EPS steering force sense control method based on friction compensation

Abstract

The invention belongs to the technical field of automobile steering control, and particularly relates to an EPS steering force sensing control method based on friction compensation, which is composed of an EPS control mechanism nonlinear friction inverse characteristic correction module, a steering system dynamics steady-state inverse characteristic correction module and an EPS steering force sensing closed-loop control module. The EPS control mechanism non-linear friction inverse characteristic correction module identifies the dry friction characteristic of the EPS control mechanism, and compensates the non-linear friction force of the control mechanism in an open-loop compensation mode; the steering system dynamics steady-state inverse characteristic correction module determines the corresponding equivalent steering resistance torque according to the steering angle position of the steering system, and further determines the power-assisted control quantity of the motor; the EPS steering force sense closed-loop control module enables the steering system after open-loop compensation to have the steering hysteresis characteristic meeting the driving feeling of a driver, and the steering force sense better meets the driving feeling requirement of the driver.

Description

Technical Field

[0001] The invention relates to the technical field of automobile steering control, and in particular to an EPS steering force sense control method based on friction compensation. Background Art

[0002] Electric power steering (EPS) is a steering system that uses an electric motor as a power source. Compared with traditional hydraulic power systems, EPS has the advantages of being more energy-efficient and environmentally friendly, simple in structure, light in weight, and highly adjustable. EPS uses the motor to precisely provide power, so that the steering force can be dynamically adjusted according to vehicle speed, steering angle, and road conditions, thereby providing the driver with a better steering force sense and control experience. EPS plays an important role in improving vehicle driving safety and comfort. The steering force sense of EPS refers to the force and feedback felt by the driver when turning the steering wheel, which directly affects driving comfort and vehicle controllability. By precisely adjusting the output torque of the motor, EPS can dynamically adjust the steering force according to factors such as vehicle speed, steering speed, and road conditions.

[0003] Invention patent CN113815717A discloses an automobile electric power steering system and a power steering method thereof. The EPS controller obtains the vehicle speed from the CAN bus. The EPS controller is connected to the torque sensor, the steering wheel angle sensor, the power motor speed sensor and the steering power regulator. The EPS controller determines the total power torque Tac according to the vehicle speed, the steering wheel hand torque, the steering wheel angle, the power motor speed and the power adjustment coefficient Factor, and controls the power motor to perform according to the total power torque Tac to provide steering assistance, assisting the driver to turn the steering wheel and complete the steering action. The invention can achieve continuous adjustment within a certain range of steering force feeling, making it convenient for the driver to obtain a suitable power feel and improving the user experience. However, the invention does not take into account the problem of nonlinear dry friction between the EPS operating mechanism and the steering actuation system during steering. The nonlinear dry friction will affect the determination of the steering power torque, making it difficult to obtain an ideal steering force feeling.

[0004] Invention patent CN116923529A discloses a steering assist technology, specifically relating to a steering force sense compensation control method, device, storage medium and vehicle. The steering force sense compensation control method obtains the total change in the steering shaft load of the current vehicle, determines the compensation torque that the steering assist motor of the vehicle needs to compensate according to the total change in the steering shaft load, and compensates the steering assist motor according to the compensation torque. The invention can compensate for the steering force sense by obtaining the total change in the axle load of the vehicle's steering shaft during the vehicle acceleration and deceleration process and the slope driving process, ensuring that the steering force sense of the vehicle is always maintained at an ideal level when driving. However, the invention only considers the impact of axle load changes on the steering assist, and does not consider the impact of the EPS control mechanism and the steering actuation system on the steering assist due to nonlinear dry friction during steering, making it difficult to compensate for the ideal steering force sense.

[0005] Therefore, in order to improve the steering force feeling of the driver when steering, it is necessary to design a compensation method for the nonlinear friction of the steering system. Based on this, the present invention proposes an EPS steering force control method based on friction compensation, which compensates for the nonlinear dry friction of EPS and at the same time, through the closed-loop control of the EPS steering force feeling, makes it conform to the steering hysteresis characteristics of the driver's driving feeling. Summary of the invention

[0006] 1. Technical issues to be resolved In view of the deficiencies in the prior art, the present invention provides an EPS steering force control method based on friction compensation, which solves the problems raised in the above background technology.

[0007] (II) Technical solution In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions: An EPS steering force control method based on friction compensation includes an EPS control mechanism nonlinear friction inverse characteristic correction module, a steering system dynamics steady-state inverse characteristic correction module and an EPS steering force closed-loop control module, and also includes the following steps: Step 1: Identify the dry friction characteristics of the EPS control mechanism and obtain the current steering wheel hysteresis characteristic curve , is the steering wheel torque, is the longitudinal velocity of the car, is the lateral acceleration of the car; Step 2: Perform steady-state inverse characteristic correction on the steering system dynamics. The steps are as follows: 201. Obtain the relationship data between the pinion angle and the steering resistance torque through experimental calibration; 202. Select the test data segment and use the power function to fit the upward and downward pinion angles and steering resistance torques respectively. The fitting formula is shown as follows: ; in, , , are the fitting parameters of the upward and downward pinion angles and steering resistance torques, Tp is the steering resistance torque, is the pinion angle, and its value varies at different vehicle speeds; 203. The middle line of the upward and downward movement is used as the steady-state inverse characteristic, and the average value of the upward and downward fitting results is the middle line of the steering resistance torque; 204. Experiments are carried out at different vehicle speeds to obtain the middle line of the steady-state inverse characteristics of the steering system dynamics at different vehicle speeds; 205. Compensate for the inverse characteristics of the steering system dynamics steady state at different vehicle speeds through the power-assist motor; Step 3: Steering force closed-loop control, the steps are as follows: 301. After the open-loop compensation of the steering system, in order to make the steering hysteresis characteristics of the steering system conform to the steering force sense of the driver, the corresponding steering hysteresis characteristics are designed as reference input; 302. Performing closed-loop control on the friction hysteresis torque through a PID controller according to the steering hysteresis characteristics and the current actual steering motor torque, and outputting the steering motor compensation torque; 303. The steering motor compensation torque signal is transmitted to the steering motor, so that the steering system meets the steering hysteresis characteristics of the driver's driving feeling, and further provides a steering force feeling that meets the driver's driving feeling.

[0008] Furthermore, in step 202, the fitting results are different at different vehicle speeds. When the vehicle speed is 80 km / h, the conventional model Power2 is: ; Coefficients (95% confidence bounds): a=321.4(-779.4,1422) b=0.01481(-0.03581,0.06543) c=-308.7(-1409,791.8) Goodness of fit: SSE: 4.828 R-square: 0.9945 Adjusted R-squared: 0.9939 RMSE: 0.4795.

[0009] Furthermore, the EPS control mechanism nonlinear friction inverse characteristic correction module identifies the dry friction characteristic of the EPS control mechanism.

[0010] Furthermore, the step 1 compensates for the nonlinear friction of the operating mechanism by means of open-loop compensation, and the steps are as follows: S1. Disconnect the steering control mechanism from the steering system below the steering pinion; S2. Install a force-measuring steering wheel to measure the steering wheel angle, steering wheel angular velocity and steering wheel torque; S3, turn the steering wheel counterclockwise to the left limit at a low speed of 50°±10° / s, a medium speed of 150°±10° / s, and a high speed of 250°±10° / s, and then turn the steering wheel counterclockwise to the right limit, and then turn the steering wheel counterclockwise to the 0° position, and record the change in steering wheel torque through the steering wheel force sensor; S4. Repeat the above experiment five times and record the data; S5. Develop a dry friction nonlinear compensation table for the EPS control mechanism and compensate for the dry friction of the steering wheel based on the compensation characteristics.

[0011] Furthermore, the steering system dynamics steady-state inverse characteristic correction module determines an equivalent steering resistance torque corresponding to the steering system angular position, and further determines a motor power assist control amount.

[0012] Furthermore, the EPS steering force closed-loop control module enables the steering system after open-loop compensation to have a steering hysteresis characteristic that meets the driver's driving feeling, so that the steering force feeling is more in line with the driver's driving feeling requirements.

[0013] (III) Beneficial effects Compared with the prior art, the present invention provides an EPS steering force control method based on friction compensation, which has the following beneficial effects: The present invention can normalize the steering system gain by correcting the steady-state inverse characteristics of the steering system dynamics, and enable the steering system after open-loop compensation to provide a steering force sense that meets the driver's driving feeling through EPS steering force closed-loop control; solve the problem that the EPS control mechanism has nonlinear dry friction during steering, resulting in poor steering hysteresis characteristics and thus unable to provide an ideal steering force sense, and propose a compensation method for nonlinear friction. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the system principle of the present invention; Figure 2 It is a schematic diagram of a solution for implementing the correction of the steady-state inverse characteristics of the dynamics of the steering system of the present invention; Figure 3 It is a schematic diagram of the inverse characteristics of the dynamic steady state of the steering system of the present invention; Figure 4 It is a schematic diagram of the hysteresis characteristic curve of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] Example like Figure 1-4 As shown, an EPS steering force control method based on friction compensation proposed in one embodiment of the present invention is composed of an EPS control mechanism nonlinear friction inverse characteristic correction module, a steering system dynamic steady-state inverse characteristic correction module and an EPS steering force closed-loop control module. The EPS control mechanism nonlinear friction inverse characteristic correction module identifies the dry friction characteristics of the EPS control mechanism and compensates for the nonlinear friction of the control mechanism by means of open-loop compensation; the steering system dynamic steady-state inverse characteristic correction module determines the corresponding equivalent steering resistance torque according to the steering system angular position and further determines the motor power control amount; the EPS steering force closed-loop control module enables the steering system after open-loop compensation to have a steering hysteresis characteristic that meets the driver's driving feeling, so that the steering force is more in line with the driver's driving feeling requirements.

[0017] The EPS steering force control method based on friction compensation is as follows: Step 1: Identify the dry friction characteristics of the EPS control mechanism and obtain the current steering wheel hysteresis characteristic curve , is the steering wheel torque, is the longitudinal velocity of the car, For the lateral acceleration of the vehicle, the nonlinear friction of the control mechanism is compensated by open-loop compensation. The steps are as follows: Disconnect the steering mechanism from the steering system below the steering pinion; Install a force-measuring steering wheel to measure the steering wheel angle, steering wheel angular velocity and steering wheel torque; Turn the steering wheel counterclockwise to the left limit position, clockwise to the right limit position, and then counterclockwise to the 0° position at a low speed of 50°±10 (i.e. 40-60)° / s, a medium speed of 150°±10 (140-160)° / s, and a high speed of 250°±10 (i.e. 240-260)° / s, and record the steering wheel torque change through the steering wheel force sensor; Repeat the above experiment five times and record the data; A nonlinear compensation table for dry friction of the EPS control mechanism is developed, and the dry friction of the steering wheel is compensated according to the compensation characteristics.

[0018] Step 2: Perform steady-state inverse characteristic correction on the steering system dynamics. The steps are as follows: Through experimental calibration, the relationship data between the pinion angle and the steering resistance torque is obtained; Select appropriate test data segments, and use power functions to fit the upward and downward pinion angles and steering resistance torques respectively. The fitting formulas are shown below: ; in, , , are the fitting parameters of the upward and downward pinion angles and steering resistance torques, Tp is the steering resistance torque, is the pinion angle, and its value is different at different vehicle speeds. The fitting results are different at different vehicle speeds. The following takes the vehicle speed of 80km / h as an example, the conventional model Power2: ; Coefficients (95% confidence bounds): a=321.4(-779.4,1422) b=0.01481(-0.03581,0.06543) c=-308.7(-1409,791.8) Goodness of fit: SSE: 4.828 R-square: 0.9945 Adjusted R-squared: 0.9939 RMSE: 0.4795; The middle line of the upward and downward directions is taken as the steady-state inverse characteristic, and the average value of the upward and downward fitting results is the middle line of the steering resistance torque; Experiments were carried out at different vehicle speeds to obtain the middle lines of the steering system dynamics steady-state inverse characteristics at different vehicle speeds.

[0019] The power-assist motor is used to compensate for the steady-state inverse characteristics of the steering system dynamics at different vehicle speeds.

[0020] Step 3: Steering force closed-loop control, the steps are as follows: After the open-loop compensation of the steering system, in order to make the steering hysteresis characteristics of the steering system consistent with the steering force sense of the driver, the corresponding steering hysteresis characteristics are designed as reference input; Through the PID controller, according to the steering hysteresis characteristics and the current actual steering motor torque, the friction hysteresis torque is closed-loop controlled to output the steering motor compensation torque; The steering motor compensation torque signal is transmitted to the steering motor, so that the steering system conforms to the steering hysteresis characteristics of the driver's driving feeling, thereby providing a steering force feel that conforms to the driver's driving feeling.

[0021] The friction and hysteresis characteristics of the EPS control mechanism are identified through experimental methods, and the friction hysteresis torque of the EPS control mechanism with nonlinear characteristics is compensated through open-loop compensation; secondly, the corresponding equivalent steering resistance torque is determined according to the steering system angular position, and the motor power control amount is further determined; finally, the closed-loop control method is used to determine the power motor torque, so that the electric power steering system can provide the driver with an ideal steering force feel.

[0022] The compensation characteristic in the above article is a steady-state inverse characteristic curve. The different vehicle speeds measured are 0, 20, 40, ..., 120, 140 km / h. The left limit position and the right limit position are the left extreme position of the steering wheel and the right extreme position of the steering wheel.

[0023] Description of relevant symbol parameters of the present invention:

[0024] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An EPS steering force control method based on friction compensation, comprising an EPS control mechanism nonlinear friction inverse characteristic correction module, a steering system dynamics steady-state inverse characteristic correction module and an EPS steering force closed-loop control module, characterized in that: The following steps are also included: Step 1: Identify the dry friction characteristics of the EPS control mechanism and obtain the current steering wheel hysteresis characteristic curve , is the steering wheel torque, is the longitudinal velocity of the car, is the lateral acceleration of the car; Step 2: Perform steady-state inverse characteristic correction on the steering system dynamics. The steps are as follows:

201. Obtain the relationship data between the pinion angle and the steering resistance torque through experimental calibration; 202. Select the test data segment and use the power function to fit the upward and downward pinion angles and steering resistance torques respectively. The fitting formula is shown as follows: ； in, , , are the fitting parameters of the upward and downward pinion angles and steering resistance torques, Tp is the steering resistance torque, is the pinion angle, and its value varies at different vehicle speeds; 203. The middle line of the upward and downward movement is used as the steady-state inverse characteristic, and the average value of the upward and downward fitting results is the middle line of the steering resistance torque; 204. Experiments are carried out at different vehicle speeds to obtain the middle line of the steady-state inverse characteristics of the steering system dynamics at different vehicle speeds; 205. Compensate for the inverse characteristics of the steering system dynamics steady state at different vehicle speeds through the power-assist motor; Step 3: Steering force closed-loop control, the steps are as follows:

301. After the open-loop compensation of the steering system, in order to make the steering hysteresis characteristics of the steering system conform to the steering force sense of the driver, the corresponding steering hysteresis characteristics are designed as reference input; 302. Performing closed-loop control on the friction hysteresis torque through a PID controller according to the steering hysteresis characteristics and the current actual steering motor torque, and outputting the steering motor compensation torque; 303. The steering motor compensation torque signal is transmitted to the steering motor, so that the steering system meets the steering hysteresis characteristics of the driver's driving feeling, and further provides a steering force feeling that meets the driver's driving feeling.

2. The EPS steering force control method based on friction compensation according to claim 1, characterized in that: In step 202, the fitting results are different at different vehicle speeds. When the vehicle speed is 80 km / h, the conventional model Power2: ； Coefficients (95% confidence bounds): a=321.4(-779.4,1422) b=0.01481(-0.03581,0.06543) c=-308.7(-1409,791.8) Goodness of fit: SSE: 4.828 R-square: 0.9945 Adjusted R-squared: 0.9939 RMSE: 0.4795.

3. The EPS steering force control method based on friction compensation according to claim 1, characterized in that: The EPS control mechanism nonlinear friction inverse characteristic correction module identifies the dry friction characteristic of the EPS control mechanism.

4. The EPS steering force control method based on friction compensation according to claim 1, characterized in that: The step 1 compensates the nonlinear friction force of the operating mechanism by means of open-loop compensation, and the steps are as follows: S1. Disconnect the steering control mechanism from the steering system below the steering pinion; S2. Install a force-measuring steering wheel to measure the steering wheel angle, steering wheel angular velocity and steering wheel torque; S3, turn the steering wheel counterclockwise to the left limit at a low speed of 50°±10° / s, a medium speed of 150°±10° / s, and a high speed of 250°±10° / s, and then turn the steering wheel counterclockwise to the right limit, and then turn the steering wheel counterclockwise to the 0° position, and record the change in steering wheel torque through the steering wheel force sensor; S4. Repeat the above experiment five times and record the data; S5. Develop a dry friction nonlinear compensation table for the EPS control mechanism and compensate for the dry friction of the steering wheel based on the compensation characteristics.

5. The EPS steering force control method based on friction compensation according to claim 1, characterized in that: The steering system dynamics steady-state inverse characteristic correction module determines the equivalent steering resistance torque corresponding to the steering system angular position, and further determines the motor power assist control amount.

6. The EPS steering force control method based on friction compensation according to claim 1, characterized in that: The EPS steering force closed-loop control module enables the steering system after open-loop compensation to have a steering hysteresis characteristic that meets the driver's driving feeling, so that the steering force feeling is more in line with the driver's driving feeling requirements.

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