Thread: AWD intelligent diesel or non-intelligent petrol?

The 2022 workshop manual describes its operation (as copied and pasted):

The twin speed transfer case is full time, permanent all wheel drive unit, with 50/50
torque distribution to the front and rear driveshafts. The transfer case is identical for all
engine derivatives and supports the following features:

Permanent all wheel drive with a bevel gear center differential, providing a 50:50
torque split

Selectable high and low range for optimum on-road and off-road performance

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, for example during parking.

The twin speed transfer case is located under the vehicle and is mounted on the cross
member, behind the automatic transmission.

The input torque is equally distributed via a bevel gear center differential. In order to
provide an optimal torque distribution to each wheel in all driving conditions, the twin
speed transfer case is equipped with an electronically controlled locking and torque-
biasing device. This device detects wheel slip via various vehicle system inputs to the
Transfer Case Control Module (TCCM) and locks the differential accordingly. The locking
torque is applied through a multiplate clutch assembly.

A planetary gear set, located in the differential assembly, allows the driver to select
high or low range. 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.

Originally Posted by one_iota

The 2022 workshop manual describes its operation (as copied and pasted):

That description is just the same as what the D3/D4 has. In fact the wording is almost identical to the D3 workshop manual description for the transfer box.

Does not explain how iAWD is different.

When iAWD was first marketed they definitely described it as being different to the normal permanent all wheel drive - even pointing out that it was different between the petrol and diesel model Defenders.

This is how it is described for the new Range Rover:



For the new RRS, similar description but they also note the use of a clutch pack to disconnect the front driveline.

My guess - the documentation for the Defender has not caught up but they are now fitting the same system used in the new Range Rover and RRS, which is a different set up to what the new Defender (and its predecessor the D3/D4) originally came with.

Originally Posted by DiscoDB

That description is just the same as what the D3/D4 has. In fact the wording is almost identical to the D3 workshop manual description for the transfer box. ....

The documentation I copied is suspiciously out of date. Whilst it refers to the 22 Defenders most of the illustrations are those of the D3/D4.

So?

Originally Posted by one_iota

The documentation I copied is suspiciously out of date. Whilst it refers to the 22 Defenders most of the illustrations are those of the D3/D4.

So?

I guess we always knew the new Defender was the replacement for the D3/D4 that we should have always had.

That manual sounds dodgy to me.

Originally Posted by DiscoDB

I guess we always knew the new Defender was the replacement for the D3/D4 that we should have always had.

That manual sounds dodgy to me.

The classic Defender was an evolutionary dead end! As much as it is revered it is an anachronism.

We need to find someone with a my23.5 Defender workshop manual!

Originally Posted by one_iota

The classic Defender was an evolutionary dead end! As much as it is revered it is an anachronism.

We need to find someone with a my23.5 Defender workshop manual!

Will check mine when I have time...and post the extract here.

Originally Posted by DiscoDB

This diagram below explains how there are now 2 clutch packs to control the split of torque from rear to front, and to also fully disconnect the front drive.

The transfer box clutch pack acts “like a differential” and can go from fully open with no drive to the front and 100% to the rear, to fully locked with 50/50 split front and rear.

The 2nd clutch pack on the front axle allows the front prop shaft and crown wheel to come to a full stop when in rear wheel drive mode to save fuel.



This diagram was prior to both systems being fully adopted across all models.

The difference with the technology today is how quickly it can respond to open and close when needed, and how it works in conjunction with the individual wheel braking for traction control.

Hi Thanks for that.

I must say the diagrams and explanations are confusing to me.

"Acts like a differential....fully open clutch with no drive to the front wheels". However, In an open traditional differential there remains torque to the front and rear wheels and indeed split exactly 50:50. Power or "drive" goes to wheels of least resistance ie no traction

" A completely closed clutch with equal torque to the front and rear as with a locked differential" . However, you always get 50:50 torque with an open diff (torque not power/drive - you cannot interchange the terms Power = torque x rpm. No rpm= no power despite infinite torque).

With a locked diff with wheels locked to the same speed (rpm) there exists anywhere between 0 to 100% torque between front and rear. It will only be 50:50 when the the traction on all wheels are the same.

Locked Diff means axles (wheels) spin at same speed and allows for uneven torque split from 0% to 100% between axles and with both torque and power in the same percentage (eg 15% torque will yield 15% power for equal rpm) sent to wheel with most resistance, where it is most needed. Power and drive will result provided the surface allows adequate traction


This video explains open vs closed difs and torque and Power transfer How 4WD Works Part 2 - Open vs. Locked Differentials - Power and Torque Transfer - YouTube
Untitled picture.jpg
So however the system works it is not "like a differential". It may work fantastically well by sending or "vectoring" (torque is a vector) torque to different wheels by whatever mechanism, cluthes.It is theoretically disappointing that only 50% can be maximally sent to the front wheels and if true, the front wheels automatically receive no torque as a priority especially if it cannot be overridden in drive mode selections

Originally Posted by DiscoDB

That description is just the same as what the D3/D4 has. In fact the wording is almost identical to the D3 workshop manual description for the transfer box.

Does not explain how iAWD is different.

When iAWD was first marketed they definitely described it as being different to the normal permanent all wheel drive - even pointing out that it was different between the petrol and diesel model Defenders.

This is how it is described for the new Range Rover:


..................

The drag reduction part (3rd para.) doesn't make sense, unless they mean mechanical drag and not aerodynamic drag.