Auxiliary Electric Tandem Transmission Oil Pump, Basic Function - GF27.57-P-2002A
724.103/114/115/120
Example illustration of electric auxiliary oil pump
Overview
This document contains information on:
- General
- Function
General
The electric auxiliary oil pump supports the oil pump (primary pump) in the following operating statuses:
- At low combustion engine speeds
- During start/stop operation
- During clutch cooling, including at high transmission oil temperatures
The auxiliary oil pump is located in the dual-clutch transmission on the fully integrated transmission control electrohydraulic controller unit.
Function
The fully integrated transmission control electrohydraulic controller unit actuates the auxiliary oil pump at low engine speeds. The auxiliary oil pump ensures the following functions at low engine speeds:
- Compensation of low oil pump (primary pump) delivery rate
- To maintain constant oil pressure
- Ensure optimum cooling of transmission components
- Ensure sufficient lubrication of transmission components
In start-stop mode, all actuators switch to a basic unloaded state when the combustion engine is stopped. This means that no gear changes can take place and the dual clutch can no longer be actuated.
In order to minimize the resulting delay between the start-off request and start-off point, the auxiliary oil pump provides the necessary oil pressure before the actual start-off procedure.
Under driving conditions such as frequent start-offs on uphill gradients or when driving with a trailer, an increased oil volume is necessary to cool the clutch.
The fully integrated transmission control electrohydraulic controller unit uses the transmission oil temperature on the clutch plates to determine what is required. If the transmission oil temperature on the clutch plates is too high, the transmission oil flow rate is increased by switching-in the auxiliary oil pump.
Heat is dissipated faster due to the increased turnover rate of the transmission oil. Heat is transmitted via the transmission oil to the transmission oil heat exchanger.
The delivery pressure of the auxiliary oil pump is dependent on the length of actuation determined by the fully integrated transmission control electrohydraulic controller unit. The delivery pressure varies between 0 and 8 bar.
The auxiliary oil pump is a combination comprising an integrated auxiliary oil pump and a dry sump pump. When rotating clockwise, it functions in combined operating mode as an integrated auxiliary oil pump and dry sump pump.
In combined operating mode (auxiliary oil pump and dry sump pump), the auxiliary oil pump draws transmission oil from the suction chamber and supplies the fully integrated transmission control electrohydraulic controller unit with transmission oil. Meanwhile, the dry sump pump pumps the transmission oil out of the gear set compartment into the suction chamber.
As a dry sump pump, the auxiliary oil pump operates in the hydraulic short circuit mode. In this operating mode, the auxiliary oil pump draws the transmission oil out of the gear set/coupling housing and is used for lubricating the gear set.