An active return method for steer-by-wire based on a return speed reference model

Abstract

The present invention discloses a method for active self-centering of a steer-by-wire system based on a self-centering speed reference model, which relates to the field of active self-centering of automobile steering wheels. The method comprises: obtaining relevant vehicle parameters; obtaining the driver's self-centering intention based on an active self-centering state judgment mechanism based on a time window; obtaining a target steering wheel self-centering speed based on the self-centering speed reference model and the current steering wheel angle; obtaining the required active self-centering torque based on the current steering wheel speed and the target self-centering speed using a control method; and obtaining the final active self-centering torque requested from the road-sensing motor based on an active self-centering torque transition mechanism. The present invention designs a self-centering speed reference model based on the dynamic model of the steer-by-wire system to achieve a smooth steering wheel self-centering process, covering low, medium, and high speed driving scenarios, and enhancing the driver's comfortable experience of steering wheel self-centering.

Description

Technical Field

[0001] The present invention relates to the field of active centering of automobile steering wheels, and in particular to an active centering method of wire-controlled steering based on a centering speed reference model. Background Art

[0002] With the rapid development of automotive technology, steer-by-wire technology has gradually emerged as an advanced technology in the field of driving control, and is attracting increasing attention from automakers and consumers. Compared with traditional mechanical steering systems, steer-by-wire systems eliminate the mechanical connection between the steering wheel and the steering wheels. Instead, they incorporate an electronic control unit, a road sensor motor, and a steering motor. This eliminates the need for mechanical connections and instead controls the vehicle's steering through electrical signals. Its flexible control methods and fast, precise response characteristics are highly compatible with the development of electrification and intelligent vehicles.

[0003] Figure 1 This is a schematic diagram of the steer-by-wire system. The system primarily consists of three components: the steering wheel assembly, the steering actuator assembly, and the main controller. The steering wheel assembly includes the steering wheel, steering wheel angle sensor, torque sensor, and road feel simulation motor. Its primary function is to transmit the driver's steering intent to the steer-by-wire main controller and receive torque signals from the main controller to provide the driver with corresponding road feel information. The steering actuator assembly, which includes the steering actuator motor, front wheel steering mechanism components, and related sensors, receives commands from the main controller to control the rotation of the steering wheel to implement the driver's steering intent.

[0004] Because the mechanical connection between the steering wheel and the steering wheel is severed, the self-centering torque applied to the steering wheel cannot be transmitted to the steering wheel through the transmission mechanism. As a result, the steering wheel will not automatically return to the center position after the driver stops steering, increasing the driver's self-centering burden and affecting driving comfort. To solve this problem, an active self-centering module is designed. After detecting that the driver's hands are off the steering wheel, the road-sensing motor outputs torque to control the steering wheel to actively return to the center position.

[0005] Active self-centering technology faces several key challenges. For example, how to design an active self-centering condition determination mechanism to accurately assess the driver's steering intent and determine whether to activate or deactivate the active self-centering system; how to determine the optimal steering wheel self-centering speed during the self-centering process at different vehicle speeds, ensuring coordination between the steering actuator and the steering wheel and a favorable vehicle self-centering posture; how to control the steering wheel self-centering process to ensure smoothness; and how to adapt the active self-centering process to sudden driver intervention to prevent discomfort caused by the active self-centering system. These issues pose the greatest obstacles to the application of active self-centering methods in steer-by-wire systems. Therefore, designing an active self-centering method with accurate self-centering condition determination, appropriate self-centering speeds at various vehicle speeds, a smooth self-centering process, and a natural transition to driver intervention is key to addressing these challenges.

[0006] The current active correction method has the following problems:

[0007] 1. Difficulty in designing the appropriate steering wheel return speed at various vehicle speeds: It is difficult to determine the most appropriate return speed for the steering wheel when returning to various states at various vehicle speeds, which affects the subsequent control of the steering wheel return speed.

[0008] 2. Lack or defects in the transition mechanism: There are defects in the transition mechanism between the active return state and the normal steering state, resulting in the steering wheel torque fluctuating when entering and exiting the active return state due to the sudden application or unloading of the active return torque, which causes discomfort to the driver to a certain extent.

[0009] 3. Misjudgment of the return condition: In certain specific situations, when the driver is steering normally, the system will mistakenly enter the active return state and apply additional active return force, resulting in a decrease in the driver's driving comfort. In other cases, after the driver releases the steering wheel, the system does not correctly enter the active return state, resulting in the steering wheel not automatically returning to the center position.

[0010] Therefore, technicians in this field are committed to developing an active self-centering method that accurately judges the self-centering working condition, has an appropriate self-centering speed at various vehicle speeds, a smooth self-centering process, and a natural transition when facing driver intervention. Summary of the Invention

[0011] To achieve the above objectives, the present invention provides an active self-centering method with accurate self-centering condition judgment, appropriate self-centering speed at various vehicle speeds, smooth self-centering process, and natural transition in the face of driver intervention.

[0012] In a first aspect, the present invention discloses a method for active self-centering of a steer-by-wire vehicle based on a self-centering speed reference model, comprising:

[0013] Step S1, obtaining relevant vehicle parameters, steering wheel mechanical parameters, model calibrated parameters, and steering wheel angle, speed, and torque parameters;

[0014] Step S2: Obtaining the driver's steering wheel intention based on the active steering state judgment mechanism based on the time window, and determining whether the current state of the steering wheel requires active steering intervention;

[0015] Step S3, determining whether the system is currently in an active return state. If the system is in an active return state, proceed to step S4; otherwise, the active return system does not intervene and returns to step S2;

[0016] Step S4, obtaining the target steering wheel return speed according to the return speed reference model and the current steering wheel angle, including

[0017] Step S401: Establish an equivalent dynamic model of the steer-by-wire system. The steer-by-wire system is considered as a rigid body and is equivalent to a second-order system. The moment of inertia and damping of each component are equivalent to the steering wheel assembly. The equivalent dynamic model is as follows:

[0018]

[0019] Where: θ is the steering wheel angle; J is the system equivalent moment of inertia; B is the system equivalent damping coefficient; T mo is the output torque of the road sensing motor; T ao is the output torque of the power assist motor; T h is the steering wheel input torque; T f is the equivalent friction torque of the system; F rack is the equivalent resistance on the rack; i mc 、i amc 、i rc J is the equivalent transmission ratio from the road sensor motor, power steering motor and rack to the steering wheel assembly; sw 、J m 、J am are the rotational inertia of the steering wheel assembly, road sensor motor and power assist motor respectively; M r is the rack mass; B sw 、B m 、B am are the damping coefficients of the steering wheel assembly, road sensor motor, and power assist motor respectively; B r is the rack damping coefficient;

[0020] The relevant parameters required by the equivalent dynamic model of the wire control steering system are: J sw 、J m 、J am 、M r 、B sw 、B m 、Bam 、B r 、i mc 、i amc 、i rc 、F rack , where F rack It can be obtained through the relevant mature wire-controlled steering rack force observation and estimation algorithm. The remaining parameters are mechanical parameters and can be obtained by consulting the relevant hardware manual or performing parameter identification tests.

[0021] In step S402, based on an assumed simplified equivalent dynamic model of the steer-by-wire system, the present invention establishes a steering wheel return speed reference model. Based on the equivalent dynamic model of the steer-by-wire system, suitable steering wheel return speeds at low, medium, and high vehicle speeds are determined. The return speed reference model is established based on the following assumptions:

[0022] 1) Due to the mechanical friction torque in the steer-by-wire system, if it is not compensated, the steering wheel angle in the reference model will not be able to return to the center position. Therefore, the present invention believes that during the return process of the speed reference model, the output torque of the steering motor can constantly compensate for the equivalent friction torque of the steering system, that is:

[0023] i amc ·T ao =T f

[0024] 2) During the active return process, the driver takes his hands off the steering wheel and does not input torque to the steering wheel. At the same time, the road sensing motor does not work and does not output torque to the steering wheel, that is:

[0025] T h =T mo =0

[0026] Based on the above assumptions, the equivalent dynamic model of steer-by-wire can be simplified as follows:

[0027]

[0028] Where: θ t is the steering wheel angle of the reference return model during the return process;

[0029] Step S403: Based on the simplified dynamic model, a reference steering wheel return speed is obtained as the target return speed at medium and low speeds. According to the above formula, the steering wheel angle and steering wheel speed at the initial moment are known. Solving the differential equation can obtain the reference return speed at each moment of the steering wheel return in the reference model.

[0030] In step S404, a virtual damping torque is applied at high speeds to obtain a corrected steering wheel reference return speed, which serves as the target return speed at high speeds. When the steering wheel angle is constant, the return torque applied to the vehicle tires increases with vehicle speed. At medium and high speeds, due to excessive return torque, the steering wheel reference return angle calculated using the return speed reference model will experience reverse overshoot oscillation. This phenomenon can significantly endanger driving safety during high-speed driving. Therefore, the present invention designs a compensation module to suppress steering wheel return overshoot and increase the virtual damping torque. The corrected return speed reference model is as follows:

[0031]

[0032] Where T d To compensate for the damping torque, the expression is as follows:

[0033]

[0034]

[0035] Where: B d To compensate for the damping torque amplitude; a d is the gradient variation coefficient of the damping torque with the steering wheel speed; v0 is the critical vehicle speed between low speed and medium-high speed; b1 and b2 are the adjustment coefficients of the compensation damping torque amplitude with vehicle speed;

[0036] The relevant parameters required for this model are: a d , v0, b1, b2 can all be obtained through calibration.

[0037] Step S5, using a control method to obtain the required active return torque according to the current steering wheel speed and the target return speed;

[0038] In step S6, based on the active self-aligning torque transition mechanism, a transition factor is obtained according to the time of entering the active self-aligning state and the steering wheel torque, and combined with the active self-aligning torque required in step S5, the final active self-aligning torque requested to the road sensing motor is obtained.

[0039] In one application scenario, step S2 may be specifically configured as follows:

[0040] The system is divided into a steering state and an active return state. The system switches between the steering state and the active return state through step S20 to judge the current system state, step S21 to enter the active return state, and step S22 to exit the active return state.

[0041] Furthermore, when the system is in the steering state, the active self-centering system does not intervene in the normal steering operation. When the system is in the active self-centering state, the active self-centering system is turned on, and the active self-centering system then calculates the required active self-centering torque and requests the required active self-centering torque from the road sensing motor.

[0042] Furthermore, if the system is currently in the steering state, step S21 is executed to enter the active return state judgment mechanism. When the system meets the following conditions at the same time, it enters the active return state:

[0043] 1) Step S211, determine the absolute value of the steering wheel angle |θ sw |Is it greater than the set return opening angle θ ent , that is, whether |θ is satisfied sw |>θ ent ;

[0044] 2) Step S212: Determine whether the steering wheel is in a stationary or returning state, that is, whether θ sw *ω sw ≤0;

[0045] 3) Step S213, determining the absolute value of the steering wheel speed |ω sw Is | less than the calibration value ω0, that is, whether |ω sw |≤ω0;

[0046] 4) Step S214, determine the absolute value of the steering wheel torque |T h |Is it less than the calibration value T low , that is, whether |T h | <T low ;

[0047] 5) Step S215: When the system determines that all four conditions are met, the timer accumulates the iteration time step. If any one of the conditions is not met, the system resets the timer and returns to step S211.

[0048] 6) Step S216, when the timer t count Greater than the time window threshold t ent When the system enters the active return state, otherwise it returns to step S211.

[0049] Parameter θ ent ,ω0,T low , t ent Obtained through real vehicle calibration.

[0050] Furthermore, if the system is currently in the active return state, step S22 is executed to determine whether to exit the active return state. The system exits the active return state when one of the following conditions is met:

[0051] 1) Step S221, determine the absolute value of the steering wheel angle |θ sw |Is it less than the set return closing angle θ? ext , that is, whether |θ is satisfied sw |<θ ext ;

[0052] 2) Step S222, determine the absolute value of the steering wheel torque |T h |Is it greater than the calibration value T high , that is, whether |T h |>T high ,

[0053] After completing step S2, execute step S3 to determine whether the system is currently in the active return state. If the system is in the active return state, proceed to subsequent steps S4 to S6. Otherwise, the active return system does not intervene and returns to step S2.

[0054] Parameter θ ext 、T high Obtained through real vehicle calibration.

[0055] In one application scenario, step S5 may be specifically configured as follows:

[0056] include,

[0057] Step S501, establishing a dynamic model of the steering wheel assembly according to the mechanical structure of the steering wheel assembly;

[0058] Step S502, defining a tracking error between the steering wheel speed and the target return speed;

[0059] Step S503 , controlling the steering wheel's return speed by a control method to obtain the output torque of the road sensing motor so that the steering wheel's return speed tracks the target return speed.

[0060] Furthermore, the control method may adopt PID control, sliding mode control, fuzzy control, adaptive control, neural network or modern control method.

[0061] In one application scenario, step S6 may be specifically configured as follows:

[0062] include,

[0063] In step S601, the active return torque transition mechanism first calculates a start transition factor K1 based on the time it takes to enter the active return state. This factor increases as the time it takes to enter the active return state increases. It is 0 when the active return state is just entered. As the time it takes to enter the active return state increases to a calibrated time threshold, the start transition factor increases to 1 and remains constant. The growth curve of the start transition factor between these two periods can be freely designed.

[0064] Step S602: After calculating the startup transition factor, the active return torque transition mechanism calculates a feel smoothing factor K2 based on the steering wheel torque measured by the sensor. This factor decreases as the steering wheel torque increases. When the steering wheel torque is less than a calibrated steering wheel torque low threshold, the feel smoothing factor is 1. When the steering wheel torque is greater than a calibrated steering wheel torque high threshold, the feel smoothing factor is 0. When the steering wheel torque is between the high and low thresholds, the curve of the change in the feel smoothing factor with the steering wheel torque can be freely designed.

[0065] Step S603: Calculate the active self-aligning torque transition factor K by combining the startup transition factor and the hand-feel smoothness factor. The active self-aligning torque transition factor is obtained by multiplying the startup transition factor and the hand-feel smoothness factor.

[0066] Step S604 , correcting the output torque of the road sense motor according to the transition factor K. Specifically, the output torque of the road sense motor obtained in step S5 is multiplied by the transition factor K to obtain the final required output torque of the road sense motor.

[0067] In a second aspect, the present invention discloses an active self-centering system for steer-by-wire based on a self-centering speed reference model, comprising:

[0068] Acquisition unit: used to obtain relevant vehicle parameters, steering wheel mechanical parameters, model calibrated parameters and steering wheel angle, speed, and torque parameters;

[0069] The first judgment unit is used to obtain the driver's return intention based on the active return state judgment mechanism based on the time window, and determine whether the current state of the steering wheel requires active return intervention;

[0070] The second judgment unit is used to judge whether the system is currently in the active return state. If the system is in the active return state, step S4 is performed; otherwise, the active return system does not intervene and returns to the first judgment unit;

[0071] The first calculation unit is used to obtain the target steering wheel return speed according to the return speed reference model and the current steering wheel angle, including

[0072] Establishing a steer-by-wire system dynamics model: Based on the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established using an existing mature steer-by-wire dynamics model establishment method.

[0073] Based on the assumption of simplifying the steer-by-wire system dynamics model, the equivalent dynamics model of the steer-by-wire system is obtained as the reference model for the return speed.

[0074] The model state is the steering wheel angle θ of the reference self-centering model during the self-centering process t, the model input is the equivalent resistance F on the rack rack ,

[0075] Based on the return speed reference model, the steering wheel reference return speed is obtained as the target return speed at medium and low speeds.

[0076] According to the reference model of the return speed, the steering wheel angle and steering wheel speed at the initial moment are known, and the reference return speed θ· t ,

[0077] Add virtual damping torque at high speed, correct the return speed reference model, and obtain the target return speed at high speed based on the corrected model;

[0078] A second calculation unit is used to obtain the required active return torque according to the current steering wheel speed and the target return speed using a control method;

[0079] The third calculation unit is used to obtain a transition factor based on the active self-aligning torque transition mechanism, according to the time of entering the active self-aligning state and the steering wheel torque, and combine it with the active self-aligning torque required in the second calculation unit to obtain the final active self-aligning torque requested from the road sensing motor.

[0080] From the above technical solution, it can be seen that the present invention discloses a method and system for active self-centering of steer-by-wire based on a self-centering speed reference model, which has the following beneficial effects:

[0081] 1. Considering the difficulty in designing a suitable steering wheel return speed at each vehicle speed, the present invention takes the dynamic physical model of the vehicle and steering system as the starting point, and designs a return speed reference model based on the dynamic model of the wire-controlled steering system to obtain the most suitable steering wheel return speed at each vehicle speed. This acquisition method takes into account the influence of vehicle speed on the steering wheel return speed and has universal applicability. The present invention establishes a dynamic model of the wire-controlled steering system, ignores the existence of mechanical friction, obtains the rack force through a rack force observation estimation algorithm or related dynamic calculations, and then obtains the reference return speed of the steering wheel return state at each vehicle speed through the dynamic model of the wire-controlled steering system, which is used as the most suitable return speed at each vehicle speed. The present invention provides a method for determining the most suitable return speed of the steering wheel when returning to each state at each vehicle speed, so that the steering wheel return condition is closer to the actual return condition of the tire, thereby reducing tire wear during the return process and enhancing the driver's comfort experience of the steering wheel return.

[0082] 2. Considering the problem of missing or defective transition mechanism, the present invention designs an active return torque transition mechanism, designs a starting transition factor based on the time of entering the active return state, and designs a hand feel smoothing factor based on the steering wheel torque measured by the sensor, and uses these two factors to achieve smooth transition. The present invention designs a starting transition factor and a hand feel smoothing factor, wherein the starting transition factor is calculated based on the time of entering the active return state. The factor increases as the time of entering the active return state increases. It is 0 when the active return state is just entered. As the time of entering the active return state increases to the calibrated time threshold, the starting transition factor increases to 1 and remains unchanged. This factor serves as the gain of the final active return force, ensuring smoothness during state switching. The hand feel smoothing factor is calculated based on the steering wheel torque measured by the sensor. The factor decreases as the steering wheel torque increases. When the steering wheel torque is less than the calibrated low-threshold steering wheel torque, the feel smoothing factor is 1; when the steering wheel torque is greater than the calibrated high-threshold steering wheel torque, the feel smoothing factor is 0. This factor, acting as a gain on the final active-righting force, ensures smooth system state transitions when the driver re-intervenes during the active-righting process. This invention enables the active-righting system to transition smoothly in the face of sudden driver intervention, avoiding the driver's sense of jerkiness during state transitions. This improves both driving comfort and safety.

[0083] 3. Considering the issue of misjudgment of the return-to-centering condition, the present invention uses a time window as a starting point and, in combination with steering wheel angle, speed, and torque, proposes a novel time-window-based active return-to-centering state determination mechanism to achieve switching between the steering state and the active return-to-centering state. The steering wheel angle, speed, and torque are used to determine whether the driver is operating the steering wheel. When all the determination conditions are met, a timer accumulates the iteration step. If any of the conditions are not met, the system resets the timer. The system enters the active return-to-center state only when the timer exceeds the time window threshold. The time window eliminates instantaneous state determination and makes it more stable, thereby reducing the misjudgment rate. The present invention accurately determines the driver's return-to-centering intention, switches the active return-to-centering system on and off, and ensures accurate and effective activation timing of the active return-to-center system. It also prevents the active return-to-center system from interfering with the driver's normal steering operation.

[0084] This invention proposes an active steer-by-wire (SWIRE) return method that covers low, medium, and high speed driving scenarios. When the driver indicates a return intention, the steering wheel is returned to the center position, achieving active return control of the SWIRE steering wheel. By designing an active return state determination mechanism, the invention accurately determines the driver's return intention, switching the active return system on and off to prevent the active return system from interfering with the driver's steering operation. To determine the most appropriate return speeds at low, medium, and high speeds, the invention designs a return speed reference model based on the dynamic model of the SWIRE system. This ensures a smooth steering wheel return process, ensuring that the steering wheel return more closely matches the actual tire return, thereby reducing tire wear during the return process and enhancing the driver's comfort experience with the steering wheel return. The invention also incorporates an active return transition mechanism. If the driver suddenly intervenes during the active return process, this mechanism ensures a smooth transition, preventing the steering wheel from causing any jerking sensations to the driver. This prevents the active return system from interfering with the driver's normal steering operation, thereby improving driving comfort and safety. When driving a steer-by-wire vehicle equipped with the active self-centering system, the present invention can assist the driver in centering the vehicle, thereby improving the driver's driving comfort.

[0085] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 It is a structural diagram of a wire-controlled steering system in the prior art.

[0087] Figure 2 This is an overall flow chart of the active correction method provided by one embodiment of the present invention.

[0088] Figure 3 This is a flow chart of a judgment mechanism for entering an active return state provided by an embodiment of the present invention.

[0089] Figure 4 This is a flow chart of a judgment mechanism for exiting the active return state provided by an embodiment of the present invention.

[0090] Figure 5 This is a flow chart for establishing a return speed reference model provided by an embodiment of the present invention.

[0091] Figure 6 This is a flow chart of an active return control module provided by an embodiment of the present invention.

[0092] Figure 7 This is a flow chart of an active aligning torque transition mechanism provided by one embodiment of the present invention.

[0093] Figure 8 This is a structural block diagram of an active righting system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0094] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0095] In the drawings, components with the same structure are denoted by the same numerical numerals, and components with similar structure or function are denoted by similar numerical numerals.

[0096] like Figure 2 As shown, it shows an active correction method, which includes six steps S1 to S6:

[0097] Step S1: Obtain relevant vehicle parameters, steering wheel parameters, model calibrated parameters, and steering wheel angle, speed, and torque parameters. Specific parameters will be described in detail in subsequent steps.

[0098] Step S2: Obtain the driver's steering intention based on the active steering state judgment mechanism based on the time window, and determine whether the current state of the steering wheel requires active steering intervention.

[0099] Step S3, determining whether the system is currently in an active return state. If the system is in an active return state, proceed to the subsequent steps; otherwise, the active return system does not intervene.

[0100] Step S4: obtaining a target steering wheel centering speed according to the centering speed reference model and the current steering wheel angle, and transmitting the target steering wheel centering speed to subsequent steps.

[0101] In step S5, the active return control module uses a control method to obtain the required active return torque based on the current steering wheel speed and the target return speed. This step preliminarily determines the required active return torque, which is then optimized in subsequent steps.

[0102] In step S6, based on the active self-aligning torque transition mechanism, a transition factor is obtained according to the steering wheel torque, and combined with the required active self-aligning torque in step S5, the final active self-aligning torque requested from the road sensing motor is obtained.

[0103] like Figure 3 As shown, further, step S2 can be specifically set as:

[0104] This mechanism divides the system into a steering state and an active self-centering state. Through steps S20, S21, and S22, the system switches between the steering state and the active self-centering state. When the system is in the steering state, the active self-centering system does not interfere with normal steering operations. When the system is in the active self-centering state, the active self-centering system is turned on, and the active self-centering system then calculates the required active self-centering torque and requests the required active self-centering torque from the road sensing motor.

[0105] Furthermore, if the system is currently in the steering state, step S21 is executed to enter the active return state judgment mechanism. When the system meets the following conditions at the same time, it enters the active return state:

[0106] 1) Step S211, determine the absolute value of the steering wheel angle |θ sw |Is it greater than the set return opening angle θ ent , that is, whether |θ is satisfied sw |>θ ent ;

[0107] 2) Step S212: Determine whether the steering wheel is in a stationary or returning state, that is, whether θ sw *ω sw ≤0;

[0108] 3) Step S213, determining the absolute value of the steering wheel speed |ω sw Is | less than the calibration value ω0, that is, whether |ω sw |≤ω0;

[0109] 4) Step S214, determine the absolute value of the steering wheel torque |T h |Is it less than the calibration value T low , that is, whether |T h | <T low .

[0110] 5) Step S215: When the system determines that all four conditions are met, the timer increments the iteration time step. If any of the conditions are not met, the system resets the timer and returns to step S211.

[0111] 6) Step S216, when the timer t count Greater than the time window threshold t ent , the system enters the active return state, otherwise returns to step S211.

[0112] like Figure 4 As shown, further, if the system is currently in the active return state, step S22 is executed to exit the active return state judgment mechanism. The system exits the active return state when one of the following conditions is met:

[0113] 1) Step S221, determine the absolute value of the steering wheel angle |θ sw |Is it less than the set return closing angle θ? ext , that is, whether |θ is satisfied sw |<θ ext ;

[0114] 2) Step S222, determine the absolute value of the steering wheel torque |T h |Is it greater than the calibration value T high , that is, whether |T h |>T high .

[0115] After completing step S2, execute step S3 to determine whether the system is currently in the active return state. If the system is in the active return state, proceed to subsequent steps S4 to S6. Otherwise, the active return system does not intervene and returns to step S2.

[0116] The relevant parameters of this mechanism θ ent ,ω0,T low , t ent ,θ ext 、T high All of them can be obtained through actual vehicle calibration.

[0117] like Figure 5 As shown, further, step S4 can be specifically configured as follows: establishing a return-to-center speed reference model to obtain a target return-to-center speed of the steering wheel at various vehicle speeds, including:

[0118] Step S401: Establish an equivalent dynamic model of the steer-by-wire system. The steer-by-wire system is considered as a rigid body and is equivalent to a second-order system. The moment of inertia and damping of each component are equivalent to the steering wheel assembly. The equivalent dynamic model is as follows:

[0119]

[0120] Where: θ is the steering wheel angle; J is the system equivalent moment of inertia; B is the system equivalent damping coefficient; T mo is the output torque of the road sensing motor; T ao is the output torque of the power assist motor; T h is the steering wheel input torque; T f is the equivalent friction torque of the system; F rack is the equivalent resistance on the rack; i mc 、i amc 、i rc J is the equivalent transmission ratio from the road sensor motor, power steering motor and rack to the steering wheel assembly; sw 、J m 、J amare the rotational inertia of the steering wheel assembly, road sensor motor and power assist motor respectively; M r is the rack mass; B sw 、B m 、B am are the damping coefficients of the steering wheel assembly, road sensor motor, and power assist motor respectively; B r is the rack damping coefficient;

[0121] The relevant parameters required by the equivalent dynamic model of the wire control steering system are: J sw 、J m 、J am 、M r 、B sw 、B m 、B am 、B r 、i mc 、i amc 、i rc 、F rack , where F rack It can be obtained through the relevant mature wire-controlled steering rack force observation and estimation algorithm. The remaining parameters are mechanical parameters and can be obtained by consulting the relevant hardware manual or performing parameter identification tests.

[0122] In step S402, based on an assumed simplified equivalent dynamic model of the steer-by-wire system, the present invention establishes a steering wheel return speed reference model. Based on the equivalent dynamic model of the steer-by-wire system, suitable steering wheel return speeds at low, medium, and high vehicle speeds are determined. The return speed reference model is established based on the following assumptions:

[0123] 1) Due to the mechanical friction torque in the steer-by-wire system, if it is not compensated, the steering wheel angle in the reference model will not be able to return to the center position. Therefore, the present invention believes that during the return process of the speed reference model, the output torque of the steering motor can constantly compensate for the equivalent friction torque of the steering system, that is:

[0124] i amc ·T ao =T f

[0125] 2) During the active return process, the driver takes his hands off the steering wheel and does not input torque to the steering wheel. At the same time, the road sensing motor does not work and does not output torque to the steering wheel, that is:

[0126] T h =T mo =0

[0127] Based on the above assumptions, the equivalent dynamic model of steer-by-wire can be simplified as follows:

[0128]

[0129] Where: θ t is the steering wheel angle of the reference return model during the return process;

[0130] Step S403: Based on the simplified dynamic model, a reference steering wheel return speed is obtained as the target return speed at medium and low speeds. According to the above formula, the steering wheel angle and steering wheel speed at the initial moment are known. Solving the differential equation can obtain the reference return speed at each moment of the steering wheel return in the reference model.

[0131] In step S404, a virtual damping torque is applied at high speeds to obtain a corrected steering wheel reference return speed, which serves as the target return speed at high speeds. When the steering wheel angle is constant, the return torque applied to the vehicle tires increases with vehicle speed. At medium and high speeds, due to excessive return torque, the steering wheel reference return angle calculated using the return speed reference model will experience reverse overshoot oscillation. This phenomenon can significantly endanger driving safety during high-speed driving. Therefore, the present invention designs a compensation module to suppress steering wheel return overshoot and increase the virtual damping torque. The corrected return speed reference model is as follows:

[0132]

[0133] Where T d To compensate for the damping torque, the expression is as follows:

[0134]

[0135] Where: B d To compensate for the damping torque amplitude; a d is the gradient variation coefficient of the damping torque with the steering wheel speed; v0 is the critical vehicle speed between low speed and medium-high speed; b1 and b2 are the adjustment coefficients of the compensation damping torque amplitude with vehicle speed;

[0136] The relevant parameters required for this model are: a d , v0, b1, b2 can all be obtained through calibration.

[0137] like Figure 6 As shown, further, step S5 can be specifically configured as follows: the active return control module is used to obtain the road sense motor output torque required to make the steering wheel return speed track the target return speed, including:

[0138] In step S501 , a dynamic model of the steering wheel assembly may be established according to the mechanical structure of the steering wheel assembly.

[0139] Step S502 : defining a tracking error between the steering wheel speed and the target return speed.

[0140] Step S503 , controlling the steering wheel's return speed by a control method to obtain the output torque of the road sensing motor so that the steering wheel's return speed tracks the target return speed.

[0141] Furthermore, the control method may adopt traditional control methods or modern control methods such as PID control, sliding mode control, fuzzy control, adaptive control and neural network.

[0142] like Figure 7 As shown, further, step S6 can make the transition between the active return state and the steering state natural, thereby reducing the frustration of the steering wheel transmitted to the driver due to the instantaneous state switching. The specific setting includes:

[0143] In step S601, the active self-aligning torque transition mechanism first calculates the starting transition factor K1 based on the time of entering the active self-aligning state. This factor increases as the time of entering the active self-aligning state increases. It is 0 when the active self-aligning state is just entered. As the time of entering the active self-aligning state increases to the calibrated time threshold, the starting transition factor increases to 1 and remains unchanged. The growth curve of the starting transition factor between these two periods can be freely designed.

[0144] In step S602, after calculating the startup transition factor, the active return torque transition mechanism calculates a feel smoothing factor, K2, based on the steering wheel torque measured by the sensor. This factor decreases as the steering wheel torque increases. When the steering wheel torque is less than a calibrated low steering wheel torque threshold, the feel smoothing factor is 1; when the steering wheel torque is greater than a calibrated high steering wheel torque threshold, the feel smoothing factor is 0. When the steering wheel torque is between the high and low thresholds, the curve of the feel smoothing factor versus steering wheel torque can be freely designed.

[0145] Step S603: Calculate the active self-aligning torque transition factor K by combining the startup transition factor and the hand-feel smoothness factor. The active self-aligning torque transition factor is obtained by multiplying the startup transition factor and the hand-feel smoothness factor.

[0146] Step S604 , correcting the output torque of the road sense motor according to the transition factor K. Specifically, the output torque of the road sense motor obtained in step S5 is multiplied by the transition factor K to obtain the final required output torque of the road sense motor.

[0147] like Figure 8 , which shows a structural block diagram of an active return system provided by an embodiment of the present invention, including:

[0148] Acquisition unit: used to obtain relevant vehicle parameters, steering wheel parameters, model calibrated parameters and steering wheel angle, speed, and torque parameters;

[0149] The first judgment unit is used to obtain the driver's return intention based on the active return state judgment mechanism based on the time window, and determine whether the current state of the steering wheel requires active return intervention;

[0150] The second judgment unit is used to judge whether the system is currently in the active return state. If the system is in the active return state, step S4 is performed; otherwise, the active return system does not intervene and returns to the first judgment unit;

[0151] The first calculation unit is used to obtain the target steering wheel return speed according to the return speed reference model and the current steering wheel angle, including

[0152] Establishing a steer-by-wire system dynamics model: Based on the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established using an existing mature steer-by-wire dynamics model establishment method.

[0153] Based on the assumption of simplifying the dynamic model of the wire-controlled steering system, the equivalent dynamic model of the wire-controlled steering system is obtained as the reference model of the return speed.

[0154] The model state is the steering wheel angle θ of the reference self-centering model during the self-centering process t , the model input is the equivalent resistance F on the rack rack ,

[0155] Based on the return speed reference model, the steering wheel reference return speed is obtained as the target return speed at medium and low speeds.

[0156] According to the reference model of the return speed, the steering wheel angle and steering wheel speed at the initial moment are known, and the reference return speed θ of the steering wheel return at each moment in the reference model is obtained by solving the differential equation · t ,

[0157] Add virtual damping torque at high speed, correct the return speed reference model, and obtain the target return speed at high speed based on the corrected model;

[0158] A second calculation unit is used to obtain the required active return torque according to the current steering wheel speed and the target return speed using a control method;

[0159] The third calculation unit is used to obtain a transition factor based on the active return torque transition mechanism according to the steering wheel torque, and combine it with the active return torque required in the second calculation unit to obtain the final active return torque requested to the road sensing motor.

[0160] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for active self-centering of steer-by-wire based on a self-centering speed reference model, characterized in that: include: Step S1, obtaining relevant vehicle parameters, steering wheel mechanical parameters, model calibrated parameters, and steering wheel angle, speed, and torque parameters; Step S2: Obtaining the driver's steering intention based on the active steering state judgment mechanism based on the time window, and determining whether the current state of the steering wheel requires active steering intervention; Step S3, determining whether the system is currently in an active return state. If the system is in an active return state, proceed to step S4; otherwise, the active return system does not intervene and returns to step S2; Step S4, obtaining a target steering wheel return speed based on the return speed reference model and the current steering wheel angle, includes: Step S401: Establish an equivalent dynamics model of the steer-by-wire system: Where: θ is the steering wheel angle; J is the system equivalent moment of inertia; B is the system equivalent damping coefficient; T mo is the output torque of the road sensing motor; T ao is the output torque of the power assist motor; T h is the steering wheel input torque; T f is the equivalent friction torque of the system; F rack is the equivalent resistance on the rack; i mc 、i amc 、i rc J is the equivalent transmission ratio from the road sensor motor, power steering motor and rack to the steering wheel assembly; sw 、J m 、J am are the rotational inertia of the steering wheel assembly, road sensor motor and power assist motor respectively; M r is the rack mass; B sw 、B m 、B am are the damping coefficients of the steering wheel assembly, road sensor motor, and power assist motor respectively; B r is the rack damping coefficient; Among them F rack It can be obtained through relevant mature wire-controlled steering rack force observation and estimation algorithms, and the remaining parameters can be obtained by consulting relevant hardware manuals or performing parameter identification tests; Step S402: Simplify the equivalent dynamics model of the steer-by-wire system and establish a steering wheel return speed reference model: Where: θ t is the steering wheel angle of the reference return model during the return process; Step S403: Based on the simplified dynamic model, a reference steering wheel return speed is obtained as the target return speed at medium and low speeds. According to the above formula, the steering wheel angle and steering wheel speed at the initial moment are known. Solving the differential equation can obtain the reference return speed at each moment of the steering wheel return in the reference model. Step S404: Apply a virtual damping torque at high speed to obtain a corrected steering wheel reference return speed as the target return speed at high speed: Where T d To compensate for the damping torque, the expression is as follows: Where: B d To compensate for the damping torque amplitude; a d is the gradient variation coefficient of the damping torque with the steering wheel speed; v0 is the critical speed of low speed and medium-high speed; b1 and b2 are the adjustment coefficients of the compensation damping torque amplitude with the vehicle speed; parameter a d , v0, b1, and b2 can all be obtained through calibration; Step S5, using a control method to obtain the required active return torque according to the current steering wheel speed and the target return speed; In step S6, based on the active self-aligning torque transition mechanism, a transition factor is obtained according to the time of entering the active self-aligning state and the steering wheel torque, and combined with the active self-aligning torque required in step S5, the final active self-aligning torque requested to the road sensing motor is obtained.

2. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 1, characterized in that: The step S2 includes: The system is divided into a steering state and an active return state. The system switches between the steering state and the active return state through step S20 to judge the current system state, step S21 to enter the active return state, and step S22 to exit the active return state.

3. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 2, characterized in that: When the system is in the steering state, the active return system does not intervene in normal steering operations. When the system is in the active return state, the active return system is turned on, and the active return system then calculates the required active return torque and requests the required active return torque from the road sensing motor.

4. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 2, characterized in that: If the system is currently in the steering state, step S21 is executed to enter the active return state judgment mechanism. When the system meets the following conditions at the same time, it enters the active return state: 1) Step S211, determine the absolute value of the steering wheel angle |θ sw |Is it greater than the set return opening angle θ ent , that is, whether |θ is satisfied sw |>θ ent ; 2) Step S212: Determine whether the steering wheel is in a stationary or returning state, that is, whether θ sw *ω sw ≤0; 3) Step S213, determining the absolute value of the steering wheel speed |ω sw Is | less than the calibration value ω0, that is, whether |ω sw |≤ω0; 4) Step S214, determine the absolute value of the steering wheel torque |T h |Is it less than the calibration value T low , that is, whether |T h | <T low ; 5) Step S215: When the system determines that all four conditions are met, the timer accumulates the iteration time step. If any one of the conditions is not met, the system resets the timer and returns to step S211. 6) Step S216, when the timer t count Greater than the time window threshold t ent When the system enters the active return state, otherwise it returns to step S211. Parameter θ ent ,ω0,T low , t ent Obtained through real vehicle calibration.

5. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 2, characterized in that: If the system is currently in the active return state, step S22 is executed to determine whether to exit the active return state. The system exits the active return state when one of the following conditions is met: 1) Step S221, determine the absolute value of the steering wheel angle |θ sw |Is it less than the set return closing angle θ? ext , that is, whether |θ is satisfied sw |<θ ext ; 2) Step S222, determine the absolute value of the steering wheel torque |T h |Is it greater than the calibration value T high , that is, whether |T h |>T high , After completing step S2, execute step S3 to determine whether the system is currently in the active return state. If the system is in the active return state, proceed to subsequent steps S4 to S6. Otherwise, the active return system does not intervene and returns to step S2. Parameter θ ext 、T high Obtained through real vehicle calibration.

6. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 1, characterized in that: The step S5 includes: Step S501, establishing a dynamic model of the steering wheel assembly according to the mechanical structure of the steering wheel assembly; Step S502, defining a tracking error between the steering wheel speed and the target return speed; Step S503 , controlling the steering wheel's return speed by a control method to obtain the output torque of the road sensing motor so that the steering wheel's return speed tracks the target return speed.

7. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 6, characterized in that: The control method may adopt PID control, sliding mode control, fuzzy control, adaptive control, neural network or modern control method.

8. The active self-centering method for steer-by-wire based on a self-centering speed reference model according to claim 6, characterized in that: The step S6 comprises: In step S601, the active return torque transition mechanism first calculates a start transition factor K1 based on the time it takes to enter the active return state. This factor increases as the time it takes to enter the active return state increases. It is 0 when the active return state is just entered. As the time it takes to enter the active return state increases to a calibrated time threshold, the start transition factor increases to 1 and remains constant. The growth curve of the start transition factor between these two periods can be freely designed. Step S602: After calculating the startup transition factor, the active return torque transition mechanism calculates a feel smoothing factor K2 based on the steering wheel torque measured by the sensor. This factor decreases as the steering wheel torque increases. When the steering wheel torque is less than a calibrated steering wheel torque low threshold, the feel smoothing factor is 1. When the steering wheel torque is greater than a calibrated steering wheel torque high threshold, the feel smoothing factor is 0. When the steering wheel torque is between the high and low thresholds, the curve of the change in the feel smoothing factor with the steering wheel torque can be freely designed. Step S603: Calculate the active self-aligning torque transition factor K by combining the startup transition factor and the hand-feel smoothness factor. The active self-aligning torque transition factor is obtained by multiplying the startup transition factor and the hand-feel smoothness factor. Step S604 , correcting the output torque of the road sense motor according to the transition factor K. Specifically, the output torque of the road sense motor obtained in step S5 is multiplied by the transition factor K to obtain the final required output torque of the road sense motor.

9. A steer-by-wire active self-centering system based on a self-centering speed reference model, the system being used to implement the active self-centering method according to claim 1, characterized in that: include: Acquisition unit: used to obtain relevant vehicle parameters, steering wheel mechanical parameters, model calibrated parameters and steering wheel angle, speed, and torque parameters; The first judgment unit is used to obtain the driver's return intention based on the active return state judgment mechanism based on the time window, and determine whether the current state of the steering wheel requires active return intervention; The second judgment unit is used to judge whether the system is currently in the active return state. If the system is in the active return state, step S4 is performed; otherwise, the active return system does not intervene and returns to the first judgment unit; The first calculation unit is used to obtain a target steering wheel return speed based on the return speed reference model and the current steering wheel angle, including: Establishing a steer-by-wire system dynamics model: Based on the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established using an existing mature steer-by-wire dynamics model establishment method. Based on the assumption of simplifying the steer-by-wire system dynamics model, the equivalent dynamics model of the steer-by-wire system is obtained as the reference model for the return speed. The model state is the steering wheel angle θ of the reference self-centering model during the self-centering process t , the model input is the equivalent resistance F on the rack rack , Based on the return speed reference model, the steering wheel reference return speed is obtained as the target return speed at medium and low speeds. According to the reference model of the return speed, the steering wheel angle and steering wheel speed at the initial moment are known, and the reference return speed θ of the steering wheel return at each moment in the reference model is obtained by solving the differential equation · t , Add virtual damping torque at high speed, correct the return speed reference model, and obtain the target return speed at high speed based on the corrected model; A second calculation unit is used to obtain the required active return torque according to the current steering wheel speed and the target return speed using a control method; The third calculation unit is used to obtain a transition factor based on the active self-aligning torque transition mechanism, according to the time of entering the active self-aligning state and the steering wheel torque, and combine it with the active self-aligning torque required in the second calculation unit to obtain the final active self-aligning torque requested from the road sensing motor.

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