The prototype development of electronic control unit for electric power steering

Electric Power Steering (EPS) in an electric car is needed to reduce the steering torque felt by the driver and to maintain good steering as a handling assist. With EPS, the driver needs only 2Nm to rotate the steering wheel in any condition. Electric power steering system consists of torque sensor, DC motor assist, current sensor, and an Electronic Control Unit (ECU). A classic proportional control method is implemented in the ECU to control the assist torque done by the DC motor assist. The proportional controller with a Kp gain of 0.6 results in a rise time of 0.1 second. Instead of direct torque sensor, an incremental encoder which is used to detect the change of steering wheel position is then converted into steering torque. Two models of EPS systems are tested, system which includes a current sensor and system which do not use a current sensor. System with a current sensor gave poorer result than the other system because of the low sensitivity and the unpredictable delay of the current sensor. The impact of using incremental encoder is that the driver has to give quite large steering torque to rotate the steering wheel in the beginning before the DC assist motor starts working.

I. Introduction

Electric Power Steering has been widely used to replace Hydraulic Power Steering in modern vehicles. In electric vehicles, electric power steering system is a better choice than the hydraulic one because EPS has lighter weight, thus it minimizes the energy consumption in the vehicle. Electric power steering system can lower the steering torque because it provides an assist torque that will help the driver to rotate the steering wheel. With EPS, the driver can perform a better handling of vehicle without being obstructed by the large steering torque. EPS also plays a great role in driving safety, especially in high speed operation. In high speed, the system can be turned off and thus the steering torque felt by the driver will be greater to ensure the safety of the driver.