gat821

With the Q5 going to be my first Audi, I've read up and become fascinated by Quattro and AWD technology.

The Torsen differential is an amazing piece of work. There are a few posts on some of the other forums on Audiworld, but fairly old. Torsen has been mentioned as being a proactive differential, compared to other diff types that are reactive, where reactive here means there has to be some wheel slippage occurring first.

But isn't that what the Torsen is responding to as well? When there's less torque on one shaft, the diff sends a multiple of that torque to the other shaft. But doesn't less torque on a shaft and it spinning faster due to wheel spin?

Seems like it's 'reacting' as well, though it's doing so faster than a viscous or clutch type diff can.

Reggie

A lot of AWD systems are FWD or RWD first and only change when they detect slippage. My RX300 is that way
http://www.rubicon-trail.com/4WD101/...e_4WD_awd.html

http://www.rallycars.com/Cars/4wd_turbo_cars.html

The best is here:

http://www.autozine.org/technical_sc...tion_4wd_2.htm

kleinbus

Lets cut the wings from this proactive right before it even flies...

Good driver can be proactive through human eyes and "butt feeling" and observe what is happening ahead that allows person to act differently if needed.

Any vehicle that senses anything through wheels is always reactive as it have to slip, no matter how much, is it just a tiny split of degree or quarter revolution, it is still slip and difference comes how quickly system reacts.

Once someone develops scanning system that is able to behave like human eye and combined with artificial intelligency, then car may become proactive as it could observe and react as needed.

In other words, there is no proactive AWD's in this world, all of them are reactive.

The driver is proactive when it shifts part time rear wheel drive pick-up to 4x4 before hitting the mud and spinning the wheels.

gat821

Those were my thoughts as well kleinbus. That's why I couldn't wrap my head around why some were calling it proactive. I was wondering if there was something I was missing on that, but you've explained it quite well.

GolfGL

I've heard Torsen described as "instantaneous" as well... maybe that is more accurate?

Coolieman1220

then there's haldex. IMO i like the torsen because its fully mechanical so it works without a problem. computers fail. and they can handle power better. haldex is all computer but it can send 100% power to any wheel where as torsen can do more of a 50/50 front rear.

gat821

Yeah, I agree - instantaneous is a better term than proactive in this case.

Reading the link from Reggie in more detail now, regarding the Porsche 959 and the Nissan GT-R's ATTESA ETS Pro, there's mention to this:

The clever electronic control system is fed by all the information that Porsche 959 had, such as G-force, boost pressure, throttle position etc, in addition, the speed of individual wheels measured by ABS wheel speed sensors. By these information, the computer knows whether the car is running out of cornering limit or not.

kleinbus, this does seem to be pretty close to being proactive. The fact that they did program all these other inputs on top of sensing for wheelspin means that there MUST be some benefit to monitoring them and directing torque as appropriate. Otherwise, why not just monitor wheelspin right? Or, or.... does the system take all these other factors into account for redirecting torque only when wheelspin occurs, not independently of it?

fastd1

Here is a video comparing the Quattro system to others:
http://video.google.com/videoplay?do...5126892796503#

Coolieman1220

if only i understood the language....

kleinbus

It's German.


Gat,

It's still reactive as it have to sense something through the sensors and it is already happening so it reacts to the situation going on like stability control does not ease your accelerator until it measures your sttering angle and senses wheel slip.

Like last month I was playing on myddy uphill to see how far Q5 goes and for my surprise it took me all the way to top while EDL was keeping that ABS sound that meant car reacted to wheel slipping and begun to brake spinning wheel(s).

Another example is automatic transmission versus manual.

During the approach to uphill automatic changes when it detects increasing rolling resistance etc that means it is reactive

Driver with manual transmission can dial down before hill to keep engine on optimum torque range and that way is proactive while taking action before the situation.

Audi's Torsen (mechanical drive) and some models from Subaru (mechanical drive) are as instant as backlash in the gears allow so generally it is instant. I better change the topic as this is heading to the direction where it becomes hair splitting...