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

Abstract

The invention relates to the technical field of vehicle control, in particular to an estimation method and device for rack force in a steer-by-wire system, a vehicle and a medium, and the method comprises the steps that 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; 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 rotation angle and the friction torque; according to the reference rack force, the steering motor output torque, the steering column rotation angle and the friction torque, the actual rack force of the steer-by-wire system is estimated. The problems that the error of the rack force obtained on the basis of a model of a steering-by-wire system in the related technology is large, and the accuracy of the rack force obtained on the basis of an estimation method is low due to lack of reference input signals are solved.

Description

Technical Field

[0001] The present application relates to the field of vehicle control technology, and in particular to a method, device, vehicle and medium for estimating rack force in a wire-controlled steering system. Background Art

[0002] As people's requirements for automobile safety, comfort, controllability and intelligence increase, traditional mechanical steering systems can no longer meet modern needs. The rapid development of autonomous driving technology has promoted the research and development and application of wire-controlled steering systems. However, in wire-controlled steering systems, since the mechanical connection between the steering wheel and the actuator is eliminated, the road feedback signal cannot be directly transmitted to the steering wheel. Therefore, how to provide real-time and accurate feedback on the road feel has become a key and difficult point in the simulation of road feel in wire-controlled steering systems.

[0003] Related technologies generally measure or estimate the rack force of the system and use the rack force as the source of road feel simulation. The measurement method is generally based on sensors, which directly measure the rack force on the steering system actuator. However, in actual vehicle applications, the arrangement of sensors is limited by the location of system components, which poses a great safety hazard. At the same time, the reliability and life of sensors in the actual use cycle of the vehicle are low, and the application cost is high. The estimation method generally obtains sufficient data through experiments to establish a steering system friction model, and the friction model outputs the current friction torque of the system. The equivalent power model of the wire-controlled steering system receives the steering motor output torque signal, the steering column angle signal and the friction torque signal, and generates the initial system rack force through calculation. However, most rack force estimation methods estimate the generalized rack force of the system. The rack force obtained includes the friction force of the system, and a single rack force cannot be obtained. In addition, due to the errors and uncertainties in the system model established by the existing estimation algorithm, there is a certain error between the initial rack force obtained and the true value. Summary of the invention

[0004] The present application provides a method, device, vehicle and medium for estimating the rack force in a wire-controlled steering system, so as to solve the problems in the related art that the rack force obtained by the wire-controlled steering system based on the model has a large error, and the rack force obtained based on the estimation method lacks a reference input signal, resulting in low accuracy of rack force estimation.

[0005] A first aspect embodiment of the present application provides a method for estimating the rack force in a steer-by-wire system, comprising the following steps: acquiring the current operating condition of a vehicle and the steering motor output torque and steering column angle of the steer-by-wire system; estimating the friction torque of the steer-by-wire system based on the current operating condition, and estimating a reference rack force of the steer-by-wire system based on the steering motor output torque, the steering column angle and the friction torque; and estimating the actual rack force of the steer-by-wire system based on the reference rack force, the steering motor output torque, the steering column angle and the friction torque.

[0006] Optionally, in one embodiment of the present application, the friction torque of the steer-by-wire system is estimated based on the current operating condition, including: inputting the current operating condition into a friction model of the steer-by-wire system, and the friction model outputting the friction torque of the steer-by-wire system, wherein the friction model calculates the friction torque under the current operating condition through a friction map.

[0007] Optionally, in one embodiment of the present application, before inputting the current operating condition into the friction model of the wire-controlled steering system, it also includes: obtaining test data of the friction characteristic test process of the wire-controlled steering system; generating a friction map of each operating condition and friction torque according to the test data, and establishing the friction model of the wire-controlled steering system according to the friction map.

[0008] Optionally, in one embodiment of the present application, a reference rack force of a steering-by-wire system is estimated based on the steering motor output torque, steering column angle and friction torque, including: inputting the steering motor output torque, steering column angle and friction torque into an equivalent dynamic model of the steering-by-wire system, and the equivalent dynamic model outputting the reference rack force of the steering-by-wire system.

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

[0010]

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

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

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

[0014]

[0015] The system state variables are: System output y=[θ,f rack ,T f ], 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] A second aspect of the present application provides an estimation device for the rack force in a wire-controlled steering system, including: an acquisition module, used to acquire the current operating condition of a vehicle and the steering motor output torque and steering column angle of the wire-controlled steering system; a first estimation module, used to estimate the friction torque of the wire-controlled steering system according to the current operating condition, and to estimate the reference rack force of the wire-controlled steering system according to the steering motor output torque, the steering column angle and the friction torque; and a second estimation module, used to estimate the actual rack force of the wire-controlled steering system according to the reference rack force, the steering motor output torque, the steering column angle and the friction torque.

[0017] A 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, wherein the processor executes the program to implement any one of the above-mentioned methods for estimating rack force in a wire-controlled steering system.

[0018] A fourth aspect of the present application provides a computer-readable storage medium having a computer program stored thereon, the program being executed by a processor to implement any of the above-mentioned methods for estimating rack force in a steer-by-wire system.

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

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

[0021] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

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

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

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

[0026] Figure 4 It is a schematic diagram of the structure of a vehicle provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0028] In the related technology, a method for fault-tolerant estimation of rack force in a wire-controlled steering system is involved, which belongs to the field of automobile wire-controlled steering technology. A dynamic modeling of the steering actuator is constructed, and the state space of the wire-controlled steering system is determined; an extended disturbance observer is designed to estimate the generalized rack force; the feedback gain of the extended disturbance observer is designed based on the stability theory; and a method for fault-tolerant estimation of rack force in a wire-controlled steering system is given. The present invention is more accurate and provides a design basis for the fault-tolerant mechanism of the observer. It has high accuracy and is less affected by motor torque fluctuations. It improves the reliability of rack force estimation and provides a strategy for observer fault tolerance. It can not only 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 feedback road feel in road feel simulation. The observation of the steering actuator motor angle, speed, and rack displacement and speed can be achieved.

[0029] Therefore, the present application provides a method for estimating the rack force in a wire-controlled steering system. First, sufficient data is obtained through experiments to establish a friction model of the wire-controlled steering system. 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 force can be separated from the generalized rack force to obtain a single rack force for the road feel simulation of the wire-controlled steering system. Then, the steering motor output torque, steering column angle and friction torque are input into the equivalent dynamic model of the wire-controlled steering system. After calculation, a reference rack force is obtained to provide a reference signal for subsequent rack force estimation, so as to obtain a more accurate rack force signal. Finally, the reference rack force, steering motor output torque, steering column angle and friction torque are input into a Kalman filter to correct the reference rack force to obtain a more accurate actual rack force. The rack force estimation method based on Kalman filtering can estimate the single rack force of the system in real time, thereby improving the accuracy of the road feel simulation of the wire-controlled steering system. At the same time, the Kalman filtering algorithm used has the advantages of low calculation amount, fast calculation speed and high accuracy, and is easy to be applied in engineering.

[0030] The following describes a method, device, vehicle, and medium for estimating rack force in a wire-controlled steering system according to an embodiment of the present application with reference to the accompanying drawings. Specifically, Figure 1 A schematic flow chart of a method for estimating rack force in a steer-by-wire system provided in an embodiment of the present application.

[0031] like Figure 1 As shown, the method for estimating the rack force in the wire-controlled steering system includes the following steps:

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

[0033] Among them, the current working condition of the vehicle covers multiple aspects such as the vehicle's driving speed, road conditions, vehicle load, driver input, external environmental factors and vehicle status. These factors jointly affect the operating state of the wire-controlled steering system and the generation and estimation of rack force; the steering motor output torque refers to the rotational torque transmitted to the steering mechanism through the output shaft of the steering motor under specific working conditions. It is the key force driving the steering mechanism to rotate and determines the sensitivity and stability of the vehicle's steering; the steering column angle refers to the angle at which the steering column rotates relative to its initial position (i.e. the position of the steering column when the vehicle is driving straight) after the driver applies torque to the steering column through the steering wheel. It is an important parameter reflecting the driver's steering intention. By measuring the steering column angle, the system can determine the degree and direction to which the driver wants the vehicle to turn, thereby adjusting the output torque of the steering motor to achieve precise control of the vehicle's steering.

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

[0035] It should be noted that the embodiments of the present application can obtain the current operating condition of the vehicle through applications, third-party automobile service platforms, on-board diagnostic systems, etc., obtain the steering motor output torque through methods such as motor nameplate and sensor measurement, and obtain the steering column angle through methods such as angle sensors and steering wheel angle indicators.

[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 embodiment of the present application will change with the change of the vehicle operating condition, and therefore it is necessary to perform real-time estimation based on the current operating condition to ensure the accuracy of the reference rack force, and the steering motor output torque, steering column angle and friction torque are key parameters for estimating the reference rack force in the equivalent dynamic model of the wire-controlled steering system, and they together determine the accuracy of the estimated reference rack force.

[0038] In an embodiment of the present application, the friction torque of the wire-controlled steering system is estimated according to the current working condition, including: inputting the current working condition into a friction model of the wire-controlled steering system, and the friction model outputting the friction torque of the wire-controlled steering system, wherein the friction model calculates the friction torque under the current working condition through a friction map.

[0039] Among them, friction torque refers to the resistance torque generated by the friction between the internal components of the wire steering system during the steering process; the friction model is a mathematical model used to describe the relationship between the friction torque and various influencing factors. In the wire steering system, the friction model can be established based on experimental data or theoretical derivation 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 a graph or table. Through the friction map, one can intuitively understand the changing trend and law of the friction torque under different working conditions.

[0040] It can be understood that the embodiment of the present application first inputs the vehicle's current driving speed, road conditions, vehicle load, driver input and other operating condition information into the friction model of the wire-controlled steering system. The friction model then calculates the estimated friction torque under the current operating condition based on the input operating condition information and the relevant information in the friction map, thereby providing more reliable basic data for the subsequent reference rack force calculation. In addition, the friction torque calculated based on the friction map can separate the friction force from the generalized rack force to obtain a single rack force, thereby improving the accuracy of the road feel simulation of the wire-controlled steering system.

[0041] In an embodiment of the present application, before inputting the current operating condition into the friction model of the wire-controlled steering system, it also includes: obtaining test data of the friction characteristic test process of the wire-controlled steering system; generating a friction map of each operating condition and friction torque according to the test data, and establishing the friction model of the wire-controlled steering system according to the friction map.

[0042] It can be understood that the embodiment of the present application must first obtain the test data of the wire-controlled steering system during the friction characteristics test process, and then generate a friction map of various working conditions and friction torques based on the test data, and then establish a friction model of the wire-controlled steering system based on the friction map. In specific applications, the friction torque under the current working condition is quickly obtained based on the input current working condition and the known friction map, and through an accurate friction model, the friction torque under different working conditions can be more accurately estimated, thereby separating the friction force from the generalized rack force and obtaining a single system rack force.

[0043] Specifically, the friction characteristics test process of the wire-controlled steering system is as follows: first, prepare the necessary test equipment such as the wire-controlled steering system, sensors, and data acquisition system. These equipment should have good precision and stability to ensure the accuracy of the test results. Then, according to the test requirements, design test conditions covering different vehicle speeds, steering speeds, road conditions, etc. These conditions should be able to fully reflect the friction characteristics of the wire-controlled steering system under different conditions. Finally, according to the design, use the test equipment to test the friction characteristics of the wire-controlled steering system. During the test, the sensor collects the friction data of the system in real time, and the data acquisition system is responsible for recording this data.

[0044] The generation process of the friction map is as follows: first, the above test data is cleaned and sorted to remove outliers and noise to ensure the accuracy and consistency of the data. Then, data analysis tools and methods are used to find the correlation between each working condition and the friction torque. Finally, based on the analysis results, the friction maps of each working condition and the friction torque are drawn. These maps usually display the relationship between the data in a graphical way to facilitate intuitive understanding and analysis. The establishment process of the friction model is as follows: first, according to the characteristics of the friction map and the nature of the test data, a suitable modeling method is selected, which can be a data-based model, a physical model or a hybrid model, etc. Then, according to the selected method, the structure of the friction model is constructed, including determining the input parameters (such as working conditions, steering angles, etc.) and output parameters (such as friction torque, etc.) of the model, as well as the relationships and formulas within the model. Finally, the model is trained and verified using test data to ensure the accuracy and reliability of the model.

[0045] In an embodiment of the present application, a reference rack force of a steering-by-wire system is estimated based on the output torque of a steering motor, a steering column angle, and a friction torque, including: inputting the output torque of the steering motor, the steering column angle, and the friction torque into an equivalent dynamic model of the steering-by-wire system, and the equivalent dynamic model outputting the reference rack force of the steering-by-wire system.

[0046] Among them, the equivalent dynamics model regards the steering motor, reduction mechanism, rack mechanism and steering column in the wire-controlled steering system as an equivalent system, and describes the motion laws 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 dynamic model of the embodiment of the present application calculates the reference rack force of the wire-controlled steering system by comprehensively considering input parameters such as the steering motor output torque, steering column angle and friction torque, as well as the physical characteristics and geometric relationships of the system. Through precise modeling and solving, the equivalent dynamic model can accurately provide the reference rack force.

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

[0049]

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

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

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

[0053]

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

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

[0056] In an embodiment of the present application, the actual rack force of the steering-by-wire system is estimated based on the reference rack force, the steering motor output torque, the steering column angle and the friction torque, including: inputting the reference rack force, the steering motor output torque, the steering column angle and the friction torque into a filter, and the filter outputting the actual rack force of the steering-by-wire system, wherein the steering column angle, the reference rack force and the friction torque are used as the system state variables and system output of the filter, the steering motor output torque is used as the system control input of the filter, and the actual rack force is calculated based on the system state variables, the system output and the system control input.

[0057] It can be understood that the embodiment of the present application selects the Kalman filter as the estimation tool, which is an optimized autoregressive data processing algorithm that can provide accurate estimation of the system in the presence of noise and uncertainty. The rack force estimation method based on Kalman filtering can perform real-time estimation of the system's single rack force, thereby improving the accuracy of the road feel simulation of the wire-controlled steering system. At the same time, the applied Kalman filter algorithm has the advantages of low computational complexity, fast computing speed, high precision, etc., and is easy to use.

[0058] Specifically, the steering column angle, reference rack force and friction torque can fully describe the dynamic behavior of the wire-controlled steering system. The steering column angle reflects the driver's steering intention, the reference rack force is the expected rack force, and the friction torque reflects the friction loss inside the system. Using 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 algorithm's operating efficiency and real-time performance. Through real-time observation and feedback of these state variables, the Kalman filter can correct system deviations in a timely manner, prevent the system state from deviating from expectations, and more accurately estimate the value of the actual rack force, thereby improving the accuracy of the estimation.

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

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

[0061]

[0062] The system state variables are: System output y=[θ,F rack ,T f ], 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; A1 is the state transfer matrix, which describes how the system state changes over time in the absence of control input and process noise; B1 is the control input matrix, which describes how the control input affects the change of the system state; G1 is the process noise matrix, which describes how the process noise affects the change of the system state; C is the observation matrix, which describes how to extract the system output from the system state variables; w(t) represents the unmodeled dynamics or external disturbances within the system; v(t) represents the error and uncertainty in the measurement process.

[0064] It can be understood that the embodiment of the present application can comprehensively consider the system state, control input, process noise and measurement noise through the state space expression of the Kalman filter, so as to more accurately estimate the actual rack force. The Kalman filter is a recursive algorithm that can process input data and update the state estimate in real time. Therefore, the estimate of the actual rack force can be obtained in real time. The filter can also cope with the instability and external interference within 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 discrete-time systems, the continuous-time state space expression needs to be discretized first, which can be done through the Euler method, as shown below:

[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 noises, and they are uncorrelated, as given by the following three equations:

[0068]

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

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

[0071] 1. Prediction estimation: Use the state estimate and control input of the previous moment to predict the state of the current moment, as shown in the following formula:

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

[0073] 2. Update the prediction estimate covariance matrix: Calculate the error covariance matrix of the prediction estimate 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 measured value, as follows:

[0076]

[0077] 4. Kalman filter estimation: Use the measurement value and 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 estimation covariance matrix: Update the error covariance matrix of the state estimate as follows:

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

[0081] At each step of the Kalman filter algorithm, an estimate of the system state x(k|k) is obtained. Since the state variable x contains the actual rack force F rack , this value can be directly extracted from the state estimate, that is, after obtaining the state estimate x(k|k) at the current moment, the value corresponding to F can be taken out. rack The corresponding components are used as estimates of the actual rack forces.

[0082] It should be noted that in the Kalman filtering process, the estimated value of the state variable is usually updated according to the dynamic characteristics and observations of the system. This means that although the initial state variable contains the reference rack force, this variable (and all other state variables) will be updated according to the new observations and system model during the filtering process. Therefore, the variable relative to the reference rack force during the filtering process will actually reflect a value closer to the actual rack force. By inputting the system values ​​x(0) and P(0) at the initial moment and applying the Kalman filtering algorithm according to the state space expression formula of the filter, the state value of the system at each moment can be gradually obtained, so that the system rack force can be output, and the single rack force of the system can be accurately estimated. The whole process uses the advantages of the Kalman filtering algorithm in processing noisy data, and can estimate the system state in real time and accurately.

[0083] In summary, if Figure 2As shown, firstly, sufficient data is obtained through experiments to establish a steering system friction model, and the friction model outputs the current friction torque of the system, so as to separate the friction force from the generalized rack force and obtain a single rack force. Then, the equivalent dynamics model of the wire-controlled steering system receives the steering motor output torque signal, the steering column angle signal and the friction torque signal, and generates a reference rack force through calculation to provide a reference for the subsequent estimation of the actual rack force. Finally, the steering column angle signal, the steering motor output torque signal, the friction torque signal and the reference rack force are input into the Kalman filter together to correct the reference rack force. The equivalent dynamics model of the wire-controlled steering system and the Kalman filter algorithm are combined to obtain a more accurate actual rack force.

[0084] Next, a rack force estimation device in a steer-by-wire system according to an embodiment of the present application will be described with reference to the accompanying drawings.

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

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

[0087] Among them, the acquisition module is used to obtain the current working condition of the vehicle and the steering motor output torque and steering column angle of the wire steering system; the first estimation module is used to estimate the friction torque of the wire steering system according to the current working condition, and estimate the reference rack force of the wire steering system according to the steering motor output torque, steering column angle and friction torque; the second estimation module is used to estimate the actual rack force of the wire steering system according to the reference rack force, steering motor output torque, steering column angle and friction torque.

[0088] It should be noted that the above explanation of the embodiment of the method for estimating the rack force in the steer-by-wire system is also applicable to the device for estimating the rack force in the steer-by-wire system in this embodiment, and will not be repeated here.

[0089] According to the device for estimating the rack force in a steer-by-wire system proposed in an embodiment of the present application, the operating condition of the vehicle and the steering motor output torque and steering column angle of the steer-by-wire system are first obtained, and the friction torque is estimated according to the current operating condition. The steering motor output torque, steering column angle and friction torque are then input into an equivalent dynamics model of the steer-by-wire system of a first estimation module to estimate a reference rack force. The reference rack force is then input as a reference signal into a Kalman filter of a second estimation module to obtain a more accurate actual rack signal. The equivalent dynamics model and the Kalman filter are combined as above, thereby solving the problems of large error in the rack force obtained based on the model of the related art steer-by-wire system and low accuracy of the rack force obtained based on the estimation method due to the lack of a reference input signal.

[0090] Figure 4 A schematic diagram of the structure of a vehicle provided in an embodiment of the present application. The vehicle may include:

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

[0092] When the processor 402 executes the program, the method for estimating the rack force in the steer-by-wire system provided in the above-mentioned embodiment is implemented.

[0093] Furthermore, the vehicle also includes:

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

[0095] The memory 401 is used to store computer programs that can be executed on the processor 402 .

[0096] The memory 401 may include a high-speed RAM (Random Access Memory) memory, and may also include a non-volatile memory, such as at least one disk memory.

[0097] If the memory 401, the processor 402 and the communication interface 403 are implemented independently, the communication interface 403, the memory 401 and the processor 402 can be connected to each other through a bus and communicate with each other. The bus can be an ISA (Industry Standard Architecture) bus, a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 4Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0098] Optionally, in a specific implementation, 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 communicate with each other through an internal interface.

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

[0100] An embodiment of the present application further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned method for estimating rack force in a steer-by-wire system.

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

[0102] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0103] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0104] It should be understood that the various parts of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, the steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array, a field programmable gate array, etc.

[0105] A person skilled in the art may understand that all or part of the steps of the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0106] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for estimating rack force in a steer-by-wire system, characterized in that: The following steps are involved: Obtain the current working condition of the vehicle and the steering motor output torque and steering column angle of the wire-controlled steering system; estimating a friction torque of a steer-by-wire system according to the current working condition, and estimating a reference rack force of the steer-by-wire system according to an output torque of the steering motor, a steering column angle, and the friction torque; An actual rack force of the steer-by-wire system is estimated based on the reference rack force, the steering motor output torque, the steering column angle, and the friction torque.

2. The method for estimating rack force in a steer-by-wire system according to claim 1, characterized in that: The estimating the friction torque of the steer-by-wire system according to the current working condition comprises: The current working condition is input into a friction model of the steer-by-wire system, and the friction model outputs a 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 method for estimating rack force in a steer-by-wire system according to claim 2, characterized in that: Before inputting the current working condition into the friction model of the wire control steering system, the method further includes: Acquiring test data of a friction characteristic test process of the steer-by-wire system; A friction map of each working condition and friction torque is generated according to the test data, and a friction model of the wire control steering system is established according to the friction map.

4. The method for estimating rack force in a steer-by-wire system according to claim 1, characterized in that: The estimating the reference rack force of the steer-by-wire system according to the steering motor output torque, the steering column angle and the friction torque comprises: The steering motor output torque, the steering column angle and the friction torque are input into an equivalent dynamics model of the steer-by-wire system, and the equivalent dynamics model outputs a reference rack force of the steer-by-wire system.

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

6. The method for estimating rack force in a steer-by-wire system according to claim 1, characterized in that: The method of estimating the actual rack force of the steer-by-wire system based on the reference rack force, the steering motor output torque, the steering column angle and the friction torque comprises: inputting the reference rack force, the steering motor output torque, 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 used as system state variables and system output of the filter, the steering motor output torque is used as system control input of the filter, and the actual rack force is calculated based on the system state variables, the system output and the system control input.

7. The method for estimating rack force in a steer-by-wire system according to claim 6, characterized in that: The state space expression formula of the filter is: The system state variables are: System output y=[θ,F rack ,T f ], system control input C = [1 0 1 1], the process noise is w(t), and the measurement noise is v(t).

8. A rack force estimation device in a steer-by-wire system, characterized in that: include: An acquisition module, used to acquire the current working condition of the vehicle and the steering motor output torque and steering column angle of the wire-controlled steering system; a first estimation module, configured to estimate a friction torque of a steer-by-wire system according to the current working condition, and to estimate a reference rack force of the steer-by-wire system according to an output torque of the steering motor, a steering column angle and the friction torque; The second estimation module is used 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 angle and the friction torque.

9. A vehicle, characterized in that: include: 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 method for estimating rack force in a wire-controlled steering system according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: The program is executed by a processor to implement the method for estimating rack force in a steer-by-wire system according to any one of claims 1 to 7.

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