Transmission oil cooling with transmission oil heat exchanger, function

P20.00-2416-79

Schematic illustration of coolant circuit (shown on engine 651)

1 Coolant pump

2 Oil/water heat exchanger

3 Crankcase

4 Cylinder head

5 Coolant collector

6 Chain case housing

7 Exhaust gas recirculation cooler

8 Radiator

9 Coolant expansion reservoir

10 Vehicle heating heat exchanger

11 Transmission oil heat exchanger

12 Bypass housing

13 Washer fluid heater heat exchanger (with code (875) Heated windshield washer system)

B Filling line

E Vent line

KG Transmission oil cooling circuit

KK Cooler circuit

KS Short-circuit circuit

KW Washer fluid heater circuit (with code (875) Heated windshield washer system)

M Engine

R Engine return line

RH Vehicle heating return line

VA Exhaust gas recirculation (EGR) circuit

VB Oil-water heat exchanger circuit

VH Vehicle heating feed line

14 Check valve

15 Washer fluid heater shutoff valve (with code (875) Heated windshield washer system)

B11/4 Coolant temperature sensor

M13/5 Coolant circulation pump

M13/7 Transmission oil cooling coolant circulation pump

R48 Coolant thermostat heating element

Y27/9 Exhaust gas recirculation actuator

Function requirements for transmission oil cooling, general

 Circuit 87 ON

 Circuit 61 (engine running)

 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 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 (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 (plate-type oil cooler).

The automatic transmission fluid flows back to the transmission from the transmission oil heat exchanger.

Coolant feed control, function sequence (engine 651)

Actuation of the coolant circulation pump for transmission oil cooling is performed on an as-required basis to match the transmission 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). The CDI control unit compares the input signals against a threshold value filed in a characteristics map and then actuates the coolant circulation pump for transmission oil cooling to match the evaluated input signal.

P27.55-2120-81

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