WO2015087516A2

WO2015087516A2 - Vehicle control apparatus

Info

Publication number: WO2015087516A2
Application number: PCT/JP2014/006048
Authority: WO
Inventors: Michihiro Miyashita
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-12-13
Filing date: 2014-12-03
Publication date: 2015-06-18
Also published as: WO2015087516A3; JP5880533B2; JP2015116085A

Abstract

A problem to be solved is that the driver is likely to have a feeling of strangeness in response to deceleration accompanied with power generation by an alternator. A target value of deceleration by the alternator during an inertial drive of a vehicle is determined, based on the speed of the vehicle (step S100). The deceleration by the alternator is then made closer to the determined target value (steps S200 to S400).

Description

VEHICLE CONTROL APPARATUS

The present invention relates to control of a vehicle.

An automobile is generally equipped with an alternator configured to generate electric power. The power generation by the alternator is performed by taking advantage of an engine torque or the inertia of the automobile. In order to improve the fuel consumption, it is effective to adequately perform power generation using the inertia (kinetic energy) of the automobile and regenerate the inertia of the vehicle as electric power. The power generation using the inertia decelerates the vehicle.

With regard to power generation using the inertia of the automobile, there is a known technique of controlling the alternator such as to generate a negative torque corresponding to a difference between current deceleration and a target deceleration. The target deceleration is calculated from, for example, the current deceleration and the throttle opening (for example, Patent Literature 1).

JP 2010-288343A

Summary

A problem of the above prior art technique is that the driver has a feeling of strangeness during an inertial drive. The inertial drive means a drive in the state that neither an accelerator pedal nor a brake pedal is depressed. The excessively large deceleration during the inertial drive may give the driver a feeling of strangeness and cause the driver to depress the accelerator pedal. Depression of the accelerator pedal reduces the fuel consumption, compared with the inertial drive. The excessively small deceleration during the inertial drive, on the other hand, gives the driver a feeling of idle running.

The invention may be implemented by any of the following aspects, in order to solve the above problem.

(1) According to one aspect of the invention, there is provided a vehicle control apparatus. This vehicle control apparatus comprises: a regenerative device configured to regenerate energy involved in a drive of a vehicle as electric power; a target deceleration determiner configured to determine a target deceleration which is a target value of deceleration during an inertial drive of the vehicle, according to vehicle speed which is speed of the vehicle; and a deceleration controller configured to control the regenerative device during the inertial drive of the vehicle and thereby perform deceleration control to make the deceleration closer to the determined target value. This aspect relieves the feeling of strangeness caused by deceleration during the inertial drive. This feeling of strangeness is expected to change according to the vehicle speed. Accordingly controlling the deceleration based on the vehicle speed can relive the feeling of strangeness.

(2) In the above aspect, it may be determined that the vehicle has an inertial drive in a state that neither of an accelerator pedal and a brake pedal provided on the vehicle is depressed. This aspect enables an inertial drive to be readily identified.

(3) In the above aspect, the target deceleration determiner may refer to a predefined relationship between allowable deceleration and the vehicle speed to obtain the allowable deceleration according to the vehicle speed and may determine the obtained allowable deceleration as the target deceleration. This aspect determines the target deceleration such as to relieve the feeling of strangeness without requiring calculation each time. The allowable deceleration denotes a value of deceleration specified in a range that does not give a feeling of strangeness to the driver.

(4) In the above aspect, the regenerative device may be an alternator and may be coupled with a driveshaft of an engine mounted on the vehicle. This aspect allows for the above control using the existing hardware configuration.

(5) In the above aspect, the deceleration controller may comprise: a target negative torque determiner configured to determine a target value of a negative torque generated by regeneration of the alternator by taking into account at least one of a rotation speed of the engine mounted on the vehicle, weight of the vehicle and the vehicle speed; and an alternator controller configured to make the negative torque closer to the determined target value, as control of the regenerative device. This aspect enables the deceleration control to be adequately performed using the alternator.

(6) In the above aspect, the alternator controller may control exciting current flowing through the alternator based on the target value of the negative torque, so as to make the negative torque closer to the determined target value. This aspect enables the negative torque of the alternator to be controlled adequately according to the characteristic of the alternator.

(7) In the above aspect, the alternator controller may set an upper limit value of the exciting current, as control of the exciting current. This aspect ensures the control suitable for the characteristic of the alternator, while avoiding an excessively large deceleration that gives a feeling of strangeness.

(8) In the above aspect, the target deceleration determiner may determine the target value to monotonically increase with an increase of the vehicle speed in at least part of a range of the vehicle speed. This aspect allows for more adequate braking of the vehicle by speed reduction at the greater deceleration in response to the high speed, in at least part of the speed range.

(9) In the above aspect, the deceleration controller may perform the deceleration control such as to increase an absolute value for a rate of change of the deceleration with respect to time in a case of decreasing the deceleration, compared with an absolute value in a case of increasing the deceleration, in at least part of the range of the vehicle speed. This aspect facilitates the approach of the deceleration to the target value in the case of decreasing the deceleration. The target value of the deceleration monotonically increases with an increase of the speed, in at least part of the speed range. Increasing the absolute value for the rate of change of the deceleration in the case of decreasing the deceleration compared with the absolute value in the case of increasing the deceleration facilitates the approach to the deceleration to the target value.

(10) In the above aspect, the target deceleration determiner may determine the target value such that a rate of change of the deceleration with respect to the vehicle speed monotonically decreases with an increase of the vehicle speed in at least part of a range of the vehicle speed. This aspect further relieves the feeling of strangeness. Monotonically decreasing the rate of change of the target value with an increase of the speed prevents an abrupt change of the target value and thereby achieves the above advantageous effect.

(11) In the above aspect, the deceleration controller may determine a rate of change of the deceleration with respect to time, according to the vehicle speed and performs the deceleration control based on the determined rate of change. This aspect facilitates the deceleration control to further relieve the feeling of strangeness.

The invention may be implemented by any of various aspects other than those described above, for example, a deceleration control method, a program for implementing this control method and a non-transitory storage medium in which this program is stored.

Fig. 1 is a block diagram illustrating components involved in a deceleration control process; Fig. 2 is a flowchart showing the deceleration control process; Fig. 3 is a graph showing relationships of overall allowable deceleration and allowable deceleration to vehicle speed; Fig. 4 is a graph showing relationship of actual deceleration to time in an accelerator-off state; Fig. 5 is a graph showing relationship of actual deceleration to time in a brake-off state; Fig. 6 is a graph showing relationships of allowable deceleration to vehicle speed (Modifications 1 and 2); Fig. 7 is a graph showing relationship between rate of change of actual deceleration with respect to vehicle speed and vehicle speed (Modification 3); Fig. 8 is a graph showing relationship between rate of change of actual deceleration with respect to vehicle speed and vehicle speed (Modification 4); and Fig. 9 is a graph showing relationship between rate of change of actual deceleration with respect to vehicle speed and vehicle speed (Modification 5).

Fig. 1 is a block diagram illustrating components involved in a deceleration control process described later among various components of a four-wheel vehicle. Fig. 1 illustrates an engine ECU 30, an alternator 40, a belt 45, a battery 50, an engine 60, a transmission 70, a driveshaft 75, drive wheels 80 and a group of sensors 90. The group of sensors 90 includes an accelerator stroke sensor 91, a brake stroke sensor 92, a throttle sensor 93, a wheel speed sensor 94, a vehicle speed sensor 95 and a battery sensor 96.

The engine ECU 30 outputs a control signal to the engine 60, for example, based on a stroke amount (depression amount) of an accelerator pedal (not shown). The engine 60 is a known internal combustion engine and generates a torque in response to the control signal input from the engine ECU 30. The torque generated by the engine 60 is transmitted through the transmission 70 and the driveshaft 75 to the drive wheels 80. The engine ECU 30 obtains values representing the rotation speed and the torque of the engine 60 from the engine 60.

The torque generated by the engine 60 rotates a rotor (not shown) of the alternator 40 via the belt 45. The alternator 40 generates electric power by the rotation of its rotor. The rotor of the alternator 40 generates a negative torque during power generation. The power generation by the alternator 40 accordingly applies a load to the engine 60 and decreases the rotation speed of the drive wheels 80 via the transmission 70, thus reducing the vehicle speed. The electric power generated by the alternator 40 is accumulated in the battery 50. The electric power accumulated in the battery 50 is supplied to electronic devices mounted on the vehicle.

The power generation by the alternator 40 is performed under control of the engine ECU 30. More specifically, the engine ECU 30 specifies a power generation voltage and a limit value of exciting current based on, for example, the rotation speed of the engine 60 and the state of charge of the battery 50 and provides the specified values to the alternator 40. The alternator 40 generates electric power at the specified power generation voltage. During such power generation, the alternator 40 is under control such that the actual flow of exciting current does not exceed the specified limit value. This control is performed by a control circuit incorporated in the alternator 40. The alternator 40 inputs the actual values of exciting current and power generation voltage to the engine ECU 30.

The accelerator stroke sensor 91 is configured to measure the stroke amount of the accelerator pedal. The brake stroke sensor 92 is configured to measure the stroke amount of a brake pedal (not shown). The throttle sensor 93 is configured to measure the opening position of a valve (not shown) for adjusting the air intake into the engine 60. The wheel speed sensor 94 is configured to obtain a pulse signal representing a rotation cycle of the drive wheels 80 and measure the rotation speed of the drive wheel 80.

The vehicle speed sensor 95 is configured to measure the driving speed of the vehicle based on, for example, the measurement result by the wheel speed sensor 94 and the position information by GPS. The battery sensor 96 is configured to estimate the state of charge of the battery 50, based on the value of a terminal voltage obtained from the battery 50. The measurement results of the group of sensors 90 described above are input into the engine ECU 30.

Fig. 2 is a flowchart showing the deceleration control process. The deceleration control process is performed by the engine ECU 30 and is triggered when both the stroke amounts of the accelerator pedal and the brake pedal become zero (shift to an inertial drive). When detecting that at least one of the stroke amounts of the accelerator pedal and the brake pedal becomes greater than zero after a start of the deceleration control process, the engine ECU 30 immediately terminates the deceleration control process and shifts to ordinary control.

The process first determines a target deceleration (step S100). The target deceleration denotes a target value of deceleration caused by a negative torque of the alternator 40. The deceleration is a value (m/s²) obtained by differentiation of the vehicle speed and takes a positive value in the state of speed reduction. The target deceleration is determined in advance relative to the vehicle speed, and its relationship is stored in the engine ECU 30.

Fig. 3 is a graph showing relationships of overall allowable deceleration and allowable deceleration to vehicle speed. The overall allowable deceleration denotes a maximum value of deceleration which does not give a feeling of strangeness to the driver and is determined by a sensory test. The driver has a feeling of strangeness when the deceleration is too large after a shift to an inertial drive. According to this embodiment, the overall allowable deceleration is determined as a function of vehicle speed, based on the finding that the overall allowable deceleration increases with an increase in vehicle speed.

As shown in Fig. 3, a curve T indicating the overall allowable deceleration of the embodiment changes logarithmically. In other words, the curve T is a curve that monotonically increases and is convex upward. The rate of change of the curve T decreases with an increase in vehicle speed.

A curve A in Fig. 3 indicates the allowable deceleration by the alternator 40. The allowable deceleration denotes a maximum value that can be allocated to the deceleration by the alternator 40. The deceleration control process is performed during an inertial drive as described above. During the inertial drive, it is preferable to maximize the negative torque of the alternator 40 and thereby increase the amount of power generation. The deceleration during the inertial drive is, however, not limitedly caused by the negative torque by the alternator 40 but is also caused by a negative torque of the engine 60 and a surface resistance of the drive wheels 80. A value obtained by subtracting the decelerations caused by factors other than the alternator 40 from the overall allowable deceleration is accordingly determined as the allowable deceleration by the alternator 40.

As shown in Fig. 3, when the vehicle speed is equal to or lower than Vm, the allowable deceleration is set to zero. This is because generation of a negative torque by the alternator 40 at the vehicle speed of or below Vm is likely to cause an engine stall.

The target deceleration set at step S100 is a value of allowable deceleration determined from the current vehicle speed and the relationship shown in Fig. 3.

The process subsequently determines a target negative torque (step S200). The target negative torque denotes a value of negative torque by the alternator 40 to achieve the target deceleration. A deceleration D by the alternator 40 is expressed by Equation (1) given below:
D= (Ta * NE) / (W * V) (1)
wherein Ta represents a negative torque (Nm) by the alternator 40, NE represents an engine rotation speed (r/s), W represents a vehicle weight (kg) and V represents a vehicle speed (m/s). The negative torque by the alternator 40 is accordingly expressed by Equation (2) given below:
Ta= (D * W * V) / NE (2)

The target negative torque Ta is calculated by substituting a value of the vehicle speed obtained from the vehicle speed sensor 95 into the vehicle speed V of Equation (2), the target deceleration into the deceleration D, a fixed value into the vehicle weight W and a value obtained from the engine 60 into the engine rotation speed Ne. The fixed value of the vehicle weight W is stored in the engine ECU 30.

The process subsequently determines a target limit value of exciting current (step S300). The target limit value of exciting current is a value used at step S400 described below. A concrete procedure of determination inputs the target negative torque calculated at step S200, the specified power generation voltage and the current engine rotation speed into a map stored in advance.

The process then makes a value actually specified as the limit value of exciting current (hereinafter referred to as "specified value") closer to the target limit value determined at step S300 (step S400). The processing of step S400 is performed over a predetermined time period, in order to ensure a smooth change of the specified value from the current value.

Fig. 4 is a graph showing relationship of actual deceleration by the alternator 40 (hereinafter referred to as "actual deceleration") to time. This graph shows the relationship when the deceleration control process is triggered by a decrease in stroke amount of the accelerator pedal to zero (hereinafter referred to as "accelerator-off state").

A time Ta1 shows the time when the processing of step S400 is started. A target deceleration Da1 is a target deceleration at the time Ta1. In the accelerator-off state, an actual deceleration Dta1 at the time Ta1 is generally smaller than the target deceleration Da1 as shown in Fig. 4. This is, however, not the essential relationship in the accelerator-off state. This is because the target deceleration of the embodiment is not determined in response to a pedal operation but is determined according to the vehicle speed. The same applies to the brake operation described below.

In the relationship illustrated in Fig. 4, the specified value is increased at step S400 to make the actual deceleration closer to the target deceleration. A concrete procedure increases the specified value over a predetermined time period, in order to prevent an abrupt increase of the actual deceleration. This results in linearly increasing the actual deceleration at a specified rate of change as shown in Fig. 4.

The process subsequently determines whether the actual deceleration converges to a target (step S500). More specifically it is determined whether the actual deceleration is within a predefined error range (for example, minus 10 percent to plus 10 percent) relative to the target deceleration. When the actual deceleration converges to the target (step S500: YES), the deceleration control process is terminated. When the actual deceleration has not yet converged to the target (step S500: NO), on the other hand, the processing of steps S100 to S400 is repeated.

A time Ta2 in Fig. 4 shows the time when step S400 is started in the second cycle. An actual deceleration Dta2 at the time Ta2 is increased by step S400 in the previous cycle to be greater than the actual deceleration Dta1 but is still smaller than a target deceleration Da2 at the time Ta2. The specified value is thus further increased at step S400, in order to further increase the actual deceleration. A target deceleration Da2 becomes smaller than the target deceleration Da1 based on the relationship shown in Fig. 3, since the vehicle speed is reduced in the time period between the time Ta1 and the time Ta2.

The actual deceleration also has an increase at a time Ta3, like at the time Ta2. The actual deceleration becomes substantially equal to a target deceleration Da4 at a time Ta4 and thereby converges to the target. Accordingly, the engine ECU 30 terminates the deceleration control process and then shifts to ordinary control to control the alternator 40.

Fig. 5 is a graph showing relationship of actual deceleration to time when the deceleration control process is triggered by a decrease in stroke amount of the brake pedal to zero (hereinafter referred to as "brake-off state").

A time Tb1 shows the time when step S400 is performed in the first cycle. An actual deceleration Dtb1 at the time Tb1 is greater than a target deceleration Db1. Accordingly the engine ECU 30 smoothly decreases the specified value to decrease the actual deceleration.

The control of decreasing the actual deceleration decreases the target deceleration with elapse of time, while decreasing the actual deceleration with elapse of time. In order to converge the actual deceleration to the target deceleration, the actual deceleration is decreased at a slope of a greater absolute value than the slope at which the actual deceleration is increased.

As shown in Fig. 5, the actual deceleration also has a decrease at a time Tb2 and at a time Tb3, like at the time Tb1 and converges to the target at a time Tb4. The engine ECU 30 shifts to the ordinary control after the time Tb4.

The embodiment described above relieves the driver's feeling of strangeness, since the control of this embodiment changes the target deceleration according to the vehicle speed and smoothly makes the actual deceleration closer to the target deceleration. This technique of control avoids, for example, an excessively large deceleration in the accelerator-off state or an excessively small deceleration in the brake-off state. Additionally, this suppresses the driver from having a feeling of strangeness in response to an excessively large actual deceleration with elapse of time after a start of an inertial drive.

Furthermore, the target deceleration is determined logarithmically relative to the vehicle speed. This further relieves the driver's feeling of strangeness. In general, the human being perceives a physical quantity logarithmically and accordingly has no significant feeling of strangeness in response to a logarithmic change.

The invention is not limited to any of the embodiments, the examples and the modifications described herein but may be implemented by a diversity of other configurations without departing from the scope of the invention. For example, the technical features of the embodiments, examples or modifications corresponding to the technical features of the respective aspects described in Summary may be replaced or combined appropriately, in order to solve part or all of the problems described above or in order to achieve part or all of the advantageous effects described above. Any of the technical features may be omitted appropriately unless the technical feature is described as essential herein. Some examples of possible modification are given below.

The allowable deceleration by the alternator may be specified in any of various manners. For example, the allowable deceleration by the alternator may be specified as a function of vehicle speed which is different from the function of the embodiment. Fig. 6 is a graph showing the relationship between the allowable deceleration and the vehicle speed (hereinafter referred to as "deceleration-vehicle speed relationship") according to one modification. As shown in Fig. 6, Modification 1 has the deceleration-vehicle speed relationship specified by a straight line. Modification 2 has the deceleration-vehicle speed relationship specified by a monotonically increasing cubic function. In another examples, the deceleration-vehicle speed relationship may be specified by a curve that does not increase monotonically (for example, a monotonically decreasing curve), by a curve that is convex downward or by any other suitable curve.

The rate of change of the actual deceleration (hereinafter simply referred to as "rate of change") with respect to the vehicle speed may be different from that of the embodiment and may be not a fixed value. Figs. 7, 8 and 9 are graphs illustrating examples of the relationship between the rate of change and the vehicle speed. Fig. 7 shows Modification 3, Fig. 8 shows Modification 4 and Fig. 9 shows Modification 5. The dimension of the rate of change is (m/s²) / (m/s)= s^-1. As shown in Figs. 7, 8 and 9, the embodiment has positive and negative fixed values as the rate of change as described above.

As shown in Figs. 7, 8 and 9,

Modifications

3, 4 and 5 have the following common characteristics with regard to the rate of change: the rate of change is equal to zero at the vehicle speed equal to the speed Vm; the positive rate of change has a monotonic increase with an increase in vehicle speed; and the negative rate of change has a monotonic decrease with an increase in vehicle speed. Modification 3 has the rate of change that is varied linearly. Modification 4 has the rate of change that is varied by a cubic curve. Modification 5 has the rate of change that is varied logarithmically.

The rate of change may be varied in any other way relative to the vehicle speed. The rate of change at the vehicle speed of Vm may not be equal to zero, and the absolute value of the rate of change may be decreased with an increase in vehicle speed.

The rate of change may be specified by a function of any suitable factor other than the vehicle speed. For example, the rate of change may be specified by a function of elapse of time since the start of the deceleration control process. The rate of change may be determined by PID control.
The deceleration control process may be continued even after convergence to the target. For example, the deceleration control process may be continued until the end of an inertial drive.
A regenerative device is not limited to the alternator but may be, for example, an assist motor. The assist motor means a motor that is capable of generating a torque to be applied to the drive wheels and the auxiliary machinery (for example, compressor).
The target deceleration may be determined, based on the driver's pedal operation. For example, different tables may be referred to in the accelerator-off state and in the brake-off state. These tables may have different characteristics with regard to the relationship between the allowable deceleration and the vehicle speed.
The deceleration control described above may be applied to transportation means other than automobiles, for example, two-wheel vehicles and train vehicles.

30 Engine ECU
40 Alternator
45 Belt
50 Battery
60 Engine
70 Transmission
75 Driveshaft
80 Drive wheels
90 Group of sensors
91 Accelerator stroke sensor
92 Brake stroke sensor
93 Throttle sensor
94 Wheel speed sensor
95 Vehicle speed sensor
96 Battery sensor

Claims

A vehicle control apparatus, comprising:
a regenerative device configured to regenerate energy involved in a drive of a vehicle as electric power;
a target deceleration determiner configured to determine a target deceleration which is a target value of deceleration during an inertial drive of the vehicle, according to vehicle speed which is speed of the vehicle; and
a deceleration controller configured to control the regenerative device during the inertial drive of the vehicle and thereby perform deceleration control to make the deceleration closer to the determined target value.
The vehicle control apparatus according to claim 1,
wherein it is determined that the vehicle has an inertial drive in a state that neither of an accelerator pedal and a brake pedal provided on the vehicle is depressed.
The vehicle control apparatus according to either claim 1 or claim 2,
wherein the target deceleration determiner refers to a predefined relationship between allowable deceleration and the vehicle speed to obtain the allowable deceleration according to the vehicle speed and determines the obtained allowable deceleration as the target deceleration.
The vehicle control apparatus according to any one of claims 1 to 3,
wherein the regenerative device is an alternator and is coupled with a driveshaft of an engine mounted on the vehicle.
The vehicle control apparatus according to claim 4,
wherein the deceleration controller comprises:
a target negative torque determiner configured to determine a target value of a negative torque generated by regeneration of the alternator by taking into account at least one of a rotation speed of the engine mounted on the vehicle, weight of the vehicle and the vehicle speed; and
an alternator controller configured to make the negative torque closer to the determined target value, as control of the regenerative device.
The vehicle control apparatus according to claim 5,
wherein the alternator controller controls exciting current flowing through the alternator based on the target value of the negative torque, so as to make the negative torque closer to the determined target value.
The vehicle control apparatus according to claim 6,
wherein the alternator controller sets an upper limit value of the exciting current, as control of the exciting current.
The vehicle control apparatus according to any one of claims 1 to 7,
wherein the target deceleration determiner determines the target value to monotonically increase with an increase of the vehicle speed in at least part of a range of the vehicle speed.
The vehicle control apparatus according to claim 8,
wherein the deceleration controller performs the deceleration control such as to increase an absolute value for a rate of change of the deceleration with respect to time in a case of decreasing the deceleration, compared with an absolute value in a case of increasing the deceleration, in at least part of the range of the vehicle speed.
The vehicle control apparatus according to any one of claims 1 to 9,
wherein the target deceleration determiner determines the target value such that a rate of change of the deceleration with respect to the vehicle speed monotonically decreases with an increase of the vehicle speed in at least part of a range of the vehicle speed.
The vehicle control apparatus according to any one of claims 1 to 10,
wherein the deceleration controller determines a rate of change of the deceleration with respect to time, according to the vehicle speed and performs the deceleration control based on the determined rate of change.