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CHRYSLER SERVICE MANUAL
STEERING—403
loaded relief valve is provided at the top of the
filter element. When oil pressure in the filter
builds up to about 5 to 7 psi., this valve opens
and permits oil to pass directly into the reser-
voir chamber.
The rotary oil pump is driven from the rear
end of the generator armature shaft through a
flexible coupling. The single rotor in the pump
draws oil from the reservoir, and discharges it
through the built-in combination flow control
valve and pressure relief valve to the valve in
the power unit assembly.
In the power steering pump, the flow control
valve and pressure relief valve are combined in
a single assembly, as shown in Figure 12. The
spring-loaded pressure relief valve is concentric
with and fits inside the spring-loaded flow con-
trol valve. When the pressure relief valve is
closed, it seats against a snap ring in the flow
control valve. An orifice in the pressure relief
valve provides the oil pressure drop that con-
trols the operation of the flow control valve.
When the oil flow from the pump tends to rise
above l
1
/^ gallons per minute, the difference in
pressure across the orifice overcomes the spring
load, and the flow control valve moves to un-
cover a passage to the intake side of the pump.
By preventing excessive oil flow, the flow con-
trol valve limits the pressure drop through the
hydraulic system and thus limits the horse-
power required to drive the pump. Oil flow of
the pump when the engine is idling is about 1%
gallons per minute.
Oil pressure in the hydraulic system builds up
to that required to overcome the resistance to
turning of the road wheels. In other words,
straight-ahead highway steering requires a rel-
atively low oil pressure, while a higher oil pres-
sure is required when turning a corner. A rapid
build-up of oil pressure tends to occur when the
road wheels are turned against a curb or when
the steering wheel is turned all the way in one
direction so that the piston reaches the end of
the stroke. To prevent excessive oil pressure,
the pressure relief valve in the pump limits the
oil pressure from 750 to 800 psi.
The entire hydraulic oil system for power
steering has a capacity of 2 quarts of SAE
10 W engine, or type "A" oil. The worm hous-
ing capacity is one pint which is separate from
the pressure system.
b. How the Coaxial Power Steering Operates
The heart of the Coaxial Power Steering Unit
has two parts; the valve and the valve body
(actually a part of the hydraulic piston, as
shown in Figure 13). Together, these two pieces
control the operation of the entire power sys-
tem. When the driver turns the steering wheel,
the valve moves with respect to the hydraulic
piston, and power asistance instantly responds.
The relative movement between the valve and
piston is very slight (it seldom excee Is .0025
inch) and must not be confused with the gen-
eral movement of the whole step'ing system
as the front wheels turn. The driver controls the
power steering unit by governing the relative
movement between the valve and hydra ilic pis-
ton. Control movements are based o. feel of
the road that comes through the steering wheel
from a hydraulic reaction chamber inside the
power unit. Relative movement of the valve and
piston affects hydraulic action as follows:
As the valve moves relative to the piston, it
regulates oil pressure and directs oil flow
through the hydraulic circuit. Consider the case
where the steering wheel is not turned and the
valve is in neutral position, as shown in Figure
13. In this position, the valve leaves openings
between it and the valve body so oil flows
through the unit quite easily with very little
flow restriction. Therefore, the oil pump has
only a slight resistance to overcome, and the oil
entering the power steering unit is under low
pressure.
Inside the unit, the oil reaches the valve
through holes drilled in the piston. At the valve
the flow divides, and oil travels toward both
ends of the valve. It flows through succeeding
openings between the valve and adjacent valve
body until it reaches the main return passage
drilled through the lower piston rod. It then
returns to the reservoir and filter. In the neutral
position, oil pressure on both sides of the power
piston is the same. Consequently, the piston
remains stationary.
When the driver turns the steering wheel, the
valve moves either up or down, depending on
which direction he turns. Suppose that he moves
the valve up slightly, relative to the piston. By
moving the valve this small amount, the driver
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