Steering-by-wire active return method based on return rotating speed reference model

Abstract

The invention discloses a steering-by-wire active return method based on a return rotating speed reference model, and relates to the field of automobile steering wheel active return. Acquiring a return intention of the driver according to an active return state judgment mechanism based on a time window; obtaining a target steering wheel aligning rotating speed according to the aligning rotating speed reference model and the current steering wheel rotating angle; acquiring required active aligning torque according to the current rotating speed of the steering wheel and the target aligning rotating speed by using a control method; and based on the active aligning torque transition mechanism, obtaining the final active aligning torque requested from the road sensing motor. According to the method, the return rotating speed reference model is designed based on the steering-by-wire system dynamics model, so that the smooth steering wheel return process is achieved, driving scenes of low, medium and high vehicle speeds are covered, and the comfort experience of a driver for steering wheel return is enhanced.

Description

Technical Field

[0001] The 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 automobile technology, steer-by-wire technology has gradually emerged as an advanced technology in the field of driving control, and has attracted more and more attention from automakers and many consumers. Compared with the traditional mechanical steering system, the steer-by-wire system eliminates the mechanical connection between the steering wheel and the steering wheel, and introduces an electronic control unit, a road sensor motor and a steering motor, so that the steering of the car is controlled by electrical signals instead of mechanical connection devices. Its flexible control method and fast and accurate response characteristics are highly in line with the development needs of modern automobile electrification and intelligence.

[0003] Figure 1 The schematic diagram of the structure of the wire steering system is mainly composed of three parts: the steering wheel assembly, the steering actuator assembly and the main controller. The steering wheel assembly includes the steering wheel, the steering wheel angle sensor, the torque sensor and the road sense simulation motor. Its main function is to transmit the driver's steering intention to the wire steering main controller, and at the same time receive the torque signal transmitted by the main controller to provide the driver with the corresponding road sense information. The steering actuator assembly includes the steering actuator motor, the front wheel steering mechanism components and related sensors, etc. Its function is to receive the instructions of the main controller to control the rotation of the steering wheel to realize the driver's steering intention.

[0004] Since the mechanical connection between the steering wheel and the steering wheel is cut off, the self-centering torque on 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, which increases the driver's self-centering burden and has a certain impact on driving comfort. To solve this problem, an active self-centering module needs to be designed. After detecting that the driver's hand is off the steering wheel, the road sensing motor outputs torque to control the steering wheel to actively return to the center position.

[0005] Active return technology faces some key problems. For example, how to design an active return condition judgment mechanism to accurately judge the driver's steering intention, so as to determine the opening and closing of the active return system; how to determine the most appropriate return speed of the steering wheel during the return process at different vehicle speeds, so that the steering actuator and the steering wheel are coordinated and the vehicle has a good return posture; how to control the return process of the steering wheel so that the return process of the steering wheel has a high degree of smoothness; how to make the active return process of the steering wheel adapt to the sudden intervention of the driver to prevent the active return system from causing discomfort to the driver. The above problems are the biggest obstacles to the use of active return methods in wire-controlled steering systems. Therefore, designing an active return method with accurate return condition judgment, appropriate return speed at various vehicle speeds, smooth return process and natural transition in the face of driver intervention is the key to solving the above problems.

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

[0007] 1. It is difficult to design the appropriate steering wheel return speed at each vehicle speed: It is difficult to determine the most appropriate return speed for the steering wheel when returning to each state at each vehicle speed, 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 to fluctuate when entering and exiting the active return state due to the sudden application or unloading of the active return torque, which brings 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 lets go, 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 return method with accurate return condition judgment, appropriate return speed at various vehicle speeds, smooth return process and natural transition when facing driver intervention. Summary of the invention

[0011] To achieve the above objectives, the present invention provides an active return method with accurate return condition judgment, appropriate return speed at various vehicle speeds, smooth return 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 wire-controlled steering system 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 return intention according to the active return state judgment mechanism based on the time window, and judging whether the current state of the steering wheel requires active return intervention;

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

[0016] Step S4, obtaining a 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 wire steering system. The wire steering system and are regarded as rigid bodies, and are equivalent to a second-order system. The moment of inertia and damping of each component are equivalent to the steering wheel assembly, and its 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 sensing motor, power assist motor and rack to the steering wheel assembly; sw , J m , J am are the rotational inertia of the steering wheel assembly, the road sensing motor and the 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 sensing motor and power assist motor respectively; B r is the rack damping coefficient;

[0020] The relevant parameters required by the equivalent dynamics model of the wire control steering system are: 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, which can be obtained by consulting the relevant hardware manual or by performing parameter identification tests.

[0021] Step S402, based on the assumption of a simplified equivalent dynamic model of the wire-controlled steering system, the present invention establishes a steering wheel return speed reference model, determines the more appropriate steering wheel return speeds at low, medium and high vehicle speeds based on the equivalent dynamic model of the wire-controlled steering system, and establishes the return speed reference model based on the following assumptions:

[0022] 1) Due to the existence of mechanical friction torque in the wire control steering system, if no compensation is given, 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 return speed reference model, the output torque of the steering motor can always 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 wire control steering can be simplified as:

[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, the reference return speed of the steering wheel 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. By solving the differential equation, the reference return speed of the steering wheel at each moment in the reference model can be obtained.

[0030] Step S404, a virtual damping torque is applied at high speed to obtain a corrected reference steering wheel return speed as the target return speed at high speed. When the steering wheel angle is constant, the return torque applied to the vehicle tire increases with the increase of the vehicle speed. At medium and high speeds, due to the excessive return torque, the reference steering wheel return angle calculated by the return speed reference model will have reverse overshoot oscillation. This phenomenon will greatly endanger driving safety during high-speed driving. Therefore, the present invention designs a compensation module to suppress the return overshoot of the steering wheel 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 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 the 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 self-centering torque according to the current steering wheel speed and the target self-centering speed;

[0038] Step S6, based on the active self-aligning torque transition mechanism, obtain the transition factor according to the time of entering the active self-aligning state and the steering wheel torque, and combine the active self-aligning torque required in step S5 to obtain the final active self-aligning torque requested to the road sensing motor.

[0039] In an application scenario, the 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 by judging the current system state in step S20, entering the judgment mechanism of the active return state in step S21, and exiting the judgment mechanism of the active return state in step S22.

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

[0043] 1) Step S211, determining 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, determining 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 the above 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] Further, if the system is currently in the active return state, the judgment mechanism of exiting the active return state is executed in step S22. When one of the following conditions is met, the system exits the active return state:

[0051] 1) Step S221, determining 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, determining 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, step S3 is executed to determine whether the system is currently in an active return state. If the system is in an active return state, subsequent steps S4 to S6 are performed. 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 an application scenario, the 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 return speed of the steering wheel by a control method to obtain the output torque of the road sensing motor so that the return speed of the steering wheel 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 an application scenario, the step S6 may be specifically configured as follows:

[0062] include,

[0063] Step S601, the active self-aligning torque transition mechanism first calculates the start transition factor K1 according to the time of entering the active self-aligning state. The factor increases as the time of entering the active self-aligning state increases. When the active self-aligning state is just entered, it is 0. As the time of entering the active self-aligning state increases to a calibrated time threshold, the start transition factor increases to 1 and remains unchanged. The growth curve of the start transition factor between these two periods can be freely designed.

[0064] Step S602, after calculating the start transition factor, the active return torque transition mechanism calculates the hand feel smoothing factor K2 according to 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 steering wheel torque low threshold, the hand feel smoothing factor is 1. When the steering wheel torque is greater than the calibrated steering wheel torque high threshold, the hand feel smoothing factor is 0. When the steering wheel torque is between the high and low thresholds, the hand feel smoothing factor versus steering wheel torque change curve can be freely designed.

[0065] Step S603, combining the start-up transition factor and the hand-feel smoothness factor, calculating the active self-aligning torque transition factor K, where the active self-aligning torque transition factor is obtained by multiplying the start-up 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, multiplying the output torque of the road sense motor obtained in step S5 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 according to the active return state judgment mechanism based on the time window, and judge 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 an active return state. If the system is in an 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: According to the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established by using an existing mature steer-by-wire dynamics model establishment method.

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

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

[0075] Based on the reference model of the return speed, the reference return speed of the steering wheel 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 according to the corrected model;

[0078] The second calculation unit is used to obtain the required active return torque according to the current steering wheel speed and the target return speed by 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 obtain the final active self-aligning torque requested to the road sensing motor in combination with the active self-aligning torque required in the second calculation unit.

[0080] It can be seen from the above technical solution that the present invention discloses a method and system for active self-centering of wire-controlled steering based on a self-centering speed reference model, and its beneficial effects include:

[0081] 1. Considering the problem that it is difficult to design a suitable steering wheel return speed at each vehicle speed, the present invention takes the dynamic physical model of the vehicle and the steering system as the starting point, and designs a return speed reference model based on the wire steering system dynamic model 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 wire steering system dynamic model, ignores the existence of mechanical friction, obtains the rack force through the rack force observation estimation algorithm or related dynamic calculation, and then obtains the reference return speed of the steering wheel return state at each vehicle speed through the wire steering system dynamic model, 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 return condition of the steering wheel is closer to the actual return condition of the tire, thereby reducing the wear of the tire 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 start-up transition factor using the time of entering the active return state, and designs a hand-feel smoothness factor using the steering wheel torque measured by the sensor, and uses these two factors to achieve smooth transition. The present invention designs a start-up transition factor and a hand-feel smoothness factor, wherein the start-up transition factor is calculated based on the time of entering the active return state, and the factor increases as the time of entering the active return state increases. It is 0 when the active return state is just entered, and as the time of entering the active return state increases to the calibrated time threshold, the start-up 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 smoothness factor is calculated based on the steering wheel torque measured by the sensor, and the factor decreases as the steering wheel torque increases. When the steering wheel torque is less than the calibrated steering wheel torque low threshold, the hand feel smoothing factor is 1; when the steering wheel torque is greater than the calibrated steering wheel torque high threshold, the hand feel smoothing factor is 0. This factor, as the gain of the final active return force, ensures that the system state switches smoothly when the driver re-intervenes during the active return process. The present invention enables the active return system to transition naturally in the face of the driver's sudden intervention, avoiding the active return system giving the driver a sense of frustration when switching states. It improves driving comfort and also improves driving safety.

[0083] 3. Considering the problem of misjudgment of the return-to-center condition, the present invention takes the time window as the starting point, combines the steering wheel angle, speed, and torque, and proposes a new active return-to-center state judgment mechanism based on the time window to realize the mutual switching of the steering state and the active return-to-center state. The steering wheel angle, speed, and torque are used to determine whether the driver is operating the steering wheel. When the judgment conditions are met, the timer accumulates the iteration step. If any one of the conditions is not met, the system clears the timer. When the timer is greater than the time window threshold, the system enters the active return-to-center state. The time window makes the state judgment not instantaneous and more stable, thereby reducing the misjudgment rate. The present invention realizes the accurate judgment of the driver's return-to-center intention, switches the opening and closing of the active return-to-center system, and makes the opening timing of the active return-to-center system accurate and effective. At the same time, it also avoids the influence of the active return-to-center system on the normal steering operation of the driver. The present invention realizes the accurate judgment of the driver's return-to-center intention, switches the opening and closing of the active return-to-center system, and makes the opening timing of the active return-to-center system accurate and effective. At the same time, it also avoids the influence of the active return-to-center system on the normal steering operation of the driver.

[0084] The present invention proposes a method for active return of wire steering, which covers driving scenarios of low, medium and high vehicle speeds, and returns the steering wheel to the middle position when the driver has the intention to return, thereby realizing the control of active return of the wire steering wheel. By designing an active return state judgment mechanism, the present invention realizes accurate judgment of the driver's return intention, so as to switch the opening and closing of the active return system and prevent the active return system from interfering with the driver's steering operation. In order to determine the most suitable return speed at low, medium and high vehicle speeds, the present invention designs a return speed reference model based on the dynamic model of the wire steering system to realize a smooth steering wheel return process, so that the return of the steering wheel is closer to the actual return of the tire, thereby reducing the wear of the tire during the return process and enhancing the driver's comfort experience of the steering wheel return. The present invention also designs an active return transition mechanism. When the driver suddenly intervenes in the active return process, the mechanism can make the system transition naturally, avoid the steering wheel giving the driver a sense of frustration, thereby avoiding the influence of the active return system on the driver's normal steering operation, and improving the 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 driving comfort of the driver.

[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 It is an overall flow chart of the active correction method provided by an embodiment of the present invention.

[0088] Figure 3 It 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 It 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 It is a flow chart of establishing a return speed reference model provided by an embodiment of the present invention.

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

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

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

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

[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 from S1 to S6:

[0097] Step S1, obtaining relevant vehicle parameters, steering wheel parameters, model calibrated parameters and steering wheel angle, speed, and torque parameters. The specific parameters are described in detail in subsequent steps.

[0098] Step S2, according to the active return state judgment mechanism based on the time window, the driver's return intention is obtained, and it is judged whether the current state of the steering wheel requires active return intervention.

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

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

[0101] Step S5, the active return control module uses a control method to obtain the required active return torque according to the current steering wheel speed and the target return speed. This step preliminarily determines the required active return torque, and optimizes this torque in subsequent steps.

[0102] Step S6, based on the active self-aligning torque transition mechanism, obtain the transition factor according to the steering wheel torque, and combine it with the required active self-aligning torque in step S5 to obtain the final active self-aligning torque requested to the road sensing motor.

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

[0106] 1) Step S211, determining 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, determining 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 the above 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.

[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. When one of the following conditions is met, the system exits the active return state:

[0113] 1) Step S221, determining 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, determining 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, step S3 is executed to determine whether the system is currently in an active return state. If the system is in an active return state, subsequent steps S4 to S6 are performed. Otherwise, the active return system does not intervene and returns to step S2.

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

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

[0118] Step S401, establish an equivalent dynamic model of the wire steering system. The wire steering system and are regarded as rigid bodies, and are equivalent to a second-order system. The moment of inertia and damping of each component are equivalent to the steering wheel assembly, and its 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 sensing motor, power assist motor and rack to the steering wheel assembly; sw , J m , J amare the rotational inertia of the steering wheel assembly, the road sensing motor and the 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 sensing motor and power assist motor respectively; B r is the rack damping coefficient;

[0121] The relevant parameters required by the equivalent dynamics model of the wire control steering system are: 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, which can be obtained by consulting the relevant hardware manual or by performing parameter identification tests.

[0122] Step S402, based on the assumption of a simplified equivalent dynamic model of the wire-controlled steering system, the present invention establishes a steering wheel return speed reference model, determines the more appropriate steering wheel return speeds at low, medium and high vehicle speeds based on the equivalent dynamic model of the wire-controlled steering system, and establishes the return speed reference model based on the following assumptions:

[0123] 1) Due to the existence of mechanical friction torque in the wire control steering system, if no compensation is given, 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 return speed reference model, the output torque of the steering motor can always 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 wire control steering can be simplified as:

[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, the reference return speed of the steering wheel 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. By solving the differential equation, the reference return speed of the steering wheel at each moment in the reference model can be obtained.

[0131] Step S404, a virtual damping torque is applied at high speed to obtain a corrected reference steering wheel return speed as the target return speed at high speed. When the steering wheel angle is constant, the return torque applied to the vehicle tire increases with the increase of the vehicle speed. At medium and high speeds, due to the excessive return torque, the reference steering wheel return angle calculated by the return speed reference model will have reverse overshoot oscillation. This phenomenon will greatly endanger driving safety during high-speed driving. Therefore, the present invention designs a compensation module to suppress the return overshoot of the steering wheel 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 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 the 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 sensing motor output torque required to make the steering wheel return speed track the target return speed, including:

[0138] 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 return speed of the steering wheel by a control method to obtain the output torque of the road sensing motor so that the return speed of the steering wheel 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, and its specific configuration includes:

[0143] Step S601, the active self-aligning torque transition mechanism first calculates the start transition factor K1 according to the time of entering the active self-aligning state. The 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 start transition factor increases to 1 and remains unchanged. The growth curve of the start transition factor between these two values ​​can be freely designed.

[0144] Step S602, after calculating the start transition factor, the active return torque transition mechanism calculates the hand feel smooth factor K2 according to the steering wheel torque measured by the sensor, and the factor decreases as the steering wheel torque increases. When the steering wheel torque is less than the calibrated steering wheel torque low threshold, the hand feel smooth factor is 1; when the steering wheel torque is greater than the calibrated steering wheel torque high threshold, the hand feel smooth factor is 0; when the steering wheel torque is between the high and low thresholds, the hand feel smooth factor can be freely designed along with the steering wheel torque change curve.

[0145] Step S603: combining the start-up transition factor and the hand-feel smoothness factor, calculate the active self-aligning torque transition factor K. The active self-aligning torque transition factor is obtained by multiplying the start-up 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, multiplying the output torque of the road sense motor obtained in step S5 by the transition factor K to obtain the final required output torque of the road sense motor.

[0147] like Figure 8 As shown, it 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 according to the active return state judgment mechanism based on the time window, and judge 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 an active return state. If the system is in an 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: According to the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established by using an existing mature steer-by-wire dynamics model establishment method.

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

[0154] The model state quantity 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 reference model of the return speed, the reference return speed of the steering wheel 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 according to the corrected model;

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

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

[0160] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for active self-centering of wire-controlled steering 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 return intention according to the active return state judgment mechanism based on the time window, and judging whether the current state of the steering wheel requires active return intervention; Step S3, determining whether the system is currently in an active return state, if the system is in an active return state, proceeding 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 according to the return speed reference model and the current steering wheel angle, including: Step S401, establishing an equivalent dynamics model of a 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 sensing motor, power assist motor and rack to the steering wheel assembly; sw , J m , J am are the rotational inertia of the steering wheel assembly, the road sensing motor and the 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; where 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 by performing parameter identification tests; Step S402, simplifying the equivalent dynamics model of the steer-by-wire system and establishing 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, the reference return speed of the steering wheel 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. By solving the differential equation, the reference return speed of the steering wheel at each moment in the reference model can be obtained. Step S404: applying a virtual damping torque at high speed to obtain a corrected reference steering wheel 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 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 self-centering torque according to the current steering wheel speed and the target self-centering speed; Step S6, based on the active self-aligning torque transition mechanism, obtain the transition factor according to the time of entering the active self-aligning state and the steering wheel torque, and combine the active self-aligning torque required in step S5 to obtain the final active self-aligning torque requested to the road sensing motor.

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 comprises: 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 by judging the current system state in step S20, entering the judgment mechanism of the active return state in step S21, and exiting the judgment mechanism of the active return state in step S22.

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 the normal steering operation. 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, determining 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, determining 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 the above 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, the judgment mechanism for exiting the active return state is executed in step S22. When one of the following conditions is met, the system exits the active return state: 1) Step S221, determining 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, determining 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, step S3 is executed to determine whether the system is currently in an active return state. If the system is in an active return state, subsequent steps S4 to S6 are performed. 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 comprises: 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 return speed of the steering wheel by a control method to obtain the output torque of the road sensing motor so that the return speed of the steering wheel 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: Step S601, the active self-aligning torque transition mechanism first calculates the start transition factor K1 according to the time of entering the active self-aligning state. The factor increases as the time of entering the active self-aligning state increases. When the active self-aligning state is just entered, it is 0. As the time of entering the active self-aligning state increases to a calibrated time threshold, the start transition factor increases to 1 and remains unchanged. The growth curve of the start transition factor between these two periods can be freely designed. Step S602, after calculating the start transition factor, the active return torque transition mechanism calculates the hand feel smoothing factor K2 according to 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 steering wheel torque low threshold, the hand feel smoothing factor is 1. When the steering wheel torque is greater than the calibrated steering wheel torque high threshold, the hand feel smoothing factor is 0. When the steering wheel torque is between the high and low thresholds, the hand feel smoothing factor versus steering wheel torque change curve can be freely designed. Step S603, combining the start-up transition factor and the hand-feel smoothness factor, calculating the active self-aligning torque transition factor K, where the active self-aligning torque transition factor is obtained by multiplying the start-up 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, multiplying the output torque of the road sense motor obtained in step S5 by the transition factor K to obtain the final required output torque of the road sense motor.

9. A wire-controlled steering active return system based on a return speed reference model, 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 according to the active return state judgment mechanism based on the time window, and judge 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 an active return state. If the system is in an 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 according to a return speed reference model and a current steering wheel angle, including: Establishing a steer-by-wire system dynamics model: According to the relevant mechanical parameters of the steer-by-wire system obtained in step S1, the steer-by-wire system dynamics model is established by using an existing mature steer-by-wire dynamics model establishment method. Based on the assumption of simplifying the dynamic model of the steer-by-wire system, the equivalent dynamic model of the steer-by-wire system is obtained as the reference model of the return speed. The model state quantity 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 reference model of the return speed, the reference return speed of the steering wheel 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 differential equation is solved to obtain the reference return speed of the steering wheel at each moment in the reference model. Add virtual damping torque at high speed, correct the return speed reference model, and obtain the target return speed at high speed according to the corrected model; The second calculation unit is used to obtain the required active return torque according to the current steering wheel speed and the target return speed by using a control method; The third calculation unit is used to calculate the active return torque transition mechanism according to the active return state. The transition factor is obtained by combining the time and steering wheel torque, and the active return torque required in the second calculation unit. The final active return torque requested from the road sensing motor is obtained.

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