Method and device for estimating system friction torque, steering-by-wire system and vehicle

Abstract

The present invention relates to a method and device for estimating system friction torque, a wire-controlled steering system and a vehicle. The estimation method is applied to the wire-controlled steering system, which includes a steering execution module, a rack of the steering execution module is hinged to a steering tie rod, the other end of the steering tie rod is hinged to a steering knuckle arm, the steering knuckle arm is fixed to a tire, and the rack pulls the steering tie rod to move back and forth to drive the steering knuckle arm and the tire to rotate around the kingpin; the estimation method includes: obtaining an estimated value of the front axle lateral force through a sliding mode observer; obtaining the front axle lateral force and the kingpin torque M kp The functional relationship between kp =F rack r arm , front axle lateral force and kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm; based on the estimated rack force, the system friction torque-rack force function model, the estimated system friction torque is obtained.

Description

Technical Field

[0001] The present invention relates to the field of vehicle technology, and in particular to a method and device for estimating a system friction torque, a wire-controlled steering system and a vehicle. Background Art

[0002] In the current EPS (Electrical Power Steering, EPS, electric power steering system) power-assisted system, the friction torque of the system is increased due to the addition of components such as reducers. In order to improve the steering feel during the steering process, a compensation constant can be set based on the system friction torque to compensate during the steering process.

[0003] Obviously, under different working conditions, the system friction torque varies, the existing compensation method is single, and the improvement of steering feel experience is limited. Summary of the invention

[0004] The present invention provides a method and device for estimating a system friction torque, a wire-controlled steering system and a vehicle, so as to solve the deficiencies in the related art.

[0005] According to a first aspect of an embodiment of the present invention, a method for estimating a friction torque of a system is provided, which is applied to a wire-controlled steering system, wherein the wire-controlled steering system comprises a steering execution module, wherein the steering execution module comprises a steering gear, a steering tie rod, a steering knuckle arm, a kingpin, and a tire; the steering gear comprises a pinion and a rack meshing with the pinion, wherein the rack is hinged to the steering tie rod, wherein the other end of the steering tie rod is hinged to the steering knuckle arm, wherein the steering knuckle arm is fixedly connected to the tire, and wherein the rack pulls the steering tie rod to reciprocate, thereby driving the steering knuckle arm and the tire to rotate around the kingpin;

[0006] The estimation method includes:

[0007] Obtaining an estimated value of the front axle lateral force by observing with a sliding mode observer;

[0008] Obtain the front axle lateral force and kingpin moment M kp The functional relationship between

[0009] Based on M kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm;

[0010] Based on the estimated rack force and the function model of system friction torque-rack force, an estimated system friction torque is obtained.

[0011] Optionally, obtaining the estimated value of the front axle lateral force through a sliding mode observer includes:

[0012] The observation state vector of the sliding mode observer is defined as The output vector is

[0013] The estimated value of the front axle lateral force is obtained according to the following sliding mode observer observation:

[0014]

[0015] Among them, I zz is the vehicle body yaw moment of inertia, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, F yf is the lateral force on the front axle of the vehicle, F yr is the lateral force on the rear axle of the vehicle, is the vehicle yaw rate, a y is the actual value of the vehicle lateral acceleration, ρ1, ρ2, ρ3, ρ4, ρ5 and ρ6 are all gain constants, sgn(e) is the sign function, those with ∧ superscript are estimated values, and those without ∧ sign are actual values.

[0016] Optionally, also include:

[0017] Obtaining the sliding mode observer according to the vehicle two-degree-of-freedom dynamics model, the sliding surface model and the gain coefficient model;

[0018] Among them, the two-degree-of-freedom dynamic model of the vehicle is:

[0019]

[0020] The sliding surface model is:

[0021]

[0022] The gain coefficient model is:

[0023]

[0024] Where, m is the vehicle mass; a y is the lateral acceleration of the vehicle; I zz is the vehicle body yaw moment of inertia; is the vehicle yaw angular velocity; l f is the distance from the vehicle's center of mass to the front axle; l r F is the distance from the vehicle's center of mass to the rear axle; yf is the lateral force on the front axle of the vehicle; Fyr is the lateral force on the rear axle of the vehicle; ρ * is the unknown gain coefficient of the sliding mode observer;

[0025] The error state vector of the sliding mode observer design model is defined as the difference between the system state vector and the observation vector, and the observation error differential equation is obtained;

[0026] The error state vector is as follows:

[0027]

[0028] The observation error differential equation is as follows:

[0029]

[0030] Among them, the superscript ~ indicates the error value

[0031] Select the gain coefficient ρ of the sliding mode observer equation * , so that the error state vector asymptotically approaches zero.

[0032] Optionally, also include:

[0033] Will Replace the sign function of sgn(e) in the sliding mode observer.

[0034] Optionally, the functional relationship between the front axle lateral force and the kingpin torque is:

[0035] M kp =F y r τ cosτcosσcosδ k +M z cosτcosσ+G f n σ cosτsinσcosσsinδ k ;

[0036] When the tire's cornering characteristics are in the linear range, M z =F y n p ;

[0037] M kp is the kingpin moment; F y =F yf is the lateral force on the front axle of the vehicle, r τ is the horizontal distance between the center of contact of the kingpin and the center of contact of the tire, τ is the castor angle of the front wheel of the vehicle, σ is the kingpin inclination angle of the front wheel of the vehicle, δ k is the front wheel kingpin angle of the vehicle, M z is the self-aligning torque of the front wheel of the vehicle, G fis the vehicle front axle load, n σ is the distance between the front wheel kingpin and the wheel center in the vehicle body length direction, n p Pneumatic trail of the tire.

[0038] Optionally, obtaining the estimated system friction torque based on the functional relationship between the rack force and the system friction torque includes:

[0039] With the preset rack force as the horizontal axis and the system friction torque budget value as the vertical axis, a discrete point diagram between the system friction torque budget value and the rack force is drawn; wherein, T f =T m i r -F rack r p , where T m The driving torque of the steering actuator motor, i r is the speed ratio of the reducer, r p is the pitch radius of the steering gear pinion, T f is the system friction torque budget value;

[0040] The above discrete point diagram is fitted to obtain the function model between the friction torque and the rack force of the system.

[0041] According to a second aspect of an embodiment of the present invention, there is provided a system friction torque estimation device, which is applied to a wire-controlled steering system, wherein the wire-controlled steering system comprises a steering execution module, wherein the steering execution module comprises a steering gear, a steering tie rod, a steering knuckle arm, a kingpin, and a tire; the steering gear comprises a pinion and a rack meshed with the pinion, wherein the rack is hinged to the steering tie rod, wherein the other end of the steering tie rod is hinged to the steering knuckle arm, wherein the steering knuckle arm is fixedly connected to the tire, and wherein the rack pulls the steering tie rod to reciprocate, thereby driving the steering knuckle arm and the tire to rotate around the kingpin;

[0042] The estimation device comprises:

[0043] An observation module, which obtains an estimated value of the front axle lateral force through a sliding mode observer;

[0044] The first acquisition module acquires the front axle lateral force and the kingpin moment M kp The functional relationship between

[0045] Estimation module, based on M kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r armis the length of the steering knuckle arm;

[0046] The second acquisition module obtains the estimated system friction torque based on the estimated rack force and the function model of the system friction torque-rack force.

[0047] According to a third aspect of an embodiment of the present invention, there is provided a wire control steering system, comprising a processor, wherein the processor is configured to execute the steps of any one of the methods described above.

[0048] According to a fourth aspect of an embodiment of the present invention, there is provided a vehicle, including a steer-by-wire system as described in any one of the above.

[0049] According to a fifth aspect of an embodiment of the present invention, there is provided a computer-readable storage medium on which computer instructions are stored, and when the instructions are executed by a processor, the steps of any of the methods described above are implemented.

[0050] The technical solution provided by the embodiments of the present invention may have the following beneficial effects:

[0051] It can be seen from the above embodiments that the sliding mode observer established by the present invention and the functional relationship between the front axle lateral force and the kingpin torque can observe the steering rack force in real time. Further combined with the rack force-system friction torque function model established by the present invention, the system friction torque of the steering execution module can be estimated in real time, which is beneficial to real-time compensation of the system friction torque during the wire-controlled steering process and optimization of the wire-controlled steering control.

[0052] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0054] Figure 1 The diagram is a schematic diagram showing the positional relationship among a rack, a steering tie rod, a steering knuckle arm and a kingpin of a steering execution module according to an exemplary embodiment.

[0055] Figure 2 The figure is a flow chart showing a method for estimating a friction torque of a system according to an exemplary embodiment.

[0056] Figure 3 The figure is a schematic diagram of a two-degree-of-freedom model of a vehicle according to an exemplary embodiment.

[0057] Figure 4 It is a comparison diagram of the estimated curve and the simulated curve of the lateral acceleration, yaw angle velocity, front axle lateral force and rear axle lateral force in the present invention.

[0058] Figure 5 The figure is a schematic diagram of the space between a front wheel and a kingpin according to an exemplary embodiment.

[0059] Figure 6 It is a comparison diagram of the estimated curve and the simulation curve of the rack force in the present invention.

[0060] Figure 7 It is a comparison diagram of the estimated curve and the simulated curve of the friction torque of the system in the present invention.

[0061] Figure 8 The figure is a block diagram of a device for estimating system friction torque according to an exemplary embodiment. DETAILED DESCRIPTION

[0062] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0063] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0064] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0065] With the rapid development of intelligent automobile technology, the technology of wire-controlled chassis has received more and more attention, and the technology of wire-controlled steering is one of the key technologies of wire-controlled chassis. The wire-controlled steering system usually includes a steering execution module, which can be used to drive the wheel to steer according to the received control signal. Figure 1As shown, the steering execution module includes a steering gear, a steering tie rod 1, a steering knuckle arm 2, a kingpin 3 and a tire 4; the steering gear includes a pinion 5 and a rack 6 meshing with the pinion 5, the rack 6 is hinged to the steering tie rod 1, the other end of the steering tie rod 1 is hinged to the steering knuckle arm 2, the steering knuckle arm 2 is fixedly connected to the tire 4, and the rack 6 pulls the steering tie rod 1 to move back and forth to drive the steering knuckle arm 2 and the tire 4 to rotate around the kingpin 3.

[0066] The applicant discovered that it is because the steering execution module has a meshing mechanism between the pinion and the rack, and the rack is connected to the steering tie rod, so the system friction torque shows an obvious load-dependent effect, that is, the system friction torque increases with the increase of the rack force of the steering execution module, and decreases with the decrease of the rack force of the steering execution module. Based on this, the applicant provides a method to estimate the system friction torque by using the rack force, thereby providing a feasible method for improving the control performance of the steering angle closed-loop control system.

[0067] like Figure 2 As shown, the method for estimating the friction torque of the system is applied to a wire-controlled steering system, and the method for estimating the friction torque of the system includes the following steps:

[0068] In step 201, an estimated value of the front axle lateral force is obtained by observing with a sliding mode observer.

[0069] In this embodiment, the estimated value of the front axle lateral force can be obtained according to the following sliding mode observer observation, wherein the observation state vector of the sliding mode observer is defined as: The output vector is

[0070] The sliding mode observer is as follows:

[0071]

[0072] Among them, I zz is the vehicle body yaw moment of inertia, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, F yf is the lateral force on the front axle of the vehicle, F yr is the lateral force on the rear axle of the vehicle, is the vehicle yaw rate, a y is the vehicle lateral acceleration, ρ1, ρ2, ρ3, ρ4, ρ5 and ρ6 are all gain constants, sgn(·) is the sign function, and those with ^ superscripts represent the estimated values ​​of the corresponding parameters, and those without ^ superscripts represent the actual values ​​of the corresponding parameters.

[0073] The sliding mode observer may be designed by obtaining the sliding mode observer based on a two-degree-of-freedom dynamics model of the vehicle, a sliding surface model, and a gain coefficient model.

[0074] Among them, Figure 3 As shown, the X-axis and Y-axis represent the global coordinate system, the X-axis and Y-axis represent the body coordinate system, the center of mass of the vehicle is taken as the coordinate origin o, the length direction of the vehicle body is the X-axis direction, the width direction of the vehicle body is the Y-axis direction, and the coordinate system xoy is established to obtain the vehicle two-degree-of-freedom model as follows:

[0075] ma y =F yf +F yr

[0076]

[0077] Among them, I zz is the vehicle body yaw moment of inertia, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, F yf is the lateral force on the front axle of the vehicle, F yr is the lateral force on the rear axle of the vehicle, is the vehicle yaw rate, a y is the lateral acceleration of the vehicle.

[0078] Further expand the dimension of the vehicle's two-degree-of-freedom dynamics model and add the lateral force F on the front axle of the vehicle yf and the lateral force F on the rear axle of the vehicle yr is the quasi-steady-state evolution equation of the vehicle:

[0079]

[0080] It should be noted that the lateral force F on the front axle of the vehicle is defined as yf and the lateral force F on the rear axle of the vehicle yr The derivative of is zero does not mean that the lateral force on the front axle of the vehicle and the lateral force on the rear axle of the vehicle remain unchanged, but only that the lateral force on the front axle of the vehicle and the lateral force on the rear axle of the vehicle are regarded as state quantities of the vehicle system, that is, variables.

[0081] The expanded two-degree-of-freedom dynamic model of the vehicle can be rewritten in the form of state space equations:

[0082]

[0083] y s =Cx s

[0084] In the formula, x sis the system state vector, A is the system state matrix, B is the system input matrix, and u is the system input vector.

[0085] Due to a y =(F yf +F yr ) / m, so the expanded vehicle two-degree-of-freedom dynamic model is obtained:

[0086]

[0087] The sliding surface model is defined as:

[0088]

[0089] The gain coefficient model is defined as:

[0090]

[0091] Then, according to the expanded vehicle two-degree-of-freedom model, sliding surface model, gain coefficient model and sign function, a sliding mode observer is obtained.

[0092] Among them, ρ in the sliding mode observer * is an unknown constant. In order to solve the gain coefficient model and prove that the observed value in the sliding mode observer in the present invention is basically equal to the actual value, the error state vector of the sliding mode observer design model can be further defined as the difference between the system state vector and the observation vector, and the observation error differential equation is obtained; the gain coefficient of the sliding mode observer equation is selected to make the error state vector asymptotically approach zero.

[0093] Among them, the error state vector is as follows;

[0094]

[0095] The observation error differential equation is as follows:

[0096]

[0097] Among them, the superscript ~ indicates the error value of the corresponding parameter.

[0098] The error state vector asymptotically approaches zero, which proves that the sliding mode observer in the present invention is a convergent function, and the observed value obtained based on the sliding mode observer is substantially equal to the actual value.

[0099] Furthermore, in order to suppress the "chattering" problem caused by the value of the sign function sgn(e) in the sliding mode observer, the approach function can be used Replace the sign function of sgn(e) in the sliding mode observer. Wherein, ε is the shaping parameter of the sigmoid function, the sign is positive, the shaping parameter is a constant, and in the process of proving the convergence and stability of the sliding mode observer, the gain coefficient can be selected at the same time to ensure that the error state vector asymptotically approaches zero.

[0100] In some embodiments, by proving the convergence of the sliding mode observer, it is found that the various parameters and shaping parameters in the gain coefficient model can be taken according to the parameters in the following table:

[0101]

[0102] Table 1

[0103] The sliding mode observer based on the above constants can complete the online estimation of the state vector of the vehicle system state and obtain the estimated value of the state vector.

[0104] Based on the above constants, the estimated value obtained by the sliding mode observer is compared with the simulation value obtained by software simulation, such as Figure 4 As shown, the simulated lateral acceleration change curve is basically consistent with the estimated lateral acceleration change curve based on the sliding mode observer, wherein the lateral acceleration change curve is the change curve of the lateral acceleration in the aforementioned embodiment, and the simulated yaw angular velocity change curve is basically consistent with the estimated yaw angular velocity change curve based on the sliding mode observer, the simulated front wheel lateral force change curve is basically consistent with the estimated front wheel lateral force change curve based on the sliding mode observer, and the simulated rear wheel lateral force change curve is basically consistent with the estimated rear wheel lateral force change curve based on the sliding mode observer. It can be seen that the experiment proves that the estimated value obtained by the sliding mode observer in the present invention is basically equivalent to the actual value and the simulation value, and the front wheel lateral force can be obtained based on the sliding mode observer.

[0105] In step 102, the functional relationship between the front axle lateral force and the kingpin torque is obtained.

[0106] In this embodiment, combined Figure 1 and Figure 5 As shown in the figure, the functional relationship between the front axle lateral force and the kingpin moment is:

[0107] M kp =F y r τ cosτcosσcosδ k +M z cosτcosσ+G f n σ cosτsinσcosσsinδ k

[0108] When the tire's cornering characteristics are in the linear range, the following conditions are met:

[0109] Mz=Fynp

[0110] Among them, M kp is the kingpin moment; F y =F yf is the lateral force on the front axle of the vehicle; r τ is the horizontal distance between the center of contact of the kingpin and the center of contact of the tire, τ is the castor angle of the front wheel of the vehicle, σ is the kingpin inclination angle of the front wheel of the vehicle, δ k is the front wheel kingpin angle of the vehicle, M z is the self-aligning torque of the front wheel of the vehicle, G f is the vehicle front axle load, n σ is the distance between the front wheel kingpin and the wheel center in the vehicle body length direction, n σ Pneumatic trail of the tire.

[0111] In step 203, based on M kp =F rack r arm , the functional relationship between the front axle lateral force and the kingpin torque and the estimated value of the front axle lateral force, to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm.

[0112] In this embodiment, based on the front axle lateral force observed by the synovial observer in the aforementioned embodiment and the functional relationship between the front axle lateral force and the kingpin torque, the estimated rack force curve is compared with the simulated rack force curve obtained by simulating the steer-by-wire system, as shown in FIG. Figure 6 As shown, the estimated rack force curve and the simulated rack force curve are basically consistent, which shows that the rack force estimated by the present invention can be considered to be basically equal to the actual rack force.

[0113] In step 204, an estimated system friction torque is obtained based on the estimated rack force and a function model of the system friction torque-rack force.

[0114] In this embodiment, the function model between the friction torque and rack force of the system can be first obtained based on the wire steering test platform. In some embodiments, on the wire steering test platform, the input voltage of the road resistance torque simulation motor is changed to simulate different levels of road resistance torque, thereby changing the load level of the steering system; the steering execution motor is controlled to make the steering execution module of the wire steering system reciprocate at a uniform speed and full stroke of the rack; the driving torque signal T of the steering execution motor is recorded. m , rack force signal F measured by the bidirectional tension pressure sensor rack 、Rack and pinion steering gear pinion angle signal θ p; Calculate the system friction torque of the wire control steering system, using the steering actuator motor drive torque as the system input T m i r , the torque converted from the rack force to the pinion shaft is taken as the system output F rack r p , the difference in system loss between input and output is used as the system friction torque, that is, T f =T m i r -F rack r p , where T m The driving torque of the steering actuator motor, i r is the speed ratio of the reducer, r p is the pitch radius of the steering gear pinion, T f The preset rack force is used as the horizontal axis, the system friction torque budget value is used as the vertical axis, and a discrete point diagram between the system friction torque budget value and the rack force is drawn; the above discrete point diagram is fitted to obtain a function model between the system friction torque and the rack force.

[0115] like Figure 7 As shown, based on the steer-by-wire test platform, the system friction torque obtained based on the estimated rack force is as follows: Figure 7 As shown in the red mark, Figure 7 The blue line in the middle is the friction torque obtained by simulation based on the friction torque model and an error range of 5%. It can be seen that the system friction torque estimated in the present invention is basically consistent with the simulation data.

[0116] Based on the technical solution of the present invention, the present invention takes into account the influence of the steering load of the steering execution module of the wire-controlled steering system on the friction torque, establishes a rack force-system friction torque function model through a wire-controlled steering test platform, and quantitatively describes the relationship between the system friction torque of the steering execution module and the rack force. Further combined with the sliding mode observer established by the present invention and the functional relationship between the front axle lateral force and the kingpin torque, the steering rack force can be observed in real time. Combined with the rack force-system friction torque function model, the system friction torque of the steering execution module can be estimated in real time, which is beneficial to real-time compensation of the system friction torque during the wire-controlled steering process and optimization of the wire-controlled steering control.

[0117] Corresponding to the above-mentioned embodiment of the estimation method, the present invention also provides an embodiment of the estimation device.

[0118] Figure 8 is a block diagram of an estimation device according to an exemplary embodiment. Figure 8, the estimation device is applied to a wire-controlled steering system, the wire-controlled steering system includes a steering execution module, the execution module includes a steering gear, a steering tie rod, a steering knuckle arm, a kingpin and a tire; the steering gear includes a pinion and a rack meshing with the pinion, the rack is hinged to the steering tie rod, the other end of the steering tie rod is hinged to the steering knuckle arm, the steering knuckle arm is fixedly connected to the tire, the rack pulls the steering tie rod to move back and forth to drive the steering knuckle arm and the tire to rotate around the kingpin; the estimation device includes an observation module 81, a first acquisition module 82, an estimation module 83 and a second acquisition module 84, wherein:

[0119] An observation module 81 is configured to obtain an estimated value of the front axle lateral force by observing the front axle lateral force through a sliding mode observer;

[0120] The first acquisition module 82 acquires the front axle lateral force and the kingpin moment M kp The functional relationship between

[0121] Estimation module 83, based on M kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm;

[0122] The second acquisition module 84 obtains the estimated system friction torque based on the estimated rack force and the function model of the system friction torque-rack force.

[0123] The various implementations of the estimation device can refer to the implementations of the aforementioned estimation method and will not be described in detail here.

[0124] The present invention also provides a wire-controlled steering system, which includes a steering execution module and a processor, wherein the execution module includes a steering gear, a steering tie rod, a steering knuckle arm, a kingpin, and a tire; the steering gear includes a pinion and a rack meshing with the pinion, the rack is hinged to the steering tie rod, the other end of the steering tie rod is hinged to the steering knuckle arm, the steering knuckle arm is fixedly connected to the tire, and the rack pulls the steering tie rod to move back and forth to drive the steering knuckle arm and the tire to rotate around the kingpin; the processor is configured to execute the steps described in any of the aforementioned methods. For example, the processor is used to execute the estimated value of the front axle lateral force obtained by observing the sliding mode observer; obtain the front axle lateral force and the kingpin torque M kp The functional relationship between kp =F rack r arm, the front axle lateral force and the kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm; based on the estimated rack force, the system friction torque-rack force function model, the estimated system friction torque is obtained.

[0125] The present invention also provides a vehicle, which includes the steer-by-wire system described in any one of the above embodiments. The vehicle includes a memory and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by one or more processors. The one or more programs include instructions for performing the following operations: obtaining an estimated value of the front axle lateral force through a sliding mode observer; obtaining the front axle lateral force and the kingpin moment M kp The functional relationship between kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The functional relationship between and the estimated value of the front axle lateral force is used to obtain the estimated rack force, where F rack is the rack force, r arm is the length of the steering knuckle arm; based on the estimated rack force, the system friction torque-rack force function model, the estimated system friction torque is obtained.

[0126] In an exemplary embodiment, a non-transitory computer-readable storage medium including instructions is also provided, such as a memory including instructions, and the instructions can be executed by a processor of the device to perform the above method. For example, the non-transitory computer-readable storage medium can be a ROM, a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, etc.

[0127] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the disclosure disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The description and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0128] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for estimating system friction torque, characterized in that: Applied to a wire-controlled steering system, the wire-controlled steering system includes a steering execution module, the steering execution module includes a steering gear, a steering tie rod, a steering knuckle arm, a kingpin and a tire; the steering gear includes a pinion and a rack meshing with the pinion, the rack is hinged to the steering tie rod, the other end of the steering tie rod is hinged to the steering knuckle arm, the steering knuckle arm is fixedly connected to the tire, the rack pulls the steering tie rod to reciprocate, so as to drive the steering knuckle arm and the tire to rotate around the kingpin; The estimation method includes: The estimated value of the lateral force on the front axle is obtained by observing the sliding mode observer; Obtain the front axle lateral force and kingpin moment M kp The functional relationship between Based on M kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The estimated rack force is obtained by the functional relationship between and the estimated value of the front axle lateral force, where F rack is the rack force, r arm is the length of the steering knuckle arm; Based on the estimated rack force, the system friction torque-rack force function model, an estimated system friction torque is obtained; The obtaining of the estimated value of the front axle lateral force by observing the sliding mode observer includes: The observation state vector of the sliding mode observer is defined as The output vector is The estimated value of the front axle lateral force is obtained according to the sliding mode observer observation, Among them, I zz is the vehicle body yaw moment of inertia, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, F yf is the lateral force on the front axle of the vehicle, F yr is the lateral force on the rear axle of the vehicle, is the vehicle yaw rate, a y is the actual value of the vehicle lateral acceleration, ρ1, ρ2, ρ3, ρ4, ρ5 and ρ6 are all gain constants, sgn(e) is the sign function, those with ∧ superscript are estimated values, and those without ∧ sign are actual values; The functional relationship between the front axle lateral force and the kingpin moment is: M kp =F y r τ cosτcosσcosδ k +M z cosτcosσ+G f n σ cosτsinσcosσsinδ k ; When the tire's cornering characteristics are in the linear range, M z =F y n p ; M kp is the kingpin moment; F y =F yf is the lateral force on the front axle of the vehicle, r τ is the horizontal distance between the center of contact of the kingpin and the center of contact of the tire, τ is the castor angle of the front wheel of the vehicle, σ is the kingpin inclination angle of the front wheel of the vehicle, δ k is the front wheel kingpin angle of the vehicle, M z is the self-aligning torque of the front wheel of the vehicle, G f is the vehicle front axle load, n σ is the distance between the front wheel kingpin and the wheel center in the vehicle body length direction, n p Pneumatic trail of the tire.

2. The estimation method according to claim 1, characterized in that: Also includes: Obtaining the sliding mode observer according to the vehicle two-degree-of-freedom dynamics model, the sliding surface model and the gain coefficient model; Among them, the two-degree-of-freedom dynamic model of the vehicle is: The sliding surface model is: The gain coefficient model is: Where, m is the vehicle mass; a y is the lateral acceleration of the vehicle; I zz is the vehicle body yaw moment of inertia; is the vehicle yaw angular velocity; l f is the distance from the vehicle's center of mass to the front axle; l r F is the distance from the vehicle's center of mass to the rear axle; yf is the lateral force on the front axle of the vehicle; F yr is the lateral force on the rear axle of the vehicle; ρ * is the unknown gain coefficient of the sliding mode observer; The error state vector of the sliding mode observer design model is defined as the difference between the system state vector and the observation vector, and the observation error differential equation is obtained; The error state vector is as follows: The observation error differential equation is as follows: Among them, the superscript ~ indicates the error value Select the gain coefficient ρ of the sliding mode observer equation * , so that the error state vector asymptotically approaches zero.

3. The estimation method according to claim 1, characterized in that: Also includes: Will Replace the sign function of sgn(e) in the sliding mode observer.

4. The estimation method according to claim 1, characterized in that: Based on the functional relationship between the rack force and the system friction torque, an estimated system friction torque is obtained, including: With the preset rack force as the horizontal axis and the system friction torque budget value as the vertical axis, a discrete point diagram between the system friction torque budget value and the rack force is drawn; wherein, T f =T m i r -F rack r p , where T m The driving torque of the steering actuator motor, i r is the speed ratio of the reducer, r p is the pitch radius of the steering gear pinion, T f is the system friction torque budget value; The above discrete point diagram is fitted to obtain the function model between the friction torque and the rack force of the system.

5. A device for estimating system friction torque, characterized in that: Applied to a wire-controlled steering system, the wire-controlled steering system includes a steering execution module, the steering execution module includes a steering gear, a steering tie rod, a steering knuckle arm, a kingpin and a tire; the steering gear includes a pinion and a rack meshing with the pinion, the rack is hinged to the steering tie rod, the other end of the steering tie rod is hinged to the steering knuckle arm, the steering knuckle arm is fixedly connected to the tire, the rack pulls the steering tie rod to reciprocate, so as to drive the steering knuckle arm and the tire to rotate around the kingpin; The estimation device comprises: An observation module obtains an estimated value of the lateral force on the front axle through observation by a sliding mode observer; The first acquisition module acquires the front axle lateral force and the kingpin moment M kp The functional relationship between Estimation module, based on M kp =F rack r arm , the front axle lateral force and the kingpin moment M kp The estimated rack force is obtained by the functional relationship between and the estimated value of the front axle lateral force, where F rack is the rack force, r arm is the length of the steering knuckle arm; A second acquisition module obtains an estimated system friction torque based on the estimated rack force and a function model of the system friction torque-rack force; The obtaining of the estimated value of the front axle lateral force by observing the sliding mode observer includes: The observation state vector of the sliding mode observer is defined as The output vector is The estimated value of the front axle lateral force is obtained according to the sliding mode observer observation, Among them, I zz is the vehicle body yaw moment of inertia, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, F yf is the lateral force on the front axle of the vehicle, F yr is the lateral force on the rear axle of the vehicle, is the vehicle yaw rate, a y is the actual value of the vehicle lateral acceleration, ρ1, ρ2, ρ3, ρ4, ρ5 and ρ6 are all gain constants, sgn(e) is the sign function, those with ∧ superscript are estimated values, and those without ∧ sign are actual values; The functional relationship between the front axle lateral force and the kingpin moment is: M kp =F y r τ cosτcosσcosδ k +M z cosτcosσ+G f n σ cosτsinσcosσsinδ k ; When the tire's cornering characteristics are in the linear range, M z =F y n p ; M kp is the kingpin moment; F y =F yf is the lateral force on the front axle of the vehicle, r τ is the horizontal distance between the center of contact of the kingpin and the center of contact of the tire, τ is the castor angle of the front wheel of the vehicle, σ is the kingpin inclination angle of the front wheel of the vehicle, δ k is the front wheel kingpin angle of the vehicle, M z is the self-aligning torque of the front wheel of the vehicle, G f is the vehicle front axle load, n σ is the distance between the front wheel kingpin and the wheel center in the vehicle body length direction, n p Pneumatic trail of the tire.

6. A steer-by-wire system, characterized in that: The method comprises a processor configured to execute the steps of the method according to any one of claims 1 to 4.

7. A vehicle, characterized in that: Comprising the steer-by-wire system as claimed in claim 6.

8. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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