center diff in Open cars?

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zerodegreec
A fully active Front, Center and Rear Diff was the height of technological advancement in the sport. You can't get the traction like they did in the Early 2000's anymore under FIA rules. 2005 was the end of the active front and rear diffs. The teams could continue to use the active center and I think that is why the STI and Evo continue to have such good controls associated with Motorsports. The technology is directly linked to the rules in the WRC between 2006 and the subsequent removal of active centers in 2011.

I think Vermont is using the best technology available for the rules in the RA series.

I'm confused.

* "we" seem to think that VTSC is using a spool/clutch "center diff" like current WRC/S2000/etc.
* rule changes/consensus seems to be that an active center diff is faster (and more $$$$) than the spool/clutch deal.
* I can't find anything in a very brief reading of the r-a rules that prohibits an active center diff in open.

If those three points are true, it certainly seems as though they're NOT using the best technology available for the rules in the RA series.

(it could be they think that the extra expense of a fancy diff isn't needed to take home yet another trophy, but what do I know?)

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KF7RWG
http://www.utahrallygroup.com

"best" is a really poor word to use in this instance.

instead, let me rephrase that to:
it certainly seems as though they're NOT using the fastest technology available for the rules in the RA series.

"best" is a delicate balancing act of speed, cost, reliability, etc.

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KF7RWG
http://www.utahrallygroup.com

ELI5: Can someone explain how the fly off hand brake works on the mechanical diff rally cars.

I've noticed when they use the hand brake in the rally cross cars they don't need to engage the clutch. This would break my car.

Instead of having a differential in the center, the transmission is directly connected to both the front and rear. In the case of the front, that's the whole story, so it's really the same as a FWD drivetrain. In the case of the rear, between the transmission and the rear there's a clutch of some sort. When you're on the gas, this clutch is engaged, so you now have a 4x4 (i.e., an AWD with a spool in the center). When you pull the hand-brake, the clutch instantly opens.

The main advantage of this approach over having a center diff with some sort of limited-slip device is that you don't have to punch the clutch when you yank the hand-brake. Also, because there's no center diff, it's not the case that the front output must suddenly rotate at twice the speed as the input (assuming a 50/50 center) when the rear output suddenly stops turning.

It was the observation that Block doesn't punch the clutch when he yanks the hand-brake in his videos that actually started this whole question. This told me that he has a Haldex (or equivalent) in the car used in the videos. I started to wonder if he has the same in the car used for RA.



Edited 2 time(s). Last edit at 04/02/2014 07:08AM by Iowa999.

You can grab a handful of parkingbrake in an awd car that has a stone age no computer viscous centerdiff without tapdancing on the clutch pedal. Block's bux certainly allow him to have all manner of fancy digital magic shyte in the drivetrain of that car but it isn't required.

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Jay Woodward
Snohomish, WA
'90 Mazdog Frankenprotege
Chronologically, 46...

http://gph.is/1bgR8Yz

That's what the center differential says to power going to the rear diff when the handbrake is pulled?

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Foard Cleveland
Blue Branch Rally Team
http://www.performancefriction.com

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Aaron Luptak
I'm confused.

That is quite apparent

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Aaron Luptak
* "we" seem to think that VTSC is using a spool/clutch "center diff" like current WRC/S2000/etc.

No, they use a Sadev as Modernbeat pointed out (twice)

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Aaron Luptak
* rule changes/consensus seems to be that an active center diff is faster (and more $$$$) than the spool/clutch deal.

WRC Rule change, has nothing to do with RA or CARS rules

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Aaron Luptak
* I can't find anything in a very brief reading of the r-a rules that prohibits an active center diff in open.

Nobody said there was such a rule. Thus that is why Vermont uses a Sadev (see above)


As modernbeat pointed out (sorry that I missed your previous mention of this);

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modernbeat
Vermont is using the Sadev box configured for Subaru use with an electronically controlled clutch.

Vermont is not using a current S2000 or WRC Spec system. I am willing to bet Block does not have any electronic diffs in his M-Sport car. There is no way that Kens car differes from the specs of THIS other than a larger displacement engine and suspension for the garbage "look at me I can slide around the same cone 50 times and film the best one" stuff that is not rally. I had seen a really good interview with Ken where he talked about the setup of his M-Sport car for GymKana "stuff" in that the car was setup more closely to gravel setting and essentially for terrible control (all floppy). He had also said that he was not very good on tarmac rally stages. Will try to remember where to find it. In fairness, very few rally drivers are good on both surfaces, there are defiantly tarmac specialists. Loeb being the exception, Sordo and Ogier being very close behind.

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Intercom and electronics dude. www.zerodegreec.ca



Edited 2 time(s). Last edit at 04/02/2014 10:10PM by zerodegreec.

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zerodegreec

Quote
Aaron Luptak
* "we" seem to think that VTSC is using a spool/clutch "center diff" like current WRC/S2000/etc.

No, they use a Sadev as Modernbeat pointed out (twice)

I cannot speak for Aaron, but here's why I found the statemant that "VTSC uses a Sadev" to not quite answer the question or, at least, leave something unclear. I've found both kinds of Sadev on the web: a Sadev with a center differential and a Sadev that is better described as a spool/clutch.

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Jay
You can grab a handful of parkingbrake in an awd car that has a stone age no computer viscous centerdiff without tapdancing on the clutch pedal.

But, to the extent that the transmission, flywheel, and engine have a decent amount of (rotational) inertia, the front wheels will leap up in speed when you do this.



Edited 1 time(s). Last edit at 04/02/2014 09:36AM by Iowa999.

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Iowa999

Quote
Jay
You can grab a handful of parkingbrake in an awd car that has a stone age no computer viscous centerdiff without tapdancing on the clutch pedal.

But, to the extent that the transmission, flywheel, and engine have a decent amount of (rotational) inertia, the front wheels will leap up in speed when you do this.

Why do you think there will be such a large leap in speed? Both front and rear diffs are at the same ratio I wouldn't expect more speed but instead more torque.

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Foard Cleveland
Blue Branch Rally Team
http://www.performancefriction.com

Quote
Iowa999
The main advantage of this approach over having a center diff with some sort of limited-slip device is that you don't have to punch the clutch when you yank the hand-brake.

Which you don't have to do anyway.
I had a 2.5RS with the upgraded centre diff and could handbrake it at will. The whole idea behind differentials is to allow either 'side' to rotate at different speeds. With the tighter diff, the car would tend to plough a bit, but it would still work. (the reality is not that the front starts to rotate faster instantly, but that the engine is bogged down)

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First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
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Last Updated, January 4, 2015

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john vanlandingham
Blame is for idiots. losers.

The flyoff is a hydraulically actuated de-coupler inline in the rear driveshaft, actuated by a 2nd master cylinder on the handbrake lever. There is a balance bar between the rear brake and flyoff so you can adjust the action of the disconnect.

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Iowa999

Quote
zerodegreec

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Aaron Luptak
* "we" seem to think that VTSC is using a spool/clutch "center diff" like current WRC/S2000/etc.

No, they use a Sadev as Modernbeat pointed out (twice)

I cannot speak for Aaron, but here's why I found the statemant that "VTSC uses a Sadev" to not quite answer the question or, at least, leave something unclear. I've found both kinds of Sadev on the web: a Sadev with a center differential and a Sadev that is better described as a spool/clutch.

^^^ Pretty much this.

Since it seems like many (most?) series no longer allow an active center diff ala WRC pre-2012, I'd imagine most of Sadev's current offerings don't have such a thing.

Don't get me wrong, I'm sure Rally-America is a HUGE player in international motorsports, with hundreds of customers knocking on Sadev and others' doors, saying "we need a 4wd sequential rally transmission with an active center diff, here's some piles of money!"

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KF7RWG
http://www.utahrallygroup.com

Uh, the system is not only used for rally. There are most certainly a large enough customer base to make these boxes for Subaru USA, and anyone else who wants one. This is a good reminder of why I don't "contribute" here anymore.you have been told what they use, google it, at the very least actually read what has been posted in this thread. Hint, modernbeat told you.

in out, you auto xers have fun. Got some actual rally stuff to do.

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Intercom and electronics dude. www.zerodegreec.ca

Quote
phlat65
The flyoff is a hydraulically actuated de-coupler inline in the rear driveshaft, actuated by a 2nd master cylinder on the handbrake lever. There is a balance bar between the rear brake and flyoff so you can adjust the action of the disconnect.

Is this something that could be adapted to a simple mans rally car, or is it proprietary to the running gear these RX/WRC cars are using?