Automobile parking front wheel automatic aligning system and method

Abstract

The invention provides an automatic front wheel aligning system and method for automobile parking, and relates to the technical field of wheel aligning control. Comprising an I MU sensor which is installed at the center of a rotating shaft of a front brake disc and a rear brake disc of a vehicle and used for obtaining a pose matrix between corresponding front and rear wheels; the controller is used for receiving the corresponding pose matrix between the front wheel and the rear wheel sent by the I MU sensor, calculating a first deflection angle of the left front wheel relative to the left rear wheel and a second deflection angle of the right front wheel relative to the right rear wheel, and obtaining an average deflection angle based on the first deflection angle and the second deflection angle; based on the average deflection angle, the left front wheel and the right front wheel are controlled to steer until the left front wheel and the right front wheel are aligned. When the automobile is parked, an algorithm is designed to obtain the steering angle difference of the front and rear wheels in real time, then the steering angle difference is converted into an electric signal to control the steering motor to operate, and high-precision automatic returning of the front wheels of the automobile is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wheel return control, and in particular relates to an automatic front wheel return system and method for parking a car. Background Art

[0002] When the car is parked, the front wheels need to be straightened to prevent the car's steering system from aging. However, in actual vehicle use, many drivers often forget this step due to habit, or deliberately do not straighten the wheels due to parking technology reasons. Some drivers even do not realize that they should straighten the wheels automatically when parking.

[0003] If the wheels are not straightened after parking, it will cause damage to the vehicle in many aspects:

[0004] (1) Failure to straighten the wheels after parking is equivalent to the power pump pumping out oil to drive the steering but not returning the oil. Negative pressure will form in the power pump, accelerating the aging of the power pump, and the oil pipe will also be under too much pressure.

[0005] (2) The wheels are not straightened after parking and are parked at an inclined angle. The weight of the vehicle body is not applied to the front frame but to the front tie bar. If this continues for a long time, the tie bar will be deformed, resulting in inaccurate steering and excessive clearance. In severe cases, it may cause an accident due to steering shake during driving.

[0006] (3) Failure to return the wheel to the correct position after parking will not only damage the above two parts, but also the tire. Under normal circumstances, the tire will maintain the state of tread contacting the ground under stress. When the wheel is not returned to the correct position, due to the existence of the kingpin inclination angle and the camber design of passenger car tires, the tire is not completely in contact with the ground with the tread, but the shoulder and part of the tread are under stress. In this case, the pressure on the sidewall of the tire is relatively large. Since the sidewall of the tire is relatively thin, if the tire is often subjected to unbalanced stress in this way, it will accelerate the aging and deformation of the tire sidewall. After the tire sidewall is aged and deformed, it is likely to cause air leakage or tire blowout.

[0007] (4) If the wheels are not straightened after parking, the vehicle may easily go off the track when it is started again, increasing the probability of a traffic accident.

[0008] The existing method of returning the wheels of a vehicle to the correct position when it is parked in the prior art usually detects the deflection angle of the steering wheel through a steering wheel angle sensor, controls the steering wheel to return to the correct position, and then controls the wheels to return to the correct position. This method often lacks the detection of whether the wheels are accurately returned to the correct position, and there may be a certain error in the return to the correct position.

[0009] In addition, there are also methods in the prior art that use wheel angle sensors to detect wheel angle signals to determine whether the wheels are aligned. When it is detected that the wheels are not aligned, the electric power steering system will align the wheels according to the wheel angle signals. For example, the technology described in the Chinese invention patent application document with the announcement number CN 102795262 A and the name of the automatic wheel alignment system. The above technology does not disclose how to specifically set the wheel angle sensor to detect the wheel angle signal. Due to the detection errors of different wheel angle sensors themselves, if the wheel angle signal detected by them has a large error, it will directly affect the accuracy of wheel alignment. Summary of the invention

[0010] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a system and method for automatic front wheel self-centering when parking a vehicle. The position and posture of each wheel are automatically acquired through two sets of IMU sensors. The two sets of IMU sensors are installed at the center of the rotation axis of the front and rear brake discs. When the vehicle is parked, an algorithm is designed to acquire the steering angle difference between the front and rear wheels in real time, and then the steering angle difference is converted into an electrical signal to control the operation of the steering motor, thereby realizing high-precision automatic self-centering of the front wheels of the vehicle.

[0011] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0012] A first aspect of the present invention provides an automatic front wheel self-centering system for parking a vehicle.

[0013] The automatic front wheel self-centering system for parking a car includes an IMU sensor and a controller, wherein:

[0014] IMU sensor, which is installed at the center of the rotation axis of the front and rear brake discs of the vehicle to obtain the corresponding position matrix between the front and rear wheels;

[0015] A controller, which is used to receive the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtain an average deflection angle based on the first deflection angle and the second deflection angle;

[0016] Based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

[0017] As an optional technical solution, two groups of IMU sensors are provided, and the two groups of IMU sensors are designed to be redundant with each other. When one group of IMU sensors fails, the other group of IMU sensors replaces the failed IMU sensors to realize the posture data acquisition function.

[0018] As an optional technical solution, the IMU sensor is used to establish the IMU coordinate system of the left rear wheel and the right rear wheel, specifically:

[0019] Take the center position of the left rear wheel and the right rear wheel as the origin, the forward direction of the left rear wheel and the right rear wheel as the positive direction of the x-axis, and determine the positive direction of the y-axis and the positive direction of the z-axis to establish the IMU coordinate system of the left rear wheel and the right rear wheel respectively.

[0020] As an optional technical solution, the IMU sensor is used to obtain the corresponding posture matrix between the front and rear wheels, and the corresponding posture matrix between the front and rear wheels includes the posture matrix of the left front wheel relative to the left rear wheel, and the posture matrix of the right front wheel relative to the right rear wheel. The specific method is:

[0021] Based on the established IMU coordinate systems of the left rear wheel and the right rear wheel, the rotation angles of the left front wheel relative to the left rear wheel and the right front wheel relative to the right rear wheel in the xyz directions are measured after parking.

[0022] Calculate the rotation matrices of the left front wheel relative to the left rear wheel, and the right front wheel relative to the right rear wheel in the xyz direction respectively;

[0023] Calculate the product of the rotation matrices corresponding to the three directions of xyz to obtain the position matrix of the left front wheel relative to the left rear wheel, and the position matrix of the right front wheel relative to the right rear wheel.

[0024] As an optional technical solution, suppose that after parking, the rotation angles of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel in the x, y, and z directions are α, β, and γ respectively, then the corresponding rotation matrices in the xyz directions are:

[0025] Rotation around the x-axis:

[0026]

[0027] Rotation around the y-axis:

[0028]

[0029] Rotation around the z-axis:

[0030]

[0031] In summary, the pose matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel is

[0032] R xyz for:

[0033] R xyz =R x (α)*R y (β)*R z (γ);

[0034] Among them, R x(α) is the x-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R y (β) is the y-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R z (γ) is the z-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel.

[0035] As an optional technical solution, the controller is used to calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and the specific method is:

[0036] Get the rotation matrix R of the front wheel relative to the rear wheel xyz , reverse the rotation angle of the front wheel relative to the rear wheel:

[0037]

[0038] The calculation formula of sy is as follows:

[0039]

[0040] In the above formula, R(i, j) represents the rotation matrix R xyz The value of the i-th row and j-th column; i = L or R, indicating left or right, respectively; α i , β i , γ i They respectively represent the first deflection angle of the left front wheel relative to the left rear wheel, and the second deflection angle of the right front wheel relative to the right rear wheel; α, β, γ are the rotation angles in the x, y, and z directions respectively.

[0041] As an optional technical solution, the controller is used to obtain an average deflection angle based on the first deflection angle and the second deflection angle by adopting a weighted summation method; the weight values ​​of the first deflection angle and the second deflection angle can be set.

[0042] As an optional technical solution, it also includes a manual switch, which is used to obtain an activation signal from a user for the automatic front wheel straightening system of the vehicle and send it to the controller;

[0043] The controller is also used to activate the automatic front wheel return function of the car when parking when receiving an activation signal.

[0044] As an optional technical solution, the controller is also used to detect the current state of the car, including whether the engine or electric drive is in working state, whether the driver has left the cab, and whether there is an obstacle within the trajectory envelope of the wheel steering;

[0045] It is also used to determine that the engine or electric drive is not in working condition, the driver has left the cab, and there are no obstacles within the trajectory envelope of the wheel steering, and to execute the automatic front wheel return function when the car is parked.

[0046] A second aspect of the present invention provides a method for automatically straightening the front wheels of a vehicle when parking.

[0047] The method for automatically returning the front wheels of a car to the correct position when parking comprises the following steps:

[0048] The IMU sensor obtains the corresponding pose matrix between the front and rear wheels;

[0049] The controller receives the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculates a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtains an average deflection angle based on the first deflection angle and the second deflection angle;

[0050] Then, based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

[0051] One or more of the above technical solutions have the following beneficial effects:

[0052] The present invention provides a system and method for automatically returning the front wheels of a vehicle to the center of the rotation axis of the front and rear brake discs through two sets of IMU sensors, and when the vehicle is parked, an algorithm is designed to obtain the steering angle difference between the front and rear wheels in real time, and then the steering angle difference is converted into an electrical signal to control the operation of the steering motor, thereby realizing high-precision automatic return of the front wheels of the vehicle.

[0053] When calculating the steering angle difference between the front and rear wheels, the present invention uses two groups of IMU sensors to respectively obtain the posture data of the left front wheel and the left rear wheel, and the posture data of the right front wheel and the right rear wheel, and respectively establishes IMU coordinate systems for the left rear wheel, the right rear wheel, the left front wheel and the right front wheel, and calculates the rotation matrix between the left rear wheel and the left front wheel, and the rotation matrix between the right rear wheel and the right front wheel, and then calculates a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtains an average deflection angle based on the first deflection angle and the second deflection angle. The average deflection angle obtained in this way is more accurate, thereby improving the accuracy of wheel return.

[0054] Before executing the automatic wheel self-centering function, the controller of the present invention detects the current state of the car, including whether the engine or electric drive is in working condition, whether the driver has left the cab, and whether there are obstacles within the trajectory envelope of the wheel steering; when the engine or electric drive is not in working condition, the driver has left the cab, and there are no obstacles within the trajectory envelope of the wheel steering, the automatic front wheel self-centering function of the car is executed to improve the safety of vehicle control.

[0055] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0057] Figure 1 This is a flow chart of the method of the first embodiment.

[0058] Figure 2 This is a diagram defining the coordinate axes of the front wheel steering angle of the first embodiment. DETAILED DESCRIPTION

[0059] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0060] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0061] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0062] Embodiment 1

[0063] This embodiment discloses an automatic front wheel self-centering system for parking a car.

[0064] like Figure 1 As shown, the automatic front wheel self-centering system for parking a car includes an IMU sensor and a controller, wherein:

[0065] IMU sensor, which is installed at the center of the rotation axis of the front and rear brake discs of the vehicle to obtain the corresponding position matrix between the front and rear wheels;

[0066] A controller, which is used to receive the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtain an average deflection angle based on the first deflection angle and the second deflection angle;

[0067] Based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

[0068] In some embodiments, the IMU sensors are provided in two groups, and the two groups of IMU sensors are designed to be redundant with each other. When one group of IMU sensors fails, the other group of IMU sensors replaces the failed IMU sensors to implement the posture data acquisition function.

[0069] In some embodiments, the IMU sensor is used to establish the IMU coordinate system of the left rear wheel and the right rear wheel, specifically:

[0070] Take the center position of the left rear wheel and the right rear wheel as the origin, the forward direction of the left rear wheel and the right rear wheel as the positive direction of the x-axis, and determine the positive direction of the y-axis and the positive direction of the z-axis to establish the IMU coordinate system of the left rear wheel and the right rear wheel respectively.

[0071] In some embodiments, the IMU sensor is used to obtain the corresponding posture matrix between the front and rear wheels, and the corresponding posture matrix between the front and rear wheels includes the posture matrix of the left front wheel relative to the left rear wheel, and the posture matrix of the right front wheel relative to the right rear wheel. The specific method is:

[0072] Based on the established IMU coordinate systems of the left rear wheel and the right rear wheel, the rotation angles of the left front wheel relative to the left rear wheel and the right front wheel relative to the right rear wheel in the xyz directions are measured after parking.

[0073] Calculate the rotation matrices of the left front wheel relative to the left rear wheel, and the right front wheel relative to the right rear wheel in the xyz direction respectively;

[0074] Calculate the product of the rotation matrices corresponding to the three directions of xyz to obtain the position matrix of the left front wheel relative to the left rear wheel, and the position matrix of the right front wheel relative to the right rear wheel.

[0075] In some embodiments, assuming that the rotation angles of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel in the x, y, and z directions after parking are α, β, and γ respectively, then the corresponding rotation matrices in the xyz directions are:

[0076] Rotation around the x-axis:

[0077]

[0078] Rotation around the y-axis:

[0079]

[0080] Rotation around the z-axis:

[0081]

[0082] In summary, the pose matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel is

[0083] R xyz for:

[0084] R xyz =R x (α)*R y (β)*R z (γ);

[0085] Among them, R x (α) is the x-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R y (β) is the y-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R z (γ) is the z-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel.

[0086] In some embodiments, the controller is used to calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and the specific method is:

[0087] Get the rotation matrix R of the front wheel relative to the rear wheel xyz , reverse the rotation angle of the front wheel relative to the rear wheel:

[0088]

[0089] The calculation formula of sy is as follows:

[0090]

[0091] In the above formula, R(i, j) represents the rotation matrix R xyz The value of the i-th row and j-th column; i = L or R, indicating left or right, respectively; α i , β i , γ i They respectively represent the first deflection angle of the left front wheel relative to the left rear wheel, and the second deflection angle of the right front wheel relative to the right rear wheel; α, β, γ are the rotation angles in the x, y, and z directions respectively.

[0092] In some embodiments, the controller is used to obtain an average deflection angle based on the first deflection angle and the second deflection angle by using a weighted summation method; the weight values ​​of the first deflection angle and the second deflection angle can be set.

[0093] In some embodiments, a manual switch is further included, wherein the manual switch is used to obtain an activation signal of the automatic front wheel return system of the vehicle parking by the user and send the activation signal to the controller;

[0094] The controller is also used to activate the automatic front wheel return function of the car when parking when receiving an activation signal.

[0095] In some embodiments, the controller is further used to detect the current state of the vehicle, including detecting whether the engine or electric drive is in working state, whether the driver has left the cab, and whether there is an obstacle within the trajectory envelope of the wheel steering;

[0096] It is also used to determine that the engine or electric drive is not in working condition, the driver has left the cab, and there are no obstacles within the trajectory envelope of the wheel steering, and to execute the automatic front wheel return function when the car is parked.

[0097] Next, the technical solution of this embodiment will be explained in detail with reference to the accompanying drawings.

[0098] This embodiment proposes a method for automatic wheel self-centering, which automatically obtains the position of each wheel through two sets of IMU sensors, which are installed at the center of the rotation axis of the front and rear brake discs. When the car is parked, the high-precision front and rear wheel steering angle difference is obtained in real time, and then converted into an electrical signal to control the operation of the steering motor to realize the automatic self-centering function of the vehicle's front wheels. The implementation principle diagram is shown in the figure below. Figure 1 shown.

[0099] (1) Enable or disable the automatic return function:

[0100] The present invention provides manual switch kinetic energy on the automobile, and if the driver needs to use the device, the driver needs to manually activate this function.

[0101] Therefore, in this embodiment, the manual switch is used to obtain the activation signal of the automatic front wheel straightening system of the vehicle parking from the user and send it to the controller;

[0102] The controller is used to activate the automatic front wheel return function of the car when it receives an activation signal.

[0103] (2) Detect the current state of the car:

[0104] After turning on this function, the controller will periodically obtain the current operating status of the car. The device will not start in the following three operating states:

[0105] 1. The engine or electric drive is in working condition;

[0106] 2. The driver has not left the cab and may have other operations at this time, so avoid affecting the driver's normal driving;

[0107] 3. If there is an obstacle in the trajectory envelope of the wheel steering, forced steering will damage the tires and steering device. In the above three states, the device is in the DISENABLE state and the device does not intervene.

[0108] The present invention executes the automatic front wheel self-centering function when the car is parked only when the engine or electric drive is not in working state, the driver leaves the cab, and there is no obstacle within the trajectory envelope of the wheel steering, thereby improving the safety of vehicle control.

[0109] (3) Obtain the position of the front and rear wheels:

[0110] After the device is started, the IMU installed on the car's brake disc collects the posture data of the front and rear wheels at a frequency of 60HZ (the sampling parameters can be set by the user);

[0111] Set the IMU coordinate system of the rear wheel to O L / R (L represents the left side, R represents the right side), the front wheel IMU coordinate system is A L / R ,like Figure 2 shown.

[0112] Then calculate the rotation matrix of the front and rear wheels Specifically, calculate the rotation matrix between the left rear wheel and the left front wheel, and the rotation matrix between the right rear wheel and the right front wheel. The specific method is:

[0113] The calculation methods of the rotation matrices for the left front, right front, left rear, and right rear are the same. Suppose the x, y, and z rotation angles of a tire after parking are α, β, and γ respectively, then the corresponding rotation matrices are shown in the following formulas. The rotation matrix is ​​calculated by the IMU sensor and is determined by the characteristics of the IMU itself, so there is no need for separate programming calculation.

[0114] Rotation around the x-axis:

[0115]

[0116] Rotation around the y-axis:

[0117]

[0118] Rotation around the z-axis:

[0119]

[0120] In summary, the pose matrix of the front wheel relative to the rear wheel is:

[0121] R xyz =R x (α)*R y (β)*R z (γ)

[0122] After obtaining the rotation matrix between the left rear wheel and the left front wheel, and the rotation matrix between the right rear wheel and the right front wheel, calculate the rotation angle β of the front wheel Y axis relative to the rear wheel i (i=1, 2, respectively, the angle difference between the left and right sides), respectively, are the first deflection angle of the left front wheel relative to the left rear wheel, and the second deflection angle of the right front wheel relative to the right rear wheel. The specific method is:

[0123] After the car stops, the rear wheels will not deflect relative to the car body. The steering of the rear wheels can be set as the reference coordinate system. When the rotation matrix R of the front wheels relative to the rear wheels is obtained, xyz , we can reversely get the rotation angle of the front wheel relative to the rear wheel:

[0124]

[0125] Where i = L, R represents the first deflection angle on the left and the second deflection angle on the right, and the calculation formula of sy is as follows:

[0126]

[0127] In the above formula, R(i, j) represents the rotational moment R xyz The value of row i and column j.

[0128] exist Figure 2 Medium, β L and β R They respectively represent a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel.

[0129] Finally, the weighted average value β of the above two groups of deflection angles, that is, the average deflection angle, is calculated; based on the average deflection angle, the left front wheel and the right front wheel are controlled to steer until the left front wheel and the right front wheel return to the straight position.

[0130] In this embodiment, in order to improve the effectiveness of the overall system, the two designed IMU groups can also be used as a redundant design. When one of the sensors fails, the remaining sensor groups can continue to work.

[0131] (4) After obtaining the deflection angle of the front wheel relative to the rear wheel, the controller converts the angle signal into a control signal for the steering motor. This control system is a negative feedback control, that is, the greater the deviation angle between the front and rear wheels, the stronger the controller's control over the steering motor.

[0132] When the deviation angle of the front and rear wheels of the car is within the set error range, the control system stops running to avoid the steering motor being in working state due to the signal error of the sensor, causing the front wheel to shake. After the front wheel steering position is consistent with the rear wheel, a complete wheel self-alignment process is completed and the system is shut down.

[0133] Embodiment 2

[0134] This embodiment discloses a method for automatically returning the front wheels of a car to the correct position when parking.

[0135] The method for automatically returning the front wheels of a car to the correct position when parking comprises the following steps:

[0136] The IMU sensor obtains the corresponding pose matrix between the front and rear wheels;

[0137] The controller receives the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculates a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtains an average deflection angle based on the first deflection angle and the second deflection angle;

[0138] Then, based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

[0139] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. The automatic front wheel self-centering system for car parking is characterized by: Includes IMU sensor and controller, including: IMU sensor, which is installed at the center of the rotation axis of the front and rear brake discs of the vehicle to obtain the corresponding position matrix between the front and rear wheels; A controller, which is used to receive the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtain an average deflection angle based on the first deflection angle and the second deflection angle; Based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

2. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 1, characterized in that: The IMU sensors are provided with two groups, and the two groups of IMU sensors are designed to be redundant with each other. When one group of IMU sensors fails, the other group of IMU sensors replaces the failed IMU sensors to realize the posture data acquisition function.

3. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 1, characterized in that: The IMU sensor is used to establish the IMU coordinate system of the left rear wheel and the right rear wheel, specifically: Take the center position of the left rear wheel and the right rear wheel as the origin, the forward direction of the left rear wheel and the right rear wheel as the positive direction of the x-axis, and determine the positive direction of the y-axis and the positive direction of the z-axis to establish the IMU coordinate system of the left rear wheel and the right rear wheel respectively.

4. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 3, characterized in that: The IMU sensor is used to obtain the corresponding posture matrix between the front and rear wheels, and the corresponding posture matrix between the front and rear wheels includes the posture matrix of the left front wheel relative to the left rear wheel, and the posture matrix of the right front wheel relative to the right rear wheel. The specific method is: Based on the established IMU coordinate systems of the left rear wheel and the right rear wheel, the rotation angles of the left front wheel relative to the left rear wheel and the right front wheel relative to the right rear wheel in the xyz directions are measured after parking. Calculate the rotation matrices of the left front wheel relative to the left rear wheel, and the right front wheel relative to the right rear wheel in the xyz direction respectively; Calculate the product of the rotation matrices corresponding to the three directions of xyz to obtain the position matrix of the left front wheel relative to the left rear wheel, and the position matrix of the right front wheel relative to the right rear wheel.

5. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 4, characterized in that: Assume that the rotation angles of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel in the x, y, and z directions after parking are α, β, and γ respectively, then the corresponding rotation matrices in the xyz directions are: Rotation around the x-axis: Rotation around the y-axis: Rotation around the z-axis: In summary, the pose matrix R of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel xyz for: R xyz =R x (a)*R y (b)*R z (c); Among them, R x (α) is the x-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R y (β) is the y-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel; R z (γ) is the z-direction rotation matrix of the left front wheel relative to the left rear wheel, or the right front wheel relative to the right rear wheel.

6. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 5, characterized in that: The controller is used to calculate a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and the specific method is: Get the rotation matrix R of the front wheel relative to the rear wheel xyz , reverse the rotation angle of the front wheel relative to the rear wheel: The calculation formula of sy is as follows: In the above formula, R(i, j) represents the rotation matrix R xyz The value of the i-th row and j-th column; i = L or R, indicating left or right, respectively; α i , β i , γ i They respectively represent the first deflection angle of the left front wheel relative to the left rear wheel, and the second deflection angle of the right front wheel relative to the right rear wheel; α, β, γ are the rotation angles in the x, y, and z directions respectively.

7. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 1, characterized in that: The controller is used to obtain an average deflection angle based on the first deflection angle and the second deflection angle by adopting a weighted summation method; the weight values ​​of the first deflection angle and the second deflection angle can be set.

8. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 1, characterized in that: It also includes a manual switch, which is used to obtain an activation signal from a user for the automatic front wheel return system of the vehicle and send it to the controller; The controller is also used to activate the automatic front wheel return function of the car when parking when receiving an activation signal.

9. The automatic front wheel self-centering system for parking a vehicle as claimed in claim 1, characterized in that: The controller is also used to detect the current state of the vehicle, including whether the engine or electric drive is in working state, whether the driver has left the cab, and whether there is an obstacle within the trajectory envelope of the wheel steering; It is also used to determine that the engine or electric drive is not in working condition, the driver has left the cab, and there are no obstacles within the trajectory envelope of the wheel steering, and to execute the automatic front wheel return function when the car is parked.

10. A method for automatically returning the front wheels of a car to the correct position when parking, characterized in that: The following steps are involved: The IMU sensor obtains the corresponding pose matrix between the front and rear wheels; The controller receives the corresponding posture matrix between the front and rear wheels sent by the IMU sensor, and calculates a first deflection angle of the left front wheel relative to the left rear wheel, and a second deflection angle of the right front wheel relative to the right rear wheel, and obtains an average deflection angle based on the first deflection angle and the second deflection angle; Then, based on the average deflection angle, the left and right front wheels are controlled to steer until they return to the straight position.

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