Figure 8-26.Control valve.
hydraulic fluid under pressure to the proper location in
the steering system. The control valve may be mounted
either in the steering mechanism or on the steering
linkage. depending on which system configuration is
POWER STEERING HOSESPower steering
hoses are high-pressure. hydraulic rubber hoses that
connect the power steering pump and the integral
gearbox or power cylinder. One line serves as a supply
line, the other acts as a return line to the reservoir of the
power steering pump.
There are three major types of power steering
systems used on modern passenger vehicles (fig. 8-27)
integral piston (linkage type), external cylinder
(linkage type), and rack and pinion. The rack and
pinion can further be divided into integral and external
power piston. The integral rack and pinion steering
system is the most common.
Integral Piston (Linkage Type)
The integral piston (linkage type) power steering
system has the hydraulic piston mounted inside the
steering gearbox. This is the most common type of
power steering system. Basically, this system consists
of a power steering pump, hydraulic lines, and a
special integral power-assist gearbox.
The integral piston power steering gearbox (fig.
8-28) contains a conventional worm and sector gear
arrangement, a hydraulic piston, and a control valve.
The control valve may be either a spool valve or a
rotary valve depending upon manufacturer.
The operation of an integral power steering system
is as follows:
With the steering wheel held straight ahead or in
NEUTRAL position, the control valve balances
hydraulic pressure on both sides of the power piston. Oil
returns to the pump reservoir from the control valve.
For a right turn, the control valve routes oil to the
left side of the power piston. The piston is pushed to the
right in the cylinder to aid pitman shaft rotation.
For a left turn, the control valve routes oil to the
right side of the power piston. The piston is pushed to
the left in the cylinder to aid pitman shaft rotation.
In both left and right turns piston movement forces
oil on the nonpressurized side of the piston back
through the control valve and to the pump.