A parking system and control method based on rear wheel traction

Abstract

This invention discloses a control method for a rear-wheel steering-based parking system, applicable to such systems. The method includes the following steps: after the vehicle's automatic parking function is activated, a target coordinate system for the parking space is established with the vehicle's position as the origin; the target parking space position is obtained, and the four corner points of the target parking space are selected as positioning targets; the parameters of the vehicle's four wheels are decomposed to obtain the vehicle's acceleration in the y-axis direction and the second derivative of the vehicle's deflection angle in the target coordinate system; the deflection angles of the front and rear wheels are calculated separately; the vehicle's center of mass is located; trajectory control is performed on the vehicle, and the parking path is calculated. This invention utilizes the original vehicle's automatic parking system and rear-wheel steering system, and through algorithm and control scheme design, fully leverages the original vehicle's execution and control systems, ultimately achieving coordinated control of the vehicle under different rear-wheel steering modes, and completing the coordinated interoperability of the two systems.

Description

Technical Field

[0001] This invention belongs to the field of automatic vehicle parking, specifically relating to a parking system and control method based on rear wheel following. Background Technology

[0002] Most current parking system control methods utilize a single steering unit for control. For example, most vehicles can only steer and operate with the front wheels to ensure that the vehicle responds to the parking system's request with a unique control trajectory, thus guaranteeing the precision of the parking action.

[0003] Current technical solutions are generally applicable to vehicles with widely used rear-wheel steering systems where the rear wheels do not follow the steering wheel. When the EPS controller receives a parking system angle request, it controls the front wheels to a predetermined position. However, it has significant limitations in vehicles equipped with rear-wheel steering systems, mainly in the following ways:

[0004] 1. In a rear-wheel-drive parking system, the different steering angles of the rear and front wheels result in different vehicle trajectories, leading to different vehicle movement trajectories under the same angle request.

[0005] 2. Rear-wheel-driven parking systems have different follow-up modes when their control modes change, such as following in the same direction and following in the opposite direction. This results in different vehicle trajectories when the parking system requests the same angle.

[0006] 3. In a rear-wheel-driven parking system, the different steering restrictions of the rear wheels result in different vehicle trajectories under the same angle request.

[0007] To address the above issues, current parking systems typically disable rear-wheel steering when the system is in operation, or maintain a fixed ratio between the rear-wheel and front-wheel steering angles. While this solves the parking system control problem, it also diminishes many advantages of rear-wheel steering, resulting in situations where, under certain conditions, the parking capability of an automatic parking system may be lower than that of a driver, thus negating the purpose of the parking system. Summary of the Invention

[0008] The purpose of this invention is to provide a parking system and control method based on rear-wheel steering. By utilizing the original vehicle's automatic parking system and rear-wheel steering system, and through algorithm and control scheme design, the original vehicle's execution and control system can be fully utilized to achieve coordinated control of the vehicle under different rear-wheel steering modes, thus completing the coordination and interoperability of the two systems.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: a rear-wheel-driven parking system control method, applied to a rear-wheel-driven parking system. This system includes an electrically connected four-wheel steering system, a central parking controller equipped with the rear-wheel-driven parking system control method, a vehicle CAN bus, an EPS controller, an ESC / TCU controller, and wheel speed sensors. The four-wheel steering system includes an electric power steering system for controlling the front wheel steering, an electric steering system for controlling the rear wheel steering, and an ECU for calculating and controlling the deflection of the rear wheel steering mechanism to adapt to the front wheel steering. The method includes the following steps:

[0010] After the vehicle activates the automatic parking function, a target coordinate system for the parking space is established with the vehicle's position as the origin, the target parking space position is obtained, and the four corner points of the target parking space are selected as the positioning targets.

[0011] The parameters of the four wheels of the vehicle are decomposed to obtain the acceleration of the vehicle in the y-axis direction and the second derivative of the vehicle's deflection angle in the target coordinate system of the parking space; where the y-axis is perpendicular to the vehicle's driving direction in the horizontal direction.

[0012] The deflection angles of the front and rear wheels were calculated separately.

[0013] Position the vehicle's quality center.

[0014] The vehicle's trajectory is controlled to calculate the parking path.

[0015] The decomposition method for the four wheel parameters of the vehicle is as follows:

[0016]

[0017] Where m is the vehicle mass, I Z Let l be the moment of inertia of the vehicle. f l is the distance from the front axle of the car to the center of gravity. r Let a be the distance from the rear axle of the vehicle to the center of gravity. y Let F be the acceleration of the vehicle in the y-axis direction. yf F represents the force on the front wheel in the y-axis direction. yr This represents the force acting on the rear wheel in the y-axis direction.

[0018] The steering angles of the front and rear wheels are calculated as follows:

[0019] Based on the relationship between the lateral force on the tire and the deflection angle:

[0020] F yf =2C αf (θ Vf -δ f cos(δ) f )

[0021] F yr =2C αr (δ r -θ Vr cos(δ) r )

[0022] Among them, C αf For the front wheel lateral stiffness, δ f θ is the steering angle of the front wheels. Vf C is the deflection angle of the front wheel. αr Let θ be the rear wheel lateral stiffness, δr be the rear wheel steering angle, and θ be the lateral stiffness. Vr This is the deflection angle of the rear wheels;

[0023] Decomposing the acceleration along the y-axis, we obtain:

[0024]

[0025] in, Let y be the acceleration of the vehicle's displacement along the y-axis, i.e., the second derivative of y. The centripetal acceleration of the vehicle;

[0026]

[0027]

[0028] Wherein, tan(θ) Vf ) is the ratio of the lateral velocity to the longitudinal velocity of the front wheel of the vehicle, tan(θ) Vr () represents the ratio of the lateral velocity to the longitudinal velocity of the rear wheel of the vehicle;

[0029] The deflection angles of the front and rear wheels are expressed as follows:

[0030]

[0031]

[0032] The specific method for locating the vehicle's quality center is as follows:

[0033] Based on the decomposition method of the four-wheel parameters of the vehicle and the calculation method of the steering angles of the front and rear wheels, the following formula is obtained:

[0034]

[0035]

[0036] During the vehicle's movement:

[0037]

[0038]

[0039] s1=2C αf cos(δ f )

[0040] s2=2C αr cos(δ r )

[0041] The location data of the vehicle's center of gravity is represented as follows:

[0042]

[0043] The positioning data at the center of the rear axle is represented as follows:

[0044]

[0045] Right now:

[0046]

[0047] Among them, X t Let Y be the target position coordinates of the vehicle in the x-axis direction, and Y be the target position coordinates of the vehicle in the y-axis direction. t Let Y be the target position coordinates of the vehicle in the Y-axis direction. Let θ be the instantaneous velocity of the vehicle in the y-direction; t This is the slip angle of the rear wheel.

[0048] The method for calculating trajectory coordinates in the trajectory control of a vehicle is as follows:

[0049]

[0050] in, This represents the vehicle's current state information, where y is the distance between the vehicle and the target location in the y-direction at the current moment. The angular change rate of the vehicle.

[0051] A rear-wheel-guided parking system is also provided, comprising an electrically connected four-wheel steering system, a central parking controller equipped with a rear-wheel-guided parking system control method, a vehicle CAN bus, an EPS controller, an ESC / TCU controller, and wheel speed sensors; wherein,

[0052] The four-wheel steering system includes an electric power steering system for controlling the steering of the front wheels, an electric steering system for controlling the steering of the rear wheels, and an ECU for calculating and controlling the deflection of the rear wheel steering mechanism to adapt to the steering of the front wheels; the vehicle CAN bus is used to provide the necessary vehicle signals collected to the central controller for processing and to transmit back the control commands processed by the central controller.

[0053] The central controller is used to establish a target coordinate system for the parking space with the vehicle's position as the origin after the automatic parking function is activated, obtain the target parking space position, and select the four corner points of the target parking space as positioning targets; decompose the parameters of the four wheels of the vehicle to obtain the acceleration of the vehicle in the y-axis direction and the second derivative of the vehicle's deflection angle in the target coordinate system; calculate the deflection angles of the front and rear wheels respectively; locate the position of the vehicle's center of mass; perform trajectory control on the vehicle and calculate the parking path;

[0054] EPS controller is used to control the steering angle of the front and rear wheels of a vehicle;

[0055] The ESC / TCU controller is used to control the automatic parking system for operations other than controlling the steering angle of the vehicle's front and rear wheels;

[0056] Wheel speed sensor, used to provide wheel speed information.

[0057] The decomposition method for the four wheel parameters of the vehicle is as follows:

[0058]

[0059] Where m is the vehicle mass, I Z Let l be the moment of inertia of the vehicle. f l is the distance from the front axle of the car to the center of gravity. r Let a be the distance from the rear axle of the vehicle to the center of gravity. y Let F be the acceleration of the vehicle in the y-axis direction. yf F represents the force on the front wheel in the y-axis direction. yr This represents the force acting on the rear wheel in the y-axis direction.

[0060] The steering angles of the front and rear wheels are calculated as follows:

[0061] Based on the relationship between the lateral force on the tire and the deflection angle:

[0062] F yf =2C αf (θ Vf -δ f cos(δ) f )

[0063] F yr =2C αr (δ r -θ Vr cos(δ) r )

[0064] Among them, C αf For the front wheel lateral stiffness, δ f θ is the steering angle of the front wheels. Vf C is the deflection angle of the front wheel. αrLet θ be the rear wheel lateral stiffness, δr be the rear wheel steering angle, and θ be the lateral stiffness. Vr Let be the deflection angle of the rear wheel; decompose the acceleration in the y-axis direction to obtain:

[0065]

[0066] in, Let y be the acceleration of the vehicle's displacement along the y-axis, i.e., the second derivative of y. The centripetal acceleration of the vehicle;

[0067]

[0068]

[0069] Wherein, tan(θ) Vf ) is the ratio of the lateral velocity to the longitudinal velocity of the front wheel of the vehicle, tan(θ) Vr () represents the ratio of the lateral velocity to the longitudinal velocity of the rear wheel of the vehicle;

[0070] The deflection angles of the front and rear wheels are expressed as follows:

[0071]

[0072]

[0073] The specific method for locating the vehicle's quality center is as follows:

[0074] Based on the decomposition method of the four-wheel parameters of the vehicle and the calculation method of the steering angles of the front and rear wheels, the following formula is obtained:

[0075]

[0076]

[0077] During the vehicle's movement:

[0078]

[0079]

[0080] s1=2C αf cos(δ f )

[0081] s2=2C αr cos(δ r )

[0082] The location data of the vehicle's center of gravity is represented as follows:

[0083]

[0084] The positioning data at the center of the rear axle is represented as follows:

[0085]

[0086] Right now:

[0087]

[0088] Among them, X t Let Y be the target position coordinates of the vehicle in the x-axis direction, and Y be the target position coordinates of the vehicle in the y-axis direction. t Let Y be the target position coordinates of the vehicle in the Y-axis direction. Let θ be the instantaneous velocity of the vehicle in the y-direction; t This is the slip angle of the rear wheel.

[0089] The method for calculating trajectory coordinates in the trajectory control of a vehicle is as follows:

[0090]

[0091] in, This represents the vehicle's current state information, where y is the distance between the vehicle and the target location in the y-direction at the current moment. The angular change rate of the vehicle.

[0092] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0093] Safety benefits: This invention can ensure the continuous use of rear wheel steering and automatic parking functions under various environmental conditions, ensuring the usage scenarios and thus guaranteeing driving safety.

[0094] Economic benefits: The design of the parking system based on rear-wheel traction control method is completed without adding any other equipment, thus saving costs.

[0095] Enterprise benefits: This invention is simple and practical, applicable to all vehicle models, can interact with rear-wheel steering systems of various models, and operates in a modular manner. Attached Figure Description

[0096] Figure 1 This is a flowchart illustrating an embodiment of the present invention;

[0097] Figure 2 This is a system architecture diagram in an embodiment of the present invention;

[0098] Figure 3 This is a flowchart of the algorithm in an embodiment of the present invention. Detailed Implementation

[0099] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0100] An invention provides a parking system control method based on rear-wheel steering. By utilizing the original vehicle's automatic parking system and rear-wheel steering system, and through algorithm and control scheme design, it fully utilizes the original vehicle's execution and control system, and ultimately achieves coordinated control of the vehicle under different rear-wheel steering modes, completing the coordination and interoperability of the two systems.

[0101] To achieve this goal, a parking system control method based on rear wheel servoing is proposed, which presents a low-cost (widely applicable) system solution.

[0102] Example 1: A parking system based on rear wheel steering

[0103] like Figure 2 As shown, the solution consists of several parts, including a four-wheel steering system that supports the basic structure of this invention, a central parking controller (with a parking system control method based on rear wheel following), a CAN bus, an EPS controller, other controllers such as ESC / TCU, and wheel speed sensors.

[0104] The four-wheel steering system refers to a 4WS system that uses electronic control and electronic power steering. The front wheels can use a conventional / electric power steering system, while the rear wheels use an electric power steering system. There are no mechanical connecting devices or hydraulic lines between the two steering gears; their structures are independent. Electronic control directly controls the steering of the front and rear wheels. During steering, signals from sensors such as the front wheel angle, vehicle speed, and yaw rate are sent to the ECU for analysis and calculation. The ECU determines the rear wheel angle and outputs a drive signal to the stepper motor, which drives the rear wheel steering mechanism to adjust the steering of the front wheels, thus achieving four-wheel steering.

[0105] The vehicle CAN bus is used to provide the central controller with the necessary vehicle signals collected for processing and to transmit back the control commands processed by the central controller.

[0106] The central controller (with an optical road spectrum detection method and technology based on air suspension) is used for: 1) storing and calculating the functional algorithms of this invention; 2) storing the angle control module; and 3) storing the algorithm programs for other normal functions.

[0107] The EPS controller is used for the unified execution of angle requests in this invention;

[0108] Other controllers such as ESC and TCU are used in the parking system and require other actions;

[0109] The wheel speed sensor provides wheel speed information and further corrects the angle information.

[0110] Example 2: A parking control method based on rear wheel traction is also provided.

[0111] like Figure 1 and Figure 3 As shown, the steps of this solution are designed as follows:

[0112] 1) Establishment of the target coordinate system for parking spaces

[0113] At time t=0, when the vehicle activates the automatic parking function and confirms its availability (mostly for finding a parking space), a coordinate system with the origin is established, and the four corner points of the target parking space are the final control targets.

[0114] 2) Decompose the parameters of the four wheels of the vehicle.

[0115]

[0116] ma y =F yf +F yr ; represents Newton's equations of motion; The equations are for torque balance;

[0117] m represents the vehicle's mass, I Z For the vehicle's moment of inertia, I f The distance from the front axle to the center of gravity of the vehicle, I r This is the distance from the rear axle to the center of gravity of the vehicle; all of these distances are known during vehicle design.

[0118] 3) Calculate the steering angle of both wheels.

[0119] Based on the relationship between the lateral force on the tire and the slip angle:

[0120] F yf =2C αf (θ Vf -δ f cos(δ) f )

[0121] F yr =2C αr (δ r -θ Vr cos(δ) r )

[0122] C αf For the front wheel lateral stiffness, δ f Let θ be the front wheel steering angle. Vf Front wheel slip angle

[0123] C αr δr is the rear wheel lateral stiffness, θ is the rear wheel steering angle, and θ is the rear wheel lateral stiffness. Vr Rear wheel slip angle

[0124] Lateral acceleration can be decomposed into acceleration generated by lateral displacement and centripetal acceleration. Decomposing the acceleration along the y-axis, we obtain:

[0125]

[0126] Let be the acceleration of the displacement in the y-axis direction. Indicates centripetal acceleration.

[0127] tan(θ Vf ), tan(θ) Vr ), which is the ratio of the vehicle's lateral speed to its longitudinal speed.

[0128] The steering angles of the two wheels are as follows:

[0129] 4) Vehicle center of mass location handling

[0130] The dynamic equations are transformed into:

[0131]

[0132]

[0133] During the vehicle's movement:

[0134]

[0135]

[0136] In the formula above:

[0137] s1=2C αf cos(δ f )

[0138] s2=2C αr cos(δ r )

[0139] The vehicle's center of gravity location data is as follows:

[0140]

[0141] The positioning data at the center of the rear axle is as follows:

[0142]

[0143] Right now:

[0144]

[0145] 5) Use real-time vehicle parameters for vehicle trajectory control.

[0146] The plan is as follows:

[0147]

[0148] in, This represents the vehicle's current state information, where y is the distance between the vehicle and the target location in the y-direction at the current moment. The angular change rate of the vehicle.

[0149] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A parking system control method based on rear-wheel servoing, characterized in that, This method is applied to a rear-wheel-driven parking system, which includes an electrically connected four-wheel steering system, a central parking controller equipped with a rear-wheel-driven parking system control method, a vehicle CAN bus, an EPS controller, an ESC / TCU controller, and wheel speed sensors. The four-wheel steering system includes an electric power steering system for controlling front wheel steering, an electric steering system for controlling rear wheel steering, and an ECU for calculating and controlling the rear wheel steering mechanism to drive the deflection to adapt to front wheel steering. The method includes the following steps: After the vehicle activates the automatic parking function, a target coordinate system for the parking space is established with the vehicle's position as the origin, the target parking space position is obtained, and the four corner points of the target parking space are selected as the positioning targets. The parameters of the four wheels of the vehicle are decomposed to obtain the acceleration of the vehicle in the y-axis direction and the second derivative of the vehicle's deflection angle in the target coordinate system of the parking space; where the y-axis is perpendicular to the vehicle's driving direction in the horizontal direction. The deflection angles of the front and rear wheels were calculated separately. Position the vehicle's quality center. The vehicle's trajectory is controlled to calculate the parking path; The decomposition method for the four wheel parameters of the vehicle is as follows: Where m is the vehicle's mass. Let be the rotational inertia of the vehicle. This is the distance from the front axle of the car to the center of gravity. This is the distance from the rear axle of the vehicle to the center of gravity. Let be the acceleration of the vehicle in the y-axis direction. This represents the force acting on the front wheel in the y-axis direction. This represents the force acting on the rear wheel in the y-axis direction. The deflection angles of the front and rear wheels are calculated as follows: Based on the relationship between the lateral force on the tire and the deflection angle: in, For the front wheel lateral stiffness, This is the steering angle of the front wheels. The deflection angle of the front wheels. For rear wheel lateral stiffness, This is the steering angle of the rear wheels. This is the deflection angle of the rear wheels; Decomposing the acceleration along the y-axis, we obtain: in, Let y be the acceleration of the vehicle's displacement along the y-axis, i.e., the second derivative of y. The centripetal acceleration of the vehicle; in, This is the ratio of the lateral velocity to the longitudinal velocity of the front wheels of the vehicle. It is the ratio of the lateral velocity to the longitudinal velocity of the rear wheel of the vehicle; The deflection angles of the front and rear wheels are expressed as follows: 。 2. The parking system control method based on rear-wheel steering according to claim 1, characterized in that, The specific method for locating the vehicle's quality center is as follows: Based on the decomposition method of the four-wheel parameters of the vehicle and the calculation method of the deflection angles of the front and rear wheels, the following formula is obtained: During the vehicle's movement: The location data of the vehicle's center of gravity is represented as follows: The positioning data at the center of the rear axle is represented as follows: Right now: in, Let x be the target position coordinates of the vehicle in the x-axis direction. Let Y be the target position coordinates of the vehicle in the Y-axis direction. Let be the instantaneous velocity of the vehicle in the y-direction; This is the slip angle of the rear wheel.

3. The parking system control method based on rear-wheel steering according to claim 2, characterized in that, The method for calculating trajectory coordinates in the trajectory control of a vehicle is as follows: in, This represents the vehicle's current state information, where y is the distance between the vehicle and the target location in the y-direction at the current moment. The angular change rate of the vehicle.

4. A parking system using the rear-wheel-drive-based parking system control method as described in claim 1, characterized in that, This includes an electrically connected four-wheel steering system, a central parking controller equipped with a rear-wheel-guided parking system control method, a vehicle CAN bus, an EPS controller, an ESC / TCU controller, and wheel speed sensors; among which, The four-wheel steering system includes an electric power steering system for controlling the steering of the front wheels, an electric steering system for controlling the steering of the rear wheels, and an ECU for calculating and controlling the deflection of the rear wheel steering mechanism to adapt to the steering of the front wheels; the vehicle CAN bus is used to provide the necessary vehicle signals collected to the central controller for processing and to transmit back the control commands processed by the central controller. The central controller is used to establish a target coordinate system for the parking space with the vehicle's position as the origin after the automatic parking function is activated, obtain the target parking space position, and select the four corner points of the target parking space as positioning targets; decompose the parameters of the four wheels of the vehicle to obtain the acceleration of the vehicle in the y-axis direction and the second derivative of the vehicle's deflection angle in the target coordinate system; calculate the deflection angles of the front and rear wheels respectively; locate the position of the vehicle's center of mass; perform trajectory control on the vehicle and calculate the parking path; EPS controller is used to control the steering angle of the front and rear wheels of a vehicle; The ESC / TCU controller is used to control the automatic parking system for operations other than controlling the steering angle of the vehicle's front and rear wheels; Wheel speed sensor, used to provide wheel speed information; The decomposition method for the four wheel parameters of the vehicle is as follows: Where m is the vehicle's mass. Let be the rotational inertia of the vehicle. This is the distance from the front axle of the car to the center of gravity. This is the distance from the rear axle of the vehicle to the center of gravity. Let be the acceleration of the vehicle in the y-axis direction. This represents the force acting on the front wheel in the y-axis direction. This represents the force acting on the rear wheel in the y-axis direction. The deflection angles of the front and rear wheels are calculated as follows: Based on the relationship between the lateral force on the tire and the deflection angle: in, For the front wheel lateral stiffness, This is the steering angle of the front wheels. The deflection angle of the front wheels. For rear wheel lateral stiffness, This is the steering angle of the rear wheels. Let be the deflection angle of the rear wheel; decompose the acceleration in the y-axis direction to obtain: in, Let y be the acceleration of the vehicle's displacement along the y-axis, i.e., the second derivative of y. The centripetal acceleration of the vehicle; in, This is the ratio of the lateral velocity to the longitudinal velocity of the front wheels of the vehicle. It is the ratio of the lateral velocity to the longitudinal velocity of the rear wheel of the vehicle; The deflection angles of the front and rear wheels are expressed as follows: 。 5. The parking system according to claim 4, characterized in that, The specific method for locating the vehicle's quality center is as follows: Based on the decomposition method of the four-wheel parameters of the vehicle and the calculation method of the deflection angles of the front and rear wheels, the following formula is obtained: During the vehicle's movement: The location data of the vehicle's center of gravity is represented as follows: The positioning data at the center of the rear axle is represented as follows: Right now: in, Let x be the target position coordinates of the vehicle in the x-axis direction. Let Y be the target position coordinates of the vehicle in the Y-axis direction. Let be the instantaneous velocity of the vehicle in the y-direction; This is the slip angle of the rear wheel.

6. The parking system according to claim 5, characterized in that, The method for calculating trajectory coordinates in the trajectory control of a vehicle is as follows: in, This represents the vehicle's current state information, where y is the distance between the vehicle and the target location in the y-direction at the current moment. The angular change rate of the vehicle.

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