Steering system rack force estimation method

Abstract

The application provides a rack force estimation method for a steering system. The method comprehensively considers the influences of a vehicle dynamics model, a PT1 dynamic transfer function, a tire steering angle, and a parking condition, and realizes estimation of the rack force through the following steps: first, calculating the lateral force of the front axle according to a two-degree-of-freedom vehicle dynamics model; second, converting the lateral force into the rack force by using the PT1 dynamic transfer function, and dynamically adjusting the transfer function in combination with the changes of the vehicle speed and the steering angle; and finally, correcting the calculated rack force through the changes of the tire steering angle and the parking condition, so as to reflect the actual steering behavior. The method can provide estimation of the rack force under various conditions, thereby improving the response speed and precision of the electric power-assisted steering system, and providing a better steering experience for the driver.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automobiles, in particular to a rack force estimation method for a steering system. BACKGROUND

[0002] With the continuous development of the automobile industry, the electric power steering system (EPS) gradually replaces the traditional hydraulic power steering system due to its high efficiency, accuracy and adjustability. The EPS system can provide appropriate auxiliary force according to the steering demand of the driver, thereby improving the driving comfort and safety. The rack force is the size of the external load, which directly affects the steering control feeling, so estimating the rack force is an important factor to provide good assist feedback.

[0003] The traditional rack force estimation method often calculates from the rack force balance, but the rack force calculated by this method is sensitive and ignores the vehicle dynamic characteristics, so the driver's feeling is poor at high vehicle speed. In order to solve this problem, the present application proposes a rack force estimation method combining a vehicle dynamics model, a PT1 dynamic transfer function, a tire steering angle and a parking condition, aiming to reduce the road feeling feedback of the car at high speed, improve the steering feeling of the driver, and meet the comfort demand of the modern automobile steering system. SUMMARY

[0004] The technical problem to be solved by the present application is how to provide a technical solution.

[0005] To solve the above technical problems, the present application provides a rack force estimation method for a steering system, comprising the following steps:

[0006] Step 1: the tire is in contact with the ground, and the tire is subjected to a lateral force and a longitudinal force when the vehicle is steering, and the lateral force controls the lateral movement of the vehicle;

[0007] Step 2: calculate the size of the front wheel lateral acceleration a yf ;

[0008] Step 3: according to the two-degree-of-freedom vehicle dynamics model, the steady-state yaw rate ω r is obtained;

[0009] Step 4: the lateral force is subjected to PT1 filtering to obtain the filtered rack force F filt , and the filtering coefficient changes according to the change of the vehicle speed and the steering wheel speed;

[0010] Step 5: calculate the coefficient factor varying with the front wheel angle and combine the filtered rack force F filt to obtain the basic rack force F rack ;

[0011] Step 6: compensate the basic rack force at low speed to calculate the parking rack force F Parking ;

[0012] Step 7: According to the results obtained in the previous six steps, the final estimated rack force F is obtained by combining the base rack force and the parking rack force.

[0013] Preferably, in step 1, the lateral force F y experienced by the front wheel is obtained according to the tire force balance y The calculation formula of F y is as follows:

[0014] F yf = a front *m front

[0015] where m yf is the front axle load of the vehicle, and a yf is the front lateral acceleration.

[0016] Preferably, in step 2, the front wheel lateral acceleration a r = ω r *u, where u is the vehicle longitudinal speed, and ω r is the steady-state yaw rate.

[0017] Preferably, in step 3, the steady-state yaw rate ω filt is obtained according to a two-degree-of-freedom vehicle dynamics model.

[0018]

[0019] where K is a stability factor.

[0020] Preferably, in step 4, the lateral force is PT1 filtered to obtain the filtered rack force F filt , and the calculation formula is as follows:

[0021]

[0022] where the input of PT1 filtering is the sum of the lateral force and the lateral force rate. T1 is the filtering coefficient, which is obtained according to the actual system and considering the vehicle speed calibration, i.e., different filtering coefficients are obtained by interpolation according to different vehicle speeds. The larger the steering wheel speed, the larger the filtering coefficient, and the PT1 filtering has better dynamic response, and the rack force responds faster to the lateral force.

[0023] Preferably, in step 5, the coefficient factor varying with the front wheel angle is calculated and combined with the filtered rack force F rack to obtain the base rack force F rack ,

[0024] F factor = R filt

[0025] wherein, in relation to the front wheel angle, the factor decreases as the front wheel angle increases.

[0026] Preferably, in step 7, the final estimated rack force F = F rack +F Parking .

[0027] The method of the present application can provide estimation of the rack force under various working conditions, thereby improving the response speed and accuracy of the electric power steering system and providing a better steering experience for the driver. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0029] Figure 1 The physical quantity diagram for calculating the size of the lateral acceleration a yf in step 2 of the present application. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described below through specific embodiments, and those skilled in the art can fully understand other advantages and technical effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied through different specific embodiments, and each detail in the present specification can be applied based on different viewpoints, and various modifications or changes can be made without departing from the general design idea of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. The following exemplary embodiments of the present application can be implemented in various forms, and should not be interpreted as being limited to the specific embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application complete and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art.

[0031] Embodiment 1

[0032] The present embodiment provides a rack force estimation method for a steering system, which is performed according to the following steps:

[0033] Step 1: The tire is in contact with the ground, and the tire is subjected to a lateral force and a longitudinal force when the vehicle is steering, and the lateral force controls the lateral movement of the vehicle. According to the force balance of the tire, the lateral force F y experienced by the front wheel is calculated.

[0034] F y = a yf *m front

[0035] wherein m front is the front axle load of the vehicle, and a yf is the front lateral acceleration.

[0036] Step 2: Calculate the front wheel lateral acceleration a yf .

[0037] As Figure 1 shown, the component of the vehicle mass center absolute acceleration along the lateral axis oy is Since the present application is based on the steady state working condition Therefore, the mass center lateral axis acceleration a y = ω r * u, while the yaw angular acceleration The front wheel lateral acceleration a yf = ω r * u can be obtained.

[0038] Where u is the vehicle longitudinal speed, and ω r is the steady state yaw angular speed.

[0039] Step 3: Obtain the steady state yaw angular speed ω r according to the two-degree-of-freedom vehicle dynamics model.

[0040]

[0041] Where K is the stability factor.

[0042] Step 4: Perform PT1 filtering on the lateral force to obtain the filtered rack force F filt

[0043]

[0044] Where the input of the PT1 filtering is the sum of the lateral force and the lateral force rate. T1 is the filtering coefficient, which is obtained according to the actual system and considering the vehicle speed calibration, that is, different filtering coefficients are obtained according to different vehicle speeds, the greater the steering wheel speed, the greater the filtering coefficient, the PT1 filtering has a better dynamic response, and the rack force responds to the lateral force faster.

[0045] Step 5: Calculate the coefficient factor varying with the front wheel steering angle and combine the filtered rack force Ffilt to obtain the basic rack force F rack .

[0046] F rack = R factor * F filt

[0047] Where R is related to the front wheel steering angle, and decreases with the increase of the front wheel steering angle.

[0048] Step 6: The rack force calculated by the vehicle model is mainly for the steering demand under general driving conditions (steady state steering), and the steering wheel needs to be frequently turned when parking, so the rack force calculated by the vehicle model is corrected. The basic rack force F rack is compensated at low speed, and the parking rack force F Parking is calculated. This force is obtained by calibration and varies with vehicle speed.

[0049] Step 7: According to the results obtained in the previous six steps, the final estimated rack force F = F rack + F Parki is obtained by combining the basic rack force and the parking rack force.

[0050] The present application has been described in detail through specific embodiments and examples, but these do not constitute a limitation on the present application. Those skilled in the art can also make many modifications and improvements without departing from the principles of the present application, and these should also be considered within the scope of protection of the present application.

Claims

1. A method for estimating rack force in a steering system, characterized in that, Comprising the steps of: Step 1: Calculate the steady-state yaw rate ω according to the two-degree-of-freedom vehicle dynamics model r ; Step 2: Calculate front wheel lateral acceleration of the size; Step 3: The tire is in contact with the ground, the tire is subjected to lateral force and longitudinal force when the vehicle turns, the lateral force controls the lateral movement of the vehicle; Step 4: PT1 filtering of the lateral force to get filtered rack force The filter coefficients vary as a function of vehicle speed and steering wheel speed. Step 5: Calculate the coefficient factor as a function of the front wheel steering angle and combine with filtered rack force Get base rack force ; Step 6: Compensate base rack force at low speed, calculate park rack force ; Step 7: The final estimated rack force is obtained by combining the base rack force and the parking rack force based on the results from the previous six steps ; In step 3, the lateral force on the front wheel is calculated according to the tire force balance , the calculation formula is: ; wherein is the front axle load of the automobile, is the front lateral acceleration; In step 4, the lateral force is filtered by PT1 to obtain the filtered rack force The calculation formula is as follows: ; wherein the input of the PT1 filter is the sum of the lateral force and the lateral force rate; is a filter coefficient, which is calibrated according to the actual system and the vehicle speed, that is, different filter coefficients are obtained by interpolation according to different vehicle speeds. The greater the steering wheel speed, the greater the filter coefficient, and the PT1 filter has a better dynamic response, and the rack force responds to the lateral force faster.

2. The steering system rack force estimation method according to claim 1, characterized by, In the step 1, the steady-state yaw rate is calculated according to a two-degree-of-freedom vehicle dynamics model ; ; wherein K is a stability factor, is the vehicle longitudinal speed.

3. The steering system rack force estimation method of claim 1, wherein, In step 2, the front wheel lateral acceleration where is the vehicle longitudinal speed, is the steady-state yaw rate.

4. The steering system rack force estimation method of claim 1, wherein, In step 5, the coefficient factor is calculated as a function of the front wheel steering angle and combined with the filtered rack force The base rack force is obtained , ; wherein, In relation to the front wheel angle, the factor decreases as the front wheel angle increases.

5. The steering system rack force estimation method of claim 1, wherein, The rack force finally estimated in step 7 .

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