|9G-TRONIC. Click to enlarge.|
Mercedes-Benz’ new E350 BlueTEC features as standard the new 9G-TRONIC, the first rear-wheel drive nine-speed automatic transmission with torque converter. 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.
The E350 with 9G-TRONIC is equipped with a 185 kW (252 hp) V6 diesel engine and delivers NEDC fuel consumption of 5.3 liters of diesel per 100 km (44.4 mpg US). The reduced fuel consumption of the E 350 BlueTEC with 9G-TRONIC compared to prior models has primarily been achieved as a result of the high level of efficiency of the transmission. As part of this, the broad ratio spread of 9.15 for gears one to nine enables a perceptible reduction in engine speed and is a decisive factor behind the high level of energy efficiency and ride comfort.
The ease of shifting of the new 9G-TRONIC—a focal point during development—is due to a comprehensive package of measures. These include the novel direct control system which enables short, barely perceptible gear changes. The combination of double torsional damper and centrifugal pendulum technology in the torque converter provides 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 for example into being able to drive at 120 km/h (75 mph) in 9th gear with an engine speed of around only 1350 rpm.
The development engineers also focused on the area of compact lightweight construction. Despite two additional gears and a maximum transferable torque of up to N·m, the new automatic transmission requires as little installation space as its predecessor and, in addition, is lighter. 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. Computer-based system analysis and mock-up made it possible to realize this goal with 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 efficient supply of the durable and shear-resistant 2nd-generation synthetic engine oil, the new automatic transmission is fitted 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 enables the flow of lubrication and coolant to be controlled actively on demand and also means that the 9G-TRONIC can benefit from a start/stop system. Due to the 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.
The higher number of gears and the broader gear ratio spread help to increase drive comfort and enable a significant enhancement to be achieved in terms of converting engine power into traction. The overall reduction in engine speed improves internal NVH comfort and cuts down external noise by up to 4 dB(A), thus reducing the strain on the environment.