A road feel feedback control method based on a high-order all-wheel drive model for steer-by-wire

Abstract

The present invention discloses a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire, comprising the following steps: S1, determining a main torque and a compensation torque, and superimposing the main torque and the compensation torque to obtain a reference torque; S2, a vehicle control unit (VCU) determining the current front wheel angle and the current reference feedback torque according to the current vehicle state, establishing the dynamic equations of the HW module and the dynamic equations of the road feel motor; S3, obtaining a control-oriented second-order state space model of the SbW system based on the dynamic model in step S2, reducing the control system's sensitivity to interference by utilizing a sliding mode, and using the HOFA method to mitigate the potential for inherent flutter and vibration in SMC applications, thereby improving the overall system performance of the HOFA-SMC and the driver's handling comfort. The road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire provided by the present invention has the effect of improving the handling, comfort, and stability of electric vehicles under various road conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle control algorithms, and in particular to a road feel feedback control method based on a steer-by-wire high-order all-wheel drive model. Background Art

[0002] Electrification and intelligence are the development trends of modern automotive chassis. Consequently, traditional mechanical connections within vehicle chassis systems are increasingly being replaced by electronic signals. In traditional steering systems, steering resistance is transmitted to the handwheel via mechanical components such as the frame and steering shaft, generating steering feel, which is correlated with steering resistance in real time. However, in steer-by-wire (SbW) vehicles, the handwheel and road wheel are mechanically decoupled. The driver's steering commands are transmitted via electrical signals to the electric motor, which then drives the road wheel. This mechanical decoupling eliminates much of the steering feel typically associated with traditional vehicles, while also improving the vehicle's fuel efficiency and maneuverability while providing greater flexibility and customization for drivers with different driving styles and preferences.

[0003] While SbW systems offer many advantages over traditional steering systems, one of their main challenges is creating the right steering feel for the driver. Ensuring a real-time correlation between steering feel and steering resistance, and a realistic steering experience, is crucial for driver safety and comfort.

[0004] Common existing methods for controlling road-sensing motor torque include open-loop control, PID control, active disturbance rejection control, and sliding mode control. However, most of these control methods suffer from significant robustness deficiencies, complex implementation, and difficulty adjusting parameters. Sliding mode control (SMC) is particularly insensitive to uncertain disturbances and system parameter variations. Therefore, designing the sliding mode control ratio is crucial, and new methods are needed to mitigate the inherent chatter and jitter of sliding mode control. Summary of the Invention

[0005] In response to the above problems, a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire is provided, aiming to solve the problems existing in the prior art.

[0006] The specific technical solutions are as follows:

[0007] A road feel feedback control method based on a steer-by-wire high-order all-wheel drive model comprises the following steps:

[0008] S1. Determine the main torque and the compensation torque, and superimpose the main torque and the compensation torque to obtain a reference torque;

[0009] S2. The vehicle control unit (VCU) determines the current front wheel angle and the current reference feedback torque based on the current vehicle state, establishes the dynamic equations of the HW module and the dynamic equations of the road sensor motor;

[0010] S3. Obtain a control-oriented second-order state space model of the SbW system based on the dynamic model in step S2;

[0011] S4, converting the second-order state space model in step S3 into a nonlinear second-order full-drive model of HW;

[0012] S5, transforming the second-order full-drive model in step S4 into an error feedback system;

[0013] S6. Establishing an equivalent control law according to the error feedback system;

[0014] S7. Proof of stability.

[0015] The above-mentioned road feel feedback control method based on the high-order all-wheel drive model of wire-controlled steering also has the following characteristics: the compensation torque includes active return torque , ensuring that the steering wheel returns to the neutral position smoothly without overshoot when the driver actively releases his hands; soft limit torque , since the SbW system has a variable gear ratio, the system can be developed to limit the steering wheel angle range to ensure safety; it also includes damping torque , friction torque and inertia torque ;

[0016] Overall reference torque as a road feel source It is expressed as follows:

[0017] .

[0018] The above-mentioned road feel feedback control method based on the high-order all-wheel drive model of steer-by-wire also has the following characteristics: the dynamic equation of the HW module is:

[0019]

[0020] Where: It represents the torque applied by the driver by adjusting the arm resistance on the handwheel; Indicates the moment of inertia of the handwheel steering column; is the handwheel damping coefficient; is the handwheel angle; represents the equivalent Coulomb friction torque of the steering column; is the torque measured by the TAS sensor;

[0021] The dynamic equation of the road sensing motor is:

[0022]

[0023] Where: Represents the output electromagnetic torque of the road sensing motor; Indicates the motor's moment of inertia; is the motor damping coefficient; Represents the equivalent Coulomb friction torque between the road sensor motor and the reduction mechanism.

[0024] The above-mentioned road feel feedback control method based on the high-order all-wheel drive model of steer-by-wire also has the following characteristics: the second-order state space model is:

[0025]

[0026] Where: is the state quantity of the steering system, and the input quantity is , is a mature friction model, and subsequent experiments have shown that it has a significant impact on control performance. Usually considered as a measurable disturbance measured by a sensor, .

[0027] The above-mentioned road feel feedback control method based on the high-order all-wheel drive model of steer-by-wire further has the following characteristics: the second-order all-wheel drive model:

[0028]

[0029]

[0030]

[0031]

[0032] Where: and is a known nonlinear function, is included and The lumped disturbance.

[0033] The above-mentioned road feel feedback control method based on the steer-by-wire high-order all-wheel drive model also has the following characteristics: the error feedback system is:

[0034]

[0035]

[0036]

[0037]

[0038] A new sliding function based on the FAS method is designed as follows:

[0039] .

[0040] The above-mentioned road feel feedback control method based on the steer-by-wire high-order all-wheel drive model also has the following characteristics: the equivalent control law is:

[0041]

[0042] According to the equivalent control law, the closed-loop dynamic equation is obtained as follows:

[0043]

[0044] Right now,

[0045]

[0046] in,

[0047] .

[0048] In summary, the beneficial effects of this solution are:

[0049] The road feel feedback control method based on a steer-by-wire high-order all-wheel drive model provided by this invention utilizes sliding mode to reduce the control system's sensitivity to disturbances and employs the HOFA method to mitigate the potential for chatter and vibration inherent in SMC applications, thereby improving the overall HOFA-SMC system performance and driver comfort. This method, based on a steer-by-wire high-order all-wheel drive model, improves the handling, comfort, and stability of electric vehicles under various road conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of a flow chart of a road feel feedback control method based on a steer-by-wire high-order all-wheel drive model of the present invention;

[0051] Figure 2 This is a control principle diagram of a road feel feedback control method based on a steer-by-wire high-order all-wheel drive model of the present invention;

[0052] Figure 3 This is a road feel composition diagram of a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire in the present invention. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0054] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0055] The present invention will be further described below with reference to specific examples, but they are not intended to limit the present invention.

[0056] Figure 1 Schematic diagram of a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire according to the present invention. Figure 2 This is a control principle diagram of a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire in the present invention. Figure 3 This is a road feel composition diagram of a road feel feedback control method based on a high-order all-wheel drive model of steer-by-wire in the present invention, as shown in FIG. Figure 1-Figure 3 As shown, the road feel feedback control method based on the steer-by-wire high-order all-wheel drive model provided in this embodiment includes the following steps:

[0057] S1. Determine the main torque and the compensation torque, and superimpose the main torque and the compensation torque to obtain a reference torque;

[0058] S2. The vehicle control unit (VCU) determines the current front wheel angle and the current reference feedback torque based on the current vehicle state, establishes the dynamic equations of the HW module and the dynamic equations of the road sensor motor;

[0059] S3. Obtain a control-oriented second-order state space model of the SbW system based on the dynamic model in step S2;

[0060] S4, converting the second-order state space model in step S3 into a nonlinear second-order full-drive model of HW;

[0061] S5, transforming the second-order full-drive model in step S4 into an error feedback system;

[0062] S6. Establish an equivalent control law based on the error feedback system;

[0063] S7. Proof of stability.

[0064] In the above embodiment, the compensation torque includes the active return torque , ensuring that the steering wheel returns to the neutral position smoothly without overshoot when the driver actively releases his hands; soft limit torque , since the SbW system has a variable gear ratio, the system can be developed to limit the steering wheel angle range to ensure safety; it also includes damping torque , friction torque and inertia torque ;

[0065] Overall reference torque as a road feel source It is expressed as follows:

[0066] .

[0067] In the above embodiment, the dynamic equation of the HW module (handwheel module) is:

[0068]

[0069] Where: It represents the torque applied by the driver by adjusting the arm resistance on the handwheel; Indicates the moment of inertia of the handwheel steering column; is the handwheel damping coefficient; is the handwheel angle; represents the equivalent Coulomb friction torque of the steering column; is the torque measured by the TAS sensor;

[0070] The dynamic equation of the road sense motor is:

[0071]

[0072] Where: Represents the output electromagnetic torque of the road sensing motor; Indicates the motor's moment of inertia; is the motor damping coefficient; Represents the equivalent Coulomb friction torque between the road sensor motor and the reduction mechanism.

[0073] It should be noted that due to its advantages of small torque fluctuation and low noise, a permanent magnet synchronous motor is used to provide driving torque, while the servo drive works in torque control mode. The dynamic equation of the road sensing motor end needs to ignore the current loop characteristics.

[0074] In the above embodiment, the second-order state space model is:

[0075]

[0076] Where: is the state quantity of the steering system, and the input quantity is , is a mature friction model, and subsequent experiments have shown that it has a significant impact on control performance. Usually considered as a measurable disturbance measured by a sensor, .

[0077] In the above embodiment, the second-order full-drive model:

[0078]

[0079]

[0080]

[0081]

[0082] Where: and is a known nonlinear function, is included and The lumped disturbance.

[0083] In the above embodiment, the error feedback system is:

[0084]

[0085]

[0086]

[0087]

[0088] A new sliding function based on the FAS method is designed as follows:

[0089] .

[0090] It should be noted that in the process of transforming the second-order full-drive model into an error feedback system, To be The reference signal to be tracked is

[0091]

[0092] Where: represents a positive scalar.

[0093] In the above embodiment, once the sliding mode occurs, an equivalent control law can be established, which is:

[0094]

[0095] Substituting the equivalent control law into the error feedback system, the closed-loop dynamic equation can be obtained as follows:

[0096]

[0097] Right now,

[0098]

[0099] in,

[0100] .

[0101] It should be noted that by constructing the sliding mode Lyapunov function and proving its stability, it can be obtained that the convergence of the closed-loop system in step 7 can reach the sliding mode surface and stay on the sliding mode surface in a finite time;

[0102] For a given positive scalar As long as the sliding surface is designed as the new sliding mode function in step 6, the state trajectory of the closed-loop system can be driven to the sliding mode surface in a finite time by the following SMC law superior:

[0103]

[0104] The choice of Lyapunov function is as follows:

[0105]

[0106] The compensation torque equation in step S1 is:

[0107]

[0108] In step S2 The calculation formula is:

[0109]

[0110] Where: is the stiffness coefficient of the angular torque sensor; Indicates the mechanical angle of the road sensor motor, Indicates the reduction ratio of the road-sensing motor reducer. It is worth noting that is consistent with the definition of SFT, and It is the torque actively applied by the driver and cannot be directly controlled by the road sensing motor.

[0111] In step S4, it is assumed that ,and is bounded, satisfied , then the output equation of the controlled output can be expressed as:

[0112]

[0113] In step S6, select:

[0114]

[0115]

[0116] in, , is a positive scalar, choose , Obviously, the eigenvalues ​​of the matrix F are and .

[0117] For any choice , all matrices and non-singular matrices All meet the following requirements:

[0118]

[0119]

[0120]

[0121] in, is an arbitrary parameter matrix satisfying ,matrix The characteristic value of and .

[0122] It can be seen that as long as the matrix is ​​selected Stable, then the closed-loop system is stable. Obviously, the degree of freedom of the control system is determined by the parameter matrix and Determined, in addition, the matrix is Hurwitz to ensure the asymptotic convergence of the system.

[0123] Working principle, high-order full-drive (HOFA) system method, this is a control-oriented system model, usually characterized as full-drive. Unlike control-based system models based on first-order state space theory, most nonlinear systems can be converted into HOFA systems through physical modeling or mathematical derivation. After obtaining the HOFA model, measurable nonlinear terms can be easily eliminated, resulting in a stable linear closed-loop system. In addition, it provides more design freedom to achieve additional system requirements. Therefore, combining SMC (sliding film control) with HOFA theory can significantly improve the system's anti-interference ability. This method aims to use sliding mode to reduce the control system's sensitivity to interference and use the HOFA method to reduce the possibility of chatter and vibration inherent in SMC applications, thereby improving the overall system performance of HOFA-SMC and the driver's operating comfort.

[0124] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A road feel feedback control method based on a high-order all-wheel drive model for steer-by-wire, characterized by: The following steps are involved: S1. Determine the main torque and the compensation torque, and superimpose the main torque and the compensation torque to obtain a reference torque; S2. The vehicle control unit determines the current front wheel angle and the current reference feedback torque according to the current vehicle state, establishes the dynamic equations of the handwheel module and the road sensor motor; S3. According to the dynamic model in step S2, a second-order state space model of the SbW system for control is obtained. The second-order state space model is: Where: is the state quantity of the steering system, and the input quantity is , is the friction model, and is considered as a measurable disturbance measured by a sensor, , Indicates the motor's moment of inertia; is the motor damping coefficient, : The reduction ratio of the road-sensing motor reducer, : Stiffness coefficient of angular torque sensor, : road sense motor angle; S4. Convert the second-order state space model in step S3 into a nonlinear second-order full-drive model of the handwheel module, wherein: ； ； ； Where: and is a known nonlinear function, is included and The lumped disturbance of S5. Transform the second-order full-drive model in step S4 into an error feedback system, where the error feedback system is: ； ； ； ； The sliding function based on the FAS method is designed as follows: In the process of transforming the second-order full-drive model into an error feedback system, assume To be The reference signal to be tracked is Where: represents a positive scalar; S6. Establish an equivalent control law according to the error feedback system. The equivalent control law is: According to the equivalent control law, the closed-loop dynamic equation is obtained as follows: Right now, in, ； S7. Proof of stability.

2. The road feel feedback control method based on a steer-by-wire high-order all-wheel drive model according to claim 1, characterized in that: The compensation torque includes an active return torque , ensuring that the steering wheel returns to the neutral position smoothly without overshoot when the driver actively releases his hands; soft limit torque , also including the damping torque , friction torque and inertia torque ; Overall reference torque as a road feel source It is expressed as follows: ； Where, : Rack and pinion torque.

3. The road feel feedback control method based on a steer-by-wire high-order all-wheel drive model according to claim 2, characterized in that: The dynamic equation of the handwheel module is: Where: It represents the torque applied by the driver by adjusting the arm resistance on the handwheel; Indicates the moment of inertia of the handwheel steering column; is the handwheel damping coefficient; is the handwheel angle; represents the equivalent Coulomb friction torque of the steering column; is the torque measured by the TAS sensor; The dynamic equation of the road sensing motor is: Where: Represents the output electromagnetic torque of the road sensing motor; Indicates the motor's moment of inertia; is the motor damping coefficient; Represents the equivalent Coulomb friction torque between the road sensor motor and the reduction mechanism.

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