November 19, 2003

Audi Direct Shift Gearbox
by Jim Kerr

Ferrari uses one. So does BMW. Now Audi has joined the club with, in my pinion, the best automatic manual gearbox in a production car and maybe one of the best transmissions ever built. Those are big words but this transmission shifts better than an automatic and shifts faster than a manual gearbox, while letting the driver have all the economy, control and the fun. Here's where to find one and how it works.

2004 Audi TT 3.2. Click image to enlarge

Audi has this transmission available in their 250 horsepower 3.2 TT Quattro. It is a manual gearbox that shifts automatically, passing power through to the Quattro all-wheel drive powertrain. Inside the car, it looks more like an automatic transmission. There is no clutch pedal. The shifter looks like an automatic transmission, with Drive position and a spring-loaded Tiptronic manual shift position. Paddle-style shift levers at the steering wheel can also shift the transmission and will put the gearbox into manual mode even though the console mounted shifter is still in the automatic position. A dash display shows if the transmission is in automatic mode or the manual gear selection.

Start your driving experience by simply placing the shifter in Drive. A Sport mode is available that will delay upshifts and downshifts for more performance in Drive mode. Step on the gas pedal and the car pulls away from a stop just like any automatic transmission but without using a torque converter. As the transmission automatically upshifts, the progression is smooth. Unless you knew, most drivers would think this car has an automatic transmission. The only sound heard from the transmission is a soft sshhfftt as the shifts occur. This sound comes from the oil flow as it engages the clutch for the next gear.

Click image to enlarge

Inside the computer controlled gearbox there are four shafts: two input shafts and two output shafts. The input shafts are concentric, with one shaft passing through the centre of the other hollow input shaft. There are two multi-plate clutch packs similar to those found in automatic transmissions. Each clutch pack connects one of the input shafts to the engine, so depending upon which is applied, either one of the two input shafts can transfer power. An oil pump at the rear of the gearbox supplies hydraulic pressure for the clutches.

The speed gears are divided between the two output shafts. First, third, fifth and reverse gear are on one output shaft while second, fourth and sixth gears are on the other shaft. Synchronisers are moved by the computer to lock each of the speed gears to their output shaft as required. Each output shaft has a pinion gear that drives the differential.

When the driver places the shift lever in drive, First gear is engaged inside the transmission, but the clutch doesn't engage until the driver steps on the gas. Because the clutch is running in oil, it can slip without burning up, allowing the car to creep along in first gear just as an automatic would. Step harder on the gas and the clutch is fully applied. A neat feature of the control system allows the driver to step on the gas and brake at the same time. Audi calls it Launch Control and it allows F1-type starts. In Sport mode with both pedals pressed, the engine revs to 3200 rpm. Release the brake and the car launches in drag strip fashion.

With the transmission engaged in first gear, the computer locks second gear to the other output shaft, but the input shaft clutch for that gear is not engaged. When it is time to shift, the computer releases the clutch for the first gear input and engages the clutch for the second gear input. In preparation for the next shift, the computer now shifts from first to third gear but leaves its clutch disengaged until the shift is requested. As the car's speed increases, the computer continues to pre-select the next gear so all it has to do is switch clutches. There is no grinding, no delays, and no shock.

By monitoring driving style, the computer predicts whether the driver will request an upshift or downshift next so it can pre-select the correct gear. It is possible to fool the computer by driving erratically, but even if the wrong gear is pre-selected it only takes a fraction of a second for it to catch up. This transmission shifts fast, with shift times in the .03 to .04 second range. Even an excellent driver has trouble matching that consistently, and this transmission can do it all day long.

This transmission concept is not new. Audi tested and won with the concept in their Sport Quattro Rally car at Pike's Peak Hill Climb in 1985. It's taken a long time to get to the street, and I hope to see much more of it soon.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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