Electronic differential control method for four-wheel independent drive automobile

Abstract

The invention relates to the technical field of automobiles, in particular to an electronic differential control method for a four-wheel independent drive automobile. Firstly, rear wheel steering angle coefficients of a front wheel steering angle and a rear wheel steering angle are dynamically adjusted through the longitudinal speed of a vehicle; electronic differential models of same-direction steering and reverse-direction steering are obtained based on the rear wheel steering angle coefficient, the flexibility of the vehicle is improved under the low-speed working condition, and the high-speed stability of the vehicle is improved under the high-speed working condition; according to the electronic differential model, obtaining the expected speed and the proportional synchronization coefficient of each wheel; and creating a four-wheel synchronous control algorithm, calculating a tracking error and a synchronous error of each wheel, endowing the synchronous error with different weights, and outputting final control. According to the electronic differential control method, accurate regulation and control of the vehicle steering process can be achieved, and good dynamic performance and use value are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of automobiles, and particularly relates to an electronic differential control method for a four-wheel independently driven vehicle. Background Art

[0002] Four-wheel independently driven electric vehicles achieve independent driving of each wheel by individually controlling each motor, and have advantages such as a compact structure, high transmission efficiency, and a large number of controllable degrees of freedom. However, since components such as the differential and drive shaft in the traditional mechanical transmission system are cancelled, the coordination between the rotational speeds of the wheels cannot be achieved. Therefore, an electronic differential control algorithm is required to dynamically adjust the rotational speeds of each motor to ensure stability during steering. Currently, the research on vehicle control technology mainly focuses on vehicles with only front-wheel steering. Compared with front-wheel steering, four-wheel steering technology involves controlling all four wheels to participate in the steering movement of the vehicle. At low speeds, the turning radius of the vehicle is reduced by reverse steering to improve the flexibility of the vehicle; at high speeds, the turning radius of the vehicle is increased by forward steering to improve the high-speed stability of the vehicle. In traditional electronic differential control, the real-time coordination between adjacent wheels is not considered, which easily leads to wheel skidding and even vehicle instability. By using a synchronous control algorithm to dynamically correct the rotational speeds of each wheel, the proportional suppression of the adjacent wheel speed difference is achieved, and the robustness of the system is improved. Summary of the Invention

[0003] The purpose of the present invention is to provide an electronic differential control method for a four-wheel independently driven vehicle, which dynamically adjusts the rotational speeds of each wheel to improve the stability of the vehicle during steering.

[0004] To achieve the above purpose, the present invention provides an electronic differential control method for a four-wheel independently driven vehicle, including the following steps:

[0005] Step 1: Establish a rear-wheel corner coefficient between the front-wheel corner and the rear-wheel corner based on the longitudinal speed of the vehicle;

[0006] Step 2: Construct forward-steering and reverse-steering electronic differential models based on the rear-wheel corner coefficient;

[0007] Step 3: Calculate the expected speed and proportional synchronization coefficient of each wheel according to the electronic differential model;

[0008] Step 4: Create a four-wheel synchronous control algorithm.

[0009] Optionally, the rear-wheel corner coefficient K between the front-wheel corner and the rear-wheel corner varies with the longitudinal speed of the vehicle, and the calculation formula is as follows:

[0010]

[0011] where m is the vehicle mass, a and b are the distances from the front and rear axles to the vehicle center of mass, C f and Cr are the cornering stiffnesses of the front and rear wheels respectively, and v is the longitudinal vehicle speed.

[0012] Optionally, the in-phase steering and counter-phase steering electronic differential models are constructed based on the rear wheel steering angle coefficient. When the rear wheel steering angle coefficient is greater than 0, the electronic differential model is in-phase steering, and when the rear wheel steering angle coefficient is less than 0, it is counter-phase steering. Then the distances l a and l b , the lateral distance R from the center line of the center of mass to the center of rotation and the distance R from the center of mass to the center of rotation g can be expressed as:

[0013]

[0014] where θ f is the front wheel steering angle.

[0015] Optionally, by dividing the turning radius of each wheel by the distance R from the center of mass to the center of rotation g calculate the proportional synchronization coefficient of each wheel, and calculate the desired speed of each wheel by multiplying the proportional synchronization coefficient of each wheel by the longitudinal vehicle speed v. The calculation formula for the turning radius of each wheel is as follows:

[0016]

[0017] where B is the wheel track, and R1, R2, R3, R4 are the turning radii of the left front wheel, right front wheel, left rear wheel, and right rear wheel.

[0018] Optionally, the four-wheel synchronization control algorithm consists of the following error of each wheel and the synchronization error. The difference between the desired wheel speed and the actual wheel speed of each wheel is divided by its respective proportional synchronization coefficient to obtain the following error, and the synchronization error is obtained by dividing the difference between adjacent wheels by their respective proportional synchronization coefficients.

[0019] Optionally, by assigning different weight values to the synchronization errors of each wheel and taking the sum with the following error as the control quantity, the calculation formula is:

[0020]

[0021] where e1, e2, e3, e4 are the tracking errors of the left front wheel, left rear wheel, right front wheel, and right rear wheel respectively; ∈ 12 , ∈ 23 , ∈ 34 , ∈ 41 are the tracking errors between the left front wheel and the left rear wheel, the left rear wheel and the right front wheel, the right front wheel and the right rear wheel, and the right rear wheel and the left front wheel respectively; a1, a2, a3, a4, a5, a6, a7, a8 are weighting coefficients; u1, u2, u3, u4 are the control quantities of the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

[0022] The present invention provides an electronic differential control method for a four-wheel independently-driven vehicle. First, a rear-wheel corner coefficient of the front-wheel corner and the rear-wheel corner is defined based on the vehicle longitudinal speed, and an electronic differential model for co-directional steering and counter-directional steering is obtained based on the rear-wheel corner coefficient. At low speed conditions, the turning radius of the vehicle is reduced through counter-directional steering to improve the flexibility of the vehicle. At high speed conditions, the turning radius of the vehicle is increased through co-directional steering to improve the high-speed stability of the vehicle. By calculating the tracking error and synchronization error of the four wheels of the electronic differential model and assigning different weights to the tracking error and synchronization error, the dynamic correction of the rotational speed of each wheel is realized, and the robustness of the system is improved. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 It is a schematic flow chart of an electronic differential control method for a four-wheel independently-driven vehicle of the present invention.

[0025] Figure 2 It is a linear two-degree-of-freedom four-wheel steering model diagram of the present invention.

[0026] Figure 3 It is a co-directional steering electronic differential model diagram of the present invention.

[0027] Figure 4 It is a counter-directional steering electronic differential model diagram of the present invention. Detailed Embodiments

[0028] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as a limitation to the present invention.

[0029] Please refer to Figure 1 , the present invention provides an electronic differential control method for a four-wheel independently-driven vehicle, including the following steps:

[0030] S1: Establish a rear-wheel corner coefficient between the front-wheel corner and the rear-wheel corner based on the vehicle longitudinal speed;

[0031] S2: Construct an electronic differential model for co-directional steering and counter-directional steering based on the rear-wheel corner coefficient;

[0032] S3: Calculate the expected speed of each wheel and the proportional synchronization coefficient according to the electronic differential model;

[0033] S4: Create a four-wheel synchronization control algorithm.

[0034] The following is a further description in combination with specific process steps;

[0035] S1: Establish the rear-wheel corner coefficient between the front-wheel corner and the rear-wheel corner based on the vehicle longitudinal speed;

[0036] Specifically, please refer to Figure 2 the provided linear two-degree-of-freedom four-wheel steering model. By analyzing the lateral motion of the vehicle, the vehicle lateral motion equation and the torque balance equation can be listed:

[0037]

[0038] Among them, m is the vehicle mass, Iz is the moment of inertia of the vehicle about the z-axis, a and b are the distances from the front and rear axles to the vehicle center of mass, ω r is the yaw rate, v and v y are the vehicle longitudinal speed and lateral speed respectively, F yf and F y X are the lateral resultant forces on the front and rear wheels of the vehicle respectively.

[0039] When the sideslip angle is small, the relationship between the lateral force on the wheel and its sideslip angle is as follows:

[0040] F yf = C f α f

[0041] F yr = C r α r

[0042] The calculation formulas for the front and rear wheel sideslip angles are as follows:

[0043]

[0044] Among them, C f and C r are the sideslip stiffnesses of the front and rear wheels respectively, α f and α r are the sideslip angles of the front and rear wheels respectively, β is the center-of-mass sideslip angle, θ f and θ r are the front and rear wheel angles respectively.

[0045] Then the motion differential equation of the four-wheel steering vehicle can be derived as:

[0046]

[0047] Further, with the centroid sideslip angle as the control target, the relationship between the rear-wheel steering angle and the front-wheel steering angle during steady-state steering is defined as θ r = Kθ f , Substituting β = 0 into the differential equation of vehicle motion, the value of K can be obtained:

[0048]

[0049] S2: Construct the in-phase steering and counter-phase steering electronic differential models based on the rear-wheel steering angle coefficient;

[0050] Specifically, please refer to Figure 3 and Figure 4 for the electronic differential model diagrams shown. The in-phase steering and counter-phase steering electronic differential models are constructed based on the rear-wheel steering angle coefficient. When the rear-wheel steering angle coefficient is greater than 0, the electronic differential model is for in-phase steering; when the rear-wheel steering angle coefficient is less than 0, it is for counter-phase steering. From the geometric relationship,

[0051] When in-phase steering:

[0052]

[0053] When counter-phase steering:

[0054]

[0055] Then the distances l a and l b from the front and rear axles to the rotation center, the lateral distance R from the centroid centerline to the rotation center, and the distance R g from the centroid to the rotation center can be expressed as:

[0056]

[0057] S3: Calculate the expected speed and proportional synchronization coefficient of each wheel according to the electronic differential model;

[0058] Specifically, define numbers 1, 2, 3, and 4 as the left front wheel, right front wheel, left rear wheel, and right rear wheel. Calculate the proportional synchronization coefficient of each wheel by dividing the turning radius of each wheel by the distance R g from the centroid to the rotation center. Calculate the expected speed of each wheel by multiplying the proportional synchronization coefficient of each wheel by the vehicle longitudinal speed v. The calculation formulas for the turning radius of each wheel are as follows:

[0059]

[0060] The expected speed and proportional synchronization coefficient of each wheel are:

[0061]

[0062] Among them, B is the wheel track, and R1, R2, R3, and R4 are the turning radii of the left front wheel, right front wheel, left rear wheel, and right rear wheel, is the expected wheel speed of the wheel numbered i, and λ i is the proportional synchronization coefficient of the wheel numbered i.

[0063] S4: Create a four-wheel synchronization control algorithm.

[0064] Specifically, the four-wheel synchronization control algorithm consists of the following error and synchronization error of each wheel. The difference between the expected wheel speed and the actual wheel speed of each wheel is divided by its respective proportional synchronization coefficient to obtain the following error, and the synchronization error is obtained by dividing the difference between adjacent wheels by their respective proportional synchronization coefficients. The calculation formula is:

[0065]

[0066] Among them, v i is the actual wheel speed of the wheel numbered i, e i is the following error of the wheel numbered i, and ∈ i，j is the synchronization error between the wheel numbered i and the adjacent wheel numbered j.

[0067] By assigning different weight values to the synchronization errors of each wheel and taking the sum with the following error as the control quantity, the final control quantity can be expressed as:

[0068]

[0069] Among them, e1, e2, e3, and e4 are the tracking errors of the left front wheel, left rear wheel, right front wheel, and right rear wheel respectively; ∈ 12 , ∈ 23 , ∈ 34 , ∈ 41 are the tracking errors between the left front wheel and the left rear wheel, left rear wheel and right front wheel, right front wheel and right rear wheel, and right rear wheel and left front wheel respectively; a1, a2, a3, a4, a5, a6, a7, and a8 are weighting coefficients; u1, u2, u3, and u4 are the control quantities of the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

Claims

1. An electronic differential control method for a four-wheel independently-driven vehicle, characterized in that, Including the following steps: Step 1: Establish a rear wheel steering angle coefficient between the front wheel steering angle and the rear wheel steering angle based on the longitudinal speed of the vehicle; Step 2: Construct a same-direction steering and reverse-direction steering electronic differential model based on the rear wheel steering angle coefficient; Step 3: Calculate the desired speed and proportional synchronization coefficient of each wheel according to the electronic differential model; Step 4: Create a four-wheel synchronization control algorithm.

2. The electronic differential control method for a four-wheel independently-driven vehicle according to claim 1, wherein The rear wheel steering angle coefficient K between the front wheel steering angle and the rear wheel steering angle changes with the longitudinal speed of the vehicle, and the calculation formula is as follows: Where m is the vehicle mass, a and b are the distances from the front and rear axles to the vehicle's center of mass, C f and C r are the cornering stiffnesses of the front and rear wheels respectively, and v is the longitudinal speed of the vehicle.

3. The electronic differential control method for a four-wheel independently-driven vehicle according to claim 1, characterized in that The co-rotating and counter-rotating electronic differential models are constructed based on the rear wheel cornering coefficient. When the rear wheel cornering coefficient is greater than 0, the electronic differential model is co-rotating, and when the rear wheel cornering coefficient is less than 0, it is counter-rotating. Then the distances l a and l b , the lateral distance R from the centroid centerline to the rotation center and the distance R from the centroid to the rotation center g can be expressed as: where θ f is the front wheel steering angle.

4. The electronic differential control method for a four-wheel independently-driven vehicle according to claim 1, characterized in that, Dividing the turning radius of each wheel by the distance R from the centroid to the rotation center g Calculate the proportional synchronization coefficient of each wheel. Multiply the proportional synchronization coefficient of each wheel by the longitudinal speed v of the vehicle to calculate the expected speed of each wheel. The calculation formula for the turning radius of each wheel is as follows: Where B is the wheel track, and R1, R2, R3, and R4 are the turning radii of the left front wheel, right front wheel, left rear wheel, and right rear wheel.

5. The electronic differential control method for a four-wheel independently-driven vehicle according to claim 1, characterized in that The four-wheel synchronization control algorithm consists of the following error and synchronization error of each wheel. The difference between the desired wheel speed and the actual wheel speed of each wheel is divided by its respective proportional synchronization coefficient to obtain the following error, and the synchronization error is obtained by dividing the difference between adjacent wheels by their respective proportional synchronization coefficients.

6. The electronic differential control method for a four-wheel independently-driven vehicle according to claim 5, wherein By assigning different weights to the synchronization errors of each wheel and taking the sum with the following error as the control quantity, the calculation formula is: where, e1, e2, e3, and e4 are the tracking errors of the left front wheel, left rear wheel, right front wheel, and right rear wheel respectively; ∈ 12 , ∈ 23 , ∈ 34 , ∈ 41 are the tracking errors between the left front wheel and the left rear wheel, left rear wheel and right front wheel, right front wheel and right rear wheel, and right rear wheel and left front wheel respectively; a1, a2, a3, a4, a5, a6, a7, a8 are synchronization coefficients; u1, u2, u3, u4 are the control quantities of the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

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