Bendix Commercial Vehicle Systems C-300N HYDRAULIC POWER STEERING1/99 - Manual (Page 4)

4
FIGURE 3 - POWER STEERING GEAR MOUNTING CONFIGURATION
TIE
ROD
DRAG
LINK
PISTON OVER
OUTPUT SHAFT
STEERING
ARM
PITMAN
ARM
TIE ROD
ARM
SPINDLE
ASSEMBLY
PISTON UNDER
OUTPUT SHAFT
When the steering gear is mounted on the vehicle in a position
similar to the piston under output shaft illustration in figure
1, the piston and spindle used will have a right hand thread.
A left hand thread is required when the steering gear is
mounted in a position similar to the piston over output
shaft illustration. In either mounting position, a right turn is
accomplished when the input shaft is rotated clockwise and
the output shaft, along with the pitman arm, rotate toward
the rear of the vehicle.
HYDRAULIC OPERATION
GENERAL
Functioning together, the spindle and valve body assemblies
serve as a means of flow and pressure control for the power
assist portion of the steering gear. All hydraulic fluid enters
and exits the power steering gear through lines connected
to the threaded ports in the valve body.
The valve body assembly forms a closure for the housing
and provides a means of retaining the spindle assembly. It
contains a series of circular channels and radial passages
which serve to direct the flow of hydraulic oil into and out of
the rotary control valve in the spindle assembly. In addition,
the valve body can contain an optional pressure relief and
bypass valve. The pressure relief valve ensures that a preset
maximum pressure is not exceeded. It is always set at a
pressure level below that of the power steering pump relief
valve and is intended to limit the power assist to a specific
maximum level. Figure 8
The optional bypass valve is intended to lessen the manual
steering effort required in the event hydraulic pressure is
lost. The bypass valve permits fluid to ‘circulate’ within the
steering gear rather than being forced to and from the power
steering pump and reservoir. Figure 9
The spindle assembly rotates on a ball bearing in the bore
of the valve body. The spindle is composed of three major
parts;, the input shaft, torsion bar, and ball screw. One end
of the input shaft is finely splined for connection to the
steering column while the other end has a coarse spline
which mates loosely with a similar spline inside the ball
screw. The coarse splines form mechanical stops which
limit the amount of relative rotation between the ball screw
and input shaft. Six evenly distributed longitudinal grooves
are machined into the outer surface of the input shaft and
correspond to six grooves machined into the bore of the
ball screw. The torsion bar is pinned to the ball screw and
input shaft and forms a spring connection between the two.
With the input shaft inserted into the ball screw the six
grooves of each of these components alternate with each
other and form the hydraulic rotary control valve. Holes on
the outside surface of the ball screw extend into the six
grooves within its bore. Figure 5
These holes allow pressurized oil to enter and exit the two
parts of the rotary control valve. There are three groups of
holes in the ball screw. Each group is made up of three
different size holes which form a diagonal line across the
surface of the ball screw. The largest hole in each group
conducts pressurized oil into the grooves of the rotary
control valve. The second largest hole in each group
conducts oil out of the rotary control valve to the side of the
power piston furthest from the rotary control valve while the
smallest hole conducts oil to the closest side of the piston.
Figures 5 & 6