Vehicle control device and vehicle control method

Abstract

In one aspect of a vehicle control device and a vehicle control method according to the present invention, in steering reaction force control, in which steering reaction force torque to be applied to a steering operation input mechanism operated by a driver is derived on the basis of the motion state of a vehicle and a reference steering reaction force characteristic indicating a characteristic of steering reaction force torque with respect to the motion state of the vehicle, the reference steering reaction force characteristic is changed in accordance with a characteristic obtained by trial driving using a prescribed trial steering reaction force characteristic. This makes it possible for the characteristics of the steering reaction torque applied to the steering operation input mechanism to be changed to characteristics that are suited to the aptitude of the driver.

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 compares a standard yaw rate calculated from the steering angle, vehicle speed, etc. with an actual yaw rate obtained from a sensor, and if it determines that understeer has occurred, it adds a steering reaction force component to the auxiliary steering torque, that is, reduces the auxiliary steering torque or outputs the auxiliary torque in the opposite direction to the steering direction, thereby warning the driver not to steer any further.

[0003] Japanese Patent Application Publication No. 11-020728

[0004] However, if the characteristics of the steering reaction torque applied to the steering operation input mechanism operated by the driver do not match the driver's aptitude, it may become difficult for the driver to operate the steering operation input mechanism as intended, which could result in a decrease in the vehicle's driving stability.

[0005] The present invention has been made in consideration of the current situation, and its purpose is to provide a vehicle control device and a vehicle control method that can change the characteristics of the steering reaction torque applied to a steering operation input mechanism to characteristics that suit the aptitude of the driver.

[0006] In one aspect, a vehicle control device according to the present invention includes a steering reaction torque calculation unit that calculates a steering reaction torque to be applied to a steering operation input mechanism operated by a driver based on a reference steering reaction torque characteristic that indicates a characteristic of the steering reaction torque relative to the vehicle's motion state and the vehicle's motion state, and a reaction force characteristic change unit that changes the reference steering reaction torque characteristic in accordance with a characteristic obtained by trial driving in which a predetermined trial steering reaction torque characteristic is used.In one aspect, a vehicle control method according to the present invention changes the characteristic of the steering reaction torque to be applied to the steering operation input mechanism in accordance with a tendency of the vehicle to sway left and right due to operation of the steering operation input mechanism by the driver when the vehicle is made to turn using a braking / driving force difference between the left and right wheels of the vehicle in a state in which the steering function of a steer-by-wire system has failed.

[0007] According to the present invention, the characteristics of the steering reaction torque applied to the steering operation input mechanism can be changed to suit the aptitude of the driver, thereby maintaining the running stability of the vehicle.

[0008] 1 is an overall configuration diagram showing a vehicle control system. FIG. 2 is a block diagram showing an overview of each control system of the vehicle control system. FIG. 3 is a block diagram showing steering reaction torque control in a first embodiment. FIG. 4 is a flowchart showing a process for changing a steering reaction force characteristic in a first embodiment. FIG. 5 is a time chart showing a difference in fluctuation of an actual yaw rate due to a steering reaction force characteristic. FIG. 6 is a flowchart showing a process for counting the number of reversals NS. FIG. 7 is a flowchart showing a second embodiment of a process for changing a steering reaction force characteristic. FIG. 8 is a flowchart showing a third embodiment of a process for changing a steering reaction force characteristic. FIG. 9 is a block diagram showing steering reaction force torque control in a fourth embodiment. FIG. 10 is a flowchart showing a process for changing a steering reaction force characteristic in a fourth embodiment. FIG. 11 is a flowchart showing a process for changing a steering reaction force characteristic in a fifth embodiment. FIG. 12 is a flowchart showing a process for changing a steering reaction force characteristic. FIG. 13 is a flowchart showing a process for changing a steering reaction force characteristic in a sixth embodiment. FIG. 14 is a flowchart showing a process for changing a steering reaction force characteristic in a sixth embodiment. FIG. 15 is a flowchart showing a process for changing a steering reaction force characteristic in a sixth embodiment. FIG. 16 is a flowchart showing a process for changing a steering reaction force characteristic in a sixth embodiment.

[0009] Hereinafter, embodiments 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 mounted on a vehicle 10. Fig. 2 is a block diagram showing the control systems for braking, driving, and steering of the vehicle control system 100. 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.

[0010] Vehicle 10 includes a driving force actuator 70 that applies driving force to vehicle 10, which includes a motor 71 that applies driving force to front wheels 11, 12 and a motor 72 that applies driving force to rear wheels 13, 14. Driving force control unit 31 acquires information on the amount of operation of accelerator pedal 73 from an accelerator pedal sensor 74. Driving force control unit 31 then sets a target driving force based on the amount of operation of accelerator pedal 73, etc., and controls the driving forces applied to front wheels 11, 12 and rear wheels 13, 14 by outputting control signals corresponding to the target driving force to motors 71, 72.

[0011] Vehicle 10 also includes a steer-by-wire system 40 as a steering device. Steer-by-wire system 40 is a steering device in which a steering wheel 51, which is a steering operation input mechanism operated by the driver of vehicle 10, is mechanically separated from left and right front wheels 11, 12, which are steered wheels. Steer-by-wire system 40 detects the steering angle θ of steering wheel 51 with a sensor, and controls an actuator based on an electrical signal of the steering angle θ of steering wheel 51, thereby turning front wheels 11, 12.

[0012] Steer-by-wire system 40 has reaction force actuator 41 that applies a steering reaction torque to steering wheel 51, wheel actuator 42 that applies a steering force to front wheels 11, 12, steering angle sensor 43 that detects steering angle δ of front wheels 11, 12, steering angle sensor 52 that detects steering angle θ of steering wheel 51 that corresponds to the operation amount of the steering operation input mechanism, and steering control unit 32 that controls reaction force actuator 41 and wheel actuator 42.

[0013] Steering angle sensor 43 detects the steering angle δ of front wheels 11, 12, for example, by detecting the position of a rack in a rack-and-pinion mechanism that constitutes wheel actuator 42. Steering angle sensor 43 can also detect the steering angle δ of front wheels 11, 12 by detecting the rotation angle of a steering motor that constitutes wheel actuator 42. Note that the steering operation input mechanism that the driver of vehicle 10 operates to change the traveling direction of vehicle 10 (in other words, the steering angle δ of front wheels 11, 12) is not limited to steering wheel 51, and may be a lever, a joystick, or the like.

[0014] Steering control unit 32 acquires information such as steering angle θ of steering wheel 51 detected by steering angle sensor 52, and calculates a target steering angle from the steering angle θ, etc. Then, steering control unit 32 controls wheel actuator 42 so that steering angle δ detected by steering angle sensor 43 approaches the target steering angle. Furthermore, as will be described in detail later, steering control unit 32 sets a target value of steering reaction torque to be applied to steering wheel 51 (in other words, target steering reaction torque) based on the motion state of vehicle 10, and controls reaction force actuator 41 to generate the target steering reaction torque.

[0015] The vehicle 10 also includes a braking system. The braking system includes a brake control unit 33, a brake pedal sensor 62 that detects the amount of operation of a brake pedal 61, brake actuators 15, 16, 17, and 18 provided on each of the wheels 11, 12, 13, and 14, and brake thrust sensors 21, 22, 23, and 24 that detect the thrust generated by the brake actuators 15, 16, 17, and 18, respectively. The brake control unit 33 controls the braking force applied to each of the wheels 11, 12, 13, and 14 by the brake actuators 15, 16, 17, and 18 based on the output of the brake pedal sensor 62 and the output of the brake thrust sensors 21, 22, 23, and 24.

[0016] The driving force control unit 31, steering control unit 32, and brake control unit 33 each include a microcomputer 31A, 32A, and 33A. Each of the microcomputers 31A, 32A, and 33A includes a microprocessor unit (MPU), read-only memory (ROM), random access memory (RAM), and other components (not shown), and various functions are realized by the MPU running programs stored in the ROM as a storage unit. The microcomputers 31A, 32A, and 33A are connected via an in-vehicle network and transmit information to one another.

[0017] The driving force control unit 31, the steering control unit 32, and the brake control unit 33 constitute a vehicle control device 30 that controls the vehicle 10. The microcomputers 31A, 32A, and 33A (in other words, the control sections of the control units 31, 32, and 33) function as a control section 30A of the vehicle control device 30.

[0018] The vehicle 10 also includes, as sensors for detecting the behavior of the vehicle 10, a yaw rate sensor 81 that detects the yaw rate γ of the vehicle 10 and a lateral acceleration sensor 82 that detects the lateral acceleration Gy of the vehicle 10. The vehicle 10 also includes a wheel speed sensor 83 that detects the wheel speeds V1-V4 of each of the wheels 11-14. The vehicle control device 30 acquires output signals from the yaw rate sensor 81, the lateral acceleration sensor 82, and the wheel speed sensor 83. The vehicle control device 30 then calculates the vehicle speed V, which is the traveling speed of the vehicle 10, based on the wheel speeds V1-V4 detected by the wheel speed sensor 83.

[0019] The following describes in detail the control of steering reaction torque (in other words, a vehicle control method related to steering reaction torque) performed by the steering control unit 32, more specifically, the microcomputer 32A serving as a control section. "First Embodiment" Fig. 3 is a block diagram of the steering control unit 32 showing a first embodiment of steering reaction torque control. The steering control unit 32 has a steering reaction torque calculation section 200 and a reaction force characteristics change section 300 as functional sections for steering reaction torque control.

[0020] The steering reaction torque calculation unit 200 calculates the steering reaction torque to be applied to the steering wheel 51 by the reaction actuator 41 based on the reference steering reaction force characteristic, which indicates the characteristic of the steering reaction torque relative to the motion state of the vehicle 10, and the motion state of the vehicle 10. Furthermore, the reaction force characteristic changing unit 300 changes the reference steering reaction force characteristic in accordance with the characteristic obtained by trial driving of the vehicle 10, in which the reference steering reaction force characteristic is set to a predetermined trial steering reaction force characteristic.

[0021] The steering reaction force characteristic in the steering reaction torque calculation unit 200 indicates the characteristic of the steering reaction force torque RT with respect to the yaw rate deviation Δγ (Δγ=γre−γac), which is the difference between the actual yaw rate γac generated in the vehicle 10 and the steering angle yaw rate γre, which is the yaw rate calculated based on the steering angle θ of the steering wheel 51 (in other words, the standard yaw rate estimated based on the steering angle θ, etc.). In other words, the steering reaction force characteristic is a characteristic that converts the yaw rate deviation Δγ, which is the motion state of the vehicle 10, into the steering reaction force torque RT.

[0022] Then, the steering reaction torque calculation unit 200 refers to the reference steering reaction force characteristic to determine the reference value RTR of the steering reaction torque RT corresponding to the yaw rate deviation Δγ at that time. Here, the steering reaction force characteristic calculation unit 200 has, as the steering reaction force characteristics, a first steering reaction force characteristic (first conversion table) in which the steering reaction force torque RT increases as the yaw rate deviation Δγ increases, and a second steering reaction force characteristic (second conversion table) in which the steering reaction force torque RT decreases as the yaw rate deviation Δγ increases.

[0023] Specifically, the steering reaction torque calculation unit 200 includes a first reference value calculation unit 201 that calculates a reference value RTR1 from the yaw rate deviation Δγ based on the first steering reaction force characteristic, and a second reference value calculation unit 202 that calculates a reference value RTR2 from the yaw rate deviation Δγ based on the second steering reaction force characteristic. The first reference value calculation unit 201 and the second reference value calculation unit 202 acquire the signal of the yaw rate deviation Δγ calculated by the steering angle yaw rate calculation unit 301 and the subtraction unit 302, and calculate the reference values ​​RTR1 and RTR2 from the acquired signal of the yaw rate deviation Δγ.

[0024] The steering angle yaw rate calculation unit 301 acquires a signal of the steering angle θ of the steering wheel 51 detected by the steering angle sensor 52 and a signal of the vehicle speed V calculated based on the wheel speeds V1-V4 detected by the wheel speed sensor 83. Then, the steering angle yaw rate calculation unit 301 calculates a steering angle yaw rate γre, which is a yaw rate estimated to occur in the vehicle 10, based on the signal of the steering angle θ and the signal of the vehicle speed V. The subtraction unit 302 calculates a yaw rate deviation Δγ by subtracting the actual yaw rate γac detected by the yaw rate sensor 81 from the steering angle yaw rate γre calculated by the steering angle yaw rate calculation unit 301, and outputs the signal of the yaw rate deviation Δγ to the first reference value calculation unit 201 and the second reference value calculation unit 202.

[0025] Then, the switch unit 203 selects either the reference value RTR1 calculated by the first reference value calculation unit 201 or the reference value RTR2 calculated by the second reference value calculation unit 202, and outputs the selected value as the reference value RTR. In other words, the steering reaction torque calculation unit 200 calculates the reference value RTR of the steering reaction torque RT using either the first steering reaction force characteristic or the second steering reaction force characteristic as the reference steering reaction force characteristic.

[0026] The steering reaction torque calculation unit 200 also has a correction term calculation unit 204 that calculates a reaction torque correction term for correcting the reference value RTR based on the motion state of the vehicle 10. The correction term calculation unit 204 sets a correction term CT that corrects the steering reaction torque to a larger value as the vehicle speed V, which is the motion state of the vehicle 10, increases. The correction term CT according to the vehicle speed V increases the steering reaction torque at high vehicle speeds, giving the driver a sense of security.

[0027] Then, the multiplier 205 multiplies the reference value RTR output by the switch 203 by the correction term CT and outputs the result as the target steering reaction torque RTtg (RTtg=RTR×CT). The steering control unit 32 controls the reaction force actuator 41 so that the target steering reaction torque RTtg is applied to the steering wheel 51.

[0028] The reaction force characteristic changing unit 300 attempts to apply a steering reaction force torque in accordance with the first steering reaction force characteristic (first trial steering reaction force characteristic) and the second steering reaction force characteristic (second trial steering reaction force characteristic) by switching the reference value RTR between the reference value RTR1 and the reference value RTR2 using the switch unit 203. Here, the behavior stability determining unit 303 determines the behavior state of the vehicle 10 during the trial drive as the characteristic obtained during the trial drive in which the steering reaction force characteristic is tried.

[0029] Then, the behavior stability determination unit 303 selects, from the first steering reaction force characteristic and the second steering reaction force characteristic, the one that more stabilizes the behavior of the vehicle 10 as the steering reaction force characteristic that better matches the driver's aptitude, and selects the selected steering reaction force characteristic as the reference steering reaction force characteristic to be used by the steering reaction force torque calculation unit 200. In other words, the behavior stability determination unit 303 outputs a selection command signal to the switch unit 203 so that the reference value RTR calculated based on the steering reaction force characteristic selected based on the behavior stability from the first steering reaction force characteristic and the second steering reaction force characteristic is output from the switch unit 203.

[0030] For example, assume that the behavioral stability of the vehicle 10 during a trial run in which a steering reaction torque is applied according to the second steering reaction torque characteristic is higher than the behavioral stability of the vehicle 10 during a trial run in which a steering reaction torque is applied according to the first steering reaction torque characteristic. In this case, the behavior stability determination unit 303 sets the switch unit 203 to output the reference value RTR2 calculated by the second reference value calculation unit 202 so that, during subsequent runs, a steering reaction torque is applied using the second steering reaction torque characteristic as the reference steering reaction torque characteristic. Note that, as will be described later, the behavior stability determination unit 303 evaluates the behavioral stability when the first steering reaction torque characteristic is applied and the behavioral stability when the second steering reaction torque characteristic is applied by determining the tendency of the vehicle 10 to sway left and right based on the actual yaw rate γac.

[0031] 4 is a flowchart showing the processing process of the steering control unit 32 (reaction force characteristic changing unit 300) for selecting a steering reaction force characteristic that matches the driver's aptitude through a trial drive that temporarily sets the steering reaction force characteristic. In step S501, the steering control unit 32 determines whether or not the current scene is a specific scene for which a trial drive is to be performed.

[0032] Specifically, in step S501, the steering control unit 32 calculates the curvature (in other words, the turning radius of the vehicle 10) from the actual yaw rate γ detected by the yaw rate sensor 81 and the vehicle speed V, and determines whether a state in which the absolute value of the change in the curvature per unit time is equal to or less than a predetermined value continues for a predetermined time. Here, a state in which the absolute value of the change in the curvature per unit time is equal to or less than the predetermined value means that the vehicle 10 is in a steady turning state or a straight-ahead state. Then, the steering control unit 32 detects a state in which the steady turning state or the straight-ahead state continues, that is, a state in which the curvature of the traveling trajectory of the vehicle 10 is stable, as a specific scene for performing a trial run.

[0033] In the trial driving in which the steering reaction force characteristic is temporarily set, the driver's steering operability changes as the steering reaction force characteristic is switched. Therefore, the steering control unit 32 avoids difficult driving situations such as changing curvature and performs the trial driving in relatively easy driving situations such as steady turning and straight driving, thereby suppressing the driver's anxiety caused by the trial driving, i.e., the switching of the steering reaction force characteristic.

[0034] If the steering control unit 32 determines in step S501 that the absolute value of the amount of change in curvature per unit time has remained equal to or less than a predetermined value for a predetermined period of time, that is, that the curvature is not stable, the process proceeds to step S502. In step S502, the steering control unit 32 performs normal steering reaction torque control, which sets the steering reaction torque in accordance with default steering reaction force characteristics (for example, first steering reaction force characteristics).

[0035] On the other hand, if the steering control unit 32 determines in step S501 that the curvature is in a stable state, that is, that the state in which the absolute value of the amount of change in the curvature per unit time is equal to or less than a predetermined value continues for a predetermined time, the process proceeds to step S503. In step S503, the steering control unit 32 performs a trial run with the first steering reaction force characteristic by setting the switch unit 203 to output the reference value RTR1 calculated by the first reference value calculation unit 201, and calculates an index value indicating the stability of the vehicle behavior during the trial run.

[0036] The steering control unit 32 calculates the number of reversals NS, which indicates the degree of sway of the actual yaw rate γac (in other words, the tendency of the vehicle 10 to sway from side to side), as an index value showing the stability of the vehicle behavior, and sets the number of reversals NS calculated during trial operation with the first steering reaction force characteristic as the first number of reversals NS1. The number of reversals NS is the number of times the sign of the differential value of the actual yaw rate γac is reversed within a set time (trial operation time), in other words, the number of times the direction of increase / decrease of the actual yaw rate γac is switched within the set time.

[0037] Here, the fewer the number of reversals NS, the less the actual yaw rate γac fluctuates (in other words, the left-right sway of the vehicle 10), indicating a more stable state of vehicle behavior. Conversely, the more the number of reversals NS, the more the actual yaw rate γac fluctuates, indicating a less stable state of vehicle behavior. If the steering reaction force characteristics do not match the driver's aptitude, it becomes difficult for the driver to operate the steering wheel 51 as intended, which tends to make the behavior of the vehicle 10 (in other words, the actual yaw rate γac) unstable.

[0038] Therefore, the steering control unit 32 can estimate that the fewer the number of reversals NS, the more the steering reaction force characteristics being tried at that time match the driver's aptitude, and conversely, the more the number of reversals NS, the more the steering reaction force characteristics being tried at that time do not match the driver's aptitude.

[0039] 5 is a time chart illustrating a change in the actual yaw rate γac when a driver for whom the behavior of the vehicle 10 is more stable with the second steering reaction force characteristic than with the first steering reaction force characteristic performs a steering operation. In this case, the first steering reaction force characteristic does not match the driver's aptitude, so when a steering reaction force torque is applied according to the first steering reaction force characteristic, the actual yaw rate γac fluctuates (the number of reversals NS) becomes large. On the other hand, the second steering reaction force characteristic matches the driver's aptitude, so when a steering reaction force torque is applied according to the second steering reaction force characteristic, the actual yaw rate γac fluctuates (the number of reversals NS) becomes small.

[0040] 6 is a flowchart showing the process of counting the number of reversals NS performed by the steering control unit 32 (behavior stability determination unit 303). In step S901, the steering control unit 32 calculates the time differential value of the actual yaw rate γac, specifically, the difference between the latest value of the actual yaw rate γac and the previous value thereof a predetermined time before.

[0041] Next, in step S902, the steering control unit 32 determines whether the sign of the time differential value of the actual yaw rate γ has reversed. That is, in step S902, the steering control unit 32 determines that a reversal has occurred when the time differential value of the actual yaw rate γ previously calculated is positive and the time differential value of the actual yaw rate γ currently calculated is negative, or when the time differential value of the actual yaw rate γ previously calculated is negative and the time differential value of the actual yaw rate γ currently calculated is positive.

[0042] If the steering control unit 32 determines that the sign of the time differential value of the actual yaw rate γ has been inverted, the steering control unit 32 proceeds to step S903. On the other hand, if the sign of the time differential value of the actual yaw rate γ remains positive or negative, the steering control unit 32 bypasses step S903 and ends this routine.

[0043] In step S903, the steering control unit 32 increments the number of reversals NS up to the previous time. Specifically, in step S903, the steering control unit 32 sets the current value of the number of reversals NS to a value obtained by adding the disturbance coefficient to the previous value of the number of reversals NS (current value of the number of reversals NS = previous value of the number of reversals NS + disturbance coefficient).

[0044] Here, the disturbance coefficient is a value that is variably set within a range of 0≦disturbance coefficient≦1.0 depending on factors that disturb the actual yaw rate γac, such as the friction coefficient μ of the road surface on which the vehicle 10 is traveling and crosswinds. Note that the steering control unit 32 can acquire disturbance information, such as the friction coefficient μ of the road surface and weather information such as wind speed and wind direction, from outside the vehicle 10 via wireless communication or the like, or from an external environment information recognition unit such as a camera provided in the vehicle 10.

[0045] The steering control unit 32 sets the disturbance coefficient to 1.0 when the road surface on which the vehicle 10 is traveling is a dry asphalt road surface and there is little crosswind, or when there is a sufficiently small disturbance. On the other hand, the steering control unit 32 brings the disturbance coefficient closer to 0 as the disturbance increases, such as when the vehicle 10 is traveling on a wet or icy road surface or when there is a strong crosswind.

[0046] By incrementing the number of reversals NS using the disturbance coefficient, the steering control unit 32 can prevent the number of reversals NS from increasing due to the influence of disturbances, and can improve the accuracy of the process of determining whether the steering reaction force characteristics match the aptitude of the driver based on the number of reversals NS. Note that the steering control unit 32 can omit changing the disturbance coefficient in response to disturbances, and can increment the number of reversals NS by a fixed value each time the sign of the time differential value of the actual yaw rate γac is reversed.

[0047] 4, the explanation will be continued. After the steering control unit 32 performs trial operation with the first steering reaction force characteristic in step S503, the process proceeds to step S504. In step S504, the steering control unit 32 performs trial operation with the second steering reaction force characteristic by setting the switch unit 203 to output the reference value RTR2 calculated by the second reference value calculation unit 202, and sets the number of reversals NS calculated at this time as the second number of reversals NS2.

[0048] The steering control unit 32 performs a trial run with the first steering reaction force characteristic in step S503, and then performs a trial run with the second steering reaction force characteristic in step S504, and then proceeds to step S505. In step S505, the steering control unit 32 compares the first number of reversals NS1 obtained during the trial run with the first steering reaction force characteristic with the second number of reversals NS2 obtained during the trial run with the second steering reaction force characteristic, and determines whether the first number of reversals NS1 is smaller than the second number of reversals NS2.

[0049] In other words, in step S505, the steering control unit 32 determines whether the vehicle 10 sways less side to side and the behavior of the vehicle 10 is more stable when the steering reaction torque is applied with the first steering reaction torque characteristic than when the steering reaction torque is applied with the second steering reaction torque characteristic. Here, if the first number of reversals NS1 is smaller than the second number of reversals NS2 and the behavior of the vehicle 10 is more stable when the steering reaction torque is applied with the first steering reaction torque characteristic than when the steering reaction torque is applied with the second steering reaction torque characteristic, the steering control unit 32 proceeds to step S506.

[0050] In step S506, the steering control unit 32 determines that the first steering reaction force characteristic is more suitable for the driver's aptitude than the second steering reaction force characteristic, and sets the steering reaction force torque to be applied in accordance with the first steering reaction force characteristic in subsequent driving. Specifically, in step S506, the steering control unit 32 sets the switch unit 203 to output the reference value RTR1 calculated by the first reference value calculation unit 201. In other words, if the steering control unit 32 confirms through the trial driving that the first steering reaction force characteristic is more suitable for the driver's aptitude than the second steering reaction force characteristic, it selects the first steering reaction force characteristic as the reference steering reaction force characteristic to be used in subsequent driving.

[0051] On the other hand, if the second reversal number NS2 is equal to or less than the first reversal number NS1 and the behavior of the vehicle 10 is more stable when the steering reaction torque is applied with the second steering reaction torque characteristic than when the steering reaction torque is applied with the first steering reaction torque characteristic, the steering control unit 32 proceeds to step S507. In step S507, the steering control unit 32 determines that the second steering reaction torque characteristic is more suited to the driver's aptitude than the first steering reaction torque characteristic, and sets the steering reaction torque to be applied in accordance with the second steering reaction torque characteristic for subsequent driving.

[0052] Specifically, in step S507, steering control unit 32 sets switch section 203 to output reference value RTR2 calculated by second reference value calculation section 202. In other words, if it is confirmed in the trial driving that the second steering reaction force characteristic is more suited to the driver's aptitude than the first steering reaction force characteristic, steering control unit 32 changes the reference steering reaction force characteristic by selecting the second steering reaction force characteristic as the reference steering reaction force characteristic to be used in subsequent normal driving.

[0053] 4, the steering control unit 32 first performs a trial of the first steering reaction force characteristic and then performs a trial of the second steering reaction force characteristic, but the order can be reversed so that the trial of the second steering reaction force characteristic is performed first and then the trial of the first steering reaction force characteristic. Furthermore, the steering control unit 32 can continue to use the steering reaction force characteristic that is selected as the one that more stabilizes the behavior of the vehicle 10 as a result of performing the trial of the first steering reaction force characteristic and the trial of the second steering reaction force characteristic until the end of the trip, and can also continue to use the steering reaction force characteristic until a change in driver is detected based on a change in the seat position of the driver's seat, etc.

[0054] Second Embodiment The second embodiment described below differs from the first embodiment in that the specific scene in which the steering reaction force characteristic is tested is when an abnormality occurs in the steering function of steer-by-wire system 40. Note that an abnormality in the steering function refers to a state in which front wheels 11, 12, which are steerable wheels, cannot be steered and the steering angle δ cannot be controlled to the target steering angle corresponding to the steering 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.

[0055] Vehicle control device 30 (control unit 30A) has a fail-safe function that, when it receives a signal indicating an abnormality in the steering function of steer-by-wire system 40, causes a difference in braking / driving force between the left and right wheels of vehicle 10, thereby causing vehicle 10 to turn. In other words, when an abnormality occurs in the steering function of steer-by-wire system 40, it becomes impossible to change steering angle δ in accordance with steering angle θ of steering wheel 51, so vehicle control device 30 generates a yaw moment in vehicle 10 in accordance with steering angle θ of steering wheel 51 due to the difference in braking / driving force between the left and right wheels.

[0056] When vehicle 10 is turned using the difference in braking / driving force between the left and right wheels, the driver experiences unique steering characteristics that differ from the steering characteristics when the turning angle δ changes in response to the steering angle θ of steering wheel 51. For this reason, whether or not the steering reaction force characteristics match the aptitude of the driver has a significant effect on steering operability.

[0057] If the steering reaction force characteristics match the aptitude of the driver, the maneuverability will improve when an abnormality occurs in the steering function and the vehicle 10 is driven to a safe location, which will contribute to vehicle safety. Therefore, the steering control unit 32 determines that the time when it acquires an abnormality signal in the steering function of the steer-by-wire system 40 is the specific scene for performing the trial drive.

[0058] As described above, the second embodiment differs from the first embodiment in the specific scenario in which trial runs (in other words, trials of the steering reaction force characteristic) are performed. However, like the first embodiment, the second embodiment performs trial runs using the first steering reaction force characteristic and trial runs using the second steering reaction force characteristic, and selects the steering reaction force characteristic based on the number of reversals NS of the actual yaw rate γac during each trial run. In other words, in the second embodiment as well, the steering control unit 32 has each function of steering reaction force torque control shown in the block diagram of FIG. 3.

[0059] 7 is a flowchart showing the process of selecting the steering reaction force characteristic in the second embodiment. In step S511, the steering control unit 32 determines whether or not an abnormality signal of the steering function of the steer-by-wire system 40 has been acquired, in other words, whether or not a malfunction of the steer-by-wire system 40 has been detected.

[0060] If steering control unit 32 has not received an abnormality signal for the steering function of steer-by-wire system 40, that is, if the steering function of steer-by-wire system 40 is normal, the process proceeds to step S512. In step S512, steering control unit 32 sets the steering reaction torque to normal. Note that the control of the steering reaction torque in step S512 can be, for example, control in which a reference steering reaction torque calculated from the yaw rate deviation Δγ based on the first steering reaction characteristic is corrected in accordance with the vehicle speed V, or control in which the steering reaction torque is set based on the steering angle θ and the vehicle speed V.

[0061] On the other hand, if the steering control unit 32 receives an abnormality signal for the steering function of the steer-by-wire system 40, that is, if the front wheels 11, 12 cannot be steered and the vehicle 10 is caused to turn by generating a difference in braking / driving force between the left and right wheels, the process proceeds to step S513 and subsequent steps. In steps S513 to S517, the steering control unit 32 executes the same processing as steps S503 to S507 described above. That is, the steering control unit 32 performs a trial of the first steering reaction force characteristic and a trial of the second steering reaction force characteristic, and selects the steering reaction force characteristic that provides higher behavior stability based on the behavior stability of the vehicle 10 during each trial run (more specifically, the number of reversals NS of the actual yaw rate γac), and thereafter controls the steering reaction force torque in accordance with the selected steering reaction force characteristic.

[0062] In addition, when the vehicle 10 is made to turn by generating a difference in braking / driving force between the left and right wheels while the front wheels 11, 12 cannot be steered, the deviation between the steering angle yaw rate γre and the actual yaw rate γac is likely to become large. Therefore, if the first steering reaction force characteristic, in which the steering reaction torque RT increases as the yaw rate deviation Δγ increases, is first tried, the steering reaction force torque becomes heavier than when the second steering reaction force characteristic is tried, allowing the driver to quickly detect an abnormality in the steering system (steer-by-wire system 40). Therefore, when trying out the steering reaction force characteristics when an abnormality signal is obtained in the steering function of the steer-by-wire system 40, it is preferable to first try the first steering reaction force characteristic and then try the second steering reaction force characteristic.

[0063] "Third Embodiment" In the above-described embodiments, the steering control unit 32 compares the behavior stability during trial operation using the first steering reaction force characteristic with the behavior stability during trial operation using the second steering reaction force characteristic, and selects either the first steering reaction force characteristic or the second steering reaction force characteristic. In contrast, in the third embodiment, if the behavior state of the vehicle 10 is sufficiently stable during trial operation using the first steering reaction force characteristic, the steering control unit 32 changes the reference steering reaction force characteristic to the first steering reaction force characteristic without performing trial operation using the second steering reaction force characteristic.

[0064] 8 is a flowchart showing the selection process for the steering reaction force characteristic in the third embodiment. In step S521, the steering control unit 32 determines whether or not it has acquired an abnormality signal for the steering function of the steer-by-wire system 40. If the steering function of the steer-by-wire system 40 is normal, the steering control unit 32 proceeds to step S522 and controls the steering reaction force torque normally.

[0065] On the other hand, when the steering control unit 32 acquires an abnormality signal of the steering function of the steer-by-wire system 40, the process proceeds to step S523, where it performs a trial run using the first steering reaction force characteristic and calculates the number of reversals NS of the actual yaw rate γac, which is an index value showing the stability of the vehicle behavior. Next, the steering control unit 32 proceeds to step S524, where it determines whether the first number of reversals NS1 counted in the trial run using the first steering reaction force characteristic is smaller than a set number. The set number is a threshold value for determining whether the number of reversals NS of the actual yaw rate γac is a value showing sufficient stability of the vehicle behavior or a value showing an unstable state of the vehicle behavior.

[0066] If the first number of reversals NS1 counted in the trial driving using the first steering reaction force characteristic is smaller than the set number, the steering control unit 32 determines that the first steering reaction force characteristic matches the driver's aptitude, and proceeds to step S527. Then, in step S527, the steering control unit 32 sets the first steering reaction force characteristic as the reference steering reaction force characteristic to be used in subsequent driving. Specifically, in step S527, the steering control unit 32 sets the switch unit 203 to output the reference value RTR1 calculated by the first reference value calculation unit 201.

[0067] In this case, trial driving using the second steering reaction force characteristic is not performed, and application of steering reaction force torque using the first steering reaction force characteristic continues from the moment an abnormality occurs in the steering function of the steer-by-wire system 40. Therefore, in a state where the vehicle 10 is turned using a braking / driving force difference between the left and right wheels, if the driver's aptitude matches the first steering reaction force characteristic, it is possible to prevent the driver from feeling uneasy due to a trial using the second steering reaction force characteristic, which does not match the driver's aptitude.

[0068] On the other hand, if the first number of reversals NS1 counted in the trial operation using the first steering reaction force characteristic is equal to or greater than the set number, the steering control unit 32 proceeds to step S525. In step S525, the steering control unit 32 performs a trial operation using the second steering reaction force characteristic and calculates the number of reversals NS of the actual yaw rate γac, which is an index value indicating the stability of the vehicle behavior.

[0069] Next, the steering control unit 32 proceeds to step S526, where it determines whether the first number of reversals NS1 counted in the preceding trial run using the first steering reaction force characteristic is smaller than the second number of reversals NS2 counted in the trial run using the second steering reaction force characteristic. If the first number of reversals NS1 is smaller than the second number of reversals NS2, the steering control unit 32 determines that the first steering reaction force characteristic is more suited to the driver's aptitude than the second steering reaction force characteristic, and it proceeds to step S527.

[0070] In step S527, the steering control unit 32 changes the reference steering reaction force characteristic to be used in subsequent driving to the first steering reaction force characteristic. Furthermore, if the first reversal number NS1 is equal to or greater than the second reversal number NS2, the steering control unit 32 proceeds to step S528 and sets the reference steering reaction force characteristic to be used in subsequent driving to the second steering reaction force characteristic. Specifically, in step S528, the steering control unit 32 sets the switch unit 203 to output the reference value RTR2 calculated by the second reference value calculation unit 202.

[0071] Fourth Embodiment The steering control unit 32 repeatedly executes weighting processing, which weights the first steering reaction force characteristic and the second steering reaction force characteristic to determine the steering reaction force torque, while changing the weighting, and can change the reference steering reaction force characteristic to a steering reaction force characteristic with weighting that stabilizes the behavior of the vehicle 10. Figure 9 is a block diagram of a fourth embodiment in which the above weighting processing is performed.

[0072] The block diagram of the fourth embodiment shown in Fig. 9 differs from the block diagram of the first embodiment shown in Fig. 3 in that it includes a first weighting unit 206, a second weighting unit 207, and an adder 208 instead of the switch unit 203. Therefore, the following will explain the first weighting unit 206, the second weighting unit 207, and the adder 208, and the same functional units as those explained in the first embodiment will be assigned the same reference numerals and explanations thereof will be omitted.

[0073] The first weighting unit 206 multiplies the reference value RTR1 calculated by the first reference value calculation unit 201 based on the yaw rate deviation Δγ by a weighting coefficient α (0≦α≦1.0), and outputs the result to the addition unit 208. The second weighting unit 207 multiplies the reference value RTR2 calculated by the second reference value calculation unit 202 based on the yaw rate deviation Δγ by a weighting coefficient “1−α”, and outputs the result to the addition unit 208.

[0074] Then, the adder 208 adds the weighted reference value RTR1 output by the first weighting unit 206 and the weighted reference value RTR2 output by the second weighting unit 207 to obtain a reference value RTR, and outputs the obtained reference value RTR to the multiplier 205. In other words, the trial steering reaction force characteristic (trial steering reaction force characteristic) is variably set depending on the weighting coefficient α.

[0075] When testing the steering reaction force characteristic, the behavior stability determination unit 303 counts the number of reversals NS while decreasing the weighting coefficient α from the initial value of 1.0, and searches for the weighting coefficient αs that minimizes the number of reversals NS, in other words, the weighting coefficient αs that most stabilizes the behavior of the vehicle 10. The process of gradually decreasing the weighting coefficient α from 1.0 is a process of gradually approaching the steering reaction force characteristic from the first steering reaction force characteristic to the second steering reaction force characteristic.

[0076] Then, when the behavior stability determination unit 303 finds the weighting coefficient αs that minimizes the number of reversals NS, it fixes the weighting coefficient α used in the first weighting unit 206 and the second weighting unit 207 to the weighting coefficient αs and changes the reference steering reaction force characteristic to the weighting coefficient αs. With this configuration, when the steering reaction force characteristic that matches the driver's aptitude is an intermediate characteristic between the first steering reaction force characteristic and the second steering reaction force characteristic, the reference steering reaction force characteristic can be changed to such an intermediate steering reaction force characteristic. In other words, compared to selecting either the first steering reaction force characteristic or the second steering reaction force characteristic, it is possible to change the reference steering reaction force characteristic to one that better matches the driver's aptitude.

[0077] 10 is a flowchart showing the process of changing to the reference steering reaction force characteristic by weighting process. In step S531, steering control unit 32 determines whether or not it has acquired an abnormality signal of the steering function of steer-by-wire system 40, in other words, whether or not it has detected a malfunction of steer-by-wire system 40. If the steering function of steer-by-wire system 40 is normal, steering control unit 32 proceeds to step S532 and controls the steering reaction force torque normally.

[0078] On the other hand, when the steering control unit 32 acquires an abnormality signal of the steering function in the steer-by-wire system 40, the process proceeds to step S533, where it performs a trial of the steering reaction torque accompanied by weighting processing. In detail, the steering control unit 32 counts the number of reversals NS of the actual yaw rate γac in a state in which the steering reaction torque set in accordance with the weighting coefficient α at that time is applied to the steering wheel 51 while gradually decreasing the weighting coefficient α from the initial value of 1.0.

[0079] In the next step S534, the steering control unit 32 determines whether the number of reversals NS, which changes as the weighting coefficient α gradually decreases, has reached a minimum value. If the number of reversals NS has not reached a minimum value, the process returns to step S533, where the weighting coefficient α is further decreased to change the steering reaction force characteristics, and the number of reversals NS for the changed steering reaction force characteristics is counted. If the number of reversals NS reaches a minimum value in the process of repeatedly decreasing the weighting coefficient α and counting the number of reversals NS, the steering control unit 32 proceeds from step S534 to step S535, where the reference steering reaction force characteristics are changed to the steering reaction force characteristics obtained by weighting with the weighting coefficient α when the number of reversals NS reaches a minimum value. In other words, after the steering control unit 32 searches for the weighting coefficient α that minimizes the number of reversals NS, the steering control unit 32 fixes the weighting coefficient α to the weighting coefficient α, thereby controlling the steering reaction torque in accordance with the weighting coefficient α when the behavior of the vehicle 10 is most stable.

[0080] The steering control unit 32 repeatedly counts the number of reversals NS while gradually decreasing the weighting coefficient α from 1.0 until the weighting coefficient α becomes 0, finds the minimum value among the number of reversals NS at each weighting coefficient α, and can use the weighting coefficient α when the minimum number of reversals NS is obtained as the weighting coefficient α that determines the reference steering reaction force characteristic. The steering control unit 32 can also count the number of reversals NS at each weighting coefficient α while gradually increasing the weighting coefficient α from 0.

[0081] Fifth Embodiment When trial driving is performed with the first steering reaction force characteristic and the second steering reaction force characteristic based on the occurrence of an abnormality in the steering function of the steer-by-wire system 40, the steering control unit 32 can determine in advance which steering reaction force characteristic to test first based on the trial driving when the steering function of the steer-by-wire system 40 is normal. FIGS. 11 to 13 are flowcharts showing the process of changing the reference steering reaction force characteristic, including the process of determining the order of trials. The fifth embodiment shown in the flowcharts of FIGS. 11 to 13 shows the process of changing the reference steering reaction force characteristic performed by the control block shown in FIG. 3.

[0082] In step S541, similarly to step S501, the steering control unit 32 determines whether a state in which the absolute value of the amount of change per unit time of the curvature calculated from the actual yaw rate γac and the vehicle speed V is equal to or less than a predetermined value (i.e., a state in which the curvature is stable) has continued for a predetermined time. If the state in which the absolute value of the amount of change per unit time of the curvature is equal to or less than the predetermined value has not continued for the predetermined time, in other words, if the driving state of the vehicle 10 is neither a steady turning state nor a straight driving state, the steering control unit 32 proceeds to step S542 and controls the steering reaction torque normally.

[0083] On the other hand, if the absolute value of the amount of change in curvature per unit time remains equal to or less than the predetermined value for a predetermined period of time, in other words, if the vehicle 10 is in a steady turning state or a straight traveling state, the steering control unit 32 proceeds to step S543. In step S543, the steering control unit 32 tries the first steering reaction force characteristic to determine the number of reversals NS1, and then tries the second steering reaction force characteristic to determine the number of reversals NS2.

[0084] Next, in step S544, the steering control unit 32 stores in memory the steering reaction force characteristic obtained when the smaller of the number of reversals NS1 and the number of reversals NS2 obtained in the trial operation in step S543 is obtained, as the steering reaction force characteristic to be tried first in the event of a failure in the steering function of the steer-by-wire system 40. In other words, when the number of reversals NS1 is smaller than the number of reversals NS2, the steering control unit 32 stores in memory the first steering reaction force characteristic which makes the behavior more stable, in other words, which is more suited to the driver's aptitude, as the steering reaction force characteristic to be tried first in the event of a failure in the steering function of the steer-by-wire system 40. Furthermore, when the number of reversals NS2 is equal to or smaller than the number of reversals NS1, the steering control unit 32 stores in memory the second steering reaction force characteristic which makes the behavior more stable, in other words, which is more suited to the driver's aptitude, as the steering reaction force characteristic to be tried first in the event of a failure in the steering function of the steer-by-wire system 40.

[0085] Once the steering control unit 32 has determined in advance the steering reaction force characteristic to be tried in advance when the steering function of the steer-by-wire system 40 fails, the process proceeds from step S544 to step S545. Then, in step S545, the steering control unit 32 determines whether or not it has acquired an abnormality signal for the steering function of the steer-by-wire system 40, in other words, whether or not it has detected a failure of the steer-by-wire system 40.

[0086] If the steering control unit 32 has not received a steering function abnormality signal, the process proceeds to step S546, where the steering reaction torque is controlled normally. On the other hand, if the steering control unit 32 receives a steering function abnormality signal, the process proceeds to step S547 (see FIG. 12), where it determines whether or not the first steering reaction force characteristic has been detected as a characteristic that stabilizes vehicle behavior in the trial of the steering reaction force characteristic when the steering function is normal, and whether or not the first steering reaction force characteristic has been stored as the steering reaction force characteristic that will precede the trial.

[0087] If the steering control unit 32 has stored the first steering reaction force characteristic as the steering reaction force characteristic that will be the first to be tried when an abnormality occurs in the steering function, the process proceeds from step S547 to step S548. In steps S548 to S553, the steering control unit 32 changes the reference steering reaction force characteristic in the same manner as in steps S523 to S528 in FIG. 8 (third embodiment) described above.

[0088] Specifically, the steering control unit 32 first performs a trial of the first steering reaction force characteristic (step S548), and if the number of reversals NS1 for the first steering reaction force characteristic is smaller than the set number, changes the reference steering reaction force characteristic to the first steering reaction force characteristic (step S549 → step S552).On the other hand, if the number of reversals NS1 for the first steering reaction force characteristic is equal to or greater than the set number, the steering control unit 32 performs a trial of the second steering reaction force characteristic (step S549 → step S550), and if the number of reversals NS1 for the first steering reaction force characteristic is smaller than the number of reversals NS2 for the second steering reaction force characteristic, changes the reference steering reaction force characteristic to the first steering reaction force characteristic (step S551 → step S552). In addition, if the number of reversals NS1 for the first steering reaction force characteristic is equal to or greater than the number of reversals NS2 for the second steering reaction force characteristic, the steering control unit 32 changes the reference steering reaction force characteristic to the second steering reaction force characteristic (step S551 → step S553).

[0089] On the other hand, in step S547, if the second steering reaction force characteristic is detected as a characteristic that stabilizes vehicle behavior in the trial of the steering reaction force characteristic when the steering function is normal and the second steering reaction force characteristic is stored as the steering reaction force characteristic to be prioritized in the trial, the steering control unit 32 proceeds from step S547 (see FIG. 12) to step S554 and subsequent steps (see FIG. 13).Then, the steering control unit 32 prioritizes the trial of the second steering reaction force characteristic (step S554), and if the number of reversals NS2 for the second steering reaction force characteristic is smaller than the set number of times, changes the reference steering reaction force characteristic to the second steering reaction force characteristic (step S555 → step S558).

[0090] If the number of reversals NS2 for the second steering reaction force characteristic is equal to or greater than the set number, the steering control unit 32 performs a trial of the first steering reaction force characteristic (step S555 → step S556), and if the number of reversals NS1 for the first steering reaction force characteristic is smaller than the number of reversals NS2 for the second steering reaction force characteristic, the steering control unit 32 changes the reference steering reaction force characteristic to the first steering reaction force characteristic (step S557 → step S559).Furthermore, if the number of reversals NS1 for the first steering reaction force characteristic is equal to or greater than the number of reversals NS2 for the second steering reaction force characteristic, the steering control unit 32 changes the reference steering reaction force characteristic to the second steering reaction force characteristic (step S557 → step S558).

[0091] Sixth Embodiment The steering control unit 32 acquires a driver-suitable characteristic of the vehicle 10 as a characteristic obtained when the steering reaction force characteristic is tested, and can change the reference steering reaction force characteristic based on the driver-suitable characteristic. Note that the driver-suitable characteristic is the suitability of the steering reaction force characteristic to the aptitude of the driver, as determined from the driver's adjustment of the steering angle θ (in other words, the operating position) of the steering wheel 51, as will be described later.

[0092] 14 is a block diagram showing a sixth embodiment in which the reference steering reaction force characteristic is changed based on the driver adaptation characteristic. The steering control unit 32 has a steering angle yaw rate calculation unit 301, a subtraction unit 302, and a reference value calculation unit 209.

[0093] The steering angle yaw rate calculation unit 301 calculates the steering angle yaw rate γre based on the steering angle θ of the steering wheel 51 and the vehicle speed V. Then, the subtraction unit 302 subtracts the actual yaw rate γac detected by the yaw rate sensor 81 from the steering angle yaw rate γre calculated by the steering angle yaw rate calculation unit 301 to calculate the yaw rate deviation Δγ (Δγ=γre−γac).

[0094] The reference value calculation unit 209 calculates a reference value RTR of the steering reaction torque RT based on the yaw rate deviation Δγ (Δγ=γre-γac) calculated by the subtraction unit 302. Here, the steering reaction force characteristic, which is the characteristic of the reference value RTR with respect to the yaw rate deviation Δγ, is variable, and the reference value calculation unit 209 calculates the reference value RTR by referring to the steering reaction force characteristic that is changed as described below.

[0095] The steering control unit 32 also has a correction term calculation section 204 and a multiplication section 205. The correction term calculation section 204 sets a correction term CT that corrects the steering reaction torque to a larger value as the vehicle speed V increases, and multiplies the reference value RTR output by a reference value calculation section 209 by the correction term CT to output the result as the target steering reaction torque RTtg.

[0096] Furthermore, the steering control unit 32 has a steering reaction force characteristic suitability determination unit 304. The steering reaction force characteristic suitability determination unit 304 determines the driver suitability characteristics of the vehicle 10, and changes the steering reaction force characteristics, which are the characteristics of the reference value RTR with respect to the yaw rate deviation Δγ in the reference value calculation unit 209, in accordance with the driver suitability characteristics.

[0097] 15 is a flowchart showing the process of changing the reference steering reaction force characteristic based on the driver suitability characteristic. In step S571, the steering control unit 32 (steering reaction force characteristic suitability determination section 304) determines whether the absolute value of the amount of change per unit time of the curvature calculated from the actual yaw rate γac and the vehicle speed V is equal to or less than a predetermined value for a predetermined time, as in step S501 of FIG. 4. The state in which the absolute value of the amount of change per unit time of the curvature is equal to or less than a predetermined value indicates a steady turning state or a straight traveling state.

[0098] If the steady turning state or straight traveling state has continued for a predetermined time, the steering control unit 32 proceeds to step S572, otherwise repeats the determination of step S571. When the steady turning state or straight traveling state has continued for a predetermined time and the process proceeds to step S572, the steering control unit 32 determines whether the absolute value of the difference between the curvature of the road ahead of the vehicle 10 acquired by a forward recognition device 85 (see FIG. 1) such as a camera provided on the vehicle 10 and the curvature calculated from the actual yaw rate γac and the vehicle speed V is equal to or less than a predetermined value.

[0099] The steering control unit 32 returns to step S571 if the absolute value of the curvature difference is greater than the predetermined value, that is, if there is a large deviation between the curvature of the road and the curvature of the turning travel of the vehicle 10. In other words, if the absolute value of the curvature difference is greater than the predetermined value, the steering control unit 32 determines that the vehicle 10 is changing lanes and is in a travel state that is not suitable for determining the driver suitability characteristics, and returns to step S571.

[0100] As will be described later, the steering control unit 32 determines the driver suitability characteristics based on the adjustment operation (turning back, turning further) of the steering angle θ of the steering wheel 51. However, since the steering angle θ is adjusted, such as turning back, even when changing lanes, the condition for determining the driver suitability characteristics is that the vehicle 10 is not changing lanes in order to distinguish between turning back for a lane change and turning back influenced by the suitability of the steering reaction torque.

[0101] On the other hand, if the absolute value of the curvature difference is equal to or less than the predetermined value and it is estimated that the vehicle 10 is not changing lanes, the steering control unit 32 proceeds to step S573. In step S573, the steering control unit 32 determines the driver suitability characteristics of the vehicle 10 based on the physical quantity related to the return of the steering wheel 51 or the rate of change of the steering angle θ (operation position).

[0102] Here, if there is an immediate return to steering or an increase in the rate of change of the steering angle θ from a state in which the curvature is stable, that is, if the driver adjusts the steering angle θ of the steering wheel 51 by returning to steering or turning it further at an increased operating speed, the steering control unit 32 determines that the steering reaction force characteristics do not match the driver's aptitude, and proceeds to step S574, where the reference steering reaction force characteristics are changed. On the other hand, if there is no return to steering or an increase in the rate of change of the steering angle θ, that is, if the driver does not adjust the steering angle θ of the steering wheel 51, the steering control unit 32 determines that the steering reaction force characteristics match the driver's aptitude, and returns to step S571, bypassing step S574, where the reference steering reaction force characteristics are changed.

[0103] In step S574, the steering control unit 32 corrects the slope of the reference value RTR corresponding to the grid of the yaw rate deviation Δγ at that time, among a plurality of grids (sections) of the yaw rate deviation Δγ of the steering reaction force characteristic (reference steering reaction force characteristic, conversion table) for calculating the reference value RTR from the yaw rate deviation Δγ, so as to suit the aptitude of the driver. For example, if the first steering reaction force characteristic is initially set as the steering reaction force characteristic in the reference value calculation unit 209, in step S574, the steering control unit 32 changes the slope of the reference value RTR for each grid so that the steering reaction force characteristic in the reference value calculation unit 209 approaches the second steering reaction force characteristic, thereby changing the steering reaction force characteristic in the reference value calculation unit 209 to a characteristic that suits the aptitude of the driver.

[0104] The vehicle 10 can be provided with an automatic driving mode in addition to a manual driving mode. In this case, in the automatic driving mode, it is not necessary to apply a steering reaction torque to the steering wheel 51, so the process for changing the steering reaction force characteristic is not performed. In the manual driving mode in which the driver operates the steering wheel 51, the process for changing the reference steering reaction force characteristic as shown in any one of the first to sixth embodiments is performed.

[0105] 16 is a flowchart showing switching of the driving program depending on the driving mode. In step S581, the vehicle control device 30 determines whether the vehicle 10 is set to the autonomous driving mode. If the vehicle 10 is set to the autonomous driving mode, the vehicle control device 30 proceeds to step S582 and controls the vehicle 10 in accordance with the autonomous driving program. Here, the autonomous driving program does not include a program for changing the steering reaction force characteristic, and therefore, no processing for changing the steering reaction force characteristic is involved.

[0106] On the other hand, if the vehicle 10 is set to the manual driving mode, the vehicle control device 30 proceeds to step S583 and controls the vehicle 10 in accordance with the manual driving program. Here, the manual driving program includes a program for changing the steering reaction force characteristics, and processing for changing the steering reaction force characteristics intervenes.

[0107] 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.

[0108] Although the vehicle 10 in the above embodiment is equipped with a steer-by-wire system 40 as a steering device, the steering device may also be an electric power steering device. The electric power steering device is a steering device in which a steering wheel 51 and the left and right front wheels 11, 12, which are steered wheels, are mechanically connected, and a motor assists the force required to operate the steering wheel 51, thereby reducing the steering force. In such an electric power steering device, the reduction in the assist torque generated by the motor is used as a component of the steering reaction torque, and the reference steering reaction force characteristic can be changed based on the characteristic obtained when the steering reaction force characteristic is set to the trial steering reaction force characteristic, as in the above embodiment.

[0109] Furthermore, instead of setting the reference value of the steering reaction torque based on the yaw rate deviation Δγ, the steering control unit 32 can set the reference value of the steering reaction torque based on, for example, a lateral acceleration deviation. Here, the lateral acceleration deviation is the deviation between the lateral acceleration estimated based on the driving state of the vehicle 10 and the actual lateral acceleration detected by a sensor. Furthermore, if the steering device is an electric power steering device, the control device of the electric power steering device can set the reference value of the steering reaction torque based on vehicle motion conditions other than the yaw rate deviation Δγ and the lateral acceleration deviation.

[0110] Furthermore, the steering reaction torque calculation section 200 has a correction term calculation section 204 that sets a correction term CT that corrects the steering reaction torque to a larger value as the vehicle speed V increases, but it may also be configured not to have the correction term calculation section 204 and to calculate the target steering reaction torque RTtg without any correction according to the vehicle speed V. Furthermore, the correction term that corrects the steering reaction torque is not limited to the correction term according to the vehicle speed V, and the steering reaction torque may be corrected by a correction term calculated based on the degree of brake saturation, for example. In this case, the steering control unit 32 corrects the steering reaction torque so that it increases as the braking force approaches the limit at which it can be output.

[0111] Furthermore, the index value indicating the stability of vehicle behavior, i.e., the characteristic obtained by trial operation with the trial steering reaction torque, is not limited to the number of reversals NS, which is the number of times the sign of the differential value of the actual yaw rate γac is reversed, and the steering control unit 32 can use an index value calculated, for example, from the timing at which the actual yaw rate γac (or lateral acceleration) switches from monotonically increasing to monotonically decreasing and the timing at which it switches from monotonically decreasing to monotonically increasing.

[0112] In addition, the duration of the trial driving using the trial steering reaction force characteristic must be long enough to ensure that the trial conditions are as consistent as possible. However, if a driver has an aptitude that matches the steering reaction force characteristic to be tested in the latter stage, the driver will be forced to drive in the former stage with a steering reaction force characteristic that does not suit his or her aptitude. Therefore, it is preferable to adjust the duration of the trial driving to be as short as possible within the range that ensures that the trial conditions are as consistent as possible.

[0113] Furthermore, the steering control unit 32 can shorten the trial driving time under conditions where differences in vehicle behavior are likely to occur depending on whether the steering reaction force characteristics match the driver's aptitude (for example, when the curvature is large or the vehicle speed V is high). Furthermore, if the number of reversals NS exceeds a set number and it is estimated that the steering reaction force characteristics being trialed do not match the driver's aptitude, the steering control unit 32 can cancel the trial driving even before the standard trial time has elapsed.

[0114] Furthermore, the steering control unit 32 tries out a plurality of steering reaction force characteristics with different slopes of the increase in the steering reaction force torque RT relative to the increase in the yaw rate deviation Δγ as the steering reaction force characteristic that the steering reaction force torque RT increases as the yaw rate deviation Δγ increases, thereby making it possible to adapt the magnitude of the slope to the aptitude of the driver. Furthermore, the steering control unit 32 tries out three or more types of steering reaction force characteristics and can select a characteristic that suits the aptitude of the driver from the three or more types of steering reaction force characteristics.

[0115] 10...vehicle, 11, 12...front wheels (steered wheels), 32...steering control unit, 40...steer-by-wire system, 41...reaction force actuator, 51...steering wheel, 52...steering angle sensor, 81...yaw rate sensor

Claims

1. A vehicle control device comprising: a steering reaction torque calculation unit that calculates a steering reaction torque to be applied to a steering operation input mechanism operated by a driver of the vehicle based on a reference steering reaction characteristic indicating the characteristics of the steering reaction torque relative to the vehicle's motion state and the vehicle's motion state; and a reaction characteristic change unit that changes the reference steering reaction characteristic in accordance with the characteristics obtained by trial driving of the vehicle to a predetermined trial steering reaction characteristic.

2. A vehicle control device according to claim 1, wherein the characteristic is a behavior state of the vehicle.

3. A vehicle control device according to claim 2, wherein the reaction force characteristic change unit performs the trial run when the state of the vehicle falls into a specific scene.

4. A vehicle control device as described in claim 3, wherein the vehicle has a steer-by-wire system that steers left and right steered wheels that are mechanically separated from the steering operation input mechanism, and the specific scene is when an abnormality signal is acquired from the steering function of the steer-by-wire system.

5. A vehicle control device according to claim 4, wherein the reaction force characteristic changing unit changes the reference steering reaction force characteristic to a steering reaction force characteristic that stabilizes the behavior state of the vehicle obtained by the trial drive.

6. A vehicle control device as described in claim 5, wherein the steering reaction torque calculation unit calculates the steering reaction torque based on the reference steering reaction characteristic which indicates the characteristic of the steering reaction torque with respect to a yaw rate deviation which is the difference between an actual yaw rate generated in the vehicle and a steering angle yaw rate calculated based on the steering angle of the steering operation input mechanism, among the motion states of the vehicle, and the speed of the vehicle among the motion states of the vehicle.

7. A vehicle control device as described in claim 6, wherein the reaction force characteristic changing unit has, as the trial steering reaction force characteristics, a first trial steering reaction force characteristic in which the steering reaction force torque increases as the yaw rate deviation increases, and a second trial steering reaction force characteristic in which the steering reaction force torque decreases as the yaw rate deviation increases, and changes the reference steering reaction force characteristic to one of the first trial steering reaction force characteristic and the second trial steering reaction force characteristic which stabilizes the behavior state of the vehicle, depending on the behavior state of the vehicle obtained by the trial operation using the first trial steering reaction force characteristic and the behavior state of the vehicle obtained by the trial operation using the second trial steering reaction force characteristic.

8. A vehicle control device as described in claim 7, wherein the reaction force characteristic changing unit performs the trial operation using the second trial steering reaction force characteristic after performing the trial operation using the first trial steering reaction force characteristic.

9. A vehicle control device as described in claim 7, wherein the reaction force characteristic changing unit changes the reference steering reaction force characteristic to the first trial steering reaction force characteristic without performing the trial operation using the second trial steering reaction force characteristic when the vehicle's behavior state is stable during the trial operation using the first trial steering reaction force characteristic.

10. A vehicle control device as described in claim 7, wherein the reaction force characteristic changing unit obtains a first reversal number, which is the number of times that the sign of the derivative value of the actual yaw rate is reversed during the trial operation using the first trial steering reaction force characteristic, obtains a second reversal number, which is the number of times that the sign of the derivative value of the actual yaw rate is reversed during the trial operation using the second trial steering reaction force characteristic, and sets the trial steering reaction force characteristic with the fewer number of reversals, either the first reversal number or the second reversal number, as the one that stabilizes the behavior state of the vehicle.

11. A vehicle control device as described in claim 6, wherein the reaction force characteristic changing unit has, as the trial steering reaction force characteristics, a first trial steering reaction force characteristic in which the steering reaction force torque increases as the yaw rate deviation increases, and a second trial steering reaction force characteristic in which the steering reaction force torque decreases as the yaw rate deviation increases, and a weighting process is repeatedly executed while changing the weighting to determine the steering reaction force torque by weighting the first trial steering reaction force characteristic and the second trial steering reaction force characteristic, and the reference steering reaction force characteristic is changed to a steering reaction force characteristic with weighting that stabilizes the behavior state of the vehicle.

12. A vehicle control device as described in claim 7, wherein the reaction force characteristic change unit, when the steering function of the steer-by-wire system is normal, acquires the behavior state of the vehicle obtained by the trial drive using the first trial steering reaction force characteristic and the behavior state of the vehicle obtained by the trial drive using the second trial steering reaction force characteristic, stores one of the first trial steering reaction force characteristic and the second trial steering reaction force characteristic which stabilizes the behavior state of the vehicle, and, when an abnormality signal of the steering function of the steer-by-wire system is acquired, performs the trial drive using the stored trial steering reaction force characteristic of the first trial steering reaction force characteristic and the second trial steering reaction force characteristic.

13. A vehicle control device as described in claim 1, wherein the characteristic is a driver-adapted characteristic of the vehicle that is acquired based on a curvature determined based on the driving state of the vehicle and a rate of change in a physical quantity or operation position related to the return of the steering operation input mechanism.

14. A vehicle control method executed by a control unit mounted on a vehicle having a steer-by-wire system that steers left and right steered wheels that are mechanically separated from a steering operation input mechanism operated by a driver of the vehicle, the method comprising: changing characteristics of a steering reaction torque applied to the steering operation input mechanism in accordance with the tendency of the vehicle to sway left and right due to operation of the steering operation input mechanism by the driver when the steering function of the steer-by-wire system has failed and the vehicle is caused to turn using a braking / driving force difference between the left and right wheels of the vehicle.

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