wec

OK a question for your motorheads ...

I've heard this phrase used in a couple of cases in refering to Audi's (& the allroad's) throttle. Could someone please explain it technically & practically?

Does it mean the gas pedal is linked directly by wire to the engine, or does it mean the opposite that it's not, but runs "by wire" through some other intermediary control system?

And what's the effect on response, driveability, etc.?

Hope this isn't a "duh" question.

Atlas Gray w/Tip & all but Nav, phone & changer

geoff-oz

Drive by wire means that there is no mechanical linkage between the "loud" pedal and the throttle body/fuel control.

All the control of the throttle is now performed by an electronic servo that is controlled by the ECU and it manages the correct amount of fuel air mixture that the engine receives for a given pedal position.

Old system used a mechanical linkage, either a braided cable with soring return or rods etc.

If you look at the accelerator you will see a small "black box" which has the position sensors and electronics for the ECU to determine how far you have pressed the pedal and how quickly etc...

Aircraft have used this term for years and it normally relates to the replacement of the cables and control rods that controlled the flaps etc. with electro-hydraulic servo systems. Nearly all modern aircraft use this system.

There is no such thing as a "duh" question, only a "duh" answer... :-)

Highland Green with dual range 6 speed.

Farmer

You lucky DOG!!!! Where are you located that you have the dual range 6 speed. I should be getting my SINGLE range 6 speed in a few days, but wish I could get the dual range. How is it? The dual range portion that is.

geoff-oz

I am in Australia and the two options we have are the Tip and a manual with Dual Range.

I haven't tried the low range as yet but I hope to get out this weekend and try it.

The low ratio is 1.54:1 so it should be able to crawl over obstacles without having to use the cluctch ( which should be avoided at all costs).

I haven't worked out why Audi only do certain options in each markt... The NZ market get the 2.5TDI engine as well as the 2.7 but both models only come in Tip, no manual...

SF Allroad

Is it a 6 speed with 1st being an ultra low gear, so that only 5 forward speeds are useful in normal driving, or is a gear that you push a lever or button or something, and it switches to an ultra low mode?

geoff-oz

The Dual Range is an extra reduction gear after the final drive output from the gear box. In normal mode the ratio is 1:1 but with the low range engaged it add a 1.54:1 reduction ratio and therefore you go slower for the same engine revs.

Most of the normal offroad 4WDs use a transfer case with up to 2:1 reduction ratios in them so they are used for the real off road tracks where slow going is the norm.

On the allroad the low ratio is engaged via a switch on the gear stick. To select low range you push the clutch in and press the button and the low ratio is electrically engaged. Will only engage below 30KPH and is limited to 50KPH

wec

It's interesting, I took a 400+ mi trip trout fishing this last weekend and used the cruise for the first time on the interstate (thankfully only 1/3 of the trip). Many cruise systems when engaged you can feel the pedal depress underfoot automatically when the system calls for more power to maintain speed (eg, uphills). The allroad did not do this ... "drive by wire"

So thanks for the confirmation/explanation. Cool.

Anyone have comments on driveability issues, concerns?

There is a "lag" mostly starting from a stop, particularly if trying to jump through traffic to make a left turn or get out of a parking lot - quite an extra thrill sometimes before the lunge. I suppose some of that is due to the turbo engine, but is this also affected by the drive by wire?

Atlas Gray allroad

hayburner3

Does the low range also improve towing, or are they unrelated?

geoff-oz

Not realy related...