Differential

[Silente]

Hi all,

i have a question about differentials.

Let's say you know differential locking effect in both power and coast side.

Exiting by a corner, each halfshaft experiences a torque connected to engine torque by the locking effect in power: so what the differential does on each halfshaft is connected to how much torque the engine gives.

But what does it happen in braking, if you are braking and turning?
The torque the differential transfers from one wheel to another is the rear brake torque?

[Silente]

Hi all,

i have a question about differentials.

Let's say you know differential locking effect in both power and coast side.

Exiting by a corner, each halfshaft experiences a torque connected to engine torque by the locking effect in power: so what the differential does on each halfshaft is connected to how much torque the engine gives.

But what does it happen in braking, if you are braking and turning?
The torque the differential transfers from one wheel to another is the rear brake torque?

[Drew Price]

What kind of diff is this?

Do you have outboard rear brake rotors, or a single inboard rear?



Best,
Drew

[Silente]

it's a zf with friction plates and ramp angles.

We have outboard brakes..

[Drew Price]

With outboard brakes the diff does not transfer any brake torque from one wheel to the other, the brake torque supplied to each rear wheel will be equal as long as all your brake components are identical for the left and right sides (assuming that the rear brakes are on the same circuit).

What does get transferred between sides through the diff when braking is the friction in the engine during overrun, when you downshift, and works the same way as accelerating does. The harder the engine is 'compression braking' the more it will force the wheels to spin the same speed for a given overrun ramp angle. The overrun ramp is usually steeper than the accel ramp angle so that the lockup effect is less.



(This is not the same diff you are using, the photos are from another forum I read.)

The 40* ramp is for accel, provides more leverage for the planet gear shafts to load the clutch packs, the 85* ramp is for overrun, and provides less leverage, so less wedging action, and clamps the clutch packs less, which allows smoother turn-in transition when coming in on the brakes. BUT, this loading only happens when you are driving the diff housing, with the drive sprocket or with an inboard rotor mounted to the diff housing. Outboard brakes do not load the housing, thus do not wedge the ramp rings apart and clamp the clutches.

It then follows that you need to make sure your diff is installed the right way around!

http://saabrally.com/member-uploads/geoff/Diffs/Assemble%2013.jpg


http://saabrally.com/member-uploads/geoff/Diffs/street%20ramp%20angles.jpg



A single inboard rear brake mounted to the diff housing can transfer brake torque between inside and outside tires up to the torque bias ratio during overrun.

Best,
Drew

[Silente]

Thx for your reply!

What i meant was that, when you are braking, wheels feel the force on the contact patch connected also to brakes action. So if you are braking and turning, the differential should work with this torque and with the torque from engine compression on its locking effect.

If when you are accelerating torque comes from the gerabox and goes to the wheels through the differential, when you are braking it comes from the brakes and goes to the gearbox through the differential..

[Scotty]

Guys,

Here is an artical we published last year.
Hope it works...

http://www.taylor-race.com/pdf...ng_differentials.pdf (http://www.taylor-race.com/pdf/understanding_differentials.pdf)

[billywight]

Scotty/Craig,

Interesting article, only slightly biased (no pun intended) toward the "Automatic Torque Biasing" differential... Though, it is interesting that the open diff is listed first in your order of preference list. I would agree on a seriously underpowered, high downforce car, or one that only goes round long sweepers, but there's not too many of those. I think if you ask any Formula Ford or Formula Continental driver (both limited to open diffs by the rules of the class) if they would rather keep their open diff or switch to a limited slip, the answer would be most certainly the limited slip!

Also, can you explain to me how the "automatic torque biasing" differential somehow violates the first law of thermodynamics and creates less heat than a Salisbury/clutch-pack diff, or furthermore how the "automatic torque biasing" diff requires less maintenance than the Salisbury/clutch-pack diff?

Seems to me that in a situation where available traction is anti-symmetric about the rear wheels (say in a corner where there is a weight transfer effect) that the diff (regardless of what type of limited slip) is simply reacting (via friction) the torque split between the two wheels. Any heat generated by this reaction will also be equal regardless of the type of differential...

Furthermore, it seems that with a clutch pack diff having a greater surface area over which to react this torque imbalance (the clutch plates) it should see lower stresses than that of an "automatic torque biasing" diff which, having less surface area to react this same torque (the ends and tips of the worm gears) will see higher stresses. Since these components are typically produced from similar steels at similar heat treatments, it follows that the "automatic torque biasing" diff will in fact require more maintenance and frequent part replacement... From my (and others) experiences, however, neither diff design requires much (if any) maintenance besides the occasional oil/grease change. Other than those points, it’s a pretty good article.