Vehicle steering device

A method of controlling a vehicle steering device, the method comprising:

• driving a steering reaction force motor to apply a steering reaction force to a steering member of a vehicle in response to a steering action of the steering member applied by a driver;
• driving a steering motor to apply a steering force to steer a vehicle wheel in accordance with the steering action of the steering member in a state where the vehicle wheel is mechanically disengaged from the steering member by controlling a switching actuator of a clutch device;
• obtaining, by a control device, an instantaneous integrated value of a current supplied to one of the steering reaction force motor and the steering motor in a manner in which:
• (i) in a time period in which a current higher than a current threshold value flows through said one of the steering reaction force motor and steering motor, the current is integrated over time;
• and (ii) in a time period in which a current lower than or equal to the current threshold value flows through said one of the steering reaction force motor and steering motor, an integrated value of a current corresponding to a decrease in temperature in the time period is subtracted, wherein the current threshold value serves as a reference for determining whether or not the steering motor is heated without a need of a temperature sensor, wherein the instantaneous integrated value of the current is based on a value calculated by multiplying the current by a predetermined cycle time;
• utilizing, by the control device, the instantaneous integrated value of the current supplied to said one of the steering reaction force motor and steering motor to determine whether or not said one of the steering reaction force motor and steering motor is in an overload state;
• determining, by the control device, that said one of the steering reaction force motor and steering motor is in the overload state when the instantaneous integrated value of the current supplied to said one of the steering reaction force motor and steering motor is higher than a predetermined threshold value;
• controlling, by the control device, the steering motor to steer the vehicle wheel in a manner that follows at least a target steering angle which is calculated based on the steering action of the steering member;
• and
• controlling, by the control device, the switching actuator of the clutch device to engage the steering member and the vehicle wheel when the overload state of said one of the steering reaction force motor and steering motor is detected.