Turning control device

1. A turning control device comprising:

a turning angle sensor configured to detect a first steering angle of a turning mechanism;

a first actuator configured to drive the turning mechanism;

a steering angle sensor configured to detect a second steering angle of a steering mechanism; and

at least one processor configured to:

calculate a target steering angle of the turning mechanism, based on at least the second steering angle;

when a third steering angle, the third steering angle being either the first steering angle or the second steering angle, is in an angular range from a maximum steering angle that the third steering angle can take to a first threshold steering angle, calculate a steering angular displacement of the third steering angle with the first threshold steering angle used as a reference;

calculate a steering angle correction value according to at least the steering angular displacement;

determine whether a steering state is a state of a driver further turning a steering wheel or a state of the driver returning the steering wheel and limit the steering angle correction value according to at least the steering state, angular velocity of the third steering angle, and the third steering angle;

by correcting the target steering angle with the steering angle correction value limited by the at least one processor, calculate a corrected target steering angle; and

control the first actuator in such a way that the first steering angle coincides with the corrected target steering angle.

2. The turning control device according to claim 1 , wherein

the at least one processor is further configured to:

calculate a torque including elastic torque based on the steering angular displacement as turning torque to be exerted on the turning mechanism; and

convert the turning torque to the steering angle correction value.

3. The turning control device according to claim 1 , wherein

the at least one processor is further configured to:

calculate a torque including at least either elastic torque based on the steering angular displacement or viscous torque based on angular velocity of the first steering angle and the steering angular displacement as turning torque to be exerted on the turning mechanism; and

convert the turning torque to the steering angle correction value.

4. The turning control device according to claim 3 , wherein

the at least one processor, by adding inertia torque based on angular acceleration of the first steering angle to at least either the elastic torque or the viscous torque, is configured to calculate the turning torque.

5. The turning control device according to claim 2 , wherein

the at least one processor, by converting the turning torque, using a coefficient depending on vehicle speed, is further configured to calculate the steering angle correction value.

6. The turning control device according to claim 1 , wherein the at least one processor is further configured to:

calculate an angular velocity correction value, based on angular velocity of the first steering angle and the steering angular displacement;

limit the angular velocity correction value according to at least the steering state, angular velocity of the third steering angle, and the third steering angle,

calculate a target angular velocity of the first steering angle, based on a difference between the corrected target steering angle and the first steering angle;

by correcting the target angular velocity with the angular velocity correction value limited by the at least one processor, calculate a corrected target angular velocity; and

control the first actuator in such a way that angular velocity of the first steering angle coincides with the corrected target angular velocity.

7. The turning control device according to claim 6 , wherein

the at least one processor is further configured to:

calculate a viscous torque to be exerted on the turning mechanism, based on the steering angular displacement and angular velocity of the first steering angle; and

convert the viscous torque to the angular velocity correction value.

8. The turning control device according to claim 7 , wherein

the at least one processor is further configured to convert the viscous torque to the angular velocity correction value, using a coefficient depending on at least either vehicle speed or whether a steering state is a state of a driver further turning a steering wheel or a state of the driver returning the steering wheel.

9. The turning control device according to claim 1 wherein the at least one processor is further configured to:

calculate a target reaction force to be applied to the steering mechanism, based on at least the second steering angle;

correct the target reaction force according to the steering angle correction value; and

apply reaction torque to the steering mechanism according to the target reaction force corrected by the at least one processor.

10. The turning control device according to claim 1 , wherein

when the third steering angle exceeds a second threshold steering angle, the second threshold steering angle being larger than the first threshold steering angle, the at least one processor is further configued to alter the first threshold steering angle according to a difference between the third steering angle and the second threshold steering angle.