A rear wheel steering control method for a vehicle based on dynamic slip rate compensation

Abstract

This invention discloses a vehicle rear-wheel steering control method based on dynamic slip ratio compensation, belonging to the field of vehicle steering control technology, including: calculating the ideal rear wheel steering angle δ. r，i Establish dynamic slip ratio: Establish the coupling relationship between slip ratio and turning radius: R eff，i =R*(1+ξ*k) i Solve for the steering angle compensation amount Δδ r，i Calculate the control output steering angle δ′ r，i This is the sum of the ideal steering angle and the compensation amount. This invention establishes a dynamic coupling model that directly correlates the slip ratio with the steering radius, breaking through the limitations of traditional static mapping and improving the stability of rear wheel steering. Furthermore, the control logic path is short and can be implemented using existing vehicle sensors and other hardware.

Description

Technical Field

[0001] This invention relates to the field of vehicle steering control technology, and more specifically to a method for controlling the rear wheel steering of a car based on dynamic slip ratio compensation. Background Technology

[0002] The vehicle chassis control system significantly improves dynamic performance by coordinating the steering angles of the front and rear wheels. In low-speed steering conditions (such as parking or navigating narrow bends), the rear-wheel reverse yaw strategy effectively reduces the turning radius and enhances vehicle maneuverability; while during high-speed lane changes or cornering, the rear-wheel same-direction compensation strategy suppresses yaw rate oscillations and strengthens driving stability.

[0003] However, due to the real-time changes in the road surface adhesion coefficient μ, such as the transition from dry asphalt to ice, nonlinear abrupt changes in tire-ground contact dynamics can occur, leading to decoupling of wheel speed signals from actual vehicle speed. Furthermore, traditional rear-wheel steering systems rely on wheel speed sensors and basic vehicle parameters such as wheelbase to estimate wheel angle values. When wheel slippage occurs, the slip ratio is not zero, and the actual wheel speed deviates significantly from the estimated value υ', resulting in distorted input steering angle, wheel slippage, and reduced vehicle stability.

[0004] The rear wheel steering angle calculation function model is δ=f(υ'、α). y Due to the distortion of the aforementioned input parameters (γ), the output control command lags or oscillates, and the function value fails to converge. Related data shows that on low-adhesion road surfaces with a road adhesion coefficient μ < 0.3, the steering angle error can reach more than 40% of the standard value, leading to instability phenomena such as oversteering or understeering of the vehicle.

[0005] Currently, most methods for coupling rear wheel steering angle and slip ratio use static mapping, lacking real-time decoupling models, which leads to instability in the vehicle's rear wheel steering control. Furthermore, the vehicle's ESP system only intervenes by braking to control the vehicle's center of gravity and cannot actively optimize wheel steering angle. Summary of the Invention

[0006] This invention provides a vehicle rear-wheel steering control method based on dynamic slip ratio compensation, aiming to solve the shortcomings of existing vehicles, such as the lack of a real-time decoupling model between the rear-wheel steering angle and slip ratio, which leads to instability in the vehicle's rear-wheel steering control.

[0007] The present invention adopts the following technical solution:

[0008] A method for rear-wheel steering control of a vehicle based on dynamic slip ratio compensation includes the following steps:

[0009] Step 1: Calculate the ideal rear wheel steering angle δ r,i ;

[0010] Step 2: Establish the dynamic slip ratio using the following formula: Among them, w i : Rotational angular velocity, R tire Tire rolling radius, v x，i : Longitudinal vehicle speed, γ: Vehicle body yaw rate, i=(L / R);

[0011] Step 3: Establish the coupling relationship between slip ratio and turning radius: R eff，i =R*(1+ξ*k) i ), where R eff，i ξ: Actual turning radius, k i Wheel slip ratio;

[0012] Step 4: Solve for the steering angle compensation amount Δδ r,i : Where K: gain coefficient, β: smoothing factor, v th Vehicle speed setting threshold, μ est : Current road surface friction coefficient; v x Vehicle longitudinal speed;

[0013] Step 5: Calculate the control output steering angle δ′ r，i δ′ is the sum of the ideal steering angle and the compensation amount. r，i =δ r，i +Δδ r,i .

[0014] The above coefficient ξ is solved by fitting the tire magic formula: Where B: tire stiffness factor; C: tire shape factor; arctan(B*k): the core nonlinear function of the tire magic formula, which describes the trend of tire slip ratio; The partial derivative of the tire lateral force with respect to its slip ratio represents the effect of changes in slip ratio on the tire lateral force, which in turn affects the vehicle's turning radius.

[0015] The gain coefficient K mentioned above is obtained using the following formula: Where β: smoothing factor, v th Vehicle speed setting threshold, μ est : Current road surface friction coefficient.

[0016] The above-mentioned ideal rear wheel steering angle δ r，i Including the ideal steering angle δ of the left rear wheel r_L Ideal steering angle δ of the right rear wheel r_R Referring to Ackermann geometry and the linear two-degree-of-freedom model of automobiles:

[0017]

[0018]

[0019] Where L is the vehicle wheelbase, R is the turning radius, and d is the rear axle track.

[0020] The longitudinal vehicle speed v in step two above x，i Including the longitudinal speed v of the left rear wheel x，L and the longitudinal speed v of the right rear wheel x，R And through IMU vehicle speed v x Corrected for yaw rate γ: υ x,L =υ x -γ*d / 2,υ x,R =υ x +γ*d / 2.

[0021] Left rear wheel slip ratio k_L: The coupling relationship between the left rear wheel slip ratio k_L and the steering radius is: R eff,L =R*(1+ξ*k_L); Right rear wheel slip ratio k_R: The coupling relationship between the right rear wheel slip ratio k_R and the steering radius is: R eff,R =R*(1+ξ*k_R).

[0022] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention establishes a dynamic coupling model that directly correlates slip ratio with steering radius, breaking through the limitations of traditional static mapping and improving the stability of rear wheel steering; moreover, the control logic path is short and can be implemented using existing vehicle sensors and other hardware.

[0024] 2. This invention adopts an asymmetric compensation method to independently handle the slippage problem of the left and right rear wheels, thus solving the instability problem caused by unilateral slippage.

[0025] 3. The gain coefficient K of the steering angle compensation in this invention is adjusted in real time according to the vehicle speed and the road friction coefficient, which further improves the accuracy of the steering angle compensation. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating an embodiment of the present invention. Detailed Implementation

[0027] Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Many details are described below to provide a comprehensive understanding of the invention; however, those skilled in the art will not need these details to implement the invention. Well-known components, methods, and processes will not be described in detail below.

[0028] Reference Figure 1This embodiment provides a method for controlling the rear-wheel steering of a vehicle based on dynamic slip ratio compensation, including the following steps:

[0029] 1. Calculate the ideal steering angle of the left rear wheel and the ideal steering angle of the right rear wheel, denoted as δ respectively. r_L δ r_R .

[0030] This embodiment specifically references the Ackermann geometric relationship and the linear two-degree-of-freedom model of a car:

[0031]

[0032]

[0033] Where L is the vehicle wheelbase, R is the turning radius, and d is the rear axle track.

[0034] II. Establish the dynamic slip ratio κ using the following formula. i The slip ratios k_L and k_R of the left rear wheel and the right rear wheel are obtained in real time.

[0035]

[0036] Among them, w i : Rotational angular velocity, R tire Tire rolling radius, v x，i : Longitudinal vehicle speed, γ: yaw rate of the vehicle body, i = (L / R); denominator max(v x.i ,0.1): When the longitudinal speed at the wheel center is less than 0.1, the value is 0.1 to avoid invalid formula calculations.

[0037] Note: i = L or R undersuffix, representing left wheel or right wheel; ki: slip ratio of the i-th wheel (slippage when ki>0, locking when <0).

[0038] Therefore, the slip ratio of the left rear wheel, k_L, is: Right rear wheel slip ratio k_R:

[0039] And through IMU vehicle speed v x Correction of yaw rate γ v x，L v x，R :

[0040] υ x,L =υ x -γ*d / 2

[0041] υ x，R =υ x +γ*d / 2

[0042] III. Establishing the coupling relationship between slip ratio and turning radius:

[0043] R eff，i =R*(1+ξ*k) i )

[0044] Among them, R eff，i Actual turning radius, k i Wheel slip ratio.

[0045] The coupling relationship between the left rear wheel slip ratio k_L and the steering radius is: R eff，L =R*(1+ξ*k_L); The coupling relationship between the right rear wheel slip ratio k_R and the steering radius is: R eff，R =R*(1+ξ*k_R).

[0046] The coefficient ξ in the above formula is solved by fitting the tire magic formula:

[0047]

[0048] Where B: tire stiffness factor; C: tire shape factor; arctan(B*k): the core nonlinear function of the tire magic formula, which describes the trend of tire slip ratio; The partial derivative of the tire lateral force with respect to its slip ratio represents the effect of changes in slip ratio on the tire lateral force, which in turn affects the vehicle's turning radius.

[0049] IV. Solving for the steering angle compensation Δδ r,i .

[0050]

[0051] Wherein, the gain coefficient K is: β: Smoothing factor, vth: Vehicle speed threshold, μ est : Current road surface friction coefficient, v x : Vehicle longitudinal speed.

[0052] Note: i = L or R underscores, representing the left or right wheel. Left rear wheel steering angle compensation: Steering angle compensation for the right rear wheel:

[0053] V. Calculate the control output steering angle δ′ r，i .

[0054] The final control output steering angle is the sum of the ideal angle and the compensation amount:

[0055] Control output: Left rear wheel steering angle Control output: Left rear wheel steering angle

[0056] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A method for rear-wheel steering control of a vehicle based on dynamic slip ratio compensation, characterized in that, Includes the following steps: Step 1: Calculate the ideal rear wheel steering angle ; Step 2: Establish the dynamic slip ratio using the following formula: , where w i : Rotational angular velocity, R tire Tire rolling radius, v x,i : Longitudinal vehicle speed, γ: Vehicle body yaw rate, i=(L / R); Step 3: Establish the coupling relationship between slip ratio and turning radius: , where R eff,i ξ: Actual turning radius, k i Wheel slip ratio; coupling coefficient ξ is solved by fitting the tire magic formula. Where B: tire stiffness factor; C: tire shape factor; The core nonlinear function of the tire magic formula describes the trend of tire slip ratio. The partial derivative of the tire lateral force with respect to its slip ratio represents the effect of changes in slip ratio on the tire lateral force, which in turn affects the vehicle's turning radius. Step 4: Solve for the steering angle compensation. : Where, K: gain coefficient, β: smoothing factor, v th Vehicle speed setting threshold, μ est : Current road surface friction coefficient, v x Vehicle longitudinal speed; the gain coefficient K is obtained using the following formula: Where β: smoothing factor, v th Vehicle speed setting threshold, μ est : Current road surface friction coefficient; Step 5: Calculate the control output steering angle , which is the sum of the ideal steering angle and the compensation amount, that is: .

2. The vehicle rear-wheel steering control method based on dynamic slip ratio compensation as described in claim 1, characterized in that: The ideal steering angle of the rear wheels Including the ideal steering angle δ of the left rear wheel r_L Ideal steering angle δ of the right rear wheel r_R Referring to Ackermann geometry and the linear two-degree-of-freedom model of automobiles: ； ； Where L is the vehicle wheelbase, R is the turning radius, and d is the rear axle track.

3. The rear-wheel steering control method for automobiles based on dynamic slip ratio compensation as described in claim 2, characterized in that: The longitudinal vehicle speed v in step two x,i Including the longitudinal speed of the left rear wheel v x,L and longitudinal speed of the right rear wheel v x,R And through IMU vehicle speed v x Corrected for yaw rate γ: , .

4. The rear-wheel steering control method for automobiles based on dynamic slip ratio compensation as described in claim 2, characterized in that, Left rear wheel slip ratio k_L: The coupling relationship between the left rear wheel slip ratio k_L and the steering radius is as follows: Right rear wheel slip ratio k_R: The coupling relationship between the right rear wheel slip ratio k_R and the steering radius is as follows: .

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