Vehicle control device and vehicle control method

Abstract

According to a vehicle control device and a vehicle control method according to the present invention, in one aspect thereof, in a vehicle provided with a steer-by-wire system, when an abnormal signal of a steering function in the steer-by-wire system is acquired, in a case where the speed of the vehicle is equal to or greater than a predetermined speed threshold value, the steering wheel is controlled to be in a locked state, and in a case where the speed of the vehicle is less than the speed threshold value, the steering wheel is controlled to be in a free state. Thus, the turning performance when an abnormality occurs in the turning function of the steer-by-wire system can be made as large as possible.

Description

Vehicle control device and vehicle control method

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

[0002] The electric vehicle steering device of Patent Document 1 is an electric vehicle steering device in which the steering unit that steers the vehicle and the turning unit that steers the vehicle's wheels are not mechanically connected, and steering is performed via a steering actuator in the turning unit in response to steering.If the steering actuator fails, the device has the function of independently controlling the driving force or braking force of the left and right wheels, controlling the turning movement of the vehicle, and applying a steering reaction force to the steering unit in response to the vehicle behavior.

[0003] JP 2009-248660 A

[0004] In a vehicle equipped with a steer-by-wire system that steers steerable wheels of the vehicle that are mechanically separated from a steering operation input mechanism such as a steering wheel, if an abnormality occurs in the steering function of the steer-by-wire system, a yaw moment can be generated in the vehicle by generating a difference in braking / driving force between the left and right wheels of the vehicle, and the steerable wheels can be steered in the turning direction of the vehicle by utilizing alignment characteristics (scrub radius), thereby making it possible to turn the vehicle. However, although the speed range in which high turning performance is achieved by generating a yaw moment is different from the speed range in which high turning performance is achieved by steering using alignment characteristics, in the past, switching of turning control according to vehicle speed has not been realized, and it has not been possible to maximize turning performance by utilizing the difference in braking / driving force between the left and right wheels.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vehicle control device and a vehicle control method that can maximize turning performance when an abnormality occurs in the steering function of a steer-by-wire system.

[0006] Therefore, in one aspect, a vehicle control device according to the present invention, when receiving an abnormality signal of the steering function in a steer-by-wire system, controls the steered wheels to a locked state if the vehicle speed is equal to or greater than a predetermined speed threshold, and controls the steered wheels to a free state if the vehicle speed is less than the speed threshold.Furthermore, in one aspect, a vehicle control method according to the present invention, when the steering function of a vehicle equipped with a steer-by-wire fails from normal operation, controls the steered wheels to a locked state if the vehicle speed is 60 km / h or greater, and controls the steered wheels to a free state if the vehicle speed is less than 30 km / h.

[0007] According to the present invention, it is possible to maximize the turning performance when an abnormality occurs in the steering function of the steer-by-wire system.

[0008] 1 is an overall configuration diagram of a vehicle control system. FIG. 2 is a block diagram that schematically shows a control system for various actuators. FIG. 3 is a block diagram that shows a steering lock / steer free switching control function. FIG. 4 is a flowchart that shows the procedure for steering lock / steer free switching control. FIG. 5 is a diagram that shows the correlation between scrub radius and maximum lateral acceleration obtained in turning control. FIG. 6 is a diagram that shows the correlation between vehicle speed and maximum lateral acceleration obtained in turning control. FIG. 7 is a diagram that shows how switching of braking / driving force control and switching between steering lock and steer free are performed according to vehicle speed. FIG. 8 is a diagram that shows a method for setting a vehicle speed threshold that performs switching between steering lock and steer free. FIG. 9 is a diagram that shows how switching between steering lock and steer free is performed during deceleration control based on the occurrence of an abnormality in the steering function.

[0009] Hereinafter, an embodiment of a vehicle control device and a vehicle control method according to the present invention will be described with reference to the drawings. Fig. 1 is an overall configuration diagram showing a vehicle control system 100 provided in a vehicle 10. Fig. 2 is a block diagram showing a control system for various actuators in the vehicle control system 100. The vehicle 10 on which the vehicle control system 100 is mounted is a four-wheeled automobile having a pair of left and right front wheels 11, 12 and a pair of left and right rear wheels 13, 14.

[0010] 1 and 2, the vehicle control system 100 will be described in detail. The vehicle 10 includes a drive unit 70 that applies a driving force to the vehicle 10. The drive unit 70 includes, as driving force actuators, a motor 71 that applies a driving force to the front wheels 11 and 12, and a motor 72 that applies a driving force to the rear wheels 13 and 14.

[0011] The driving force control unit 31 acquires a signal indicating the amount of operation of the accelerator pedal 73 output by the accelerator pedal sensor 74. The driving force control unit 31 then outputs a control signal corresponding to a target driving force based on the amount of operation of the accelerator pedal 73 to the motors 71, 72, thereby controlling the driving forces applied to the front wheels 11, 12 and the rear wheels 13, 14.

[0012] Vehicle 10 also includes a steer-by-wire system 40 as a steering device, in which a steering wheel 51 as a steering operation input mechanism is mechanically separated from front wheels 11, 12, which are steered wheels. Steer-by-wire system 40 includes a reaction force actuator 41 that applies an operation reaction torque to steering wheel 51, a wheel actuator 42 that applies a steering force to front wheels 11, 12, and a steering control unit 32 that controls reaction force actuator 41 and wheel actuator 42. Steering wheel 51 also includes an operation angle sensor 52 that detects an operation angle θ, which is the rotation angle of steering wheel 51.

[0013] Steering control unit 32 acquires signals such as a signal of steering angle θ of steering wheel 51 detected by steering angle sensor 52 and signals of rotational speeds WS1-WS4 of each of wheels 11-14 detected by wheel speed sensor 53, and calculates a target steering angle and a target reaction torque. Steering control unit 32 then controls wheel actuator 42 so that the steering angle of front wheels 11, 12, which are steered wheels, becomes the target steering angle, and also controls reaction force actuator 41 so that the target reaction torque is applied to steering wheel 51.

[0014] The vehicle 10 also includes a braking device 60 that applies braking force to each of the wheels 11-14. The braking device 60 includes a brake control unit 33, a brake pedal sensor 62 that detects the amount of operation of a brake pedal 61, and brake actuators 15, 16, 17, and 18 that are provided on each of the wheels 11, 12, 13, and 14. The brake control unit 33 controls the braking force that the brake actuators 15, 16, 17, and 18 apply to each of the wheels 11, 12, 13, and 14 based on the output of the brake pedal sensor 62, etc. The braking device 60 is a device that can individually adjust the braking force that is applied to each of the wheels 11, 12, 13, and 14.

[0015] The vehicle 10 also has an integrated control unit 34, which is a higher-level control unit than the driving force control unit 31, steering control unit 32, and brake control unit 33. The driving force control unit 31, steering control unit 32, brake control unit 33, and integrated control unit 34 are connected to an in-vehicle network and configured to be able to communicate with each other.

[0016] As will be described in detail later, integrated control unit 34 receives from steering control unit 32 a signal indicating the diagnosis result of the steering function of steer-by-wire system 40. When integrated control unit 34 receives an abnormality signal for the steering function of steer-by-wire system 40, integrated control unit 34 outputs a command to brake control unit 33 to generate a braking / driving force difference between the left and right wheels of vehicle 10 to turn vehicle 10, and also outputs a switching command to switch steering lock actuator 91 of steering lock switching mechanism 90 between a locked state and a free state.

[0017] In this embodiment, a braking force difference is generated between the left and right wheels to turn the vehicle 10, but in the case of a vehicle in which each wheel is provided with an in-wheel motor as a driving force actuator, a driving force difference can be generated between the left and right wheels to turn the vehicle 10. In other words, in this embodiment, turning control when an abnormality occurs in the steering function of the steer-by-wire system 40 can be achieved by the braking / driving force difference between the left and right wheels.

[0018] Note that an abnormality in the steering function refers to a state in which the front wheels 11, 12, which are the steerable wheels, cannot be steered and the steering angle of the front wheels 11, 12 cannot be controlled to the target steering angle corresponding to the operation angle θ of the steering wheel 51, and is caused by a malfunction of the wheel actuator 42, a malfunction of the drive circuit of the wheel actuator 42, a malfunction of various sensors, etc. When an abnormality in the steering function occurs, the integrated control unit 34 generates a braking / driving force difference between the left and right wheels to turn the vehicle 10, while decelerating and stopping the vehicle 10, thereby realizing a limp home (evacuation control).

[0019] The steering lock switching mechanism 90 is a mechanism that selectively stops the steering movement of the front wheels 11, 12, which are steered wheels, in response to a control command from the integrated control unit 34. In other words, the locked state of the steering lock switching mechanism 90 (hereinafter also referred to as the "steer lock state") is a state in which the steering movement of the front wheels 11, 12 is stopped and steering is not possible. The free state (hereinafter also referred to as the "steer free state") is a normal state in which the steering movement of the front wheels 11, 12 is permitted, and is maintained in the free state if the steering function of the steer-by-wire system 40 is normal.

[0020] The steering lock switching mechanism 90 is a mechanism that stops the rotation of the pinion shaft in the rack and pinion mechanism and the axial movement of the rack bar by mechanically engaging or hitting a locking member, or by electromagnetic force. Furthermore, the wheel actuator 42 can be used as a steering lock actuator 91 by controlling it to generate a steering force that resists changes in the steering angle of the front wheels 11, 12.

[0021] The driving force control unit 31, steering control unit 32, brake control unit 33, and integrated control unit 34 are each equipped with a microcomputer 31A, 32A, 33A, and 34A, respectively. The microcomputers 31A, 32A, 33A, and 34A are each equipped with a microprocessor unit (MPU), read-only memory (ROM), random access memory (RAM), and the like (not shown), and various functions are realized by causing the MPU to run programs stored in the ROM as a storage unit.

[0022] The driving force control unit 31, the steering control unit 32, the brake control unit 33, and the integrated control unit 34 constitute a vehicle control device 30 that controls the vehicle 10. The microcomputers 31A, 32A, 33A, and 34A function as a control section 30A of the vehicle control device 30.

[0023] The following describes in detail the turning control that is performed when an abnormality occurs in the steering function of steer-by-wire system 40. Figure 3 is a block diagram showing the turning control function of control unit 30A. Note that braking / driving force actuator 95 shown in Figure 3 includes at least brake actuators 15-18, and also includes a driving force actuator provided for each wheel if the driving force for each wheel can be controlled individually, such as when each wheel of vehicle 10 is equipped with an in-wheel motor as a driving force actuator.

[0024] Control unit 30A includes functional units, namely, a steering lock command calculation unit 21, a steering free command calculation unit 22, and a steering lock state switching determination unit 23. Steering lock command calculation unit 21 and steer free command calculation unit 22 acquire signals such as a target steering angle signal and a vehicle speed signal estimated from the output of wheel speed sensor 53 from steer-by-wire system 40.

[0025] When steering lock actuator 91 is controlled so that front wheels 11, 12 are locked, steering lock command calculation unit 21 calculates a braking / driving force command (first braking / driving force) based on the target steering angle, vehicle speed, etc., to generate a braking / driving force difference between front wheels 11, 12 and rear wheels 13, 14, thereby generating a yaw moment that turns vehicle 10 in the direction of steering wheel 51. In other words, steering lock command calculation unit 21 performs vehicle yaw moment control, which is control that generates a yaw moment that turns vehicle 10 in the direction of steering wheel 51, by, for example, making the braking force applied to the front and rear inner wheels greater than the braking force applied to the front and rear outer wheels.

[0026] On the other hand, when steering lock actuator 91 is controlled so that front wheels 11, 12 are in a free state, steer-free command calculation unit 22 calculates, based on the target steering angle, vehicle speed, etc., braking / driving force commands to be applied to the inside and outside turning wheels to achieve steering control of front wheels 11, 12 in accordance with the setting of the scrub radius (kingpin offset) of front wheels 11, 12. For example, when the scrub radius of front wheels 11, 12 is negative, applying braking force to left front wheel 11 can steer front wheels 11, 12 to the right, and conversely, applying braking force to right front wheel 12 can steer front wheels 11, 12 to the left. Furthermore, when the scrub radius of the front wheels 11 and 12 is positive, the front wheels 11 and 12 can be steered to the left by applying a braking force to the left front wheel 11, and conversely, the front wheels 11 and 12 can be steered to the right by applying a braking force to the right front wheel 12.

[0027] Therefore, for example, when the scrub radius of the front wheels 11, 12 is negative, the steer-free command calculation unit 22 calculates a braking / driving force command to apply a braking force to the outside wheel of the turning front wheels 11, 12. On the other hand, when the scrub radius of the front wheels 11, 12 is positive, the steer-free command calculation unit 22 calculates a braking / driving force command to apply a braking force to the inside wheel of the turning front wheels 11, 12. Furthermore, in controlling the braking / driving force of the rear wheels 13, 14, the steer-free command calculation unit 22 calculates a braking / driving force command to make the braking force applied to the inside wheel of the turning rear wheels 13, 14 greater than the braking force applied to the outside wheel of the turning rear wheels 13, 14.

[0028] Therefore, when the scrub radius of the front wheels 11, 12 is positive, a larger braking force is applied to, for example, the inner wheel of the turning front wheels 11, 12 in both the steer-lock state and the steer-free state. Here, in the steer-lock state, the front wheels 11, 12 cannot be steered, generating a yaw moment in the turning direction, while in the steer-free state, the front wheels 11, 12 are steered in the turning direction. In other words, when the scrub radius of the front wheels 11, 12 is positive, switching between the steer-lock state and the steer-free state switches between vehicle yaw moment control and steering control.

[0029] On the other hand, when the scrub radius of the front wheels 11, 12 is negative, if the vehicle is in a steering lock state, a yaw moment in the turning direction can be generated by increasing the braking force applied to the inner turning wheel of the front wheels 11, 12. However, if the braking force applied to the inner turning wheel of the front wheels 11, 12 is increased in a steer-free state, the front wheels 11, 12 will be steered in the opposite direction to the turning direction. Therefore, the braking force applied to the outer turning wheel of the front wheels 11, 12 is increased to steer the front wheels 11, 12 in the turning direction. In other words, when the scrub radius of the front wheels 11, 12 is negative, the pattern of the braking / driving force difference between the front wheels 11, 12 is reversed between the steering lock state and the steer-free state.

[0030] The steering lock state switching determination unit 23 receives from the steer-by-wire system 40 an abnormality signal indicating whether or not there is an abnormality in the steering function, and a signal of the vehicle speed estimated from the output of the wheel speed sensor 53. If an abnormality has occurred in the steering function of the steer-by-wire system 40, the steering lock state switching determination unit 23 outputs a switching signal (on / off command signal) to the steering lock actuator 91 depending on whether the vehicle speed is equal to or greater than a threshold value or less than a threshold value, thereby switching the steering lock switching mechanism 90 between the locked state and the free state.

[0031] Here, the steering lock state switching determination unit 23 switches the steering lock switching mechanism 90 to the locked state if the vehicle speed is equal to or greater than the threshold value, and switches the steering lock switching mechanism 90 to the free state if the vehicle speed is less than the threshold value. When the steering lock state switching determination unit 23 locks the steering lock switching mechanism 90 (in other words, when the vehicle speed is equal to or greater than the threshold value), it outputs the braking / driving force command calculated by the steering lock command calculation unit 21 (vehicle yaw moment control) to the braking / driving force actuator 95 (brake actuators 15-18). On the other hand, when the steering lock state switching determination unit 23 frees the steering lock switching mechanism 90 (in other words, when the vehicle speed is less than the threshold value), it outputs the braking / driving force command calculated by the steering free command calculation unit 22 (steering control) to the braking / driving force actuator 95 (brake actuators 15-18).

[0032] 4 is a flowchart showing the procedure for turning control when an abnormality occurs in the steering function of the steer-by-wire system 40. In step S101, the control unit 30A determines whether or not an abnormality has occurred in the steering function of the steer-by-wire system 40, in other words, whether or not the steer-by-wire system 40 has malfunctioned.

[0033] If the steering function of the steer-by-wire system 40 is normal, the control unit 30A repeats the determination of whether the steering function is normal or abnormal in step S101 without proceeding to the abnormality processing from step S102 onwards. Note that while the steering function of the steer-by-wire system 40 is normal, the steering lock switching mechanism 90 is held in a free state, and steering control by the steer-by-wire system 40 is carried out normally.

[0034] On the other hand, if an abnormality occurs in the steering function of steer-by-wire system 40, control unit 30A proceeds from step S101 to step S102 to determine whether or not the vehicle speed is below a threshold value. If the vehicle speed is equal to or greater than the threshold value, control unit 30A proceeds to step S103 to switch steering lock switching mechanism 90 to the locked state and to provide a braking / driving force command from steering lock command calculation unit 21 to braking / driving force actuator 95 (brake actuators 15-18), thereby executing vehicle yaw moment control.

[0035] On the other hand, if the vehicle speed is less than the threshold value, control unit 30A proceeds to step S104, switches steering lock switching mechanism 90 to the free state, and issues a braking / driving force command from steering-free command calculation unit 22 to braking / driving force actuator 95 (brake actuators 15-18), thereby executing steering control. Then, in the next step S105, control unit 30A ends turning control when vehicle 10 decelerates and stops.

[0036] Below, we will explain the action and effect of the turning control, which switches the steering lock switching mechanism 90 between a locked state and a free state depending on the vehicle speed when an abnormality occurs in the steering function of the steer-by-wire system 40, and switches the vehicle turning method between vehicle yaw moment control and steering control depending on the switching.

[0037] Fig. 5 is a diagram showing the correlation between the maximum lateral acceleration obtained by vehicle yaw moment control in the locked state and the maximum lateral acceleration obtained by steering control in the free state, and the scrub radius of the front wheels 11, 12. Fig. 6 is a diagram showing the correlation between the maximum lateral acceleration obtained by vehicle yaw moment control in the locked state and the maximum lateral acceleration obtained by steering control in the free state, and the vehicle speed (speed of the vehicle 10) when the scrub radius of the front wheels 11, 12 is a certain value.

[0038] The maximum lateral acceleration obtained by vehicle yaw moment control in the locked state is not affected by the scrub radius of the front wheels 11, 12 as shown in Figure 5 because no steering is performed, but it increases as the vehicle speed increases as shown in Figure 6. On the other hand, the maximum lateral acceleration obtained by steering control in the free state changes depending on the scrub radius of the front wheels 11, 12 as shown in Figure 5, but is not affected by the vehicle speed as shown in Figure 6. Here, as shown in Figure 6, the maximum lateral acceleration obtained by vehicle yaw moment control in the locked state and the maximum lateral acceleration obtained by steering control in the free state intersect (becoming the same maximum lateral acceleration) when the vehicle speed is a predetermined speed.

[0039] Furthermore, at speeds slower than the maximum lateral acceleration intersection point, performing steering control in the free state results in a higher maximum lateral acceleration than performing vehicle yaw moment control in the locked state. Conversely, at speeds faster than the maximum lateral acceleration intersection point, performing vehicle yaw moment control in the locked state results in a higher maximum lateral acceleration than performing steering control in the free state. Therefore, by switching between vehicle yaw moment control in the locked state and steering control in the free state depending on whether the vehicle speed at that time is slower or faster than the maximum lateral acceleration intersection point, the lateral acceleration that can be generated by the braking / driving force difference between the left and right wheels, i.e., cornering performance, can be maximized.

[0040] 7 is a state diagram that shows a schematic diagram of switching between vehicle yaw moment control in a locked state and steering control in a free state based on a comparison between the vehicle speed and a threshold value. If the vehicle speed is equal to or greater than the threshold value, the steering is locked and a difference in braking / driving force is generated between the left and right front wheels 11, 12, thereby executing vehicle yaw moment control to generate a yaw moment in the vehicle 10. For example, when turning left, the steering is locked and a braking force is applied to the left front wheel 11, which is the inside wheel of the turn, to generate a yaw moment in the left turning direction.

[0041] Furthermore, if the vehicle speed is below a threshold, the system switches to a steer-free state, and then performs steering control to steer the front wheels 11, 12 in the turning direction by generating a difference in braking / driving force between the left and right front wheels 11, 12. For example, if the scrub radius of the front wheels 11, 12 is negative and the vehicle 10 is to turn left, braking force is applied to the right front wheel 12, which is the outside wheel of the turn, to steer the front wheels 11, 12 to the left.

[0042] Since the maximum lateral acceleration that can be generated by steering control in the free state varies depending on the scrub radius, as well as on vehicle specifications such as vehicle weight, vehicle length, tread, and wheelbase, a vehicle speed threshold value for switching between vehicle yaw moment control in the locked state and steering control in the free state is determined based on these factors. In the case of vehicle 10 in which the scrub radius of front wheels 11, 12, which are steered wheels, is variable, control unit 30A can variably set the threshold value depending on the scrub radius at that time, and can also output a command to return the scrub radius to the specified scrub radius if the scrub radius has been changed from the specified scrub radius that matches the threshold value.

[0043] As described above, the threshold value is changed depending on vehicle specifications including the scrub radius of the front wheels 11, 12, but generally, the front wheels 11, 12 are switched between locked and unlocked states within the following vehicle speed ranges: In the case of a typical vehicle 10, at least in the high-speed range of 60 km / h or higher, the front wheels 11, 12 are placed in a steering lock state and vehicle yaw moment control is performed, and at least in the low-speed range of less than 30 km / h, the front wheels 11, 12 are placed in a steering-free state and steering control is performed.

[0044] That is, in the case of a typical vehicle 10, the vehicle speed threshold is set within a speed range of 30 km / h or more and less than 60 km / h. Therefore, according to the vehicle control device 30 having the above-described turning control function, when the steering function of the steer-by-wire system 40 fails from normal operation, the front wheels 11, 12 are controlled to be in a steering locked state if the vehicle speed is in a high speed range of 60 km / h or more, and the front wheels 11, 12 are controlled to be in a steer-free state if the vehicle speed is in a low speed range of less than 30 km / h.

[0045] 8 is a diagram showing a method for setting the vehicle speed threshold based on the scrub radius. Assuming that the scrub radius of the vehicle 10 is R1 (a predetermined negative value), the maximum lateral acceleration generated at this scrub radius R1 is the maximum lateral acceleration αymax1 that can be generated by steering control in the free state. Then, the vehicle speed V1 at which the maximum lateral acceleration αymax1 is generated by vehicle yaw moment control in the locked state is set as the threshold.

[0046] By setting this vehicle speed threshold, when the vehicle speed is below the threshold, steering control in the free state is performed to obtain the maximum lateral acceleration αymax1, and when vehicle yaw moment control in the locked state is performed when the vehicle speed is equal to or greater than the threshold, the maximum lateral acceleration that can be generated is higher than the maximum lateral acceleration αymax1. In other words, the free state and the locked state are switched so as to generate the greater maximum lateral acceleration between the maximum lateral acceleration obtained by steering control in the free state and the maximum lateral acceleration obtained by vehicle yaw moment control in the locked state. Note that the threshold can be set to a vehicle speed that deviates from the vehicle speed V1 at which the maximum lateral acceleration αymax1 is generated in vehicle yaw moment control in the locked state, and the vehicle speed V1 at which the maximum lateral acceleration αymax1 is generated in vehicle yaw moment control in the locked state is not necessarily set as the threshold.

[0047] 9 is a time chart showing how the steering lock switching mechanism 90 switches between lock / free and turning control during deceleration control when an abnormality occurs in the steering function of the steer-by-wire system 40 while the vehicle 10 is traveling. In FIG. 9, when an abnormality occurs in the steering function of the steer-by-wire system 40 at time t1, the vehicle speed at that time is equal to or greater than a threshold, so the front wheels 11, 12 are placed in a steering lock state and vehicle yaw moment control is performed.

[0048] Then, as the vehicle decelerates from time t1, when the vehicle speed falls below a threshold at time t2, steering control is implemented with the front wheels 11, 12 in a steer-free state, and deceleration continues with steering control being carried out in this steer-free state, until the vehicle 10 comes to a stop (vehicle speed = 0 km / h) at time t3. Here, if the vehicle speed when an abnormality occurs in the steering function of the steer-by-wire system 40 is below the threshold, the front wheels 11, 12 will not be placed in a steer-lock state and vehicle yaw moment control will not be carried out, and steering control will be carried out in a steer-free state from the start.

[0049] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0050] For example, vehicle 10 may be a vehicle in which the rear wheels are steered by steer-by-wire system 40. Furthermore, turning control by distributing braking and driving forces to the front and rear wheels is not limited to being performed by the driver in manual driving mode, but can also be applied when an abnormality occurs in the steering function of the steer-by-wire system in autonomous driving mode. Furthermore, the steering operation input mechanism in steer-by-wire system 40 is not limited to steering wheel 51, but may be a lever, joystick, or the like.

[0051] Furthermore, the control unit that controls the steering lock switching mechanism 90 (steering lock actuator 91) is not limited to the integrated control unit 34. For example, the steering control unit 32, the brake control unit 33, etc. may be included in the system that controls the steering lock switching mechanism 90 (steering lock actuator 91). Furthermore, the system may include a control unit for controlling the steering lock switching mechanism 90 at the same level as the steering control unit 32, the brake control unit 33, etc.

[0052] 10... vehicle, 11, 12... front wheels (steered wheels), 15-18... brake actuator, 30... vehicle control device, 30A... control unit, 40... steer-by-wire system, 90... steering lock switching mechanism, 91... steering lock actuator

Claims

1. A vehicle control device provided in a vehicle equipped with a steer-by-wire system that steers steerable wheels among the vehicle's wheels and is mechanically separated from a steering operation input mechanism, wherein a control unit provided in the vehicle control device, when receiving an abnormality signal from the steering function of the steer-by-wire system, controls the steerable wheels to be in a locked state if the speed of the vehicle is equal to or greater than a predetermined speed threshold, and controls the steerable wheels to be in a free state if the speed of the vehicle is below the speed threshold.

2. A vehicle control device according to claim 1, wherein the control unit changes the speed threshold value in accordance with the size of a scrub radius of the steered wheels.

3. A vehicle control device as claimed in claim 1, wherein the control unit, when the steered wheels are controlled to be in a locked state, applies a first braking / driving force to the steered wheels, thereby executing vehicle yaw moment control to generate a yaw moment in the vehicle; and, when the steered wheels are controlled to be in a free state, calculates a second braking / driving force to be applied to the turning inner wheel and turning outer wheel of the vehicle at the steered wheels in accordance with the setting of a scrub radius at the steered wheels, and executes steering control of the steered wheels based on the second braking / driving force.

4. A vehicle control method executed by a control unit of a vehicle equipped with a steer-by-wire system, which, when the steering function of the vehicle fails from normal operation, controls the steered wheels to be in a locked state if the vehicle speed is 60 km / h or more, and controls the steered wheels to be in a free state if the vehicle speed is less than 30 km / h.

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