Track tracking control method and system for four-wheel distributed drive automatic driving vehicle

Abstract

This invention discloses a trajectory tracking control method and system for autonomous vehicles based on four-wheel distributed drive, comprising: obtaining the current speed of the four-wheel distributed drive vehicle and the user's desired speed; simplifying the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel; determining the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculating the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtaining the desired trajectory of the four-wheel distributed drive vehicle; calculating the basic rotational speed of each wheel of the four-wheel distributed drive vehicle; calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle; and obtaining the total desired rotational speed of each wheel based on the basic speed and the compensation speed of each wheel. This invention achieves trajectory tracking control of a four-wheel distributed drive vehicle with strong real-time performance.

Description

Technical Field

[0001] This invention belongs to the field of autonomous driving technology, and particularly relates to a method and system for trajectory tracking control of autonomous vehicles based on four-wheel distributed drive. Background Technology

[0002] Distributed drive vehicles, developed in recent years, typically operate by having several drive motors output independently controllable speeds and torques to perform steering and movement. Benefiting from their high reliability and energy efficiency, distributed drive vehicles are widely used in various fields such as park delivery, urban shuttle services, and scientific research. However, they also suffer from drawbacks such as poor control stability and insufficient control sensitivity, limiting their large-scale promotion and industrial application in certain aspects. Currently, only a few solution providers both domestically and internationally have developed control methods that can be deployed on various platforms and operate effectively, and it is difficult for ordinary users to customize them for specific needs. Distributed drive solutions involve hardware and software coordination between multiple drive units, and the debugging process is cumbersome, significantly raising the barrier to entry for autonomous driving in the aforementioned scenarios. Many factors affect the ability of distributed drive vehicles to follow a desired trajectory. Errors in the perception and positioning equipment can affect the monitoring of kinematic states such as pose and heading, indirectly interfering with the output of the execution unit; the pre-determined desired trajectory may contain dead zones that do not meet the vehicle's dynamic constraints, leading to loss of control conditions such as excessive slip rate during trajectory tracking, causing the path error to gradually increase. These factors have a significant negative impact on driving safety and limit the realization of autonomous driving functions. Therefore, designing control methods to correct following errors is a problem that the industry must currently address. For four-wheel distributed drive vehicles that cannot adjust steering angles, significant wheel slippage and wear will occur under conditions other than straight-line driving. This not only damages the vehicle's mechanical structure and shortens its service life, but also affects the vehicle's trajectory tracking performance, requiring a significant amount of time to converge errors when the deviation from the desired trajectory is too large. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a trajectory tracking control method and system for autonomous vehicles based on four-wheel distributed drive. This method can significantly improve the accuracy and real-time performance of trajectory tracking while minimizing vehicle slippage, and achieve effective multi-dimensional tracking of heading and speed.

[0004] To achieve the above objectives, this invention provides a trajectory tracking and control method for autonomous vehicles based on four-wheel distributed drive, comprising:

[0005] Obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed;

[0006] The four-wheeled distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, which includes an ideal rear wheel and an ideal front wheel;

[0007] Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle;

[0008] Calculate the basic rotational speed of each wheel of the four-wheel distributed drive vehicle;

[0009] Calculate the compensated speed of each wheel of the four-wheel distributed drive vehicle;

[0010] Based on the basic speed and the compensation speed of each wheel, the total expected rotational speed of each wheel is obtained.

[0011] The trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention simplifies the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, including:

[0012] The left and right front wheels of the four-wheel distributed drive vehicle are equivalently transformed into ideal front wheels, and the left and right rear wheels are equivalently transformed into ideal rear wheels, with both the ideal front wheels and the ideal rear wheels located on the longitudinal centerline of the vehicle.

[0013] According to the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention, the method for calculating the turning radius of the ideal two-degree-of-freedom bicycle model is as follows:

[0014] absolute position p t and expected tracking point p tar The distance between them is l;

[0015] Ideal rear wheel rolling direction and straight line p t p tar The angle between them is θ;

[0016] absolute position p t To the expected tracking point p tar During the tracking process, the path traveled by the ideal rear wheel is an arc. The turning radius R of the ideal two-degree-of-freedom bicycle model is calculated as follows:

[0017] OP t =Op tar ,

[0018] According to the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention, the method for calculating the turning angle of the ideal front wheel of the ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line containing the ideal front wheel and the straight line containing the ideal rear wheel is the turning center; the angle between the two straight lines is equal to the front wheel turning angle δ; and the distance from the ideal front wheel to the ideal rear wheel is l. d ;

[0019] The rotation angle of the ideal front wheel in the ideal two-degree-of-freedom bicycle model is calculated as follows:

[0020] Substitution have to

[0021] According to the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention, the method for calculating the basic rotational speed of each wheel of the four-wheel distributed drive vehicle is as follows:

[0022] Based on an ideal two-degree-of-freedom bicycle model, the yaw rate ω is calculated as follows:

[0023]

[0024] The basic rotational speed is calculated based on the yaw rate:

[0025]

[0026] Where, n lf n lr n rf n rr These are the rotational speeds of the left front wheel, left rear wheel, right front wheel, and right rear wheel, respectively. R w v is the radius of the wheel. t The current speed of the four-wheel distributed drive vehicle; d y is the distance between the ideal front wheel and the ideal rear wheel; b is the track width.

[0027] According to the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention, the method for calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle is as follows:

[0028] The compensation speed Δn of each wheel is calculated based on the speed error. v :

[0029]

[0030] Where e(j) represents the velocity difference error at the j-th sampling time; k p The speed error proportionality coefficient; e(t) is the speed error; k i The integral coefficient for velocity error;

[0031] The compensation speed Δn of each wheel is calculated based on the heading error. d :

[0032]

[0033] Among them, e d (t) represents the heading error; k dd e is the differential coefficient for heading error; d (j) represents the heading error at time j; T represents the control period; ψ t ψ is the angle between the current vehicle heading and the x-axis of the geodetic coordinate system. tar This represents the angle between the tangent to the desired trajectory at the desired tracking point and the x-axis of the geodetic coordinate system.

[0034] The compensation speed Δn of each wheel is calculated based on the lateral error. l :

[0035]

[0036] Among them, e l (t) represents the distance from the current vehicle position to the projection point on the desired trajectory; k l and B l These are the adjustable proportional coefficient and the base, respectively.

[0037] According to the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive provided by the present invention, the method for obtaining the total desired rotational speed of each wheel based on the basic speed and the compensation speed of each wheel is as follows:

[0038]

[0039] Where lf, rf, lr, and rr are the subscripts of the relevant physical quantities of the left front wheel, right front wheel, left rear wheel, and right rear wheel of the four-wheel distributed drive vehicle, respectively; Δn lf , Δn rf , Δn lr , Δn rr Let Δn be the total expected speed of the left front wheel, the total expected speed of the right front wheel, the total expected speed of the left rear wheel, and the total expected speed of the right rear wheel of the four-wheel distributed drive vehicle; v The compensated rotational speed for each wheel; Δn d The compensated rotational speed for each wheel; Δn l This refers to the compensation speed for each wheel.

[0040] On the other hand, in order to achieve the above objectives, the present invention also provides an autonomous vehicle trajectory tracking control system based on four-wheel distributed drive, including: a speed acquisition module, a model construction module, a vehicle desired trajectory acquisition module, a vehicle basic speed calculation module, a vehicle compensation speed calculation module, and a vehicle total desired speed calculation module;

[0041] The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed;

[0042] The model building module is used to simplify a four-wheeled distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel;

[0043] The vehicle expected trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle.

[0044] The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of the four-wheel distributed drive vehicle;

[0045] The vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle.

[0046] The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel.

[0047] Technical advantages of this invention: This invention discloses a trajectory tracking control method and system for autonomous vehicles based on four-wheel distributed drive. It solves the problem that traditional control methods for differential steering vehicles cannot meet kinematic requirements. By introducing a desired tracking point and ideal front and rear wheels, the difficult-to-analyze differential steering model is transformed into an ideal two-degree-of-freedom model, and the basic rotational speed is calculated. The trajectory is then optimized from three aspects: lateral error, heading error, and speed, and the compensation rotational speed is solved. Based on multi-dimensional rotational speed compensation, trajectory tracking control of four-wheel distributed drive vehicles is achieved with strong real-time performance while minimizing wheel slippage and wear. This invention has good results in engineering applications, lowering the threshold for the implementation of autonomous driving of distributed drive vehicles. Attached Figure Description

[0048] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0049] Figure 1This is a flowchart illustrating the trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive, according to an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the trajectory tracking control system for autonomous vehicles based on four-wheel distributed drive, according to an embodiment of the present invention.

[0051] Figure 3 This is a schematic diagram illustrating the calculation of the turning radius according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram illustrating the solution of the ideal front wheel steering angle in an embodiment of the present invention. Detailed Implementation

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0054] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0055] like Figure 1 As shown, this embodiment provides a trajectory tracking and control method for autonomous vehicles based on four-wheel distributed drive, including:

[0056] Obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed;

[0057] The four-wheeled distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, which includes an ideal rear wheel and an ideal front wheel;

[0058] Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle.

[0059] Calculate the basic rotational speed of each wheel in a four-wheel distributed drive vehicle;

[0060] Calculate the compensated speed of each wheel of a four-wheel distributed drive vehicle;

[0061] Based on the basic speed and the compensation speed of each wheel, the total expected rotational speed of each wheel is obtained.

[0062] Specifically, the vehicle's kinematic state is collected by wheel speed sensors and inertial measurement units to calculate the vehicle speed, which, together with the desired vehicle speed command from the user, is input to the vehicle controller.

[0063] Furthermore, simplifying the four-wheeled distributed drive vehicle into an ideal two-degree-of-freedom bicycle model includes:

[0064] The left and right front wheels of the four-wheel distributed drive vehicle are equivalently transformed into ideal front wheels, and the left and right rear wheels are equivalently transformed into ideal rear wheels, with both ideal front wheels and ideal rear wheels located on the longitudinal centerline of the vehicle.

[0065] Specifically, the complex four-wheel differential model is transformed into a simple two-degree-of-freedom monorail model; after solving for the intermediate quantity of the front wheel steering angle required by the monorail model, the basic speed required for each wheel is obtained by reverse calculation, thus achieving the expected technical goal of four-wheel differential steering.

[0066] Furthermore, such as Figure 3 As shown, the method for calculating the turning radius of an ideal two-degree-of-freedom bicycle model is as follows:

[0067] absolute position p t and expected tracking point p tar The distance between them is l;

[0068] Ideal rear wheel rolling direction and straight line p t p tar The angle between them is θ;

[0069] absolute position p t To the expected tracking point p tar During the tracking process, the path traveled by the ideal rear wheel is an arc. The turning radius R of the ideal two-degree-of-freedom bicycle model is calculated as follows:

[0070] Op t =Op tar ,

[0071] Furthermore, such as Figure 4 As shown, the method for calculating the steering angle of the ideal front wheel in an ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line containing the ideal front wheel and the straight line containing the ideal rear wheel is the steering center; the angle between the two straight lines is equal to the front wheel steering angle δ; and the distance from the ideal front wheel to the ideal rear wheel is l. d ;

[0072] The rotation angle of the ideal front wheel in an ideal two-degree-of-freedom bicycle model is calculated as follows:

[0073] Substitution have to

[0074] Furthermore, the method for calculating the basic rotational speed of each wheel in a four-wheel distributed drive vehicle is as follows:

[0075] Based on an ideal two-degree-of-freedom bicycle model, the yaw rate ω is calculated as follows:

[0076]

[0077] The basic rotational speed is calculated based on the yaw rate:

[0078]

[0079] Where, n lf n lr n rf n rr These are the rotational speeds of the left front wheel, left rear wheel, right front wheel, and right rear wheel, respectively. R w v is the radius of the wheel. t The current speed of the four-wheel distributed drive vehicle; d denoted by , where b is the distance from the ideal front wheel to the ideal rear wheel; and b is the wheelbase. When the vehicle deviates from the desired trajectory, the trajectory is optimized from three aspects: heading error, lateral error, and speed, until convergence is achieved, thus realizing high-precision tracking control.

[0080] Furthermore, the method for calculating the compensated speed of each wheel in a four-wheel distributed drive vehicle is as follows:

[0081] The compensation speed Δn of each wheel is calculated based on the speed error. v :

[0082]

[0083] Where e(j) represents the velocity difference error at the j-th sampling time; k p The speed error proportionality coefficient; e(t) is the speed error; k i This represents the speed error integral coefficient; specifically, a PI controller is used to ensure that the vehicle's actual speed gradually converges to the desired speed as it approaches the tracking point, until the error is zero. Since the platform used in this patent is a differential steering vehicle, the compensation speed Δn... v It acts on each wheel without affecting the steering angle or yaw rate;

[0084] The compensation speed Δn of each wheel is calculated based on the heading error. d :

[0085]

[0086] Among them, e d (t) represents the heading error; k dd e is the differential coefficient for heading error; d (j) represents the heading error at time j; T represents the control period; ψ t ψ is the angle between the current vehicle heading and the x-axis of the geodetic coordinate system. tarThis represents the angle between the tangent of the desired trajectory at the desired tracking point and the x-axis of the geodetic coordinate system. Specifically, a PD controller is used to ensure that the vehicle's actual heading gradually and smoothly converges to the desired heading as it approaches the tracking point, avoiding high-frequency jitter. Since the platform used in this patent is a differential steering vehicle, the compensation speed Δn... d The effect is applied to both front wheels, with the changes in rotational speed of the inner and outer wheels being respectively... and

[0087] The compensation speed Δn of each wheel is calculated based on the lateral error. l :

[0088]

[0089] Among them, e l (t) represents the distance from the current vehicle position to the projection point on the desired trajectory; k l and B l These are the manually adjustable proportional coefficient and the base; specifically, an exponential function relationship is used so that the lateral error of the vehicle gradually approaches zero as it approaches the tracking point. Due to the compensation speed Δn d This has already been applied to both front wheels. Considering the constraints of the hardware's execution capabilities, the compensation speed Δn will be adjusted. l Used for both rear wheels, where the speed changes of the inner and outer wheels are respectively and

[0090] Furthermore, based on the basic speed and compensation speed of each wheel, the method for obtaining the total expected rotational speed of each wheel is as follows:

[0091]

[0092]

[0093] Where lf, rf, lr, and rr are the subscripts of the relevant physical quantities of the left front wheel, right front wheel, left rear wheel, and right rear wheel of the four-wheel distributed drive vehicle, respectively; Δn lf , Δn rf , Δn lr , Δn rr Let Δn be the total expected speed of the left front wheel, the total expected speed of the right front wheel, the total expected speed of the left rear wheel, and the total expected speed of the right rear wheel of the four-wheel distributed drive vehicle; v The compensated rotational speed for each wheel; Δn d The compensated rotational speed for each wheel; Δn l This refers to the compensation speed for each wheel.

[0094] Specifically, a PD controller is used to smoothly converge the vehicle's actual heading to the desired heading, avoiding high-frequency oscillations. The required compensation speed Δn... d The force is applied to both front wheels to ensure the vehicle's responsiveness to this quantity; a PI controller is used to rapidly converge the vehicle's real-time speed to the desired speed until the error is eliminated. The required compensation speed Δn is... l Acting on each wheel, it does not affect the yaw rate of differential steering. An exponential function controller is used to quickly converge the vehicle's lateral error to zero. The required compensation speed Δn d It acts on both rear wheels to protect each wheel from rotating beyond the constraints of the hardware's execution capabilities.

[0095] like Figure 2 As shown, this embodiment also provides an autonomous vehicle trajectory tracking and control system based on four-wheel distributed drive, including: a speed acquisition module, a model construction module, a vehicle desired trajectory acquisition module, a vehicle basic speed calculation module, a vehicle compensation speed calculation module, and a vehicle total desired speed calculation module;

[0096] The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed;

[0097] A model module is constructed to simplify a four-wheeled distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, which includes an ideal rear wheel and an ideal front wheel;

[0098] The vehicle expected trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius and the turning angle of the ideal front wheel of the ideal two-degree-of-freedom bicycle model, and obtain the expected trajectory of the four-wheel distributed drive vehicle.

[0099] The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of a four-wheel distributed drive vehicle.

[0100] The vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of a four-wheel distributed drive vehicle.

[0101] The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed and the compensation speed of each wheel.

[0102] This invention discloses a trajectory tracking control method and system for autonomous vehicles based on four-wheel distributed drive. It solves the problem that traditional control methods for differential steering vehicles cannot meet kinematic requirements. By introducing a desired tracking point and ideal front and rear wheels, the difficult-to-analyze differential steering model is transformed into an ideal two-degree-of-freedom model, and the basic rotational speed is calculated. The trajectory is then optimized from three aspects: lateral error, heading error, and velocity, and the compensation rotational speed is solved. Based on multi-dimensional rotational speed compensation, trajectory tracking control of four-wheel distributed drive vehicles is achieved with strong real-time performance while minimizing wheel slippage and wear. This invention has shown good results in engineering applications, lowering the threshold for the implementation of autonomous driving of distributed drive vehicles.

[0103] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive, characterized in that, include: Obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed; The four-wheeled distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, which includes an ideal rear wheel and an ideal front wheel; Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle; Calculate the basic rotational speed of each wheel of the four-wheel distributed drive vehicle; Calculate the compensated speed of each wheel of the four-wheel distributed drive vehicle; Based on the basic speed and the compensated speed of each wheel, the total expected rotational speed of each wheel is obtained; The method for calculating the compensated speed of each wheel of the four-wheel distributed drive vehicle is as follows: The compensated rotational speed of each wheel is calculated based on the speed error. : , ， in, Indicates the first The velocity difference error at each sampling time; This is the speed error proportionality coefficient; For speed error; The integral coefficient for velocity error; The compensated rotational speed of each wheel is calculated based on the heading error. : , ， in, For heading error; These are the differential coefficients for the heading error; Let be the heading error at time j; To control the cycle; The angle between the current vehicle heading and the x-axis of the geodetic coordinate system. This represents the angle between the tangent to the desired trajectory at the desired tracking point and the x-axis of the geodetic coordinate system. The compensated speed of each wheel is calculated based on the lateral error. : , in, This represents the distance from the current vehicle position to the projection point on the desired trajectory; and These are the adjustable proportional coefficient and the base, respectively; The method for obtaining the total expected rotational speed of each wheel based on the basic speed and the compensated speed of each wheel is as follows: ， ， ， ， in, These are subscripts for the physical quantities related to the left front wheel, right front wheel, left rear wheel, and right rear wheel of a four-wheeled distributed drive vehicle. , , , The total expected speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel of the four-wheel distributed drive vehicle are: To calculate the compensated rotational speed of each wheel based on the speed error; To calculate the compensated rotational speed of each wheel based on the heading error; To calculate the compensated rotational speed of each wheel based on the lateral error.

2. The trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive as described in claim 1, characterized in that, Simplifying a four-wheeled distributed drive vehicle into an ideal two-degree-of-freedom bicycle model includes: The left and right front wheels of the four-wheel distributed drive vehicle are equivalently transformed into ideal front wheels, and the left and right rear wheels are equivalently transformed into ideal rear wheels, with both the ideal front wheels and the ideal rear wheels located on the longitudinal centerline of the vehicle.

3. The trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive as described in claim 1, characterized in that, The method for calculating the turning radius of the ideal two-degree-of-freedom bicycle model is as follows: Absolute position and expected tracking points The distance between them is ; Ideal rear wheel rolling direction and straight line The included angle between them is ; Absolute position To the expected tracking point During the tracking process, the ideal rear wheel travels a circular arc. Calculate the turning radius of the ideal two-degree-of-freedom bicycle model. for: = ， , 。 4. The trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive as described in claim 1, characterized in that, The method for calculating the steering angle of the ideal front wheel in the ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line containing the ideal front wheel and the straight line containing the ideal rear wheel is the steering center, and the angle between the two lines and the steering angle of the front wheel are calculated. Equal, the distance from the ideal front wheel to the ideal rear wheel is ; The rotation angle of the ideal front wheel in the ideal two-degree-of-freedom bicycle model is calculated as follows: , Substitute have to .

5. The trajectory tracking control method for autonomous vehicles based on four-wheel distributed drive as described in claim 1, characterized in that, The method for calculating the basic rotational speed of each wheel of the four-wheel distributed drive vehicle is as follows: Calculate the yaw rate based on an ideal two-degree-of-freedom bicycle model. for: ， The basic rotational speed is calculated based on the yaw rate: ， ， in, , These are the rotational speeds of the left front wheel, left rear wheel, right front wheel, and right rear wheel, respectively. The radius of the wheel; This represents the current speed of the four-wheel distributed drive vehicle. The distance between the ideal front wheel and the ideal rear wheel; This refers to the wheel track.

6. A system for trajectory tracking control of an autonomous vehicle based on four-wheel distributed drive according to any one of claims 1-5, characterized in that, include: The system includes a speed acquisition module, a model building module, a vehicle desired trajectory acquisition module, a vehicle basic speed calculation module, a vehicle compensation speed calculation module, and a vehicle total desired speed calculation module. The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's desired speed; The model building module is used to simplify a four-wheeled distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel; The vehicle desired trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the desired trajectory of the four-wheel distributed drive vehicle. The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of the four-wheel distributed drive vehicle; The vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle. The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel.

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