Oil supply for automatic transmission, function - GF27.57-P-1000AHO

TRANSMISSION 724.2 in MODEL 212 

Function requirements for automatic transmission oil supply, general 

• Transmitter key (A8/1) inserted

Oil supply for automatic transmission, general 

With the combustion engine running, the primary pump delivers oil to the electrohydraulically controlled automatic transmission. The primary pump is driven by the wet clutch drive shaft. The primary pump is installed in the transmission bell housing in front of the wet clutch.

Oil supply for automatic transmission with stopped internal combustion engine 

On the automatic transmission with electrohydraulic control and oil pump drive through the wet clutch drive shaft the oil supply stops when the internal combustion engine is switched off. With this, all the control elements and actuators change to a basic state under no load and the automatic transmission power flow stops. The electrical transmission oil pump secures the oil supply and the cooling of the control elements and actuators in the automatic transmission during internal combustion engine standstill.

The electrical transmission oil pump is part of the fully integrated transmission control controller unit (Y3/8) and it is active under the following operating conditions:

• During preparation for an internal combustion engine start through the electrical machine (A79/1), transmitter key inserted (circuit 87 (circuit 15 switched) OFF)
• During preparation for an internal combustion engine start through the electrical machine (circuit 87 (circuit 15 switched) ON)
• During coast down shifting to support the primary pump (upshifts and downshifts) (internal combustion engine running)
• For cooling requests by the fully integrated transmission control unit
• At vehicle standstill (internal combustion engine standstill), to keep the gear oil pressure in the hydraulic control elements constant
• In the electric drive mode (electrical machine ON, internal combustion engine standstill) for oil supply and cooling of the control elements and actuators in the automatic transmission

The electrical transmission oil pump secures the oil supply for the control elements and actuators n the automatic transmission when the internal combustion engine is at a standstill, and following an internal combustion engine start it reduces any time lost, between the drive-off request and the drive-off time.

The electrical transmission oil pump in electric drive mode is responsible for the oil supply and cooling (speed-controlled, depending on volumetric flow requirement) or it supports the primary pump in hybrid drive mode.

Automatic transmission fluid

The transmission fluid used for the automatic transmission generation has a lower viscosity which coupled with a new additive package, changes the maintenance intervals and optimizes fuel consumption.

The new gear oil is colored blue, which enables it to be differentiated from the previously used red-colored ATF.