DSP-based electric power assisted steering using BLDC

S¯adhan¯a Vol. 33, Part 5, October 2008, pp. 581–590. © Printed in India

DSP-based electric power assisted steering using BLDC

motor

R MURUGAN, S NANDAKUMAR and M S MOHIYADEEN

Bharat Electronics Limited, Nandambakkam, Chennai 600 089

e-mail: muruganr@bel.co.in; nandakumars@bel.co.in; mohiyadeenms@bel.co.in

Abstract. This paper introduces a design and implementation of electrically

assisted power steering (EAS) using BLDC motor for a vehicle. The control architecture consists of two layers of control, namely the vehicle speed associated control

and the torque assist control. In the higher level of control architecture, the vehicle

speed controller works as an assistance level controller for the steering effort. In

the lower level, the torque controller gives the effort level control. This has been

realized by torque sensor and vehicle sensor interfaced in the DSP. For implementing

in the system, a DSP-based BLDC motor controller with three-phase inverter

module is specially designed using Hall-effect sensor feedback and a single dc-link

current sensor. This work is implemented in a Light Commercial Vehicle having

a recirculating ball type gear. This is for the first time (EAS) being implemented

for this type of vehicle any where in the world. Generally, EAS having clutch to

disconnect the motor in high speed or abnormal conditions from the gear box. In

this implementation the motor is directly coupled to gearbox without clutch and all

abnormalities are handled by the processor. This is implemented without modifying

the vehicle supply system like changing the existing alternator or rating of the

battery and using the existing sensors. The design is such a way that the feel of the

driver assistance can be varied easily at any time. The performance of the control

system is experimentally verified and it is tested in one of the Light Commercial

Vehicle (LCV).

Keywords. BLDC motor; EAS; steering.

1. Introduction

Power steering is a system for reducing the steering effort on vehicles by using external

source to assist in turning the wheels. Most new generation vehicles now have power steering, owing to the trends toward greater vehicle mass and wider tires, all increase the steering effort needed. Modern vehicles would be difficult to maneuver at low speeds (e.g. when parking) without assistance. Most power steering systems work by using a belt-driven pump to provide hydraulic pressure to the system. This hydraulic pressure is generated by a pump which is driven by the vehicle’s engine. While the power steering is not used, i.e. driving in a straight line, twin hydraulic lines provide equal pressure to both sides of the steering wheel gear.

R Murugan, S Nandakumar and M S Mohiyadeen

When torque is applied to the steering wheel, the hydraulic lines provide unequal pressures and hence assist in turning the wheels in the intended direction.

Electric Power Steering systems use electric components with no hydraulic systems at

all. Sensors detect the motion and torque of the steering column and a computer module applies assistive power via an electric motor coupled directly to either the steering gear