JP2004306860A - Steering apparatus for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering apparatus for a vehicle facilitating the layout of components around a steering shaft. <P>SOLUTION: In a so-called "rack assist type" electric power steering apparatus 1, a plurality of electric motors 17, 18 are provided so as to face a rack 6, and to adjoin each other in the axial direction of the rack 6, and to concentrically surround the rack 6. The rotation of the output shafts of the respective electric motors 17, 18 is converted into the axial movement of the rack 6 via movement transformation mechanisms 19, 20, such as ball screw mechanisms, corresponding to the respective electric motors 17, 18 in order to assist the steering action. The so-called "rack assist type" electric power steering apparatus 1 is applicable to a so-called "steering by wire type" steering apparatus for a vehicle. In the so-called "steering by wire type" steering apparatus, a steering member 2 is not mechanically connected to a steering mechanism. The trouble that the layout of surrounding components becomes difficult when a plurality of electric motors are provided to drive the rack (steering rod), can be eliminated by the so-called "rack assist type" electric power steering apparatus 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a vehicle steering system including a plurality of motors for driving a steering shaft extending in the left-right direction of a vehicle.
[0002]
[Prior art]
2. Description of the Related Art In recent years, electric power steering devices have been widely used instead of hydraulic power steering devices. For example, in order to obtain a steering assist force comparable to a hydraulic actuator, a plurality of electric motors are provided in parallel with a rack shaft as a steering shaft, and the rack shaft is rotated from each electric motor via a steering gear on the steering shaft. 2. Description of the Related Art An electric power steering device that performs assist driving in a direction is provided (for example, Patent Document 1).
[0003]
Further, in a so-called steer-by-wire vehicle steering device in which a steering wheel as a steering means is arranged without being mechanically connected to a steering mechanism, a main steering motor on a rack shaft and a rack via a pinion are provided. There has been proposed a vehicle steering system in which a sub-steering motor that applies a steering force to a shaft is provided, and the vehicle is normally steered by a combined force of both motors, and when an abnormality occurs in any of the motors, the steering is performed only by a normal motor ( For example, Patent Document 2).
[0004]
[Patent Document 1]
JP-A-5-155343 [Patent Document 2]
Japanese Patent Application Laid-Open No. Hei 10-218000
[Problems to be solved by the invention]
However, when a plurality of motors are used, for example, as in Patent Literature 1, all of these motors require a large space on the side of the rack shaft, or, as in Patent Literature 2, They overhanged in a direction substantially perpendicular to the axis. For this reason, there has been a problem that the layout of components around the rack axis becomes difficult.
[0006]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicle steering device in which a layout of components around a steering axis is easy.
[0007]
Means for Solving the Problems and Effects of the Invention
In order to achieve the above object, a first invention is a vehicle steering system including a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle, wherein the plurality of motors are opposed in the axial direction of the steering shaft. And concentrically surrounds each of the steering shafts. According to the present invention, the plurality of motors are compactly laid out around the steering shaft, and there is no concern of interference with surrounding components.
[0008]
According to a second aspect, in the first aspect, a plurality of motion conversion mechanisms for converting the rotation of the rotor of each motor into the axial movement of the steering shaft are provided, and each motion conversion mechanism is integrated with the rotor of the corresponding motor. Each of the rotary cylinders includes a rotatable rotary cylinder that surrounds the periphery of the steering shaft, and an elastic member is interposed between adjacent rotary cylinders. According to the present invention, the adjacent rotary cylinders are pre-pressed in opposite directions to each other, so that the play in the axial direction can be eliminated, so that the response of the steering shaft drive by the motor is improved.
[0009]
According to a third invention, in the first invention, the plurality of motors include one of a common stator and a common rotor. According to the present invention, the manufacturing cost can be significantly reduced by using a common member.
A fourth invention is characterized in that, in the first, second or third invention, the plurality of motors include a common rotor rotation angle detection means, and are driven based on a detection signal of the rotor rotation angle detection means. Is what you do. In the present invention, the manufacturing cost can be significantly reduced by using a rotor rotation angle detecting means such as a resolver in common for a plurality of motors.
[0010]
In a fifth aspect based on the first, second, or third aspect, each of the plurality of motors includes a rotor rotation angle detection unit, and based on a comparison between detection signals of the plurality of motors, the rotation of the rotor is determined. It is characterized by further comprising an angle detecting means or a means for judging abnormality of the motor. According to the present invention, the following operation and effect can be obtained. That is, if an abnormality is determined based on the current value of the motor, the motor load has already increased at the time when the abnormality is determined. On the other hand, in the present invention, the abnormality is determined based on the detection signal of the rotor rotation angle detecting means for controlling the motor, so that the abnormality can be quickly determined, for example, at a stage where the motor load does not increase so much. .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering system according to a first embodiment of the present invention. With reference to FIG. 1, in the present embodiment, description will be made on the assumption that the vehicle steering device is an electric power steering device (EPS) 1, but the present invention is not limited to this, and for example, a steering wheel or the like is used. It can also be applied to a so-called steer-by-wire (SBW) system in which the mechanical connection between the steering member 2 and the steering mechanism is eliminated.
[0012]
The electric power steering device 1 includes a steering shaft 3 connected to a steering member 2, a pinion 4 connected to the steering shaft 3 via an intermediate shaft 100, and a rack 5 that meshes with the pinion 4. A rack shaft 6 as a steering shaft extending in the left-right direction.
Tie rods 7 are respectively connected to both ends of the rack shaft 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, the rotation is converted by the pinion 4 and the rack 5 into a linear motion of the rack shaft 6 along the left-right direction of the vehicle. Thereby, steering of the wheel 8 is achieved.
[0013]
The steering shaft 3 is divided into an input shaft 9 connected to the steering member 2 and an output shaft 10 connected to the pinion 4. These input and output shafts 9 and 10 are mutually connected on the same axis via a torsion bar 11. Are linked.
A torque sensor 12 for detecting a steering torque based on the relative rotational displacement between the input and output shafts 9 and 10 via the torsion bar 11 is provided, and a torque detection result of the torque sensor 12 is transmitted to a control unit (electronic control unit: ECU). ) 13. The control unit 13 controls a supply current to a plurality of electric motors 17 and 18 for assisting steering via respective drivers 15 and 16 based on a torque detection result, a vehicle speed detection result from a vehicle speed sensor 14, and the like. . The control unit 13 includes a CPU 13a, a ROM 13b storing a control program and the like, a RAM 13c used as a work area, and the like.
[0014]
The output rotation of each of the electric motors 17 and 18 is converted into the axial movement of the rack shaft 6 via the corresponding motion conversion mechanism 19 or 20 such as a ball screw mechanism, and the steering is assisted. The electric power steering device 1 is a so-called rack assist type.
The electric motors 17 and 18 are, for example, brushless motors, are arranged adjacent to each other in the axial direction of the rack shaft 6 and concentrically surround the rack shaft 6.
[0015]
The electric motors 17 and 18 are rotatably supported via cylindrical stators 22 and 23 fixed to the inner periphery of the rack housing 21 and bearings 24 and 25 corresponding to the rack housing 21, respectively. And rotors 26 and 27 inserted into the insides 22 and 23, respectively. Although not shown, a coil composed of a plurality of excitation phases that winds a part of the stators 22 and 23 is provided, and the outer circumferences of the rotors 26 and 27 are opposed to the stators 22 and 23. , A cylindrical driving magnet is provided. The driving magnet is magnetized so as to alternately form N and S poles in the circumferential direction.
[0016]
The electric motors 17 and 18 are provided with resolvers 41 and 42 for detecting the rotational positions (rotation angles) of the rotors 26 and 27, respectively. Each of the resolvers 41 and 42 includes a stator 43 fixed to the rack housing 21 and a rotor 44 that rotates integrally with the corresponding rotors 26 and 27. Since a predetermined voltage is induced in the stator section 43 in accordance with the rotational position of the rotor section 44, the rotational position (phase) of the rotor section 44, that is, the rotors 26 and 27 can be determined by measuring this voltage. .
[0017]
Based on the rotational position (phase) of each of the rotors 26 and 27 output from each of the resolvers 41 and 42, the control unit 13 controls each of the coils divided in the rotational direction of the stators 22 and 23 of the corresponding electric motors 17 and 18. A current is sequentially supplied to the excitation phase (not shown), and as a result, the electric motors 17 and 18 composed of brushless motors are driven and controlled to generate a predetermined rotation output.
As the motion converting mechanisms 19 and 20, a ball screw mechanism or a bearing screw mechanism (for example, Japanese Patent Application Laid-Open No. 2000-46136) can be used to convert rotary motion into linear motion. In the present embodiment, description will be made in accordance with an example in which a ball screw mechanism is used. The motion conversion mechanisms 19 and 20 have ball nuts 28 and 29 as rotating cylinders that surround the rack shaft 6. The ball nuts 28, 29 are screwed into ball screw grooves 6 a formed in the middle of the rack shaft 6 via balls 30, thereby constituting motion conversion mechanisms 19, 20.
[0018]
Corresponding ball nuts 28 and 29 are press-fitted and fixed to opposed ends of the rotors 26 and 27 of the electric motors 17 and 18, and opposite ends of the rotors 26 and 27 are racked via corresponding bearings 24 and 25. The housing 21 is rotatably supported.
The bearings 24 and 25 contact the positioning steps on the outer peripheral surfaces of the corresponding rotors 26 and 27, thereby restricting the corresponding rotors 26 and 27 from moving away from each other.
[0019]
On the other hand, an elastic member 31 such as a compression coil spring or an annular rubber is interposed between the opposing ends of the ball nuts 28 and 29, and urges the ball nuts 28 and 29 in a direction away from each other. As a result, the ball nuts 28 and 29 are pre-pressed in opposite directions so that there is no backlash in the axial direction. As a result, the responsiveness of driving the rack shaft 6 by the electric motors 17 and 18 increases.
The control unit 13 determines the control amount of the electric motors 17 and 18 based on the above-described torque detection result, vehicle speed detection result, and the like, and adjusts the electric motors 17 and 18 to the rotation angles detected by the corresponding resolvers 41 and 42. Drive control is performed so as to obtain a predetermined output based on the output.
[0020]
The driving forces (rotational forces of the output shafts) of the electric motors 17 and 18 are converted into linear motions in the axial direction (vehicle width direction) of the rack shaft 6 by the corresponding motion conversion mechanisms 19 and 20, whereby the wheels are driven. The required steering assist force for turning 8 is obtained.
According to the present embodiment, by using a plurality of motors 17 and 18 concentrically arranged on the rack shaft 6 so as to be opposed to each other in the axial direction of the rack shaft 6, the power generation unit is provided around the rack shaft 6. Since the layout can be made compact, there is no fear of interference with surrounding parts.
[0021]
In addition, the adjacent ball nuts 28 and 29 are pre-pressed in opposite directions by the elastic member 31 interposed therebetween, so that play in the axial direction can be eliminated. As a result, the response of steering assist by the electric motors 17 and 18 is improved. Become.
Next, FIGS. 2A and 2B are schematic cross-sectional views of main parts of a vehicle steering system according to another embodiment of the present invention. In the embodiment of FIG. 2A, the plurality of electric motors 17 and 18 include a rotor unit 32 as a common rotor. The rotor unit 32 includes rotor portions 32a and 32b corresponding to the electric motors 17 and 18, respectively, which are integrally rotatably connected via a rotary cylinder 32c such as a ball nut.
[0022]
On the other hand, in the embodiment of FIG. 2B, the plurality of electric motors 17 and 18 have a common long stator 33. 2A and 2B, the same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. According to the embodiment shown in FIGS. 2A and 2B, the manufacturing cost can be significantly reduced due to the common use of the members. Further, it is possible to contribute to downsizing of the vehicle steering system.
Next, FIG. 3 shows still another embodiment of the present invention. In the embodiment of FIG. 3, a resolver 35 is used as a common rotor rotation angle detecting means in the plurality of electric motors 17 and 18. In the case where the electric motors 17 and 18 individually have rotors (see FIG. 1), although not shown in FIG. 3, the rotor portion of the resolver 35 is integrated with the rotor of one of the electric motors 17 and 18. It should just be attached so that it may rotate. When a common rotor unit 32 is used between the electric motors 17 and 18 (see FIG. 2A), the rotor of the resolver 35 may be attached to the rotor unit 32.
[0023]
In the present embodiment, by using the resolver 35 as the rotor rotation angle detecting means common to the plurality of electric motors 17 and 18, the manufacturing cost can be reduced and the steering device for the vehicle can be reduced in size. be able to. Further, since the detection signal from the common resolver 35 may be processed, the control load on the control unit 13 can be reduced.
Next, FIG. 4 shows still another embodiment of the present invention. In the embodiment of FIG. 4, a plurality of control units (ECUs) 131 and 132 are provided as a measure against failure. As in the embodiment of FIG. 3, a common resolver 35 is used by the plurality of electric motors 17 and 18, and a detection signal from the resolver 35 is given to each of the control units 131 and 132. Usually, the drive control of the plurality of electric motors 17 and 18 is performed using each one of the control units 131 through the separate control lines a and b. The other control unit 132 drives and controls the electric motors 17 and 18 via the respective control lines c and d. In the present embodiment, since a control system for a failure is provided in a separate system, reliability is high.
[0024]
Next, FIG. 5 shows still another embodiment of the present invention. In the embodiment of FIG. 5, output signals are provided to a plurality of control units 131 and 132 from resolvers 41 and 42 provided in each of the electric motors 17 and 18 via two lines e and f. Normally, one control unit 131 drives and controls a plurality of electric motors 17 and 18 via respective control lines a and b using a detection signal of one resolver 41.
[0025]
When the one resolver 41 breaks down, the one control unit 131 drives and controls the plurality of electric motors 17 and 18 through the respective control lines a and b using the other resolver 42. Further, when one of the control units 131 fails, the other control unit 132 is used as in the embodiment of FIG. In the embodiment of FIG. 5, by providing the plurality of resolvers 41 and 42 and the plurality of control units 131 and 132, good control can be performed even in the case of a failure.
[0026]
Next, FIG. 6 shows still another embodiment of the present invention. The embodiment of FIG. 6 differs from the embodiment of FIG. 5 in that a plurality of control units 131 and 132 monitor each other via a signal transmission line g and compare signals from the resolvers 41 and 42. The failure of the resolvers 41 and 42 or the electric motors 17 and 18 is determined based on the determination, and a warning is given by the notification member 50. As the notification member 50, a lamp, a liquid crystal display, a buzzer, or the like can be used.
[0027]
Specifically, as shown in the flowchart of FIG. 7, detection signals m1 and m2 from a plurality of resolvers 41 and 42 are input (step S1), and the difference Δm (Δm = m1−m2) is calculated (step S1). Step S2), it is monitored whether the obtained difference Δm exceeds the first threshold value K1 (Δm> K1) (step S3).
If the difference Δm exceeds the first threshold value K1 (YES in step S3), a second threshold value K2 larger than the first threshold value K1 is adopted as a new threshold value, and the difference Δm (Δm> K2) is determined (step S4).
[0028]
When the difference Δm exceeds the second threshold value K2 (Δm> K2) (YES in step S4), it is determined that one of the electric motors 17 or 18 is stopped, and for example, by sound or display, etc. The driver is notified that an abnormality has occurred, and a warning is given (step S5). The change to the second threshold value K2 is performed while the vehicle is running. The value of the first threshold value K1 is set to a value slightly larger than the phase difference in consideration of the mechanical phase difference (play) in the rotation direction existing between the plurality of electric motors 17 and 18.
[0029]
In the embodiment shown in FIGS. 6 and 7, the abnormality is determined based on the detection signals of the resolvers 41 and 42 as the rotor rotation angle detecting means for controlling the motor. Abnormality can be determined at the same time, and quick failure response is possible.
On the other hand, in the conventional case where the abnormality is determined based on the current value of the motor, the motor load has already increased at the time when the abnormality is determined, and there is a possibility that the failure response may be delayed.
[0030]
The reason why the threshold value is set to two levels as in the above-mentioned flowchart is to distinguish and cope with a case in which only the resolver serving as the detecting means is abnormal and a case in which the electric motor itself is abnormal. That is, the output abnormality of the resolver 41 or 42 is mainly determined by comparing the difference Δm with the smaller first threshold value K1 (step S3), and the difference Δm is compared with the larger second threshold value K2 (step S3). In step S4), an abnormality such as disconnection of the electric motor 17 or 18 is mainly determined.
[0031]
Further, in the embodiment of FIG. 7, the control unit that performs the abnormality determination may be a main control unit (ECU) that controls the entire vehicle. In this case, the detection signals of the resolvers 41 and 42 are provided to the main control unit via a communication means such as a CAN (Controller Area Network), and the main control unit performs an abnormality determination and activates the notification member. You may do it.
It should be noted that the present invention is not limited to the above embodiments, and the present invention can be applied to a so-called steer-by-wire vehicle steering system. Various changes can be made.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device as a vehicle steering device according to an embodiment of the present invention.
FIGS. 2A and 2B are schematic cross-sectional views of main parts of a vehicle steering system according to another embodiment of the present invention.
FIG. 3 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 4 is a schematic view of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 5 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 6 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 7 is a flowchart showing a flow of determining a failure in the embodiment of FIG. 6;
[Explanation of symbols]
1 electric power steering system (vehicle steering system)
2 Steering member 6 Rack shaft (steering shaft)
13 Control unit (ECU)
15, 16 Driver 17, 18 Electric motor 19, 20 Motion conversion mechanism 21 Rack housing 22, 23 Stator 24, 25 Bearing 26, 27 Rotor 28, 29 Ball nut (rotary cylinder)
30 ball 31 elastic member 32 rotor unit (common rotor)
33 (common) stator 35 (common) resolver (rotor rotation angle detecting means)
41, 42 resolver (rotor rotation angle detecting means)
131, 132 control unit (ECU; means for determining abnormality)

Claims (5)

In a vehicle steering system including a plurality of motors for driving a steering shaft extending in a left-right direction of a vehicle, the plurality of motors may face each other in the axial direction of the steering shaft and concentrically surround the steering shaft. A steering device for a vehicle. 2. The motor control system according to claim 1, further comprising a plurality of motion converting mechanisms for converting the rotation of the rotor of each motor into the axial movement of the steering shaft, wherein each of the motion converting mechanisms is integrally rotatable with the corresponding motor rotor. A steering apparatus for a vehicle, comprising: a rotary cylinder surrounding each of the rotary cylinders, wherein an elastic member is interposed between adjacent rotary cylinders. 2. The vehicle steering system according to claim 1, wherein the plurality of motors include one of a common stator and a common rotor. 4. The vehicle steering system according to claim 1, wherein the plurality of motors include a common rotor rotation angle detection unit, and are driven based on a detection signal of the rotor rotation angle detection unit. 4. The motor according to claim 1, 2 or 3, wherein each of the plurality of motors includes a rotor rotation angle detection unit, and based on a comparison between detection signals of the rotor rotation angle detection units of the plurality of motors, an abnormality in the rotor rotation angle detection unit or the motor. A vehicle steering system, further comprising: means for determining a vehicle steering angle.

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