Steer-by-wire automobile stability control method, device and equipment considering time delay

Abstract

The invention discloses a steer-by-wire automobile stability control method, device and equipment considering time delay. The method comprises the steps that a steer-by-wire system model is established; establishing a non-linear time delay model existing in steer-by-wire; based on the steer-by-wire system model, performing linearization processing on the nonlinear time lag model to obtain a transfer function of a steer-by-wire actuating mechanism containing time lag; and based on the transfer function of the steer-by-wire executing mechanism containing the time delay, stability control is conducted on the automobile. Therefore, aiming at the delay problem existing in a steer-by-wire system, compared with passive control based on a wave variable theory and a dissipation theory, the operability is reduced, and the tracking precision cannot be ensured; according to the method, on the premise that the robust stability of the system is guaranteed, the tracking capacity, the anti-interference capacity and the like of the system under the condition of random delay can be guaranteed at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile stability control, and in particular to a method, device and equipment for controlling the stability of a steer-by-wire automobile taking into account time lag. Background Art

[0002] With the accelerated advancement of the research and development and industrialization of autonomous driving technology, my country's "Medium- and Long-Term Development Plan for the Automobile Industry" clearly states that highly and fully autonomous driving vehicles will be commercialized by 2025. In this context, the wire-controlled steering system is becoming the core development direction of intelligent driving steering systems due to its fast response characteristics, flexibly designed angle / force transmission ratio and high integration advantages.

[0003] This technical system replaces the traditional mechanical transmission structure with electronic signal control, and is mainly composed of three functional modules: the road sense feedback module integrates the road sense motor, deceleration device and torque angle sensor through the steering wheel assembly, and converts the torque command output by the controller into driving tactile feedback in real time; the steering execution module is driven by the steering motor to drive the rack and pinion mechanism, and cooperates with the tension and pressure sensor to achieve precise tracking and control of the front wheel angle of the car; the electronic control unit serves as the central system to coordinate the operation of each module. This mechatronic design not only optimizes the system layout space, but also significantly improves the control response speed and integrated control capabilities, providing key technical support for autonomous driving.

[0004] However, the time lag problem in the system has become the main bottleneck restricting its performance improvement. The sources of time lag include physical factors such as gap friction in the mechanical execution link, as well as communication delays in the transmission of electronic signals. Studies have shown that when the network delay exceeds 50ms, the conventional PI control strategy will cause system instability; if the probability of communication cycle delay exceeds 10%, it will cause functional failure. The specific impact is reflected in two aspects: first, the delay in road feel feedback will cause the driver's perception to lag behind the actual road conditions, directly affecting the timeliness of the steering operation; second, the delay in vehicle state feedback will lead to a decrease in the accuracy of preview control and increase the risk of driving trajectory deviation. These time lag effects not only prolong the system adjustment time and increase the control overshoot, but in severe cases will induce system oscillation or even loss of control.

[0005] In view of the time-delay characteristics, current research focuses on developing control algorithms with adaptive compensation capabilities, which can improve system robustness and dynamic response quality by identifying delay parameters in real time and dynamically adjusting control strategies. This has become a key technical direction to break through the performance bottleneck of the wire-controlled steering system. Summary of the invention

[0006] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a steer-by-wire vehicle stability control method, device and equipment taking into account time lag, so as to achieve linear approximation of nonlinear time lag and build a rack-and-pinion steer-by-wire actuator model.

[0007] In order to achieve the above object, the technical solution of the embodiment of the present invention is:

[0008] In a first aspect, the present invention provides a steer-by-wire vehicle stability control method taking into account time lag, the method comprising:

[0009] S1, establishing a steer-by-wire system model; the steer-by-wire system model is:

[0010]

[0011] In the formula, G i (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f (s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k 0 is the proportionality coefficient between the front wheel steering angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio;

[0012] S2, establishing a nonlinear time-lag model in the steer-by-wire process; the nonlinear time-lag model is:

[0013]

[0014] In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; i sm (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c(s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator;

[0015] S3, based on the steer-by-wire system model, linearize the nonlinear time-delay model to obtain a transfer function of the steer-by-wire actuator with time delay: M(s)=G i (s)*G d (s)(3);

[0016] S4, performing stability control on the vehicle based on the transfer function of the wire-controlled steer actuator with time lag.

[0017] In a second aspect, the present invention provides a steer-by-wire vehicle stability control device taking into account time lag, the device comprising:

[0018] Establishing a module for establishing a wire-controlled steering system model; the wire-controlled steering system model is:

[0019]

[0020] In the formula, G i (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f (s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k 0 is the proportionality coefficient between the front wheel steering angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio;

[0021] The establishment module is also used to establish a nonlinear time-lag model in the wire control steering; the nonlinear time-lag model is:

[0022] In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; ism (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c (s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator;

[0023] A processing module is used to linearize the nonlinear time-delay model based on the wire-controlled steering system model to obtain a transfer function of the wire-controlled steering actuator with time delay: M(s)=G i (s)*G d (s)(3);

[0024] The control module is used for performing stability control on the vehicle based on the transfer function of the wire control steering actuator with time lag.

[0025] In some embodiments, the establishment module is further used to use equations (4) and (5) to respectively determine the output matrices of the steering actuator and the reducer; T m =K t *i(4);T g =N*T m =N*K t *i(5); where T m is the motor shaft output torque, T g The output torque of the reducer;

[0026] According to the connection characteristics between the reducer and the gear rack, the force analysis of the gear rack is carried out, and T g =F*r p (6);

[0027] Considering Coulomb friction and steering return force, and according to Newton's second law F = m*a, the force of the gear rack can be obtained: F = m r *a+B r *v+F c +F z (7); where F c Coulomb force is used as interference input; F z is the return force; a is the acceleration of the gear rack; v is the speed of the gear rack;

[0028] You can get: In the formula, is the second-order derivative of rack displacement; is the first-order derivative of the rack displacement;

[0029] And by F z =ρ f *tanh(δ) / L s ; tanh(δ)=δ(9); where, ξ f is the Coulomb friction torque constant; δ is the front wheel turning angle of the car; is the first-order derivative of the front wheel steering angle of the car; is the sign function; h(δ) is the hyperbolic tangent function;

[0030] Based on formula (8) and formula (9), we can get:

[0031] After performing Laplace transformation on equation (10), we can get:

[0032]

[0033] Based on the relationship between wheel angle and rack displacement We can get:

[0034]

[0035] After processing formula (12), we can get:

[0036]

[0037] δ(s)=G i (s)*i(s)+G f (s)*F c (s)(14);

[0038] The wire control steering system model is obtained:

[0039]

[0040] In some embodiments, the establishment module is further used to determine the ideal front wheel angle of the vehicle based on the obtained ideal steering wheel angle and the rack displacement; determine the cross-correlation function between the ideal steering wheel angle and the ideal front wheel angle of the vehicle; the cross-correlation function is expressed as: R wf =R[δ sw (t)δ f (t+T h )](15); the cross-correlation between the two is calculated as:

[0041] In the formula, R wf is the cross-correlation function between the steering wheel angle and the front wheel angle of the car; R is the correlation coefficient between the steering wheel angle and the front wheel angle of the car; δ sw is the ideal steering wheel angle; δ sw (t) is the ideal steering wheel angle at time t; t is the current time; T h is the delay time when the mutual correlation coefficient is maximum; δ fis the ideal front wheel turning angle of the car; μ sw and μ f is the mean of the ideal steering wheel angle and the ideal front wheel angle of the car, σ sw and σ f is the standard deviation of the ideal steering wheel angle and the ideal front wheel angle of the car;

[0042] Based on the ideal steering wheel angle and the ideal front wheel angle of the vehicle, the time-delay steering wheel angle, the time-delay front wheel angle of the vehicle and the current after the steering actuator has a time lag are determined; expressed as:

[0043] δ swd (t) = δ sw (t-τ); δ fd (t) = δ f (t-τ);i sm (t) = i c (t-τ); (17)

[0044] In the formula, δ swd is the time-delay steering wheel angle; δ swd (t) is the steering wheel angle after the time lag at time t; δ fd is the front wheel steering angle of the time-delayed vehicle; δ fd (t) is the front wheel turning angle of the vehicle at time t; i sm (t) is the control current of the steering actuator motor at time t;

[0045] The transfer function that determines the current is:

[0046] In some embodiments, the processing module is further used to perform time lag approximation on equation (2) using the following method: 1) Taylor approximation is:

[0047]

[0048] 2) Pade approximation is:

[0049]

[0050] 3) The full pole approximation is:

[0051]

[0052] The nonlinear time-delay model is linearized using first-order full poles, and the following is obtained:

[0053]

[0054] Based on equations (1) and (21), the transfer function of the wire-controlled steering actuator with time lag is obtained as follows: M(s) = G i(s)*G d (s)(3).

[0055] In a third aspect, an embodiment of the present invention provides an electronic device, comprising: a memory for storing executable instructions; and a processor for implementing the above-mentioned steer-by-wire vehicle stability control method taking into account time lag when executing the executable instructions stored in the memory.

[0056] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium storing executable instructions for causing a processor to execute the executable instructions to implement the above-mentioned steer-by-wire vehicle stability control method taking into account time delay.

[0057] The invention provides a method, device and storage medium for controlling the stability of a steer-by-wire automobile considering time delay. First, a steer-by-wire system model is established; a nonlinear time delay model existing in the steer-by-wire is established; secondly, based on the steer-by-wire system model, the nonlinear time delay model is linearized to obtain a transfer function of a steer-by-wire actuator containing time delay; finally, based on the transfer function of the steer-by-wire actuator containing time delay, the automobile is controlled for stability. In this way, the invention addresses the delay problem existing in the steer-by-wire system. Compared with the passive control based on the wave variable theory and the dissipation theory, which causes the operability to be reduced and the tracking accuracy cannot be guaranteed, and other current control limitations such as overshoot and instability caused by the traditional PI control, the invention can ensure the tracking and anti-interference capabilities of the system under random delay conditions while ensuring the robust stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a schematic structural diagram of a steer-by-wire vehicle stability control system taking into account time lag provided by an embodiment of the present invention;

[0059] Figure 2 is a schematic flow chart of a steer-by-wire vehicle stability control method considering time lag provided by an embodiment of the present invention;

[0060] Figure 3 It is a schematic diagram of the process framework of the nonlinear time-delay linearization modeling method of the steer-by-wire system provided by an embodiment of the present invention;

[0061] Figure 4 It is a schematic diagram of the composition structure of a steer-by-wire vehicle stability control device taking into account time lag provided by an embodiment of the present invention;

[0062] Figure 5 The figure is a schematic diagram of the composition structure of a steer-by-wire vehicle stability control device taking into account time lag provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings. The described embodiments should not be regarded as limiting the present invention. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0064] In the following description, reference is made to "some embodiments," which describe a subset of all possible embodiments, but it is understood that "some embodiments" may be the same subset or different subsets of all possible embodiments, and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the present invention have the same meaning as commonly understood by those skilled in the art to which the embodiments of the present invention pertain. The terms used in the embodiments of the present invention are for the purpose of describing the embodiments of the present invention only and are not intended to limit the present invention.

[0065] The following describes an exemplary application of a time-delay-considered wire-controlled automobile stability control device according to an embodiment of the present invention. The time-delay-considered wire-controlled automobile stability control device provided by the embodiment of the present invention can be implemented as a terminal or a server. In one implementation, the time-delay-considered wire-controlled automobile stability control device provided by the embodiment of the present invention can be implemented as various types of terminals such as laptop computers, tablet computers, desktop computers, and mobile devices; in another implementation, the time-delay-considered wire-controlled automobile stability control device provided by the embodiment of the present invention can also be implemented as a server, wherein the server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, content distribution networks (CDN, Content Delivery Network), and big data and artificial intelligence platforms. The terminal and the server can be directly or indirectly connected by wired or wireless communication, which is not limited in the embodiment of the present invention. The following describes an exemplary application of the time-delay-considered wire-controlled automobile stability control device as a server.

[0066] See also Figure 1 , Figure 11 is a schematic diagram of the structure of a steer-by-wire vehicle stability control system 10 considering time lag provided by an embodiment of the present invention. In order to achieve the assessment of flood risk, an embodiment of the present invention can provide a steer-by-wire vehicle stability control platform considering time lag, and the steer-by-wire vehicle stability control platform considering time lag can be implemented as a steer-by-wire vehicle stability control application considering time lag. The steer-by-wire vehicle stability control system 100 considering time lag provided by an embodiment of the present invention includes a terminal 110, a network 120 and a server 130, wherein the server 130 is a server of the steer-by-wire vehicle stability control application considering time lag. The server 130 can constitute a steer-by-wire vehicle stability control device considering time lag according to an embodiment of the present invention. The terminal 110 is connected to the server 130 via the network 120, and the network 120 can be a wide area network or a local area network, or a combination of the two.

[0067] In some embodiments, please refer to Figure 1 When the stability control of the steer-by-wire vehicle is performed, the terminal 110 sends the received vehicle stability control task to the server 130 through the network 120. The server 130 establishes a steer-by-wire system model in response to the vehicle stability control task sent by the terminal 110; establishes a nonlinear time-delay model existing in the steer-by-wire; based on the steer-by-wire system model, the nonlinear time-delay model is linearized to obtain a transfer function of the steer-by-wire actuator with time delay; based on the transfer function of the steer-by-wire actuator with time delay, the vehicle is stability controlled to obtain a vehicle stability control result. After obtaining the vehicle stability control result, the server 130 sends the vehicle stability control result to the terminal 110 through the network 120.

[0068] The embodiment of the present invention provides a steer-by-wire vehicle stability control method taking into account time lag, see Figure 2 , Figure 2 is a flow chart of a method for controlling the stability of a steer-by-wire vehicle taking into account time lag provided by an embodiment of the present invention, which is combined with Figure 2 The steps shown are explained.

[0069] Step S1, establishing a steer-by-wire system model.

[0070] Here, the steer-by-wire system model is:

[0071]

[0072] In the formula, G i (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f(s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k 0 is the proportionality coefficient between the front wheel steering angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio.

[0073] Step S2, establishing a nonlinear time-lag model in steer-by-wire.

[0074] Here, the nonlinear time-lag model is:

[0075] In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; i sm (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c (s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator.

[0076] Step S3: Based on the steer-by-wire system model, linearize the nonlinear time-delay model to obtain a transfer function of the steer-by-wire actuator with time delay.

[0077] Here, the transfer function of the wire-controlled steering actuator with time lag is: M(s) = G i (s)*G d (s).

[0078] Step S4, performing stability control on the vehicle based on the transfer function of the steer-by-wire actuator with time lag.

[0079] The invention provides a method, device and storage medium for controlling the stability of a steer-by-wire automobile considering time delay. First, a steer-by-wire system model is established; a nonlinear time delay model existing in the steer-by-wire is established; secondly, based on the steer-by-wire system model, the nonlinear time delay model is linearized to obtain a transfer function of a steer-by-wire actuator containing time delay; finally, based on the transfer function of the steer-by-wire actuator containing time delay, the automobile is controlled for stability. In this way, the invention addresses the delay problem existing in the steer-by-wire system. Compared with the passive control based on the wave variable theory and the dissipation theory, which causes the operability to be reduced and the tracking accuracy cannot be guaranteed, and other current control limitations such as overshoot and instability caused by the traditional PI control, the invention can ensure the tracking and anti-interference capabilities of the system under random delay conditions while ensuring the robust stability of the system.

[0080] In some embodiments, the above step S1 can be implemented in the following ways:

[0081] Using equations (4) and (5), the output matrices of the steering actuator and the reducer are determined respectively; T m =K t *i(4);T g =N*T m =N*K t *i(5); where T m is the motor shaft output torque, T g The output torque of the reducer;

[0082] According to the connection characteristics between the reducer and the gear rack, the force analysis of the gear rack is carried out, and T g =F*r p (6);

[0083] Considering Coulomb friction and steering return force, and according to Newton's second law F = m*a, the force of the gear rack can be obtained: F = m r *a+B r *v+F c +F z (7); where F c Coulomb force is used as interference input; F z is the return force; a is the acceleration of the gear rack; v is the speed of the gear rack;

[0084] You can get: In the formula, is the second-order derivative of rack displacement; is the first-order derivative of the rack displacement;

[0085] And by F z =ρ f*tanh(δ) / L s ; tanh(δ)=δ(9); where, ξ f is the Coulomb friction torque constant; δ is the front wheel turning angle of the car; is the first-order derivative of the front wheel steering angle of the car; is the sign function; h(δ) is the hyperbolic tangent function;

[0086] Based on formula (8) and formula (9), we can get:

[0087] After performing Laplace transformation on equation (10), we can get:

[0088]

[0089] Based on the relationship between wheel angle and rack displacement We can get:

[0090]

[0091] After processing formula (12), we can get:

[0092]

[0093] δ(s)=G i (s)*i(s)+G f (s)*F c (s)(14);

[0094] The wire control steering system model is obtained:

[0095]

[0096] In some embodiments, the above step S2 can be implemented in the following manner:

[0097] Determining an ideal front wheel angle of the vehicle based on the obtained ideal steering wheel angle and the rack displacement;

[0098] Determine the cross-correlation function between the ideal steering wheel angle and the ideal front wheel angle of the vehicle; the cross-correlation function is expressed as: wf =R[δ sw (t)δ f (t+T h )](15);

[0099] The cross-correlation between the two is calculated as:

[0100] In the formula, R wfis the cross-correlation function between the steering wheel angle and the front wheel angle of the car; R is the correlation coefficient between the steering wheel angle and the front wheel angle of the car; δ sw is the ideal steering wheel angle; δ sw (t) is the ideal steering wheel angle at time t; t is the current time; T h is the delay time when the mutual correlation coefficient is maximum; δ f is the ideal front wheel turning angle of the car; μ sw and μ f is the mean of the ideal steering wheel angle and the ideal front wheel angle of the car, σ sw and σ f is the standard deviation of the ideal steering wheel angle and the ideal front wheel angle of the car;

[0101] Based on the ideal steering wheel angle and the ideal front wheel angle of the vehicle, the time-delay steering wheel angle, the time-delay front wheel angle of the vehicle and the current after the steering actuator has a time delay are determined, which is expressed as: δ swd (t) = δ sw (t-τ); δ fd (t) = δ f (t-τ);i sm (t) = i c (t-τ); (17);

[0102] In the formula, δ swd is the time-delay steering wheel angle; δ swd (t) is the steering wheel angle after the time lag at time t; δ fd is the front wheel steering angle of the time-delayed vehicle; δ fd (t) is the front wheel turning angle of the vehicle at time t; i sm (t) is the control current of the steering actuator motor at time t;

[0103] The transfer function that determines the current is:

[0104] In some embodiments, the above step S3 can be implemented in the following ways:

[0105] The following method is used to perform time-delay approximation on equation (2):

[0106] 1)Taylor approximation is:

[0107]

[0108] 2) Pade approximation is:

[0109]

[0110] 3) The full pole approximation is:

[0111]

[0112] The nonlinear time-delay model is linearized using first-order full poles, and the following is obtained:

[0113]

[0114] Based on equations (1) and (21), the transfer function of the wire-controlled steering actuator with time lag is obtained as follows: M(s) = G i (s)*G d (s)(3).

[0115] The following is an explanation of an exemplary application of the embodiments of the present application in a practical application scenario.

[0116] The control process of the present invention is as follows: the driver applies a steering command to the vehicle, the sensor receives the steering command, and the controller processes the signal and sends a control signal to the steering execution motor and the reducer to output torque, thereby driving the gear rack mechanism to move, and the front wheels of the vehicle are rotated through the steering trapezoid. In the control process, due to the network communication time delay in signal acquisition, processing and transmission and the friction and damping of mechanical structures such as gears and racks, the steering angle of the front wheels output by the vehicle lags behind the steering command issued by the driver, and excessive time delay may cause instability of the control system, so it is necessary to compensate for the time delay. The nonlinear time delay is linearized by the full pole approximation method, which can avoid the generation of right half plane zero points, and does not introduce non-minimum phase, ensuring the stability of the system, providing convenience for the subsequent time delay compensation and the solution of the lateral stability controller, and is more suitable for subsequent linearization control.

[0117] The present invention provides a nonlinear time-delay linearization modeling method for a wire-controlled steering system, the control method comprising the following steps:

[0118] Step 1) establishing a steer-by-wire system model and analyzing it;

[0119] Step 2) establishing a nonlinear time-delay model that may occur in the steer-by-wire process;

[0120] Step 3) Linearize the nonlinear model in step 2 and combine it with the steer-by-wire model in step 1.

[0121] Furthermore, the specific method of establishing the control method of the present invention is:

[0122] 1. The steer-by-wire system model in step 1) is:

[0123] First, let's focus on the motor part. The wire-controlled steering actuator motor (i.e., the wire-controlled steering actuator in the above embodiment) usually uses a DC motor or a permanent magnet synchronous motor, but its specific model has no effect on the modeling, so it can be simplified to a DC motor model. According to the structure and characteristics of the DC motor, the torque of the DC motor is proportional to the current, that is: T m =K t *i; where T m is the motor shaft output torque; K t is the torque constant; i is the input current of the wire-controlled steering actuator.

[0124] The steer-by-wire actuator directly controls the motor to generate torque by current. At this time, the electrical part is already controlled by the current loop, so it can be simplified to the torque output being proportional to the current. The torque generated by the motor is directly determined by the input current, and there is no need to consider the delay of the inductance. It is assumed that the current control is ideal, that is, the current can instantly reach a given value and there is no need to consider the dynamics of the motor, including the inertia and friction of the motor's rotor.

[0125] Secondly, the reducer is connected to the output shaft of the steering actuator motor. The function of the reducer is to reduce the speed and increase the torque. The reduction ratio of the reducer is set to be the output speed of the reducer is the output shaft speed of the motor. The output torque of the reducer is N times that of the motor output shaft. Assuming the reducer is ideal, ignoring inertia and elastic deformation, the reducer model is simplified to the link of torque amplification and speed reduction. At this time, the output torque of the reducer is: T g =N*T m =N*K t *i; where T g is the output torque of the reducer; N is the reduction ratio.

[0126] The output shaft of the reducer is connected to the pinion of the rack and pinion mechanism. For the rack and pinion model, the input torque is T of the output shaft of the reducer. g , and the stress analysis can be obtained to obtain T g =F*r p ,so In the formula, r p is the radius of the gear; F is the force on the gear rack; considering the influence of Coulomb friction and steering return force, the force analysis and Newton's second law F = m*a shows that: F = m r *a+B r *v+F c +F z Where, F c Coulomb force is used as interference input; F z is the return force; a is the acceleration of the gear rack; v is the speed of the gear rack.

[0127] At the same time, we know that:

[0128] So we can get:

[0129] After processing:

[0130] Where x is the displacement of the rack; and: F z =ρ f *tanh(δ) / L s ;

[0131]

[0132] The hyperbolic tangent function is used to linearly approximate it: tanh(δ) = δ;

[0133] So we get:

[0134] After Laplace transformation, we can get:

[0135]

[0136] Because the relationship between the front wheel steering angle and the rack displacement is

[0137] So we have:

[0138] After processing, we can get:

[0139] So: δ(s)=G i (s)*i(s)+G f (s)*F c (s);

[0140] The wire control steering system model is obtained:

[0141]

[0142] Furthermore, the nonlinear time lag model that may appear in the wire control steering in step 2) is:

[0143] The analysis of the time lag link includes two parts. The first part is the time lag caused by the mechanical friction and damping caused by the steering actuator due to its own structure. The second part is the time lag caused by the sensor, network communication and signal processing of the driver and the vehicle steering system, as well as the transmission delay of the driver's steering angle and the transmission delay of the vehicle parameters output by the vehicle. In the steering actuator assembly of the steer-by-wire system, the command transmission time lag caused by the damping and friction of mechanical components such as the steering actuator reflects the response ability and operation execution ability of the steering actuator itself.

[0144] This method uses the steering wheel angle as the overall input and the actual front wheel angle of the vehicle as the output to calculate the delay time of the steering actuator. The actual steering wheel angle is obtained by the torque angle sensor, the rack displacement is obtained by the linear displacement sensor, and the front wheel angle of the vehicle is obtained by the steering trapezoid. It can be concluded that the final output of the front wheel angle of the vehicle has a certain amount of time lag compared to the steering wheel angle input. The relationship between the mutual correlation coefficient and the time delay is calculated. First, the steering wheel angle δ sw and the front wheel turning angle δ f The cross-correlation function between the two is calculated:

[0145] R wf =R[δ sw (t)δ f (t+T h )];

[0146] The cross-correlation between the two is further calculated as:

[0147] In the formula, R wf is the cross-correlation function between the steering wheel angle and the front wheel angle of the car; R is the correlation coefficient between the steering wheel angle and the front wheel angle of the car; δ sw is the ideal steering wheel angle; δ sw (t) is the ideal steering wheel angle at time t; t is the current time; T h is the delay time when the mutual correlation coefficient is maximum; δ f is the ideal front wheel turning angle of the car; μ sw and μ f is the mean of the ideal steering wheel angle and the ideal front wheel angle of the car, σ sw and σ f is the standard deviation of the ideal steering wheel angle and the ideal car front wheel angle.

[0148] There is a certain amount of time lag in the process of automotive sensors collecting signals, processors processing signals, and local area network or bus transmission of signals. There is also a communication lag between the driver turning the steering wheel and the steering actuator executing the command, including the ideal processing time of communication and the transmission time of the signal in the network or bus transmission. The idealization of communication is related to the hardware and software capabilities of sensors, processors, and acquisition systems, while the transmission time of signals is usually related to communication congestion, transmission speed, and transmission distance. The longer the signal transmission distance, the greater the time lag.

[0149] In view of the time lag caused by the steering actuator in signal acquisition, transmission, and processing, it is assumed that δ fd is the front wheel steering angle after time lag, δ f The ideal front wheel steering angle of the vehicle is used as a reference. The time delay specifically includes the transmission delay of the expected front wheel steering angle signal and the signal processing and transmission delay of the actual front wheel steering angle of the vehicle; the other is the actuator execution delay caused by the damping and friction of the mechanical components in the steering actuator. Set i c is the control current of the steering actuator, i sm is the steering actuator control current after time lag, and the expression is as follows:

[0150] The steering wheel angle and front wheel angle after time lag are: δ swd (t) = δ sw (t-τ); δ fd (t) = δ f (t-τ);

[0151] The current in the steering actuator motor after time lag is: i sm (t) = i c (t-τ);

[0152] The transfer function of current is:

[0153] Furthermore, the nonlinear model of the steer-by-wire system in step 3) is linearized:

[0154] The transfer function of the control current of the steering actuator is: The control current of the steering actuator is approximated by time lag according to the commonly used approximation method:

[0155] 1)Taylor approximation is:

[0156]

[0157] 2) Pade approximation is:

[0158]

[0159] 3) The full pole approximation is:

[0160]

[0161] The nonlinear time-delay model is linearized using first-order full poles, and the following is obtained:

[0162]

[0163] The full-pole approximation does not have a non-minimum phase part and is conducive to the structural integrity of the subsequent controller. The output transfer function of the front wheel steering angle controlled by the steer-by-wire actuator current is obtained according to the steer-by-wire actuator modeling method in step (1):

[0164] Therefore, the transfer function of the wire-controlled steering actuator model with time lag is obtained as follows:

[0165] M(s)=G i (s)*G d (s).

[0166] Figure 3 A schematic diagram of the process framework structure of the nonlinear time-delay linearization modeling method for a steer-by-wire system provided in an embodiment of the present invention is shown in FIG. Figure 3 As shown, the module structure of a nonlinear time-delay linearization modeling method under the stability control of a wire-controlled steering vehicle considering time lag of the present invention includes: 1. driver model, 2. ideal vehicle model, 3. steering wheel assembly model, 4. real vehicle model, 5. steering time-delay model, 6. steering execution assembly controller based on time lag, and 7. yaw stability controller. The driver turns the steering wheel to give the steering wheel assembly a steering angle and torque signal. The ideal vehicle model calculates the current ideal state parameters based on the current information and generates the front wheel steering angle under the action of the yaw stability controller by making a difference with the parameters of the real vehicle model. However, due to the communication time lag and the friction and damping of each mechanical component, the steering angle is not accurate, and the nonlinearity of the time lag is not easy to handle. Therefore, the time-delay linearization processing of the present invention is connected in series with the steering actuator to form a wire-controlled steering actuator assembly model containing time lag, which can then be subsequently optimized and compensated.

[0167] Figure 4 FIG. 1 is a schematic diagram of the structure of a steer-by-wire vehicle stability control device taking into account time lag provided by an embodiment of the present invention. Figure 4 As shown, the steer-by-wire vehicle stability control device 400 considering time lag includes: an establishment module 401, used to establish a steer-by-wire system model; the steer-by-wire system model is:

[0168]

[0169] In the formula, Gi (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f (s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k 0 is the proportionality coefficient between the front wheel steering angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio;

[0170] The establishment module 401 is also used to establish a nonlinear time-lag model in the steer-by-wire system; the nonlinear time-lag model is:

[0171] In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; i sm (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c (s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator;

[0172] The processing module 402 is used to linearize the nonlinear time-delay model based on the steer-by-wire system model to obtain the transfer function of the steer-by-wire actuator with time delay: M(s)=G i (s)*G d (s)(3);

[0173] The control module 403 is used to perform stability control on the vehicle based on the transfer function of the steer-by-wire actuator with time lag.

[0174] It should be noted that the description of the device of the embodiment of the present invention is similar to the description of the above method embodiment, and has similar beneficial effects as the same method embodiment, so it will not be repeated. For technical details not disclosed in the embodiment of the device, please refer to the description of the method embodiment of the present invention for understanding.

[0175] It should be noted that, in the embodiment of the present invention, if the above-mentioned wire-controlled steering vehicle stability control method considering time delay is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. According to this understanding, the technical solution of the embodiment of the present invention, or the part that contributes to the relevant technology, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including a number of instructions for a terminal to execute all or part of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a U disk, a mobile hard disk, a read-only memory (ROM, Read Only Memory), a magnetic disk or an optical disk. In this way, the embodiment of the present invention is not limited to any specific combination of hardware and software.

[0176] Correspondingly, an embodiment of the present invention provides a steer-by-wire vehicle stability control device taking into account time lag, Figure 5 FIG. 1 is a schematic diagram of the structure of a steer-by-wire vehicle stability control device taking into account time lag provided by an embodiment of the present invention. Figure 5 As shown, the steer-by-wire vehicle stability control device 500 considering time delay comprises at least: a processor 501 and a computer-readable storage medium 502 configured to store executable instructions, wherein the processor 501 generally controls the overall operation of the steer-by-wire vehicle stability control device 500 considering time delay. The computer-readable storage medium 502 is configured to store instructions and applications executable by the processor 501, and can also cache data to be processed or processed by each module in the processor 501 and the steer-by-wire vehicle stability control device 500 considering time delay, which can be implemented by flash memory (FLASH) or random access memory (RAM, Random Access Memory).

[0177] An embodiment of the present invention provides a storage medium storing executable instructions, wherein the executable instructions are stored. When the executable instructions are executed by a processor, the processor will be caused to execute the method provided by the embodiment of the present invention, for example, Figure 2 The method shown.

[0178] In some embodiments, the storage medium can be a computer-readable storage medium, for example, a ferroelectric random access memory (FRAM), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, a magnetic surface memory, an optical disk, or a compact disk read-only memory (CD-ROM), etc.; it can also be various devices including one or any combination of the above memories.

[0179] In some embodiments, executable instructions may be in the form of a program, software, software module, script or code, written in any form of programming language (including compiled or interpreted languages, or declarative or procedural languages), and may be deployed in any form, including as a stand-alone program or as a module, component, subroutine or other unit suitable for use in a computing environment.

[0180] As an example, executable instructions may, but need not, correspond to a file in a file system, may be stored as part of a file storing other programs or data, for example, in one or more scripts in a HyperText Markup Language (HTML) document, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files storing one or more modules, subroutines, or code portions). As an example, executable instructions may be deployed to be executed on one electronic device, or on multiple electronic devices located at one location, or on multiple electronic devices distributed at multiple locations and interconnected by a communication network.

[0181] The above description is only an embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement and improvement made within the spirit and scope of the present invention are included in the protection scope of the present invention.

[0182] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present invention, the size of the serial number of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention. The serial numbers of the above-mentioned embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments.

[0183] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or device. In the absence of further restrictions, an element defined by the statement "comprises one..." does not exclude the presence of other identical elements in the process, method, article or device including the element. In several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another system, or some features can be ignored, or not executed.

[0184] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A steer-by-wire vehicle stability control method considering time lag, characterized in that: The method comprises: S1, establishing a steer-by-wire system model; the steer-by-wire system model is: In the formula, G i (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f (s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k0 is the proportionality coefficient between the front wheel angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio; S2, establishing a nonlinear time-lag model in the steer-by-wire process; the nonlinear time-lag model is: In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; i sm (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c (s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator; S3, based on the steer-by-wire system model, linearize the nonlinear time-delay model to obtain a transfer function of the steer-by-wire actuator with time delay: M(s)=G i (s)*G d (s)(3); S4, performing stability control on the vehicle based on the transfer function of the wire-controlled steer actuator with time lag.

2. The method according to claim 1, characterized in that The step of establishing a wire control steering system model comprises: Using equations (4) and (5), the output matrices of the steering actuator and the reducer are determined respectively; T m =K t *i(4);T g =N*T m =N*K t *i(5); where T m is the motor shaft output torque, T g The output torque of the reducer; According to the connection characteristics between the reducer and the gear rack, the force analysis of the gear rack is carried out, and T g =F*r p (6); Considering Coulomb friction and steering return force, and according to Newton's second law F = m*a, the force of the gear rack can be obtained: F = m r *a+B r *v+F c +F z (7); where F c Coulomb force is used as interference input; F z is the return force; a is the acceleration of the gear rack; v is the speed of the gear rack; You can get: In the formula, is the second-order derivative of rack displacement; is the first-order derivative of the rack displacement; And by In the formula, ξ f is the Coulomb friction torque constant; δ is the front wheel turning angle of the car; is the first-order derivative of the front wheel steering angle of the car; is the sign function; h(δ) is the hyperbolic tangent function; Based on equations (8) and (9), we can get: After performing Laplace transformation on equation (10), we can get: Based on the relationship between wheel angle and rack displacement We can get: After processing formula (12), we can get: δ(s)=G i (s)*i(s)+G f (s)*F c (s)(14); The wire control steering system model is obtained:

3. The method according to claim 2, characterized in that The method of establishing a nonlinear time-lag model in the steer-by-wire process comprises: Determining an ideal front wheel angle of the vehicle based on the obtained ideal steering wheel angle and the rack displacement; Determine the cross-correlation function between the ideal steering wheel angle and the ideal front wheel angle of the vehicle; the cross-correlation function is expressed as: wf =R[δ sw (t)δ f (t+T h )](15); The cross-correlation between the two is calculated as: In the formula, R wf is the cross-correlation function between the steering wheel angle and the front wheel angle of the car; R is the correlation coefficient between the steering wheel angle and the front wheel angle of the car; δ sw is the ideal steering wheel angle; δ sw (t) is the ideal steering wheel angle at time t; t is the current time; T h is the delay time when the mutual correlation coefficient is maximum; δ f is the ideal front wheel turning angle of the car; μ sw and μ f is the mean of the ideal steering wheel angle and the ideal front wheel angle of the car, σ sw and σ f is the standard deviation of the ideal steering wheel angle and the ideal front wheel angle of the car; Based on the ideal steering wheel angle and the ideal front wheel angle of the vehicle, the time-delay steering wheel angle, the time-delay front wheel angle of the vehicle and the current after the steering actuator has a time delay are determined, which is expressed as: δ swd (t) = δ sw (t-τ); δ fd (t) = δ f (t-τ);i sm (t) = i c (t-τ); (17); In the formula, δ swd is the time-delay steering wheel angle; δ swd (t) is the steering wheel angle after the time lag at time t; δ fd is the front wheel turning angle of the time-delayed vehicle; δ fd (t) is the front wheel turning angle of the vehicle at time t; i sm (t) is the control current of the steering actuator motor at time t; The transfer function that determines the current is:

4. The method according to claim 3, characterized in that The method of linearizing the nonlinear time-delay model based on the steer-by-wire system model to obtain a transfer function of the steer-by-wire actuator with time-delay includes: The following method is used to perform time-delay approximation on equation (2): 1)Taylor approximation is: 2) Pade approximation is: 3) The full pole approximation is: The nonlinear time-delay model is linearized using first-order full poles, and the following is obtained: Based on equations (1) and (21), the transfer function of the wire-controlled steering actuator with time lag is obtained as follows: M(s) = G i (s)*G d (s)(3).

5. A steer-by-wire vehicle stability control device taking into account time lag, characterized in that: The device comprises: Establishing a module for establishing a wire-controlled steering system model; the wire-controlled steering system model is: In the formula, G i (s) is the transfer function of the steering actuator that uses the steering control current as input, drives the reduction mechanism to output torque to the rack and pinion mechanism through the steering motor output shaft, and drives the front wheel angle of the vehicle as output through the steering trapezoid; G f (s) is the Coulomb friction force in the steer-by-wire actuator as the disturbance input; k0 is the proportionality coefficient between the front wheel angle and the rack displacement; s is the Laplace variable, complex frequency; L s is the equivalent force arm of the steering trapezoidal mechanism; ρ f is the self-aligning torque coefficient; r p is the gear radius; m r is the equivalent mass of the gear rack; B r is the equivalent damping coefficient; K t is the torque constant; i is the input current of the wire-controlled steering actuator; N is the reduction ratio; The establishment module is also used to establish a nonlinear time-lag model in the wire control steering; the nonlinear time-lag model is: In the formula, G d (s) is the transfer function of the control current of the wire-controlled steering actuator after time lag; the time lag τ causes the current control of the wire-controlled steering actuator to be executed with lag, and the current command issued by the controller of the wire-controlled steering actuator is i c ;i sm is the control current of the wire-controlled steering actuator after time lag; i sm (s) is the control current of the steer-by-wire actuator after Laplace transformation; i c (s) is the transfer function of the control current of the steer-by-wire actuator after Laplace transformation; τ is the time lag in the steer-by-wire actuator; A processing module is used to linearize the nonlinear time-delay model based on the wire-controlled steering system model to obtain a transfer function of the wire-controlled steering actuator with time delay: M(s)=G i (s)*G d (s)(3); The control module is used for performing stability control on the vehicle based on the transfer function of the wire control steering actuator with time lag.

6. An electronic device, characterized in that: include: A memory for storing executable instructions; The processor is used to implement the steer-by-wire vehicle stability control method considering time delay as described in any one of claims 1 to 4 when executing the executable instructions stored in the memory.

7. A computer-readable storage medium, characterized in that: Executable instructions are stored, which are used to cause the processor to execute the executable instructions to implement the steer-by-wire vehicle stability control method considering time delay as described in any one of claims 1 to 4.

Images