differential

[grakson]

how do you achieve that center differential (torsen, clutch or open type) doesn't split equal amount of torque between front and rear drive shaft.
So normaly differential provide both axels with the same amount of torque, but center diferential is usualy designed to provide 40/60 front/rear.

 

[BrianPetersen]

One way to do it is to use a planetary gear-set. Drive the planet carrier as you would normally drive the differential carrier. Sun gear goes to the end with less desired torque, ring gear goes to the end with more desired torque. Obviously this is still locked to a fixed ratio.

Other designs use clutches with various engagement strategies, or viscous couplings that in some way overrule or get superimposed on top of what the differential (either conventional or planetary) is doing. In these cases, the "torque split" would appear to be smoke and mirrors because it depends how much the clutches are engaged.

 

[murpia]

I've never heard of a Torsen diff that has an unequal torque split, although in theory it could be done.

You have to imagine a conventional diff as a set of rotating levers. Then it becomes clear how an unequal torque split is achieved by levers of different 'length'.

As well as planetary gears, side-by-side spur gears can be used to make a diff. You have two 'sun' gears of different sizes and connect them with a pairs of intermeshed spur gears running on the diff carrier. (This is one of those picture / thousand word scenarios...)

Regards, Ian

 

[grakson]

none of you two guys are making any sense!

you BrianPetersen said "one way to do it is"... and then you said "this is still locked to a fixed ratio"

Other designs use clutches or viscos...

FIrstly we must differ clutch or visco type LSD and clutch or visco units. differential has thre axles (input and two outputs), clutch or visco unit has only output and input, and clutch type units are usualy computer controled.

surely with visco diff you can't set torque split ratio, because visco is only added to open diff, and fluid comes in action when there is difference betwen two output shafts speed not torque. It's the same with clutch type LSD.
but if you talk about computer controled clutch unit you can control torque split. (this kind of system uses BMW Xdrive)

ands you murphia Quattro uses Torsen center diff on cars with longitudial mount engines and they say power is transferd front to rear in 40 to 60 ratio.

and yes some scheme or picture will be good, like you said thousand words scenario

 

[grakson]

and please explain me the difference between open and planetary diff as I taught this is the same. also some scheme or picture will be apriciated.

 

[murpia]

Grakson, can you provide a reference to which Audi has a 40/60 Torsen diff? I'd like to see that. Like I said it is possible but I never heard of it before.

To clarify, it is possible to design an open diff (no locking mechanism, clutches, viscous elements, or fixed geared torque bias) to split torque unequally.

Such a diff is usually planetary, but could be spur gear based.

It is still considered open because the torque bias is still fixed. Say it's designed to be 1.0:1.5 front:rear (a 40%/60% diff). If you lift the front wheels into the air, you get no torque at the rear wheels. 1.5 times zero is still zero.

A normal diff has a fixed torque bias of 1:1, it's just a special case of the general possibility to design any torque bias.

Non-open diffs can vary the torque bias with a locking mechanism, clutches, viscous elements etc. and can still transmit torque if one axle is in the air.

Hope that helps,

Regards, Ian

 

[murpia]

So, looking in the obvious place I can see how Torsen have done it:

http://www.torsen.com/files/Torsen T-3 Technical Sheet.pdf

Pretty neat I have to say.

Regards, Ian

 

[NickE]

One neat way to provide the torque split, and make the viscous coupling have a better (more consistant, quicker) reaction time is to provide it with a "preload" of sorts... IE a center diff with a 1:1.1 ratio. Then you just use the opposite ratios at the front/rear axel diffs to provide your overall ratio.



Nick
I love materials science!