May 15, 2003
Mercedes-Benz introduces world’s first seven-speed automatic transmission
Stuttgart, Germany – The world’s first seven-speed automatic transmission for passenger cars will be a standard feature of the E 500, S 430, S 500, CL 500 and SL 500 models beginning this Fall. It will replace the standard five-speed automatic transmissions.
Mercedes-Benz reports that the newly developed seven-speed automatic transmission reduces fuel consumption in the NEDC driving cycle by as much as 0.6 litres per 100 kilometres (depending on the car), increases acceleration from 0 to 100 km/h by up to 0.3 seconds, and allows significantly quicker intermediate sprints from 60 to 120 km/h. At the same time, shifting is smoother than with the current five-speed automatics.
Mercedes engineers have achieved these advances through the use of seven gear ratios. These allow the automatic transmission to retain the small increases in engine speed which are important in ensuring optimum gear ratios, whilst at the same time offering a larger ratio spread between the lowest and highest gear. 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 – a clear plus point in terms of both cutting fuel consumption and keeping the lid on noise levels.
When the driver switches down rapidly through the gears (kickdown), the new transmission does not always select the individual gears in strict order. Instead, the 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, one feature of the new seven-speed automatic transmission is a lockup clutch in the hydrodynamic torque converter. In many situations, this 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 barely any larger or heavier than the five-speed automatic transmission currently fitted in Mercedes passenger cars. Credit for this achievement goes in particular to the transmission casing, which is constructed of lightweight magnesium – also a world premiere in volume production.
The new seven-speed automatic transmission will be produced at the Mercedes plant at Stuttgart-Untert