GF27.55-P-2003AHW Transmission Oil Cooling With Transmission Oil Heat Exchanger, Function

GF27.55-P-2003AHW Transmission Oil Cooling With Transmission Oil Heat Exchanger, Function
TRANSMISSION 722.9 in MODEL 204 with ENGINE 271, 651 as of model year 2012 /YoM 11 model refinement package
TRANSMISSION 722.9 in MODEL 204 with ENGINE 274 as of model year 2013 /YoM 12

Function requirements for transmission cooling, general
^ Circuit 87 ON
^ Circuit 61 (engine running)
^ Threshold for transmission oil temperature exceeded

Transmission cooling, general
To keep the operating temperature of the transmission constant in a temperature range to match the respective operating state, the transmission oil cooling is regulated as required.
The transmission oil temperature can be lowered through transmission oil cooling and help prevent damage to the transmission due to overheating.

Transmission oil heat exchanger
The transmission oil heat exchanger is designed as a plate-type oil cooler. Its operating principle means it can be kept small and provide high efficiency when cooling the automatic transmission fluid.
The transmission oil heat exchanger is located on the front axle carrier.

Function sequence for transmission oil cooling
The function sequence is subdivided into the following steps:
^ Function sequence for transmission oil preheating
^ Function sequence for transmission oil cooling
^ Coolant feed control, function sequence (with engine 651)

Function sequence for transmission oil preheating
At a transmission oil temperature of <80 °C (cold starting phase) the transmission oil is additionally heated as from a coolant temperature of >57°C through the transmission oil heat exchanger, to ensure that the ideal operating temperature for the automatic transmission fluid is reached as quickly as possible.
Transmission oil preheating continues until the automatic transmission fluid has reached the coolant temperature. The duration of the transmission oil preheating is also dependent on the load request from the driver, the active ancillary assemblies, the shift operations and the ambient temperature.

Function sequence for transmission oil cooling
The automatic transmission fluid is pumped by the transmission oil pump (primary pump) from the transmission to the transmission oil heat exchanger. The transmission oil heat exchanger forms the interface between the automatic transmission fluid and the coolant circuit. The waste heat of the automatic transmission fluid is absorbed by the coolant within the transmission oil heat exchanger.
The automatic transmission fluid flows back to the transmission from the transmission oil heat exchanger.

Coolant feed control, function sequence (with engine 651)
The actuation of the heat exchanger shutoff valve (Y58/13) is demand-controlled to match the automatic transmission fluid temperature. The transmission oil temperature is recorded by the transmission oil temperature sensor (Y3/8s2) and sent by the fully integrated transmission control unit (Y3/8n4) over the drive train CAN (CAN C) to the CDI control unit (N3/9). The CDI control unit compares the input signals against a threshold value filed in a characteristics map and then actuates the heat exchanger shutoff valve to match the evaluated input signal.
With the thermostat closed and the heat exchanger shutoff valve closed, the feed to the transmission oil heat exchanger is interrupted. When the thermostat is operating, the transmission cooler is supplied with cold coolant from the radiator.





View of transmission oil heat exchanger

63 Transmission oil heat exchanger

B Automatic transmission fluid feed to transmission oil heat exchanger
C Return line for automatic transmission fluid from transmission oil heat exchanger
E Coolant feed to transmission oil heat exchanger
F Return line to coolant circuit





View of heat exchanger shutoff valve (with engine 651)

1 Electrical connector

Y58/13 Heat exchanger shutoff valve

A Feed from engine oil cooler
B Return line to coolant circuit
C Feed to transmission oil heat exchanger

The heat exchanger shutoff valve is an electromagnetically actuated 3-way valve.