Transmission oil cooling with transmission oil heat exchanger, function - GF27.55-P-2003AHO
TRANSMISSION 724.2 in MODEL 212 with ENGINE 651
Schematic diagram of coolant circuit
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
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 gear oil temperature can be lowered through the transmission oil cooling and any risk of overheating damage can be avoided.
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 gear oil.
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
- Function sequence for transmission oil circuit control
- Function sequence for coolant supply control
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 gear oil is reached as quickly as possible.
Transmission oil preheating continues until the gear oil 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 gear oil 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 gear oil and the coolant circuit. The waste heat of the gear oil is absorbed by the coolant within the transmission oil heat exchanger (plate-type oil cooler).
The gear oil flows back to the transmission from the transmission oil heat exchanger.
Function sequence for transmission oil circuit control
The supply of gear oil from the transmission to the transmission oil heat exchanger is regulated by the transmission oil thermostat. The transmission oil thermostat is screwed into the housing of the transmission bell housing and it opens or closes the feed to the transmission oil heat exchanger, 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 volumetric flow rate is routed over the transmission oil heat exchanger (large circuit), to also additionally heat or cool the gear oil.
Function sequence for coolant supply control
The transmission cooling coolant circulation pump is actuated to match demand depending on the gear oil 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). This compensates for the input signal with a threshold value filed in the characteristics map, and actuates the transmission cooling coolant circulation pump by way of the transmission cooling coolant circulation pump relay (K40/10kS) to match the evaluated input signal.
View of transmission oil heat exchanger
| Overview of system components for automatic transmission (AT) | 722.9 in model 172 | GF27.10-P-9992AHN |