Electronic stability control system for vehicle

Abstract

A vehicle electronic stability control system which allows a vehicle to have improved movement performance and limit performance without causing a driver to feel uncomfortable, by actuating electronic stability control from a state where a lateral slip is relatively less likely to occur. The system prevents a skid of a vehicle. The system is provided with a stability determination module that obtains information indicating vehicle behavior from a sensor, and determines whether the vehicle is in an unstable or less stable state, on the basis of the information. The system is further provided with a braking/driving force control module which, when the stability determination module determines that the vehicle is in the unstable or less stable state, applies a braking force to one of the drive wheels, and simultaneously applies a driving force to the motor for the other drive wheel.

Claims

1. An electronic stability control system for vehicle comprising a plurality of wheels including at least a pair of left and right drive wheels, wherein the vehicle has motors for individually driving the pair of left and right drive wheels, respectively, a sensor configured to detect at least one predetermined vehicle behavior, and friction brakes each configured to apply a frictional braking force to the respective one of the plurality of drive wheels, and the electronic stability control system comprises: a stability determination module configured to obtain information indicating the vehicle behavior from the sensor, and to determine whether or not the vehicle is in an unstable state or in a less stable state before the unstable state is reached, on the basis of the obtained information indicating the vehicle behavior; and a braking/driving force control module configured to, when the stability determination module determines that the vehicle is in the unstable state or in the less stable state, apply, to one drive wheel of the pair of left and right drive wheels, a braking force using one of or both a regenerative brake of the motor associated with the one drive wheel and the friction brake associated with the one drive wheel, and simultaneously apply a driving force to the motor for the other drive wheel, the pair of left and right drive wheels include a pair of left and right front drive wheels of the plurality of drive wheels, the determination by the stability determination module as to whether or not the vehicle is in the unstable state or in the less stable state includes determination as to whether or not the vehicle is in an oversteer state, and when the stability determination module determines that the vehicle is in the oversteer state, the braking/driving force control module applies a braking force to a cornering outer wheel on a curved travel path, of the pair of left and right front drive wheels, and simultaneously applies a driving force to a cornering inner wheel on the curved travel path, of the pair of left and right front drive wheels, the applied braking force and the driving force having the same absolute value.

2. The electronic stability control system as claimed in claim 1, wherein the sensor includes a vehicle speed sensor configured to detect a vehicle speed, a lateral acceleration sensor configured to detect a lateral acceleration, and a yaw rate sensor configured to detect a yaw rate, the stability determination module calculates a sideslip angle change rate deviation that is a deviation between a threshold and a sideslip angle change rate, the sideslip angle change rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor, the lateral acceleration detected by the lateral acceleration sensor, and the yaw rate detected by the yaw rate sensor, and the braking/driving force control module determines magnitudes of the braking force and the driving force to be applied, in accordance with the sideslip angle change rate deviation.

3. The electronic stability control system as claimed in claim 1, wherein the sensor includes a vehicle speed sensor configured to detect a vehicle speed, a steering angle sensor configured to detect a steering angle, and a yaw rate sensor configured to detect a yaw rate, the stability determination module calculates a yaw rate deviation that is a deviation between a reference yaw rate and the yaw rate detected by the yaw rate sensor, the reference yaw rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor and the steering angle detected by the steering angle sensor, and the braking/driving force control module determines magnitudes of the braking force and the driving force to be applied, in accordance with the yaw rate deviation.

4. The electronic stability control system as claimed in claim 1, wherein the sensor includes a vehicle speed sensor configured to detect a vehicle speed, a lateral acceleration sensor configured to detect a lateral acceleration, a steering angle sensor configured to detect a steering angle, and a yaw rate sensor configured to detect a yaw rate, the stability determination module calculates a sideslip angle change rate deviation that is a deviation between a threshold and a sideslip angle change rate and a yaw rate deviation that is a deviation between a reference yaw rate and the yaw rate detected by the yaw rate sensor, the sideslip angle change rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor, the lateral acceleration detected by the lateral acceleration sensor, and the yaw rate detected by the yaw rate sensor, the reference yaw rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor and the steering angle detected by the steering angle sensor, and the braking/driving force control module determines magnitudes of the braking force and the driving force to be applied, in accordance with one of or both the sideslip angle change rate deviation and the yaw rate deviation.

5. The electronic stability control system as claimed in claim 1, wherein the braking/driving force control module applies the braking force by a regenerative torque on the motor associated with the wheel to which the braking force is to be applied.

6. The electronic stability control system as claimed in claim 5, wherein the braking/driving force control module includes a braking force determination module configured to determine whether or not a target braking force exceeds a maximum braking force that the motor is capable of generating, and a braking force shortfall addition module configured to, when the braking force determination module determines that the target braking force exceeds the maximum braking force, apply the excess braking force to the wheel to which the braking force is to be applied, using the friction brake.

7. The electronic stability control system as claimed in claim 1, wherein the stability determination module has a sideslip degree calculation unit configured to calculate a sideslip degree of drive wheels, and the braking/driving force control module has a braking/driving force distributor configured to add a braking force to the braking force and the driving force to be applied to the respective ones of the pair of left and right drive wheels to cause a deceleration as the function of the sideslip degree calculated by the sideslip degree calculation unit.

8. An electronic stability control system for vehicle comprising a plurality of wheels including at least a pair of left and right drive wheels, wherein the vehicle has motors for individually driving the pair of left and right drive wheels, respectively, a sensor configured to detect at least one predetermined vehicle behavior, and friction brakes each configured to apply a frictional braking force to the respective one of the plurality of drive wheels, and the electronic stability control system comprises: a stability determination module configured to obtain information indicating the vehicle behavior from the sensor, and to determine whether or not the vehicle is in an unstable state or in a less stable state before the unstable state is reached, on the basis of the obtained information indicating the vehicle behavior; and a braking/driving force control module configured to, when the stability determination module determines that the vehicle is in the unstable state or in the less stable state, apply, to one drive wheel of the pair of left and right drive wheels, a braking force using one of or both a regenerative brake of the motor associated with the one drive wheel and the friction brake associated with the one drive wheel, and simultaneously apply a driving force to the motor for the other drive wheel, the pair of left and right drive wheels include a pair of left and right rear drive wheels of the plurality of wheels, the determination by the stability determination module as to whether or not the vehicle is in the unstable state or in the less stable state includes determination as to whether or not the vehicle is in an understeer state, and when the stability determination module determines that the vehicle is in the understeer state, the braking/driving force control module applies a braking force to a cornering inner wheel on a curved travel path, of the pair of left and right rear drive wheels, and simultaneously applies a driving force to a cornering outer wheel on the curved travel path, of the pair of left and right rear drive wheels, the applied braking force and the driving force having the same absolute value.

9. The electronic stability control system as claimed in claim 8, wherein the stability determination module has a sideslip degree calculation unit configured to calculate a sideslip degree of drive wheels, and the braking/driving force control module has a braking/driving force distributor configured to add a braking force to the braking force and the driving force to be applied to the respective ones of the pair of left and right drive wheels to cause a deceleration as the function of the sideslip degree calculated by the sideslip degree calculation unit.

10. The electronic stability control system as claimed in claim 8, wherein the sensor includes a vehicle speed sensor configured to detect a vehicle speed, a steering angle sensor configured to detect a steering angle, and a yaw rate sensor configured to detect a yaw rate, the stability determination module calculates a yaw rate deviation that is a deviation between a reference yaw rate and the yaw rate detected by the yaw rate sensor, the reference yaw rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor and the steering angle detected by the steering angle sensor, and the braking/driving force control module determines magnitudes of the braking force and the driving force to be applied, in accordance with the yaw rate deviation.

11. The electronic stability control system as claimed in claim 8, wherein the sensor includes a vehicle speed sensor configured to detect a vehicle speed, a lateral acceleration sensor configured to detect a lateral acceleration, a steering angle sensor configured to detect a steering angle, and a yaw rate sensor configured to detect a yaw rate, the stability determination module calculates a sideslip angle change rate deviation that is a deviation between a threshold and a sideslip angle change rate and a yaw rate deviation that is a deviation between a reference yaw rate and the yaw rate detected by the yaw rate sensor, the sideslip angle change rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor, the lateral acceleration detected by the lateral acceleration sensor, and the yaw rate detected by the yaw rate sensor, the reference yaw rate being obtained on the basis of the vehicle speed detected by the vehicle speed sensor and the steering angle detected by the steering angle sensor, and the braking/driving force control module determines magnitudes of the braking force and the driving force to be applied, in accordance with one of or both the sideslip angle change rate deviation and the yaw rate deviation.

12. The electronic stability control system as claimed in claim 8, wherein the braking/driving force control module applies the braking force by a regenerative torque on the motor associated with the wheel to which the braking force is to be applied.

13. The electronic stability control system as claimed in claim 12, wherein the braking/driving force control module includes a braking force determination module configured to determine whether or not a target braking force exceeds a maximum braking force that the motor is capable of generating, and a braking force shortfall addition module configured to, when the braking force determination module determines that the target braking force exceeds the maximum braking force, apply the excess braking force to the wheel to which the braking force is to be applied, using the friction brake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims.

(2) In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and:

(3) FIG. 1 is a plan view schematically showing a system configuration of a vehicle electronic stability control system according to a first embodiment of is the present invention;

(4) FIG. 2 is a cross-sectional view of an in-wheel motor drive device in the vehicle of FIG. 1;

(5) FIG. 3 is a control block diagram of the electronic stability control system of FIG. 1;

(6) FIG. 4 is a diagram showing a relationship between the stability of the vehicle achieved by the electronic stability control system of FIG. 1 and a weight coefficient;

(7) FIG. 5A is a diagram schematically showing a real vehicle test example when the vehicle of FIG. 1 or the like is oversteering; and

(8) FIG. 5B is a diagram schematically showing a real vehicle test example when the vehicle of FIG. 1 or the like is understeering.

DESCRIPTION OF EMBODIMENTS

(9) A vehicle electronic stability control system according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

(10) FIG. 1 is a plan view schematically showing a system configuration of the vehicle electronic stability control system 5. The electronic stability control system 5 is for preventing a vehicle from skidding. In this embodiment, a vehicle 100 is a four-wheel drive automobile which includes the electronic stability control system 5. The vehicle 100 includes a pair of left and right front wheels 1, 1 and a pair of left and right rear wheels 2, 2. The wheels are individually driven by the respective motors 3.

(11) Each motor 3 includes an in-wheel motor drive device IWM described below. The pair of left and right front wheels 1, 1 can be turned by a turning mechanism (not shown), and are steered by a steering wheel through the turning mechanism. This vehicle includes friction brakes 4 which apply frictional braking forces to the respective wheels 1 and 2. Each friction brake 4 may include a hydraulic or electric mechanical brake.

(12) The vehicle has a control system including: an ECU 6 including an ESC 5; a higher-level ECU 7 which is higher-level control device than the ECU 6; and inverter devices 8. The ECU 6 and the higher-level ECU 7 each include a computer, a program executable by the computer, various electronic circuits and the like. The higher-level ECU 7 is, for example, an electronic control unit which performs coordinated control and centralized control of the entire vehicle. The higher-level ECU 7 includes a torque distribution module 7a. The torque distribution module 7a receives an acceleration command from an accelerator operating device 9, and a deceleration command from a brake operating device 10. The torque distribution module 7a distributes a braking/driving command corresponding to the difference between the acceleration command and the deceleration command to the motors 3 through the ECU 6 and the respective inverter devices 8. The braking/driving command is, for example, a torque command.

(13) Each of the inverter devices 8 has a power circuit unit 8a provided for the associated motor 3, and a motor control unit 8b which controls the power circuit unit 8a. The power circuit units 8a can be independently controlled so that different motor torques are provided. Each motor control unit 8b outputs, to the ECU 6, various kinds of information such as detected values, control values, and the like related to the in-wheel motor drive devices IWM associated therewith. Each motor control unit 8b also converts a braking/driving torque command value inputted from the ECU 6 into an electric current command to be outputted to a PWM driver of the power circuit unit 8a.

(14) This vehicle includes at least one detection device 30. This detection device may include a steering angle sensor 11 which detects a steering angle, a vehicle speed detection device 12 which detects a vehicle speed, a yaw rate sensor 13 which detects a yaw rate, and a lateral acceleration sensor 14 which detects a lateral acceleration.

(15) FIG. 2 is a cross-sectional view of the in-wheel motor drive device IWM. Each in-wheel motor drive device IWM has the motor 3, a speed reducer 15, and a wheel bearing 16, which are partly of entirely disposed within the wheel. The rotation of the motor 3 is transferred to the drive wheel 1 (2) through the speed reducer 15 and the wheel bearing 16. A brake rotor 17 is fixed to a flange portion of a hub ring 16a of the wheel bearing 16, so that the brake rotor 17 rotates together with the drive wheel 1 (2). The motor 3 is, for example, an embedded magnet synchronous motor in which a permanent magnet is incorporated in a core portion of a rotor 3a. In the motor 3, a radial gap is provided between a stator 3b fixed to a housing 18 and the rotor 3a attached to a rotation output shaft 19.

(16) FIG. 3 is a control block diagram of the electronic stability control system 5. In the following description, FIG. 1 is also referred to as appropriate. FIG. 3 shows yaw rate feedback control. The electronic stability control system 5 has a stability determination module 20 and a braking/driving force control module 21. That is, the stability determination module 20 and the braking/driving force control module 21 are provided in the ESC 5. The stability determination module 20 obtains information indicating at least one predetermined vehicle behavior, from the detection device 30, and determines whether or not the vehicle is in an unstable state or in a less stable state before the unstable state is reached, on the basis of the obtained information indicating the vehicle behavior.

(17) The stability determination module 20 has a reference yaw rate calculation unit 22, a controller 23, a reference sideslip angle calculation unit 29, a sideslip degree calculator 24, and a stability determiner 25. In the yaw rate feedback control shown in FIG. 3, the reference yaw rate calculation unit 22 calculates the following reference yaw rate .sub.ref from a vehicle speed V detected by the vehicle speed detection device 12 and a steering angle .sub.h detected by the steering angle sensor 11, using a vehicle model.

(18) $\begin{array}{cc}{}_{\mathrm{ref}}\left(s\right)=G_{}^{}\left(0\right)\frac{{}_n^2\left(T_{}s+1\right)}{s^2+2{}_{n}s+{}_n^2}{}_h\left(s\right)& \left[\mathrm{Math}.1\right]\end{array}$
where G.sub..sup.(0) is a yaw rate gain constant, .sub.n is the natural frequency of the vehicle, is a damping ratio, and T.sub. is a constant. The natural frequency .sub.n of the vehicle and the damping ratio depend on the vehicle speed V.

(19) A deviation calculation unit 31 calculates a deviation (yaw rate deviation between the reference yaw rate .sub.ref calculated above and an actual yaw rate detected by the yaw rate sensor 13.

(20) Alternatively, in sideslip angle change rate feedback control, a sideslip angle change rate d/dt is calculated using the following equation, and a deviation (sideslip angle change rate deviation) (d/dt)) from a preset threshold is calculated by the deviation calculation unit 31.

(21) $\begin{array}{cc}\frac{d}{\mathrm{dt}}=-\frac{G_y}{V}& \left[\mathrm{Math}.2\right]\end{array}$
where G.sub. represents a yaw rate gain.

(22) The controller 23 determines a target yaw moment M.sub.t on the basis of the yaw rate deviation or the sideslip angle change rate deviation (d/dt). The yaw rate feedback control will now be described.
M.sub.t=K.sub.p+K.sub.I+K.sub.D((n1)(n))
where K.sub.p, K.sub.I, and K.sub.D are gain constants in proportion calculation, integration calculation, and differentiation calculation, respectively.

(23) The stability determiner 25 determines whether or not the vehicle is in an oversteer state or in an understeer state, on the basis of information indicating a vehicle behavior, such as the yaw rate , the yaw rate deviation , is the vehicle speed V, the lateral acceleration, and the like. For example, if the absolute value of the actual yaw rate is lower than the absolute value of the reference yaw rate, the stability determiner 25 determines that the vehicle is in the understeer state. Also, if the sideslip change rate d/dt is greater than the preset threshold, the stability determiner 25 determines that the vehicle is in the oversteer state.

(24) If the stability determination module 20 determines that the vehicle is in the unstable state or in the less stable state, e.g., the stability determination module 20 determines that the vehicle is in the oversteer state or in the understeer state, the braking/driving force control module 21 applies a braking force to one drive wheel 1 (2) of the pair of left and right drive wheels 1, 1 (2, 2) using one of or both a regenerative brake of the motor 3 and the friction brake 4 corresponding to that drive wheel 1 (2). Simultaneously the braking/driving force control module 21 applies a driving force to the motor 3 for the other drive wheel 1 (2).

(25) If the stability determiner 25 determines that the vehicle is in the understeer state, a braking/driving force distributor 26 calculates temporary braking/driving force command values having the same absolute value for a braking force to an inner rear wheel 2 and a driving force to an outer rear wheel 2 so that the braking force is to be applied to the inner rear wheel 2 and the driving force is to be applied to the outer rear wheel 2 (see FIG. 5B). Furthermore, the sideslip degree calculator 24 calculates a sideslip degree. The braking/driving force distributor 26 determines a target deceleration rate in accordance with the sideslip degree, and adds a decelerating force corresponding to the target deceleration rate to the temporary braking/driving force command values for the outer rear wheel 2 and the inner rear wheel 2.

(26) The braking/driving force distributor 26 has a braking force determination module 26a and a braking force shortfall addition module 26b. The braking force determination module 26a determines whether a target command braking torque (target braking force) exceeds the maximum torque that can be outputted (the maximum braking force that can be generated) by the motor 3. The maximum output torque is determined by, for example, the rated output of the motor 3. If the command braking torque exceeds the maximum torque that can be outputted by the motor 3, the braking force shortfall addition module 26b applies the excess braking force using the friction brake 4 to the wheel 1 (2) to which the braking force is to be applied. With a great yaw moment, a deceleration is caused, but the vehicle can be stabilized by the deceleration.

(27) The sideslip degree calculator 24 calculates a reference sideslip angle .sub.ref from the vehicle speed V detected by the vehicle speed detection device 12 and the steering angle .sub.h detected by the steering angle sensor 11, using a vehicle model.

(28) $\begin{array}{cc}{}_{\mathrm{ref}}\left(s\right)=G_{}^{}\left(0\right)\frac{{}_n^2\left(T_{}s+1\right)}{s^2+2{}_{n}s+{}_n^2}{}_h\left(s\right)& \left[\mathrm{Math}.3\right]\end{array}$
where G.sub..sup.(0) is a sideslip angle gain constant, .sub.n is the natural frequency of the vehicle, is a damping ratio, and T.sub. is a constant. The natural frequency .sub.n of the vehicle and the damping ratio depend on the vehicle speed V.

(29) A deviation (sideslip angle deviation) between the reference sideslip angle .sub.ref calculated above and an actual sideslip angle detected by a sideslip angle sensor 13 is calculated. A relationship between the magnitude of the deviation and the sideslip degree is predetermined on the basis of the results of experiments, simulations, or the like. The actual sideslip angle may be estimated by integration of the sideslip angle change rate d/dt.

(30) The sideslip degree is calculated from, for example, the magnitude of the sideslip angle as described above. The target deceleration rate may be set to zero when the sideslip degree is relatively low, and may be set to higher as the is sideslip degree increases.

(31) By adding a decelerating force corresponding to the sideslip degree to the temporary braking/driving command values for the outer rear wheel 2 and the inner rear wheel 2, a deceleration is caused, and therefore, the cornering center can be made at the forward part of the vehicle, resulting in an improvement in course tracing performance.

(32) Furthermore, since a deceleration is not caused while the sideslip degree is relatively low, the driver does not feel uncomfortable and the movement performance of the vehicle does not decrease. However, while the sideslip degree is high, a deceleration is caused, and therefore, the cornering center can be made at the forward part of the vehicle, resulting in an improvement in course tracing performance. During cornering, a load on a cornering inner wheel decreases, and therefore, in conventional electronic stability control in which only a braking force to an inner rear wheel is applied, a great braking force may not be generated, so that a sufficient yaw moment may not be generated. In contrast to this, in this control, a driving force to the outer rear wheel 2 is also applied, and therefore, a sufficient yaw moment can be reliably generated.

(33) When the stability determiner 25 determines that the vehicle is in the oversteer state, the braking/driving force distributor 26 in the braking/driving force control module 21 applies a driving force to the inner front wheel 1 and a braking force to the outer front wheel 1, the driving force and the braking force having the same absolute value and different directions, so that the in-wheel motor drive devices IWM provide a target yaw moment (see FIG. 5A). As a result, an outward yaw moment A1 is generated in the vehicle (see FIG. 5A), and therefore, oversteer tendency can be reduced. In addition, a deceleration is not caused, and therefore, even if a threshold which is a condition for taking measures to prevent a skid is set to low in the electronic stability control, the driver does not feel uncomfortable and the movement performance does not decrease.

(34) When the vehicle is in the unstable state and the sideslip degree is high, the target deceleration rate may be determined in accordance with the sideslip degree, and a decelerating force corresponding to the target deceleration rate may be added to the braking/driving force command values for the outer front wheel 1 and the inner front wheel 1, as in the case of the understeer state. Thus, the braking/driving force distributor 26 can add a braking force corresponding to a sideslip degree as described above to generate a deceleration, so that the cornering center can be made at the forward part of the vehicle, resulting in an improvement in course tracing performance.

(35) A driving force and a braking force are generated not by separate devices, for example, a driving force distribution device and a mechanical brake, but by the in-wheel motor drive device IWM. Therefore, the driver is not likely to feel uncomfortable at the time of switching between a driving force and a braking force. In addition, when a braking force is applied by the regenerative torque of the motor 3, the kinetic energy of the vehicle is converted into electric energy, which can then be used. Therefore, compared to the case where only the friction brake 4 is used, a decrease in electrical efficiency is reduced.

(36) Direct yaw moment (abbreviated to DYC) control may be performed by other control algorithms in a normal state where the stability of the vehicle is high. In this case, the braking/driving force control module 21 calculates a weighted sum of a driving force command value T.sub.DYC provided by DYC control performed by a DYC control unit 28 and a braking/driving force command value T.sub.ESC provided by the electronic stability control, as represented by the following equation, and adds the weighted sum to the braking/driving torque command value to obtain a braking/driving torque command value T.sub.IWM to the in-wheel motor drive device IWM.
T.sub.IWM=(1)T.sub.DYC+T.sub.ESC
where is a weight coefficient.

(37) The braking/driving torque command value to which the weighted sum is added is the value that is calculated according to amounts of operation of the accelerator operating device 9 or the brake operating device 10.

(38) FIG. 4 is a diagram showing a relationship between the stability of the vehicle achieved by the electronic stability control system and the weight coefficient . Regarding the weighting for the driving force command value T.sub.DYC and the braking/driving force command value T.sub.ESC, only the driving force command value provided by the DYC control is weighted in a state where the vehicle stability is high. As the stability decreases, the proportion of the DYC driving force command value is decreased, and the proportion of the braking/driving force command value provided by the electronic stability control is increased.

(39) As a result, the driving force command value provided by the DYC control and the braking/driving force command value provided by the electronic stability control is be smoothly changed without interference therebetween, and therefore, the driver is not likely to feel uncomfortable. The braking/driving torque command value T.sub.IWM is inputted to an anti-lock brake system (abbreviated to ABS)/traction control system (abbreviated to TCS) controller 27 in the inverter device 8. The ABS/TCS controller 27 performs anti-lock brake control and traction control to prevent the wheels 1 and 2 from being locked or spinning due to a braking/driving torque venerated by the electronic stability control.

(40) The vehicle electronic stability control system may be implemented in a two-wheel drive vehicle in which a pair of left and right wheels, i.e., two wheels, are independently driven. In this case, oversteer tendency can be reduced in a front-wheel drive vehicle in which a pair of left and right front wheels, i.e., two wheels, are independently driven. Understeer tendency can be reduced in a rear-wheel drive vehicle in which a pair of left and right rear wheels, i.e., two wheels, are independently driven.

(41) In the in-wheel motor drive device, a cycloidal speed reducer, a planetary speed reducer, a speed reducer with two parallel shafts, and other speed reducers can be employed. Alternatively, the in-wheel motor drive device may be of a so-called direct motor type in which a speed reducer is not employed.

(42) The respective units included in the stability determination module 20 and the braking/driving force control module 21, i.e., the reference yaw rate calculation unit 22, the stability determiner 25, the controller 23, the reference sideslip angle calculation unit 29 and the sideslip degree calculator 24, and the braking/driving force distributor 26, are preferably implemented by a processor executing a software program. Alternatively, the above units may be implemented by a combination of an adder, a subtractor, a differentiator, an integrator, and/or a comparator, or the like, so that the units can be implemented by hardware.

(43) The present invention is in no way limited to the above embodiments. Various additions, changes, or deletions can be made thereto without departing from the spirit and scope of the present invention.

REFERENCE NUMERALS

(44) 1 . . . front wheel (drive wheel)

(45) 2 . . . rear wheel (drive wheel)

(46) 3 . . . motor

(47) 4 . . . friction brake

(48) 30 (11, 12, 13, 14) . . . detection device

(49) 20 . . . stability determination module

(50) 21 . . . braking/driving force control module