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Torsen Differential

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jhu42 View Drop Down
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    Posted: Feb/05/2009 at 11:19am
Hey All,

I was looking at the Torsen Differential University Special, http://www.torsen.com/fsae/fsaefaqframes.htm , and wondering if any other teams had had success/failure with using a differential system on their car.

We have always just used a solid drive shaft on our vehicle. If you have used a limited slip differential did the improvement in the handling of the car out weigh the downsides, i.e. packaging, weight, $$$ ?

Thanks,
Adam

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dillon_b12 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 11:34am
I didn't work on driveline so I can't tell you if ours outweighed the downsides but I do know that our car's turning circle was reduced significantly and the car handled great with it.

One problem we ran into was that the friction material in the diff has already worn completely off.  This is more likely a problem with lube leaking out of the housing than the diff's fault.  Also, the diff we used is made for the front of a 4x4 ATV so it isn't supposed to be running all the time.  Luckily, clutch packs for the diff are only $50.  We are hoping that it lasts better when properly lubed and if not we will replace the clutch packs after each race.

We we're running our LSD when we won the Louisville Midnight Mayhem race.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kenneth Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 12:29pm
An LSD is one of the major changes on our car this year, and we looked at pretty much every type that exists. We ended up ruling out the Torsen even though its theoretical performance is the best because if one wheel cannot transmit torque, then it acts open. That's probably fine for an on-road vehicle, but in Baja, we spend just as much time on 3 wheels or less as we do on all 4. The only true failsafe for a Torsen would be to install cutting brakes, but it seems like a huge band-aid fix for an improperly selected differential.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jarmumd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 2:11pm
Has anyone every looked into modifying an LSD to accept a pin, such that the pin would lock one of the shafts to the diff (thus locking the whole shebang)?  I suppose you could create a level mechanism to the cockpit, but I was thinking something you would have to do manually.  Since it's always on the car, i would think that its a feature you could engage and disengage for each event/endurance?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jhu42 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 2:40pm
Going back to the torsen diff for a second.  Agreed it spins when it goes up on 3 wheels, but how is this different from when the car is on say on some ice on one side and not on the other.  

Also I have seen that the torsen differentials are run in the audi quattro as a center diff.  How would the torque biasing in that system work?  If it senses that there is more resistance on the back wheels does it send more of the torqe to that location?

Also if the free tire spins when it is on 3 wheels, how is this setup any different from an open differential?

Thanks, these devices are confusing,
Adam 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kenneth Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 3:17pm
The diff doesn't actually care if the wheel is on the ground or not, rather as its name suggests, it "senses" the torque difference between the two, and splits drive torque accordingly. The diff runs at 50-50 most of the time, but when torque to the drive wheels differs significantly, it can bias up to some maximum like 20% to the inside and 80% to the outside. So if you have less friction force to the ground than that 20%, you'll only get a fraction of that 20% of total torque put down and about 4 times that to the outside wheel. With the one wheel in the air, you get no torque on that wheel (or say 1% for the sake of math working out) and 4 times that, or 4% of your torque on the outside wheel. Needless to say, that's gonna be pretty useless for getting you unstuck from something that you needed a lot of torque to get stuck in.

Marc, we did consider an external locking mechanism on our diff, but decided that the complexity and weight wasn't worth it for our application, and that a properly designed diff setup shouldn't need it. I'm not saying that ours will be that properly designed, but we sure as hell will try!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote seanbronee Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 4:02pm
We looked into the torsen diff but it is rather heavy and large. Instead we are using a cam and pawl diff from a honda ATV. Although it has similar characteristics, it is half the size and weight. We will be putting a locking mechanism on it so that we can lock the system for mudbogging and tractor pull.
If we were living in a post-nuclear-war, dystopian society, with Mel Gibson tearing around in a tractor-trailer, a BAJA car would be ideal!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dillon_b12 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 5:20pm
The way that offroaders who run Torsens(some Hummers) get around the one wheel in the air situation is by applying the brakes lightly.  The braking gives enough drag so that the other wheel will engage.
 
What do you mean by "cam and pawl"?  What type of ATV is it out of?

We ran a factory Honda atv diff and it was terrible compared to the new LSD that we run.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jarmumd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 5:57pm
I had to turn around the gears in my 84 4runner's true-trac so that I could run it up front.  Let me know if anyone wants pictures of the internals.  That diff comes with some preload available, but compared to the engine output - you need to drag the brakes if in the air.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scotty82 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 6:48pm

Guys.

I am new to the Baja stuff..
But I have been supplying  around 160 FSAE teams world wide with there diffs and drive lines for about 8 years now.
 
I am gonna come out see what you guys are all about in April at the Alabama compitition.
Looks  like a good time.
 
Dillon... Here is an artical that Craig wrote last year. It will break down most of the diffs used in racing. The Cam and Pawl has been around for a bit. It is a diff that needs attention when you run the snot out of it.
 
 
 
 
 


Edited by scotty82 - Feb/05/2009 at 6:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dillon_b12 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 9:07pm
Upon looking at pictures, I believe the original Honda diff we used was a cam and pawl style.  The problems we had we're outline exactly in the info you provided.

"In setting up the car the weaker tire must remain on the ground to
apply enough torque for locking. If the tire lifts free of the ground it will spin
freely, with no forward thrust on the “good” tire."

The diff we use now is closer to a Salisbury type.  It uses clutch packs but unlike what your article mentions it is unable to ever fully unlock the inside tire.  This works great for us because we get the advantage of a tighter turning circle while not completely unlocking the inside tire.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote seanbronee Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 11:38pm

The cam and pawl diff is now used as the front differential in all Honda ATVs post 2004 with the exception of the Big Red UTV. We test drove a Foreman 450 on a very icy parkinglot with this same diff and it seemed to work quite well. It did however spin out one wheel when there was no resistance however, tapping the brakes got it transfering torque quite agressively to the opposite wheel. The Honda system known as "SureTrac" appears very different to the diff shown in that document. It has a completely different internal structure and is a torque biasing unit rather than a lockup unit.

Using a diff is going to be a new step for us and the way I see it, as long as we keep moving I can't see us having any problems. Worst case scenario, we keep it locked or if its really useless, we will identify this in testing and just swap to a spool.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dillon_b12 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/05/2009 at 11:50pm
You'll like it but it isn't the best option available.  You just have to know how to drive it.  If you go in hard and lift the rear tire it WILL spin.  Frustrating when you are trying to make a pass on someone by running in deep.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jarmumd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 2:40am
well it's funny, desert racers and rock crawlers use spools or locking diffs...  Rally cars (sandblast is in 24ish hours) use limited slips... 

I really   really like the idea of having part of the endurance course on pavement heh heh, and we are looking to do something like that

i think part of the issue is that to run an lsd, you need power...  that's how many rally cars do it...  baja cars just dont have the HP, and traction is always needed...  My point of view is to control oversteer with a combination of swaybar, rearsteer, tire pressure - instead of with an LSD... 

of course this IS one of those places where being heavier (locking LSD) could make you faster instead of lighter (AL spool)

my .02
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kenneth Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 10:31am
Desert racers can run spools because they don't need to turn much. Their top priority is having the travel to bomb through giant holes at really high speeds. Rally cars do well with LSD's (and usually clutch-type ones) because they do need to turn a lot in low-traction conditions where an open diff won't allow them to put power to the ground. I've heard of FWD rally cars running spools for durability, but they are very understeer-prone.

Our diff-less cars have always been great on endurance courses where we're able to carry tons of speed through the huge wide corners, but it wasn't until recently that they were truly competitive maneuverability cars. This took some pretty crazy suspension geometry and nearly perpetual tricycling, and we still have trouble with low-speed turnarounds and loops on some surfaces. This is where the diff comes into play, making the car drive more like a road car than a drifter. If we were on pavement, we probably could get away with an open diff, but like I said before, varied terrain brings with it the risk of getting stuck with a wheel in the air.

I do like the idea of having some pavement on course, as I've been trying to get our team to take our car autocrossing so we can show the local FSAE teams how it's done! I'd do it myself, but most of the time I'd rather be racing my own car.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scotty82 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 10:55am
I am starting to see more of the bike powerd buggy manufactures call me about the ATB diffs.
It will turn in like an open diff. But will bias the torque when power is laid down.
This discussion on diffs is the main reason I want to come out and see what you guys do.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adrive7 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 1:12pm
Our team actually went from using open diffs back to a spool setup and it served us well. Since we build our own gearbox, I considered incorporating a Torsen diff into it, but the more I thought about it, we have never been in a situation in a race or in testing where we were hurt by the spool setup. Our rear sus is designed to lighten up the inside tire so you can pretty much always break the rear loose.

Obviously a pavement section could pose some issues, but the majority of any race is on a loose surface.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dillon_b12 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 1:46pm
Originally posted by scotty82 scotty82 wrote:

I am starting to see more of the bike powerd buggy manufactures call me about the ATB diffs.
It will turn in like an open diff. But will bias the torque when power is laid down.
This discussion on diffs is the main reason I want to come out and see what you guys do.


I would love if we could run a Torsen style diff provided that the cost wasn't outrageous.

I have run a Zexel-Torsen in my truck for years and it has been outstanding.  I never even know it is there.

One place where I think our diff shined was on the S&T Course at Montreal.  It looked like to me that after just coming off that jump it would be very hard to throw the car hard enough to get it to slide and make the turn for the shortcut.  After watching countless people miss that turn, our car made it with zero problems.

Also, I hate the idea of a pavement section on the endurance course.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote karman1970 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/06/2009 at 10:14pm
LSDs work great when both driven tires have traction and are on the ground most of the time. We've run a clutch LSD from a Yamaha Timberwolf pretty successfully for the last two years, but it sometimes takes a while for the clutchs to grab (might help if we'd ever bothered rebuilt it). What you really need in low-traction situations is a speed-sensing diff. We're running a Detroit this year. No push (which is good on an IRS car) yet the traction of a spool.
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