Automotive Engineer

Shifting through the gears of a manual transmission, if done correctly, can be the most efficient way to change gear and improve fuel economy. But most drivers don’t necessarily know when the best time is to change up or down.

Putting the emphasis on the vehicle to take control of the shift pattern means drivers can save fuel without the pressure of checking the tachometer, road layout or the topography of the land.

A traditional torque converter may be simple but it is not efficient. It was Porsche’s introduction of the dual-clutch transmission in its 1980s Le Mans cars and Volkswagen’s subsequent development of the technology to series production levels, that has helped to improve automated transmissions so they match the efficiency of the perfect manual gear change. But the technology was first developed nearly 100 years ago by Adolphe Kégresse, although it never reached the mass market.

Kégresse was a military engineer who invented the half-track. He was born in Héricourt, eastern France, in 1879 and educated in Montbélliard, before moving to Russia to work for the Tsar, Nicholas II.

He returned to France in 1919, but during his 14 years in Russia developed the Kégresse track, which used canvas instead of metal, to turn standard vehicles into half-tracks.

Kégresse continued his work on the technology while working for Citroën, but after leaving the company in the mid-1930s focused his engineering abilities on another technology: transmissions.

Manual transmissions of the time were cumbersome and because they required the driver to slide the gears on to the shaft, needed careful control of the throttle and good timing. Kégresse’s system addressed this by automating the gearshift.

In 1935, he patented his Autoserve transmission design, that used two clutches; the first engaged even gears, while the second engaged odd gears.

It was an ingenious design that meant driving was made simpler and easier, doing away with the complexity of manually changing gear. The design was based on a concentric clutch arrangement, where both clutches shared the same plane.

Kégresse installed his system on a 1939 Citroën Traction Avant to test his technology. It worked, but even with its undoubted benefits the system was never taken any further because traditional torque converter automatic technology was more cost effective.

For all of Kégresse’s foresight, his system was not looked at again until the 1980s, when Porsche adopted dual-clutch transmissions for its 956 and 962 Le Mans racing cars and Audi used the technology in its successful Audi Quattro rally car.

But it was another 20 years before dual-clutch technology was adopted by production vehicles. The fourth generation VW Golf used the transmission system in the high performance R32 variant in 2003.

The technology has been improved since Kégresse’s original concentric arrangement. Many of the latest designs use identically-sized clutches arranged in parallel, controlling up to seven speeds.

Clutch types have also improved. Both wet and dry clutches mean that dual-clutch transmissions can be applied to a wider variety of vehicles. Wet clutches can be used in high performance cars, such as the McLaren MP4-12C, which uses a twin-turbo V8 gasoline engine, while dry clutches mean even small B-segment vehicles, such as the VW Polo, can benefit from the technology’s smooth shifting pattern and improved efficiency.

Kégresse’s invention made the shifting of gears less reliant on the driver’s ability to manipulate the throttle and time their gear change so they could slide the gear on to the shaft themselves.

We can thank a persistent engineer who began his career developing half-track vehicles for the military. And although his invention was not a commercial success in his lifetime, the technology is now making vehicles more efficient.