A robust stability control method for steer-by-wire vehicles

Abstract

The application provides a robust stability control method for a steer-by-wire vehicle, which comprises the following steps: firstly, a two-degree-of-freedom vehicle dynamics model is established, and the lateral velocity and the mass center side slip angle of the vehicle under a steady state condition are solved; then, the control target of the vehicle stability control is further modified, and a reference model for designing a robust controller is established based on the two-degree-of-freedom vehicle dynamics model; finally, a steer-by-wire vehicle robust stability controller based on a hybrid sensitivity control is designed and solved, and is used for performing the steer-by-wire vehicle robust stability control. The method can effectively improve the robust stability and the trajectory tracking performance of the steer-by-wire vehicle.

Description

Technical Field

[0001] The present invention relates to the field of automobile assisted driving, and in particular to a robust stability control method for an intelligent steer-by-wire vehicle. Background Art

[0002] Vehicle stability is directly related to occupant comfort and overall vehicle safety. However, common stability control technologies rarely consider both the system's actual control output and the system's robustness to uncertain interference when controlling vehicle stability. This often means that a larger control output is required to achieve the desired control effect when pursuing system stability, and the system's resistance to internal and external interference is relatively weak.

[0003] For front-wheel steering-by-wire vehicles, on the one hand, the front wheel steering angle cannot be increased indefinitely. On the other hand, considering the nonlinear characteristics of the tire, the cornering force will tend to saturate or even decrease with the increase of the cornering angle. In addition, the nonlinearity of the vehicle system and the complexity of the driving conditions require consideration of not only the robust stability of the vehicle but also the control output of the control system and the dynamic response performance of the system in the design process of the vehicle stability controller. That is, the robust stability of the vehicle should be achieved with as small a control output as possible. Summary of the Invention

[0004] The purpose of the present invention is to propose a robust stability control method for an intelligent steer-by-wire vehicle, which can effectively improve the robust stability and trajectory tracking performance of the intelligent steer-by-wire vehicle.

[0005] To achieve the above objectives, the technical solution of the present invention is: a method for robust stability control of an intelligent steer-by-wire vehicle, comprising the following steps:

[0006] S1. Establish a two-degree-of-freedom vehicle dynamics model under the conditions of small angle assumption and linear tire model;

[0007] S2. Based on the established two-degree-of-freedom vehicle dynamics model, solve the vehicle's yaw rate and sideslip angle under steady-state conditions;

[0008] S3. Considering the limitations of road adhesion conditions during actual driving, set a control target for vehicle stability control;

[0009] S4. Establish a reference model for robust controller design based on a two-degree-of-freedom vehicle dynamics model;

[0010] S5. Design and solve the problem based on H2 / H ∞ A hybrid sensitivity controlled steer-by-wire vehicle robust stability controller is provided for robust stability control of a steer-by-wire vehicle.

[0011] Preferably, the two-degree-of-freedom vehicle dynamics model under the small angle assumption and linear tire model conditions in S1 is specifically as follows:

[0012]

[0013] Where, v x is the longitudinal velocity of the vehicle; γ is the yaw rate of the vehicle; β is the sideslip angle of the center of mass of the vehicle; m is the mass of the vehicle; I z is the moment of inertia of the vehicle around the Z axis; a is the distance from the center of mass of the vehicle to the front axle; b is the distance from the center of mass of the vehicle to the rear axle; k f is the front wheel cornering stiffness; k r is the rear wheel cornering stiffness; δ f is the front wheel angle resulting from driver input.

[0014] Preferably, the yaw rate and sideslip angle of the vehicle under steady-state conditions are solved in S2 as follows:

[0015]

[0016] Where, is the stability factor; L=a+b is the wheelbase of the vehicle.

[0017] Preferably, the control target for vehicle stability control in S3 is specifically as follows:

[0018]

[0019] Where μ is the road adhesion coefficient; g is the acceleration of gravity; γ d is the reference yaw rate; β d is the sideslip angle of the reference center of mass.

[0020] Preferably, the reference model for the robust controller design in S4 is as follows:

[0021]

[0022] Where, F yw is the side wind force; l yw is the distance from the side wind action point to the center of mass; Δδ f Additional front wheel steering angle for controller input.

[0023] Preferably, the design steps of the steer-by-wire vehicle robust stability controller in S5 are as follows:

[0024] S5.1. Select additional front wheel turning angle Δδ f As the control input, that is, u=[Δδ f ]; the vehicle's yaw rate γ and center of mass sideslip angle β are used as state variables, that is, x = [βγ]T ; In addition, the reference center of mass side slip angle β d , reference yaw rate γ d , the driver inputs the equivalent front wheel steering angle δ f and the side wind disturbance F yw As the interference input signal, that is, w=[β d γ d δ f F yw ] T The tracking error of the sideslip angle and yaw rate is used as the measurement output, i.e. y = [e1 e2] T =[ΔβΔγ] T =[β d -βγ d -γ] T ; Select z ∞ =[z ∞1 z ∞2 z ∞3 z ∞4 ] T =[βγΔβΔγ] T As the controlled system H ∞ Performance; Select z2=[Δδ f ]H2 performance as the controlled system;

[0025] S5.2, build on H2 / H ∞ The state space of vehicle robust stability control with mixed sensitivity control is:

[0026]

[0027] Where, D 12 =[0] 4x1 ; C2 = [0] 1x2 ;D 21 =[0] 1x4 ;D 22 =[1] 1x1 ;

[0028]

[0029] S5.3. Based on the established state space, derive the generalized control object and closed-loop system for robust stability control of steer-by-wire vehicles:

[0030]

[0031]

[0032]

[0033] Where P(s) is the generalized control object; K(s) is the robust stability controller; Z1 = [Z ∞3 Z ∞4 ] T and Z3=[Z ∞ 1Z ∞2 ] T is the output of the controlled system, where Z1 represents the target tracking performance and interference suppression performance of the controlled system, Z3 represents the robust stability and noise suppression performance of the controlled system; Z2 represents the size of the controller output; W1=diag{W 11 ,W 12}、W2=diag{W 21 ,W 22} and W3 represent the weighting functions of the three performances Z1, Z3 and Z2 respectively; is the transfer function from disturbance input to controlled output, G 11 , G 12 are δ f 、F yw Transfer function to the sideslip angle β, G 13 , G 14 are δ f 、F yw Transfer function to yaw rate γ; G0 = [G 01 G 02 ] T is the transfer function from the controller output to the controlled output, G 01 , G 02 Represents Δδ respectively f Transfer function to the sideslip angle β and yaw rate γ of the center of mass;

[0034] S5.4. Solve the robust stability controller K(s) to make the closed-loop system stable and satisfy the following constraints:

[0035]

[0036] Where, and w=[β d γ d δ f F yw ] T Transfer function to Z1, Z2, and Z3; η is a constant.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] Designed H2 / H ∞The hybrid sensitivity controller balances the robustness of intelligent steer-by-wire vehicles with the controller's output performance, improving the vehicle's stability and dynamic response under uncertain disturbances. Furthermore, the robust stability controller design simultaneously considers the vehicle's yaw rate and center-of-mass sideslip angle tracking, thereby improving both robust stability and trajectory tracking performance. Therefore, this design holds great promise for market application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of robust stability control for an intelligent steer-by-wire vehicle according to the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] The present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0042] The present invention discloses a robust stability control method for an intelligent steer-by-wire vehicle. The steps of the robust stability control method for an intelligent steer-by-wire vehicle are as follows:

[0043] S1. Establish a two-degree-of-freedom vehicle dynamics model under the conditions of small angle assumption and linear tire model;

[0044]

[0045] Where, v x is the longitudinal velocity of the vehicle; γ is the yaw rate of the vehicle; β is the sideslip angle of the center of mass of the vehicle; m is the mass of the vehicle; I z is the moment of inertia of the vehicle around the Z axis; a is the distance from the center of mass of the vehicle to the front axle; b is the distance from the center of mass of the vehicle to the rear axle; k f is the front wheel cornering stiffness; k r is the rear wheel cornering stiffness; δ f is the front wheel angle resulting from driver input.

[0046] S2. Based on the established two-degree-of-freedom vehicle dynamics model, solve the vehicle's yaw rate and sideslip angle under steady-state conditions:

[0047]

[0048] Where, is the stability factor; L=a+b is the wheelbase of the vehicle.

[0049] S3. Considering the limitations of the road adhesion conditions during actual driving, the control objective of vehicle stability control is further modified to:

[0050]

[0051] Where μ is the road adhesion coefficient; g is the acceleration of gravity; γ d is the reference yaw rate; β d is the sideslip angle of the reference center of mass.

[0052] S4. Establish a reference model for robust controller design based on the two-degree-of-freedom vehicle dynamics model, namely:

[0053]

[0054] Where, F yw is the side wind force; l yw is the distance from the side wind action point to the center of mass; Δδ f Additional front wheel steering angle for controller input.

[0055] S5. Design and solve the problem based on H2 / H ∞ Robust stability controller for steer-by-wire vehicles with hybrid sensitivity control.

[0056] like Figure 1 As shown, the design steps of the steer-by-wire vehicle robust stability controller are as follows:

[0057] S5.1. Select additional front wheel turning angle Δδ f As the control input, that is, u=[Δδ f ]; the vehicle's yaw rate γ and center of mass sideslip angle β are used as state variables, that is, x = [βγ] T ; In addition, the reference center of mass side slip angle β d , reference yaw rate γ d , the driver inputs the equivalent front wheel steering angle δ f and the side wind disturbance F yw As the interference input signal, that is, w=[β d γ d δ f F yw ] T The tracking error of the sideslip angle and yaw rate is used as the measurement output, i.e. y = [e1 e2] T =[ΔβΔγ] T =[β d -βγ d -γ] T ; Select z ∞ =[z ∞1 z ∞2 z∞3 z ∞4 ] T =[βγΔβΔγ] T As the controlled system H ∞ Performance; Select z2=[Δδ f ] as the H2 performance of the controlled system.

[0058] S5.2, build on H2 / H ∞ The state space of vehicle robust stability control with mixed sensitivity control is:

[0059]

[0060] Where, D 12 =[0] 4x1 ; C2 = [0] 1x2 ;D 21 =[0] 1x4 ;D 22 =[1] 1x1 ;

[0061]

[0062] S5.3. Based on the established state space, derive the generalized control object and closed-loop system for robust stability control of steer-by-wire vehicles:

[0063]

[0064]

[0065]

[0066] Where P(s) is the generalized control object; K(s) is the robust stability controller; Z1 = [Z ∞3 Z ∞4 ] T and Z3=[Z ∞ 1Z ∞2 ] T is the output of the controlled system, where Z1 represents the target tracking performance and interference suppression performance of the controlled system, Z3 represents the robust stability and noise suppression performance of the controlled system; Z2 represents the size of the controller output; W1 = diag{W 11 ,W 12}、W2=diag{W 21 ,W 22} and W3 represent the weighting functions of the three performances Z1, Z3 and Z2 respectively; is the transfer function from disturbance input to controlled output, G 11 , G12 are δ f 、F yw Transfer function to the sideslip angle β, G 13 , G 14 are δ f 、F yw Transfer function to yaw rate γ; G0 = [G 01 G 02 ] T is the transfer function from the controller output to the controlled output, G 01 , G 02 Represents Δδ respectively f Transfer function to the sideslip angle β and yaw rate γ of the center of mass.

[0067] S5.4. Solve the robust stability controller K(s) to make the closed-loop system stable and satisfy the following constraints:

[0068]

[0069] Where, and w=[β d γ d δ f F yw ] T Transfer function to Z1, Z2, and Z3; η is a constant.

[0070] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[0071] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A robust stability control method for an intelligent steer-by-wire vehicle, characterized in that: Here are the steps: S1. Establish a two-degree-of-freedom vehicle dynamics model under the conditions of small angle assumption and linear tire model; S2. Based on the established two-degree-of-freedom vehicle dynamics model, solve the vehicle's yaw rate and sideslip angle under steady-state conditions; S3. Considering the limitations of road adhesion conditions during actual driving, set a control target for vehicle stability control; S4. Establish a reference model for robust controller design based on a two-degree-of-freedom vehicle dynamics model; S5. Design and solve the problem based on H2 / H ∞ A hybrid sensitivity controlled steer-by-wire vehicle robust stability controller is used to perform robust stability control of a steer-by-wire vehicle; The design steps of the robust stability controller for the S5 steer-by-wire vehicle are as follows: S5.

1. Select additional front wheel turning angle Δδ f As the control input, that is, u=[Δδ f ]; the vehicle's yaw rate γ and center of mass sideslip angle β are used as state variables, that is, x = [β γ] T ; In addition, the reference center of mass side slip angle β d , reference yaw rate γ d , the driver inputs the equivalent front wheel steering angle δ f and the side wind disturbance F yw As the interference input signal, that is, w=[β d γ d δ f F yw ] T The tracking error of the sideslip angle and yaw rate is used as the measurement output, i.e. y = [e1 e2] T =[Δβ Δγ] T =[β d -β γ d -γ] T ; Select z ∞ =[z ∞1 z ∞2 z ∞3 z ∞4 ] T =[β γ Δβ Δγ] T As the controlled system H ∞ Performance; Select z2=[Δδ f ]H2 performance as the controlled system; S5.2, build on H2 / H ∞ The state space of vehicle robust stability control with mixed sensitivity control is: Where, D 12 =[0] 4x1 ; C2 = [0] 1x2 ;D 21 =[0] 1x4 ;D 22 =[1] 1x1 ; S5.

3. Based on the established state space, derive the generalized control object and closed-loop system for robust stability control of steer-by-wire vehicles: Where P(s) is the generalized control object; K(s) is the robust stability controller; Z1 = [Z ∞3 Z ∞4 ] T and Z3=[Z ∞1 Z ∞2 ] T is the output of the controlled system, where Z1 represents the target tracking performance and interference suppression performance of the controlled system, Z3 represents the robust stability and noise suppression performance of the controlled system; Z2 represents the size of the controller output; W1=diag{W 11 ,W 12 }、W2=diag{W 21 ,W 22 } and W3 represent the weighting functions of the three performances Z1, Z3 and Z2 respectively; is the transfer function from disturbance input to controlled output, G 11 , G 12 are δ f 、F yw Transfer function to the sideslip angle β, G 13 , G 14 are δ f 、F yw Transfer function to yaw rate γ; G0 = [G 01 G 02 ] T is the transfer function from the controller output to the controlled output, G 01 , G 02 Represents Δδ respectively f Transfer function to the sideslip angle β and yaw rate γ of the center of mass; S5.

4. Solve the robust stability controller K(s) to make the closed-loop system stable and satisfy the following constraints: Where, and w=[β d γ d δ f F yw ] T Transfer function to Z1, Z2, and Z3; η is a constant.

2. The method for robust stability control of an intelligent steer-by-wire vehicle according to claim 1, characterized in that: The two-degree-of-freedom vehicle dynamics model under the small angle assumption and linear tire model conditions in S1 is as follows: Where, v x is the longitudinal velocity of the vehicle; γ is the yaw rate of the vehicle; β is the sideslip angle of the center of mass of the vehicle; m is the mass of the vehicle; I z is the moment of inertia of the vehicle around the Z axis; a is the distance from the center of mass of the vehicle to the front axle; b is the distance from the center of mass of the vehicle to the rear axle; k f is the front wheel cornering stiffness; k r is the rear wheel cornering stiffness; δ f is the front wheel angle resulting from driver input.

3. The method for robust stability control of an intelligent steer-by-wire vehicle according to claim 1, characterized in that: The yaw rate and sideslip angle of the vehicle under steady-state conditions are calculated in S2 as follows: Where, is the stability factor; L=a+b is the wheelbase of the vehicle.

4. The method for robust stability control of an intelligent steer-by-wire vehicle according to claim 1, characterized in that: The control objectives of the vehicle stability control in S3 are as follows: Where μ is the road adhesion coefficient; g is the acceleration of gravity; γ d is the reference yaw rate; β d is the sideslip angle of the reference center of mass.

5. The method for robust stability control of an intelligent steer-by-wire vehicle according to claim 1, characterized in that: The reference model for the robust controller design in S4 is as follows: Where, F yw is the side wind force; l yw is the distance from the side wind action point to the center of mass; Δδ f Additional front wheel steering angle for controller input.

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