Vehicle control device, vehicle control method, and vehicle control system

Abstract

According to an aspect of a vehicle control device, a vehicle control method, and a vehicle control system of the present invention: a target vehicle momentum indicating a target yaw rate or a target lateral acceleration is acquired on the basis of an operation angle of a steering wheel; when the steered angle of a steered wheel cannot be detected, a control command for generating a yaw moment in the vehicle by a wheel other than the steered wheel on the basis of the target vehicle momentum is output; and a braking / driving force command for providing a braking / driving force to the steered wheel is output on the basis of a steered angle estimated on the basis of a difference between the actual vehicle momentum generated in the vehicle by the control command and the target vehicle momentum. This enables turning control to be carried out by means of the braking / driving force with high precision, even if the information of the steered angle has been lost.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a failure detection / management system for a steering angle sensor of a steer-by-wire system. The failure detection / management system of Patent Document 1 obtains an estimated steering angle based on a yaw rate or lateral acceleration, and compares the estimated steering angle with a detected value of the steering angle by a steering angle sensor to detect a failure of the steering angle sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when the steer-by-wire system fails and the steering of the steered wheels becomes impossible, by controlling the difference between the braking / driving force applied to the wheels on the inner side of the turn and the braking / driving force applied to the wheels on the outer side of the turn, a yaw moment can be generated in the vehicle to turn the vehicle in the operation direction of the steering wheel. However, when performing turning control by such braking / driving force, if the information on the steering angle of the steered wheels is also lost, it becomes impossible to control the braking / driving force appropriately according to the steering angle, and there is a problem that the accuracy of the turning control decreases.

[0005] The present invention has been made in view of the conventional situation, and an object thereof is to provide a vehicle control device, a vehicle control method, and a vehicle control system that can perform turning control by braking / driving force with high accuracy even when the information on the steering angle of the steered wheels is lost.

Means for Solving the Problems

[0006] According to the vehicle control device, vehicle control method, and vehicle control system of the present invention, in one embodiment, a target vehicle momentum indicating a target yaw rate or target lateral acceleration to be generated in the vehicle is acquired based on the steering wheel operating angle, and if the detection feasibility information, which is information regarding whether or not the steering angle of the steering wheel can be detected, indicates that detection is not possible, a control command is output to generate a yaw moment in the vehicle with the wheels of the vehicle other than the steering wheel based on the target vehicle momentum, an actual vehicle momentum corresponding to the target vehicle momentum generated in the vehicle by the control command is acquired, an estimated steering angle, which is an estimated value of the steering angle of the steering wheel, is acquired based on the difference between the target vehicle momentum and the actual vehicle momentum, and a first braking force command is output to apply a braking force to the steering wheel based on the estimated steering angle. [Effects of the Invention]

[0007] According to the present invention, even if information on the steering angle of the steering wheels is lost, turning control using braking and driving forces can be performed with high precision. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing the vehicle control system. [Figure 2] This is a block diagram illustrating the schematics of each control system in a vehicle control system. [Figure 3] This flowchart shows the turning control process that estimates the steering angle from the yaw rate difference. [Figure 4] This flowchart shows the turning control process that estimates the steering angle from the yaw rate difference. [Figure 5] This is a state diagram illustrating the control state of braking and driving forces when estimating the steering angle. [Figure 6] This is a state diagram illustrating the control state of braking and driving forces implemented using the estimated steering angle. [Figure 7] This flowchart shows the process of turn control, which estimates the steering angle from the difference in lateral acceleration. [Figure 8] This flowchart shows the process of turn control, which estimates the steering angle from the difference in lateral acceleration. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the vehicle control device, vehicle control method, and vehicle control system according to the present invention will be described with reference to the drawings. Figure 1 is an overall configuration diagram showing the vehicle control system 100 installed in the vehicle 10. Figure 2 is a block diagram schematically showing the braking, driving, and steering control systems of the vehicle control system 100. The vehicle 10 is equipped with a pair of left and right front wheels 11, 12 and a pair of left and right rear wheels 13, 14.

[0010] Furthermore, the vehicle 10 includes a drive force actuator 70 that provides driving force to the vehicle 10, comprising a motor 71 that provides driving force to the front wheels 11 and 12, and a motor 72 that provides driving force to the rear wheels 13 and 14. The drive force control unit 31 acquires information on the amount of operation of the accelerator pedal 73 from the accelerator pedal sensor 74 and outputs control signals to the motors 71 and 72 according to the target drive force based on the amount of operation of the accelerator pedal 73, thereby applying drive force corresponding to the amount of operation of the accelerator pedal 73 to the front wheels 11 and 12 and the rear wheels 13 and 14.

[0011] Furthermore, the vehicle 10 is equipped with a steer-by-wire system 40 in which the steering wheel 51 and the front wheels 11 and 12, which are the steering wheels, are mechanically separated as a steering device. The steer-by-wire system 40 includes a reaction force actuator 41 that applies an operating reaction force torque to the steering wheel 51, a wheel actuator 42 that applies steering force to the front wheels 11 and 12, a steering angle sensor 43 that detects the steering angle δ of the front wheels 11 and 12 (in other words, the tire angle of the front wheels 11 and 12), and a steering control unit 32 that controls the reaction force actuator 41 and the wheel actuator 42.

[0012] In addition, the steering wheel 51 includes an operation angle sensor 52 that detects an operation angle θ, which is the rotation angle of the steering wheel 51. The steering angle sensor 43 detects the steering angle δ of the front wheels 11, 12 by detecting the rotation angle of the steering motor that constitutes the wheel actuator 42 or the rack position in the rack and pinion mechanism that converts the rotational force of the steering motor into linear movement.

[0013] The steering control unit 32 acquires information on the operation angle θ of the steering wheel 51 detected by the operation angle sensor 52, and obtains a target steering angle and a target reaction force torque from the operation angle θ, which is a steering angle command. Then, the steering control unit 32 controls the wheel actuator 42 so that the steering angle δ detected by the steering angle sensor 43 approaches the target steering angle, and controls the reaction force actuator 41 so that a target reaction force torque is applied to the steering wheel 51.

[0014] In addition, the vehicle 10 includes a braking device. The braking device includes a brake control unit 33, a brake pedal sensor 62 that detects the operation amount of the brake pedal 61, brake actuators 15, 16, 17, 18 provided on each of the wheels 11, 12, 13, 14, and brake thrust sensors 21, 22, 23, 24 that detect the thrust generated by the brake actuators 15, 16, 17, 18, respectively.

[0015] The brake control unit 33 controls the braking force applied by the brake actuators 15, 16, 17, 18 to each of the wheels 11, 12, 13, 14 based on the output of the brake pedal sensor 62 and the outputs of the brake thrust sensors 21, 22, 23, 24. The brake actuators 15, 16, 17, 18 and the driving force actuator 70 constitute the control and drive actuators of the vehicle control system 100.

[0016] The driving force control unit 31, the steering control unit 32, and the brake control unit 33 each include a microcomputer 31A, 32A, 33A. The microcomputers 31A, 32A, 33A each include an MPU (Microprocessor Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., which are not shown in the figure. By operating the programs stored in the ROM as a storage unit with the MPU, various functions are realized.

[0017] Note that 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. Also, the microcomputers 31A, 32A, 33A function as a control unit 30A of the vehicle control device 30.

[0018] The vehicle 10 also includes 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 as sensors for detecting the behavior 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 control unit 30A acquires the output signals of the above yaw rate sensor 81, lateral acceleration sensor 82, and wheel speed sensor 83.

[0019] In such a vehicle control system 100, the control unit 30A, specifically, the microcomputer 32A of the steering control unit 3 diagnosticates the presence or absence of an abnormality in the steering function in the steer-by-wire system 40. Note that an abnormality in the steering function means a state where the front wheels 11, 12, which are the steering wheels, cannot be steered and the steering angle δ cannot be controlled to the target steering angle corresponding to the operation angle θ of the steering wheel 51, which is due to a failure of the wheel actuator 42, an abnormality in the drive circuit of the wheel actuator 42, a failure of various sensors, etc.

[0020] When the control unit 30A acquires information indicating an abnormality in the steering function of the steer-by-wire system 40, it outputs a braking force command that creates a difference in braking force between the left and right wheels, thereby generating a yaw moment in the vehicle 10 corresponding to the operating angle θ of the steering wheel 51, and causing the vehicle 10 to turn in the direction of the steering wheel 51's operation. The control that creates a difference in braking and driving force between the front wheels 11 and 12 is a control that makes one of the following values ​​greater than the other: the sum of the driving and braking force applied to the outer front wheel 11 and 12 during a turn, and the sum of the driving and braking force applied to the inner front wheel 11 and 12 during a turn, when the driving force is a positive physical quantity and the braking force is a negative physical quantity.

[0021] Here, between the front wheels 11 and 12, whether the braking force on the outer side of the turn is smaller than the braking force on the inner side of the turn, or conversely, whether the braking force on the inner side of the turn is smaller than the braking force on the outer side of the turn, is determined based on the alignment characteristics of the front wheels 11 and 12, specifically the setting of the scrub radius. If the scrub radius of the front wheels 11 and 12 is negative, the vehicle control device 30 outputs a braking force command in the braking force control of the front wheels 11 and 12 such that the braking force on the outer side of the turn is smaller than the braking force on the inner side of the turn.

[0022] If the scrub radius of the front wheels 11 and 12 is negative, for example, if braking force is applied to the right front wheel 12 for a right turn, the front wheels 11 and 12 will turn to the left, opposite to the target turning direction, and similarly, if braking force is applied to the left front wheel 11 for a left turn, the front wheels 11 and 12 will turn to the right, opposite to the target turning direction. In other words, if the scrub radius of the front wheels 11 and 12 is negative, making the braking force on the inside of the turn smaller than the braking force on the outside of the turn will change the steering angle δ of the front wheels 11 and 12 in a direction that cancels out the yaw moment generated by the difference in braking force between the front wheels 11 and 12. Furthermore, if the yaw moment caused by the change in steering angle δ is significant, the vehicle may turn in the opposite direction to the turning direction expected from the difference in braking and driving forces applied to the front wheels 11 and 12.

[0023] Therefore, when the scrub radius of the front wheels 11 and 12 is negative, the control unit 30A outputs a braking force command such that the braking force on the outside of the turn is smaller than the braking force on the inside of the turn. This allows the front wheels 11 and 12 to be steered in a direction corresponding to the steering wheel 51's operating angle θ, and the lateral force of the tires generated by the steering of the front wheels 11 and 12 in the turning direction can be used to turn the vehicle 10 in a direction corresponding to the steering wheel 51's operating angle θ.

[0024] On the other hand, when the scrub radius at the front wheels 11 and 12 is positive, the direction of the steering angle change due to the difference in braking and driving forces between the left and right sides is the opposite of the negative case. Therefore, when the scrub radius of the front wheels 11 and 12 is positive, the control unit 30A outputs a braking force command to make the braking force on the inner side of the turn smaller than the braking force on the outer side of the turn, in order to generate a yaw moment in the vehicle 10 by utilizing the steering due to the alignment characteristics and the difference in braking force between the left and right sides.

[0025] Furthermore, the rear wheels 13 and 14, which are not steering wheels, are relatively less affected by the scrub radius as an alignment characteristic. Therefore, when the control unit 30A controls the braking and driving forces of the rear wheels 13 and 14 to generate a yaw moment in the vehicle 10, assuming that the driving force is a positive physical quantity and the braking force is a negative physical quantity, it outputs braking and driving force commands for the rear wheels 13 and 14 such that the sum of the driving force and braking force applied to the rear wheel on the inside of the turn is less than the sum of the driving force and braking force applied to the rear wheel on the outside of the turn.

[0026] Furthermore, the microcomputer 32A of the steering control unit 32 can detect abnormal steering function information in the steer-by-wire system 40, and transmit this information to the drive force control unit 31 and the brake control unit 33 via a higher-level vehicle integrated control unit or the like. Furthermore, a higher-level unit, such as a vehicle integrated control unit, can diagnose whether or not there is an abnormality in the steering function of the steer-by-wire system 40, and if an abnormality occurs in the steering function, the higher-level unit can output abnormality information to the lower-level units, the drive force control unit 31 and the brake control unit 33.

[0027] However, when the control unit 30A performs turning control that creates a difference in braking and driving force between the left and right wheels, if it loses the detection information, which is information indicating the detected value of the steering angle δ, in other words, if the steering angle δ cannot be detected, it will not be able to control the braking and driving force to an appropriate level that takes into account the lateral force generated in accordance with the steering angle δ, and the accuracy of the turning control will decrease. Therefore, if the control unit 30A has lost the information regarding the steering angle δ, it estimates the steering angle δ from the equation of motion of the vehicle 10 and uses the estimated information of the steering angle δ for turning control.

[0028] The control unit 30A, as a process for estimating the steering angle δ, outputs a control command to generate a target yaw rate corresponding to the operating angle θ of the steering wheel 51 by controlling the braking and driving forces of the rear wheels 13 and 14, which are wheels other than the steering wheels. The control unit 30A then estimates the steering angle δ based on the difference between the actual yaw rate generated by the braking and driving force control of the rear wheels 13 and 14 and the target yaw rate.

[0029] Here, the control unit 30A, in the process of estimating the steering angle δ, does not generate a braking and driving force difference for the front wheels 11 and 12, which are the steering wheels, but generates a braking and driving force difference for the rear wheels 13 and 14. This is because if a braking and driving force difference is generated for the front wheels 11 and 12, the steering angle δ will change according to the alignment characteristics, as described above, and the accuracy of the steering angle δ estimation will decrease. Therefore, when the steering angle δ cannot be detected, the control unit 30A generates a yaw moment in the vehicle 10 by controlling the braking and driving force of the wheels other than the steering wheels, i.e., the rear wheels 13 and 14. After estimating the steering angle δ from the yaw moment generated at this time, the control unit 30A uses the estimated steering angle δ information to perform braking and driving force control on the steering wheels, the front wheels 11 and 12.

[0030] The following section provides a more detailed explanation of the turning control (in other words, the vehicle control method) when an abnormality occurs in the steering function of the steer-by-wire system 40. Figures 3 and 4 are flowcharts showing the rotation control process performed by the control unit 30A.

[0031] In step S201, the control unit 30A determines whether both the drive system (drive force actuator 70) and the braking system (brake actuators 15, 16, 17, 18) are functioning normally and whether the braking and driving forces can be controlled. Furthermore, the presence or absence of abnormalities in the drivetrain is diagnosed by the drive force control unit 31, and the presence or absence of abnormalities in the braking system is diagnosed by the brake control unit 33. Then, if both the braking system and the drive system are functioning normally, the control unit 30A proceeds to step S202. If there is an abnormality in at least one of the braking system or the drive system, the control unit terminates this routine because it is not possible to perform turning control using braking and driving forces.

[0032] In step S202, the control unit 30A determines whether it has acquired information indicating an abnormality in the steering function of the steer-by-wire system 40, or more specifically, whether the steering control unit 32 has diagnosed an abnormality in the steering function. Then, if the steering function of the steer-by-wire system 40 is abnormal, the control unit 30A proceeds to step S203. On the other hand, the control unit 30A terminates this routine if the steering function of the steer-by-wire system 40 is normal and the front wheels 11 and 12 are steered according to the operating angle θ of the steering wheel 51, as cornering control by braking and driving force is unnecessary.

[0033] In step S203, the control unit 30A determines whether it has obtained information indicating that the steering angle δ cannot be detected, or information indicating that it can be detected, as information regarding whether the steering angle δ can be detected. In other words, in step S203, the control unit 30A determines whether the steering angle δ is unknown or whether the steering angle δ is being detected correctly.

[0034] If the control unit 30A is in a state where the steering angle δ can be detected, it proceeds to step S204 or later and performs turning control using braking and driving force based on the steering angle δ detected by the steering angle sensor 43. On the other hand, if the control unit 30A is in a state where it cannot detect the steering angle δ and has lost information about the steering angle δ, it proceeds to step S209 or later and performs turning control using braking and driving forces, which includes the process of determining the estimated steering angle δe, which is an estimated value of the steering angle δ.

[0035] First, the turning control from step S204 onward, when the steering angle δ is detectable, will be explained below. In step S204, the control unit 30A calculates the target yaw rate γ* as the target vehicle momentum based on the operating angle θ of the steering wheel 51 detected by the operating angle sensor 52 and the vehicle speed V (in other words, the vehicle body speed) obtained from the signal of the wheel speed sensor 83.

[0036] Next, in step S205, the control unit 30A calculates the target longitudinal acceleration α* based on the amount of operation of the brake pedal 61 detected by the brake pedal sensor 62 and the amount of operation of the accelerator pedal 73 detected by the accelerator pedal sensor 74. Then, in step S206, the control unit 30A calculates the target braking and driving forces Ffl, Ffr, Frl, and Frr for each wheel 11-14 to achieve the target yaw rate γ* and target longitudinal acceleration α*, based on the target yaw rate γ*, the target longitudinal acceleration α*, and the steering angle δ detected by the steering angle sensor 43. From now on, unless otherwise specified, the target braking force for each wheel will be collectively referred to as "Fxx".

[0037] Next, in step S207, the control unit 30A calculates the target braking force Tbxx for each wheel 11-14, which is generated by the brake actuators 15, 16, 17, and 18, and the drive torque Tmxx for each wheel 11-14, which is generated by the motors 71 and 72, from the target braking force Fxx for each wheel 11-14. Then, in step S208, the control unit 30A outputs a braking force command as a control command to the brake actuators 15, 16, 17, and 18 based on the target braking force Tbxx, and outputs a drive force command as a control command to the drive force actuator 70 based on the target drive torque Tmxx.

[0038] In other words, when the steering function of the steer-by-wire system 40 is abnormal, if the steering angle δ can be detected, the estimation process for the steering angle δ is unnecessary, and braking and driving force control can be performed using the detected value of the steering angle δ. Therefore, the control unit 30A outputs a braking force command that applies braking force to the front wheels 11 and 12 based on the target yaw rate γ*, without performing the process of estimating the steering angle δ by applying braking force only to the rear wheels 13 and 14, which will be described later. Furthermore, the braking force command based on the target yaw rate γ* corresponds to a second braking force command that applies braking force to the front wheels 11 and 12 based on the target vehicle momentum.

[0039] As described above, if the steering function of the steer-by-wire system 40 is abnormal, the control unit 30A, if the steering angle δ can be detected, controls the braking and driving forces applied to the front wheels 11, 12 and the rear wheels 13, 14, taking into account the information of the steering angle δ, thereby generating the yaw moment requested by the driver of the vehicle 10 in the vehicle 10. In other words, if the steering function of the steer-by-wire system 40 is abnormal and the steering angle δ is detectable, the control unit 30A outputs a braking force command to apply braking force to the front wheels 11, 12 and the rear wheels 13, 14 based on the target yaw rate γ*.

[0040] Next, the turning control performed from step S209 onward, which is carried out when the steering function of the steer-by-wire system 40 is abnormal and the steering angle δ cannot be detected, will be described below. First, in step S209, the control unit 30A calculates the target yaw rate γ* as the target vehicle momentum based on the steering wheel 51's operating angle θ and the vehicle speed V. Furthermore, the control unit 30A can correct the target yaw rate γ* according to the vehicle conditions.

[0041] Next, in step S210, the control unit 30A calculates the target longitudinal acceleration α* based on the amount of operation of the brake pedal 61 and the amount of operation of the accelerator pedal 73. Then, in step S211, the control unit 30A determines the target braking and driving forces Frl and Frr for the rear wheels 13 and 14, which are the wheels other than the steering wheels, based on the target yaw rate γ* and the target longitudinal acceleration α*. In other words, the control unit 30A controls the braking and driving forces of the rear wheels 13 and 14 to determine the target braking and driving forces Frl and Frr of the rear wheels 13 and 14 so that the vehicle 10 generates a target yaw rate γ*.

[0042] Next, in step S212, the control unit 30A calculates the target braking force Tbrl, Tbrr for the rear wheels 13 and 14, which will be generated by the brake actuators 17 and 18, and the drive torque Tmrl, Tmrr for the rear wheels 13 and 14, which will be generated by the motor 72, from the target braking force Frl, Frr of the rear wheels 13 and 14. Then, in step S213, the control unit 30A controls the brake actuators 17 and 18 of the rear wheels 13 and 14 based on the target braking forces Tbrl and Tbrr, and controls the motor 72 that drives the rear wheels 13 and 14 based on the target drive torques Tmrl and Tmrr.

[0043] Next, in step S214, the control unit 30A detects the vehicle speed V from the signal of the wheel speed sensor 83. Then, in step S215, the control unit 30A determines whether the vehicle speed V is greater than or equal to a predetermined threshold value VT.

[0044] Here, the threshold value VT for the vehicle speed V in step S215 is a value used by the control unit 30A to switch between detecting the yaw rate γ actually occurring in the vehicle 10 using the yaw rate sensor 81 or estimating it from the driving conditions of the vehicle 10. Since the detection accuracy of the yaw rate γ by the yaw rate sensor 81 decreases as the vehicle speed V decreases, the lower limit of the vehicle speed V at which the yaw rate sensor 81 can detect the yaw rate γ with sufficient accuracy is set as a threshold.

[0045] In other words, when the vehicle speed V is greater than or equal to the threshold VT, the detection accuracy of the yaw rate γ by the yaw rate sensor 81 is ensured, and when the vehicle speed V is less than the threshold VT, the yaw rate sensor 81 is unable to detect the yaw rate γ with sufficient accuracy. Therefore, if the control unit 30A determines in step S215 that the vehicle speed V is greater than or equal to the threshold VT, it proceeds to step S216 and detects the actual yaw rate γa as the actual vehicle momentum from the output signal of the yaw rate sensor 81.

[0046] On the other hand, when the control unit 30A determines that the vehicle speed V is less than the threshold VT, it proceeds to step S217 and estimates the actual yaw rate γa as actual vehicle momentum based on the wheel speed detected by the wheel speed sensor 83 and the tread of the vehicle 10, according to equation 1.

number

[0047] Furthermore, if the vehicle 10 is not equipped with a yaw rate sensor 81, or if the yaw rate sensor 81 equipped in the vehicle 10 is lost and the yaw rate γ cannot be detected, the control unit 30A can perform the process of step S217, which estimates the actual yaw rate γa from the wheel speed, etc.

[0048] The control unit 30A determines the actual yaw rate γa in step S216 or step S217, then proceeds to step S218 to determine the difference Δγ (Δγ = γ* - γa) between the target yaw rate γ* and the actual yaw rate γa. Next, in step S219, the control unit 30A calculates the estimated steering angle δe, which is an estimated value of the steering angle δ at the present moment, based on the difference Δγ between the target yaw rate γ* and the actual yaw rate γa, in other words, the difference between the target vehicle momentum and the actual vehicle momentum.

[0049] In detail, in step S219, the control unit 30A determines the estimated steering angle δe based on the difference Δγ according to the equation of motion of the vehicle 10 shown in Equation 2.

number

[0050] In the next step S220, the control unit 30A calculates the target braking and driving forces Ffl, Ffr, Frl, and Frr for each wheel 11-14 to achieve the target yaw rate γ* and target longitudinal acceleration α*, based on the target yaw rate γ*, target longitudinal acceleration α*, and estimated steering angle δe. Next, in step S221, the control unit 30A calculates the target braking force Tbxx for each wheel 11-14 generated by the brake actuators 15, 16, 17, and 18, and the drive torque Tmxx for each wheel 11-14 generated by the motors 71 and 72, based on the target braking force Fxx for each wheel 11-14.

[0051] Then, in step S222, the control unit 30A outputs braking force commands to the brake actuators 15, 16, 17, and 18 of the front wheels 11, 12 and rear wheels 13, 14 based on the target braking force Tbxx, and outputs driving force commands to the motors 71 and 72, which are the driving force actuators 70 of the front wheels 11, 12 and rear wheels 13, 14, based on the target driving torque Tmxx. In other words, the control unit 30A obtains an estimated steering angle δe by controlling the braking and driving force of the rear wheels 13 and 14, and then outputs a braking and driving force command, that is, a first braking and driving force command, which applies braking and driving force to the front wheels 11 and 12 based on the estimated steering angle δe.

[0052] Furthermore, the braking and driving force command that the control unit 30A outputs in step S222, which applies braking and driving force to the front wheels 11 and 12, is determined, as described above, based on whether the scrub radius setting for the front wheels 11 and 12 is negative or positive. In other words, when the scrub radius of the front wheels 11 and 12 is negative, the control unit 30A outputs a braking force command such that the braking force on the outside of the turn is smaller than the braking force on the inside of the turn.

[0053] This allows the front wheels 11 and 12 to be steered in a direction corresponding to the steering wheel 51's operating angle θ, and the lateral force of the tires generated by the steering of the front wheels 11 and 12 in the turning direction can be used to turn the vehicle 10 in a direction corresponding to the steering wheel 51's operating angle θ. On the other hand, if the scrub radius of the front wheels 11 and 12 is positive, the control unit 30A outputs a braking force command to make the braking force on the inner side of the turn smaller than the braking force on the outer side of the turn, in order to generate a yaw moment in the vehicle 10 by utilizing the steering due to the alignment characteristics and the difference in braking force between the left and right sides.

[0054] Figures 5 and 6 show a schematic diagram of the braking and driving force control (in other words, the vehicle control method) executed by the control unit 30A when the steering function of the steer-by-wire system 40 is abnormal and the steering angle δ cannot be detected. Figure 5 is a diagram showing the state when the braking and driving forces of the rear wheels 13 and 14 are controlled to generate the target yaw rate γ*, and Figure 6 is a diagram showing the state when the braking and driving forces of the front wheels 11 and 12 and the rear wheels 13 and 14 are controlled based on the estimated steering angle δe to generate the target yaw rate γ*.

[0055] Figures 5 and 6 illustrate an example where the driver of vehicle 10 operates the steering wheel 51 in the rightward turning direction. In other words, the driver is requesting the vehicle 10 to turn to the right by operating the steering wheel 51, but the steer-by-wire system 40 malfunctions, making it impossible to change the direction of the steering wheels, the front wheels 11 and 12, to the right.

[0056] At this time, the control unit 30A first does not perform braking and driving force control to generate yaw moment for the front wheels 11 and 12, which are the steering wheels, but instead outputs braking and driving force commands for the rear wheels 13 and 14, which are the wheels other than the steering wheels, thereby generating the target yaw rate γ*, which is the yaw moment requested by the driver (see Figure 5). The braking and driving force command for the rear wheels 13 and 14 is, for example, a command to apply braking force to the right rear wheel 14, as shown in Figure 5.

[0057] In other words, when the driving force is a positive physical quantity and the braking force is a negative physical quantity, the control unit 30A outputs a braking force command that makes the sum of the driving force and braking force applied to the right rear wheel 14, which is the inner wheel of the vehicle 10 during a turn, less than the sum of the driving force and braking force applied to the left rear wheel 13, which is the outer wheel of the vehicle 10 during a turn, among the rear wheels 13 and 14, which are the wheels other than the steering wheels 11 and 12. The control unit 30A then calculates the estimated steering angle δe at the current moment from the difference Δγ between the actual yaw rate γ and the target yaw rate γ* by controlling the braking and driving forces of the rear wheels 13 and 14.

[0058] Furthermore, if the front wheels 11 and 12 are included in the braking and driving force control used to determine the estimated steering angle δe, the steering angle δ of the front wheels 11 and 12 will change with the braking and driving force control, which will reduce the accuracy of the calculation of the estimated steering angle δe. Therefore, the control unit 30A excludes the front wheels 11 and 12, which are the steering wheels, from the braking and driving force control target for determining the estimated steering angle δe, and performs braking and driving force control on the rear wheels 13 and 14, which are the wheels other than the steering wheels, thereby improving the accuracy of the calculation of the estimated steering angle δe.

[0059] Once the steering angle δ is estimated, the estimated steering angle δe can be used in the braking and driving force control that generates the yaw moment requested by the driver. Using the estimated steering angle δe improves the accuracy of yaw moment control. Therefore, the control unit 30A takes into account the estimated steering angle δe and determines the target braking and driving force Fxx for the front wheels 11, 12 and rear wheels 13, 14 in order to achieve the target yaw rate γ* and target longitudinal acceleration α*.

[0060] The control unit 30A then controls the braking force of the front wheels 11, 12 and the rear wheels 13, 14 based on the target braking force Fxx, thereby generating the yaw moment, or target yaw rate γ*, requested by the driver (see Figure 6). In other words, when the steering angle δ cannot be detected, the control unit 30A first controls the braking and driving force on the rear wheels 13 and 14, which are the wheels other than the steering wheels 11 and 12, to generate a yaw moment in the vehicle 10. Then, in the second stage, it outputs a braking and driving force command that also applies braking and driving force to the steering wheels 11 and 12, thereby generating a yaw moment in the vehicle 10.

[0061] The first stage provides an opportunity to estimate the steering angle δ with high accuracy from the difference Δγ between the actual yaw rate γa and the target yaw rate γ*. In the second stage, when applying braking and driving forces to the front wheels 11 and 12, which are the steering wheels, the estimated result of the steering angle δ is reflected in the control of the braking and driving forces, thereby enabling the generation of a yaw moment in accordance with the driver's operation of the steering wheel 51 with high accuracy. Therefore, even when the steering function in the steer-by-wire system 40 is abnormal, the control unit 30A can perform turning control using braking and driving forces with high precision, even if it loses information on the steering angle δ of the front wheels 11 and 12, which are the steering wheels.

[0062] Incidentally, instead of calculating the estimated steering angle δe from the yaw rate difference Δγ, the control unit 30A can calculate the estimated steering angle δe from the difference ΔGy between the actual lateral acceleration Gya generated as a result of controlling the braking and driving forces of the rear wheels 13 and 14 to generate the target lateral acceleration Gy* and the target lateral acceleration Gy*. Furthermore, yaw rate γ has less delay and noise compared to lateral acceleration Gy. Therefore, the process of calculating the estimated steering angle δe from the yaw rate difference Δγ enables more accurate turning control compared to the process of calculating the estimated steering angle δe from the lateral acceleration difference ΔGy.

[0063] The flowcharts in Figures 7 and 8 illustrate the turning control process when calculating the estimated steering angle δe from the difference ΔGy of lateral acceleration Gy. In the following, we will mainly explain the steps S301-S322 in the flowcharts of Figures 7 and 8 that have different processing content than the steps S201-S222 in the flowcharts of Figures 3 and 4, and will omit detailed explanations of the steps that have the same processing content.

[0064] If the steering function of the steer-by-wire system 40 is abnormal but the steering angle δ can be detected, the control unit 30A calculates the target lateral acceleration Gy* to be generated in the vehicle 10 from the operating angle θ of the steering wheel 51 and the vehicle speed V in step S304. Then, in step S306, the control unit 30A calculates the target braking and driving forces Ffl, Ffr, Frl, and Frr for each wheel 11-14 to achieve the target lateral acceleration Gy* and target longitudinal acceleration α*, based on the target lateral acceleration Gy*, the target longitudinal acceleration α*, and the steering angle δ detected by the steering angle sensor 43.

[0065] On the other hand, if the steering function of the steer-by-wire system 40 is abnormal and the steering angle δ cannot be detected, the control unit 30A calculates a target lateral acceleration Gy* to be generated in the vehicle 10 in step S309 based on the operating angle θ of the steering wheel 51 and the vehicle speed V. Then, in step S311, the control unit 30A calculates the target braking and driving forces Frl and Frr for the rear wheels 13 and 14, which are wheels other than the steering wheels, based on the target lateral acceleration Gy* and the target longitudinal acceleration α*.

[0066] Next, in steps S312 and S313, the control unit 30A controls the braking force and driving force of the rear wheels 13 and 14 based on the target braking and driving forces Frl and Frr. In steps S315-S317, the control unit 30A determines the actual lateral acceleration Gya when the braking force of the rear wheels 13 and 14 is controlled based on the target braking and driving forces Frl and Frr.

[0067] Furthermore, if the vehicle speed V is below a threshold, or if the lateral acceleration sensor 82 cannot detect lateral acceleration, the control unit 30A can estimate the actual lateral acceleration Gya by substituting the actual yaw rate γa and V=(V1+V2) / 2, which are obtained according to formula 1, into Gya=V·γa.

[0068] Then, in step S318, the control unit 30A calculates the difference ΔGy (ΔGy = Gy* - Gya) between the actual lateral acceleration Gya and the target lateral acceleration Gy*. Next, in step S319, the control unit 30A determines the estimated steering angle δe based on the difference ΔGy according to the equation of motion of the vehicle 10 shown in equation 3.

number

[0069] In step S319, the control unit 30A obtains the estimated steering angle δe, and in step S320, it calculates the target lateral acceleration Gy*, the target longitudinal acceleration α*, and further calculates the target braking and driving forces Ffl, Ffr, Frl, and Frr for each wheel to achieve the target lateral acceleration Gy* and target longitudinal acceleration α* from the estimated steering angle δe. Then, in step S321, the control unit 30A calculates the target braking force Tbxx and drive torque Tmxx for each of the wheels 11-14, and in the next step S322, it controls the brake actuators 15, 16, 17, and 18 based on the target braking force Tbxx, and controls the motors 71 and 72 as drive force actuators 70 based on the target drive torque Tmxx.

[0070] Even when the control unit 30A determines the estimated steering angle δe from the lateral acceleration difference ΔGy, it performs braking and driving force control on wheels other than the steering wheels in the braking and driving force control for determining the estimated steering angle δe, so that the estimated steering angle δe can be determined with high accuracy. Furthermore, since the control unit 30A takes into account the estimated steering angle δe to perform braking and driving force control for each wheel 11-14, it can perform turning control using braking and driving force with high accuracy even if the information on the steering angle δ of the steering wheel is lost.

[0071] The technical concepts 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 will be obvious to those skilled in the art that various modifications can be taken based on the basic technical concept and teachings of the present invention.

[0072] The steer-by-wire system in the above embodiment is a steering system that steers the front wheels of a vehicle, but the vehicle may be a work vehicle such as a forklift or construction equipment that is equipped with a steer-by-wire system that steers the rear wheels. In the case of a vehicle equipped with a steer-by-wire system that steers the rear wheels, the control unit of the vehicle control device controls the braking and driving force of the front wheels (the wheels other than the steering wheels) so that a target yaw rate or target lateral acceleration is generated. At this time, the steering angle δ of the rear wheels (the steering wheels) is estimated from the difference between the actual yaw rate or actual lateral acceleration generated and the target, and the braking and driving force control of the rear wheels is performed by reflecting the estimated result of the steering angle δ of the rear wheels.

[0073] Furthermore, in a vehicle control system that includes a higher-level control unit such as a vehicle integrated control unit above the control units for each actuator, including the drive force control unit 31, the steering control unit 32, and the brake control unit 33, the higher-level control unit can output a braking force control command to the control unit for each actuator when an abnormality occurs in the steering function of the steer-by-wire system. In this case, the higher-level control unit corresponds to a vehicle control device equipped with a control section. [Explanation of Symbols]

[0074] 10…Vehicle, 11,12…Front wheels (steering wheels), 13,14…Rear wheels, 15,16,17,18…Brake actuators, 30…Vehicle control device, 30A…Control unit, 40…Steer-by-wire system, 51…Steering wheel, 70…Drive force actuator, 81…Yaw rate sensor, 100…Vehicle control system

Claims

1. A vehicle control device installed in a vehicle, The vehicle has a steer-by-wire system that steers the vehicle's steering wheels, which are mechanically disconnected from the steering wheel. The control unit of the aforementioned vehicle control device is The detection feasibility information, which is information regarding whether or not the steering angle of the steering wheel can be detected, is obtained. Based on the steering wheel operation angle, a target vehicle momentum is obtained that represents a target yaw rate or target lateral acceleration to be generated in the vehicle. If the detection availability information indicates that detection is not possible, a control command is output to generate a yaw moment in the vehicle using the wheels of the vehicle other than the steering wheels, based on the target vehicle momentum. The control command acquires the actual vehicle momentum corresponding to the target vehicle momentum generated in the vehicle, Based on the difference between the target vehicle momentum and the actual vehicle momentum, an estimated steering angle, which is an estimated value of the steering angle of the steering wheel, is obtained. Based on the estimated steering angle, a first braking force command is output to apply braking force to the steering wheel. Vehicle control device.

2. A vehicle control device according to claim 1, The target vehicle momentum is the target yaw rate, and the actual vehicle momentum is the actual yaw rate. Vehicle control device.

3. A vehicle control device according to claim 1, The target vehicle momentum is the target lateral acceleration, and the actual vehicle momentum is the actual lateral acceleration. Vehicle control device.

4. A vehicle control device according to claim 1, The control unit is If information indicating an abnormality in the steering function of the steer-by-wire system is acquired, and the detection availability information indicates that detection is possible, a second braking force command is output to apply braking force to the steering wheel based on the target vehicle momentum. Vehicle control device.

5. A vehicle control device according to claim 1, The steering wheel is either the front or rear wheel of the vehicle. Vehicle control device.

6. A vehicle control device according to claim 5, The aforementioned steering wheel is the front wheel. Vehicle control device.

7. A vehicle control device according to claim 5, The aforementioned control command is When the driving force is a positive physical quantity and the braking force is a negative physical quantity, this is a braking force command that makes the sum of the driving force and braking force applied to the inner wheel of the vehicle during a turn, among the wheels other than the steering wheel, less than the sum of the driving force and braking force applied to the outer wheel of the vehicle during a turn. Vehicle control device.

8. A vehicle control device according to claim 5, The first braking force command is, When the driving force is a positive physical quantity and the braking force is a negative physical quantity, the braking force command makes one of the following two values ​​greater than the other: the sum of the driving force and braking force applied to the outer steering wheel of the vehicle during a turn, and the sum of the driving force and braking force applied to the inner steering wheel of the vehicle during a turn. The braking force command is determined based on the setting of the scrub radius in the steering wheel. Vehicle control device.

9. A vehicle control device according to claim 5, In the aforementioned vehicle, the scrub radius of the steering wheel is set to a negative value. The first braking force command is, When the driving force is a positive physical quantity and the braking force is a negative physical quantity, the braking force command is such that the sum of the driving force and braking force applied to the outer steering wheel of the vehicle during a turn is less than the sum of the driving force and braking force applied to the inner steering wheel of the vehicle during a turn. Vehicle control device.

10. A vehicle control device according to claim 5, The first braking force command is, When the driving force is a positive physical quantity and the braking force is a negative physical quantity, the braking force command is such that the sum of the driving force and braking force applied to the inner steering wheel of the vehicle during a turn is less than the sum of the driving force and braking force applied to the outer steering wheel of the vehicle during a turn. Vehicle control device.

11. A vehicle control device according to claim 1, The control unit is When the vehicle's speed is less than a predetermined value, when the vehicle's yaw rate is undetectable, or when the vehicle's lateral acceleration is undetectable, the actual vehicle momentum is estimated based on the vehicle's wheel speed. Vehicle control device.

12. A vehicle control method performed by a control unit installed in a vehicle, The vehicle has a steer-by-wire system that steers the vehicle's steering wheels, which are mechanically disconnected from the steering wheel. The control unit is The detection feasibility information, which is information regarding whether or not the steering angle of the steering wheel can be detected, is obtained. Based on the steering wheel operation angle, a target vehicle momentum is obtained that represents a target yaw rate or target lateral acceleration to be generated in the vehicle. If the detection availability information indicates that detection is not possible, a control command is output to generate a yaw moment in the vehicle using the wheels of the vehicle other than the steering wheels, based on the target vehicle momentum. The control command acquires the actual vehicle momentum corresponding to the target vehicle momentum generated in the vehicle, Based on the difference between the target vehicle momentum and the actual vehicle momentum, an estimated steering angle, which is an estimated value of the steering angle of the steering wheel, is obtained. Based on the estimated steering angle, a first braking force command is output to apply braking force to the steering wheel. Vehicle control method.

13. A steer-by-wire system that steers the vehicle's steering wheels, mechanically disconnected from the steering wheel, When the steering angle of the steering wheel cannot be detected, a control unit generates a yaw moment in the vehicle using the other wheels of the vehicle, and then outputs a braking force command to apply braking force to the steering wheel. A braking actuator that applies braking force to the steering wheel based on the braking force command, A vehicle control system equipped with the following features.

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