Steer-by-wire system and control method

Abstract

The application discloses a kind of steer-by-wire systems and control method, specifically relates to steering control unit technical field, system initialization after motor enters current closed loop mode, motor torque is applied to make rack uniform speed move to left or right;When satisfying motor torque size is greater than threshold value and motor angle no longer changes, record the point A n , motor angle x n And motor turns r n ;If n is not greater than threshold value, change motor torque direction, make rack move in opposite direction;Otherwise, according to record motor turns r n And motor angle x n , calculate the total angle of motor rotation between each adjacent two point, obtain rack full stroke angle range S;In current loop control mode, apply opposite direction torque to make rack move S / 2, reach rack zero position vicinity;After zero position determination, TAS rotation angle is converted using motor rotation angle and TAS rotation angle transmission ratio, realize rotation angle closed loop control;Vehicle is in low-speed straight line driving, rack zero position is constantly corrected, and power-off zero position is stored.

Description

Technical Field

[0001] This invention relates to the field of steering control unit technology, and more specifically to a steer-by-wire system and control method. Background Technology

[0002] Most current SBW systems use traditional DP-EPS or RP-EPS structures for their front wheel actuators (RWA). Although they do not require a pinion input shaft (because there is no intermediate shaft), they still retain the rack and pinion drive pair and TAS sensor (or AOS sensor) to achieve position tracking control in order to obtain the rack position more accurately.

[0003] The design and assembly of gear and rack transmission pairs are very complex. The housing and rack are difficult to manufacture and costly, and they are also prone to noise problems caused by misalignment. However, the function of the SBW system is only to realize the angle sensor, which has a very low "cost-effectiveness".

[0004] TAS or AOS sensors are expensive and have certain technological barriers, with only a few suppliers possessing the relevant technology. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention provides the following technical solution: a steer-by-wire control method, the control method comprising:

[0007] Step 1: First, perform system initialization;

[0008] Step 2: The motor enters the current loop control mode, and the motor torque is applied to make the rack move to the left or right at a constant speed; it is determined in real time that the motor torque is greater than the torque threshold k_t and the motor angle no longer changes.

[0009] Step 3: When the motor torque is greater than the torque threshold k_t and the motor angle no longer changes, record point A. n Motor angle x n and motor revolutions r n Where n represents point A n Motor angle x n and motor revolutions r n The nth data, ;

[0010] If n is not greater than the number of times threshold k_n, change the direction of the motor torque so that the rack moves in the opposite direction;

[0011] Otherwise, based on the recorded motor revolutions r n and motor angle xn Calculate the total angle of motor rotation between each pair of adjacent points {S1,S2,...,S}. n}, thus obtaining the rack's full stroke angle range S = (S1 + S2 + ... S n ) / k_n;

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

[0013] Step 5: After zero position determination, the TAS angle is calculated 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 straight line at low speed, the rack zero position is continuously corrected and stored after power-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 of the actual motor angle x0, and the theoretical value of the motor angle Theta0 is initialized to 0; the number of rotations r of the motor is initialized to 0, and then the number of rotations is accumulated sequentially during the clockwise rotation process and decreased sequentially during the counterclockwise rotation process.

[0015] Using a continuously changing ramp curve as a reference angle, the motor is made to rotate at a constant speed in one direction through closed-loop control of the rotation angle, that is, the rack moves at a constant speed towards the end.

[0016] Preferably, under closed-loop cornering control, the motor rotates at a constant speed in one direction, and the rack moves at a constant speed towards its end, including:

[0017] The difference between the reference angle and the actual angle is used to obtain the planned desired angular velocity through the P controller;

[0018] The difference between the desired angular velocity and the actual rotational speed is used to obtain the final motor torque through a PI controller, which can drive the rack to move at a constant speed towards the end.

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

[0020] During the angle closed-loop control process, when the theoretical value of the motor angle no longer changes and the motor torque exceeds the set motor torque threshold, it indicates that the rack is near the end, i.e., the mechanical stop. To avoid damaging the motor and protect the end of the rack, the motor torque output is temporarily cut off.

[0021] Preferably, in step 3, the motor angle does not change and the motor torque is greater than the threshold, at which point the rack is near its end; based on the rack end point A in the current direction... n Motor angle x n and motor revolutions r nCalculate the theoretical value of the motor angle at one end of the rack: Theta n To comprehensively consider the entire stroke angle range S n Provide data.

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

[0023] Preferably, in step 3, n is recorded as not greater than k, and the direction of the motor torque is changed accordingly to make the rack move in the opposite direction; when the rack reaches the end position, the direction of the motor torque is changed again to drive the rack to move to the other end, and the theoretical value of the motor angle Theta at the other end of the rack is obtained. n To ensure data accuracy, k rack movements and point recordings are required {Theta1, Theta2, ..., Theta}. n}

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

[0025] Among them, the motor angle range S of the entire stroke from the left end to the right end of the rack. n = |Theta n - Theta n-1 |

[0026] Preferably, in step 5, a force in the opposite direction is applied to move the rack by S / 2 to the vicinity of the rack zero position, thus completing the zero position determination; after the zero position determination, the current motor position is taken as the rack zero position, and the TAS angle is calculated as the actual steering wheel angle using the transmission ratio K between the motor angle and the TAS angle, thereby realizing the closed-loop control of the steering angle StrAng = Theta / K.

[0027] The difference between the reference angle and the actual angle is used to obtain the desired angular velocity through the P controller; the difference between the desired angular velocity and the actual rotational speed is used to obtain the motor torque through the PI controller, thus realizing closed-loop control of the rotation angle.

[0028] When the vehicle is traveling at low speed in a straight line, the rack position is constantly adjusted to zero.

[0029] Based on driver intent recognition, it is determined that the current driver intent is to drive in a straight line at low speed. The rack force is then corrected to zero, specifically including:

[0030] If the wheel 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, the current state is determined to be low-speed straight driving.

[0031] Under low-speed straight-line driving conditions, record the current steering wheel angle and determine whether correction is needed;

[0032] If the current steering wheel angle is greater than 3 degrees, 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; otherwise, the currently determined angle zero position is maintained.

[0033] StrAng_Real = StrAng - Ang_Offset;

[0034] Wherein, StrAng_Real represents the corrected steering wheel angle calculated based on the current steering wheel angle StrAng, and Ang_Offset represents the current steering wheel angle recorded when the vehicle is stationary, used for angle offset compensation;

[0035] Zero position storage is completed upon power-down. The zero angle position is stored before power-down for angle initialization upon the next power-up.

[0036] The present invention also discloses a steer-by-wire system for implementing the above-described method.

[0037] The present invention has the following advantages:

[0038] This invention first initializes the steer-by-wire system. After initialization, the motor enters a current loop control mode, applying torque to move the rack. During movement, the end position of the rack is determined by monitoring the motor torque and angle, and relevant point data is recorded. After multiple measurements, the full stroke angle range of the rack is calculated to determine the zero position. Closed-loop control of the steering angle is achieved using the transmission ratio between the motor rotation angle and the TAS rotation angle, precisely controlling the vehicle's steering angle. During low-speed movement, the rack zero position is continuously monitored and corrected to ensure the accuracy of steering control. Compared with existing technologies, this invention eliminates the need for TAS / AOS sensors and related transmission mechanisms, greatly simplifying the system design, reducing manufacturing complexity, saving costs, and improving system reliability. It also eliminates the need for linear displacement sensors, thus avoiding the need for sensor mounting and transmission reduction mechanisms on the housing. This invention uses a high-precision, high-safety redundant scheme for the motor rotor position sensor (MPS) 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. Attached Figure Description

[0039] Figure 1 A schematic flowchart illustrating the steer-by-wire system and control method provided by the present invention;

[0040] Figure 2 This is a schematic diagram illustrating the specific relationship between the motor angle and the theoretical value of the motor angle provided by the present invention. Detailed Implementation

[0041] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] like Figure 1 As shown, the present invention provides a steer-by-wire control method, the control method comprising:

[0043] Step 1: First, perform system initialization;

[0044] In one exemplary instance, the system initialization is as follows: the motor rotor position sensor MPS is initialized to obtain the initial value of the actual motor angle x0, and the theoretical value of the motor angle Theta0 is initialized to 0; the number of motor rotations r is initialized to 0, and then the number of rotations is accumulated sequentially during the clockwise rotation process and sequentially decreased during the counterclockwise rotation process.

[0045] Step 2: The motor enters the current loop control mode, and the motor torque is applied to make the rack move to the left or right at a constant speed; it is determined in real time that the motor torque is greater than the torque threshold k_t and the motor angle no longer changes.

[0046] A continuously changing ramp curve is used as a reference angle; through dual closed-loop angle control, the motor rotates at a constant speed in one direction, that is, the rack moves at a constant speed towards the end.

[0047] In one exemplary instance, 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 its end, including:

[0048] The difference between the reference angle and the actual angle is used to obtain the planned desired angular velocity through the P controller;

[0049] The difference between the desired angular velocity and the actual rotational speed is used to obtain the final motor torque through a PI controller, which can drive the rack to move at a constant speed towards the end.

[0050] In one exemplary instance, the magnitude of the motor torque is determined in real time, whether it exceeds a certain threshold, and whether the motor angle no longer changes.

[0051] During the closed-loop control of the rotation angle, when the theoretical value of the motor angle no longer changes and the motor torque exceeds the set motor torque threshold k_t, it indicates that the rack is near the end, i.e., the mechanical stop point. To avoid damaging the motor and protect the end of the rack, the motor torque output is temporarily cut off.

[0052] Step 3: When the motor torque is greater than the torque threshold k_t and the motor angle no longer changes, record point A. n Motor angle x n and motor revolutions r n Where n represents point A n Motor angle x n and motor revolutions r n The nth data, ;

[0053] If n is not greater than the number of times threshold k_n, change the direction of the motor torque so that the rack moves in the opposite direction;

[0054] Otherwise, based on the recorded motor angle x n and motor revolutions r n Calculate the total angle of motor rotation between each pair of adjacent points {S1,S2,...,S}. n}, thus obtaining the rack's full stroke angle range S = (S1 + S2 + ... S n ) / k_n;

[0055] In one exemplary instance, the motor angle remains unchanged and the motor torque is greater than the number of cycles threshold k_t, at which point the rack is near its end; based on the rack end point A in the current direction... n Motor angle x n and motor revolutions r n Calculate the theoretical value of the motor angle at one end of the rack: Theta n To comprehensively consider the entire stroke angle range S n Provide data; motor angle x n Theta, the theoretical value of the motor angle n See diagram Figure 2 .

[0056] Theta n = (360 - x0) + (r n -1)*360 + x n .

[0057] In one exemplary instance, n is recorded as not exceeding a threshold number of attempts k_n. The direction of the motor torque is then changed to move the rack in the opposite direction. Once the rack reaches its end position, the direction of the motor torque is changed again, driving the rack to move to the other end. The theoretical value of the motor angle at the other end of the rack, Theta, is then obtained. n To ensure data accuracy, k_n rack movements and point recordings are required {Theta1, Theta2, ..., Theta}. n}

[0058] In one exemplary instance, when n is greater than the number of times threshold k_n, the total angle of motor rotation between each pair of adjacent points {S1, S2, ..., S_n} is calculated. n}, thus obtaining the rack's total travel range S = (S1+S2+...+S n ) / k_n;

[0059] Calculate the motor angle range Sn = |Theta| for the entire stroke from the left end to the right end of the rack. n - Theta n-1 |

[0060] Step 4: In current loop control mode, apply a reverse torque to move the rack by S / 2 until it reaches near the zero position of the rack;

[0061] Step 5: After zero position determination, the TAS angle is calculated 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 straight line at low speed, the rack zero position is continuously corrected and stored after power-off.

[0062] In one exemplary instance, a force in the opposite direction is applied to move the rack by S / 2 to the vicinity of the rack zero position, thus completing the zero position determination. After the zero position determination, the current motor position is taken as the rack zero position, and the TAS angle is calculated as the actual steering wheel angle using the transmission ratio K between the motor angle and the TAS angle, thereby realizing closed-loop control of the steering angle: StrAng = Theta / K.

[0063] The difference between the reference angle and the actual angle is used to obtain the desired angular velocity through the P controller; the difference between the desired angular velocity and the actual rotational speed is used to obtain the motor torque through the PI controller, thus realizing closed-loop control of the rotation angle.

[0064] When the vehicle is traveling at low speed in a straight line, the rack position is constantly adjusted to zero.

[0065] Based on driver intent recognition, it is determined that the current driver intent is to drive in a straight line at low speed. The rack force is then corrected to zero, specifically including:

[0066] If the wheel 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, the current state is determined to be low-speed straight driving.

[0067] Under low-speed straight-line driving conditions, record the current steering wheel angle and determine whether correction is needed;

[0068] If the current steering wheel angle is greater than 3 degrees, 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; otherwise, the currently determined angle zero position is maintained.

[0069] StrAng_Real = StrAng - Ang_Offset;

[0070] Wherein, StrAng_Real represents the corrected steering wheel angle calculated based on the current steering wheel angle StrAng, and Ang_Offset represents the current steering wheel angle recorded when the vehicle is stationary, used for angle offset compensation;

[0071] Zero position storage is completed upon power-down. The zero angle position is stored before power-down for angle initialization upon the next power-up.

[0072] The present invention also discloses a steer-by-wire system for implementing the above-described method.

[0073] This embodiment demonstrates the application of the steer-by-wire control method in an autonomous driving scenario:

[0074] 1. Initialization phase:

[0075] When an autonomous vehicle starts, the steer-by-wire system is initialized first. The motor rotor position sensor (MPS) is initialized, acquiring the initial actual motor angle value x0 = 10°, while the theoretical motor angle value Theta0 is initialized to 0°, and the number of motor rotations r is initialized to 0°. At this point, the system establishes the initial reference state for the motor angle.

[0076] 2. Rack movement and end-effector detection:

[0077] The autonomous driving system issues a command to instruct the vehicle to prepare to steer and adjust its driving route. The motor enters current loop control mode, applying motor torque to move the rack to the right at a constant speed.

[0078] During movement, the system continuously monitors the motor torque and angle changes. When the motor torque reaches a set threshold (e.g., 5 N·m, assumed value) and the motor angle no longer changes, it indicates that the rack has reached near its end (mechanical stop). At this point, the system temporarily cuts off the motor torque output. Record the point A1, the motor angle x1 = 30°, and the number of motor revolutions r1 = 2, and calculate the theoretical value of the motor angle Theta1 = (360 - 10) + (2 - 1) * 360 + 30 = 740°.

[0079] 3. Calculation of angles throughout the entire stroke:

[0080] Assuming k_n = 3 (averaging of 3 measurements), change the direction of the motor torque to move the rack to the left, and repeat the above process to obtain data A2 and A3 at two other points, along with their corresponding motor angles and rotation counts. After completing 3 measurements, calculate the total angles S1, S2, and S3 of the motor rotation between each pair of adjacent points. For example, if S1 = 200°, S2 = 210°, and S3 = 190°, then the rack's full stroke angle range S = (S1 + S2 + S3) / k_n = (200 + 210 + 190) / 3 = 200°.

[0081] 4. Zero-point determination and closed-loop control:

[0082] In current loop control mode, a counter-torque is applied to move the rack by S / 2 = 100°, bringing it to near the rack's zero position. After zero-position determination, given the transmission ratio K = 10 (assumed value) between the motor angle and the TAS angle, the TAS angle is calculated using this ratio. Assuming the theoretical motor angle Theta = 50°, the actual steering wheel angle StrAng = Theta / K = 50 / 10 = 5°. The difference between the reference angle and the actual angle is used to obtain the desired angular velocity via a P controller; the difference between the desired angular velocity and the actual rotational speed is used to obtain the motor torque via a PI controller, thus achieving closed-loop angle control.

[0083] 5. Correction for low-speed straight-line driving:

[0084] When the autonomous vehicle is traveling at low speed in a straight line (determined by checking that the wheel speed deviation of the left and right front wheels is less than a threshold, and the steering wheel angle change is less than a certain threshold), the current steering wheel angle is recorded. Assuming the current steering wheel angle is 4°, which is greater than 3°, it is considered that the current steering wheel angle zero point needs correction, and the current steering wheel angle is recorded for angle offset compensation. The corrected steering wheel angle StrAng_Real = StrAng - Ang_Offset is calculated to ensure the accuracy of the vehicle's driving direction. When the vehicle is powered off, the zero point is stored so that the angle can be initialized upon the next power-on.

[0085] This embodiment provides an intelligent parking scenario. When the vehicle enters intelligent parking mode, the steer-by-wire system is initialized first. After initialization, the motor enters current loop control mode. According to the path instructions 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 relevant point data is recorded. After multiple measurements, the full stroke angle range of the rack is calculated, and the zero position is determined. During parking, the transmission ratio between the motor angle and the TAS angle is used to achieve closed-loop control of the steering angle, precisely controlling the vehicle's steering angle. For example, when the vehicle needs to park parallel to the parking space, the system uses the steer-by-wire system to precisely adjust the steering wheel angle based on the parking space distance and vehicle position information fed back by sensors, so that the vehicle accurately stops 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.

[0086] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A steer-by-wire control method, characterized in that: Control methods include: Step 1: First, perform system initialization; Step 2: The motor enters the current closed-loop control mode, and the motor torque is applied to make the rack move to the left or right at a constant speed; it is judged in real time whether the motor torque is greater than the torque threshold k_t and the motor angle no longer changes; Step 3: When the motor torque is greater than the torque threshold k_t and the motor angle no longer changes, record point A. n Motor angle x n and motor revolutions r n Where n represents point A n Motor angle x n and motor revolutions r n The nth data, ; If n is not greater than the number of times threshold k_n, change the direction of the motor torque so that the rack moves in the opposite direction; Otherwise, according to the recorded motor revolution number r n and the motor angle x n , the total angle of the motor revolution between each adjacent two points is calculated {S1, S2,..., S n}, and the full stroke angle range of the rack is obtained S = (S1 + S2 +... S n ) / k_n; Step 4: In current loop control mode, apply a reverse torque to move the rack by S / 2 until it reaches near the zero position of the rack; Step 5: After zero position determination, the TAS angle is calculated using the transmission ratio between the motor angle and the TAS angle to achieve closed-loop angle control; when the vehicle is traveling in a straight line at low speed, the rack zero position is continuously corrected and stored after power-off.

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

3. The steer-by-wire control method according to claim 2, characterized in that: In step 3, the motor angle does not change and the motor torque is greater than the torque threshold k_t, at this time the rack is near the end; according to the current direction of the rack end point A n , the motor angle x n , and the motor number of turns r n ; calculate the motor angle theoretical value Theta n at the end of the rack, which provides data for subsequent comprehensive consideration of the full stroke angle range S n . Theta n = (360 - x0) + (r n -1)*360 + x n 。 4. The steer-by-wire control method according to claim 3, characterized in that: In step 3, record that n is no greater than the threshold number of attempts k_n, and then change the direction of the motor torque to make the rack move 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 data accuracy, k_n rack movements and point recordings are performed {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 the threshold number k_n, the total angle of motor rotation between each pair of adjacent points {S1, S2, ..., S_n} is calculated. n }, thus obtaining the rack's total travel range S = (S1 + S2 + ... + S n ) / k_n; Among them, the motor angle range S of the entire stroke from one end of the rack to the other end. 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 until it reaches near the rack zero position, completing the zero-position determination. After the zero-position determination, the current motor position is taken as the rack zero position, and the TAS angle is calculated using the transmission ratio K between the motor angle and the TAS angle as the actual steering wheel angle, thus realizing closed-loop control of the steering angle. StrAng = Theta / K; The difference between the reference angle and the actual angle is used to obtain the desired angular velocity through the P controller; the difference between the desired angular velocity and the actual rotational speed is used to obtain the motor torque through the PI controller, thus realizing closed-loop control of the rotation angle. When the vehicle is traveling at low speed in a straight line, the rack position is constantly adjusted to zero. Based on driver intent recognition, it is determined that the current driver intent is to drive in a straight line at low speed. The rack zero position is then corrected, specifically including: If the wheel 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, the current state is determined to be low-speed straight driving. Under low-speed straight-line driving conditions, record the current steering wheel angle and determine whether correction is needed; If the current steering wheel angle is greater than 3 degrees, 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; otherwise, the currently determined angle zero position is maintained. StrAng_Real = StrAng - Ang_Offset; Wherein, StrAng_Real represents the corrected steering wheel angle calculated based on the actual steering wheel angle StrAng, and Ang_Offset represents the current steering wheel angle recorded when the vehicle is stationary, used for angle offset compensation; Zero position storage is completed upon power-down. The zero angle position is stored before power-down for angle initialization upon the next power-up.

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

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