor 30 to rotate the drive shaft 22 in the reverse direction when the battery 94 still has a small energy with a remaining capacity BRM not exceeding the reference minimum level Bmin. In this case, an energy flow is between the gasoline engine 50, the clutch motor 30, the assist motor 40 and the battery 94 as shown in Fig. 12(c).

The power output device 20 of the first embodiment can find another application, which is given as a second embodiment of the present invention. In the first embodiment, the assist motor 40 is controlled to perform the reverse power operation to move the vehicle in the reverse direction. However, the vehicle can be driven in reverse by the power operation of the clutch motor 30. In the second embodiment, the clutch motor 30 is controlled to perform the power operation with the electric energy stored in the battery 94 while the crankshaft 56 of the gasoline engine 50 is stopped. The clutch motor 30 thus generates a torque not greater than the maximum static friction torque of the crankshaft 56 of the gasoline engine 50 and allows the drive shaft 22 to rotate opposite to the original rotation of the crankshaft 56.

Fig. 13 shows torques applied to the respective shafts of the power output device in the second embodiment. In the structure of the second embodiment, the crankshaft 56, which originally rotates in the direction of the dot-dash open arrow, has finished rotating, and the rotation speed Ne of the crankshaft 56 (engine speed) is zero. The clutch motor 30 is controlled to perform the power operation and rotate the drive shaft 22 in the opposite direction to the original rotation of the crankshaft 56, as shown by the solid open arrow in Fig. 13. Under such conditions, the following torques are applied to the crankshaft 56 and the drive shaft 22. The crankshaft 56 receives the torque Tc generated by the clutch motor 30 and a static friction torque Tef of the crankshaft 56, which act in opposite directions and cancel each other. The drive shaft 22 receives the torque Tc generated by the clutch motor 30 and a static friction torque Tdf of the drive shaft 22, which act in opposite directions and cancel each other out. The torque Tc of the clutch motor 30 applied to the crankshaft 56 is a counterforce to the torque Tc applied to the drive shaft 22.

The condition required to prevent the clutch motor 30 from rotating the crankshaft 56 of the gasoline engine 50 is given as follows:

Tefmax ≥ Tef = Tc (5)

where Tefmax denotes the maximum static friction moment of the crankshaft 56.

The condition required to enable the drive shaft 22 to rotate opposite to the original rotation of the crankshaft 56 is given as follows:

Td > 0 (6),

where Td denotes the output torque of the drive shaft 22, which is equal to Tc-Tdf. The expression (6) is therefore written as:

Tc > Tdf (7)

Expressions (5) and (7) can be combined and written as:

Tefmax ≤ Tc < Tdf (8)

When the conditions of expression (8) are satisfied, the clutch motor 30 can rotate the drive shaft 22 in the opposite direction to the original rotation of the crankshaft 56 without rotating the crankshaft 56 of the gasoline engine 50. The maximum static friction torque of the crankshaft 56 includes not only a torque generated by the actual friction but also a torque due to the resistance generated in the process of compressing the air in a cylinder with a piston in the gasoline engine 50.

Fig. 14 is a flowchart showing a control procedure of the second embodiment, which is executed by the control CPU 90 to drive the vehicle in reverse. This control routine is executed on the assumption that the gasoline engine 50 has stopped its operation and that the crankshaft 56 has stopped rotating. In the same manner as the control routine of Fig. 10, when the program enters the routine, the control CPU 90 of the controller 80 first reads the select lever position SP output from the select lever position sensor 84 in step S300 and determines whether the select lever 82 is in the reverse gear position in step S302. If the select lever 82 is in the reverse gear position, the program proceeds to step S306. On the other hand, if the select lever 82 is not in the reverse gear position, the program exits the routine.

The control CPU 90 reads the accelerator pedal position AP output from the accelerator pedal position sensor 65 in step S306, and calculates the output torque command value Td* (of the drive shaft 22) in accordance with the input accelerator pedal position AP in step S308. Like the output torque command value Td* calculated in step S208 in the flowchart of Fig. 10, the output torque command value Td* calculated in step S308 has a negative sign, whereas the output torque command value Td* calculated in step S102 in the flowchart of Fig. 6 has a positive sign.

In step S310, the control CPU 90 receives the output of the remaining capacity measuring device 99 and compares the remaining capacity BRM of the battery 94 with the reference minimum level Bmin. If the remaining capacity BRM is above the reference minimum level Bmin, the program determines that the remaining capacity BRM of the battery 94 is sufficient and proceeds to step S312. On the other hand, if the remaining capacity BRM is not above the reference minimum level Bmin, the program determines that the remaining capacity BRM of the battery 94 is insufficient and exits the routine. The control routine of the second embodiment is under the assumption that the electric energy stored in the battery 94 is used for the power operation of the clutch motor 30. The program thus terminates the processing when the remaining capacity BRM of the battery 94 is insufficient.

In step S312, the output torque command value Td* calculated in step S308 is compared with a predetermined maximum static friction torque Tefmax of the crankshaft 56 of the gasoline engine 50. If the output torque command value Td* is equal to or less than the maximum static friction torque Tefmax, the program proceeds to step S314 to set the torque command value Tc* of the clutch motor 30 equal to the output torque command value Td* requested by the driver. On the other hand, if the output torque command value Td* is greater than the maximum static friction torque Tefmax, the torque command value Tc* of the clutch motor 30 is set equal to the maximum static friction torque Tefmax in step S316 so that the conditions of expression (8) are satisfied.

After setting the torque command value Tc* of the clutch motor 30, the program proceeds to step S318 to control the clutch motor 30 based on the torque command value Tc* of the clutch motor 30 set in either step S314 or step S316. The concrete procedure of the clutch motor control is identical to that shown in the flowchart of Fig. 7.

According to the control routine explained above, the clutch motor 30 can rotate the drive shaft 22 opposite to the original rotation of the crankshaft 56 without rotating the crankshaft 56 of the gasoline engine 50, thereby moving the vehicle in reverse.

Although the operation of the assist motor 40 is not specifically mentioned in the above description, the assist motor 40 may comply with any of the following options. The first option is to keep the assist motor 40 at rest. In this case, the vehicle is driven only by the clutch motor 30 in reverse. The second option is to cause the assist motor 40 to perform the power operation. In this case, the torque generated by the assist motor 40 acts to amplify the rotation of the drive shaft 22 in the opposite direction to the original rotation of the crankshaft 56. The vehicle is thus driven in reverse by both the clutch motor 30 and the assist motor 40. The third option is to cause the assist motor 40 to perform the regeneration operation. In this case, the torque generated by the assist motor 40 acts in the direction in which the torque generated by the clutch motor 30 is cancelled. This results in a decrease in the output torque of the drive shaft 22, but the electric energy regenerated by the assist motor 40 can partially cover the energy required for the vehicle to move backwards, thus reducing the consumption of electric energy stored in the battery 94.

Although the power output device 20 is applied to the controller of the second embodiment in the above description, the second embodiment is not limited to this structure. For example, the assist motor is not an essential part of the process of moving the vehicle in reverse by the clutch motor 30 as long as the power output device includes the clutch motor 30, the gasoline engine 50 and the battery 94.

In the second embodiment, the clutch motor 30 is controlled to rotate the drive shaft 22 in the opposite direction to the original rotation of the crankshaft 56 while the crankshaft 56 is stopped. However, the crankshaft 56 may be rotated during the control operation. The clutch motor 30 may rotate the drive shaft 22 in the opposite direction to the original rotation of the crankshaft 56 as long as the crankshaft 56 receives the torque having a magnitude equal to or greater than the torque Tc generated by the clutch motor 30 but acting in the opposite direction to the torque Tc. Therefore, it makes no difference whether the crankshaft 56 rotates or not.

When the clutch motor 30 rotates the drive shaft 22 opposite to the original rotation of the crankshaft 56 while the crankshaft 56 is rotating, the crankshaft 56 receives a kinetic stiction torque of the crankshaft 56 of the gasoline engine 50 that acts opposite to the torque Tc of the clutch motor 30 and cancels the torque Tc. Under such conditions, it makes no difference whether the gasoline engine 50 is driven or not because the gasoline engine 50 enters a state similar to braking. The kinetic stiction torque of the crankshaft 56 includes not only a torque generated by actual friction but also torques due to the resistance generated in the process of compressing air in a cylinder by a piston in the gasoline engine 50. or the resistance generated in the process of taking air into the cylinder. When the gasoline engine 50 has the function of an exhaust brake, a high torque can be generated by the operation of the exhaust brake.

The power output device 20 of the first embodiment can find another application, which is given as a third embodiment of the present invention. In order to reduce the speed of the vehicle traveling in reverse, that is, to brake the drive shaft 22 rotating in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50, it is necessary that either the assist motor 40 or the clutch motor 30 performs the regeneration operation and carries out regenerative braking. When the remaining capacity BRM of the battery 94 is equal to or greater than a maximum reference level Bmax, the battery 94 is in the fully charged state and cannot store additional electric energy. This means that the battery 94 cannot absorb the electric energy regenerated by either the assist motor 40 or the clutch motor 30. Failure to use the regenerated power results in a reduction in the speed of the vehicle traveling in reverse. In the third embodiment, the assist motor 40 is controlled to perform the regenerative operation when the gasoline engine 50 is at rest and to apply a regenerative braking force to the drive shaft 22, while the electric power regenerated by the assist motor 40 is supplied to the clutch motor 30, which then performs the power operation with the regenerated power.

Fig. 15 shows torques applied to the respective shafts of the power output device in the third embodiment. In the structure of the third embodiment, the gasoline engine 50 is in the rest state, and the crankshaft 56, which originally rotates in the direction of the dashed open arrow, has stopped rotating (engine speed Ne = 0). The drive shaft 22 is rotated opposite to the original rotation of the crankshaft 56 as shown by the solid open arrow in Fig. 15. Under the condition that the assist motor 40 performs the regeneration operation and that the clutch motor 30 performs the power operation, the following torques are applied to the crankshaft 56 and the drive shaft 22. As in the second embodiment shown in Fig. 13, the crankshaft 56 receives the torque Tc generated by the clutch motor 30 and the static friction torque Tef of the crankshaft 56, which act in opposite directions and cancel each other out. The drive shaft 22 receives the torque Tc generated by the clutch motor 30 and the torque Ta generated by the assist motor 40. The torque Tc acts in the direction of increasing the rotation of the drive shaft 22, while the torque Ta acts in the direction of decelerating the rotation of the drive shaft 22. The torque Tc of the clutch motor 30 is thus opposite to the direction of the torque Ta of the assist motor 40. The torque Tc of the clutch motor 30 applied to the crankshaft 56 is a counterforce to the torque Tc applied to the drive shaft 22. The explanation does not take into account the static friction moment of the drive shaft 22.

The energy Pa regenerated by the assist motor 40 as electrical energy is expressed as:

Pa = Ksa · Ta · Nd (9)

where Ksa denotes an efficiency of the regeneration operation in the assist motor 40, and Nd stands for the rotational speed of the drive shaft 22.

Energy Pc consumed by the clutch motor 30 is given as:

Pc = (1/ksc) Tc Nc (10),

where ksc denotes a power operation efficiency in the clutch motor 30, and Nc represents the rotational speed of the clutch motor 30 (i.e., the rotational speed difference between the crankshaft 56 and the drive shaft 22).

There is a certain amount of energy loss in the process of transferring the energy regenerated by the assist motor 40 as electric energy to the clutch motor 30. The energy Pa generated by the assist motor 40 is therefore larger than the energy Pc consumed by the clutch motor 30:

Pa > Pc (11)

Since the crankshaft 56 has stopped rotating, the rotational speed Nc of the clutch motor 30 is equal to the rotational speed Nd of the drive shaft 22. Substituting equations (9) and (10) into expression (11) gives:

Ksa x Ta > (1/ksc) Tc (12)

Assuming that both the efficiency of the regeneration operation Ksa in the assist motor 40 and the efficiency of the power operation ksc in the clutch motor 30 are close to the value '1', the expression (12) is further rewritten as:

Ta > Tc (13)

As clearly shown in Fig. 15, the output torque Td of the drive shaft 22 is Ta - Tc. The expression (13) is therefore further modified to:

Td = Ta - Tc > 0 (14)

Expression (14) shows that the output torque Td acts in the opposite direction to the rotation of the drive shaft 22 and therefore decelerates the drive shaft 22. That is, the drive shaft 22 undergoes deceleration (i.e., acceleration in the opposite direction to the rotation of the drive shaft 22), which reduces the speed of the vehicle traveling in reverse.

As explained above in the second embodiment, the condition of expression (5) should be satisfied in order to prevent the clutch motor 30 from rotating the crankshaft 56 of the gasoline engine 50.

Fig. 16 is a flow chart showing a control procedure of the third embodiment, which is performed by the control CPU 90 to reduce the speed of the vehicle traveling in reverse. This control routine is executed under the assumption that the vehicle is traveling in reverse (ie, the drive shaft 22 rotates in the opposite direction to the rotation of the crankshaft 56), the gasoline engine 50 is operating has stopped and the crankshaft 56 has stopped rotating. When the program enters the routine of Fig. 16, the control CPU 90 first determines in step S400 whether a brake pedal (not shown) has been depressed. The driver generally depresses the brake pedal when he wishes to reduce the speed of the vehicle or to stop the vehicle. In response to depression of the brake pedal, the program determines that the driver wishes to reduce the speed of the vehicle and performs the reducing operation as described below.

The control CPU 90 receives the output of the remaining capacity measuring device 99 and compares the remaining capacity BRM of the battery 94 with a maximum reference level Bmax in step S402. If the remaining capacity BRM of the battery 94 is below the maximum reference level Bmax, the program determines that the battery 94 still has a small capacity for storing additional electric energy and exits the routine of Fig. 16. In this case, another reduction process is performed using the battery 94. For example, the clutch motor 30 or the assist motor 40 is controlled to perform the regeneration operation and carry out regenerative braking while storing the regenerated power in the battery 94. On the other hand, if the remaining capacity BRM of the battery 94 is equal to or greater than the maximum reference level Bmax, the program determines that the battery 94 is in the fully charged state and cannot store any more electric energy, and proceeds to step S404.

Based on the maximum static friction torque Tefmax of the crankshaft 56 of the gasoline engine 50, the torque command value Tc* of the clutch motor 30 is Step S404 is determined so that the condition of expression (5) is satisfied. The control CPU 90 then receives data on the rotational speed Nd of the drive shaft 22 in step S406. Since the crankshaft 56 of the gasoline engine 50 is in the rest state as mentioned above, the rotational speed Nc of the clutch motor 30 is equal to the rotational speed Nd of the drive shaft 22. In step S406, the control CPU 90 thus receives data on the rotational speed Nc of the clutch motor 30 and the rotational speed Nd of the drive shaft 22.

In the subsequent step S408, the control CPU 90 calculates the electric power Pc consumed by the clutch motor 30 from the torque command value Tc* of the clutch motor 30 set in step S404 and the rotational speed Nc of the clutch motor 30 input in step S406 according to the above-mentioned equation (10). The electric power Pa to be regenerated by the assist motor 40 is derived from the consumed power Pc in step S410 by taking into account the energy loss in the transmission operation. The control CPU 90 calculates the torque command value Ta* of the assist motor 40 in step S412 from the rotational speed Nd of the drive shaft 22 read in step S406 and the regenerated power Pa derived in step S410 according to the above-mentioned equation (9).

In step S414, the control CPU 90 controls the clutch motor 30 based on the torque command value Tc* of the clutch motor 30 set in step S404. The concrete procedure of the clutch motor control is identical to that described above according to the flowchart of Fig. 7. In the following step S416, the control CPU 90 controls the assist motor 40 based on the torque command value Ta* of the assist motor 40 set in step S412. The concrete procedure of the assist motor control is similar to the processing of step S140 and subsequent steps in the flowcharts of Figs. 8 and 9. In the flowchart of Fig. 16, for convenience of illustration, the control operations of the clutch motor 30 and the assist motor 40 are shown as separate steps. However, in the actual procedure, these control operations are collectively executed. For example, the control CPU 90 simultaneously controls the clutch motor 30 and the assist motor 40 by interrupt processing.

The control operation explained above enables the assist motor 40 to perform the regenerative operation and apply a regenerative braking force to the drive shaft 22, and at the same time enables the clutch motor 30 to perform the power operation and consume the electric energy regenerated by the assist motor 40. The structure of the third embodiment can brake the drive shaft 22 and reduce the speed of the vehicle traveling in reverse while allowing the clutch motor 30 to absorb the electric energy regenerated by the assist motor 40.

The magnitude of the output torque Td is varied by controlling the operating conditions of the clutch motor 30 and the assist motor 40 to change the amount of energy loss in the respective motors 30 and 40 (for example, by varying the efficiency of the regenerative operation Ksa in the assist motor 40 and the efficiency of the power operation ksc in the clutch motor 30).

As in the second embodiment, the control operation of the third embodiment is carried out while the crankshaft 56 is at a standstill. However, the crankshaft 56 may be rotated during the operation of braking the drive shaft 22 and reducing the vehicle speed.

Fig. 17 schematically illustrates an essential part of another power output device 20A as a fourth embodiment of the present invention. Although in the power output device 20 of Fig. 1, the assist motor 40 is attached to the drive shaft 22, in the power output device 20A of Fig. 17, an assist motor 40A is attached to the crankshaft 56 of the gasoline engine 50.

The power output device 20A of Fig. 17 has a structure similar to that of the power output device 20 of Fig. 1, except that the assist motor 40A is mounted on the crankshaft 56 disposed between the gasoline engine 50 and a clutch motor 30A. In the power output device 20A of Fig. 17, like numerals and symbols denote like elements as those of the power output device 20 of Fig. 1. Unless otherwise indicated, the symbols used in the description have like meanings.

The following describes the essential operation of the power output device 20A shown in Fig. 17. First, the operation of the fourth embodiment which is carried out to drive the vehicle in the forward direction, that is, to rotate the drive shaft 22 in the direction of rotation of the crankshaft 56 of the gasoline engine 50. For example, assume that the gasoline engine 50 is driven with a torque Te and at a rotational speed Ne. Consequently, when a torque Ta is added to the crankshaft 56 by the assist motor 40A connected to the crankshaft 56, the sum of the torques (Te + Ta) acts on the crankshaft 56. When the clutch motor 30A is controlled to produce the torque Tc equal to the sum of the torques (Te + Ta), the torque Tc (= Te + Ta) is transmitted to the drive shaft 22.

When the rotational speed Nd of the drive shaft 22 is lower than the rotational speed Ne of the gasoline engine 50 (Nd < Ne), the clutch motor 30A regenerates electric power based on the rotational speed difference Nc between the rotational speed Ne of the gasoline engine 50 and the rotational speed Nd of the drive shaft 22. The regenerated power is supplied to the assist motor 40A via the first and second drive circuits 91 and 92 to activate the assist motor 40A. Provided that the torque Ta of the assist motor 40A is set to a value that enables the assist motor 40A to consume the electric energy substantially equivalent to the electric energy regenerated by the clutch motor 30A, free torque conversion is permitted for the energy output from the gasoline engine 50 within a range that satisfies the relationship of the equation (15) given below. Since the relationship of the equation (15) represents the ideal state with an efficiency of 100%, (Tc · Nd) is a little less than (Te · Ne) in the actual state.

Te · Ne = Tc · Nd (15)

When the rotational speed Nd of the drive shaft 22 is higher than the rotational speed Ne of the gasoline engine 50 (Nd > Ne), the clutch motor 30A operates as a normal motor. The clutch motor 30A consequently increases the rotational speed of the inner rotor 34 relative to the outer rotor 32. Provided that the torque Ta of the assist motor 40A is set to a negative value that enables the assist motor 40A to regenerate electric energy substantially equivalent to the electric energy consumed by the clutch motor 30A, free torque conversion within a range that satisfies the relationship of the above-mentioned equation (15) is also permitted for the energy output from the gasoline engine 50.

The following describes the operation of the fourth embodiment, which is performed to drive the vehicle in reverse, i.e., to rotate the drive shaft 22 in the opposite direction to the rotation of the crankshaft 56 of the gasoline engine 50. Any of the following four control operations can be applied to this embodiment to move the vehicle backward.

According to a first control process, the control CPU 90 sends an instruction to the EFIECU 70 by communication. The EFIECU 70, which receives the instruction, controls the gasoline engine 50 to stop the operation of the gasoline engine 50 and the rotation of the crankshaft 56. The control CPU 90 then controls the second drive circuit 92 to hold the crankshaft 56 in the assist motor 40A via the electromagnetic coupling of the stator 43 to the rotor 42. This is achieved by achieved by enabling the three-phase windings 44 to generate not a rotating magnetic field but a standing magnetic field. The control CPU 90 then controls the first drive circuit 91 to enable the clutch motor 30A to perform the power operation and rotate the drive shaft 22 opposite to the original rotation of the crankshaft 56. The electric energy stored in the battery 94 is used to drive the assist motor 40A and the clutch motor 30A.

Fig. 18 shows torques applied to the respective shafts in the power output device 20A of Fig. 17. When the clutch motor 30A rotates the drive shaft 22 opposite to the original rotation of the crankshaft 56 (shown by the dashed open arrow) as shown by the solid open arrow, the crankshaft 56 receives the torque Tc generated by the clutch motor 30A. The torque Tc of the clutch motor 30A acts in the direction of the original rotation of the crankshaft 56 and is opposite to the direction of the torque Ta generated by the assist motor 40A. This prevents the crankshaft 56 from rotating. The drive shaft 22 can thus continue to rotate opposite to the original rotation of the crankshaft 56 due to the support by the stationary crankshaft 56. Under practical conditions, the crankshaft 56 also receives the static static friction torque Tef of the crankshaft 56 generated by the gasoline engine 50. The sum of the static static friction torque Tef and the torque Ta of the assist motor 40A thus cancels the torque Tc of the clutch motor 30A.

When the electromagnetic coupling of the stator 43 with the rotor 42 in the assist motor 40A is released, only the static friction torque Tef of the crankshaft 56 in the gasoline engine 50 acts to hold the crankshaft 56. Under such conditions, the power output device 20A enters the state identical to that described in the second embodiment.

According to a second control operation, the control CPU 90 controls the second drive circuit 92 to enable the assist motor 40A to perform the regeneration operation while the gasoline engine 50 is in the operating state and the crankshaft 56 is rotated. The control CPU 90 then controls the first drive circuit 91 to enable the clutch motor 30A to perform the power operation with the electric energy regenerated by the assist motor 40A and to rotate the drive shaft 22 in the opposite direction to the rotation of the crankshaft 56. In the second operation, the electric energy stored in the battery 94 is not used for the control operation.

Fig. 19 also shows torques applied to the respective shafts in the power output device 20A of Fig. 17. When the assist motor 40A is controlled to perform the regenerative operation while the crankshaft 56 rotates in the direction of the closed arrow, the crankshaft 56 receives the regenerative torque Ta generated by the assist motor 40A. Meanwhile, the clutch motor 30A performs the power operation and applies the torque Tc to the crankshaft 56, which acts in the rotation direction of the crankshaft 56 and cancels the torque Ta (provided that the crankshaft 56 is rotated at a constant speed). According to the law of action and reaction, the clutch motor 30A also applies the torque Tc to the drive shaft 22 which acts in opposition to the rotation of the crankshaft 56. This torque Tc is output as the output torque Td from the drive shaft 22.

Fig. 20 is a graph schematically illustrating an amount of energy regenerated by the assist motor 40A and an amount of energy consumed by the clutch motor 30A under the condition of Fig. 19. As clearly shown in Fig. 20, the gasoline engine 50 rotating at an engine speed Ne and an engine torque Te generates energy corresponding to an area Ge. The assist motor 40A regenerates energy corresponding to the sum of the areas Ge + Gm as electric energy. The regenerated power is supplied to the clutch motor 30A, which generates energy corresponding to the sum of the areas Gd + Gm and rotates the drive shaft 22 at a rotational speed Nd opposite to the rotation of the crankshaft 56. This means that the energy in the area Ge is converted into that in the area Gd. The drive shaft 22 thus outputs the torque difference (Te - Ta) as the output torque Td, i.e. the drive shaft 22 outputs the energy in the range Ge.

There is a certain amount of energy loss in the process of regenerating electric energy in the assist motor 40A, transmitting the regenerated power to the clutch motor 30A, and consuming the transmitted power in the clutch motor 30A. Therefore, the energy in the region Ge rarely exactly matches the energy in the region Gd in practical operation, even if the energy loss in the Clutch motor 30A and assist motor 40A is comparatively low.

Fig. 21 shows a flow of energy between the gasoline engine 50, the clutch motor 30A and the assist motor 40A. The assist motor 40A receives mechanical energy Te · Ne generated by the gasoline engine 50 in the area Ge and mechanical energy Tc · Ne transmitted by the clutch motor 30A in the area Gm. The assist motor 40A converts all the mechanical energy into electrical energy Ta · Na corresponding to the sum of the areas Gm + Ge. The converted electrical energy is supplied to the clutch motor 30A. The clutch motor 30A then converts the electrical energy supplied by the assist motor 40A into mechanical energy Tc · Nc corresponding to the sum of the areas Gm + Gd. A part of the mechanical energy Tc · Ne corresponding to the range Gm is transmitted to the assist motor 40A, while the remaining mechanical energy Td · Nd corresponding to the range Gd is output from the drive shaft 22.

According to a third control operation, as in the second control operation, the control CPU 90 activates the regeneration operation of the assist motor 40A and the power operation of the clutch motor 30A. In this operation, the electric power regenerated by the assist motor 40A is not entirely transmitted to the clutch motor 30A, but is partially supplied to the battery 94. This operation enables the battery 94 to be charged with the regenerated power while the drive shaft 22 is rotated in the opposite direction to the rotation of the crankshaft 56.

According to a fourth control operation, as in the second control operation, the control CPU 90 activates the regenerative operation of the assist motor 40A and the power operation of the clutch motor 30A. In this operation, the clutch motor 30A performs the power operation not only with the energy regenerated by the assist motor 40A but also with the electric energy stored in the battery 94. This operation enables a high torque to be output to the drive shaft 22 rotating in the opposite direction to the rotation of the crankshaft 56.

The power output device 20A having the structure shown in Fig. 17 can rotate the drive shaft 22 in accordance with any of the above-mentioned four control operations in the opposite direction to the rotation of the crankshaft 56.

Many other modifications, variations and changes can be made without departing from the scope or spirit of the invention. It is therefore to be understood that the above embodiments are intended to be illustrative only and not restrictive. Some examples of modifications are given below.

In the structure of the power output device 20 shown in Fig. 1, the clutch motor 30 and the assist motor 40 are separately mounted at different locations on the drive shaft 22. However, as in a modified power output device 20B illustrated in Fig. 22, the clutch motor and the assist motor may be fixedly mounted to each other. A clutch motor 30B of the power output device 20B has an inner rotor 34 connected to the crankshaft 56 and an outer rotor 34 connected to the drive shaft 22. 32B. Three-phase coils 36 are mounted on the inner rotor 34, and permanent magnets 35B are arranged on the outer rotor 32B so that the outer surface and the inner surface thereof have different magnetic poles. An assist motor 40B includes the outer rotor 32B of the clutch motor 30B and a stator 43 having three-phase windings 44 mounted thereon. In this structure, the outer rotor 32B of the clutch motor 30B also functions as a rotor of the assist motor 40B. Since the three-phase windings 36 are mounted on the inner rotor 34 which is connected to the crankshaft 56, a rotary transformer 38 for supplying electric power to the three-phase windings 36 of the clutch motor 30B is mounted on the crankshaft 56.

In the power output device 20B, the voltage applied to the three-phase windings 36 on the inner rotor 34 is controlled against the inner surface magnetic pole of the permanent magnet 35B mounted on the outer rotor 32B. This allows the clutch motor 30B to operate in the same manner as the clutch motor 30 of the power output device 20 shown in Fig. 1. The voltage applied to the three-phase windings 44 on the stator 43 is controlled against the outer surface magnetic pole of the permanent magnet 35B mounted on the outer rotor 32B. This allows the assist motor 40B to operate in the same manner as the assist motor 40 of the power output device 20. The control operations explained as the first to third embodiments are applicable to the power output device 20B shown in Fig. 22, which thus produces the same effects as the power output device 20 shown in Fig. 1.

In the power output device 20B of Fig. 22, the clutch motor 30B and the assist motor 40B are integrally assembled, thereby shortening the length of the power output device 20B along the drive shaft 22. The outer rotor 32B simultaneously functions as one of the rotors in the clutch motor 30B and the rotor of the assist motor 40B, thereby effectively reducing the size and weight of the entire power output device 20B.

The modified structure in which the outer rotor 32B functions as one of the rotors in the clutch motor 30B and as the rotor of the assist motor 40B causes the clutch motor 30B and the assist motor 40B to interfere with each other magnetically and thus have a negative effect on each other. In order to prevent strong magnetic interference, the outer rotor 32B may be designed as a double cylinder structure with two concentric cylinders. One of the cylinders is associated with the rotor of the clutch motor 30B and the other with the rotor of the assist motor 40B. The two cylinders separated by a predetermined distance are connected to the drive shaft 22. A magnetic shield member for blocking the magnetic lines of force is also effective for preventing the magnetic interference.

In the power output device 20A of Fig. 17, which is given as the fourth embodiment discussed above, the assist motor 40A is mounted at a location between the gasoline engine 50 and the clutch motor 30A on the crankshaft 56. However, as in another power output device 20C illustrated in Fig. 23, the gasoline engine 50 may be mounted between a clutch motor 30C and an assist motor 40C, each of which is connected to the crankshaft 56. The control operations performed by the power output device 20A of Fig. 17 are also applicable to the power output device 20C, which thus performs similar operations and produces similar effects.

In the power output device 20A of Fig. 17, the clutch motor 30A and the assist motor 40A are separately mounted at different positions of the crankshaft 56. However, as in a power output device 20D shown in Fig. 24, the clutch motor and the assist motor may be fixedly mounted to each other. A clutch motor 30D of the power output device 20D includes an outer rotor 32D connected to the crankshaft 56 and an inner rotor 34 connected to the drive shaft 22. Three-phase coils 36 are mounted on the inner rotor 34, and permanent magnets 35D are arranged on the outer rotor 32D so that its outer and inner surfaces have different magnetic poles. An assist motor 40D includes the outer rotor 32D of the clutch motor 30D and a stator 43 having three-phase windings 44 mounted thereon. In this structure, the outer rotor 32D of the clutch motor 30D also functions as a rotor of the assist motor 40D.

In the power output device 20D, the voltage applied to the three-phase windings 36 on the inner rotor 34 is controlled against the inner surface magnetic pole of the permanent magnet 35D arranged on the outer rotor 32D. This enables the clutch motor 30D to operate in the same manner as the clutch motor 30A of the power output device 20A shown in Fig. 17. The voltage applied to the three-phase windings 44 on the stator 43 is controlled against the outer surface magnetic pole of the permanent magnet 35D arranged on the outer rotor 32D. This enables the assist motor 40D to operate in the same manner as the assist motor 40A of the power output device 20A. The control operations of the fourth embodiment explained above are also applicable to the power output device 20D shown in Fig. 24, which thus produces the same effects as the power output device 20A shown in Fig. 17.

As in the case of the power output device 20B shown in Fig. 22, in the power output device 20D of Fig. 24, the clutch motor 30D and the assist motor 40D are integrally assembled, thereby shortening the length of the power output device 20D along the drive shaft 22. The outer rotor 32D simultaneously functions as one of the rotors in the clutch motor 30D and the rotor of the assist motor 40D, thereby effectively reducing the size and weight of the entire power output device 20D.

The gasoline-powered gasoline engine 50 is used as an internal combustion engine in the above power output devices. However, the principle of the invention is applicable to other internal combustion engines and external combustion engines such as diesel engines, turbine engines and jet engines.

Permanent magnet (PM) type synchronous motors are used in the above-described power output devices for the clutch motor 30 and the assist motor 40. Other motors such as variable magnet resistance (VR) type synchronous motors, vernier thrusters, DC motors, induction motors and superconductor motors can be used for both the regeneration operation and power operation, while stepper motors can only be used for power operation.

In the above-described power output device, the outer rotor 32 of the clutch motor 30 is coupled to the crankshaft 56, while the inner rotor 34 is connected to the drive shaft 22. Alternatively, the outer rotor 32 may be coupled to the drive shaft 22 and the inner rotor 34 may be coupled to the crankshaft 56. Opposed disk rotors may be used instead of the outer rotor 32 and the inner rotor 34.

The rotary transformer 38 used as a means for transmitting electric energy to the clutch motor 30 may be replaced by a slip ring brush contact, a slip ring mercury contact, a magnetic energy semiconductor coupling or the like.

In the above power output device, transistor inverters are used for the first and second drive circuits 91 and 92. Other examples applicable to the drive circuits 91 and 92 include IGBT (insulated gate bipolar mode transistor) inverters, thyristor inverters, voltage PWM (pulse width modulation) inverters, square wave inverters (voltage inverters and current inverters), and resonance inverters.

The battery 94 may include Pb cells, NiMH cells, Li cells and the like. A capacitor may be used instead of the battery 94. The battery 94 also functions as a means for receiving the regenerated power. A variety of electrical devices (e.g., lighting, sound and cooling devices), installed in the vehicle may be used for the means for receiving the regenerated power other than the battery 94.

Although the power output device is installed in a vehicle in the above embodiments, it can also be installed in other transportation devices such as ships and aircraft, as well as a variety of industrial machines.

The scope and spirit of the present invention are limited only by the appended claims.

Claims (24)

1. A power output device for outputting power to a drive shaft, the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, and the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; a first motor drive device (91) for exchanging electrical currents with the first motor (30) to vary the electromagnetic coupling of the first rotor with the second rotor; a second motor (40) having a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; a second motor drive device (92) for exchanging electrical currents with the second motor (40) to vary the electromagnetic coupling of the stator with the third rotor; and a control device (90) for controlling the second motor drive device (92) for driving the second motor (40) such that the drive shaft (22) is caused to rotate in a second direction which is opposite to the first direction; characterized by a storage device (94) for storing electrical energy; and wherein the control device (90) comprises means for controlling the first motor drive device (91) to set a torque (Tc) generated by the first motor (30) to at most a predetermined level (Tmin) and controlling the second motor drive device (92) to supply the electrical energy stored in the storage device (94) to the second motor (40). 2. A power output device according to claim 1, wherein the torque (Tc) generated by the first motor (30) is substantially zero (S212). 3. A power output device for outputting power to a drive shaft, the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which between the output shaft (56) of the internal combustion engine and the drive shaft (22) power is transmitted via the electromagnetic coupling of the first and second rotors; a first motor drive device (91) for exchanging electrical currents with the first motor (30) to vary the electromagnetic coupling of the first rotor with the second rotor; a second motor (40) having a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; a second motor drive device (92) for exchanging electrical currents with the second motor (40) to vary the electromagnetic coupling of the stator with the third rotor; and a control device (90) for controlling the second motor drive device (92) for driving the second motor (40) such that the drive shaft (22) is caused to rotate in a second direction which is opposite to the first direction; characterized by a storage device (94) for storing electrical energy; wherein the control device (90) comprises means for controlling the first motor drive device (91) to enable the first motor (30) to generate electrical energy, and controlling the second motor drive device (92), a) to supply the generated electrical energy and the electrical energy stored in the storage device (94) to the second motor (40), or b) to supply the generated electrical energy to the second motor (40) and at least partially the storage device (94) to be stored. 4. The power output device according to claim 3, wherein the power output device further comprises: a residual capacity measuring device (99) for measuring a residual capacity (BRM) of electrical energy stored in the storage device (94); and a power generation amplifying device for increasing (S222) the rotational speed (Ne) of the output shaft (56) of the internal combustion engine to amplify the electric power generated by the first motor (30) when the residual capacity (BRM) measured by the remaining capacity measuring device is not larger than a predetermined value (Bmin). 5. A power output device for outputting power to a drive shaft (22), the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; a motor drive device (91) for exchanging electric currents with the first motor (30) for varying the electromagnetic coupling of the first rotor with the second rotor; a storage device (94) for storing electrical energy; characterized by a control device (90) for controlling the motor drive device (91) to supply the electrical energy stored in the storage device (94) to the motor to drive the motor (30) and further to enable the motor to generate a torque (Tc) acting in a second direction opposite to the first direction and to apply the torque (Tc) to the drive shaft (22), thereby rotating the drive shaft (22) in the second direction. 6. A power output device according to claim 5, wherein the control device (90) comprises means for controlling (S312) the motor drive device (91) to enable the motor (30) to generate the torque (Tc) which is not greater than a maximum static friction torque (Tefmax) of the output shaft (56) of the internal combustion engine and to apply the torque (Tc) to the drive shaft (22) when the output shaft (56) of the internal combustion engine is in the rest state. 7. A power output device according to claim 5 or 6, wherein the power output device further comprises: a residual capacity measuring device (99) for measuring a residual capacity (BRM) of electrical energy stored in the storage device (94); means for enabling (S310) the control device (90) to carry out the control of the motor drive device (91) when the residual capacity (BRM) measured by the residual capacity measuring device (99) is greater than a predetermined value (Bmin). 8. A power output device for outputting power to a drive shaft (22), the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; a first motor drive device (91) for exchanging electrical currents with the first motor (40) to vary the electromagnetic coupling of the first rotor with the second rotor; a second motor (40) having a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; and a second motor drive device (92) for exchanging electrical currents with the second Motor (40) for varying the electromagnetic coupling of the stator with the third rotor; characterized by a control device (90) for controlling the second motor drive device (92) when the drive shaft (22) rotates in a second direction opposite to the first direction to enable (S412) the second motor (40) to generate electrical energy, generate a first torque (Ta) acting in the first direction, and apply the first torque (Ta) to the drive shaft (22), wherein the control device (90) simultaneously controls the first motor drive device (91) to supply the generated electrical energy (Pa) to the first motor (30) to drive the first motor (30) and further enable the first motor (30) to generate a second torque (Tc) acting in the second direction and apply the second torque (Tc) to the drive shaft. 9. A power output device according to claim 8, wherein the first torque (Ta) generated by the second motor (40) and applied to the drive shaft (22) is greater than the second torque (Tc) generated by the first motor (30) and applied to the drive shaft (22). 10. A power output device according to claim 8 or 9, wherein the control device (90) comprises means for controlling (5404) the first motor drive device (91) to enable the first motor (30) to generate the second torque (Tc) which is not greater than a maximum static friction torque (Tefmax) of the output shaft (56) of the internal combustion engine, and second torque (Tc) to the drive shaft when the output shaft (56) of the internal combustion engine is at rest. 11. A power output device according to any one of the preceding claims, wherein the third rotor is attached to the second rotor connected to the drive shaft (22). 12. Power output device for outputting power to a drive shaft (22), the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30A) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; a first motor drive device (91) for exchanging electric currents with the first motor (30A) to vary the electromagnetic coupling of the first rotor with the second rotor; a second motor (40A) having a stator and a third rotor connected to the output shaft (56) of the internal combustion engine, the stator being electromagnetically coupled to the third rotor; and a second motor drive device (92) for exchanging electrical currents with the second motor (40A) to vary the electromagnetic coupling of the stator with the third rotor; a control device (90) for controlling the first motor drive device (91) for driving the first motor (30A) to cause the drive shaft (56) to rotate in a second direction which is opposite to the first direction; characterized in that the power output device further comprises a storage device (94) for storing electrical energy; and the control device has means for controlling the second motor drive device (92), a) to supply the electrical energy stored in the storage device (94) to the second motor (40A) and to enable the second motor (40) to hold the output shaft (56) of the internal combustion engine and to prevent the output shaft (56) of the internal combustion engine from rotating, and to control the first motor drive device (91) to supply the electrical energy stored in the storage device (94) to the first motor (30A); or c) to enable the second motor (40A) to generate electrical energy and to control the first motor drive device (91) to supply the generated electrical energy to the first motor (30A) and at least partially to the storage device (94) to be stored; or b) to enable the second motor (40A) to generate electrical energy and to control the first motor drive device (91) to supply the generated electrical energy and the electrical energy stored in the storage device (94) to the first motor (30A). 13. A power output device according to claim 12, wherein the third rotor is attached to the first rotor connected to the output shaft (56) of the internal combustion engine (50). 14. Power output device according to one of claims 1 to 7 or 11 to 13, wherein the power output device further comprises: an input device (84) for inputting a command regarding a direction of rotation of the drive shaft (22); and Means for enabling (S202, S302) the control device (90) to execute the control to rotate the drive shaft (22) in the second direction when the input device (84) inputs the command to set the second direction as the rotation direction. 15. A method for controlling a power output device for outputting power to a drive shaft (22), the method comprising the steps of: (a) providing an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; and a second motor (40) having a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; and (b) driving the second motor (40) to cause the drive shaft (22) to rotate in a second direction opposite to the first direction; characterized in that step (a) comprises the step of providing a storage device (94) for storing electrical energy; and step (b) comprises the steps: (b-1) setting a torque (Tc) generated by the first motor (30) to at most a predetermined level (Tmin); and (b-2) supplying the electrical energy stored in the storage device (94) to the second motor (40). 16. A method for controlling a power output device for outputting power to a drive shaft (22), the method comprising the step of: (a) providing an internal combustion engine (50) having an output shaft (56), the internal combustion engine the output shaft (56) rotates in a first direction; a motor (30) with a first rotor which is connected to the output shaft (56) of the internal combustion engine and a second rotor which is connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; and a storage device (94) for storing electrical energy; characterized by the step (b) supplying the electrical energy stored in the storage device (94) to the motor (30) to drive the motor (30) and further enabling the motor (30) to generate a torque (Tc) acting in a second direction opposite to the first direction and to apply the torque (Tc) to the drive shaft (22), thereby rotating the drive shaft (22) in the second direction. 17. The method of claim 16, wherein step (b) comprises the step of: Enabling the motor (30) to generate the torque (Tc) which is not greater than a maximum static friction torque (Tefmax) of the output shaft (56) of the internal combustion engine and to apply the torque (Tc) to the drive shaft (22) when the output shaft (56) of the internal combustion engine is in the idle state. 18. A method of controlling a power output device to output power to a drive shaft, the method comprising the step of: (a) providing an internal combustion engine (50) with an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) with a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; and a second motor (40) with a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; characterized by the steps (b) enabling the second motor (40) to generate electrical energy, to generate a first torque (Ta) acting in the first direction, and to apply the first torque (Ta) to the drive shaft (22) when the drive shaft (22) rotates in a second direction opposite to the first direction; and (c) supplying the generated electrical energy to the first motor (30) to drive the first motor (30) and further enabling the first motor (30) to generate a second torque (Tc) acting in the second direction and to apply the second torque (Tc) to the drive shaft (22). 19. The method of claim 18, wherein step (c) comprises the steps of: enabling the first motor (30) to generate the second torque (Tc) that is not greater than a maximum static friction torque (Tefmax) of the output shaft (56) of the internal combustion engine, and applying the second torque (Tc) to the drive shaft (22) when the output shaft (56) of the internal combustion engine is at rest. 20. A method for controlling a power output device for outputting power to a drive shaft (22), the method comprising the steps of: (a) providing an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30A) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which a transmission between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic Coupling of the first and second rotors power is transmitted; and a second motor (40A) having a stator and a third rotor connected to the output shaft (56) of the internal combustion engine, the stator being electromagnetically coupled to the third rotor; and (b) driving the first motor (30A) to cause the drive shaft (22) to rotate in a second direction opposite to the first direction; characterized in that step (a) comprises the step of providing a storage device (94) for storing electrical energy; and step (b) comprises the steps: (b-1) supplying the electrical energy stored in the storage device (94) to the second motor (40A) and enabling the second motor (40A) to hold the output shaft (56) of the internal combustion engine and prevent the output shaft (56) of the internal combustion engine from rotating; and (b-2) Supplying the electrical energy stored in the storage device (94) to the first motor (30A). 21. A power output device for outputting power to a drive shaft, the power output device comprising: an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; and a second motor (40) having a stator and a third rotor connected to the drive shaft (22), the stator being electromagnetically coupled to the third rotor; characterized by a first inverter (91) for exchanging electric currents with the first motor (30) for varying the electromagnetic coupling of the first rotor with the second rotor; a second inverter (92) for exchanging electric currents with the second motor (40) for varying the electromagnetic coupling of the stator with the third rotor; a control device (90) for controlling the second inverter (92) for driving the second motor (40) to cause the drive shaft (22) to rotate in a second direction opposite to the first direction; wherein the control device (90) comprises means for controlling the first inverter (91) to enable the first motor (30) to generate electrical energy, and for controlling the second inverter (92) to supply the generated electrical energy to the second motor (40). 22. The power output device of claim 21, wherein the power output device further comprises; a power generation amplifying device for increasing (S222) the rotational speed of the output shaft (56) of the internal combustion engine to amplify the electric power generated by the first motor (30). 23. A power output device according to claim 21 or 22, wherein the third rotor is attached to the second rotor connected to the drive shaft (22). 24. A method for controlling a power output device for outputting power to a drive shaft (22), the method comprising the steps of: (a) providing an internal combustion engine (50) having an output shaft (56), the internal combustion engine rotating the output shaft (56) in a first direction; a first motor (30) having a first rotor connected to the output shaft (56) of the internal combustion engine and a second rotor connected to the drive shaft (22), the second rotor being arranged coaxially with the first rotor and being rotatable relative thereto, the first and second rotors being electromagnetically coupled to one another, as a result of which power is transmitted between the output shaft (56) of the internal combustion engine and the drive shaft (22) via the electromagnetic coupling of the first and second rotors; and a second motor (40) having a stator and a third rotor connected to the drive shaft (22), wherein the stator is electromagnetically coupled to the third rotor; and (b) driving the second motor (40) to cause the drive shaft (22) to rotate in a second direction opposite to the first direction; characterized in that step (b) comprises the step of: (b-1) controlling a first inverter (91) to enable the first motor (30) to generate electrical energy; and (b-2) controlling a second inverter (92) to supply the generated electrical energy to the second motor (40).