Oil supply using two pumps

To ensure supply of the 2nd-generation synthetic engine oil, the 9G-TRONIC is fitted with two pumps. The mechanical main pump installed “off-axis” lies next to the main shaft and is driven via a chain. In an automatic transmission such as 7G-TRONIC, the main oil pump previously ringed the transmission shaft and was directly driven. This meant that the diameter of the transmission shaft prevented the pump from being reduced in size as desired. For this reason the vane cell pump is now placed alongside the main shaft (“off-axis”), and is reduced in size to suit requirements.

The mechanical main pump, which ensures the oil supply to the electrohydraulically controlled automatic transmission when the internal combustion engine is running, is backed up by a separate electric auxiliary pump. On the one hand this design enables the flow of lubrication and coolant to be controlled actively on demand, and at the same time also means that the 9G-TRONIC can benefit from a start/stop system. In subsequent hybrid applications, this additional oil delivery also allows so-called “sailing”, i.e. maintaining a constant speed without using the internal combustion engine.

When the engine is off – for example at a red traffic light in start/stop mode – the electric auxiliary pump is actuated, ensuring a defined basic pressure and guaranteeing that all necessary functions are maintained. When the driver wishes to move off on a green light, oil delivery by the electric pump after engine-starting guarantees acceleration. In certain operating states with the engine running, the auxiliary pump also assists the main pump, for example at very low engine speeds or in very high temperatures. In this case the flow of oil is added as needed to ensure smooth gear shifts or when there is a higher cooling requirement.