Patent ID: 8666602

Claim:
A method of operating a motor-driven power steering system of a vehicle, the method comprising: providing a vehicle comprising an engine and a motor-driven power steering system, the motor-driven power steering system comprising a steering motor, a control circuit, and a temperature sensor located at a sensor location other than on the steering motor, the temperature sensor being configured to measure sensor temperature at the sensor location during operation of the vehicle, the control circuit being configured to estimate motor temperature of the steering motor based on the measured sensor temperature and electric current supplied to the steering motor, wherein the sensor temperature at a first stoppage of the engine is defined as a first sensor temperature, wherein the electric current at the first stoppage of the engine is defined as a first electric current; providing a first temperature map indicative of changes in the sensor temperature over time after stoppage of the engine; providing a second temperature map indicative of temperature changes of the steering motor over time after stoppage of the engine; storing the first sensor temperature; estimating a first motor temperature using the first sensor temperature and the first electric current; upon start of the engine that is immediately after the first stoppage, measuring a second sensor temperature at the sensor location using the temperature sensor; estimating a time length between the first stoppage of the engine and the start of the engine using the first sensor temperature, the second sensor temperature and the first temperature map; estimating a second motor temperature of the steering motor using the estimated time length, the first motor temperature and the second temperature map; and controlling an electric power supplied to the steering motor based on the second motor temperature.