A vehicle positioning method

Abstract

The present invention provides a vehicle positioning method, which includes: step 1, establishing a calibration environment, wherein the calibration environment includes an Ackerman steering model and preset calibration conditions; step 2, calibrating the wheelbase under the calibration environment; step 3, calibrating the steering transmission ratio according to the wheelbase under the calibration environment; step 4, determining the vehicle position according to the calibration result. The present invention does not require expensive RTK equipment, and the calibration accuracy is higher than that of the RTK equipment, which effectively improves the calculation accuracy of the vehicle odometer.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic parking, and in particular to a vehicle positioning method. Background Art

[0002] In automatic parking technology, the accuracy of the vehicle positioning system is of paramount importance. In order to improve positioning accuracy, the vehicle's steering wheel angle transmission ratio needs to be calibrated in advance. Although the steering wheel angle transmission ratio coefficient is determined when the vehicle steering structure is developed, the steering wheel angle transmission ratio coefficient is actually affected by ground friction and road surface flatness when the vehicle odometer is calculated, and needs to be recalibrated on a flat road to improve positioning accuracy.

[0003] The existing steering wheel angle transmission ratio coefficient calibration scheme generally uses the positioning result output by the RTK (Real-time kinematic) device as the true value of the vehicle's motion trajectory. However, RTK devices are not only expensive, but also have poor practicality and usability. First, RTK devices must rely on the signal of a specific base station in actual application. It is difficult to obtain accurate positioning signals when the base station signal is blocked; second, when studying the vehicle's driving trajectory, the rear axle center of the vehicle is generally used as the object. However, it is difficult to install the RTK device exactly at the rear axle center of the vehicle during actual installation, or it is difficult to accurately measure the distance from the positioning antenna of the RTK device to the rear axle center. At this time, the path output by the RTK device will deviate from the trajectory of the real rear axle center, resulting in a large error in the vehicle's odometer, which in turn affects the performance of the automatic parking system. Summary of the invention

[0004] The present invention provides a vehicle positioning method, aiming to solve the defects in the prior art and effectively improve the calculation accuracy of the vehicle odometer.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a vehicle positioning method, comprising:

[0007] Step 1: establishing a calibration environment, wherein the calibration environment includes an Ackerman steering model and preset calibration conditions;

[0008] Step 2, calibrating the wheelbase under the calibration environment;

[0009] Step 3, calibrating the steering transmission ratio according to the wheelbase under the calibration environment;

[0010] Step 4: Determine the vehicle position based on the calibration results.

[0011] Specifically, the step 2 includes:

[0012] Step 201, control the vehicle to make a circular motion and return to the starting point;

[0013] Step 202, obtaining the number of pulses generated by the rear left wheel and the rear right wheel in the process;

[0014] Step 203: calculating the turning radius of the rear left wheel and the rear right wheel according to the first preset relationship;

[0015] Step 204: Calculate the wheelbase according to the second preset relationship.

[0016] Specifically, the first preset relationship is:

[0017]

[0018] The second preset relationship is:

[0019] W v =R l -R r

[0020] Where Wv represents the wheelbase, R l Represents the turning radius of the rear left wheel, R r Represents the turning radius of the rear right wheel, P l and P r are the pulse numbers of the rear left wheel and rear right wheel respectively, and ΔP is the actual driving distance corresponding to a single pulse number of the vehicle.

[0021] Specifically, the step 3 includes:

[0022] Step 301, controlling the steering wheel to turn from the left limit to the right limit at a preset angle step, and determining the turning radius of the vehicle according to a third preset relationship;

[0023] Step 302: determining the front wheel equivalent turning angle according to a fourth preset relationship;

[0024] Step 303: Determine the steering transmission ratio according to the steering wheel angle and the front wheel equivalent angle.

[0025] Specifically, the third preset relationship is:

[0026]

[0027] Among them, R is the turning radius of the vehicle, Wv is the wheelbase, P l and P r They are the pulse numbers of the rear left wheel and rear right wheel respectively.

[0028] Specifically, the fourth preset relationship is:

[0029]

[0030] Among them, L is the wheelbase of the front and rear axles, and R is the turning radius of the vehicle.

[0031] Specifically, step 4 includes:

[0032] Step 401, establishing a global coordinate system;

[0033] Step 402, calculating the left unit driving distance of the rear left wheel and the right unit driving distance of the rear right wheel in unit time;

[0034] Step 403, judging the vehicle driving type according to the left unit driving distance and the right unit driving distance;

[0035] Step 404: Calculate the vehicle's current position and posture based on the vehicle's driving type and driving direction.

[0036] Specifically, step 404 includes: if the vehicle driving type is straight driving, determining the current position of the center point of the rear axle of the vehicle according to a fifth preset relationship, and the fifth preset relationship is:

[0037]

[0038] θ c (k+1)=θ c (k)

[0039] x r (k+1)=x r (k)+λS r (Δt)cos(θ c (k))

[0040] y r (k+1)=y r (k)+λS r (Δt)sin(θ c (k))

[0041] θ r (k+1)=θ c (k)

[0042] x l (k+1)=x l (k)+λS l (Δt)cos(θ c (k))

[0043] y l (k+1)=y l (k)+λS l (Δt)sin(θ c (k))

[0044] θl (k+1)=θ c (k)

[0045] Among them, (x c (k+1),y c (k+1),θ c (k+1)) represents the current position of the rear axle center point, (x l (k+1),y l (k+1),θ l (k+1)) represents the current position of the left wheel, (x r (k+1),y r (k+1),θ r (k+1)) represents the current position of the right wheel, (x l (k),y k (k)) represents the coordinates of the left wheel at the previous moment, (x r (k),y r (k)) represents the coordinate of the right wheel at the previous moment, S l (Δt) represents the unit travel distance on the left side, S r (Δt) represents the unit driving distance on the right side, θ c (k) represents the angle between the center point of the rear axle and the positive direction of the X-axis of the global coordinate system at the previous moment, λ is the direction factor, λ=1 when the vehicle is moving forward, and λ=-1 when the vehicle is moving backward.

[0046] Specifically, step 404 includes: if the vehicle driving type is curved driving, determining the current position of the center point of the rear axle of the vehicle according to a first preset rule, wherein the first preset rule is:

[0047] Step A1, according to the calibrated steering gear ratio, the turning radius of the rear axle center point at the previous moment is obtained from the steering wheel angle at the previous moment;

[0048] Step A2, calculating the unit driving distance of the center point of the rear axle of the vehicle in unit time;

[0049] Step A3, determining the change in the vehicle heading angle per unit time according to the turning radius of the rear axle center point at the previous moment and the unit driving distance of the center point;

[0050] Step A4, determining the length of the arc chord corresponding to the arc trajectory per unit time and the first angle between the arc chord and the X-axis of the global coordinate system according to the change in the vehicle heading angle per unit time;

[0051] Step A5: determining the current position of the center point of the rear axle of the vehicle according to the position of the vehicle at the previous moment, the chord length and the first angle.

[0052] Specifically, the step A5 includes: determining the current position of the center point of the rear axle of the vehicle according to a sixth preset relationship, wherein the sixth preset relationship is:

[0053]

[0054] θ c (k+1)=θ c (k)+λεΔθ

[0055] in:

[0056] When the vehicle turns left:

[0057] x l (k+1)=x l (k)-εl l cosα l

[0058] y l (k+1)=y l (k)+λεl l sinα l

[0059] λ l (k+1)=θ c (k)+λεΔθ

[0060] x r (k+1)=x r (k)-εl r cosα r

[0061] y r (k+1)=y r (k)+λεl r sinα r

[0062] θ r (k+1)=θ c (k)+λεΔθ

[0063] When the vehicle turns right:

[0064] x l (k+1)=x l (k)-εl l cosα l

[0065] y l (k+1)=y l (k)-λεl l sinα l

[0066] θl (k+1)=θ c (k)+λεΔθ

[0067] x r (k+1)=x r (k)-εl r cosα r

[0068] y r (k+1)=y r (k)-λεl r sinα r

[0069] θ r (k+1)=θ c (k)+λεΔθ

[0070] In the formula, (x c (k+1),y c (k+1),θ c (k+1)) represents the current position of the rear axle center point, (x l (k+1),y l (k+1),θ l (k+1)) represents the current position of the left wheel, (x r (k+1),y r (k+1),θ r (k+1)) represents the current position of the right wheel, (x l (k),y l (k)) represents the coordinates of the left wheel at the previous moment, (x r (k),y r (k)) represents the coordinate of the right wheel at the previous moment, S l (Δt) represents the unit travel distance on the left side, S r (Δt) represents the unit driving distance on the right side, θ c (k) represents the angle between the center point of the rear axle and the positive direction of the X-axis of the global coordinate system at the previous moment, Δθ represents the change in the vehicle heading angle per unit time, l l , l r They represent the length of the arc chord corresponding to the arc trajectory of the rear left wheel and the rear right wheel in unit time, respectively, l , α r They represent the first angles corresponding to the rear left wheel and the rear right wheel respectively, λ is the direction factor, λ=1 when the vehicle is moving forward, λ=-1 when the vehicle is moving backward, ε represents the rotation direction, ε=1 when the vehicle turns left, and ε=-1 when the vehicle turns right.

[0071] The beneficial effects of the present invention are as follows: the present invention establishes an Ackerman steering model and presets calibration conditions, calibrates the wheelbase, calibrates the steering transmission ratio according to the wheelbase, and finally determines the vehicle position according to the calibration result, thereby achieving the goal of completing the calibration of the vehicle steering wheel angle transmission ratio only according to the vehicle body size parameters and the wheel speed sensor signal, without the need for expensive RTK equipment, and the calibration accuracy is higher than that of the RTK equipment, thereby effectively improving the calculation accuracy of the vehicle odometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 It is a schematic flow chart of the vehicle positioning method of the present invention;

[0073] Figure 2 It is a schematic diagram of a vehicle plane model of the present invention;

[0074] Figure 3 is the Ackerman steering geometry model of the present invention;

[0075] Figure 4 It is a schematic diagram of wheelbase calibration of the present invention;

[0076] Figure 5 is a schematic diagram of vehicle motion of the present invention;

[0077] Figure 6 It is a schematic diagram of the arc trajectory and the first angle of the present invention. DETAILED DESCRIPTION

[0078] The following specifically describes the embodiments of the present invention in conjunction with the accompanying drawings, which are only for reference and illustration and do not constitute a limitation on the scope of patent protection of the present invention.

[0079] In the process described in the specification, claims or drawings of the present invention, the serial numbers of each step (such as step 10, 20, etc.) are included. The serial numbers are only used to distinguish the steps, and the serial numbers themselves do not represent any execution order. It should be noted that the descriptions such as "first" and "second" in this article are only used to distinguish the description objects, etc., and do not represent the order of precedence, nor do they mean that "first", "second", etc. are different types.

[0080] like Figure 1 As shown, this embodiment provides a vehicle positioning method, including:

[0081] Step 1: Establish a calibration environment, wherein the calibration environment includes an Ackerman steering model and preset calibration conditions.

[0082] Figure 2 is a schematic diagram of a vehicle plane model of this embodiment, in which θ is the vehicle heading angle, is the equivalent steering angle of the front wheel, and the coordinate of the center point of the rear axle is R(x r ,y r); L is the wheelbase of the front and rear axles, L f is the front overhang length, L r is the rear overhang length, W v For wheelbase.

[0083] In this embodiment, the preset calibration conditions are: during calibration, the vehicle speed is controlled to be less than 5 km / h, which is a low-speed operating condition, the vehicle has no sideslip, the tire side deviation is negligible, and the center point of the vehicle's rear axle is used as the reference point.

[0084] Figure 3 It is the Ackerman steering geometry model. During the vehicle steering process, under the condition that the steering wheel angle remains unchanged, the turning angle of the inner wheel will be greater than the turning angle of the outer wheel. At this time, the steering vertical lines of the four wheels intersect at one point (on the extension line of the rear axle), and the intersection is the instantaneous steering center.

[0085] exist Figure 3 In the Ackerman steering geometry shown, the left and right front wheel steering angles and vehicle dimensions satisfy:

[0086]

[0087] Where W v is the wheelbase, L is the front and rear axle wheelbase, α 1 and α 2 are the left and right front wheel steering angles respectively.

[0088] From the above formula, we can see that the vehicle steering can be simplified into circular motion, and the front wheel equivalent turning angle and the left and right front wheel steering angles satisfy:

[0089]

[0090] In the formula, is the front wheel equivalent steering angle.

[0091] Vehicle turning radius R and front wheel equivalent turning angle The relationship satisfies:

[0092]

[0093] Where R is the turning radius of the vehicle (i.e. the turning radius of the midpoint of the rear axle of the vehicle), and L is the wheelbase between the front and rear axles.

[0094] From the above Ackerman steering geometry model, it can be seen that when the vehicle turning radius R is measured, the front wheel equivalent turning angle can be calculated according to the front and rear axle wheelbase L The corresponding relationship between the steering wheel angle and the front wheel equivalent angle can be determined.

[0095] Step 2: calibrate the wheelbase Wv under the calibration environment.

[0096] It can be seen from the Ackermann steering geometry model that the wheelbase Wv is determined by the contact point between the wheel and the ground, and the rotation of the wheel is sensed by the wheel speed pulse sensor on the wheel side. The odometer calculation relies entirely on the wheel speed pulse signal, so it is necessary to calibrate the actual distance between the wheel speed pulse sensors on the two rear wheels of the vehicle based on the wheel speed pulses of the left and right rear wheels.

[0097] From the Ackerman steering geometry model, we can know that under the condition of a fixed steering wheel angle, all points on the vehicle body rotate around the instantaneous steering center, the angular velocity of each point is consistent, and the linear velocity is proportional to the distance from the point to the instantaneous steering center, that is, in unit time, the central angle swept by each point is equal and the path length traversed is proportional to the corresponding one.

[0098] Due to the influence of sensor installation, the wheel speed sensor spacing cannot directly use the vehicle's rear axle track data. Figure 4 As shown, this step provides a wheelbase calibration method, including:

[0099] Step 201, control the vehicle to make a circular motion and return to the starting point;

[0100] Step 202: Obtain the number of pulses P generated by the rear left wheel and the rear right wheel during the process. l , P r .

[0101] Step 203: Calculate the turning radius R of the rear left wheel and the rear right wheel according to the first preset relationship. l , R r .

[0102] In this embodiment, the first preset relationship is:

[0103]

[0104] Among them, R l Represents the turning radius of the rear left wheel, R r Represents the turning radius of the rear right wheel, P l and P r are the pulse numbers of the rear left wheel and rear right wheel respectively, and ΔP is the actual driving distance corresponding to a single pulse number of the vehicle.

[0105] Step 204: Calculate the wheelbase Wv according to the second preset relationship.

[0106] In this embodiment, the second preset relationship is:

[0107] W v =R l -R r

[0108] Among them, R l Represents the turning radius of the rear left wheel, Rr Indicates the turning radius of the rear right wheel.

[0109] Step 3: calibrate the steering transmission ratio γ according to the wheelbase Wv under the calibration environment.

[0110] The steering gear ratio indicates the relationship between the steering wheel rotation angle and the wheel rotation angle, and the calculation formula is: steering gear ratio = wheel rotation angle / steering wheel rotation angle.

[0111] In this embodiment, step 3 includes:

[0112] Step 301: Control the steering wheel to steer from the left limit to the right limit at a preset angle step, and determine the vehicle turning radius according to a third preset relationship.

[0113] In this embodiment, the preset angle step is 30°.

[0114] In this embodiment, the third preset relationship is:

[0115]

[0116] Among them, R is the turning radius of the vehicle, Wv is the wheelbase, P l and P r They are the pulse numbers of the rear left wheel and rear right wheel respectively.

[0117] Step 302: Determine the front wheel equivalent turning angle according to the fourth preset relationship

[0118] In this embodiment, the fourth preset relationship is:

[0119]

[0120] Among them, L is the wheelbase of the front and rear axles, and R is the turning radius of the vehicle.

[0121] Step 303: According to the steering wheel angle Φ and the front wheel equivalent angle Determine the steering gear ratio γ.

[0122] In this embodiment, the steering gear ratio

[0123] Step 4: Determine the vehicle position based on the calibration results.

[0124] In specific implementation, within the unit time Δt, it is considered that the vehicle steering wheel angle and vehicle speed remain unchanged, that is, the vehicle performs uniform linear motion or uniform circular motion.

[0125] like Figure 5 As shown, S l (Δt) and S r(Δt) are the lengths of the paths traveled by the left and right rear wheels in unit time Δt, and Δθ is the change in the vehicle heading angle in unit time Δt.

[0126] In this embodiment, step 4 includes:

[0127] Step 401: Establish a global coordinate system.

[0128] Step 402: Calculate the left unit travel distance S of the rear left wheel within the unit time Δt. l (Δt), right unit travel distance S of the rear right wheel r (Δt).

[0129] In this embodiment:

[0130] S l (Δt)=P l (Δt)ΔP,S r (Δt)=P r (Δt)ΔP

[0131] Among them, P l (Δt) and P r (Δt) are the pulse numbers of the rear left wheel and rear right wheel in unit time Δt, and ΔP is the actual driving distance corresponding to a single pulse number of the vehicle.

[0132] Step 403: According to the left unit driving distance S l (Δt), right unit travel distance S r (Δt) Determine the vehicle driving type.

[0133] In this embodiment, step 403 includes: if the left unit travel distance S l (Δt) and the right unit travel distance S r (Δt) are equal, the vehicle driving type is judged to be straight driving, otherwise the vehicle driving type is judged to be curved driving.

[0134] Step 404: Calculate the vehicle's current position and posture based on the vehicle's driving type and driving direction.

[0135] In this embodiment, step 404 includes:

[0136] 1) If the vehicle driving type is straight driving, the current position of the center point of the rear axle of the vehicle is determined according to the fifth preset relationship, and the fifth preset relationship is:

[0137]

[0138] θ c (k+1)=θ c (k)

[0139] x r (k+1)=x r (k)+λS r (Δt)cos(θ c (k))

[0140] y r (k+1)=y r (k)+λS r (Δt)sin(θ c (k))

[0141] θ r (k+1)=θ c (k)

[0142] x l (k+1)=x l (k)+λS l (Δt)cos(θ c (k))

[0143] y l (k+1)=y l (k)+λS l (Δt)sin(θ c (k))

[0144] θ l (k+1)=θ c (k)

[0145] Among them, (x c (k+1),y c (k+1),θ c (k+1)) represents the current position of the rear axle center point, (x l (k+1),y l (k+1),θ l (k+1)) represents the current position of the left wheel, (x r (k+1),y r (k+1),θ r (k+1)) represents the current position of the right wheel, (x l (k),y l (k)) represents the coordinates of the left wheel at the previous moment, (x r (k),y r (k)) represents the coordinate of the right wheel at the previous moment, S l (Δt) represents the unit travel distance on the left side, S r (Δt) represents the unit driving distance on the right side, θ c(k) represents the angle between the center point of the rear axle and the positive direction of the X-axis of the global coordinate system at the previous moment, λ is the direction factor, λ=1 when the vehicle is moving forward, and λ=-1 when the vehicle is moving backward.

[0146] 2) If the vehicle driving type is curved driving, the current position of the center point of the rear axle of the vehicle is determined according to a first preset rule, wherein the first preset rule is:

[0147] Step A1: According to the calibrated steering transmission ratio γ, the turning radius R of the rear axle center point at the previous moment is obtained from the steering wheel angle δ(k) at the previous moment. c (k).

[0148] Step A2: Calculate the unit driving distance S of the center point of the rear axle of the vehicle within the unit time Δt. c (Δt).

[0149]

[0150] Step A3: according to the turning radius R of the rear axle center point at the previous moment c (k), the center point unit driving distance S c (Δt), determine the change Δθ of the vehicle heading angle per unit time.

[0151] In this embodiment, the calculation formula of the change Δθ of the vehicle heading angle per unit time is as follows:

[0152]

[0153] Step A4, determining the chord length l of the arc chord corresponding to the arc trajectory within the unit time Δt and the first angle α between the arc chord and the X-axis of the global coordinate system according to the change Δθ of the vehicle heading angle within the unit time.

[0154] When the vehicle is traveling at a low speed, the tire side slip can be ignored and it is assumed that the vehicle as a whole rotates around the instantaneous steering center. The corresponding yaw angle changes of the left and right wheels on the rear axle are consistent.

[0155] Take the left wheel as an example. Figure 6 As shown, A is the starting point of the vehicle movement and B is the end point of the vehicle movement. In △O'AB, the first angle α is denoted by α l , the length of the arc chord is l l , from the geometric relationship in the figure we can get:

[0156]

[0157] Similarly, for the rear right wheel, we have:

[0158]

[0159] Among them, θl (k),θ r (k) respectively represents the angle between the horizontal axis of the rear left wheel and the rear right wheel and the positive direction of the X-axis of the global coordinate system.

[0160] Generally speaking, we have: l (k) = θ r (k).

[0161] Step A5: determining the current position of the center point of the rear axle of the vehicle according to the position of the vehicle at the previous moment, the chord length l and the first angle α.

[0162] In this embodiment, step A5 includes: determining the current position of the center point of the rear axle of the vehicle according to a sixth preset relationship, and the sixth preset relationship is:

[0163]

[0164] θ c (k+1)=θ c (k)+λεΔθ

[0165] in:

[0166] When the vehicle turns left:

[0167] x l (k+1)=x l (k)-εl l cosα l

[0168] y l (k+1)=y l (k)+λεl l sinα l

[0169] θ l (k+1)=θ c (k)+λεΔθ

[0170] x r (k+1)=x r (k)-εl r cosα r

[0171] y r (k+1)=y r (k)+λεl r sinα r

[0172] θ r (k+1)=θ c (k)+λεΔθ

[0173] When the vehicle turns right:

[0174] x l (k+1)=x l (k)-εl l cosα l

[0175] y l (k+1)=y l (k)-λεl l sinα l

[0176] θ l (k+1)=θ c (k)+λεΔθ

[0177] x r (k+1)=x r (k)-εl r cosα r

[0178] y r (k+1)=y r (k)-λεl r sinα r

[0179] θ r (k+1)=θ c (k)+λεΔθ

[0180] In the formula, (x c (k+1),y c (k+1),θ c (k+1)) represents the current position of the rear axle center point, (x l (k+1),y l (k+1),θ l (k+1)) represents the current position of the left wheel, (x r (k+1),y r (k+1),θ r (k+1)) represents the current position of the right wheel, (x l (k),y l (k)) represents the coordinates of the left wheel at the previous moment, (x r (k),y r (k)) represents the coordinate of the right wheel at the previous moment, S l (Δt) represents the unit travel distance on the left side, S r (Δt) represents the unit driving distance on the right side, θ c (k) represents the angle between the center point of the rear axle and the positive direction of the X-axis of the global coordinate system at the previous moment, Δθ represents the change in the vehicle heading angle per unit time, ll , l r They represent the length of the arc chord corresponding to the arc trajectory of the rear left wheel and the rear right wheel in unit time, respectively, l , α r They represent the first angles corresponding to the rear left wheel and the rear right wheel respectively, λ is the direction factor, λ=1 when the vehicle is moving forward, λ=-1 when the vehicle is moving backward, ε represents the rotation direction, ε=1 when the vehicle turns left, and ε=-1 when the vehicle turns right.

[0181] The above disclosure is only a preferred embodiment of the present invention, which cannot be used to limit the scope of protection of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope covered by the present invention.

Claims

1. A vehicle positioning method, characterized in that: include: Step 1, establishing a calibration environment, wherein the calibration environment includes an Ackerman steering model and preset calibration conditions, wherein the preset calibration conditions are: during calibration, the vehicle speed is controlled to be less than 5 km / h, which is a low-speed working condition, the vehicle has no sideslip, the tire side slip is ignored, and the center point of the vehicle rear axle is taken as the reference point; Step 2, calibrating the wheelbase under the calibration environment; Step 3, calibrating the steering transmission ratio according to the wheelbase under the calibration environment; Step 4: Determine the vehicle position according to the calibration result; The step 4 comprises: Step 401, establishing a global coordinate system; Step 402, calculating the left unit driving distance of the rear left wheel and the right unit driving distance of the rear right wheel in unit time; Step 403, judging the vehicle driving type according to the left unit driving distance and the right unit driving distance; Step 404: Calculate the current position and posture of the vehicle according to the driving type and driving direction of the vehicle; The step 404 includes: if the vehicle driving type is curved driving, determining the current position of the center point of the rear axle of the vehicle according to a first preset rule, wherein the first preset rule is: Step A1, according to the calibrated steering gear ratio, the turning radius of the rear axle center point at the previous moment is obtained from the steering wheel angle at the previous moment; Step A2, calculating the unit driving distance of the center point of the rear axle of the vehicle in unit time; Step A3, determining the change in the vehicle heading angle per unit time according to the turning radius of the rear axle center point at the previous moment and the unit driving distance of the center point; Step A4, determining the length of the arc chord corresponding to the arc trajectory per unit time and the first angle between the arc chord and the X-axis of the global coordinate system according to the change in the vehicle heading angle per unit time; Step A5: determining the current position of the center point of the rear axle of the vehicle according to the position of the vehicle at the previous moment, the chord length and the first angle.

2. The vehicle positioning method according to claim 1, characterized in that: The step 2 comprises: Step 201, control the vehicle to make a circular motion and return to the starting point; Step 202, obtaining the number of pulses generated by the rear left wheel and the rear right wheel in the process; Step 203, calculating the turning radius of the rear left wheel and the rear right wheel according to the first preset relationship; Step 204: Calculate the wheelbase according to the second preset relationship.

3. The vehicle positioning method according to claim 2, characterized in that: The first preset relationship is: The second preset relationship is: in, W Indicates wheelbase, R l Represents the turning radius of the rear left wheel, R r Represents the turning radius of the rear right wheel, P l and P r are the pulse numbers of the rear left wheel and rear right wheel respectively, and ΔP is the actual driving distance corresponding to a single pulse number of the vehicle.

4. The vehicle positioning method according to claim 3, characterized in that: The step 3 comprises: Step 301, controlling the steering wheel to turn from the left limit to the right limit at a preset angle step, and determining the turning radius of the vehicle according to a third preset relationship; Step 302: determining the front wheel equivalent turning angle according to a fourth preset relationship; Step 303: Determine the steering transmission ratio according to the steering wheel angle and the front wheel equivalent angle.

5. The vehicle positioning method according to claim 4, characterized in that: The third preset relationship is: Where R is the turning radius of the vehicle.

6. The vehicle positioning method according to claim 5, characterized in that: The fourth preset relationship is: Among them, L is the wheelbase of the front and rear axles.

7. The vehicle positioning method according to claim 1, characterized in that: The step A5 includes: determining the current position of the center point of the rear axle of the vehicle according to a sixth preset relationship, wherein the sixth preset relationship is: in: When the vehicle turns left: When the vehicle turns right: In the formula, Indicates the current position of the rear axle center point. Indicates the current position of the left wheel. Indicates the current position of the right wheel. represents the coordinates of the left wheel at the previous moment, represents the coordinates of the right wheel at the previous moment, Indicates the unit driving distance on the left side, Indicates the unit driving distance on the right side, It represents the angle between the center point of the rear axle and the positive direction of the X-axis of the global coordinate system at the previous moment, Δθ represents the change of the vehicle heading angle per unit time, l l , l r They represent the length of the arc chord corresponding to the arc trajectory of the rear left wheel and the rear right wheel in unit time, respectively, l , α r They represent the first angles corresponding to the rear left wheel and the rear right wheel respectively. λ is the direction factor. When the vehicle moves forward, λ=1; when the vehicle moves backward, λ=-1. ε represents the rotation direction. When the vehicle turns left, ε=1; when the vehicle turns right, ε=-1.

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