Electric power steering apparatus and control method thereof

1. An electric power steering apparatus comprising:

a motor comprising a first motor coupled to a worm wheel of a steering shaft and configured to rotate the worm wheel to move a rack and a second motor coupled to the worm wheel of the steering shaft and configured to rotate the worm wheel to move the rack in synchronization with the first motor;

a sensor comprising a torque angle sensor configured to detect a torque value and a steering angle in response to manipulation of a steering wheel and an angle sensor configured to detect an angle of rotation of a sector shaft; and

a controller configured to control the first and second motors, respectively, in response to the manipulation of the steering wheel,

wherein the controller is configured to calculate an amount of compensation rotation of the motor based on the detected steering angle and the detected angle of rotation, and control an amount of rotation of the motor in accordance with the calculated amount of compensation rotation, and

wherein the controller is configured to,

when the calculated amount of compensation rotation is less than a predetermined value, only drive the first motor to move the rack in accordance with the calculated amount of compensation rotation, and

when the calculated amount of compensation rotation is equal to or greater than the predetermined value, drive both of the first motor and the second motor to move the rack in accordance with the calculated amount of compensation rotation.

2. The electric power steering apparatus according to claim 1 , wherein the motor is driven to transfer power to a ball screw of a second reducer having a power transmission structure comprised of the ball screw and a ball nut via a first reducer having a power transmission structure provided by engagement of worm gears and a worm wheel, so that the power is transferred to the rack.

3. The electric power steering apparatus according to claim 2 , wherein the torque angle sensor is connected to the steering shaft, in a location between the steering wheel and the first reducer, to detect the torque value and the steering angle due to torsion and rotation of the steering shaft.

4. The electric power steering apparatus according to claim 2 , wherein the angle sensor is disposed on the sector shaft to detect the angle of rotation of the sector shaft, the sector shaft rotating in response to sliding of the ball nut of the second reducer.

5. The electric power steering apparatus according to claim 4 , wherein the angle sensor includes:

one or more magnets disposed on surface portions of a sector gear provided on an outer circumferential surface of the sector shaft to be engaged with the ball nut; and

a magnetic sensor detecting magnetic force generated by the magnets, response to the sector gear rotating along with the sliding of the ball nut.

6. The electric power steering apparatus according to claim 5 , the magnetic sensor disposed in a housing to face the magnets, the housing surrounding the sector shaft and the sector gear.

7. The electric power steering apparatus according to claim 1 , wherein the controller configured to calculate a first amount of rotation of a vehicle's wheel in accordance with the detected steering angle and a second amount of rotation of the vehicle's wheel in accordance with the detected angle of rotation, calculate the amount of compensation rotation by comparing the first amount of rotation and the second amount of rotation, and apply a compensation current based on the amount of compensation rotation to the motor.

8. The electric power steering apparatus according to claim 7 , wherein the controller is configured to perform position control to the motor by proportional integral control.

9. A control method of an electric power steering apparatus of a vehicle, the method comprising:

controlling a motor in response to manipulation of a steering wheel, wherein the motor comprising a first motor coupled to a worm wheel of a steering shaft and configured to rotates the worm wheel to move a rack and a second motor coupled to the worm wheel of the steering shaft and configured to rotate the worm wheel to move the rack in synchronization with the first motor;

detecting a torque value and a steering angle in response to the manipulation of the steering wheel;

detecting an angle of rotation of a sector shaft;

calculating an amount of compensation rotation of the motor by comparing the steering angle and the angle of rotation; and

controlling, in accordance with the amount of compensation rotation, a first amount of rotation of the first motor and a second amount of rotation of the second motor, respectively

wherein the controller,

when the calculated amount of compensation rotation is less than a predetermined value, only drives the first motor to move the rack in accordance with the calculated amount of compensation rotation, and

when the calculated amount of compensation rotation is equal to or greater than the predetermined value, drives both of the first motor and the second motor to move the rack in accordance with the calculated amount of compensation rotation.

10. The control method according to claim 9 , wherein the detection of the torque value and the steering angle comprises detecting the torque value and the steering angle in response to torsion and rotation of the steering shaft.

11. The control method according to claim 10 , wherein the detection of the angle of rotation of the sector shaft comprises detecting the angle of rotation of the sector shaft by detecting magnetic force generated by one or more magnets disposed on the sector shaft.

12. An electric power steering apparatus comprising:

a motor comprising a first motor coupled to a worm wheel of a steering shaft and configured to rotate the worm wheel to move a rack and a second motor coupled to the worm wheel of the steering shaft and configured to rotate the worm wheel to move the rack in synchronization with the first motor;

a sensor comprising a vehicle speed sensor configured to obtain a vehicle speed of a host vehicle, a steering angle sensor configured to obtain a steering angular velocity due to manipulation of a steering wheel, and a front sensor configured to obtain a distance to a preceding vehicle; and

a controller configured to control an operation of the first motor and an operation of the second motor, respectively, so that the vehicle's wheel is steered in response to the manipulation of the steering wheel,

wherein the controller is configured to:

determine a normal mode and an emergency mode to drive the motor in accordance with at least one selected from among the vehicle speed, the steering angular velocity, the distance to a preceding vehicle, or combinations thereof,

only drive the first motor in the normal node, and

drive both the first motor and the second motor in an emergency mode.

13. The electric power steering apparatus according to claim 12 , wherein the motor is configured to drive to transfer power to a ball screw of a second reducer having a power transmission structure comprised of the ball screw and a ball nut via a first reducer having a power transmission structure provided by engagement of worm gears and a worm wheel, so that the power is transferred to the rack.

14. The electric power steering apparatus according to claim 13 , wherein the sensor further comprises an angle sensor disposed on a sector shaft to detect an angle of rotation of the sector shaft, the sector shaft rotating in response to sliding of the ball nut.

15. The electric power steering apparatus according to claim 14 , wherein the controller is configured to calculate additional assistance steering power required in the emergency mode, in accordance with a steering angle of the steering wheel and the angle of rotation of the sector shaft, and drives the second motor to provide the additional assistance steering power.

16. The electric power steering apparatus according to claim 12 , wherein the controller is configured to operate in the emergency mode when the vehicle speed is equal to or greater than a predetermined reference value, the steering angular velocity is equal to or greater than a predetermined reference value, and the distance to a preceding vehicle is equal to or less than a predetermined reference value.

17. The electric power steering apparatus according to claim 12 , wherein the controller is configured to determine the emergency mode to increase assistance steering power with increases in the vehicle speed, increases in the steering angular velocity, and decreases in the distance to a preceding vehicle.

18. The electric power steering apparatus according to claim 12 , wherein a center of rotation of the steering wheel is movable up and down about a center of the steering wheel.

19. The electric power steering apparatus according to claim 18 ,

wherein the sensor comprises a first sensor configured to obtain position of the center of rotation of the steering wheel and a second sensor configured to detect an area of the steering wheel held by a driver, and

wherein the controller is configured to control driving of the first motor and the second motor in accordance with the vehicle speed, the position of the center of rotation, and the area of the steering wheel held the driver.

20. The electric power steering apparatus according to claim 12 ,

wherein the sensor further comprises an angle sensor configured to obtain an angle of rotation of a sector shaft, and

wherein the controller is configured to calculate an amount of compensation rotation of the motor in accordance with a steering angle of the steering wheel and an angle of rotation of a sector shaft, and control an amount of rotation of the motor in accordance with the amount of compensation rotation.