Vehicle behavior control system

Abstract

To provide a vehicle behavior control device which can make a travel path of a rear wheel coincide with a travel path of a front wheel.SOLUTION: A vehicle behavior control device 10 for controlling the behavior of the vehicle comprises a processor 14 and a memory 16, wherein the processor 14 is configured to: obtain a front wheel path Tf; calculate a front wheel curvature Kf that is a curvature of the front wheel path Tf at each of a plurality of front wheel passing points constituting the front wheel path Tf; sequentially calculate a rear wheel steering angle Br at which a curvature Kr(t2) of a rear wheel path at each of the plurality of front wheel passing points Pf coincides with the curvature Kf(t1) of the front wheel path Tf at each of the plurality of front wheel passing points Pf; and control driving of the front wheel 40 and driving of the rear wheel 42 based on the rear wheel steering angle Br that is calculated and a front wheel steering angle Bf.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This specification discloses a vehicle behavior control device that controls the behavior of a vehicle.

Background Art

[0002] Conventionally, a four-wheel steering vehicle capable of steering both the front wheels and the rear wheels of a vehicle has been known. According to such a four-wheel steering vehicle, the behavior of the vehicle can be more appropriately controlled. Patent Document 1 discloses a vehicle behavior control device capable of steering both the front wheels and the rear wheels. The device described in Patent Document 1 calculates a target slip angle of the vehicle based on a driving instruction, corrects the target slip angle based on the road environment, and controls the steering of the front wheels and the rear wheels so as to achieve the corrected slip angle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, usually, when a vehicle turns, the trajectories of the front wheels and the rear wheels deviate from each other, and an inner wheel difference and an outer wheel difference (hereinafter referred to as "wheel difference") occur. Usually, since a driver steers considering such a wheel difference, the wheel difference does not become a major problem. However, under specific conditions such as when passing through a narrow road, if a wheel difference occurs, it may become difficult to control the running of the vehicle. In Patent Document 1, such a wheel difference is not considered at all.

[0005] Therefore, this specification discloses a vehicle behavior control device capable of making the running trajectory of the rear wheels coincide with the running trajectory of the front wheels.

Means for Solving the Problems

[0006] The vehicle behavior control device disclosed herein is a vehicle behavior control device for controlling the behavior of a vehicle, comprising a processor and a memory, wherein the processor acquires a front wheel trajectory, calculates the curvature of the front wheel trajectory at each of a plurality of front wheel passing points constituting the front wheel trajectory as the front wheel curvature, sequentially calculates a rear wheel steering angle at which the curvature of the rear wheel trajectory at a predetermined front wheel passing point matches the curvature of the front wheel trajectory at the predetermined front wheel passing point, and controls the driving of the front wheels and rear wheels based on the calculated rear wheel steering angle and front wheel steering angle. [Effects of the Invention]

[0007] The vehicle behavior control device disclosed herein makes it possible to make the trajectory of the rear wheels match the trajectory of the front wheels. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing the configuration of a vehicle behavior control system. [Figure 2] This is a schematic diagram of a two-wheeled model. [Figure 3] This diagram shows the process of calculating the rear wheel steering angle for driving along ruts. [Figure 4] This is a schematic diagram of a rigid body model. [Figure 5] This is a flowchart showing the flow of the 6-component force control process. [Figure 6] This is a flowchart showing the flow of rut-tracking control. [Modes for carrying out the invention]

[0009] The configuration of the vehicle behavior control device 10 will be described below with reference to the drawings. Figure 1 is a block diagram showing the configuration of the vehicle behavior control device 10. The vehicle behavior control device 10 shown in Figure 1 is applied to a four-wheeled vehicle.

[0010] The vehicle behavior control device 10 controls the vehicle's behavior based on driving instructions. Driving instructions are instructions regarding the vehicle's acceleration, deceleration, and steering. For example, the driver of the vehicle outputs driving instructions by operating the accelerator pedal, brake pedal, and steering wheel. The driver's inputs are detected by the accelerator pedal sensor 18, brake pedal sensor 20, and steering sensor 22, and input to the vehicle behavior controller 12 as driving instructions. Also, if the vehicle is driving autonomously with the autonomous driving system 24, this autonomous driving system 24 outputs driving instructions. The autonomous driving system 24 is a system for performing automated driving or advanced driver assistance. The autonomous driving system 24 includes multiple sensors and a computer, and automatically controls the vehicle's acceleration, deceleration, and steering. The trajectory sensor 23 is a sensor that detects the trajectory of the front wheels 40. Such a trajectory sensor 23 is, for example, a GPS that sequentially detects the position of the front wheels 40.

[0011] The vehicle behavior controller 12 controls the vehicle's behavior, particularly steering, based on driving instructions. Details of the control by the vehicle behavior controller 12 will be described later. Physically, the vehicle behavior controller 12 is a computer including a processor 14 and memory 16. In Figure 1, the vehicle behavior controller 12 is shown as a single computer. However, the vehicle behavior controller 12 may be composed of multiple computers that are physically separated. Furthermore, part or all of the vehicle behavior controller 12 may function as part of the autonomous driving system 24. In addition, part of the vehicle behavior controller 12 may be located outside the vehicle. In this case, the vehicle behavior controller 12 has wireless communication capabilities.

[0012] The vehicle control actuator group 26 includes multiple actuators to control the behavior of the vehicle. For example, the vehicle control actuator group 26 includes a drive actuator 28, a brake actuator 30, a front wheel steering actuator 32, a rear wheel steering actuator 34, an active stabilizer 36, and an active suspension 38.

[0013] The drive actuator 28 controls the amount of air supplied to the engine (throttle opening) in response to a control command from the vehicle behavior controller 12, thereby controlling the driving force of the vehicle. If the vehicle is equipped with a motor (not shown) as a power source, the vehicle behavior controller 12 outputs a control command to the motor to control the driving force. In this case, the motor corresponds to the drive actuator 28. The drive actuator 28 may also be capable of changing the distribution of driving force to the front wheels and the driving force to the rear wheels. The brake actuator 30 controls the brake system (not shown) in response to a control command from the vehicle behavior controller 12, thereby controlling the braking force of the vehicle.

[0014] The front wheel steering actuator 32 controls the steering angle of the front wheels in response to control commands from the vehicle behavior controller 12. The rear wheel steering actuator 34 controls the steering angle of the rear wheels in response to control commands from the vehicle behavior controller 12.

[0015] The active stabilizer 36 controls the twist angle of the stabilizer bar (not shown) in response to control commands from the vehicle behavior controller 12. The active suspension 38 controls the suspension characteristics in response to control commands from the vehicle behavior controller 12.

[0016] Next, the control of the vehicle's behavior by the vehicle behavior controller 12 will be explained. Based on the driving instructions, the vehicle behavior controller 12 calculates the slip angle B at the vehicle's center of gravity, the vehicle speed Vv, and the yaw rate Θ necessary to achieve the desired behavior. Subsequently, the vehicle behavior controller 12 takes the calculated slip angle B, vehicle speed Vv, and yaw rate Θ as input and performs a 6-component force control process.

[0017] The six-force control process is a process of controlling the steering and driving forces of the front and rear wheels based on the behavior at the vehicle's center of gravity. The behavior at the vehicle's center of gravity is, for example, the slip angle B, vehicle speed Vv, and yaw rate Θ at the center of gravity point of the vehicle. In the six-force control process, the vehicle behavior controller 12 calculates the six forces (hereinafter referred to as "center-of-gravity six forces") at the center of gravity point of the vehicle based on the slip angle B and the like. Further, the vehicle behavior controller 12 outputs a control command to the vehicle control actuator group 26 so that the calculated center-of-gravity six forces are output. This six-force control process is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2022-021715 and Japanese Unexamined Patent Application Publication No. 2022-165535. Therefore, hereinafter, only the outline of the six-force control process will be briefly described. FIG. 5 is a flowchart showing the flow of the six-force control process.

[0018] The center-of-gravity six forces are composed of the longitudinal force Fx, lateral force Fy, vertical force Fz, roll moment Mx, pitch moment My, and yaw moment Mz at the center of gravity point of the vehicle. The vehicle behavior controller 12 applies known conversion formulas to the slip angle B, vehicle speed Vv, and yaw rate Θ to calculate the planar three forces (S10). The planar three forces are composed of the longitudinal force Fx, lateral force Fy, and yaw moment Mz.

[0019] Subsequently, the vehicle behavior controller 12 applies the obtained planar three forces to an inertial motion model to calculate the three forces above the spring (S12). The inertial motion model is a vehicle model that takes into account inertial forces and suspension reaction forces. The three forces above the spring are composed of the vertical force Fz, roll moment Mx, and pitch moment My.

[0020] The six component forces of the center of gravity (Fx, Fy, Fz, Mx, My, Mz) are composed of the three component forces on this spring (Fz, Mx, My) and the three component forces on the plane (Fx, Fy, Mz). Based on the calculated six component forces of the center of gravity, the vehicle behavior controller 12 calculates the tire three component forces for each of the four wheels (S14). The tire three component forces are composed of the longitudinal force Fxi of the tire, the lateral force Fyi, and the vertical force Fzi. Subsequently, based on the calculated tire three component forces, the vehicle behavior controller 12 calculates a control command and outputs it to the vehicle control actuator group 26 (S16). As is clear from the above description, the vehicle behavior controller 12 disclosed in this specification can appropriately control the behavior of the vehicle based on the slip angle B, vehicle speed Vv, and yaw rate Θ by using the above-described six component force control process.

[0021] Here, as described above, in order to obtain the slip angle B, vehicle speed Vv, and yaw rate Θ, the target speed vector VECf of the front wheels 40 and the target speed vector VECr of the rear wheels 42 are required. The target speed vector VECf of the front wheels 40 is defined by the front wheel steering angle Bf and the front wheel speed Vf. The target speed vector VECr of the rear wheels 42 is defined by the rear wheel steering angle Br and the rear wheel speed Vr.

[0022] Normally, the front wheel steering angle Bf and the front wheel speed Vf are calculated from the driving instruction. The rear wheel speed Vr is the same as the front wheel speed Vf. The rear wheel steering angle Br is often set as it happens. When the rear wheel steering angle Br is set as it happens, when the vehicle turns, an inside wheel difference and an outside wheel difference (hereinafter collectively referred to as "wheel difference") in which the rear wheel trajectory Tr deviates from the front wheel trajectory Tf occur. Under specific conditions, for example, when the vehicle passes through a narrow road, such wheel differences may become a problem.

[0023] Therefore, the vehicle behavior controller 12 disclosed herein calculates target velocity vectors VECf,VECr so that the front wheels 40 and rear wheels 42 follow the same trajectory, when requested by the driver or the autonomous driving system 24. When the rear wheels 42 follow the same trajectory as the front wheels 40, the rear wheels 42 will move in the ruts formed by the front wheels 40. Hereinafter, the driving mode in which the trajectory of the rear wheels 42 matches the trajectory of the front wheels 40 will be referred to as "rut driving".

[0024] The following explains the principle for calculating the target velocity vectors VECf and VECr for track driving. In the following explanation, the curvature of the front wheel trajectory Tf will be referred to as "front wheel curvature Kf," and the curvature of the rear wheel trajectory Tr will be referred to as "rear wheel curvature Kr." Furthermore, points on the front wheel trajectory Tf will be referred to as "front wheel passing points."

[0025] The target velocity vectors VECf and VECr are calculated based on the two-wheel model. Figure 2 is a schematic diagram of the two-wheel model. In the two-wheel model, the front wheel curvature Kf and rear wheel curvature Kr are expressed by the following equations (1) and (2). In equations (1) and (2), Lwb is the wheelbase Lwb. The wheelbase Lwb is a known constant. The front wheel steering angle Bf and front wheel speed Vf are calculated from the driving instructions as described above.

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[0026] In the case of rutting, the vehicle behavior controller 12 positions the rear wheels 42 at the points where the front wheels pass, and sequentially steers the rear wheels 42 so that the curvature Kr of the rear wheels at these points matches the curvature Kf of the front wheels. By matching the curvature Kr of the rear wheels with the curvature Kf at points where the front wheels pass, the rear wheel trajectory Tr matches the front wheel trajectory Tf.

[0027] To achieve this control, the vehicle behavior controller 12 sequentially acquires the front wheel curvature Kf at each of the multiple front wheel passing points and temporarily stores it in the memory 16. The front wheel curvature Kf may be calculated, for example, from the results detected by the trajectory sensor 23. That is, the vehicle behavior controller 12 calculates the front wheel trajectory Tf from the detection results of the trajectory sensor 23. Furthermore, the vehicle behavior controller 12 calculates the front wheel curvature Kf at each front wheel passing point from the front wheel trajectory Tf. Alternatively, the vehicle behavior controller 12 may calculate the front wheel curvature Kf by sequentially performing the calculation in equation (1).

[0028] The vehicle behavior controller 12 calculates the rear wheel steering angle Br such that when the rear wheel 42 is located at a predetermined front wheel passing point, the rear wheel curvature Kr at that point matches the front wheel curvature Kf. For example, consider the case in Figure 3 where, at time t1, the front wheel 40 passes a predetermined front wheel passing point Pf. Let the front wheel curvature Kf at this front wheel passing point Pf be Kf(t1). Then, at time t2, suppose the rear wheel 42 reaches the front wheel passing point Pf. If the rear wheel curvature Kr at this front wheel passing point Pf is Kr(t2), the vehicle behavior controller 12 calculates the rear wheel steering angle Br that satisfies Kf(t1)=Kr(t2).

[0029] Specifically, the vehicle behavior controller 12 solves equation (3) for the rear wheel steering angle Br. The vehicle behavior controller 12 uses the value temporarily stored in memory 16 as the value of Kf(t1).

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[0030] By solving equation (3), the rear wheel steering angle Br that allows for rutting can be obtained. The front wheel steering angle Bf, front wheel speed Vf, and rear wheel speed Vr can be calculated from the driving instructions as described above. Therefore, once the rear wheel steering angle Br is calculated, the target speed vectors VECf and VECr that allow for rutting can be obtained. Subsequently, the vehicle behavior controller 12 sequentially calculates the target speed vectors VECf and VECr that allow for rutting using the same procedure.

[0031] Note that rutting must begin with the rear wheels 42 positioned at the point where the front wheels pass. However, if the vehicle begins to turn without performing rutting, a wheel difference will occur. Therefore, in this case, it is difficult to position the rear wheels 42 at the point where the front wheels pass. Thus, rutting may be started while the vehicle is traveling in a straight line. When traveling in a straight line, the rear wheels 42 can be easily positioned at the point where the front wheels pass without complex calculations.

[0032] Incidentally, the rear wheel steering angle Br calculated here is the steering angle for a two-wheeled model. Therefore, the calculated rear wheel steering angle Br cannot be directly applied to a four-wheeled vehicle, except in special circumstances. These special circumstances refer to situations where the vehicle is moving at a low speed and the slip angle can be ignored. In this case, the calculated rear wheel steering angle Br and front wheel steering angle Bf can be directly applied to a four-wheeled vehicle.

[0033] On the other hand, when the vehicle speed Vv is relatively large, the slip angle cannot be ignored. In this case, the vehicle behavior controller 12 converts the two-wheeled vehicle model into a rigid body model. Figure 4 is a schematic diagram of the rigid body model. The rigid body model represents the vehicle's behavior using the vehicle speed Vv at the vehicle's center of gravity, the slip angle B, and the yaw rate Θ. The slip angle B, vehicle speed Vv, and yaw rate Θ can be calculated by applying the target velocity vectors VECf and VECr to known conversion formulas.

[0034] Figure 6 is a flowchart showing the flow of rut-following control. When rut-following is performed, the vehicle behavior controller 12 calculates the front wheel steering angle Bf and the front wheel speed Vf based on the driving instruction (S20). Next, the vehicle behavior controller 12 identifies the front wheel curvature Kf at the current position of the rear wheels 42 (e.g., the point Pf the front wheels pass through) (S22). Hereafter, the front wheel curvature Kf identified in step S22 will be denoted as "Kf(t1)".

[0035] The vehicle behavior controller 12 solves equation 3 above, assuming the current rear wheel curvature is Kr(t2), to calculate the rear wheel steering angle Br that satisfies Kf(t1)=Kr(t2) (S24). Next, the vehicle behavior controller 12 converts the two-wheel model into a rigid body model and calculates the slip angle B, vehicle speed Vv, and yaw rate Θ based on the two target velocity vectors VECf and VECr (S26). Once B, Vv, and Θ are calculated, the vehicle behavior controller 12 uses these as inputs to perform a 6-component force control process (S28). The same process is repeated until the rut driving is completed.

[0036] As is clear from the above explanation, the vehicle behavior controller 12 disclosed herein sequentially calculates a rear wheel steering angle Br in which the rear wheel curvature Kr matches the front wheel curvature Kf, in order to enable rut driving. Then, the vehicle behavior controller 12 steers the wheels based on the obtained rear wheel steering angle Br. This enables smooth rut driving.

[0037] Furthermore, the vehicle behavior controller 12 disclosed herein converts the target velocity vectors VECf and VECr obtained in the two-wheel model into a lower-dimensional rigid body model. By converting to a rigid body model, the 6-component force control processing disclosed in Japanese Patent Application Publication No. 2022-021715 and Japanese Patent Application Publication No. 2022-165535 can be easily utilized.

[0038] It should be noted that the configuration described above is merely an example, and other configurations may be changed as long as the configuration described in claim 1 is met. For example, in the above description, a 6-component force control process is used to calculate the control command for achieving rutted driving. However, the control command for the vehicle control actuator group 26 may be calculated directly from the target speed vectors VECf and VECr without using the 6-component force control process. [Explanation of Symbols]

[0039] 10 Vehicle behavior control device, 12 Vehicle behavior controller, 14 Processor, 16 Memory, 18 Accelerator pedal sensor, 20 Brake pedal sensor, 22 Steering sensor, 23 Trajectory sensor, 24 Autonomous driving system, 26 Vehicle control actuator group, 28 Drive actuator, 30 Brake actuator, 32 Front wheel steering actuator, 34 Rear wheel steering actuator, 36 Active stabilizer, 38 Active suspension, 40 Front wheel, 42 Rear wheel, B Slip angle, Bf Front wheel steering angle, Br Rear wheel steering angle, Kf Front wheel curvature, Kr Rear wheel curvature, Lwb Wheelbase, Pf Front wheel passing point, Tf Front wheel trajectory, Vf Front wheel speed, Vv Vehicle speed, Θ Yaw rate.

Claims

1. A vehicle behavior control device for controlling the behavior of a vehicle, Equipped with a processor and memory, The aforementioned processor, Obtain the front wheel trajectory, The curvature of the front wheel trajectory at each of the multiple points through which the front wheel passes, which constitute the aforementioned front wheel trajectory, is calculated as the front wheel curvature. The curvature of the rear wheel trajectory at a predetermined point where the front wheel passes coincides with the curvature of the front wheel trajectory at the predetermined point where the front wheel passes is calculated sequentially. Based on the calculated rear wheel steering angle and front wheel steering angle, the drive of the front and rear wheels is controlled. It is configured in such a way, A vehicle behavior control device characterized in that, when the curvature of the front wheel trajectory at the predetermined front wheel passing point is Kf(t1), the wheelbase is Lwb, the front wheel speed is Vf, the front wheel steering angle is Bf, and the rear wheel steering angle is Br, the rear wheel steering angle is a steering angle that satisfies the following equation 3. [Math 1]

2. A vehicle behavior control device for controlling the behavior of a vehicle, Equipped with a processor and memory, The aforementioned processor, Obtain the front wheel trajectory, The curvature of the front wheel trajectory at each of the multiple points through which the front wheel passes, which constitute the aforementioned front wheel trajectory, is calculated as the front wheel curvature. The curvature of the rear wheel trajectory at a predetermined point where the front wheel passes coincides with the curvature of the front wheel trajectory at the predetermined point where the front wheel passes is calculated sequentially. Based on the calculated rear wheel steering angle and front wheel steering angle, the drive of the front and rear wheels is controlled. It is configured in such a way, The aforementioned vehicle is a four-wheeled vehicle having two front wheels and two rear wheels. The aforementioned processor, Based on the two-wheel model, the target velocity vectors for the front wheel and the rear wheel are calculated. Based on the aforementioned target velocity vector, the behavior of the vehicle at its center of gravity is calculated. Based on the behavior of the vehicle's center of gravity, the steering and driving force of the four wheels are controlled. A vehicle behavior control device characterized by being configured in such a way.

3. A vehicle behavior control device according to claim 1 or 2, Furthermore, it is equipped with a trajectory sensor that detects the front wheel trajectory, The processor is configured to calculate the curvature of the front wheel trajectory at multiple points where the front wheel passes, based on the detected front wheel trajectory. A vehicle behavior control device characterized by the following:

4. A vehicle behavior control device for controlling the behavior of a vehicle, Equipped with a processor and memory, The aforementioned processor, Obtain the front wheel trajectory, The curvature of the front wheel trajectory at each of the multiple points through which the front wheel passes, which constitute the aforementioned front wheel trajectory, is calculated as the front wheel curvature. The curvature of the rear wheel trajectory at a predetermined point where the front wheel passes coincides with the curvature of the front wheel trajectory at the predetermined point where the front wheel passes is calculated sequentially. Based on the calculated rear wheel steering angle and front wheel steering angle, the drive of the front and rear wheels is controlled. It is configured in such a way, The vehicle behavior control device is characterized in that the processor is configured to start calculating a rear wheel steering angle such that the curvature of the rear wheel trajectory at a predetermined front wheel passing point matches the curvature of the front wheel trajectory at the predetermined front wheel passing point, during the period when the vehicle is traveling in a straight line.

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