Steering control device

1. A steering control device for a steering system including a housing, a turning shaft that is accommodated in the housing such that the turning shaft is able to reciprocate, and an actuator that applies a motor torque for causing the turning shaft to reciprocate using a motor as a drive source, the steering control device comprising:

an absolute steering angle detecting unit configured to detect an absolute steering angle which is a rotation angle of a rotation shaft which is able to be converted into a turning angle of turning wheels connected to the turning shaft and which is expressed as an absolute angle including a range exceeding 360°; and

a current command value calculating unit configured to calculate a current command value corresponding to a target value of the motor torque output from the motor, wherein

the steering control device is configured to control activation of the motor such that an actual current value which is supplied to the motor reaches the current command value,

the current command value calculating unit is configured to store an end-position-corresponding angle which is an angle indicating an end position at which movement of the turning shaft is limited due to end contact in which the turning shaft comes into contact with the housing and which is correlated with the absolute steering angle,

the current command value calculating unit is configured to perform end contact relaxation control for correcting the current command value such that a decrease of an end separation angle indicating a distance of the absolute steering angle from the end-position-corresponding angle is limited when the end separation angle is equal to or less than a predetermined angle,

the current command value calculating unit is configured to perform partial release control for decreasing a correction value of the current command value due to execution of the end contact relaxation control when a vehicle is tried to be turned at the time of execution of the end contact relaxation control, and

the current command value calculating unit is configured to stop the partial release control when the current command value which is calculated at the time of execution of the partial release control is a value which is not affected by decreasing the correction value based on execution of the partial release control.

2. The steering control device according to claim 1 , wherein the current command value calculating unit is configured to calculate the current command value such that an increase of the end separation angle is not limited through the end contact relaxation control when the end separation angle is equal to or less than the predetermined angle.

3. The steering control device according to claim 1 , wherein:

the current command value calculating unit is configured to calculate a steering angle limit value which decreases with a decrease of the end separation angle when the end separation angle is equal to or less than the predetermined angle;

the current command value calculating unit is configured to perform the end contact relaxation control by limiting an absolute value of the current command value to the steering angle limit value;

the current command value calculating unit is configured to perform the partial release control by increasing the steering angle limit value; and

the current command value calculating unit is configured to stop the partial release control based on a result of comparison between the current command value which is calculated at the time of execution of the partial release control and a stop determination value based on the steering angle limit value which is not increased due to execution of the partial release control.

4. The steering control device according to claim 3 , wherein, when a sign of the current command value for causing the motor to generate the motor torque for turning the turning wheels in one of rightward and leftward directions is defined as being positive and the sign of the current command value for causing the motor to generate the motor torque for turning the turning wheels in the other direction is defined as being negative, the current command value calculating unit is configured to stop the partial release control when the end separation angle is equal to or less than the predetermined angle by turning the turning wheels in the one direction and the current command value calculated at the time of execution of the partial release control is less than the stop determination value which is positive, and to stop the partial release control when the end separation angle is equal to or less than the predetermined angle by turning the turning wheels in the other direction and the current command value calculated at the time of execution of the partial release control is greater than the stop determination value which is negative.

5. The steering control device according to claim 3 , wherein:

the current command value calculating unit is configured to calculate an angle limiting component which decreases as the end separation angle increases;

the current command value calculating unit is configured to calculate the steering angle limit value based on a value obtained by subtracting the angle limiting component from a rated current of the motor; and

the current command value calculating unit is configured to calculate the angle limiting component such that the angle limiting component is less at the time of execution of the partial release control than at the time of non-execution of the partial release control.