Automatic Transmission (At), Function - GF27.10-D-0001TSA

Transmission 725.0 in model 907 

Block diagram 

Automatic transmission (AT), general 

The 9G-TRONIC 725.0 automatic transmission is an electronically controlled automatic transmission with 9 forward gears and one reverse gear. The gear ratios for the gear ranges are achieved by planetary gear sets. All the transmission functions and components for this automatic transmission are combined in one assembly module. The fully integrated transmission control (VGS) electric controller unit (N15/15) arranged in the automatic transmission minimizes the number of interfaces to the subharness in the vehicle. Use of the VGS electric controller unit results in the following additional advantages:

• High electromagnetic compatibility (prevention of interaction between multiple electronic components)
• Fast current control as well as the compensation of on-board electrical system fluctuations, which leads to increased 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 measures:

• A new transmission set-up with 9 gears and gear ratio spread of 9.15
• New, optimized transmission components
• Reduction of working pressure
• Implementation of a completely new software with additional comfort and dynamic functions
• New actuator concept with two oil pumps (primary pump and electrical auxiliary oil pump (M42))

The automatic transmission can be subdivided into the following assemblies:

• Torque converter with torsional damper, centrifugal pendulum and torque converter lockup clutch
• New oil pump (primary pump) in "off-axis design" for generating the required 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)
• VGS electric control unit

Further subfunctions are described in separate documents:

• Automatic transmission (AT), drive programs 
• Shift operation, function 
• Transmission control, function 
• Engage gear range, function 
• Parking interlock controller, function 
• Key-P function 
• Emergency-P function 
• Power flow with forward travel function 
• Power flow with reverse travel function 
• Torque converter lockup clutch control, function 
• Oil circuit - as-built configuration 
• A/T oil supply, function 
• Working/lubrication/shift pressure, function 
• Torque converter lock-up clutch control pressure, function 
• Limp-home mode, function