Middle position self-learning method, middle position deviation compensation method and system of rear wheel steering mechanism

Abstract

The invention provides a neutral position self-learning method for a rear wheel steering mechanism. The neutral position self-learning method comprises the steps that S1, a motor assembly of the rear wheel steering mechanism is provided with an MPS sensor; s2, a motor drives a rack of a rear wheel steering mechanism to move leftwards to a left limit position and a right limit position, an MPS sensor records an MPS measured value of the rack moving leftwards to the left limit position, and a rack position measured value is calculated; s3, the deviation between the middle point of the rack and the initial scale when the LPS sensor is powered on is calculated; s4, correcting the actual position of the rack by using the deviation between the middle point of the rack and the initial scale when the LPS sensor is electrified, and correcting the initial scale when the LPS sensor is electrified; s5, calculating a linear error of the LPS sensor; and S6, repeating the step S5 for multiple times, and establishing a mapping relationship between the LPS measurement values of the LPS sensors when the rack moves to different positions and the linear errors of the corresponding LPS sensors. According to the invention, the accuracy of neutral position calibration of the rear wheel steering mechanism is ensured, and the error of neutral position deviation compensation is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rear wheel steering control, in particular to a mid-position self-learning method, a mid-position deviation compensation method and a system for a rear wheel steering mechanism. Background Art

[0002] With the rapid development of vehicle technology, vehicle handling stability and safety are becoming increasingly important. The driver directly controls the vehicle through the vehicle steering system, so the vehicle steering system is a key component that directly affects vehicle safety.

[0003] The vehicle steering system must be kept in the neutral position to ensure the vehicle's smoothness and safety. After the vehicle steering system assembly rolls off the production line, it is impossible to determine whether the steering system is in the neutral position. A neutral position correction is required to ensure that the vehicle steering system can remain in the neutral position after installation, laying the foundation for subsequent calibration corrections of the vehicle off the production line.

[0004] At present, the mid-position self-learning of the vehicle steering system is mainly focused on the mid-position self-learning of the front-wheel steering mechanism after the vehicle rolls off the production line and during power-on initialization. There is almost no research on the mid-position self-learning method of the rear-wheel steering mechanism.

[0005] The advantages of the rear-wheel steering mechanism are obvious. It can improve the stability of the vehicle, reduce the turning radius of the vehicle, and make the vehicle more sensitive at low speeds and more stable when cornering at high speeds. Therefore, studying the median self-learning method of the rear-wheel steering mechanism and filling the gap in the research method of median correction after the assembly steering system is offline has very important engineering significance for vehicle safety.

[0006] The center-position self-learning of existing vehicle steering systems is mainly focused on the center-position self-learning of the front-wheel steering mechanism after the vehicle rolls off the production line and during power-on initialization. The application scenarios are too narrow, and in actual production and manufacturing, it is impossible to only consider the center-position correction function during vehicle driving.

[0007] The median self-learning of the existing vehicle steering system is mainly concentrated on the median self-learning of the front-wheel steering mechanism after the vehicle rolls off the production line and during power-on initialization. Before loading and after the rear-wheel steering mechanism rolls off the production line, the median deviation of the rear-wheel steering mechanism is not corrected, which makes the subsequent loading procedures cumbersome and increases the difficulty of loading. Summary of the invention

[0008] The present invention proposes a median self-learning method, a median deviation compensation method and a system for a rear-wheel steering mechanism, so as to solve the technical problem in the prior art that before loading and after the rear-wheel steering mechanism is offline, the median deviation of the rear-wheel steering mechanism is not corrected, which makes the subsequent loading procedure cumbersome and increases the difficulty of loading.

[0009] One aspect of the present invention is to provide a mid-position self-learning method for a rear-wheel steering mechanism, the mid-position self-learning method comprising the following method steps:

[0010] S1. The motor assembly of the rear wheel steering mechanism is equipped with an MPS sensor; wherein the motor assembly includes a motor; the motor is used to drive the rack of the rear wheel steering mechanism to move left and right;

[0011] The MPS sensor is used to measure the rotor angle of the motor, thereby measuring the MPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism;

[0012] The rear wheel steering mechanism is equipped with an LPS sensor, and the LPS sensor is used to measure the LPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism;

[0013] S2, the motor drives the rack of the rear wheel steering mechanism to move left to the left limit position, and the MPS sensor records the MPS measurement value when the rack moves left to the left limit position;

[0014] Calculate the rack position measurement value when the rack moves to the left limit position: C = L0 + M;

[0015] Among them, C represents the rack position measurement value when the rack moves to the left limit position, L0 represents the initial scale value when the LPS sensor is powered on, and M represents the MPS measurement value when the rack moves to the left limit position;

[0016] The motor drives the rack of the rear wheel steering mechanism to move right to the right limit position, and the MPS sensor records the MPS measurement value when the rack moves right to the right limit position;

[0017] Calculate the measured value of the rack position when the rack moves right to the right limit position: C'=L0+M';

[0018] Among them, C' represents the rack position measurement value when the rack moves right to the right limit position, L0 represents the initial scale value when the LPS sensor is powered on, and M' represents the MPS measurement value when the rack moves right to the right limit position;

[0019] S3, repeat step S2 at least once, obtain multiple rack position measurement values ​​C1, C2, ..., Cn when the rack moves to the left to the left limit position, and multiple rack position measurement values ​​C1', C2', ..., Cn' when the rack moves to the right to the right limit position;

[0020] Calculate the deviation between the rack midpoint of the rear wheel steering mechanism and the initial scale when the LPS sensor is powered on:

[0021] Δσ1=(C1+C2+...+Cn+C1'+C2'+...+Cn') / 2n;

[0022] Wherein, Δσ1 represents the deviation between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on, C1, C2, ..., Cn represent the rack position measurement values ​​when the rack is moved to the left limit position multiple times, C1', C2', ..., Cn' represent the rack position measurement values ​​when the rack is moved to the right limit position multiple times, and n represents the number of times step S2 is repeated;

[0023] S4, using the deviation Δσ1 between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on, correcting the actual position of the rack, and correcting the initial scale when the LPS sensor is powered on, to calibrate the midpoint of the rear wheel steering mechanism;

[0024] S5, the motor drives the rack of the rear wheel steering mechanism to move to a certain position, the MPS sensor records the MPS measurement value of the rack moving to a certain position, and uses the LPS sensor corrected by the initial scale at power-on to record the LPS measurement value of the rack moving to a certain position;

[0025] Using the MPS measurement value when the rack moves to a certain position, calculate the rack position measurement value when the rack moves to a certain position: C”=M”+L0-Δσ1;

[0026] Among them, C” represents the rack position measurement when the rack moves to a certain position, and M” represents the MPS measurement value when the rack moves to a certain position;

[0027] The linear error of the LPS sensor is calculated using the rack position measurement value when the rack moves to a certain position: Δσ2 = C”-L;

[0028] Among them, Δσ2 represents the linear error of the LPS sensor, and L represents the LPS measurement value recorded by the LPS sensor after the initial scale correction at power-on when the rack moves to a certain position;

[0029] S6, repeat step S5 multiple times to calculate the linear error Δσ2 of multiple LPS sensors;

[0030] The mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor is established to complete the mid-position self-learning of the rear-wheel steering mechanism.

[0031] In a preferred embodiment, in step S2, the rack moves to the left limit position or the rack moves to the right limit position, which is determined by the following method:

[0032] When the rotor torque of the motor is greater than a preset threshold, and the rack speed is less than a preset threshold and lasts for a period of time;

[0033] The motor enters a stalled state, and the position where the rack moves to the left is the left limit position or the position where the rack moves to the right is the right limit position.

[0034] In a preferred embodiment, the rotor torque of the motor is calculated by the following method:

[0035] S201, obtaining a rack displacement instruction; the motor drives the rack of the rear wheel steering mechanism to move left or right according to the rack displacement instruction;

[0036] S202, the LPS sensor collects the actual displacement of the rack after the rack moves left or right;

[0037] S203, filtering the actual displacement of the rack to obtain the filtered actual displacement of the rack;

[0038] S204, calculating the rotor torque of the motor using the rack displacement command and the filtered actual rack displacement.

[0039] In a preferred embodiment, in step S204, the rack displacement is feedforward controlled and PI controlled by using the rack displacement command and the filtered actual rack displacement to generate a rack speed command;

[0040] The filtered actual rack displacement is converted into the actual rack speed; the rack speed is controlled by PI using the rack speed command and the actual rack speed to generate the rotor torque command of the motor.

[0041] In a preferred embodiment, in step S6, linear interpolation is performed on the linear errors Δσ2 of the plurality of LPS sensors to obtain a plurality of linear interpolation results;

[0042] Using the results of multiple linear interpolation, a mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor is established.

[0043] Another aspect of the present invention is to provide a method for compensating for a center deviation of a rear wheel steering mechanism, the method comprising the following steps:

[0044] Step 1, the motor drives the rack of the rear wheel steering mechanism to move left or right;

[0045] Step 2, the LPS sensor records the LPS measurement value when the rack moves left or right;

[0046] Step 3, find the mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor by the median self-learning method of the present invention;

[0047] Get the LPS measurement value recorded by the LPS sensor when the rack moves left or right, and the corresponding linear error Δσ2 of the LPS sensor;

[0048] Step 4: Use the obtained linear error Δσ2 of the LPS sensor to compensate the LPS measurement value of the rack moving left or right recorded by the LPS sensor to complete the median deviation compensation of the back-wheel steering mechanism.

[0049] Another aspect of the present invention is to provide a mid-position self-learning system for a rear-wheel steering mechanism, wherein the mid-position self-learning system is used to execute a mid-position self-learning method for a rear-wheel steering mechanism provided by the present invention, comprising:

[0050] An MPS sensor configured for a motor assembly of a rear-wheel steering mechanism; the motor assembly includes a motor; the motor is used to drive the rack of the rear-wheel steering mechanism to move left and right;

[0051] The MPS sensor is used to measure the rotor angle of the motor, thereby measuring the MPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism;

[0052] The rear wheel steering mechanism is equipped with an LPS sensor, and the LPS sensor is used to measure the LPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism;

[0053] The motor assembly integrates a limit position judgment module, a rack midpoint deviation calculation module, a mid-position calibration module and a mapping relationship generation module;

[0054] The limit position judgment module is used to determine whether the rack of the motor-driven rear wheel steering mechanism moves to the left limit position or the rack moves to the right limit position;

[0055] The rack midpoint deviation calculation module is used to calculate the deviation between the rack midpoint of the rack of the rear wheel steering mechanism and the initial scale when the LPS sensor is powered on;

[0056] The center position calibration module uses the deviation between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on to correct the actual position of the rack and correct the initial scale when the LPS sensor is powered on to calibrate the center position of the rear wheel steering mechanism;

[0057] The mapping relationship generating module is used to calculate the linear errors of multiple LPS sensors and establish a mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor.

[0058] In a preferred embodiment, the limit position judgment module includes a filtering module, a control module and a stall state judgment module;

[0059] The control module obtains a rack displacement instruction and controls the motor to drive the rack of the rear wheel steering mechanism to move left or right;

[0060] The filtering module is used to filter the actual displacement of the rack after the rack moves left or right, which is collected by the LPS sensor, to obtain the filtered actual displacement of the rack;

[0061] The control module calculates the rotor torque of the motor using the rack displacement command and the filtered actual rack displacement;

[0062] The stall state judgment module is used to judge whether the motor enters a stall state:

[0063] When the rotor torque of the motor is greater than a preset threshold value, and the rack speed is less than a preset threshold value and lasts for a period of time, the motor enters a stalled state, otherwise the motor does not enter a stalled state;

[0064] When the motor enters a stalled state, the limit position determination module determines that the rack moves left to a left limit position or the rack moves right to a right limit position.

[0065] In a preferred embodiment, the control module uses the rack displacement command and the filtered actual rack displacement to perform feedforward control and PI control on the rack displacement to generate a rack speed command;

[0066] The filtered actual rack displacement is converted into the actual rack speed; the rack speed is controlled by PI using the rack speed command and the actual rack speed to generate the rotor torque command of the motor.

[0067] Another aspect of the present invention is to provide a median deviation compensation system for a rear-wheel steering mechanism, wherein the median deviation compensation system is used to execute a median deviation compensation method for a rear-wheel steering mechanism provided by the present invention.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] The present invention proposes a mid-position self-learning method, a mid-position deviation compensation method and a system for a rear-wheel steering mechanism. Based on the MPS measurement value of the rack of the rear-wheel steering mechanism when it moves to the left limit displacement and the MPS measurement value of the rack when it moves to the right limit displacement, the rack position measurement values ​​when the rack moves to the left limit position multiple times and the rack position measurement values ​​when the rack moves to the left limit position multiple times are calculated, thereby calculating the deviation between the midpoint of the rack of the rear-wheel steering mechanism and the initial scale when the LPS sensor is powered on, correcting the actual position of the rack, and correcting the initial scale when the LPS sensor is powered on, and calibrating the mid-position of the rear-wheel steering mechanism. The whole process is free of human interference and there is no error caused by human factors, which greatly reduces the error and ensures the accuracy of the mid-position calibration of the rear-wheel steering mechanism.

[0070] The present invention proposes a mid-position self-learning method, a mid-position deviation compensation method and a system for a rear-wheel steering mechanism. After the mid-position of the rear-wheel steering mechanism is calibrated, the rack of the rear-wheel steering mechanism is moved to multiple positions. The linear errors of multiple LPS sensors are calculated by using the MPS measurement value, the initial scale value of the LPS sensor when it is powered on, the deviation between the rack midpoint of the rack and the initial scale of the LPS sensor when it is powered on, and the LPS measurement value recorded by the LPS sensor after the initial scale is corrected when it is powered on. A mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error of the corresponding LPS sensor is established, thereby correcting the linear error of the LPS sensor when measuring a large stroke of the rack, ensuring the accuracy of the LPS sensor after the mid-position calibration of the rear-wheel steering mechanism, and reducing the mid-position deviation of the rear-wheel steering mechanism.

[0071] The present invention proposes a mid-position self-learning method, a mid-position deviation compensation method and a system for a rear-wheel steering mechanism, which increase the application scenarios of the mid-position self-learning function of the vehicle steering system, simplify the loading process, and ensure the functionality and safety of the mid-position correction after the vehicle steering system assembly is off the production line. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the specific implementation of the present invention or the technical solution in the prior art, the following briefly introduces the drawings required for use in the specific implementation or the prior art description. Obviously, the drawings described below are some implementations of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0073] Figure 1 It is a structural schematic diagram of the rear wheel steering mechanism of the present invention.

[0074] Figure 2 The present invention is a flowchart of a mid-position self-learning method of a rear wheel steering mechanism.

[0075] Figure 3 It is a structural diagram of the rack midpoint deviation of the rack after the rear wheel steering mechanism is offline in one embodiment of the present invention.

[0076] Figure 4 It is a structural diagram of the rack of the rear wheel steering mechanism of the present invention moving left to the left extreme position.

[0077] Figure 5 The present invention is a simplified structural diagram of a rack of a rear wheel steering mechanism that moves right to a right limit position.

[0078] Figure 6 It is a simplified structural diagram of a rear wheel steering mechanism in which the rack is moved to the left to multiple positions in one embodiment of the present invention.

[0079] Figure 7 It is a simplified structural diagram of a rear wheel steering mechanism in which the rack is moved rightward to multiple positions in one embodiment of the present invention.

[0080] Figure 8 The present invention is a structural block diagram of a mid-position self-learning system of a rear wheel steering mechanism.

[0081] Fig. 9 It is a structural block diagram of the limit position judgment module of the present invention.

[0082] Fig.10 It is a structural block diagram of the control module of the present invention. DETAILED DESCRIPTION

[0083] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0084] Combination Figure 1 and Figure 2 According to an embodiment of the present invention, a method for self-learning a mid-position of a rear-wheel steering mechanism is provided. In order to explain the present invention more clearly, it is necessary to explain the rear-wheel steering mechanism of the present invention.

[0085] Figure 1 As shown, the rear wheel steering mechanism includes a motor assembly 1, a reducer transmission mechanism 2 and a rack 3, and both ends of the rack 3 are connected to the rear wheels 6 of the vehicle.

[0086] The motor assembly 1 includes a motor 101 (such as Figure 8 The motor 101 is used to drive the rack 3 of the rear wheel steering mechanism to move left and right. Specifically, the rotor of the motor 101 is connected to the rack 3 through the reducer transmission mechanism 2, and the motor 101 converts the rotational motion of the rotor of the motor 101 into the left and right motion of the rack 3 through the reducer transmission mechanism 2, so that the rack 3 pulls the rear wheel 6 of the vehicle to deflect and steer.

[0087] The motor assembly 1 of the rear wheel steering mechanism is equipped with an MPS sensor 4 (MPS, Motor Position Sensor, motor rotor position sensor). The MPS sensor 4 is used to measure the rotor angle (rotor position) of the motor 101, thereby measuring the MPS measurement value of the left and right movement of the rack 3 of the rear wheel steering mechanism.

[0088] Specifically, since the rotor of the motor 101 is connected to the rack 3 through the reducer transmission mechanism 2, when the rotor of the motor 101 rotates an angle, the rack 3 moves a displacement to the left or right. The rotation angle of the rotor of the motor 101 and the displacement of the rack 3 to the left or right have a one-to-one correspondence, so that the MPS sensor 4 measures the MPS measurement value of the left and right movement of the rack 3 of the rear wheel steering mechanism by measuring the rotor angle (rotor position) of the motor 101.

[0089] The rear wheel steering mechanism is equipped with an LPS sensor 5 (LPS, Linear Position Sensor). The LPS sensor 5 is used to measure the LPS measurement value of the left and right movement of the rack 3 of the rear wheel steering mechanism.

[0090] Before the vehicle is loaded, after the rear wheel steering mechanism is offline, the zero point of the LPS sensor 5 of the rear wheel steering mechanism and the rack midpoint O of the rack 3 (such as Figure 3 As shown) is misaligned, and the rack 3 of the rear-wheel steering mechanism has a certain offset (the center deviation of the rear-wheel steering mechanism is not corrected).

[0091] For example, Figure 3 As shown, after the rear wheel steering mechanism is offline, the rack 3 of the rear wheel steering mechanism is offset to the left by a distance d. That is, the rack midpoint O of the rack 3 is offset to the left by a distance d from the correct position O'. That is, the actual position of the rack 3 is offset to the left by a distance d from the correct position, and the mid-position deviation of the rear wheel steering mechanism needs to be corrected.

[0092] Combination Figures 2 to 7 According to an embodiment of the present invention, a method for self-learning a mid-position of a rear-wheel steering mechanism is provided, comprising the following steps:

[0093] Step S1, the motor assembly 1 of the rear wheel steering mechanism is equipped with the MPS sensor 4. The motor assembly 1 includes a motor 101; the motor 101 is used to drive the rack 3 of the rear wheel steering mechanism to move left and right.

[0094] The MPS sensor 4 is used to measure the rotor angle of the motor 101, thereby measuring the MPS measurement value of the left-right movement of the rack 3 of the rear wheel steering mechanism.

[0095] The rear wheel steering mechanism is equipped with an LPS sensor 5. The LPS sensor 5 is used to measure the LPS measurement value of the left and right movement of the rack 3 of the rear wheel steering mechanism.

[0096] Step S2: The motor 101 drives the rack 3 of the rear wheel steering mechanism to move left to the left limit position, and the MPS sensor 4 records the MPS measurement value when the rack 3 moves left to the left limit position, such as Figure 4 shown.

[0097] Calculate the rack position measurement value when rack 3 moves left to the left limit position: C = L0 + M;

[0098] Wherein, C represents the rack position measurement value when the rack 3 moves left to the left limit position, L0 represents the initial scale value when the LPS sensor 5 is powered on, and M represents the MPS measurement value when the rack 3 moves left to the left limit position.

[0099] The motor 101 drives the rack 3 of the rear wheel steering mechanism to move right to the right limit position, and the MPS sensor 4 records the right limit displacement of the rack 3 when it moves right to the right limit position, such as Figure 5 shown.

[0100] Calculate the rack position measurement value when the rack 3 moves right to the right limit position: C'=L0+M';

[0101] Wherein, C' represents the rack position measurement value when the rack 3 moves right to the right limit position, L0 represents the initial scale value when the LPS sensor 5 is powered on, and M' represents the MPS measurement value when the rack 3 moves right to the right limit position.

[0102] Specifically, by applying a rack displacement instruction to the motor 101, the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left to the left limit position or right to the right limit position.

[0103] Further, the rack 3 moves to the left limit position or the rack 3 moves to the right limit position, which is determined by the following method:

[0104] When the rotor torque of the motor 101 is greater than a preset threshold, and the rack speed of the rack 3 is less than a preset threshold and lasts for a period of time;

[0105] The motor 101 enters a stalled state, and the position where the rack 3 moves to the left is the left limit position or the position where the rack 3 moves to the right is the limit position.

[0106] Furthermore, the rotor torque of the motor 101 is calculated by the following method:

[0107] Step S201, obtaining a rack displacement instruction; the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left or right according to the rack displacement instruction.

[0108] For example, it is assumed that the maximum stroke of the rack 3 moving to the left is -60 mm, and the maximum stroke of the rack 3 moving to the right is 60 mm.

[0109] A rack displacement instruction of -100 mm to the left is applied to the motor 101 to control the motor 101 to drive the rack 3 of the rear wheel steering mechanism to move left.

[0110] A rack displacement instruction of 100 mm to the right is applied to the motor 101, so as to control the motor 101 to drive the rack 3 of the rear wheel steering mechanism to move right.

[0111] In this embodiment, applying a rack displacement instruction of -100 mm to the left and a rack displacement instruction of 100 mm to the right to the motor 101 is only exemplary. In some embodiments, as long as the rack displacement instruction is greater than the maximum stroke (-60 mm, 60 mm), it is sufficient to ensure that the rack 3 can reach the leftmost end or the rightmost end.

[0112] Step S202: The LPS sensor 5 collects the actual displacement of the rack 3 after the rack 3 moves left or right.

[0113] When the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left or right according to the rack displacement instruction, the LPS sensor 5 collects the actual rack displacement after the rack 3 moves left or right in real time.

[0114] Step S203: filter the actual rack displacement to obtain the filtered actual rack displacement.

[0115] The actual rack displacement after the rack 3 moves left or right, which is collected in real time by the LPS sensor 5, is filtered to obtain the filtered actual rack displacement.

[0116] Step S204 : Calculate the rotor torque of the motor 101 by using the rack displacement command and the filtered actual rack displacement.

[0117] Specifically, the rack displacement command and the filtered actual rack displacement are used to perform feedforward control and PI control on the rack displacement to generate a rack speed command.

[0118] The filtered actual rack displacement is converted into the actual rack speed; the rack speed is PI controlled using the rack speed command and the actual rack speed to generate the rotor torque command of the motor 101.

[0119] When the rotor torque of the motor 101 is greater than a preset threshold, and the rack speed of the rack 3 (the actual rack speed) is less than the preset threshold and lasts for a period of time;

[0120] The motor 101 enters a stalled state, and the position where the rack 3 moves to the left is the left limit position or the position where the rack 3 moves to the right is the right limit position.

[0121] When the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left to the left limit position, the MPS sensor 4 records the MPS measurement value when the rack 3 moves left to the left limit position, such as Figure 4 shown.

[0122] Calculate the rack position measurement value when rack 3 moves left to the left limit position: C = L0 + M;

[0123] Wherein, C represents the rack position measurement value when the rack 3 moves left to the left limit position, L0 represents the initial scale value when the LPS sensor 5 is powered on, and M represents the MPS measurement value when the rack 3 moves left to the left limit position.

[0124] For example, the motor 101 enters a stalled state, and the left limit position of the rack 3 moving to the left is -40 mm, that is, the rack 3 moves to the left to -40 mm.

[0125] like Figure 3 As shown, after the rear-wheel steering mechanism is offline, the actual position of the rack 3 is offset to the left by a distance d from the correct position, and the zero position of the MPS sensor 4 is aligned with the rack midpoint O of the rack 3. When the rack 3 moves to the left at -40 mm, the MPS measurement value of the rack 3 moved to the left extreme position recorded by the MPS sensor 4 is -39 mm, that is, the rack 3 actually moves to the left by -39 mm.

[0126] Assuming that the initial scale value of the LPS sensor 5 read when it is powered on is 1 mm, the rack position measurement value when the rack 3 moves left to the left limit position is calculated by the following method:

[0127] C=L0+M=1mm-39mm=-38mm.

[0128] When the motor 101 drives the rack 3 of the rear wheel steering mechanism to move right to the right limit position, the MPS sensor 4 records the MPS measurement value when the rack 3 moves right to the right limit position, such as Figure 5 shown.

[0129] Calculate the rack position measurement value when the rack 3 moves right to the right limit position: C'=L0+M';

[0130] Wherein, C' represents the rack position measurement value when the rack 3 moves right to the right limit position, L0 represents the initial scale value when the LPS sensor 5 is powered on, and M' represents the MPS measurement value when the rack 3 moves right to the right limit position.

[0131] For example, the motor 101 enters a stalled state, and the right limit position of the rack 3 moving to the right is 40 mm, that is, the rack 3 moves to the right to 40 mm.

[0132] like Figure 3 As shown, after the rear-wheel steering mechanism is offline, the actual position of the rack 3 is offset to the left by a distance d from the correct position, and the zero position of the MPS sensor 4 is aligned with the rack midpoint O of the rack 3. When the rack 3 moves to the right to 40 mm, the MPS measurement value of the rack 3 moving to the right extreme position recorded by the MPS sensor 4 is 41 mm, that is, the rack 3 actually moves to the right by 41 mm.

[0133] Assuming that the initial scale value of sensor 5 read by LPS when it is powered on is 1 mm, the rack position measurement value when rack 3 moves right to the right limit position is calculated by the following method:

[0134] C'=L0+M'=1mm+41mm=42mm.

[0135] Step S3, repeat step S2 at least once, obtain multiple rack position measurement values ​​C1, C2, ..., Cn when the rack 3 moves to the left extreme position, and multiple rack position measurement values ​​C1', C2', ..., Cn' when the rack 3 moves to the right extreme position.

[0136] Calculate the deviation between the rack midpoint O of the rack 3 of the rear wheel steering mechanism and the initial scale of the LPS sensor 5 when it is powered on:

[0137] Δσ1=(C1+C2+...+Cn+C1'+C2'+...+Cn') / 2n

[0138] Among them, Δσ1 represents the deviation between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on, C1, C2, ..., Cn represent the rack position measurement values ​​when the rack 3 is moved to the left limit position multiple times, C1', C2', ..., Cn' represent the rack position measurement values ​​when the rack 3 is moved to the right limit position multiple times, and n represents the number of times step S2 is repeated.

[0139] For example, in this embodiment, step S2 is repeated once, the motor 101 enters a stalled state, and when the rack 3 moves to the left at -40 mm, the MPS measurement value recorded by the MPS sensor 4 when the rack 3 moves to the left limit position is -38 mm.

[0140] Assuming that the initial scale value of sensor 5 read by LPS when it is powered on is 1 mm, the rack position measurement value when rack 3 moves left to the left limit position is calculated by the following method:

[0141] C=L0+M=1mm-38mm=-37mm.

[0142] The motor 101 enters a stalled state, and when the rack 3 moves to the right to a position of 40 mm, the MPS measurement value of the rack 3 moving to the right limit position recorded by the MPS sensor 4 is 42 mm.

[0143] Assuming that the initial scale value of sensor 5 read by LPS when it is powered on is 1 mm, the rack position measurement value when rack 3 moves right to the right limit position is calculated by the following method:

[0144] C'=L0+M'=1mm+42mm=43mm.

[0145] In order to explain the present invention more clearly, the rack position measurement value C when the rack 3 moves left to the left limit position for the first time is recorded as C1, C1=C=L0+M=1mm-39mm=-38mm.

[0146] The rack position measurement value C when the rack 3 moves to the left limit position for the second time is recorded as C2.

[0147] C2=C=L0+M=1mm-38mm=-37mm.

[0148] The rack position measurement value C' when the rack 3 moves right to the right limit position for the first time is recorded as C1', C1'=C'=L0+M'=1mm+41mm=42mm.

[0149] The rack position measurement value C' when the rack 3 moves rightward to the right limit position for the second time is recorded as C2', C2'=C'=L0+M'=1mm+42mm=43mm.

[0150] Using the rack position measurement values ​​when the rack 3 moves to the left extreme position and to the right extreme position twice: C1 = -38 mm, C2 = -37 mm, C1' = 42 mm, C2' = 43 mm, calculate the deviation between the rack midpoint O of the rack 3 of the rear wheel steering mechanism and the initial scale when the LPS sensor 5 is powered on:

[0151] Δσ1=(C1+C2+C2'+...+Cn') / 4=(-38mm-37mm+42mm+43mm) / 4=2.5mm.

[0152] Step S4, using the deviation Δσ1 between the rack midpoint O of the rack 3 and the initial scale when the LPS sensor 5 is powered on, correct the actual position of the rack 3, and correct the initial scale when the LPS sensor 5 is powered on, to calibrate the center position of the rear wheel steering mechanism.

[0153] For example, the calculated deviation between the rack midpoint O of the rack 3 of the rear wheel steering mechanism and the initial scale of the LPS sensor 5 when powered on is Δσ1=2.5mm, and the initial scale value of the sensor 5 read by the LPS when powered on is 1mm, thereby obtaining the distance d=L0-Δσ1=1mm-2.5mm=-1.5mm that the rack midpoint O of the rack 3 is offset to the left from the correct position O'. That is, the actual position of the rack 3 is offset to the left from the correct position by d=-1.5mm.

[0154] Move rack 3 1.5m to the right to return the rack midpoint O of rack 3 to the correct position O', correct the actual position of rack 3, and adjust the initial scale 1mm of LPS sensor 5 when it is powered on to zero position, correct the initial scale of LPS sensor 5 when it is powered on, so that the zero position of LPS sensor 5 is aligned with the rack midpoint O of rack 3, and calibrate the center position of the rear wheel steering mechanism.

[0155] Step S5, the motor 101 drives the rack 3 of the rear wheel steering mechanism to move to a certain position, the MPS sensor 4 records the MPS measurement value of the rack 3 moving to a certain position, and uses the LPS sensor 5 corrected by the initial scale when power is turned on to record the LPS measurement value of the rack 3 moving to a certain position.

[0156] The MPS measurement value when the rack 3 moves to a certain position is used to calculate the rack position measurement value when the rack 3 moves to a certain position: C" = M" + L0 - Δσ1;

[0157] Among them, C" represents the rack position measurement when the rack 3 moves to a certain position, M" represents the MPS measurement value when the rack 3 moves to a certain position, L0 represents the initial scale value when the LPS sensor 5 is powered on (the initial scale value when the LPS sensor 5 is powered on before correction), and Δσ1 represents the deviation between the rack midpoint O of the rack 3 and the initial scale when the LPS sensor 5 is powered on.

[0158] The linear error of the LPS sensor is calculated using the rack position measurement value when the rack 3 moves to a certain position: Δσ2 = C”-L;

[0159] Wherein, Δσ2 represents the linear error of the LPS sensor 5 , and L represents the LPS measurement value when the rack 3 moves to a certain position and recorded by the LPS sensor 5 after the initial scale correction at power-on.

[0160] In step S1 to step S4, although the actual position of the rack 3 and the initial scale of the LPS sensor when it is powered on have been corrected, the center position of the rear wheel steering mechanism has been calibrated. However, since the LPS sensor 5 has a linear error when measuring the large stroke of the rack 3, the accuracy of the LPS sensor 5 is affected. The present invention corrects the linear error of the LPS sensor 5 after the center position of the rear wheel steering mechanism is calibrated through steps S5 to S6.

[0161] like Figure 6 As shown, in one embodiment, the motor 101 drives the rack 3 of the rear-wheel steering mechanism to move leftward to the first position W1.

[0162] In this embodiment, the first position W1 is set to -30mm. Since the rack 3 moves 1.5mm to the right, the actual position of the rack 3 has been corrected, and the rack midpoint O of the rack 3 returns to the correct position O'. The rack midpoint O of the rack 3 differs from the zero position of the MPS sensor 4 by -1.5mm, that is, the deviation between the rack midpoint O of the rack 3 and the zero position of the MPS sensor 4 is d=L0-Δσ1=-1.5mm.

[0163] At this time, when the rack 3 moves to the left to the first position W1 = -30 mm, the MPS measurement value recorded by the MPS sensor 4 when the rack 3 moves to the first position W1 = -30 mm is -28.5 mm.

[0164] Using the MPS measurement value when the rack 3 moves to the left to the first position W1 = -30 mm, calculate the rack position measurement value when the rack 3 moves to the first position W1 = -30 mm:

[0165] C”=M”+L0-Δσ1=-28.5mm+1mm-2.5mm=-30mm.

[0166] In step S1 to step S4, the zero position of the LPS sensor 5 is aligned with the rack midpoint O of the rack 3. However, due to the linear error of the LPS sensor 5 when measuring the maximum stroke of the rack 3, there is an error in the LPS measurement value recorded by the LPS sensor 5 after the initial scale correction when the rack 3 moves to W1 = -30 mm when powered on.

[0167] For example, in this embodiment, when the rack 3 moves to the left to the first position W1 = -30 mm, the LPS measurement value of the rack 3 moving to the first position W1 = -30 mm recorded by the LPS sensor 5 after the initial scale correction at power-on is -29.6 mm.

[0168] The linear error of the LPS sensor 5 is calculated using the rack position measurement value when the rack 3 moves to the left to the first position W1 = -30 mm:

[0169] Δσ2=C”-L=-30mm-(-29.6mm)=-0.4mm.

[0170] Step S6, repeating step S5 multiple times to calculate the linear errors Δσ2 of multiple LPS sensors 5;

[0171] A mapping relationship between the LPS measurement value of the LPS sensor 5 when the rack 3 moves to different positions and the linear error Δσ2 of the corresponding LPS sensor 5 is established to complete the mid-position self-learning of the rear-wheel steering mechanism.

[0172] Combination Figure 6 and Figure 7In this embodiment, the second position W2=-15mm, the third position W3=15mm, and the fourth position W4=30mm are set, and step S5 is repeated. The linear error of the LPS sensor is calculated using the rack position measurement value when the rack 3 moves to the left to the second position W2=-15mm:

[0173] Δσ2=C”-L=-15mm-(-14.8mm)=-0.2mm.

[0174] The linear error of the LPS sensor is calculated using the rack position measurement value when the rack 3 moves to the right to the third position W3 = 15 mm:

[0175] Δσ2=C”-L=15mm-14.8mm=0.2mm.

[0176] The linear error of the LPS sensor is calculated using the rack position measurement value when the rack 3 moves to the right to the fourth position W4 = 30 mm:

[0177] Δσ2=C”-L=30mm-29.6mm=0.4mm.

[0178] A mapping relationship between the LPS measurement value of the LPS sensor when the rack 3 moves to the first position W1, the second position W2, the third position W3 and the fourth position W4 and the linear error Δσ2 of the corresponding LPS sensor 5 is established to complete the mid-position self-learning of the rear-wheel steering mechanism.

[0179] Specifically, in this embodiment, a mapping relationship is established between the LPS measurement value -29.6 mm of the LPS sensor when the rack 3 moves to the first position W1 and the linear error Δσ2 = -0.4 mm of the corresponding LPS sensor 5 .

[0180] A mapping relationship between the LPS measurement value -14.8 mm of the LPS sensor when the rack 3 moves to the second position W2 and the linear error Δσ2 = -0.2 mm of the corresponding LPS sensor 5 is established.

[0181] A mapping relationship between the LPS measurement value 14.8 mm of the LPS sensor when the rack 3 moves to the third position W3 and the linear error Δσ2=0.2 mm of the corresponding LPS sensor 5 is established.

[0182] A mapping relationship between the LPS measurement value 29.6 mm of the LPS sensor when the rack 3 moves to the fourth position W3 and the linear error Δσ2=0.4 mm of the corresponding LPS sensor 5 is established.

[0183] A lookup table is prepared by mapping the established LPS measurement values ​​of the LPS sensor 5 when the rack 3 moves to different positions with the corresponding linear error Δσ2 of the LPS sensor 5. In the lookup table, the LPS measurement values ​​of multiple LPS sensors correspond to the linear errors of multiple LPS sensors 5 one by one, and the mid-position self-learning of the rear-wheel steering mechanism is completed.

[0184] In some preferred embodiments, since it is impossible to exhaust every position where the rack 3 moves, linear interpolation is performed on the linear errors Δσ2 of multiple LPS sensors 5 to obtain multiple linear interpolation results.

[0185] By using the results of multiple linear interpolations, a mapping relationship between the LPS measurement value of the LPS sensor 5 when the rack 3 moves to different positions and the linear error Δσ2 of the corresponding LPS sensor 5 is established.

[0186] In the present invention, in step S1 to step S4, the actual position of the rack 3 and the initial scale of the LPS sensor 5 when it is powered on are corrected, so that the zero position of the LPS sensor 5 is aligned with the rack midpoint O of the rack 3, and the center position of the rear-wheel steering mechanism is calibrated. There is no error caused by human factors in the whole process, which greatly reduces the error and ensures the accuracy of the center position calibration of the rear-wheel steering mechanism.

[0187] After the present invention calibrates the middle position of the rear wheel steering mechanism, since the LPS sensor 5 has a linear error when measuring the maximum stroke of the rack 3, the present invention corrects the linear error of the LPS sensor 5 through steps S5 to S6, thereby ensuring the accuracy of the LPS sensor.

[0188] According to an embodiment of the present invention, a method for compensating for a center deviation of a rear-wheel steering mechanism is provided, comprising the following method steps:

[0189] Step 1: The motor 101 drives the rack 3 of the rear wheel steering mechanism to move left or right.

[0190] Step 2: The LPS sensor 4 records the LPS measurement value of the rack 3 moving to the left or right.

[0191] Step 3, find the mapping relationship (lookup table) between the LPS measurement value of the LPS sensor 5 when the rack moves to different positions established by the mid-position self-learning method of the rear-wheel steering mechanism of the present invention and the linear error Δσ2 of the corresponding LPS sensor 5.

[0192] The LPS measurement value of the rack moving to the left or right recorded by the LPS sensor 5 is obtained, and the linear error Δσ2 of the corresponding LPS sensor is obtained.

[0193] Step 4: Use the obtained linear error Δσ2 of the LPS sensor to compensate the LPS measurement value of the rack moving left or right recorded by the LPS sensor, so as to complete the median deviation compensation of the back-wheel steering mechanism.

[0194] Combination Figure 1 , Figures 8 to 10 According to an embodiment of the present invention, a mid-position self-learning system of a rear-wheel steering mechanism is provided, which is used to execute a mid-position self-learning method of a rear-wheel steering mechanism provided by the present invention, comprising:

[0195] The motor assembly 1 of the rear wheel steering mechanism is equipped with an MPS sensor 4. The motor assembly 1 includes a motor 101. The motor 101 is used to drive the rack 3 of the rear wheel steering mechanism to move left and right.

[0196] The MPS sensor 4 is used to measure the rotor angle of the motor 101, thereby measuring the MPS measurement value of the left-right movement of the rack 3 of the rear wheel steering mechanism.

[0197] The rear wheel steering mechanism is equipped with an LPS sensor 5. The LPS sensor 5 is used to measure the LPS measurement value of the left and right movement of the rack 3 of the rear wheel steering mechanism.

[0198] The motor assembly 1 integrates a limit position judgment module 102 , a rack midpoint deviation calculation module 103 , a mid-position calibration module 104 and a mapping relationship generation module 105 .

[0199] The limit position determination module 102 is used to determine whether the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left to the left limit position or the rack 3 to move right to the right limit position.

[0200] Specifically, Figure 8 As shown, the limit position determination module 102 includes a filtering module 1021 , a control module 1022 and a stall state determination module 1023 .

[0201] The control module 1022 obtains the rack displacement instruction and controls the motor 101 to drive the rack 3 of the rear wheel steering mechanism to move left or right.

[0202] When the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left or right according to the rack displacement instruction, the LPS sensor 5 collects the actual rack displacement after the rack 3 moves left or right in real time.

[0203] The filtering module 1021 is used to filter the actual rack displacement after the rack 3 moves left or right, which is collected by the LPS sensor 5, to obtain the filtered actual rack displacement.

[0204] The control module 1022 calculates the rotor torque of the motor using the rack displacement command and the filtered actual rack displacement.

[0205] Specifically, Fig.10 As shown, the control module 1022 uses the rack displacement instruction and the filtered actual rack displacement to perform feedforward control and PI control on the rack displacement to generate a rack speed instruction.

[0206] The filtered actual rack displacement is converted into the actual rack speed; the rack speed is PI controlled using the rack speed command and the actual rack speed to generate the rotor torque of the motor 101.

[0207] The stall state determination module 1023 is used to determine whether the motor 101 enters a stall state:

[0208] When the rotor torque of the motor 101 is greater than a preset threshold, and the rack speed (actual rack speed) is less than the preset threshold and lasts for a period of time, the motor 101 enters a stalled state, otherwise the motor 101 does not enter a stalled state.

[0209] When the motor 101 enters the stalled state, the limit position determination module 102 determines that the rack 3 moves to the left limit position or moves to the right limit position.

[0210] When the limit position judgment module 102 determines that the motor 101 drives the rack 3 of the rear wheel steering mechanism to move left to the left limit position, the MPS sensor 4 records the MPS measurement value of the rack 3 moving left to the left limit position; when the limit position judgment module 102 determines that the motor 101 drives the rack 3 of the rear wheel steering mechanism to move right to the right limit position, the MPS sensor 4 records the MPS measurement value of the rack 3 moving right to the right limit position.

[0211] The rack midpoint deviation calculation module 103 is used to calculate the deviation between the rack midpoint of the rack 3 of the rear wheel steering mechanism and the initial scale when the LPS sensor 5 is powered on.

[0212] Specifically, the rack 3 moves to the left extreme position and the rack 3 moves to the right extreme position at least once, and the rack position measurement values ​​C1, C2, ..., Cn when the rack 3 moves to the left extreme position multiple times, and the rack position measurement values ​​C1', C2', ..., Cn' when the rack 3 moves to the right extreme position multiple times are calculated.

[0213] Calculate the deviation between the rack midpoint O of the rack 3 of the rear wheel steering mechanism and the initial scale of the LPS sensor 5 when it is powered on:

[0214] Δσ1=(C1+C2+...+Cn+C1'+C2'+...+Cn') / 2n

[0215] Among them, Δσ1 represents the deviation between the midpoint of the rack 3 of the rack and the initial scale when the LPS sensor 5 is powered on, C1, C2, ..., Cn represent the rack position measurement values ​​when the rack 3 moves to the left limit position multiple times, C1', C2', ..., Cn' represent the rack position measurement values ​​when the rack 3 moves to the right limit position multiple times, and n represents the number of times step S2 is repeated.

[0216] The center position calibration module 104 uses the deviation between the rack midpoint O of the rack 3 and the initial scale when the LPS sensor 5 is powered on to correct the actual position of the rack 3 and the initial scale when the LPS sensor 5 is powered on to calibrate the center position of the rear wheel steering mechanism.

[0217] The mapping relationship generating module 105 is used to calculate the linear errors of the plurality of LPS sensors and establish a mapping relationship between the LPS measurement values ​​of the LPS sensors when the rack moves to different positions and the linear errors Δσ2 of the corresponding LPS sensors.

[0218] According to an embodiment of the present invention, a center deviation compensation system of a rear-wheel steering mechanism is provided, which is used to execute a center deviation compensation method of a rear-wheel steering mechanism provided by the present invention.

[0219] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A mid-position self-learning method for a rear-wheel steering mechanism, characterized in that: The median self-learning method comprises the following steps: S1. The motor assembly of the rear wheel steering mechanism is equipped with an MPS sensor; wherein the motor assembly includes a motor; the motor is used to drive the rack of the rear wheel steering mechanism to move left and right; The MPS sensor is used to measure the rotor angle of the motor, thereby measuring the MPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism; The rear wheel steering mechanism is equipped with an LPS sensor, and the LPS sensor is used to measure the LPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism; S2, the motor drives the rack of the rear wheel steering mechanism to move left to the left limit position, and the MPS sensor records the MPS measurement value when the rack moves left to the left limit position; Calculate the rack position measurement value when the rack moves to the left limit position: C = L0 + M; Among them, C represents the rack position measurement value when the rack moves to the left limit position, L0 represents the initial scale value when the LPS sensor is powered on, and M represents the MPS measurement value when the rack moves to the left limit position; The motor drives the rack of the rear wheel steering mechanism to move right to the right limit position, and the MPS sensor records the MPS measurement value when the rack moves right to the right limit position; Calculate the measured value of the rack position when the rack moves right to the right limit position: C'=L0+M'; Among them, C' represents the rack position measurement value when the rack moves right to the right limit position, L0 represents the initial scale value when the LPS sensor is powered on, and M' represents the MPS measurement value when the rack moves right to the right limit position; S3, repeat step S2 at least once, obtain multiple rack position measurement values ​​C1, C2, ..., Cn when the rack moves to the left to the left limit position, and multiple rack position measurement values ​​C1', C2', ..., Cn' when the rack moves to the right to the right limit position; Calculate the deviation between the rack midpoint of the rear wheel steering mechanism and the initial scale when the LPS sensor is powered on: Δσ1=(C1+C2+...+Cn+C1'+C2'+...+Cn') / 2n; Wherein, Δσ1 represents the deviation between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on, C1, C2, ..., Cn represent the rack position measurement values ​​when the rack is moved to the left limit position multiple times, C1', C2', ..., Cn' represent the rack position measurement values ​​when the rack is moved to the right limit position multiple times, and n represents the number of times step S2 is repeated; S4, using the deviation Δσ1 between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on, correcting the actual position of the rack, and correcting the initial scale when the LPS sensor is powered on, to calibrate the midpoint of the rear wheel steering mechanism; S5, the motor drives the rack of the rear wheel steering mechanism to move to a certain position, the MPS sensor records the MPS measurement value of the rack moving to a certain position, and uses the LPS sensor corrected by the initial scale at power-on to record the LPS measurement value of the rack moving to a certain position; Using the MPS measurement value when the rack moves to a certain position, calculate the rack position measurement value when the rack moves to a certain position: C”=M”+L0-Δσ1; Among them, C” represents the rack position measurement when the rack moves to a certain position, and M” represents the MPS measurement value when the rack moves to a certain position; The linear error of the LPS sensor is calculated using the rack position measurement value when the rack moves to a certain position: Δσ2 = C”-L; Among them, Δσ2 represents the linear error of the LPS sensor, and L represents the LPS measurement value recorded by the LPS sensor after the initial scale correction at power-on when the rack moves to a certain position; S6, repeat step S5 multiple times to calculate the linear error Δσ2 of multiple LPS sensors; The mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor is established to complete the mid-position self-learning of the rear-wheel steering mechanism.

2. The median self-learning method according to claim 1, characterized in that: In step S2, the rack moves to the left limit position or the rack moves to the right limit position, which is determined by the following method: When the rotor torque of the motor is greater than a preset threshold, and the rack speed is less than a preset threshold and lasts for a period of time; The motor enters a stalled state, and the position where the rack moves to the left is the left limit position or the position where the rack moves to the right is the right limit position.

3. The median self-learning method according to claim 2, characterized in that: The rotor torque of the motor is calculated by the following method: S201, obtaining a rack displacement instruction; the motor drives the rack of the rear wheel steering mechanism to move left or right according to the rack displacement instruction; S202, the LPS sensor collects the actual displacement of the rack after the rack moves left or right; S203, filtering the actual displacement of the rack to obtain the filtered actual displacement of the rack; S204, calculating the rotor torque of the motor using the rack displacement command and the filtered actual rack displacement.

4. The median self-learning method according to claim 3, characterized in that: In step S204, the rack displacement is fed-forward controlled and PI controlled by using the rack displacement command and the filtered actual rack displacement to generate a rack speed command; The filtered actual rack displacement is converted into the actual rack speed; the rack speed is controlled by PI using the rack speed command and the actual rack speed to generate the rotor torque command of the motor.

5. The median self-learning method according to claim 1, characterized in that: In step S6, linear interpolation is performed on the linear errors Δσ2 of the plurality of LPS sensors to obtain a plurality of linear interpolation results; Using the results of multiple linear interpolations, a mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor is established.

6. A method for compensating for a mid-position deviation of a rear-wheel steering mechanism, characterized in that: The median deviation compensation method comprises the following method steps: Step 1, the motor drives the rack of the rear wheel steering mechanism to move left or right; Step 2, the LPS sensor records the LPS measurement value when the rack moves left or right; Step 3, searching for the median self-learning method described in any one of claims 1 to 5, and establishing a mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor; Obtain the LPS measurement value of the LPS sensor recording tooth bar moving left or right, and the corresponding linear error Δσ2 of the LPS sensor; Step 4: Use the obtained linear error Δσ2 of the LPS sensor to compensate the LPS measurement value of the rack moving left or right recorded by the LPS sensor to complete the median deviation compensation of the back-wheel steering mechanism.

7. A mid-position self-learning system for a rear wheel steering mechanism, characterized in that: The median self-learning system is used to execute the median self-learning method according to any one of claims 1 to 5, comprising: An MPS sensor configured for a motor assembly of a rear-wheel steering mechanism; the motor assembly includes a motor; the motor is used to drive the rack of the rear-wheel steering mechanism to move left and right; The MPS sensor is used to measure the rotor angle of the motor, thereby measuring the MPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism; The rear wheel steering mechanism is equipped with an LPS sensor, and the LPS sensor is used to measure the LPS measurement value of the left and right movement of the rack of the rear wheel steering mechanism; The motor assembly integrates a limit position judgment module, a rack midpoint deviation calculation module, a mid-position calibration module and a mapping relationship generation module; The limit position judgment module is used to determine whether the rack of the motor-driven rear wheel steering mechanism moves to the left limit position or the rack moves to the right limit position; The rack midpoint deviation calculation module is used to calculate the deviation between the rack midpoint of the rack of the rear wheel steering mechanism and the initial scale when the LPS sensor is powered on; The center position calibration module uses the deviation between the rack midpoint of the rack and the initial scale when the LPS sensor is powered on to correct the actual position of the rack and correct the initial scale when the LPS sensor is powered on to calibrate the center position of the rear wheel steering mechanism; The mapping relationship generating module is used to calculate the linear errors of multiple LPS sensors and establish a mapping relationship between the LPS measurement value of the LPS sensor when the rack moves to different positions and the linear error Δσ2 of the corresponding LPS sensor.

8. The median self-learning system according to claim 7, characterized in that: The limit position judgment module includes a filtering module, a control module and a stall state judgment module; The control module obtains a rack displacement instruction and controls the motor to drive the rack of the rear wheel steering mechanism to move left or right; The filtering module is used to filter the actual displacement of the rack after the rack moves left or right, which is collected by the LPS sensor, to obtain the filtered actual displacement of the rack; The control module calculates the rotor torque of the motor using the rack displacement command and the filtered actual rack displacement; The stall state judgment module is used to judge whether the motor enters a stall state: When the rotor torque of the motor is greater than a preset threshold value, and the rack speed is less than a preset threshold value and lasts for a period of time, the motor enters a stalled state, otherwise the motor does not enter a stalled state; When the motor enters a stalled state, the limit position determination module determines that the rack moves left to a left limit position or the rack moves right to a right limit position.

9. The median self-learning system according to claim 8, characterized in that: The control module uses the rack displacement command and the filtered actual rack displacement to perform feedforward control and PI control on the rack displacement to generate a rack speed command; The filtered actual rack displacement is converted into the actual rack speed; the rack speed is controlled by PI using the rack speed command and the actual rack speed to generate the rotor torque command of the motor.

10. A mid-position deviation compensation system for a rear wheel steering mechanism, characterized in that: The median deviation compensation system is used to execute the median deviation compensation method described in claim 6.

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