A vehicle active front wheel steering and direct yaw moment cooperative control method

Abstract

The application discloses a vehicle active front wheel steering and direct yaw moment cooperative control method, which firstly acquires vehicle state information and establishes an ideal yaw angular velocity and ideal mass center side slip angle reference model based on a two-degree-of-freedom vehicle model; secondly, a mass center side slip angle-mass center side slip angular velocity phase plane is established, and an instability index representing vehicle transient stability is calculated; then, a sliding mode control algorithm is adopted to calculate a total additional yaw moment required for maintaining vehicle stability; subsequently, according to the relationship between the instability index and a preset threshold, the total moment is decomposed into target moments of the active front wheel steering and the direct yaw moment through dynamic weight distribution; finally, the target moments are converted into front wheel active superimposed steering angles and four-wheel longitudinal force moments and are sent to corresponding actuators.

Description

Technical Field

[0001] This invention relates to a method for coordinated control of active front wheel steering and direct yaw moment in a vehicle. Background Technology

[0002] With the development of automotive steer-by-wire technology, Active Front Steering (AFS) and Direct Yaw Torque Control (DYC) systems are widely used to improve vehicle handling stability and active safety. AFS effectively regulates vehicle yaw response by superimposing an active control angle on top of the driver's steering wheel angle. However, when the ground adhesion coefficient is low or the vehicle is in extreme steering conditions, the lateral force of the front tires easily reaches saturation, at which point the control effect of AFS will significantly diminish or even fail. DYC generates additional yaw torque through independent distribution of four-wheel drive / braking torque, possessing strong intervention capabilities in the tire nonlinear region and under extreme conditions. However, frequent intervention of DYC can lead to unexpected speed drops and abrupt jerking sensations, severely impacting driving comfort. Existing chassis control methods mostly involve independent control of AFS and DYC or simple threshold switching, lacking a collaborative control method that can achieve a smooth transition between the vehicle's linear and nonlinear regions and fully leverage the complementary advantages of both. Summary of the Invention

[0003] The present invention provides a method for coordinated control of active front wheel steering and direct yaw moment of a vehicle in order to solve the problems existing in the prior art.

[0004] The technical solutions adopted in this invention are as follows:

[0005] A method for coordinated control of active front wheel steering and direct yaw moment in a vehicle includes the following steps:

[0006] Acquire vehicle status information and calculate ideal yaw rate and ideal center of mass sideslip angle based on a two-degree-of-freedom vehicle model;

[0007] Obtain the vehicle's current sideslip angle and sideslip velocity, establish the sideslip angle-slip velocity phase plane, and calculate the instability index.

[0008] Using a sliding mode control algorithm, with the control objective being that the yaw rate tracks the ideal yaw rate and the center of gravity sideslip angle tends to the ideal center of gravity sideslip angle, the total additional yaw moment required to maintain the stability of the vehicle is calculated.

[0009] Based on the comparison results between the instability index and the preset first threshold and second threshold, the total additional yaw moment is decomposed into the active front wheel steering target yaw moment and the direct yaw moment target yaw moment through weight allocation. The first threshold and the second threshold are set based on the stability boundary parameters of the phase plane.

[0010] The active front wheel steering target yaw moment is converted into the active superimposed steering angle of the front wheels and sent to the steering actuator. The direct yaw moment target yaw moment is converted into the longitudinal moment of the four wheels and sent to the brake actuator or drive actuator.

[0011] Furthermore, the formula for calculating the instability index is as follows:

[0012] ,

[0013] in, Instability index The sideslip angle is the angle of the center of mass. The angular velocity of the center of mass deflection. This is the slope parameter of the stable boundary line of the phase plane.

[0014] Furthermore, the stability boundary of the phase plane is represented using the biline method, and its boundary equation is:

[0015] ,

[0016] in, The intercept parameter is the boundary value for stability.

[0017] Furthermore, the weight allocation adopts a standard cubic polynomial smoothed step function, and the direct yaw moment allocation weight coefficient is defined as follows:

[0018] ,

[0019] in, It is a normalized variable calculated based on the instability index and the first and second thresholds.

[0020] Furthermore, the normalized variable The calculation formula is:

[0021] ,

[0022] in, Instability index The first threshold, This is the second threshold.

[0023] Furthermore, the sliding mode control algorithm includes:

[0024] Constructing a joint sliding surface ,in This is the error in the centroid sideslip angle. For yaw rate error, and The sliding surface weight coefficient is greater than zero;

[0025] Based on saturation function Calculate the total additional yaw moment, where This represents the boundary layer thickness.

[0026] Furthermore, the saturation function The expression is:

[0027] .

[0028] Furthermore, the vehicle status information includes vehicle speed, steering wheel angle, yaw rate, lateral acceleration, as well as the distance from the vehicle's center of gravity to the front and rear axles, vehicle mass, and lateral stiffness of the front and rear wheels.

[0029] Furthermore, the formula for calculating the ideal yaw rate is as follows:

[0030] ,

[0031] in, For longitudinal vehicle speed, Wheelbase For the overall vehicle quality, The distance from the center of gravity to the front axle. The distance from the center of gravity to the rear axle. For the front wheel lateral stiffness, For rear wheel lateral stiffness, For the front wheel steering angle, The road surface adhesion coefficient, This is the acceleration due to gravity.

[0032] Furthermore, when the instability index is less than the first threshold, the direct yaw moment target yaw moment is zero, and the active front wheel steering target yaw moment is equal to the total additional yaw moment;

[0033] When the instability index is greater than the second threshold, the target yaw moment of the active front wheel steering is zero, and the target yaw moment of the direct yaw moment is equal to the total additional yaw moment.

[0034] When the instability index is between the first threshold and the second threshold, the active front wheel steering target yaw moment and the direct yaw moment target yaw moment are non-linearly and smoothly transitioned according to the weight allocation.

[0035] The present invention has the following beneficial effects:

[0036] (1) By continuously assessing the vehicle stability status through the instability index, active front wheel steering is used to make fine adjustments in the linear stability zone, which effectively avoids the unexpected speed drop and jerking caused by direct yaw torque intervention, and improves the smoothness of daily driving.

[0037] (2) When the vehicle enters the nonlinear region or extreme working conditions, direct yaw moment control is seamlessly introduced through dynamic weight allocation, and the longitudinal moment difference is used to strongly correct the deviation, effectively suppressing the vehicle instability trend and improving safety under extreme working conditions.

[0038] (3) The instability index based on phase plane theory is used as the basis for weight allocation. Compared with the traditional single-sided acceleration threshold switching method, it can reflect the dynamic transient changes of the vehicle earlier and more continuously, making the control logic more robust.

[0039] (4) The weight allocation adopts a standard cubic polynomial smooth step function to achieve a nonlinear smooth transition between the weight of active front wheel steering and direct yaw moment, avoiding abrupt changes in the control system at the threshold switching point and ensuring the continuous adjustability of vehicle handling stability. Attached Figure Description

[0040] Figure 1 This is a flowchart of the present invention.

[0041] Figure 2 This is a two-degree-of-freedom vehicle dynamics model.

[0042] Figure 3 for Phase plane diagram.

[0043] Figure 4 This is a schematic diagram of the weight allocation curves for AFS and DYC. Detailed Implementation

[0044] The invention will now be further described with reference to the accompanying drawings.

[0045] This invention discloses a method for coordinated control of active front wheel steering and direct yaw moment in a vehicle. Figure 1 The flowchart of this method shows that the entire process is executed in a closed loop, following the sequence of vehicle state information acquisition and ideal reference model establishment, phase plane stability assessment, total additional yaw moment calculation, cooperative weight allocation, and actuator control output.

[0046] During vehicle operation, onboard sensors acquire real-time signals of longitudinal vehicle speed, steering wheel angle, yaw rate, and lateral acceleration. The distance from the vehicle's center of gravity to the front axle is known to be... The distance from the center of mass to the rear axle is Wheelbase L = a + b, vehicle mass is The front wheel lateral stiffness is The rear wheel lateral stiffness is The ideal yaw rate under the current operating conditions is calculated based on the linear two-degree-of-freedom dynamic model of the vehicle. The formula for calculating the ideal yaw rate is:

[0047] ,

[0048] in, It is the road surface adhesion coefficient. It is gravitational acceleration. It is a symbolic function. This refers to the steering angle of the front wheels.

[0049] In this embodiment, the ideal centroid sideslip angle is... It is set to 0, which serves as the core control objective for vehicle lateral stability.

[0050] Obtain the vehicle's current center of gravity sideslip angle and the angular velocity of the center of mass deflection Establish the phase plane of the center of mass sideslip angle and the center of mass sideslip angular velocity. Figure 2 The two-degree-of-freedom vehicle dynamics model used in this embodiment maintains a constant longitudinal vehicle speed. Based on the two-degree-of-freedom vehicle dynamics model, the vehicle dynamics differential equation is obtained as follows:

[0051] ,

[0052] In the formula, The moment of inertia of the entire vehicle. and These are the lateral forces on the front and rear wheels, respectively.

[0053] Ignoring vehicle dynamic load transfer, and influenced by the center of gravity position, the vertical loads on the front and rear wheels are as follows:

[0054] ,

[0055] In the formula, and These represent the vertical loads on the front and rear wheels, respectively. During vehicle operation, the forces on each wheel differ, resulting in varying slip angles. A nonlinear tire model is established based on the magic formula to accurately obtain the tire lateral force. The tire lateral force calculation formula is as follows:

[0056] ,

[0057] In the formula, This refers to the lateral force of the tire. Let be the tire slip angle, and B, C, D, and E be functions of the tire vertical load and camber angle, which can be obtained by fitting the tire model parameters.

[0058] Based on the fitting of the above dynamic model and tire model, the following results were obtained: The stability boundary of the phase plane is represented by the biline method, and the boundary equation is obtained by fitting the biline method. ,in The slope parameter of the phase trajectory boundary line. For the intercept parameters of the stable boundary, Figure 3 for Phase plane diagram.

[0059] To continuously quantify the current transient stability of a vehicle, an instability index is defined. , Reflects the current status point of the vehicle The weighted distance along the direction perpendicular to the boundary line from the absolute stability center of the phase plane, i.e., the origin. The higher the value, the higher the likelihood of vehicle instability.

[0060] The sliding mode control algorithm is used to calculate the total additional yaw moment ΔM required to maintain vehicle stability, and the actual yaw rate γ is used to track the ideal yaw rate. Actual centroid sideslip angle Approaching the ideal centroid side slip angle To control the target, the yaw rate error is defined. Centroid side slip angle error Design of joint sliding surface The formula for calculating the total additional yaw moment is:

[0061] ,

[0062] in:

[0063] , ,

[0064] sat(·) is a saturation function, and its expression is:

[0065] Ф represents the boundary layer thickness; and The sliding surface weight coefficient is greater than zero. and The approach law adjustment parameter is greater than zero. The use of the saturation function can effectively suppress the chattering problem inherent in sliding mode control and improve control smoothness.

[0066] The vehicle control range is divided based on the nonlinear characteristics of the tire magic formula, and a first threshold is set. The corresponding linear range of tire lateral force serves as the boundary point for the vehicle's stability region, and a second threshold is set. This corresponds to the tire lateral force saturation value and the vehicle stability boundary; based on the instability index. Calculate the normalized variable based on the relationship between the two thresholds. The calculation formula is: In the transition zone Inside, .

[0067] The weighting is applied using a standard cubic polynomial smoothed step function, directly assigning weighting coefficients to the yaw moment. Active front wheel steering weighting coefficient .

[0068] Figure 4 This is a schematic diagram of the weight distribution curves for active front wheel steering and direct yaw moment, visually demonstrating the non-linear, smooth transition relationship between the two weights as the vehicle transitions from a stable state to a state of extreme instability; coordinated control logic is executed according to the control interval:

[0069] when At that time, the vehicle is in the linear stability region. , The active front-wheel steering system is fully responsible for fine-tuning vehicle stability.

[0070] when When the vehicle enters the nonlinear transition zone, the active front wheel steering and direct yaw moment are coupled and controlled in a dual-effect manner.

[0071] when At that time, the vehicle was in the extreme instability zone. , The direct yaw moment system takes complete control to prevent vehicle sideslip.

[0072] The active front wheel steering target yaw moment after coordinated distribution is converted into the active superimposed front wheel steering angle. The formula for calculating the actual front wheel steering angle is as follows:

[0073] ,

[0074] And satisfy The steering angle constraint sends the actual steering angle command of the front wheels to the steering actuator; the direct yaw moment target yaw moment is input into the lower torque distributor to calculate the longitudinal moment of the four wheels, and the torque command is sent to the hydraulic braking system or independent drive motor. Additional yaw moment is generated through the independent distribution of the four-wheel drive / braking torque. Combined with the superimposed steering angle adjustment of the active front wheel steering, the vehicle's handling stability and driving comfort are optimized in all working conditions. While ensuring safety in extreme working conditions, the vehicle speed loss is minimized and the active safety performance of the vehicle is improved.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for coordinated control of active front wheel steering and direct yaw moment in a vehicle, characterized in that: Includes the following steps: Acquire vehicle status information and calculate ideal yaw rate and ideal center of mass sideslip angle based on a two-degree-of-freedom vehicle model; Obtain the vehicle's current sideslip angle and sideslip velocity, establish the sideslip angle-slip velocity phase plane, and calculate the instability index. Using a sliding mode control algorithm, with the control objective being that the yaw rate tracks the ideal yaw rate and the center of gravity sideslip angle tends to the ideal center of gravity sideslip angle, the total additional yaw moment required to maintain the stability of the vehicle is calculated. Based on the comparison results between the instability index and the preset first threshold and second threshold, the total additional yaw moment is decomposed into the active front wheel steering target yaw moment and the direct yaw moment target yaw moment through weight allocation. The first threshold and the second threshold are set based on the stability boundary parameters of the phase plane. The active front wheel steering target yaw moment is converted into the active superimposed steering angle of the front wheels and sent to the steering actuator. The direct yaw moment target yaw moment is converted into the longitudinal moment of the four wheels and sent to the brake actuator or drive actuator.

2. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: The formula for calculating the instability index is as follows: ， in, Instability index The sideslip angle is the angle of the centroid. The angular velocity of the center of mass deflection. This represents the slope parameter of the stable boundary line of the phase plane.

3. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 2, characterized in that: The stability boundary of the phase plane is represented by the biline method, and its boundary equation is: ， in, The intercept parameter is the boundary value for stability.

4. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: The weighting allocation adopts a standard cubic polynomial smoothed step function, and the direct yaw moment allocation weighting coefficient is defined as follows: ， in, It is a normalized variable calculated based on the instability index and the first and second thresholds.

5. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 4, characterized in that: The normalized variable The calculation formula is: ， in, Instability index The first threshold, This is the second threshold.

6. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 5, characterized in that: The sliding mode control algorithm includes: Constructing a joint sliding surface ,in This is the error in the centroid sideslip angle. For yaw rate error, and The sliding surface weight coefficient is greater than zero; Based on saturation function Calculate the total additional yaw moment, where This represents the boundary layer thickness.

7. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: The saturation function The expression is: 。 8. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: The vehicle status information includes vehicle speed, steering wheel angle, yaw rate, lateral acceleration, distance from the vehicle's center of gravity to the front and rear axles, vehicle mass, and lateral stiffness of the front and rear wheels.

9. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: The formula for calculating the ideal yaw rate is: ， in, For longitudinal vehicle speed, Wheelbase For the overall vehicle quality, The distance from the center of gravity to the front axle. The distance from the center of gravity to the rear axle. For the front wheel lateral stiffness, For rear wheel lateral stiffness, For the front wheel steering angle, The road surface adhesion coefficient, This is the acceleration due to gravity.

10. The method for coordinated control of active front wheel steering and direct yaw moment of a vehicle as described in claim 1, characterized in that: When the instability index is less than the first threshold, the direct yaw moment target yaw moment is zero, and the active front wheel steering target yaw moment is equal to the total additional yaw moment. When the instability index is greater than the second threshold, the target yaw moment of the active front wheel steering is zero, and the target yaw moment of the direct yaw moment is equal to the total additional yaw moment. When the instability index is between the first threshold and the second threshold, the target yaw moment of the active front wheel steering and the target yaw moment of the direct yaw moment undergo a non-linear smooth transition according to the weight allocation.

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