A method and system for driving a small radius turn of a vehicle

Abstract

The application relates to a method for driving small-radius steering of a vehicle, comprising the following steps: acquiring front wheel steering angle data based on the transmission ratio and the maximum steering angle of a steering wheel input, calculating expected yaw angular velocity data of the vehicle based on the opening of a throttle pedal, calculating yaw angular acceleration data based on the current yaw angular velocity of the vehicle and the expected yaw angular velocity data; locking one side rear wheel as a steering center wheel, acquiring the rotational inertia data of the vehicle steering with the steering center wheel as the center, and calculating total yaw torque data of the vehicle steering based on the yaw angular acceleration data and the rotational inertia data. The method and system for driving small-radius steering of the vehicle lock one side rear wheel as a steering center and cooperatively control the torque of the remaining three wheels, so that the vehicle rotates around a body contour point, thereby breaking through the geometric radius limitation of traditional steering, realizing extremely small-radius steering, and significantly improving the maneuvering flexibility of the vehicle in scenes such as U-turns on narrow roads and parking in compact parking spaces.

Description

Technical Field

[0001] This invention relates to the field of vehicle steering technology, and more specifically to a method and system for driving a vehicle to steer with a small radius. Background Technology

[0002] Currently, urban travel scenarios are becoming increasingly complex, and there is an urgent need for vehicles to have greater maneuverability in narrow spaces (such as U-turns on narrow roads and parking in mechanical parking spaces). This places extremely high demands on their steering capabilities. Small-radius steering technology aims to significantly reduce the minimum turning radius of vehicles, thus becoming a key to improving vehicle maneuverability. As a key indicator for measuring vehicle maneuverability, small-radius steering capability has become one of the research focuses in the field of new energy vehicles.

[0003] In traditional centralized drive vehicles, small-radius steering is mainly achieved through the cooperation of the mechanical steering system and the differential. This method is limited by the steering angle limit of the mechanical structure and the lag of the differential response, so the steering radius of such vehicles is difficult to further reduce. In extremely narrow scenarios, multiple forward and backward adjustments are often required to complete the steering, resulting in low traffic efficiency. Some technologies adopt a stationary steering scheme, which controls the wheels on both sides to rotate in opposite directions, so that the vehicle rotates around its own center, thereby achieving theoretical zero-radius steering. However, this scheme consumes a lot of energy, puts a heavy burden on the motor and battery system, and the sliding friction between the tires and the ground will seriously wear down the tires and damage the ground. Summary of the Invention

[0004] This application provides a method and system for driving a vehicle to make small-radius steering. By locking the inner rear wheel and dynamically distributing the torque of the other three motors, the slip ratio of the wheel is adjusted, thereby changing the longitudinal and lateral forces exerted by the ground on the tire. This allows the vehicle to make extremely small-radius steering around the wheel as the steering center, significantly reducing the steering radius, while also reducing wheel wear and improving traffic efficiency.

[0005] In a first aspect, embodiments of this application provide a method for driving a vehicle to perform small-radius steering, comprising the following steps: The front wheel steering angle data is obtained based on the transmission ratio and maximum steering angle input from the steering wheel. The vehicle's expected yaw rate data is calculated based on the opening degree of the accelerator pedal. The yaw acceleration data is calculated based on the vehicle's current yaw rate and expected yaw rate data. One rear wheel is locked as the steering center wheel. The rotational inertia data of the vehicle turning around the steering center wheel is obtained. Based on the yaw angle acceleration data and rotational inertia data, the total yaw torque data of the vehicle is calculated. The total yaw torque data is divided into first yaw torque data, second yaw torque data and third yaw torque data according to a preset ratio and distributed to the other three wheels except the steering center wheel. Based on the acquired first yaw torque data, second yaw torque data, and third yaw torque data, the target slip ratio of the corresponding wheel is calculated using the tire model; the longitudinal velocity data of the other three wheels is calculated based on the vehicle's current yaw rate and vehicle geometric parameters; and the target wheel speed data of the other three wheels is calculated based on the acquired target slip ratio and longitudinal velocity data. The system acquires the actual wheel speed data of the three wheels other than the steering center wheel. Based on the acquired target wheel speed data and actual wheel speed data, it acquires the motor output torque data of the three wheels other than the steering center wheel. It calculates the braking torque of the steering center wheel and controls the corresponding wheel to achieve steering based on the acquired motor output torque data and braking torque.

[0006] In conjunction with the first aspect, in one implementation, the yaw acceleration data is obtained using the following formula: ; ; in, This is the proportionality coefficient. The integral coefficient is... The differential coefficients are... To track errors, For the desired yaw rate data, This represents the current yaw rate.

[0007] In conjunction with the first aspect, in one implementation, the total yaw torque data is obtained using the following formula: ; in, For rotational inertia data, This is the yaw acceleration data. The longitudinal force is applied to the front wheel on the side closest to the steering center wheel. For the longitudinal force of the other front wheel, The lateral force on the front wheel closest to the steering center wheel. The lateral force on the other front wheel, Let L be the longitudinal force on the rear wheel other than the steering center wheel, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, Let L be the geometric auxiliary angle determined by L and B.

[0008] In conjunction with the first aspect, in one embodiment, the tire model is a composite brush tire model.

[0009] In conjunction with the first aspect, in one implementation, the longitudinal velocity data is obtained using the following formula: ; ; ; in, Let L be the current yaw rate, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, Let L be the geometric auxiliary angle determined by L and B.

[0010] In conjunction with the first aspect, in one implementation, the target wheel speed data is obtained using the following formula: ; Where i represents the other three wheels. The target slip ratios for the remaining three wheels are... For which wheel's longitudinal velocity data it corresponds to. The radius is the wheel radius.

[0011] In conjunction with the first aspect, in one embodiment, the motor output torque data is calculated using the following formula: ; ; in, For the remaining three wheels, the longitudinal torque data is as follows. For the wheel radius, For rotational inertia data, , and These are the proportional coefficient, integral coefficient, and differential coefficient for the other three wheels, respectively. The remaining three wheels correspond to the rotational speed error. For the target wheel speed data corresponding to the other three wheels, This refers to the actual wheel speed data for the remaining three wheels.

[0012] In conjunction with the first aspect, in one implementation, after obtaining the motor output torque data of the three wheels other than the steering center wheel based on the acquired target wheel speed data and actual wheel speed data, the method further includes: Obtain the motor's maximum output torque and maximum output power data; Determine the maximum permissible torque of the motors corresponding to the other three wheels at the current wheel speed; The motor output torque data of the three wheels other than the steering center wheel are compared with the corresponding maximum allowable torque, and the smaller one is taken as the final output torque data.

[0013] In conjunction with the first aspect, in one embodiment, the braking torque of the steering center wheel is obtained by the following formula: ; in, is the proportionality constant, m is the vehicle mass, and g is the gravitational acceleration.

[0014] Secondly, embodiments of this application provide a system for a method of driving a vehicle to perform small-radius steering, comprising: The control module, which responds to steering commands, is configured to lock one rear wheel as the steering center wheel based on the steering command. The data acquisition module is configured to acquire the transmission ratio of the steering wheel input, the maximum steering angle, the opening of the accelerator pedal, the current yaw rate of the vehicle, the moment of inertia data for steering, the vehicle's geometric parameters, and the actual wheel speed data of the three wheels other than the steering center wheel. The processing module, connected to the control module and the data acquisition module, is configured to acquire front wheel steering angle data based on the transmission ratio and maximum steering angle; calculate the vehicle's desired yaw rate data based on the accelerator pedal opening; calculate yaw acceleration data based on the vehicle's current yaw rate and desired yaw rate data; calculate the total yaw torque data based on the yaw acceleration data and moment of inertia data; divide the total yaw torque data into first yaw torque data, second yaw torque data, and third yaw torque data according to a preset ratio, and distribute them to the three wheels other than the steering center wheel; and based on the acquired data... The first, second, and third yaw torque data are used to calculate the target slip ratio of the corresponding wheels using the tire model. Based on the vehicle's current yaw rate and vehicle geometry, the longitudinal velocity data of the other three wheels are calculated. Based on the acquired target slip ratio and longitudinal velocity data, the target wheel speed data of the other three wheels is calculated. The actual wheel speed data of the other three wheels (excluding the steering wheel) is obtained. Based on the acquired target wheel speed data and actual wheel speed data, the motor output torque data of the other three wheels (excluding the steering wheel) is obtained, and the braking torque of the steering wheel is calculated. The execution module, which is connected to the processing module, is configured to control the corresponding wheels to achieve steering based on the acquired motor output torque data and braking torque.

[0015] The beneficial effects of the technical solutions provided in this application include: 1. The method and system for driving vehicles with small radius steering lock one rear wheel as the steering center and coordinates the torque of the other three wheels to make the vehicle rotate around the body contour point, thereby breaking through the geometric radius limitation of traditional steering and realizing extremely small radius steering, thus significantly improving the maneuverability of the vehicle in scenarios such as U-turns in narrow roads and parking in tight spaces.

[0016] 2. The method and system for driving vehicles with small radius steering can accurately calculate the yaw torque required to maintain the desired steering posture in real time by using PID closed-loop control based on yaw rate. By using a composite brush tire model, the torque distribution requirements are transformed into precise wheel slip ratio and target wheel speed control, which ensures the smoothness of the small radius steering process and the dynamic stability of the vehicle, and avoids vehicle instability or impact.

[0017] 3. The method and system for driving vehicles with small radius steering uses a composite brush tire model to precisely control the slip ratio of wheels other than the steering center wheel within the ideal low range for generating the target tire force. This ensures that the tires always work in the low-wear zone where rolling friction is dominant, thereby reducing energy loss during steering and effectively mitigating abnormal tire wear and damage to the ground. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the main method steps of the present invention; Figure 2 This is a schematic diagram of the geometric auxiliary angle in an embodiment of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0021] Example 1: Please see Figure 1 This application provides a method for driving a vehicle to turn with a small radius, including the following steps: S1. Obtain front wheel steering angle data based on the transmission ratio and maximum steering angle input by the steering wheel; calculate the vehicle's desired yaw rate data based on the opening degree of the accelerator pedal; and calculate yaw acceleration data based on the vehicle's current yaw rate and desired yaw rate data. ① When the driver engages the small-radius steering and turns the steering wheel, the front wheel steering angle data is obtained based on the gear ratio and maximum steering angle input by the steering wheel. The front wheel steering angle data is specifically obtained through the following formula: ; in, The gear ratio input via the steering wheel. This is the maximum steering wheel angle.

[0022] ② The desired yaw rate of the vehicle is calculated based on the accelerator pedal opening, specifically obtained using the following formula: ; in, The yaw rate coefficient, This refers to the opening degree of the accelerator pedal.

[0023] ③ Calculate the yaw acceleration data based on the vehicle's current yaw rate and desired yaw rate data, specifically using the following formula: Get the vehicle's current yaw rate ; in, ; in addition, This is a scaling factor used to quickly reduce the current error; These are the integral coefficients used to eliminate steady-state errors; These are the differential coefficients, used to suppress overshoot and improve system stability; To track errors, For the desired yaw rate data, This represents the current yaw rate.

[0024] It is important to note that , , , All of these are constants determined through calibration based on the target vehicle parameters. During the vehicle development phase, based on parameters such as vehicle weight, wheelbase, and tire characteristics, conventional parameter tuning methods in this field are used to test and calibrate under typical road conditions to obtain a set of optimal parameter values ​​that enable fast, stable yaw rate tracking response with small overshoot. Once the parameters are determined, they can be stored in the vehicle's control unit for use by this method.

[0025] S2. Lock one rear wheel as the steering center wheel, obtain the rotational inertia data of the vehicle turning around the steering center wheel, calculate the total yaw torque data of the vehicle turning based on the yaw angle acceleration data and rotational inertia data, divide the total yaw torque data into the first yaw torque data, the second yaw torque data and the third yaw torque data according to the preset ratio, and distribute them to the other three wheels except the steering center wheel. This embodiment uses the left rear wheel as the steering center wheel for explanation: ① Obtain rotational inertia data: This is the rotational inertia of the vehicle as it rotates around the steering center wheel. This parameter is an inherent property of the vehicle and can be predetermined by calculation or experimental measurement based on geometric parameters such as the vehicle's curb weight, mass distribution, wheelbase, and track width. It is stored in the vehicle's control unit and can be directly obtained when in use. ② Calculate the total yaw torque data for vehicle steering based on yaw acceleration and moment of inertia data, specifically using the following formula: ; in, For rotational inertia data, This is the yaw acceleration data. The longitudinal force is on the left front wheel. The longitudinal force is on the right front wheel. The lateral force on the left front wheel, The lateral force is on the right front wheel. Let L be the longitudinal force on the right rear wheel, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, The geometric auxiliary angle determined by L and B (e.g.) Figure 2 (as shown) ③ Divide the total yaw torque data into first yaw torque data, second yaw torque data, and third yaw torque data according to a preset ratio, and distribute them to the three wheels other than the steering center wheel. Specifically: In this embodiment, the preset proportions of the left front wheel, right front wheel, and right rear wheel are as follows: And there are Then, the first yaw torque data, the second yaw torque data, and the third yaw torque data can be represented as follows: ; ; ; Since the sideslip angle is fixed, the yaw moment contribution of each wheel is mainly affected by its respective slip ratio, which can be expressed as follows: ; ; ; in, The slip ratio of the left front wheel. The slip ratio of the right front wheel. This represents the slip ratio of the right rear wheel.

[0026] S3. Based on the acquired first yaw torque data, second yaw torque data, and third yaw torque data, calculate the target slip ratio of the corresponding wheel using the tire model; calculate the longitudinal velocity data of the other three wheels based on the vehicle's current yaw rate and vehicle geometric parameters; and calculate the target wheel speed data of the other three wheels based on the acquired target slip ratio and longitudinal velocity data. ① Calculate the target slip ratio of the corresponding wheel using a tire model: The tire model in this embodiment is a composite brush tire model, specifically as follows: ; in, This refers to tire torque. This refers to the tire's combined slip. For the corresponding lateral stiffness, For vertical loads, The composite slip threshold, The coefficient of friction of the road surface; For vertical loads Since the vehicle's speed is low when turning with a small radius, it can be approximated that the vertical load on each wheel is the same, that is: ; Where m is the mass of the vehicle and g is the acceleration due to gravity.

[0027] The composite slip is a function of longitudinal slip and lateral deflection: ; in, For longitudinal slip ratio, The lateral slip ratio can be calculated as follows:

[0028] in, This refers to the tire's slip ratio. This refers to the tire slip angle.

[0029] Obtain the left and right track widths of the vehicle. The front and rear track width is , Since the vehicle is turning counterclockwise around the left rear wheel, the slip angles of the left and right front wheels can be calculated using the following formula:

[0030] in, The side slip angle of the left front wheel. The side slip angle of the right front wheel; Because step ③ of step S2 above divides the total yaw torque data into first yaw torque data, second yaw torque data, and third yaw torque data (F) according to a preset ratio, and distributes them to the other three wheels besides the steering center wheel, the slip ratios of the left front wheel, right front wheel, and right rear wheel can be solved using the composite brush tire model. , and .

[0031] In addition, the parameters in the composite brush tire model include the tire's lateral stiffness. and composite slip threshold These are all inherent characteristic parameters of the tire. These parameters can be determined in advance through standard tire mechanical tests (such as bench tests), or by the tire supplier providing a data mapping table for different vertical loads for the model to use.

[0032] ② Calculate the longitudinal velocity data of the other three wheels based on the vehicle's current yaw rate and vehicle geometry parameters. This can be obtained using the following formula: ; ; ; in, Let L be the current yaw rate, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, Let L be the geometric auxiliary angle determined by L and B.

[0033] ③ Calculate the target wheel speed data for the remaining three wheels based on the acquired target slip ratio and longitudinal velocity data. Specifically, this can be obtained using the following formula: ; ; ; in, , and These are the slip ratios of the left front wheel, right front wheel, and right rear wheel, respectively. , and The data are the longitudinal speeds of the left front wheel, right front wheel, and right rear wheel, respectively. The radius is the wheel radius.

[0034] S4. Obtain the actual wheel speed data of the three wheels of the vehicle other than the steering center wheel. Based on the obtained target wheel speed data and actual wheel speed data, obtain the motor output torque data of the three wheels other than the steering center wheel. Calculate the braking torque of the steering center wheel. Based on the obtained motor output torque data and braking torque, control the corresponding wheel to achieve steering.

[0035] ① Based on the acquired target wheel speed data and actual wheel speed data, obtain the motor output torque data for the three wheels other than the steering center wheel, specifically using the following formula: ; in, ; in addition, For the remaining three wheels, the longitudinal torque data is as follows. For the wheel radius, For rotational inertia data, , and These are the proportional coefficient, integral coefficient, and differential coefficient for the other three wheels, respectively. The remaining three wheels correspond to the rotational speed error. For the target wheel speed data corresponding to the other three wheels, This refers to the actual wheel speed data for the remaining three wheels.

[0036] Based on step ③ of step S2 above, which divides the total yaw torque data into first yaw torque data, second yaw torque data and third yaw torque data according to a preset ratio, and the target wheel speed data obtained in step ③ of step S3, the motor output torque data of the left front wheel, right front wheel and right rear wheel can be obtained by using the above formula.

[0037] In addition, the proportionality coefficient Integral coefficient and differential coefficients These are the proportional, integral, and derivative gains used for closed-loop control of wheel speed. These parameters are determined through engineering calibration based on the motor's moment of inertia, torque response characteristics, and the vehicle's actual dynamic response. The specific calibration process can be carried out on a test bench or in a real vehicle using conventional parameter tuning methods in the field, so that the wheel speed can quickly, smoothly, and accurately track the target speed, and the overshoot is within the allowable range.

[0038] It is important to note that after obtaining the motor output torque data for the three wheels, the following is also included: ② Limiting of motor output torque: To ensure the safety and reliability of the electric drive system, the initially calculated motor output torque needs to be limited to ensure that it does not exceed the physical output capacity of the motor at the current speed. The process is as follows: Obtain the maximum output torque data of the motors corresponding to the left front wheel, right front wheel, and right rear wheel. and maximum output power data ; Determine the motors corresponding to the left front wheel, right front wheel, and right rear wheel at the current wheel speed. Maximum permissible torque ; ; Compare the motor output torque data of the left front wheel, right front wheel, and right rear wheel with the corresponding maximum permissible torque. The smaller value is used as the final output torque data.

[0039] ③ Calculate the braking torque of the steering center wheel; In this embodiment, the braking torque of the left rear wheel is calculated using the following formula: ; in, is the proportionality constant, m is the vehicle mass, and g is the gravitational acceleration.

[0040] In addition, the proportionality coefficient The safety factor is greater than 1, and its specific value is determined through engineering calibration. It is necessary to ensure that the generated braking torque is sufficient to overcome the maximum static friction torque that the ground may exert on the wheel, so as to reliably lock it as the steering center. In the calibration, the working conditions of different road surface adhesion coefficients need to be comprehensively considered to ensure that the wheel can be effectively locked on both high and low adhesion road surfaces.

[0041] Example 2: Embodiment 2 of this application also provides a system for a method of driving a vehicle to perform small-radius steering, including: The control module, which is the system's triggering unit, is used to respond to small-radius steering commands issued by the driver through a human-machine interface (such as physical buttons or a touch screen), and thereby lock one rear wheel as the steering center wheel. The data acquisition module communicates with the vehicle's bus network (such as CAN bus) and various sensors (such as steering wheel angle sensor, yaw rate sensor, wheel speed sensor, etc.). It is configured to acquire the transmission ratio of the steering wheel input, the maximum steering angle, the opening of the accelerator pedal, the current yaw rate of the vehicle, the moment of inertia data for steering, the vehicle's geometric parameters, and the actual wheel speed data of the three wheels other than the steering center wheel. The processing module, typically implemented by one or more electronic control units (ECUs) of the vehicle, establishes a communication connection with the control module and data acquisition module, receives relevant instructions and data, and has embedded a control program configured to execute all the calculation and decision-making logic as described in Example 1, including but not limited to: acquiring front wheel steering angle data based on the gear ratio and maximum steering angle; calculating the vehicle's desired yaw rate data based on the accelerator pedal opening; calculating yaw acceleration data based on the vehicle's current yaw rate and desired yaw rate data; calculating the total yaw torque data of the vehicle's steering based on the yaw acceleration data and moment of inertia data; and dividing the total yaw torque data into first yaw torque data and second yaw torque data according to a preset ratio. The system collects data, including the first, second, and third yaw torque data, and distributes them to the three wheels other than the steering center wheel. Based on the acquired first, second, and third yaw torque data, it calculates the target slip ratio of the corresponding wheel using a tire model. Based on the vehicle's current yaw rate and vehicle geometry, it calculates the longitudinal velocity data of the other three wheels. Based on the acquired target slip ratio and longitudinal velocity data, it calculates the target wheel speed data corresponding to the other three wheels. It also acquires the actual wheel speed data of the three wheels other than the steering center wheel. Based on the acquired target wheel speed data and actual wheel speed data, it acquires the motor output torque data of the three wheels other than the steering center wheel and calculates the braking torque of the steering center wheel. The execution module mainly includes the drivers of multiple wheel-side motors or hub motors that drive the vehicle, as well as an electronic braking system (such as ESC / EPB). This module is connected to the processing module, receives the torque command issued by it, drives the corresponding motor to output precise torque, and applies braking force to the steering center wheel, ultimately achieving a small-radius steering action in a coordinated manner.

[0042] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0043] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0044] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for driving a vehicle to turn with a small radius, characterized in that, Includes the following steps: The front wheel steering angle data is obtained based on the transmission ratio and maximum steering angle input from the steering wheel. The vehicle's expected yaw rate data is calculated based on the opening degree of the accelerator pedal. The yaw acceleration data is calculated based on the vehicle's current yaw rate and expected yaw rate data. One rear wheel is locked as the steering center wheel. The rotational inertia data of the vehicle turning around the steering center wheel is obtained. Based on the yaw angle acceleration data and rotational inertia data, the total yaw torque data of the vehicle is calculated. The total yaw torque data is divided into first yaw torque data, second yaw torque data and third yaw torque data according to a preset ratio and distributed to the other three wheels except the steering center wheel. Based on the acquired first yaw torque data, second yaw torque data, and third yaw torque data, the target slip ratio of the corresponding wheel is calculated using the tire model; the longitudinal velocity data of the other three wheels is calculated based on the vehicle's current yaw rate and vehicle geometric parameters; and the target wheel speed data of the other three wheels is calculated based on the acquired target slip ratio and longitudinal velocity data. Obtain the actual wheel speed data of the three wheels of the vehicle other than the steering center wheel, and obtain the motor output torque data of the three wheels other than the steering center wheel based on the obtained target wheel speed data and actual wheel speed data. The braking torque of the steering center wheel is calculated, and the corresponding wheel is controlled to achieve steering based on the acquired motor output torque data and braking torque.

2. The method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The yaw acceleration data is obtained using the following formula: ； ; in, This is the proportionality coefficient. The integral coefficient is... The differential coefficients are... To track errors, For the desired yaw rate data, This represents the current yaw rate.

3. The method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The total yaw torque data is obtained using the following formula: ； in, For rotational inertia data, This is the yaw acceleration data. The longitudinal force is applied to the front wheel on the side closest to the steering center wheel. For the longitudinal force of the other front wheel, The lateral force on the front wheel closest to the steering center wheel. The lateral force on the other front wheel, Let L be the longitudinal force on the rear wheel other than the steering center wheel, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, Let L be the geometric auxiliary angle determined by L and B.

4. The method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The tire model is a composite brush tire model.

5. A method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The longitudinal velocity data is obtained using the following formula: ； ； ； in, Let L be the current yaw rate, L be the wheelbase between the front and rear wheels, and B be the track width between the left and right wheels. The front wheel steering angle data is for the front wheel closest to the steering center wheel. For the front wheel steering angle data of the other front wheel, Let L be the geometric auxiliary angle determined by L and B.

6. The method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The target wheel speed data is obtained using the following formula: ； Where i represents the other three wheels. The target slip ratios for the remaining three wheels are... For which wheel's longitudinal velocity data it corresponds to. The radius is the wheel radius.

7. A method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The motor output torque data is calculated using the following formula: ； ； in, For the remaining three wheels, the longitudinal torque data is as follows. For the wheel radius, For rotational inertia data, , and These are the proportional coefficient, integral coefficient, and differential coefficient for the other three wheels, respectively. The remaining three wheels correspond to the rotational speed error. For the target wheel speed data corresponding to the other three wheels, This refers to the actual wheel speed data for the remaining three wheels.

8. A method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, After obtaining the motor output torque data of the three wheels other than the steering center wheel based on the acquired target wheel speed data and actual wheel speed data, the process also includes: Obtain the motor's maximum output torque and maximum output power data; Determine the maximum permissible torque of the motors corresponding to the other three wheels at the current wheel speed; The motor output torque data of the three wheels other than the steering center wheel are compared with the corresponding maximum allowable torque, and the smaller one is taken as the final output torque data.

9. A method for driving a vehicle to turn with a small radius according to claim 1, characterized in that, The braking torque of the steering center wheel is obtained by the following formula: ； in, is the proportionality constant, m is the vehicle mass, and g is the gravitational acceleration.

10. A system based on the method for driving a vehicle with small-radius steering as described in claim 1, characterized in that, include: The control module, which responds to steering commands, is configured to lock one rear wheel as the steering center wheel based on the steering command. The data acquisition module is configured to acquire the transmission ratio of the steering wheel input, the maximum steering angle, the opening of the accelerator pedal, the current yaw rate of the vehicle, the moment of inertia data for steering, the vehicle's geometric parameters, and the actual wheel speed data of the three wheels other than the steering center wheel. The processing module, connected to the control module and the data acquisition module, is configured to acquire front wheel steering angle data based on the transmission ratio and maximum steering angle; calculate the vehicle's desired yaw rate data based on the accelerator pedal opening; calculate yaw acceleration data based on the vehicle's current yaw rate and desired yaw rate data; calculate the total yaw torque data based on the yaw acceleration data and moment of inertia data; divide the total yaw torque data into first yaw torque data, second yaw torque data, and third yaw torque data according to a preset ratio, and distribute them to the three wheels other than the steering center wheel; and based on the acquired data... The first, second, and third yaw torque data are used to calculate the target slip ratio of the corresponding wheels using the tire model. Based on the vehicle's current yaw rate and vehicle geometry, the longitudinal velocity data of the other three wheels are calculated. Based on the acquired target slip ratio and longitudinal velocity data, the target wheel speed data of the other three wheels is calculated. The actual wheel speed data of the other three wheels (excluding the steering wheel) is obtained. Based on the acquired target wheel speed data and actual wheel speed data, the motor output torque data of the other three wheels (excluding the steering wheel) is obtained, and the braking torque of the steering wheel is calculated. The execution module, which is connected to the processing module, is configured to control the corresponding wheels to achieve steering based on the acquired motor output torque data and braking torque.

Images