LR3/Disco 3
GENERAL
The DD295 transfer box is a full time, permanent four-wheel-drive unit, with 50/50 torque distribution to the front and rear
driveshafts. The unit is manufactured by Magna Steyr Powertrain in Graz, Austria and supports the following features:
Permanent four-wheel-drive with a bevel gear centre differential, providing a 50:50 torque split
Selectable high and low range for optimum on-road and off-road performance
Two-speed, fully synchronized 'shift-on-the-move' system allows the driver to change the range without having to
stop the vehicle
Electronically controlled multi-plate clutch providing a centre differential lock and torque biasing function to give
improved traction performance and vehicle dynamic stability.
A strategy, to electronically control the centre differential multi plate clutch assembly, has been developed to provide:
a pre-loading function, increasing locking torque with increased driving torque
a slip controller to increase locking torque under off-road conditions and decrease locking torque for optimum
comfort, e.g. parking.
The unit is located under the vehicle and is mounted on the cross-member, behind the transmission. The unit is identical
for all engine derivatives.
The transfer box receives a torque input from the transmission output shaft, which is passed through the unit to two
outputs for the front and rear drive shafts.
The input torque is equally distributed via a bevel gear type differential. In order to provide an optimal torque distribution
to each wheel in all driving conditions, the unit is equipped with an electronically controlled locking and torque-biasing
device. This device detects wheel slip via various vehicle system inputs to the transfer box control module and locks the
differential accordingly. The locking torque is applied through a multi-plate clutch assembly.
A planetary gear set, located in the differential assembly, allows the driver to select high or low range whilst driving, this is
known as 'shift on the move'. When in low range, the planetary gear set provides a ratio of 2.93:1, which gives the vehicle
an extremely low crawl speed for off road driving and trailer towing. High range is a direct drive from the transmission
output shaft and provides a 1:1 ratio.
Both the centre differential locking and biasing and the 'shift on the move' features are actuated via a DC transfer box
motor, which is controlled by the transfer box control module, via a Pulse Width Modulation (PWM) signal.
57
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Thrust washer
58
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Spacer ring
59
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Oil pump assembly
60
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Needle roller bearing
61
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Input shaft
62
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O-ring
63
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Circlip
64
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Disc spring, 2 off
65
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Bolt, 19 off
66
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Dowel pin (2 off)
67
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Front housing
68
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Breather cartridge
69
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Bearing
70
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Circlip
71
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Seal ring
72
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Front output flange
73
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Seal ring
74
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Circlip
75
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Bearing
