Run Quaife backwards?

[Chuckster]

Anyone know if that makes a difference? I'd like to turn it around to get the ring gear flange on the other side. I'm not in FSAE but I reckon many of you have taken one apart and might have feel for opposite sense rotation and function. On first glance, I don't see where a worm gear/worm wheel pair actually care.

Chuck

[Chuckster]

Anyone know if that makes a difference? I'd like to turn it around to get the ring gear flange on the other side. I'm not in FSAE but I reckon many of you have taken one apart and might have feel for opposite sense rotation and function. On first glance, I don't see where a worm gear/worm wheel pair actually care.

Chuck

[exFSAE]

Reason we went with a TRE / Quaife differential is so we wouldn't have to take it apart..

I'm not sure how the internals work to be honest. Differentials are one thing I understand poorly. I do know on some types you can have very different power-on vs coast performance, which would then be direction sensitive.

Why not just email the guys at Taylor Race or at Quaife and get the answer straight from the horses mouth? The Taylor Race guys (Scotty, etc) are typically very helpful.

[Erich Ohlde]

i'm pretty sure the quaife doesn't work right if you run it backwards. It deals with the thrust and friction on the internal gears. Craig Taylor or Scotty can give a much more detailed explanation.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jayhawk_electrical:
i'm pretty sure the quaife doesn't work right if you run it backwards. It deals with the thrust and friction on the internal gears. Craig Taylor or Scotty can give a much more detailed explanation. </div></BLOCKQUOTE>
Best not run one in a single-rear-disc-on-diff-carrier car, then...

Regards, Ian

[Composites Guy]

I called Quaife USA to ask that exact question a year ago. They said its operating characteristics are the same in either direction. I hope that they are right, as their other answers to me have NOT inspired confidence (i.e. they swear that this is a sealed diff when in fact grease is designed to run out through spiral cut grooves between the stub axles and the housing to lubricate that interface, see http://fsae.com/eve/forums/a/tpc/f/125607348/m/82810580...0041341#24610041341) (http://fsae.com/eve/forums/a/tpc/f/125607348/m/82810580341?r=24610041341#24610041341)). On my personal car I am running the diff with the bolt flange on the drivers side... the car is only partly built and has not driven yet.

IF... if indeed the diff works the same in both forward and reverse it makes for some REALLY COOL thoughts about running a single inboard brake mounted on the diff (something Quaife says don't do, because "that's not the way race cars do it".) My thoughts are that under braking the diff should bias the braking torque to the wheel with more grip. However, under hard cornering/braking if your lateral weight transfer exceeds the torque bias of the diff you should see inside rear wheel slip/possible reversal.

In other words... using a single, diff mounted brake: under cornering/braking the inner rear wheel is more lightly loaded... the diff should bias braking torque to the outter rear wheel providing a cool way of maximizing rear braking. Contrast this with two outboard brakes where there is equal braking torque to each rear wheel, and you are more likely to drag (lock) the lightly loaded inner wheel under hard braking. Back to the single, diff- mounted rear brake.... this "cool way of maximizing rear braking grip" would work as long as the weight transfer does not exceed the torque bias of the diff. If it does, then the inner stub shaft is going to rotate in the opposite direction of the outter stub shaft with respect to the housing. As an example, say that you brake really hard and lock up the rear single brake (meaning the housing doesn't move)... if the weight transfer exceeds the torque bias then the the inner wheel will spin backwards... if the torque bias exceeds the weight transfer then both wheels do not rotate (i.e. your rear is in a full on skid). I give that example only to demonstrate the opperating characteristics of the system...neither situation there would be good... but you aren't trying to lock the brakes during normal racing. Up to the point of locking, providing the favorable weight transfer setup (which you control by keeping a low center of gravity in your design with respect to track width) then YOU SHOULD HAVE A BETTER REAR BRAKING GRIP WITH A SINGLE BRAKE DISC MOUNTED ON THE QUAIFE DIFF, THAN WITH TWO OUTBOARD BRAKES.

This kinda goes against traditional thought, and it hinges on the Quaife acting the same in either direction. Please read this CAREFULLY and let me know your thoughts. I may be wrong.

[Pete M]

I don't think anyone claimed running dual rear brakes gave you better grip under braking. As you mention, with a diff between the brake and the wheels, the diff can do its job and distribute the braking torque unequally between the wheels. Ok, so now you've got a higher braking force on your outside wheel and you're attempting to enter the corner. Except the brakes are trying to pull the car out of the corner, creating understeer while trail braking. Hence why some teams run dual rear brakes.

[Erich Ohlde]

i don't know of the guys at quaife USA. but i do know that Scotty and Craig Taylor know a LOT about these diffs. I'm suprised scotty hasn't responded to this. Probably pretty busy

[billywight]

The quaife will work the same if you run it forwards or backwards, it doesn't matter. Take one apart and have a look, it's not that complicated.

But, do you really want a rotor on the housing of a Quaife??? The quaife (or taylor, taggert, torsen) diff does not bias torque from the lightly loaded wheel the the heavier loaded wheel as their marketing team would like you to think... See:

http://dsrforum.yuku.com/topic/1568

for more info. Read the entire post, and keep in mind that it's an internet forum and some points points made are correct, and some are just wrong. (I'll leave that for you to figure out.)

The short of it is, though, that under hard braking you WILL exceed the bias ratio of tbe quaife and you will loose overall braking power as you are limited to (Bias Ratio)*(Torque lightly loaded wheel can take) rather than the torque the higher loaded wheel can take. The torque the higher loaded wheel can take will certainly be higher than 4 * the torque the lightly loaded wheel can take. (Quaife max bias ratio is about 4)

[Brian Evans]

Actually, an open diff will also distribute braking torque equally to both rear wheels with one disc, up to the point of lockup on one side. Per Mark Oritz, anyway.

[Scotty]

The stub axles helix are designed to go one direction.
As you accelerate the stubs will be pushed outward towards the thrust plates on the outer ends of the diff.
If the helix of the stubs is going the other direction. The stubs will close in on each other which will increase the pre-load of the bellville stack. All this will do is make the diff feel a little notchy when you are off and back on the gas.
Running the brake off the diff is more of a customer preferance.I have never had any complaints.
But the majority of our multiple championships in numerous classes over the last 10 years including FSAE ,and a new track record that was just laid down last weekend,have all ran out board brakes.
And yes they are not very complicated,that is why they are so fast and reliable.

[billywight]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Actually, an open diff will also distribute braking torque equally to both rear wheels with one disc, up to the point of lockup on one side. Per Mark Oritz, anyway. </div></BLOCKQUOTE>

True, but when does that one wheel lockup? In a tight turn with a lot of load transfer, the lightly loaded wheel will lockup fairly easily and you are left with the tracktive braking capability of that one lightly loaded wheel (not much braking).

This statement is true for the quaife as well, but the quaife will give you about 4X as much braking capability, though 4X not much is still not much... This is why you see dual outboard brakes on all "real" racecars because the max braking is determined by the most highly loaded wheel, not the lowest loaded wheel. (though there are other reasons as well)

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> The stubs will close in on each other which will increase the pre-load of the bellville stack. All this will do is make the diff feel a little notchy when you are off and back on the gas. </div></BLOCKQUOTE>

True, let me rephrase my original statement:
The planet gears won't care if the diff is run forwards or backwards, but the stub axle gears will behave slightly differnt. On acceleration they thrust outwards agains the housing, on braking (or acceleration if the diff is run backwards) they thrust into each other compressing the preloading assembly. If enough thrust is present they will compress the preloading assembly until they are thrusting against each other and will act the same as in acceleration.

Chuckster, if you're looking to flip the diff around for chain alignment reasons, it will work OK, but for it to work its best you should look into preloading the side gears the other direction (against the housing). Stay away from the diff mounted brake for the reasons listed above.

Or, better yet, avaoid the whole Quaife mess and run a Salisbury. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Scotty]

Billy,

Touché my freind.

Even though brakes are overrated......
In my world 4 big ones give me a good piece of mind.
Are you going to VIR. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[billywight]

Probably not, I tend to keet to the west coast. I'll probably only make it to a few west coast races, FSAE West, Heartland Peak Toparka, and the ARRC.

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by billywight:
Stay away from the diff mounted brake for the reasons listed above. </div></BLOCKQUOTE>

Let's not forget that all that heat has to go somewhere. If the brakes are outboard, it's the air. If the rotor is buried in the rear of the car it will go into the diff housing. And depending on the case construction the brake torque may load the case torsionally, like when using the Torsens.

Heat was the main thing that kept us away from that orientation. That, and the possibility of losing a halfshaft/CV joint eliminating any rear braking effort.

Design decisions, design decisions...

Best,
Drew

[Steve O]

Let me just say first off that brakes are for pansies. Second, because of the size of these cars all of these concerns with the rear breaks do not really apply to these cars. The stock setup on most quads weighing around the same as our cars is a clutchpack diff of sorts with an inboard rear brake.

Back on topic though I am pretty sure that if you flip it around you have to flip around the thrust plates as well, considering they are directional. The two center plates when put together should have a hole in the center that form either a triangle (1-way) or an asymmetrical diamond (1.5 way) with the steep angle in the direction of thrust under acceleration the flat side or narrow angle side is the direction of neg. acceleration. This is because the diffs are set up to only lock under certain conditions. It would only be completely bi-directional if you had a 2-way diff which is a bad idea for a formula car... it's more what you would look for in a drifter or dirt track car. The diamond in the center of a 2 way diff is symmetrical and therefore acts the same in both ways... wheels lock under accel or neg. accel.

Steve

[Alan]

If I were to go back and work on FSAE again, the brakes and the diff are two areas I would focus on a lot more than I did previously. I can't tell if you are being sarcastic or not with the "brakes are for pansies" comment, but I would definitely not trivialize the rear brakes on any application.

Not too sure what this 1, 1.5, or 2 way thing is you're talking about (the ramps on a Salisbury type diff?), but again I think its too general to say you don't want the rear wheels locked together under decel on a formula car.

[Scotty]

Chuckster,

Back to your main question...If this is the Civic diff...
And you want to to move the ring gear flange from the left side to the right.
Put the diff in a press,this will make it easier to remove the bolts on the end cap due to the fact there is pre-load.
Take all the internals .worm gears and stub gear and move them from the left to the right.
You will see the stubs are directional when you take them out.
When you are ready for final assembly .put it in the press again and press the end plate down till it bottoms. This will make the bolts happy bein they will not be trying to crush pre-load.
We do hundreds of Quaif diffs a year.
Call me or send me an e-mail if you have any question

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alan:
If I were to go back and work on FSAE again, the brakes and the diff are two areas I would focus on a lot more than I did previously. I can't tell if you are being sarcastic or not with the "brakes are for pansies" comment, but I would definitely not trivialize the rear brakes on any application. </div></BLOCKQUOTE>

Brakes only make you go slower. Why would anyone want that.

In all seriousness though I wish I understood differentials and impact on vehicle performance better. Moreso.. how to tell when the differential is the item to change.

If the car is understeer on entry and exit.. when is it best to tune with dampers, or roll bars, or differential? Likewise for oversteer, or any combination really.

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
Let me just say first off that brakes are for pansies. Second, because of the size of these cars all of these concerns with the rear breaks do not really apply to these cars. The stock setup on most quads weighing around the same as our cars is a clutchpack diff of sorts with an inboard rear brake.

Back on topic though I am pretty sure that if you flip it around you have to flip around the thrust plates as well, considering they are directional. The two center plates when put together should have a hole in the center that form either a triangle (1-way) or an asymmetrical diamond (1.5 way) with the steep angle in the direction of thrust under acceleration the flat side or narrow angle side is the direction of neg. acceleration. This is because the diffs are set up to only lock under certain conditions. It would only be completely bi-directional if you had a 2-way diff which is a bad idea for a formula car... it's more what you would look for in a drifter or dirt track car. The diamond in the center of a 2 way diff is symmetrical and therefore acts the same in both ways... wheels lock under accel or neg. accel.

Steve </div></BLOCKQUOTE>


I've never really felt compelled to bash anyone on a public forum.....but that was perhaps one of the most ignorant posts I have ever read. I seriously hope you were just kidding. If not, please go do your homework.

And if you think that 2-way differentials have no place in formula cars, go check out an Atlantic car, a (former) Champ Car, or any one of the other open wheel series that have run salisburys.

(P.S.- the topic was about Quaife's anyway)

[Underthefloor]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Composites Guy:

IF... if indeed the diff works the same in both forward and reverse it makes for some REALLY COOL thoughts about running a single inboard brake mounted on the diff (something Quaife says don't do, because "that's not the way race cars do it".) My thoughts are that under braking the diff should bias the braking torque to the wheel with more grip. However, under hard cornering/braking if your lateral weight transfer exceeds the torque bias of the diff you should see inside rear wheel slip/possible reversal.

In other words... using a single, diff mounted brake: under cornering/braking the inner rear wheel is more lightly loaded... the diff should bias braking torque to the outter rear wheel providing a cool way of maximizing rear braking. Contrast this with two outboard brakes where there is equal braking torque to each rear wheel, and you are more likely to drag (lock) the lightly loaded inner wheel under hard braking. Back to the single, diff- mounted rear brake.... this "cool way of maximizing rear braking grip" would work as long as the weight transfer does not exceed the torque bias of the diff. If it does, then the inner stub shaft is going to rotate in the opposite direction of the outter stub shaft with respect to the housing. As an example, say that you brake really hard and lock up the rear single brake (meaning the housing doesn't move)... if the weight transfer exceeds the torque bias then the the inner wheel will spin backwards... if the torque bias exceeds the weight transfer then both wheels do not rotate (i.e. your rear is in a full on skid). I give that example only to demonstrate the opperating characteristics of the system...neither situation there would be good... but you aren't trying to lock the brakes during normal racing. Up to the point of locking, providing the favorable weight transfer setup (which you control by keeping a low center of gravity in your design with respect to track width) then YOU SHOULD HAVE A BETTER REAR BRAKING GRIP WITH A SINGLE BRAKE DISC MOUNTED ON THE QUAIFE DIFF, THAN WITH TWO OUTBOARD BRAKES.
</div></BLOCKQUOTE>

The Quaife and any other friction based LSD will always bias torque to the slower moving wheel, not the wheel with the most grip (yeh, they are usually going to be the same wheel). In the case of braking into a turn, the outside wheel is moving 'slowest' (with respect to the input/braking force which is going in the opposite direction). Because the outside wheel is moving 'slower' than the inside wheel, it will have the amount of torque of the inside wheel torque * TBR. This means that on every turn, your single rear brake car will be breaking heavily on the outside wheel which will cause an under steer moment.

Its important to remember that every time the wheels are spinning at different speeds, the LSD is biasing at full TBR to the slower moving wheel(with respect to the input force).

[A Richards]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
Let me just say first off that brakes are for pansies. Steve </div></BLOCKQUOTE>

Really. Well if that truely is the case then i dont think you will mind me cutting the brake lines on your car when your not watching.

What a stupid thing to say.

[Scotty]

WOW.......

[exFSAE]

I think some people 'round here aren't picking up on sarcasm...

[Composites Guy]

Great thread guys... you have given me things to think about. Although for my car I have no intention of turning the diff around, nor do I think over-heating the diff with a center mounted brake will be an issue for the 90 second autocrossing my car will see. I haven't opened up the Quaife diff yet as I really want that lifetime warranty! :-)

BillyWright wrote "4X of not much is still not much" and "The short of it is, though, that under hard braking you WILL exceed the bias ratio of tbe quaife and you will loose overall braking power as you are limited to (Bias Ratio)*(Torque lightly loaded wheel can take) rather than the torque the higher loaded wheel can take. The torque the higher loaded wheel can take will certainly be higher than 4 * the torque the lightly loaded wheel can take. (Quaife max bias ratio is about 4)"


I have to take issue with Billy Wright's statements. I think that you can design your car with a low CG such that under hard braking/cornering you never see less than 20% of the rear weight over the lightly loaded (inner) wheel.

Its hard to argue with the track record of outboard brakes. The past XX number of FSAE winners had them right? But perhaps that is because they had ties to good racers/designers who not only told them to use outboard brakes (because that's what works in larger, more powerful race cars), but helped them develop a good overall comprehensive FSAE program. I mean by the same logic RMIT 2006 shouldn't have used a single cylinder/ultralight car because that is so different from previous winners.

[Steve O]

WOW... I was not publicly bashing anything... the brakes thing, a total joke, just as someone else in this post said... brakes just make you slow down, what do you need that for? JUST A JOKE...obviously we need brakes, so I am sorry for not making that clear. You guys REALLY need to get out of the fumes in those shops because to not realize that is a joke is ignorant! Thanks exFSAE for picking up on the sarcasm... at least someone here still has a sense of humor!

As for the diff portion of it I don't see where there is even any sarcasm or anything that could be construed as bashing. A quaife diff IS a clutch diff so I am not sure what your "P.S." comment is supposed to mean.


As for the 2 way diff I think you need to do your homework. If you have a 2 way diff unless you had completely no deccel or accel... completely neutral and rev's matched through the corner (I know in theory you should be, but it doesn't mean you will be...what if you have to quickly avoid something a locking rear end from pulling the throttle coupled with a quick turn would cause you to spin) your diff would lock up and you would never go into an open diff state, which means your rear wheels would want to spin out... let me rephrase my comment and say 2 ways are not typically used on formula cars. Typically a 1.5 way diff is used on a formula car, that allows lock on deccel but as soon as you start to corner the clutches will slip and still allow the wheels to spin at different rates in an open diff state...if your wheels are locked all the time when cornering on dry pavement, what is the point of having a diff, why not run a solid axle? Again, that is something used for low traction tracks where you want your rear end to slide out...hence the reason they use them on drifters. This is not referring to the brakes being able to lock up the wheels... just the torque from the engine. The point of running a LIMITED slip differential on a formula car is so that it locks sometimes but allows the open differential state in cornering so your inside wheel can move slower than your outside wheel.

To sum that up now and avoid any confusion...

1) yes a formula cars need brakes I understand this. http://fsae.com/groupee_common/emoticons/icon_wink.gif
2)yes differential locking under accel and deccel is important but you want the deccel locking to be able to slip in cornering.
3) If I hurt anyone's feelings I am sorry, I would never bash on a topic that isn't ridiculous, and this wasn't ridiculous. It was a serious question and besides the first joke it was a serious answer.
4) jdstuff- thats funny how instead of questioning my motives first you are quick to bash me on a public forum despite your comment about not liking to bash people. If you had a question about my post you could have been inquisitive as Alan was and I would have explained myself more...if at that point I was still coming off as some public bashing jerk off then go for it and call me out on it. So either way, sorry to offend you, I hope this post clears things up for you. If not I will be more than happy to have a private discussion about differentials and cornering physics with you.
5) If anyone cuts my brake lines (as suggested above) at the competition I will kick you in the junk. Not because I plan on using them, because of course they aren't necessary, but because it will make a real big mess everywhere... that brake fluid just sucks to clean up. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Steve

[jdstuff]

Steve,

Apologies for the harshness of my previous post. Guess I took your comments completely the wrong way.

Based on Chuckster's first post referring to worm gears, I would assume that we are talking about a Quaife TBD and not a LSD....which is why I assumed you were just spouting off random information. Chuck, if I am wrong, please correct me and I'd be happy to shut up!

Now, since the topic has steered toward LSD operation, I'd like to throw a few more comments into the discussion. I'm sure we could sit here and argue 1.5 or 2 way until we're both blue in the face, but I don't think that will achieve anything. I'm sure that you could get either to work properly, for the same reason race cars can get torsens, open diffs, or anything else to work.....it's dependent on the rest of the system.

One thing that I think we need to clarify is the terminology that is being used here. You mentioned the diff locking and unlocking under accel/decel...and threw in the comment of 'why not run a solid axle.' A LSD will not fully lock under any conditions, unless you are running so much preload that you cannot overcome the torsional difference needed between the inside/outside tires to get everything rotating in the first place. With a limited slip, you will only achieve a percentage of lockup....hence the LIMTED slip. Since you brought low-traction into the picture...real 4x4's, rock-crawlers, etc will always choose Lockers over LSDs. Lockers allow them to fully lock the axle together as if it were solid; whereas a LSD will never give them that...one wheel will always spin more than the other.

Back to LSDs: 2-way refers to equal percentages of lockup on accel/decel, which is why the drifters like them since the diff will behave the same either jumping on the throttle or stepping off of it. 1.5 way refers to a diff that can achieve different percentages of lockup under accel/decel. I agree that this is probably more desirable for a formula car. The only time either of these diffs will be 'open' is during the instant between the accel/decel transition, if you are running zero preload. Don't confuse the terms 'open' and 'differentiation,' which I think you have done......they are two very different things!

Perhaps it is just a confusion of terminology here, but I still feel like you don't have a full grasp on the operational theory of LSDs & Salisburys. (Correct me if I am wrong.) Sorry again for the previous bash...I realize now that you were actually trying to meaningfully contribute to the discussion and not just spouting BS. I think that this is shaping up to be another really good differential discussion!

Chuckster,
Back to the original question. It's been a LONG time since I've had a Quaife TBD apart, but based on what I remember and how it works I don't think you will have any big issues with running it backwards. I could be wrong, though, having never done it....

[A Richards]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Steve O:
WOW... I was not publicly bashing anything... the brakes thing, a total joke, just as someone else in this post said... brakes just make you slow down, what do you need that for? JUST A JOKE...obviously we need brakes, so I am sorry for not making that clear.
Steve </div></BLOCKQUOTE>


Hahahahaha, I was just taking the piss man, nothing serious.

Regards,

Ashley Richards

[Boston]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Underthefloor:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Composites Guy:

IF... if indeed the diff works the same in both forward and reverse it makes for some REALLY COOL thoughts about running a single inboard brake mounted on the diff (something Quaife says don't do, because "that's not the way race cars do it".) My thoughts are that under braking the diff should bias the braking torque to the wheel with more grip. However, under hard cornering/braking if your lateral weight transfer exceeds the torque bias of the diff you should see inside rear wheel slip/possible reversal.

In other words... using a single, diff mounted brake: under cornering/braking the inner rear wheel is more lightly loaded... the diff should bias braking torque to the outter rear wheel providing a cool way of maximizing rear braking. Contrast this with two outboard brakes where there is equal braking torque to each rear wheel, and you are more likely to drag (lock) the lightly loaded inner wheel under hard braking. Back to the single, diff- mounted rear brake.... this "cool way of maximizing rear braking grip" would work as long as the weight transfer does not exceed the torque bias of the diff. If it does, then the inner stub shaft is going to rotate in the opposite direction of the outter stub shaft with respect to the housing. As an example, say that you brake really hard and lock up the rear single brake (meaning the housing doesn't move)... if the weight transfer exceeds the torque bias then the the inner wheel will spin backwards... if the torque bias exceeds the weight transfer then both wheels do not rotate (i.e. your rear is in a full on skid). I give that example only to demonstrate the opperating characteristics of the system...neither situation there would be good... but you aren't trying to lock the brakes during normal racing. Up to the point of locking, providing the favorable weight transfer setup (which you control by keeping a low center of gravity in your design with respect to track width) then YOU SHOULD HAVE A BETTER REAR BRAKING GRIP WITH A SINGLE BRAKE DISC MOUNTED ON THE QUAIFE DIFF, THAN WITH TWO OUTBOARD BRAKES.
</div></BLOCKQUOTE>

The Quaife and any other friction based LSD will always bias torque to the slower moving wheel, not the wheel with the most grip (yeh, they are usually going to be the same wheel). In the case of braking into a turn, the outside wheel is moving 'slowest' (with respect to the input/braking force which is going in the opposite direction). Because the outside wheel is moving 'slower' than the inside wheel, it will have the amount of torque of the inside wheel torque * TBR. This means that on every turn, your single rear brake car will be breaking heavily on the outside wheel which will cause an under steer moment.

Its important to remember that every time the wheels are spinning at different speeds, the LSD is biasing at full TBR to the slower moving wheel(with respect to the input force). </div></BLOCKQUOTE>

The inside wheel should be turning slower with respect to the differential compared to the outside, since the inside wheel has a smaller radius, thus shorter distance to cover. The torsen and quaife are unique because they should actually provide oversteer under braking (corner entry with trailbraking) and understeer durring corner exit. The former only true with a single rear brake.

[Steve O]

Jason,

Apology accepted! I agree with everything you said in the post... I agree that I was not using the right word there... just a slip up. Also, I had misread the initial post and for some reason was thinking he was talking of an LSD. Other than that, I understand my post was extremely simplified, but I was trying to keep it that way as all he would have needed to know (if he was talking about an LSD) is that the ramps would have to be in the right direction... unless he had a 2 way ramp. The comment about the live axle was more retaliatory than anything else; I understand that the amount of "lock" is limited.

I will never claim to be any diff. expert and would also welcome a more in depth discussion on diff's as I pretty much just know what I have needed to know!

Steve

[Underthefloor]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Boston:

The inside wheel should be turning slower with respect to the differential compared to the outside, since the inside wheel has a smaller radius, thus shorter distance to cover. The torsen and quaife are unique because they should actually provide oversteer under braking (corner entry with trailbraking) and understeer durring corner exit. The former only true with a single rear brake. </div></BLOCKQUOTE>

I don't think that the Quaife or Torsen are unique, clutch packs and Salisburys will work the same way. The difference being any preload increases the TBR under low torque.

If you are using a center brake, when braking into a corner, the diff will cause an under steer moment.

You need to look at the wheel speeds with respect to the differential and the input torque. If the wheels are spinning at the same speed, then with respect to the differential, they are both stationary. In this case, the wheel with the most grip will get the most torque up to the TBR.

Now when turning and the wheels are spinning at different speeds, with respect to the differential, they will be moving in opposite directions. If there is torque being applied one wheel will be rotating in the same direction as the input torque and one will be rotating in the opposite direction. The wheel moving in the opposite direction of the input torque will always have the full TBR*torque of the other wheel.

When braking into a corner with a center brake, the input torque(from the brake) is in the opposite direction that the diff is rotating. When you look at the wheel speeds with respect to the differential, the outside wheel is rotating in the opposite direction as the input torque. That means that the outside wheel will get most of the braking torque.

Its kind of confusing and Im not that good at explaining how the TBR works. If you use the car as your reference frame, then under acceleration, the slower moving wheel will get more torque. Under braking(center brake/trail braking) the faster moving wheel will get more torque.

[Underthefloor]

Someone should write a paper on how the different diffs transfer torque in different situations. I get the impression that a lot of people get confused by the marketing phrase 'sends power to the wheel with more grip' A good paper on the subject could save FSAE students hundreds of man hours every year.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Underthefloor:
Someone should write a paper on how the different diffs transfer torque in different situations. I get the impression that a lot of people get confused by the marketing phrase 'sends power to the wheel with more grip' A good paper on the subject could save FSAE students hundreds of man hours every year. </div></BLOCKQUOTE>
It really wouldn't be very hard to test this stuff on a rig. Transmission dynos are commonplace in OEM and / or motorsports developemnt these days, just a pair of eddy current brakes on each driveshaft output from the diff. You can power it with an electric motor, as long as the relative speeds across the diff and the torques are correct you only need it to rotate at a few hundred rpm.

Alternatively, strain-gauging of driveshafts is relatively straightforward and a simple wireless transmission system is easy enough these days. Like the system Pi sells but without the ££££s. A good project for an old car, fit it with all the diffs you can find and both single or twin rear brake systems.

Regards, Ian