Power steering was invented earlier in the century
to deal with the excessive weight of modern

Power steering relies on a simple principle- a
hydraulic pump running off a belt driven by the
engine places a small amount of fluid under
pressure, which in turn assists the steering
mechanism in directing the tires as you turn the
steering wheel. The system typically includes a
pump, a pressure hose assembly, a control valve,
and a return line.

There are three types of power steering systems
used on passenger vehicles. The first and most
popular is known as power rack-and-pinion
steering. It utilizes a power unit built directly into
the rack assembly. When the wheel turns, an
internal rotary valve directs the flow of power
steering fluid to the proper end of the power
cylinder. The difference in pressure on either side
of this cylinder assists in moving the rack, thereby
easing steering. A control valve then returns
excess fluid to the main reservoir.

The second system, used mostly on larger
vehicles (SUVs and pickup trucks) is called
recirculating-ball steering. In this system, a series
of steel balls act as rolling threads between the
steering shaft and the rack piston. The rack piston
moves up (right turn) or down (left turn), assisted
by hydraulic pressure. As in the system above,
fluid pressure is regulated by a control valve.

The third is in many of todays newer vehicles. It is
Electric Power Assist. There is no belt driven
power steering pump, pressure or return lines or
fluid. This system uses an electric motor, control
module, and sensors in the steering column to
produce the power assist. If there is a problem in
the system, a
warning light will come on the dash
or the Driver Information Center.
Everything About Power Steering

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