Estimation method and device of rack force in steer-by-wire system, vehicle and medium

Abstract

The application relates to the technical field of vehicle control, in particular to a rack force estimation method and device in a steer-by-wire system, a vehicle and a medium, wherein the method comprises the following steps: acquiring a current working condition of the vehicle and a steering motor output torque and a steering column rotation angle of the steer-by-wire system; estimating a friction torque of the steer-by-wire system according to the current working condition, estimating a reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque; and estimating an actual rack force of the steer-by-wire system according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque, thereby solving the problems that the rack force error obtained by a related technology steer-by-wire system based on a model is relatively large and the rack force obtained by an estimation method is relatively low in accuracy due to the lack of reference input signals.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vehicle control, in particular to a rack force estimation method and device in a steer-by-wire system, a vehicle and a medium. BACKGROUND

[0002] With the increasing demand for safety, comfort, handling and intelligence of vehicles, traditional mechanical steering systems have been difficult to meet modern needs. The rapid development of automatic driving technology has further promoted the research and application of steer-by-wire systems. However, in the steer-by-wire system, the mechanical connection between the steering wheel and the actuator is cancelled, and the road feedback signal cannot be directly transmitted to the steering wheel. Therefore, how to accurately and timely feedback the road feeling has become a key point in the road feeling simulation of the steer-by-wire system.

[0003] In related technologies, the rack force is generally measured or estimated as the source of road feeling simulation. The measurement method is generally based on sensors to directly measure the rack force on the steering system actuator. However, in real vehicle applications, the arrangement of sensors is limited by the position of system components, which poses a great safety hazard. In addition, the reliability and service life of sensors are low during the actual use cycle of the vehicle, and the application cost is high. The estimation method generally obtains sufficient data through experiments to establish a steering system friction model. The friction model outputs the current friction torque of the system. The steer-by-wire system equivalent power model receives the steering motor output torque signal, the steering column rotation angle signal and the friction torque signal, and generates the initial system rack force after calculation. However, the rack force estimation method mostly estimates the generalized rack force of the system, and the obtained rack force contains the friction force of the system. The single rack force cannot be obtained. Moreover, due to the errors and uncertainties in the system model established by the existing estimation method, there is a certain error between the initial rack force obtained and the true value. SUMMARY

[0004] The present application provides a rack force estimation method, device, vehicle and medium in a steer-by-wire system to solve the problems of large rack force error obtained by the steer-by-wire system based on the model, lack of reference input signal of the rack force obtained based on the estimation method, and low accuracy of rack force estimation in related technologies.

[0005] The first aspect embodiment of the present application provides a rack force estimation method in a steer-by-wire system, comprising the following steps: obtaining the current working condition of the vehicle and the steering motor output torque and the steering column rotation angle of the steer-by-wire system; estimating the friction torque of the steer-by-wire system according to the current working condition, and estimating the reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque; and estimating the actual rack force of the steer-by-wire system according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque.

[0006] Optionally, in an embodiment of the present application, the friction torque of the steer-by-wire system is estimated according to the current working condition, comprising: inputting the current working condition into a friction model of the steer-by-wire system, the friction model outputting the friction torque of the steer-by-wire system, wherein the friction model calculates the friction torque under the current working condition through a friction map.

[0007] Optionally, in an embodiment of the present application, before the current working condition is inputted into the friction model of the steer-by-wire system, it further comprises: obtaining test data of a friction characteristic test process of the steer-by-wire system; generating a friction map of each working condition and the friction torque according to the test data, and establishing the friction model of the steer-by-wire system according to the friction map.

[0008] Optionally, in an embodiment of the present application, the reference rack force of the steer-by-wire system is estimated according to the output torque of the steering motor, the steering column angle and the friction torque, comprising: inputting the output torque of the steering motor, the steering column angle and the friction torque into an equivalent dynamics model of the steer-by-wire system, the equivalent dynamics model outputting the reference rack force of the steer-by-wire system.

[0009] Optionally, in an embodiment of the present application, the formula of the equivalent dynamics model is:

[0010]

[0011] wherein J is the equivalent rotational inertia of the system, C is the equivalent damping of the system, θ is the steering column angle, T is the output torque of the steering motor, i is the speed reduction ratio from the motor shaft to the steering shaft, F is the reference rack force of the steering system, i is the generalized transmission ratio from the steering link to the steering column shaft, and T is the friction torque of the steering system. m mc rackini rc f

[0012] Optionally, in an embodiment of the present application, the actual rack force of the steer-by-wire system is estimated according to the reference rack force, the output torque of the steering motor, the steering column angle and the friction torque, comprising: inputting the reference rack force, the output torque of the steering motor, the steering column angle and the friction torque into a filter, the filter outputting the actual rack force of the steer-by-wire system, wherein the steering column angle, the reference rack force and the friction torque are taken as the system state variables and the system output of the filter, the output torque of the steering motor is taken as the system control input of the filter, and the actual rack force is calculated according to the system state variables, the system output and the system control input.

[0013] Optionally, in an embodiment of the present application, the state space expression formula of the filter is:

[0014] ​​​​​

[0015] wherein the system state variable is The system output y = [θ, f rack f ] and the system control input u = T m , C = [1 0 1 1], the process noise is w(t), and the measurement noise is v(t).

[0016] The second aspect of the present application provides a rack force estimation device in a steer-by-wire system, comprising: an acquisition module, configured to acquire a current working condition of a vehicle and a steering motor output torque and a steering column rotation angle of the steer-by-wire system; a first estimation module, configured to estimate a friction torque of the steer-by-wire system according to the current working condition, and estimate a reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque; and a second estimation module, configured to estimate an actual rack force of the steer-by-wire system according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque.

[0017] The third aspect of the present application provides a vehicle, comprising: a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor executes the program to implement the rack force estimation method in the steer-by-wire system of any one of the above aspects.

[0018] The fourth aspect of the present application provides a computer readable storage medium, having a computer program stored thereon, and the program is executed by a processor to implement the rack force estimation method in the steer-by-wire system of any one of the above aspects.

[0019] Therefore, the present application has at least the following beneficial effects:

[0020] The embodiments of the present application can establish a friction model of the steer-by-wire system under different working conditions through experimental means, and form a friction atlas using test data in the friction characteristic test, obtain system friction under each working condition based on the friction atlas, thereby stripping the friction force from the generalized rack force to obtain a single rack force; the reference rack force calculated by the equivalent dynamic model of the steer-by-wire system is input into the Kalman filter, thereby providing a reference value for the estimation of the actual rack force, obtaining a more accurate rack force signal, avoiding the problems of large rack force error based on the model and lack of reference input signal based on the estimation method, and improving the accuracy of rack force estimation.

[0021] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0022] ​The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings of exemplary embodiments of the present application, wherein:

[0023] Figure 1 A flow chart of a rack force estimation method in a steer-by-wire system according to an embodiment of the present application;

[0024] Figure 2 A control block diagram of a rack force estimation method in a steer-by-wire system according to an embodiment of the present application;

[0025] Figure 3 A block schematic diagram of a rack force estimation device in a steer-by-wire system according to an embodiment of the present application;

[0026] Figure 4 A structural schematic diagram of a vehicle according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein the same or like reference numerals and characters throughout the figures denote the same or like components or elements having the same or similar functions. The embodiments described below are exemplary and are intended to be illustrative of the present application and are not to be construed as limiting thereof.

[0028] In the related art, a rack force fault-tolerant estimation method for a steer-by-wire system belongs to the technical field of automobile steer-by-wire. Dynamics modeling of a steering actuator is constructed, and a state space of the steer-by-wire system is determined; an extended disturbance observer is designed to estimate a generalized rack force; feedback gain of the extended disturbance observer is designed based on stability theory; and the rack force fault-tolerant estimation method for the steer-by-wire system is given. The present application is more accurate, and provides a design basis for the fault-tolerant mechanism of the observer. It has high precision and is less affected by motor torque fluctuations. The reliability of rack force estimation is improved, and a fault-tolerant strategy for the observer is provided. Not only can it be used to design a feedforward controller in steering follow-up control to improve the accuracy of angle tracking, but also can be used to design a feedback road feel in road feel simulation. It can realize observation of steering motor angle, speed, and rack displacement and speed.

[0029] Therefore, the application provides a rack force estimation method in a steer-by-wire system, first, a sufficient amount of data is obtained through experiments to establish a friction model of the steer-by-wire system, and the friction torque under the current working condition is quickly obtained according to the input current working condition and the known friction map, so that the friction can be separated from the generalized rack force to obtain a single rack force for road feeling simulation in the steer-by-wire system, then the steering motor output torque, the steering column rotation angle and the friction torque are input into the equivalent dynamics model of the steer-by-wire system, and the reference rack force is obtained through calculation, which provides a reference signal for subsequent estimation of the rack force, so as to obtain a more accurate rack force signal, finally, the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque are input into the Kalman filter, and the reference rack force is corrected to obtain a more accurate actual rack force, and the rack force estimation method based on Kalman filtering can estimate the single rack force of the system in real time, improve the accuracy of the road feeling simulation of the steer-by-wire system, and the Kalman filtering algorithm applied has the advantages of less calculation amount, fast operation speed, high precision and easy application in engineering.

[0030] The rack force estimation method, device, vehicle and medium of the embodiment of the application are described below with reference to the drawings, in particular, Figure 1 The rack force estimation method in the steer-by-wire system provided by the embodiment of the application is shown in the flowchart.

[0031] As Figure 1 shown, the rack force estimation method in the steer-by-wire system includes the following steps:

[0032] In step S101, the current working condition of the vehicle and the steering motor output torque and the steering column rotation angle of the steer-by-wire system are obtained.

[0033] The current working condition of the vehicle covers the driving speed of the vehicle, the road condition, the vehicle load, the driver input, the external environmental factors and the vehicle state, etc., which jointly affect the operation state of the steer-by-wire system and the generation and estimation of the rack force; the steering motor output torque refers to the rotational torque transmitted to the steering mechanism by the output shaft of the steering motor under a specific working condition, which is the key force to drive the rotation of the steering mechanism and determines the sensitivity and stability of the vehicle steering; the steering column rotation angle refers to the angle rotated by the steering column relative to its initial position (i.e. the position of the steering column when the vehicle is straight) after the driver applies torque to the steering column through the steering wheel, which is an important parameter reflecting the steering intention of the driver, and through the measurement of the steering column rotation angle, the system can determine the degree and direction of the steering of the vehicle desired by the driver, so as to adjust the output torque of the steering motor and realize precise control of the vehicle steering.

[0034] It can be understood that the embodiments of the present application can more accurately estimate the friction torque of the subsequent steer-by-wire system by acquiring the current working condition of the vehicle. The steering motor output torque is the key force to drive the steering mechanism to rotate, directly affects the generation of the rack force, and is an important input parameter for estimating the rack force. The steering column angle reflects the steering intention of the driver and the motion state of the steering mechanism, and is closely related to the rack force. By measuring the steering column angle, the estimation model of the rack force can be further corrected and improved.

[0035] It should be noted that the embodiments of the present application can acquire the current working condition of the vehicle through application, third-party automobile service platform, on-board diagnostic system, etc. The steering motor output torque can be acquired through motor nameplate and sensor measurement, etc. The steering column angle can be acquired through angle sensor and steering wheel angle indicator, etc.

[0036] In step S102, the friction torque of the steer-by-wire system is estimated according to the current working condition, and the reference rack force of the steer-by-wire system is estimated according to the steering motor output torque, the steering column angle and the friction torque.

[0037] It can be understood that the friction torque of the embodiments of the present application will change with the change of the working condition of the vehicle, so it is necessary to estimate it in real time according to the current working condition to ensure the accuracy of the reference rack force. The steering motor output torque, the steering column angle and the friction torque are the key parameters for estimating the reference rack force of the steer-by-wire system equivalent dynamics model, which jointly determine the accuracy of the estimated reference rack force.

[0038] In the embodiments of the present application, the friction torque of the steer-by-wire system is estimated according to the current working condition, which includes: inputting the current working condition into the friction model of the steer-by-wire system, and the friction model outputs the friction torque of the steer-by-wire system, wherein the friction model calculates the friction torque under the current working condition through the friction map.

[0039] Wherein, the friction torque refers to the resistance torque generated by the friction between the internal components of the steer-by-wire system during steering; the friction model is a mathematical model used to describe the relationship between the friction torque and various influencing factors. In the steer-by-wire system, the friction model can be established based on experimental data or theoretical derivation, and is used to estimate the friction torque under different working conditions; the friction map is a tool that represents the relationship between the friction torque and various influencing factors (such as speed, temperature, load, etc.) in the form of graphs or tables. Through the friction map, the change trend and law of the friction torque under different working conditions can be intuitively understood.

[0040] It can be understood that the embodiment of the application first inputs the current driving speed of the vehicle, the road condition, the vehicle load, the driver input and other working condition information into the friction model of the steer-by-wire system, and the friction model calculates the friction torque estimation value in the current working condition according to the input working condition information and the related information in the friction map, thereby providing more reliable basic data for subsequent calculation of the rack force reference, and the friction torque calculated based on the friction map can realize stripping of the friction force from the generalized rack force to obtain a single rack force, and improve the accuracy of the road feel simulation of the steer-by-wire system.

[0041] In the embodiment of the application, before the current working condition is input into the friction model of the steer-by-wire system, the method further includes: acquiring test data of a friction characteristic test process of the steer-by-wire system; generating a friction map of each working condition and the friction torque according to the test data, and establishing the friction model of the steer-by-wire system according to the friction map.

[0042] It can be understood that the embodiment of the application first acquires test data of the steer-by-wire system in a friction characteristic test process, then generates a friction map of each working condition and the friction torque according to the test data, and establishes the friction model of the steer-by-wire system according to the friction map, and in specific application, the friction torque in the current working condition is quickly obtained according to the input current working condition and the known friction map, and the friction torque in different working conditions can be more accurately estimated through the accurate friction model, so that the friction force is stripped from the generalized rack force to obtain a single system rack force.

[0043] Specifically, the friction characteristic test process of the steer-by-wire system is as follows: first, prepare necessary test equipment such as the steer-by-wire system, sensors and a data acquisition system, and these devices should have good precision and stability to ensure the accuracy of the test results, then design test working conditions covering different vehicle speeds, steering speeds, road conditions and the like according to test requirements, these working conditions should be able to comprehensively reflect the friction characteristics of the steer-by-wire system under different conditions, and finally, according to the design, use the test equipment to test the friction characteristics of the steer-by-wire system, and in the test process, the sensors collect friction data of the system in real time, and the data acquisition system is responsible for recording these data.

[0044] The generation process of the friction map is as follows: first, the test data is cleaned and arranged to remove outliers and noise, ensuring the accuracy and consistency of the data, then the correlation between various working conditions and friction torque is found out using data analysis tools and methods, and finally the friction map of various working conditions and friction torque is drawn according to the analysis results, which usually shows the relationship between data in a graphical way, facilitating intuitive understanding and analysis; the establishment process of the friction model is as follows: first, select the appropriate modeling method according to the characteristics of the friction map and the nature of the test data, which can be based on data-based models, physical models or hybrid models, etc., then build the structure of the friction model according to the selected method, including determining the input parameters (such as working conditions, steering angle, etc.) and output parameters (such as friction torque, etc.) of the model, as well as the internal relationships and formulas of the model, and finally train and verify the model using test data to ensure the accuracy and reliability of the model.

[0045] In the embodiment of the present application, the reference rack force of the steer-by-wire system is estimated according to the output torque of the steering motor, the steering column angle and the friction torque, which includes: inputting the output torque of the steering motor, the steering column angle and the friction torque into the equivalent dynamics model of the steer-by-wire system, and the equivalent dynamics model outputs the reference rack force of the steer-by-wire system.

[0046] The equivalent dynamics model is to regard the steering motor, the reduction mechanism, the rack mechanism and the steering column in the steer-by-wire system as an equivalent system, and to describe the motion law of this system in time and space through mathematical equations. This model helps to understand and predict the dynamic behavior of the system, and provides theoretical support for the control and optimization of the system.

[0047] It can be understood that the equivalent dynamics model of the embodiment of the present application calculates the reference rack force of the steer-by-wire system by comprehensively considering the input parameters such as the output torque of the steering motor, the steering column angle and the friction torque, as well as the physical characteristics and geometric relationships of the system, and the equivalent dynamics model can accurately provide the reference rack force through accurate modeling and solving.

[0048] In the embodiment of the present application, the formula of the equivalent dynamics model is:

[0049]

[0050] Where J is the equivalent moment of inertia of the system, C is the equivalent damping of the system, θ is the steering column angle, T m is the output torque of the steering motor, i mc is the reduction ratio from the motor shaft to the steering shaft, F rackini is the reference rack force of the steering system, i rc is the generalized transmission ratio from the steering link to the steering column shaft, T f is the friction torque of the steering system.

[0051] It can be understood that the formula of the equivalent dynamic model of the embodiments of the present application can more accurately calculate the reference rack force than the traditional empirical formula or the simplified model, has higher calculation accuracy, thereby providing a benchmark value for subsequent estimation of the actual rack force, and improving the accuracy and accuracy of the estimation.

[0052] Specifically, the system equivalent moment of inertia J in the model and the system equivalent damping C can be measured by experiment or simulation, an angle sensor is installed on the steering column to measure the steering column rotation angle θ in real time, the steering motor output torque T m is calculated according to the technical parameters of the steering motor and the control strategy of the motor, the reduction ratio i mc from the motor shaft to the steering shaft is calculated according to the design parameters of the reducer (such as gear ratio, transmission efficiency, etc.), and the generalized transmission ratio i rc is calculated according to the geometric relationship of the steering rod and the steering column shaft and the design parameters of the transmission mechanism (such as the length of the connecting rod, the angle, etc.), and the friction torque T f is calculated by the friction map, and the reference rack force F rackini estimated based on the system model is obtained by substituting the above parameters into the formula of the equivalent dynamic model, as shown in the following formula:

[0053]

[0054] In step S103, the actual rack force of the steer-by-wire system is estimated according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque.

[0055] It can be understood that the reference rack force obtained by the embodiments of the present application needs to be input into the Kalman filter together with the steering motor output torque, the steering column rotation angle and the friction torque, and the reference rack force is corrected by the Kalman filtering algorithm to obtain a more accurate actual rack force.

[0056] In the embodiments of the present application, the actual rack force of the steer-by-wire system is estimated according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque, including: inputting the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque into the filter, and the filter outputs the actual rack force of the steer-by-wire system, wherein the steering column rotation angle, the reference rack force and the friction torque are taken as the system state variables and the system output of the filter, the steering motor output torque is taken as the system control input of the filter, and the actual rack force is calculated according to the system state variables, the system output and the system control input.

[0057] It can be understood that the Kalman filter is selected as the estimation tool in the embodiment of the application, which is an optimal autoregressive data processing algorithm, can provide accurate estimation for the system in the presence of noise and uncertainty, and the rack force estimation method based on Kalman filtering can perform real-time estimation on the single rack force of the system, improve the accuracy of the road feeling simulation of the steer-by-wire system, and the applied Kalman filtering algorithm has the advantages of less calculation amount, fast operation speed, high precision, and is easy to use.

[0058] Specifically, the steering column rotation angle, the reference rack force and the friction torque can comprehensively describe the dynamic behavior of the steer-by-wire system, the steering column rotation angle reflects the steering intention of the driver, the reference rack force is the expected rack force, and the friction torque reflects the friction loss inside the system. Taking these parameters as the system state variables and system outputs of the Kalman filter can ensure that the filter can fully consider the real-time state of the system in the prediction and update stages, thereby improving the filtering accuracy, optimizing the calculation process of the filtering algorithm, and improving the operation efficiency and real-time performance of the algorithm. Through real-time observation and feedback of these state variables, the Kalman filter can timely correct the system deviation, prevent the system state from deviating from the expectation, more accurately estimate the value of the actual rack force, and improve the estimation accuracy.

[0059] The steering motor output torque is a key control variable of the steer-by-wire system, which directly determines the generation and change of the rack force. Taking the steering motor output torque as the control input can significantly improve the estimation accuracy in the process of estimating the actual rack force by the Kalman filter, enhance the robustness and stability of the system, and optimize the control strategy.

[0060] In the embodiment of the application, the state space expression formula of the filter is:

[0061]

[0062] Among them, the system state variable is The system output y = [θ, F rack ,T f ] and the system control input u = T m , c = [1 0 1 1], the process noise is w(t), and the measurement noise is v(t).

[0063] Among them, F rackis the actual rack force, which is the key quantity that the filter needs to accurately estimate; A1is a state transition matrix, which describes how the system state changes over time without control input and process noise; B1is a control input matrix, which describes how the control input affects the change of the system state; G1is a process noise matrix, which describes how the process noise affects the change of the system state; C is an observation matrix, which describes how to extract the system output from the system state variables; w(t) represents the internal unmodeled dynamics or external disturbances of the system; v(t) represents the errors and uncertainties in the measurement process.

[0064] It can be understood that, through the state space expression of the Kalman filter, the system state, the control input, the process noise and the measurement noise can be comprehensively considered, so that the actual rack force can be more accurately estimated, and the Kalman filter is a recursive algorithm, which can process the input data in real time and update the state estimation value, so that the estimation value of the actual rack force can be obtained in real time. The filter can also cope with internal instability and external disturbances of the system, thereby improving the robustness of the system in estimating the actual rack force.

[0065] Specifically, since the Kalman filter algorithm is usually applied to a discrete-time system, it is necessary to discretize the continuous-time state space expression, which can be completed by the Euler method, as follows:

[0066]

[0067] In addition, the Kalman filter algorithm requires that the process noise w(k) and the measurement noise v(k) are zero-mean Gaussian white noise, and they are not correlated, which is given by the following three equations:

[0068]

[0069] e[w(k)v T (k)]=0

[0070] wherein Q(k) and R(k) are the covariance matrices of the process noise and the observation noise respectively, which describe the statistical characteristics of the process noise and the measurement noise respectively; assuming that the current state of the system is k, the Kalman filter algorithm is applied to estimate the system state, which is divided into the following steps:

[0071] 1. Prediction estimation: the state estimation at the last moment and the control input are used to predict the state at the current moment, as follows:

[0072] x(k|k-1)=A1(k)x(k-1|k-1)+B1(k)u(k-1)

[0073] 2. Update the prediction estimation covariance matrix: calculate the error covariance matrix of the prediction estimation, as follows:

[0074] P(k|k-1) = A(k)P(k-1|k-1)A T (k) + Q(k)

[0075] 3. Kalman filter gain matrix: Calculate the Kalman gain, which is used to weigh the relative trust between the predicted estimate and the measurement value, as follows:

[0076]

[0077] 4. Kalman filter estimate: Use the measurement value and the Kalman gain to update the state estimate, as follows:

[0078] x(k|k) = x(k|k-1) + K(k)(y(k) - C(k)x(k|k-1)

[0079] 5. Kalman filter estimate covariance matrix: Update the error covariance matrix of the state estimate, as follows:

[0080] P(k|k) = (I - K(k)C(k))P(k|k-1)

[0081] In each step of the Kalman filter algorithm, an estimate of the system state x(k|k) is obtained, and since the state variable x contains the actual rack force F rack , this value can be directly extracted from the state estimate, i.e. after obtaining the state estimate x(k|k) at the current time, the component corresponding to F rack is taken as the estimated value of the actual rack force.

[0082] It should be noted that in the Kalman filter process, the estimate of the state variable is usually updated according to the dynamic characteristics of the system and the observation value, which means that although the initial state variable contains the reference rack force, during the filtering process, this variable (as well as all other state variables) will be updated according to new observation values and system models, so that during the filtering process, the variable corresponding to the reference rack force will actually reflect a value closer to the actual rack force. By inputting the values of the system at the initial time x(0) and P(0), and applying the Kalman filter algorithm according to the state space expression formula of the filter, the state value of the system at each time can be obtained step by step, so that the rack force of the system can be output, and accurate estimation of the single rack force of the system can be completed. The whole process takes advantage of the Kalman filter algorithm in handling noisy data, and can estimate the system state in real time and accurately.

[0083] In summary, as Figure 2As shown, first, sufficient data is acquired by experiment to establish a steering system friction model, and the current friction torque of the system is output from the friction model, so as to realize stripping of the friction force from the generalized rack force, to obtain a single rack force, then the steer-by-wire system equivalent dynamics model receives the steering motor output torque signal, the steering column rotation angle signal and the friction torque signal, and generates a reference rack force after calculation, to provide a reference for subsequent estimation of the actual rack force, finally, the steering column rotation angle signal, the steering motor output torque signal, the friction torque signal and the reference rack force are input into a Kalman filter together, to correct the reference rack force, and the steer-by-wire system equivalent dynamics model and the Kalman filtering algorithm are combined to obtain a more accurate actual rack force.

[0084] Secondly, the rack force estimation device in the steer-by-wire system according to the embodiment of the application is described with reference to the accompanying drawings.

[0085] Figure 3 is a block schematic diagram of the rack force estimation device in the steer-by-wire system according to the embodiment of the application.

[0086] As shown in Figure 3 , the rack force estimation device 30 in the steer-by-wire system comprises an acquisition module 310, a first estimation module 320 and a second estimation module 330.

[0087] The acquisition module is configured to acquire the current working condition of the vehicle and the steering motor output torque and the steering column rotation angle of the steer-by-wire system. The first estimation module is configured to estimate the friction torque of the steer-by-wire system according to the current working condition, and estimate the reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque. The second estimation module is configured to estimate the actual rack force of the steer-by-wire system according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque.

[0088] It should be noted that the above explanation and description of the rack force estimation method in the steer-by-wire system also apply to the rack force estimation device in the steer-by-wire system of the embodiment, which will not be described here again.

[0089] The rack force estimation device of the steer-by-wire system provided by the embodiment of the application first acquires the working condition of the vehicle and the output torque of the steering motor and the steering column angle of the steer-by-wire system, estimates the friction torque according to the current working condition, then inputs the output torque of the steering motor, the steering column angle and the friction torque into the equivalent dynamics model of the steer-by-wire system of the first estimation module to estimate the reference rack force, and then inputs the reference rack force as a reference signal into the Kalman filter of the second estimation module, so as to obtain a more accurate actual rack signal. The above combines the equivalent dynamics model and the Kalman filter, thereby solving the problems of the rack force error of the steer-by-wire system based on the model being large and the rack force based on the estimation algorithm being low in accuracy due to the lack of reference input signals and the like.

[0090] Figure 4 The vehicle provided by the embodiment of the application is shown in the structural schematic diagram. The vehicle can include:

[0091] The memory 401, the processor 402 and the computer program stored in the memory 401 and executable on the processor 402.

[0092] The processor 402 implements the rack force estimation method of the steer-by-wire system provided in the above embodiment when executing the program.

[0093] Further, the vehicle further includes:

[0094] The communication interface 403 is used for communication between the memory 401 and the processor 402.

[0095] The memory 401 is used for storing the computer program executable on the processor 402.

[0096] The memory 401 can include a high-speed RAM (Random Access Memory, random access memory) memory, and can also include a non-volatile memory, for example, at least one disk memory.

[0097] If the memory 401, the processor 402 and the communication interface 403 are independently implemented, the communication interface 403, the memory 401 and the processor 402 can be connected to each other through a bus and complete the communication between each other. The bus can be an ISA (Industry Standard Architecture, industry standard architecture) bus, a PCI (Peripheral Component, peripheral component interconnect) bus or an EISA (Extended Industry Standard Architecture, extended industry standard architecture) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For the convenience of representation, Figure 4Only one bus or only one type of bus can exist, however.

[0098] Optionally, if the memory 401, the processor 402 and the communication interface 403 are integrated on a chip, the memory 401, the processor 402 and the communication interface 403 can complete the communication among each other through an internal interface.

[0099] The processor 402 can be a CPU (Central Processing Unit, central processor), or an ASIC (Application Specific Integrated Circuit, specific integrated circuit), or one or more integrated circuits configured to implement the embodiments of the present application.

[0100] The embodiments of the present application also provide a computer readable storage medium, which has stored a computer program, and the program is executed by a processor to implement the rack force estimation method in the steer-by-wire system as described above.

[0101] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0102] In addition, the terms "first", "second" are only used for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "N" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited.

[0103] Any process or method described in a flowchart or otherwise described herein can be understood as representing code modules, segments, or portions of code that include one or more executable instructions for implementing the specified logical functions or steps, and the various embodiments of the application include alternative implementations of the described processes or methods, in which the order of steps can be changed, including the use of simultaneous steps or reverse order of steps, where necessary and / or desirable, and in which certain steps can be combined, deleted, modified, or changed to other data processing procedures, as will be apparent to those skilled in the art.

[0104] It should be understood that portions of the application can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. As such, if implemented in hardware, and in another embodiment, any of the following technologies, or a combination thereof, can be used: discrete logic circuitry having logic gates for implementing logic functions upon an application of data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays, field programmable gate arrays, and the like.

[0105] Those of ordinary skill in the art can understand that all or part of the steps carried out by the method of the above-mentioned embodiments can be completed by a program instructing the relevant hardware, and the program can be stored in a computer readable storage medium, and when the program is executed, it includes one or a combination of the steps of the method embodiments.

[0106] Although the embodiments of the application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the application, and those of ordinary skill in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the application.

Claims

1. A method of estimating rack force in a steer-by-wire system, characterized by, The method comprises the following steps: acquiring a current working condition of a vehicle and a steering motor output torque and a steering column rotation angle of a steer-by-wire system; estimating a friction torque of the steer-by-wire system according to the current working condition, and estimating a reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque; estimating an actual rack force of the steer-by-wire system according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque, comprising: inputting the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque into a filter, the filter outputting the actual rack force of the steer-by-wire system, wherein the steering column rotation angle, the reference rack force and the friction torque are taken as system state variables and system outputs of the filter, the steering motor output torque is taken as a system control input of the filter, and the actual rack force is calculated according to the system state variables, the system outputs and the system control input.

2. The rack force estimation method in a steer-by-wire system according to claim 1, characterized by, The estimation of the friction torque of the steer-by-wire system according to the current working condition comprises: inputting the current working condition into a friction model of the steer-by-wire system, the friction model outputting the friction torque of the steer-by-wire system, wherein the friction model calculates the friction torque under the current working condition through a friction map.

3. The rack force estimation method in a steer-by-wire system according to claim 2, characterized by, Before the inputting of the current working condition into the friction model of the steer-by-wire system, the method further comprises: acquiring test data of a friction characteristic test process of the steer-by-wire system; generating a friction map of each working condition and friction torque according to the test data, and establishing the friction model of the steer-by-wire system according to the friction map.

4. The rack force estimation method in a steer-by-wire system according to claim 1, characterized by, The estimation of the reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque comprises: inputting the steering motor output torque, the steering column rotation angle and the friction torque into an equivalent dynamics model of the steer-by-wire system, the equivalent dynamics model outputting the reference rack force of the steer-by-wire system.

5. The rack force estimation method in a steer-by-wire system according to claim 4, characterized by, The formula of the equivalent dynamics model is: where J is the system equivalent moment of inertia, C is the system equivalent damping, θ is the steering column rotation angle, T m is the steering motor output torque, i mc is the motor shaft to steering shaft reduction ratio, F rackini is the steering system reference rack force, i rc is the steering tie rod to steering column shaft generalized transmission ratio, T f is the steering system friction torque.

6. The rack force estimation method in a steer-by-wire system according to claim 1, characterized by, The state space expression formula of the filter is: where the system state variable is , the system output , the system control input , , , , , the process noise , and the measurement noise .

7. A device for estimating rack force in a steer-by-wire system, characterized in that, comprising: an acquiring module, configured to acquire a current working condition of a vehicle and a steering motor output torque and a steering column rotation angle of a steer-by-wire system; a first estimating module, configured to estimate a friction torque of the steer-by-wire system according to the current working condition, and estimate a reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column rotation angle and the friction torque; The second estimation module is configured to estimate the actual rack force of the steer-by-wire system according to the reference rack force, the output torque of the steering motor, the steering column rotation angle and the friction torque, and comprises: inputting the reference rack force, the output torque of the steering motor, the steering column rotation angle and the friction torque into a filter, and outputting the actual rack force of the steer-by-wire system by the filter, wherein the steering column rotation angle, the reference rack force and the friction torque are taken as system state variables and system outputs of the filter, the output torque of the steering motor is taken as a system control input of the filter, and the actual rack force is calculated according to the system state variables, the system outputs and the system control input.

8. A vehicle characterized by comprising: The application further provides a computer program product, comprising: A memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the rack force estimation method in the steer-by-wire system according to any one of claims 1-6.

9. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the rack force estimation method in the steer-by-wire system according to any one of claims 1-6.

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