AWD without a Centre Diff

Gannon · Post by **Gannon** » Wed Jan 24, 2007 7:26 pm

Have you ever heard of a torque limiter (the thing found on PTO driven farm equipment to protect your tractors gearbox when you hit a stump)

They also use them in manufacturing www.ringspann.de/uk/products/p45/p45rs.htm

What if you were add one of these between the gearbox and the rear diff.

You would have engine power to all 4 wheels, but it would slip (but still maintains preset torque) under high strain and enable your car to corner without binding up the gearbox.

The ones designed for slashers are about 6" in diameter and have 8-10 springs that allow the pressure/torque threshold to be adjusted

Just a crazy idea i had

What do you think

Post by **Captain Obvious** » Wed Jan 24, 2007 8:53 pm

hmmmm could work kinda like a viscous diff in a lib box me thinks

AndrewT · Post by **AndrewT** » Wed Jan 24, 2007 9:32 pm

That is just a rather agricultural (pun intended) LSD isnt it?

Brumby Boy · Post by **Brumby Boy** » Wed Jan 24, 2007 10:24 pm

Suparoo wrote:
Just a crazy idea i had

What do you think

Dont we live on crazy ideas around here???

mattims · Post by **mattims** » Thu Jan 25, 2007 9:04 am

i believe it would be pretty harsh. It relies on static friction so it would grip and bind the gearbox then slip with a clunk and grip again.

BlackMale · Post by **BlackMale** » Thu Jan 25, 2007 9:07 am

I agree with Mattims. Also how you going to bind it up so it dose not release for 4WD? or are you just talking about on road use only.

Gannon · Post by **Gannon** » Thu Jan 25, 2007 3:57 pm

Yeah i was thinking on road use only.

My thoughts originated from the viscous coupling in the early AWD auto forester and liberty gearboxes. I read somewhere that the front wheels are connected permamently to the engine, and there is a proportion sent to the rear axle, controlled by the viscous coupling.
Or something along those lines.

I thought about it binding and releasing with a clunk, but i read this on a website...

During the slipping process, input and output rotate relative to each other and the preset limit torque continues to be transmitted.

So i figured that it shouldnt be all that bad (clutch LSD's work in a similar way)

Are there any other ways of achieving what i wanna achieve? What do other AWD systems use?

Lets make this a brain storming session!!!

YouTube · Post by **El_Freddo** » Tue Jan 17, 2012 1:41 pm

Hey Gannon, Just dug up this while doing a search.

Sorry to see the discussion didn't go any further - did you actually look any further into it? I'm guessing not

I reckon the easiest way to test it would be on a part time 4wd gearbox, locking in 4wd with the PTO's torque limiter hanging out the back of the gearbox...

Cheers

Bennie

Gannon · Post by **Gannon** » Tue Jan 17, 2012 2:50 pm

El_Freddo wrote: I reckon the easiest way to test it would be on a part time 4wd gearbox, locking in 4wd with the PTO's torque limiter hanging out the back of the gearbox...

Yeah my fab skills weren't all that good at that stage, but my idea was to attach it to the centre bearing carrier between the gearbox and the diff.

revmax · Post by **revmax** » Tue Jan 17, 2012 3:21 pm

good idea. would it withstand 6000rpm/200kmh or 3000/100kmh

Gannon · Post by **Gannon** » Tue Jan 17, 2012 5:10 pm

Most PTO driven equipment is designed for 540rpm, but some machines also run on 1000rpm. Id say if it was balanced properly, it would be ok

vincentvega · Post by **vincentvega** » Tue Jan 17, 2012 10:53 pm

cant see it lasting 5 minutes. its designed as an overload protection not something that is slipping every time you turn a corner

discopotato03 · Post by **discopotato03** » Wed Jan 18, 2012 5:51 am

Corect and thats why it wouldn't work . They are designed to be an overload protection device and they would not take kindly to constant slipage .

And erm no , the gearbox drives the center diffs hemisphere which drives the cross pins and then the planet gears on these pins drive the side gears . One side gear is effectively the front diff pinion and the other turns the riser or "transfer" gears to the rear output and tailshaft . The load is balanced driving in a straight line or around corners till a wheel slips . Then the power (torque) goes out the path to the most lightly loaded wheel ie the slipping/spinning one . The viscous hub is just there to limit how fast one side gear can turn compared to the other side one . Being really road cars these need to be quiet and unobtrusive which also limits their effectiveness as an off road traction aid . If they had a serious middle LSD they do clank and do bind and thats part of the compromise .

For an all out competition tarmac car the 4 Matic system is best because it gives the best trade off of RWD characteristics with all paw traction . Its the system Nissan used in the original GTRs though in race trim they flicked all the G sensor electronic control gear .
What they do is have fixed RWD as in an inline engine and gearbox . The back of the gearbox has a transfer case with a multiplate wet clutch a la motorbike and a front output shaft connected to a front diff housed in the side of an aluminium engine sump . They use hydraulic pressure to vary the load from free to direct drive , smartys use the power steering pump as the pressure/fluid provider . In the road cars the wheel speed sensors detect slip and the ECU signals the wet clutch to progressively power the front diff .
The system doesn't wind up because when the wet clutch lets go all the drive is from the rear diff .
The race cars had what looked like a hydraulic handbrake with 5 or 6 steps ie from free to direct front diff drive , aside from launching the drivers set it to taste and left it alone . No way Nissan could do this with road cars so they have all the problematic electronic crap . They still had to build understeer into the roadies because Joe average wood duck always kills himself in cars designed to oversteer or understeer less anyway ...

There is no ultimate system other than long travel coil suspension attached to 6WD and four lockable diffs . In other words buy a 6WD Pinzgauer .

NachaLuva · Post by **NachaLuva** » Wed Jan 18, 2012 1:01 pm

discopotato03 wrote: There is no ultimate system other than long travel coil suspension attached to 6WD and four lockable diffs . In other words buy a 6WD Pinzgauer.

http://www.4x4road.com/tipspinz.html

Oh yeah baby

Make those stupid Landcruisers look lame lol

spike · Post by **spike** » Wed Jan 18, 2012 3:08 pm

thinking about all this traction is fine, but i do not accept the old saying

who needs articulation if you've got lockers

we can lock the front and rear but until we start going mad with lift and flex. While offroading (rock hopping) isnt really my scene i know that this system doesnt do it all.

i think a rear locker would be better, then lock the center up

Gannon · Post by **Gannon** » Wed Jan 18, 2012 7:49 pm

You do realise this thread is 5 years old?

spike · Post by **spike** » Wed Jan 18, 2012 8:03 pm

yeah ahaha wondered why it got opened up again

YouTube · Post by **El_Freddo** » Wed Jan 18, 2012 8:11 pm

spike wrote:yeah ahaha wondered why it got opened up again

My fault

Interesting discussion though, I reckon it'd work - if you've ever used one of these on farm machinery they cop a beating! Longevity wouldn't be an issue, the issue would be the rotational speed.

Gannon, don't take people's comments personally - they're not out to attack you, even if it seems like they are. Some of the best idea came from something crazy!

Cheers

Bennie

spike · Post by **spike** » Wed Jan 18, 2012 8:21 pm

El_Freddo wrote: Gannon, don't take people's comments personally - they're not out to attack you, even if it seems like they are. Some of the best idea came from something crazy!

sorry gannon wasnt aiming anything at you just throwing my ball into the room

the idea would work, but the revs and duration would be the problem
and the work in hooking it up and having to replace it would be outragous

discopotato03 · Post by **discopotato03** » Wed Jan 18, 2012 10:52 pm

I think the issue with Subarus is suspension travel , even if you could lock every diff can you keep enough feet on the ground to keep moving .
Don't think 6WDs with diff locks can't have every wheel turning at the same speed without actually moving . A bit exciting when it weights 24 tonnes and trying to drag it up steep rock shelves !
I think the most unstopable one I ever drove was an army prototype Leyland Mastiff 6WD . Big wide 18Rx22.5 super singles tyres and real good suspension travel .