Automatic Transmission Oil Supply, Basic Function - GF27.57-P-1003A

Model all with transmission 725 

Overview 

This document contains information on:

• General 
• Function requirements 
  • Primary pump 
  • Electric auxiliary oil pump 
• Function 

General 

With the combustion engine running, the oil pump (primary pump) delivers oil to the electrohydraulically actuated automatic transmission. The oil pump is driven through a chain drive by the drive shaft.

Function requirements 

• Primary pump 
  • Engine in operation
• Electric auxiliary oil pump
  • Ignition ON (circuit 15)

Function 

If the oil supply fails whilst the combustion engine is switched off, all control elements and actuators switch to the unloaded basic condition.

The frictional connection to the combustion engine is therefore interrupted.

When starting the combustion engine, a gear engagement process from N to D1 must be carried out after establishing the oil supply. The resulting time loss between the start-off request and the start-off time is minimized by the electric oil pump.

The electric auxiliary oil pump is activated in start/stop mode and takes over the basic supply of control elements and actuators. The oil pressure is maintained by the electric auxiliary oil pump.

The electric auxiliary oil pump supports the primary pump at low engine speeds of the combustion engine. The flow volume, added as required by the electric auxiliary oil pump, is requested in the combustion engine's low-speed range during shift operations or when increased cooling is required.