Steering apparatus for vehicle and method for controlling the same

1. A steering apparatus for use in a vehicle, in which the steering apparatus includes a steering transmission system for transmitting rotation of a steering wheel to a steered wheel, the steering apparatus comprising:

a drive unit arrangable in the steering transmission system for changing a steering angle of the steered wheel;

a calculation unit for calculating a control target amount of the steering angle based on a vehicle model;

a control unit for controlling the drive unit to change the steering angle based on the control target amount;

a determination unit for determining whether or not the absolute value of at least one of yaw rate of the vehicle and lateral acceleration of the vehicle is greater than or equal to a predetermined value when velocity of the vehicle is less than or equal to a predetermined velocity, wherein the control unit refrains from executing the control based on the control target amount when the absolute value is not greater than or equal to the predetermined value.

2. The steering apparatus according to claim 1 , wherein the control unit executes the control based on the control target amount when the absolute value is greater than or equal to the predetermined value.

3. The steering apparatus according to claim 1 , further comprising:

a second determination unit for determining a steering characteristic of the vehicle based on the vehicle model, the control unit controlling the drive unit to change the steering angle in a direction opposite the direction of a yaw moment when the steering characteristic is determined as being oversteer, and the control unit controlling the drive unit to decrease the steering angle when the steering characteristic is determined as being understeer.

4. The steering apparatus according to claim 3 , wherein the control unit does not execute the control based on the second determination unit when the absolute value is greater than or equal to the predetermined value.

5. The steering apparatus according to claim 1 , wherein the drive unit includes a motor, and the steering angle of the steered wheel includes a first steering angle based on rotation of the steering wheel and a second steering angle based on drive of the motor, the second steering angle being added to the first steering angle to vary a transmission ratio of the steering angle of the steered wheel relative to the rotational angle of the steering wheel.

6. A steering apparatus for use in a vehicle, in which the steering apparatus includes a steering transmission system for transmitting rotation of a steering wheel to a steered wheel, the steering apparatus comprising:

a drive unit arrangable in the steering transmission system for changing a steering angle of the steered wheel;

a calculation unit for calculating a control target amount of the steering angle based on a vehicle model;

a control unit for controlling the drive unit to change the steering angle based on the control target amount;

a gain calculation unit for calculating a correction gain that reduces the control target amount based on at least one of yaw rate of the vehicle and lateral acceleration of the vehicle; and

a correction unit for correcting the control target amount based on the correction gain, wherein the control unit controls the drive unit to change the steering angle based on the control target amount that has been corrected when velocity of the vehicle is less than or equal to a predetermined velocity.

7. The steering apparatus according to claim 6 , further comprising:

a determination unit for determining a steering characteristic of the vehicle based on the vehicle model, the control unit controlling the drive unit to change the steering angle in a direction opposite the direction of a yaw moment when the steering characteristic is determined as being oversteer, and the control unit controlling the drive unit to decrease the steering angle when the steering characteristic is determined as being understeer.

8. The steering apparatus according to claim 6 , wherein the drive unit includes a motor, and the steering angle of the steered wheel includes a first steering angle based on rotation of the steering wheel and a second steering angle based on drive of the motor, the second steering angle being added to the first steering angle to vary a transmission ratio of the steering angle of the steered wheel relative to the rotational angle of the steering wheel.

9. A method for controlling steering of a steered wheel of a vehicle, the method comprising:

calculating a control target amount for a steering angle of the steered wheel based on a vehicle model;

controlling the steering angle based on the control target amount;

determining whether or not the absolute value of at least one of yaw rate of the vehicle and lateral acceleration of the vehicle is greater than or equal to a predetermined value when velocity of the vehicle is less than or equal to a predetermined velocity; and

refraining from controlling the steering angle based on the control target amount when the absolute value is not greater than or equal to the predetermined value.

10. The method according to claim 9 , further comprising controlling the steering angle based on the control target amount when the absolute value is greater than or equal to the predetermined value.

11. A-method for controlling steering of a steered wheel of a vehicle, the method comprising:

calculating a control target amount for a steering angle of the steered wheel based on a vehicle model;

controlling the steering angle based on the control target amount;

calculating a correction gain for reducing the control target amount based on at least one of yaw rate of the vehicle and lateral acceleration of the vehicle;

correcting the control target amount based on the correction gain; and

controlling the steering angle based on the control target amount that has been corrected when velocity of the vehicle is less than or equal to a predetermined velocity.