Vehicle control device and vehicle control method

Abstract

A vehicle control device according to the present invention sets the size of the scrub radius of a steering wheel to a first positive value or a first negative value when an abnormality occurs in the steering function of a steer-by-wire system. In addition, in a vehicle control method according to the present invention, the size of the scrub radius of a steering wheel is changed when the steering function of a steer-by-wire system ceases to operate normally. Accordingly, it is possible to suppress a decrease in turning performance due to the specification of the scrub radius of the steering wheel when an abnormality occurs in the turning function of the steer-by-wire system.

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 vehicle steering device of Patent Document 1 includes a knuckle that supports an upper support point and a lower support point on the vehicle body via suspension members, with the upper support point being located more inward than the inner side surface of the wheel in the vehicle width direction; a kingpin axis changing device that has a first degree of freedom for changing the kingpin offset amount and a second degree of freedom for changing the kingpin inclination angle and is capable of moving the lower support point between a position more inward and a position more outward than the side surface; a steering control device that controls the steering angle of the wheel based on a target steering angle θ; and a kingpin axis control device that controls the kingpin axis changing device in accordance with the target steering angle θ.

[0003] Japanese Patent Application Laid-Open No. 2009-202606

[0004] In a vehicle equipped with a steer-by-wire system that steers steerable wheels that are mechanically disconnected 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, causing the vehicle to turn, by generating a difference in braking / driving force between the left and right wheels of the vehicle. Furthermore, when a difference in braking / driving force between the left and right steerable wheels is generated, the steerable wheels turn according to the scrub radius, which is an alignment characteristic. Therefore, by allocating braking / driving force to the steerable wheels to steer the steerable wheels in the turning direction of the vehicle, turning performance can be improved. However, depending on the specifications of the scrub radius of the steerable wheels, allocating braking / driving force to the steerable wheels may not provide a sufficient turning effect due to the steering of the steered wheels.

[0005] Therefore, an object of the present invention is to provide a vehicle control device and a vehicle control method that can prevent the turning performance from being reduced due to the specifications of the scrub radius of the steered wheels when an abnormality occurs in the steering function of the steer-by-wire system.

[0006] Therefore, in one aspect, a vehicle control device according to the present invention controls an actuator that changes the size of the scrub radius of the steered wheels when an abnormality signal is received in the steering function of the steer-by-wire system, so that the size of the scrub radius of the steered wheels is set to a first positive value or a first negative value. Also, in one aspect, a vehicle control method according to the present invention changes the size of the scrub radius of the steered wheels by controlling an actuator when the steering function of the steer-by-wire system has failed from normal operation.

[0007] According to the present invention, when an abnormality occurs in the steering function of the steer-by-wire system, the specifications of the scrub radius of the steered wheels can prevent the turning performance from being reduced.

[0008] 1 is an overall configuration diagram of a vehicle control system; FIG. 2 is a block diagram showing a schematic diagram of a control system for various actuators; FIG. 3 is a diagram showing an example of the correlation between scrub radius and lateral force in a front wheel; FIG. 4 is a flowchart showing the flow of turning control; FIG. 5 is a time chart showing the start timing of braking / driving force distribution in turning control; FIG. 6 is a diagram showing one embodiment of the configuration of an active suspension; FIG. 7 is a diagram showing a state in which the scrub radius is changed using the active suspension; and FIG. 8 is a diagram showing one embodiment of an actuator attached to a suspension arm.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle control device and a vehicle control method according to an embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a diagram showing the overall configuration of 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.

[0010] As will be described in detail later, when an abnormality occurs in the steering function of the steer-by-wire system of the vehicle 10, the vehicle control system 100 turns the vehicle 10 by distributing braking / driving force to the front and rear wheels, and when implementing this braking / driving force distribution, executes control to change the scrub radius of the front wheels, which are the steered wheels. Below, the vehicle control system 100 will be described in detail with reference to Figures 1 and 2.

[0011] 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. The front wheels 11, 12 are first wheels that are steered wheels, and the rear wheels 13, 14 are second wheels that are not steered wheels.

[0012] The vehicle 10 includes a drive device 70 that applies a driving force to the vehicle 10. The drive device 70 includes, as driving force actuators, a motor 71 that applies a driving force to the front wheels 11, 12 and a motor 72 that applies a driving force to the rear wheels 13, 14. The drive force control unit 31 acquires information such as the amount of operation of an accelerator pedal 73 from an accelerator pedal sensor 74. The drive force control unit 31 then controls the driving forces applied to the front wheels 11, 12 and the rear wheels 13, 14 by outputting control signals to the motors 71, 72 in accordance with a target driving force based on the amount of operation of the accelerator pedal 73, etc.

[0013] Vehicle 10 also includes, as a steering device, a steer-by-wire system 40 in which a steering wheel 51 serving 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.

[0014] Steering control unit 32 acquires information such as the operation angle θ of steering wheel 51 detected by operation angle sensor 52, and calculates a target steering angle and a target reaction torque from the operation angle θ, etc. Steering control unit 32 then controls wheel actuator 42 so that the steering angle of front wheels 11, 12 becomes the target steering angle, and also controls reaction force actuator 41 so that the target reaction torque is applied to steering wheel 51.

[0015] The vehicle 10 also includes a braking device 60 that applies braking forces to 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 the wheels 11, 12, 13, and 14. The brake control unit 33 controls the braking forces that the brake actuators 15, 16, 17, and 18 apply to the wheels 11, 12, 13, and 14 based on the output of the brake pedal sensor 62 and the like.

[0016] The vehicle 10 also includes a scrub radius variable device 80. The scrub radius variable device 80 has scrub radius variable actuators 81, 82 that vary the scrub radius of the front wheels 11, 12, and a suspension control unit 34 that controls the scrub radius variable actuators 81, 82. The scrub radius variable actuators 81, 82 will be described in detail later, but may be, for example, actuators attached to suspension arms of the vehicle 10 or active suspensions provided on the vehicle 10.

[0017] As will be described in detail later, when suspension control unit 34 acquires an abnormality signal in the steering function of steer-by-wire system 40, it controls scrub radius variable actuators 81, 82 so that the magnitude of the scrub radius of front wheels 11, 12 is set to a predetermined target value (first positive value or first negative value). In other words, when the steering function of steer-by-wire system 40 fails from normal operation, suspension control unit 34 controls scrub radius variable actuators 81, 82 to change the magnitude of the scrub radius of front wheels 11, 12.

[0018] When an abnormality occurs in the steering function of the steer-by-wire system 40, the driving force control unit 31 and the brake control unit 33 perform turning control to turn the vehicle 10 by distributing the braking and driving forces of the wheels 11-14. In order to stably obtain the turning effect by steering the front wheels 11, 12 during such turning control, the suspension control unit 34 has a function to change the scrub radius of the front wheels 11, 12 from the standard specification value to a target value suitable for turning control.

[0019] The driving force control unit 31, steering control unit 32, brake control unit 33, and suspension control unit 34 are each equipped with a microcomputer 31A, 32A, 33A, and 34A, respectively. Each of the microcomputers 31A, 32A, 33A, and 34A is equipped with a microprocessor unit (MPU), read-only memory (ROM), random access memory (RAM), and the like, all of which are not shown, and various functions are realized by causing the MPU to run programs stored in the ROM, which serves as a storage unit.

[0020] The driving force control unit 31, the steering control unit 32, the brake control unit 33, and the suspension 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.

[0021] Communication is possible between the steering control unit 32 and the brake control unit 33, between the steering control unit 32 and the driving force control unit 31, and further between the steering control unit 32 and the suspension control unit 34. When the brake control unit 33, the driving force control unit 31, and the suspension control unit 34 receive an abnormality signal from the steering control unit 32 regarding the steering function of the steer-by-wire system 40, they perform turning control to change the direction of travel of the vehicle 10 in place of the steer-by-wire system 40.

[0022] That is, steering control unit 32 has a function of diagnosing whether or not there is an abnormality in the steering function of steer-by-wire system 40. Note that an abnormality in the steering function is a state in which front wheels 11, 12, which are steerable wheels, cannot be steered and the steering angle of front wheels 11, 12 cannot be controlled to a target steering angle corresponding to the operating angle θ of steering wheel 51, and is caused by a malfunction of wheel actuator 42, an abnormality in the drive circuit of wheel actuator 42, malfunctions of various sensors, etc.

[0023] Here, the vehicle control device 30 can have a vehicle integrated control unit that is a higher-level control unit than the driving force control unit 31, steering control unit 32, brake control unit 33, and suspension control unit 34. The vehicle integrated control unit can be configured to acquire an abnormality signal regarding the steering function from the steering control unit 32, and output a turning control command signal to the brake control unit 33, driving force control unit 31, and suspension control unit 34.

[0024] 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. The turning control that is performed by brake control unit 33 and driving force control unit 31 includes vehicle yaw moment control that generates a yaw moment in vehicle 10, and steering control that steers front wheels 11, 12 by utilizing alignment characteristics.

[0025] Vehicle yaw moment control is a control that generates a difference in braking / driving force between the left and right rear wheels 13, 14, thereby generating a yaw moment in the vehicle 10 according to the operating angle θ of the steering wheel 51, and turns the vehicle 10 in the operating direction of the steering wheel 51. For example, when turning the vehicle 10 to the right, a braking force is applied to the right rear wheel 14 to generate a yaw moment that turns the vehicle 10 to the right.

[0026] The steering control is a control that generates a difference in braking / driving force between the front wheels 11, 12, and thereby steers the front wheels 11, 12 in a direction according to the operating angle θ of the steering wheel 51 according to the alignment characteristics (scrub radius). For example, when turning the vehicle 10 to the right, if the scrub radius of the front wheels 11, 12 is negative, the front wheels 11, 12 can be steered to the right by applying a braking force to the left front wheel 11.

[0027] Depending on the specifications of the scrub radii of the front wheels 11, 12, a sufficient turning effect may not be obtained even when braking / driving force distribution (for example, application of braking force to one wheel) is performed to steer the front wheels 11, 12. Therefore, when an abnormality occurs in the steering function of the steer-by-wire system 40, the suspension control unit 34 changes the scrub radii of the front wheels 11, 12 from the standard specifications to a target scrub radius that is pre-set as a scrub radius that provides a sufficient turning effect through braking / driving force distribution to the front wheels 11, 12. Then, the brake control unit 33 and the driving force control unit 31 perform braking / driving force distribution (in other words, steering control) for the front wheels 11, 12 with the scrub radii of the front wheels 11, 12 changed to the target scrub radii.

[0028] 3 is a diagram showing an example of the correlation between the scrub radius of the front wheels 11, 12 and the lateral force (in other words, the turning effect) generated by the front wheels 11, 12 when braking / driving force distribution is performed between the front wheels 11, 12. Note that the correlation between the scrub radius and the lateral force shown in FIG. 3 varies depending on the tread and wheelbase of the vehicle 10.

[0029] 3, the range of scrub radii where the lateral force is equal to or less than the threshold value is a region where steering of the front wheels 11, 12 cannot be expected to have a turning effect even if braking / driving force distribution is performed on the front wheels 11, 12. When the scrub radii of the front wheels 11, 12 are negative and the vehicle 10 is to turn right, braking force is applied to the left front wheel 11, for example, to steer the front wheels 11, 12 to the right. However, applying braking force to the left front wheel 11 generates a yaw moment in a direction that turns the vehicle 10 left.

[0030] Therefore, if the turning effect of steering to the right is small, the turning effect of the steering is canceled out by the yaw moment in the direction that turns the vehicle 10 in the opposite direction, and no turning effect can be expected from the steering. Therefore, if the target scrub radius is set to be negative, the size of the target scrub radius (more specifically, the absolute value of the distance) needs to be made large to some extent so that the turning effect of the steering exceeds the turning force caused by the yaw moment that occurs in the opposite direction.

[0031] On the other hand, when the scrub radius of the front wheels 11, 12 is positive and the vehicle 10 is to turn right, for example, braking force is applied to the right front wheel 12 to steer the front wheels 11, 12 to the right. The braking / driving force distribution for steering the front wheels 11, 12 to the right also generates a yaw moment that turns the vehicle 10 to the right. Therefore, when the target scrub radius is positive, the turning effect of the steering can be obtained even if the target scrub radius is shorter than when the target scrub radius is negative. Therefore, the range of scrub radii where the lateral force is equal to or less than the threshold value includes a larger negative region, and in the example of FIG. 3 , it ranges from near zero scrub to a predetermined negative value.

[0032] The target scrub radius is set to a first negative value or a first positive value outside the range of scrub radii where the lateral force is equal to or less than the threshold value. If the braking / driving force distribution to the front wheels 11, 12 is implemented after the scrub radius change control is executed, the turning effect due to steering is prevented from being offset by the yaw moment generated by the braking / driving force distribution, regardless of the scrub radius specifications of the vehicle 10, and the turning effect due to steering the front wheels 11, 12 is sufficiently obtained.

[0033] 4 is a flowchart showing the flow of turning control (in other words, a vehicle control method) when an abnormality occurs in the steering function of the steer-by-wire system 40. In the vehicle control system 100, the driving force control unit 31, steering control unit 32, brake control unit 33, and suspension control unit 34 cooperate to execute turning control, but for the sake of simplicity, the description will be given assuming that the control unit 30A of the vehicle control device 30 executes the control.

[0034] In step S101, control unit 30A diagnoses the steering function of steer-by-wire system 40. Control unit 30A can diagnose the steering function based on, for example, changes in the absolute value of the deviation between the target steering angle and the actual steering angle, and can diagnose the occurrence of an abnormality in the steering function when the absolute value of the deviation remains equal to or greater than a threshold value for a predetermined period of time.

[0035] Next, in step S102, control unit 30A determines whether or not an abnormality in the steering function has been diagnosed as a result of diagnosing the steering function of steer-by-wire system 40. Here, if control unit 30A diagnoses that steer-by-wire system 40 is normal and that the steering angle of front wheels 11, 12 can be controlled to the target steering angle, control unit 30A proceeds to step S103.

[0036] In step S103, the control unit 30A calculates the target steering angle (in other words, the target tire angle) of the front wheels 11, 12, which are the steered wheels, based on the operation angle θ of the steering wheel 51, etc. Then, the control unit 30A controls the wheel actuator 42 of the steer-by-wire system 40 based on the target steering angle, and steers the front wheels 11, 12 to the target steering angle.

[0037] On the other hand, if an abnormality occurs in the steer-by-wire system 40 and it becomes impossible to control the steering angle of the front wheels 11, 12 to the target steering angle, the control unit 30A proceeds from step S102 to step S105 and thereafter, and performs turning control to change the direction of travel of the vehicle 10 by allocating braking / driving force to the wheels 11-14, instead of the steer-by-wire system 40. Furthermore, the control unit 30A performs control to change the scrub radius of the front wheels 11, 12 as necessary in the turning control based on braking / driving force allocation.

[0038] In other words, when the microcomputer 34A of the steering control unit 32 detects an abnormality in the steering function of the steer-by-wire system 40, it outputs an abnormality signal to the brake control unit 33, the driving force control unit 31, and the suspension control unit 34 to command the implementation of turning control. Then, the brake control unit 33 and the driving force control unit 31 implement braking / driving force distribution, and the suspension control unit 34 implements change of the scrub radius of the front wheels 11, 12.

[0039] In step S105, the control unit 30A determines whether the standard scrub radii of the front wheels 11, 12 are within a predetermined range defined as a range in which no turning effect can be expected from steering. If the standard scrub radii of the front wheels 11, 12 are within the range in which no turning effect can be expected from steering, the control unit 30A determines that the target scrub radii must be changed to a value outside that range (see FIG. 3). In other words, the control unit 30A controls the scrub radius variable actuators 81, 82 to change the scrub radii of the front wheels 11, 12 from the standard specifications only if the standard scrub radii of the front wheels 11, 12 are smaller than a predetermined value.

[0040] If it is necessary to change the scrub radius of the front wheels 11, 12, that is, if the standard specifications for the scrub radius of the front wheels 11, 12 are within a range in which no turning effect can be expected from steering, the control unit 30A proceeds to step S106 and subsequent steps. On the other hand, if it is not necessary to change the scrub radius of the front wheels 11, 12, that is, if the standard specifications for the scrub radius of the front wheels 11, 12 are within a range in which no turning effect can be expected from steering, the control unit 30A bypasses steps S106 to S109 and proceeds to step S110, where it cancels the scrub radius change process.

[0041] In step S106, the control unit 30A calculates braking / driving force commands for the rear wheels 13, 14 based on the driver's operation amounts, specifically, the accelerator operation amount, the brake operation amount, and the operation angle θ of the steering wheel 51. That is, in step S106, the control unit 30A determines a braking / driving force distribution for the rear wheels 13, 14 for generating a yaw moment in the vehicle 10 according to the operation angle θ of the steering wheel 51 while responding to the driver's acceleration / deceleration request.

[0042] Next, in step S107, the control unit 30A controls the scrub radius variable actuators 81, 82 to change the scrub radius of the front wheels 11, 12 from the standard specification to a target scrub radius (more specifically, a first positive value or a first negative value) for turning control when the steer-by-wire system 40 fails. The target scrub radius can be fixed in advance to either the first positive value or the first negative value. The control unit 30A can also select either the first positive value or the first negative value based on the standard specification of the scrub radius of the front wheels 11, 12 (or the scrub radius of the front wheels 11, 12 when an abnormality occurs in the steering function), the variable range of the scrub radius by the scrub radius variable actuators 81, 82, etc.

[0043] In step S108, control unit 30A controls the braking / driving force applied to each of rear wheels 13, 14 based on the braking / driving force command calculated in step S106, thereby generating a difference in braking / driving force between the left and right rear wheels 13, 14 and generating a yaw moment in vehicle 10. In other words, in step S108, control unit 30A turns vehicle 10 by controlling the braking / driving force at rear wheels 13, 14, which are wheels other than the steered wheels (front wheels 11, 12).

[0044] In step S109, the control unit 30A determines whether the change control of the scrub radius of the front wheels 11, 12 has been completed and the scrub radius of the front wheels 11, 12 has been changed to the target scrub radius, or whether the scrub radius of the front wheels 11, 12 is in a transient state in which it is changing toward the target scrub radius. If the scrub radius of the front wheels 11, 12 is in a transient state in which it has not yet reached the target scrub radius, the control unit 30A returns to step S108 and turns the vehicle 10 by controlling the braking / driving force at the rear wheels 13, 14.

[0045] On the other hand, when the scrub radius of the front wheels 11, 12 reaches the target scrub radius, the control unit 30A proceeds from step S109 to step S110, and calculates the braking / driving force commands for the rear wheels 13, 14 based on the amount of operation by the driver, as in step S106. Next, the control unit 30A proceeds to step S111, and controls the braking / driving force applied to the rear wheels 13, 14 based on the braking / driving force commands for the rear wheels 13, 14 calculated in step S110, and also controls the braking / driving force applied to the front wheels 11, 12 so as to generate a difference in braking / driving force between the front wheels 11, 12 in order to steer the front wheels 11, 12 in the turning direction corresponding to the operation angle θ of the steering wheel 51.

[0046] In other words, when a change in the scrub radius of the front wheels 11, 12 is requested, the control unit 30A executes turning control through braking / driving force distribution to the rear wheels 13, 14 (in other words, vehicle yaw moment control) until the scrub radius of the front wheels 11, 12 is set to the target scrub radius, and then, after the change in the scrub radius is completed and the scrub radius is set to the target scrub radius, executes turning control through braking / driving force distribution to the front wheels 11, 12. On the other hand, if a change in the scrub radius of the front wheels 11, 12 is not necessary and the process proceeds from step S102 to step S110, the control unit 30A starts turning control through braking / driving force distribution to the rear wheels 13, 14 and turning control through braking / driving force distribution to the front wheels 11, 12 in parallel.

[0047] Figure 5 is a time chart showing differences in the timing at which braking / driving force distribution starts during turning control that requires a change in the scrub radius of the front wheels 11, 12. At time t1 in Figure 5, when it is diagnosed that the steering function of steer-by-wire system 40 has malfunctioned from normal operation, an abnormality flag for the steering function is raised. Then, based on the raising of the abnormality flag for the steering function, control is initiated to change the scrub radius of the front wheels 11, 12 to a target scrub radius for turning control, and the scrub radius of the front wheels 11, 12 changes from the standard specification toward the target scrub radius.

[0048] Furthermore, when the steering function abnormality flag is raised, a yaw moment is generated in the vehicle 10 due to the difference in braking / driving force between the left and right rear wheels 13, 14, and braking / driving force control is initiated to turn the vehicle 10 in the turning direction intended by the driver. For example, when turning the vehicle 10 to the right, braking force is applied to the right rear wheel 14 to generate a yaw rate in the right turning direction.

[0049] Then, at time t2, when a yaw moment is being generated by the braking / driving force distribution of the rear wheels 13, 14, and the scrub radius of the front wheels 11, 12 reaches the target scrub radius, braking / driving force distribution that generates a braking / driving force difference between the left and right front wheels 11, 12 is initiated, thereby steering the front wheels 11, 12 in the turning direction. For example, when turning the vehicle 10 to the right, if the target scrub radius is set to a first negative value, applying braking force to the left front wheel 11 causes the front wheels 11, 12 to turn right.

[0050] As described above, the turning effect caused by steering can be stably achieved by starting the braking / driving force control of the front wheels 11, 12 after the scrub radius of the front wheels 11, 12 reaches the target scrub radius. Note that the control unit 30A can start the braking / driving force control of the front wheels 11, 12 when the scrub radius of the front wheels 11, 12 approaches the target scrub radius to a certain extent (in other words, when it reaches an intermediate value between the standard specification and the target scrub radius).

[0051] The variable scrub radius actuators 81, 82 will be described in detail below. Figure 6 is a front view showing one embodiment of the configuration of an active suspension as the variable scrub radius actuators 81, 82. The front wheels 11, 12 each have a tire 91 on the outer periphery and a wheel 92 in the center. The wheel 92 is attached to a hub 93, and a brake disc 94 that constitutes the braking device 60 is attached to the hub 93.

[0052] The hub 93 is attached to the vehicle body 10A via an upper arm 95 and a lower arm 96, and an active suspension 97 is provided between the upper arm 95 and the vehicle body 10A. The active suspension 97 is a mechanism that can arbitrarily change the vehicle height of the vehicle 10.

[0053] 7 shows a state in which the scrub radius of the front wheels 11, 12 shown in FIG. 6 has been changed from the standard specification state to a target scrub radius based on the occurrence of an abnormality in the steering function. When changing the scrub radius, the active suspension 97 is stroked to roll the vehicle body 10A, which tilts the upper arm 95 and lower arm 96 connected to the vehicle body 10A, generating a camber angle at the front wheels 11, 12 and changing the scrub radius of the front wheels 11, 12. In other words, when the vehicle 10 is equipped with the active suspension 97, the control unit 30A can change the scrub radius of the front wheels 11, 12 to the target scrub radius by controlling the stroke amount of the active suspension 97.

[0054] 8 is a diagram showing one embodiment of actuators attached to suspension arms as variable scrub radius actuators 81, 82. The front wheels 11, 12 each have a tire 91 on the outer periphery and a wheel 92 in the center. The wheel 92 is attached to a hub 93, and a brake disc 94 that constitutes the braking device 60 is attached to the hub 93.

[0055] The hub 93 is supported by an upper arm 95 and a lower arm 96, and a shock absorber 98 is provided between the lower arm 96 and the vehicle body 10A. The knuckle 99 has an upper support point moving device 99A and a lower support point moving device 99B, and is further provided with actuators 100A and 100B that act on the upper support point moving device 99A and the lower support point moving device 99B to move the position of the knuckle 99. The control unit 30A controls the actuators 100A and 100B to change the kingpin position (shown by the dotted line in FIG. 8 ) and change the scrub radius to the target scrub radius.

[0056] 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.

[0057] For example, the vehicle may have a first wheel, which is a steered wheel steered by the steer-by-wire system, as a rear wheel, and a second wheel, which is not a steered wheel, as a front wheel. Also, turning control by distributing braking and driving force to the front and rear wheels is not limited to being performed in a manual driving mode by the driver, but can also be applied when an abnormality occurs in the steering function of the steer-by-wire system in an automated driving mode.

[0058] Furthermore, the target value of the scrub radius of the steered wheels when an abnormality occurs in the steering function of the steer-by-wire system (more specifically, the first negative value or the first positive value) can be changed depending on the driving state of the vehicle 10 at that time and driving conditions such as the unevenness of the road surface on which the vehicle 10 is traveling. Furthermore, the steering operation input mechanism in the steer-by-wire system is not limited to the steering wheel, and may be a lever, a joystick, or the like.

[0059] 10... Vehicle, 11, 12... Front wheels (steered wheels, first wheels), 13, 14... Rear wheels (second wheels other than steered wheels), 30... Vehicle control device, 30A... Control unit, 40... Steer-by-wire system, 60... Braking device, 70... Drive device, 81, 82... Scrub radius variable actuator (actuator)

Claims

1. A vehicle control device provided on a vehicle, comprising: a steer-by-wire system that steers a first wheel that is mechanically disconnected from a steering operation input mechanism when the first wheel is a steerable wheel among the vehicle's wheels; and an actuator that is controlled to change the size of the scrub radius of the first wheel, wherein a control unit provided in the vehicle control device controls the actuator so that the size of the scrub radius of the first wheel is set to a first positive value or a first negative value when an abnormality signal is acquired from the steering function of the steer-by-wire system.

2. A vehicle control device according to claim 1, wherein the control unit applies a braking / driving force to the first wheel and executes steering control of the first wheel after the magnitude of the scrub radius of the first wheel is set to the first positive value or the first negative value.

3. A vehicle control device as described in claim 2, wherein, when a wheel other than a steered wheel among the wheels is designated as the second wheel, the control unit applies a braking / driving force to the second wheel until the magnitude of the scrub radius of the first wheel is set to the first positive value or the first negative value, thereby executing vehicle yaw moment control to generate a yaw moment in the vehicle.

4. A vehicle control device according to claim 1, wherein the control unit controls the actuator when an abnormality signal is acquired from the steering function of the steer-by-wire system, only if the size of the scrub radius of the first wheel is smaller than a predetermined value.

5. A vehicle control device according to claim 1, wherein the actuator is an actuator attached to a suspension arm of the vehicle.

6. A vehicle control device according to claim 1, wherein the actuator is an active suspension provided on the vehicle.

7. A vehicle control method executed by a control unit provided in a vehicle equipped with a steer-by-wire system that steers steerable wheels that are mechanically separated from a steering operation input mechanism, and an actuator that changes the size of the scrub radius of the steerable wheels by being controlled, wherein when the steering function of the steer-by-wire system fails to function normally, the size of the scrub radius of the steerable wheels is changed by controlling the actuator.

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