Vehicle control device and vehicle control procedure

Abstract

In a mode of a vehicle control device and vehicle control method according to the present invention, when a disturbance occurs in a steering function in a steer-by-wire system, brake torque control is executed to generate a yaw moment in the vehicle by utilizing a friction braking force exerted on the vehicle's road wheels based on a steering input into the steering wheel. In brake torque control, a braking torque force exerted on first road wheels, which are the steered road wheels, and on second road wheels, which are the other road wheels, is distributed based on the vehicle's state. As a result, brake torque control can operate stably even if a vehicle state changes.

Description

TECHNICAL AREA

[0001] The present invention relates to vehicle control devices and vehicle control methods. BACKGROUND OF THE TECHNOLOGY

[0002] Patent document 1 discloses a steering control device for a vehicle. This steering control device comprises an actuator for assisting the steering process of steered road wheels based on a steering torque. If a fault or malfunction occurs in the actuator, the steering control device applies a braking force differential based on the steering torque to a braking device for the right and left road wheels. REFERENCE MARK LIST PATENT DOCUMENT

[0003] Patent Document 1: JP 2000-190863 A SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0004] When an anomaly occurs in the steering function of a steer-by-wire system, there are cases where a friction braking device creates a difference in friction braking force between the left and right wheels, generating a yaw moment that causes the vehicle to rotate. If, in these cases, the friction braking force for rotation is distributed evenly between the individual wheels during the rotation, a reduction in the vehicle's range (travel time) or a deterioration in steering performance may occur, depending on the vehicle's condition.

[0005] The present invention was made with regard to conventional factual circumstances, and it is an object of the present invention to provide a vehicle control device and a vehicle control method that can stably operate a brake torque control for generating a yaw moment in a vehicle by applying or exerting a friction braking force on a road wheel, even when the vehicle condition changes. MEANS TO SOLVE THE PROBLEM

[0006] In one mode of a vehicle control device according to the present invention, when a disturbance occurs in a steering function in a steer-by-wire system, brake torque control is performed to generate a yaw moment in the vehicle by utilizing a friction braking force exerted on the vehicle's road wheels based on a steering input into the steering wheel. During brake torque control, a brake torque braking force exerted on first road wheels, which are the steered road wheels, and second road wheels, which are the other road wheels, is distributed based on the vehicle's state.

[0007] Furthermore, in a mode of a vehicle control method according to the present invention, when a steering wheel is turned to the right in a state where a disturbance in a steering function has occurred in the steer-by-wire system, the friction braking force is applied to the right rear wheel if the temperature of a friction braking device that exerts a friction braking force on the right rear wheel of the vehicle is 100 degrees Celsius. If the temperature of the friction braking device that exerts the friction braking force on the right rear wheel is 300 degrees Celsius, the friction braking force is applied to the right front wheel of the front wheels. EFFECTS OF INVENTION

[0008] According to the present invention, a brake torque control can be operated stably even when the vehicle condition changes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 illustrates an overall configuration of a vehicle control system. Fig. Figure 2 is a block diagram illustrating the driving, braking, and steering control systems in the vehicle control system. Fig. 3 is the first half of a flowchart illustrating a brake torque control process. Fig. 4 is the second half of the flowchart, which illustrates the brake torque control process. Fig. Figure 5 illustrates an example of a distribution of driving and braking forces when a requested acceleration is zero and when a friction braking force is applied to a rear road wheel. Fig. Figure 6 illustrates an example of a distribution of driving and braking forces when the requested acceleration is zero and when a friction braking force is applied to a front road wheel. Fig. Figure 7 illustrates an example of a distribution of driving and braking forces when acceleration is requested and when a friction braking force is applied to a rear road wheel. Fig. Figure 8 illustrates an example of a distribution of driving and braking forces when deceleration is requested and when a friction braking force is applied to a rear road wheel. Fig. Figure 9 illustrates an example of a distribution of drive and braking forces that generate a moment to turn or rotate the front road wheels. Fig. Figure 10 illustrates an exemplary situation in which the direction of rotation requested by a driver differs from the direction of the front road wheels. Fig. Figure 11 illustrates an example of the distribution of driving and braking forces when the front road wheels have been turned or rotated, although driving straight ahead is requested. Fig. 12 is the first half of a flowchart illustrating a brake torque control process that includes a control to return the front road wheels to their neutral position or close to it. Fig. 13 is the second half of the flowchart, illustrating the brake torque control process, which includes the control to return the front road wheels to their neutral position or close to it. Fig. Figure 14 illustrates an example of a distribution of driving and braking forces to return the front road wheels to their neutral position or close to it. Fig. 15 is the first half of a flowchart illustrating a brake torque control process that includes slip correction control. Fig. 16 is the second half of the flowchart, which illustrates the process of brake torque control, including slip correction control. Fig. Figure 17 is a flowchart illustrating a slip correction control process. Fig. Figure 18 illustrates an example of a distribution of drive and braking forces in slip correction control. MODE FOR EXECUTING THE INVENTION

[0009] An example of a vehicle control device and a vehicle control method according to the present invention is described below with reference to the drawings.

[0010] Fig. Figure 1 illustrates an overall configuration of a vehicle control system 100 mounted in a vehicle.

[0011] Fig. Figure 2 is a block diagram that schematically illustrates the braking, drive and steering control systems in the vehicle control system 100.

[0012] Vehicle 10 is a four-wheeled vehicle comprising a pair of left and right front road wheels 11 and 12 and a pair of left and right rear road wheels 13 and 14.

[0013] Among the road wheels 11, 12, 13 and 14 of the vehicle 10, the front road wheels 11 and 12 are the first road wheels, which are the steered road wheels.

[0014] Furthermore, the rear road wheels 13 and 14 are second road wheels, which are the other road wheels besides the steered road wheels.

[0015] Furthermore, the vehicle 10 includes, as a drive and brake force actuator 70, a first electric motor 71, which exerts drive and brake force on the front road wheels 11 and 12, and a second electric motor 72, which exerts drive and brake force on the rear road wheels 13 and 14.

[0016] A unit 31 for controlling drive and braking forces receives information about the actuation value of an accelerator pedal 73 from an accelerator pedal sensor 74 and outputs a control signal, corresponding to a target drive force, to the electric motors 71 and 72 based on the actuation value of the accelerator pedal 73. The electric motors 71 and 72 then exert the drive force corresponding to the actuation value of the accelerator pedal 73 on the front road wheels 11 and 12 and the rear road wheels 13 and 14.

[0017] Furthermore, the unit 31 controls the drive and braking forces by operating the electric motors 71 and 72 as generators, regenerative braking, which uses the rotational resistance at the time of energy or current generation as a braking force, and causes the front road wheels 11 and 12 and the rear road wheels 13 and 14 to generate a force during regenerative braking.

[0018] Furthermore, the vehicle 10 includes a steer-by-wire system 40 in which a steering wheel 51 is mechanically separated as a steering device from the front road wheels 11 and 12, which are the steered road wheels.

[0019] The steer-by-wire system 40 comprises a reaction force actuator 41, which applies an actuation reaction force torque to the steering wheel 51, a wheel actuator 42, which applies a steering or rotation force to the front road wheels 11 and 12, a steering or rotation angle sensor 43, which detects a steering or rotation angle δ of the front road wheels 11 and 12 (in other words, the tire angle of the front road wheels 11 and 12), and a steering control unit 32, which controls the reaction force actuator 41 and the wheel actuator 42.

[0020] Furthermore, the steering wheel 51 includes an actuation angle sensor 52, which detects an actuation angle θ, which is the rotation angle of the steering wheel 51.

[0021] The rotation angle sensor 43 detects the rotation angle δ of the front road wheels 11 and 12 by detecting the rotation angle of a rotary motor forming the wheel actuator 42 or the rack position of a rack mechanism or rack and pinion mechanism that converts the rotational force of the rotary motor into a linear motion.

[0022] The steering control unit 32 acquires information about the actuation angle θ of the steering wheel 51 (in other words, information about the steering actuation), which is detected by the actuation angle sensor 52, and calculates a target rotation angle and a target reaction force torque, for example, from the actuation angle θ.

[0023] The steering control unit 32 controls the wheel actuator 42 such that the rotation angle δ detected by the rotation angle sensor 43 approaches the target rotation angle, and controls the reaction force actuator 41 such that the target reaction force torque is applied to the steering wheel 51.

[0024] In addition, the vehicle 10 includes a friction braking system that exerts a friction braking force on the road wheels 11, 12, 13 and 14.

[0025] The friction braking system comprises a brake control unit 33, a brake pedal sensor 62 which detects the actuation magnitude of a brake pedal 61, brake actuators 15, 16, 17 and 18 which are arranged on the road wheels 11, 12, 13 and 14 respectively, and brake pressure force sensors 21, 22, 23 and 24 which detect a pressure force (thrust) generated by the brake actuators 15, 16, 17 and 18 respectively.

[0026] The brake control unit 33 controls friction braking forces exerted by the brake actuators 15, 16, 17 and 18 on their respective road wheels 11, 12, 13 and 14, based on the output of the brake pedal sensor 62 and the output of the brake thrust sensors 21, 22, 23 and 24.

[0027] The brake actuators 15, 16, 17 and 18 are friction braking devices that exert friction braking forces on the road wheels 11, 12, 13 and 14.

[0028] The unit 31 for controlling drive and braking forces, the steering control unit 32 and the brake control unit 33 contain microcomputers 31A, 32A and 33A respectively.

[0029] Each of the 31A, 32A and 33A microcomputers includes a microprocessor unit (MPU), a read-only memory (ROM), a random access memory (RAM), etc., which are not illustrated, and implements various types of functions by causing its MPU to execute a program stored in a ROM as a memory unit.

[0030] The unit 31 for controlling drive and braking forces, the steering control unit 32 and the brake control unit 33 form a vehicle control device 30 that controls the vehicle 10.

[0031] The microcomputers 31A, 32A and 33A function as a control unit 30A of the vehicle control device 30.

[0032] Furthermore, the vehicle 10 includes, as sensors that detect the behavior of the vehicle 10, a yaw rate sensor 81, which detects a yaw rate γ of the vehicle 10, and a lateral acceleration sensor 82, which detects a lateral acceleration Gy of the vehicle 10.

[0033] The vehicle 10 also includes a road wheel speed sensor 83, which records the road wheel speeds V1 to V4 of the road wheels 11, 12, 13 and 14.

[0034] The control unit 30A (the microcomputers 31A, 32A and 33A) receives output signals from the yaw rate sensor 81, the lateral acceleration sensor 82 and the road wheel speed sensor 83, which are described above.

[0035] In the vehicle control system 100, the steering control unit 32 (the microcomputer 32A) determines whether or not there is an anomaly in the steering or turning function in the steer-by-wire system 40.

[0036] “An anomaly in the steering or turning function” refers to a condition in which the turning angle δ of the front road wheels 11 and 12, which are the steered road wheels, cannot be controlled to the target turning angle based on the actuation angle θ of the steering wheel 51 (in other words, based on the steering actuation input into the steer-by-wire system 40).

[0037] An anomaly in the rotation function occurs, for example, due to a malfunction of the wheel actuator 42, an anomaly of a drive circuit of the wheel actuator 42, or a malfunction of any of the various types of sensors.

[0038] When the steering control unit 32 detects an anomaly in the rotational function in the steer-by-wire system 40 (in other words, detects a signal indicating an anomaly in the rotational function), the steering control unit 32 issues a brake force command to generate a difference in the friction braking force between the right and left road wheels. As a result, a yaw moment is generated in the vehicle 10 based on the steering wheel 51's operating angle θ, and the vehicle 10 is consequently rotated in the direction of steering wheel 51 operation.

[0039] That is, if an anomaly occurs in the steering function in the steer-by-wire system 40, the steering control unit 32 changes the direction of the vehicle 10 by generating a yaw moment based on a friction braking force difference between the right and left road wheels (hereinafter referred to as brake torque control), instead of controlling the rotation angle δ of the front road wheels 11 and 12.

[0040] Fig. 3 and Fig. Figure 4 are flowcharts illustrating a mode of a brake torque control procedure (a sequence of a vehicle control procedure) performed by the steering control unit 32.

[0041] Although the steering control unit 32 performs the brake torque control in this system, a control unit such as a vehicle integration control unit, which is superior to the steering control unit 32, may be configured to monitor the steering function in the steer-by-wire system 40 and perform the brake torque control if an anomaly occurs in the steering function.

[0042] In step S201, the steering control unit 32 detects an anomaly in the steering function in the steer-by-wire system 40.

[0043] Next, in step S202, the steering control unit 32 determines whether the anomaly in the steer-by-wire system 40 has overridden or rendered ineffective the rotation of the front road wheels 11 and 12.

[0044] If the steer-by-wire system 40 is normal or functioning and the front road wheels 11 and 12 can be turned, the steering control unit 32 proceeds to step S203.

[0045] In step S203, the steering control unit 32 calculates a target rotation angle δtg of the front road wheels 11 and 12 based on the actuation angle θ of the steering wheel 51.

[0046] Next, in step S204, the steering control unit 32 performs a normal steering control operation, in which the steering control unit 32 controls the wheel actuator 42 such that the rotation angle δ of the front road wheels 11 and 12 approaches the target rotation angle δtg.

[0047] This means that if the steer-by-wire system 40 is functioning normally, the steering control unit 32 uses the steer-by-wire system 40 to implement the turning or steering operation of the vehicle 10.

[0048] If, on the other hand, the steering control unit 32 determines that there is an anomaly in the steering function in the steer-by-wire system 40 and that the steer-by-wire system 40 cannot turn the front road wheels 11 and 12, the process proceeds to step S205 to implement the steering operation of the vehicle 10 by executing the brake torque control instead of executing the drive control of the steer-by-wire system 40.

[0049] In step S205, the steering control unit 32 determines whether the temperature of the brake actuator (the friction brake device) of one of the brake target or road wheels to be braked, on which the friction brake force is exerted by the brake torque control, is a first threshold temperature TH1 or lower.

[0050] The road wheels to be braked, on which the friction braking force is applied in order to implement the steering function through the brake torque control, are the rotating inner road wheel of the rear road wheels 13 and 14 and the rotating inner road wheel of the front road wheels 11 and 12.

[0051] The steering control unit 32 determines the direction of rotation based on the actuation angle θ of the steering wheel 51.

[0052] As described below, if a negative scrub radius is set for the front road wheels 11 and 12, it is possible to generate the force to rotate the front road wheels 11 and 12 in the direction of rotation by increasing the driving force exerted on the rotating inner road wheel of the front road wheels 11 and 12 so that it is greater than the driving force exerted on the rotating outer road wheel, or by exerting a friction braking force on the rotating outer road wheel of the front road wheels 11 and 12.

[0053] In this case, the road wheel to be braked, on which the friction braking force is applied to implement the steering function by the brake torque control, is the rotating outer road wheel of the front road wheels 11 and 12.

[0054] Furthermore, the temperatures of the brake actuators 15, 16, 17 and 18 (friction brake devices) are, for example, the temperatures of the brake rotors.

[0055] As described below, the steering control unit 32 estimates the temperature of a brake actuator by estimating the amount of any increase from the initial temperature of the brake actuator due to brake torque control, for example, from brake pressure and vehicle speed. In step S205, the steering control unit 32 compares the estimated temperature with the first threshold temperature TH1.

[0056] The initial temperature can be a pre-defined temperature stored in a memory. In step S205, at the start of the brake torque control, the steering control unit 32 compares this initial temperature with the first threshold temperature TH1.

[0057] If the vehicle contains 10 temperature sensors, each of which detects the temperature of a corresponding brake actuator 15, 16, 17 and 18, the steering control unit 32 can detect the temperatures of the brake actuators 15, 16, 17 and 18 output by their respective temperature sensors and can use the detected temperatures for temperature determination in steps S205 and S207.

[0058] The first threshold temperature TH1 is a temperature that exceeds the permissible operating temperature of brake actuators 15, 16, 17, and 18 (friction brake devices). If the temperature of a brake actuator exceeds the first threshold, this means that the temperature falls into a temperature range (in other words, a prohibited operating temperature range) in which, for example, deformation of the brake rotor or a reduction in friction braking force relative to the brake pressure occurs.

[0059] For example, the first threshold temperature TH1 is set at approximately 350 degrees Celsius.

[0060] If the temperature of any of the brake actuators of the road wheels to be braked, on which the friction braking force is exerted by the brake torque control, exceeds the first threshold temperature TH1, the steering control unit 32 determines that the brake torque control cannot be executed. Thus, the process continues from step S205 to step S206.

[0061] In step S206, the steering control unit 32 calculates the friction braking force generated in the brake actuators 15, 16, 17 and 18, which stops the vehicle 10, as the control target and makes adjustments to stop the application of the driving force to any of the road wheels without receiving a driving request from the driver.

[0062] As described above, if the temperature of any of the brake actuators of the road wheels to be braked rises excessively and if the execution of the brake torque control, in other words, the steering operation by applying the friction braking force, cannot be implemented, the steering control unit 32 ensures the safety of the vehicle 10 by requesting a stop of the vehicle 10 (automatic stop process).

[0063] If, on the other hand, all temperatures of the brake actuators of the road wheels to be braked, on which the friction braking force is exerted by the brake torque control, are the first threshold temperature TH1 or lower, the steering control unit 32 determines that the brake torque control can be carried out, and the process continues from step S205 to step S207.

[0064] In step S207, the steering control unit 32 determines whether the temperature of the brake actuator of the rotating inner road wheel of the rear road wheels 13 and 14 is a second threshold temperature TH2 or higher.

[0065] The second threshold temperature TH2 is a temperature that is lower than the first threshold temperature TH1 (TH2 < TH1), and is a threshold to determine whether the temperature meets a temperature condition below which continuous use of the brake actuator is permissible.

[0066] For example, the second threshold temperature TH2 is set at approximately 200 degrees Celsius.

[0067] If the steering control unit 32 determines that the temperature of the brake actuator of the rotating inner road wheel of the rear road wheels 13 and 14 is the second threshold temperature TH2 or lower, the process proceeds to step S208.

[0068] In step S208, the steering control unit 32 performs a distribution setting in which the target road wheel on which the friction braking force (braking force for a braking torque) is applied by the brake torque control is set to the rotating inner road wheel of the rear road wheels 13 and 14, in other words, a setting to generate a torque based on the difference of the left and right braking force between the rear road wheels 13 and 14.

[0069] If, on the other hand, the steering control unit 32 determines that the temperature of the brake actuator of the rotating inner road wheel of the rear road wheels 13 and 14 is the second threshold temperature TH2 or higher, the process proceeds to step S209.

[0070] Next, in step S209, the steering control unit 32 performs a distribution setting in which the target road wheel on which the friction braking force is applied by the brake torque control is set to the rotating inner road wheel (or the rotating outer road wheel) of the front road wheels 11 and 12, in other words, a setting to generate a torque based on the difference of the left and right braking force between the front road wheels 11 and 12, which are the steered road wheels.

[0071] This means that, in the standard setting of the brake torque control, the steering control unit 32 generates a difference in the left and right braking force between the rear road wheels 13 and 14. The steering control unit 32 continues to generate the difference in the left and right braking force between the rear road wheels 13 and 14 until either of the temperatures of the brake actuators of the rear road wheels 13 and 14 reaches the second threshold temperature TH2 or higher.

[0072] If any of the temperatures of the brake actuators on which the friction braking force is applied reaches the second threshold temperature TH2 or higher due to the continuous application of the friction braking force to the rear road wheels 13 and 14, the steering control unit 32 switches the target road wheels between which the difference of the left and right braking force is generated from the rear road wheels 13 and 14 to the front road wheels 11 and 12.

[0073] As described above, the steering control unit 32 distributes the braking torque braking force exerted by the brake torque control on the front road wheels 11 and 12 (first road wheels) and the rear road wheels 13 and 14 (second road wheels), based on a condition of the vehicle 10, in particular the temperatures of the brake actuators 17 and 18 (friction brake devices) of the rear road wheels 13 and 14.

[0074] This configuration prevents excessive temperature increases in any of the brake actuators and allows continuous execution of brake torque control for a longer period of time (for a longer driving distance).

[0075] Furthermore, if the difference in left and right braking force is generated between the front road wheels 11 and 12, unstable rotation occurs due to the alignment characteristics (steering roll radius) of the front road wheels 11 and 12, and the control accuracy of the yaw moment may deteriorate.

[0076] In contrast, even when the difference in left and right braking force is generated between the rear road wheels 13 and 14, which are not steered, no rotation occurs. Therefore, it is possible to obtain a yaw moment based on the difference in left and right braking force with high accuracy.

[0077] Thus, in brake torque control, the steering control unit 32 first performs the control to generate a difference in the left and right braking force between the rear road wheels 13 and 14, from which a high degree of control accuracy can be expected.

[0078] If next any of the temperatures of the brake actuators of the rear road wheels 13 and 14 increase, the steering control unit 32 switches to control to generate a difference in left and right braking force between the front road wheels 11 and 12, although the accuracy of the torque control deteriorates.

[0079] Thus, it is possible to improve the accuracy of the brake torque control as much as possible, while extending the time (the distance) over which the brake torque control can continue.

[0080] After the steering control unit 32 has set the target road wheels between which the difference of the left and right braking force is generated to the pair of rear road wheels 13 and 14 or the pair of front road wheels 11 and 12 in step S208 or step S209 described above, the process continues to step S210 and the steering control unit 32 performs the brake force control.

[0081] In step S210, the steering control unit 32 calculates a target yaw rate γ* from the actuation angle θ of the steering wheel 51 and the vehicle speed V and calculates a target acceleration α* from the actuation value of the accelerator pedal 73 and the actuation value of the brake pedal 61.

[0082] Next, in step S211, the steering control unit 32 calculates the target drive and braking forces applied to the road wheels 11, 12, 13 and 14, based on the target yaw rate γ*, the target acceleration α* and the friction braking force distribution setting in the brake torque control.

[0083] Next, in step S212, the steering control unit 32 issues a brake force control command to the brake control unit 33 and issues a drive force control command to the unit 31 to control drive and brake forces based on the target drive and brake forces applied to the road wheels 11, 12, 13 and 14.

[0084] Next, in step S213, the steering control unit 32 estimates all temperatures of the brake actuators 15, 16, 17 and 18 based on the brake pressure and vehicle speed.

[0085] In steps S205 and S207, the steering control unit 32 compares the estimated temperatures obtained in step S213 with threshold temperatures.

[0086] The brake control unit 33 can estimate the temperatures of the brake actuators 15, 16, 17 and 18, and the steering control unit 32 can obtain information about the temperatures estimated by the brake control unit 33 and can use the information obtained for brake torque control.

[0087] As described above, the second threshold temperature TH2, which is used to determine the change or switching of the road wheel to which the braking torque / braking force is distributed, is set to approximately 200 degrees Celsius.

[0088] Thus, in a state where a malfunction occurs in the steering function of the steer-by-wire system 40, for example, when the steering wheel 51 is turned to the right, the friction braking force is applied to the right rear wheel 14 if the temperature of the brake actuator 18, which applies the friction braking force to the right rear wheel 14 of the rear wheels 13 and 14, is 100 degrees Celsius. If the temperature of the brake actuator 18 is 300 degrees Celsius, the friction braking force is applied to the right front wheel 12 of the front wheels 11 and 12.

[0089] The following section describes in more detail the distribution of drive and braking forces in the brake torque control.

[0090] Fig. 5 and Fig. Figure 6 illustrates an example of changing or switching the distribution of drive and brake forces based on the temperatures of the brake actuators in a state where the driver requests a right turn of the vehicle 10 by turning the steering wheel 51 from the neutral position to the right, and in a state where the acceleration / deceleration request by the driver (in other words, the acceleration / deceleration requested by the vehicle 10) is zero, that is, in a driving condition at constant speed.

[0091] The acceleration / deceleration request by the driver is determined from the actuation magnitude of the accelerator pedal 73 and the actuation magnitude of the brake pedal 61.

[0092] Fig. Figure 5 illustrates an initial state of a drive and brake force distribution when a disturbance occurs in the steering function in the steer-by-wire system 40 and when the steering control unit 32 starts the brake torque control.

[0093] The steering control unit 32, acting as the brake torque control, distributes the braking torque (friction braking force) to the right rear wheel 14, which is the rotating inner wheel of the rear wheels 13 and 14, in order to generate a drive and braking force difference between the left rear wheel 13 and the right rear wheel 14. In this way, a torque is generated to turn or steer the vehicle 10 in the right direction.

[0094] In the Fig. In the brake torque-braking force distribution illustrated in Figure 5, the brake torque braking force is applied to one of the left and right road wheels, and no brake torque braking force is applied to the other. However, this distribution can instead be one in which a friction braking force is applied to both the left and right road wheels, thus creating a difference between the friction braking force applied to one of the left and right road wheels and the friction braking force applied to the other.

[0095] In addition, the steering control unit 32 issues a command for regenerative braking to generate a force during regenerative braking in the front road wheels 11 and 12.

[0096] Furthermore, the steering control unit 32 implements the driving of the vehicle 10 by performing a drive control, in which a drive command to generate a drive force in the rear road wheels 13 and 14 is issued to the unit 31 for controlling drive and braking forces.

[0097] Assuming that the driving force is represented by a positive physical quantity and the braking force is represented by a negative physical quantity, the steering control unit 32 performs a control such that the sum of the friction braking force exerted on the right rear road wheel 14 by the brake torque control, the force exerted on the front road wheels 11 and 12 during regenerative braking by the regenerative braking control, and the driving force exerted on the rear road wheels 13 and 14 by the drive control will be zero.

[0098] By setting the sum of the friction braking force, the force during regenerative braking and the drive force to zero for the entire vehicle, as described above, the steering control unit 32 adjusts the drive and brake force distribution to the state in which the acceleration / deceleration requirement is zero.

[0099] Fig. Figure 5 illustrates the condition in which there is a difference in the driving force between the left and right rear road wheels 13 and 14. This means that the driving force of the left and right rear road wheels 13 and 14 differs depending on the function of the differential gear for transmitting the output or power of the second electric motor 72 to the left rear road wheel 13 and the right rear road wheel 14.

[0100] As described above, by generating a force during regenerative braking in the front road wheels 11 and 12, to which no braking torque is distributed during brake torque control, energy efficiency through regeneration is improved and a temperature increase of the brake actuators 15 and 16 of the front road wheels 11 and 12 is reduced.

[0101] Furthermore, in the state in Fig. 5, in which the braking torque braking force is distributed to the right rear road wheel 14, the same value of force is applied during regenerative braking to the front road wheels 11 and 12, which are the steered road wheels, and no drive and braking force difference is generated between the front road wheels 11 and 12.

[0102] Since the front road wheels 11 and 12 are not rotated by the difference in drive and braking force between the front road wheels 11 and 12, a torque for rotating the vehicle 10 can thus be controlled with high accuracy by adjusting the friction braking force exerted on the right rear road wheel 14.

[0103] In this case, if the in Fig. As the illustrated state of the drive and brake force distribution continues, the temperature of the brake actuator 18, which applies the brake torque braking force to the right rear road wheel 14, which is a rotating inner road wheel, is increased by frictional heat.

[0104] If the temperature of the brake actuator 18 reaches the second threshold temperature TH2 or higher, the steering control unit 32 determines that the brake actuator 18 can no longer be used and switches the drive and brake force distribution to the one specified in Fig. 6 illustrated distribution.

[0105] Fig. Figure 6 illustrates a drive and braking force distribution, in which the forces exerted on the front road wheels 11 and 12 and the forces exerted on the rear road wheels 13 and 14, which are in Fig. 5 are illustrated, have been exchanged or changed.

[0106] This means that, in the brake torque control, the steering control unit 32 distributes the brake torque braking force to the right front road wheel 12, which is the rotating inner road wheel of the front road wheels 11 and 12, in order to generate a drive and braking force difference between the left front road wheel 11 and the right front road wheel 12. In this way, a torque is generated to turn or steer the vehicle 10 in the right direction.

[0107] Furthermore, the steering control unit 32 applies the force during regenerative braking to the rear road wheels 13 and 14 and applies the driving force to the front road wheels 11 and 12.

[0108] Assuming that the driving force is represented by a positive physical quantity and the braking force is represented by a negative physical quantity, the steering control unit 32 performs a control such that the sum of the friction braking force exerted on the right front road wheel 12 by the brake torque control, the force exerted on the rear road wheels 13 and 14 by the regenerative braking control during regenerative braking, and the driving force exerted on the front road wheels 11 and 12 by the drive control will be zero.

[0109] When the driver requests a left turn or curve of the vehicle 10 by turning the steering wheel 51 from the neutral position to the left, the steering control unit 32 first distributes the braking torque braking force to the left rear road wheel 13 to generate a torque to turn or steer the vehicle 10 to the left.

[0110] Next, when the temperature of the brake actuator 17, which applies the friction braking force to the left rear road wheel 13, reaches the second threshold temperature TH2 or higher, the steering control unit 32 distributes the braking torque braking force to the left front road wheel 11 in order to switch the current state to the state in which a torque is generated to steer the vehicle 10 in the left direction.

[0111] As described above, the steering control unit 32 switches the road wheel to which the braking torque braking force is distributed, based on the temperature increase of the corresponding brake actuator, from the rotating inner road wheel of the rear road wheels 13 and 14 to the rotating inner road wheel of the front road wheels 11 and 12.

[0112] This brake torque control can continuously generate torque in a direction of rotation or steering requested by the driver, while preventing an excessive increase in the temperature of a corresponding brake actuator.

[0113] Fig. Figure 7 illustrates a condition in which the driver requests a right turn and acceleration of the vehicle 10, and illustrates an example of a drive and brake force distribution when the temperature of the brake actuator 18 of the right rear road wheel 14, which is a rotating inner road wheel, is lower than the second threshold temperature TH2.

[0114] In this case, the steering control unit 32 distributes the braking torque braking force to the right rear road wheel 14, which is the rotating inner road wheel of the rear road wheels 13 and 14.

[0115] Furthermore, the steering control unit 32 implements driving by applying a driving force to the rear road wheels 13 and 14 and applies a driving force to the front road wheels 11 and 12 based on the acceleration request by the driver.

[0116] In the Fig. Figure 7 illustrates the state of drive and brake force distribution. When the temperature of the brake actuator 18, which exerts the friction braking force on the right rear road wheel 14, reaches the second threshold temperature TH2 or higher, the steering control unit 32 switches the drive and brake force distribution between the pair of front road wheels 11 and 12 and the pair of rear road wheels 13 and 14.

[0117] Fig. Figure 8 illustrates a condition in which the driver requests a right turn and deceleration of the vehicle 10, and illustrates an example of a drive and brake force distribution when the temperature of the brake actuator 18 of the right rear road wheel 14, which is a rotating inner road wheel, is lower than the second threshold temperature TH2.

[0118] In this case, the steering control unit 32 distributes the braking torque braking force to the right rear road wheel 14, which is the rotating inner road wheel of the rear road wheels 13 and 14.

[0119] Furthermore, the steering control unit 32 implements driving by applying a drive force to the rear road wheels 13 and 14 and applies a force to the front road wheels 11 and 12 during regenerative braking based on a deceleration request.

[0120] In the Fig. Figure 8 illustrates the state of drive and brake force distribution. When the temperature of the brake actuator 18, which exerts the friction braking force on the right rear road wheel 14, reaches the second threshold temperature TH2 or higher, the steering control unit 32 switches the drive and brake force distribution between the pair of front road wheels 11 and 12 and the pair of rear road wheels 13 and 14.

[0121] As described above, when the steering control unit 32 distributes the braking torque braking force to one of the rear road wheels 13 and 14, the steering control unit 32 fulfills the acceleration / deceleration request of the driver by controlling the driving and braking forces exerted on the front road wheels 11 and 12.

[0122] Furthermore, when the steering control unit 32 distributes the braking torque braking force to one of the front road wheels 11 and 12, the steering control unit 32 fulfills the acceleration / deceleration request of the driver by controlling the driving and braking forces exerted on the rear road wheels 13 and 14.

[0123] If an anomaly occurs in the steering function in the steer-by-wire system 40, it is possible, for example, in addition to a function to change the direction of travel of the vehicle 10 to the side of the road, to execute an emergency operation or emergency drive (limp home) that moves the vehicle 10 to a stopping position requested by the driver by implementing acceleration / deceleration based on the driver's request.

[0124] Furthermore, if the temperature of the brake actuator of the rotating inner wheel of the rear wheels 13 and 14 increases, the steering control unit 32 distributes the braking torque to one of the front wheels 11 and 12, creating a difference between the left and right braking forces. In this way, it is possible to rotate the front wheels 11 and 12 in the direction of rotation or steering requested by the driver by utilizing the alignment characteristics (steering roll radius) of the front wheels 11 and 12.

[0125] Fig. Figure 9 illustrates a condition in which the braking torque braking force is distributed to one of the front road wheels 11 and 12 when the temperature of the brake actuator 18 of the right rear road wheel 14, which is the rotating inner road wheel of the rear road wheels 13 and 14, has reached the second threshold temperature TH2 or higher in a condition in which the steering wheel 51 is turned to the right.

[0126] This case assumes that the steering scrub radius of the front road wheels 11 and 12 is negative.

[0127] In this case, the steering control unit 32 distributes the braking torque braking force to the left front road wheel 11, which is the rotating outer road wheel of the front road wheels 11 and 12.

[0128] If the front road wheels 11 and 12 of the vehicle 10 have a negative scrub radius, the application of the braking force to the front road wheels 11 and 12 generates a moment that rotates the front road wheels 11 and 12 about the center of an axis extending in the transverse direction of the vehicle.

[0129] If the rotation mechanism of the front road wheels 11 and 12 is a mechanism in which the front road wheels 11 and 12 are coupled to each other via a tie rod and in which the rotation angle of the front road wheel 11 and the rotation angle of the front road wheel 12 are changed integrally, the moments generated in the front road wheels 11 and 12 cancel each other out if the same braking force is applied to the two front road wheels 11 and 12, so that the rotation angle of the front road wheels 11 and 12 does not change.

[0130] In contrast, if there is a difference between the braking force applied to the front road wheel 11 and the braking force applied to the front road wheel 12, different moments are generated in the front road wheels 11 and 12, which changes the angle of rotation of the front road wheels 11 and 12.

[0131] For example, if a greater braking force is applied to the left front wheel 11 of the front wheels 11 and 12, the front wheels 11 and 12 will rotate to the right. If a greater braking force is applied to the right front wheel 12 of the front wheels 11 and 12, the front wheels 11 and 12 will rotate to the left.

[0132] That means if a right turn or curve, as in Fig. As illustrated in Figure 9, applying a braking force to the left front road wheel 11, which is a rotating outer road wheel, can actively rotate the front road wheels 11 and 12 in the right direction, which is the direction of the turn. As a result, the vehicle 10 is turned or steered to the right by the lateral force generated by the rotation of the front road wheels 11 and 12.

[0133] As described above, switching the brake torque / braking force distribution based on the temperature of the corresponding brake actuator is not limited to switching from the rotating inner wheel of the rear wheels 13 and 14 to the rotating inner wheel of the front wheels 11 and 12. If the steering roll radius is negative, switching from the rotating inner wheel of the rear wheels 13 and 14 to the rotating outer wheel of the front wheels 11 and 12 is possible.

[0134] Furthermore, if a fault occurs in the steering function in the steer-by-wire system 40, the steering control unit 32 can return the rotation angle of the front road wheels 11 and 12 to the neutral position or close to it by generating a braking force difference between the front road wheels 11 and 12 and by rotating the front road wheels 11 and 12 in a desired direction.

[0135] Fig. Figure 10 illustrates a case in which, when a fault occurs in the steering function in the steer-by-wire system 40, the front road wheels 11 and 12 have already been turned in the left direction, which is opposite to the direction to steer to the right, which is the steering direction requested by the driver.

[0136] In this state, the steering control unit 32 exerts the friction braking force on the rotating inner road wheel of the rear road wheels 13 and 14. Even if the driver attempts to turn or steer the vehicle 10 in the right direction, the tire lateral force generated in the front road wheels 11 and 12 is exerted to steer the vehicle 10 in the left direction, thereby reducing the effect of the brake torque control.

[0137] Fig. Figure 11 illustrates a case in which, when a fault occurs in the steering function in the steer-by-wire system 40, the front road wheels 11 and 12 have already been turned to the right, even though the driver requests or desires to drive straight ahead.

[0138] In this case, since the front road wheels 11 and 12 have been turned to the right to drive the vehicle 10 straight ahead, it is necessary to exert a braking force on the left rear road wheel 13 and to generate a braking force differential between the rear road wheels 13 and 14. As a result, a torque is generated to counteract the torque produced by the angle of rotation of the front road wheels 11 and 12.

[0139] This means that if a fault occurs in the steering function in the steer-by-wire system 40, it is necessary, if the front road wheels 11 and 12 have already been turned, in particular if the angle of rotation of the front road wheels 11 and 12 has already exceeded a predetermined angle in order to drive the vehicle 10 straight ahead, to continuously exert a friction braking force on one of the rear road wheels 13 and 14.

[0140] If the friction braking force is applied continuously, the temperature of the corresponding brake actuator can rise and the tire can wear unevenly.

[0141] Thus, if a disturbance occurs in the steering function of the steer-by-wire system 40, the steering control unit 32 generates a braking force differential between the front road wheels 11 and 12 in order to return the rotation angle of the front road wheels 11 and 12 to the neutral position or close to it. In this way, the rotation function based on brake torque control can be maintained stably, and the need to continuously apply the friction braking force to drive the vehicle 10 straight ahead is reduced.

[0142] Fig. 12 and Fig. Figure 13 are flowcharts illustrating a brake torque control procedure performed by the steering control unit 32, wherein the brake torque control includes a process to return the front road wheels 11 and 12 to the neutral position or near it.

[0143] Steps S301 to S304 in the flowchart in Fig. 12 are the same as steps S201 to S204 in the flowchart in Fig. 3. Furthermore, steps S307 to S313 are shown in the flowchart in Fig. 13 the same as steps S207 to S213 in the flowchart in Fig. 4.

[0144] Therefore, the description of the processing contents of steps S301 to S304 and steps S307 to S313 is omitted, and the processing contents in steps S305 and S306 are described in detail below.

[0145] If the steering control unit 32 determines in step S302 that the steer-by-wire system 40 cannot turn the front road wheels 11 and 12, the process proceeds to step S305.

[0146] In step S305, the steering control unit 32 determines whether the absolute value of the rotation angle δ [degrees] of the front road wheels 11 and 12 is a predetermined value δth or less.

[0147] The rotation angle δ is zero in the neutral position. Based on the positive or negative sign, the steering control unit 32 determines whether the rotation angle δ falls into a range in the right direction from the neutral position or into a range in the left direction from the neutral position.

[0148] Thus, in step S305, the steering control unit 32 determines whether the front road wheels 11 and 12 are in the neutral position or close to it.

[0149] Furthermore, the rotation angle δ determined by the steering control unit 32 in step S305 is a detected value obtained by means of a rotation angle sensor 43 or an estimated value of the rotation angle δ.

[0150] In this, the steering control unit 32 can, for example, generate a drive and brake force difference between the rear road wheels 13 and 14 such that the target yaw rate or target lateral acceleration is generated, and can estimate the rotation angle δ of the front road wheels 11 and 12 based on the difference between the target yaw rate or target lateral acceleration and the actually generated yaw rate or lateral acceleration.

[0151] If the steering control unit 32 determines in step S305 that the absolute value of the rotation angle δ is above the predetermined angle δth and that the front road wheels 11 and 12 have been turned to the right or to the left by a predetermined angle or more, the process proceeds to step S306.

[0152] In step S306, the steering control unit 32 performs a process such that the absolute value of the rotation angle δ of the front road wheels 11 and 12 falls below the predetermined angle δth, in other words, a process to return the rotation angle δ of the front road wheels 11 and 12 to the neutral position or close to it, without using the steer-by-wire system 40.

[0153] This means that the predetermined angle δth in step S305 is a threshold value to determine whether the current rotation angle δ can be left unchanged, as is the case when performing brake torque control, or whether the current rotation angle δ must be reduced.

[0154] If, on the other hand, the steering control unit 32 determines in step S305 that the absolute value of the rotation angle δ is the predetermined angle δth or less, in other words, that the rotation angle δ is in the neutral position or close to it, the process bypasses step S306 and proceeds to step S307.

[0155] This means that if the absolute value of the rotation angle δ is the predetermined angle δth or less, the steering control unit 32 determines that the process of returning the rotation angle δ of the front road wheels 11 and 12 to the neutral position or close to it is not necessary.

[0156] In step S306, the steering control unit 32 generates a braking force difference between the front road wheels 11 and 12 such that the absolute value of the rotation angle δ of the front road wheels 11 and 12 reaches the predetermined angle δth or less.

[0157] For example, if the steering roll radius of the front road wheels 11 and 12 is negative and if the front road wheels 11 and 12 have been turned to the right from the neutral position, the steering control unit 32 causes the brake actuator 16 to exert a friction braking force on the right front road wheel 12 in order to return the front road wheels 11 and 12 to the neutral position.

[0158] If the steering roll radius of the front road wheels 11 and 12 is negative and if the front road wheels 11 and 12 have been turned to the left from the neutral position, the steering control unit 32 in step S306 causes the brake actuator 15 to apply a friction braking force to the left front road wheel 11 in order to return the front road wheels 11 and 12 to the neutral position.

[0159] After the steering control unit 32 has returned the front road wheels 11 and 12 to the neutral position as described above, the process continues to step S307. In step S307, the steering control unit 32 executes the brake torque control to switch the right and left road wheels, between which a braking force differential is generated, from the rear road wheels 13 and 14 to the front road wheels 11 and 12 based on the increase in temperature of the corresponding brake actuator.

[0160] When the steering control unit 32 returns the front road wheels 11 and 12 to the neutral position in step S306, the steering control unit 32 applies the braking torque braking force, which is the friction braking force, to the rotating inner road wheel of the rear road wheels 13 and 14 to generate a torque.

[0161] As a result, it is possible to avoid a situation in which no torque can be generated during the process of returning the front road wheels 11 and 12 to the neutral position and in which the steering process is delayed.

[0162] Fig. Figure 14 is a state diagram illustrating a control operation of the process to return the front road wheels 11 and 12 to the neutral position or close to it.

[0163] Fig. Figure 14 illustrates an exemplary case in which the steering roll radius of the front road wheels 11 and 12 is negative, the driver requests a right turn and the front road wheels 11 and 12 have already been turned to the right, when a disturbance in the steering function in the steer-by-wire system 40 occurs.

[0164] In this case, the steering control unit 32 applies the friction braking force to the right front road wheel 12 of the front road wheels 11 and 12 to generate a torque that rotates the right front road wheel 12 to the left. By rotating the left front road wheel 11 to the left together with the right front road wheel 12 to the left, the steering control unit 32 returns the front road wheels 11 and 12 to the neutral position or close to it.

[0165] Furthermore, the steering control unit 32, in conjunction with the return of the front road wheels 11 and 12, distributes the braking torque braking force to the right rear road wheel 14, which is the rotating inner road wheel of the rear road wheels 13 and 14, in order to generate a torque requested by the driver in the right direction.

[0166] After returning the front road wheels 11 and 12 to the neutral position, the steering control unit 32 switches to normal brake torque control as described above. Fig. 5 illustrates this.

[0167] Before on the in Fig. When the control state illustrated in 5 is switched, the steering control unit 32 has returned the front road wheels 11 and 12 to the neutral position, ensuring the control accuracy of the torque generated by applying the friction braking force to the right rear road wheel 14 and consequently improving the steering performance.

[0168] Furthermore, when the driver requests the vehicle 10 to travel straight ahead, the steering control unit 32 actively returns the front road wheels 11 and 12 to the neutral position. In this way, the steering control unit 32 can drive the vehicle 10 straight ahead without distributing any braking torque or braking force.

[0169] This means that in order to drive the vehicle 10 straight ahead, if the front road wheels 11 and 12 have already been turned or rotated, it is necessary to generate a torque to counteract the torque caused by the rotation of the front road wheels 11 and 12 by creating a driving and braking force difference between the left and right road wheels.

[0170] In contrast, by returning the front road wheels 11 and 12 to the neutral position beforehand, there is no need to generate torque by creating a difference in driving and braking force between the left and right road wheels. This means it is possible to prevent the temperature of the corresponding brake actuator from rising or to prevent uneven tire wear.

[0171] If a road wheel that generates torque slips or slides during the execution of the brake torque control, the desired torque cannot be generated and the steering performance deteriorates.

[0172] The following describes a mode of brake torque control that prevents such a deterioration of steering performance due to slippage of a road wheel.

[0173] Fig. Figures 15 to 17 are flowcharts illustrating a mode of a brake torque control procedure that can prevent a deterioration in steering performance due to the occurrence of slippage.

[0174] As described in detail below, the flowcharts in Fig. Figures 15 to 17 illustrate brake torque control, a control system for preventing a deterioration of steering performance due to the occurrence of wheel slip. Specifically, the steering control unit 32 distributes a brake torque braking force applied to one of the front road wheels 11 and 12 (first road wheels) and one of the rear road wheels 13 and 14 (second road wheels) based on a wheel slip condition, which is the state of the vehicle 10.

[0175] Steps S401 to S411 in Fig. 15 and Fig. 16 are the same as steps S201 to S211 in Fig. 3 and Fig. 4. Furthermore, steps S413 and S414 are in Fig. 16 the same as steps S212 and S213 in Fig. 4.

[0176] Thus, in the flowcharts in Fig. 15 and Fig. 16. A detailed description of each step except step S412 has been omitted, and step S412 is described in detail.

[0177] In step S412, the steering control unit 32 performs a slip correction control, which is a control to correct the distribution of drive and braking forces when a road wheel in which a torque is generated exhibits slip.

[0178] Fig. Figure 17 is a flowchart that specifically illustrates the processing content in step S412.

[0179] In step S412A, the steering control unit 32 determines whether slippage has occurred in at least one (one or both of the left and right road wheels) of the front road wheels 11 and 12 or rear road wheels 13 and 14 in which the torque is currently being generated.

[0180] If the tire slip ratio obtained from the output of the road wheel speed sensor 83 exceeds a threshold value, the steering control unit 32 determines that slip has occurred.

[0181] If no slip has occurred in any of the left and right road wheels where the torque is currently being generated, the steering control unit 32 does not execute the slip correction control and the process continues to step S413.

[0182] If, on the other hand, the steering control unit 32 determines that slippage has occurred in at least one of the road wheels in which the torque is currently being generated, the process continues to step S412B.

[0183] In step S412B, the steering control unit 32 determines whether no slip has occurred in the right or left road wheel opposite the slipping road wheel, or whether slip has occurred in both the left and right road wheels.

[0184] If the steering control unit 32 determines that no slippage has occurred in the right or left road wheel opposite the slipping road wheel, the process proceeds to step S412C.

[0185] In step S412C, the steering control unit 32 reduces the drive and braking forces applied to the slipping road wheel and increases the drive and braking forces applied to one of the left and right road wheels, the road wheel being opposite the slipping road wheel, in order to reduce the slipping of the slipping road wheel and ensure the requested torque.

[0186] For example, if, in a state where torque is being generated, the rotating outer road wheel of the rear road wheels 13 and 14 slips due to the application of the friction braking force to the rotating inner road wheel of the rear road wheels 13 and 14, the steering control unit 32 reduces the driving force applied to the rear road wheels 13 and 14 and increases the friction braking force applied to the rotating inner road wheel that is not slipping.

[0187] In this way, the slippage of the rotating outer road wheel is reduced, the drive and braking force difference between the rear road wheels 13 and 14 is maintained, and the required torque is ensured.

[0188] In this case, the steering control unit 32 implements the requested acceleration / deceleration by adjusting the drive and braking forces exerted on the front road wheels 11 and 12.

[0189] If, on the other hand, the steering control unit 32 determines that both the right and left road wheels are slipping, the process continues to step S412D.

[0190] In step S412D, the steering control unit 32 determines whether the temperature of the brake actuator of the rotating inner road wheel, on which the friction braking force is applied to generate a torque, is the first threshold temperature TH1 or lower.

[0191] If the steering control unit 32 determines that the temperature of the brake actuator of the rotating inner road wheel is above the first threshold temperature TH1, the process proceeds to step S412F. In step S412F, the steering control unit 32 calculates, as the control target, the friction braking force generated in the brake actuators 15, 16, 17 and 18 to stop the vehicle 10, as in step S206.

[0192] If, on the other hand, the steering control unit 32 determines that the temperature of the brake actuator of the rotating inner road wheel is the first threshold temperature TH1 or lower, the process proceeds to step S412E.

[0193] In step S412E, the steering control unit 32 corrects the target drive and braking forces (sizes of the distribution between front and rear) calculated in step S411, which are applied to the road wheels 11, 12, 13 and 14 to reduce slippage and generate the necessary torque.

[0194] For example, if the rear road wheels 13 and 14 slip in a state where the braking torque braking force, which is a friction braking force, is exerted on the rotating inner road wheel of the rear road wheels 13 and 14, the steering control unit 32 reduces the slippage of the rear road wheels 13 and 14 by reducing the drive and braking forces exerted on the rear road wheels 13 and 14 in step S412E.

[0195] Furthermore, in step S412E, the steering control unit 32 compensates for the lack of steering torque caused by the reduction of the drive and braking forces applied to the rear road wheels 13 and 14 by applying the braking torque braking force to the rotating inner road wheel of the front road wheels 11 and 12.

[0196] Fig. Figure 18 illustrates an example of the correction (distribution correction) of drive and braking forces in step S412E by using a condition in which a driver requests a right turn.

[0197] Since a right turn or curve is requested, the steering control unit 32 executes a brake torque control to apply the brake torque braking force, which is a friction braking force, to the right rear road wheel 14, which is the rotating inner road wheel of the rear road wheels 13 and 14, and executes a drive control to apply the drive force to the rear road wheels 13 and 14.

[0198] If, in this condition, the left rear road wheel 13 and the right rear road wheel 14 slip, the steering control unit 32 reduces the drive and braking forces applied to the rear road wheels 13 and 14 in the brake torque control and drive control in order to reduce the slippage.

[0199] If the steering control unit 32 reduces the driving and braking forces applied to the rear road wheels 13 and 14, the torque generated in the rear road wheels 13 and 14 is reduced because the difference in driving and braking forces between the rear road wheels 13 and 14 is reduced, and it can no longer meet the torque requested by the driver.

[0200] To resolve this, the steering control unit 32 applies the braking torque force, which is a frictional braking force, to the right front road wheel 12, which is the rotating inner wheel of the front road wheels 11 and 12, thus compensating for the lack of torque. As a result, the torque requested by the driver is generated.

[0201] As described above, the slip correction control can prevent the steering performance from deteriorating due to the occurrence of slippage, and the brake torque control can be operated stably.

[0202] If one of the road wheels in which a torque is generated exhibits slip or slippage, the steering control unit 32 can also switch to the distribution in which the friction braking force is applied to the rotating inner road wheel of the front road wheels 11 and 12 and the rotating inner road wheel of the rear road wheels 13 and 14, as shown in Fig. 18 illustrated.

[0203] Furthermore, the steering control unit 32 can perform the control to distribute the braking torque braking force to one of the front road wheels 11 and 12 and one of the rear road wheels 13 and 14 based on the slip state of the road wheels, instead of performing the control to distribute the braking torque braking force to one of the front road wheels 11 and 12 and one of the rear road wheels 13 and 14 based on the temperatures of the corresponding brake actuators.

[0204] The individual technical concepts described in the example above can be combined and used appropriately, as long as no conflict arises.

[0205] Although the present invention has thus been described in detail with reference to a preferred example, it will be obvious to the person skilled in the art that various types of modified modes are possible based on the basic technical concepts and teachings of the present invention.

[0206] For example, if the vehicle control device 30 (steering control unit 32) switches from the state in which the braking torque is distributed to one of the rear road wheels 13 and 14 to the state in which the braking torque is distributed to one of the front road wheels 11 and 12, where the front road wheels 11 and 12 are the steered road wheels, the vehicle control device 30 (steering control unit 32) can temporarily distribute the braking torque to one of the rear road wheels 13 and 14 and one of the front road wheels 11 and 12.

[0207] Furthermore, the vehicle control device 30 (steering control unit 32) can distribute the braking torque braking force to one of the rear road wheels 13 and 14 and one of the front road wheels 11 and 12 in a ratio based on a ratio between the temperature of the brake actuator of the rotating inner road wheel of the rear road wheels 13 and 14 and the temperature of the brake actuator of the rotating inner road wheel (or the rotating outer road wheel) of the front road wheels 11 and 12.

[0208] Furthermore, the vehicle 10 can, for example, be a work vehicle, such as a forklift or construction machine, which includes a steer-by-wire system for turning or rotating the rear road wheels 13 and 14.

[0209] If the vehicle 10 includes a steer-by-wire system for rotating the rear road wheels 13 and 14, the vehicle control device 30 distributes the braking torque force to the rotating inner road wheel of the front road wheels 11 and 12 if the temperature of the friction braking device, which exerts a friction braking force on the rotating inner road wheel of the front road wheels 11 and 12, is lower than the first threshold temperature TH1. If the temperature of the friction braking device, which exerts a friction braking force on the rotating inner road wheel of the front road wheels 11 and 12, exceeds the first threshold temperature TH1, the vehicle control device 30 distributes the braking torque force to the rotating inner road wheel of the rear road wheels 13 and 14, which are the steered road wheels.

[0210] This means that the steered road wheels turned or rotated by means of the steer-by-wire system can be the pair of front road wheels 11 and 12 or the pair of rear road wheels 13 and 14.

[0211] Furthermore, vehicle 10 comprises at least four road wheels, consisting of a pair of left and right road wheels (first road wheels), which are the steered road wheels, and a pair of left and right road wheels (second road wheels), which are the other road wheels besides the steered road wheels. In other words, vehicle 10 can be a six-wheeled vehicle.

[0212] Furthermore, vehicle 10 can be a vehicle that has an internal combustion engine as its power source instead of electric motors 71 and 72. Alternatively, vehicle 10 can be a vehicle in which a driving force is exerted on one pair of front road wheels and one pair of rear road wheels by an internal combustion engine, and driving and braking forces are exerted on the other pair by an electric motor.

[0213] Furthermore, in the example above, the vehicle control device 30 (steering control unit 32) distributes a braking torque / braking force applied to the first road wheels, which are the steered road wheels, and the second road wheels, which are the other road wheels, based on the temperature of a friction braking device or the slip state of a road wheel as a vehicle condition. However, the vehicle condition is not limited to this.

[0214] For example, the vehicle control unit 30 (steering control unit 32) can distribute a braking torque / braking force exerted on the first road wheels, which are the steered road wheels, and the second road wheels, which are the other road wheels, based on physical quantities that influence a torque generated by a difference in driving and braking forces between the left and right road wheels. These physical quantities can include the wheel load, tire pressure, the degree of tire deterioration or wear (amount of wear), the coefficient of friction of the road surface, etc. REFERENCE MARK LIST 10 vehicles 11, 12 Front road wheel (steered road wheel, first road wheel) 13, 14 Rear road wheel (second road wheel) 15, 16, 17, 18 Brake actuator (friction brake device) 30 Vehicle control unit 30A control unit 32 Steering control unit 40 Steer-by-Wire system 51 Steering wheel 71 First electric motor 72 Second electric motor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2000-190863 A

[0003]

Claims

[1] Vehicle control device arranged in a vehicle comprising a steer-by-wire system which, assuming that the steered road wheels under the road wheels of the vehicle are first road wheels which are mechanically separated from a steering wheel and that the road wheels other than the steered road wheels of the road wheels are second road wheels, rotates the first road wheels and comprises friction braking devices which exert a friction braking force on the road wheels, wherein, if a control unit contained in the vehicle control device detects a signal indicating an anomaly in a steering function in the steer-by-wire system, the control unit performs a brake torque control to generate a yaw moment in the vehicle by using the friction braking force exerted on the road wheels based on a steering input into the steering wheel and In brake torque control, the control unit distributes a brake torque braking force, which is applied to the first road wheels and the second road wheels, based on the vehicle's condition. [2] Vehicle control device according to claim 1, wherein the control unit distributes the braking torque braking force to a rotating inner road wheel of the first road wheels or a rotating inner road wheel of the second road wheels based on, under the conditions of the vehicle, a temperature of the friction braking device which exerts the friction braking force on the rotating inner road wheel of the second road wheels. [3] Vehicle control device according to claim 2, wherein the vehicle comprises a first electric motor that exerts driving and braking forces on the first road wheels, and a second electric motor that exerts driving and braking forces on the second road wheels, wherein, when the control unit distributes the braking torque braking force to the first road wheels, the control unit performs a regenerative braking control to generate a force during regenerative braking in the second road wheels and where, when the control unit distributes the braking torque braking force to the second road wheels, the control unit performs a regenerative braking control to generate a force during regenerative braking in the first road wheels. [4] Vehicle control device according to claim 3, where, if a requested acceleration / deceleration demanded by the vehicle is zero, the control unit, if the control unit distributes the braking torque braking force to the first road wheels, performs a drive control to generate a driving force in the first road wheels, where, if the control unit distributes the braking torque / braking force to the second road wheels, the control unit performs a drive control to generate a driving force in the second road wheels, where, assuming that the driving force is represented by a positive physical quantity and the braking force is represented by a negative physical quantity, the control unit performs a control such that the sum of the friction braking force through the brake torque control, the force during regenerative braking through the regenerative braking control, and the driving force through the drive control is zero. [5] Vehicle control device according to claim 2, wherein, if the temperature of the friction brake device which exerts the friction brake force on the rotating inner road wheel of the second road wheels is less than a second threshold temperature, the control unit distributes the brake torque brake force to the rotating inner road wheel of the second road wheels. [6] Vehicle control device according to claim 5, wherein, when the temperature of the friction braking device which exerts the friction braking force on the rotating inner road wheel of the second road wheels is above a first threshold temperature which is higher than the second threshold temperature, the control unit exerts a predetermined braking force on the road wheels. [7] Vehicle control device according to claim 2, wherein the first road wheels are front road wheels of the vehicle and the second road wheels are rear road wheels of the vehicle. [8] Vehicle control device according to claim 1, wherein the control unit distributes the braking torque braking force to a rotating inner road wheel of the first road wheels and a rotating inner road wheel of the second road wheels based on, under the conditions of the vehicle, a slip condition of the second road wheels. [9] Vehicle control device according to claim 1, where a negative scrub radius is specified for the first road wheels and where, if the control unit distributes the braking torque braking force to the first road wheels based on the vehicle's states, the control unit distributes the braking torque braking force to a rotating outer road wheel of the first road wheels. [10] Vehicle control device according to claim 1, wherein, when the control unit detects the signal indicating the anomaly in the steering function in the steer-by-wire system, if the rotation angle of the first road wheels is above a predetermined angle, the control unit causes the corresponding friction brake devices to exert a friction braking force on the first road wheels such that the rotation angle of the first road wheels falls below the predetermined angle. [11] Vehicle control method performed by a control unit located in a vehicle comprising a steer-by-wire system that rotates first road wheels which are mechanically separated from a steering wheel and which are steered road wheels of the vehicle, and friction braking devices which exert a friction braking force on the road wheels of the vehicle, wherein, if the steering wheel is turned to the right in a state where a fault has occurred in a steering function in the steer-by-wire system, the friction braking force is exerted on the right rear wheel if the temperature of the friction braking device that exerts the friction braking force on a right rear wheel of the vehicle's rear wheels is 100 degrees Celsius and wherein, if the temperature of the friction braking device which exerts the friction braking force on the right rear road wheel is 300 degrees Celsius, the friction braking force is exerted on a right front road wheel of the front road wheels.

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