Steering system rack force estimation method

Abstract

The invention provides a steering system rack force estimation method. The method comprehensively considers the influence of a vehicle dynamics model, a PT1 dynamic transfer function, a tire steering angle and a parking working condition, and realizes estimation of the rack force through the following steps: firstly, calculating the lateral force of a front axle according to a two-degree-of-freedom vehicle dynamics model; secondly, converting a lateral force into a rack force by utilizing a PT1 dynamic transfer function, and dynamically adjusting the transfer function in combination with the change of the vehicle speed and the steering angle; and finally, correcting the calculated rack force through the change of the steering angle of the tire and the parking working condition so as to reflect the actual control behavior. According to the method, estimation of the rack force can be provided under various working conditions, so that the response speed and precision of the electric power steering system are improved, and better control experience is provided for a driver.

Description

Technical Field

[0001] The invention relates to the field of automobiles, and in particular to a method for estimating rack force of a steering system. Background Art

[0002] With the continuous development of the automobile industry, the electric power steering system (EPS) has gradually replaced the traditional hydraulic power steering system due to its high efficiency, precision and adjustability. The EPS system can provide appropriate auxiliary force according to the driver's steering needs, thereby improving driving comfort and safety. The rack force is the size of the external load and directly affects the steering control feeling. Therefore, estimating the rack force is an important factor in providing good power feedback.

[0003] Traditional rack force estimation methods often calculate from the rack force balance, but the rack force calculated by this method is relatively sensitive and ignores the dynamic characteristics of the vehicle, resulting in poor driver feel at high speeds. In order to solve this problem, the present invention proposes a rack force estimation method that combines a vehicle dynamics model, a PT1 dynamic transfer function, a tire steering angle, and a parking condition, aiming to reduce the road feel feedback of the car at high speeds, improve the driver's steering feel, and meet the comfort requirements of modern car steering systems. Summary of the invention

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

[0005] In order to solve the above technical problems, the present invention provides a steering system rack force estimation method, comprising the following steps:

[0006] Step 1: The tire is in contact with the ground. When the vehicle turns, the tire is subjected to lateral and longitudinal forces. The lateral force controls the lateral movement of the vehicle.

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

[0008] Step 3: Calculate the steady-state yaw rate ω based on the two-degree-of-freedom vehicle dynamics model r ;

[0009] Step 4: Perform PT1 filtering on the lateral force to obtain the filtered rack force F filt , the filter coefficient changes according to the vehicle speed and steering wheel speed;

[0010] Step 5: Calculate the coefficient factor that changes with the front wheel angle and combine it with the filtered rack force F filt Get the basic rack force F rack ;

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

[0012] Step 7: Based on the results obtained in the first six steps, the basic rack force and the parking rack force are combined to obtain the final estimated rack force F.

[0013] Preferably, in step 1, the lateral force F exerted on the front wheel is calculated based on the tire force balance. y , the F y The calculation formula is:

[0014] F y =a yf *m front

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

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

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

[0018]

[0019] Where K is the stability factor.

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

[0021]

[0022] Among them, the input of PT1 filter is the sum of lateral force and lateral force change rate ratio. T1 is the filter coefficient, which is obtained according to the actual system and vehicle speed calibration, that is, different filter coefficients are interpolated according to different vehicle speeds. The greater the steering wheel speed, the greater the filter coefficient, the better the dynamic response of PT1 filter, and the faster the rack force responds to the lateral force.

[0023] Preferably, in step 5, the coefficient factor that changes with the front wheel angle is calculated and combined with the filtered rack force F filt Get the basic rack force F rack ,

[0024] F rack =R factor *F filt

[0025] Among them, is related to the front wheel turning angle. As the front wheel turning angle increases, the factor decreases.

[0026] Preferably, in step 7, the rack force F is finally estimated to be F rack +F Parking .

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

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0029] Figure 1 The lateral acceleration a is calculated in step 2 of the present invention. yf Schematic diagram of the physical quantity of the size of . DETAILED DESCRIPTION

[0030] The following describes the implementation methods of the present invention through specific specific embodiments, and those skilled in the art can fully understand other advantages and technical effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through different specific implementation methods, and the details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without deviating from the overall design concept of the invention. It should be noted that the following embodiments and the features in the embodiments can be combined with each other in the absence of conflict. The following exemplary embodiments of the present invention can be implemented in a variety of different 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 invention thorough and complete, and to fully convey the technical solutions of these exemplary specific embodiments to those skilled in the art.

[0031] Example 1

[0032] This embodiment provides a steering system rack force estimation method, which is performed in the following steps:

[0033] Step 1: The tire is in contact with the ground. When the vehicle turns, the tire is subjected to lateral force and longitudinal force. The lateral force controls the lateral movement of the vehicle. According to the tire force balance, calculate the lateral force F on the front wheel. y .

[0034] F y =a yf *m front

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

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

[0037] like Figure 1 As shown, the component of the absolute acceleration of the center of mass of the car along the horizontal axis oy is Since the present invention is based on steady-state conditions Therefore, the horizontal acceleration of the center of mass is a y =ω r *u, yaw angular acceleration The lateral acceleration of the front wheel is a yf =ω r *u.

[0038] Where u is the longitudinal velocity of the vehicle, ω r is the steady-state yaw rate.

[0039] Step 3: Calculate the steady-state yaw rate ω based on the two-degree-of-freedom vehicle dynamics model r .

[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] Among them, the input of PT1 filter is the sum of lateral force and lateral force change rate ratio. T1 is the filter coefficient, which is obtained according to the actual system and vehicle speed calibration, that is, different filter coefficients are interpolated according to different vehicle speeds. The greater the steering wheel speed, the greater the filter coefficient, the better the dynamic response of PT1 filter, and the faster the rack force responds to the lateral force.

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

[0046] F rack =R factor *F filt

[0047] Among them, is related to the front wheel turning angle. As the front wheel turning angle increases, the factor decreases.

[0048] Step 6: The rack force calculated by the vehicle model is mainly applicable to the steering requirements under general driving conditions (steady-state steering). Frequent steering of the steering wheel is required when parking, so the rack force calculated by the vehicle model is corrected. rack Compensate and calculate the parking rack force F Parking This force is obtained by calibration and varies with vehicle speed.

[0049] Step 7: Based on the results obtained in the first six steps, the basic rack force and the parking rack force are combined to obtain the final estimated rack force F = F rack +F Parki .

[0050] The present invention has been described in detail above through specific implementation modes and embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may also make many variations and improvements, which should also be regarded as the protection scope of the present invention.

Claims

1. A method for estimating the rack force of a steering system, characterized in that: The following steps are involved: Step 1: The tire is in contact with the ground. When the vehicle turns, the tire is subjected to lateral and longitudinal forces. The lateral force controls the lateral movement of the vehicle. Step 2: Calculate the front wheel lateral acceleration a yf size; Step 3: Calculate the steady-state yaw rate ω based on the two-degree-of-freedom vehicle dynamics model r ; Step 4: Perform PT1 filtering on the lateral force to obtain the filtered rack force F filt , the filter coefficient changes according to the vehicle speed and steering wheel speed; Step 5: Calculate the coefficient factor that changes with the front wheel angle and combine it with the filtered rack force F filt Get the basic rack force F rack ; Step 6: Compensate the basic rack force at low speed and calculate the parking rack force F Parking ; Step 7: Based on the results obtained in the first six steps, the basic rack force and the parking rack force are combined to obtain the final estimated rack force F.

2. The steering system rack force estimation method according to claim 1, characterized in that: In step 1, the lateral force F exerted on the front wheel is calculated based on the tire force balance. y , the F y The calculation formula is: F y =a yf *m front Where m front is the front axle load of the vehicle, a yf is the front lateral acceleration.

3. The steering system rack force estimation method according to claim 1, characterized in that: In step 2, the front wheel lateral acceleration a yf =ω r *u, where u is the longitudinal velocity of the vehicle, ω r is the steady-state yaw rate.

4. The steering system rack force estimation method according to claim 1, characterized in that: In step 3, the steady-state yaw rate ω is calculated based on the two-degree-of-freedom vehicle dynamics model. r . Where K is the stability factor.

5. The steering system rack force estimation method according to claim 1, characterized in that: In step 4, the lateral force is subjected to PT1 filtering to obtain the filtered rack force F filt , the calculation formula is as follows: Among them, the input of PT1 filter is the sum of lateral force and lateral force change rate ratio. T1 is the filter coefficient, which is obtained according to the actual system and vehicle speed calibration, that is, different filter coefficients are interpolated according to different vehicle speeds. The greater the steering wheel speed, the greater the filter coefficient, the better the dynamic response of PT1 filter, and the faster the rack force responds to the lateral force.

6. The steering system rack force estimation method according to claim 1, characterized in that: In step 5, the coefficient factor that changes with the front wheel angle is calculated and combined with the filtered rack force F filt Get the basic rack force F rack , F rack =R factor *F filt Among them, is related to the front wheel turning angle. As the front wheel turning angle increases, the factor decreases.

7. The steering system rack force estimation method according to claim 1, characterized in that: In step 7, the rack force F is finally estimated to be F rack +F Parking .

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