Transmission and Drivetrain: Description and Operation

GF35.00-P-0001CE Rear Axle Cooling, Function
MODEL 204.377
- with CODE (P98) Black Series





1 Rear axle differential
1a Rear axle differential end cover
2 Oil intake line to oil pump
3 Oil feed line to oil cooler
4 Rear axle differential oil cooler
5 Oil return line to rear axle differential
6 Oil line connecting point
M75 Rear axle differential coolant circuit oil pump
S25/1 Rear axle differential coolant circuit temperature switch
A Rear axle differential coolant circuit temperature switch electrical connector
B Rear axle differential coolant circuit oil pump electrical connector

Function requirements, general
^ Circuit 15 ON (rear axle differential coolant circuit relay (K36/3), switched on ground side)

Rear axle cooling, general
The great forces which act on the rear axle differential while the vehicle is being driven, make demand-based cooling of the rear axle oil necessary.
This prevents damage caused by overheating of the rear axle differential components.

The rear axle cooling system consists of the following subfunctions:
^ Function sequence for cooling circuit control
^ Function sequence for cooling circuit

Function sequence for cooling circuit control
The system is controlled by the following components:
- Rear axle differential coolant circuit temperature switch
- Rear axle differential coolant circuit oil pump
- Rear axle gear coolant circuit relay

The rear axle differential coolant circuit temperature switch is screwed into the bottom of the rear axle differential end cover. At an oil temperature of approx. 100 °C and higher, the bimetal contact of the rear axle differential coolant circuit temperature switch closes. The control circuit is thus closed (on the ground side), the rear axle differential coolant circuit relay picks up and closes the load-current circuit so that the rear axle differential coolant circuit oil pump is energized.
If the oil temperature drops below a threshold value (greater than 93 °C, hysteresis 5K ±2K), the bimetal contact of the rear axle differential coolant circuit temperature switch opens again and energization of the rear axle differential coolant circuit oil pump is interrupted.

Hysteresis
The hysteresis is a "hold condition" which occurs following a change in status and continues to exist within a defined framework.
In the case of temperature control by means of the rear axle differential coolant circuit temperature switch, continuous activation and deactivation (surging) of the rear axle differential coolant circuit oil pump at the temperature threshold is to be avoided

Function sequence for cooling circuit
When the rear axle differential coolant circuit oil pump is switched on, the heated rear axle oil is drawn through the oil intake pipe and fed to the rear axle differential coolant circuit transmission oil pump, and from there it is delivered to the rear axle differential oil cooler via the oil feed line.
The rear axle oil flows through the rear axle differential oil cooler where it dissipates part of its heat to the fins of the rear axle differential oil cooler.
The air flowing past the radiator fins absorbs the waste heat and carries it away.
The rear axle oil cooled in this way is fed back to the rear axle differential via the oil return line.