Steering control device and steering system

1. A steering system comprising:

an actuator comprising a motor as a drive source;

a steering control device configured to control the motor in the steering system in which a steering torque required for steering a steering wheel is changed using a motor torque applied from an actuator with a motor as a drive source,

the steering control device comprising a processing circuit, and the processing circuit being configured to:

calculate a torque command value that is a target value of a motor torque when operation of the motor is controlled such that the motor torque is generated;

calculate a torque component used to calculate the torque command value based on a state variable changing according to operation of the steering system;

calculate a calculational hysteresis component for adding, to the torque component, a hysteresis characteristic with respect to change of a specific state variable changing with steering of the steering system, the calculational hysteresis component being acquired using, as an origin, a value of the specific state variable set at a predetermined timing;

calculate, in a first calculation situation, the calculational hysteresis component for adding a first hysteresis characteristic to the torque component is calculated; and

calculate, in a second calculation situation, the calculational hysteresis component for adding a second hysteresis characteristic having a hysteresis width larger than a hysteresis width of the first hysteresis characteristic to the torque component,

wherein, in the second calculation situation after change from the first calculation situation, the processing circuit includes a zero point calculating unit configured to calculate a value corresponding to the origin in the second hysteresis characteristic at a time when the calculational hysteresis component enabling a value of the calculational hysteresis component at a timing of the change from the first calculation situation to be maintained is calculated, and calculates the calculational hysteresis component using the value calculated by the zero point calculating unit as the origin;

reflect, in the torque component, the calculational hysteresis component acquired through calculation in the first calculation situation, in a first state in which a vehicle is able to be determined to be in a traveling state that does not include a stopped state; and

reflect, in the torque component, the calculational hysteresis component acquired through calculation in the second calculation situation, in a second state in which the vehicle is able to be determined to be in a traveling state including the stopped state,

wherein the motor torque used for changing the steering torque required for steering the steering wheel of the vehicle is based on the torque component.

2. The steering system according to claim 1 , wherein:

the processing circuit is configured to calculate a base component of an angle axial force as the torque component, the angle axial force being determined according to an angle that is convertible to a turning angle of turning wheels of a vehicle, and the angle axial force being an axial force in which road surface information is not reflected; and

the processing circuit is configured to calculate the calculational hysteresis component that is added to the base component.

3. The steering system according to claim 1 , wherein:

in a situation in which a vehicle speed is a second vehicle speed determined to correspond to the second state after change from a first vehicle speed determined to correspond to the first state, the processing circuit calculates the calculational hysteresis component enabling a value of the calculational hysteresis component at a timing of the change from the first vehicle speed to be maintained.

4. The steering system according to claim 1 , wherein:

the processing circuit is configured to calculate a vehicle speed coefficient changing according to a vehicle speed such that the vehicle speed is reflected in the calculational hysteresis component when the first hysteresis characteristic or the second hysteresis characteristic is added to the torque component; and

in a situation in which the calculated vehicle speed coefficient is a second vehicle speed coefficient calculated at a second vehicle speed determined to correspond to the second state after change from a first vehicle speed coefficient calculated at a first vehicle speed determined to correspond to the first state, the processing circuit calculates the calculational hysteresis component enabling a value of the calculational hysteresis component at a timing of the change from the first vehicle speed coefficient to be maintained.