The first nine-speed automatic transmission with torque converter, the 9G-TRONIC for premium vehicles, is now celebrating its debut: equipped with the innovative power transmission, the E 350 BlueTEC is set to become one of the most fuel-efficient six-cylinder diesel models in its class. Thanks to the high efficiency level of the patented transmission design, NEDC fuel consumption in the E-Class is reduced to 5.3 litres of diesel per 100 km. As is typical of the brand, the transmission offers outstanding comfort and barely perceptible gear changes.
In the E 350 BlueTEC, which is available in Saloon and Estate models and comes equipped with the new 9G-TRONIC as standard, the 185 kW (252 hp) V6 diesel engine has an average NEDC fuel consumption of 5.3 litres of diesel per 100 km (44.38 mpg/US, 18.86 km/l) (Estate: 5.5 l/100 km/42.76 mpg/US, 18.18 km/l), corresponding to CO2 emissions of 138 g/km (Estate: 144 g/km). As a result, the new models with 9G-TRONIC undercut their predecessors in terms of both consumption and CO2 emissions. The higher number of gears and the broader gear ratio spread help to increase drive comfort and allow a significant enhancement to be achieved in terms of converting engine power into traction.
On the one hand, the overall reduction in engine speed improves NVH comfort and therefore the pleasant sense of well-being on board the E-Class, and on the other also cuts down external noise by up to 4 dB(A), thus reducing the strain on the environment. The reduced fuel consumption of the E 350 BlueTEC with 9G-TRONIC has primarily been achieved as a result of the high efficiency level of the transmission. As part of this, the broad ratio spread of 9.15 for gears one to nine allows a clearly perceptible reduction in engine speed and is a decisive factor behind the high level of energy efficiency and ride comfort. Shortened shift and reaction times ensure optimum spontaneity combined with outstanding ease of shifting. In manual mode and S mode in particular, the 9G-TRONIC responds significantly more spontaneously and enhances driving pleasure.
The particular ease of shifting of the new 9G-TRONIC – a focal point during development and a hallmark feature of a Mercedes-Benz automatic transmission – comes courtesy of a comprehensive package of measures. These include the novel direct control system which enables short, barely perceptible gear changes. The combination of twin-turbine torsional damper and centrifugal pendulum technology in the torque converter ensures outstanding drive comfort. Together with the extended gear ratio spread, higher speeds can now be driven at lower engine speeds for even greater comfort. In reality this translates into being able to drive at 120 km/h (75 mph) in 9th gear with an engine speed of around only 1350 rpm, for example.
Advanced technology for superior power transmission
In the case of the 9-speed automatic transmission, the development engineers also focussed on the area of “compact lightweight construction.” Despite two additional gears and a maximum transferable torque of up to 1000 Nm (738 lb-ft), the new automatic transmission requires as little installation space as its predecessor and is also lighter in weight. The two-piece housing design has been retained: the torque converter housing is made of lightweight aluminium, while the transmission housing with weight-optimised plastic oil pan is made of an even lighter magnesium alloy.
Another goal was to implement the nine gears with a minimal number of planetary gear sets and shift elements. Intensive, computer-based system analysis and mock-up made it possible to realise this goal with just four simple planetary gear sets and six shift elements. Three speed sensors monitor operation and provide the transmission control system with corresponding data for effective shifting. Here it is possible for several gears to be jumped when accelerating or decelerating, should the driving conditions call for it.
To ensure the reliable and at the same time energy efficient supply of the durable and shear-resistant second-generation synthetic fuel economy engine oil, the new automatic transmission is equipped with two pumps. The considerably smaller mechanical main pump, featuring an off-axis design, is located next to the main shaft and is chain-driven and fed by a separate electric auxiliary pump. This design allows the flow of lubricating and cooling oil to be controlled actively on demand, and also means that 9G-TRONIC can benefit from a start/stop system. Thanks to the world’s first direct control system in a planetary automatic transmission with nine gears, it has also been possible to significantly increase hydraulic efficiency within the transmission.
Around 22 million automatic transmissions from Mercedes-Benz since 1961
Mercedes-Benz has been developing and producing high-quality automatic transmissions featuring outstanding ease of shifting, optimum energy efficiency and dependable durability for more than 50 years. To date, a total of around 22 million automatic passenger car transmissions have left the manufacturing plant in Stuttgart-Hedelfingen, close to the corporate headquarters in Stuttgart-Untertürkheim.
The 9G-TRONIC is suitable for rear-wheel and all-wheel drives as well as hybrid and plug-in hybrid drive systems, and will be used in almost all model series and engines in the coming years.