5 replies to this topic

[rhm]

Ok, the technical forum has been a bit thin of traffic lately so I figure I can ask this:

On Top Gear a few weeks ago they had the Prodrive technology demonstrator car which had an active awd system like they run on WRC cars. Being that it was Top Gear they made a big thing about how it was impossble to understand how it worked which I thought was a bit presumptuous of their audience! Even though they bothered to film a prodrive employee explaining it, they didn't let us hear that explanation, they just showed Clarkson making stupid faces. Anyway...

Specifically, how does an active centre-diff improve traction in turns? I can see how an LSD of some description would improve traction in a front or rear wheel drive vehicle, but how does an active centre-diff improve things. Also, do these cars have open front and rear diffs or do they use a torsen or something like that?

[zac510]

The car may well suffer from the ruddy weight bias, engine location and understeer that Subaru's WRX does, given the similarities in the drivetrain.

To be honest I had to search the net to find out which end the engine was in, such was Top Gear's lack of useful information. I was hoping it would be in the rear, but it is not to be.

Surely if Prodrive fitted their whizzbang centre diff and torsen front and rear diffs to a standard WRX, Mr Clarkson would be impressed too.

[Calorus]

Originally posted by rhm
Ok, the technical forum has been a bit thin of traffic lately so I figure I can ask this:

On Top Gear a few weeks ago they had the Prodrive technology demonstrator car which had an active awd system like they run on WRC cars. Being that it was Top Gear they made a big thing about how it was impossble to understand how it worked which I thought was a bit presumptuous of their audience! Even though they bothered to film a prodrive employee explaining it, they didn't let us hear that explanation, they just showed Clarkson making stupid faces. Anyway...

Specifically, how does an active centre-diff improve traction in turns? I can see how an LSD of some description would improve traction in a front or rear wheel drive vehicle, but how does an active centre-diff improve things. Also, do these cars have open front and rear diffs or do they use a torsen or something like that?

Okay the computer knows each wheel's speed and the from that the slowest is taken to be roadspeed at the inside corner. A VCD varies the torque in the same way as an LSD between the front and rear to apportion a quantity of power proportional to the amount of grip; i.e. inverse to the amount of slip. This allows the car to lay down as much power as possible, by balancing the majority of wheelspin with the steering angle to allow slightly more wheelspin on the unloaded wheels whilst forcing the majority of power to the most loaded whel on the most loaded axle.

That's what I know about the Nismo system, rather than the Prodrive one, but logic argues...

[zac510]

That is the kind of technology that Nissan and Mitsubishi have been using on performance road cars for several years but it might be the P2 that applies it with enough processing power to control every corner of the car individually on a road car. If Prodrive were to make it...

I still think the difference between the special centre diff and the non-special centre diff is exaggerated by the chassis.

Nobody has really done it with a mid mounted engine unless you consider the 959. I guess Prodrive wanted to keep it cheap.

[pio!pio!]

I think it's the same active center differential on regular STi model Imprezas

[J. Edlund]

http://www.prodrive....and by wire.pdf