Torsen Question

[erasedhammer]

So a couple days ago I went out for some off roading and came off a small slope at an angle, which caused two wheels to be off the ground (one in rear, one in front). Without brake modulation, The vehicle would not move at all with more throttle.

As far as I know and understand the torsen differential, the wheel with traction should receive 4 times more torque than the spinning wheel.

So theoretically if the wheel off the ground was getting 100 ft lbs of torque, wouldn't the wheel on the ground get 400 ft lbs of torque and the vehicle should move?
So why didn't I move?

The torsen website doesn't mention anything about brake modulation, but is that the only way to keep it from acting like an open diff?

After a small amount of brake pressure I was able to glide right on off the slope, as expected.

Extra info I found:
Looked at wikipedia... found that normal torsens act like open diffs when one wheel is airbourne. Interesting, any one know why that happens and not when both wheels are on a surface?

Also, looks like torsen made a differential that solved that problem, the T2R racemaster? I think I saw one in a 4:1 TBR... I wonder if putting that in a humvee would better its ability to move forward regardless of wheel slippage...(could eliminate the fact that brake modulation is only fighting your engine)?

 

[Wire Fox]

Very cool subject to read into. The T1 and T2 differentials are incompatible, but it looks like thanks to ABS existing in the Hummer H1, we might have off-the-shelf parts to make this possible. The H1 through 1998 should have been without ABS and used the standard T1 differential that the HMMWVs are all equipped with. Allegedly in 1999 with the ABS addition, they switched to a T2 differential with a lower bias ratio so that it would not stay locked and fight against the ABS/TT4 system. However, like you've pointed out, the T2R has a higher torque bias ratio that comes close to matching our T1, but also has some applications where it has a running clutch to pre-load the differential and allow it to remain locked without BTM. The T2 and T2R are compatible to some extent, so it should be possible to interchange the two in an application built to accept them.

I'm nowhere even close to an expert on these, but it looks like it might be possible to switch to the differential setup for the 1999-2002 H1, then switch in a T2R differential to get the effect you're wanting. The T2Rs were listed at about $650 each, plus the cost of all of the H1 parts you would need... Very expensive, but it looks technically possible.

EDIT I may fundamentally understand how these are assembled. The more I read now, the less confident I am about everything I said except for the later H1s having a T2-type Torsen.

 

[Retiredwarhorses]

I wouldn't try to copy anything from the TT4 setup on a Hummer H1. Just learn how to BTM.
The best years for the Hummer line was 97.5-1998, 1999 was by far the worst IMO "TT4"

 

[erasedhammer]

I wouldn't try to copy anything from the TT4 setup on a Hummer H1. Just learn how to BTM.
The best years for the Hummer line was 97.5-1998, 1999 was by far the worst IMO "TT4"

I agree, I much prefer the T1 with the high TBR ratio. I was just looking into why the torsen acts like an open diff when a wheel is airbourne.

 

[NDT]

I agree, I much prefer the T1 with the high TBR ratio. I was just looking into why the torsen acts like an open diff when a wheel is airbourne.

It's supposed to act as an open differential until you lock it with brake throttle modulation (BTM).

 

[erasedhammer]

It's supposed to act as an open differential until you lock it with brake throttle modulation (BTM).

Yes, but why, like whats the concept of operation when a wheel is off the ground? And why does it differ when one wheel is on a surface and slipping? Just looking for some food for thought

 

[snowtrac nome]

because of the way the helical gears work against each other you need some friction to initiate the lock up once this happens you have all the pull you need. in mud or on snow you should have enough friction to make it work on ice or one wheel air borne you will need to add friction with brakes