Vehicle control device and vehicle control method

Abstract

In a vehicle control device and a vehicle control method according to one aspect of the present invention, when an abnormality signal of a braking actuator that controls a braking force applied to the wheel of a vehicle is acquired, a suspension actuator that controls the orientation or the height of the vehicle is controlled in response to a signal pertaining to a turning request requested for the vehicle or a signal pertaining to a braking request requested for the vehicle. As a result, when an abnormality occurs in the braking actuator, it is possible to suppress a decrease in the braking force or the vehicle body turning performance due to the braking force in the entire vehicle body.

Description

Vehicle control device and vehicle control method

[0001] The present invention relates to a vehicle control device and a vehicle control method.

[0002] When the vehicle control device disclosed in Patent Document 1 acquires an abnormality signal of a steering function in a steer-by-wire steering system, when the driving force is defined as a positive physical quantity and the braking force is defined as a negative physical quantity in accordance with the steering operation input to a steering operation input member, the sum of the driving force and the braking force applied to the rear wheel on the inner side of the vehicle's turn is made smaller than the sum of the driving force and the braking force applied to the rear wheel on the outer side of the vehicle's turn; an upward force is generated by a first rear suspension actuator corresponding to the rear wheel on the outer side of the turn, a downward force is generated by a second rear suspension actuator corresponding to the rear wheel on the inner side of the turn, and an upward force is generated by a first front suspension actuator corresponding to the front wheel on the outer side of the turn.

[0003] Japanese Patent Laid-Open No. 2024-101243

[0004] However, the conventional vehicle control device is a technology for improving turning performance through control of a suspension actuator when an abnormality occurs in a steer-by-wire steering system and the vehicle body is turned by controlling braking and driving forces, and no consideration is given to a case where an abnormality occurs in a braking actuator. Therefore, when an abnormality occurs in a braking actuator, there are problems that the braking force of the entire vehicle body becomes insufficient, or the vehicle turning performance by braking force control decreases.

[0005] The present invention has been made in view of the conventional circumstances, and an object of the present invention is to provide a vehicle control device and a vehicle control method that can suppress a decrease in the braking force of the entire vehicle body or the vehicle turning performance provided by the braking force when an abnormality occurs in a braking actuator.

[0006] According to one aspect of the vehicle control device and the vehicle control method according to the present invention, when an abnormality signal of a braking actuator is acquired, the suspension actuator is controlled in accordance with a signal related to a turning request required for the vehicle or a signal related to a braking request required for the vehicle.

[0007] According to the present invention, when a malfunction occurs in the braking actuator, it is possible to prevent a decrease in the braking force of the entire vehicle or the vehicle turning performance due to the braking force.

[0008] This is an overall configuration diagram showing the vehicle control system. This is a block diagram schematically showing the control system of the vehicle control system. This is a flowchart showing one aspect of turning assist control. This is a diagram showing the correlation between suspension stroke and toe angle. This is a state diagram illustrating a control pattern for turning assist control. This is a time chart illustrating the correlation of each signal in turning assist control. This is a flowchart showing one aspect of braking assist control. This is a state diagram showing braking assist control when the left rear wheel is an abnormal wheel. This is a state diagram showing braking assist control when the left front wheel and left rear wheel are abnormal wheels. This is a state diagram showing braking assist control when the left rear wheel and right rear wheel are abnormal wheels. This is a state diagram showing braking assist control when the left front wheel and right rear wheel are abnormal wheels. This is a flowchart showing steer-by-wire control in braking assist control. This is a time chart illustrating the correlation of each signal in braking assist control.

[0009] Hereinafter, embodiments of the vehicle control device and vehicle control method according to the present invention will be described with reference to the drawings. Figure 1 is an overall configuration diagram of the vehicle control system 100 mounted on a vehicle 10. The vehicle 10 is a four-wheeled automobile equipped with a pair of left and right front wheels 11, 12 and a pair of left and right rear wheels 13, 14, and includes a suspension system, a steering system, and a braking system. Figure 2 is a schematic block diagram showing the control systems of the suspension system, steering system, and braking system, which are part of the vehicle control system 100.

[0010] Vehicle 10 is equipped with an active suspension 70 as its suspension system. The active suspension 70 has an energy source such as hydraulic or pneumatic pressure and is a suspension system that can adjust the attitude or ride height of vehicle 10 by independently controlling the pressure of suspension actuators 71-74 provided on each of the wheels 11-14. The suspension control unit 31 outputs control signals to the suspension actuators 71-74 in response to an attitude request signal or a ride height request signal, thereby controlling the upward or downward force in the vertical direction of vehicle 10 generated by the suspension actuators 71-74.

[0011] Furthermore, the vehicle 10 is equipped with a steer-by-wire system 40 (SBW) as a steering device, in which the steering input member, the steering wheel 51, and the steering wheels, the front wheels 11 and 12, are mechanically separated. Note that the steering input member is not limited to the steering wheel 51, but may be a lever, joystick, or the like.

[0012] The steer-by-wire system 40 includes a reaction force actuator 41 that applies an operating reaction force torque to the steering wheel 51, a wheel actuator 42 that applies steering force to the front wheels 11 and 12, a steering angle sensor 43 that detects the steering angle δ of the front wheels 11 and 12 (in other words, the front wheel tire angle), a steering control unit 32 that controls the reaction force actuator 41 and the wheel actuator 42, and an operating angle sensor 52 that detects the operating angle θ, which is the rotation angle of the steering wheel 51.

[0013] The steering control unit 32 acquires the signal of the steering wheel 51's operating angle θ detected by the operating angle sensor 52, and determines the target steering angle (target tire angle) and target reaction torque from the operating angle θ and other factors. The steering control unit 32 then outputs a control signal to the wheel actuator 42 so that the steering angle δ detected by the steering angle sensor 43 approaches the target steering angle, and also outputs a control signal to the reaction force actuator 41 so that the target reaction torque is applied to the steering wheel 51. Furthermore, the steering control unit 32 controls the wheel actuator 42 in response to turning requests in the vehicle 10's autonomous driving or driver assistance.

[0014] The vehicle 10 is equipped with a braking system 80 that includes braking actuators 15-18 that control the braking force applied to each wheel 11-14 of the vehicle 10. The braking system 80 includes a braking control unit 33, a brake pedal sensor 62 that detects the amount of operation of the brake pedal 61, braking actuators 15-18 provided on each wheel 11-14, and thrust sensors 21-24 that detect the thrust generated by each braking actuator 15-18. The braking control unit 33 outputs control signals to the braking actuators 15-18 in accordance with the output of the brake pedal sensor 62, etc., to control the braking force applied to each wheel 11-14.

[0015] The suspension control unit 31, the steering control unit 32, and the braking control unit 33 each include a microcomputer 31A, 32A, and 33A as their control units. Each of the microcomputers 31A, 32A, and 33A includes an MPU (Microprocessor Unit), ROM (Read Only Memory), and RAM (Random Access Memory), respectively (not shown in the diagram), and various functions are realized by running a program stored in the ROM (which acts as a memory unit) using the MPU. Furthermore, the microcomputers 31A, 32A, and 33A that make up the suspension control unit 31, the steering control unit 32, and the braking control unit 33 are connected to a communication bus line 91 of an in-vehicle network such as a CAN (Controller Area Network), and communicate with each other via the in-vehicle network.

[0016] The suspension control unit 31, steering control unit 32, and braking control unit 33 constitute a vehicle control device 30 that controls the vehicle 10. The microcomputers 31A, 32A, and 33A function as the control unit 30A of the vehicle control device 30. The control unit 30A is configured to perform vehicle control, including steering, braking, and suspension control, and is the main body that executes the vehicle control method.

[0017] Here, the control unit 30A of the vehicle control device 30 has functional redundancy that, in addition to normal control that individually controls steering, braking, and suspension, compensates for the steering and braking functions by controlling other devices when an abnormality occurs in the steering or braking device. Specifically, when the control unit 30A of the vehicle control device 30 acquires a signal indicating an abnormality in the steering function of the steer-by-wire system 40, it performs braking force distribution control, which is a control that changes the direction of travel of the vehicle 10 by controlling the difference in braking force between the left and right wheels instead of steering by the steer-by-wire system 40. Furthermore, when the control unit 30A of the vehicle control device 30 performs braking force distribution control based on an abnormality in the steering function of the steer-by-wire system 40, if it acquires an abnormality signal from the braking actuators 15-18, it performs turning assist control that controls the suspension actuators 71-74 in response to a signal related to a turning request in order to suppress the deterioration of turning performance due to the abnormality of the braking actuators 15-18.

[0018] Furthermore, when the control unit 30A of the vehicle control device 30 acquires an abnormal signal from the brake actuators 15-18 and acquires information about the abnormal wheel, which is the wheel in which the brake actuator 15-18 has malfunctioned, it performs brake assist control by controlling the suspension actuators 71-74 in response to a signal related to a brake request. In this way, when the control unit 30A of the vehicle control device 30 acquires an abnormal signal from the brake actuators 15-18, it performs either turn assist control by controlling the suspension actuators 71-74 in response to a signal related to a turn request requested by the vehicle 10, or brake assist control by controlling the suspension actuators 71-74 in response to a signal related to a brake request requested by the vehicle 10.

[0019] The following describes in more detail the turning assist control and braking assist control performed by the vehicle control device 30 (control unit 30A). Figure 3 is a flowchart showing one aspect of the turning assist control. In step S101, the vehicle control device 30 (control unit 30A) acquires a turning request based on the driver's operation of the steering wheel 51, or a turning request based on automatic driving or driver assistance. The signal related to the turning request requested to the vehicle 10 includes the amount of steering wheel 51 operation, the target steering angle of the front wheels 11 and 12, the target lateral acceleration, the target yaw rate, etc.

[0020] Next, in step S102, the vehicle control device 30 detects whether there is an abnormality in the steering function, specifically whether the steering angle δ of the front wheels 11 and 12 cannot be changed in accordance with the command signal in the steer-by-wire system 40. Then, in step S103, the vehicle control device 30 determines whether or not an abnormality has occurred in the steering function of the steer-by-wire system 40.

[0021] If the steering function of the steer-by-wire system 40 is normal, the vehicle control device 30 proceeds to step S104 and calculates a target steering angle according to the amount of steering wheel 51 is operated. Then, in step S105, the vehicle control device 30 controls the wheel actuator 42 (steering actuator) based on the target steering angle to control the steering angle of the front wheels 11 and 12 to the target steering angle.

[0022] On the other hand, if the steering function of the steer-by-wire system 40 is abnormal (in other words, if the front wheels 11 and 12 cannot be steered), the vehicle control device 30 proceeds to step S106 to determine whether or not there is an abnormality in any of the braking actuators 15-18. An abnormality in the braking actuators 15-18 includes not only an abnormality in which no braking force is generated at all, but also an abnormality in which only a braking force lower than the intended braking force can be generated. If the braking actuators 15-18 are normal, the vehicle control device 30 proceeds to step S107 or later to perform braking force distribution control, which changes the direction of travel of the vehicle 10 by controlling the difference in braking force between the left and right wheels, instead of steering by the steer-by-wire system 40.

[0023] In step S107, the vehicle control device 30 calculates the target yaw rate based on the steering wheel 51's operating angle θ and the vehicle speed (vehicle body speed). Next, in step S108, the vehicle control device 30 calculates the target longitudinal acceleration based, for example, the amount of operation of the brake pedal 61 detected by the brake pedal sensor 62 and the amount of operation of the accelerator pedal detected by an accelerator pedal sensor (not shown). When autonomous driving or driver assistance is implemented, the vehicle control device 30 acquires the target yaw rate and target longitudinal acceleration as required values ​​for autonomous driving or driver assistance.

[0024] In step S109, the vehicle control device 30 calculates the target braking force for each of the wheels 11-14 in order to achieve the target yaw rate and target longitudinal acceleration. Next, in step S110, the vehicle control device 30 calculates the target braking force for each of the wheels 11-14 to be generated by each of the braking actuators 15-18, and the driving torque to be generated by a driving actuator such as a motor (not shown), from the target braking force for each of the wheels 11-14. Then, in step S111, the vehicle control device 30 outputs a control command (braking force command) to the braking actuators 15-18 based on the target braking force and a control command (driving force command) to the driving actuator based on the target driving torque.

[0025] On the other hand, if the steering function in the steer-by-wire system 40 is abnormal and an abnormality occurs in any of the braking actuators 15-18, the vehicle control device 30 proceeds to step S112 and determines the yaw rate that is insufficient to be achieved due to the abnormality of the braking actuators 15-18 from the target yaw rate. Next, in step S113, the vehicle control device 30 determines the control amount of the suspension actuators 71-74 to compensate for the insufficient yaw rate. Then, in step S114, the vehicle control device 30 drives and controls the suspension actuators 71-74 according to the control amount determined in step S113.

[0026] The following specifically illustrates the control of the suspension actuators 71-74 in the turning assist control shown in the flowchart of Figure 3. Figure 4 is a diagram showing the correlation between suspension stroke and toe angle in the suspension geometry of vehicle 10. In one aspect of the suspension geometry of vehicle 10, the toe angle switches from toe-out to toe-in in response to an increase in suspension stroke, and conversely, switches from toe-in to toe-out in response to a decrease in suspension stroke.

[0027] Figure 5 is a state diagram showing one aspect of the control pattern of the suspension actuators 71-74 when the turning assist control shown in the flowchart of Figure 3 is implemented in a vehicle 10 having the suspension geometry shown in Figure 4. Figure 5 shows a case where, when there is a request to turn the vehicle 10 to the right, an abnormality occurs in the steering function of the steer-by-wire system 40, and a yaw moment is generated that turns the vehicle 10 to the right due to the difference in braking force between the left and right sides. Furthermore, Figure 5 assumes a case where, due to an abnormality in the braking actuators 15-18, the yaw moment that can be generated by the difference in braking force between the left and right sides is less than required.

[0028] At this time, the vehicle control device 30 (suspension control unit 31) controls the suspension actuators 71-74 so that the left front wheel 11 and left rear wheel 13 on the outside of the turn generate an upward force in the vertical direction of the vehicle 10, and the right front wheel 12 and right rear wheel 14 on the inside of the turn generate a downward force in the vertical direction of the vehicle 10. The control pattern of the suspension actuators 71-74 common to both the left and right turning directions is as follows.

[0029] The vehicle control device 30 generates an upward force using the first rear wheel suspension actuator, which corresponds to the outer rear wheel of the vehicle 10 during a turn, and generates a downward force using the second rear wheel suspension actuator, which corresponds to the inner rear wheel of the vehicle 10 during a turn, among the suspension actuators 71-74. Furthermore, the vehicle control device 30 generates an upward force using the first front wheel suspension actuator, which corresponds to the outer front wheel of the vehicle 10 during a turn, among the suspension actuators 71-74, and generates a downward force using the second front wheel suspension actuator, which corresponds to the inner front wheel of the vehicle 10 during a turn, among the suspension actuators 71-74.

[0030] When vehicle 10 turns, a roll generally occurs where the inner side of the turn lifts and the outer side sinks. However, the control of the suspension actuators 71-74 described above generates a reverse roll, where the inner side of the turn sinks and the outer side lifts. Here, the suspension geometry of vehicle 10 has the characteristic of switching from toe-out to toe-in in response to an increase in suspension stroke, and switching from toe-in to toe-out in response to a decrease in suspension stroke.

[0031] Therefore, as shown in Figure 5, when the suspension actuators 71-74 are controlled to generate a reverse roll where the inner side of the turn sinks and the outer side of the turn rises, the tire angle of the inner wheel (the left wheel in the example of Figure 5) changes to toe-out, and the tire angle of the outer wheel (the right wheel in the example of Figure 5) changes to toe-in. In other words, by controlling the suspension actuators 71-74 to generate a reverse roll, the tire angles of the wheels 11-14 can be directed toward the inner side of the turn, thereby generating a yaw moment toward the inner side of the turn, compensating for the yaw rate that is insufficient due to a malfunction of the braking actuators 15-18, and enabling the desired turning motion to be achieved.

[0032] Figure 6 is a time chart showing the switching of various flags and changes in roll angle when cornering assist control is performed on a vehicle 10 having the suspension geometry shown in Figure 4. At time t1, when the cornering request state is in effect, if the SBW abnormality flag, which indicates an abnormality in the steering function of the steer-by-wire system 40, is raised, braking force distribution control is started to change the direction of travel of the vehicle 10 by controlling the difference in braking force between the left and right wheels.

[0033] At time t2, when the braking force distribution control is being performed, if a braking abnormality flag indicating an abnormality in any of the braking actuators 15-18 is raised, turning assist control is performed by changing the toe angle of the wheels 11-14 through the control of the suspension actuators 71-74. In this turning assist control for the vehicle 10 having the suspension geometry shown in Figure 4, the suspension actuators 71-74 are controlled to generate a reverse roll, where the direction of roll is opposite to the direction of turning. With this turning assist control, the yaw rate is maintained even if an abnormality occurs in any of the braking actuators 15-18, and a decrease in turning performance can be suppressed.

[0034] Furthermore, even if the suspension geometry of the vehicle 10 has characteristics opposite to those shown in Figure 4, where it switches from toe-in to toe-out in response to an increase in suspension stroke and from toe-out to toe-in in response to a decrease in suspension stroke, cornering assist control can still be achieved. In this case, the vehicle control device 30 (suspension control unit 31) controls the suspension actuators 71-74 to generate a downward force in the vertical direction of the vehicle 10 at the outer wheel during cornering, and an upward force in the vertical direction of the vehicle 10 at the inner wheel during cornering.

[0035] In other words, in turning assist control, the vehicle control device 30 controls the suspension actuators 71-74 to generate an upward force in the vertical direction of the vehicle 10 on one of the sides of the turning outer wheel and the turning inner wheel, and to generate a downward force in the vertical direction of the vehicle 10 on the other side, according to the suspension geometry of the vehicle 10. However, turning assist control is not limited to controlling the suspension actuators on both the turning outer wheel and turning inner wheel sides, and it is possible to control the suspension actuator on either the turning outer wheel side or the turning inner wheel side so that the tire angle faces inward during the turn by changing the toe angle. Furthermore, the turning assist control is not limited to a configuration in which it is performed on both the front wheels 11, 12 and the rear wheels 13, 14, and for example, it is possible to control the suspension actuators 71, 72 of the front wheels 11, 12 to change only the toe angle of the front wheels 11, 12.

[0036] Figure 7 is a flowchart illustrating one aspect of brake assist control, which is the control of the suspension actuators 71-74 to improve the overall deceleration performance of the vehicle body when a malfunction occurs in the brake actuators 15-18. In step S201, the vehicle control device 30 (control unit 30A) acquires an abnormality signal from the brake actuators 15-18 and determines whether or not a malfunction has occurred in any of the brake actuators 15-18. If all of the brake actuators 15-18 are normal, the vehicle control device 30 returns to step S201 and repeats the abnormality determination process.

[0037] On the other hand, if an abnormality occurs in any of the braking actuators 15-18, the vehicle control device 30 proceeds to step S202, where it obtains a signal regarding the abnormal wheel, which is the wheel corresponding to the abnormal braking actuator among the braking actuators 15-18 that is experiencing the abnormality, and identifies the abnormal wheel. Next, in step S203, the vehicle control device 30 calculates the control amount for the suspension actuators 71-74, that is, the control amount in braking assist control, based on the information about the abnormal wheel, in order to suppress the reduction in braking force of the entire vehicle. Then, in step S204, the vehicle control device 30 drives and controls the suspension actuators 71-74 according to the control amount obtained in step S203.

[0038] Figure 8 is a state diagram showing one aspect of the control pattern of the suspension actuators 71-74 when the turning assist control shown in the flowchart of Figure 7 is implemented. Figure 8 shows the control state of the suspension actuators 71-74 when the braking actuator 17 of the left rear wheel 13 fails and the braking actuator 17 is unable to generate braking force (in other words, when the left rear wheel 13 is an abnormal wheel). Here, the vehicle control device 30 controls the suspension actuators 71-74 to change the roll angle and pitch angle of the vehicle body so that the wheel load on the wheels 11-12, 14 (normal wheels) corresponding to the normal braking actuators 15-16, 18 increases, and the wheel load on the abnormal left rear wheel 13 decreases.

[0039] In detail, the vehicle control device 30 controls the suspension actuator 73 to generate an upward force in the vertical direction of the vehicle 10 at the left rear wheel 13, which is an abnormal wheel, and controls the suspension actuators 71-72 and 74 to generate a downward force in the vertical direction of the vehicle 10 at the left and right front wheels 11 and 12 and the right rear wheel 14, which are normal wheels. Through the control of the suspension actuators 71-74, the roll angle changes so that the left side of the vehicle body lifts and the right side sinks, and the pitch angle changes so that the front side of the vehicle body sinks and the rear side lifts, causing the center of gravity of the vehicle 10 to move forward and to the right compared to when braking assist control is not performed. As the center of gravity moves forward and to the right, the wheel load of the left rear wheel 13, which is an abnormal wheel, decreases, while the wheel load of the left and right front wheels 11 and 12 and the right rear wheel 14, which are normal wheels, increases. Since braking force cannot be generated at the left rear wheel 13, which is an abnormal wheel, the braking force generated at the normal wheels increases, improving the deceleration performance of the entire vehicle.

[0040] In the control pattern shown in Figure 7, the suspension actuators 71-72, 74 corresponding to the normal left and right front wheels 11, 12 and the right rear wheel 14 generate a downward force in the vertical direction of the vehicle 10. However, the braking assist control is not limited to generating a downward force in all normal wheels. In other words, the vehicle control device 30 can be programmed to generate a downward force in the vertical direction of the vehicle 10 using at least the suspension actuator 72 of the right front wheel 12, which is located diagonally opposite to the abnormal left rear wheel 13.

[0041] Therefore, if a malfunction occurs in the braking actuator 17 (braking device) of the left rear wheel 13 and the driver of the vehicle 10 presses the brake pedal 61, the vehicle control device 30 (control unit 30A) will generate an upward force in the vertical direction of the vehicle 10 by the suspension actuator 73, which is an active suspension corresponding to the left rear wheel 13, and will generate a downward force in the vertical direction of the vehicle 10 by the suspension actuator 72, which is an active suspension corresponding to at least the right front wheel 12 of the vehicle 10.

[0042] Figure 8 shows the case where the left rear wheel 13 is an abnormal wheel. However, if any one of the wheels 11-14 is an abnormal wheel, the vehicle control device 30 can change the vehicle's posture by controlling the suspension actuators 71-74 to generate an upward force in the vertical direction of the vehicle 10 on the abnormal wheel and a downward force in the vertical direction of the vehicle 10 on the normal wheel, thereby reducing the wheel load on the abnormal wheel and increasing the wheel load on the normal wheel. Similarly, if the left and right front wheels 11, 12 (front two wheels), left and right rear wheels 13, 14 (rear two wheels), front and rear right wheels 12, 14 (right two wheels), or front and rear left wheels 11, 13 (left two wheels) are abnormal wheels, the vehicle control device 30 can also change the vehicle's posture by controlling the suspension actuators 71-74 to generate an upward force in the vertical direction of the vehicle 10 on the abnormal wheel and a downward force in the vertical direction of the vehicle 10 on the normal wheel, thereby reducing the wheel load on the abnormal wheel and increasing the wheel load on the normal wheel.

[0043] Fig. 9 shows the control state of suspension actuators 71-74 by braking assist control when the braking actuator 15 of the left front wheel 11 and the braking actuator 17 of the left rear wheel 13 fail, and the braking actuator 15 and the braking actuator 17 cannot generate braking force (in other words, when the two wheels on the left side are abnormal wheels). In this case, the vehicle control device 30 controls the suspension actuators 71-74 such that the left front wheel 11 and the left rear wheel 13, which are abnormal wheels, generate an upward force in the vertical direction of the vehicle 10, and the right front wheel 12 and the right rear wheel 14, which are normal wheels, generate a downward force in the vertical direction of the vehicle 10.

[0044] This causes a roll in which the right side of the vehicle body sinks and the left side of the vehicle body floats, and the position of the center of gravity of the vehicle 10 moves to the right side of the vehicle body. Therefore, the wheel load of the two left wheels, which are abnormal wheels, decreases, and the wheel load of the two right wheels, which are normal wheels, increases. Accordingly, the braking force generated by the two right normal wheels increases corresponding to the braking force that cannot be generated by the two left abnormal wheels, and the deceleration performance of the entire vehicle body is improved. When the two right wheels are abnormal wheels, the vehicle control device 30 controls the suspension actuators 71-74 such that the two right abnormal wheels generate an upward force in the vertical direction of the vehicle 10, and the two left normal wheels generate a downward force in the vertical direction of the vehicle 10.

[0045] Fig. 10 shows the control state of suspension actuators 71-74 by braking assist control when the braking actuator 17 of the left rear wheel 13 and the braking actuator 18 of the right rear wheel 14 fail, and the braking actuator 17 and the braking actuator 18 cannot generate braking force (in other words, when the two rear wheels are abnormal wheels). In this case, the vehicle control device 30 controls the suspension actuators 71-74 such that the left rear wheel 13 and the right rear wheel 14, which are abnormal wheels, generate an upward force in the vertical direction of the vehicle 10, and the left front wheel 11 and the right front wheel 12, which are normal wheels, generate a downward force in the vertical direction of the vehicle 10.

[0046] As a result, a pitching behavior occurs in which the front side of the vehicle body sinks and the rear side of the vehicle body floats, and the center of gravity position of the vehicle 10 moves forward of the vehicle body. Therefore, the wheel load of the two rear wheels, which are abnormal wheels, decreases, and the wheel load of the two front wheels, which are normal wheels, increases. Therefore, since braking force cannot be generated by the two rear wheels that are abnormal wheels, the braking force generated by the two front wheels that are normal wheels increases, and the deceleration performance of the entire vehicle body is improved. In the case where the two front wheels are abnormal wheels, the vehicle control device 30 controls the suspension actuators 71 to 74 such that the two front wheels that are abnormal wheels generate an upward force in the vertical direction of the vehicle 10, and the two rear wheels that are normal wheels generate a downward force in the vertical direction of the vehicle 10.

[0047] FIG. 11 shows the control state of the suspension actuators 71 to 74 by the braking assist control when the abnormal wheels are two wheels positioned diagonally to the vehicle 10 with respect to each other. FIG. 11 exemplifies a case where the brake actuator 15 of the left front wheel 11 and the brake actuator 18 of the right rear wheel 14 have failed, and the brake actuator 15 and the brake actuator 18 cannot generate braking force.

[0048] At this time, the vehicle control device 30 performs control to retract the suspension actuator 71 corresponding to the left front wheel 11 that is an abnormal wheel and the suspension actuator 74 corresponding to the right rear wheel 14 that is also an abnormal wheel. Further, the vehicle control device 30 performs control to extend the suspension actuator 72 corresponding to the right front wheel 12 that is a normal wheel and the suspension actuator 73 corresponding to the left rear wheel 13 that is also a normal wheel.

[0049] Here, the control for retracting the suspension actuator is control to pull the wheel toward the vehicle body side, and the control for extending the suspension actuator is control to push the wheel downward from the vehicle body. By the expansion / contraction control of the suspension actuators 71 to 74, wheel load can be applied to the right front wheel 12 and the left rear wheel 13 which are normal wheels positioned in the diagonal direction of the vehicle 10 (in other words, the wheels other than the abnormal wheels positioned in the diagonal direction of the vehicle 10), so that the braking force generated at the right front wheel 12 and the left rear wheel 13 which are normal wheels increases, and the deceleration performance of the entire vehicle body is improved.

[0050] Furthermore, even if the braking actuator 16 of the right front wheel 12 and the braking actuator 17 of the left rear wheel 13 fail, and the braking actuators 16 and 17 are unable to generate braking force, the vehicle control device 30 will still perform extension and retraction control of the suspension actuators according to the normal and abnormal wheels. Specifically, the vehicle control device 30 will retract the suspension actuator 72 corresponding to the abnormal right front wheel 12 and the suspension actuator 73 corresponding to the abnormal left rear wheel 13, and will extend the suspension actuator 71 corresponding to the normal left front wheel 11 and the suspension actuator 74 corresponding to the normal right rear wheel 14. In this way, if the abnormal wheels are two wheels located diagonally opposite each other on the vehicle 10, the vehicle control device 30 will retract the suspension actuators corresponding to the abnormal wheels and extend the suspension actuators corresponding to the wheels excluding the abnormal wheels.

[0051] As described above, when a malfunction occurs in the braking actuators 15-18, the vehicle control device 30 performs braking assist control by controlling the suspension actuators 71-74 to prevent a decrease in the overall deceleration performance of the vehicle body. However, at this time, a difference in braking force may occur between the wheels regardless of the turning request, which may cause the vehicle's posture to become unstable. Therefore, the vehicle control device 30 can be equipped with a function to control the steer-by-wire system 40 according to the difference between the requested yaw rate included in the signal related to the turning request and the estimated yaw rate of the vehicle 10.

[0052] Figure 12 is a flowchart showing the control of the steer-by-wire system 40 when brake assist control is performed. In step S301, the vehicle control device 30 (control unit 30A) acquires a signal related to a braking request based on the driver's operation of the brake pedal 61, or a braking request based on automatic driving or driver assistance. The signal related to the braking request includes signals such as the amount of operation of the brake pedal 61, the target braking force, and the target deceleration.

[0053] Next, in step S302, the vehicle control device 30 determines whether or not an abnormality has occurred in any of the braking actuators 15-18. If all of the braking actuators 15-18 are functioning normally, the vehicle control device 30 proceeds to step S303 and determines the control amount (for example, the target brake fluid pressure) of the braking actuators 15-18 based on the braking request. Then, in the next step S304, the vehicle control device 30 controls the braking actuators 15-18 according to the control amount determined in step S303.

[0054] On the other hand, if there is a malfunction in any of the braking actuators 15-18, the vehicle control device 30 proceeds to step S305 and acquires information about the abnormal wheel, which is the wheel corresponding to the malfunctioning braking actuator 15-18. Upon acquiring the information about the abnormal wheel, the vehicle control device 30 performs control of the suspension actuators 71-74 (braking assist control) in step S306, based on the information about the abnormal wheel, to change the vehicle's posture so that the wheel load on the abnormal wheel decreases and the wheel load on the normal wheel increases. Details of the braking assist control in step S306 are as explained with reference to Figures 8-11, etc.

[0055] Next, in step S307, the vehicle control device 30 determines the estimated yaw rate, which is the yaw rate that is estimated to occur when braking is performed while an abnormality has occurred in any of the braking actuators 15-18. Then, in the next step S308, the vehicle control device 30 compares the requested yaw rate, which corresponds to a turning request based on the driver's operation of the steering wheel 51, or a turning request based on automated driving or driver assistance, with the estimated yaw rate obtained in step S307, and determines whether there is a difference of a predetermined value or more between the requested yaw rate and the estimated yaw rate.

[0056] If the difference between the requested yaw rate and the estimated yaw rate is greater than or equal to a predetermined value, the vehicle control device 30 proceeds to step S309 and determines a control amount for the steering angle δ of the front wheels 11 and 12 corresponding to the difference between the requested yaw rate and the estimated yaw rate. In other words, the vehicle control device 30 determines a correction amount for the steering angle δ of the front wheels 11 and 12 so that the estimated yaw rate approaches the requested yaw rate.

[0057] Then, in the next step S310, the vehicle control device 30 controls the wheel actuator 42 of the steer-by-wire system 40 according to the control amount (correction amount of the steering angle δ of the front wheels 11 and 12) obtained in step S309, and then proceeds to control the suspension actuators 71-74 from step S311 onwards. By performing this control of the steer-by-wire system 40, the difference between the required yaw rate and the estimated yaw rate is reduced, and the vehicle behavior can be stabilized in the event of a malfunction in any of the braking actuators 15-18.

[0058] Furthermore, the vehicle control device 30 can perform reaction force control, which controls the reaction force generated by the reaction force actuator 41, in order to control the steer-by-wire system 40 to bring the estimated yaw rate closer to the required yaw rate, by guiding the driver's operation of the steering wheel 51 in a direction that brings the estimated yaw rate closer to the required yaw rate. In addition, the vehicle control device 30 can perform the above reaction force control in parallel with the steering angle δ correction control, or in place of the steering angle δ correction control.

[0059] On the other hand, if the difference between the requested yaw rate and the estimated yaw rate is less than a predetermined value, the vehicle control device 30 determines that correction control of the steer-by-wire system 40 is unnecessary, and bypasses steps S309 and S310, proceeding to the braking assist control from step S311 onwards. In step S311, the vehicle control device 30 calculates the control amount for the suspension actuators 71-74 based on information about the abnormal wheel where the braking actuators 15-18 are malfunctioning. Then, in step S312, the vehicle control device 30 drives the suspension actuators 71-74 according to the control amount obtained in step S311, thereby preventing a decrease in the overall braking force of the vehicle due to the malfunction of the braking actuators 15-18.

[0060] Figure 13 is a time chart showing the switching of various flags and changes in steering angle when braking assist control is implemented according to the flowchart in Figure 12. At time t11, the brake pedal 61 is pressed and the braking actuators 15-18 begin to generate braking force, causing deceleration.

[0061] At time T12 in the deceleration state, if a braking abnormality flag is raised indicating that an abnormality has occurred in any of the braking actuators 15-18, braking assist control, which controls the suspension actuators 71-74 to increase the wheel load on the normal wheels, is initiated, and the suspension control flag is raised. On the other hand, if a disturbance occurs in the yaw rate due to an abnormality in any of the braking actuators 15-18, counter-steer control is implemented to correct the steering angle in order to stabilize the disturbance in the yaw rate.

[0062] The technical ideas described in the above embodiments can be used in appropriate combinations, provided that no contradictions arise. Furthermore, although the content of the present invention has been specifically described with reference to preferred embodiments, it will be obvious to those skilled in the art that various modifications can be taken based on the basic technical ideas and teachings of the present invention.

[0063] For example, in braking assist control, the vehicle control device 30 can vary the amount of wheel load distribution, or in other words, the amount of change in the vehicle's posture, based on a comparison between the braking force required for each wheel and the braking force that may be generated in an abnormal state of the braking actuators 15-18. Furthermore, the braking actuators 15-18 are not limited to braking actuators that generate friction braking force, but may also be braking actuators that generate regenerative braking force, or even braking actuators that use both friction braking force and regenerative braking force.

[0064] Furthermore, abnormalities in the braking actuators 15-18 include a state in which the generated braking force is limited to a lower level than normal due to factors such as a rise in the temperature of the braking actuators 15-18. In addition, the vehicle control device 30 can be programmed to control at least one of the braking assist control and the turning assist control.

[0065] Furthermore, the vehicle control device 30 can control the turning force by controlling the difference in driving force between the left and right sides in addition to the difference in braking force between the left and right sides when steering by the steer-by-wire system 40 becomes impossible. In addition, a control unit positioned above the suspension control unit 31, steering control unit 32, and braking control unit 33 can be a system that integrates braking assist control and turning assist control.

[0066] 10...Vehicle, 11, 12...Front wheels, 13, 14...Rear wheels, 15-18...Brake actuators, 30...Vehicle control device, 30A...Control unit, 31...Suspension control unit 31, 32...Steering control unit, 33...Brake control unit, 40...Steer-by-wire system, 51...Steering wheel, 70...Active suspension, 71-74...Suspension actuators, 80...Brake device, 100...Vehicle control system

Claims

1. A vehicle control device provided in a vehicle, comprising: a braking actuator for controlling the braking force applied to the wheels of the vehicle; and a suspension actuator for controlling the attitude or height of the vehicle, wherein the control unit of the vehicle control device, when it receives an abnormal signal from the braking actuator, controls the suspension actuator in response to a signal relating to a turning request or a braking request required for the vehicle.

2. A vehicle control device according to claim 1, wherein the vehicle is equipped with a steer-by-wire system, and the control unit, upon acquiring an abnormal signal of the steering function in the steer-by-wire system and an abnormal signal of the braking actuator, controls the suspension actuator in accordance with a signal relating to a turning request required of the vehicle.

3. A vehicle control device according to claim 2, wherein the control unit controls the suspension actuator to generate an upward force in the vertical direction of the vehicle on one of the sides of the vehicle's pivoting outer wheel and pivoting inner wheel, and a downward force in the vertical direction of the vehicle on the other side, according to the geometry of the vehicle.

4. A vehicle control device according to claim 1, wherein the control unit acquires an abnormal signal from the braking actuator and acquires information regarding an abnormal wheel corresponding to the braking actuator in which the abnormality occurred, and controls the suspension actuator in accordance with a signal relating to a braking request required by the vehicle.

5. A vehicle control device according to claim 4, wherein the control unit controls the suspension actuator to generate an upward force in the vertical direction of the vehicle on the abnormal wheel, and generates a downward force in the vertical direction of the vehicle on the wheels excluding the abnormal wheel, when the abnormal wheel is one of the wheels, two right wheels, two left wheels, two front wheels, or two rear wheels.

6. A vehicle control device according to claim 4, wherein the control unit, when the abnormal wheel is two wheels located diagonally opposite each other on the vehicle, performs control to retract the suspension actuator corresponding to the abnormal wheel and performs control to extend the suspension actuator corresponding to the wheels excluding the abnormal wheel.

7. A vehicle control device according to claim 4, wherein the vehicle is equipped with a steer-by-wire system, and the control unit controls the steer-by-wire system according to the difference between the requested yaw rate included in the signal relating to the turning request and the estimated yaw rate of the vehicle.

8. A vehicle control method performed by a control unit of a vehicle equipped with a braking system and an active suspension, wherein, when an abnormality occurs in the braking system of the left rear wheel of the vehicle and the driver of the vehicle presses the brake pedal, the active suspension corresponding to the left rear wheel of the vehicle generates an upward force in the vertical direction of the vehicle, and at least the active suspension corresponding to the right front wheel of the vehicle generates a downward force in the vertical direction of the vehicle.

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