CN117681959B - Vehicle state control method for four-wheel independent steering vehicle - Google Patents

Abstract

The invention relates to a vehicle state control method of a four-wheel independent steering vehicle, belongs to the technical field of automobile steering failure, and aims at solving the technical problem that steering failure cannot be handled by single wheel redundancy control. The method comprises the following steps: based on the chassis architecture of the four-wheel independent steering vehicle, an equation set of the running state of the vehicle and the corners of all the wheels is obtained through analysis, and the running state of the vehicle is controlled by actively controlling the corners of the four wheels. The invention provides a method for controlling the running state of a vehicle through other wheel corners when a single wheel fails, a double wheel fails and a three-wheel fails, and simultaneously provides a method for reducing the maximum value of four side deflection angles to reduce the abrasion of tires, ensure that the abrasion of each wheel is uniform and the service life is consistent, reduce the lateral force born by a suspension and improve the control margin of the longitudinal force of the tires when the four wheels are in normal steering.

Description

Vehicle state control method for four-wheel independent steering vehicle

Technical Field

The invention relates to the technical field of automobile steering failure, and in particular to a vehicle state control method for a four-wheel independent steering vehicle.

Background technique

In recent years, the emerging development of four-wheel independent steering architecture vehicles based on steer-by-wire technology has brought greater freedom and adjustment space to vehicle control. However, compared with traditional mechanical steering, the reliability of steer-by-wire is not high. When the line or communication fails, one or more wheels lose the steering ability, making the vehicle uncontrolled and prone to danger. At present, the redundant control research of steer-by-wire mainly focuses on hardware and software redundancy of a certain wheel steering mechanism.

However, most of the hardware or software redundant control involved nowadays is to control a certain wheel individually, but when one or more wheels fail to turn, the single wheel redundant control will not work. Therefore, it is particularly important for steer-by-wire vehicles to study a control method for wheel steering failure. Even if there is a wheel steering failure, the vehicle can still drive or stop safely according to the driver's intention, ensuring the safety of the driver and passengers, and improving the safety of steer-by-wire vehicles.

Summary of the invention

The present invention aims to solve the technical problem in the prior art that redundant control of a single wheel cannot cope with steering failure, and provides a vehicle state control method for a four-wheel independent steering vehicle.

In order to solve the above technical problems, the technical solutions of the present invention are as follows:

A vehicle state control method for a four-wheel independent steering vehicle comprises the following steps: based on the chassis structure of the four-wheel independent steering vehicle, analyzing and obtaining a set of equations of the vehicle driving state and the turning angles of each wheel, and controlling the vehicle driving state by actively controlling the turning angles of the four wheels.

In the above technical solution, the vehicle state control method specifically includes the steps of:

The side slip angle of the wheel is obtained by the wheel turning angle and the speed direction at the wheel contact point;

The lateral force of each wheel is obtained based on the tire's cornering characteristics;

Combined with the tire longitudinal force and the structural parameters of the four-wheel independent steering vehicle, the equations of the longitudinal acceleration, lateral acceleration and yaw angular acceleration at the center of mass of the three components of the vehicle state with respect to the four wheel angles are established;

The vehicle state is controlled based on the chassis dynamics model.

In the above technical solution, the vehicle state control method specifically includes the steps of:

When the four-wheel steering is normal, in order to reduce the wear of the four wheels, the side slip angle of the wheel with the maximum side slip angle among the four wheels is reduced, and the other wheel steering angles are controlled to make the vehicle driving state meet the expected value;

When a single wheel steering fails, the wheel angle is treated as a fixed value, and the three expected driving state components are achieved by adjusting the other three wheel angles, so that the vehicle can run in the expected state;

When the two-wheel steering fails, the two wheel angles are treated as fixed values. At this time, the vehicle driving state is degraded and the lateral acceleration and yaw acceleration are adjusted to meet the expected values. The longitudinal acceleration is not considered to maintain the vehicle handling stability.

When the three-wheel steering fails, the three wheel angles are treated as constants, and the vehicle's driving state is also downgraded by adjusting the only normal steering wheel angle to meet the expected yaw acceleration and reduce the yaw rate to alleviate the vehicle's tail-spinning phenomenon, which poses a greater risk.

In the above technical solution, the vehicle state control method specifically includes the following steps:

First, the velocity direction of each wheel contact point is analyzed to obtain the lateral force of the tire;

Secondly, the chassis dynamics model is analyzed and modeled. The center of mass of the vehicle is taken as the research object. The force on the tire is applied to the center of mass, and the equations of the center of mass longitudinal acceleration, lateral acceleration and yaw angular acceleration related to the ground force on the tire are obtained.

When the steering functions of the four wheels are normal, they are individually controlled through the steering motor, and the control target is determined to reduce the maximum side slip angle of the wheel;

When a single wheel steering fails, its steering angle value is treated as a fixed value, and the unique steering angle value of other wheels is solved. By controlling the steering angles of the three wheels, the lateral acceleration, longitudinal acceleration and yaw acceleration fully reach the expected driving state;

When the two-wheel steering fails, the steering angle control of the other two wheels gives priority to satisfying the lateral acceleration and yaw acceleration to reach the expected values;

When the three-wheel steering fails, the vehicle's yaw acceleration is guaranteed by controlling the steering angle of the normal wheels.

In the above technical solution, the center-of-mass velocity and the yaw angular velocity are acquired by a gyroscope and a speed sensor arranged at the center of mass of the vehicle.

In the above technical solution, when both wheels fail, the vehicle longitudinal acceleration control is in braking.

The present invention has the following beneficial effects:

The vehicle state control method of the four-wheel independent steering vehicle of the present invention determines the precise mathematical relationship between the vehicle driving state and the tire turning angle based on the chassis dynamics model of the four-wheel independent steering frame vehicle.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the four-wheel steering is normal, this equation group is a four-element equation group of three driving state components about the four wheel angles. At this time, the maximum value of the four sideslip angles can be reduced, and the expected three driving state components can still be met by adjusting the remaining wheel angles, so as to reduce tire wear, make the wear amount of each wheel uniform and the life consistent, reduce the lateral force on the suspension and improve the tire longitudinal force control margin.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the single-wheel steering fails, the wheel angle is treated as a constant. This equation group is a ternary equation group of three driving state components about the three wheel angles. At this time, the other three wheel angles have a unique solution. By adjusting the three wheel angles, the expected three driving state components can be fully achieved, so that the vehicle can travel according to the expected state.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the two-wheel steering fails, the two wheel angles are treated as constants. This equation group is a binary equation group of three driving state components about the two wheel angles. At this time, the vehicle driving state is degraded and controlled. By adjusting the remaining two wheel angles, the lateral acceleration and yaw angle acceleration are preferentially satisfied to reach the expected values. The longitudinal acceleration is not considered to maintain the vehicle handling stability. The longitudinal acceleration control of the vehicle does not need to be precisely controlled, and braking is sufficient.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When three-wheel steering fails, the three wheel angles are treated as constant values, and the vehicle driving state is also degraded and controlled. The yaw angular acceleration is satisfied to reach the expected value by adjusting the only normal steering wheel angle, thereby reducing the yaw angular velocity and alleviating the greater danger of the vehicle's tail-swinging phenomenon.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 is a schematic diagram of the speed direction analysis of each wheel contact point.

Figure 2 is a schematic diagram of the vehicle chassis dynamics model.

FIG. 3 is a schematic flow chart of the steps of a vehicle state control method for a four-wheel independent steering vehicle according to the present invention.

Detailed ways

The inventive concept of the present invention is:

The present invention provides a vehicle state control method for a four-wheel independent steering vehicle, which takes the four-wheel steering into account in a unified manner. The vehicle driving state can be obtained through the turning angles of the four wheels, thereby inferring the turning angles required for the normal steering wheels to provide when the expected driving state is reached. The method can cope with steering failures such as single-wheel steering failure, double-wheel steering failure and three-wheel steering failure. When the four-wheel steering is fault-free, the maximum side slip angle of the four wheels can be reduced, the tire wear can be reduced, and the service life of the four tires can be closer.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention, when one or more wheels fail to turn, the angle of the vehicle is controlled by other wheels with normal steering so that the vehicle can reach the expected driving state. When the expected vehicle control cannot be met, downgrade control is performed to give priority to ensuring the safety of the driving vehicle.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention, as shown in Figure 3, includes the following steps: based on the chassis architecture of the four-wheel independent steering vehicle, a group of equations of the vehicle driving state and the turning angle of each wheel are obtained through dynamic analysis, and the vehicle driving state is controlled by actively controlling the turning angles of the four wheels.

The vehicle state control method of the present invention is specifically described, comprising the steps of:

The side slip angle of the wheel is obtained by analyzing the wheel turning angle and the speed direction at the wheel contact point;

The lateral force of each wheel is obtained based on the tire's cornering characteristics;

Combined with the tire longitudinal force and the structural parameters of the four-wheel independent steering vehicle, the equations of the longitudinal acceleration, lateral acceleration and yaw angular acceleration at the center of mass of the three components of the vehicle state with respect to the four wheel angles are established;

The vehicle state is controlled based on the chassis dynamics model.

The vehicle state control method specifically comprises the following steps:

First, the velocity direction of each wheel contact point is analyzed to obtain the lateral force of the tire;

Secondly, the chassis dynamics model is analyzed and modeled. The center of mass of the vehicle is taken as the research object. The force on the tire is applied to the center of mass, and the equations of the center of mass longitudinal acceleration, lateral acceleration and yaw angular acceleration related to the ground force on the tire are obtained.

When the steering functions of the four wheels are normal, they are controlled individually through the steering motor. At this time, the control target is determined to reduce the maximum slip angle of the wheel as much as possible. When the four-wheel steering functions are normal, in order to reduce the wear of the four wheels, the slip angle of the wheel with the maximum slip angle among the four wheels is reduced, and the other wheel angles are controlled to make the vehicle driving state meet the expected value.

When a single wheel steering fails, its steering angle value is treated as a constant value, and the unique steering angle value of other wheels is solved. By controlling the steering angles of the three wheels, the lateral acceleration, longitudinal acceleration and yaw acceleration can fully achieve the expected driving state; when a single wheel steering fails, the steering angle of the wheel is treated as a constant value, and the three expected driving state components can be fully achieved by adjusting the steering angles of the other three wheels, so that the vehicle can drive according to the expected state;

When the two-wheel steering fails, the lateral acceleration and yaw acceleration are controlled by the other two wheels to meet the expected values. When the two-wheel steering fails, the two wheel angles are treated as fixed values. At this time, the vehicle driving state is degraded and the lateral acceleration and yaw acceleration are controlled by adjusting the other two wheel angles to meet the expected values. The longitudinal acceleration is not considered to maintain the vehicle handling stability.

When the three-wheel steering fails, the vehicle's yaw acceleration is ensured by controlling the steering angle of the normal steering wheel. When the three-wheel steering fails, the three wheel angles are treated as fixed values, and the vehicle's driving state is also degraded. By adjusting the only normal steering wheel angle to meet the yaw acceleration to reach the expected value, the yaw velocity is reduced to alleviate the vehicle's tail-swinging phenomenon, which causes greater danger.

The center of mass velocity and yaw rate are acquired by the gyroscope and speed sensor arranged at the center of mass of the vehicle. When both wheels fail, the vehicle longitudinal acceleration control is in braking.

The present invention is described in detail below with reference to the accompanying drawings.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention comprises the following steps:

First, the gyroscope and speed sensor are arranged at the center of mass of the vehicle, so that the yaw angular velocity of the vehicle and the speed direction at the center of mass can be obtained, thereby obtaining the instantaneous speed direction of each wheel contact point.

As shown in FIG1 , the speed direction analysis of each wheel contact point is performed by obtaining the speed and angular velocity at the center of mass obtained by the sensor, as well as the vehicle structure parameters, to obtain the speed direction at each wheel.

Speed direction of the left front wheel at the contact point:

; (0.1)

Speed direction of the right front wheel at the contact point:

; (0.2)

Speed direction of the left rear wheel at the contact point:

; (0.3)

Speed direction of the right rear wheel at the contact point:

; (0.4)

In the formula, , , and are the speed directions of the left front, right front, left rear and right rear wheels at the contact points, is the velocity at the center of mass of the vehicle, is the velocity direction at the vehicle’s center of mass, is the angular velocity at the center of mass of the vehicle, is the front and rear wheelbase of the vehicle, The distance from the vehicle's center of mass to the front axle , For the left and right wheel tracks.

Specify the vehicle's center of mass speed The direction of rotation is clockwise from the front of the vehicle, and the angular velocity The direction is clockwise, and the speed at the wheel contact point is The direction is clockwise from the front of the vehicle.

Next, the vehicle chassis dynamics model is analyzed and modeled. According to the tire's side slip characteristics and the dynamic analysis of the center of mass, the relationship between the longitudinal acceleration, lateral acceleration and yaw angular acceleration at the center of mass can be obtained, including variables such as wheel angle, tire contact point velocity direction and tire longitudinal force.

As shown in FIG2 , in the chassis dynamics analysis of the four-wheel independent steering vehicle, the longitudinal force and lateral force of each tire jointly determine the acceleration at the center of mass and the yaw angular acceleration, and determine the driving state of the vehicle. The desired vehicle control effect can be achieved by controlling the tire force.

The longitudinal acceleration at the center of mass is:

; (0.5)

The lateral acceleration at the center of mass is:

; (0.6)

The vehicle yaw angular acceleration at the center of mass is:

; (0.7)

In the formula, is the longitudinal acceleration of the vehicle at the center of mass, is the lateral acceleration of the vehicle at the center of mass, is the vehicle yaw angular acceleration at the center of mass, , , and are the longitudinal forces on the left front, right front, left rear and right rear wheels respectively. , , and are the lateral forces on the left front wheel, right front wheel, left rear wheel and right rear wheel respectively. , , and are the turning angles of the left front, right front, left rear and right rear wheels respectively. is the total mass of the vehicle, is the moment of inertia of the vehicle with its center of mass as the center of rotation.

Among them, the cornering stiffness of each tire takes the same value. According to the cornering characteristics of the tire,

; (0.8)

In the formula, is the slip angle of the wheel, is the cornering stiffness of the tire.

Specify the wheel angle The direction is counterclockwise from the front of the vehicle, which is positive, and the wheel slip angle The direction of the wheel contact point speed The direction is counterclockwise, the range is To ensure that the tire cornering characteristics are roughly in the linear region.

Since the wheel slip angle has a range limit, when the wheel steering angle value solved by formula (0.8) makes the expected tire slip angle exceed the specified limit range, the execution slip angle takes the maximum tire slip angle that can be achieved in the direction close to the expected value, so that the control result is closer to the expected vehicle driving state. All wheel steering angle adjustments must ensure that the slip angle is within the specified range to avoid exceeding the lateral force that the suspension can withstand, while increasing the margin for longitudinal adhesion and reducing tire wear. If the steering angle adjustment range in the specified linear region of cornering stiffness is not enough to meet the requirements, the relationship between cornering stiffness and slip angle can be established or expanded to the nonlinear region by looking up the median value table to increase the adjustable steering angle range.

Substituting formula (0.8) into formulas (0.5), (0.6) and (0.7), we get , and About variables , , and The system of equations:

; (0.9)

Longitudinal acceleration , lateral acceleration and yaw angular acceleration Determines the driving state of the vehicle, that is, , , and By analyzing formula (0.9), it can be obtained that the three equations contain four unknown quantities and have two degrees of freedom. In the following four cases, the characteristics of the four-wheel independent steering vehicle can improve the vehicle's handling stability and driving safety.

Case 1: Four-wheel steering is normal

When all wheels are turning normally, , , and The four wheel angles can be controlled by the steering motor. At this time, the equation group has two degrees of freedom. The control target is to reduce the side slip angle of the wheel as much as possible to reduce tire wear, reduce the lateral force on the suspension, and increase the tire longitudinal force control margin. For example, when the sensor determines that the left front wheel has the largest side slip angle, the value of the left front wheel with the largest side slip angle can be reduced by controlling the change of the side slip angles of other wheels, so that the wear of each wheel is uniform and the life is consistent. According to the adhesion ellipse, when the tire lateral force decreases, the longitudinal adhesion increases.

Case 2: Single-wheel steering failure

When any wheel is out of control, the wheel angle sensor reads the current position of the wheel and obtains its angle. At this time, the lateral acceleration can be increased by controlling the angles of other wheels. , longitudinal acceleration and yaw angular acceleration For example, when the left front wheel steering fails, Uncontrollable, treated as a constant, read the real value through the angle sensor. and the expected vehicle state lateral acceleration , longitudinal acceleration and yaw angular acceleration Substituting the numerical value into formula (0.9), the turning angle values of the other three wheels can be solved , and , and it is the only solution. That is, when the left front wheel fails, the expected driving state can be fully achieved by controlling the steering angles of the other three wheels.

Case 3: Dual-wheel steering failure

When any two wheels fail to turn, the wheel angle sensor reads the current position of the two wheels, and the other two wheels are controlled to give priority to satisfying the lateral acceleration. and yaw angular acceleration Reach the expected value, longitudinal acceleration Ignore it, maintain the vehicle's handling stability, and do not need to precisely control the vehicle's longitudinal acceleration, just brake. For example, when the left front wheel and left rear wheel steering fail, and It is uncontrollable and is also treated as a constant value. The real value is read out through the steering angle sensor. , left rear wheel angle and the expected vehicle state lateral acceleration and yaw angular acceleration Substituting the numerical value into formula (0.9), the turning angles of the other two wheels can be solved. and , and it is the only solution. That is, when the left front wheel and the left rear wheel steering fail, the vehicle can be driven safely by controlling the steering angles of the other two wheels.

Case 4: Three-wheel steering failure

When any three wheels fail to turn, the current positions of these wheels are read through the wheel angle sensors. At this time, the yaw acceleration is given priority through the steering angle control of the only normal wheel. To achieve the expected value, reduce the yaw rate. For example, when only the right rear wheel is steering normally, , and Uncontrollable, treated as a constant, read the real value through the angle sensor. , and and the expected vehicle state yaw acceleration Substituting the numerical value into formula (0.9), the turning angle of the right rear wheel can be solved , and it is the only solution. That is, when the three wheel steering fails, the yaw acceleration of the vehicle can be guaranteed by controlling the steering angle of the normal wheel, so as to alleviate the greater danger of the vehicle's tail-swinging phenomenon.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention determines the precise mathematical relationship between the vehicle driving state and the tire turning angle based on the chassis dynamics model of the four-wheel independent steering frame vehicle.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the four-wheel steering is normal, this equation group is a four-element equation group of three driving state components about the four wheel angles. At this time, the maximum value of the four sideslip angles can be reduced, and the expected three driving state components can still be met by adjusting the remaining wheel angles, so as to reduce tire wear, make the wear amount of each wheel uniform and the life consistent, reduce the lateral force on the suspension and improve the tire longitudinal force control margin.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the single-wheel steering fails, the wheel angle is treated as a constant. This equation group is a ternary equation group of three driving state components about the three wheel angles. At this time, the other three wheel angles have a unique solution. By adjusting the three wheel angles, the expected three driving state components can be fully achieved, so that the vehicle can travel according to the expected state.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When the two-wheel steering fails, the two wheel angles are treated as constants. This equation group is a binary equation group of three driving state components about the two wheel angles. At this time, the vehicle driving state is degraded and controlled. By adjusting the remaining two wheel angles, the lateral acceleration and yaw angle acceleration are preferentially satisfied to reach the expected values. The longitudinal acceleration is not considered to maintain the vehicle handling stability. The longitudinal acceleration control of the vehicle does not need to be precisely controlled, and braking is sufficient.

The vehicle state control method of the four-wheel independent steering vehicle of the present invention is obtained by analyzing the obtained relationship. When three-wheel steering fails, the three wheel angles are treated as constant values, and the vehicle driving state is also degraded and controlled. The yaw angular acceleration is satisfied to reach the expected value by adjusting the only normal steering wheel angle, thereby reducing the yaw angular velocity and alleviating the greater danger of the vehicle's tail-swinging phenomenon.

Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims (1)

1. The vehicle state control method of the four-wheel independent steering vehicle is characterized by comprising the following steps of analyzing and obtaining an equation set of a vehicle running state and the corners of all wheels based on a chassis framework of the four-wheel independent steering vehicle, and controlling the vehicle running state by actively controlling the corners of the four wheels;

the vehicle state control method includes the steps of: obtaining a slip angle of the wheel through the wheel corner and the speed direction at the wheel grounding point; obtaining the lateral force of each wheel according to the lateral deflection characteristics of the tire; establishing an equation set of longitudinal acceleration, transverse acceleration and yaw angular acceleration of the vehicle at the mass center of three components of the vehicle state according to the longitudinal force of the tire and the structural parameters of the four-wheel independent steering vehicle; controlling the vehicle state based on the chassis dynamics model;

The method specifically comprises the following steps:

Firstly, arranging a gyroscope and a speed sensor at the barycenter of a vehicle, so as to obtain the yaw rate of the vehicle and the speed direction at the barycenter, and further obtain the instantaneous speed direction of the grounding point of each wheel;

the ground point speed direction of each wheel is analyzed, and the speed direction of each wheel is obtained through the speed and the angular speed of the center of mass and the vehicle structural parameters;

speed direction at the ground point of the left front wheel:

；

speed direction at right front wheel ground point:

；

left rear wheel ground point speed direction:

；

speed direction at right rear wheel ground point:

；

in the method, in the process of the invention, 、、、The speed directions of the ground points of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel are respectively,As the speed at the centroid of the vehicle,Is the direction of the velocity at the centroid of the vehicle,The angular velocity at the center of mass of the vehicle is L, the front-rear wheelbase of the vehicle is L, a is the distance between the center of mass of the vehicle and the front axle, and b is the left-right wheelbase;

specifying speed at vehicle centroid Clockwise rotation from the direction of the head to positive, angular velocityClockwise positive, wheel ground speedThe clockwise rotation of the direction of the head is positive;

Then, analyzing and modeling a vehicle chassis dynamics model, and according to the cornering characteristics of the tire and the dynamics analysis of the center of mass, obtaining a longitudinal acceleration, lateral acceleration and yaw angular acceleration relation at the center of mass, wherein the relation comprises the variables of the wheel rotation angle, the tire grounding point speed direction and the tire longitudinal force;

The four-wheel independent steering vehicle chassis dynamics analysis is carried out, the longitudinal force and the lateral force of each tire jointly determine the acceleration and the yaw acceleration at the centroid, the running state of the vehicle is determined, and the expected vehicle control effect can be realized by controlling the tire force;

the longitudinal acceleration at the centroid is:

；

the lateral acceleration at the centroid is:

；

the vehicle yaw acceleration at the centroid is:

；

In the method, in the process of the invention, Is the longitudinal acceleration of the vehicle at the centroid,Is the lateral acceleration of the vehicle at the centroid,Is the vehicle yaw acceleration at the centroid,、、AndThe left front, the right front, the left rear and the right rear wheels are respectively stressed by longitudinal force,、、AndThe left front, right front, left back and right back wheels are respectively stressed by lateral force,、、AndThe corners of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel are respectively,For the total mass of the vehicle,A moment of inertia about the center of rotation of the vehicle at the centroid;

wherein the cornering stiffness of each tire takes the same value, and is known according to the cornering properties of the tire

；

In the method, in the process of the invention,As the slip angle of the wheel,Is the cornering stiffness of the tyre;

defining the rotation angle of each wheel The direction is rotated anticlockwise from the direction of the headstock to be positive, and the wheel slip angle is changedFrom the direction of the wheel ground contact pointThe anticlockwise rotation of the direction is positive, the rangeIn the inner part, the cornering characteristic of the tire is ensured to be in a linear region;

because of the range limitation of the wheel slip angle, when the expected tire slip angle exceeds the specified limit range by the wheel corner value solved according to the formula (0.8), the slip angle is executed to obtain the maximum tire slip angle which is close to the expected value direction, so that the control result is more approximate to the expected vehicle running state; all wheel rotation angle adjustment needs to ensure that the side deflection angle is within a specified range so as not to exceed the lateral force born by the suspension, and simultaneously improves the margin for the longitudinal adhesive force and reduces the tire abrasion; if the angular adjustment range of the specified cornering stiffness linear region is insufficient to meet the requirement, a relation of the cornering stiffness relative to the cornering angle can be established or expanded to a nonlinear region by a median table look-up mode, and the angular adjustment range is increased;

by taking the formula (0.8) into the formulas (0.5), (0.6) and (0.7), it is possible to obtain 、AndWith respect to variables、、AndIs set of equations:

；

Longitudinal acceleration Lateral accelerationYaw accelerationDetermining the running state of the vehicle, i.e. by、、AndDetermining; as can be obtained by analysis of the formula (0.9), three equations contain four unknowns, have two degrees of freedom, and can improve the steering stability and running safety of the vehicle by the characteristics of the four-wheel independent steering vehicle in the following four cases;

case one: normal four-wheel steering

When all wheels turn normally, i.e.、、AndThe four wheel corners can be controlled by a steering motor, and the equation set has two degrees of freedom, so that the control target is determined to reduce the slip angle of the wheels as much as possible;

And a second case: failure of single wheel steering

When any wheel steering is uncontrolled, the current position of the wheel is read through a wheel angle sensor to obtain the angle of the wheel, and at the moment, the transverse acceleration can be caused through the angle control of other wheelsLongitudinal accelerationYaw accelerationReaching the expected value;

And a third case: failure of two-wheel steering

When any two wheels fail in steering, the current positions of the two wheels are read through the wheel angle sensors, and at the moment, the transverse acceleration is preferentially met through angle control of the other two wheelsYaw accelerationReaching the expected value, longitudinal accelerationRegardless of the control method, the vehicle steering stability is maintained, the vehicle longitudinal acceleration control is not required to be accurately controlled, and the vehicle is braked;

Case four: three-wheel steering failure

When any three wheels fail in steering, the current positions of the wheels are read through the wheel angle sensors, and the yaw acceleration is preferentially met through the control of the normal wheel angle of the only steeringReaching the desired value, the yaw rate is reduced.