Steer-by-wire system and control method

Abstract

The invention discloses a steer-by-wire system and a control method, and particularly relates to the technical field of steering control units, after the system is initialized, a motor enters a current closed-loop mode, and motor torque is applied to enable a rack to move leftwards or rightwards at a constant speed; when the motor torque is larger than the threshold value and the motor angle does not change any more, the point A < n >, the motor angle x < n > and the number of turns rn of the motor are recorded; if n is not greater than the threshold value, changing the torque direction of the motor to enable the rack to move reversely; otherwise, according to the recorded number of turns rn of the motor and the angle xn of the motor, the total angle of rotation of the motor between every two adjacent point positions is calculated, and the total stroke angle range S of the rack is obtained; in the current loop control mode, applying a reverse direction torque to enable the rack to move S / 2 to reach the position near the rack zero position; after zero position judgment, the transmission ratio of the motor rotation angle to the TAS rotation angle is used for converting the TAS rotation angle, and rotation angle closed-loop control is achieved; when the vehicle runs in a low-speed straight line, the rack zero position is continuously corrected, and the power-off zero position is stored.

Description

Technical Field

[0001] The present invention relates to the technical field of steering control units, and in particular to a steer-by-wire system and a control method. Background Art

[0002] Most of the current front wheel actuators (RWA) of SBW systems borrow the traditional DP-EPS or RP-EPS structural solutions. Although a pinion input shaft is not required (because there is no intermediate shaft), in order to obtain the rack position more accurately, the rack and pinion transmission pair and TAS sensor (or AOS sensor) are retained to achieve position tracking control.

[0003] The design and assembly of the gear rack transmission structure are very complex. The processing and manufacturing cost of the housing and rack is high and difficult. It is also prone to noise problems caused by the matching. However, for the SBW system, the only function it realizes is the angle sensor, and the "cost-effectiveness" is very low.

[0004] TAS or AOS sensors are relatively expensive and have certain technical barriers, and only a few suppliers have the relevant technologies. Summary of the Invention

[0005] To this end, the present invention provides a steer-by-wire system and a control method to solve the problems raised in the background art.

[0006] In order to achieve the above object, the present invention provides the following technical solution: a steer-by-wire control method, the control method comprising:

[0007] Step 1: First initialize the system;

[0008] Step 2: The motor enters current loop control mode and applies motor torque to move the rack to the left or right at a constant speed. The motor torque is determined in real time to be greater than the threshold and the motor angle remains unchanged.

[0009] Step 3: When the motor torque is greater than the threshold k and the motor angle no longer changes, record the point A. n , motor angle x n And the number of motor turns r n , where n represents point A n , motor angle x n And the number of motor turns r n The nth data, n∈{1,2,3,...};

[0010] If n is not greater than the threshold k, change the direction of the motor torque to move the rack in the opposite direction;

[0011] Otherwise, according to the recorded motor revolutions r n and motor angle x n, calculate the total angle of motor rotation between each two adjacent points {S1, S2, ..., S n}, the rack full stroke angle range S=(S1+S2+...S n ) / k;

[0012] Step 4: In the current loop control mode, apply a reverse torque to move the rack by S / 2 until it reaches near the rack zero position.

[0013] Step 5: After the zero position is determined, the TAS angle is converted using the transmission ratio between the motor angle and the TAS angle to achieve closed-loop angle control. Finally, when the vehicle is traveling in a low-speed straight line, the rack zero position is continuously corrected and the zero position is stored when the power is turned off.

[0014] Preferably, the system initialization is as follows: in step 1, the motor rotor position sensor MPS is initialized to obtain the initial value x0 of the actual motor angle, and the theoretical value Theta0 of the motor angle is initialized to 0; the number of revolutions r of the motor is initialized to 0, and then the number of revolutions in the clockwise rotation process of the motor is accumulated successively, and the number of revolutions in the counterclockwise rotation process is accumulated successively.

[0015] A continuously changing ramp curve is used as the reference angle; through angle closed-loop control, the motor rotates uniformly in one direction, that is, the rack moves uniformly toward the end.

[0016] Preferably, under the closed-loop control of the rotation angle, the motor rotates at a constant speed in one direction, and the rack moves at a constant speed toward the end, including:

[0017] The difference between the reference angle and the actual angle is calculated and the desired angular velocity after planning is obtained through the P controller.

[0018] The difference between the expected angular velocity and the actual speed is calculated, and the final motor torque is obtained through the PI controller, which can drive the rack to move at a constant speed toward the end.

[0019] Preferably, it is determined in real time whether the motor torque is greater than a certain threshold and the motor angle no longer changes;

[0020] During angle closed-loop control, if the theoretical motor angle stops changing and the motor torque exceeds the set torque threshold, indicating that the rack is near its end, i.e., its mechanical stop, the motor torque output is temporarily cut off to avoid damage to the motor and protect the rack end.

[0021] Preferably, in step 3, the motor angle does not change and the motor torque is greater than the threshold value, at which time the rack is near the end; according to the rack end point A in the current direction n , motor angle x n And the number of motor turns r n , calculate the theoretical value of the motor angle Theta at the end of the rackn , for the subsequent comprehensive consideration of the full stroke angle range S n Provide data.

[0022] Theta n =(360-x0)+(r n -1)*360+x n .

[0023] Preferably, in step 3, record that n is not greater than k, and then change the direction of the motor torque to move the rack in the opposite direction; when the rack reaches the end position, change the direction of the motor torque to drive the rack to move to the other end, and obtain the theoretical value of the motor angle Theta at the other end of the rack n To ensure the accuracy of the data, k rack movements and point records {Theta1, Theta2, ..., Theta n}.

[0024] Preferably, in step 3, when n is greater than k, the total angle of rotation of the motor between each two adjacent points {S1, S2, ..., S n}, the rack full travel range S=(S1+S2+...+S n ) / k;

[0025] The motor angle range S of the full stroke from the left end to the right end of the rack is n =|Theta n -Theta n-1 |.

[0026] Preferably, in step 5, a force in the opposite direction is applied to move the rack S / 2 to near the rack zero position, completing the zero position determination; after the zero position determination, the current motor position is used as the rack zero position, and the transmission ratio K between the motor angle and the TAS angle is used to convert the TAS angle as the actual steering wheel angle to achieve angle closed-loop control

[0027] StrAng=Theta / K;

[0028] The reference angle is subtracted from the actual angle, and the desired angular velocity is obtained through the P controller. The desired angular velocity is subtracted from the actual speed, and the motor torque is obtained through the PI controller to achieve closed-loop control of the angle.

[0029] When the vehicle is traveling in a straight line at low speed, the rack zero position is constantly corrected;

[0030] Based on the driver's intention recognition, it is determined that the current driver's intention is to drive in a straight line at low speed, and the rack force zero position is corrected, specifically including:

[0031] If the speed deviation of the left front wheel and the right front wheel is less than the threshold, and the steering wheel angle change is less than a certain threshold, it is determined that the current state is low-speed straight driving;

[0032] Under low-speed straight-line driving conditions, the current steering wheel angle is recorded to determine whether correction is needed;

[0033] If the current steering wheel angle is greater than 3 degrees, the current steering wheel angle zero position needs to be corrected and the current steering wheel angle is recorded for angle offset compensation; otherwise, the currently determined angle zero position is maintained;

[0034] StrAng_Real=StrAng-Ang_Offset;

[0035] Among them, StrAng_Real represents the corrected steering wheel angle calculated based on the current steering wheel angle StrAng, and Ang_Offset represents the recording of the current steering wheel angle for angle offset compensation when the vehicle is stationary;

[0036] The zero position is stored when the power is turned off. The angle zero position is stored before the power is turned off and is used for angle initialization after the next power-on.

[0037] The present invention also discloses a wire-controlled steering system, which is used to implement the above method.

[0038] The present invention has the following advantages:

[0039] The present invention first initializes the wire-controlled steering system. After the initialization is completed, the motor enters the current loop control mode and applies torque through the motor to move the rack. During the movement, the end position of the rack is determined by monitoring the motor torque and angle, and the relevant point position data is recorded. After multiple measurements, the full stroke angle range of the rack is calculated to determine the zero position. The transmission ratio of the motor angle and the TAS angle is used to achieve angle closed-loop control and accurately control the vehicle steering angle. During low-speed movement, the rack zero position is continuously monitored and corrected to ensure the accuracy of steering control. Compared with the existing technology, the TAS / AOS sensor and related transmission mechanism are eliminated, which greatly simplifies the system solution, reduces the complexity of production and manufacturing, saves costs, and improves the reliability of the system. Linear displacement sensors are not used, and there is no need to design sensor installation and transmission reduction mechanisms on the housing. The present invention uses a motor rotor position sensor MPS with a high-precision, high-safety redundant solution to obtain safe and high-precision position information. After obtaining the initial position, the MPS can be used as a reference to calculate the accurate rack position. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic flow chart of the steer-by-wire system and control method provided by the present invention;

[0041] Figure 2 A schematic diagram of the specific relationship between the motor angle and the theoretical value of the motor angle provided by the present invention. DETAILED DESCRIPTION

[0042] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0043] like Figure 1 As shown, the present invention provides a wire-controlled steering control method, the control method comprising:

[0044] Step 1: First initialize the system;

[0045] In an exemplary embodiment, the system initialization is as follows: the motor rotor position sensor MPS is initialized to obtain the initial value x0 of the actual motor angle, and the theoretical value Theta0 of the motor angle is initialized to 0; the number of revolutions r of the motor is initialized to 0, and then the number of revolutions in the clockwise rotation process of the motor is accumulated successively, and the number of revolutions in the counterclockwise rotation process is accumulated successively.

[0046] Step 2: The motor enters current loop control mode and applies motor torque to move the rack to the left or right at a constant speed. The motor torque is determined in real time to be greater than the threshold and the motor angle remains unchanged.

[0047] A continuously changing ramp curve is used as the reference angle; through double closed-loop angle control, the motor rotates uniformly in one direction, that is, the rack moves uniformly toward the end.

[0048] In an exemplary embodiment, under dual closed-loop angle control, the motor rotates at a constant speed in one direction, and the rack moves at a constant speed toward the end, including:

[0049] The difference between the reference angle and the actual angle is calculated and the desired angular velocity after planning is obtained through the P controller.

[0050] The difference between the expected angular velocity and the actual speed is calculated, and the final motor torque is obtained through the PI controller, which can drive the rack to move at a constant speed toward the end.

[0051] In an exemplary embodiment, it is determined in real time whether the motor torque is greater than a certain threshold and the motor angle no longer changes;

[0052] During angle closed-loop control, if the theoretical motor angle stops changing and the motor torque exceeds the set torque threshold, indicating that the rack is near its end, i.e., the mechanical dead center, the motor torque output is temporarily cut off to avoid damage to the motor and protect the rack end.

[0053] Step 3: When the motor torque is greater than the threshold and the motor angle no longer changes, record the point A. n , motor angle x n And the number of motor turns r n , where n represents point A n , motor angle x n And the number of motor turns r n The nth data, n∈{1,2,3,...};

[0054] If n is not greater than k, change the direction of the motor torque to move the rack in the opposite direction;

[0055] Otherwise, according to the recorded motor angle x n And the number of motor turns r n , calculate the total angle of motor rotation between each two adjacent points {S1, S2, ..., S n}, the rack full stroke angle range S=(S1+S2+...S n ) / k;

[0056] In an exemplary embodiment, the motor angle does not change and the motor torque is greater than the threshold value, and the rack is near the end; according to the rack end point A in the current direction n , motor angle x n And the number of motor turns r n , calculate the theoretical value of the motor angle Theta at the end of the rack n , for the subsequent comprehensive consideration of the full stroke angle range S n Provide data; motor angle x n and the theoretical value of the motor angle Theta n See the schematic diagram Figure 2 .

[0057] Theta n =(360-x0)+(r n -1)*360+x n .

[0058] In an exemplary embodiment, record n ​​is not greater than k, and then change the direction of the motor torque to move the rack in the opposite direction; when the rack reaches the end position, change the direction of the motor torque to drive the rack to move to the other end, and obtain the theoretical value of the motor angle Theta at the other end of the rack nTo ensure the accuracy of the data, k rack movements and point records {Theta1, Theta2, ..., Theta n}.

[0059] In an exemplary embodiment, when n is greater than k, the total angle of rotation of the motor between each two adjacent points {S1, S2, ..., S n}, the rack full travel range S=(S1+S2+...+S n ) / k; calculate the motor angle range S of the full stroke from the left end to the right end of the rack n ; The average rack travel range is obtained based on the average value of k groups of data:

[0060] S=(S1+S2+...+S n ) / k;

[0061] Calculate the motor angle range Sn for the full stroke from the left end to the right end of the rack = |Theta n -Theta n-1 |.

[0062] Step 4: In the current loop control mode, apply a reverse torque to move the rack by S / 2 until it reaches near the rack zero position.

[0063] Step 5: After the zero position is determined, the TAS angle is converted using the transmission ratio between the motor angle and the TAS angle to achieve closed-loop angle control. Finally, when the vehicle is traveling in a low-speed straight line, the rack zero position is continuously corrected and the zero position is stored when the power is turned off.

[0064] In an exemplary embodiment, a force in the opposite direction is applied to move the rack S / 2 to near the rack zero position, completing the zero position determination. After the zero position determination, the current motor position is used as the rack zero position, and the transmission ratio K between the motor angle and the TAS angle is used to convert the TAS angle as the actual steering wheel angle to achieve angle closed-loop control.

[0065] StrAng=Theta / K;

[0066] The reference angle is subtracted from the actual angle, and the desired angular velocity is obtained through the P controller. The desired angular velocity is subtracted from the actual speed, and the motor torque is obtained through the PI controller to achieve closed-loop control of the angle.

[0067] When the vehicle is traveling in a straight line at low speed, the rack zero position is constantly corrected;

[0068] Based on the driver's intention recognition, it is determined that the current driver's intention is to drive in a straight line at low speed, and the rack force zero position is corrected, specifically including:

[0069] If the speed deviation of the left front wheel and the right front wheel is less than the threshold, and the steering wheel angle change is less than a certain threshold, it is determined that the current state is low-speed straight driving;

[0070] Under low-speed straight-line driving conditions, the current steering wheel angle is recorded to determine whether correction is needed;

[0071] If the current steering wheel angle is greater than 3 degrees, the current steering wheel angle zero position needs to be corrected and the current steering wheel angle is recorded for angle offset compensation; otherwise, the currently determined angle zero position is maintained;

[0072] StrAng_Real=StrAng-Ang_Offset;

[0073] Among them, StrAng_Real represents the corrected steering wheel angle calculated based on the current steering wheel angle StrAng, and Ang_Offset represents the recording of the current steering wheel angle for angle offset compensation when the vehicle is stationary;

[0074] The zero position is stored when the power is turned off. The angle zero position is stored before the power is turned off and is used for angle initialization after the next power-on.

[0075] The present invention also discloses a wire-controlled steering system, which is used to implement the above method.

[0076] This embodiment is an application of the wire-controlled steering method to the scenario of autonomous driving of a car:

[0077] 1. Initialization phase:

[0078] When a self-driving car starts, the steer-by-wire system is initialized. The motor rotor position sensor (MPS) is initialized, obtaining the initial value of the actual motor angle (x0) of 10°. The theoretical motor angle (Theta0) is initialized to 0°, and the number of motor revolutions (r) is initialized to 0°. At this point, the system establishes an initial baseline state for the motor angle.

[0079] 2. Rack movement and end detection:

[0080] The autonomous driving system issues a command, preparing the vehicle to turn and adjust its route. The motor enters current loop control mode, applying motor torque to move the rack to the right at a constant speed.

[0081] During movement, the system determines the motor torque and angle changes in real time. When the motor torque reaches a set threshold (e.g., 5 N·m, assumed) and the motor angle stops changing, indicating the rack has reached its end (mechanical dead center), the system temporarily cuts off the motor torque output. The system records this point, A1, the motor angle, x1 = 30°, and the number of motor revolutions, r1 = 2, and calculates the theoretical motor angle, Theta1 = (360 - 10) + (2 - 1) * 360 + 30 = 740°.

[0082] 3. Full stroke angle calculation:

[0083] Assuming k = 3 (taking three measurements and taking the average), change the direction of the motor torque to move the rack to the left. Repeat the above process to obtain data for two additional points, A2 and A3, along with their corresponding motor angles and number of revolutions. After completing three measurements, calculate the total motor rotation angles S1, S2, and S3 between each adjacent point. For example, if S1 = 200°, S2 = 210°, and S3 = 190°, then the full rack travel angle range S = (S1 + S2 + S3) / k = (200 + 210 + 190) / 3 = 200°.

[0084] 4. Zero position determination and closed-loop control:

[0085] In current loop control mode, applying a counter-torque causes the rack to move S / 2 = 100°, reaching near zero position. After zero position determination, the transmission ratio between the motor angle and the TAS angle is known to be K = 10 (an assumed value). This transmission ratio is used to convert the TAS angle. Assuming the theoretical motor angle value, Theta, is 50°, the actual steering wheel angle, StrAng, is calculated as Theta / K = 50 / 10 = 5°. The difference between the reference angle and the actual angle is used to obtain the desired angular velocity through a P controller. The difference between the desired angular velocity and the actual speed is used to obtain the motor torque through a PI controller, achieving closed-loop angle control.

[0086] 5. Correction for low-speed straight driving:

[0087] When the autonomous vehicle is in a low-speed straight-line driving state (determined by judging that the wheel speed deviation of the left front wheel and the right front wheel is less than a threshold, and the steering wheel angle change amplitude is less than a certain threshold), the current steering wheel angle is recorded. Assuming that the current steering wheel angle is 4°, which is greater than 3°, it is considered that the current steering wheel angle zero position needs to be corrected, and the current steering wheel angle is recorded for angle offset compensation. The corrected steering wheel angle StrAng_Real is calculated as StrAng-Ang_Offset to ensure the accuracy of the vehicle's driving direction. When the vehicle is powered off, the zero position storage is completed so that the angle can be initialized after the next power-on.

[0088] This embodiment provides an intelligent parking scenario. When the vehicle enters the intelligent parking mode, the wire-controlled steering system is also initialized first. After the initialization is completed, the motor enters the current loop control mode. According to the path instruction planned by the parking system, the motor applies torque to move the rack. During the movement, the end position of the rack is determined by monitoring the motor torque and angle, and the relevant point data is recorded. After multiple measurements, the full stroke angle range of the rack is calculated to determine the zero position. During the parking process, the transmission ratio of the motor angle and the TAS angle is used to achieve angle closed-loop control and accurately control the vehicle's steering angle. For example, when the vehicle needs to be parked parallel to a parking space, the system accurately adjusts the steering wheel angle through the wire-controlled steering system based on the parking space distance and vehicle position information fed back by the sensor, so that the vehicle is parked accurately in the parking space. During low-speed movement, the rack zero position is continuously monitored and corrected to ensure the accuracy of steering control and complete the intelligent parking operation.

[0089] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A steer-by-wire control method, characterized in that: Control methods include: Step 1: First initialize the system; Step 2: The motor enters the current closed-loop control mode and applies motor torque to move the rack to the left or right at a constant speed. The system then determines in real time whether the motor torque is greater than a threshold value k and the motor angle remains unchanged. Step 3: When the motor torque is greater than the threshold k and the motor angle no longer changes, record the point A. n , motor angle x n And the number of motor turns r n , where n represents point A n , motor angle x n And the number of motor turns r n The nth data, n∈{1,2,3,...}; If n is not greater than the threshold k, change the direction of the motor torque to move the rack in the opposite direction; Otherwise, according to the recorded motor revolutions r n and motor angle x n , calculate the total angle of motor rotation between each two adjacent points {S1, S2, ..., S n }, the rack full stroke angle range S=(S1+S2+...S n ) / k; Step 4: In the current loop control mode, apply a reverse torque to move the rack by S / 2 until it reaches near the rack zero position. Step 5: After the zero position is determined, the TAS angle is converted using the transmission ratio between the motor angle and the TAS angle to achieve angle closed-loop control. When the vehicle is traveling in a low-speed straight line, the rack zero position is continuously corrected and the zero position is stored when the power is turned off.

2. The steer-by-wire control method according to claim 1, wherein: The system initialization is as follows: In step 1, the motor rotor position sensor MPS is initialized to obtain the initial value x0 of the actual motor angle, and the theoretical value Theta0 of the motor angle is initialized to 0; the number of motor rotations r is initialized to 0, and then the number of rotations in the clockwise rotation process of the motor is accumulated in sequence, and the number of rotations in the counterclockwise rotation process is accumulated in sequence.

3. The steer-by-wire control method according to claim 1, wherein: In step 3, the motor angle does not change and the motor torque is greater than the threshold. At this time, the rack is near the end. According to the rack end point A in the current direction, n , motor angle x n And the number of motor turns r n ; Calculate the theoretical value of the motor angle Theta at the end of the rack n , for the subsequent comprehensive consideration of the full stroke angle range S n Provide data; Theta n =(360-x0)+(r n -1)*360+x n 。 4. The steer-by-wire control method according to claim 3, wherein: In step 3, record that n is not greater than k, and then change the direction of the motor torque to move the rack in the opposite direction; when the rack reaches the end position, change the direction of the motor torque to drive the rack to the other end, and obtain the theoretical value of the motor angle Theta at the other end of the rack n ; To ensure the accuracy of the data, perform k rack movements and point records {Theta1, Theta2, ..., Theta n }.

5. The steer-by-wire control method according to claim 4, characterized in that: In step 3, when n is greater than k, calculate the total angle of motor rotation between each two adjacent points {S1, S2, ..., S n }, the rack full travel range S=(S1+S2+...+S n ) / k; The motor angle range S of the full stroke from one end of the rack to the other end is n =|Theta n -Theta n-1 |.

6. The steer-by-wire control method according to claim 5, characterized in that: In step 4, a force in the opposite direction is applied to move the rack by S / 2 to near the rack zero position, completing the zero position determination. After the zero position determination, the current motor position is used as the rack zero position, and the transmission ratio K between the motor angle and the TAS angle is used to convert the TAS angle into the actual steering wheel angle, thus achieving angle closed-loop control: StrAng=Theta / K; The reference angle is subtracted from the actual angle, and the desired angular velocity is obtained through the P controller. The desired angular velocity is subtracted from the actual speed, and the motor torque is obtained through the PI controller to achieve closed-loop control of the angle. When the vehicle is traveling in a straight line at low speed, the rack zero position is constantly corrected; Based on the driver's intention recognition, it is determined that the current driver's intention is to drive in a straight line at low speed, and the rack force zero position is corrected, specifically including: If the speed deviation of the left front wheel and the right front wheel is less than the threshold, and the steering wheel angle change is less than a certain threshold, it is determined that the current state is low-speed straight driving; Under low-speed straight-line driving conditions, the current steering wheel angle is recorded to determine whether correction is needed; If the current steering wheel angle is greater than 3 degrees, the current steering wheel angle zero position needs to be corrected and the current steering wheel angle is recorded for angle offset compensation; otherwise, the currently determined angle zero position is maintained; StrAng_Real=StrAng-Ang_Offset; Among them, StrAng_Real represents the corrected steering wheel angle calculated based on the actual steering wheel angle StrAng, and Ang_Offset represents the recording of the current steering wheel angle for angle offset compensation when the vehicle is stationary; The zero position is stored when the power is turned off. The angle zero position is stored before the power is turned off and is used for angle initialization after the next power-on.

7. A steer-by-wire system, characterized in that: Used to implement the method according to any one of claims 1 to 6.

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