Sliding mode fault-tolerant control method of automobile steer-by-wire system, terminal and storage medium

Abstract

The invention relates to the technical field of automobile fault-tolerant control, and discloses a sliding mode fault-tolerant control method of an automobile steer-by-wire system, a terminal and a storage medium. The method comprises the following steps: firstly, establishing a nonlinear bonding graph model of the steer-by-wire system so as to establish a dynamic model of a front wheel subsystem in the steer-by-wire system; then, based on a dynamic model of a front wheel subsystem, a sliding mode controller is adopted to control the actual angle of a front wheel to track the reference angle of the front wheel, so that the automobile travels on an expected track; and when it is detected that the sensor of the automobile breaks down, the fault value of the sensor is estimated through the sliding-mode observer, the fault influence is eliminated, and fault-tolerant control is achieved. According to the invention, the fault tolerance problem when the vehicle breaks down in the driving process is solved.

Description

Technical Field

[0001] The invention relates to the technical field of automobile fault-tolerant control, and in particular to a sliding mode fault-tolerant control method, a terminal and a storage medium of an automobile wire-controlled steering system. Background Art

[0002] With the development of the automobile industry, consumers have put forward higher requirements for automobile safety, energy saving and environmental protection performance, and traditional automobile steering systems are gradually unable to meet modern needs.

[0003] Early automobile steering systems mainly adopted mechanical structures, with a fixed transmission ratio between the steering wheel and the steering wheel, resulting in poor steering dynamics and kinematic characteristics of the car. In addition, the mechanical steering system has the disadvantages of large steering torque and difficult control by the driver. To improve this problem, the hydraulic power steering system was introduced. The system is powered by the engine, which improves the lightness and flexibility of the steering, but its energy consumption is high.

[0004] With the widespread application of electronic technology, the electric power steering system (EPS) has gradually developed and been widely used, which has improved the steering stability to a certain extent. However, the traditional steering system still relies on the steering drive shaft, which may cause serious impact damage to the driver in the event of a traffic accident. In order to solve this problem, the steering-by-wire (SBW) system came into being. The steering-by-wire system eliminates the mechanical connection and relies on sensors, actuators and electronic control units (ECUs) to complete steering control, which improves safety and driving comfort. However, the system is highly dependent on sensors and is easily affected by sensor failures, thus affecting driving safety. Therefore, timely detection, tracking and compensation of faults are crucial for the steering-by-wire system.

[0005] During long-term use, the sensors of the steer-by-wire system may fail due to aging or environmental influences. If the failure cannot be detected in time or there is a lack of effective compensation mechanism, it may lead to loss of steering control, posing a serious safety hazard. However, the prior art still lacks a sliding mode fault-tolerant control method for automotive steer-by-wire systems to effectively deal with sensor failures, which needs to be solved urgently. Summary of the invention

[0006] In order to overcome the defects in the above-mentioned prior art, the present invention provides a sliding mode fault-tolerant control method, a terminal and a storage medium for an automobile steer-by-wire system, which solves the fault-tolerant problem when a vehicle fails during driving.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention discloses a sliding mode fault-tolerant control method for a vehicle steer-by-wire system, comprising the following steps:

[0009] S1. Establish a non - linear bond graph model of the steer - by - wire system, and based on this, establish the dynamic model of the front - wheel subsystem in the steer - by - wire system;

[0010] S2. Based on the dynamic model of the front - wheel subsystem, use a sliding - mode controller to control the actual angle of the front wheel to track its reference angle, so that the vehicle travels on the desired trajectory;

[0011] S3. When it is detected that the vehicle's sensor fails, estimate the sensor fault value through a sliding - mode observer, eliminate the fault influence, and achieve fault - tolerant control.

[0012] As a further improvement of the above - mentioned scheme, step S1 includes the following specific steps:

[0013] S11. Divide the steer - by - wire system into a steering - wheel subsystem and a front - wheel subsystem; among them, the steering - wheel subsystem includes a steering wheel, a feedback motor, a reducer, a feedback - motor driver, a steering - wheel angle sensor, and a feedback - motor angle sensor, and the front - wheel subsystem includes a steering - motor driver, a steering motor, a reducer, a gear, a rack, a front wheel, a steering - motor angle sensor, a gear - angle sensor, and a front - wheel angle sensor;

[0014] S12. Construct a non - linear bond graph model based on the bond - graph theory; among them, the basic elements of the non - linear bond graph model include a one - port element, a two - port element, and a multi - port element; the one - port element includes a potential source Se, a flow source Sf, a dissipative element R, an inertial element I, a capacitive element C, and flow sensors {Df 1 , Df 2 , …, Df 5}; the two - port element includes a transformer TF and a gyrator GY; the multi - port element includes a 1 - type junction and a 0 - type junction;

[0015] S13. Establish the dynamic model of the front - wheel subsystem through the non - linear bond graph model, and its expression is as follows:

[0016]

[0017] In the formula, K s is the torque constant of the steering motor; U 2 is the input voltage of the steering motor; R m is the viscous friction coefficient of the steering motor; θ s is the angle of the steering motor, and are the first - order derivative and the second - order derivative of θ s respectively; C s is the stiffness of the steering - motor shaft; x r is the rack displacement; G p1is the reduction ratio of the reducer; r p is the gear radius; J s is the moment of inertia of the rotor of the steering motor; R p represents the friction force of the rack; C p represents the rack stiffness; G p2 represents the ratio of the linear velocity of the rack to the angular velocity of the front wheel; θ fw is the actual steering angle of the front wheel; M p represents the mass of the rack; θ fk is the steering angle of the front wheel; R fk is the friction force between the tire and the ground; J fk is the moment of inertia of the front wheel; g m is the friction torque characteristic function of the steering motor, g r is the friction torque characteristic function of the gear, g fk is the friction torque characteristic function of the front wheel. The expression formulas of the three are where, T s,i and T c,i are the Coulomb friction torque and the static friction torque of the corresponding components respectively, and λ i is a constant characterizing the transition between T s,i and T c,i with μ as the independent variable; T e is the self-aligning torque.

[0018] As a further improvement of the above solution, step S2 includes the following specific steps:

[0019] S21. Set the system state and system input according to the dynamic model of the front wheel subsystem; where, the system input is the input voltage u of the steering motor driver, and the expression formula of the system state x(t) is:

[0020]

[0021] In the formula, t represents time; the superscript T is the transpose symbol;

[0022] S22. Establish the state space model of the steer-by-wire system in the healthy state, and the expression formula is:

[0023]

[0024] In the formula, is the derivative of the system state variable; y(t) is the system output, that is, the steering angle of the front wheel; u(t) is the sliding mode control rate, that is, the function of the input voltage u of the steering motor driver changing with time; f(x,t) is the nonlinear term; Ψ(x,t) is the lumped disturbance; A, B, and C are the state transition coefficient matrix, the input coefficient matrix, and the output coefficient matrix respectively;

[0025] S23. After simplifying the dynamic model of the front wheel system, the dynamic equation of the front wheel system is obtained:

[0026]

[0027] In the formula, J eq is the equivalent moment of inertia; B eq is the equivalent damping coefficient; T f is the non - linear frictional torque; K e is the motor output torque coefficient;

[0028] S24. Combining the dynamic equation, a sliding - mode control law is set. A sliding - mode controller is used to control the input voltage signal of the steering motor driver according to the sliding - mode control law, so that the actual angle of the front wheel tracks its reference angle; among them, the calculation formula for the input voltage u of the steering motor driver is:

[0029]

[0030] In the formula, θ fwd is the reference signal of the front - wheel steering angle; c>0; s is the sliding - mode surface; εsgn(·) is the sign - function term, and k>0 is the linear term.

[0031] As a further improvement of the above - mentioned solution, in step S3, when it is detected that the sensor fails, the sliding - mode observer automatically controls the motor output according to its own design to achieve fault tolerance; among them, the design method of the sliding - mode observer includes the following specific steps:

[0032] S31. Establish a state - space model of the steer - by - wire system under sensor failure, and the expression formula is:

[0033]

[0034] In the formula, is the state variable of the vehicle, y s (t) is the output of the steer - by - wire system; u r (t) is the control input, that is, the input voltage of the steering motor driver; K r is the feedback motor torque constant, J w is the moment of inertia of the front wheel, B w is the viscous friction coefficient of the front wheel; B s =[0 K r / G r J w T , G r is the transmission ratio between the rack displacement and the front - wheel steering angle; C sy =[1 0] is the output gain matrix; ​is the non - linear term in the steer - by - wire system; E s =[0 1] T ; ψ 3 (x s , t) is the lumped disturbance; M s = 1; f s (t) is the sensor fault;

[0035] S32. Augment and reconstruct the state - space model of the steer - by - wire system under sensor fault to obtain the augmented matrix:

[0036]

[0037] In the formula, is the augmented state variable, where z(t) is a user - defined variable and can be the output y s (t) to implement low - pass filtering and satisfy the formula: A f is a stable filtering matrix, defined as a diagonal positive - definite matrix;

[0038] S33. Design a sliding - mode observer using the augmented matrix, and the expression formula is:

[0039]

[0040] In the formula, is the estimated value of ; is the estimated value of ; is the augmented transpose of τ s (x s , t), that is v is the discontinuous term in the sliding - mode observer; L 1 is the sliding - mode observer gain matrix.

[0041] As a further improvement of the above scheme, after the design of the sliding - mode observer is completed, calculate the estimated value of the sensor fault, that is, the discontinuous term v in the sliding - mode observer, and the expression formula is:

[0042]

[0043] In the formula, e y and ρ 1 are positive scalar gains, ρ 1 >β fs ; H 1 is an arbitrary matrix that satisfies the formula ; P 1 is a 3×3 real - symmetric matrix; δ 1is a positive scalar;

[0044] Calculate where is the estimated value of f s (t);

[0045] The fault tolerance of the faulty sensor is completed using the following formula:

[0046]

[0047] In the formula, is the front wheel steering angle after fault tolerance; y 3 (t) is the actual output of the faulty sensor; is the sensor fault estimation error, which can converge to zero within a finite time.

[0048] The present invention also discloses a computer terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the sliding mode fault tolerance control method of the steer-by-wire system of the vehicle as described above are implemented.

[0049] The present invention also provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the steps of the sliding mode fault tolerance control method of the steer-by-wire system of the vehicle as described above are implemented.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] The present invention provides a sliding mode fault tolerance control method for a steer-by-wire system of a vehicle based on a bond graph model, which solves the problem of fault tolerance when the vehicle fails during driving. By adopting sliding mode control and controlling the front wheel steering angle according to the steering wheel torque, the ideal output state can be better tracked. By using a sliding mode observer based on the data of the non-faulty sensor, a fault reconstruction model is established and fault tolerance control is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a flowchart of the sliding mode fault tolerance control method of the steer-by-wire system of the vehicle in Embodiment 1 of the present invention.

[0053] Figure 2 is the bond graph of the steering wheel part of the steer-by-wire system in Embodiment 1 of the present invention.

[0054] Figure 3 is the bond graph of the feedback motor and reducer parts of the steer-by-wire system in Embodiment 1 of the present invention.

[0055] Figure 4It is the bond graph of the feedback motor driver part in the steer-by-wire system of Embodiment 1 of the present invention.

[0056] Figure 5 It is the bond graph of the steering motor driver part in the steer-by-wire system of Embodiment 1 of the present invention.

[0057] Figure 6 It is the bond graph of the steering motor part in the steer-by-wire system of Embodiment 1 of the present invention.

[0058] Figure 7 It is the bond graph of the rack and pinion part in the steer-by-wire system of Embodiment 1 of the present invention.

[0059] Figure 8 It is the bond graph of the front wheel part in the steer-by-wire system of Embodiment 1 of the present invention.

[0060] Figure 9 It is the schematic diagram of the steering wheel input module of the rear-end model in Embodiment 1 of the present invention.

[0061] Figure 10 It is the schematic diagram of the input module of the friction of the handwheel in Embodiment 1 of the present invention.

[0062] Figure 11 It is the schematic diagram of the steering wheel input module and the "To Workplace" module in Embodiment 1 of the present invention, where the data is exported to the workspace.

[0063] Figure 12 It is the "To File" module in Embodiment 1 of the present invention, where the data is exported to generate a.mat file.

[0064] Figure 13 It is the schematic diagram of the co-simulation module of CarSim and MATLAB in Embodiment 1 of the present invention.

[0065] Figure 14 It is the software interface diagram of the model state under the input sine wave signal and without faults in Embodiment 1 of the present invention.

[0066] Figure 15 It is the software interface diagram of the model state under the input sine wave signal and under gradual faults in Embodiment 1 of the present invention.

[0067] Figure 16 It is the software interface diagram of the model state under the input ramp signal and under intermittent faults in Embodiment 1 of the present invention.

[0068] Figure 17 It is the software interface diagram of the model state under the input ramp signal and under gradual faults in Embodiment 1 of the present invention.

[0069] Figure 18This is the error evaluation software interface diagram for the input sine wave signal in Embodiment 1 of the present invention under fault-free conditions.

[0070] Figure 19 This is the error evaluation software interface diagram for the input sine wave signal in Embodiment 1 of the present invention under gradually changing fault conditions.

[0071] Figure 20 This is the error evaluation software interface diagram for the input ramp signal in Embodiment 1 of the present invention under intermittent fault conditions.

[0072] Figure 21 This is the error evaluation software interface diagram for the input ramp signal in Embodiment 1 of the present invention under gradually changing fault conditions.

[0073] Figure 22 This is the schematic diagram of the computer terminal structure in Embodiment 2 of the present invention. Detailed implementation manners

[0074] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0075] Embodiment 1

[0076] Please refer to Figure 1 , this embodiment provides a sliding mode fault-tolerant control method for an automotive steer-by-wire system, including the following steps, namely S1 to S3.

[0077] S1. Establish a non-linear bond graph model of the steer-by-wire system, and thereby establish a dynamic model of the front wheel subsystem in the steer-by-wire system.

[0078] Step S1 includes the following specific steps, namely S11 to S13.

[0079] S11. Divide the steer-by-wire system into a steering wheel subsystem and a front wheel subsystem; wherein, the steering wheel subsystem includes a steering wheel, a feedback motor, a reducer, a feedback motor driver, a steering wheel angle sensor, and a feedback motor angle sensor, and the front wheel subsystem includes a steering motor driver, a steering motor, a reducer, a gear, a rack, a front wheel, a steering motor angle sensor, a gear angle sensor, and a front wheel angle sensor.

[0080] S12. Construct a non - linear bond graph model based on bond graph theory; wherein, the basic elements of the non - linear bond graph model include a one - port element, a two - port element, and a multi - port element; the one - port element includes a potential source Se, a flow source Sf, a dissipative element R, an inertial element I, a capacitive element C, and flow sensors {Df 1 , Df 2 , …, Df 5}; the two - port element includes a transformer TF and a gyrator GY; the multi - port element includes a 1 - type node and a 0 - type node.

[0081] The non - linear bond graph model of the steer - by - wire system of the front - wheel - steering vehicle in this embodiment can be divided into seven parts: the steering wheel part, the feedback motor and reducer part, the feedback motor driver part, the steering motor driver part, the steering motor part, the rack - and - pinion part, and the front - wheel part. Their bond graphs are specifically as Figures 2 to 8 shown.

[0082] The elements included in the modeling of the steering wheel part are the potential source Se: T h , the dissipative element R: R w , the inertial element l: J w , the capacitive element and the flow sensor wherein, T h represents the input torque of the steering wheel, R w represents the mechanical friction force received by the steering wheel, J w represents the moment of inertia of the steering wheel, K h represents the stiffness of the steering column connected to the steering wheel, represents the angular velocity of the steering wheel.

[0083] The elements included in the feedback motor and reducer part are the transformer TF: G fm , the dissipative element {R: R mr1 , R: R mr2}, the inertial element I: J fm , the gyrator GY: K fm and the flow sensor wherein, G fm is the reduction ratio, R mr1 is the mechanical friction force of the feedback motor, R mr2 is the resistance of the electrical part of the feedback motor, J fm is the moment of inertia of the rotor of the feedback motor, K fm is the current - torque constant, is the angular velocity of the feedback motor.

[0084] The elements included in the feedback motor driver part are the transformer Tf: K 1 and the flow source Sf: U 1. Among them, K 1 represents the voltage-current ratio, and U 1 is the input voltage of the feedback motor driver.

[0085] The components included in the steering motor driver part are the current source Sf:U 2 and the converter TF:K 2 . Among them, K 2 represents the voltage-current ratio, and U 2 is the input voltage of the steering motor driver.

[0086] The components included in the steering motor part are the dissipative elements {R:R s1 ,R:R s2}, the gyrator GY:K m , the inertial element I:J s , the capacitive element and the current sensor Among them, R s1 is the resistance of the electrical part of the steering motor, and R s2 is the mechanical friction of the steering motor, K m is the current-torque constant, J s is the moment of inertia of the steering motor rotor, K s is the stiffness of the steering motor shaft, is the angular velocity of the steering motor.

[0087] The components included in the rack and pinion part are the converter the dissipative element R:R r , the inertial element I:M r , the converter TF:G r2 , the capacitive element and the current sensor Among them, G r1 is the reduction ratio, r p is the gear radius, R r is the mechanical friction of the rack, M r is the mass of the rack, G r2 is the ratio of the rack linear velocity to the front wheel angular velocity, K r is the stiffness of the rack, is the linear velocity of the rack.

[0088] The components included in the front wheel part are the dissipative element R:R f , the inertial element I:J f , the potential source Se:T e and the current sensor Among them, R f is the friction between the front wheel and the road surface, J f is the moment of inertia, T e is the self-aligning torque, is the angular velocity of the front wheel.

[0089] The five mechanical frictions {R w , R mr1 , R s2 , R r , R f} in the steer-by-wire system are all non-linear, and the constitutive relations of their potential and flow can be expressed as:

[0090]

[0091] In the formula, B v , T v,c , and T v,s represent the viscous friction coefficient, Coulomb friction torque, and static friction torque respectively, v ∈ {w, mr1, s2, r, f}, e h , and f h , h ∈ {2, 9, 22, 29, 36}, represent the potential and flow of the corresponding power bond respectively.

[0092] Figure 4 In is the feedback motor driver controller, E 1 is the difference between the reference value T rf of the steering wheel feedback torque and the actual value T af . Among them, N v is the speed coefficient, N f is the torque transmission ratio between the steering wheel and the front wheels; In Figure 5 , is the steering motor driver controller, is the difference between the desired front wheel angle and the actual front wheel angle, where N θ is the steering transmission ratio.

[0093] S13. Establish the dynamic model of the front wheel subsystem through the non-linear bond graph model. Since the focus of the present invention is on the front wheel angle tracking performance of the steer-by-wire system when the front wheel subsystem sensor fails, only the dynamic model of the front wheel subsystem is established, and its expression is as follows:

[0094]

[0095] In the formula, K s is the steering motor torque constant; U 2 is the input voltage of the steering motor; R m is the viscous friction coefficient of the steering motor; θ s is the steering motor angle, and are respectively θ sThe first derivative and the second derivative of; C s is the stiffness of the steering motor shaft; x r is the rack displacement; G p1 is the reduction ratio of the reducer; r p is the gear radius; J s is the moment of inertia of the steering motor rotor;

[0096] R p represents the frictional force of the rack; C p represents the rack stiffness; G p2 represents the ratio of the rack linear velocity to the front wheel angular velocity; θ fw is the actual front wheel angle; M p represents the mass of the rack; θ fk is the front wheel angle; R fk is the frictional force between the tire and the ground; J fk is the moment of inertia of the front wheel; g m is the steering motor frictional torque characteristic function, g r is the gear frictional torque characteristic function, g fk is the front wheel frictional torque characteristic function, and the expression formulas of the three are i ∈ {m, r, fk}, where, T s,i and T c,i are the Coulomb frictional torque and the static frictional torque of the corresponding components respectively, λ i is a constant characterizing the transition between T s,i and T c,i and μ is the independent variable; T e is the self-aligning torque.

[0097] S2. Based on the dynamic model of the front wheel subsystem, a sliding mode controller is used to control the actual angle of the front wheel to track its reference angle, so that the vehicle travels on the desired trajectory.

[0098] Step S2 includes the following specific steps, namely S21~S24.

[0099] S21. Set the system state and system input according to the dynamic model of the front wheel subsystem; where, the system input is the input voltage u of the steering motor driver, and the expression formula of the system state x(t) is:

[0100]

[0101] In the formula, t represents time; the superscript T is the transpose symbol.

[0102] S22. Establish the state space model of the steer-by-wire system in the healthy state, and the expression formula is:

[0103]

[0104] In the formula, is the derivative of the system state variable; y(t) is the system output, i.e., the front wheel steering angle; u(t) is the sliding mode control rate, i.e., the function of the input voltage u of the steering motor driver changing with time; f(x,t) is the non-linear term; Ψ(x,t) is the lumped disturbance; A, B, and C are the state transition coefficient matrix, input coefficient matrix, and output coefficient matrix, respectively.

[0105] S23. After simplifying the dynamic model of the front wheel subsystem, the dynamic equation of the front wheel subsystem is obtained:

[0106]

[0107] In the formula, J eq is the equivalent moment of inertia; B eq is the equivalent damping coefficient; T f is the non-linear frictional torque; K e is the motor output torque coefficient.

[0108] S24. Combine the dynamic equation to set the sliding mode control rate, and use a sliding mode controller to control the input voltage signal of the steering motor driver according to the sliding mode control rate, so that the actual angle of the front wheel tracks its reference angle. Among them, the sliding mode surface s of the sliding mode controller is:

[0109]

[0110] In the formula, c>0; e = θ fwd -θ fw ; θ fwd is the reference signal of the front wheel steering angle;

[0111] The reaching law of the sliding mode controller is:

[0112]

[0113] In the formula, εsgn(s) is the sign function term, and k>0 is the linear term;

[0114] The calculation formula of the input voltage u of the steering motor driver is:

[0115]

[0116] In the formula, θ fwd is the reference signal of the front wheel steering angle; c>0; s is the sliding mode surface; εsgn(·) is the sign function term, and k>0 is the linear term.

[0117] S3. When it is detected that the sensor of the vehicle fails, estimate the sensor fault value through a sliding mode observer, eliminate the fault influence, and achieve fault-tolerant control.

[0118] In step S3, when a sensor failure is detected, the sliding mode observer automatically controls the motor output according to its own design to achieve fault tolerance.

[0119] It should be noted that how to detect sensor faults is not the inventive point. In this embodiment, the technical content in the published invention CN118011799A can be referred to for implementation.

[0120] The design method of the sliding mode observer includes the following specific steps, namely S31 to S33.

[0121] S31. The present invention mainly considers the failure of the front wheel angle sensor. Since the state space model in step S22 is too complex, it is quite challenging to directly design a fault reconstruction strategy to estimate the fault value. To solve this problem, the present invention performs a certain model transformation and reconstruction before fault reconstruction. Therefore, a state space model of the steer-by-wire system under sensor failure is established, and the expression formula is:

[0122]

[0123] In the formula, is the state variable of the vehicle, y s (t) is the output of the steer-by-wire system; u r (t) is the control input, that is, the input voltage of the steering motor driver; K r is the feedback motor torque constant, J w is the moment of inertia of the front wheel, B w is the viscous friction coefficient of the front wheel; B s =[0 K r / G r J w T , G r is the transmission ratio between the rack displacement and the front wheel steering angle; C sy =[1 0] is the output gain matrix; is the non-linear term in the steer-by-wire system; E s =[0 1] T ; Ψ 3 (x s , t) is the lumped disturbance; M s =1; f s (t) is the sensor fault.

[0124] S32. To build a sliding mode observer, first, the state space model of the steer-by-wire system under sensor failure will be augmented and reconstructed to obtain an augmented matrix:

[0125] ​

[0126] In the formula, is the augmented state variable, where z(t) is a user-defined variable and can be the output y s ( t) implements low-pass filtering and satisfies the formula: A f is a stable filtering matrix, defined as a diagonal positive definite matrix;

[0127] S33. Design a sliding mode observer using the augmented matrix, and the expression formula is:

[0128]

[0129] In the formula, is 's estimated value; is 's estimated value; is τ s (x s ,t)'s augmented transpose, that is v is the discontinuous term in the sliding mode observer, used to adjust the system state estimation; L 1 is the sliding mode observer gain matrix, used to adjust the system rapidity.

[0130] After completing the design of the sliding mode observer, calculate the sensor fault estimated value, that is, the discontinuous term v in the sliding mode observer, and the expression formula is:

[0131]

[0132] In the formula, e y and ρ 1 are positive scalar gains, ρ 1 > β fs ; H 1 is an arbitrary matrix that satisfies the formula P 1 is a 3×3 real symmetric matrix, used to determine and ensure system stability; δ 1 is a positive scalar, used to reduce the chattering caused by v.

[0133] Calculate Among them, is the estimated value of f s (t).

[0134] Complete the fault tolerance of the faulty sensor using the following formula, and the fault tolerance formula is as follows:

[0135]

[0136] In the formula, is the front wheel steering angle after fault tolerance; y 3 (t) is the actual output of the faulty sensor; is the sensor fault estimation error, which can converge to zero within a finite time.

[0137] In this embodiment, the front-end environment is also established using MATLAB software, connected to the back-end model, for parameter adjustment and model state observation. And a co-simulation is carried out with CarSim to observe the traveling state of the vehicle model.

[0138] 1. Overall front-end functions

[0139] 1.1 Parameter settings: Set parameters such as the input waveform, sliding mode surface parameters, reaching law chattering control, reaching law approaching rate, moment of inertia, damping coefficient, mechanical friction, etc.

[0140] 1.2 Sensor fault injection: Select fault modes such as no fault, gradual fault, intermittent fault, failure fault, sudden fault, etc.

[0141] 1.3 Simulation content: Steering wheel input waveform, front wheel steering angle tracking waveform, vehicle trajectory diagram waveform, fault image waveform.

[0142] 1.4 Error evaluation: Monitor the front wheel tracking error and fault estimation error in real time.

[0143] 2. Jumping between APP interfaces

[0144] One APP interface corresponds to one MATLAB APP file, and the jumping of the APP interface is realized by opening and closing the file. The specific implementation process is as follows:

[0145] Add a "button" module to the APP interface and add a callback function to it.

[0146] For example: run("CANSHU1.mlapp");

[0147] delete(app);

[0148] Indicates closing the current interface and opening the interface corresponding to "CANSHU1.mlapp".

[0149] 3. Data transfer between the front end and the back end

[0150] 3.1 Front-end data input to the back-end model

[0151] Add modules such as "drop-down box" and "edit field (numeric)" to the APP interface and add callback functions to them.

[0152] Example 1: When selecting different input waveforms, the "Drop - down box" module can be used, and different waveform names are added to its drop - down items. Then add a callback function:

[0153] value = app.DropDown.Value;

[0154] global a4;

[0155] switch value

[0156] case 'Sine wave'

[0157] a4 = 1;

[0158] case 'Constant'

[0159] a4 = 2;

[0160] case 'Ramp'

[0161] a4 = 3;

[0162] end

[0163] Inctrl = a4;

[0164] assignin("base","Inctrl",Inctrl);

[0165] If the drop - down box selects "Sine wave", the corresponding value of Inctrl is 1 (as Figure 9 shown), and the model outputs a sine wave.

[0166] Example 2: When setting model parameters, the "Edit Field (Numeric)" module can be used, and a callback function is added to it:

[0167] Bh = app.EditField.Value;

[0168] assignin("base","Bh",Bh);

[0169] If 0.01 is entered in the "Edit Field (Numeric)" module, then the value of Bh in the model (as Figure 10 shown) is 0.01, and the corresponding friction of the steering wheel, i.e., the handwheel, is 0.01.

[0170] 3.2. Input of Back - end Model Data to the Front - end Interface

[0171] Add a "To Workspace" module to the model to transfer data to the workspace, and then call it through code in the front - end, or add a "To File" module to transfer data to a *.mat file, and then call it through code in the front - end.

[0172] Example 1: When drawing a static diagram of the steering wheel input waveform on the APP interface, add a "To Workspace" module at the steering wheel waveform input of the model (as shown in Figure 11 ), then add a "Coordinate Area" module and a "Button" module to the APP interface, and add a callback function to the "Button" module:

[0173] cla(app.UIAxes_2);

[0174] out = sim("test01");

[0175] IN = out.IN;

[0176] plot(IN, 'Parent', app.UIAxes_2, 'Color', 'r');

[0177] hold(app.UIAxes_2, "on");

[0178] After pressing the "Button", the static diagram of the steering wheel input waveform will be displayed in the coordinate area.

[0179] Example 2: When drawing a dynamic diagram of the front wheel steering angle tracking on the APP interface, add a "ToFile" module at the front wheel steering angle output of the model (as shown in Figure 12 ), and change the "Save Format" in the "To File" module to "Array", then add a "Coordinate Area" module and a "Button" module to the APP interface, and add a callback function to the "Button" module:

[0180] sim("test01");

[0181] load OUT1.mat;

[0182] x = OUT1(1, :);

[0183] y = OUT1(2, :);

[0184] h1 = animatedline(app.UIAxes, "Color", 'b', 'LineWidth', 1);

[0185] a = tic;

[0186] for i = 1:(length(x))

[0187] addpoints(h1, x(i), y(i));

[0188] b = toc(a);

[0189] if b>(1 / 100)

[0190] drawnow

[0191] a=tic;

[0192] end

[0193] end

[0194] drawnow

[0195] After pressing the button, the axes area will display a dynamic plot of the front wheel angle tracking.

[0196] 4. Joint simulation of Simulink and CarSim

[0197] First, configure the car environment of CarSim, such as car model, road, etc., and connect CarSim and Simulink using the "Run Control withSimulink" module in CarSim. Then set the input and output parameters.

[0198] like Figure 13 As shown in the figure, in the CarSim and MATLAB joint simulation module, the input is the front wheel steering angle of the car (i.e. vs_sf), and the output is the X and Y components of the car model's trajectory (i.e. X.mat, Y.mat). In CarSim, you can see the 3D graph of the car model's movement, and in the APP interface, the "coordinate area" is used to display the dynamic vehicle trajectory curve.

[0199] In this embodiment, the nominal values ​​of the parameters of the wire control steering system are shown in Table 1 below:

[0200] Parameter Nominal value Parameter Nominal value Parameter Nominal value <![CDATA[B w > 0.05 Nm / rad <![CDATA[J s > <![CDATA[2.8e -4 kg·m 2 > <![CDATA[T mr1,s > 0.06 Nm <![CDATA[J w > <![CDATA[0.028kg·m 2 > <![CDATA[K s > 1 Nm / rad <![CDATA[T s2,c > 0.05 Nm <![CDATA[K h > 4 Nm / rad <![CDATA[G r1 > 15 <![CDATA[T s2,s > 0.69 Nm <![CDATA[G fm > 5 <![CDATA[r p > 0.08m <![CDATA[T r,c > 0.6 Nm <![CDATA[B mr1 > <![CDATA[2.06e -4 Nm / rad]]> <![CDATA[B r > 20 Nm / rad <![CDATA[T r,s > 0.61 Nm <![CDATA[J fm > <![CDATA[4.5e -5 kg·m 2 > <![CDATA[M r > 3 kg <![CDATA[T f,c > 0.6 Nm <![CDATA[K fm > 0.123 Nm / A <![CDATA[G r2 > 1.4 <![CDATA[T f,s > 0.7 Nm <![CDATA[R mr2 > 0.22 Ω <![CDATA[K r > 250 Nm / rad <![CDATA[N v > 0.19 <![CDATA[K 1 > 1 A / V <![CDATA[B f > 25 Nm / rad <![CDATA[N f > 700 <![CDATA[K 2 > 7 A / V <![CDATA[J f > <![CDATA[0.05kg·m 2 > <![CDATA[N θ > 12 <![CDATA[R s1 > 0.03 Ω <![CDATA[T w,c > 0.33 Nm <![CDATA[α s2 > 0.007 <![CDATA[K m > 0.097 Nm / A <![CDATA[T w,s > 0.331 Nm <![CDATA[α r > 0.006 <![CDATA[B s2 > 0.0124 Nm / rad <![CDATA[T mr1,c > 0.059 Nm <![CDATA[α w ,α mr1 ,α f > 0.001

[0201] This embodiment uses CarSim and MATLAB APP to establish a front-end environment, which is connected to the back-end model, and can conveniently adjust model parameters, observe model status and the trajectory of the car model.

[0202] See also Figures 14 to 21 When the system is in a sinusoidal or ramp input, different fault conditions are added. Figures 14 - 17 It can be seen that the actual front wheel steering angle values ​​can stably follow the ideal value, and the vehicle model's trajectory is consistent with expectations, which verifies that the sliding mode fault-tolerant control method of the present invention is effective. Figures 18 - 21 It can be seen that the front wheel tracking error is controlled within 0.03 rad, and the fault estimation error is controlled within 0.05 rad, which further verifies the excellent fault tolerance effect of the present invention when a fault occurs during vehicle driving.

[0203] Example 2

[0204] This embodiment provides a computer terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the sliding mode fault-tolerant control method of the steer-by-wire system of an automobile as described in Embodiment 1 are implemented.

[0205] As Figure 22 shown, the computer terminal provided in this embodiment includes: at least one processor 101 and a memory 102 connected to at least one processor 101. In this embodiment, the specific connection medium between the processor 101 and the memory 102 is not limited. Figure 22 Here, it is taken as an example that the processor 101 and the memory 102 are connected through a bus 100. The bus 100 is represented by a thick line in Figure 22 here. The connection manners between other components are only illustrative and not restrictive. The bus 100 can be divided into an address bus, a data bus, a control bus, etc. For the convenience of representation, Figure 22 it is only represented by a thick line in here, but it does not mean that there is only one bus or one type of bus. Alternatively, the processor 101 can also be called a controller, and there is no limit to the name.

[0206] In this embodiment, the memory 102 stores instructions executable by at least one processor 101. By executing the instructions stored in the memory 102, at least one processor 101 can execute the foregoing method.

[0207] Among them, the processor 101 is the control center of the device, and can connect various parts of the entire control device through various interfaces and lines. By running or executing the instructions stored in the memory 102 and calling the data stored in the memory 102, various functions of the device and process data, so as to monitor the device as a whole.

[0208] In a possible design, the processor 101 may include one or more processing units. The processor 101 may integrate an application processor and a modem processor. Among them, the application processor mainly processes the operating system, user interface, application programs, etc., and the modem processor mainly processes wireless communication. It can be understood that the foregoing modem processor may not be integrated into the processor 101. In some embodiments, the processor 101 and the memory 102 can be implemented on the same chip, and in some embodiments, they can also be separately implemented on independent chips.

[0209] The processor 101 can be a general-purpose processor, such as a central processing unit (CPU), a digital signal processor, an application-specific integrated circuit, a field-programmable gate array, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, and can implement or execute the various methods, steps, and logic block diagrams disclosed in the embodiments. The general-purpose processor can be a microprocessor or any conventional processor, etc. The steps of the sliding mode fault-tolerant control method of the steer-by-wire system of the vehicle disclosed in conjunction with Embodiment 1 can be directly embodied as being executed by the hardware processor, or executed by a combination of hardware and software modules in the processor 101.

[0210] The memory 102, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. The memory 102 can include at least one type of storage medium, for example, it can include flash memory, a hard disk, a multimedia card, a card-type memory, a random access memory (RAM), a static random access memory (SRAM), a programmable read-only memory (PROM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a magnetic memory, a magnetic disk, an optical disk, and so on. The memory 102 is any other medium that can be used to carry or store the desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited to this. The memory 102 in this embodiment can also be a circuit or any other device capable of implementing a storage function, for storing program instructions and / or data.

[0211] By programming the design of the processor 101, the code corresponding to the security verification method introduced in the foregoing embodiments can be solidified into the chip, so that the chip can execute Figure 1 the steps of the method shown. How to program the design of the processor 101 is a well-known technology to those skilled in the art and will not be elaborated herein.

[0212] Embodiment 3

[0213] This embodiment provides a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps of the sliding mode fault-tolerant control method of the steer-by-wire system of the vehicle as described in Embodiment 1.

[0214] The computer-readable storage medium may include flash memory, a hard disk, a multimedia card, a card-type memory (e.g., SD or DX memory, etc.), a random access memory (RAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, etc. In some embodiments, the storage medium may be an internal storage unit of the computer device, such as the hard disk or memory of the computer device. In other embodiments, the storage medium may also be an external storage device of the computer device, such as a plug-in hard disk equipped on the computer device, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, etc. Of course, the storage medium may also include both the internal storage unit and the external storage device of the computer device. In this embodiment, the memory is generally used to store the operating system installed on the computer device and various application software. In addition, the memory may also be used to temporarily store various data that have been output or are to be output.

[0215] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, making equivalent substitutions or changes should be covered by the protection scope of the present invention.

Claims

1. A sliding mode fault-tolerant control method for a vehicle steer-by-wire system, characterized in that: The following steps are involved: S1. Establish a nonlinear bond graph model of the steer-by-wire system, and thereby establish a dynamic model of the front wheel subsystem in the steer-by-wire system; S2. Based on the dynamic model of the front wheel subsystem, a sliding mode controller is used to control the actual angle of the front wheel to track its reference angle so that the car moves on the desired trajectory; S3. When a fault is detected in the vehicle sensor, the sensor fault value is estimated through the sliding mode observer to eliminate the fault impact and achieve fault-tolerant control.

2. The sliding mode fault-tolerant control method of the automotive steer-by-wire system based on the bond graph model according to claim 1, characterized in that: Step S1 includes the following specific steps: S11. The steer-by-wire system is divided into a steering subsystem and a front wheel subsystem; wherein the steering subsystem includes a steering wheel, a feedback motor, a reducer, a feedback motor driver, a steering wheel angle sensor, and a feedback motor angle sensor; and the front wheel subsystem includes a steering motor driver, a steering motor, a reducer, a gear, a rack, a front wheel, a steering motor angle sensor, a gear angle sensor, and a front wheel angle sensor; S12. Construct a nonlinear bond graph model based on bond graph theory; wherein the basic elements of the nonlinear bond graph model include a one-port element, a two-port element and a multi-port element; the one-port element includes a potential source Se, a flow source Sf, a dissipative element R, an inertial element I, a capacitive element C and a flow sensor {Df1, Df2, ..., Df5}; the two-port element includes a transformer TF and a gyrator GY; the multi-port element includes a 1-type node and a 0-type node; S13. The dynamic model of the front wheel subsystem is established through the nonlinear bond graph model, and its expression is as follows: In the formula, K s is the steering motor torque constant; U2 is the input voltage of the steering motor; R m is the viscous friction coefficient of the steering motor; θ s is the steering motor angle, and They are θ s The first and second derivatives of C s is the stiffness of the steering motor shaft; x r is the rack displacement; G p1 is the reduction ratio of the reducer; r p is the gear radius; J s is the moment of inertia of the steering motor rotor; R p Represents the friction force of the rack; C p Represents the rack stiffness; G p2 Represents the ratio of rack linear velocity to front wheel angular velocity; θ fw is the actual turning angle of the front wheel; M p Represents the quality of the rack; θ fk is the front wheel turning angle; R fk is the friction between the tire and the ground; J fk is the moment of inertia of the front wheel; g m is the steering motor friction torque characteristic function, g r is the gear friction torque characteristic function, g fk is the characteristic function of the front wheel friction torque, and the expression formula of the three is Among them, T s,i and T c,i are the Coulomb friction torque and static friction torque of the corresponding components, λ i It is a representation of T s,i and T c,i The constant of transition between e is the self-aligning torque.

3. The sliding mode fault-tolerant control method of the automotive steer-by-wire system according to claim 2, characterized in that: Step S2 includes the following specific steps: S21. Set the system state and system input according to the dynamic model of the front wheel subsystem; wherein the system input is the input voltage u of the steering motor driver, and the expression formula of the system state x(t) is: In the formula, t represents time; superscript T is the transposition symbol; S22. Establish a state space model of the steer-by-wire system in a healthy state, expressed as: In the formula, is the derivative of the system state variable; y(t) is the system output, i.e., the front wheel steering angle; u(t) is the sliding mode control rate, i.e., the time-varying function of the input voltage u of the steering motor driver; f(x, t) is the nonlinear term; Ψ(x, t) is the lumped disturbance; A, B, and C are the state transfer coefficient matrix, input coefficient matrix, and output coefficient matrix, respectively; S23. After simplifying the dynamic model of the front wheel system, the dynamic equation of the front wheel system is obtained: In the formula, J eq is the equivalent moment of inertia; B eq is the equivalent damping coefficient; T f is the nonlinear friction torque; K e is the motor output torque coefficient; S24. The sliding mode control rate is set in combination with the dynamic equation, and the input voltage signal of the steering motor driver is controlled by the sliding mode controller according to the sliding mode control rate so that the actual angle of the front wheel tracks its reference angle; wherein the calculation formula of the input voltage u of the steering motor driver is: In the formula, θ fwd is the reference signal of the front wheel steering angle; c>0; s is the sliding surface; εsgn(·) is the sign function term, and k>0 is the linear term.

4. The sliding mode fault-tolerant control method of the automotive steer-by-wire system according to claim 3, characterized in that: In step S3, when a sensor failure is detected, the sliding mode observer automatically controls the motor output size according to its own design to achieve fault tolerance; wherein the design method of the sliding mode observer includes the following specific steps: S31. Establish a state space model of the steer-by-wire system under sensor failure, expressed as: In the formula, is the state variable of the car, y s (t) is the output of the steer-by-wire system; u r (t) is the control input, i.e., the input voltage of the steering motor driver; K r is the feedback motor torque constant, J w is the moment of inertia of the front wheel, B w is the viscous friction coefficient of the front wheel; B s =[0K r / G r J w ] T , G r is the transmission ratio between rack displacement and front wheel steering angle; C sy =[1 0] is the output gain matrix; is the nonlinear term in the steer-by-wire system; E s =[0 1] T ; ψ3(x s ,t) is the aggregate interference; M s =1; f s (t) is sensor failure; S32. Perform augmented reconstruction on the state space model of the steer-by-wire system under sensor failure to obtain an augmented matrix: In the formula, is the augmented state variable, where z(t) is a custom variable and can be the output y s (t) realizes low-pass filtering and satisfies the formula: A f is a stable filter matrix, defined as a diagonal positive definite matrix; S33. Using the augmented matrix to design a sliding mode observer, the expression formula is: In the formula, for The estimated value of for The estimated value of is τ s (x s ,t), that is, v is the discontinuous term in the sliding mode observer; L1 is the sliding mode observer gain matrix.

5. The sliding mode fault-tolerant control method of the automotive steer-by-wire system according to claim 4, characterized in that: After completing the design of the sliding mode observer, the sensor fault estimation value, i.e., the discontinuous term v in the sliding mode observer, is calculated, and the expression formula is: In the formula, e y and ρ1 is a positive scalar gain, ρ1>β fs ; H1 satisfies the formula Any matrix of, P1 is a 3×3 order real symmetric matrix; δ1 is a positive scalar; calculate in, f s (t) is an estimated value; The following formula is used to complete the fault tolerance of the faulty sensor. The fault tolerance formula is as follows: In the formula, is the front wheel steering angle after fault tolerance; y3(t) is the actual output of the fault sensor; is the sensor fault estimation error, which can converge to zero in a finite time.

6. A computer terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the sliding mode fault-tolerant control method of the automotive steer-by-wire system as claimed in any one of claims 1 to 5 are implemented.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the sliding mode fault-tolerant control method of a vehicle steer-by-wire system as claimed in any one of claims 1 to 5 are implemented.

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