Specifications

Chassis Specialist : Electric Power Steering
Page 5
EPS Motor
The EPS motor can either be a brushless or brushed reversible
motor. Depending upon the motor’s location it will provide assist at
the steering gear or the steering column. The motors used in non-
Hybrid vehicles are 12 volts DC and will be rated between 35 and
80 amps. On some applications the motor will also be a part of the
power steering control module (PSCM). The motor will either drive
a worm gear in the steering column internally through a
recirculating ball screw assembly or through the steering gear
pinion. The motors used on Hybrid vehicles will vary from a 12
volt system up to a 50 volt system depending upon the application.
EPS Sensors
Depending upon the manufacturer, the EPS system will have
one or two sensors. The systems that use a single sensor will
have a steering wheel torque sensor. The sensor measures the
torsional twist that occurs when the steering wheel is turned.
The power steering control module uses this sensor to
determine the amount of assist required based on vehicle
speed and tire size. The sensor typically consists of a
compensation coil, a detecting coil and three detecting rings.
To measure the torque in the steering column the detecting
rings have toothed edges that face each other. Detecting ring
#1 is mounted to the steering column output shaft while
detecting rings #2 and #3 are both mounted to the input shaft. The detecting coil is mounted around the
toothed edges of detecting rings 1 and 2. As the steering wheel is turned the alignment of the toothed
edges changes due to the torque on the shaft. This changes the signal voltage of the detecting coil. The
power steering control module PSCM interprets the change in voltage as torque being applied to the
shaft.