BMW 3 Owners & Service Manuals

BMW 3: Oil supply

The basic functions of the oil circuit of the GA8P75HZ transmission correspond to those of the GA8HP70Z transmission. The oil has the following tasks:

  • Lubrication
  • Control of the shift elements
  • Cooling

It is a conventional pressure circulating system. In addition to the mechanical transmission oil pump known from the GA8HP70Z, an auxiliary electrical transmission oil pump was integrated into the automatic transmission of the G20 PHEV.

Automatic transmission
Transmission oil pump GA8P75HZ transmission

  1. Mechanical transmission oil pump
  2. Electrical transmission oil pump

The mechanical transmission oil pump is driven by a rolling tooth chain on the transmission input shaft. If the separation clutch is open, drive is accomplished via the electrical machine; if the separation clutch is closed, drive is accomplished through a combination of the combustion engine and the electrical machine.

In operating phases with insufficient speed at the transmission input shaft, the auxiliary electric oil pump compensates for insufficient pressure in the hydraulic system, in order to reduce the response time of the transmission in the event of a load request.

The auxiliary electric transmission oil pump is a vane-type compressor, like the mechanical transmission oil pump. It is driven by a brushless direct current motor. The control electronics are integrated in the housing of the auxiliary electric oil pump and are activated by the electronic transmission control (EGS). The electrical transmission oil pump can be operated as of a transmission oil temperature of -5 ºC (23 ºF). In special cases, such as in the event of a failure of the electrical machine, the electrical transmission oil pump can be operated from a temperature of -15 ºC (5 ºF) in an emergency operation, in order to close the separation clutch. This enables the driver to continue the journey, also in the event of failure of the electrical machine.

In the GA8P75HZ transmission, the electrical oil pump occupies the space of the hydraulic pressure accumulator known from the GA8HP70Z. Like the hydraulic pressure accumulator, the electrical transmission oil pump can also be replaced in the event of a fault.

Automatic transmission
Installation location of electrical transmission oil pump GA8P75HZ transmission

  1. Intake pipe
  2. Bolting points of the electrical transmission oil pump
  3. Electrical connection

Oil cooling

Automatic transmission
Engine oil cooling GA8P75HZ transmission

  1. Transmission oil cooler
  2. Electric motor
  3. Connection of transmission oil lines (for cooling the electrical machine)
  4. Automatic transmission
  5. Connection of transmission oil lines (for cooling the automatic transmission)
  6. Transmission oil thermostat

There is an additional transmission oil cooler in front of the coolant radiator. With the aid of a thermostat, the oil circuit is directed through the transmission oil cooler when corresponding transmission oil temperatures are reached.

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