vi number JAGUAR X308 1998 2.G Manual Online

Power Steering - Power Steering
Description an
d Operation

Parts List
The power steering system is a rack and pinion design, with an engine-dri ve n pump providing the steering assistance. The
system features variable steering assistance with vehicle spee d, a variable ratio steering rack, and a hydraulic control valve
which has a torsion bar arrangement giving improved center feel to the steering.
Absolute cleanliness must be observed wh en replenishing the fluid or dismantling any part of the system. If any major
component is renewed a new fluid rese rvoir must be fitted. New fluid from a sealed container must be used.
It
em
Par
t Number
De
scription
1—Steeri

ng rack assembly
2—Power as

sisted steering pump
3—F

luid reservoir
4—F

luid cooler
5—Hoses and pipework
6—In-

line quick-fit connector

The steering rack assembly :
Is mounted on the
rear face of the
front suspension crossbeam by two forg ed mounting brackets with resilient
bushes. The bushes are handed (pinion side and non-pinion side) and are orientated according to the vehicle range
application.
Convert s
the rotary motion of the steering wheel, via the steering gear pinion, to the lateral motion of the rack.
F
e
atures a variable ratio steering
rack with integral hydraulic po wer steering cylinder and piston.
Has a hydrauli
c control valve with Servotronic co
ntrol and positive center feel torsion bar.
The basic steering rack assembly is not serviceable. The following components are serviceable items:
Transfer pipework
.
Servotronic valve. Cent
ralizing cap.

O
u
ter ball joint.
Rac
k
gaiter.
Clips and

fittings.
Steering Rack Components
It e
m
Par
t
Number
De
scr
iption
1—Front
su
spension crossbeam
2—Steeri
ng rack housi
ng
3—Hydraulic

control valve housing
4—Moun
ting bracke
t
5—Gait
er

6—Tie
rod

7—O
u
ter ball joint

Steering R
a
ck Assembly

P
arts List
It

em
Par
t Number
De
scription
1—Steeri

ng rack
2—Hydrau

lic control valve
3—Torsio

n bar
4—Pin

ion
5—O

perating cylinder and piston
6—Inne

r ball joint
7—Tie

rod

P a
rts List
The variable ratio rack:
Incorporates teeth
of varying pitch and angle of contact, giving a variable pi
tch circle diameter which is a minimum
at the center of the rack and a maximum at the ends.
R e
duces excessive response to on-center stee
ring inputs during motorway driving.
Causes the steering action to become pro
gressively more
direct as the stee ring wheel is turned from the center
position.
Allows a low n u
mber of turns of the
steering wheel from lock to lock.
Ite
m
Par
t
Number
De
scr
iption
1—Steeri
ng rack
2—Tooth contact an
gle at
center of rack
3—Tooth c o
ntact angle
at ends of rack

Variable Ratio Steering Rack

P
arts List
The positive center-feel torsion bar improves the straight ahead feel of the steering in the region where very small amounts
of hydraulic pressure, and hence re action pressure, are generated.
The torsion bar assembly forms part of the hydraulic control valve assembly , and includes an axially pre-loaded metal
bellows spring, which is arranged co-axially with the torsion bar. The torsion bar is positively connected between the end
piece and the input shaft. One end of the bellows spring is attached to the input shaft, while the other end is attached to a
centering device. The centering device has two prism-shaped recesses with ca ged, guided, ball bearings arranged between
the recesses, and determines the zero-torsion position of the bellows spring.
On turning the steering wheel from the straight ahead position, the spring fo rces of the torsion bar assembly must be
overcome. Initially, the bellows spring produces substantial additional torsional resistance. However, after an angular
movement of approximately 0.2 degrees the torsional rigidity decreases and becomes similar to a conventional torsion bar.
It
em
Par
t Number
De
scription
1—End piece
2—Torsio

n bar
3—Caged ball bearing

s
4—Centering device
5—Bel

lows spring
6—In

put shaft


Positive Center-Feel Torsion Bar

Torsio
n Bar Components

P a
rts List
The power assisted steering pump:
Is mo u
nted on a bracket installe
d on the front of the engine.
Provides hydraul
ic pressure fo
r the power steering system.
Is of the roll
er vane type.
Is belt driven from th
e en
gine crankshaft.
Will provide 1
05 bar f
luid pressure.
The pump is not serviceable and should be renewed as a complete assembly.
Fluid Reservoir
Re
servoir and Hoses

Ite
m
Par
t
Number
De
scr
iption
1—Power as
si
sted steering pump
2—Engine
m
ounting bracket
3—High
pressure port

Power Assisted Steering Pump

The fluid reservo
ir:
Is lo

cated in the engine compartment, mounted on the engine compartment fuse box bracket.
Incorporates

a 10 micron, li
fetime, integral filter.
Has a cap
acity of 0.4 liter.
Has a dipsti

ck incorporated into the filler cap for checking the fluid level.
A new reservoir must be fitted if the steering rack, pump or fluid cooler are renewed.
Fluid C
ooler

P
arts List
The fluid cooler:
Is
resiliently mounted on th
e front body cross member.
Coo
ls the fluid before it is
returned to the reservoir.
Is
of the wire-bound tube type.
Has i

ntegral hoses.
Supply and Return Hoses a

nd Pipework
The supply and return h
oses and
pipework deliver fluid at high pressure from the pump to th e steering rack assembly. The
fluid is then returned to th e reservoir through the cooler tube. The high pressure supply hose contains two cable-type
attenuators, one at each end, to reduce nois e. The return pipe is clipped to the steering rack housing by a resilient
mounting.
It
em
Par
t Number
De
scription
1—Fl

uid reservoir
2—Supply line
3—R

eturn line
4—Fi

ller cap
It

em
Par
t Number
De
scription
1—Front body cross member
2—F

luid cooler
3—Inte

gral hoses
4—Cooler m

ounting


P
arts List

P a
rts List
The supply and return pipes are secured to the hydraulic control valve housing by a latch-plate having a single fixing screw.
The latch-plate is captive to the supply pipe. Each pipe has an O-ri ng which is a serviceable item.
In-Line Quick-Fit Connector

Parts List

Ite
m
Par
t
Number
De
scr
iption
1—Return
pipe (RH drive)
2—Supply pipe (RH
drive)
3—Latc
h-plate
4—Latch-
plate securing screw
It
e
m
Par
t
Number
De
scr
iption
1—Qu
ic
k-fit connector
2—Return
pipe

Latch
-Plate Location

m
ember. The quick-fit connector O-rings are not serviceable.
Special tool JD 182 is required to disconnect the quick-fit connector.
Hydraulic System


P
arts List
Hydraulic System

Op
erating Principle
The rot
ary motion of the steering wheel is converted, via the st
eering rack pinion, to the lateral motion of the rack. Steering
assistance is provided by pressurized fluid being directed against a piston operating within the rack cylinder. Rack
movement is achieved by diffe rential pressures being applied on either si de of the rack piston, caused by unequal
restrictions within the hydraulic control valve.
The main components of the hydraulic control valve are the rota ry distributor, control sleeve and hydraulic reaction piston.
It
em
Par
t Number
De
scription
1—F

luid reservoir
2—Pum

p
3—Pressure and fl

ow limiting valve
4—Supply line
5—R

eturn line
6—Steeri

ng rack
7—Pin

ion
8—O

perating cylinder and piston
9—Hydrau

lic control valve
10—Hydraulic reaction

piston
11—Control

sleeve
12—R

otary distributor
13—F

luid cooler


A
quick-fit connector with double O-ring se
als is incorporated in the return line and is clipped to the right-hand chassis side

The rotary distri
butor and control sleeve turn relative to ea
ch other, forming the unequal restrictions which create the
differential pressures to operat e the rack piston; the displacement of the di stributor and sleeve being controlled by the
elastic deformation of a torsion bar which is concentric with the pinion and valve. Refer to Positive Center-Feel Torsion Bar
in this sub-sectio n.
The hydraulic reaction piston moves axially, relative to th e rotary distributor, and is connected to the control sleeve by a
three-bearing helical screw. Pressure applied either side of the hydraulic reaction piston is translated into a rotational force
which increases steering effort. For detail s of Servotronic speed-sensitive steering control, refer to Servotronic Control in
this sub-section.
When the vehicle is travelling straight ah ead, the valve restrictions are balanced, thus providing equal pressures on either
side of the rack piston. When load is a pplied at the steering wheel, the two halves of the control valve (rotary distributor
and control sleeve) are displaced making the restrictions unequa l. The resulting differential pressures on either side of the
rack piston, assist the steering rack to mo ve to left or right. As the turning load is removed, the pressures equalize again
and the steering return s to the straight ahead position , aided by suspension geometry.
Serv
otronic Control

P a
rts List
The Servotronic system provides steering assistance which is pr oportional to vehicle speed. It comprises the steering control
module, and Servotronic valve forming part of the hydraulic control valve assembly.
The Servotronic valve is an electro-hydrauli c device with a variable orifice, which varies in size according to the position of a
needle valve. The needle valve is controlled by a solenoid in response to a variable current input from the steering control
Ite
m
Part
Number
Descr
iption
1—Vehi
cl
e speed input
2—Steeri
ng control
module
3—Servotronic valve
4—Hydraulic

control valve housing
5—PAS stee
rin
g pump
6—Batt
ery