Steer-by-wire system and control method thereof

1. A steer-by-wire system comprising:

a reaction motor generating a reaction in a direction opposite to a direction in which a steering wheel is manipulated, in response to the steering wheel being manipulated by a driver;

a current sensor sensing a phase current output by the reaction motor;

a motor position sensor sensing an angle of rotation of the reaction motor;

a state and disturbance observer estimating a plurality of state variables and a driver torque by receiving information regarding the phase current and information regarding the angle of rotation of the reaction motor, and at least one information of a damping coefficient of the steering wheel, a damping coefficient of the reaction motor, an inertia of the steering wheel, or an inertia of the reaction motor; and

a reaction controller determining a reaction torque output by the reaction motor, in accordance with the plurality of state variables and the driver torque estimated by the state and disturbance observer,

wherein estimated values of plurality of state variables, calculated by the state and disturbance observer, include at least one of a driver torque, a steering angle of the steering wheel, a steering angular speed of the steering wheel, a torsion bar torque, a difference in angular speed between the steering wheel and the reaction motor, or combinations thereof.

2. The steer-by-wire system according to claim 1 , wherein the state and disturbance observer possesses information regarding a base estimator gain defined using a Kalman filter and estimates the plurality of state variables by applying the base estimator gain to a differential phase equation.

3. The steer-by-wire system according to claim 1 , further comprising:

a steering motor steering a vehicle wheel; and

a steering controller controlling a steering torque output by the steering motor by receiving estimated values of the plurality of state variables from the state and disturbance observer.

4. The steer-by-wire system according to claim 1 , wherein the state and disturbance observer recalculates estimated values of the plurality of state variables if the plurality of state variables differ from at least one of the information regarding the angle of rotation of the reaction motor, the information regarding the phase current of the reaction motor, or a combination thereof, by a predetermined value or more.

5. The steer-by-wire system according to claim 1 , further comprising a torque sensor sensing a torque occurring in response to the steering wheel being manipulated,

wherein the state and disturbance observer determines whether or not the torque sensor malfunctions by comparing a torsion bar torque sensed by the torque sensor with a torsion bar torque estimated by the state and disturbance observer.

6. The steer-by-wire system according to claim 1 , further comprising a steering angle sensor sensing a steering angle of the steering wheel,

wherein the state and disturbance observer determines whether or not the steering angle sensor malfunctions by comparing a steering angle of the steering wheel, sensed by the steering wheel sensor, with a steering angle of the steering wheel, estimated by the state and disturbance observer.

7. A control method of a steer-by-wire system, comprising:

sensing a phase current output by a reaction motor generating a reaction in a direction opposite to a direction in which a steering wheel is manipulated, in response to the steering wheel being manipulated by a driver;

sensing an angle of rotation of the reaction motor;

estimating a plurality of state variables and a driver torque by receiving information regarding the phase current and information regarding the angle of rotation of the reaction motor, and at least one information of a damping coefficient of the steering wheel, a damping coefficient of the reaction motor, an inertia of the steering wheel, or an inertia of the reaction motor; and

determining a reaction torque output by the reaction motor, in accordance with the plurality of state variables and the driver torque,

wherein estimated values of the plurality of state variables include at least one of a driver torque, a steering angle of the steering wheel, a steering angular speed of the steering wheel, a torsion bar torque, a difference in angular speed between the steering wheel and the reaction motor, or combinations thereof.

8. The control method according to claim 7 , wherein the estimation of the plurality of state variables estimates the plurality of state variables by applying a base estimator gain defined using a Kalman filter to a differential phase equation.

9. The control method according to claim 7 , further comprising controlling a current provided to a steering motor of a vehicle wheel by receiving estimated values of the plurality of state variables.

10. The control method according to claim 7 , further comprising recalculating estimated values of the plurality of state variables if the plurality of state variables differ from at least one of the information regarding the angle of rotation of the reaction motor, the information regarding the phase current of the reaction motor, or a combination thereof, by a predetermined value or more.

11. The control method according to claim 7 , further comprising:

sensing, by a torque sensor, a torsion bar torque of a steering column; and

determining whether or not the torque sensor malfunctions by comparing the torsion bar torque, sensed by the torque sensor, with a torsion bar torque from among estimated values of the plurality of state variables.

12. The control method according to claim 7 , further comprising:

sensing, by a steering angle sensor, a steering angle of the steering wheel; and

determining whether or not the steering angle sensor malfunctions by comparing the steering angle of the steering wheel, sensed by the steering wheel sensor, with a steering angle of the steering wheel from among estimated values of the plurality of state variables.