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

Abstract

A vehicle control device, a vehicle control method, and a vehicle control system are provided that can realize a turning function including tire steering using braking and driving forces. [Solution] A vehicle control device is provided in a vehicle 10 having a steer-by-wire system that steers left and right steerable wheels (front wheels 11, 12) that are mechanically separated from the steering wheel. When the steering wheel is operated, a control section provided in this vehicle control device calculates braking / driving commands to turn the steered wheels in the direction of steering wheel operation so that one of the sum of the driving force and braking force applied to the steered wheel on the outside of the turning vehicle of the left and right steerable wheels and the sum of the driving force and braking force applied to the steered wheel on the inside of the turning vehicle of the left and right steerable wheels is larger than the other, based on a setting of a scrub radius of the steered wheels, and outputs the calculated braking / driving commands.

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 technology]

[0002] With the recent increase in development of autonomous driving technology, research and development into steer-by-wire (SBW) steering mechanisms is progressing. Ensuring reliability is important in steer-by-wire technology, and systems are made redundant, but redundancy leads to increased system costs. For this reason, for example, in Patent Document 1, when the steering function of the SBW steering mechanism fails, a vehicle yaw moment is generated by distributing the braking force of each wheel, thereby realizing turning function. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-190863 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the steering function fails, controlling the vehicle yaw moment alone may not necessarily achieve the desired turning, considering the effects of braking force, driving force (braking / driving force), and tire steering caused by alignment.

[0005] In other words, when braking force is applied to one front wheel to turn, the turning direction changes depending on the kingpin offset setting. In this case, if a vehicle has a negative scrub radius, braking the right front wheel to turn right will cause the front wheel to turn left, which is the opposite of the target turning direction, and the tire will be steered in a direction that suppresses the turning caused by the braking force. Similarly, braking the left front wheel to turn left will also cause the tire to be steered in a direction that suppresses the turning caused by the braking force.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a vehicle control device, a vehicle control method, and a vehicle control system that can realize a turning function including tire steering using braking / driving force. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a vehicle control device and a vehicle control method having a steer-by-wire system that steers left and right steerable wheels that are mechanically separated from a steering wheel, wherein, when the steering wheel is operated, a control unit included in the vehicle control device determines a braking / driving command to turn the steerable wheels in the direction of operation of the steering wheel based on a setting of a scrub radius of the steerable wheels so that one of the sum of the driving force and braking force to be applied to the steerable wheel on the outside of a turn of the vehicle and the sum of the driving force and braking force to be applied to the steerable wheel on the inside of a turn of the vehicle is larger than the other, where driving force is a positive physical quantity and braking force is a negative physical quantity, and outputs the determined braking / driving command.

[0008] According to another aspect of the present invention, there is provided a vehicle control system including the vehicle control device and a braking / driving actuator that applies braking / driving forces to the left and right steered wheels based on the braking / driving commands output from the control unit. [Effects of the Invention]

[0009] In this invention, not only is a vehicle yaw moment generated by using the difference in braking / driving force between the left and right sides of the vehicle, but turning is achieved by using the braking / driving force generated at each wheel and tire steering due to alignment. As a result, the invention can provide a vehicle control device, vehicle control method, and vehicle control system that can achieve turning functions including tire steering using braking / driving force. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram of a vehicle control device and a vehicle control system according to a first embodiment of the present invention. [Figure 2] 2 is a flowchart showing an outline of a vehicle control method in the vehicle control device and vehicle control system shown in FIG. [Figure 3A] 10A and 10B are diagrams for explaining the movement of a vehicle in response to braking / driving forces when turning; [Figure 3B] FIG. 2 is a diagram for explaining the movement of tires in response to braking / driving forces during cornering. [Figure 4] 10A and 10B are diagrams for explaining the movement of the vehicle under another control method using braking / driving forces. [Figure 5] FIG. 10 is a diagram illustrating yet another control method using braking / driving forces, which illustrates the movement of the vehicle when the driving forces of each wheel can be controlled. [Figure 6] FIG. 10 is a flowchart illustrating a vehicle control device, a vehicle control method, and a vehicle control system according to a second embodiment of the present invention, and is an outline of a vehicle control method when the steer-by-wire system is normal and controls the tire angle to assist steering. [Figure 7] 7 is a diagram for explaining the movement of the vehicle under control using braking / driving forces in the vehicle control method shown in FIG. 6. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a configuration diagram of a vehicle control device and a vehicle control system according to an embodiment of the present invention. A vehicle 10 is equipped with a motor 72 that drives front wheels (tires) 11 and 12 and a motor 73 that drives rear wheels (tires) 13 and 14. The motors 72 and 73 function as drive actuators and drive the front wheels 11 and 12 and the rear wheels 13 and 14, respectively, in response to the amount of operation of an accelerator pedal 71 input to a powertrain control unit 33.

[0012] This vehicle 10 is equipped with a steer-by-wire steering mechanism (steer-by-wire system) in which the steering wheel 51 and the front wheels (steered wheels) 11, 12 are not physically connected but are mechanically separated. In other words, unlike conventional steering mechanisms, this steering mechanism does not have a steering shaft. When the driver operates the steering wheel 51, the steering angle is detected by the steering angle sensor 52, and the target tire angle and target reaction force according to the conditions at the time of operation are calculated by the steering control unit 31. The target tire angle is then 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 in order to apply a steering reaction torque to the steering wheel 51, thereby performing steering control.

[0013] The brake control unit 32 also performs braking by means of brake actuators (braking actuators) 15, 16, 17, and 18 based on the amount of operation of the brake pedal 61 and the outputs of brake thrust sensors 21, 22, 23, and 24 that detect the thrust generated by the brake.

[0014] The steering control unit 31, the brake control unit 32, and the powertrain control unit 33 function as the control section 30 of the vehicle control device. The steering control unit 31 detects a system failure and, when it acquires an abnormality signal for the steering function, controls the braking force by the brakes and the driving force by the motors 72, 73 according to the steering operation input to the steering wheel 51 by the brake control unit 32 and the powertrain control unit 33.

[0015] Then, a braking command is selectively output from brake control unit 32 to brake actuators 15, 16, 17, 18, and a drive command is selectively output from powertrain control unit 33 to motors 72, 73 so that the total value of the driving force and braking force applied to the steered wheel on the outside of the turning of vehicle 10 is smaller than the total value of the driving force and braking force applied to the steered wheel on the inside of the turning of vehicle 10.

[0016] Fig. 2 is a flowchart showing an outline of a vehicle control method in the vehicle control device shown in Fig. 1. When the ignition of the vehicle 10 is turned on, the steering control unit 31 detects a malfunction in the SBW system (step S1). It is determined whether a malfunction that makes it impossible to steer the tires has occurred (step S2). If a malfunction has occurred, a target yaw rate (γ * Next, the brake control unit 32 and the power train 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 * ) is calculated (step S4).

[0017] Next, the target yaw rate (γ * ) and the target longitudinal acceleration (α x * ) to calculate the target braking / driving force (F fl ,F fr ,F rl ,F rr ) is calculated (step S5). From this point on, unless otherwise specified, the target braking forces of the individual wheels are collectively referred to as "F xx " is written as ". In the next step S6, the target braking / driving force (F xx ) to generate the target braking force (Tb xx ) and the target drive torque (Tm xx ) is calculated. In the next step S7, the target braking force (Tb xx ), the brake control unit 32 drives the brake actuators 15, 16, 17, and 18 to generate the target driving torque (Tm xx ) and the power train control unit 33 drives the motors 72 and 73, and the process ends.

[0018] On the other hand, if it is determined in step S2 that no malfunction has occurred, the target tire angle (σ) is calculated from the steering wheel angle detected by the steering angle sensor 52 (step S8). Thereafter, the wheel actuator 42 is driven from the target tire angle (σ) and the process ends (step S9).

[0019] 3A and 3B are diagrams for explaining the movement of the vehicle and tires in response to braking / driving forces during cornering. In this example, the movement is explained when the scrub radius (γσ) of the front wheels is negative (the kingpin axis KP is located outside the tire center). The moment (m BF2 ) is expressed by the following equation (1).

number

[0020] In addition, when a lateral force (SF) occurs due to the steering of the tire angle, the moment (m SF ) is expressed in relation to the caster rail (ζ) by the following equation (2):

number

[0021] From the previous equations (1) and (2), the tire angular acceleration (σ ** ) is expressed by the following equation (3). The tire angle (σ) is calculated from the second order integral of this equation (3).

number

[0022] The tire angle (σ) calculated in the previous equation (3), the vehicle speed (V), the yaw rate (γ), and the distance from the center of gravity of the vehicle to the front axle (l f ), vehicle body side slip angle (β), front wheel cornering power (C f ), the lateral force (SF) is expressed by the following equation (4).

number

[0023] The yaw moment (M C ) is expressed by the following equation (5).

number

[0024] In this way, the front wheels are steered by the braking force (BF1) in the previous equation (1) to the tire angle (σ) and the vehicle yaw moment (M ST ) and the yaw moment (M BF1 ), the vehicle yaw moment (M BF2 ) can be controlled to allow the vehicle 10 to turn. In addition, the braking force (BF2) of the rear wheels may be used to increase the amount of slip of the tire (right rear wheel 14) during cornering, thereby reducing the lateral force of the tire (right rear wheel 14), and the balance of lateral forces with the front wheels may be changed to increase the yaw moment generated in the vehicle, thereby enabling cornering.

[0025] As described above, even if an abnormality occurs in the steering function of the steer-by-wire system in a vehicle with a negative scrub radius, it is possible to turn the vehicle in the direction desired by the driver by making the braking / driving force smaller on the outer wheels than on the inner wheels (for example, by applying a larger force in the braking direction). When a wheel with a scrub radius is set, braking generates a moment in the direction that causes the tire to turn. In particular, when a wheel with a negative scrub radius is set, the tire turns in a direction that cancels out the vehicle yaw moment generated by the braking force (tire steering generates a side force, which generates a vehicle yaw moment). In particular, vehicles that are significantly affected by the vehicle yaw moment due to this steering may end up turning in the opposite direction to the intended turning direction. In a vehicle with such characteristics, cornering can be achieved by using the side force generated by steering, by making the total value of the braking and driving forces on the outer wheels smaller than that on the inner wheels.

[0026] In the present invention, the front wheels generate a braking / driving force difference for steering the tires depending on the alignment characteristics, while the rear wheels generate a braking force difference for realizing the vehicle yaw moment because the influence of the alignment characteristics is relatively small. This not only enables redundancy between functions in the event of a SBW failure to generate a vehicle yaw moment using the difference in braking and driving force, but also enables tire steering using alignment characteristics, thereby achieving a cornering function using braking and driving force.

[0027] Therefore, with the vehicle control device, vehicle control method, and vehicle control system described above, turning can be achieved by utilizing the braking force difference generated in the front wheels and tire steering due to alignment, and the rear wheels can be turned by generating a vehicle yaw moment using the braking force difference between the left and right wheels, thereby realizing a turning function using tire steering due to braking force and vehicle yaw moment.

[0028] FIG. 4 is a diagram illustrating the movement of a vehicle under another control method using braking / driving forces. The scrub radius of this vehicle 10 is also set to a negative value. To generate a moment around the kingpin axis at the front wheels 11, 12 using driving forces TF2, TF1 and braking force BF2, a driving force difference is generated by generating torque from the motor 72 and driving the brake actuator 15 of the left front wheel 11. This causes the front wheels 11, 12 to turn in the turning direction, and a vehicle yaw moment is generated by braking force BF1 on the right rear wheel 14, thereby realizing the turning of the vehicle 10.

[0029] When using braking / driving force, the target longitudinal acceleration (α x * ) and distributes the braking and driving force to achieve the target longitudinal acceleration (α x * ) cannot be achieved, the required turning is achieved by distributing the braking and driving forces of each wheel so that the generated longitudinal acceleration is on the deceleration side, for example. Furthermore, if the force that can be generated at each wheel becomes saturated due to a change in load, etc., the braking / driving force is reallocated so that force is generated at another wheel. For example, in Figure 4, if the braking force BF1 that can be generated at the right rear wheel 14 becomes saturated, the braking / driving force is reallocated so that driving force is generated at the left rear wheel 13. Furthermore, if wheel slip of a predetermined value or more is detected at any wheel, the braking / driving forces are redistributed so as not to increase the slip.

[0030] FIG. 5 illustrates yet another control method using braking / driving forces, illustrating vehicle movement when the driving force of each wheel can be controlled. This example is applied to a so-called in-wheel motor vehicle 10, in which motors 81, 82, 83, and 84 are installed on each wheel. This vehicle 10 also has a negative scrub radius. Using these motors 81 and 82, the right front wheel 12 generates a driving force TF1 at motor 82 to generate a moment around the kingpin axis, generating a driving force difference to steer the front wheels 11 and 12. Furthermore, using motors 83 and 84, a vehicle yaw moment is generated by the braking force BF1 of brake actuator 18 on the right rear wheel 14 and the driving force from motor 83 on the left rear wheel, thereby realizing turning of the vehicle 10.

[0031] 6 is a flowchart illustrating an outline of a vehicle control method for explaining a vehicle control device, a vehicle control method, and a vehicle control system according to a second embodiment of the present invention. The second embodiment controls the tire angle to assist steering when the steer-by-wire system is normal. First, the steering control unit 31 calculates the target tire angle (σ* ) is calculated (step S11). Next, the target tire angle (σ * ) and tire angle (σ) from the difference e ) is calculated (step S12).

[0032] Next, the brake control unit 32 and the power train 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 * ) is calculated (step S13). Then, the tire angle deviation (σ e ) and the target longitudinal acceleration (α x * ) to calculate the target braking / driving force (F fl ,F fr ,F rl ,F rr ) is calculated (step S14). Hereafter, unless otherwise specified, the target braking forces of the individual wheels are collectively referred to as "F xx " is written as ". Next, the target braking / driving force of each wheel (F xx ) to generate the target braking force (Tb xx ) and the target drive torque (Tm xx ) is calculated (step S15).

[0033] Next, the target braking force (Tb xx ), the brake control unit 32 drives the brake actuators 15, 16, 17, and 18 in accordance with the target drive torque (Tm xx ) and drives the motors 72 and 73 (step S16). Then, the wheel actuator 42 is driven from the target tire angle (σ) (step S17).

[0034] According to this control method, the tire angle can be controlled to assist steering. Furthermore, the steering assist according to the second embodiment can be similarly applied to steering systems (EPS) that are not steer-by-wire (SBW) type, as long as the scrub radius of the steering wheel is negative.

[0035] Figure 7 is a diagram for explaining the movement of the vehicle under control using braking and driving forces in the vehicle control method shown in Figure 6. The front wheels 11, 12, which are steered wheels, generate a moment around the kingpin axis with driving forces TF2, TF1 and braking force BF2, so torque is generated by motor 72 and brake actuator 15 of left front wheel 11 is driven, thereby generating a driving force difference and assisting the steering of the front wheels 11, 12. When braking / driving force is used, the target longitudinal acceleration (α x * ) and distributes the braking and driving force to achieve the target longitudinal acceleration (α x * ) cannot be achieved, for example, the target longitudinal acceleration (α x * ) to assist in steering of the tires by using a braking / driving force difference equivalent to

[0036] According to the above-described configuration and method, the vehicle is turned by utilizing the braking force difference generated on the front wheels and tire steering due to alignment, while the rear wheels are turned by generating a vehicle yaw moment using the braking force difference between the left and right wheels. Therefore, if the SBW tire steering function fails, it is possible to realize the turning requested by the system using braking / driving force regardless of the vehicle alignment. Furthermore, by realizing the turning function using braking / driving force regardless of the alignment characteristics, redundancy in the SBW can be reduced and costs can be reduced. As a result, a vehicle control device, vehicle control method, and vehicle control system can be obtained that can realize the turning function using tire steering due to braking force and vehicle yaw moment.

[0037] It should be noted that the configurations, methods, etc. described in the first and second embodiments are merely outlined to enable the present invention to be understood and practiced. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical idea set forth in the claims.

[0038] For example, although the target longitudinal acceleration is calculated by the steering control unit 31, it may be configured to be calculated by another control unit within the control section 30. Furthermore, it goes without saying that the calculations performed by the control units 31, 32, and 33 within the control section 30 may be performed by another control unit, and a dedicated control unit may be provided to realize the turning function when the steering function fails. [Explanation of symbols]

[0039] 10...vehicle, 11, 12...front wheels (tires), 13, 14...rear wheels (tires), 15, 16, 17, 18...brake actuator, 21, 22, 23, 24...brake thrust sensor, 30...control section, 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 that steers left and right steerable wheels that are mechanically separated from a steering wheel, The control unit of the vehicle control device includes: When the steering wheel is operated, determining a braking / driving command for steering the steered wheels in the direction of operation of the steering wheel based on a setting of a scrub radius of the steered wheels so that one of a total value of the driving force and the braking force applied to the steered wheel on the outside of the turning of the vehicle among the left and right steered wheels and a total value of the driving force and the braking force applied to the steered wheel on the inside of the turning of the vehicle among the left and right steered wheels is larger than the other, when the driving force is a positive physical quantity and the braking force is a negative physical quantity; outputting the determined braking / driving command; Vehicle control device.

2. The vehicle control device according to claim 1, The control unit an abnormality signal of a steering function in the steer-by-wire system is acquired, and when the steering wheel is operated, the braking / driving command is requested; A vehicle control device characterized by:

3. The vehicle control device according to claim 1, The steered wheels are front wheels. A vehicle control device characterized by:

4. A vehicle control method executed by a control unit provided in a vehicle having a steer-by-wire system that steers left and right steerable wheels that are mechanically separated from a steering wheel, comprising: When the steering wheel is operated, determining a braking / driving command for steering the steered wheels in the direction of operation of the steering wheel based on a setting of a scrub radius of the steered wheels so that one of a total value of the driving force and the braking force applied to the steered wheel on the outside of the turning of the vehicle among the left and right steered wheels and a total value of the driving force and the braking force applied to the steered wheel on the inside of the turning of the vehicle among the left and right steered wheels is larger than the other, when the driving force is a positive physical quantity and the braking force is a negative physical quantity; outputting the determined braking / driving command; Vehicle control method.

5. A steer-by-wire system that steers the left and right steered wheels that are mechanically separated from the steering wheel, A control unit provided in a vehicle, When the steering wheel is operated, determining a braking / driving command for steering the steered wheels in the direction of operation of the steering wheel based on a setting of a scrub radius of the steered wheels so that one of a total value of the driving force and the braking force applied to the steered wheel on the outside of the turning of the vehicle among the left and right steered wheels and a total value of the driving force and the braking force applied to the steered wheel on the inside of the turning of the vehicle among the left and right steered wheels is larger than the other, when the driving force is a positive physical quantity and the braking force is a negative physical quantity; the control unit that outputs the determined braking / driving command; a braking / driving actuator that applies braking / driving forces to the left and right steered wheels based on the braking / driving command; A vehicle control system comprising:

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