Steering assist apparatus of vehicle and method for steering assist apparatus

1. A steering assist apparatus of a vehicle provided with a steering input apparatus that inputs a steering angle and a steering apparatus that steers wheels of the vehicle with a turning angle, the steering input apparatus and the steering apparatus performing a differential operation with a transmission ratio which is a ratio of a change amount of the steering angle to a change amount of the turning angle, the steering assist apparatus comprising:

a steering drive that drives the steering apparatus;

a processor configured to perform functions including:

a steering control that executes an automatic steering mode in which the steering drive is controlled such that a turning angle is determined based on at least either a running state of the vehicle or road information to accomplish the turning angle; and

a transmission ratio determination that determines, based on a turning curvature and at least either a running state of the vehicle or the road information, a first transmission ratio in the automatic steering mode to be a value different from a second transmission ratio in a manual steering mode in which the steering apparatus operates in accordance with the steering angle inputted via the steering input apparatus,

wherein

the transmission ratio determination changes the transmission ratio such that the larger the turning curvature, the larger the transmission ratio is.

2. The steering assist apparatus according to claim 1 , wherein the transmission ratio determination further determines the first transmission ratio based on the turning angle.

3. The steering assist apparatus according to claim 2 , wherein the transmission ratio determination unit determines the first transmission ratio such that the larger the turning angle, the larger the first transmission ratio is.

4. The steering assist apparatus according to claim 1 , wherein the transmission ratio determination unit determines the first transmission ratio based on a change rate of the turning angle.

5. The steering assist apparatus according to claim 4 , wherein the transmission ratio determination determines the first transmission ratio such that the larger the change rate of the turning angle, the larger the first transmission ratio is.

6. The steering assist apparatus according to claim 1 , wherein the transmission ratio determination further determines the first transmission ratio based on a travelling speed of the vehicle.

7. The steering assist apparatus according to claim 1 , wherein the transmission ratio determination further determines the first transmission ratio based on a confidence degree of the steering assist apparatus.

8. The steering assist apparatus according to claim 7 , wherein the transmission ratio determination determines the first transmission ratio such that the smaller the confidence degree, the smaller the first transmission ratio is.

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

a variable steering angle apparatus that generates a differential angle between the steering angle and the turning angle; and

the steering control controls the variable steering angle apparatus so as to further generate a differential angle based on the first transmission ratio or the second transmission ratio.

10. The steering assist apparatus according to claim 9 , wherein

the steering control controls, when the vehicle changes a direction from straight forward travelling to turning travelling or from the turning traveling to the straight forward travelling, the variable steering angle apparatus with the first transmission ratio to change the steering angle before changing the turning angle.

11. The steering assist apparatus according to claim 1 , wherein

the steering control further determines, during the manual steering mode, the turning angle by using the steering angle and the second transmission ratio, and controls the steering drive so as to accomplish the turning angle.

12. The steering assist apparatus according to claim 11 , further comprising:

a steering input drive apparatus that drives the steering input apparatus; and

the steering control further controls, when the vehicle changes a direction from straight forward travelling to turning travelling or from the turning traveling to the straight forward travelling, the steering input drive apparatus with the first transmission ratio so as to change the steering angle before changing the turning angle.

13. A computer-implemented method for steering assist of a vehicle provided with a steering input apparatus that inputs a steering angle and a steering apparatus that steers wheels of the vehicle with a turning angle, the steering input apparatus and the steering apparatus performing a differential operation with a transmission ratio which is a ratio of a change amount of the steering angle to a change amount of the turning angle, the method comprising steps of:

determining, based on at least either a running state of the vehicle or road information, a first transmission ratio in an automatic steering mode to be a value different from a second transmission ratio in a manual steering mode in which the steering apparatus operates in accordance with the steering angle inputted via the steering input apparatus;

executing the automatic steering mode in which a steering drive is controlled such that a turning angle is determined based on a turning curvature and at least either the running state of the vehicle or the road information to accomplish the turning angle; and

changing the transmission ratio such that the larger the turning curvature, the larger the transmission ratio is.