Multi-shaft distributed steering system and fault-tolerant control method thereof

Abstract

The invention discloses a multi-axle distributed steering system and a fault-tolerant control method thereof. The multi-axle distributed steering system comprises a steering wheel assembly, a front axle steering controller, a double-rear axle steering controller and a multi-axle distributed steering execution assembly. The steering wheel assembly is used for receiving operation information of a driver and providing road feeling feedback; the front axle steering controller controls the multi-axle distributed steering execution assembly to complete steering and controls the road feeling motor to provide road feeling feedback according to steering wheel torque and steering angle information input by a driver and the vehicle running state. The double-rear-axle steering controller and the front-axle steering controller together control the multi-axle distributed steering execution assembly to complete steering and control the road feeling motor to provide road feeling feedback according to steering wheel torque and steering angle information input by a driver and the vehicle running state. According to the method, the safety redundancy performance of the multi-shaft distributed steer-by-wire system can be effectively improved, and the fault-tolerant capability and the driving safety of the vehicle are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed steering systems, and in particular relates to a multi-axis distributed steering system and a fault-tolerant control method thereof. Background Art

[0002] The distributed steering system can independently control the angle of each wheel through electrical signals, providing a new, optimal steering platform for intelligent driving. Furthermore, its four steering actuator assemblies provide a degree of redundancy compared to front-wheel steer-by-wire, compensating for the reduced reliability associated with steer-by-wire technology. Steering flexibility and safety are crucial for multi-axle vehicles under complex operating conditions. Traditional distributed steering systems, when faced with component failures, can be disrupted by a single-winding motor-driven steering system. If a short circuit or open circuit occurs in the motor winding, steering assistance will cease to function properly, posing significant risks to vehicle control. Furthermore, the system utilizes multiple, frequently operating steer-by-wire assemblies, leading to increased complexity in the event of a failure.

[0003] There have been some studies on fault-tolerant control of distributed steering systems, but most solutions use hardware redundancy design to achieve fault tolerance, such as adding a mechanical transmission mechanism as a backup for electrical signal failure, and setting up dual motors as a backup for motor failure. The use of hardware redundancy greatly increases the cost and size of the system and cannot fully utilize the advantages of wire-controlled steering. To address the above problems, Chinese invention patent application number CN201810340702.2, entitled "A Fault-Tolerant Control System and Control Method for a Wire-Controlled Four-Wheel Independent Steering System," discloses a calculation method for how to switch modes and allocate steering angles after a wire-controlled four-wheel independent steering system fails. However, when a system failure occurs, only two modes, front-wheel steering and rear-wheel steering, are set, which cannot fully utilize the advantages of distributed steering. At the same time, it does not distinguish between different fault types, which can easily lead to misjudgment due to sensor failure. The Chinese invention patent application number is CN202310469257.0, entitled "A dual-winding distributed wire-controlled steering system and its fault-tolerant control method", which discloses the realization of fault-tolerant control of the dual-winding distributed wire-controlled steering system under various fault conditions. However, in terms of system complexity and cost, a dual-winding motor needs to be installed on each wheel, which greatly increases the cost and redundancy, and the steering of the four wheels needs to be independently controlled and coordinated. The control algorithm is complex and has high requirements on the computing power and real-time performance of the controller. It is necessary to accurately judge the fault type and switch the control strategy in a short time, otherwise it is easy to cause the vehicle steering to lose control.

[0004] Therefore, in response to the above problems, the present invention proposes a multi-axis distributed wire-controlled steering system and a control method thereof. When the steering function of a vehicle fails, the performance advantages of the multi-axis distributed steering can be maximized while ensuring safety, and fault-tolerant control of the multi-axis distributed wire-controlled steering system with dual windings on the front axle can be achieved under various fault conditions. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a multi-axis distributed steering system and a fault-tolerant control method thereof, so as to solve the problems of the existing distributed wire-controlled steering fault-tolerant control method in the fault state, such as the single fault-tolerant control mode, complex control algorithm calculation, and excessively high cost. The present invention can effectively improve the safety redundancy performance of the multi-axis distributed wire-controlled steering system, and improve the vehicle's fault tolerance capability and driving safety.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a multi-axis distributed wire-controlled steering system, comprising: a steering wheel assembly, a front axle steering controller, a dual rear axle steering controller and a multi-axis distributed steering execution assembly; wherein,

[0008] The steering wheel assembly is arranged between the front axle and the dual rear axles, and is used to receive the driver's operating information and provide road feel feedback. It includes: a steering wheel, a steering column, a rotation angle torque sensor and a road feel motor. The steering wheel is connected to the steering column, and the rotation angle torque sensor and the road feel motor are both installed on the steering column. The rotation angle torque sensor and the road feel motor are respectively connected to the front axle steering controller and the dual rear axle steering controller;

[0009] The front axle steering controller is arranged between the steering wheel assembly and the front axle, and is connected to the steering wheel assembly and the multi-axis distributed steering actuator assembly through the vehicle bus. It controls the multi-axis distributed steering actuator assembly to complete steering and controls the road feel motor to provide road feel feedback based on the steering wheel torque and angle information input by the driver and the vehicle operating status.

[0010] The dual rear axle steering controller is arranged between the steering wheel assembly and the dual rear axles and is connected to the steering wheel assembly and the multi-axis distributed steering actuator assembly via the vehicle bus. Based on the steering wheel torque and steering angle information input by the driver and the vehicle operating status, it works together with the front axle steering controller to control the multi-axis distributed steering actuator assembly to complete steering and control the road feel motor to provide road feel feedback.

[0011] The multi-axis distributed steering execution assembly is respectively arranged on the two wheels of the front axle and the four wheels of the double rear axles, and includes: two front axle single-wheel steering execution assemblies, four rear axle single-wheel steering execution assemblies and three steering tie rod mechanisms. The front axle single-wheel steering assembly is distributed on the two front wheels, and the four rear axle single-wheel steering execution assemblies are distributed on the four wheels of the double rear axles. One of the three steering tie rod mechanisms is arranged between the two wheels of the front axle, and two are arranged between the four wheels of the double rear axles.

[0012] Furthermore, the front axle single-wheel steering execution assembly includes: a front axle dual-winding steering motor controller, a front axle dual-winding steering motor, a front axle dual-winding steering motor sensor, a first reducer assembly, a front axle wheel angle sensor, a front axle steering arm, a first column and a first shock absorber; the front axle dual-winding steering motor controller is connected to the front axle dual-winding steering motor, the output shaft of the front axle dual-winding steering motor is connected to the total input end of the first reducer, and is installed on the frame above the two wheels of the front axle, the output end of the first reducer assembly is connected to the front axle steering arm through a spline to transmit torque; the front axle steering arm is connected to the first column by a fastening bolt, and the first shock absorber is installed on the first column; the front axle dual-winding steering motor sensor is connected to the front axle dual-winding steering motor controller; the front axle wheel angle sensor is connected to the front axle steering controller.

[0013] Furthermore, the rear axle single-wheel steering execution assembly includes: a dual rear axle steering motor controller, a dual rear axle steering motor, a dual rear axle steering motor sensor, a second reducer assembly, a dual rear axle wheel angle sensor, a dual rear axle steering arm, a second column and a second shock absorber; the dual rear axle steering motor controller is connected to the dual rear axle steering motor, the output shaft of the dual rear axle steering motor is connected to the input end of the second reducer assembly, and is installed on the frame above the four wheels of the dual rear axles, the output end of the second reducer assembly is connected to the dual rear axle steering arm through a spline to transmit torque; the dual rear axle steering arm is connected to the second column by a fastening bolt, and the second shock absorber is installed on the second column; the dual rear axle steering motor sensor is connected to the dual rear axle steering motor controller; the dual rear axle wheel angle sensor is connected to the dual rear axle steering controller.

[0014] Furthermore, the three steering tie rod mechanisms are respectively installed on the front axle steering arm and the dual rear axle steering arms, which include a steering tie rod and an electromagnetic clutch. The electromagnetic clutch is set in the middle position of the steering tie rod, and the electromagnetic clutch is respectively connected to the front axle steering controller and the dual rear axle steering controller through the vehicle bus.

[0015] Furthermore, the first reducer assembly and the second reducer assembly are both two-stage reduction devices using a first-stage planetary gear reducer and a second-stage worm gear reducer.

[0016] Furthermore, the front axle dual-winding steering motor is a six-phase permanent magnet synchronous motor.

[0017] Furthermore, the dual rear axle steering motor is a three-phase permanent magnet synchronous motor.

[0018] Furthermore, the vehicle bus is a CAN bus or a Flex Ray bus.

[0019] In the present invention, under normal working conditions, the electromagnetic clutch device is in a disconnected state, and the rotation of the two wheels on the front axle and the four wheels on the dual rear axles do not interfere with each other; when the vehicle steering function fails, the front axle single-wheel steering execution assembly or the rear axle single-wheel steering execution assembly loses steering ability, and the electromagnetic clutch engages under the control of the front axle steering controller and the dual rear axle steering controller respectively, so that the front axle single-wheel steering execution assembly or the rear axle single-wheel steering execution assembly that has lost steering ability can follow the steering.

[0020] When the front axle single-wheel steering execution assembly is working, the front axle dual-winding steering motor controller controls the rotation of the front axle dual-winding steering motor according to the steering angle command of the front axle steering controller. The torque output by the front axle steering motor is decelerated and increased by the first reducer assembly, driving the front axle steering arm and the two wheels of the front axle to rotate together.

[0021] When the rear axle single-wheel steering execution assembly is working, the dual rear axle steering motor controller controls the rotation of the dual rear axle steering motor according to the steering angle command of the dual rear axle steering controller. The torque output by the dual rear axle steering motor is decelerated and increased by the second reducer assembly, driving the dual rear axle steering arm and the four wheels of the dual rear axle to rotate together.

[0022] The present invention also provides a fault-tolerant control method for a multi-axis distributed steer-by-wire system. Based on the above system, the steps are as follows:

[0023] 1) Collect the steering angle information and torque information input by the driver and send them to the front axle steering controller and the dual rear axle steering controller respectively; collect the front axle wheel angle information and send it to the front axle steering controller; collect the dual rear axle wheel angle information and send it to the dual rear axle steering controller;

[0024] 2) determining whether the multi-axis distributed steer-by-wire system is in a normal operating condition based on the steering angle and torque information input by the driver and the vehicle operating status; if it is in a normal operating condition, proceeding to step 3); if it is in a faulty operating condition, proceeding to step 4);

[0025] 3) Calculating the steering angle distribution instructions for the two front axle wheels and the four rear axle wheels, and controlling the front axle single-wheel steering actuating assembly and the rear axle single-wheel steering actuating assembly to execute the corresponding wheel steering angle distribution instructions;

[0026] 4) Determine the specific location of the fault. If the fault location is a front axle dual-winding steering motor fault, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to perform fault-tolerant control on the faulty front axle dual-winding steering motor; if the fault location is a dual rear axle steering motor fault, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location of the fault, so that the dual rear axle steering motor that still has normal steering function among the four wheels of the dual rear axle drives the faulty dual rear axle steering motor to rotate to complete the steering; if the fault location is a multiple steering fault of the front axle dual-winding steering motor and the dual rear axle steering motor, the differential torque required for the front axle differential steering is solved; finally, the current status of the multi-axis distributed steering system is fed back to the vehicle controller.

[0027] Furthermore, the vehicle operating state in step 2) includes: wheel angle, vehicle speed, vehicle yaw angular velocity, vehicle roll angular velocity and vehicle center of mass sideslip angle.

[0028] Furthermore, the determination method in step 2) specifically includes:

[0029] The front axle steering controller uses a state observer to obtain the real-time estimated state of the two front axle wheels, and subtracts it from the measured value of the front axle wheel angle sensor to obtain a first residual sequence; if the first residual sequence is within the set threshold, the front axle dual-winding steering motor is in normal working condition; if the first residual sequence exceeds the set threshold, the front axle dual-winding steering motor is in a faulty state; the dual rear axle steering controller uses a state observer to obtain the real-time estimated state of the four wheels of the dual rear axles, and subtracts it from the measured value of the dual rear axle wheel angle sensor to obtain a second residual sequence; if the second residual sequence is within the set threshold, the dual rear axle steering motor is in normal working condition; if the second residual sequence exceeds the set threshold, the dual rear axle steering motor is in a faulty state; if both the first residual sequence and the second residual sequence exceed the corresponding set thresholds, it is determined that both the front axle dual-winding motor and the dual rear axle steering motor are in a faulty state.

[0030] Furthermore, the state observer is a sliding mode observer or a Lumberg observer.

[0031] Furthermore, in step 2), the state observer calculates the steering angles of the two front axle wheels and the steering angles of the four rear axle wheels using the vehicle roll angular velocity and the vehicle yaw angular velocity, and determines whether the vehicle is in a normal working state by the residual error and the residual norm of the steering angle value. The expression is as follows:

[0032]

[0033] Where ω represents the vehicle's yaw rate, δ ii Indicates the turning angle of the two wheels on the front axle or the four wheels on the dual rear axles, u indicates the vehicle speed, Le represents the equivalent wheelbase, K represents the stability coefficient of the vehicle, m represents the vehicle mass, l f Indicates the distance from the front axle to the center of mass of the vehicle, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r k represents the distance between the second rear axle and the vehicle's center of mass. f is the tire cornering stiffness of the front axle, k m is the tire cornering stiffness of the first rear axle in the dual rear axle, k r is the tire cornering stiffness of the second rear axle in the dual rear axle, p is the vehicle roll angular velocity, φ is the vehicle roll angle; L′=l f +l r , L1=l f +l m , L2=l m +l r , L' is the distance between the front axle and the second rear axle of the dual rear axles; L1 is the distance between the front axle and the first rear axle of the dual rear axles; L2 is the sum of the distance between the front axle and the first rear axle of the dual rear axles and the distance between the front axle and the second rear axle of the dual rear axles;

[0034] The residual sequence of the vehicle's yaw rate, roll rate, and sideslip angle exceeds the set threshold to determine whether the steering angles of the two front axle wheels and the steering angles of the four rear axles calculated by the state observer are correct and satisfy the following formula:

[0035]

[0036] Among them, e ωm 、e pm 、e βm are the upper limits of the yaw rate residual, roll rate residual and center of mass sideslip angle residual respectively; σ ω , σ p , σ β are the measurement errors of yaw rate, roll rate and sideslip angle respectively; e ω is the yaw rate residual, e p is the roll angular velocity residual, e β is the center of mass sideslip angle residual, Δω is the error between the yaw rate measurement and the ideal value, Δp is the error between the roll rate measurement and the ideal value, Δβ is the error between the center of mass sideslip angle measurement and the ideal value, |.| max Indicates the maximum absolute value.

[0037] Furthermore, the step 3) specifically includes:

[0038] The current equivalent front axle transmission ratio and equivalent dual rear axle transmission ratio are determined based on the input steering wheel angle and vehicle operating status. The equivalent front axle angle and equivalent dual rear axle angle are then calculated and the steering center is determined. The wheel angle adjustment amount is calculated based on the position of the steering center.

[0039] Genetic algorithms and neural network algorithms are used to determine the current equivalent front axle transmission ratio and the equivalent dual rear axle transmission ratio. The solution expressions for the current equivalent front axle angle and the equivalent dual rear axle angle are as follows:

[0040]

[0041] Among them, δ f , δ m , δ r are the equivalent front axle angle, the equivalent first dual rear axle angle, and the equivalent second dual rear axle angle, θ sw is the input steering wheel angle, G f , G m , G r They are the equivalent front axle transmission ratio, the equivalent dual rear axle first axle transmission ratio and the equivalent dual rear axle second axle transmission ratio respectively;

[0042] The instantaneous steering center position is determined based on the equivalent front axle angle, the equivalent first axis angle of the dual rear axles, and the equivalent second axis angle of the dual rear axles. The expression is as follows:

[0043]

[0044] Among them, L B is the vehicle width, L c It is the vertical distance from the inner side of the turning vehicle to the turning center;

[0045] Calculate the steering angle adjustment of each wheel, the expression is as follows:

[0046]

[0047] Among them, v y is the vehicle lateral velocity, v x is the vehicle longitudinal velocity, Δ f , Δ m , Δ r They are the equivalent front axle angle adjustment, the equivalent dual rear axle first axle angle adjustment and the equivalent dual rear axle second axle angle adjustment respectively;

[0048] Calculate the distribution value of the steering angle of each wheel. The expression is as follows:

[0049]

[0050] Among them, δ fl is the left front wheel turning angle, δfr is the right front wheel turning angle, δ ml is the left turning angle of the first rear axle in the double rear axle, δ mr is the right turning angle of the first rear axle in the dual rear axles, δ rl is the left turning angle of the second rear axle in the double rear axle, δ rr It is the right turning angle of the second rear axle in the double rear axle.

[0051] Furthermore, in step 4), after the front axle dual-winding steering motor sensor detects that the front axle dual-winding steering motor has failed, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to optimize the control of the front axle dual-winding steering motor after the motor failure by using a control algorithm based on model predictive control principles and PID;

[0052] The control algorithm based on the model predictive control principle and PID is divided into an angle control loop and a current control loop. The input of the angle control loop is the calculated desired steering angle of the two wheels on the front axle, and the output is the reference current of the dq axes of the front axle dual-winding steering motor; the input of the current control loop is the reference current and actual current of the dq axes of the front axle dual-winding steering motor, and the output is the voltage control amount of the dq axes of the front axle dual-winding steering motor; the obtained voltage control amount of the dq axes of the front axle dual-winding steering motor is subjected to VSD coordinate transformation and vector PWM modulation, and then acts on the front axle dual-winding steering motor to control the front axle dual-winding steering motor;

[0053] The calculation steps of the control algorithm based on the model predictive control principle and PID include: using the model predictive control as an outer loop controller to predict the future expected current value of the system and calculate the optimal current value; using the PID controller as an inner loop controller to adjust the current demand for a period of time in the future predicted by the model predictive control based on the motor model and fault information according to the error between the expected current value provided by the model predictive control and the actual output value; then using the current demand as the set value of the PID controller, and the PID controller adjusts the input voltage of the motor according to the error between the actual current and the set value, thereby realizing control of the front axle dual-winding steering motor;

[0054] Optimization control is performed based on the principle that the stator magnetomotive force remains unchanged before and after the fault. The prediction model after the fault is corrected based on the optimized mathematical model. The reference phase current after the fault is solved with the minimum stator current amplitude as the optimization goal for tracking control of the current loop.

[0055] The state space equation of the prediction model after the front axle dual-winding steering motor fails is expressed as follows:

[0056] x(k+1)=Ax(k)+Bu(k)

[0057] y(k)=Cx(k)

[0058] Among them, A, B, and C are all coefficient matrices; x(k) is the state quantity at time k, x(k+1) is the state quantity at time k+1, y(k) is the output quantity at time k, and u(k) is the control quantity at time k; the A, B, and C matrices are:

[0059]

[0060] Where, R is the stator resistance; L d , L q is the dq axis stator inductance; L z is the stator leakage inductance; T s is the sampling period; ω e (k) represents the motor angular velocity sampled at time k;

[0061] The output expression after optimized control is:

[0062] Y=ψξ(k)+ΘΔU

[0063] Among them, Y is the output; ψ and Θ are coefficient matrices; Y, ψ, and Θ are respectively:

[0064]

[0065] Where ξ(k) is the state matrix obtained after iteration; ΔU is the control increment matrix obtained after iteration; A, B, and C are all coefficient matrices; y(k+i|k) represents the output within the prediction step, i = 1, 2, ..., N p ; Δu(k+i) is the control quantity increment within the control step, i=1,2,…,N c ;

[0066] The cost function J of model predictive control is:

[0067]

[0068] Where Np is the prediction step size; N c is the control step size; y ref (k+i|k) is the reference value of the output; Δu(k+i) is the control increment within the control step; Q and R are the weight coefficient matrices of the output and the control increment, respectively;

[0069] The problem of calculating the current control variable through model predictive control is transformed into a quadratic programming problem, which is expressed as follows:

[0070]

[0071] st△U min ≤ΔU≤ΔU max

[0072] Where H and g are solvable matrices; ΔU min and ΔU max are the minimum and maximum values ​​of the control increment respectively.

[0073] Furthermore, in step 4), when the fault location is a dual rear axle steering motor failure, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location where the fault occurs, so that the dual rear axle single-wheel steering execution assembly with normal steering of the four wheels of the dual rear axle still drives the faulty dual rear axle single-wheel steering execution assembly to rotate, thereby completing the steering.

[0074] Furthermore, in step 4), when the fault location is a multiple steering fault of the front axle dual-winding steering motor and the dual rear axle steering motors, the front axle steering controller solves the differential torque required for the front axle differential steering based on a sliding mode control method. The specific process is as follows: when the multi-axis distributed steering system fails, the differential steering is activated, and the steering wheel input is interpreted into the desired yaw angular velocity of the vehicle using the sliding mode control method, ensuring that the vehicle's yaw angular velocity tracks the desired yaw angular velocity, thereby obtaining the required differential torque;

[0075] The desired yaw rate of the vehicle is expressed as:

[0076]

[0077] Among them, ω a represents the desired yaw rate of the vehicle, δ h Represented as the input of the steering wheel, L e Indicates the equivalent wheelbase; K e represents the stability factor, v x Indicates the longitudinal speed of the vehicle;

[0078] According to the desired yaw rate of the vehicle, the sliding surface of the sliding mode control is defined as:

[0079]

[0080] Where c is the proportional function; ω a represents the desired yaw rate of the vehicle; ω represents the yaw rate of the vehicle;

[0081] The output of the sliding mode controller is obtained as follows:

[0082] u=u eq +u sw

[0083] Where u is the output of the sliding mode controller, u eq is equivalent control, which means the control quantity that moves stably along the sliding surface under ideal conditions; u sw is the switching control quantity;

[0084] The differential torque required for differential steering of the left and right wheels on the front axle is calculated as follows:

[0085]

[0086] Among them, ΔM is the differential torque required for the left and right wheels of the front axle to perform differential steering, C f is the front axle equivalent cornering stiffness, C m is the equivalent cornering stiffness of the first axis of the dual rear axles, C r is the equivalent cornering stiffness of the second rear axle, ω a represents the desired yaw rate of the vehicle, ω is the yaw rate of the vehicle, is a function of the yaw rate, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r Indicates the distance between the second rear axle and the vehicle's center of mass, l f Indicates the distance from the front axle to the vehicle's center of mass.

[0087] Beneficial effects of the present invention:

[0088] The present invention can achieve fault-tolerant control of a multi-axis distributed wire-controlled steering system under various position fault conditions; compared with the traditional wire-controlled four-wheel steering method, the present invention significantly reduces redundancy costs and has low fault-tolerant control complexity, which can effectively improve the fault-tolerant capability of the multi-axis distributed wire-controlled steering system and the driving safety of the vehicle.

[0089] 1. This invention improves the fault tolerance of the multi-axis distributed steering system, ensuring that the system can maintain stable operation in the event of a fault. The front axle uses a dual-winding motor as the steering motor, greatly improving the hardware fault tolerance of the distributed wire-controlled steering system. The vehicle will have obvious advantages in driving safety, cost control, lightweight design, etc.

[0090] 2. The present invention adopts a front axle dual-winding motor fault tolerance method combining model predictive control and PID, and a multiple steering fault tolerance method based on sliding mode control for the front axle dual-winding steering motor and the dual rear axle steering motor. It can perform fault-tolerant control of various position fault conditions, and fault-tolerant control of conditions where multiple position faults exist at the same time, thereby improving the fault tolerance capability of multi-axle distributed steering vehicles for fault types and the driving safety of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 Schematic diagram of the structure of the system of the present invention;

[0092] Figure 2 This is a schematic structural diagram of the front axle single-wheel steering actuator assembly of the present invention;

[0093] Figure 3 This is a flow chart of the fault-tolerant control method of the present invention;

[0094] Figure 4 This is a flow chart of the fault-tolerant control algorithm based on model prediction principle and PID motor;

[0095] Figure 5 This is the flow chart of the differential steering fault-tolerant control algorithm based on sliding mode control. DETAILED DESCRIPTION

[0096] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and drawings. The contents mentioned in the embodiments are not intended to limit the present invention.

[0097] Reference Figure 1 、 Figure 2 As shown, a multi-axis distributed wire-controlled steering system of the present invention includes: a steering wheel assembly 1, a front axle steering controller 2, a dual rear axle steering controller 3 and a multi-axis distributed steering execution assembly 4; wherein,

[0098] The steering wheel assembly 1 is arranged between the front axle and the dual rear axles, and is used to receive the driver's operation information and provide road feel feedback. It includes: a steering wheel 101, a steering column 102, a rotation angle torque sensor 103 and a road feel motor 104. The steering wheel 101 is connected to the steering column 102, and the rotation angle torque sensor 103 and the road feel motor 104 are both installed on the steering column 102. The rotation angle torque sensor 103 and the road feel motor 104 are respectively connected to the front axle steering controller 2 and the dual rear axle steering controller 3;

[0099] The front axle steering controller 2 is arranged between the steering wheel assembly 1 and the front axle, and is connected to the steering wheel assembly and the multi-axis distributed steering execution assembly through the vehicle bus; it controls the multi-axis distributed steering execution assembly 4 to complete the steering and controls the road sense motor 104 to provide road sense feedback according to the steering wheel torque, steering angle information and vehicle operating status input by the driver;

[0100] The dual rear axle steering controller 3 is arranged between the steering wheel assembly and the dual rear axles, and is connected to the steering wheel assembly and the multi-axis distributed steering execution assembly through the vehicle bus. Based on the steering wheel torque and angle information input by the driver and the vehicle operating status, it controls the multi-axis distributed steering execution assembly 4 together with the front axle steering controller to complete the steering and control the road sense motor 104 to provide road sense feedback.

[0101] The multi-axis distributed steering execution assembly 4 is respectively arranged on the two wheels 4018 of the front axle and the four wheels 4018 of the double rear axles, and includes: two front axle single-wheel steering execution assemblies 401, four rear axle single-wheel steering execution assemblies 402 and three steering tie rod mechanisms 403. The front axle single-wheel steering assembly is distributed on the two front wheels, and the four rear axle single-wheel steering execution assemblies are distributed on the four wheels of the double rear axles. One of the three steering tie rod mechanisms is arranged between the two wheels of the front axle, and two are arranged between the four wheels of the double rear axles.

[0102] Specifically, the front axle single-wheel steering execution assembly 401 includes: a front axle dual-winding steering motor controller 4011, a front axle dual-winding steering motor 4012, a front axle dual-winding steering motor sensor 4013, a first reducer assembly 4015, a front axle wheel angle sensor 4016, a front axle steering arm 4017, a first column 4019 and a first shock absorber 40110; the front axle dual-winding steering motor controller 4011 is connected to the front axle dual-winding steering motor 4012, and the output shaft of the front axle dual-winding steering motor 4012 is connected to the first reducer assembly The input end of the first reducer assembly 4015 is connected to the front axle and is installed on the frame 4014 above the two wheels 4018 of the front axle. The output end of the first reducer assembly 4015 is connected to the front axle steering arm 4017 through a spline to transmit torque; the front axle steering arm 4017 is connected to the first column 4019 through a fastening bolt, and the first shock absorber 40110 is installed on the first column 4019; the front axle dual-winding steering motor sensor 4013 is connected to the front axle dual-winding steering motor controller 4011; the front axle wheel angle sensor 4016 is connected to the front axle steering controller 2.

[0103] Specifically, the rear axle single-wheel steering execution assembly includes: a dual rear axle steering motor controller, a dual rear axle steering motor, a dual rear axle steering motor sensor, a second reducer assembly, a dual rear axle wheel angle sensor, a dual rear axle steering arm, a second column and a second shock absorber; the dual rear axle steering motor controller is connected to the dual rear axle steering motor, the output shaft of the dual rear axle steering motor is connected to the input end of the second reducer assembly, and is installed on the frame above the four wheels of the dual rear axles, the output end of the second reducer assembly is connected to the dual rear axle steering arm through a spline to transmit torque; the dual rear axle steering arm is connected to the second column by a fastening bolt, and the second shock absorber is installed on the second column; the dual rear axle steering motor sensor is connected to the dual rear axle steering motor controller; the dual rear axle wheel angle sensor is connected to the dual rear axle steering controller.

[0104] Specifically, the three steering tie rod mechanisms are respectively installed on the front axle steering arm and the dual rear axle steering arms, which include a steering tie rod and an electromagnetic clutch. The electromagnetic clutch is set in the middle position of the steering tie rod, and the electromagnetic clutch is connected to the front axle steering controller and the dual rear axle steering controller respectively through the vehicle bus.

[0105] Specifically, the first reducer assembly and the second reducer assembly are both two-stage reduction devices using a first-stage planetary gear reducer and a second-stage worm gear reducer.

[0106] Specifically, the front axle dual-winding steering motor is a six-phase permanent magnet synchronous motor.

[0107] Specifically, the dual rear axle steering motor is a three-phase permanent magnet synchronous motor.

[0108] Specifically, the vehicle bus is a CAN bus or a Flex Ray bus.

[0109] In the present invention, under normal working conditions, the electromagnetic clutch device is in a disconnected state, and the rotation of the two wheels on the front axle and the four wheels on the dual rear axles do not interfere with each other; when the vehicle steering function fails, the front axle single-wheel steering execution assembly or the rear axle single-wheel steering execution assembly loses steering ability, and the electromagnetic clutch engages under the control of the front axle steering controller and the dual rear axle steering controller respectively, so that the front axle single-wheel steering execution assembly or the rear axle single-wheel steering execution assembly that has lost steering ability can follow the steering.

[0110] When the front axle single-wheel steering execution assembly is working, the front axle dual-winding steering motor controller controls the rotation of the front axle dual-winding steering motor according to the steering angle command of the front axle steering controller. The torque output by the front axle steering motor is decelerated and increased by the first reducer assembly, driving the front axle steering arm and the two wheels of the front axle to rotate together.

[0111] When the rear axle single-wheel steering execution assembly is working, the dual rear axle steering motor controller controls the rotation of the dual rear axle steering motor according to the steering angle command of the dual rear axle steering controller. The torque output by the dual rear axle steering motor is decelerated and increased by the second reducer assembly, driving the dual rear axle steering arm and the four wheels of the dual rear axle to rotate together.

[0112] Reference Figures 3 to 5 As shown, the present invention also provides a fault-tolerant control method for a multi-axis distributed steer-by-wire system. Based on the above system, the steps are as follows:

[0113] 1) Collect the steering angle information and torque information input by the driver and send them to the front axle steering controller and the dual rear axle steering controller respectively; collect the front axle wheel angle information and send it to the front axle steering controller; collect the dual rear axle wheel angle information and send it to the dual rear axle steering controller;

[0114] 2) determining whether the multi-axis distributed steer-by-wire system is in a normal operating condition based on the steering angle and torque information input by the driver and the vehicle operating status; if it is in a normal operating condition, proceeding to step 3); if it is in a faulty operating condition, proceeding to step 4);

[0115] The vehicle operating state in step 2) includes: wheel angle, vehicle speed, vehicle yaw angular velocity, vehicle roll angular velocity and vehicle center of mass sideslip angle.

[0116] Specifically, the judgment method in step 2) includes:

[0117] The front axle steering controller uses a state observer to obtain the real-time estimated state of the two front axle wheels, and subtracts it from the measured value of the front axle wheel angle sensor to obtain a first residual sequence; if the first residual sequence is within the set threshold, the front axle dual-winding steering motor is in normal working condition; if the first residual sequence exceeds the set threshold, the front axle dual-winding steering motor is in a faulty state; the dual rear axle steering controller uses a state observer to obtain the real-time estimated state of the four wheels of the dual rear axles, and subtracts it from the measured value of the dual rear axle wheel angle sensor to obtain a second residual sequence; if the second residual sequence is within the set threshold, the dual rear axle steering motor is in normal working condition; if the second residual sequence exceeds the set threshold, the dual rear axle steering motor is in a faulty state; if both the first residual sequence and the second residual sequence exceed the corresponding set thresholds, it is determined that both the front axle dual-winding motor and the dual rear axle steering motor are in a faulty state.

[0118] The state observer is a sliding mode observer or a Lumberg observer.

[0119] In step 2), the state observer calculates the turning angles of the two front axle wheels and the turning angles of the four rear axle wheels using the vehicle roll angular velocity and the vehicle yaw angular velocity, and determines whether the state is in a normal working state by the residual and residual norm of the turning angle value. The expression is as follows:

[0120]

[0121] Where ω represents the vehicle's yaw rate, δ ii Indicates the turning angle of the two wheels on the front axle or the four wheels on the dual rear axles, u indicates the vehicle speed, L e represents the equivalent wheelbase, K represents the stability coefficient of the vehicle, m represents the vehicle mass, l f Indicates the distance from the front axle to the center of mass of the vehicle, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r k represents the distance between the second rear axle and the vehicle's center of mass. f is the tire cornering stiffness of the front axle, k m is the tire cornering stiffness of the first rear axle in the dual rear axle, kr is the tire cornering stiffness of the second rear axle in the dual rear axle, p is the vehicle roll angular velocity, φ is the vehicle roll angle; L′=l f +l r , L1=l f +l m , L2=l m +l r , L' is the distance between the front axle and the second rear axle of the dual rear axles; L1 is the distance between the front axle and the first rear axle of the dual rear axles; L2 is the sum of the distance between the front axle and the first rear axle of the dual rear axles and the distance between the front axle and the second rear axle of the dual rear axles;

[0122] The residual sequence of the vehicle's yaw rate, roll rate, and sideslip angle exceeds the set threshold to determine whether the steering angles of the two front axle wheels and the steering angles of the four rear axles calculated by the state observer are correct and satisfy the following formula:

[0123]

[0124] Among them, e ωm 、e pm 、e βm are the upper limits of the yaw rate residual, roll rate residual and center of mass sideslip angle residual respectively; σ ω , σ p , σ β are the measurement errors of yaw rate, roll rate and sideslip angle respectively; e ω is the yaw rate residual, e p is the roll angular velocity residual, e β is the center of mass sideslip angle residual, Δω is the error between the yaw rate measurement and the ideal value, Δp is the error between the roll rate measurement and the ideal value, Δβ is the error between the center of mass sideslip angle measurement and the ideal value, |.| max Indicates the maximum absolute value.

[0125] 3) Calculating the steering angle distribution instructions for the two front axle wheels and the four rear axle wheels, and controlling the front axle single-wheel steering execution assembly and the rear axle single-wheel steering execution assembly to execute the corresponding wheel steering angle distribution instructions; specifically including:

[0126] The current equivalent front axle transmission ratio and equivalent dual rear axle transmission ratio are determined based on the input steering wheel angle and vehicle operating status. The equivalent front axle angle and equivalent dual rear axle angle are then calculated and the steering center is determined. The wheel angle adjustment amount is calculated based on the position of the steering center.

[0127] Genetic algorithms and neural network algorithms are used to determine the current equivalent front axle transmission ratio and the equivalent dual rear axle transmission ratio. The solution expressions for the current equivalent front axle angle and the equivalent dual rear axle angle are as follows:

[0128]

[0129] Among them, δ f , δ m , δ r are the equivalent front axle angle, the equivalent first dual rear axle angle, and the equivalent second dual rear axle angle, θ sw is the input steering wheel angle, G f , G m , G r They are the equivalent front axle transmission ratio, the equivalent dual rear axle first axle transmission ratio and the equivalent dual rear axle second axle transmission ratio respectively;

[0130] The instantaneous steering center position is determined based on the equivalent front axle angle, the equivalent first axis angle of the dual rear axles, and the equivalent second axis angle of the dual rear axles. The expression is as follows:

[0131]

[0132] Among them, L B is the vehicle width, L c It is the vertical distance from the inner side of the turning vehicle to the turning center;

[0133] Calculate the steering angle adjustment of each wheel, the expression is as follows:

[0134]

[0135] Among them, v y is the vehicle lateral velocity, v x is the vehicle longitudinal velocity, Δ f , Δ m , Δ r They are the equivalent front axle angle adjustment, the equivalent dual rear axle first axle angle adjustment and the equivalent dual rear axle second axle angle adjustment respectively;

[0136] Calculate the distribution value of the steering angle of each wheel. The expression is as follows:

[0137]

[0138] Among them, δ fl is the left front wheel turning angle, δ fr is the right front wheel turning angle, δ ml is the left turning angle of the first rear axle in the double rear axle, δ mr is the right turning angle of the first rear axle in the dual rear axles, δ rl is the left turning angle of the second rear axle in the double rear axle, δ rrIt is the right turning angle of the second rear axle in the double rear axle.

[0139] 4) Determine the specific location of the fault. If the fault is located in the front axle dual-winding steering motor, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to perform fault-tolerant control on the faulty front axle dual-winding steering motor. If the fault is located in the dual rear axle steering motor, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location of the fault, so that the dual rear axle steering motor that still has normal steering function among the four wheels of the dual rear axle drives the faulty dual rear axle steering motor to rotate to complete the steering. If the fault is located in the front axle dual-winding steering motor and the dual rear axle steering motor with multiple steering faults, the differential torque required for the front axle differential steering is solved. Finally, the current state of the multi-axis distributed steering system is fed back to the vehicle controller.

[0140] Wherein, in said step 4), after the front axle dual-winding steering motor sensor detects that the front axle dual-winding steering motor has a fault, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to optimize the control of the front axle dual-winding steering motor after the motor fault by using a control algorithm based on model predictive control principle and PID;

[0141] The control algorithm based on the model predictive control principle and PID is divided into an angle control loop and a current control loop. The input of the angle control loop is the calculated desired steering angle of the two wheels on the front axle, and the output is the reference current of the dq axes of the front axle dual-winding steering motor; the input of the current control loop is the reference current and actual current of the dq axes of the front axle dual-winding steering motor, and the output is the voltage control amount of the dq axes of the front axle dual-winding steering motor; the obtained voltage control amount of the dq axes of the front axle dual-winding steering motor is subjected to VSD coordinate transformation and vector PWM modulation, and then acts on the front axle dual-winding steering motor to control the front axle dual-winding steering motor;

[0142] The calculation steps of the control algorithm based on the model predictive control principle and PID include: using the model predictive control as an outer loop controller to predict the future expected current value of the system and calculate the optimal current value; using the PID controller as an inner loop controller to adjust the current demand for a period of time in the future predicted by the model predictive control based on the motor model and fault information according to the error between the expected current value provided by the model predictive control and the actual output value; then using the current demand as the set value of the PID controller, and the PID controller adjusts the input voltage of the motor according to the error between the actual current and the set value, thereby realizing control of the front axle dual-winding steering motor;

[0143] Optimization control is performed based on the principle that the stator magnetomotive force remains unchanged before and after the fault. The prediction model after the fault is corrected based on the optimized mathematical model. The reference phase current after the fault is solved with the minimum stator current amplitude as the optimization goal for tracking control of the current loop.

[0144] The state space equation of the prediction model after the front axle dual-winding steering motor fails is expressed as follows:

[0145] x(k+1)=Ax(k)+Bu(k)

[0146] y(k)=Cx(k)

[0147] Among them, A, B, and C are all coefficient matrices; x(k) is the state quantity at time k, x(k+1) is the state quantity at time k+1, y(k) is the output quantity at time k, and u(k) is the control quantity at time k; the A, B, and C matrices are:

[0148]

[0149] Where, R is the stator resistance; L d , L q is the dq axis stator inductance; L z is the stator leakage inductance; T s is the sampling period; ω e (k) represents the motor angular velocity sampled at time k;

[0150] The output expression after optimized control is:

[0151] Y=ψξ(k)+ΘΔU

[0152] Among them, Y is the output; ψ and Θ are coefficient matrices; Y, ψ, and Θ are respectively:

[0153]

[0154] Where ξ(k) is the state matrix obtained after iteration; ΔU is the control increment matrix obtained after iteration; A, B, and C are all coefficient matrices; y(k+i|k) represents the output within the prediction step, i = 1, 2, ..., N p ; Δu(k+i) is the control quantity increment within the control step, i=1,2,…,N c ;

[0155] The cost function J of model predictive control is:

[0156]

[0157] Where Np is the prediction step size; N c is the control step size; y ref(k+i|k) is the reference value of the output; Δu(k+i) is the control increment within the control step; Q and R are the weight coefficient matrices of the output and the control increment, respectively;

[0158] The problem of calculating the current control variable through model predictive control is transformed into a quadratic programming problem, which is expressed as follows:

[0159]

[0160] St△U min ≤ΔU≤ΔU max

[0161] Where H and g are solvable matrices; ΔU min and ΔU max are the minimum and maximum values ​​of the control increment respectively.

[0162] In step 4), when the fault location is a dual rear axle steering motor fault, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location where the fault occurs, so that the dual rear axle single-wheel steering execution assembly with normal steering of the four wheels of the dual rear axle still drives the faulty dual rear axle single-wheel steering execution assembly to rotate, thereby completing the steering.

[0163] In step 4), if the fault location is a multiple steering fault of the front axle dual-winding steering motor and the dual rear axle steering motors, the front axle steering controller solves the differential torque required for front axle differential steering based on a sliding mode control method. The specific process is as follows: in the event of a failure of the multi-axis distributed steering system, differential steering is activated, and the steering wheel input is interpreted into a desired yaw angular velocity of the vehicle using the sliding mode control method, ensuring that the vehicle's yaw angular velocity tracks the desired yaw angular velocity, thereby obtaining the desired differential torque.

[0164] The desired yaw rate of the vehicle is expressed as:

[0165]

[0166] Among them, ω a represents the desired yaw rate of the vehicle, δ h Represented as the input of the steering wheel, L e Indicates the equivalent wheelbase; K e represents the stability factor, v x Indicates the longitudinal speed of the vehicle;

[0167] According to the desired yaw rate of the vehicle, the sliding surface of the sliding mode control is defined as:

[0168]

[0169] Where c is the proportional function; ωa represents the desired yaw rate of the vehicle; ω represents the yaw rate of the vehicle;

[0170] The output of the sliding mode controller is obtained as follows:

[0171] u=u eq +u sw

[0172] Where u is the output of the sliding mode controller, u eq is equivalent control, which means the control quantity that moves stably along the sliding surface under ideal conditions; u sw is the switching control quantity;

[0173] The differential torque required for differential steering of the left and right wheels on the front axle is calculated as follows:

[0174]

[0175] Among them, ΔM is the differential torque required for the left and right wheels of the front axle to perform differential steering, C f is the front axle equivalent cornering stiffness, C m is the equivalent cornering stiffness of the first axis of the dual rear axles, C r is the equivalent cornering stiffness of the second rear axle, ω a represents the desired yaw rate of the vehicle, ω is the yaw rate of the vehicle, is a function of the yaw rate, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r Indicates the distance between the second rear axle and the vehicle's center of mass, l f Indicates the distance from the front axle to the vehicle's center of mass.

[0176] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be considered as the scope of protection of the present invention.

Claims

1. A multi-axis distributed steer-by-wire system, characterized in that: include: Steering wheel assembly, front axle steering controller, dual rear axle steering controller and multi-axis distributed steering execution assembly; among them, The steering wheel assembly is arranged between the front axle and the dual rear axles, and is used to receive the driver's operating information and provide road feel feedback. It includes: a steering wheel, a steering column, a rotation angle torque sensor and a road feel motor. The steering wheel is connected to the steering column, and the rotation angle torque sensor and the road feel motor are both installed on the steering column. The rotation angle torque sensor and the road feel motor are respectively connected to the front axle steering controller and the dual rear axle steering controller; The front axle steering controller is arranged between the steering wheel assembly and the front axle, and is connected to the steering wheel assembly and the multi-axis distributed steering actuator assembly through the vehicle bus. It controls the multi-axis distributed steering actuator assembly to complete steering and controls the road feel motor to provide road feel feedback based on the steering wheel torque and angle information input by the driver and the vehicle operating status. The dual rear axle steering controller is arranged between the steering wheel assembly and the dual rear axles and is connected to the steering wheel assembly and the multi-axis distributed steering actuator assembly via the vehicle bus. Based on the steering wheel torque and steering angle information input by the driver and the vehicle operating status, it works together with the front axle steering controller to control the multi-axis distributed steering actuator assembly to complete steering and control the road feel motor to provide road feel feedback. The multi-axis distributed steering execution assembly is respectively arranged on the two wheels of the front axle and the four wheels of the double rear axles, and includes: two front axle single-wheel steering execution assemblies, four rear axle single-wheel steering execution assemblies and three steering tie rod mechanisms. The front axle single-wheel steering assembly is distributed on the two front wheels, and the four rear axle single-wheel steering execution assemblies are distributed on the four wheels of the double rear axles. One of the three steering tie rod mechanisms is arranged between the two wheels of the front axle, and two are arranged between the four wheels of the double rear axles.

2. The multi-axis distributed steer-by-wire system according to claim 1, characterized in that: The front axle single-wheel steering execution assembly includes: a front axle dual-winding steering motor controller, a front axle dual-winding steering motor, a front axle dual-winding steering motor sensor, a first reducer assembly, a front axle wheel angle sensor, a front axle steering arm, a first column and a first shock absorber; the front axle dual-winding steering motor controller is connected to the front axle dual-winding steering motor, the output shaft of the front axle dual-winding steering motor is connected to the total input end of the first reducer and is installed on the frame above the two wheels of the front axle, the output end of the first reducer assembly is connected to the front axle steering arm through a spline to transmit torque; the front axle steering arm is connected to the first column by a fastening bolt, and the first shock absorber is installed on the first column; the front axle dual-winding steering motor sensor is connected to the front axle dual-winding steering motor controller; the front axle wheel angle sensor is connected to the front axle steering controller.

3. The multi-axis distributed steer-by-wire system according to claim 1, characterized in that: The rear axle single-wheel steering execution assembly includes: a dual rear axle steering motor controller, a dual rear axle steering motor, a dual rear axle steering motor sensor, a second reducer assembly, a dual rear axle wheel angle sensor, a dual rear axle steering arm, a second column and a second shock absorber; the dual rear axle steering motor controller is connected to the dual rear axle steering motor, the output shaft of the dual rear axle steering motor is connected to the input end of the second reducer assembly and is installed on the frame above the four wheels of the dual rear axles, the output end of the second reducer assembly is connected to the dual rear axle steering arm through a spline to transmit torque; the dual rear axle steering arm is connected to the second column by a fastening bolt, and the second shock absorber is installed on the second column; the dual rear axle steering motor sensor is connected to the dual rear axle steering motor controller; the dual rear axle wheel angle sensor is connected to the dual rear axle steering controller.

4. A fault-tolerant control method for a multi-axis distributed steer-by-wire system, based on the system according to any one of claims 1 to 3, characterized in that: The steps are as follows: 1) Collect the steering angle information and torque information input by the driver and send them to the front axle steering controller and the dual rear axle steering controller respectively; collect the front axle wheel angle information and send it to the front axle steering controller; collect the dual rear axle wheel angle information and send it to the dual rear axle steering controller; 2) determining whether the multi-axis distributed steer-by-wire system is in a normal operating condition based on the steering angle and torque information input by the driver and the vehicle operating status; if it is in a normal operating condition, proceeding to step 3); if it is in a faulty operating condition, proceeding to step 4); 3) Calculating the steering angle distribution instructions for the two front axle wheels and the four rear axle wheels, and controlling the front axle single-wheel steering actuating assembly and the rear axle single-wheel steering actuating assembly to execute the corresponding wheel steering angle distribution instructions; 4) Determine the specific location of the fault. If the fault location is a front axle dual-winding steering motor fault, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to perform fault-tolerant control on the faulty front axle dual-winding steering motor; if the fault location is a dual rear axle steering motor fault, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location of the fault, so that the dual rear axle steering motor that still has normal steering function among the four wheels of the dual rear axle drives the faulty dual rear axle steering motor to rotate to complete the steering; if the fault location is a multiple steering fault of the front axle dual-winding steering motor and the dual rear axle steering motor, the differential torque required for the front axle differential steering is solved; finally, the current status of the multi-axis distributed steering system is fed back to the vehicle controller.

5. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 4, characterized in that: The judgment method in step 2) specifically includes: The front axle steering controller uses a state observer to obtain the real-time estimated state of the two front axle wheels, and subtracts it from the measured value of the front axle wheel angle sensor to obtain a first residual sequence; if the first residual sequence is within the set threshold, the front axle dual-winding steering motor is in normal working condition; if the first residual sequence exceeds the set threshold, the front axle dual-winding steering motor is in a faulty state; the dual rear axle steering controller uses a state observer to obtain the real-time estimated state of the four wheels of the dual rear axles, and subtracts it from the measured value of the dual rear axle wheel angle sensor to obtain a second residual sequence; if the second residual sequence is within the set threshold, the dual rear axle steering motor is in normal working condition; if the second residual sequence exceeds the set threshold, the dual rear axle steering motor is in a faulty state; if both the first residual sequence and the second residual sequence exceed the corresponding set thresholds, it is determined that both the front axle dual-winding motor and the dual rear axle steering motor are in a faulty state.

6. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 5, characterized in that: In step 2), the state observer calculates the turning angles of the two front axle wheels and the turning angles of the four rear axle wheels using the vehicle roll angular velocity and the vehicle yaw angular velocity, and determines whether the state is in a normal working state by the residual and residual norm of the turning angle value. The expression is as follows: Where ω represents the vehicle's yaw rate, δ ii Indicates the turning angle of the two wheels on the front axle or the four wheels on the dual rear axles, u indicates the vehicle speed, L e represents the equivalent wheelbase, K represents the stability coefficient of the vehicle, m represents the vehicle mass, l f Indicates the distance from the front axle to the center of mass of the vehicle, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r k represents the distance between the second rear axle and the vehicle's center of mass. f is the tire cornering stiffness of the front axle, k m is the tire cornering stiffness of the first rear axle in the dual rear axle, k r is the tire cornering stiffness of the second rear axle in the dual rear axle, p is the vehicle roll angular velocity, φ is the vehicle roll angle; L′=l f +l r , L1=l f +l m , L2=l m +l r , L' is the distance between the front axle and the second rear axle of the dual rear axles; L1 is the distance between the front axle and the first rear axle of the dual rear axles; L2 is the sum of the distance between the front axle and the first rear axle of the dual rear axles and the distance between the front axle and the second rear axle of the dual rear axles; The residual sequence of the vehicle's yaw rate, roll rate, and sideslip angle exceeds the set threshold to determine whether the steering angles of the two front axle wheels and the steering angles of the four rear axles calculated by the state observer are correct and satisfy the following formula: Among them, e ωm 、e pm 、e βm are the upper limits of the yaw rate residual, roll rate residual and center of mass sideslip angle residual respectively; σ ω , σ p , σ β are the measurement errors of yaw rate, roll rate and sideslip angle respectively; e ω is the yaw rate residual, e p is the roll angular velocity residual, e β is the center of mass sideslip angle residual, Δω is the error between the yaw rate measurement and the ideal value, Δp is the error between the roll rate measurement and the ideal value, Δβ is the error between the center of mass sideslip angle measurement and the ideal value, |.| max Indicates the maximum absolute value.

7. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 4, characterized in that: The step 3) specifically includes: The current equivalent front axle transmission ratio and equivalent dual rear axle transmission ratio are determined based on the input steering wheel angle and vehicle operating status. The equivalent front axle angle and equivalent dual rear axle angle are then calculated and the steering center is determined. The wheel angle adjustment amount is calculated based on the position of the steering center. Genetic algorithms and neural network algorithms are used to determine the current equivalent front axle transmission ratio and the equivalent dual rear axle transmission ratio; The solution expressions for the current equivalent front axle angle and the equivalent dual rear axle angle are as follows: Among them, δ f , δ m , δ r are the equivalent front axle angle, the equivalent first dual rear axle angle, and the equivalent second dual rear axle angle, θ sw is the input steering wheel angle, G f , G m , G r They are the equivalent front axle transmission ratio, the equivalent dual rear axle first axle transmission ratio and the equivalent dual rear axle second axle transmission ratio respectively; The instantaneous steering center position is determined based on the equivalent front axle angle, the equivalent first axis angle of the dual rear axles, and the equivalent second axis angle of the dual rear axles. The expression is as follows: Among them, L B is the vehicle width, L c It is the vertical distance from the inner side of the turning vehicle to the turning center; Calculate the steering angle adjustment of each wheel, the expression is as follows: Among them, v y is the vehicle lateral velocity, v x is the vehicle longitudinal velocity, Δ f , Δ m , Δ r They are the equivalent front axle angle adjustment, the equivalent dual rear axle first axle angle adjustment and the equivalent dual rear axle second axle angle adjustment respectively; Calculate the distribution value of the steering angle of each wheel. The expression is as follows: Among them, δ fl is the left front wheel turning angle, δ fr is the right front wheel turning angle, δ ml is the left turning angle of the first rear axle in the double rear axle, δ mr is the right turning angle of the first rear axle in the dual rear axles, δ rl is the left turning angle of the second rear axle in the double rear axle, δ rr It is the right turning angle of the second rear axle in the double rear axle.

8. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 4, characterized in that: In step 4), after the front axle dual-winding steering motor sensor detects that the front axle dual-winding steering motor has failed, the front axle steering controller controls the corresponding front axle dual-winding steering motor controller to optimize the control of the front axle dual-winding steering motor after the motor failure by using a control algorithm based on model predictive control principle and PID; The control algorithm based on the model predictive control principle and PID is divided into an angle control loop and a current control loop. The input of the angle control loop is the calculated desired steering angle of the two wheels on the front axle, and the output is the reference current of the dq axes of the front axle dual-winding steering motor; the input of the current control loop is the reference current and actual current of the dq axes of the front axle dual-winding steering motor, and the output is the voltage control amount of the dq axes of the front axle dual-winding steering motor; the obtained voltage control amount of the dq axes of the front axle dual-winding steering motor is subjected to VSD coordinate transformation and vector PWM modulation, and then acts on the front axle dual-winding steering motor to control the front axle dual-winding steering motor; The calculation steps of the control algorithm based on the model predictive control principle and PID include: using the model predictive control as an outer loop controller to predict the future expected current value of the system and calculate the optimal current value; using the PID controller as an inner loop controller to adjust the current demand for a period of time in the future predicted by the model predictive control based on the motor model and fault information according to the error between the expected current value provided by the model predictive control and the actual output value; then using the current demand as the set value of the PID controller, and the PID controller adjusts the input voltage of the motor according to the error between the actual current and the set value, thereby realizing control of the front axle dual-winding steering motor; Optimization control is performed based on the principle that the stator magnetomotive force remains unchanged before and after the fault. The prediction model after the fault is corrected based on the optimized mathematical model. The reference phase current after the fault is solved with the minimum stator current amplitude as the optimization goal for tracking control of the current loop. The state space equation of the prediction model after the front axle dual-winding steering motor fails is expressed as follows: x(k+1)=Ax(k)+Bu(k) y(k)=Cx(k) Among them, A, B, and C are all coefficient matrices; x(k) is the state quantity at time k, x(k+1) is the state quantity at time k+1, y(k) is the output quantity at time k, and u(k) is the control quantity at time k; the A, B, and C matrices are: Where, R is the stator resistance; L d , L q is the dq axis stator inductance; L z is the stator leakage inductance; T s is the sampling period; ω e (k) represents the motor angular velocity sampled at time k; The output expression after optimized control is: Y=ψξ(k)+ΘΔU Among them, Y is the output; ψ and Θ are coefficient matrices; Y, ψ, and Θ are respectively: Where ξ(k) is the state matrix obtained after iteration; ΔU is the control increment matrix obtained after iteration; A, B, and C are all coefficient matrices; y(k+i|k) represents the output within the prediction step, i = 1, 2, ..., N p ; Δu(k+i) is the control quantity increment within the control step, i=1,2,…,N c ; The cost function J of model predictive control is: Where Np is the prediction step size; N c is the control step size; y ref (k+i|k) is the reference value of the output; Δu(k+i) is the control increment within the control step; Q and R are the weight coefficient matrices of the output and the control increment, respectively; The problem of calculating the current control variable through model predictive control is transformed into a quadratic programming problem, which is expressed as follows: s.tΔU min ≤ΔU≤ΔU maX Where H and g are solvable matrices; ΔU min and ΔU max are the minimum and maximum values ​​of the control increment respectively.

9. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 8, characterized in that: In step 4), when the fault location is a dual rear axle steering motor fault, the dual rear axle steering controller controls the corresponding steering tie rod mechanism to engage according to the location where the fault occurs, so that the dual rear axle single-wheel steering execution assembly with normal steering of the four wheels of the dual rear axle still drives the faulty dual rear axle single-wheel steering execution assembly to rotate, thereby completing the steering.

10. The fault-tolerant control method for a multi-axis distributed steer-by-wire system according to claim 9, characterized in that: In step 4), if the fault location is a multiple steering fault of the front axle dual-winding steering motor and the dual rear axle steering motors, the front axle steering controller solves the differential torque required for front axle differential steering based on a sliding mode control method. The specific process is as follows: in the event of a failure of the multi-axis distributed steering system, the differential steering is activated, and the steering wheel input is interpreted into a desired yaw angular velocity of the vehicle using the sliding mode control method, ensuring that the vehicle's yaw angular velocity tracks the desired yaw angular velocity, thereby obtaining the desired differential torque; The desired yaw rate of the vehicle is expressed as: Among them, ω a represents the desired yaw rate of the vehicle, δ h Represented as the input of the steering wheel, L e Indicates the equivalent wheelbase; K e represents the stability factor, v x Indicates the longitudinal speed of the vehicle; According to the desired yaw rate of the vehicle, the sliding surface of the sliding mode control is defined as: Where c is the proportional function; ω a represents the desired yaw rate of the vehicle; ω represents the yaw rate of the vehicle; The output of the sliding mode controller is obtained as follows: in=in eq +in sw Where u is the output of the sliding mode controller, u eq is equivalent control, which means the control quantity that moves stably along the sliding surface under ideal conditions; u sw is the switching control quantity; The differential torque required for differential steering of the left and right wheels on the front axle is calculated as follows: Among them, ΔM is the differential torque required for the left and right wheels of the front axle to perform differential steering, C f is the front axle equivalent cornering stiffness, C m is the equivalent cornering stiffness of the first axis of the dual rear axles, C r is the equivalent cornering stiffness of the second rear axle, ω a represents the desired yaw rate of the vehicle, ω is the yaw rate of the vehicle, is a function of the yaw rate, l m Indicates the distance between the first rear axle of the dual rear axles and the vehicle's center of mass, l r Indicates the distance between the second rear axle and the vehicle's center of mass, l f Indicates the distance from the front axle to the vehicle's center of mass.

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