Thursday 7th May 2009

Audi Sport Diff Takes Off

S4's torque-vectoring diff reaches A5 and S5 cabrio, with more to come

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Audi is expanding the reach of its torque-vectoring Sport Differential option, which is now available on A5 and S5 cabriolet models, as well as the recently introduced S4.

Torque-vectoring diffs have been around for a while, and the new system that has been introduced on the S4 will migrate to other performance models imminently, says Audi. If you want the clever rear diff on an S4 you’ll need to specify the £990 Drive Select system plus an extra £460 for the Sport Differential itself.

The Audi system uses electronically-controlled and hydraulically-actuated clutches to adjust torque to each rear wheel, and works with Audi’s front/rear torque-splitting quattro system to maximise directional stability and minimise understeer.

'With the new sport differential influencing drive to the rear wheels, the S4 exhibits exceptional traction and stability,' says Audi. 'Close to the car’s handling limits, it acts like ESP, but with the principle reversed: corrective movements are not initiated solely by altering the engine settings or applying the brakes, but also by controlled redistribution of tractive force. As a result the car’s progress is distinctly smoother and more free-flowing, since ESP comes into action much less frequently.'

For those of us without an engineering degree, Audi offers the following explanation of its system: 'Depending on steering angle, lateral acceleration, yaw angle, road speed and other signals, the car’s control unit calculates the most suitable distribution of torque to the wheels for

How the Sports Diff integrates

every driving situation. When the steering wheel is turned, for example, or the car accelerated in a corner, power is redirected in a controlled manner to the outer rear wheel. This has the effect of 'forcing' the car into the corner so that the angle of the front wheels is followed accurately. The difference in tractive force between the left and right rear wheels also exerts a steering effect, so that the usual steering corrections by the driver are no longer needed. As a result understeer, or the tendency for the car to run wide at the front, is to all intents and purposes eliminated.'

 

[PhatPhil]

Good to see that Audi have signed up to the plain english campaign...

[Pentoman]

Interesting to see Audi coming up with some stuff to improve the driving experience recently - magnetic ride, opposite corners with connected dampers (like a metro on hydragas?), now this.

Perhaps they've pinned the 1998 launch reviews of the S4 V6 to the engineer's walls.

[Jessop]

Have to love innovative engineering ides =]

[paulmurr]

Is this more effective than a mechanical limited slip diff? It sounds rather overcomplicated to me.

[brogenville]

So they've basically come up with active yaw control (albeit under a different name), as designed by mitsubish oh... 13 years ago?

[kambites]

brogenville said:

So they've basically come up with active yaw control (albeit under a different name), as designed by mitsubish oh... 13 years ago?

Pretty much.

[Neomagic]

kambites said:

brogenville said:

So they've basically come up with active yaw control (albeit under a different name), as designed by mitsubish oh... 13 years ago?

Pretty much.

Not quite since, there many more variables in all the systems of the car.

[daveco]

Why don't Audi just place the engine further into the engine bay on the RS models? This would help a fair amount to alleviate understeer.

Actually why do they position the engine that far forward?

[kambites]

daveco said:

Why don't Audi just place the engine further into the engine bay on the RS models? This would help a fair amount to alleviate understeer.

Actually why do they position the engine that far forward?

I think it's to do with now the centre diff is arranged with Quatro. I was under the impression that the new A4 platform pushed the engine behind the axle line though, I'm sure I read that somewhere?

[toohuge]

kambites said:

daveco said:

Why don't Audi just place the engine further into the engine bay on the RS models? This would help a fair amount to alleviate understeer.

Actually why do they position the engine that far forward?

I think it's to do with now the centre diff is arranged with Quatro. I was under the impression that the new A4 platform pushed the engine behind the axle line though, I'm sure I read that somewhere?

Yes, the a4's engine is mounted behind the front axle. By mounting the engine further away from the cabin, it creates a lot more room.
Personally, i am not convinced by all this electronic differential business.

[gumsie]

As a result understeer, or the tendency for the car to run wide at the front, is to all intents and purposes eliminated.

What a bunch of fools.

[anonymous-user]

I think they should be applauded for trying! Audi make some very fine cars spoilt by average handling! they are at last listening to the critisism and doing somthing about it!

[nekrum]

Pentoman said:

Interesting to see Audi coming up with some stuff to improve the driving experience recently - magnetic ride, opposite corners with connected dampers (like a metro on hydragas?), now this.

Perhaps they've pinned the 1998 launch reviews of the S4 V6 to the engineer's walls.

Perhaps they did but if it's anything like the DRC systems fitted to RS models it's inherently floored!..

[anonymous-user]

Pistonheads 'Negativity matters'

[Dr G]

nekrum said:

Pentoman said:

Interesting to see Audi coming up with some stuff to improve the driving experience recently - magnetic ride, opposite corners with connected dampers (like a metro on hydragas?), now this.

Perhaps they've pinned the 1998 launch reviews of the S4 V6 to the engineer's walls.

Perhaps they did but if it's anything like the DRC systems fitted to RS models it's inherently floored!..

What inherent flaw would that be? I see no problem with making suspension out of Cadbury's milk chocolate.

Oh wait....

[nekrum]

Dr G said:

nekrum said:

Pentoman said:

Interesting to see Audi coming up with some stuff to improve the driving experience recently - magnetic ride, opposite corners with connected dampers (like a metro on hydragas?), now this.

Perhaps they've pinned the 1998 launch reviews of the S4 V6 to the engineer's walls.

Perhaps they did but if it's anything like the DRC systems fitted to RS models it's inherently floored!..

What inherent flaw would that be? I see no problem with making suspension out of Cadbury's milk chocolate.

Oh wait....

Cadbury's - they'd never use Cadbury's it's consistently good!..

[E21_Ross]

i don't see why people are slating RS models here? I have been fortunate to spend many, many hours in a '57 plate RS4 avant, and that thing doesn't have any problems going round corners, i can tell you that much!

[nekrum]

E21_Ross said:

i don't see why people are slating RS models here? I have been fortunate to spend many, many hours in a '57 plate RS4 avant, and that thing doesn't have any problems going round corners, i can tell you that much!

Not slating RS models, own an RS6 myself - don't have problems going around corners when the DRC isn't broken but many RS owners are choosing to replace DRC not for ride, but for reliability..

Edited by nekrum on Thursday 7th May 16:35

[fluffnik]

Neomagic said:

Not quite since, there many more variables in all the systems of the car.

It seems to use all the same inputs and do the same thing as the system in my 13 year old Mitsubishi...

...probably there to counteract the nose heavy understeeryness just like it does (rather well) in my 13 year old Mitsubishi.

The only thing I don't have is the variable damping.

ETA: ...or funky steering

Edited by fluffnik on Thursday 7th May 17:12

[anonymous-user]

fluffnik said:

Neomagic said:

Not quite since, there many more variables in all the systems of the car.

It seems to use all the same inputs and do the same thing as the system in my 13 year old Mitsubishi...

...probably there to counteract the nose heavy understeeryness just like it does (rather well) in my 13 year old Mitsubishi.

The only thing I don't have is the variable damping.

ETA: ...or funky steering

Edited by fluffnik on Thursday 7th May 17:12

So its like you old Mitsubish only newer and better with more features