7G-TRONIC: World’s first 7-speed autobox for cars
The world’s first 7-speed automatic transmission for passenger cars is here and it’s from Mercedes-Benz. Known as the 7G-TRONIC, it will be a standard feature of the E500, S430, S500, CL500 and SL500 models from the end of 2003, replacing the 5-speed automatic version currently fitted.
The newly-developed automatic transmission is claimed to reduce 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 said to be even smoother, and therefore more comfortable, than with the automatic transmission presently used.
By having seven gear ratios, it is possible for 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.
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What’s more, 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, 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.
Shift quality, meanwhile, also hits new heights, it is claimed. The new transmission glides through the gears extremely smoothly and yet with impressive speed. Gear-changes are barely noticeable, especially in the higher gears.
An outstanding feature of the new 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 significant technical advances, the 7G-TRONIC automatic transmission is barely any larger or heavier than the well-proven 5-speed automatic transmission currently fitted in Mercedes models. Credit for this impressive achievement goes in particular to the transmission casing, which is constructed in lightweight magnesium – also a world first in volume production.
The 7G-TRONIC transmission development represents the fifth generation of automatic transmissions made by the Mercedes-Benz brand, and in so doing continues an impressive tradition. Since 1959, the carmaker has produced over eleven million automatic transmissions. Whilst the automatic transmission is part of the standard equipment in the S-Class, around 88% of all Mercedes E-Class customers currently order their car with automatic transmission, and the figure stands at some 65% for the C-Class Saloons, Estates and Sports Coupés… and this figure is on the rise.
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| SL500 will get 7-speed autobox as standard |
