2010 JAGUAR XFR Workshop Manual

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Page 745 of 3039

JAGUAR XFR 2010 1.G Workshop Manual 1 Locknut ( 2 off) 2 RH (right-hand) tie-rod 3 Steering gear boot (2 off) 4 Steering gear 5 Bolt and washer (3 off) 6 Servotronic valve 7 Valve unit 8 Input shaft 9 LH (left-hand) tie-rod 10 Steering

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JAGUAR XFR 2010 1.G Workshop Manual 1 Pressure/return to/from steering gear 2 Return fluid chamber 3 Cut-off valve 4 Radial groove 5 Servotronic transducer valve 6 Fluid feed radial groove 7 Radial groove 8 Orifice 9 Balls 10 Compressio

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JAGUAR XFR 2010 1.G Workshop Manual 18 Pinion 19 Steering gear rack bar 20 Valve sleeve The valve unit is an integral part of the steering gear. The principle function of the valve unit is to provide power assistance
(i.e. when parking

18 Pinion 19 Steering gear rack bar 20 Valve sleeve The valve unit is an integral part of the steering gear. The principle function of the valve unit is to provide power assistance
(i.e. when parking) to optimize the effort required to turn the steering wheel.

The pinion housing of the valve is an integral part of the main steering gear casting. The pinion housing has four machined
ports which provide connections for pressure feed from the power steering pump, return fluid to the reservoir and pressure
feeds to each side of the cylinder piston.

The valve unit comprises an outer sleeve, an input shaft, a torsion bar and a pinion shaft. The valve unit is co-axial with the
pinion shaft which is connected to the steering column via the input shaft. The valve unit components are located in the
steering gear pinion housing which is sealed with a cap.

The outer sleeve is located in the main bore of the pinion housing. Three annular grooves are machined on its outer diameter.
PTFE (polytetrafluoroethylene) rings are located between the grooves and seal against the bore of the pinion housing. Holes
are drilled radially in each annular groove through the wall of the sleeve. The bore of the outer sleeve is machined to accept
the input shaft. Six equally spaced slots are machined in the bore of the sleeve. The ends of the slots are closed and do not
continue to the end of the outer sleeve. The radial holes in the outer sleeve are drilled into each slot.

The input shaft has two machined flats at its outer end which allow for the attachment of the steering column intermediate
shaft yoke. The flats ensure that the intermediate shaft is fitted in the correct position. The inner end of the input shaft forms
a dog-tooth which mates with a slot in the pinion shaft. The fit of the dog-tooth in the slot allows a small amount of relative
rotation between the input shaft and the pinion shaft before the dog-tooth contacts the wall of the slot. This ensures that, if
the power assistance fails, the steering can be operated manually without over stressing the torsion bar. The central portion of
the input shaft has equally spaced longitudinal slots machined in its circumference. The slots are arranged alternately around
the input shaft.

The torsion bar is fitted inside the input shaft and is an interference fit in the pinion shaft. The torsion bar is connected to the
input shaft by a drive pin. The torsion bar is machined to a smaller diameter in its central section. The smaller diameter allows
the torsion bar to twist in response to torque applied from the steering wheel in relation to the grip of the tyres on the road
surface.

The pinion shaft has machined teeth on its central diameter which mate with teeth on the steering gear rack. A slot, machined
in the upper end of the pinion shaft mates with the dog-tooth on the input shaft. The pinion shaft locates in the pinion
housing and rotates on ball and roller bearings.

Servotronic Valve

The Servotronic transducer valve is located in a port in the side of the steering gear valve housing. The valve is sealed in the
housing with an O-ring seal and is secured with two long screws into threaded holes in the housing. The Servotronic valve is a
transducer controlled valve which responds to control signals supplied from Servotronic software in the instrument cluster.

The Servotronic valve determines the hydraulic reaction at the steering gear rotary valve and controls the input torque required
to turn the steering wheel. The Servotronic system allows the steering to be turned with the optimum effort when the vehicle
is stationary or manoeuvred at slow speed. The hydraulic reaction changes proportional to the vehicle speed, with the required
steering effort increasing as the vehicle moves faster. At high speeds, the Servotronic system provides the driver with a good
feedback through the steering providing precise steering and improved stability.

The instrument cluster receives road speed signals from the ABS module and calculates the correct controlling signal for the Servotronic valve. The Servotronic software within the instrument cluster has a diagnostic capability which allows a Jaguar
approved diagnostic system to check the tune of the steering and retrieve fault codes relating to the Servotronic valve. Two
fault codes are stored relating to the valve for positive connection short to ground or battery and negative connection short to
ground or battery.

The Servotronic software within the instrument cluster also contains a number of steering maps which are selected via the car
configuration file depending on the vehicle model and tire fitment.

If a failure of the Servotronic valve or software occurs, the system will suspend Servotronic assistance and only a default level
of assistance will be available. Fault codes relating to the fault are stored in the instrument cluster. No warning lamps are
illuminated and the driver may be aware of the steering being 'heavier' than usual.
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Page 748 of 3039

JAGUAR XFR 2010 1.G Workshop Manual NOTE: V8 pump shown

Page 749 of 3039

JAGUAR XFR 2010 1.G Workshop Manual 1 Power steering fluid inlet port 2 Flow control valve 3 Power steering fluid outlet port 4 Variable Orifice 5 Pump rotor 6 High pressure 7 Adapter ring 8 Cam Ring 9 Low pressure The pump consists of

1 Power steering fluid inlet port 2 Flow control valve 3 Power steering fluid outlet port 4 Variable Orifice 5 Pump rotor 6 High pressure 7 Adapter ring 8 Cam Ring 9 Low pressure The pump consists of a shaft containing a number of slots into which vanes are inserted and these vanes run within a cam ring
in the pump body. The centerline of the shaft is not concentric with that of the bore of the body and this creates the expanding
and contracting cavities that form the pumping action.

The vanes rotate within the cam ring and are driven by the shaft. As the vanes rotate, the cam ring causes the space between
the vanes to increase. This causes a depression between the vanes and fluid is drawn from the reservoir via the suction hose
into the space between the vanes. As the shaft rotates, the inlet port is closed to the vanes which have drawn in fluid,
trapping the fluid between the vanes. The cam ring causes the space between the vanes to reduce and consequentially
compresses and pressurizes the hydraulic fluid trapped between them. Further rotation of the shaft moves the vanes to the
outlet port. As the vanes pass the port plate the pressurized fluid passes from the pump outlet port into the pressure hose to
the steering gear.

The cam ring in the pump body can move within the valve body. By moving the cam ring it is possible to vary the eccentricity of
the shaft and the vanes in relation to the cam ring. As the eccentricity is decreased, the volume of hydraulic fluid trapped
between the vanes decreases, maintaining the flow in response to pump speed. This reduces the load required to turn the
pump and therefore improves engine output and economy. This allows the flow rate to be matched to the system demands and
increased flow rate is only required when the steering wheel is turned.

The pump has an internal regulating valve which controls the eccentricity of the cam ring and therefore varies the flow rate
according to demand. The regulating relief valve limits the maximum pressure supplied to the steering gear to 110 bar (1595
lbf in2) ± 4 bar (58 lbf in2) and also limits the maximum flow to 8.5 l/min (1.86 gal/min) ± 0.5 l/min (0.1 gal/min) regardless
of engine speed.

Page 750 of 3039

JAGUAR XFR 2010 1.G Workshop Manual 1 Bolt and washer (2 off) 2 Rubber mounting (2 off) 3 Cap 4 Reservoir body 5 Return connection 6 Suction hose connection 7 Max/Min level 8 Lanyard The reservoir is located in the engine compartment, o

Page 751 of 3039

JAGUAR XFR 2010 1.G Workshop Manual A V8 naturally aspirated and 3.0 V6 B V8 supercharged 1 Fluid cooler 2 Hose - return to fluid reservoir 3 Hose - Return from steering gear valve unit The fluid cooler is located in the return circuit

Page 752 of 3039

JAGUAR XFR 2010 1.G Workshop Manual Published: 11-May-2011
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