Electric power steering apparatus

1. An electric power steering apparatus including a motor, the apparatus comprising:

a steering torque sensor configured to detect a steering torque applied to a steering wheel and output a steering torque signal corresponding to the steering torque;

a speed sensor configured to detect a speed of a vehicle and output a speed signal corresponding to the speed of the vehicle;

an auxiliary steering force setting unit configured to output a signal representing a linear change of a gradual increase or decrease;

a map setter configured to receive a signal output from the auxiliary steering force setting unit and to set an auxiliary steering force map where a maximum steering torque, a maximum target motor current, or a ratio of a target motor current to a steering torque at a specific speed gradually increases or decreases;

a current signal supply configured to output the steering torque signal and a target motor current signal corresponding to the speed signal according to the auxiliary steering force map; and

a motor driving unit configured to supply a current corresponding to the target motor current signal to the motor.

2. The electric power steering apparatus as claimed in claim 1 , wherein the auxiliary steering force setting unit outputs the signal representing a linear change of a gradual increase or decrease based on manipulation of a driver.

3. The electric power steering apparatus as claimed in claim 1 , wherein the auxiliary steering force setting unit includes a continuously moving switch or knob, or a touch screen for displaying a continuous movement.

4. The electric power steering apparatus as claimed in claim 1 , further comprising:

a feedback unit configured to output a current difference signal obtained from a target motor current signal input from the current signal supply and an actual motor current signal corresponding to an actual current flowing through the motor;

a motor current controller configured to receive the current difference signal from the feedback unit and to output a control signal for compensating for a difference between a target motor current and an actual motor current; and

a current detecting unit configured to detect a motor current flowing through the motor and to output the actual motor current signal corresponding to the detected motor current to the feedback unit.

5. The electric power steering apparatus as claimed in claim 1 , further comprising a boundary value comparator configured to judge if the maximum steering torque, the maximum target motor current, or the ratio is within a boundary value.

6. An electric power assisting method implemented by an electric power steering apparatus including a motor, the method comprising steps of:

detecting a steering torque applied to a steering wheel and outputting a steering torque signal corresponding to the steering torque;

detecting a speed of a vehicle and outputting a speed signal corresponding to the speed of the vehicle;

outputting a signal representing a linear change of a gradual increase or decrease;

receiving a signal output from an auxiliary steering force setting unit and setting an auxiliary steering force map where a maximum steering torque, a maximum target motor current, or a ratio of a target motor current to a steering torque at a specific speed gradually increases or decreases;

outputting the steering torque signal and a target motor current signal corresponding to the speed signal according to the auxiliary steering force map; and

supplying a current corresponding to the target motor current signal to the motor.

7. The electric power assisting method as claimed in claim 6 , wherein the signal representing a linear change of a gradual increase or decrease is based on manipulation of a driver.

8. The electric power assisting method as claimed in claim 6 , wherein the signal representing a linear change of a gradual increase or decrease is based on a continuously moving switch or knob, or a touch screen for displaying a continuous movement.

9. The electric power assisting method as claimed in claim 6 , further comprising steps of:

outputting a current difference signal obtained from a target motor current signal input from a current signal supply and an actual motor current signal corresponding to an actual current flowing through the motor;

outputting a control signal for compensating for a difference between a target motor current and an actual motor current by receiving the current difference signal; and

detecting a motor current flowing through the motor and outputting the actual motor current signal corresponding to the detected motor current to a feedback unit.

10. The electric power assisting method as claimed in claim 6 , further comprising the step of judging if the maximum steering torque, the maximum target motor current, or the ratio is within a boundary value.