Rear-wheel steering system and controlling method thereof

1. A rear-wheel steering system comprising:

a rack configured to transmit a driving force generated from a rear-wheel steering motor to rear wheels;

a first correction module configured to, when an engine is started, detect a first position of the rack using a displacement sensor and calculate a first correction value that is a difference between the first position and a neutral position;

a second correction module configured to, when the engine is started, detect a second position of the rack using a motor position sensor that detects a rotation angle of the rear-wheel steering motor and calculate a second correction value that is a difference between the second position and the neutral position;

a comparison determiner configured to compare the first correction value and the second correction value to determine whether the displacement sensor has malfunctioned; and

a steering controller configured to control an operation of the rear-wheel steering motor,

wherein, when the first correction value is out of a preset error range for the second correction value, the comparison determiner determines that the displacement sensor has malfunctioned and displays a malfunction of the displacement sensor to a driver.

2. The rear-wheel steering system of claim 1 , wherein the second correction module includes:

a start controller configured to transmit a control signal to the steering controller to drive the rear-wheel steering motor sequentially in forward and reverse directions so that the rack sequentially moves from a starting position to both side ends of a rack stroke within the rack stroke; and

a second correction value calculator configured to identify the starting position of the rack using the rotation angle and a rotation direction of the rear-wheel steering motor detected by the motor position sensor when the rack moves within the rack stroke.

3. The rear-wheel steering system of claim 2 , wherein the second correction value calculator has pre-stored information about a relationship between the rotation angle of the rear-wheel steering motor and a length of the rack stroke, and

wherein the second correction value identifies the starting position of the rack by applying the rotation angle and the rotation direction of the rear-wheel steering motor detected by the motor position sensor to the length of the rack stroke.

4. The rear-wheel steering system of claim 2 , wherein, when the comparison determiner completes a determination on the displacement sensor, the steering controller returns the rack to the neutral position by controlling the operation of the rear-wheel steering motor such that the rack moves by half of a length of the rack stroke.

5. The rear-wheel steering system of claim 1 , wherein, when the engine is turned off, the steering controller controls the rack to return to the neutral position by operating the rear-wheel steering motor and stores information about a current position of the rack in a memory when the control is completed, and

wherein, when the engine is turned on, the steering controller checks the information about the position of the rack at the time of turning off the engine and operates the first correction module and the second correction module when the rack is not located in the neutral position.

6. A rear-wheel steering system comprising:

a rack configured to transmit a driving force generated from a rear-wheel steering motor to rear wheels;

a motor position sensor configured to detect a rotation angle of the rear-wheel steering motor;

a steering controller configured to control an operation of the rear-wheel steering motor;

a start controller configured to, when an engine is started, transmit a control signal to the steering controller to drive the rear-wheel steering motor sequentially in forward and reverse directions so that the rack sequentially moves from a starting position to both side ends of a rack stroke within the rack stroke; and

a correction value calculator configured to identify a starting position of the rack using the rotation angle of the rear-wheel steering motor detected by the motor position sensor when the rack moves within the rack stroke,

wherein, when the first correction value is out of a preset error range for the second correction value, the comparison determiner determines that the displacement sensor has malfunctioned and displays a malfunction of the displacement sensor to a driver.

7. A controlling method of a rear-wheel steering system, comprising:

detecting an absolute value for a position of a rack which transmits a driving force generated from a rear-wheel steering motor to rear wheels when an engine is started and calculating a first correction value that is a difference between the position of the rack and a neutral position;

detecting a position of the rack using a rotation angle of the rear-wheel steering motor and calculating a second correction value that is a difference between the detected position of the rack and the neutral position; and

comparing the first correction value and the second correction value to verify accuracy of the first correction value,

wherein the comparing the first correction value and the second correction value includes:

determining that a displacement sensor which detects the absolute value of the position of the rack has malfunctioned when the first correction value is out of a preset error range for the second correction value, and

displaying a malfunction of the displacement sensor to a driver.

8. The controlling method of claim 7 , wherein the calculating a second correction value includes:

controlling the rack to sequentially move from a starting position of the rack to both side ends of a rack stroke within the rack stroke by sequentially driving the rear-wheel steering motor in forward and reverse directions; and

identifying the starting position of the rack using the rotation angle of the rear-wheel steering motor detected by a motor position sensor when the rack moves within the rack stroke.

9. The controlling method of claim 8 , wherein the identifying the start position includes:

identifying the starting position of the rack using information about a length of the rack stroke that matches an already possessed rotation angle of the rear-wheel steering motor, and

applying the rotation angle and a rotation direction of the rear-wheel steering motor, which are detected by the motor position sensor, to the length of the rack stroke.

10. The controlling method of claim 8 , further comprising, after the comparing, returning the rack to the neutral position by controlling an operation of the rear-wheel steering motor such that the rack moves by half of a length of the rack stroke.

11. The controlling method of claim 8 , further comprising:

controlling the rack to return to the neutral position by operating the rear-wheel steering motor when the engine is turned off; and

when the control is completed, storing information about a current position of the rack in a memory,

wherein, when the rack is not located in the neutral position when the engine is started, the calculating a first correction value and the calculating a second correction value are performed.