Steering control method and equipment for four-wheel independent driving and steering electric automobile

Abstract

The invention provides a steering control method and equipment for a four-wheel independent driving and steering electric automobile, and belongs to the field of automobile steering. When the fault detector detects that the steering actuator breaks down, the fault state at the moment is quantified and transmitted to the self-adaptive fault-tolerant controller in real time, and the fault-tolerant controller calculates the needed additional yawing moment according to the current residual state of the steering actuator and the driving state of the vehicle; and then the vehicle steering function is jointly completed through hub motor differential drive and a residual steering actuator, and if the vehicle cannot be kept in a stable area after the steering actuator breaks down, steering degradation and parking processing are conducted. According to different failure types of the steer-by-wire system, vehicle steering can be completed through differential drive of the four-wheel hub motor and the residual steering actuator, and the cost is reduced while it is guaranteed that the vehicle has the steering function.

Description

Technical Field

[0001] The invention belongs to the field of automobile steering, and in particular relates to a steering control method and equipment for a four-wheel independent drive and steering electric vehicle. Background Art

[0002] Four-wheel independent drive and steering electric vehicles integrate drive, braking, steering and suspension, achieving a high degree of integration of the chassis system; it can travel in all directions, such as front-wheel steering, four-wheel steering, diagonal driving, on-the-spot steering, crab walking and other driving modes; this architecture also provides a good development platform for intelligent driving. Due to the complete decoupling between its wheels, the four wheels are independently controllable, and steering requires four steering motors to complete. The increase in steering actuators makes steering redundancy more important. When the steering actuator fails, formulating a suitable fault-tolerant control strategy can greatly reduce the impact of the failure on the system, thereby improving the stability of the system.

[0003] Existing redundancy technologies can be roughly divided into two categories: one is hardware backup redundancy technology, and the other is algorithm fault-tolerant technology. Hardware backup provides backup for important components and components prone to failure, such as a dual actuator or dual controller structure. This method can effectively increase vehicle safety but will increase the quality and cost of the system; algorithm fault tolerance mainly relies on the controller's fault-tolerant algorithm to improve the redundancy of the entire system. When a steering system fails, the remaining steering system devices that are working normally are controlled, or the remaining devices are used to complete the current work.

[0004] In-wheel motor-driven electric vehicles, the wheel hub motor is directly installed in or near the drive wheel, which has the characteristics of simple structure, short transmission path, high transmission efficiency, etc. Since the drive motor can be controlled separately, the vehicle can be turned by using the different drive torques output by the left and right motors to generate additional yaw torque. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a steering control method and device for a four-wheel independent drive and steering electric vehicle when a steering actuator of the four-wheel independent drive and steering electric vehicle fails.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a steering control method for a four-wheel independent drive and steering electric vehicle, comprising:

[0008] Input the desired steering wheel angle, obtain the desired wheel angle through the Ackerman steering relationship, and transmit it to the steering actuator for execution;

[0009] When the deviation between the actual wheel steering angle of the steering actuator and the expected wheel steering angle exceeds the upper limit of the stable error value, the steering actuator is determined to be faulty, and then the vehicle is judged whether it is in a stable state based on the vehicle's yaw angular velocity: if so, steering redundancy control is adopted, and the vehicle is steered using the residual functions of the normal steering actuator and the faulty steering actuator; if not, steering degradation processing is adopted, and differential braking is used to generate four wheel braking torque and increase the front wheel toe to stop the vehicle.

[0010] When a vehicle steering actuator fails, the four wheel angles are output according to the failure type and degree, and steering is completed using the residual functions of the normal steering actuator and the faulty steering actuator; if steering cannot be completed, differential steering is used for auxiliary steering.

[0011] When the vehicle becomes unstable or encounters dangerous situations, the differential drive / braking system is used to generate additional yaw torque to park the vehicle while maintaining the stability of the vehicle body.

[0012] Optionally, judging whether the vehicle is in a stable state according to the yaw angular velocity of the vehicle is specifically as follows:

[0013] When the deviation between the actual yaw rate and the expected yaw rate exceeds the upper limit of the stability error value, the vehicle is in an unstable state; otherwise, the vehicle is in a stable state.

[0014] Optionally, when the fault detector detects that the steering actuator fails, the hub motor differential drive and the residual steering actuator are used to jointly complete the steering redundancy control. The process of steering redundancy control includes:

[0015] Identify the fault type of the steering actuator, set the fault factor of the input adaptive fault-tolerant controller according to the fault type, the adaptive fault-tolerant controller outputs the four wheel angles to the vehicle, and the vehicle feeds back the actual yaw rate For sliding mode controller;

[0016] Output the desired yaw rate through the four-wheel independent steering two-degree-of-freedom vehicle model The sliding mode controller is given a sliding mode controller. and , combined with the set constraints and objective function, output the four wheel driving torque to the vehicle.

[0017] Optionally, if the steering actuator fails and the vehicle cannot remain in the stable area, the steering is degraded and the vehicle is parked. The process of steering degradation includes:

[0018] The vehicle feedbacks the actual yaw rate The sliding mode controller outputs the desired yaw rate through the four-wheel independent steering two-degree-of-freedom vehicle model The sliding mode controller is given a sliding mode controller. and , combined with the set constraints and objective function, output the four wheel driving torque to the vehicle;

[0019] The vehicle controls the wheels to rotate toward the central axis to increase the front wheel toe and outputs four wheel steering angles to the vehicle.

[0020] Optionally, during the steering redundant control process, the adaptive fault-tolerant controller outputs four wheel steering angles to the vehicle, specifically:

[0021] Construct the state-space equations for the vehicle when the steering actuator fails:

[0022] ;

[0023] Among them, the state quantity , and are the actual sideslip angle and yaw rate of the center of mass, respectively. Denotes differential, superscript Represents transpose; input , , , and are the wheel angles of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; represents the system matrix, represents the input matrix;

[0024] Defining Tracking Error for:

[0025] ;

[0026] In the formula, , and are the desired sideslip angle and yaw rate of the center of mass, respectively;

[0027] According to the state space equation and tracking error calculation , is any positive constant;

[0028] Adaptive fault-tolerant controller based on Output four wheel angles , , and To the vehicle.

[0029] Optionally, during the steering redundant control process, the four-wheel independent steering two-degree-of-freedom vehicle model is:

[0030] ;

[0031] In the formula, and are the actual sideslip angle and yaw rate of the center of mass, respectively. represents differential; and are the distances from the center of mass to the front and rear axes respectively; Indicates the mass of the vehicle; and are the cornering stiffness of the front and rear wheels respectively; is the vehicle longitudinal velocity; , , and are the wheel angles of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It's a car around The moment of inertia of the shaft.

[0032] Optionally, during the steering redundant control process, the sliding mode controller outputs four wheel driving torques to the vehicle, specifically:

[0033] The sliding mode controller is based on the yaw rate error Select the sliding surface and calculate the resultant torque of the four wheel driving torques ;

[0034] The dynamic model of the differential steering system is constructed as follows:

[0035] ;

[0036] In the formula, the subscript ; and They are the effective moments of inertia of the front and rear differential steering systems respectively; and They are the effective damping of the front and rear differential steering systems; and are the front and rear wheel turning angles respectively; and are the steering torque differences around the kingpin of the front and rear wheels respectively; and are the additional yaw moments of the front and rear wheels, ; and are the driving torques of the right front wheel and the right rear wheel respectively; and are the driving torques of the left front wheel and the left rear wheel respectively; and are the total return torque of the front and rear differential steering systems respectively; and are the cornering stiffness of the front and rear wheels respectively; and are the slip angles of the front and rear wheels respectively; Half the wheelbase; Half of the tire trail; The kingpin offset; is the wheel radius; Denotes differential, superscript represents the second derivative;

[0037] Under the differential steering system dynamics model, the constraints are set as follows:

[0038] ;

[0039] In the formula, the subscript , respectively the left front wheel, the right front wheel, the left rear wheel and the right rear wheel; is the maximum torque output by the motor; , and are the lateral force, longitudinal force and vertical force of the wheel respectively; is the road friction factor of the wheel;

[0040] Tire load rate The minimum is the objective function, set the objective function to:

[0041] ;

[0042] According to the objective function and constraints, the driving torque of the four wheels is obtained.

[0043] Optionally, the process of steering degradation processing satisfies the following vehicle status:

[0044] ;

[0045] In the formula, is the moment of inertia of the vehicle around the Z axis; is the actual yaw rate; , , and are the lateral forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the longitudinal forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It is half the wheelbase; and are the distances from the center of mass to the front and rear axles, respectively; and Respectively, the front and rear wheel turning angles.

[0046] Optionally, during the steering degradation process, the sliding mode controller outputs four wheel driving torques to the vehicle, specifically:

[0047] In the vehicle state, set the constraints as follows:

[0048] ;

[0049] In the formula, , , and They are the braking forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the vertical forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the road friction factors of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively;

[0050] Tire load rate The minimum is the objective function, set the objective function to:

[0051] ;

[0052] In the formula, the subscript ;

[0053] According to the objective function and constraints, the driving torque of the four wheels is obtained.

[0054] In a second aspect, the present invention provides an electronic device comprising: 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 steering control method of the four-wheel independent drive and steering electric vehicle of the first aspect is implemented.

[0055] The beneficial effects of the present invention are as follows: the present invention can formulate a suitable fault-tolerant control strategy when a steering actuator fails, thereby greatly reducing the impact of the failure on the system, thereby improving the stability of the system; the present invention can target different failure types of the wire-controlled steering system, utilize four-wheel hub motor differential drive and residual steering actuators to complete vehicle steering, thereby reducing costs while ensuring that the vehicle has a steering function. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a force analysis diagram of the tires of a four-wheel steering vehicle.

[0057] Figure 2 It is a steering control flow chart of a four-wheel independent drive and steering electric vehicle.

[0058] Figure 3 It is a steering control strategy diagram of a four-wheel independent drive and steering electric vehicle.

[0059] Figure 4 It is a schematic diagram of the dynamic model of the differential steering system. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0061] In one embodiment, the present invention provides a steering control method for a four-wheel independent drive and steering electric vehicle, wherein the tire force of the four-wheel steering vehicle is as follows: Figure 1 As shown. Since the four wheels are independently controllable, when the steering actuator partially fails, the normal steering actuator and the residual functions of the faulty steering actuator are used to complete the steering of the vehicle. At the same time, in order to ensure the stability of the vehicle, the differential drive / brake is used to provide additional yaw force to ensure the stability of the vehicle.

[0062] When the vehicle controller detects that the vehicle body angle does not turn according to the steering wheel angle, it is determined that the steering system has failed, and the steering fault-tolerant control system intervenes. The vehicle controller obtains the driver's desired wheel angle based on the driver's steering wheel angle, and obtains the steering wheel angle, longitudinal vehicle speed signal, yaw angular velocity and center of mass sideslip angle of the running vehicle. At this time, it is determined whether the vehicle steering actuator is faulty. According to the fault tree, the actuator faults are divided into three categories: partial failure, communication interruption, and stuck fault, as shown in Table 1. and is the failure factor.

[0063] Table 1 Actuator fault types

[0064] Fault type ε λ normal 1 0 Partial failure 0-1 0,1 Communication interruption 0 0,1 Stuck fault 0 0,1

[0065] It is worth noting that the above faults are classified for a certain steering actuator. This embodiment is for a vehicle that is a four-wheel independent drive and steering electric vehicle. The vehicle has a total of four steering actuators, each of which is independently controllable. The purpose of this embodiment is to use the vehicle's four independently controllable steering wheels to complete steering according to different failure types and failure degrees of the steering actuator.

[0066] Defining Steering Actuator Fault Input for:

[0067] (1);

[0068] In the formula, Indicates a stuck fault. Indicates partial failure of the steering actuator and communication interruption fault. Indicates the four wheels: left front wheel, right front wheel, left rear wheel and right rear wheel. , Indicates the fault factor corresponding to the wheel.

[0069] According to the four-wheel independent steering two-degree-of-freedom vehicle model:

[0070] (2);

[0071] In the formula, and are the actual sideslip angle and yaw rate of the center of mass, respectively. represents differential; and are the distances from the center of mass to the front and rear axes respectively; Indicates the mass of the vehicle; and are the cornering stiffness of the front and rear wheels respectively; is the vehicle longitudinal velocity; , , and are the wheel angles of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It's a car around The moment of inertia of the shaft.

[0072] The state space equation can be obtained by equation (2):

[0073] (3);

[0074] In the formula, the state quantity , input , Indicates the output quantity; is the system matrix, is the input matrix, is the output matrix.

[0075] The steering control process of four-wheel independent drive and steering electric vehicles is as follows Figure 2As shown, when the vehicle is turning normally, after the driver inputs the desired steering wheel angle, the wheel angles of the four wheels can be obtained through the Ackerman steering relationship and transmitted to the four steering actuators. When the actual angle executed by the vehicle steering actuator deviates too much from the expected angle, that is, when equation (4) is not satisfied, it is considered that the steering actuator has a fault and the adaptive fault-tolerant controller intervenes. After the fault-tolerant controller intervenes, in order to ensure the stability of the vehicle, this embodiment jointly determines the safety range of the vehicle based on the wheel angle and yaw angular velocity:

[0076] (4);

[0077] (5);

[0078] in, and In order to stabilize the upper bound of the error value, the specific value can be obtained through experiments for different vehicle models. When formula (5) is not satisfied, the vehicle will be in an unstable state. and denote the actual and desired wheel angles, respectively, and represent the actual and expected yaw angular velocity respectively. When both equations (4) and (5) are satisfied, it is determined that the steering actuator has no fault. , .

[0079] When the steering actuator is normal, the steering redundancy controller does not intervene and only uses the steering actuator to complete vehicle steering.

[0080] Partial failure means that the steering actuator can steer at a certain angle but cannot reach the driver's expected angle. At this time, the vehicle steering is completed by using the remaining normal steering actuators, the residual functions of the faulty steering actuator and differential steering.

[0081] When the steering actuator communication fails, only differential steering is used to complete the steering. When the steering actuator is stuck, if equation (5) is satisfied, the faulty motor is locked and the remaining normal steering actuator is used to complete the vehicle steering. If equation (5) is not satisfied, the steering is degraded and differential braking is used to keep the vehicle stable and parked.

[0082] In summary, if Figure 3 As shown in the figure, when the steering actuator fails, the steering redundant controller outputs the four wheel angles according to the failure type and failure degree, and completes the steering using the residual functions of the normal steering actuator and the faulty steering actuator. If the steering cannot be completed, the differential steering is used for auxiliary steering. When the vehicle is in a dangerous situation such as instability, the differential drive / brake is used to generate additional yaw torque to maintain the stability of the vehicle body while parking.

[0083] According to the different types of failure modes and failure degrees of the steering system, and The values ​​are different. The specific values ​​are as follows:

[0084] When a certain steering actuator does not satisfy equation (4) but the vehicle body state satisfies equation (5), it is considered that the steering actuator of the vehicle is partially failed. , is the maximum angle that the wheel can reach at this time, is the wheel turning angle desired by the driver.

[0085] When the wheel angle does not respond to the steering wheel angle for two consecutive cycles, if the vehicle controller can receive the feedback signal sent back by the steering controller, it is considered to be a steering actuator stuck fault. If the vehicle controller cannot receive the feedback signal sent by the steering actuator, it is considered to be a signal interruption.

[0086] When it is a stuck fault, the actuator , the remaining normal steering actuators and differential steering are used to complete vehicle steering.

[0087] When the communication is interrupted, the steering actuator cannot normally receive the command from the vehicle controller and stops controlling the steering motor. , using four-wheel differential drive to complete vehicle steering.

[0088] It is worth noting that in any fault state, when the vehicle body state does not satisfy equation (5), that is, the vehicle has exceeded the stability boundary, Steering downgrade is performed, and differential braking is used to generate additional yaw torque and increase the front wheel toe to stabilize the vehicle.

[0089] When the vehicle is in a steering downgrade state, the front wheel toe is increased by controlling the wheels to rotate toward the center axis, that is, the left wheel rotates to the right and the right wheel rotates to the left.

[0090] By controlling the braking torque of the four wheels, additional yaw rate is generated to balance the extra yaw rate of the vehicle, so that the vehicle can stop stably. For the current vehicle state:

[0091] (6);

[0092] In the formula, is the moment of inertia of the vehicle around the Z axis; is the actual yaw rate; , , and are the lateral forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the longitudinal forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It is half the wheelbase; and are the distances from the center of mass to the front and rear axles, respectively; and are the front and rear wheel turning angles respectively. At this time, the total braking force of the four wheels should be The radius of the attachment circle is Indicates the maximum braking force that the ground can provide:

[0093] (7);

[0094] In the formula, , , and They are the braking forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the vertical forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the road friction factors for the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

[0095] Taking the lowest tire load rate as the objective function, the driving torque of the left and right wheels is calculated according to the constraints. Objective function:

[0096] (8);

[0097] The driving torque of the four wheels can be obtained by combining equations (6), (7) and (8).

[0098] When the vehicle steering system fails but the vehicle is still in the stable area, that is, it does not satisfy equation (4) but satisfies equation (5). At this time, the residual functions of the normal steering actuator and the faulty steering actuator and the differential steering of the left and right wheel hub motors are used to enable the vehicle to steer accurately according to the driver's intention. At this time, the input of the four wheel angles is , which is the input when the steering actuator fails. From equations (1) and (3), the state space equation at this time is:

[0099] (9);

[0100] Defining Tracking Error for:

[0101] (10);

[0102] In the formula, , and are the desired sideslip angle and yaw rate of the center of mass, respectively;

[0103] Design Input , is an arbitrary positive number used to ensure the stability of the control system.

[0104] Select the Lyapunov function :

[0105] (11);

[0106] right The derivative is:

[0107] (12);

[0108] Available , it can be seen that the designed steering redundant controller is stable.

[0109] In order to enable the vehicle to complete steering according to the driver's intention when the steering system fails to varying degrees, the present embodiment uses differential steering to perform auxiliary steering under fault conditions.

[0110] Firstly, the additional yaw moment required to track the reference model is obtained using a sliding mode controller.

[0111] According to the yaw rate error Select sliding surface for:

[0112] (13);

[0113] In the formula, The value is a positive constant and is the controller parameter that satisfies the Routh–Hurwitz stability criterion.

[0114] Select the exponential approach law to reduce system jitter, that is:

[0115] (14);

[0116] In the formula, and are controller parameters, all greater than zero. At the same time reduce It can make the transition smoother during sliding mode switching. From the characteristics of the sliding mode controller, we can see , we can get:

[0117] (15);

[0118] Therefore, the required resultant torque can be obtained for:

[0119] (16);

[0120] Since the differential torque and the wheel angle are approximately in a linear relationship, this embodiment approximately assumes that the front and rear wheel angles and the front and rear axle differential torque have the following proportional relationship:

[0121] (17);

[0122] In the formula, and Indicates the differential torque required by the front and rear axles of the vehicle. When the front and rear wheels of the vehicle have the same turning angle direction, is positive, vice versa The value is negative. .

[0123] Build as Figure 4 The differential steering system dynamics model is shown:

[0124] (18);

[0125] In the formula, the subscript ; and They are the effective moments of inertia of the front and rear differential steering systems respectively; and They are the effective damping of the front and rear differential steering systems; and are the front and rear wheel turning angles respectively; and are the steering torque differences around the kingpin of the front and rear wheels respectively; and are the additional yaw moments of the front and rear wheels, ; and are the driving torques of the right front wheel and the right rear wheel respectively; and are the driving torques of the left front wheel and the left rear wheel respectively; and are the total return torque of the front and rear differential steering systems respectively; and are the cornering stiffness of the front and rear wheels respectively; and are the slip angles of the front and rear wheels respectively; Half the wheelbase; Half of the tire trail; The kingpin offset; is the wheel radius.

[0126] In order to achieve steering when the steering system fails, the residual steering actuator and the wheel hub motor differential drive are used to achieve stable parking when the vehicle is uncontrollable. The constraints are formulated as follows:

[0127] (19);

[0128] In the formula, is the maximum torque output by the motor.

[0129] According to equations (8), (16)-(19), the driving torque of the four wheels can be calculated, so that the vehicle can complete the steering according to the driver's intention.

[0130] In another embodiment, the present invention proposes an electronic device, comprising: 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 steering control method of the four-wheel independent drive and steering electric vehicle of the aforementioned embodiment is implemented.

[0131] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0132] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A steering control method for a four-wheel independent drive and steering electric vehicle, characterized in that: include: Input the desired steering wheel angle, obtain the desired wheel angle through the Ackerman steering relationship, and transmit it to the steering actuator for execution; When the deviation between the actual wheel steering angle of the steering actuator and the expected wheel steering angle exceeds the upper limit of the stable error value, the steering actuator is determined to be faulty, and then the vehicle is judged whether it is in a stable state based on the vehicle's yaw angular velocity: if so, steering redundancy control is adopted, and the vehicle is steered using the residual functions of the normal steering actuator and the faulty steering actuator; if not, steering degradation processing is adopted, and differential braking is used to generate four wheel braking torque and increase the front wheel toe to stop the vehicle.

2. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 1, characterized in that: The method of judging whether the vehicle is in a stable state according to the yaw angular velocity of the vehicle is specifically as follows: When the deviation between the actual yaw rate and the expected yaw rate exceeds the upper limit of the stability error value, the vehicle is in an unstable state; otherwise, the vehicle is in a stable state.

3. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 1, characterized in that: The process of switching to redundant control includes: Identify the fault type of the steering actuator, set the fault factor of the input adaptive fault-tolerant controller according to the fault type, the adaptive fault-tolerant controller outputs the four wheel angles to the vehicle, and the vehicle feeds back the actual yaw rate For sliding mode controller; Output the desired yaw rate through the four-wheel independent steering two-degree-of-freedom vehicle model The sliding mode controller is given a sliding mode controller. and , combined with the set constraints and objective function, output the four wheel driving torque to the vehicle.

4. The steering control method of a four-wheel independent drive and steering electric vehicle as claimed in claim 1, characterized in that: The process of turning to downgrade processing includes: The vehicle feedbacks the actual yaw rate The sliding mode controller outputs the desired yaw rate through the four-wheel independent steering two-degree-of-freedom vehicle model The sliding mode controller is given a sliding mode controller. and , combined with the set constraints and objective function, output the four wheel driving torque to the vehicle; The vehicle controls the wheels to rotate toward the central axis to increase the front wheel toe and outputs four wheel steering angles to the vehicle.

5. The steering control method of a four-wheel independent drive and steering electric vehicle as claimed in claim 3, characterized in that: During the steering redundant control process, the adaptive fault-tolerant controller outputs four wheel steering angles to the vehicle, specifically: Construct the state-space equations for the vehicle when the steering actuator fails: ； Among them, the state quantity , and are the actual sideslip angle and yaw rate of the center of mass, respectively. Denotes differential, superscript Represents transpose; input , , , and are the wheel angles of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; represents the system matrix, represents the input matrix; Defining Tracking Error for: ； In the formula, , and are the desired sideslip angle and yaw rate of the center of mass, respectively; According to the state space equation and tracking error calculation , is any positive constant; Adaptive fault-tolerant controller based on Output four wheel angles , , and To the vehicle.

6. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 3, characterized in that: During the steering redundant control process, the four-wheel independent steering two-degree-of-freedom vehicle model is: ； In the formula, and are the actual sideslip angle and yaw rate of the center of mass, respectively. represents differential; and are the distances from the center of mass to the front and rear axes respectively; Indicates the mass of the vehicle; and are the cornering stiffness of the front and rear wheels respectively; is the vehicle longitudinal velocity; , , and are the wheel angles of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It's a car around The moment of inertia of the shaft.

7. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 3, characterized in that: During the steering redundant control process, the sliding mode controller outputs four wheel driving torques to the vehicle, specifically: The sliding mode controller is based on the yaw rate error Select the sliding surface and calculate the resultant torque of the four wheel driving torques ; The dynamic model of the differential steering system is constructed as follows: ； In the formula, the subscript ; and They are the effective moments of inertia of the front and rear differential steering systems respectively; and They are the effective damping of the front and rear differential steering systems; and are the front and rear wheel turning angles respectively; and are the steering torque differences about the kingpin of the front and rear wheels respectively; and are the additional yaw moments of the front and rear wheels, ; and are the driving torques of the right front wheel and the right rear wheel respectively; and are the driving torques of the left front wheel and the left rear wheel respectively; and are the total return torque of the front and rear differential steering systems respectively; and are the cornering stiffness of the front and rear wheels respectively; and are the slip angles of the front and rear wheels respectively; Half the wheelbase; Half of the tire trail; The kingpin offset; is the wheel radius; Denotes differential, superscript represents the second derivative; Under the differential steering system dynamics model, the constraints are set as follows: ； In the formula, the subscript , respectively the left front wheel, the right front wheel, the left rear wheel and the right rear wheel; is the maximum torque output by the motor; , and are the lateral force, longitudinal force and vertical force of the wheel respectively; is the road friction factor of the wheel; Tire load rate The minimum is the objective function, set the objective function to: ； According to the objective function and constraints, the driving torque of the four wheels is obtained.

8. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 4, characterized in that: The process of the steering degradation process satisfies the following vehicle conditions: ； In the formula, is the moment of inertia of the vehicle around the Z axis; is the actual yaw rate; , , and are the lateral forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the longitudinal forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; It is half the wheelbase; and are the distances from the center of mass to the front and rear axles, respectively; and Respectively, the front and rear wheel turning angles.

9. A steering control method for a four-wheel independent drive and steering electric vehicle as claimed in claim 8, characterized in that: During the steering degradation process, the sliding mode controller outputs four wheel driving torques to the vehicle, specifically: In the vehicle state, set the constraints as follows: ； In the formula, , , and They are the braking forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the vertical forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; , , and are the road friction factors of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively; Tire load rate The minimum is the objective function, set the objective function to: ； In the formula, the subscript ; According to the objective function and constraints, the driving torque of the four wheels is obtained.

10. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steering control method for the four-wheel independent drive and steering electric vehicle as described in any one of claims 1 to 9 is implemented.

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