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

Abstract

Provided are a vehicle control device, a vehicle control method, and a vehicle control system capable of implementing a turning function including tire steering due to brake driving force. A vehicle control device is provided with a steer-by-wire system that steers left and right steered wheels mechanically separated from a steering wheel, and is provided in a vehicle in which the ground radius of the steered wheels is set to be negative. The vehicle control device is characterized in that when an abnormal signal of a steering function of a steer-by-wire system is acquired, a control unit of the vehicle control device outputs a brake drive command when a driving force is set to a positive physical quantity and a braking force is set to a negative physical quantity according to a steering operation input to a steering wheel. The brake drive command makes the total value of the driving force and the braking force applied to the steering wheel on the outer side of the turning of the vehicle smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the turning of the vehicle among the left and right steering wheels.

Description

Technical Field

[0001] The present invention relates to a vehicle control device, a vehicle control method and a vehicle control system for controlling a vehicle equipped with a steer-by-wire system. Background Art

[0002] With the active development of autonomous driving technology in recent years, research and development related to steer-by-wire (SBW) steering mechanisms are being promoted. In steer-by-wire technology, it is important to ensure reliability, and the system will be redundant, but redundancy will lead to an increase in system costs. Therefore, for example, in Patent Document 1, when the steering function of the SBW steering mechanism fails, the turning function is achieved by distributing the braking force of each wheel to generate a vehicle yaw moment.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent document 1: (Japanese) Unexamined Patent Application Publication No. 2000-190863. Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] However, in the case of a steering failure, the target turn may not necessarily be achieved by controlling the vehicle yaw moment alone, taking into account the influence of tire steering caused by braking force, driving force (braking driving force) and wheel alignment.

[0008] That is, when a braking force is applied to one of the front wheels to achieve a turn, the turning direction changes according to the setting of the kingpin offset. At this time, in a vehicle with a tire wear radius set to a negative value, the right front wheel is braked to make a right turn. Since the front wheel faces the left direction, it becomes the opposite direction of the target turning direction, and the tire turns in the direction that suppresses the turning by the braking force. Similarly, when the left front wheel is braked to make a left turn, the tire also turns in the direction that suppresses the turning by the braking force.

[0009] The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to provide a vehicle control device, a vehicle control method, and a vehicle control system capable of realizing a turning function including tire steering by braking and driving forces.

[0010] Technical solutions for solving technical problems

[0011] According to one aspect of the present invention, a vehicle control device and a vehicle control method are provided, wherein the vehicle control device has a steer-by-wire system for steering left and right steering wheels mechanically separated from a steering wheel, and is provided on a vehicle in which a tire radius of the steering wheel is set to negative, wherein a control unit of the vehicle control device, upon obtaining an abnormal signal of a steering function of the steer-by-wire system, outputs a first braking drive instruction when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity based on a steering operation input to the steering wheel, wherein the first braking drive instruction makes the total value of the driving force and the braking force applied to the steering wheel on the outer side of the turn of the left and right steering wheels of the vehicle smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the turn of the left and right steering wheels of the vehicle.

[0012] According to another aspect of the present invention, there is provided a vehicle control system including the vehicle control device and a brake drive actuator that applies a brake drive force to the left and right steering wheels based on the first brake drive command output from the control unit.

[0013] Effects of the Invention

[0014] In the present invention, not only the left and right braking-driving force difference of the vehicle is used to generate the vehicle yaw moment, but also the tire steering realized by the braking-driving force generated on each wheel and the wheel positioning can be used to realize the turning realized by the braking-driving force. Therefore, according to the present invention, a vehicle control device, a vehicle control method and a vehicle control system that can realize the turning function including the tire steering realized by the braking-driving force can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a configuration diagram of a vehicle control device and a vehicle control system according to a first embodiment of the present invention.

[0016] Figure 2 Yes means Figure 1 A flowchart schematically showing a vehicle control method of a vehicle control device and a vehicle control system shown.

[0017] Figure 3A This is a diagram for explaining the behavior of the vehicle with respect to the braking and driving forces when turning.

[0018] Figure 3B This is a diagram for explaining the behavior of the tires with respect to the braking and driving forces during cornering.

[0019] Figure 4 This is a diagram for explaining the behavior of the vehicle due to another control method using the braking and driving forces.

[0020] Figure 5This is another control method using the braking and driving forces, and is a diagram for explaining the behavior of the vehicle when the driving force of each wheel can be controlled.

[0021] Figure 6 A diagram for explaining a vehicle control device, a vehicle control method, and a vehicle control system according to a second embodiment of the present invention, and is a flowchart showing an overview of a vehicle control method when a steer-by-wire system controls tire angles to assist steering in a normal state.

[0022] Figure 7 is used for Figure 6 FIG. 2 is a diagram for explaining the behavior of a vehicle caused by control using braking or driving force in the vehicle control method shown. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0024] Figure 1 1 is a configuration diagram of a vehicle control device and a vehicle control system according to an embodiment of the present invention. The vehicle 10 includes a motor 72 for driving the front wheels (tires) 11 and 12 and a motor 73 for driving the rear wheels (tires) 13 and 14. The motors 72 and 73 work as drive actuators and drive the front wheels 11 and 12 and the rear wheels 13 and 14, respectively, according to the operation amount of the accelerator pedal 71 input to the powertrain control unit 33.

[0025] The vehicle 10 is equipped with a steer-by-wire steering mechanism (steer-by-wire system) in which the steering wheel 51 is not physically connected to the front wheels (steered wheels) 11, 12 but is mechanically separated. That is, unlike conventional steering mechanisms, this steering mechanism does not have a steering shaft.

[0026] When the driver operates the steering wheel 51, the steering angle sensor 52 detects the steering angle, and the target tire angle and target reaction force corresponding to the operating conditions are obtained through the steering control unit 31. Then, the target tire angle is output from the steering control unit 31 to the wheel actuator 42, and the target reaction force is output to the reaction force actuator 41 to perform steering control in order to apply the steering reaction force torque to the steering wheel 51.

[0027] The brake control unit 32 causes the brake actuators (brake actuators) 15 , 16 , 17 , 18 to apply the brake based on the amount of operation of the brake pedal 61 and the outputs of the brake thrust sensors 21 , 22 , 23 , 24 that detect thrust generated by braking.

[0028] The steering control unit 31, the brake control unit 32, and the powertrain control unit 33 function as the control unit 30 of the vehicle control device. In addition, the steering control unit 31 is used to detect system failures. When an abnormal signal of the steering function is obtained, the brake control unit 32 and the powertrain control unit 33 are used to control the braking force achieved by the brake and the driving force achieved by the motors 72 and 73 according to the steering operation input to the steering wheel 51.

[0029] Then, a braking command is selectively output from the braking control unit 32 to the braking actuators 15, 16, 17, and 18, and a driving command is selectively output from the powertrain control unit 33 to the motors 72, 73, so that the total value of the driving force and the braking force applied to the steering wheel on the outer side of the turning of the vehicle 10 among the left and right steering wheels is smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the turning of the vehicle 10 among the left and right steering wheels.

[0030] Figure 2 Yes means Figure 1 Flowchart of an overview of the vehicle control method in the vehicle control device shown. When the ignition of the vehicle 10 is turned on, the steering control unit 31 detects a SBW system failure (step S1). It is determined whether a failure occurs that makes the steering of the tire impossible (step S2). If a failure occurs, the target yaw rate (γ*) is calculated based on the steering wheel angle and vehicle speed (V) detected by the steering angle sensor 52 (step S3). Next, the brake control unit 32 and the powertrain control unit 33 detect the operation amount of the brake pedal 61 and the accelerator pedal 71, and the steering control unit 31 calculates the target front and rear acceleration (α x *)(Step S4).

[0031] Next, according to the target yaw rate (γ*) and the target front and rear acceleration (α x *) Calculate the target braking force (F) of each wheel fl 、F fr 、F rl 、F rr )(Step S5). It should be noted that, hereinafter, unless otherwise specified, the target braking force of each wheel is uniformly expressed as “F xx ”.

[0032] In the next step S6, the target braking force (F xx ), calculate the target braking force (Tb) generated by the brake actuators 15, 16, 17, 18 xx ) and the target drive torque (Tm) generated by the motors 72 and 73 xx ).

[0033] In the next step S7, according to the target braking force (Tb xx ) The brake control unit 32 drives the brake actuators 15, 16, 17, 18 according to the target driving torque (Tm xx ) The powertrain control unit 33 drives the motors 72 and 73 and ends.

[0034] On the other hand, when it is determined in step S2 that no failure has occurred, the target tire angle (σ) is calculated based on the steering wheel angle detected by the steering angle sensor 52 (step S8).

[0035] Then, the wheel actuator 42 is driven according to the target tire angle (σ) and the process ends (step S9).

[0036] Figure 3A and Figure 3B The diagrams are used to illustrate the behavior of the vehicle and tires relative to the braking and driving forces when turning. σ ) is negative (the kingpin axis KP is located at a position further outward than the tire center). The moment (m BF2 ) is shown in the following formula (1).

[0037] [Formula 1]

[0038] m BF2 =γ δ *BF2…(1)

[0039] Furthermore, when a lateral force (SF) is generated by turning the tire angle, the moment (m SF ), according to the relationship with the caster angle drag moment (ζ), it is shown in the following formula (2).

[0040] [Formula 2]

[0041] m SF =ζ*SF…(2)

[0042] Based on the above equations (1) and (2), the tire angular acceleration (σ**) is expressed as in the following equation (3). The tire angle (σ) is calculated by the double integral of the equation (3).

[0043] [Formula 3]

[0044]

[0045] According to the tire angle (σ), vehicle speed (V), and yaw rate (γ) calculated from the previous formula (3), the distance from the center of gravity of the vehicle to the front axle (l f ), the sideslip angle of the vehicle body (β), the cornering force of the front wheel (C f), the lateral force (SF) is expressed as follows (4).

[0046] [Formula 4]

[0047]

[0048] According to the braking force (BF1, BF2) and the lateral force (SF), the yaw moment (M C ) is shown in the following formula (5).

[0049] [Formula 5]

[0050] M c =M BF1 -M BF2 +M ST …(5)

[0051] Thus, for the front wheels, the vehicle yaw moment (M) is generated by the tire angle (σ) turned by the braking force (BF1) of the above formula (1) and the lateral force (SF) generated by the tire angle (σ). ST ), the yaw moment (M) generated by the braking force (BF1) BF1 ), the vehicle yaw moment (M) generated by the rear wheel braking force (BF2) BF2 ) control enables the vehicle 10 to turn.

[0052] Furthermore, when turning, the lateral force of the tire (right rear wheel 14) can be reduced by increasing the slip of the tire (right rear wheel 14) through the braking force (BF2) of the rear wheel, and the yaw moment generated in the vehicle can be increased by changing the balance with the lateral force of the front wheel.

[0053] As described above, in a vehicle with a negative tire radius, even if the steering function of the wire-controlled steer system is malfunctioning, the vehicle can be turned in the direction requested by the driver by making the braking drive force on the outer wheel smaller than that on the inner wheel (for example, applying a larger force in the braking direction).

[0054] The wheel with a set tire radius generates a moment in the direction in which the tire is turned by braking. In particular, for a wheel with a negative tire radius, the tire turns in a direction to offset the vehicle yaw moment generated by the braking force (the lateral force generated by the tire turning generates the vehicle yaw moment). In particular, in a vehicle that is greatly affected by the vehicle yaw moment caused by the turning, there is a possibility that the vehicle turns in the opposite direction to the intended turning direction.

[0055] In a vehicle having such characteristics, by making the total value of the braking and driving forces smaller at the outer wheel than at the inner wheel, it is possible to achieve turning using the lateral force generated by the steering.

[0056] In the present invention, the front wheels generate a braking-driving force difference for steering the tires according to the wheel alignment characteristics, and the rear wheels generate a braking force difference for realizing the vehicle yaw moment because the influence of the wheel alignment characteristics is relatively small.

[0057] As a result, not only is the vehicle yaw moment generated by using the braking-driving force difference through redundancy between functions when the SBW fails, but tire steering using wheel alignment characteristics can also be achieved, thereby realizing a turning function based on the braking-driving force.

[0058] Therefore, according to the above-mentioned vehicle control device, vehicle control method and vehicle control system, the front wheels can turn by using the tire steering generated by the braking force difference and the wheel positioning, and the rear wheels can turn by using the left and right braking force difference to generate the vehicle yaw moment, thereby realizing the turning function using the tire steering based on the braking force and the vehicle yaw moment.

[0059] Figure 4 This is a diagram for explaining the behavior of the vehicle caused by other control methods using braking driving force. The tire radius of the vehicle 10 is set to be negative. The front wheels 11 and 12 generate a moment around the kingpin axis by using the driving force TF2 and TF1 and the braking force BF2, and the motor 72 generates torque to drive the brake actuator 15 of the left front wheel 11 to generate a driving force difference. As a result, the front wheels 11 and 12 are turned in the turning direction, and the braking force BF1 of the right rear wheel 14 is used to generate a vehicle yaw moment to achieve the turning of the vehicle 10.

[0060] When using braking force, the braking force is distributed to achieve the target front and rear acceleration (α x *). Also, the acceleration (α x *) cannot be achieved, for example, the braking and driving forces of each wheel are distributed so that the generated front and rear acceleration becomes the deceleration side to achieve the required turning.

[0061] In addition, when the force that can be generated by each wheel is saturated due to load changes, the braking and driving forces are redistributed so that force is generated at other wheels. Figure 4 In the case where the braking force BF1 that can be generated by the right rear wheel 14 is saturated, the braking-driving force is distributed so that the driving force is generated at the left rear wheel 13 .

[0062] Furthermore, when wheel slip greater than a predetermined value is detected at each wheel, the braking / driving force is redistributed so as not to encourage slip.

[0063] Figure 5It is another control method using braking driving force, and is a diagram for explaining the action of a vehicle when the driving force of each wheel can be controlled. This example is applicable to a vehicle 10 in which each wheel is provided with a so-called hub motor of motors 81, 82, 83, and 84. The tire radius of the vehicle 10 is also set to be negative. Using these motors 81 and 82, the right front wheel 12 generates a driving force TF1 by the motor 82 in order to generate a torque around the kingpin axis, and the front wheels 11 and 12 are turned by generating a driving force difference. In addition, using motors 83 and 84, the vehicle yaw moment is generated by utilizing the braking force BF1 of the brake actuator 18 of the right rear wheel 14 and the driving force based on the motor 83 of the left rear wheel to achieve the turning of the vehicle 10.

[0064] Figure 6 The second embodiment of the present invention is used to explain a vehicle control device, a vehicle control method, and a vehicle control system, and is a flowchart showing an overview of the vehicle control method. The second embodiment controls the tire angle to assist steering when the steer-by-wire system is normal.

[0065] First, the steering control unit 31 calculates a target tire angle (σ*) based on the steering wheel angle detected by the steering angle sensor 52 (step S11 ).

[0066] Next, the tire angle deviation (σ) is calculated from the difference between the target tire angle (σ*) and the tire angle (σ). e )(Step S12).

[0067] Next, the brake control unit 32 and the powertrain control unit 33 detect the operation amounts of the brake pedal 61 and the accelerator pedal 71, and the steering control unit 31 calculates the target longitudinal acceleration (α x *)(Step S13).

[0068] Then, according to the tire angle deviation (σ e ) and the target front and rear acceleration (α x *) Calculate the target braking force (F) of each wheel fl 、F fr 、F rl 、F rr ) (Step S14). It should be noted that, in the following, unless otherwise specified, the target braking force of each wheel is uniformly expressed as “F xx ”.

[0069] Next, according to the target braking force (F xx ) calculates the target braking force (Tb) generated by the brake actuators 15, 16, 17, 18 xx ) and the target drive torque (Tm) generated by the motors 72 and 73 xx)(Step S15).

[0070] Next, according to the target braking force (Tb xx ) The brake control unit 32 drives the brake actuators 15, 16, 17, 18 according to the target driving torque (Tm xx ) The powertrain control unit 33 drives the motors 72 and 73 (step S16).

[0071] Then, the wheel actuator 42 is driven according to the target tire angle (σ) (step S17).

[0072] According to such a control method, the tire angle can be controlled to assist steering. Furthermore, the steering assistance of the second embodiment can be similarly applied to a steering device (EPS) that is not a steer-by-wire (SBW) type when the wheel radius of the steered wheel is negative.

[0073] Figure 7 is used for Figure 6 FIG. 1 is a diagram for explaining the behavior of a vehicle caused by the control using the braking driving force in the vehicle control method shown. In order to generate a moment about the kingpin axis using the driving force TF2, TF1 and the braking force BF2, the front wheels 11, 12 as steering wheels generate a driving force difference by generating a torque by the motor 72 and driving the brake actuator 15 of the left front wheel 11 to assist the steering of the front wheels 11, 12.

[0074] Furthermore, when the braking and driving forces are used, the braking and driving forces are distributed so as to achieve the target longitudinal acceleration (α x *). In addition, the acceleration (α x *) cannot be achieved, for example, using a velocity equivalent to the target forward and backward acceleration (α x *) to assist the tire's steering.

[0075] According to the above structure and method, the front wheel turns by using the tire steering generated by the braking force difference and the wheel alignment, and the rear wheel turns by using the left and right braking force difference to generate the vehicle yaw moment. Therefore, in the case where the tire steering function of the SBW fails, the braking driving force can be used to achieve the turning required by the system regardless of the wheel alignment of the vehicle. In addition, regardless of the wheel alignment characteristics, the cost can be reduced by reducing the redundancy of the SBW by realizing the turning function based on the braking driving force. As a result, a vehicle control device, a vehicle control method, and a vehicle control system that can realize the turning function using the tire steering based on the braking force and the vehicle yaw moment can be obtained.

[0076] It should be noted that the structures, methods, etc. described in the first and second embodiments are merely summarized to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be changed into various forms as long as it does not depart from the scope of the technical ideas represented in the patent claims.

[0077] For example, the steering control unit 31 calculates the target longitudinal acceleration, but it may be configured so that it is calculated by other control units in the control unit 30. Furthermore, it is of course possible to use other control units to perform the calculations performed by the control units 31, 32, and 33 in the control unit 30, or to provide a dedicated control unit for realizing the turning function in the event of a steering function failure.

[0078] Description of Reference Numerals

[0079] 10…Vehicle; 11, 12…Front wheel (tire); 13, 14…Rear wheel (tire); 15, 16, 17, 18…Brake actuator; 21, 22, 23, 24…Brake thrust sensor; 30…Control unit; 31…Steering control unit; 32…Brake control unit; 33…Powertrain control unit; 41…Reaction force actuator; 42…Wheel actuator; 51…Steering wheel; 52…Steering angle sensor; 61…Brake pedal; 71…Accelerator pedal; 72, 73, 81, 82, 83, 84…Motor.

Claims

1. A vehicle control device having a steer-by-wire system for steering left and right steering wheels mechanically separated from a steering wheel, and a vehicle in which a tire wear radius provided in the steering wheels is set to be negative, characterized in that: The control unit of the vehicle control device outputs a first braking drive instruction when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity according to the steering operation input to the steering wheel when an abnormal signal of the steering function in the wire control steer system is obtained, The first brake drive instruction makes the total value of the driving force and the braking force applied to the steering wheel on the outer side of the vehicle's turning outer side smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the vehicle's turning inner side.

2. The vehicle control device according to claim 1, characterized in that: The steering wheel is a front wheel.

3. The vehicle control device according to claim 2, characterized in that: The control unit outputs a second brake drive instruction when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity according to the steering operation input to the steering wheel, The second brake-drive command makes the total value of the driving force and the braking force applied to the rear wheel on the inner side of the vehicle when turning smaller than the total value of the driving force and the braking force applied to the rear wheel on the outer side of the vehicle when turning.

4. The vehicle control device according to claim 3, characterized in that: The control unit outputs a slip control instruction according to the steering operation input to the steering wheel, The slip control command increases a slip amount of a rear wheel on an inner side of a turn of the vehicle, of the left and right rear wheels.

5. The vehicle control device according to claim 2, characterized in that: The first brake drive command is a command to apply a braking force to a front wheel on the outer side of a turn of the vehicle.

6. The vehicle control device according to claim 2, characterized in that: The first braking-driving instruction is an instruction to apply a driving force to the front wheel on the inner side of the turning of the vehicle.

7. The vehicle control device according to claim 2, characterized in that: The first brake-drive command is a command to apply a driving force and a braking force to the front wheel on the outer side of the turning of the vehicle and to apply a driving force to the front wheel on the inner side of the turning of the vehicle.

8. The vehicle control device according to claim 3, characterized in that: The first brake drive instruction is an instruction to apply a braking force to the front wheel on the outer side of the turning of the vehicle. The second braking-driving instruction is an instruction to apply a driving force to a rear wheel on an outer side of a turning of the vehicle and to apply a braking force to a rear wheel on an inner side of a turning of the vehicle.

9. The vehicle control device according to claim 3, characterized in that: The first brake drive command is a command to apply a driving force to the front wheel on the inner side of the turning of the vehicle. The second braking-driving instruction is an instruction to apply a driving force to a rear wheel on the outer side of the turning of the vehicle and to apply a braking force to a rear wheel on the inner side of the turning of the vehicle.

10. The vehicle control device according to claim 3, characterized in that: The first brake drive instruction is an instruction to apply a driving force and a braking force to the front wheel on the outer side of the turning of the vehicle and to apply a driving force to the front wheel on the inner side of the turning of the vehicle. The second braking-driving instruction is an instruction to apply a driving force to a rear wheel on the outer side of the turning of the vehicle and to apply a braking force to a rear wheel on the inner side of the turning of the vehicle.

11. A vehicle control method, executed by a control unit having a steer-by-wire system for steering left and right steering wheels mechanically separated from a steering wheel, and a vehicle in which a tire wear radius provided in the steering wheels is set to be negative, characterized in that: When the control unit obtains an abnormal signal of the steering function in the steer-by-wire system, the control unit outputs a first brake drive instruction when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity according to the steering operation input to the steering wheel, The first drive instruction makes the total value of the driving force and the braking force applied to the steering wheel on the outer side of the vehicle's turning outer side smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the vehicle's turning inner side.

12. A vehicle control system, characterized in that: have: a steer-by-wire system that steers left and right steering wheels that are mechanically decoupled from the steering wheel; A control unit is provided on a vehicle in which the tire radius of the steering wheel is set to be negative, wherein, when an abnormal signal of the steering function of the wire control steering system is obtained, a first braking drive instruction is output when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity according to the steering operation output to the steering wheel, The first brake drive instruction makes the total value of the driving force and the braking force applied to the steering wheel on the outer side of the vehicle when turning out of the left and right steering wheels smaller than the total value of the driving force and the braking force applied to the steering wheel on the inner side of the vehicle when turning out of the left and right steering wheels; A brake drive actuator applies a brake drive force to the left and right steering wheels based on the first brake drive instruction.

13. A vehicle control device having a steer-by-wire system for steering left and right steering wheels mechanically separated from a steering wheel, characterized in that: The control unit of the vehicle control device obtains a braking drive instruction based on the setting of the tire radius in the steering wheel when the driving force is set to a positive physical quantity and the braking force is set to a negative physical quantity according to the steering operation input to the steering wheel, The brake drive command makes one of the total value of the driving force and the braking force applied to the steering wheel on the outer side of the vehicle turning out of the left and right steering wheels and the total value of the driving force and the braking force applied to the steering wheel on the inner side of the vehicle turning out of the left and right steering wheels greater than the other. The obtained brake drive command is output.

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