A compensation algorithm for a rear-wheel steering sensor system

Abstract

The present invention discloses a compensation algorithm for a rear-wheel steering sensor system, which relates to the technical field of vehicle control. Aiming at the performance limitations of sensors, failures of mechanical components, and transmission accuracy problems, the controller receives the corner request from an external controller, controls the rotational speed and torque of the motor, and the rotational speed and torque of the motor are transmitted to a ball screw mechanism through a belt and a pulley. The ball screw mechanism converts the rotational motion of the motor into the linear motion of the screw. The displacement of the screw is detected by a motor position sensor and a linear position sensor. The controller combines the position of the linear displacement sensor and the degree of the motor position sensor to determine the number of turns the motor needs to rotate when the screw returns to the middle position, and a compensation algorithm that meets the functional safety requirements, solving the problem of screw position deviation caused by mechanical system and sensor errors, and meeting the requirements of the functional safety level.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle control, and particularly relates to a compensation algorithm for a rear-wheel steering sensor system. Background Art

[0002] With the development of automotive electronic control and intelligence, rear-wheel steering sensors are applied to mid- to high-end sedans. At low speeds, the rear-wheel steering gear can reduce the turning radius of the vehicle and increase its flexibility; at high speeds, the rear-wheel steering gear can improve the driving stability of the vehicle. The rear-wheel steering gear belongs to steer-by-wire. If the rear-wheel steering gear malfunctions or its accuracy decreases, it is very likely to cause safety accidents.

[0003] In the prior art, there are two types of rear-wheel steering sensors used in the rear-wheel steering system to monitor the position of the lead screw: a linear displacement sensor and a motor position sensor. The linear displacement sensor can directly monitor the displacement of the lead screw, and the motor position sensor can monitor the number of rotations and position of the motor, and outputs the rotation angle and number of rotations of the motor, which is converted into the displacement of the lead screw through the transmission ratio. However, the linear displacement sensor and the motor position sensor have the following problems.

[0004] 1. When the vehicle is powered off, the readings of the motor position sensor cannot be written into the program. As a result, each time the vehicle is powered on, the motor position sensor only knows the current position of the number of turns and has no idea how many turns the motor has rotated. Therefore, it is impossible to know the actual position of the lead screw. 2. Due to the limitations of the technology of the linear displacement sensor itself, its accuracy decreases at high temperatures, and there are large transmission errors in the mechanical assembly at high temperatures or under large external forces. Coupled with the long-term wear of mechanical components, there will be a large error between the position of the lead screw sent by the motor position sensor and the actual position of the lead screw, resulting in an unexpected rotation angle of the rear wheel. This situation can cause the vehicle to deviate from its course and even become unstable. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention conceives a compensation algorithm for a rear-wheel steering sensor system, provides a compensation algorithm for the performance limitations of the sensor, faults of mechanical components, and transmission accuracy problems to meet the requirements of the functional safety level.

[0006] The technical solution adopted to implement the present invention is: a compensation algorithm for a rear-wheel steering sensor system, the rear-wheel steering sensor system comprising: a motor, a controller, a ball screw mechanism, a belt and a pulley, a pull rod, a linear displacement sensor and a motor position sensor, the controller receiving a cornering request and controlling the rotational speed N and torque T of the motor, the rotational speed and torque of the motor being transmitted to the ball screw mechanism through the belt and pulley, the ball screw mechanism converting the rotational motion of the motor into a linear motion of the lead screw, and detecting the displacement of the lead screw through the motor position sensor and the linear position sensor, characterized in that the compensation algorithm for the rear-wheel steering sensor system comprises the following steps:

[0007] 1) Check the difference S between the two signals S1 and S2 of the linear displacement sensor, i.e., S = S1 - S2, and the critical value S D = 0.2 mm. If S > S D , it is determined that the linear displacement sensor fails, report a general fault, and the motor position sensor controls it to rotate back to zero and maintain the zero position. The controller no longer accepts the cornering request and reports to the instrument to remind the driver; when the difference resumes S ≤ S D , restore the normal monitoring mechanism of the linear displacement sensor, and calculate the lead screw displacement speed Vs = ρS / ρt through the displacement ρS at the current moment ρt and the next moment;

[0008] 2) Check the difference δ between the two signals δ1 and δ2 of the motor position sensor, i.e., δ = δ1 - δ2, and the critical value is δ D . If δ > δ D , it is determined that the motor position sensor fails, report a serious fault, cut off the motor power at the same time and keep it in place, and report to the instrument to remind the driver of a serious fault and stop driving. The controller no longer accepts the cornering request, and calculate the external thrust F of the ball screw according to formula (1):

[0009] F × Vs = T × N × η / 9550 (1)

[0010] Where: F is the external lead screw thrust, Vs is the lead screw speed, T is the motor torque, N is the motor speed, and η is the total mechanical transmission efficiency;

[0011] Convert the motor speed N into the displacement S of the lead screw R = n × i / P,

[0012] Where: n is the number of turns of the motor rotation, i is the transmission ratio, and P is the lead screw pitch;

[0013] 3) F A is the limit external force value affecting the transmission accuracy at room temperature, F A = 1 KN, T Ais the critical upper limit value of the mechanical assembly temperature, T A = 60 °C, the critical value S A = 0.4 mm, S L is the lead screw displacement monitored by the stroke sensor, S R is the lead screw displacement monitored by the motor position sensor. If |S L - S R | ≤ S A , the angular displacement of the motor does not need to be corrected; if |S L - S R | > S A , when the external force F < F A , and the mechanical assembly temperature < TA, the lead screw displacement monitoring mechanism takes effect, and the angular displacement of the motor is compensated and corrected. The angular displacement compensation mechanism of the motor calculates the actual compensation value Sn of the current cycle according to formula (2),

[0014] Sn = (S B - Sn-1)K + Sn-1(2)

[0015] In the formula: S B is the target compensation displacement; Sn-1 is the actual compensation value of the previous cycle; the calibration coefficient K ≤ 0.5;

[0016] If S n ≤ S A , the target displacement adjustment amount is reached, and no further compensation is required at this time; if |S L - S R | ≥ S C , when the set value S C = 2 mm, an alarm signal is issued, the internal mechanical components are damaged, and the components need to be replaced.

[0017] Furthermore, the motor is a variable frequency speed control motor.

[0018] Furthermore, the ball screw mechanism is a circulating guide vane type.

[0019] Furthermore, both ends of the linear displacement sensor have a 4 mm buffer stroke, and the accuracy is 0.05% - 0.02% FS.

[0020] Furthermore, the motor position sensor is a proximity sensor.

[0021] Furthermore, the controller is a microprogram controller.

[0022] The beneficial effects of a compensation algorithm for a rear-wheel steering sensor system according to the present invention are as follows:

[0023] A compensation algorithm for a rear-wheel steering sensor system, which receives a corner request from an external controller through a controller, controls the speed and torque of a motor, and the speed and torque of the motor are transmitted to a ball screw mechanism through a belt and a pulley. The ball screw mechanism converts the rotational motion of the motor into a linear motion of the screw. The displacement of the screw is detected by a motor position sensor and a linear position sensor. The controller combines the position of the linear displacement sensor and the degree of the motor position sensor to determine the number of turns the motor needs to rotate when the screw returns to the middle position, and a compensation algorithm that meets the functional safety requirements is used to solve the problem of screw position deviation caused by mechanical system and sensor errors. Brief Description of the Drawings

[0024] Figure 1 is a flowchart of a compensation algorithm for a rear-wheel steering sensor system;

[0025] Figure 2 is a system schematic diagram of a rear-wheel steering sensor system;

[0026] Figure 3 is a schematic diagram of the position of a roller screw mechanism in a rear-wheel steering sensor system. Detailed Embodiment

[0027] The following combines the attached Figures 1 to 3 drawings and specific embodiments to further describe the present invention in detail. To make the purpose, technical solution and advantages of the embodiments clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. The specific embodiments described here are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] As shown in the attached Figure 2 drawings, the rear-wheel steering sensor system includes: a motor, a controller, a roller screw mechanism, a belt and a pulley, a pull rod, a linear displacement sensor and a motor position sensor. The motor is a variable-frequency speed-regulating motor, the roller screw mechanism is a circulating guide type, both ends of the linear displacement sensor have a 4-mm buffer stroke, and the accuracy is 0.05% - 0.02% FS. The motor position sensor is a proximity sensor, and the controller is a microprogram controller. The controller receives a corner request and controls the speed N and torque T of the motor. The speed and torque of the motor are transmitted to the ball screw mechanism through the belt and the pulley. The ball screw mechanism converts the rotational motion of the motor into a linear motion of the screw. The displacement of the screw is detected by the motor position sensor and the linear position sensor. By monitoring the displacement of the screw and through the conversion ratio of the screw displacement and the rear-wheel corner.

[0029] As shown in the attached Figure 1 drawings, a compensation algorithm for a rear-wheel steering sensor system includes the following steps:

[0030] 1) Check the difference S of the two signals S1 and S2 of the linear displacement sensor, that is, S = S1 - S2, and the critical value S D = 0.2 mm. If S > S D , it is determined that the linear displacement sensor fails, report a general fault, return to zero and hold the zero position under the control of the motor position sensor, the controller no longer accepts the corner request, and report to the instrument to remind the driver; when the difference resumes S ≤ S D , restore the normal monitoring mechanism of the linear displacement sensor, and calculate the lead screw displacement speed Vs = ρS / ρt through the displacement ρS at the current moment ρt and the next moment;

[0031] 2) Check the difference δ of the two signals δ1 and δ2 of the motor position sensor, that is, δ = δ1 - δ2, and the critical value is δ D . If δ > δ D , it is determined that the motor position sensor fails, report a serious fault, cut off the motor power at the same time and keep it in place, and report to the instrument to remind the driver and then turn to a serious fault, stop driving, the controller no longer accepts the corner request, and calculate the external thrust F of the ball screw according to formula (1),

[0032] F × Vs = T × N × η / 9550 (1)

[0033] In the formula: F is the external lead screw thrust, Vs is the lead screw speed, T is the motor torque, N is the motor speed, and η is the total mechanical transmission efficiency;

[0034] Convert the motor speed N into the displacement S of the lead screw R = n × i / P,

[0035] In the formula: n is the number of turns of the motor rotation, i is the transmission ratio, and P is the lead screw pitch;

[0036] 3) F A is the limit external force value affecting the transmission accuracy at room temperature, F A = 1 KN, T A is the critical upper limit value of the mechanical assembly temperature accuracy, T A = 60 °C, the critical value S A = 0.4 mm, S L is the lead screw displacement monitored by the travel sensor, S R is the lead screw displacement monitored by the motor position sensor. If |S L - S R | ≤ S A , there is no need to correct the angular displacement of the motor; if |S L - S R | > S A , when the external force F < FA and the temperature of the mechanical assembly < T A When this occurs, the lead screw displacement monitoring mechanism becomes effective, compensating and correcting the angular displacement of the motor. The angular displacement compensation mechanism of the motor calculates the actual compensation value Sn for the current cycle according to formula (2).

[0037] Sn = (S B - Sn-1)K + Sn-1 (2)

[0038] where: S B is the target compensation displacement; Sn-1 is the actual compensation value of the previous cycle; the calibration coefficient K ≤ 0.5;

[0039] If S n ≤ S A , the target displacement adjustment amount is reached and no further compensation is made at this time; if |S L -S R | ≥ S C , when the set value S C = 2 mm, an alarm signal is issued, indicating that the internal mechanical components are damaged and need to be replaced.

[0040] When the cumulative error between the linear displacement sensor and the mechanical assembly exceeds a certain threshold, the motor will be unable to calculate the actual position of the lead screw. As shown in the appendix Figure 3 , it is not clear whether it should rotate three or four turns to reach the current lead screw position. At this time, it is necessary to judge according to the external force and temperature threshold. If it is within the range, the lead screw position is corrected at this time to reduce the error.

[0041] The above is only the preferred mode of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A compensation algorithm for a rear-wheel steering sensor system, the rear-wheel steering sensor system comprises: a motor, a controller, a roller screw mechanism, a belt and a pulley, a pull rod, a linear displacement sensor and a motor position sensor. The controller receives a corner request and controls the rotational speed N and torque T of the motor. The rotational speed and torque of the motor are transmitted to the ball screw mechanism through the belt and pulley. The ball screw mechanism converts the rotational motion of the motor into the linear motion of the screw. The displacement of the screw is detected by the motor position sensor and the linear position sensor. The compensation algorithm for the rear-wheel steering sensor system is characterized by the following steps: 1) Check the difference S between the two signals S1 and S2 of the linear displacement sensor, that is, S = S1 - S2. The critical value SD = 0.2 mm. If S > SD, it is determined that the linear displacement sensor fails, and a general fault is reported. The motor position sensor controls the motor to rotate back to zero and maintain the zero position. The controller no longer accepts the corner request and reports to the instrument to remind the driver. When the difference recovers to S ≤ SD, restore the normal monitoring mechanism of the linear displacement sensor. Calculate the screw displacement speed Vs through the current moment ρt and the displacement amount ρS at the next moment. 2) Check the difference δ between the two signals δ1 and δ2 of the motor position sensor, that is, δ = δ1 - δ2. The critical value is δD. If δ > δD, it is determined that the motor position sensor fails, and a serious fault is reported. At the same time, cut off the power of the motor and keep it in place, and report to the instrument to remind the driver of a serious fault and stop driving. The controller no longer accepts the corner request. If δ ≤ δD, calculate the external thrust F of the ball screw according to formula (1). F×Vs = T×N×η / 9550 (1) In the formula: F is the external thrust of the ball screw, Vs is the screw speed, T is the motor torque, N is the motor speed, and η is the total mechanical transmission efficiency; Convert the motor speed N into the displacement SR of the screw = n×i / P, In the formula: n is the number of turns of the motor rotation, i is the transmission ratio, and P is the screw lead; 3) When S ≤ SD and δ ≤ δD, FA is the limit external force value affecting the transmission accuracy at room temperature, FA = 1 KN, TA is the critical upper limit value of the mechanical assembly temperature accuracy, TA = 60 °C, the critical value SA = 0.4 mm, SL is the screw displacement monitored by the linear displacement sensor, SR is the screw displacement monitored by the motor position sensor. If |SL - SR| ≤ SA, no correction is required for the corner displacement of the motor. If |SL - SR| > SA, when F < FA and the mechanical assembly temperature < TA, the screw displacement monitoring mechanism takes effect, and the corner displacement of the motor is compensated and corrected. The corner displacement compensation mechanism of the motor calculates the actual compensation value Sn of the current cycle according to formula (2). Sn = (SB - Sn-1)K + Sn-1(2) In the formula: SB is the target compensation displacement; Sn-1 is the actual compensation value of the previous cycle; the calibration coefficient K ≤ 0.5; When Sn ≤ SA, the target displacement adjustment amount is reached and no further compensation is required. When |SL - SR| ≥ SC and the set value SC = 2 mm, an alarm signal is issued, indicating that the internal mechanical components are damaged and need to be replaced.

2. A compensation algorithm for a rear-wheel steering sensor system according to claim 1, characterized in that the motor is a variable-frequency speed-regulating motor.

3. A compensation algorithm for a rear-wheel steering sensor system according to claim 1, characterized in that the ball screw mechanism is a circulating guide vane type.

4. A compensation algorithm for a rear-wheel steering sensor system according to claim 1, characterized in that both ends of the linear displacement sensor have a 4-mm buffer stroke.

5. A compensation algorithm for a rear-wheel steering sensor system according to claim 1, characterized in that the motor position sensor is a proximity sensor.

6. A compensation algorithm for a rear-wheel steering sensor system according to claim 1, characterized in that the controller is a microprogram controller.

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