Saturn Saturn ASTRA Specifications download pdf (Page 5)

Chassis Specialist : Electric Power Steering

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Electric Power Steering Systems

Power steering systems were originally developed in the early 1950’s; the first production vehicle

being the 1951 Chrysler Imperial. These systems were hydraulic with a pump being driven by the

vehicle’s engine. As it is difficult to turn the steering wheel at low speeds, automobile manufacturers

were forced to install very large steering wheels. The large steering wheel was required to provide a

driver enough mechanical advantage at low speeds when the tire to pavement friction is at the highest.

The introduction of power steering allowed for smaller steering wheels and redesigned interior space.

The hydraulic systems used in the 1950’s are very similar to the systems still in use today. Granted,

development has progressed on the power steering pumps and hydraulic valves. Power steering systems

still require engine horsepower to operate. As fuel economy standards tightened and power train

packaging decreased in size, engineers were forced to develop new power steering systems. This course

will look at the electric power steering (EPS) systems used by Ford, General Motors, Honda and

Toyota. The first electric power steering system on a production vehicle debuted in 1993 in the Acura

NSX.

Currently, there are four different electric power steering system configurations. The Acura NSX uses a

rack assembly with a motor mounted internally. The double pinion style EPS system uses an electric

motor mounted externally to the pinion. The third configuration is having the electric motor mounted

internally in the pinion. The forth and final EPS system has the electric motor mounted on the steering

column. This is the most common system found on today’s vehicles. These systems are currently

manufactured by Koyo Seiko, Delphi, NSK, ZF and TRW Automotive.

The first system offered on a production vehicle was on the Acura NSX. This system is very complex

using an electric motor and a recirculating ball and screw assembly all mounted inside the steering

rack. The DC motor armature rotates around the steering rack and drives a helical gear that is meshed

to the ball screw assembly. The ball screw assembly is clamped to the rack which will transfer the

steering motion directly to the rack. The steering wheel torque sensor is mounted in the pinion housing

and a steering wheel speed sensor is mounted in the steering column. Based on the data from the torque

sensor and speed sensor along with the vehicle speed input from the engine control module (ECM) the

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Saturn Saturn ASTRA Specifications Page 5