Transmission: Ready for the future with nine gears

Jun 28, 2014
Depending on the model, the CLS Coupé and CLS Shooting Brake have the standard 7-speed automatic transmission 7G-TRONIC PLUS or new 9G-TRONIC, the world's first nine-speed automatic transmission with hydrodynamic torque converter in the premium segment.
This innovation builds on the strengths of 7G-TRONIC PLUS, which continues to champion efficiency, comfort and dynamism. With two additional forward gears 9G-TRONIC lowers fuel consumption further whilst simultaneously boosting ease of shifting and agility.
The following models are equipped with new 9G-TRONIC as standard: CLS 220 BlueTEC, CLS 250 BlueTEC, CLS 350 BlueTEC and CLS 500. The 7G-TRONIC PLUS automatic transmission is installed in the CLS 400 and the 4MATIC models. Among the traits of the latest evolutionary stage of the seven-speed automatic transmission from Mercedes-Benz are the new torque converter with reduced slip, an ECO transmission mode with improved gear spread, as well as an auxiliary oil pump that maintains the operating pressure when the engine is automatically switched off. What is more, friction-optimised components in conjunction with low-friction oil make it possible to lower the operating pressure. The upsides of this are very smooth gear changes and a dynamic response.
9G-TRONIC from Mercedes-Benz is the world's first nine-speed automatic transmission in the premium segment. Its broad ratio spread (9.15) for gears one to nine allows an overall reduction in engine speed - a key factor behind the high level of energy efficiency and ride comfort. Shortened shift and response times ensure optimum immediacy combined with outstanding ease of shifting. In manual mode and S mode in particular, 9G-TRONIC responds immediately and enhances driving pleasure. This is linked to the transmission's high efficiency, which is a noticeable advantage in terms of fuel consumption.
The particular ease of shifting of new 9G-TRONIC comes courtesy of a comprehensive package of measures. These include a 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 road speeds can be driven at lower engine speed for even greater comfort. In reality this translates into being able to drive at 120 km/h in ninth gear with an engine speed of around only 1350 rpm, for example.
Advanced technology for superior power transmission
Despite two additional gears and a maximum transferable torque of up to 1000 Nm, the transmission requires as little installation space as the 7G-TRONIC 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. 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 long-lasting 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.
In addition, the engineers have improved the hydraulic circuit in the torque converter in new 9G-TRONIC and increased its efficiency to up to 92 percent. This extraordinarily good figure is important for fuel economy because the losses imposed by physics when transferring the engine torque to the transmission's input shaft are kept to a minimum. In short: 9G-TRONIC converts a very high proportion of the engine power into tractive power.
One of the most comfort-enhancing and at the same time fuel-saving features is the torsional damper, which compensates even more effectively for eccentricities and vibrations within the transmission. Moreover, the optimised damping enables slip in the torque converter lock-up clutch to be reduced considerably even at low loads, which likewise contributes to fuel economy.
Variety of modes: Economy, Sport, Manual and "Short-term M"
With three transmission modes, 9G-TRONIC offers a control strategy that is adapted to the relevant traffic situation or the driver's personal preferences. In ECO mode upshifts are performed sooner, and the handling is gentler overall to support an economical driving style at lower engine speeds. In SPORT or MANUAL modes the control strategy shortens the response and shift times, and there is higher revving in the gears to support a dynamic and sporty driving style. Transmission modes are activated with a switch on the centre console.
Like 7G-TRONIC PLUS before it, 9G-TRONIC also has the automatic mode "Short-term M". This is activated in ECO and SPORT mode if the driver engages the required gear using the shift paddles. "Short-term M" remains active if there are repeated manual gear shifts or a sporty driving style is maintained with higher linear and lateral acceleration levels. In contrast to permanently activated MANUAL mode (with AMG Line only), however, "Short-term M" is deactivated after a certain period without higher power requirements, and the transmission reverts to the original mode.
Mercedes-Benz CLS-Class model year 2014, technology, CLS 63 AMG, AMG SPEEDSHIFT MCT
Mercedes-Benz CLS-Class model year 2014, technology, 9G-TRONIC