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Centre Diff Problems / Questions / Suggestions
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(33 posts, started )
Centre Diff Problems / Questions / Suggestions
A) There needs to be the option to have a locked centre diff (or no diff, really).

B) The "Torque Split" option is ambiguous. How is that acheived? Why can we adjust the viscous diff's and also the torque split - how is THAT achieved mechanically? And why can I adjust the torque split with an "open" centre differential?

C) Please add the option for a clutch pack differential as a centre diff; and of course a torsen diff would be nice as has already been mentioned - but would suit a centre diff quite well.

I'm confused as to how the torque split is created if it's not action of the centre diff itself...
I'm currently reading though this: http://en.wikipedia.org/wiki/Four-wheel_drive

No doubt it will shed some light on the situation.

Edit: as I'm reading through there seems to be some major factual errors in there, e.g.: "the left front wheel actually turns four times as fast as it should be turning, preventing the other three wheels from turning."

Funny, but when in the inside wheel spins I don't recall all other 3 wheels locking and the car braking to a halt. The text describes a possible specific situation, when trying to pull away, but most of the time you're already going to be moving, so it's incorrect as a general assumption.

Edit again: OK, read most of it now, doesn't really answer your questions.
I made an open differential out of legos (it had the case for it, I just added the gears). If you hold one of the wheels still, then the other wheel does not spin any faster then it was before you locked the other wheel. It did with my lego diff at least!
#4 - Osco
Quote from wheel4hummer :I made an open differential out of legos (it had the case for it, I just added the gears). If you hold one of the wheels still, then the other wheel does not spin any faster then it was before you locked the other wheel. It did with my lego diff at least!

something like this?

Quote from Ball Bearing Turbo :A) There needs to be the option to have a locked centre diff (or no diff, really).

B) The "Torque Split" option is ambiguous. How is that acheived? Why can we adjust the viscous diff's and also the torque split - how is THAT achieved mechanically? And why can I adjust the torque split with an "open" centre differential?

C) Please add the option for a clutch pack differential as a centre diff; and of course a torsen diff would be nice as has already been mentioned - but would suit a centre diff quite well.

I'm confused as to how the torque split is created if it's not action of the centre diff itself...

I dont think anyone ever created a car with locked central diff for racing. It wouldnt be very healthy for a gearbox i think.

Torque split on different axles is realised with different size of wheels, belonging to both axles, in the mechanism of differential.
#7 - Osco
Quote from wheel4hummer :Yes, the same exact tires too!

I built the same one, only the center pinion doesn't run smooth so it's like an lsd
I have those lego diffs as well, and in fact the wheel you don't hold does turn faster, as it should.

I realise that a locked centre diff would not be healthy, but I would still like the option anyway - especially if/when we get rally tracks with no tarmac in them.

So based on what's been said, I think something is "interesting" in the way we can adjust things on the RB4/FXR...
Quote from Osco :I built the same one, only the center pinion doesn't run smooth so it's like an lsd

I guess there is no actual such thing as a fully open diff anyway. There will always be some amount of friction on the pinion gears. I want to make a torsen diff out of legos, but I have VERY few legos. I will have to buy some off of ebay or something.
Quote from himself :I dont think anyone ever created a car with locked central diff for racing. It wouldnt be very healthy for a gearbox i think.

Torque split on different axles is realised with different size of wheels, belonging to both axles, in the mechanism of differential.

Actually, locked center diff 4WDs were the first ever built and tested to race, though for obvious reasons they didn't do too well on sticky tarmac due to the locked center diff.

Locked diff centers should never be used unless you're off-road. That's why all real off-roaders either have part time 4WD that uses 2WD only on tarmac or have open or viscous/torsen/etc center diffs that are mechanically lockable. When wheels start getting serious differences in load front to back (e.g. steep hillclimb), locked center diffs are still the best practical choice. One could combine Torsen center LSD and brake based TC for the theoretically ultimate system, though the only car I know of that does this for now is the TC equipped Pajero.

A torsen center LSD would be great in LFS, though I would not want locked diffs in LFS unless they are unlockable in car like RL 4WDs. ACD would be ideal, though the rally pack remains neglected to this day.
any chance to get back to the actual question which was how is that torque bias achieved ?
Quote from Shotglass :any chance to get back to the actual question which was how is that torque bias achieved ?

Isn't it just simply two gears which one of them is bigger and smaller? It's has an always constant ratio.
Quote from geeman1 :Isn't it just simply two gears which one of them is bigger and smaller? It's has an always constant ratio.

that would mean different rotation speeds though wuldnt it ?
I've never heard of that before. The Torsen website has a variety of ways to acheive this with particular differentials, but my whole point is WHY is the torque split adjustable when there is no torque sensing differential or LSD of any type available in LFS for a centre diff? If you have a conventional open centre diff, you're not going to be adjusting the torque split according to anything I've ever read... And viscous diffs are speed sensing; not torque sensing - so why can I adjust the torque split in LFS?

Here is an amazing torque biasing diff which is not 50/50 by default. ()
http://www.torsen.com/files/To ... 3%20Technical%20Sheet.pdf

Here are more typical torque sensing diffs , 50/50 with a built in torque bias ratio
http://www.torsen.com/files/To ... 2%20Technical%20Sheet.pdf
http://www.torsen.com/files/To ... 1%20Technical%20Sheet.pdf

Again, my question is - what is this torque split in LFS actually doing and why is it available on systems that it shouldn't be - as far as I can tell. The centre diff is what determines the torque split unless I have some serious gaps in drivetrain knowledge - and if I do, please point them out so I can learn from it.
Quote from Shotglass :any chance to get back to the actual question which was how is that torque bias achieved ?

Look at the attached pic. The torque split is realised simply by making one of the wheels (1 or 2) smaller or bigger. This makes one axle turn with more/less torque.
Attached images
diff.jpg
Quote from himself :Look at the attached pic. The torque split is realised simply by making one of the wheels (1 or 2) smaller or bigger. This makes one axle turn with more/less torque.

Doesn't it also alter the RPM though?
himself - nope, still not with you. Those wheels (1 and 2 in the diagram) a) surely have to be the same size for it to work mechanically and b) they have teeth so surely that makes small changes in size irrelevant, they're forced to turn at the same rate?

wheel4hummer - you can put your sig back now, you know.
Quote from Bob Smith :wheel4hummer - you can put your sig back now, you know.

Oh yeah, different avatar.

EDIT: I think I found another way to achieve torque bias. You place a clutch in between the front and rear differentials. Then you power the driveshaft that you want to have more torque. Since there is a clutch, the wheels spin at the same speed while getting different amounts of torque.

EDIT AGAIN: ROFL! All I posted was a basic clutch-pack differential. I feel stupid.

#21 - w126
Quote from Bob Smith :Those wheels (1 and 2 in the diagram) a) surely have to be the same size for it to work mechanically

You can achieve the same with additional gears (2:1 ratio for example) on one of the output shafts of the central differential or different final drive ratios of front and rear differentials. When driving in the straight line the front and rear wheels turn at the same speeds (approximately), therefore the output shafts of the central diff don't have the same speeds (the additional gears convert both torque and rotational speed), nothing unusual for a differential.
IMO all the differential settings available in LFS are possible mechanically.
No, all that would happen (under hard accel) is that the side with less resistance (due to gearing in this case) will slip first - whilst the side with more resitance would still receive the same amount of torque as the other side, since an open diff insists on a 50/50 split by it's very nature. (nothing unusual for a differential )

next.
#23 - w126
The torques at the output shafts of the central differential would be equal (for open differential), but the torques delivered to front and rear wheels would be different. Isn't that what we really wanted?
That's starting to make a bit more sense now.
Quote from w126 :The torques at the output shafts of the central differential would be equal (for open differential), but the torques delivered to front and rear wheels would be different. Isn't that what we really wanted?

Imagine you and I are holding on to a shaft. You're the front or rear wheels and I'm the diff, if I twist with __ torque you'll get the same torque.

After doing a bit of checking, it appears the Torsen diff, mathematically speaking, is identical to the clutch pack diff without the preload. So for all practical purposes, until the preload was added to the diffs recently, everyone using a clutch pack diff has already been driving a Torsen diff.

The Torsen appears to do exactly the same thing as the clutch LSD, it's just doing it through a beautiful arrangement of gears without any clutches or preload. Mechanically it's a great design, but for simulation purposes at this level it's identical.
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Centre Diff Problems / Questions / Suggestions
(33 posts, started )
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