Transmission oil cooling, function - GF27.55-P-2000AHO

TRANSMISSION 724.2 in MODEL 212 with ENGINE 276 

Function requirements for transmission oil cooling, general 

• Circuit 87 ON
• Internal combustion engine running and/or electrical machine (A79/1) ON
• Threshold for transmission oil temperature exceeded

Transmission oil cooling, general 

While driving, fast peak temperatures are generated on severely stressed transmission components such as, e.g. multidisk clutches and multidisk brakes, for example on lengthy ascents in conjunction with frequent shifting or at high load requirements.

These are rinsed and lubricated by gear oil.

To avoid any thermal damage to individual transmission components or even their failure or a break in the lubricating film, the gear oil has to be cooled.

On vehicles with engine 276 this is done by a transmission cooler integrated into the radiator module below the low-temperature cooler. The gear oil's waste heat is dissipated over the transmission cooler through the blowby air or the air flow generated by the cooling fan.

Function sequence for transmission oil cooling 

The function sequence is subdivided into the following steps:

• Function sequence for transmission oil circuit control 
• Function sequence for transmission oil cooling 

Function sequence for transmission oil circuit control 

The supply of gear oil from the transmission to the transmission cooler is regulated by the transmission oil thermostat. The transmission oil thermostat is screwed into the transmission bell housing, and it opens or closes the supply to the transmission cooler depending on the instantaneous transmission oil temperature (stroke start at approx. 70 °C, maximum stroke as of approx. 90 °C). When closed (cold-start phase), the gear oil is quickly brought up to operating temperature in the small circuit within the transmission. When open, the gear oil is routed over the transmission cooler (large circuit), to cool down the gear oil.

Function sequence for transmission oil cooling 

The gear oil is pumped from the transmission over a feed line to the transmission cooler when the transmission oil thermostat is open by the transmission oil pump (primary pump). The gear oil waste heat is dissipated to the blowby air through the radiator fins of the transmission cooler.

The gear oil flows from the transmission cooler over the return line and back to the transmission.