Control method and system of four-wheel steering system, computer storage medium and program

Abstract

The invention discloses a control method of a four-wheel steering system, which comprises the following steps of: establishing a motion model of the four-wheel steering system, and outputting a side slip angle and a yaw velocity signal according to a steering operation signal of a driver and a front and rear wheel steering angle control signal output by a sliding mode prediction controller; a two-degree-of-freedom reference model of the four-wheel steering system is established, and a side slip angle reference signal and a yaw velocity reference signal are output according to a steering operation signal of a driver; a sliding mode prediction controller is established and outputs front and rear wheel turning angle control signals according to the difference between the side slip angle and yaw velocity signals and the side slip angle and yaw velocity reference signals and a steering operation signal of a driver, so that the output of the motion model tends to be consistent with the output of the two-degree-of-freedom reference model; and the four-wheel steering system is controlled by the front and rear wheel steering angle control signal. The invention further discloses a corresponding control system, a storage medium and a program. The dynamic response capability of the system is improved.

Description

Technical Field

[0001] The invention relates to a steering system control method and system, a computer storage medium and a program, and belongs to the technical field of vehicle steering control. Background Art

[0002] Four-wheel steering (4WS) technology is a key technology of automobile intelligent system, which can effectively improve vehicle handling stability and active safety.

[0003] It monitors vehicle status information in real time, controls the size of the front and rear wheel turning angles, improves the vehicle's driving safety at high speeds and steering maneuverability at low speeds, and thus improves the vehicle's handling performance.

[0004] Four-wheel steering control technology mainly collects vehicle driving state parameters (yaw rate, center of mass slip angle, vehicle speed, etc.) and road adhesion conditions, and uses four-wheel steering control strategies to determine the front and rear wheel steering angles of the vehicle to meet the lateral stability control requirements. However, single control methods such as traditional PID and optimal control methods are difficult to achieve rapid decoupling control of the center of mass slip angle and yaw rate under high-speed conditions. There is a significant phase delay, which increases the risk of vehicle over / understeering. It is also difficult to simultaneously meet the dual indicators of center of mass slip angle tracking accuracy and yaw rate convergence speed. The conflict between the two is more significant under high-speed conditions. The traditional sliding mode controller uses a symbolic function to generate the control law, which causes high-frequency jitter during the convergence of the vehicle's center of mass slip angle, aggravating tire wear and affecting driving comfort. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the task of the present invention is to provide a control method and system for a four-wheel steering system, the purpose of which is to improve the dynamic response capability of the control system to the model, while meeting the requirements of the center of mass sideslip angle tracking accuracy and the yaw angular velocity convergence speed, and enhancing the robustness of the system. The present invention also provides a computer storage medium and a program for implementing the control method.

[0006] The technical solution of the present invention is as follows: A control method for a four-wheel steering system, comprising: Establishing a motion model of a four-wheel steering system, wherein the motion model outputs a mass center sideslip angle and a yaw rate signal according to a steering operation signal of a driver and a front and rear wheel steering angle control signal output by a sliding mode prediction controller; Establishing a two-degree-of-freedom reference model of a four-wheel steering system, wherein the two-degree-of-freedom reference model outputs a center of mass sideslip angle and a yaw rate reference signal according to a steering operation signal of a driver; A sliding mode predictive controller is established, which outputs front and rear wheel steering angle control signals according to the differences between the center of mass sideslip angle and yaw velocity signals and the center of mass sideslip angle and yaw velocity reference signals and the driver's steering operation signal, so that the output of the motion model is consistent with the output of the two-degree-of-freedom reference model, and the four-wheel steering system is controlled by the front and rear wheel steering angle control signals.

[0007] Furthermore, the state equation of the motion model is: , , , , in, An angular step input of the front wheels generated by the driver's steering operation signal; The steering angle is generated by the front and rear wheel steering angle control signals output by the sliding mode predictive controller; are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; M is the vehicle mass; V is the vehicle speed; are the distances from the center of mass to the front and rear axles, respectively; is the yaw moment of inertia about the center of mass; is the input distribution ratio of the sliding mode predictive controller to the front and rear wheels.

[0008] Furthermore, the state equation of the two-degree-of-freedom reference model is: , , , in, The angular step input of the front wheel generated by the driver's steering operation signal, is the yaw rate time constant, is the time constant of the sideslip angle of the center of mass, , in, are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; M is the vehicle mass; V is the vehicle speed; are the distances from the center of mass to the front and rear axles, respectively; .

[0009] Further, 0.1~0.25, It is 0.1~0.25.

[0010] Furthermore, the sliding surface of the sliding mode predictive controller is expressed as: , The objective function of the sliding mode predictive controller is: , The control law of the sliding mode predictive controller is: , in, T is the sampling time; is the sideslip angle of the center of mass of the motion model; is the sideslip angle of the center of mass of the two-DOF reference model; are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; are the distances from the center of mass to the front and rear axles, respectively; is the yaw angular velocity; M is the vehicle mass; V is the vehicle speed; The angular step input of the front wheel generated by the driver's steering operation signal, is the input allocation ratio of the sliding mode predictive controller to the front and rear wheels; is a constant, which indicates the response speed of the sliding mode controller to the yaw rate deviation.

[0011] Furthermore, the control law of the sliding mode predictive controller is: , in is the saturation function, k , q is the setting coefficient.

[0012] Further, .

[0013] Another technical solution of the present invention is: a control system of a four-wheel steering system, comprising: Motion model module: used to establish a motion model of the four-wheel steering system, the motion model outputs the center of mass sideslip angle and yaw rate signal according to the driver's steering operation signal and the front and rear wheel steering angle control signal output by the sliding mode prediction controller; Reference model module: used to establish a two-degree-of-freedom reference model of the four-wheel steering system, wherein the two-degree-of-freedom reference model outputs a center of mass sideslip angle and a yaw rate reference signal according to the driver's steering operation signal; Controller module: used to establish a sliding mode prediction controller, which outputs front and rear wheel steering angle control signals according to the difference between the center of mass sideslip angle and yaw velocity signals and the center of mass sideslip angle and yaw velocity reference signals and the driver's steering operation signal, so that the output of the motion model tends to be consistent with the output of the two-degree-of-freedom reference model, and controls the four-wheel steering system with the front and rear wheel steering angle control signals.

[0014] Another technical solution of the present invention is: a computer storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the aforementioned control method of the four-wheel steering system is implemented.

[0015] Yet another technical solution of the present invention is: a computer program, which, when executed by a processor, implements the aforementioned control method of the four-wheel steering system.

[0016] The advantages of the present invention compared with the prior art are: The present invention adopts a sliding mode predictive control method based on model reference, selects an ideal two-degree-of-freedom automobile steering model as a reference, and makes the dynamic characteristics of the controlled object and the known reference model as close as possible.

[0017] The present invention adopts a sliding mode predictive control method. On the basis of having the high robustness and rapid responsiveness of traditional sliding mode control, it combines the advantages of predictive control, so that the sideslip angle of the center of mass and the yaw angular velocity converge rapidly at different vehicle speeds, and the sliding mode control performance is optimized.

[0018] The sliding mode predictive controller uses a saturation function instead of a sign function to reduce the system's chattering. The high-frequency chattering amplitude of the sideslip angle and yaw rate during the convergence process is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the module of the control system of the four-wheel steering system.

[0020] Figure 2 Schematic diagram of the flow chart of the control method of the four-wheel steering system.

[0021] Figure 3 Schematic diagram of the vehicle's linear two-degree-of-freedom model.

[0022] Figure 4 It is the center of mass sideslip angle curve obtained by the present invention at 20 km / h.

[0023] Figure 5 This is the yaw rate curve obtained by the present invention at 20 km / h.

[0024] Figure 6 It is the center of mass sideslip angle curve obtained by the present invention at 50 km / h.

[0025] Figure 7 This is the yaw rate curve obtained by the present invention at 50 km / h.

[0026] Figure 8 It is the center of mass sideslip angle curve obtained by the present invention at 80 km / h.

[0027] Fig. 9 This is the yaw rate curve obtained by the present invention at 80 km / h. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the embodiments, but are not intended to limit the present invention.

[0029] Please combine Figure 1 As shown, this embodiment constructs a control system of a four-wheel steering system including: The motion model module 100 is used to establish a motion model of the four-wheel steering system. The motion model outputs a mass center side slip angle and a yaw rate signal according to the driver's steering operation signal and the front and rear wheel steering angle control signal output by the sliding mode prediction controller. Reference model module 200: used to establish a two-degree-of-freedom reference model of the four-wheel steering system, the two-degree-of-freedom reference model outputs a center of mass sideslip angle and a yaw rate reference signal according to the driver's steering operation signal; Controller module 300: used to establish a sliding mode prediction controller, which outputs front and rear wheel steering angle control signals according to the difference between the center of mass sideslip angle and yaw rate signals and the center of mass sideslip angle and yaw rate reference signals and the driver's steering operation signal, so that the output of the motion model tends to be consistent with the output of the two-degree-of-freedom reference model, and controls the four-wheel steering system with the front and rear wheel steering angle control signals.

[0030] Please refer to the specific control method of the four-wheel steering system implemented by the control system of the four-wheel steering system. Figure 2 As shown, it includes the following parts.

[0031] 1. Establish the motion model of the four-wheel steering system.

[0032] The motion model outputs the sideslip angle and yaw rate signals of the center of mass according to the driver's steering operation signal and the front and rear wheel steering angle control signals output by the sliding mode prediction controller.

[0033] Please combine the specific Figure 3 As shown in the figure, the influence of the suspension is not considered, and it is assumed that the car only moves in a plane parallel to the ground, that is, the car only has yaw motion around the center of mass and lateral motion along the y-axis. In addition, the lateral acceleration of the car is controlled below 0.4g.

[0034] The differential equation of motion of the motion model is:

[0035] In formula (1), M is the vehicle mass; V is the vehicle speed; u is the forward speed along the x-axis; v is the lateral acceleration along the y-axis; is the sideslip angle of the center of mass; is the yaw angular velocity; is the yaw moment of inertia about the center of mass; are the front and rear wheel turning angles respectively; are the distances from the center of mass to the front and rear axles, respectively; ; and are the front and rear wheel cornering forces respectively.

[0036] Because the front and rear wheel turning angles are small, it can be approximately considered that , then formula (1) can be written as:

[0037] in, .

[0038] are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; They are the front and rear tire slip angles respectively.

[0039] and: .

[0040] Further establish the state space expression of the four-wheel steering system motion model From formula (2), it can be seen that the sum of the front and rear wheel angles mainly affects the lateral motion of the car, and the difference between the front and rear wheel angles mainly affects the yaw motion of the vehicle. Considering that the driver's steering operation controls the front wheel angle, the controller controls the front and rear wheel angles according to the information feedback of the vehicle's center of mass sideslip angle and yaw angular velocity. Therefore, the actual steering angles of the front and rear wheels can be established as:

[0041]

[0042] An angular step input of the front wheels generated by the driver's steering operation signal; The steering angle is generated by the front and rear wheel steering angle control signals output by the sliding mode predictive controller; is the input distribution ratio of the sliding mode predictive controller to the front and rear wheels. changes, the sum of the front and rear wheel angles remains unchanged. The change in the lateral motion of the vehicle will have little effect.

[0043] Select state variables , the state equation is obtained from the differential equation (2):

[0044] in, , , .

[0045] 2. Establish a two-degree-of-freedom reference model of the four-wheel steering system.

[0046] The two-degree-of-freedom reference model outputs the center-of-mass sideslip angle and yaw rate reference signals according to the driver's steering operation signal. Figure 3 The vehicle linear two-degree-of-freedom model shown can well reflect the relationship between the vehicle front wheel steering angle input and lateral yaw motion under stable driving conditions. Therefore, a two-degree-of-freedom reference model is constructed based on the vehicle linear two-degree-of-freedom model as the control target, and its state equation expression is:

[0047] in, , , in, is the yaw rate time constant, is the time constant of the sideslip angle of the center of mass, It is an empirical value, generally 0.1 to 0.25, and 0.15 is taken in this embodiment.

[0048] .

[0049] 3. Establish a sliding mode predictive controller.

[0050] Predictive control is based on the prediction of future output by the model. Combined with the fast response characteristics of sliding mode control, SMPC (sliding mode predictive control) has excellent dynamic performance and can quickly track the reference signal. Therefore, the present invention adopts this method to achieve the establishment of the controller.

[0051] The sliding mode predictive controller outputs front and rear wheel steering angle control signals according to the difference between the sideslip angle and yaw rate signals and the reference signals of the sideslip angle and yaw rate as well as the driver's steering operation signal, so that the output of the motion model is consistent with the output of the two-degree-of-freedom reference model, and the four-wheel steering system is controlled by the front and rear wheel steering angle control signals.

[0052] First, define the sliding surface as , here is the mass center side slip angle of the two-degree-of-freedom reference model. To ensure the stability of the system, .but:

[0053] In the formula, is a constant, which indicates the response speed of the sliding mode controller to the yaw rate deviation.

[0054] From formula (2), we can get:

[0055] therefore,

[0056] Then from formula (3) and formula (4), we can get:

[0057] Thoughts controlled by predictions, predictions of the passage of time T ( T The sliding surface of the sampling time (0.1s in this embodiment) is expressed as:

[0058] The predictive control objective is ,Right now: .

[0059] Assume that the objective function of sliding mode predictive control is:

[0060] To achieve optimal control, Right now:

[0061] We can get: ,Right now: .

[0062] Substituting into formula (10) we can get:

[0063] Therefore, the control law of the sliding mode predictive controller is:

[0064] In order to eliminate the chattering phenomenon of the system, the exponential approach rate is increased for the above control law, and the saturation function is added .

[0065] That is, the control law is modified as follows:

[0066] in, , based on simulation optimization, the coefficients k=0.5 and q=0.1 are set.

[0067] Based on the motion model, two-degree-of-freedom reference model and sliding mode predictive controller established above, control is performed. The motion model outputs center of mass sideslip angle and yaw rate signals according to the driver's steering operation signal and the front and rear wheel steering angle control signals output by the sliding mode predictive controller. The two-degree-of-freedom reference model outputs center of mass sideslip angle and yaw rate reference signals according to the driver's steering operation signal. The sliding mode predictive controller outputs front and rear wheel steering angle control signals according to the difference between the center of mass sideslip angle and yaw rate signals output by the motion model and the center of mass sideslip angle and yaw rate reference signals output by the two-degree-of-freedom reference model and the driver's steering operation signal, so that the output of the motion model is consistent with the output of the two-degree-of-freedom reference model, and the four-wheel steering system is controlled by the front and rear wheel steering angle control signals.

[0068] In order to verify the effect of the control method of the present invention, simulation experiments were carried out at different speeds. The experimental results are as follows: Figures 4 to 9 As shown in the figure, at the three vehicle speeds of 20km / h, 50km / h and 80km / h, the sideslip angle of the center of mass and the yaw angular velocity tracked the reference model well and achieved an ideal control effect.

[0069] Finally, it should be pointed out that the specific methods of the above embodiments can form a computer program product. Therefore, the computer program product implemented in this application can be stored on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.).

Claims

1. A control method for a four-wheel steering system, characterized in that: include: Establishing a motion model of a four-wheel steering system, wherein the motion model outputs a mass center sideslip angle and a yaw rate signal according to a steering operation signal of a driver and a front and rear wheel steering angle control signal output by a sliding mode prediction controller; Establishing a two-degree-of-freedom reference model of a four-wheel steering system, wherein the two-degree-of-freedom reference model outputs a center of mass sideslip angle and a yaw rate reference signal according to a steering operation signal of a driver; A sliding mode predictive controller is established, which outputs front and rear wheel steering angle control signals according to the differences between the center of mass sideslip angle and yaw velocity signals and the center of mass sideslip angle and yaw velocity reference signals and the driver's steering operation signal, so that the output of the motion model is consistent with the output of the two-degree-of-freedom reference model, and the four-wheel steering system is controlled by the front and rear wheel steering angle control signals.

2. The control method of the four-wheel steering system according to claim 1, characterized in that: The state equation of the motion model is: , , , , in, An angular step input of the front wheels generated by the driver's steering operation signal; The steering angle is generated by the front and rear wheel steering angle control signals output by the sliding mode predictive controller; are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; M is the vehicle mass; V is the vehicle speed; are the distances from the center of mass to the front and rear axles, respectively; is the yaw moment of inertia about the center of mass; is the input distribution ratio of the sliding mode predictive controller to the front and rear wheels.

3. The control method of the four-wheel steering system according to claim 1, characterized in that: The state equation of the two-degree-of-freedom reference model is: , , , in, The angular step input of the front wheel generated by the driver's steering operation signal, is the yaw rate time constant, is the time constant of the sideslip angle of the center of mass, ， in, are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; M is the vehicle mass; V is the vehicle speed; are the distances from the center of mass to the front and rear axles, respectively; .

4. The control method of the four-wheel steering system according to claim 3, characterized in that: 0.1~0.25, It is 0.1~0.

25.

5. The control method of the four-wheel steering system according to claim 1, characterized in that: The sliding surface of the sliding mode predictive controller is expressed as: ， The objective function of the sliding mode predictive controller is: ， The control law of the sliding mode predictive controller is: ， in, T is the sampling time; is the sideslip angle of the center of mass of the motion model; is the sideslip angle of the center of mass of the two-DOF reference model; are the tire cornering stiffness of the front and rear wheels, respectively, and take negative values; are the distances from the center of mass to the front and rear axles, respectively; is the yaw angular velocity; M is the vehicle mass; V is the vehicle speed; The angular step input of the front wheel generated by the driver's steering operation signal, is the input allocation ratio of the sliding mode predictive controller to the front and rear wheels; is a constant, which indicates the response speed of the sliding mode controller to the yaw rate deviation.

6. The control method of the four-wheel steering system according to claim 5, characterized in that: The control law of the sliding mode predictive controller is: ， in is a saturation function, k , q is the setting coefficient.

7. The control method of the four-wheel steering system according to claim 6, characterized in that: 。 8. A control system for a four-wheel steering system, characterized in that: include: Motion model module: used to establish a motion model of the four-wheel steering system, the motion model outputs the center of mass sideslip angle and yaw rate signal according to the driver's steering operation signal and the front and rear wheel steering angle control signal output by the sliding mode prediction controller; Reference model module: used to establish a two-degree-of-freedom reference model of the four-wheel steering system, wherein the two-degree-of-freedom reference model outputs a center of mass sideslip angle and a yaw rate reference signal according to the driver's steering operation signal; Controller module: used to establish a sliding mode prediction controller, which outputs front and rear wheel steering angle control signals according to the difference between the center of mass sideslip angle and yaw velocity signals and the center of mass sideslip angle and yaw velocity reference signals and the driver's steering operation signal, so that the output of the motion model tends to be consistent with the output of the two-degree-of-freedom reference model, and controls the four-wheel steering system with the front and rear wheel steering angle control signals.

9. A computer storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the control method of the four-wheel steering system according to any one of claims 1 to 8 is implemented.

10. A computer program, characterized in that When the computer program is executed by a processor, the control method of the four-wheel steering system according to any one of claims 1 to 8 is implemented.

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