A four-wheel active steering control mode switching system

Abstract

The application discloses a four-wheel active steering control mode switching system, which comprises a running information measuring module, an active steering multi-mode switching threshold value parameter calculating module, an active steering mode selecting module and an active steering mode executing module. The running information measuring module is used for measuring the vehicle speed, the road adhesion coefficient, the mass center side slip angle, the yaw angular velocity, the lateral acceleration and the steering wheel rotation angle. The active steering multi-mode switching threshold value parameter calculating module is used for calculating the comprehensive stability control factor and the multi-mode switching threshold value in different road adhesion coefficient intervals. The active steering mode selecting module selects the automobile steering mode according to the active steering multi-mode switching threshold value parameter. The active steering mode executing module is used for switching the automobile steering mode, including the automobile front wheel steering mode, the four-wheel steering mode under the sliding mode control and the four-wheel steering mode under the optimal control.

Description

TECHNICAL FIELD

[0001] The present application relates to a four-wheel active steering control mode switching system. BACKGROUND

[0002] With the progress of the automotive industry, consumers' demand for vehicle performance is also increasing, not only requiring vehicles to provide higher driving speed and more stable handling performance, but also requiring vehicles to perform best handling performance in various driving states and working conditions. However, the traditional front-wheel steering vehicle is prone to instability in some special road conditions, and has been unable to meet the needs of consumers for safety, so more advanced active safety technology needs to be used to improve the safety performance of the vehicle.

[0003] As an advanced active safety technology, the four-wheel active steering control mode switching system can automatically adjust the steering angle and steering speed of the four wheels according to the driving state and working condition of the vehicle, thereby effectively improving the handling performance and active safety of the vehicle. However, it still has certain limitations in a single control mode, such as the optimal control strategy being prone to instability when the vehicle speed is too high, and the four-wheel active steering vehicle controlled by the sliding mode control strategy having poor handling stability when the vehicle speed is low. In order to improve these problems, the present application provides a four-wheel active steering control mode switching system. SUMMARY

[0004] The purpose of the present application is to provide a four-wheel active steering control mode switching system to solve the problems faced in the background art.

[0005] To achieve the above purpose, the present application provides the following technical solution: a four-wheel active steering control mode switching system, comprising a driving information measurement module, an active steering multi-mode switching threshold value parameter calculation module, an active steering mode selection module, and an active steering mode execution module.

[0006] The driving information measurement module is used to measure the vehicle speed v, the road adhesion coefficient μ, the mass center side slip angle β, the yaw angular velocity r, the lateral acceleration a y , and the steering wheel angle θ.

[0007] The active steering multi-mode switching threshold value parameter calculation module is used to calculate the comprehensive stability control factor J T and the multi-mode switching threshold values v TH，i in different road adhesion coefficient intervals: the first threshold value v TH，1 , the second threshold value v TH，2 , the third threshold value v TH，3 , the fourth threshold value v TH，4 , the fifth threshold value v TH，5 , the sixth threshold value v TH，6 , and the seventh threshold value vTH，7 , the eighth threshold value v TH，8 , the ninth threshold value v TH，9 , the tenth threshold value v TH，10 ;

[0008] The active steering mode selection module is configured to select the steering mode of the vehicle according to the active steering multi-mode switching threshold value parameters, and when the comprehensive stability control factor J T is less than the vehicle stability threshold value J0, the front wheel steering mode is adopted, and when the comprehensive stability control factor J T is greater than the vehicle stability threshold value J0, the four-wheel steering mode is adopted; the control mode of the four-wheel steering mode is determined according to the multi-mode switching threshold value v TH，i of the vehicle speed v, the road adhesion coefficient μ and the mass center side slip angle β of the current state of the vehicle, and the sliding mode control mode and the optimal control mode of the four-wheel steering are switched: when v i < v TH，i the vehicle four-wheel steering adopts the sliding mode control mode, and when v i > v TH，i the vehicle four-wheel steering adopts the optimal control mode.

[0009] The active steering mode execution module is configured to switch the steering mode of the vehicle, wherein the steering mode of the vehicle is the front wheel steering mode and the four-wheel steering mode; when the vehicle is switched to the front wheel steering mode, the vehicle four-wheel steering control system only outputs the front wheel steering angle, and the output value of the rear wheel steering is zero; when the vehicle is switched to the four-wheel steering mode, the vehicle four-wheel steering control system simultaneously outputs the calculated front wheel steering angle and rear wheel steering angle of the vehicle according to the control mode.

[0010] The comprehensive stability control factor J T in the active steering multi-mode switching threshold value parameter calculation module is determined by the following formula:

[0011]

[0012] The weight coefficients w1 and w2 are determined by the following formula:

[0013]

[0014] w2 = ε (1-w min ) (1-w2) + w min ;

[0015] Wherein E is the stability margin, w min is the minimum value of the weight factor, and ε is the adjustment factor.

[0016] The lateral acceleration stability control factor is determined by the following formula:

[0017]

[0018] Yaw rate stability control factor J r is determined by the following equation:

[0019]

[0020] where n is the number of sampling points, Δt represents the interval of sampling time, and the subscripts i and o represent instantaneous and steady-state values, respectively.

[0021] The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameter in the lower road adhesion interval according to the following method:

[0022] According to the measured road adhesion coefficient μ of the automobile, it is divided into the following 10 intervals: interval I, II, III, IV, V, VI, VII, VIII, IX, X, and the corresponding μ ranges are: the range of μ corresponding to interval I is 0 < μ ≤ 0.1, the range of μ corresponding to interval II is 0.1 < μ ≤ 0.2, the range of μ corresponding to interval III is 0.2 < μ ≤ 0.3, the range of μ corresponding to interval IV is 0.3 < μ ≤ 0.4, the range of μ corresponding to interval V is 0.4 < μ ≤ 0.5, the range of μ corresponding to interval VI is 0.5 < μ ≤ 0.6, the range of μ corresponding to interval VII is 0.6 < μ ≤ 0.7, the range of μ corresponding to interval VIII is 0.7 < μ ≤ 0.8, the range of μ corresponding to interval IX is 0.8 < μ ≤ 0.9, and the range of μ corresponding to interval X is 0.9 < μ ≤ 1.0.

[0023] When the road adhesion coefficient is in the I to V interval, the first to fifth threshold values are obtained by the following formula: wherein is the vehicle speed value that makes the center of mass side slip angle zero in the four-wheel steering mode of the sliding mode control of the automobile in different road adhesion coefficient intervals, is the vehicle speed value that makes the center of mass side slip angle zero in the four-wheel steering mode of the optimal control of the automobile in different road adhesion coefficient intervals.

[0024] The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameter in the high road adhesion interval according to the following method:

[0025] When the road adhesion coefficient is in the VI to X interval, the optimal control strategy appears unstable when the vehicle speed is too high; therefore, under the condition of high road adhesion coefficient, the sixth to tenth threshold values are obtained by the following formula: wherein n values of vehicle speed at which the absolute value of the side slip angle of the mass center of the four-wheel steering mode of the vehicle in the different road surface adhesion coefficient interval sliding mode control is equal to the absolute value of the side slip angle of the mass center of the four-wheel steering mode of the optimal control.

[0026] The active steering mode selection module switches the steering mode of the vehicle according to the following rules:

[0027] When the comprehensive stability control factor J T is less than the vehicle stability threshold J0, the front-wheel steering mode is adopted; when the comprehensive stability control factor J T is greater than the vehicle stability threshold J0, the four-wheel steering mode is adopted.

[0028] The active steering mode selection module switches the four-wheel steering mode according to the following rules:

[0029] When the road surface adhesion coefficient μ is in the first interval, the vehicle speed v is greater than the first threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the first threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the second interval, the vehicle speed v is greater than the second threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the second threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the third interval, the vehicle speed v is greater than the third threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the third threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the fourth interval, the vehicle speed v is greater than the fourth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the fourth threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the fifth interval, the vehicle speed v is greater than the fifth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the fifth threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the sixth interval, the vehicle speed v is greater than the sixth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the sixth threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the seventh interval, the vehicle speed v is greater than the seventh threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the seventh threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the eighth interval, the vehicle speed v is greater than the eighth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the eighth threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the ninth interval, the vehicle speed v is greater than the ninth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the ninth threshold, the four-wheel steering of the vehicle adopts the optimal control; when the road surface adhesion coefficient μ is in the tenth interval, the vehicle speed v is greater than the tenth threshold, the four-wheel steering of the vehicle adopts the sliding mode control, and the vehicle speed v is less than the tenth threshold, the four-wheel steering of the vehicle adopts the optimal control.

[0030] The active steering mode execution module is used for switching different steering modes, when the automobile is switched to the front wheel steering mode, the automobile four-wheel steering control system only outputs the front wheel steering angle, and the output value of the rear wheel steering is zero; when the automobile is switched to the four-wheel steering mode, the automobile four-wheel steering control system simultaneously outputs the calculated automobile front wheel steering angle and rear wheel steering angle according to the control mode.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] 1. A four-wheel active steering control mode switching system according to the current state of the automobile speed v, the road adhesion coefficient μ, the mass center side slip angle β, the yaw angular velocity r, the lateral acceleration a y , the steering wheel steering angle θ, the comprehensive stability control factor and the multi-mode switching threshold value in different road adhesion coefficient intervals are obtained.

[0033] 2. The present application calculates the comprehensive stability control factor and the multi-mode switching threshold value in different road adhesion coefficient intervals by the active steering multi-mode switching threshold value parameter calculation module, so as to select the automobile driving mode under the driving condition of different adhesion coefficient intervals, so that the automobile can drive in the optimal control mode under different conditions.

[0034] 3. The steering mode of the present application includes the automobile front wheel steering mode, the four-wheel steering mode under the sliding mode control and the four-wheel steering mode under the optimal control, and the steering mode of the automobile is switched, so that the steering stability and the active safety of the automobile are kept at all times. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application will be further described below in combination with the drawings:

[0036] Figure 1 A four-wheel active steering control mode switching system is provided in the present application. DETAILED DESCRIPTION

[0037] The present application will be further described below in combination with the drawings and specific embodiments.

[0038] As Figure 1 shown, the present application is a four-wheel active steering control mode switching system, which comprises a driving information measurement module, an active steering multi-mode switching threshold value parameter calculation module, an active steering mode selection module and an active steering mode execution module.

[0039] The driving information measurement module is used for measuring the speed v, the road adhesion coefficient μ, the mass center side slip angle β, the yaw angular velocity r, the lateral acceleration a y and the steering wheel steering angle θ.

[0040] The active steering multi-mode switching threshold parameter calculation module is configured to calculate a comprehensive stability control factor J T and different road adhesion coefficient intervals TH，i : a first threshold value v TH，1 , a second threshold value v TH，2 , a third threshold value v TH，3 , a fourth threshold value v TH，4 , a fifth threshold value v TH，5 , a sixth threshold value v TH，6 , a seventh threshold value v TH，7 , an eighth threshold value v TH，8 , a ninth threshold value v TH，9 , a tenth threshold value v TH，10 .

[0041] The active steering mode selection module is configured to select a steering mode of the vehicle according to the active steering multi-mode switching threshold parameters, and when the comprehensive stability control factor J T is less than a vehicle stability threshold J0, a front-wheel steering mode is adopted, and when the comprehensive stability control factor J T is greater than the vehicle stability threshold J0, a four-wheel steering mode is adopted; the control mode of the four-wheel steering mode is determined according to multi-mode switching threshold values v TH，i of the vehicle speed v, the road adhesion coefficient μ and the mass center side slip angle β of the current state of the vehicle; the four-wheel steering mode is switched between a sliding mode control mode and an optimal control mode, and when v i < v TH，i , the vehicle four-wheel steering adopts the sliding mode control mode, and when v i > v TH，i , the vehicle four-wheel steering adopts the optimal control mode.

[0042] The active steering mode execution module is configured to switch the steering mode of the vehicle, wherein the steering mode of the vehicle is the front-wheel steering mode and the four-wheel steering mode; when the vehicle is switched to the front-wheel steering mode, the vehicle four-wheel steering control system only outputs a front-wheel steering angle, and the output value of the rear-wheel steering is zero; when the vehicle is switched to the four-wheel steering mode, the vehicle four-wheel steering control system simultaneously outputs the calculated front-wheel steering angle and rear-wheel steering angle according to the control mode.

[0043] The comprehensive stability control factor J T in the active steering multi-mode switching threshold parameter calculation module is determined by the following formula:

[0044]

[0045] The weight coefficients w1 and w2 are determined by the following formula:

[0046]

[0047] w2 = ε(1 - w min )(1 - w2) + w min ;

[0048] where E is a stability margin, w min is a minimum value of a weighting factor, and ε is a tuning factor;

[0049] lateral acceleration stability control factor is determined by the following equation:

[0050]

[0051] yaw rate stability control factor J r is determined by the following equation:

[0052]

[0053] where n is the number of sampling points, Δt is the sampling time interval, and the subscripts i and o represent instantaneous and steady-state values, respectively.

[0054] The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameter in the lower road adhesion interval according to the following method:

[0055] According to the measured road adhesion coefficient μ of the automobile, it is divided into the following 10 intervals: interval I, II, III, IV, V, VI, VII, VIII, IX, X corresponding to the μ range respectively: the μ range corresponding to interval I is 0 < μ ≤ 0.1, the μ range corresponding to interval II is 0.1 < μ ≤ 0.2, the μ range corresponding to interval III is 0.2 < μ ≤ 0.3, the μ range corresponding to interval IV is 0.3 < μ ≤ 0.4, the μ range corresponding to interval V is 0.4 < μ ≤ 0.5, the μ range corresponding to interval VI is 0.5 < μ ≤ 0.6, the μ range corresponding to interval VII is 0.6 < μ ≤ 0.7, the μ range corresponding to interval VIII is 0.7 < μ ≤ 0.8, the μ range corresponding to interval IX is 0.8 < μ ≤ 0.9, and the μ range corresponding to interval X is 0.9 < μ ≤ 1.0.

[0056] When the road adhesion coefficient is in the I to V interval, the first to fifth threshold values are obtained by the following formula: wherein is the vehicle speed value at which the center of mass side slip angle is zero in the four-wheel steering mode of the sliding mode control of the automobile in different road adhesion coefficient intervals, is the vehicle speed value at which the center of mass side slip angle is zero in the four-wheel steering mode of the optimal control of the automobile in different road adhesion coefficient intervals.

[0057] The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameter in the high road adhesion interval according to the following method:

[0058] When the road adhesion coefficient is in the interval of VI to X, the optimal control strategy appears instability phenomenon at high vehicle speed; therefore, the acquisition formula of the sixth to tenth threshold value under the condition of high road adhesion coefficient is Wherein The n vehicle speed values at which the absolute value of the four-wheel steering mode of the vehicle in different road adhesion coefficient intervals is equal to the absolute value of the four-wheel steering mode of the optimal control.

[0059] The active steering mode selection module switches the steering mode of the vehicle according to the following rules:

[0060] When the comprehensive stability control factor J T is less than the vehicle stability threshold J0, the front-wheel steering mode is adopted; when the comprehensive stability control factor J T is greater than the vehicle stability threshold J0, the four-wheel steering mode is adopted.

[0061] The active steering mode selection module switches the four-wheel steering mode according to the following rules:

[0062] In the first interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the first threshold value, and adopts the optimal control when the vehicle speed v is less than the first threshold value; in the second interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the second threshold value, and adopts the optimal control when the vehicle speed v is less than the second threshold value; in the third interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the third threshold value, and adopts the optimal control when the vehicle speed v is less than the third threshold value; in the fourth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the fourth threshold value, and adopts the optimal control when the vehicle speed v is less than the fourth threshold value; in the fifth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the fifth threshold value, and adopts the optimal control when the vehicle speed v is less than the fifth threshold value; in the sixth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the sixth threshold value, and adopts the optimal control when the vehicle speed v is less than the sixth threshold value; in the seventh interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the seventh threshold value, and adopts the optimal control when the vehicle speed v is less than the seventh threshold value; in the eighth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the eighth threshold value, and adopts the optimal control when the vehicle speed v is less than the eighth threshold value; in the ninth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the ninth threshold value, and adopts the optimal control when the vehicle speed v is less than the ninth threshold value; in the tenth interval of the road adhesion coefficient μ, the vehicle four-wheel steering adopts the sliding mode control when the vehicle speed v is greater than the tenth threshold value, and adopts the optimal control when the vehicle speed v is less than the tenth threshold value.

[0063] The active steering mode execution module is configured to switch different steering modes, and when the vehicle switches to the front-wheel steering mode, the vehicle four-wheel steering control system only outputs the front-wheel steering angle, and the output value of the rear-wheel steering is zero; when the vehicle switches to the four-wheel steering mode, the vehicle four-wheel steering control system simultaneously outputs the calculated front-wheel steering angle and rear-wheel steering angle according to the control mode.

Claims

1. A four-wheel active steering control mode switching system, characterized in that, Includes the following: The system includes a driving information calculation module, an active steering multi-mode switching threshold parameter calculation module, an active steering mode selection module, and an active steering mode execution module. The driving information calculation module is used to measure vehicle speed v, road adhesion coefficient μ, center of gravity sideslip angle β, yaw rate r, and lateral acceleration a. y Steering wheel angle θ; The active steering multi-mode switching threshold parameter calculation module is used to calculate the comprehensive stability control factor J. T The multi-mode switching threshold parameter v within different road surface adhesion coefficient ranges TH，i First threshold value v TH，1 Second threshold value v TH，2 Third threshold value v TH，3 Fourth threshold value v TH，4 Fifth threshold value v TH，5 The sixth threshold value v TH，6 The seventh threshold value v TH，7 Eighth threshold value v TH，8 Ninth threshold value v TH，9 The tenth threshold value v TH，10 ; The active steering mode selection module is used to select the vehicle steering mode according to the above-mentioned multi-mode switching threshold parameters: when the comprehensive stability control factor J T When the vehicle stability threshold J0 is less than the vehicle stability threshold value, front-wheel steering mode is used; when the comprehensive stability control factor J... T When the vehicle stability threshold J0 is exceeded, four-wheel steering mode is activated. The control mode of four-wheel steering mode is determined by the multi-mode switching threshold v based on the vehicle speed v, road adhesion coefficient μ, and center of gravity sideslip angle β. TH，i Switching between sliding mode and optimal control mode for four-wheel steering: When v... i >v TH，i The car's four-wheel steering uses a sliding mode control, when v i <v TH，i The car's four-wheel steering uses an optimal control mode; The comprehensive stability control factor J in the active steering multi-mode switching threshold parameter calculation module T Determined by the following formula: ； The weighting coefficients w1 and w2 are determined by the following formula: ； ； Where E is the stability margin, w min ε is the minimum value of the weighting factor, and ε is the adjustment factor; Lateral acceleration stability control factor Determined by the following formula: ； Yaw rate stability control factor Determined by the following formula: ； In the above two formulas, n is the number of sampling points, Δt represents the sampling time interval, and the subscripts i and o represent the instantaneous value and the steady-state value, respectively. The active steering mode execution module is used to switch the vehicle steering mode, which is a front-wheel steering mode and a four-wheel steering mode. When the vehicle is switched to front-wheel steering mode, the four-wheel steering control system only outputs the front wheel angle, and the output value of the rear wheel steering is zero. When the vehicle is switched to four-wheel steering mode, the four-wheel steering control system outputs the calculated front wheel angle and rear wheel angle simultaneously according to the control mode.

2. The four-wheel active steering control mode switching system according to claim 1, characterized in that: The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameter in the lower road surface adhesion range according to the following method: Based on the calculated vehicle road adhesion coefficient μ, it is divided into the following 10 intervals: the ranges of μ corresponding to intervals I, II, III, IV, V, VI, VII, VIII, IX, and X are as follows: the range of μ corresponding to interval I is 0 < μ ≤ 0.1, the range of μ corresponding to interval II is 0.1 < μ ≤ 0.2, the range of μ corresponding to interval III is 0.2 < μ ≤ 0.3, the range of μ corresponding to interval IV is 0.3 < μ ≤ 0.4, the range of μ corresponding to interval V is 0.4 < μ ≤ 0.5, the range of μ corresponding to interval VI is 0.5 < μ ≤ 0.6, the range of μ corresponding to interval VII is 0.6 < μ ≤ 0.7, the range of μ corresponding to interval VIII is 0.7 < μ ≤ 0.8, the range of μ corresponding to interval IX is 0.8 < μ ≤ 0.9, and the range of μ corresponding to interval X is 0.9 < μ ≤ 1.0; The formulas for obtaining the first to fifth threshold values ​​of the road surface adhesion coefficient within the range of I to V are as follows: i = 1, 2, 3, 4, 5; in This refers to the vehicle speed when the center of gravity sideslip angle is zero under four-wheel steering mode with sliding mode control in different road surface adhesion coefficient ranges. This refers to the vehicle speed when the center of gravity sideslip angle is zero under the optimal four-wheel steering mode for controlling the vehicle in different road surface adhesion coefficient ranges.

3. The four-wheel active steering control mode switching system according to claim 1, characterized in that: The active steering multi-mode switching threshold parameter calculation module calculates the multi-mode switching threshold parameters in the high road adhesion range according to the following method: When the road surface adhesion coefficient is between VI and X, the optimal control strategy becomes unstable at excessively high vehicle speeds. Therefore, under high road surface adhesion coefficient conditions, the formula for obtaining the sixth to tenth threshold values ​​is: i = 6, 7, 8, 9, 10; in The n vehicle speed values ​​represent the absolute values ​​of the sideslip angle of the center of gravity in the sliding mode control of the four-wheel steering mode under different road surface adhesion coefficient ranges, which are equal to the absolute value of the sideslip angle of the center of gravity in the optimal control of the four-wheel steering mode.

4. The four-wheel active steering control mode switching system according to claim 1, characterized in that: The active steering mode selection module switches the four-wheel steering mode according to the following rules: When the road surface adhesion coefficient μ is in interval I, and the vehicle speed v is greater than the first threshold, the four-wheel steering uses sliding mode control; when the vehicle speed is less than the first threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval II, and the vehicle speed v is greater than the second threshold, the four-wheel steering uses sliding mode control; when the vehicle speed is less than the second threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval III, and the vehicle speed v is greater than the third threshold, the four-wheel steering uses sliding mode control; when the vehicle speed is less than the third threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval IV, and the vehicle speed v is greater than the fourth threshold, the four-wheel steering uses sliding mode control; when the vehicle speed is less than the fourth threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval V, and the vehicle speed v is greater than the fifth threshold, the four-wheel steering uses sliding mode control; when the vehicle speed is less than the fifth threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval VI, if the vehicle speed v is greater than the sixth threshold, the four-wheel steering uses sliding mode control; if the vehicle speed is less than the sixth threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval VII, if the vehicle speed v is greater than the seventh threshold, the four-wheel steering uses sliding mode control; if the vehicle speed is less than the seventh threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval VIII, if the vehicle speed v is greater than the eighth threshold, the four-wheel steering uses sliding mode control; if the vehicle speed is less than the eighth threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval IX, if the vehicle speed v is greater than the ninth threshold, the four-wheel steering uses sliding mode control; if the vehicle speed is less than the ninth threshold, the four-wheel steering uses optimal control. When the road surface adhesion coefficient μ is in interval X, if the vehicle speed v is greater than the tenth threshold, the four-wheel steering uses sliding mode control; if the vehicle speed is less than the tenth threshold, the four-wheel steering uses optimal control.

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