Electric auxiliary oil pump, basic function

P27.19-2725-76

Overview

This document contains information on:

 General

 Function

General

The electric auxiliary oil pump has the following tasks:

 Supporting the working pressure supply

 Support of cooling and lubrication

 Start/stop qualification

 Emergency engaging and emergency release of park pawl

Function

Supporting the working pressure supply

If additional volumetric flow is required (e. g. during shift operations), the electric auxiliary oil pump supports the mechanically operated primary pump in accordance with requirements. The electric auxiliary oil pump provides supporting flow volume. This counteracts working pressure drops due to undersupply.

Support of cooling and lubrication

In order to provide additional flow volume, the electric auxiliary oil pump is actuated as needed to meet high cooling and lubrication requirements. The primary pump can be downsized due to the option of providing an additional flow volume. This lowers the CO2 output.

Start/stop qualification

If the combustion engine or the electric machine is not in operation during the stop phase, then the electric auxiliary oil pump provides a basic pressure level. As a result, the hydraulic ducts of the electrohydraulic control and the piston chambers of the shift elements remain filled. Through electrically-controlled operation of the electric auxiliary oil pump, the exact oil filling capacity necessary to compensate for leakage in the electrohydraulic actuator  (EHS) is delivered. This makes it possible to reduce the power consumption of the electric auxiliary oil pump to a minimum at the start/stop operating point.

Emergency engaging and emergency release of park pawl

If the combustion engine or the electric machine is not in operation and the park pawl lift solenoid is intact, then the electric auxiliary oil pump hydraulically activates the park pawl (Not-P). The park pawl is engaged mechanically by means of a spring.

When the park pawl lift solenoid is defective, the park pawl actuator is released hydraulically. If the combustion engine is not in operation, then the electric auxiliary oil pump is requested. Emergency release/emergency engaging is only possible in direction P, but not from P to Not P.

P27.56-0002-76

Oil pan

Oil is supplied to the electric auxiliary oil pump by a separate filter (4) integrated into the oil pan (3). The drawn-in transmission oil is supplied into the working pressure duct of the electrohydraulic control by the electric auxiliary oil pump.

 In the case of operation solely with the electric auxiliary oil pump (where the combustion engine or electric machine is at a standstill), leakage via the stationary oil pump (primary pump) is prevented by a check valve.