Rear wheel steering apparatus and control method thereof
The present disclosure relates to a rear wheel steering apparatus and a control method thereof, which can detect stick-slip that may occur during the operation of a rear wheel steering (RWS) system, thereby controlling the performance of a motor in a variable manner, and can control the motor to operate in a limited operation mode only when the stick-slip has occurred during the operation of the RWS system, thereby reducing the noise generated by the stick-slip and the shock transmitted to a vehicle.
1. A rear wheel steering apparatus for controlling a steering angle of rear wheels based on a command received from a vehicle electronic control unit (ECU), the rear wheel steering apparatus comprising:
a motor for moving a rear wheel steering rail connected to the rear wheels in left and right directions; and
a rear wheel steering ECU configured to control the motor to move the rear wheel steering rail to a target movement distance based on the command and to determine whether stick-slip occurs based on the target movement distance and an actual movement distance of the rear wheel steering rail.
2. The rear wheel steering apparatus of claim 1 , further comprising a linear position sensor for sensing the actual movement distance of the rear wheel steering rail, wherein the rear wheel steering ECU receives the actual movement distance from the linear position sensor.
3. The rear wheel steering apparatus of claim 2 , wherein the rear wheel steering ECU determines that the stick-slip has occurred in response to determining that a first condition, in which a difference between the target movement distance and the actual movement distance occurring for a predetermined unit time is equal to or greater than a first predetermined reference distance, is satisfied.
4. The rear wheel steering apparatus of claim 3 , wherein the rear wheel steering ECU determines whether the stick-slip occurs by further using at least one of an estimated movement distance obtained based on a rotation angle of the motor or a current output of the motor.
5. The rear wheel steering apparatus of claim 4 , further comprising a motor position sensor for sensing the rotation angle of the motor, wherein the rear wheel steering ECU receives the rotation angle from the motor position sensor and obtains the estimated movement distance of the rear wheel rail based on the rotation angle.
6. The rear wheel steering apparatus of claim 5 , wherein, in a state where the first condition is satisfied, the rear wheel steering ECU determines that the stick-slip has occurred in response to determining that at least one of a second condition, in which the current output of the motor is equal to or greater than a predetermined reference output when the actual movement distance for the unit time reaches a second predetermined reference distance or more at one go, or a third condition, in which a difference between the estimated movement distance and the actual movement distance is equal to or greater than a third predetermined distance, is satisfied.
7. The rear wheel steering apparatus of claim 6 , wherein the rear wheel steering ECU sequentially determines whether the first condition, the second condition, and the third condition are satisfied according to a predetermined sequence, determines that the stick-slip has occurred in response to determining that all the first condition, the second condition, and the third condition are satisfied, and determines that the stick-slip has not occurred in response to determining that any one of the first condition, the second condition, and the third condition is not satisfied.
8. The rear wheel steering apparatus of claim 6 , wherein, in response to determining that the stick-slip has occurred, the rear wheel steering ECU controls the motor to operate in a limited operation mode.
9. The rear wheel steering apparatus of claim 8 , wherein the rear wheel steering ECU controls the motor to operate in the limited operation mode in which the rear wheel steering rail moves by a limited movement distance obtained based on the target movement distance using a predetermined limit ratio.
10. The rear wheel steering apparatus of claim 9 , wherein the rear wheel steering ECU controls the motor to operate in the limited operation mode having different limit ratios depending on a level of the stick-slip that has occurred.
11. The rear wheel steering apparatus of claim 10 , wherein, in response to determining that the level of the stick-slip is within a first stick-slip level, at which only one of the second condition and the third condition is satisfied in a state where the first condition is satisfied, the rear wheel steering ECU controls the motor to operate in the limited operation mode in which the rear wheel steering rail moves by a first limited movement distance obtained based on the target movement distance using a first predetermined limit ratio, and
wherein, in response to determining that the level of the stick-slip is equal to a second stick-slip level, at which all the first condition, the second condition, and the third condition are satisfied, the rear wheel steering ECU controls the motor to operate in the limited operation mode in which the rear wheel steering rail moves by a second limited movement distance obtained based on the target movement distance using a second predetermined limit ratio having a value lower than the first limit ratio.
12. The rear wheel steering apparatus of claim 8 , wherein the rear wheel steering ECU performs an operation of determining whether the stick-slip occurs and an operation of controlling the motor to operate in the limited operation mode only once at a beginning of an operation of the rear wheel steering apparatus, or continuously performs the operation of determining whether the stick-slip occurs and the operation of controlling the motor to operate in the limited operation mode during the operation of the rear wheel steering apparatus.
13. A vehicle comprising a vehicle electronic control unit (ECU) and the rear wheel steering apparatus of claim 1 .
14. A control method of a rear wheel steering apparatus, the rear wheel steering apparatus configured to control a steering angle of rear wheels based on a command received from a vehicle electronic control unit (ECU) and comprising: a motor for moving a rear wheel steering rail connected to the rear wheels in left and right directions; and a rear wheel steering ECU for controlling the motor to move the rear wheel steering rail to a target movement distance based on the command, the control method comprising determining, by the rear wheel steering ECU, whether stick-slip occurs based on the target movement distance and an actual movement distance of the rear wheel steering rail.
15. The control method of a rear wheel steering apparatus of claim 14 , wherein the determining whether the stick-slip occurs comprises determining whether the stick-slip occurs based on the actual movement distance received from a linear position sensor.
16. The control method of a rear wheel steering apparatus of claim 15 , wherein the determining whether the stick-slip occurs comprises determining that the stick-slip has occurred in response to determining that a first condition, in which a difference between the target movement distance and the actual movement distance occurring for a predetermined unit time is equal to or greater than a first predetermined reference distance, is satisfied.
17. The control method of a rear wheel steering apparatus of claim 16 , wherein the determining whether the stick-slip occurs comprises determining whether the stick-slip occurs by further using at least one of an estimated movement distance obtained based on a rotation angle of the motor or a current output of the motor.
18. The control method of a rear wheel steering apparatus of claim 17 , wherein the determining whether the stick-slip occurs comprises obtaining the estimated movement distance of the rear wheel steering rail based on the rotation angle received from a motor position sensor.
19. The control method of a rear wheel steering apparatus of claim 18 , wherein the determining whether the stick-slip occurs comprises determining that the stick-slip has occurred, in a state where the first condition is satisfied, in response to determining that at least one of a second condition, in which the current output of the motor is equal to or greater than a predetermined reference output when the actual movement distance for the unit time reaches a second predetermined reference distance or more at one go, or a third condition, in which a difference between the estimated movement distance and the actual movement distance is equal to or greater than a third predetermined distance, is satisfied.
20. The control method of a rear wheel steering apparatus of claim 19 , wherein the determining whether the stick-slip occurs comprises sequentially determining whether the first condition, the second condition, and the third condition are satisfied according to a predetermined sequence, determining that the stick-slip occurs in response to determining that all the first condition, the second condition, and the third condition are satisfied, and determining that the stick-slip has not occurred in response to determining that any one of the first condition, the second condition, and the third condition is not satisfied.
21. The control method of a rear wheel steering apparatus of claim 19 , further comprising controlling, by the rear wheel steering ECU, the motor to operate in a limited operation mode in response to determining that the stick-slip has occurred.
22. A non-transitory computer-readable medium storing computer-executable instructions when executed by a processor, causing the processor to perform the control method according to claim 14 .
23. A rear wheel steering apparatus for controlling a steering angle of rear wheels based on a command received from a vehicle electronic control unit (ECU), the rear wheel steering apparatus comprising:
a motor for moving a rear wheel steering rail connected to the rear wheels in left and right directions; and
a rear wheel steering ECU configured to:
determine whether stick-slip occurs based on a target movement distance and an actual movement distance of the rear wheel steering rail, and
control the motor to operate in a limited operation mode, in which the rear wheel steering rail moves by a limited movement distance smaller than the target movement distance, in response to determining that the stick-slip has occurred.
24. The rear wheel steering apparatus of claim 23 , wherein the rear wheel steering ECU is further configured to control the motor to operate in a normal operation mode, in which the rear wheel steering rail moves by the target movement distance based on the command received from the vehicle ECU, in response to determining that the stick-slip has not occurred.
25. The rear wheel steering apparatus of claim 23 , wherein the limited movement distance is determined by the target movement distance multiplied by a predetermined limit ratio.
26. The rear wheel steering apparatus of claim 25 , wherein the rear wheel steering ECU controls the motor to operate in the limited operation mode having different limit ratios depending on a level of the stick-slip that has occurred.