1999 LAND ROVER DISCOVERY steering

STEERING
DESCRIPTION AND OPERATION 57-7
Reservoir
1Filler cap
2Reservoir body (dual PAS/ACE shown )
3Filter4Supply connection
5Return connection
The fluid reservoir is made of moulded plastic and is located on LH side of the engine compartment, on a bracket
which is attached to the inner wing. Dependent on the vehicles specification the reservoir may be a dual PAS/ACE,
or PAS only reservoir. Both types of reservoir are similar to each other the dual PAS/ACE reservoir has two chambers,
the PAS only reservoir has one chamber of a larger capacity. On both types of reservoir the PAS chamber has its own
filler cap and is identified by lettering on the reservoir body.
A filter of fine polyester mesh is moulded into the base of the chamber. The filter removes particulate matter from the
fluid before it is drawn into the supply connection and is non-serviceable. Upper and lower level marks are moulded
into the reservoir body, the reservoir is fitted with filler cap, a seal in the cap prevents leakage. The filler cap is pushed
onto a latch and turned through 90° to lock. A breather hole is incorporated in the cap to allow venting of air due to
fluid level changes during operation. The breather hole also allows air that may be in the fluid to separate out and vent
to atmosphere.
The reservoir holds hydraulic fluid and allows for expansion and contraction of the fluid due to temperature variations.
With the reservoir correctly filled the inlet to the PAS pump will be kept covered at normal operational attitudes. The
fluid flowing to the reservoir is cooled by convection from the pipe surfaces, the fluid held in the reservoir also allows
convection from the sides of the reservoir to take place. The total capacity of the reservoir with PAS only is 1000 cc
(0.264 US gallons), for vehicles fitted with PAS and ACE the total capacity of the reservoir is 500 cc (0.132 US
gallons).

STEERING
57-8 DESCRIPTION AND OPERATION
Steering box
The steering box is located behind the first cross member of the chassis and is secured to the chassis rail with four
bolts. The steering box is of the worm and roller type and has a rotary control valve. The steering box is connected to
the steering knuckles of the front road wheels by the drop arm, drag link and track rod. The steering box is lubricated
by the hydraulic fluid in the housing. The input shaft is attached to the steering wheel via the intermediate shaft and
steering column. The drop arm is secured to the output shaft with a nut and tab washer. A ball joint allows movement
between drop arm and drag link, the ball joint is secured with a locknut. The steering box requries approximately 3.5
turns from lock to lock.
As a maintenance aid, an alignment bolt can be used to lock the drop arm at the steering box centre position. The bolt
fits in a groove in the rear face of the drop arm and screws in to a threaded hole on the bottom of the steering box
housing.
Cross section through steering box
1Relief valve stop 2 off
2Relief valve 2 off
3Piston
4Rack
5Housing
6Output shaft
7Roller
8Valve rotor9Torsion bar
10Input shaft
11Pin
12Valve sleeve
13Course spline
14Worm gear
15Spline (worm gear to torsion bar)

STEERING
DESCRIPTION AND OPERATION 57-9
Principle of operation
Movement of the input shaft is transferred through the pin to the torsion bar and valve rotor on the input shaft. As the
input shaft turns, the spline of the torsion bar turns the worm gear. This action causes the roller to rotate on its bearings
and move. As the roller is located by a pin to a yoke on the output shaft, the output shaft rotates in the steering box
housing. As the amount of torque acting on the input shaft increases the torsion bar starts to twist. As the torsion bar
twists the valve rotor turns in the valve sleeve. When the ports in the valve rotor and valve sleeve are turned, hydraulic
fluid is directed to chamber 'A' or 'B' in the power cylinder.
With hydraulic fluid in one chamber under high pressure, the piston moves. The return line ports in the rotary valve,
aligned by the movement of the valve rotor, allow the fluid in the opposite chamber to flow to return. The teeth of the
rack move and transfer the force from the piston to the output shaft, giving assistance to move the drop arm. As the
output shaft rotates the torsion bar load is decreased. The rotor on the input shaft will return as the torsion bar
unwinds, the rotary valve will then be in a neutral position and the pressure in chambers 'A' and 'B' will equalise. With
no high pressure acting on the piston, force on the piston and rack is released.
To prevent heat accumulation at full steering lock due to excessive pressure, a relief valve inside the steering box is
opened as the box approaches full lock. The relief valve pins are located in the cylinder cover and housing and are
not to be adjusted.
The steering box design ensures a mechanical link through the course spline on the control valve rotor, the spline will
become engaged if:
lThe hydraulic pressure fails.
lThe steering box rotary control valve fails.
The coarse spline may also engage in some full lock situations if sufficient torque is applied to the input shaft.

STEERING
57-10 DESCRIPTION AND OPERATION
Rotary control valve
The rotary valve assembly comprises of three parts. The valve sleeve is fixed inside one end of the worm gear, the
valve sleeve has ports through it to allow the passage of hydraulic fluid. The input shaft has a valve rotor machined
on one end, the valve rotor also has ports through it and can rotate in the valve sleeve. A torsion bar is attached to
the input shaft by a pin, the torsion bar goes through the input shaft and valve rotor and is engaged by a spline into
the worm gear.
The coarse spline on the end of the valve rotor is loosely engaged in the worm gear, the coarse spline can make
contact and drive the worm gear in some full lock and in no pressure conditions. In the event of a torsion bar failure,
power assistance will be lost, the coarse spline will drive the worm gear and enable the vehicle to be steered and
driver control maintained.
Rotary control valve at neutral
1Worm gear
2Torsion bar
3Valve sleeve
4Pin5Input shaft and valve rotor
6Piston/rack
7Coarse spline
8Spline (torque shaft to worm gear)
When there is no demand for assistance the torsion bar holds the ports in the valve sleeve and valve rotor in a neutral
relationship to one another. The ports in the valve sleeve and the valve rotor are so aligned to allow equal (low) fluid
pressure on each side of the piston. Excess fluid flows through ports in the valve rotor through the valve sleeve and
back to the reservoir.

STEERING
DESCRIPTION AND OPERATION 57-11
Rotary control valve in demand mode
1Worm gear
2Torsion bar
3Valve sleeve
4Pin5Input shaft and valve rotor
6Piston/rack
7Coarse spline
8Spline (torque shaft to worm gear)
When the steering wheel and input shaft is turned steering resistance transmitted to the worm causes the torsion bar
to be wound up and the valve ports in the valve rotor and valve sleeve to be aligned for a right or left turn. The
alignment of the valve ports directs fluid pressure 'A' from the PAS pump to one side of the piston/rack . The other
side of the piston/rack is now connected to return 'B' (due the valves port alignment) and displaced fluid returns to the
reservoir. The pressure difference in the cylinder on each side of the piston gives the power assistance to move the
rack and so turn the steering.
The greater the resistance of the road wheels to the steering rotary movement, the greater torque acting on the torsion
bar and input shaft causing greater changes of alignment of the ports in the valve. As the change of alignment
becomes greater, the fluid pressure passing to the applicable side of the piston/rack increases.
Only when the steering wheel stops turning and the torsion bar has unwound, will the valve rotor return to the neutral
position. In the neutral position the fluid circulates through the ports in the valve rotor and valve sleeve and back to
the reservoir where it is cooled.

STEERING
57-12 DESCRIPTION AND OPERATION
PAS pump - V8
1Bolt 2 off
2Nut
3Stud
4Auxiliary housing
5PAS pump6Outlet
7Inlet
8Bolt 3 off
9Drive pulley
The PAS pump is located on the auxiliary housing and is attached by two bolts, the bolts go through flanged bushes
in the auxiliary housing. A stud passes through the PAS pump and through a flanged bush in the auxiliary housing,
the auxiliary housing and PAS pump are secured by a nut. As the two bolts and nut are tightened the bushes move
slightly and the flange of each bush clamps the PAS pump. A drive pulley is attached to the pump drive shaft with
three bolts, and is belt driven at a ratio of 1.4 crankshaft revolutions to 1 of the drive pulley. Fluid is drawn into the
PAS pump inlet from the reservoir through a flexible hose at low (suction) pressure. Fluid at high pressure from the
PAS pump outlet is supplied to the rotary control valve on the steering box.
The PAS pump is a roller vane type and has an internal pressure regulator and flow control valve. The roller vanes
can move in slots in the pumps rotor and are moved outwards by centrifugal force as the pump rotates. The pump
rotor rotates in the pump housing, the internal shape of the housing forms a 'cam' shape. Due to the 'cam' shape the
volume of the housing decreases between the inlet and outlet ports.
As the pump rotor rotates towards the pump inlet the volume between the roller vanes and the pump housing
increases, this action causes a depression in the chamber between the pump roller vanes and the housing. As the
rotation continues the chamber is opened to the pump inlet, and the depression in the chamber causes fluid to be
drawn in. The roller vanes continue past the inlet port, closing off the inlet port and trapping the fluid in the chamber
between the rollers and the pump housing.

STEERING
DESCRIPTION AND OPERATION 57-13
The internal 'cam' shape of the pump housing causes the rollers to move closer together as the pump rotor rotates
towards the outlet port. The reduced volume of the chamber between the roller vanes causes the fluid to become
pressurised. When the chamber is opened to the outlet port of the pump the fluid escapes at high pressure. The roller
vanes continue turning and go past the outlet port, closing off the chamber between the two roller vanes.
As rotation continues the inlet sequence begins again. The inlet and pressurisation/outlet sequences continue as the
pump rotates, and is repeated between each two roller vanes. The pump is a positive displacement type and the
potential pump output increases with engine (drive pulley) speed. The pressure relief and flow control valve regulates
flow/pressure by diverting fluid back to the pump inlet through internal recirculation passages in the pump body.

STEERING
57-14 DESCRIPTION AND OPERATION
PAS pump - diesel
1Drive pulley
2Mounting bracket
3Bolt 2 off
4Bolt
5PAS pump
6Coupling7Auxiliary housing
8Outlet
9Inlet adaptor pipe and seal
10Bolt 2 off
11Bolt 2 off
12Bolt 3 off
The PAS pump is located on the auxiliary housing, two bolts go through the PAS pump, mounting bracket and into
the auxiliary housing. One bolt also attaches the mounting bracket to the PAS pump, two bolts secure the mounting
bracket to the auxiliary housing. An inlet adaptor pipe with a seal is secured to the bottom of the pump with two bolts.
A drive pulley is attached to the pump drive shaft with three bolts, and is belt driven at a ratio of 1.35 crankshaft
revolutions to 1 of the drive pulley. A coupling on the rear of the PAS pump rotates the water pump impeller located
in the auxiliary housing. Fluid is supplied to the PAS pump inlet from the reservoir through a flexible hose at low
(suction) pressure. Fluid at high pressure from the PAS pump outlet is supplied to the rotary control valve on the
steering box.
The PAS pump is a roller vane type and has an internal pressure regulator and flow control valve. The roller vanes
can move in slots in the pumps rotor and are moved outwards by centrifugal force as the pump rotates. The pump
rotor rotates in the pump housing, the internal shape of the housing forms a 'cam' shape. Due to the 'cam' shape the
volume of the housing decreases between the inlet and outlet ports.