A four-wheel independent steering control method for a horizontal four-rudder wheel chassis vehicle

Abstract

A four-wheel independent steering control method for a horizontal four-rudder wheel chassis vehicle, the method comprising: a vehicle controller (VCU) obtaining a control instruction, recognizing a driving intention, and calculating a vehicle driving mode, a desired vehicle speed, and a desired vehicle turning angle; the vehicle controller (VCU) receiving a sensor signal to recognize the vehicle state, i.e., calculating the current vehicle speed and the current four-wheel turning angle through the four-wheel encoder signal and the rotating speed signal of the rotating speed sensor; obtaining the rear wheel desired turning angle from the current vehicle speed and the desired vehicle turning angle through the current driving mode; obtaining the desired four-wheel turning angle according to the variable instantaneous center Ackerman steering turning angle relationship; obtaining the desired four-wheel rotating speed from the current four-wheel turning angle and the desired vehicle speed; and then sending the desired four-wheel turning angle and the desired four-wheel rotating speed to the steering motor and the walking motor through a message to complete the desired action. The application can improve the efficiency and accuracy of the driver's driving operation, and further improve the safety and efficiency of the operation.

Description

Technical Field

[0001] This invention relates to the field of four-wheel independent steering control, and specifically to a method for four-wheel independent steering control of a horizontal four-steering wheel chassis vehicle. Background Technology

[0002] Vehicles using a horizontal four-wheel steering chassis can perform independent four-wheel steering, offering agile steering and free movement in confined spaces. Because vehicles with steer-by-wire four-wheel independent steering chassis have many degrees of freedom, suitable algorithms are needed to control the angles and speeds of the four wheels to reduce the turning radius and tire wear. Current four-wheel independent steering algorithms mainly establish single-wheel models for the front and rear wheels, distributing their angles and speeds to ensure the front two wheels have the same angle and speed, and the rear two wheels have the same speed and angle, but they do not establish a four-wheel angle and speed distribution algorithm. Some four-wheel angle and speed distribution algorithms only establish a longitudinally fixed instantaneous center Ackermann four-wheel angle and speed distribution algorithm, where the instantaneous center of the front wheel speed lies on the axial extension line of the rear wheel, and vice versa, resulting in inconsistent instantaneous centers of speed. All of the above-mentioned control algorithms lead to excessively large turning radii and accelerated tire wear in four-wheel independent steering vehicles. Therefore, this paper proposes a four-wheel independent steering control method for vehicles with a horizontal four-wheel steering chassis. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to optimize the four-wheel steering angle and speed distribution of the omnidirectional vehicle, reduce the turning radius, reduce tire wear, increase control precision, improve the safety and accuracy of the driver's driving operation, and improve the safety and efficiency of operation. In order to solve the above problems, a four-wheel independent steering control method for a horizontal four-steering wheel chassis vehicle is provided.

[0004] The object of this invention is achieved in the following manner:

[0005] A method for four-wheel independent steering control of a horizontal four-wheel chassis vehicle, the method comprising:

[0006] Step S1: The vehicle control unit (VCU) acquires control commands, identifies driving intentions, and calculates the vehicle driving mode, desired vehicle speed, and desired vehicle steering angle.

[0007] Step S2: The vehicle control unit (VCU) receives sensor signals to identify the vehicle status, that is, it calculates the current vehicle speed and the current four-wheel steering angle by analyzing the signals from the four-wheel encoders and the speed sensors.

[0008] Step S3: Using the current driving mode, obtain the desired rear wheel steering angle from the current vehicle speed and the desired overall vehicle steering angle;

[0009] The desired four-wheel steering angle is obtained based on the instantaneous center of gravity Ackermann steering angle relationship; the desired four-wheel speed is obtained from the current four-wheel steering angle and the desired vehicle speed; then the desired four-wheel steering angle and the desired four-wheel speed are sent to the steering motor and the travel motor via messages to complete the desired action.

[0010] The vehicle driving modes include normal driving, stationary turning, lateral movement, diagonal movement, changing direction, or pulse reset mode.

[0011] In step S2, if the current driving mode is normal driving mode, the current four-wheel steering angle and speed signals obtained from the speed sensors of the four-wheel encoder and the drive motor are used to identify the current vehicle status.

[0012] (1) If If the average front wheel steering angle is less than 0.5°, the vehicle can be considered to be moving straight, and the current engine speed is... Where, δ fl δ represents the current steering angle of the left front wheel. fr The current steering angle of the right front wheel, u A u B u C u D These are the current rotational speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively, and u is the current overall vehicle speed;

[0013] (2) If This allows us to determine if the entire vehicle is turning left, where δ fl δ represents the current steering angle of the left front wheel. fr The current steering angle of the right front wheel is shown in the following formula; the overall vehicle speed is calculated as follows.

[0014]

[0015]

[0016]

[0017]

[0018] (3) When The vehicle can then be determined to be turning right, and the vehicle speed is calculated using the following formula;

[0019]

[0020]

[0021]

[0022] The steering angle command issued by the control command will be used as the steering angle of the front main steering wheel at the next moment. The rear main steering wheel angle at the next moment is obtained based on the vehicle's mass, speed, wheelbase, and center of gravity position. As shown in the formula below;

[0023]

[0024] Where m is the total vehicle mass, L f L is the distance from the center of mass to the front axle. r L is the distance from the center of mass to the rear axle, and K is the wheelbase. r Here, denoted as tire lateral stiffness, and u is the vehicle speed.

[0025] Based on the relationship between the instantaneous center of gravity and the Ackermann four-wheel steering angles, and the steering angles of the front and rear main steering wheels, we have And L = a ′ +b ′ , can be obtained

[0026]

[0027] The following formulas are used to obtain Δf and Δr.

[0028] ,

[0029]

[0030] And thus obtain This is the expected steering angle of the four steering wheels at the next moment, as shown in the following formula.

[0031]

[0032] in, and The signs are opposite, meaning the front and rear wheels are turning in opposite directions;

[0033] From the current four-wheel steering angle δ fl δ fr δ rl δ rr and the desired vehicle speed u issued by the control command N The expected rotational speed u of the four steering wheels at the next moment is calculated. AN u BN u CN u DN Similarly, it is necessary to identify the vehicle status, which includes turning left, turning right, or going straight;

[0034] like If the average steering angle of the front wheels is less than 0.5°, the vehicle can be considered to be moving straight. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0035] u AN =uN u BN =u N u CN =u N u DN =u N ;

[0036] like If the average steering angle of the front wheels is greater than 0.5°, the vehicle can be considered to be turning left. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0037]

[0038]

[0039]

[0040]

[0041] when When the average steering angle of the front wheels is less than -0.5°, the vehicle can be considered to be turning right. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0042]

[0043]

[0044]

[0045] In stationary steering mode, the vehicle body rotates around its geometric center, and the expected steering angle of the four wheels conforms to the following formula;

[0046]

[0047] Left turn is positive, right turn is negative; when the vehicle rotates counterclockwise, the expected speed of the four wheels is set to 400 r / min for the drive motor; when the vehicle rotates clockwise, the expected speed of the four wheels is set to -400 r / min for the drive motor.

[0048] In lateral movement mode, the desired steering angle of all four wheels is set to -90°, and the desired speed of the four wheels is the desired speed of the whole vehicle issued by the control command, as shown in the following formula.

[0049]

[0050] u AN =u BN =u CN =u DN =u N .

[0051] In diagonal driving mode, the desired steering angle of the four wheels is set to the desired steering angle of the entire vehicle as issued by the control command. The desired speed of the four wheels is set to the desired speed of the entire vehicle issued by the control command, as shown in the following formula;

[0052]

[0053] u AN =u BN =u CN =u DN =u N .

[0054] In the variable-head mode, the vehicle changes from a longitudinal head to a transverse head, and the definitions of wheelbase and track width are reversed. The four-wheel speed and steering angle in the transverse head mode are obtained according to the calculation method in the normal driving mode.

[0055] In pulse zeroing mode, the rotary motor enters relative position mode and moves in the opposite direction according to the rotation angle obtained from the encoder feedback, and then the pulse is zeroed, so that the wheel can automatically return to the zero position.

[0056] The beneficial effects of this invention are as follows: Compared with the prior art, the horizontal four-wheel independent steering control method of this invention, employing a variable instantaneous center Ackermann four-wheel steering angle relationship, where the instantaneous center of speed is determined jointly by the four wheel steering angles, enables the instantaneous centers of speed of the four wheels to converge at a single point. Furthermore, by distributing the rotational speeds of the four wheels, tire wear is minimized to the greatest extent possible. Simultaneously, the front and rear wheels steer in opposite directions during turns, minimizing the turning radius. Multiple movement modes are added to meet the movement requirements under various working conditions. In summary, this control method can improve the efficiency and accuracy of driver operation, thereby enhancing operational safety and work efficiency. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of a horizontal four-wheel steering control system for a vehicle with a four-wheel steering wheel chassis, as described in an embodiment of the present invention.

[0058] Figure 2 This is a flowchart of the algorithm in an embodiment of the present invention;

[0059] Figure 3 This is a schematic diagram of a horizontal four-wheel steering chassis vehicle with variable instantaneous center of gravity Ackermann four-wheel independent steering in an embodiment of the present invention;

[0060] Figure 4 This is a schematic diagram of the stationary turning mode of a horizontal four-steering wheel chassis vehicle in an embodiment of the present invention;

[0061] Figure 5 This is a schematic diagram of the lateral movement mode of a horizontal four-steering wheel chassis vehicle in an embodiment of the present invention;

[0062] Figure 6 This is a schematic diagram of the horizontal four-steering wheel chassis vehicle in the oblique driving mode in an embodiment of the present invention;

[0063] Figure 7 This is a schematic diagram of the horizontal four-steering wheel chassis vehicle changing head mode in an embodiment of the present invention;

[0064] in, Figure 3 In the middle, L f L is the distance from the center of mass to the front axle. r Let L be the distance from the center of mass to the rear axle, K be the wheelbase, a be the distance from the instantaneous center of velocity to the front axle, b be the distance from the instantaneous center of velocity to the rear axle, and δ be the distance from the center of mass to the rear axle. fl δ represents the current steering angle of the left front wheel. fr δ is the current steering angle of the right front wheel. rl δ is the current left rear wheel steering angle. rr δ is the current steering angle of the right rear wheel. f δ is the current front main steering wheel angle. r This refers to the steering angle of the front and rear main steering wheels. Detailed Implementation

[0065] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0066] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0067] like Figure 1 As shown, this invention is based on a horizontal four-wheel chassis vehicle four-wheel independent steering control system. The control system includes a motion execution module, the structure of which can be referenced from the structure of the motion execution module in the existing patent CN202121472277.6, an intelligent omnidirectional baggage transfer platform control system for airports. The motion execution module includes a vehicle controller, which is wiredly connected to a host computer to receive motion commands sent by the host computer.

[0068] The motor driver assembly is connected to the vehicle controller and receives commands sent by the vehicle controller.

[0069] The traveling mechanism, connected to the motor drive assembly, is located under the vehicle and includes at least four steering wheel assemblies. Each steering wheel assembly includes a steering wheel slewing bearing mounted on the bottom of the chassis. Wheels are mounted on the lower part of the steering wheel slewing bearing, and the wheels are connected to steering wheel travel motors, which are also mounted on the bottom of the chassis. A steering wheel steering motor is mounted on the lower part of the chassis. The output shaft of the steering wheel steering motor is connected to the steering wheel slewing bearing via gear engagement. The motor drive assembly controls the operation of the steering wheel steering motor and the steering wheel travel motor, receives data from the built-in encoders of the steering wheel steering motor and the steering wheel travel motor, calculates feedback values ​​for the steering wheel speed and deflection angle, and sends them to the vehicle controller. The vehicle controller is communicatively connected to a wired handheld control box, which sends control messages to provide control commands to the vehicle. The wired handheld control box also sends vehicle speed and deflection angle commands to the vehicle controller.

[0070] like Figure 2 The diagram shows a flowchart of a four-wheel independent steering control method for a horizontal four-wheel chassis vehicle provided by an embodiment of the present invention. The method includes:

[0071] Step S1: The vehicle controller (VCU) acquires control commands, which include messages sent from the handheld control box. The VCU identifies the driving intention and calculates the vehicle driving mode (normal driving, stationary turning, lateral movement, diagonal movement, change of direction or pulse zeroing mode), the desired vehicle speed, and the desired vehicle turning angle.

[0072] Step S2: The vehicle control unit (VCU) receives sensor signals to identify the vehicle status, that is, it calculates the current vehicle speed and the current four-wheel steering angle by analyzing the signals from the four-wheel encoders and the speed sensors.

[0073] Step S3: Using the current driving mode, obtain the desired rear wheel steering angle from the current vehicle speed and the desired overall vehicle steering angle;

[0074] The desired four-wheel steering angle is obtained based on the instantaneous center of gravity Ackermann steering angle relationship; the desired four-wheel speed is obtained from the current four-wheel steering angle and the desired vehicle speed; then the desired four-wheel steering angle and the desired four-wheel speed are sent to the steering motor and the travel motor via messages to complete the desired action.

[0075] The vehicle driving modes include normal driving, stationary turning, lateral movement, diagonal movement, changing direction, or pulse reset mode.

[0076] Specifically, such as Figure 3The diagram shows the vehicle's steering, and the current vehicle speed is calculated as follows. If the current driving mode is normal driving mode, the current four-wheel steering angle and speed signals obtained from the four-wheel encoder and the speed sensors of the drive motor are used to determine the current vehicle status.

[0077] (1) If If the average front wheel steering angle is less than 0.5°, the vehicle can be considered to be moving straight, and the current engine speed is... Where, δ fl δ represents the current steering angle of the left front wheel. fr The current steering angle of the right front wheel, u A u B u C u D These are the current rotational speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively, and u is the current overall vehicle speed;

[0078] (2) If This allows us to determine if the entire vehicle is turning left, where δ fl δ represents the current steering angle of the left front wheel. fr The current steering angle of the right front wheel is shown in the following formula; the overall vehicle speed is calculated as follows.

[0079]

[0080]

[0081]

[0082]

[0083] Where, δ fl δ represents the current steering angle of the left front wheel. fr Let L be the current steering angle of the right front wheel, 'a' be the distance from the instantaneous center of velocity to the front axle, 'b' be the distance from the instantaneous center of velocity to the rear axle, and L be the distance from the right front wheel to the front axle. f L is the distance from the center of mass to the front axle. r L is the distance from the center of gravity to the rear axle, K is the wheelbase, and δ is the track width. f δ is the current front main steering wheel angle. r The current and rear main steering wheel angle, u A u B u C u D These represent the rotational speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel, respectively, and u represents the current overall vehicle speed; point O is the instantaneous center of velocity, O' is the vehicle's center of gravity, and OO', OA, OB, OC, and OD are units of length, see [reference]. Figure 3 .

[0084] (3) When The vehicle can then be determined to be turning right, and the vehicle speed is calculated using the following formula;

[0085]

[0086]

[0087]

[0088] Furthermore, the steering angle command issued in the control command is used as the steering angle of the front main steering wheel at the next moment. The rear main steering wheel angle at the next moment is obtained based on the vehicle's mass, speed, wheelbase, and center of gravity position. As shown in the formula below; the front main steering wheel is a virtual wheel, see Figure 3 Dashed line wheel.

[0089]

[0090] Where m is the total vehicle mass, L f L is the distance from the center of mass to the front axle. r L is the distance from the center of mass to the rear axle, and K is the wheelbase. r Where is the tire lateral stiffness, u is the vehicle speed, and C1 is a user-defined coefficient. The rear main steering wheel angle is obtained by multiplying the front main steering wheel angle by C1.

[0091] Based on the relationship between the instantaneous center of gravity and the Ackermann four-wheel steering angles, and the steering angles of the front and rear main steering wheels, we have

[0092] And L = a ′ +b ′ , can be obtained

[0093]

[0094] a' is the expected distance of the instantaneous center of velocity from the front axle at the next moment, b' is the expected distance of the instantaneous center of velocity from the rear axle at the next moment; B' is the calculated expected value at the next moment.

[0095] The following formulas are used to obtain Δf and Δr.

[0096] ,

[0097]

[0098] And thus obtain This is the expected steering angle of the four steering wheels at the next moment, as shown in the following formula.

[0099]

[0100] in, and The signs are opposite, meaning the front and rear wheels are turning in opposite directions.

[0101] Furthermore, based on the current four-wheel steering angle δ fl δ fr δ rl δ rr and the desired vehicle speed u issued by the control command N The expected rotational speed u of the four steering wheels at the next moment is calculated. AN u BN u CN u DN Similarly, it is necessary to identify the vehicle's status (turning left, turning right, or going straight).

[0102] like If the average steering angle of the front wheels is less than 0.5°, the vehicle can be considered to be moving straight. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0103] u AN =u N u BN =u N u CN =u N u DN =u N .

[0104] like If the average steering angle of the front wheels is greater than 0.5°, the vehicle can be considered to be turning left. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0105]

[0106]

[0107]

[0108]

[0109] when When the average steering angle of the front wheels is less than -0.5°, the vehicle can be considered to be turning right. The expected rotational speed of the four wheels at the next moment is shown in the following formula.

[0110]

[0111]

[0112]

[0113] Furthermore, in order to enable the horizontal four-wheel chassis vehicle to move flexibly and move freely in special locations, the present invention also provides a variety of driving modes, including turning on the spot, lateral movement, diagonal movement, and changing the vehicle's direction, to meet the movement requirements in complex working environments such as on decks and inside cabins.

[0114] In stationary turning mode, the vehicle rotates around its geometric center, such as... Figure 4 As shown. At this point, the expected steering angle of the four wheels conforms to the following formula;

[0115]

[0116] Left turn is positive, right turn is negative; when the vehicle rotates counterclockwise, the expected speed of the four wheels is set to 400 r / min for the drive motor; when the vehicle rotates clockwise, the expected speed of the four wheels is set to -400 r / min for the drive motor.

[0117] In lateral mode, the vehicle moves laterally, such as... Figure 5 As shown, the desired steering angle of all four wheels is set to -90°, and the desired speed of the four wheels is the desired speed of the whole vehicle issued by the control command, as shown in the following formula.

[0118]

[0119] u AN =u BN =u CN =u DN =u N .

[0120] In diagonal mode, the vehicle can travel at any angle, such as... Figure 6 As shown. The desired steering angle for all four wheels is set to the desired steering angle of the entire vehicle as issued by the control command. The desired speed of the four wheels is set to the desired speed of the entire vehicle issued by the control command, as shown in the following formula;

[0121]

[0122] u AN =u BN =u CN =u DN =u N .

[0123] Furthermore, the horizontal four-wheel chassis vehicle proposed in this invention can change its front end as needed during operation, therefore a variable front end mode is provided, such as... Figure 7 As shown. In the variable-head mode, the vehicle changes from a longitudinal front to a transverse front, and the definitions of wheelbase and track width are reversed. The four-wheel speed and steering angle in the transverse-head mode are obtained according to the calculation method in the normal driving mode.

[0124] Expecting four-wheel cornering The desired four-wheel speed u is converted into a control command message and sent to the steering motor. AN u BN u CN u DN The signal is converted into a control command message and sent to the travel motor, which enables the vehicle to complete the expected action.

[0125] Furthermore, due to factors such as heavy vehicle loads and wheel-ground friction, a discrepancy may arise between the desired wheel rotation angle and the actual rotation angle obtained from the encoder feedback. Therefore, a pulse zeroing mode is added. The rotary motor enters a relative position mode and moves in the opposite direction based on the rotation angle obtained from the encoder feedback, then performs a pulse zeroing, allowing the wheel to automatically return to its zero position. The pulse zeroing mode proposed in this invention can automatically calibrate the wheel using encoders arranged on the four wheels after it loses its zero position, eliminating the tedious process of repeatedly connecting to a host computer for manual calibration.

[0126] This invention provides a method for independent steering control of four wheels of a horizontal four-wheel chassis vehicle, which optimizes the distribution of steering angle and speed of the four wheels of the omnidirectional vehicle, reduces the turning radius, reduces tire wear, increases control precision, improves the safety and accuracy of the driver's vehicle control, and improves the safety and efficiency of operation.

[0127] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for independent steering control of four wheels of a horizontal four-wheel chassis vehicle, characterized in that: The method includes: Step S1: The vehicle control unit (VCU) acquires control commands, identifies driving intentions, and calculates the vehicle driving mode, desired vehicle speed, and desired vehicle steering angle. Step S2: The vehicle control unit (VCU) receives sensor signals to identify the vehicle status, that is, it calculates the current vehicle speed and the current four-wheel steering angle by analyzing the signals from the four-wheel encoders and the speed sensors. Step S3: Using the current driving mode, obtain the desired rear wheel steering angle from the current vehicle speed and the desired overall vehicle steering angle; The desired four-wheel steering angle is obtained based on the instantaneous center of gravity Ackermann steering angle relationship; the desired four-wheel speed is obtained from the current four-wheel steering angle and the desired overall vehicle speed; then the desired four-wheel steering angle and the desired four-wheel speed are sent to the steering motor and the travel motor via messages to complete the desired action; In step S2, if the current driving mode is normal driving mode, the current four-wheel steering angle and speed signals obtained from the speed sensors of the four-wheel encoder and the drive motor are used to identify the current vehicle status. (1) If If the average front wheel steering angle is less than 0.5°, the vehicle can be considered to be moving straight, and the current engine speed is... ,in, The current steering angle of the left front wheel. The current steering angle of the right front wheel, u A The current speed of the left front wheel, u B The current speed of the right front wheel, u C The current speed of the left rear wheel, u D The current rotational speed of the right rear wheel is denoted by 'u', and the current speed of the entire vehicle is denoted by 'u'. (2) If This allows us to determine if the entire vehicle is turning left. The current steering angle of the left front wheel. The current steering angle of the right front wheel; the overall vehicle speed is calculated using the following formula: ， ； ， ， ， ， ； ； Where 'a' is the distance from the instantaneous center of velocity to the front axle, 'B' is an intermediate calculation variable, and 'L' is the wheelbase. δ is the steering angle of the current and rear main steering wheels. f b is the current front main steering wheel angle; b is the instantaneous distance from the center of velocity to the rear axle; K is the track width; L f The distance from the center of gravity to the front axle (3) When This allows us to determine if the vehicle is turning right, and the vehicle speed is calculated using the following formula; ， ， ， ， ； ； OO', OA, OB, OC, and OD are units of length. OO' is the length from the instantaneous center of velocity to the center of gravity of the vehicle; OA is the length from the instantaneous center of velocity to wheel A; OB is the length from the instantaneous center of velocity to wheel B; OC is the length from the instantaneous center of velocity to wheel C; and OD is the length from the instantaneous center of velocity to wheel D. The steering angle command issued by the control command will be used as the steering angle of the front main steering wheel at the next moment. The rear main steering wheel angle at the next moment is obtained based on the vehicle's mass, speed, wheelbase, and center of gravity position. As shown in the formula below; ， ； Where m is the total vehicle mass. This is the distance from the center of gravity to the front axle. L is the distance from the center of mass to the rear axle, and L is the wheelbase. Here, denoted as tire lateral stiffness, and u is the vehicle speed. Based on the relationship between the instantaneous center of gravity and the Ackermann four-wheel steering angles, and the steering angles of the front and rear main steering wheels, we have , And there are , can be obtained ， ， ； a' is the expected distance of the instantaneous center of velocity from the front axle at the next moment, b' is the expected distance of the instantaneous center of velocity from the rear axle at the next moment; B' is the calculated expected value at the next moment. The intermediate parameters Δf and Δr for distributing the four wheel steering angles are obtained from the following formulas. ， ； And thus obtain , , , , The desired steering angle for the left front wheel. The desired steering angle for the right front wheel. The desired steering angle for the left rear wheel. The desired steering angle of the right rear wheel is given by the following formula: ， ， ， ； in, and The signs are opposite, meaning the front and rear wheels are turning in opposite directions; From the current four-wheel turning angle , , , and the desired vehicle speed issued by the control command The expected rotational speeds of the four steering wheels at the next moment are calculated. , , , Similarly, it is necessary to identify the vehicle status, which includes turning left, turning right, or going straight; like If the average steering angle of the front wheels is less than 0.5°, the vehicle can be considered to be moving straight. The expected rotational speed of the four wheels at the next moment is shown in the following formula. ， ， ， ； like If the average steering angle of the front wheels is greater than 0.5°, the vehicle can be considered to be turning left. The expected rotational speed of the four wheels at the next moment is shown in the following formula. ， ； ， ， ， ， ； ， ， ， ； when When the average steering angle of the front wheels is less than -0.5°, the vehicle can be considered to be turning right. The expected rotational speed of the four wheels at the next moment is shown in the following formula. ， ， ， ， ； ， ， ， 。 2. The four-wheel steering control method for a horizontal four-steering wheel chassis vehicle according to claim 1, characterized in that: The vehicle driving modes include normal driving, stationary turning, lateral movement, diagonal movement, changing direction, or pulse reset mode.

3. The four-wheel steering control method for a horizontal four-wheel chassis vehicle according to claim 2, characterized in that: In stationary steering mode, the vehicle body rotates around its geometric center, and the expected steering angle of the four wheels conforms to the following formula; ， ， ， ； Left turn is positive, right turn is negative; when the vehicle rotates counterclockwise, the expected speed of the four wheels is set to 400 r / min for the drive motor; when the vehicle rotates clockwise, the expected speed of the four wheels is set to -400 r / min for the drive motor.

4. The four-wheel steering control method for a horizontal four-steering wheel chassis vehicle according to claim 2, characterized in that: In lateral movement mode, the desired steering angle for all four wheels is set to -90°, and the desired speed for all four wheels is the desired speed of the entire vehicle as specified in the control command, as shown in the following formula: ； 。 5. The four-wheel steering control method for a horizontal four-steering wheel chassis vehicle according to claim 2, characterized in that: In diagonal driving mode, the desired steering angle of the four wheels is set to the desired steering angle of the entire vehicle as issued by the control command. The desired speed of the four wheels is set to the desired speed of the whole vehicle issued by the control command, as shown in the following formula; ； 。 6. The four-wheel steering control method for a horizontal four-steering wheel chassis vehicle according to claim 2, characterized in that: In the variable-head mode, the vehicle changes from a longitudinal head to a transverse head, and the definitions of wheelbase and track width are reversed. The four-wheel speed and steering angle in the transverse head mode are obtained according to the calculation method in the normal driving mode.

7. The four-wheel steering control method for a horizontal four-wheel chassis vehicle according to claim 2, characterized in that: In pulse zeroing mode, the rotary motor enters relative position mode and moves in the opposite direction according to the rotation angle obtained from the encoder feedback, and then the pulse is zeroed, so that the wheel can automatically return to the zero position.

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