Chapter 25 Steering Systems 509
Power Steering Components
All modern power steering systems are
integral systems. In these systems, hydraulic
pressure is applied directly within the steer-
ing gear housing. The steering gear and hous-
ings used in integral systems are known as
self-contained power steering gears. Pressure
is provided by a hydraulic pump, usually belt
driven by the engine, to produce the necessary
hydraulic pressure. A few are driven by an elec-
tric motor. A typical integral power steering sys-
tem used with parallelogram linkage is shown
in Figure 25-21. A rack-and-pinion power steer-
ing system is shown in Figure 25-22.
In all self-contained power steering gears, a
control valve is actuated by the driver’s steer-
ing effort. This valve admits oil, under pressure,
to one side of a power piston. The pressure the
oil creates against the piston is transferred to the
inner tie rods (rack-and-pinion steering) or to
the pitman shaft (parallelogram steering), assist-
ing the driver in turning the front wheels.
Control Valve
On modern vehicles, all power steering
control valves are rotary spool valves. Rotary
spool valves are used on both rack-and-pinion
and parallelogram steering systems. A rotary
spool valve assembly consists of inner and outer
spools that contain oil pressure passages, a
housing, and a torsion bar. The inner spool can
rotate a small amount inside the outer spool. The
spools have a very close fi t in the valve hous-
ing to reduce pressure leakage. Figure 25-23 is a
cutaway view of a rotary spool valve installed in
the housing. Pressurized fl uid enters the valve
from the power steering pump.
The torsion bar is designed to twist when it
is turned. The top of the torsion bar is connected
Worm
Roller
Pitman
shaft
Lock
washer
Nut
Bushings
Adjusting
screw
Locknut
Pitman arm
Bearing
Worm
Bearing
Shims
Bearing
Case
Roller assembly
Figure 25-20.
Cross-sections of a worm-and-roller manual steering gear.
Toyota
Adjusting bolt
Spool
Ball nut
Cross shaft
Torsion bar
Gearbox
cutaway view
Oil reservoir
Idler
arm
Oil pump
Relay rod
Tie rod
Gear box
Steering
column
Oil pump
cutaway view
Rotor
Figure 25-21.
Integral power steering system. Note the gearbox and oil pump cutaways.
Chrysler