Abstract: The electric power steering system controls motor output torque by the controller ECU according to signal of the hand torque,vehicle speed senor etc.The thermal management for ECU and motor is the key to control cost and security of system.This article puts forward the distinction between fast and slow temperature rising by theoretic model to get the system's temperature increasing value in different heating conditions and the relationship between the motor current and the immediate temperature to calculate the motor temperature.Simulation and experiments show that the thermal management analysis and the design method can effectively solve the problem of the heating system and successfully realize the unification of the system cost and system safety.

Key words: electric power steering system;fast and slow temperature rising;motor temperature;increasing temperature value