P27.57-2068-79
1 | Auxiliary oil pump (electric tandem pump) |
Overview
This document contains information on:
General
Location
Function
General
The job of the auxiliary oil pump is to support the oil pump (primary pump) in the following operating states:
At low combustion engine speeds
Start/stop mode
Support of clutch cooling including at high transmission oil temperatures
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, e.g. frequent start-off operations 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 bar and 8 bar.
Location
The auxiliary oil pump is located in the dual-clutch transmission on the fully integrated transmission control electrohydraulic controller unit.
Function
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 oil from the suction chamber and supplies the fully integrated transmission control electrohydraulic controller unit with oil. Meanwhile, the dry sump pump pumps the 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 oil out of the gear set/coupling housing and is used for lubricating the gear set.