ATB Diffs

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Originally Posted by Eevo

i have a stupid question, whats an ATB?

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An Ashcroft ATB, Quaife ATB, Torsen type II, WaveTrac and TruTrac all operate on the same principle where they use helical gears in pockets. There are detail differences, including the amount of preload used, and the TruTrac uses a cast case and only three gears vs six in the others.

I started to write up a description but this from Ashcrofts site is better (easier!)


The helical gear type ATB has many advantages that overcome the objections to other designs. There is a minimal pre-load necessary to engage the gears but this does not cause excessive wear or harshness, the helical gear type is virtually invisible to the driver on normal road use as the gear/pocket friction simply does not occur.
So how does this 'helical gear' ATB work, as stated earlier there are six sets of helical gears, mounted parallel to the axle, each side 'sun' gear drives six helical gears, these mesh with six corresponding helical gears which in turn drive the opposite side 'sun' gear. The important factor is the fact that these helical gears are mounted in 'pockets' in the center carrier, so any radial load on the helical gears causes them the press against the side of the pocket creating friction. This is why we use six pockets as opposed to three in another well known brand, more pockets more friction and better ATB effect.

One of the drawbacks of the ATB is that it is always necessary to have some load on one wheel per axle. if there a no load situation eg cross axle the wheel with traction would only see approx three times the load on the wheel with no traction ie nothing!!. To overcome this, as stated earlier, the ATB is fitted with some preload springs to provide some loading to the side with no traction in the event of a cross axle, where this pre-load is not providing sufficient traction to the other side then one favourite trick is to apply a small amount of left foot brake whilst applying more throttle. This manouver fools the diff by providing load to the non-traction side which is multiplied by the ATB (approx 3:1) to the other side, the loss of drive attributed to the brakes which are acting equally on both wheels is overcome by the additional throttle. In a car fitted with Automatic Traction Control this braking all takes effect automatically and the ATB provides additional traction by multiplying the ATC effect.

Ashcroft Transmissions

TruTrac <em>https://www.youtube.com/watch?v=lZms...ature=youtu.be

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Originally Posted by Marty90

Automatic Torque Biasing Limited Slip Differential.
Can someone who has them tell me.My Puma has TC which works well but I hate that the wheel which has lost traction needs to spin madly before TC activates and often some momentum is still needed.Would an ATB reduce the initial spinning. I'm looking at E-lockers just so that once activated,it should be easier on the vehicle.

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I have the Ashcroft ATB on the front. You don't notice it is there, apart from the initial slight wanting to return to centre with the steering. Only been on the sand with them, most notable difference is TC doesn't seem to come on as much. And the Disco seems to take the soft deep sand a little better. Could be my imagination, of course, but there is a difference, for the better. The idea was to put a locker in the back, finances don't permit that, so another ATB may be going there. If I live long enough to save the money. [bigsmile1]

For the price on 1 elocker you can get 2 ATBs. Cheers

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Originally Posted by rick130

To overcome this, as stated earlier, the ATB is fitted with some preload springs to provide some loading to the side with no traction in the event of a cross axle, where this pre-load is not providing sufficient traction to the other side then one favourite trick is to apply a small amount of left foot brake whilst applying more throttle. This manouver fools the diff by providing load to the non-traction side which is multiplied by the ATB (approx 3:1) to the other side, the loss of drive attributed to the brakes which are acting equally on both wheels is overcome by the additional throttle. In a car fitted with Automatic Traction Control this braking all takes effect automatically and the ATB provides additional traction by multiplying the ATC effect.

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I had wondered about the applying of the brake pedal as whether this would help overcome the wheel just spinning freely in the air and send drive to the wheel with traction..... Still u need some extra throttle to do this and that might not suit in every situation especially slow is the go and wheel placement is crucial....
But for those that mostly do offroad touring with the odd harder track thrown in, I'm assuming the ATB's in the Front/Rear and possibly the TC would or should be good enough ???

I posted on the D2 section because from what i read the D2's traction control works very well with the ATB and you have 90 percent of a locker without the drawbacks...ie you can still steer fine with it in the front; you don't get the vehicle stepping sideways; you don't have to turn it on and off; you get the benefit on high speed dirt. I would think there is very little between an ATB equipped D2 and a fully locked D2. Cheers

Cheers

This link is from the Ashcroft web site, offered to users as a critique of the ATB.

DEFENDER2.NET - View topic - ATB (torsen) front and rear install

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Originally Posted by ozscott

An ATB shouldn't throw you sideways on a side slope. Cheers

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A feature often overlooked. (I will see your "shouldn't" and raise with a first hand experienced "doesn't, much")

Have seen it repeatedly when unavoidably traversing slippery side slopes with no ruts or other features to help by hooking wheels into a line:
- diff(s) locked: Every 2" forward matched by 2" sideways slip down hill while steering straight ahead. hard to predict what happens with any steering input other than increased slippage sideways downslope (eg steer uphill but front slips downhill even worse!).
- diff(s) unlocked, open diffs: uphill wheels (unloaded) spin too easily on slippery stuff.

- with ATBs: typically can drive and steer predictably with much reduced sideways downslope slip.

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Originally Posted by Robmacca

I had wondered about the applying of the brake pedal as whether this would help overcome the wheel just spinning freely in the air and send drive to the wheel with traction..... Still u need some extra throttle to do this and that might not suit in every situation especially slow is the go and wheel placement is crucial....
But for those that mostly do offroad touring with the odd harder track thrown in, I'm assuming the ATB's in the Front/Rear and possibly the TC would or should be good enough ???

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Again with the benefit of first hand experience, because my Malaysian assembled 2013 TDCi DCPU doesn't have TC: Deft left foot braking does work with ATBs fitted.
- No need to be too heavy footed on the brake, just enough to stop the spinning wheel from free-spin. To control/reduce the spinning, not necessarily stop it totally.
- the brake calipers on wheels either side of an ATB bite equally on their associated brake disks
- there is still going to be an imbalance across the ATB as the previously free spinning wheel will still be turning faster/easier than the wheel on the ground (which now will have BOTH the brake caliper + some ground traction to deal with). Causing the ATB to do its biassing magic and get some useful drive to the wheel on the ground.

- As for this being perhaps unsuited to "slow is the go" situations. Maybe. It'd be down to the skill of the operator largely. One doesn't need to stab/jab on the brake pedal roughly...


- LFBraking with an ATB doesn't work as well as TC+ATB. For sure. And of course a full on selectable locker or an unlocker (like a detroit) will be better still at getting drive to the wheel on the ground

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Originally Posted by steane

If you are just comparing lockers and ATBs, it's easiest to view it on a scale of 1 - 10, 1 being the absolute best.

Slow, challenging off-road

1 - Lockers
2 - ATBs with TC
3 - ATBs

Every other situation

1 - ATBs
v
v
v
v
10 - Open diffs

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Absolutely!! You have nailed it so well steane.



And to make it clear to those who didn't get it. Where steane writes comparing lockers and ATBs:

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Originally Posted by steane

Every other situation

1 - ATBs
v
v
v
v
10 - Open diffs

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Steane didn't forget to show where "lockers" are on the 1-10 scale for "Every other situation" .

"10 - Open diffs" is what you have when selectable lockers are unlocked - and unlocked is the norm for selectable lockers in pretty much "Every other situation"


Meanwhile ATBs (with or without TC) are not totally useless in that one area where selectable lockers shine, and on top of that are an asset in all other onroad and offroad scenarios.

(Edit: For completeness: There are some exceptions to "open diff is what you have when selectable lockers are unlocked". The Ashcroft centre ATB for Land Rovers retains the ability to selectively lock the centre diff. KAM lockers used to have an ATB diff that was a selectably lockable. Obviously when these are "unlocked" one does not have an open diff, one has an ATB.)