Automatic Transmission, Basic Function - GF27.00-D-9901A

Model All with transmission 725.0 

Courtesy of MERCEDES-BENZ USA

Example illustration of automatic transmission with torque converter and integrated centrifugal pendulum 

General 

Combustion engines operate in a limited rpm range. The automatic transmission converts the engine torque into the tractive force required by the wheels to overcome motion resistance.

The automatic transmission is an entirely electronically controlled automatic transmission with nine forward gears and one reverse gear. The gear ratios for the gear ranges are achieved by planetary gear sets. In the automatic transmission, all transmission functions and components are combined in one assembly module.

The fully integrated transmission control controller unit located in the automatic transmission minimizes interfaces to the subharness in the vehicle.

Using the fully integrated transmission control provides the following additional advantages:

• High electromagnetic compatibility (prevention of interaction between multiple electronic components)
• Fast current control as well as compensation for on-board electrical system fluctuations (increasing shift quality)
• Accurate determination of measurements relevant to shift operations and faster evaluation of the measured values

Increased service life, reduced fuel consumption and maximum gearshift comfort can be achieved with the following:

• Transmission set-up with nine gears and gear ratio spread of 9.15
• Optimized transmission components
• Reduction of working pressure
• Software with additional comfort and dynamic functions
• Actuation concept with two oil pumps

The transmission can be subdivided into the following assemblies:

• Torque converter with torsional damper, centrifugal pendulum and torque converter lockup clutch
• Oil pump (primary pump) for generating the necessary oil pressure and for reliable lubrication of the shift elements and bearing points
• Electrical auxiliary oil pump for generating required oil pressure, for guaranteeing lubrication of shift elements and bearing points at engine OFF and for supporting the primary pump
• Transmission housing with mechanical transmission components (planetary gear sets, electrohydraulically operated park pawl, multidisk clutches and multidisk brakes)
• Fully integrated transmission control controller unit with integrated fully integrated transmission control unit