Range Rover. Manual - part 174
STEERING
5
DESCRIPTION AND OPERATION
Hydraulic fluid flow
Fluid from the hydraulic pump (18) flows into an
annular chamber and surrounds the part of the valve
body which houses the two valve spools. When the
valve is in the neutral position, see illustration
57M7022, the fluid flows through the inlet grooves
(13) and (14) to the radial grooves (7) and (8). The
radial grooves are connected via oilways to the right
and left hand cylinder chambers. Fluid also flows back
to the fluid reservoir (17) through the open return
grooves (15) and (16). When the steering wheel is
turned clockwise, see illustration 57M7023, the piston
(2) moves to the right in the power cylinder. At the
same time the valve spools are moved into their
working position. Valve spool (11) moves to the right,
inlet groove (13) is opened. Valve spool (12) moves to
the left, closing inlet groove (14). Pressure fluid now
flows via radial groove (8) to the left hand side of the
cylinder, assisting movement of the steering wheel.
The fluid in the right hand cylinder is pushed out by
the piston, and flows back to the fluid reservoir via
radial groove (7) and return groove (15). When the
steering wheel is turned anti-clockwise the valve
operation is reversed, pressure fluid flowing to the
right hand side of the cylinder.
The quantity of fluid required for the system is
adjusted by the pressure and flow limiting valve (19) in
the PAS pump. The flow limiting valve ensures that
maximum demand for pressure fluid is met regardless
of engine speed.
Steering limit valve
A steering limit valve is incorporated in the piston
head (2) as a safeguard against overloading the
steering linkage, lock stops and hydraulic pump. This
ball valve is always shut by pressure in the left or right
hand cylinder. However shortly before the piston
reaches full travel in either direction, the valve is
opened by a pin, resulting in pressure drop. Hydraulic
assistance is greatly reduced, and full lock can only
be achieved with increased manual effort by the
driver.
Adjustment
The shape of the sector shaft gearing makes axial
adjustment of the shaft possible. This allows any play
between the two gears, which might occur after a long
period in service, to be eliminated using the sector
shaft adjuster screw.