Understanding differentials

[wormdoggy]

I don't profess to be mechanically inclined as some of the members of this forum, but I do believe in educating myself before I make or attempt to make any modifications to my car. I'm just thankful I have mechanics who are friends and in the family that can help me when its time for the modification.

My question is on differentials. Why is it that in ordinary open ended differentials, power is shifted to the wheel with less traction or least resistance? Is it a matter of cost or is there some kind of engineering behind this method? It would seem much more practical and SAFER to have traction applied to the wheel with the greater traction and not the one with less traction. After all, if I'm in a jam or need power , I would want it to go the wheel with the most traction........

I don;t understand why automotive manufacturers don't implement the QUAIFE system or similar on all cars. I just seems like a much safer way to drive. Its gotta be cost!

Yes..........if you haven;t guess it by now I am thinking of purchasing the QUAIFE but just want to understand the mechanics behind it better.

Thanks
Patrick

 

[SweetRed04]

Cost is the driving reason.

To prevent the drive wheels from skidding during normal cornering a differential of some kind is needed. The standard "open" differential is the lowest cost way to accomplish that function. There are several other options that allow varing amouts of torque to go to the tire with less traction that I am aware, such as free wheeling types (no-spin), posi types (clutches that add some torque to the traction limited wheel that are usually energized by the differential gear separating forces), Torsen (a gear type which uses gear friction to split the torque to the wheels based on the rotation of the tires through their operational arcs), hydraulically locking (active clutch type differentials that are automatically (via computer inputs or as a function of speed between the axles) or manually controlled to selective fully lock both axles together), electro rehtoric (sp) differentials (a differential that locks up its clutch when electric current is applied to an electrically active fluid that hardens when voltage is applied). I don't know what type the Quaife is.

 

[GR8_ASP]

I believe the Quaife is a torsen-gleason style differential. Which as you indicate uses gear methodology. Most simplictically described like a worm gear where it is difficult for the driven side to apply torque through the worm gear back to the source or toward the other output.

The differential for most is really a planetary system. And in a planetary system when one constraint is lost the motion transfers to the location of the lost constraint. Thus if one wheel loses traction the motion will transfer through to that location. That motion comes with little torque, thus the torque applied to the other wheel is minimal (note the torque is equal to both sides).

 

[Vipermann]

...
The differential for most is really a planetary system. And in a planetary system when one constraint is lost the motion transfers to the location of the lost constraint. Thus if one wheel loses traction the motion will transfer through to that location. That motion comes with little torque, thus the torque applied to the other wheel is minimal (note the torque is equal to both sides).

hey ... pass me some of that stuff

 

[kmg99]

FYI, the viper uses an expensive speed sensing limited slip differential in the rear axle referred to as a hydra-lok by DANA. The differential uses a small pump that is activated by a speed difference between the two rear tires (ie. one spinning). As the pump builds pressure from one tire spinning faster than the other it applies this pressure to a clutch pack, transferring torque across the differential bringing the other, slower turning tire up to speed. This differential has the ability to transfer up to 100% of the torques across the rear axle from side to side. It is not a planetary differential, it uses bevel gears. The disadvantage to this system is that it can be a bit slow to react. The advantage is that it can transfer 100% of the torque from side to side.

The quaife is a torque biasing (not speed) sensing differential. It reacts to torque differences between the two rear tires and transfers torque across the differential very rapidly in result to any split in values. Generally speaking this is a better solution for on-road situations where the relative reaction torque available at the two tires is fairly equal, and where speed differences are to be expected (when cornering). This system can only multiply torque differences between the two wheels (usually a max of 3-4X) and cannot transfer 100% of the vehicle torque to one side or the other as the Hydra-Lok is capable of achieving.

The hydra-lok was originally developed for off-road situations and was first launched on the Jeep Grand Cherokee. As you can imagine, in an off-road situation one tire may be in the air climbing rocks, offering no torque and you need a system that can transfer 100% across the system to the other wheel.

I think the tooling was in place for the hydra-lok, volumes where at a point that DCX chose it over better on-road oriented solutions. BTW, the Grand uses the Dana 44 geometry identical to the inner workings of the Viper rear axle, so you now understand how decisions are made based on economics and not always the utlimate solutions. That said, for a factory application you are still getting a pretty high tech solution.

In a past life I engineered automotive drivelines for the big 3.

 

[jk]

An informative tutorial if you want to learn the basics of differentials:

http://www.houseofthud.com/differentials.htm

 

[SnakeEye]

Interesting topic...

kmg99, thx quite insightful.

 

[Viper X]

Another issue, besides traction and reaction advantages is that the Quaife comes with a lifetime warranty against mechanical failure, even when racing. The one proviso, as with all things mechanical, is that you change your fluid regularly. Also, it is a whole bunch stronger and works much better. Torque is very transfered smoothly and the car almost wants to straighten itself out under power with the Quaife. With the hydralok, it wants to go sideways under power.

After having 8 Viper diff failures, 7 hydralok (two blew up, 5 ring/pinion issues) and 1 Gen II clutch pack failure (clutches locked / unlocked unpredictably one day at Willow - wife spun twice), I purchased one Quaife for each car. 10,000 miles on the SRT (750 rwhp) and no issues. 2,500 miles on GTS (550 rwhp), no issues.

Call Unitrax. They will take care of you.

Dan

 

[YoungDoc]

Viper X have you noticed alot of traction gain with the Quaife system?? I noticed you had an SRT10 at 750 rwhp... I plan on getting a viper and slapping a paxton on... i would like to run decent times with just streets tires, AKA low 11's.. So like I said just how much traction gain are we talking here on street tires with that my rwhp? thanks in advance

 

[wormdoggy]

Wow.......great information guys.



Thanks
Patrick

 

[Viper X]

YoungDoc,

This depends on the "street" tires that you run. Kumhos work pretty well. PS Cups don't. Pilot Sports are lousy too, whether run flat or not from a dry traction higher hp car standpoint. Pirelli's are about the same. I really wish that Michelin would make PS2's in sizes to fit the rear of the Viper.

I have ended up running Nitto drag radials on the street for many reasons as follows:

1)traction
2)traction
3)traction
2)ride quality is greatly improved when cruising and handling is very good for a drag radial.

I occasionally indulge myself and get into some spirited street driving. Haven't lost yet to many more expensive cars. As a side note, engine should make about 900+ rwhp after most recent changes.

The Quaife does help with traction on the street, at the drags and on the race track.

Dan