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D3 / D4 / RRS D3 / D4 zone is the place for all that specialist D3 / D4 info (and the RRS stuff even though they don't like to think of it as a disco).

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Old 7th July 2008, 09:57 AM
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Disco 3 Centre Differential

Hi. I'm just wondering what kind of diff the Discovery 3 has in the centre. I understand it's an e-diff but is it viscous coupling or a torsen diff or what?

Thanks.
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Old 7th July 2008, 09:35 PM
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Hello Doogs911, welcome aboard!

This may answer your question.

Quote:
Originally Posted by Land Rover
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.
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Old 7th July 2008, 11:41 PM
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Thanks, Jamo. I'd be interested in pulling apart a transfer case... Or perhaps we should just get a Disco 3
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Old 11th August 2008, 09:58 AM
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Another inquiry: Are the front and rear differentials in the Discovery 3 in the centre of the vehicle or are they offset?
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Old 11th August 2008, 08:45 PM
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Offset to the left hand side.
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Old 12th August 2008, 12:41 AM
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doogs, this is what the transfer case looks like inside: (from Vehicle Cutaways and Automotive Projects - Mike McGhee - Cutaway Creations)



If you go to that site, they have cutaways of a RRS rolling chassis (virtually identical to the D3) with good details of the drivetrain.
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Old 21st January 2009, 03:32 PM
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Good one Leo. On inspection, this site has a cut-away of a full D3. Some fascinating photos showing just how complex the D3 is under the skin. It is a bit like watching a cross between CSI and Top Gear!
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Old 21st January 2009, 03:40 PM
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Quote:
Originally Posted by sniegy View Post
Offset to the left hand side.
Isn't the rear diff in the centre ?
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Old 23rd January 2009, 07:34 PM
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