Motor-driven power steering system and control method thereof

1. A motor-driven power steering system that assists in steering by transmitting auxiliary steering power by driving a motor when a steering wheel is steered, the motor-driven power steering system comprising:

a motor driver configured to drive the motor; and

a controller electrically connected to the motor driver,

wherein the controller is configured to:

receive a first rotation angle obtained by a steering wheel angle sensor according to steering of the steering wheel and a second rotation angle obtained by a motor position sensor,

when a steered position of the steering wheel is in an auxiliary steering limit section and a difference value between the first rotation angle and the second rotation angle is different from a predetermined reference value, change a rotation position of the steering wheel angle sensor and a rotation position of the motor position sensor to an initial original position,

when changed to the initial original position, receive the first rotation angle obtained by the steering wheel angle sensor according to steering of the steering wheel and the second rotation angle obtained by the motor position sensor again, and

control the motor driver to perform auxiliary steering based on the first rotation angle and the second rotation angle received again.

2. The motor-driven power steering system of claim 1 , wherein, when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, the controller is configured to determine that a slip between a worm wheel, engaged with a worm connected to the motor, and an auxiliary pinion occurs.

3. The motor-driven power steering system of claim 1 , wherein the controller is configured to:

when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, further receive a rotation speed obtained by the motor position sensor and a steering torque obtained by a torque sensor,

when the rotation speed and the steering torque are in a forward direction, further determine whether a first difference value between the second rotation angle and the first rotation angle is greater than a first predetermined reference value,

when the first difference value is greater than the first predetermined reference value, further determine whether a first holding time during which the first difference value remains greater than the first predetermined reference value is longer than a first predetermined reference time, and

when the first holding time is longer than the first predetermined reference time, further change the rotation position of the steering wheel angle sensor and the rotation position of the motor position sensor to the initial original position.

4. The motor-driven power steering system of claim 1 , wherein the controller is configured to:

when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, further receive a rotation speed obtained by the motor position sensor and a steering torque obtained by a torque sensor,

when the rotation speed and the steering torque are in a reverse direction, further determine whether a second difference value between the second rotation angle and the first rotation angle is less than a second predetermined reference value,

when the second difference value is less than the second predetermined reference value, further determine whether a second holding time during which the second difference value remains less than the second predetermined reference value is longer than a second predetermined reference time, and

when the second holding time is longer than the second predetermined reference time, further change the rotation position of the steering wheel angle sensor and the rotation position of the motor position sensor to the initial original position.

5. The motor-driven power steering system of claim 1 , wherein the controller is configured to be electrically connected to an ignition switch, and

after the ignition switch is turned on, synchronize and receive the first rotation angle obtained by the steering wheel angle sensor and the second rotation angle obtained by the motor position sensor.

6. The motor-driven power steering system of claim 1 , wherein, when changed to the initial original position, the controller is configured to synchronize and receive the first rotation angle obtained by the steering wheel angle sensor and the second rotation angle obtained by the motor position sensor again.

7. A control method of a motor-driven power steering system that assists in steering by transmitting auxiliary steering power by driving a motor when a steering wheel is steered, the control method comprising:

receiving a first rotation angle obtained by a steering wheel angle sensor according to steering of the steering wheel and a second rotation angle obtained by a motor position sensor;

determining whether a steered position of the steering wheel is in an auxiliary steering limit section;

determining whether the steered position of the steering wheel is in the auxiliary steering limit section and a difference value between the first rotation angle and the second rotation angle is different from a predetermined reference value;

when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, changing a rotation position of the steering wheel angle sensor and a rotation position of the motor position sensor to an initial original position,

when changed to the initial original position, receiving the first rotation angle obtained by the steering wheel angle sensor according to steering of the steering wheel and the second rotation angle obtained by the motor position sensor again, and

performing auxiliary steering based on the first rotation angle and the second rotation angle received again.

8. The control method of claim 7 , wherein, when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, it is determined that a slip between a worm wheel, engaged with a worm connected to the motor, and an auxiliary pinion occurs.

9. The control method of claim 7 , wherein, when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, the changing to the initial original position further receives a rotation speed obtained by the motor position sensor and a steering torque obtained by a torque sensor,

further determines whether the rotation speed and the steering torque are in a forward direction,

when the rotation speed and the steering torque are in the forward direction, further determines whether a first difference value between the second rotation angle and the first rotation angle is greater than a first predetermined reference value,

when the first difference value is greater than the first predetermined reference value, further determines whether a first holding time during which the first difference value remains greater than the first predetermined reference value is longer than a first predetermined reference time, and

when the first holding time is longer than the first predetermined reference time, further changes the rotation position of the steering wheel angle sensor and the rotation position of the motor position sensor to the initial original position.

10. The control method of claim 7 , wherein, when the difference value between the first rotation angle and the second rotation angle is different from the predetermined reference value, the changing to the initial original position further receives a rotation speed obtained by the motor position sensor and a steering torque obtained by a torque sensor,

further determines whether the rotation speed and the steering torque are in a reverse direction,

when the rotation speed and the steering torque are in the reverse direction, further determines whether a second difference value between the second rotation angle and the first rotation angle is less than a second predetermined reference value,

when the second difference value is less than the second predetermined reference value, further determines whether a second holding time during which the second difference value remains less than the second predetermined reference value is longer than a second predetermined reference time, and

when the second holding time is longer than the second predetermined reference time, further changes the rotation position of the steering wheel angle sensor and the rotation position of the motor position sensor to the initial original position.

11. The control method of claim 7 , wherein the receiving of the first rotation angle and the second rotation angle synchronizes and receives the first rotation angle obtained by the steering wheel angle sensor and the second rotation angle obtained by the motor position sensor, after an ignition switch for starting the motor-driven power steering system is turned on.

12. The control method of claim 7 , wherein, when changed to the initial original position, the receiving of the first rotation angle and the second rotation angle again synchronizes and receives the first rotation angle obtained by the steering wheel angle sensor and the second rotation angle obtained by the motor position sensor again.