TRACTION control

[RJG18]

Originally Posted by p76rangie

A centre diff lock in older LRs do not lock up all the wheels. Basically with no centre diff lock your car is one wheel drive. That is, lift any wheel and it will not go anywhere. With the centre diff lock engaged it becomes 2 wheel drive. That is, you have to lift one front and one rear wheel to loose drive. add a rear diff lock and it becomes a 3 wheel drive and then add a front locker and it is a true 4 wheel drive.

Ian

Exactly. That's one thing I didn't mention in my overly long rambling post. If you don't have a centre diff lock, but DO have front and rear axle diffs locked, then it still allows the front pair of wheels and the back pairs of wheels to turn at different rates, and receive different amounts of power. So if the front two wheels are spinning in mud, but the back two wheels still have traction, then without a CDL all the power will go to spinning the front wheels, and the back wheels won't turn at all.

The combinations of how T/C and/or D/Ls worl varries in different combinations. Might to do a simple ASCII diagram of how they work (this could go badly wrong):

[nfrey2]

So most D2's have a completely open center diff? Most RRC's have a viscous coupling, and D1's have full locking center diffs. Listed in order of effectiveness.

[RJG18]

(follow on from above post) :

Ok, so our ASCII Landy looks like this:


[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


The (F) is the front diff, (C) is centre diff and (R) is rear diff. Ignore the dots to the left, they're just needed to get the spaing right...


1. WITHOUT DIFF LOCK or T/C:

If the back right wheel gets stuck in mud and loses all grip then all the drive follows the drive train as indicated below:

[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


Or, If both right wheels have lost grip in mud, power will all be used to spin these wheels, and the vehicle will remain stuck:


[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


Or if both front laft and back right wheels have lost grip, the power will be transfered to these wheels, again meaning the wheels that DO have grip still have now traction:


[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


So in all of the above cases, without T/C or D/L, you are stuck.




2. WITH DIFF LOCKS

We'll use the third scenario from above (hey this is just like being a teacher!). Front left and back right wheels spinning in mud, as shown below:


[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]

If we lock the just the front dif. All that will happen here is that the front left wheel (previously spinning in mud) is now locked to the front right, so has traction, but this of course means that the whole front axel (both front wheels) now have greater traction than the back right wheel (which is still in mud) so all the power follows the centre diff backwards, and just spins the back right wheel - so the car goes nowhere:

[]--(L)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]

Continued in next post...

[RJG18]

... continued from above...

Locking just the centre diff on it's own does not help either, as this will just mean that the front and rear prop shafts (the vertical lines) will both turn together, and when the drive reaches the axel diffs, it will turn the wheel with the least reistance, i.e. the front left and back right wheels that are stuck in mud:

[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


However, if you lock all three diffs, then both shafts and both axels will turn together, and power will go to all 4 wheels (i.e. you have true four wheel drive). This means that although the two stuck wheels will still spin, the two wheels with grip will also spins, and you'll move

[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


3. WITH TRACTION CONTROL (and no Diff Locks):

This is how a Disco 2 works.

If we take our original scenario, where front left and back right wheels are spinning in mud:

[]--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--[]


What the D2 does is detect that these two wheels are spinning, and apply the brakes to them:

XX--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--XX

This then locks the front left and back right wheels (that were stuck in mud) meaning that although the other two wheels DO still have some resistance (i.e. they are gripping the ground) this resistance is less than the front left and back right wheels, which are now full locked by the brakes. This means that the wheels with the grip DO receive the power:

XX--(F)--[]
......|
......|
.....(C)
......|
......|
[]--(R)--XX

[FlyWheel]

Excellent job on the ASCII.......and well explained.....

[Jupiter Rover]

oohh ok.. that makes it ALOT easier to understand how TC works and locks. and so on. because i really didnt have a clue. im new to wheelin**.. thanks bud. this helps. i gota good picture in my mind of what now goes on when i get stuck in mud. THANKS

pete