Active return logic design method for steer-by-wire system

Abstract

The invention discloses an active return logic design method for a steer-by-wire system, which comprises the following steps: acquiring state information of a driver and a vehicle, performing decision processing to obtain an active return state flag bit, if the active return state flag bit is to start active return, determining an active return moment according to the state information, and if the active return moment is not to start active return, determining an active return moment; according to the method, accurate control over vehicle steering can be achieved, the accuracy of active return control is improved, and therefore the operation stability of the vehicle and the performance of a steer-by-wire system are improved; in conclusion, the active return control realizes that the steering wheel can automatically and stably return to the middle position after the driver releases the steering wheel by monitoring the vehicle speed and the steering torque of the steering wheel in real time and combining the power-assisted characteristic curve, the closed-loop fuzzy PID control strategy and the return compensation mode, so that the driving stability and comfort of the vehicle are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of active return of a wire-controlled steering system, and in particular to an active return logic design method of a wire-controlled steering system. Background Art

[0002] With the development of science and technology, smart cars have become an important direction for the development of future cars. As one of the core technologies of smart cars, the wire-controlled steering system eliminates the mechanical connection between the steering wheel and the steering assembly, and transmits control commands through electrical signals to achieve the steering of the steering actuator. This system can flexibly design its force transmission and angle transmission characteristics to improve the safety and comfort of the vehicle.

[0003] A common active return control strategy is a closed-loop PID (proportional-integral-differential) control based on the steering wheel angle. This strategy compares the deviation between the target steering wheel position and the actual steering wheel position, outputs a control voltage, and enables the power-assisted motor to bring the steering wheel to the neutral position.

[0004] There are some problems with the existing active return control method of the wire-controlled steering system, such as high-speed return overshoot and low-speed return insufficient. These problems will cause the vehicle's handling stability to be affected due to factors such as its own structure and system friction when the vehicle is driving at different speeds and road conditions. Therefore, a more accurate and stable active return logic design method is needed to improve the performance of the wire-controlled steering system. Summary of the invention

[0005] The present invention aims to provide a simple, efficient and reliable method for designing active self-centering logic of a steer-by-wire system, so as to improve the self-centering performance and driving safety of the system, and to improve the working condition adaptability and driving safety of a steer-by-wire vehicle.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for designing active return logic of a wire-controlled steering system comprises the following steps:

[0008] S1. Obtaining basic data for active return control, including driver and vehicle status information;

[0009] S2. According to the vehicle speed and steering torque, the system calculates the required power assist value through the preset power assist characteristic curve, and then determines the power assist current that the power assist motor should generate;

[0010] S3, performing active return judgment, making a decision on the state information through a wire-controlled steering active return state decision, and obtaining an active return state flag;

[0011] S4, calculating the active return torque, and determining whether to perform active return according to the active return flag. If active return is performed, the active return torque is calculated;

[0012] S5. Apply a certain self-aligning torque through the power-assisting motor to assist in active self-alignment.

[0013] As a further feature of the method of the present invention, in S1, the state information includes vehicle speed, steering wheel speed, steering wheel angle and steering wheel torque.

[0014] As a further step in the method of the present invention, in S1, the vehicle speed and the steering torque of the steering wheel are monitored in real time by a vehicle speed sensor and a steering wheel torque sensor.

[0015] As a further step in the method of the present invention, in S1, the acquired information is processed accordingly, the steering wheel angle is processed in a dead zone, and the steering wheel speed and the steering wheel torque are low-pass filtered.

[0016] As a further step in the method of the present invention, S31, determining whether the vehicle is in a stable driving state, if the vehicle is in a stable driving state, proceeding to the next step, if the vehicle is in an unstable driving state (such as rapid acceleration, rapid deceleration, sharp turn, etc.), no active return control is performed;

[0017] S32, determining whether the steering wheel is near the neutral position, if the steering wheel is near the neutral position (e.g., within a range of ±5°), proceeding to the next step, if the steering wheel deviates far from the neutral position, no active return control is performed;

[0018] S33: determining whether the driver has released the steering wheel; if the driver has released the steering wheel, performing active centering control; if the driver is still holding the steering wheel, not performing active centering control.

[0019] As a further step in the method of the present invention, in S4, the calculation method of active return is to calculate the angular error between the current position of the steering wheel and the zero position, and output the target return speed and the motor target return torque respectively through angle dead zone, angle loop fuzzy PI and speed loop fuzzy PI control, thereby driving the motor to realize active return of the steering wheel.

[0020] As a further step in the method of the present invention, S51, when driving at a low speed, the ECU (electronic control unit) controls the power-assisting motor to apply a certain return-to-center torque to help the steering system return to center;

[0021] S52. When the vehicle is traveling at high speed, the ECU will appropriately reduce the power-assist torque and use the resistance torque generated by the power-assist motor itself to apply corresponding return damping to the steering system to avoid excessive return and improve system stability.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention proposes an active return logic design method for a wire-controlled steering system, which collects status information of the driver and the vehicle and performs decision processing to obtain an active return status flag. If the active return status flag is to turn on active return, the active return torque is determined according to the status information, and then the active return target torque is determined, and the motor is driven and controlled to complete the vehicle steering. This method can achieve precise control of vehicle steering, improve the accuracy of active return control, so as to improve the return performance and driving safety of the system, thereby improving the vehicle's handling stability and the performance of the wire-controlled steering system, and improving the working condition adaptability and driving safety of the wire-controlled steering vehicle;

[0023] The active return control monitors the vehicle speed and steering wheel steering torque in real time, combines the power assist characteristic curve and closed-loop fuzzy PID control strategy, and the return compensation mode, so that the steering wheel can automatically and smoothly return to the middle position after the driver releases the steering wheel, thereby ensuring the vehicle's driving stability and comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a block diagram of active return control in the method of the present invention;

[0025] Figure 2 It is the fuzzy PID control flow chart in the method of the present invention;

[0026] Figure 3 Generate a block diagram for the embedded code in the method of the present invention;

[0027] Figure 4 This is the active return test in the method of the present invention. Figure 1 ;

[0028] Figure 5 This is the active return test in the method of the present invention. Figure 2 . DETAILED DESCRIPTION

[0029] The content of the present invention can be more easily understood by selecting the following detailed description of the preferred implementation method of the present invention and the embodiments included. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. When there is a conflict, the definition in this specification shall prevail.

[0030] As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0031] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0032] Singular forms include plural references unless the context clearly indicates otherwise. "Optional" or "either" means that the subsequently described event or incident may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0033] Approximate terms in the specification and claims are used to modify quantities, indicating that the present invention is not limited to the specific quantity, but also includes acceptable and modified parts close to the quantity without causing changes in the relevant basic functions. Accordingly, the use of "about", "approximately", etc. to modify a numerical value means that the present invention is not limited to the exact numerical value. In some examples, the approximate terms may correspond to the accuracy of the instrument for measuring the numerical value. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all subranges contained therein.

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0035] Embodiment 1

[0036] Active return control is an advanced technology used in steer-by-wire (SBW) systems. Its main purpose is to automatically return the steering wheel to the middle position through motor assistance after the driver releases the steering wheel, thereby maintaining the vehicle's straight-line driving state and improving driving stability and comfort.

[0037] The purpose of this patent is to provide a method for designing active return logic for a wire-controlled steering system, which can be based on the actual driving state of the vehicle and the driver's operating intention, as well as the phenomenon of insufficient vehicle return at low speed and overshoot of vehicle return at high speed in the prior art.

[0038] This method collects the status information of the driver and the vehicle, and performs decision processing to obtain the active return state flag. If the active return state flag is to turn on active return, the active return torque is determined according to the status information, and then the active return target torque is determined, and the motor is driven and controlled to complete the vehicle steering. This method can achieve precise control of vehicle steering, improve the accuracy of active return control, and thus improve the vehicle's handling stability and the performance of the wire control steering system.

[0039] Reference Figure 1-Figure 2 , specifically including the following steps: First, the system monitors the vehicle speed in real time through the vehicle speed sensor, and monitors the steering wheel speed, steering wheel angle and steering wheel torque in real time through the steering wheel torque sensor. These signals are the basic data for active return control;

[0040] Then, the acquired information is processed accordingly, such as the dead zone processing of the steering wheel angle, the low-pass filtering of the steering wheel speed and steering wheel torque, etc.

[0041] Next, an active return judgment is performed, and the state information is processed by a wire-controlled steering active return state decision to obtain an active return state flag.

[0042] In the method of the present invention, the decision on the active return state of the wire control steering can be made according to the following algorithm: determine whether the vehicle is in a stable driving state. If the vehicle is in a stable driving state, proceed to the next step; if the vehicle is in an unstable driving state (such as sudden acceleration, sudden deceleration, sharp turn, etc.), no active return control is performed, and it is determined whether the steering wheel is near the center position. If the steering wheel is near the center position (such as within the range of ±5°), proceed to the next step; if the steering wheel deviates far from the center position, no active return control is performed, and it is determined whether the driver has released the steering wheel. If the driver releases the steering wheel, active return control is performed; if the driver still holds the steering wheel, no active return control is performed;

[0043] Then, whether to perform active return is determined according to the active return flag. If active return is performed, the active return torque is calculated;

[0044] The calculation method of active return is to calculate the angle error between the current position of the steering wheel and the zero position, and output the target return speed and the motor target return torque respectively through the angle dead zone, angle loop fuzzy PI and speed loop fuzzy PI control, so as to drive the motor to realize the active return of the steering wheel;

[0045] Then, according to the vehicle speed and steering torque, the system calculates the required power assist value through the preset power assist characteristic curve, and then determines the power assist current that the power assist motor should generate. The quality of the power assist characteristic curve directly determines the steering lightness, steering road feel and handling stability of the SBW system.

[0046] When driving at low speed, the ECU (electronic control unit) will control the power-assist motor to apply a certain self-centering torque to help the steering system return to center. When the vehicle is driving at high speed, the ECU will appropriately reduce the power-assist torque and use the resistance torque generated by the power-assist motor itself to apply corresponding self-centering damping to the steering system to avoid excessive self-centering and improve system stability.

[0047] A common active return control strategy is a closed-loop PID (proportional-integral-differential) control based on the steering wheel angle. This strategy compares the deviation between the target steering wheel position and the actual steering wheel position, outputs a control voltage, and causes the power-assist motor to bring the steering wheel to the center position.

[0048] Based on the above, in order to compensate for the loss of returning force caused by steering system resistance, steering system inertia, motor inertia, etc. during the vehicle's returning process, the system will also adopt a returning compensation mode to further improve the vehicle's returning performance.

[0049] In summary, active return control achieves the goal of automatically and smoothly returning the steering wheel to the middle position after the driver releases the steering wheel by real-time monitoring of vehicle speed and steering wheel steering torque, combined with the power assist characteristic curve and closed-loop fuzzy PID control strategy, as well as the return compensation mode, thereby ensuring the vehicle's driving stability and comfort.

[0050] Embodiment 2

[0051] In order to verify the actual effect of the method proposed in the present invention, the model is generated into embedded code through the following steps: Figure 3 ; Flash the code into the controller through the flashing software and perform an active return test. The test results are shown in the figure below. Figure 4 , Figure 4 Turn left (720°10km / h), Figure 5 , Figure 5 Right (720°10km / h), it can be seen from the figure that the residual angle of return is about 1 degree, and the return time is about 3.5s. According to the return standard, the residual is ≤10 degrees, and the return time is 2-4s. This design strategy meets the requirements.

[0052] The examples referred to herein are merely illustrative and are used to explain some features of the method of the present invention. The appended claims are intended to claim the widest possible range that can be imagined, and the embodiments presented herein are only illustrations of selected implementations according to the combination of all possible embodiments. Therefore, it is the applicant's intention that the appended claims are not limited by the selection of examples that illustrate the features of the present invention. Some numerical ranges used in the claims also include sub-ranges within them, and changes in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for designing active return logic of a wire-controlled steering system, characterized in that: The following steps are involved: S1. Obtaining basic data for active return control, including driver and vehicle status information; S2. According to the vehicle speed and steering torque, the system calculates the required power assist value through the preset power assist characteristic curve, and then determines the power assist current that the power assist motor should generate; S3, performing active return judgment, making a decision on the state information through a wire-controlled steering active return state decision, and obtaining an active return state flag; S4, calculating the active return torque, and determining whether to perform active return according to the active return flag. If active return is performed, the active return torque is calculated; S5. Apply a certain self-aligning torque through the power-assisting motor to assist in active self-alignment.

2. The active return logic design method of a wire-controlled steering system according to claim 1, characterized in that: In S1, the state information includes vehicle speed, steering wheel speed, steering wheel angle and steering wheel torque.

3. The active return logic design method of a wire-controlled steering system according to claim 2, characterized in that: In S1, the vehicle speed and steering torque of the steering wheel are monitored in real time through the vehicle speed sensor and the steering wheel torque sensor.

4. The active return logic design method of a wire-controlled steering system according to claim 3, characterized in that: In S1, the acquired information is processed accordingly, the steering wheel angle is processed in the dead zone, and the steering wheel speed and steering wheel torque are low-pass filtered.

5. The active return logic design method of a steer-by-wire system according to claim 1, characterized in that: S31, determining whether the vehicle is in a stable driving state, if the vehicle is in a stable driving state, proceeding to the next step, if the vehicle is in an unstable driving state, not performing active return control; S32, determining whether the steering wheel is near the neutral position, if the steering wheel is near the neutral position, proceeding to the next step, if the steering wheel deviates far from the neutral position, not performing active return control; S33: determining whether the driver has released the steering wheel; if the driver has released the steering wheel, performing active centering control; if the driver is still holding the steering wheel, not performing active centering control.

6. The active return logic design method of a steer-by-wire system according to claim 1, characterized in that: In S4, the calculation method of active return is to calculate the angular error between the current position of the steering wheel and the zero position, and output the target return speed and the motor target return torque respectively through the angle dead zone, angle loop fuzzy PI and speed loop fuzzy PI control, so as to drive the motor to realize the active return of the steering wheel.

7. The active return logic design method of a steer-by-wire system according to claim 1, characterized in that: S51: When driving at low speed, the ECU will control the power-assisting motor to apply a certain return-to-center torque to help the steering system return to center; S52. When the vehicle is traveling at high speed, the ECU will appropriately reduce the power-assist torque and use the resistance torque generated by the power-assist motor itself to apply corresponding return damping to the steering system to avoid excessive return and improve system stability.

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