THE NEW AUTOMATIC TRANSMISSION 9G-TRONIC from Mercedes -Benz, Dr. Christoph Dörr Senior manager automatic transmission projects Daimler AG, Germany Manfred Homm Senior manager automatic transmission mechatronics and torque converter Daimler AG, Germany Guenter Indlekofer Senior m anager automatic transmission hardware Daimler AG, Germany SUMMARY The first nine -speed automatic transmission with torque converter, the 9G -TRONIC for premium vehicles, is celebrating its world premiere. 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 level of efficiency of the patented transmission design, NEDC fuel consumption in the E -Class is re duced to 5.3 liters of diesel per 100 km. As is typical of the brand, the transmission features outstanding comfort and barely perceptible gear changes. The E 350 BLUETEC featuring the 9G -TRONIC as new standard and is available to order in continental Eur ope with immediate effect. HISTORY OF AUTOMATIC TRANSMISSION AND SYSTEM IDENTIFICATION Mercedes -Benz develops a nd produces planetary gear set automatic transmissions for the rear wheel drivetrains for more than 50 years. The first generation automatic tra nsmission started in 1960 as K4A025, a 4 speed planetary gear set – automatic transmission with hydraulic clutch as starting element, see figure 1. In former times the search process for planetary gear systems was done analytically [1, 2] . Due to the high effort first computer programs were designed to support the calculation. In order to search a new high efficient transmission system for the 9G -TRONIC an innovative consistent software tool had to be developed. With the specific boundary conditions of • Size • Spread • Number of gears • Optimum gear teeth efficiency several billions of planetary couple systems were analyzed, evaluated and partly designed. The selected system of the 9G -TRONIC got world -wide patented in 2008. The system is designed for a torque capacity up to 1.000 Nm. Figure 1: Development of planetary gear set automatic transmissi on generations at Mercedes -Benz TRANSMIS SION SYSTEM The s ystem design of the 9G -TRONIC is shown in figure 2 . It consists of 4 standard planetary gear sets and 6 shift elements, which are 3 clutches and 3 brakes. With these gear sets and shift elements the 9G -TRONIC realizes nine forward speeds and one reverse speed . Figure 2: Planetary gear system and shift pattern of 9G -TRONIC. The number of coupled elements for the transmission is a minimum for 9 speeds under the set of constraints. For a modern planetary gear system with more than 8 speeds and a high ratio an extremely long input shaft is characteristic. The shaft is coupled in the trans mission system to the 4th planetary gear set. The transmission system is designed that the number of speeds correlates to the overall ratio. With 9 speeds an optimized gear ratio hat to between 8 and 10. T hus a harmonic st epping for the 9G -TRONIC is possible which leads in a comfortable driving. THE MECHANICS OF THE 9G -TRONIC The design of the automatic transmission 9G -TRONIC is shown in figure 3. Compared with predecessor transmissions the 9G -TRONIC is completely new due to the revolutionary transmission concept . Figure 3: Design of the 9G -TRONIC with essential components The mechanics of the transmission is laid -out as a compact design unit for standard drivetrain configuration, see figure 3. Similar to the predecessor transmission a two -piece case concept was implemented with the aluminum torque converter case and for light weight a magnesium transmission case [3, 4] . Main advantage of the two -piece case is high modularity with possibility to adapt easily to different engines as well as the simple modular impleme ntatio