Audi: An automatic that trumps manual

Are you one those who don't like automatic gear shifting because it's too dull? Forget about it and try Audi - although the DSG is developed by Audi, they don't call it DSG any more but S-tronic.

Ladies and gentlemen, we have a breakthrough, one of those points in the evolution of the automobile where something new eclipses what went before, sets new standards and changes the way we think and the way things will be done.

For the first time, we have an automatic transmission that outperforms a manual.

Until now, it has been a given that an automatic transmission brings with it a penalty in both fuel consumption and performance, especially acceleration. But the Audi/VW Direct Shift Gearbox (DSG) not only allows faster acceleration than its manual counterpart, it results in better fuel mileage.

First, the facts. The 200-horsepower 2007 VW GTi, equipped with a six-speed manual transmission, accelerates from rest to 100 kilometres an hour in 7.2 seconds. With the six-speed DSG automatic, that drops to 6.9 seconds.

The six-speed manual is rated at 10 litres per 100 km in the city, and the DSG at 9.4. The highway ratings are identical at 6.9.

Where the DSG gets the edge over conventional automatics is the fact it combines the comfort and convenience of an automatic with the agility, efficiency and economy of a manual. It is also far more refined than the clutchless manuals.

The whole game is that of maximizing efficiency. In the hunt to improve mileage and minimize emissions from the internal combustion engine, engineers strive to keep it within a narrow operating range, where it is most efficient.

That is easier to do as you increase the number of gears available, resulting in less of a drop in revs when going from one to the next. Five-speed transmissions have become the norm, with six-speeds growing in popularity. Mercedes offers a seven-speed and Lexus has an eight-speed on the way.

Conventional automatics, regardless of the number of gears, are inefficient, depending on hydraulics and slippage to change gears.

First introduced on the Audi TT several years ago, the DSG uses two clutches and two rows of gear ratios. One clutch and shaft operate reverse, first, third and fifth gears on a centre shaft, while second, fourth and sixth are on an outer hollow shaft operated by a separate clutch.

During operation, two gears are actually engaged at the same time, one on each shaft. But only one clutch is engaged and transmitting power to the wheels.

Let's say you're accelerating in second gear. Then third is pre-selected and whether you ask for a shift with a paddle on the wheel, the lever on the console or let the fully automatic mode make the decision for you, the clutch on the shaft containing second gear is released and the other one closes.

Since the opening and closing actions of the two clutches overlap slightly, a smooth shifts results. Once the shift is made, the next gear up or down is then pre-selected on the other shaft and remains on standby until its clutch is engaged.

You're actually changing clutches as much as changing gears.

The gear changes are accomplished in three- to four-hundredths of a second, quicker than any human is capable of with a manual and faster than a conventional automatic.

Other than the speed and refinement of the shifts, one of the most noticeable advantages of the DSG occurs when pulling out to pass.

In a conventional automatic, the unit has to work its way down through fifth and then fourth to third, for example. With the DSG, it goes directly from sixth to third in less than a tenth of a second.

This ability to shift gears with a minimal interruption of power delivery is the key to its advantage.

Continuously variable transmissions or CVTs are seen by some as an alternative to the DSG, but, generally speaking, they are a better match with small engines and hybrids, while the DSG is suitable across the spectrum and very happy with high-output, larger engines.

It's sort of like the battle between cassettes and eight-tracks, VHS and Betamax — one will emerge the better choice. My money's on DSG.

Related news: Foursprung, P4MR, Audi, VW, gear shifting

Source: The Globe and Mail

Read more

Read what others are saying about it: Bloglines, Feedster, Technorati