JP2010195089A - Steering control device and method for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the movement to the side of a low μ road of a wheel grounded on the side of a high μ road, and to suppress the rotational displacement to the yaw direction of a vehicle. <P>SOLUTION: When the vehicle travels on a split μ road, and a braking force is generated in wheels, a yaw moment arithmetic part 18 calculates a yaw moment to be generated in a vehicle due to the difference of the braking force between right and left wheels. Also, when the yaw moment is equal to or more than a first set value, a braking time front-and-rear wheel steering angle calculation part 21 reduces a target yaw rate. Moreover, the braking time front-and-rear wheel steering angle calculation part 21 reduces a target lateral deceleration in comparison with the case that the yaw moment is less than a second set value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle steering control device and a vehicle steering control method for steering at least one of a front wheel and a rear wheel of a vehicle.

  On so-called split μ roads where the left and right wheels run on different road surfaces, when braking is applied, only the wheels on the high friction coefficient road surface (hereinafter also referred to as “high μ roads”) generate braking force. The wheel on the low friction coefficient road surface (hereinafter also referred to as “low μ road”) does not generate a sufficient braking force. Therefore, the difference between the braking force generated by the wheels on the high μ road side and the braking force generated by the wheels on the low μ road side generates a yaw moment that causes the vehicle to turn to the high μ road side. As a result, the vehicle may be rotationally displaced in the yaw direction by the yaw moment.

  Conventionally, in order to suppress the rotational displacement in the yaw direction, for example, there is a technique described in Patent Document 1. In the technique described in Patent Document 1, when the driver performs a braking operation while the vehicle is traveling on a split μ road, the front wheel on the high μ road side is steered in the toe-in direction, and the front wheel on the low μ road side is In the current direction. As a result, a yaw moment for turning the vehicle toward the low μ road is generated, and a yaw moment for turning the vehicle toward the low μ road is canceled.

JP 2007-261478 A

However, in the above conventional technique, the front wheel on the high μ road side is steered in the toe-in direction, that is, on the low μ road side, so that a lateral force directed to the low μ road side is generated on the front wheel on the high μ road side. The vehicle moves to the low μ road side. Further, the wheel that is grounded on the high μ road side by the movement enters the low μ road side, so that the lateral force of the wheel that is grounded on the high μ road side may be reduced. As a result, rotational displacement in the yaw direction may occur in the vehicle.
The present invention pays attention to the above points, and it is an object of the present invention to suppress the movement of the wheels that are in contact with the high μ road side to the low μ road side and to suppress the rotational displacement of the vehicle in the yaw direction. Yes.

  In order to solve the above problems, the present invention sets a target yaw rate and a target lateral speed based on a steering state by a driver, and determines at least one of a front wheel and a rear wheel of the vehicle based on the target yaw rate and the target lateral speed. I tried to steer. When the yaw moment generated by the difference in braking force between the left and right wheels becomes larger than the first set value, the target lateral speed is reduced. Further, when the yaw moment becomes larger than the second set value which is larger than the first set value, the target yaw rate is reduced.

  According to the present invention, for example, when a yaw moment is generated in the vehicle due to a braking force difference between the left and right wheels when traveling on a split μ road, first, the yaw moment becomes larger than the first set value, so that the target lateral speed is increased. Is reduced. Thereby, the movement of the vehicle in the lateral direction can be suppressed, and the movement of the wheel on the high μ road side to the low μ road side can be suppressed. Subsequently, when the yaw moment becomes larger than the second set value, the target yaw rate is also reduced. Thereby, the rotational displacement to the yaw direction of a vehicle can be suppressed. Therefore, the control for suppressing the movement of the vehicle in the lateral direction can be started before the control for suppressing the rotational displacement in the yaw direction is started. As a result, it is possible to suppress the movement of the wheels that are in contact with the high μ road side to the low μ road side, and to suppress the rotational displacement of the vehicle in the yaw direction.

It is a lineblock diagram of vehicles equipped with a steering control device for vehicles of a 1st embodiment. It is a block diagram showing the content of the arithmetic processing which the steering control controller 12 performs. It is a block diagram which shows the structure of the front and rear wheel steering angle calculating part 14 at the time of braking. 5 is a flowchart showing a processing procedure executed by a split μ road determination calculation unit 19. It is a figure for _{demonstrating} the setting method of split micro determination flag _FSPL . It is a figure for _{demonstrating} the setting method of split micro determination flag _FSPL . 3 is a block diagram showing a configuration of a target value correction gain calculation unit 20. FIG. It is a figure which shows a target yaw rate correction | amendment gain map. 3 is a block diagram showing a configuration of a front wheel steering angle output correction calculation unit 22. FIG. It is a figure which shows a target front wheel steering angle correction gain map. It is a flowchart which shows the process sequence which the steering control controller 12 performs. It is a figure for demonstrating operation | movement of a vehicle. It is a figure for demonstrating a comparative example. It is a block diagram of the front-wheel steering angle output correction calculating part 22 of 2nd Embodiment. It is a figure which shows a target front wheel steering angle correction gain map.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a configuration diagram of a vehicle equipped with the vehicle steering control device of the present embodiment.
As shown in FIG. 1, the vehicle includes the following various sensors. The sensors are a steering angle sensor 1, a vehicle speed sensor 2, a hydraulic pressure sensor 3, and a lateral G sensor 4. These sensors output detection signals to the steering control controller 12.

The steering angle sensor 1 detects the front wheel steering angle θ of the steering wheel. For example, a rotary encoder attached to the steering column can be used.
The vehicle speed sensor 2 detects the number of rotations of the wheels 5FL to 5RR. And the vehicle speed V is detected based on the detected rotation speed of the wheels 5FL to 5RR. As the vehicle speed sensor 2, for example, a rotary encoder attached to the wheels 5FL to 5RR can be used.

The hydraulic pressure sensor 3 detects brake hydraulic pressures P _{FL to} P _RR in wheel cylinders 11FL ′ to 11RR ′ (described later) of the wheels 5FL to 5RR.
The lateral G sensor 4 detects lateral acceleration Y _G generated in the vehicle. For example, a device configured using a piezoelectric element or the like can be used.
The vehicle also includes a front wheel steering controller 6, a front wheel steering actuator 7, a rear wheel steering controller 8, a rear wheel steering actuator 9, a braking control controller 10, and brake actuators 11FL to 11RR.

The front wheel steering controller 6 determines the front wheel steering angle command value I _θ based on the final target front wheel steering angle θ ^* ”(described later) output from the steering control controller 12 and the front wheel motor rotation angle (described later) output from the front wheel steering actuator 7. The front wheel steering angle command value _Iθ is a command value for making the actual front wheel steering angle θ coincide with the final target front wheel steering angle θ ^* ”. Then, the front wheel steering controller 6 outputs the calculated front wheel steering angle command value _Iθ to the front wheel steering actuator 7.

Front-wheel steering actuator 7, depending on the front wheel steering angle command value I _theta front wheel steering controller 6 outputs, to control the front wheel 5FL, turning angle of 5FR. As the front wheel steering actuator 7, for example, a variable gear ratio mechanism that changes the ratio of the turning angle of the front wheels 5FL and 5FR with respect to the steering angle of the steering wheel between the motor and the reduction gear can be used. With this motor and reduction gear, the turning angle of the front wheels 5FL and 5FR can be changed regardless of the front wheel steering angle.

The front wheel steering actuator 7 detects the front wheel motor rotation angle. The front wheel motor rotation angle is the rotation angle of the motor that changes the ratio of the turning angles of the front wheels 5FL and 5FR. Then, the front wheel steering actuator 7 outputs the detection result to the front wheel steering controller 6.
The rear wheel steering controller 8 determines a rear wheel steering angle command based on the final target rear wheel steering angle δ ^* ”(described later) output from the steering control controller 12 and the rear wheel steering angle (described later) output from the rear wheel steering actuator 9. to calculate the value I _[delta] wheels and steering angle command value I _[delta] after., which is a command value to match the actual rear wheel steering angle to the final target rear wheel steering angle [delta] ^* ". Then, the rear wheel steering controller 8 outputs a rear wheel steering angle command value I _δ to the rear wheel steering actuator 9.

Rear wheel steering actuator 9 in accordance with the wheel steering angle command value I _[delta] After the rear wheel steering controller 8 outputs, the rear wheels 5RL, controls the steering angle of 5RR. For example, it is possible to use a mechanism that is provided in the rear wheel steering mechanism and moves the rack shaft of the rear wheel steering mechanism in the vehicle width direction using a motor and a speed reducer. By this movement of the rack shaft, the turning angle of the rear wheels 5RL and 5RR can be changed.
The rear wheel steering actuator 9 detects the turning angle of the rear wheels 5RL and 5RR. Then, the detection result is output to the front wheel steering controller 6 as the rear wheel steering angle.

The braking controller 10 calculates the target brake fluid pressure based on the operation amount of the brake pedal. Based on the target brake fluid pressure, the brake fluid pressures P _{FL to} P _RR in the wheel cylinders 11FL ′ to 11RR ′ are controlled.
Moreover, the braking control controller 10 performs ABS (antilocked braking system) control. The ABS control is a control in which the brake fluid pressures P _{FL to} P _RR are repeatedly reduced and increased with respect to the wheel cylinders 11FL ′ to 11RR ′ of the locked wheels 5FL to 5RR.

Further, when the ABS control is being executed, the braking controller 10 sets the ABS operation flag F _ABS to “1”. The ABS operation flag F _ABS is a flag indicating whether or not ABS control is being executed. When the flag value is “1”, the ABS operation flag F _ABS indicates that the ABS control is being executed, and when the flag value is “0”, the ABS control is not being executed. Represents. Then, the braking control controller 10 outputs the set ABS operation flag F _ABS to the steering control controller 12.

The brake actuators 11FL to 11RR have wheel cylinders 11FL ′ to 11RR ′. Wheel cylinders 11FL ′ to 11RR ′ are provided on the respective wheels 5FL to 5RR. A braking force is generated on the wheels 5FL to 5RR in accordance with the control of the brake fluid pressures P _{FL to} P _RR controlled by the braking controller 10. As the brake actuators 11FL to 11RR, for example, a disc brake or a drum brake can be used.

The vehicle also includes a steering control controller 12.
The steering controller 12 performs arithmetic processing on the signals detected by the various sensors 1 to 4 to calculate a final target front wheel steering angle θ ^* ″ and a final target rear wheel steering angle δ ^* ″. Then, the steering control controller 12 outputs the final target front wheel steering angle θ ^* ″ as the calculation result to the front wheel steering controller 6, and outputs the final target rear wheel steering angle δ ^* ″ to the rear wheel steering controller 8. As the steering control controller 12, for example, a microprocessor can be used.

Next, the contents of the arithmetic processing executed by the steering control controller 12 will be described using a block diagram.
FIG. 2 is a block diagram showing the contents of the arithmetic processing executed by the steering controller 12.
As shown in FIG. 2, the block diagram includes a target value calculation unit 13, a braking front / rear wheel steering angle calculation unit 14, and a front / rear wheel steering angle output selection unit 15.
The target value calculator 13 calculates the target yaw rate dφ ^* / dt and the target lateral speed Vy ^* based on the front wheel steering angle θ output from the steering angle sensor 1 and the vehicle speed V output from the vehicle speed sensor 2. The target yaw rate dφ ^* / dt is a target value of the yaw rate dφ / dt generated in the vehicle. Further, the target lateral speed Vy ^* is a target value of the lateral speed Vy generated in the vehicle.

Further, the target value calculation unit 13 calculates the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* based on the target yaw rate dφ ^* / dt and the target lateral speed Vy ^* . The target front wheel steering angle θ ^* is a target value of the front wheel steering angle θ required for the vehicle to generate the target yaw rate dφ ^* / dt and the target lateral velocity Vy ^* . The target rear wheel steering angle δ ^* is a target value of the rear wheel steering angle δ necessary for the vehicle to generate the target yaw rate dφ ^* / dt and the target lateral velocity Vy ^* .
Specifically, first, a model describing the motion of the vehicle is introduced in order to calculate the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* . For example, a two-wheel model that approximates the motion of a two-wheel vehicle can be used. In the two-wheel model, the vehicle speed V is constant, the yaw angle is sufficiently small, the lateral speed Vy is sufficiently small compared to the longitudinal speed, and in a motion state in which the saturation characteristics of the tire lateral force do not appear significantly, the following (1) It can be approximated as

Here, dφ / dt is the yaw rate, Vy is the lateral velocity, θ is the front wheel steering angle, δ is the rear wheel steering angle, Iz is the vehicle inertia moment, M is the vehicle weight, L _F is the front axis-centroid point distance, L _r Is the center-of-gravity point-rear axle distance, N is the steering gear ratio, and Vx is the longitudinal speed. K _F is a front wheel cornering power, Kr is a rear wheel cornering power, C _F is a front wheel cornering force, and Cr is a rear wheel cornering force.
Further, based on the two-wheel model of the above formula (1), the following formula (2) can be obtained as a transfer function of the yaw rate dφ / dt with respect to the front wheel steering angle θ.

  The transfer function of the yaw rate dφ / dt in the above equation (2) can be summarized as the following equation (3).

  Similarly, the following equation (4) can be obtained as a transfer function of the lateral velocity Vy with respect to the front wheel steering angle θ based on the two-wheel model of the above equation (1).

  Further, the transfer function of the lateral velocity Vy in the above equation (4) can be summarized as the following equation (5).

  By the above formulas (3) and (5) obtained as described above, vehicle parameters are obtained.

を算出する。
次に、これら車両パラメータを用い、目標ヨーレイトdφ^*/dtの伝達関数として、下記（６）式を設定する。

Is calculated.
Next, using these vehicle parameters, the following equation (6) is set as a transfer function of the target yaw rate dφ ^* / dt.

Here, yrate-gain-map is the yaw rate steady gain, yrate-omegn-map is the yaw rate response (natural frequency), yrate-zeta-map is the yaw rate attenuation factor, and yrate-zero-map is the yaw rate advance element. These are tuning parameters for adjusting the characteristics of the target yaw rate dφ ^* / dt.
Similarly, the following equation (7) is set as a transfer function of the target lateral speed Vy ^* based on the calculated vehicle parameters.

Where vy-gain-map is the transverse velocity steady gain, vy-omegn-map is the transverse velocity response (natural frequency), vy-zeta-map is the transverse velocity damping factor, and vy-zero-map is the transverse velocity advance factor. It is. These are tuning parameters for adjusting the characteristics of the target lateral velocity Vy ^* .
Based on the vehicle parameters calculated from the above equations (3) and (5), the target yaw rate dφ ^* / dt and the target lateral velocity Vy ^* are calculated from the above equations (6) and (7) obtained as described above. Then, the target yaw rate dφ ^* / dt and the target lateral velocity Vy ^* calculated in this way are output to the front and rear wheel steering angle output selection unit 15.
Next, based on the two-wheel model of (1) above, as a relational expression of the target yaw rate dφ ^* / dt, the target lateral speed Vy ^* , the target front wheel steering angle θ ^* , and the target rear wheel steering angle δ ^* , the following (8) Set the expression.

  Moreover, said (8) Formula can be put together like following (9) Formula.

Based on the above equation (9), the calculation formulas for the target front wheel steering angle dθ ^* / dt and the target rear wheel steering angle dδ ^* / dt can be summarized as the following equation (10).

From the above equation (10) obtained as described above, based on the target yaw rate dφ ^* / dt and the target lateral velocity Vy ^* calculated from the above equations (6) and (7), the target front wheel steering angle θ ^* and the target rear wheel The steering angle δ ^* is calculated. Then, the target front wheel steering angle θ ^* and the target rear wheel steering angle δ ^* calculated in this way are output to the front and rear wheel steering angle calculation unit 14 during braking.

FIG. 3 is a block diagram illustrating a configuration of the front and rear wheel steering angle calculation unit 14 during braking.
As shown in FIG. 3, the front and rear wheel steering angle calculation unit 14 during braking includes a first adder 16, a second adder 17, a yaw moment calculation unit 18, a split μ road determination calculation unit 19, and a target value correction gain calculation unit. 20, a braking front / rear wheel steering angle calculation unit 21 and a front wheel steering angle output correction calculation unit 22 are provided.
The first adder 16 subtracts the brake fluid pressure P · F _R from the brake fluid pressure P _FL output from the fluid pressure sensor 3. Then, outputs the subtraction result, the yaw moment calculating unit 18 and a split μ road determination computing unit 19 as a front wheel lateral Br hydraulic pressure difference [Delta] P _F.

The second adder 17 subtracts the brake fluid pressure P _RR from the brake fluid pressure P _RL output from the fluid pressure sensor 3. Then, the subtraction result, and outputs the yaw moment calculating section 18 as the rear wheel left and right Br hydraulic pressure difference [Delta] P _R.
Yaw moment calculation unit 18, based on the wheel left Br hydraulic pressure difference [Delta] P _R after the front wheel lateral Br hydraulic pressure difference [Delta] P _F, that and a second adder 17 where the first adder 16 outputs the output, yaw accordance with the following equation (11) The moment estimated value Id ² φs / dt ² is calculated. The yaw moment estimated value Id ² φs / dt ² is an estimated value of the yaw moment generated around the center of gravity of the vehicle due to a difference in braking force between the left and right wheels 5FL to 5RR. Then, the yaw moment calculator 18 outputs the estimated yaw moment value Id ² φs / dt ² to the target value correction gain calculator 20 and the front and rear wheel steering angle calculator 21 during braking.

Here, I is yaw direction of the inertia moment of the vehicle, S _F is the piston area front wheel brake, S _R is the rear wheel brake piston area, mu _R is rear brake pad friction coefficient, mu _F front wheel brake pad friction coefficient, R _BF is a front wheel brake effective radius, and R _BR is a rear wheel brake effective radius. Also, R _TR rear wheel tire radius, R _TF is front tire radius, T _F is the rear wheel tire radius, T _R is the front tire radius.

The split μ road determination calculation unit 19 determines whether the traveling road surface of the vehicle is a split μ road having different friction coefficients of the road surface on which the left and right wheels travel. Then, the split μ determination flag F _SPL is set according to the determination result. The split μ determination flag F _SPL is a flag indicating whether or not the traveling road surface of the vehicle is a split μ road. For example, when the flag value is “1”, it indicates that the traveling road surface of the vehicle is a split μ road, and when the flag value is “0”, it indicates that the traveling road surface of the vehicle is not a split μ road. To express.

Here, the calculation processing for setting the split μ determination flag F _SPL executed by the split μ road determination calculation unit 19 will be specifically described.
FIG. 4 is a flowchart showing the procedure for setting the split μ determination flag F _SPL . 5 and 6 are diagrams for explaining a method of setting the split μ determination flag F _SPL .
As shown in FIG. 4, in this calculation process, first, in step S101, it is determined whether or not the split μ determination flag F _SPL is set to “0” when this calculation process was executed last time. If it is determined that the split μ determination flag F _SPL is set to “0” (YES), the process proceeds to step S102. Also, when this calculation process is executed for the first time, the process proceeds to step S102. On the other hand, if it is determined that the split μ determination flag F _SPL is set to “1” (NO), the process proceeds to step S108.

Next, in step S102, the left and right front wheels 5FL, friction coefficient of a road surface on which 5FR travels (hereinafter, also referred to as a "road surface μ") the difference between is equal to or greater than the set value N _1. The set value N ₁ is the minimum value of the difference between the road surfaces μ that can be determined to be traveling on the split μ road.
Specifically, the left and right front wheels 5FL, a difference between the road surface of a road surface on which 5FR travels mu, between the front right and left Br hydraulic pressure difference [Delta] P _F Noting that there is a certain correlation, the first adder 16 There absolute value of the front wheel left and right Br hydraulic pressure difference [Delta] P _F which outputs | determines the greater than the set value P _Hi | [Delta] P _F. The set value P _Hi is the front wheel left / right Br hydraulic pressure difference ΔP · F that can be taken when the difference between the road surface μ of the road surface on which the left and right front wheels 5FL, 5FR travel is set to the set value N ₁ . Then, the absolute value of the front wheel left and right Br hydraulic pressure difference ΔP _F | ΔP _F | if is determined to greater than the set value P _Hi (YES), the difference between the road surface μ of a road surface on which the left and right front wheels is traveling the set value N It determines with it being larger than _1, and transfers to step S103. If it is determined that the value is equal to or less than the set value P _Hi (NO), it is determined that the difference between the road surface μ of the road surface on which the left and right front wheels are traveling is equal to or less than the set value N ₁ , and the calculation process is terminated. . When this calculation process is terminated, the split μ determination flag F _SPL “0” is output to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering angle output selection unit 15.

Next, in step S103, it is determined whether or not the absolute value | Y _G | of the lateral acceleration Y _G output from the lateral G sensor 4 is greater than a set value G _Hi . The set value G _Hi is the minimum value of the lateral acceleration Y _{G that} can be determined when the vehicle moves in the lateral direction. If it is determined that the absolute value | Y _G | of the lateral acceleration Y _G is larger than the set value G _Hi (YES), it is determined that the vehicle moves in the lateral direction, and the process proceeds to step S104. On the other hand, when it is determined that the value is equal to or less than the set value G _Hi (NO), it is determined that the vehicle does not move in the lateral direction, and the calculation process is terminated. When this calculation process is terminated, the split μ determination flag F _SPL “0” is output to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering angle output selection unit 15.

Next, in step S104, it is determined whether or not the absolute value | θ | of the front wheel steering angle θ detected by the steering angle sensor 1 is greater than a set value θ _Hi . The set value θ _Hi is the minimum value of the front wheel steering angle θ that can be determined that the driver is performing the steering operation. If it is determined that the absolute value | θ | of the front wheel steering angle θ is larger than the set value θ _Hi (YES), it is determined that the driver is performing a steering operation, and the process proceeds to step S105. On the other hand, if it is determined that the value is equal to or less than the set value θ _Hi (NO), it is determined that the driver is not performing a steering operation, and this calculation process is terminated. When this calculation process is terminated, the split μ determination flag F _SPL “0” is output to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering angle output selection unit 15.

Next, in step S105, it is determined whether or not the ABS operation flag F _ABS output from the braking controller 10 is “1”. When it is determined that the ABS operation flag F _ABS is “1” (YES), the process proceeds to step S106. On the other hand, if it is determined that the value is “0” (NO), the calculation process is terminated. When this calculation process is terminated, the split μ determination flag F _SPL “0” is output to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering angle output selection unit 15.

Next, in step S106, as shown in FIG. 5, all the conditions in steps S101 to S105, that is, | ΔP _F |> P _Hi , | Y _G |> G _Hi , | θ |> θ _Hi , .F It is determined whether or not all the conditions of _ABS = 1 are satisfied for a set time T ₁ (for example, 0.1 sec.) Or longer. Then, when it is determined to be satisfied for a time above T ₁ sets all conditions proceeds to (YES) step S107. On the other hand, if it is determined that the time during which all the conditions can be satisfied is shorter than the set time T ₁ (NO), this determination is repeated.

Next, in step S107, the value of the split μ determination flag F _SPL is set to “1”, and the split μ determination flag F _SPL is set to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering. After the output to the corner output selection unit 15, this calculation process is terminated.
On the other hand, in step S108, it is determined whether or not the difference between the road surface μ of the road surface on which the left and right front wheels 5FL and 5FR travel is smaller than a set value N ₂ (<N ₁ ).

Specifically, the left and right front wheels 5FL, a difference between the road surface of a road surface on which 5FR travels mu, between the front right and left Br hydraulic pressure difference [Delta] P _F Noting that there is a certain correlation, the first adder 16 There absolute value of the front wheel left and right Br hydraulic pressure difference [Delta] P _F which outputs | [Delta] P _F | is equal to or setpoint P _Low (<P _Hi) is smaller than. Then, the absolute value of the front wheel left and right Br hydraulic pressure difference ΔP _F | ΔP _F | if is determined that the setting value P _Low smaller (YES), the difference between the road surface μ of a road surface on which the left and right front wheels is traveling the set value N It determines with it being smaller than _2, and transfers to step S112. If it is determined that the value is equal to or greater than the set value P _Low (NO), it is determined that the difference between the road surface μ on the road surface on which the left and right front wheels travel is equal to or greater than the set value N ₂ , and the process proceeds to step S109.

Next, in step S109, it is determined whether or not the absolute value | Y _G | of the lateral acceleration Y _G output from the lateral G sensor 4 is smaller than a set value G _Low (<G _Hi ). And when it determines with it being smaller than setting value _GLow (YES), it transfers to said step S112. On the other hand, if it is determined that the value is equal to or greater than the set value G _Low (NO), the process proceeds to step S110.
Next, in step S110, it is determined whether or not the absolute value | θ | of the front wheel steering angle θ detected by the steering angle sensor 1 is smaller than a set value θ _Low (<θ _Hi ). If it is determined that the value is smaller than the set value θ _Low (YES), the process proceeds to step S112. On the other hand, if it is determined that the value is equal to or greater than the set value θ _Low (NO), the process proceeds to step S111.

Next, in step S111, it is determined whether or not the ABS operation flag F _ABS output from the braking controller 10 is “0”. And when it determines with it being "0" (YES), it transfers to the said step S112. If it is determined to be “1” (NO), this calculation process is terminated. When this calculation process is terminated, the split μ determination flag F _SPL “1” is output to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering angle output selection unit 15.

Next, in step S112, as shown in FIG. 6, all the conditions in steps S108 to S111, that is, | ΔP _F | <P _Low , | Y _G | <G _Low , | θ | <θ _Low ,. It is determined whether or not all the conditions of _ABS = 0 are satisfied for a set time T ₂ (for example, 0.1 sec.) Or longer. Then, when it is determined to be satisfied for the time T ₂ or more sets all conditions proceeds to (YES) step S113. On the other hand, if it is determined that the time during which all the conditions can be satisfied is shorter than the set time T ₂ (NO), the calculation process is terminated.
Next, in step S113, the value of the split μ determination flag F _SPL is set to “0”, and the split μ determination flag F _SPL is set to the target value correction gain calculation unit 20, the braking front / rear wheel steering angle calculation unit 21, and the front / rear wheel steering. After the output to the corner output selection unit 15, this calculation process is terminated.

FIG. 7 is a block diagram illustrating a configuration of the target value correction gain calculation unit 20.
As shown in FIG. 7, the target value correction gain calculation unit 20 includes a first multiplier 23, a target yaw rate correction gain setting unit 24, and a target lateral velocity correction gain setting unit 25.
The first multiplier 23 multiplies the yaw moment estimated value Id ² φs / dt ² output from the yaw moment calculator 18 by the split μ path determination flag F _SPL output from the split μ path determination calculator 19. Then, and outputs the multiplication result ^{Id 2 φs / dt 2 · F} SPL, as yaw moment estimated value of the corrected target yaw rate correction gain setting unit 24 and a target lateral velocity correction gain setting unit 25.
The target yaw rate correction gain setting unit 24 calculates the target yaw rate correction gain G _{dφT / dt} based on the corrected yaw moment estimated value Id ² φs / dt ² · F _SPL output from the first multiplier 23. A target yaw rate correction gain _G dφT _{/ dt} is a gain for correcting the target yaw rate d.phi ^* / dt by multiplying the target yaw rate dφ ^* / dt.

FIG. 8 is a diagram showing a target yaw rate correction gain map.
Specifically, the target yaw rate correction gain setting unit 24, based on the yaw moment estimated value ^{Id 2 φs / dt 2 · F} SPL corrected, with reference to the target yaw rate correction gain map shown in FIG. 8, the target yaw rate corrected The gain G _{dφT / dt} is calculated. The target yaw rate correction gain map is a map representing the relationship between the corrected yaw moment estimated value absolute value | Id ² φs / dt ² · F _SPL | and the target yaw rate correction gain G _{dφT / dt} . In the target yaw rate correction gain map, the target yaw rate correction gain G _{dφT / dt} is in the range where | Id ² φs / dt ² · F _SPL | is 0 or more and the second set value Id ² φs ₂ / dt ² (> 0) or less. Is “1”. In addition, | Id ² φs / dt ² · F _SPL | is larger than the second set value Id ² φs ₂ / dt ^{2 and} less than the third set value Id ² φs ₃ / dt ² (> Id ² φs ”/ dt ² ). In this range, the target yaw rate correction gain G _{dφT / dt} is linearly decreased from “1” to “0” as | Id ² φs / dt ² · F _SPL | Further, in a range where | Id ² φs / dt ² · F _SPL | is larger than the third set value Id ² φs ₃ / dt ² , the target yaw rate correction gain G _{dφT / dt} is set to “0”. Then, the target yaw rate correction gain G _{dφT / dt} calculated in this way is output to the front and rear wheel steering angle calculation unit 21 during braking.

Returning to FIG. 7, the target lateral speed correction gain setting unit 25 calculates the target deceleration correction gain G _Vy based on the corrected yaw moment estimated value Id ² φs / dt ² · F _SPL output from the first multiplier 23. Is calculated. The target deceleration correction gain G _Vy is a gain for correcting the target deceleration Vy ^* by multiplying the target deceleration Vy ^* .
Specifically, the target lateral speed correction gain setting unit 25, based on the yaw moment estimated value ^{Id 2 φs / dt 2 · F} SPL after correction, referring to the target deceleration correction gain map shown in FIG. 8 (b) Then, the target deceleration correction gain G _Vy is calculated. The target deceleration correction gain map is a map that represents the relationship between the corrected absolute value of the yaw moment | Id ² φs / dt ² · F _SPL | and the target deceleration correction gain G _Vy . In the target deceleration correction gain map, in the range where | Id ² φs / dt ² · _FSPL | is 0 or more and less than the first set value Id ² φs ₁ / dt ² (<Id ² φs ₂ ”/ dt ² ) The target deceleration correction gain G _{Vy is set} to “1”. In the range where | Id ² φs / dt ² · F _SPL | is greater than the first set value Id ² φs ₁ / dt ² and less than or equal to the second set value Id ² φs ₂ / dt ² , | Id ² φs / dt ^{2. The} target deceleration correction gain G _Vy is linearly decreased from “1” to “0” as ² · F _SPL | increases. Further, the target deceleration correction gain G _Vy is set to “0” in a range where | Id ² φs / dt ² · F _SPL | is larger than the second set value Id ² φs ₂ / dt ² . Then, the target deceleration correction gain G _Vy calculated in this way is output to the front and rear wheel steering angle calculation unit 21 during braking.

Thus, the target yaw rate correction gain setting unit 24 reduces the target deceleration correction gain G _Vy when | Id ² φs / dt ² · F _SPL | becomes larger than the first set value Id ² φs ₁ / dt ^2. . Further, the target lateral velocity correction gain setting unit 25 reduces the target yaw rate correction gain G _{dφT / dt} when | Id ² φs / dt ² · F _SPL | becomes larger than the second set value Id ² φs ₂ / dt ^2. . Therefore, if | Id ² φs / dt ² · F _SPL | is increasing, first, | Id ² φs / dt ² · F _SPL | becomes larger than the first set value Id ² φs ₁ / dt ^2. The target deceleration correction gain G _Vy decreases. Subsequently, when | Id ² φs / dt ² · F _SPL | becomes larger than the second set value Id ² φs ₂ / dt ² , the target yaw rate correction gain G _{dφT / dt} is also reduced.

Returning to FIG. 3, the front and rear wheel steering angle calculation unit 21 during braking is based on outputs from the yaw moment calculation unit 18, the split μ road determination calculation unit 19, and the target value correction gain calculation unit 20 before the target front wheel steering angle before correction. θ ^* ′ and target rear wheel steering angle δ ^* ′ are calculated.
Specifically, the target yaw rate dφ ^* / dt output from the target value calculation unit 13 is multiplied by the target yaw rate correction gain G _{dφT / dt} output from the target value correction gain calculation unit 20. Then, the multiplication result dφ ^* / dt · G _{dφT / dt} is set as a corrected target yaw rate dφ _T ^* / dt.

Further, the target lateral speed Vy ^* output from the target value calculation unit 13 is multiplied by the target deceleration correction gain G _Vy output from the target value correction gain calculation unit 20. Then, the multiplication result Vy ^* · G _Vy is set as a corrected target deceleration Vy _T ^* .
Further, based on the two-wheel model of the above equation (1), the corrected target yaw rate dφ _T ^* / dt, the corrected target deceleration Vy _T ^* , the target front wheel steering angle θ ^* ′, and the target rear wheel steering angle δ ^* The following equation (12) is set as the relational expression '.

Moreover, said (12) Formula can be put together into the following (13) Formula based on the said (11) Formula.

Furthermore, the above equation (13) can be summarized as the following (14).

Based on the corrected target yaw rate dφ _T ^* / dt and the corrected target deceleration Vy _T ^* , the target front wheel steering angle θ ^* ′ before correction and the target rear wheel are calculated based on the above-described equation (14). Steering angle δ ^* 'is calculated. Then, the pre-correction target front wheel steering angle θ ^* ′ and the target rear wheel steering angle δ ^* ′ calculated in this way are output to the front wheel steering angle output correction calculation unit 22.

As described above, the braking front / rear wheel steering angle calculation unit 21 calculates the corrected target yaw rate dφ _T ^* / dt by multiplying the target yaw rate dφ ^* / dt by the target yaw rate correction gain G _{dφT / dt} . In addition, the braking front / rear wheel steering angle calculation unit 21 calculates the corrected target deceleration Vy _T ^* by multiplying the target lateral speed Vy ^* by the target deceleration correction gain G _Vy . Therefore, when | Id ² φs / dt ² · F _SPL | is increased, first, the target deceleration correction gain G _Vy is decreased, so that the corrected target deceleration Vy _T ^* is decreased. Subsequently, the target yaw rate correction gain G _{dφT / dt} is reduced, so that the corrected target yaw rate dφ _T ^* / dt is also reduced.

Further, in the braking front / rear wheel steering angle calculation unit 21, the vehicle generates the corrected target yaw rate dφ ^* / dt and the corrected target lateral velocity Vy ^* with the external force moment Id ² φs / dt ² added. Therefore, the target front wheel steering angle θ ^* ′ and the target rear wheel steering angle δ ^* ′ before correction are calculated. Therefore, the calculated uncorrected target front wheel steering angle θ ^* 'is adjusted so that the high μ road side front wheel is steered in the toe-in direction and the low μ road side front wheel is turned in the toe out direction so as to cancel out the external force moment Id ² φs / dt ^2. It will steer. Further, the calculated target rear wheel steering angle δ ^* ′ is such that the high μ road side rear wheel is steered in the toe-out direction and the low μ road side rear wheel is steered in the toe-in direction.

FIG. 9 is a block diagram illustrating a configuration of the front wheel steering angle output correction calculation unit 22.
As shown in FIG. 9, the front wheel steering angle output correction calculation unit 22 includes a target front wheel steering angle gain setting unit 26 and a second multiplier 27.
The target front wheel rudder angle gain setting unit 26 applies the target front wheel rudder angle θ during braking based on the target front wheel rudder angle θ ^* ′ before correction and the target rear wheel rudder angle δ ^* ′ output by the front and rear wheel rudder angle calculating unit 21 during braking. _s ^* is calculated.

FIG. 10 is a diagram illustrating a target front wheel steering angle correction gain map.
Specifically, the target front wheel steering angle gain setting unit 26 based on the target rear wheel steering angle [delta] ^* ', with reference to the target front wheel steering angle correction gain map shown in FIG. 10, the target front wheel steering angle correction gain G _F Is calculated. The target front wheel steering angle correction gain map, and after the target wheel steering angle [delta] ^* ', a map representing the relationship between the target front wheel steering angle correction gain G _F. The target front wheel steering angle correction gain map, | δ ^* '| is "0" and the target front wheel steering angle correction gain G _F in and the first set value [delta] _Max1 the range greater than or equal to 0. The first set value δ _Max1 is the maximum turning angle that the rear wheels 5RL and _5RR can physically take. Moreover, | [delta] ^* '| is the large and second set value δ _Max2 (> δ _Max1) the range from the first set value δ _Max1, | δ ^*' | As increases, the target front wheel steering angle correction gain G _F is increased linearly from “0” to the maximum gain G _Max . The maximum gain G _Max is a tuning parameter for adjusting the characteristic of the front wheel auxiliary steering angle θ ^* ′. Furthermore, | δ ^* '| is the target front wheel steering angle correction gain G _F and the maximum gain G _Max in the second set value [delta] _Max2 larger range. The outputs thus calculated target front wheel steering angle correction gain G _F to the second multiplier 27.

Returning to FIG. 9, the second multiplier 27 adds the target front wheel steering angle output from the target front wheel steering angle gain setting unit 26 to the target front wheel steering angle θ ^* ′ before correction output from the front and rear wheel steering angle calculation unit 21 during braking. It is multiplied by the correction gain G _F. Then, the multiplication result θ ^* '· G _F, and outputs the front and rear wheel steering angle output selection unit 15 as the braking target front wheel steering angle theta _s ^*.
Thus, the target front wheel steering angle gain setting unit 26, | δ ^* '| if is first set value [delta] _Max1 following first set value, the target front wheel steering angle correction gain G _F as "0" To do. In the second multiplier 27 multiplies the correction before the target front wheel steering angle theta ^* 'to the target front wheel steering angle correction gain G _F, to obtain a target front wheel steering angle theta _s ^* during braking. Therefore, when | δ ^* ′ | is equal to or _smaller than the first set value δ _Max1 ^* , the braking target front wheel steering angle θ _s ^* is “0”.

Returning to FIG. 2, the front and rear wheel steering angle output selection unit 15 determines the final target front wheel steering angle θ ^* ”and the final target rear wheel based on outputs from the target value calculation unit 13 and the front and rear wheel steering angle calculation unit 14 during braking. Set the rudder angle δ ^* ”.
Specifically, the front and rear wheel steering angle output selection unit 15 determines whether or not the split μ road determination flag F _SPL output from the front and rear wheel steering angle calculation unit 14 during braking is “1”. If it is “1”, the braking target front wheel steering angle θ ^* ′ output from the braking front / rear wheel steering angle calculation unit 14 is set as the final target front wheel steering angle θ ”, and the braking target rear wheel steering angle δ. ^* 'Is the final target rear wheel steering angle δ ". On the other hand, when it is “0”, the target front wheel steering angle θ ^* output by the target value calculation unit 13 is set as the final target front wheel steering angle θ ″, and the target rear wheel steering angle δ ^* is set as the final target rear wheel steering angle δ. ".

(Operation)
Next, the operation of the embodiment of the present invention will be described.
FIG. 11 is a flowchart showing a processing procedure executed by the steering control controller 12.
FIG. 12 is a diagram for explaining the operation of the vehicle.
First, as shown in FIG. 2, the steering controller 12 periodically acquires the front wheel steering angle θ, the vehicle speed V, the brake fluid pressures P _{FL to} P _RR , the ABS operation flag F _ABS , and the lateral G.
Subsequently, the target value calculation unit 13 calculates the target yaw rate dφ ^* / dt and the target lateral deceleration V _y ^* based on the front wheel steering angle θ and the vehicle speed V, and based on the calculation results, the target front wheel steering angle θ ^*. And the target rear wheel steering angle δ ^* is calculated. Then, the target yaw rate dφ ^* / dt and the target lateral deceleration Vy ^* are output to the front / rear wheel rudder angle calculation unit 14 during braking, and the target front wheel rudder angle θ ^* and the target rear wheel rudder angle δ ^* are selected as front / rear wheel rudder angle outputs. It outputs to the part 15 (step S201 of FIG. 11).

  Here, as shown in FIG. 12A, when the vehicle is traveling on the split μ road, the driver performs a braking operation, and a braking force difference is generated between the left and right wheels 5FL to 5RR. Suppose you are in a state. Then, it is assumed that a yaw moment that causes the vehicle to turn to the high μ road side is generated in the vehicle due to the braking difference, and the driver steers so as to cancel the yaw moment. Further, it is assumed that the braking controller 10 starts executing the ABS control by the braking.

Then, as shown in FIG. 3, the yaw moment calculation unit 18 estimates the yaw moment estimated value Id ² φs / dt generated by the braking force difference between the left and right wheels 5FL to 5RR based on the brake fluid pressures P _{FL to} P _RR. ² is calculated. Then, the calculation result is output to the target value correction gain calculation unit 20 and the braking front and rear wheel steering angle calculation unit 21 (step S202 in FIG. 11).
At the same time, the split μ road determination calculation unit 19 determines that the traveling road surface of the vehicle is a split μ road based on the front wheel steering angle θ, the lateral GY _G , and the ABS operation flag F _ABS , and the split μ road determination flag F _SPL Is set to “1”. Then, the setting result is output to the front and rear wheel steering angle output selection unit 15, the target value correction gain calculation unit 20, and the braking front and rear wheel steering angle calculation unit 21.

Here, the yaw moment is relatively small, and the estimated yaw moment value Id ² φs / dt ² is not less than the first set value Id ² φs ₁ / dt ^{2 and} less than the second set value Id ² φs ₂ / dt ^2. Suppose.
Then, the target value correction gain calculation unit 20 _{sets the} target yaw rate correction gain G _{dφT / dt} to “1” based on the yaw moment estimated value Id ² φs / dt ² and the split μ road determination flag F _SPL and reduces the target decrease. The speed correction gain G _Vy is set to a positive value of “1” or less. Then, the setting result is output to the front and rear wheel steering angle calculation unit 21 during braking (step S203 in FIG. 11).

Subsequently, the braking front / rear wheel steering angle calculation unit 21 multiplies the target yaw rate correction gain G _{dφT / dt} by the target yaw rate dφ ^* / dt, and _sets the multiplication result as the corrected target yaw rate dφ _T ^* / dt. . Further, the target deceleration correction gain G _Vy is multiplied by the target yaw rate dφ ^* / dt, and the multiplication result is set as a corrected target yaw rate dφ _T ^* / dt.
As a result, the corrected target yaw rate dφ _T ^* / dt is equal to the target yaw rate dφ ^* / dt, and the corrected target lateral velocity Vy _T ^* is smaller than the target lateral velocity Vy ^* .

Subsequently, the front / rear wheel steering angle calculation unit 21 during braking uses the corrected target yaw rate dφ _T ^* / dt and the corrected target lateral velocity Vy _T ^* based on the corrected target front wheel steering angle θ ^* ′ and the target rear wheel. Steering angle δ ^* 'is calculated. This pre-correction target front wheel steering angle θ ^* ′ is such that the high μ road side front wheel is steered in the toe-in direction and the low μ road side front wheel is steered in the toe out direction so as to cancel out Id ² φs / dt ² . Further, the target rear wheel steering angle δ ^* ′ is such that the high μ road side rear wheel is steered in the toe-out direction and the low μ road side rear wheel is steered in the toe-in direction. Then, the braking front / rear wheel steering angle calculation unit 21 outputs the calculation result to the front wheel steering angle output correction calculation unit 22 (step S204 in FIG. 11).

Here, it is assumed that the target rear wheel steering angle δ ^* ′ is larger than the second set value δ _Max2 .
Then, the front wheel steering angle output correction calculation unit 22, based on the following target wheel steering angle [delta] ^* ', sets the target front wheel steering angle correction gain G _F to "1". Subsequently, based on the setting result, the target front wheel steering angle θ ^* ′ is set as the target front wheel steering angle θ _s ^* during braking. Further, the target rear wheel steering angle δ ^* ′ is set as a target rear wheel steering angle δ _s ^* during braking. Then, the braking target front wheel steering angle θ _s ^* and the braking target rear wheel steering angle δ ^* ′ are output to the front and rear wheel steering angle output selection unit 15 (step S205).

Subsequently, returning to FIG. 2, the front and rear wheel steering angle output selection unit 15 determines the target front wheel steering angle θ ^* , the target rear wheel steering angle δ _s ^* , the braking target, based on the split μ road determination flag F _SPL “1”. The target front wheel steering angle θ ^* and the target rear wheel steering angle δ _s ^* are selected from the front wheel steering angle θ _s ^* and the braking target rear wheel steering angle δ _s ^* . Then, the selected target front wheel steering angle θ ^* is output to the front wheel steering controller 6 as the final target front wheel steering angle θ ^* ”. Further, the target rear wheel steering angle δ _s ^* is output as the final target rear wheel steering angle δ ^*. "Is output to the rear wheel steering controller 8 (step S206 in FIG. 11).

Subsequently, the front wheel steering controller 6 calculates a front wheel steering angle command value I _θ based on the final target front wheel steering angle θ ^* ″, and outputs the calculation result to the front wheel steering actuator 7. Subsequently, the front wheel steering actuator 7 but the front wheels 5FL according to front wheel steering angle command value I _theta, steers 5RR. Thus, the front-wheel steering angle theta is equal to the final target front wheel steering angle theta ^* ".
At the same time, the rear wheel steering controller 8 calculates a rear wheel steering angle command value I _δ based on the final target rear wheel steering angle δ ^* ″, and outputs the calculation result to the rear wheel steering actuator 9. Subsequently, the rear The wheel steering actuator 9 steers the rear wheels 5RL and 5RR in accordance with the rear wheel steering angle command value I _δ , whereby the rear wheel steering angle δ matches the final target front wheel steering angle δ ^* ″.

Accordingly, as shown in FIG. 12B, the high μ road side front wheels are steered in the toe-in direction, and the low μ road side front wheels are steered in the toe-out direction. Further, the high μ road side rear wheels are steered in the toe-out direction, and the low μ road side rear wheels are steered in the toe-in direction. As a result, the yaw rate according to the driver's steering operation can be generated, and the lateral speed Vy of the vehicle can be reduced.
The above flow is repeated periodically.

Further, it is assumed that the yaw moment increases and the yaw moment estimated value Id ² φs / dt ² becomes larger than the second set value Id ² φs ₂ / dt ² as the above flow is repeated.
Then, the target value correction gain calculation unit 20 _{sets the} target yaw rate correction gain G _{dφT / dt} to a positive value of “1” or less based on the yaw moment estimated value Id ² φs / dt ² and the split μ road determination flag F _SPL. The target deceleration correction gain G _Vy is set to “0”. Then, the setting result is output to the front and rear wheel steering angle calculation unit 21 during braking (step S203 in FIG. 11).

As a result, the corrected target yaw rate dφ _T ^* / dt is smaller than the target yaw rate dφ ^* / dt, and the corrected target lateral velocity Vy _T ^* becomes “0”.
As a result, as shown in FIG. 12B, the turning of the high μ road side front wheels in the toe-in direction increases, and the turning amount of the low μ road side front wheels in the toe-out direction is steered. Further, the turning amount of the high μ road side rear wheel in the toe-out direction increases, and the turning amount of the low μ road side rear wheel in the toe-in direction increases. As a result, the yaw rate of the vehicle is reduced, and the lateral speed Vy of the vehicle becomes “0”.
With the above operation, the control for suppressing the lateral movement of the vehicle can be started before the control for suppressing the rotational displacement in the yaw direction is started. As a result, it is possible to suppress the movement of the wheels that are in contact with the high μ road side to the low μ road side, and to suppress the rotational displacement of the vehicle in the yaw direction.

FIG. 13 is a diagram for explaining a comparative example.
By the way, when the yaw moment is generated in the vehicle due to the difference in braking force between the left and right wheels, in the method in which the control for suppressing the lateral movement of the vehicle is not performed, as shown in FIGS. When 5FL and 5FR are steered to the low μ road side, a lateral force directed toward the low μ road side is generated. Then, as shown in FIG. 13 (c), the vehicle has moved to the low μ road side due to the lateral force, and the wheel that was in contact with the high μ road side has entered the low μ road side and has been in contact with the high μ road side. The lateral force of the wheel may be reduced. As a result, rotational displacement in the yaw direction may occur in the vehicle.

  Here, in the present embodiment, the steering angle sensor 1 of FIG. 2 constitutes a steering state detection means. In the same manner, the target value calculation unit 13, the braking front and rear wheel steering angle calculation unit 14 and the target value correction gain calculation unit 20 in FIG. 2, the braking front and rear wheel steering angle calculation unit 21 in FIG. 3, and the target yaw rate correction in FIG. The gain setting unit 24 and the target lateral speed correction gain setting unit 25 constitute a target setting unit. Also, the target value calculation unit 13, the braking front / rear wheel steering angle calculation unit 14, the front / rear wheel steering angle output selection unit 15, the front wheel steering controller 6, the front wheel steering actuator 7, the rear wheel steering controller 8, and the rear wheel steering actuator shown in FIG. 9 and the braking front / rear wheel steering angle calculation unit 21 and front wheel steering angle output correction calculation unit 22 in FIG. 3 constitute a steering means. Further, the braking front / rear wheel steering angle calculation unit 14 in FIG. 2 and the split μ road determination calculation unit 19 in FIG. 3 constitute split μ road determination means. Further, the brake actuators 11FL to 11RR in FIG. 1 and the braking controller 10 in FIG. 2 constitute a braking force generating means. Further, the front / rear wheel steering angle calculator 14 in FIG. 2 and the yaw moment calculator 18 in FIG. 3 constitute a yaw moment detector. Further, the front and rear wheel steering angle calculation unit 14 in FIG. 2, the front wheel steering angle output correction calculation unit 22 in FIG. 3, and the target front wheel steering angle gain setting unit 26 in FIG. 9 constitute rear wheel steering angle determination means. Further, the wheel cylinders 1111FL 'to 11RR' of FIG. 1 constitute a wheel cylinder. Further, the hydraulic pressure sensor 3 of FIGS. 1 and 2 constitutes a brake hydraulic pressure detecting means.

(Effect of this embodiment)
(1) In the present embodiment, the steering means sets the target yaw rate and the target lateral speed based on the steering state by the driver, and based on the target yaw rate and the target lateral speed, at least the front wheels and the rear wheels of the vehicle. One side was steered. The target setting means reduces the target lateral speed when the yaw moment generated by the difference in braking force between the left and right wheels is greater than the first set value. Further, when the yaw moment becomes larger than the second set value which is larger than the first set value, the target yaw rate is reduced.

  According to this configuration, for example, when a yaw moment is generated in the vehicle due to a braking force difference between the left and right wheels when traveling on a split μ road, first, the yaw moment becomes larger than the first set value, so that the target lateral speed is increased. Is reduced. Thereby, the movement of the vehicle in the lateral direction can be suppressed, and the movement of the wheels on the high μ road side to the low μ road side can be suppressed. Subsequently, when the yaw moment becomes larger than the second set value, the target yaw rate is also reduced. Thereby, the rotational displacement to the yaw direction of a vehicle can be suppressed. Therefore, the control for suppressing the movement of the vehicle in the lateral direction can be started before the control for suppressing the rotational displacement in the yaw direction is started. As a result, it is possible to suppress the movement of the wheels that are in contact with the high μ road side to the low μ road side, and to suppress the rotational displacement of the vehicle in the yaw direction.

(2) The steering means steers the high μ road side front wheels in the toe-in direction, executes front wheel steering control to steer the low μ road side front wheels in the toe out direction, and steers the high μ road side rear wheels in the toe out direction. Then, rear wheel turning control for turning the low μ road side rear wheel in the toe-in direction is executed.
Therefore, the front wheels can be steered in the low μ road side direction, and the rear wheels can be steered in the high μ road side direction. Then, a lateral force directed to the low μ road side can be generated at the front wheels, and the yaw moment generated by the braking force difference between the left and right wheels can be reduced by the yaw moment accompanying the lateral force. In addition, the lateral force can be generated on the rear wheels toward the high μ road side, and the lateral force can reduce the lateral force acting on the low μ road side due to the lateral force generated on the front wheels. The yaw moment generated by the difference in braking force between the left and right wheels can also be reduced. As a result, it is possible to more appropriately suppress the rotational displacement of the vehicle in the yaw direction and the movement of the wheels that are in contact with the high μ road side to the low μ road side.
Furthermore, the amount of steering of the rear wheel toward the high μ road side is increased, and the lateral force generated by the rear wheel toward the high μ road side is increased, so that the vehicle can be moved to the high μ road side. As a result, it is possible to more appropriately suppress the movement of the wheel that is in contact with the high μ road side to the low μ road side.

(3) The steering means starts executing the front wheel steering control after starting the execution of the rear wheel steering control.
Therefore, it is possible to suppress the front wheels from generating lateral force directed to the low μ road side as compared with a method that always executes both front wheel steering control and rear wheel steering control. As a result, it is possible to more appropriately suppress the movement of the wheel that is in contact with the high μ road side to the low μ road side.

(4) When the turning means determines that the turning angle of the rear wheel is equal to or less than the maximum turning angle, only the rear wheel turning control is executed, and the turning angle of the rear wheel is the maximum turning. When it is determined that the angle is larger than the angle, both the front wheel steering control and the rear wheel steering control are executed.
Therefore, when the target yaw rate and target deceleration can be achieved only by turning the rear wheel, only the steering control is executed, and when the target yaw rate and target deceleration cannot be realized only by turning the rear wheel, Both front wheel steering control and rear wheel steering control can be executed. Therefore, the front wheel steering control can be started when the front wheels need to be steered.

(5) The split μ road determination means determines whether the traveling road surface of the vehicle is a split μ road based on the brake fluid pressures of the left and right wheels.
Therefore, by using the brake fluid pressure that correlates with the braking force that directly reflects the reaction force of the ground contact surface of the wheel, it is possible to accurately determine whether the road is a split μ road with high responsiveness.

(Application examples)
(1) In the present embodiment, the example in which the steering means steers both the front wheels and the rear wheels has been described, but other configurations can also be adopted. For example, only the rear wheels may be steered, the high μ road side rear wheels may be steered in the toe-out direction, and the low μ road side rear wheels may be steered in the toe-in direction.
By doing so, for example, the rear wheels can be steered in the high μ road side direction. Further, a lateral force directed to the high μ road side can be generated at the rear wheel, and the yaw moment generated by the difference in braking force between the left and right wheels can be reduced by the yaw moment accompanying the lateral force. Therefore, unlike the method of turning both the front wheels and the rear wheels, it is possible to suppress the occurrence of lateral force directed to the low μ road side at the front wheels. As a result, it is possible to more appropriately suppress the movement of the wheel that is in contact with the high μ road side to the low μ road side.

(Second Embodiment)
Next, a second embodiment according to the present invention will be described with reference to the drawings.
In addition, about the structure similar to the said 1st Embodiment, the same code | symbol is attached | subjected and demonstrated.
FIG. 14 is a block diagram of the front wheel steering angle output correction calculation unit 22 of the second embodiment.
FIG. 15 is a diagram illustrating a target front wheel steering angle correction gain map.

(Constitution)
The basic configuration of the vehicle of this embodiment is the same as that of the first embodiment. However, as shown in FIG. 14, the target front wheel steering angle gain setting unit 26 refers to the second target front wheel steering angle correction gain map shown in FIG. 15 based on the estimated yaw moment value Id ² φs / dt ² , It calculates a target front wheel steering angle correction gain G _F. The second target front wheel steering angle correction gain map, the yaw moment estimated value Id ² .phi.s / dt ^2, a map representing the relationship between the target front wheel steering angle correction gain G _F. The target front wheel steering angle correction gain ^{map, | Id 2 φs / dt 2} | a is the target front wheel steering angle correction gain G _F in and the first set value Id ² φ _Max1 / dt ² or less in the range greater than or equal to 0 and "0" To do. The first set value Id ² φ _Max1 / dt ² can be generated by the maximum value of the yaw moment that can be generated by turning the rear wheels 5RL and _5RR , that is, the maximum turning angle δ _Max1 of the rear wheels 5RL and _5RR . Yaw moment. ^{Moreover, | Id 2 φs / dt 2} | in the large and second set value _{^{Id 2 φ Max2 / dt 2 (}} > Id 2 φ Max1 / dt 2) the range from the first set value Id ² phi _Max1 / dt ² is ^{, | Id 2 φs / dt 2} | as increases linearly increasing the target front wheel steering angle correction gain G _F from "0" to "1". ^{Furthermore, | Id 2 φs / dt 2} | is the second set value Id ² phi _Max2 / dt ² is greater than the range to the target front wheel steering angle correction gain G _F as "1". The outputs thus calculated target front wheel steering angle correction gain G _F to the second multiplier 27.
Here, in the present embodiment, the target front wheel steering angle gain setting unit 26 of FIG. 14 constitutes a yaw moment determination means.

(Effect of this embodiment)
(1) In this embodiment, when the steering means determines that the yaw moment generated in the vehicle due to the difference in braking force between the left and right wheels is equal to or less than the maximum yaw moment, only the rear wheel steering control is executed. I tried to do it. When it is determined that the yaw moment is greater than the maximum yaw moment, both the front wheel turning control and the rear wheel turning control are executed.
Therefore, if the yaw moment generated in the vehicle due to the difference in braking force between the left and right wheels is relatively small and the target yaw rate and the target lateral acceleration can be achieved only by the rear wheel steering control, only the steering control is executed. it can. Further, when the yaw moment is relatively large and the target yaw rate or the like cannot be realized only by the rear wheel steering control, both the front wheel steering control and the rear wheel steering control can be executed. Therefore, the front wheel steering control can be started when the front wheels need to be steered.

1 is a steering angle sensor (steering state detecting means), 3 is a hydraulic pressure sensor (braking / driving force detecting means), 6 is a front wheel steering controller (steering means), 7 is a front wheel steering actuator (steering means), and 8 is a rear wheel. Wheel steering controller (steering means), 9 is a rear wheel steering actuator (steering means), 10 is a braking control controller (braking force generating means), 11FL to 11RR are brake actuators (braking force generating means), and 13 is a target value. Calculation unit (target setting means, steering means), 14 is a front and rear wheel steering angle calculation part (target setting means, steering means, split μ road determination means, yaw moment detection means, rear wheel steering angle determination means) during braking, Reference numeral 15 denotes a front / rear wheel steering angle output selection unit (steering means), 18 a yaw moment calculation unit (yaw moment detection means), 19 a road determination calculation unit (split μ road determination means), and 20 a target value correction gain. A calculation unit (target setting means), 21 is a front / rear wheel steering angle calculation unit (target setting means, steering means), and 22 is a front wheel steering angle output correction calculation unit (steering means, yaw moment determination means, rear wheel steering). Angle determination unit), 24 is a target yaw rate correction gain setting unit (target setting unit), 25 is a target lateral acceleration correction gain setting unit (target setting unit), and 26 is a target front wheel steering angle gain setting unit (rear wheel steering angle determination unit). , Yaw moment determination means), 27 is a second multiplier

Claims (8)

Steering state detecting means for detecting the steering state by the driver;
Target setting means for setting a target yaw rate and a target lateral speed based on the steering state detected by the driver detected by the steering state detection means;
Steering means for turning at least one of the front wheel and the rear wheel of the vehicle based on the target yaw rate and the target lateral speed set by the target setting means;
Split μ road determination means for determining whether the road surface of the vehicle is a split μ road having different friction coefficients of the road surface on which the left and right wheels travel;
Braking force generating means for generating braking force on the wheels;
When the split μ road determination means determines that the traveling road surface of the vehicle is a split μ road and the braking force generation means generates a braking force on the wheels, the split μ road determination means A yaw moment detecting means for detecting a yaw moment generated in the vehicle,
When the yaw moment detected by the yaw moment detecting means is equal to or greater than a first set value, the target setting means is configured to reduce the target lateral deceleration as compared with the case where the yaw moment is less than the first set value. When the yaw moment detected by the yaw moment detector is equal to or greater than the second set value greater than the first set value, the yaw moment is less than the second set value. A vehicle steering control device that reduces the target yaw rate. 2. The vehicle steering control device according to claim 1, wherein the steering means steers a high μ road side rear wheel in a toe-out direction and steers a low μ road side rear wheel in a toe-in direction.   The steering means steers the high μ road side front wheels in the toe-in direction, performs front wheel steering control to steer the low μ road side front wheels in the toe out direction, and steers the high μ road side rear wheels in the toe out direction. 2. The vehicle steering control device according to claim 1, wherein rear wheel steering control is performed to steer the low μ road-side rear wheel in a toe-in direction.   The vehicle steering control device according to claim 3, wherein the steering means starts execution of the front wheel steering control after starting execution of the rear wheel steering control. A rear wheel steering angle determination means for determining whether or not the rear wheel steering angle is larger than the maximum steering angle;
The steering means performs only the rear wheel steering control when the rear wheel steering angle determination means determines that the rear wheel steering angle is equal to or less than the maximum steering angle, and determines the rear wheel steering angle determination. 5. The vehicle according to claim 4, wherein when the means determines that the turning angle of the rear wheel is larger than the maximum turning angle, both the front wheel turning control and the rear wheel turning control are executed. Steering control device. A yaw moment determination means for determining whether the yaw moment detected by the yaw moment detection means is greater than the maximum yaw moment that can be generated by the rear wheel;
The steering means performs only the rear wheel turning control when the yaw moment determining means determines that the yaw moment is equal to or less than the maximum yaw moment, and the yaw moment determining means 5. The vehicle steering control device according to claim 4, wherein when it is determined that the yaw moment is greater than the maximum yaw moment, both the front wheel steering control and the rear wheel steering control are executed. 6. The braking force generation means includes a wheel cylinder that is provided on each of the wheels, and generates a braking force on the wheels according to an internal brake fluid pressure,
Brake fluid pressure detecting means for detecting the brake fluid pressure of the wheel cylinder,
The split μ road determination means determines whether or not the traveling road surface of the vehicle is a split μ road based on the brake fluid pressure of the left and right wheels detected by the brake fluid pressure detection means. Item 7. The vehicle steering control device according to any one of Items 1 to 6. A vehicle steering control method that sets a target yaw rate and a target lateral speed based on a steering state by a driver, and steers at least one of a front wheel and a rear wheel of the vehicle based on the target yaw rate and the target lateral speed. ,
When the vehicle is traveling on a split μ road, if a braking force is generated on the wheel, the yaw moment generated on the vehicle is calculated based on the difference in the braking force between the left and right wheels,
When the calculation result is greater than or equal to the first set value, the target lateral deceleration is reduced compared to the case where the yaw moment is less than the first set value, and the calculated result is the first set value. A vehicle steering control method, wherein the target yaw rate is reduced when the yaw moment is less than the second set value when the yaw moment is greater than the second set value.

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