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3-16
GROUP 3-SUSPENSION, STEERING, WHEELS AND TIRES
(040)
SECTOR---
SHAFT
FIG.
2-Power Steering Gear
and input shaft assembly can twist
in the actuator, and thus move it
up and down. This movement results
from a short length of helical splines
on the inside diameter of the actua-
tor which engage the outside diam-
eter of the input shaft. The actuator
is held in the spool by a snap ring.
Therefore, as the torsion bar twists,
its radial motion is transferred into
axial motion hy helical threads. Thus,
the valve spool is moved off center,
and fluid is directed to one side of
the piston or the other (Fig. 3).
The restricting of the fluid flow
to one side of the piston increases
the fluid pressure proportionately to
the reaction of turning the front
wheels.
The resistance of the torsion har
gives the driver a feel of the road
at all times. The more •he torsion
bar twists, the greater the feel of
the road and at the same time the
driver is receiving a greater power
assist in steering.
HORN GROUND WIRE
CONNECTION
G1087-B
FIG. 3-
Valve Detail
STRAIGHT -AHEAD POSITION
When the power unit is not assist-
ing in the steering effort, the valve
spool is in the neutral (straight-
ahead) position (Fig. 4). The fluid
flows from the pump, through the
open-center valve, and returns to the
pump through the worm bearing.
Therefore, no area of the valve spool
or steering gear is under high pres-
sure in this position. The amount of
pressure in neutral position is ap-
proximately 30 psi at normal opera-
ting temperatures.
The pump has no influence on the
valve spool, but the spool, housing,
and power cylinder are full of fluid
at all times when the pump- operates.
RIGHT TURN
When the steering wheel is turned
to the right, the ball nut on the worm
resists being turned due to load on
the sector shaft from the front end
weight of the vehicle. Thus the tor-
sion bar will start to twist (Fig. 4).
For a right turn the valve spool
moves up, allowing fluid from the
pump to enter against the upper side
of the power piston. The fluid on the
lower side of the piston is free to
return through the valve to the pump.
Therefore, the power assist is to the
upper side of the piston, pushing it
downward and providing assist in
turning of the sector shaft.
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