Mercedes-Benz will fit 7G-TRONIC seven-speed automatic transmissions to its E 500, S 430, S 500, CL 500 and SL 500 models towards the end of the year.

Mercedes-Benz will fit 7G-TRONIC seven-speed automatic transmissions to its E 500, S 430, S 500, CL 500 and SL 500 models towards the end of the year.

The Stuttgart-based manufacturer claims that the new ‘box will be the world’s first production-fitted seven-speed automatic and would yield improvements in fuel consumption, acceleration and smoother gear changes.

The 7G-TRONIC transmission represents the fifth generation of automatic transmissions made by the Mercedes-Benz brand and will replace the marque’s five-speed ‘boxes on certain models

According to the manufacturer, the seven-speed automatic transmission reduces fuel consumption in the NEDC driving cycle by up to 0,6 litres per 100 kilometres (depending on the derivative the gearbox is fitted to), increases acceleration from 0 to 100 km/h by up to 0,3 seconds and allows quicker acceleration from 60 to 120 km/h. At the same time, shifting is apparently smoother than with the automatic transmission presently used.

The use of seven gear ratios has allowed the transmission to retain the small increases in engine speed that ensure optimum gear ratios, while offering a larger ratio spread between the lowest and highest gear. According to a Mercedes-Benz spokesman, this gives the electronic control unit more flexibility to adjust shifting in such as way as to keep fuel consumption low and the transmission’s reactions fast. It also lowers the average engine speed.

When the driver switches down rapidly through the gears (kickdown), the new transmission does not always select the individual gears in strict order. Instead, 7G-TRONIC will miss out a particular gear if necessary, switching from seventh gear straight down to fifth, for example, and from there directly to third. In this situation, only two gear changes are actually required - instead of the normal four - in order to accelerate quickly using kickdown.

As in its predecessor, the new seven-speed automatic transmission has a lockup clutch in the hydrodynamic torque converter. The system largely eliminates slip between the pump and turbine rotor. It does this by establishing a virtually fixed connection wherever possible between the engine shaft and transmission shaft, creating an extremely effective barrier to output loss.

In contrast to conventional automatic transmissions, in which torque converter lockup is only possible in higher gears, the lockup clutch in the new seven-speed automatic transmission from Mercedes-Benz is active from the first gear up.

Despite these technical advances, the 7G-TRONIC automatic transmission is similar in size and weight to Mercedes’ five-speed automatic gearbox. The weight reduction was achieved by constructing the transmission casing from lightweight magnesium.

Speaking to CARtoday.com on Thursday, DaimlerChrysler technical specialist Hans Leithgöb said the seven-speed automatic gearbox would appear on South African models at the same time as it was released in Germany.

"The 7G-TRONIC will first be introduced in eight-cylinder derivatives and added to other models, such as the V12-engined S600, SL600 and CL600 at a later stage," he said.