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Thermal Management, Function - GF07.10-P-1012MRA

Engine 274.9 in model 205 (except 205.047/053/054/147/247/253) 

Engine 274.9 in model 253 (except 253.354/954) 

Function requirements for thermal management, general points 

Thermal management, general 

The coolant temperature of the engine is regulated with the thermal management controlled by the ME-SFI control unit (N3/10). The following advantages arise from this:

Thermal management controlling is dependent on the following sensors and signals:

Schematic diagram of the coolant circuit (for code M014 (Uprated engined) and code 494 (USA version)) 

G12933909Courtesy of MERCEDES-BENZ USA

Function sequence for thermal management 

The thermal management is described in the following points:

Function sequence for coolant thermostat regulation 

The mechanically influenced opening and closing of the ball rotary valve in the coolant thermostat takes place via the temperature-dependent expansion or contraction of the wax expansion element in a temperature range of approx. 102°C to 118°C. Target temperature is approx. 105°C. At 118°C the ball rotary valve is fully open.

In addition, opening and closing of the coolant thermostat heating element can be electronically influenced through actuation of the coolant thermostat heating element (R48). This occurs fully variable and dependent on the motoric requests.

The ball rotary slide in the coolant thermostat can take the following positions:

Closed 

The ball rotary slide of the coolant thermostat is closed if the following conditions are fulfilled:

Through rapid warming the engine reaches its operating temperature quicker which is favorable for fuel consumption.

View of coolant thermostat closed 

G12933910Courtesy of MERCEDES-BENZ USA

Open (mixed-fuel mode) 

The ball rotary slide begins to open if one of the following conditions is fulfilled:

Open (radiator operation)  "For exceeding of a coolant temperature of about 118°C the ball rotary slide is opened completely and the coolant can flow unheeded over the engine radiator.

View of the coolant thermostat opened 

G12933911Courtesy of MERCEDES-BENZ USA

Electronic regulation 

Complete opening can also take place at lower temperatures when the coolant thermostat heating element from the ME-SFI [ME] control unit actuated dependent on the operating conditions.

The following data are read in directly by the ME-SFI [ME] control unit:

The compressor is actuated via a ground signal. The power supply takers place over "circuit 87 M2".

Dependent on the motoric requests, a higher or a lower coolant target temperature is adjusted.

For a high coolant specified temperature (approx. 105°C) the mechanical regulation is supported by additional heating of the wax expansion element from 106°C onwards. For 110°C the heating element is fully energized, which results in the full opening of the ball rotary slide. An increased coolant temperature produces in partial-load range a favorable performance level, which works very positively on the fuel consumption.

The low coolant specified temperature lies at approx. 85°C. In doing so the heating element is subject to a pre-control, which is variably adapted to the ambient conditions. In summer, at high outside temperatures, the heating element can already be fully energized for 80°C in order to avoid critical temperature ranges. In winter and for lower outside temperatures the heating element is energized at 30 to 50 % of the maximum output.

A low coolant temperature in the wide open throttle operation has a positive effect on the engine power, since the intake air is less warmed.

Function sequence for post-start phase with electric coolant pump 

In the post-start phase the coolant circulation stopped through cutting out of the electrical coolant pump. Due to missing cooling the engine warms quicker and the exhaust emission are reduced.

The electric coolant pump is switched off for a cold start if the following conditions are fulfilled:

The electrical coolant pump switches on in response to the request "Heat". In this way the FIR is heated quickly.

If the conditions for shutoff of the electric coolant pump are no longer fulfilled, the ME-SFI [ME] control unit stops actuation of the electric coolant pump. The coolant circulation is therefore achieved again.

View of electric coolant pump 

G12933912Courtesy of MERCEDES-BENZ USA

Function sequence for cutting out of heating system (for code M014 (Uprated engined) and code 494 (USA version)) 

For a cold start and rapid heating up of the engine, the ME-SFI [ME] control unit switches off the heating system coolant flow by actuating the heating system shutoff valve (Y16/2) in the short term. If the engine or the coolant in the engine cooling circuit reaches a certain temperature, the feed flow to the heating system is freed up again.

Function sequence for overheating protection 

In a case of thermal overload the overheating protection protects the catalytic converters against engine damage and overheating damage.

The following measures are taken for overheating protection:

IMPORTANT A warning message in the instrument cluster is shown for an excessively high coolant temperature. To do this the ME-SFI [ME] control unit transmits an appropriate signal via the drive train CAN to the powertrain control unit and via the suspension FlexRay, electronic ignition lock control unit and user interface CAN on the IC.

Function sequence for fan control 

The powertrain control unit actuates the fan motor (M4/7). In doing so, the actuation takes place over the drivetrain LIN (LIN C3) and all rotational speeds between 0 and 100% can be set. For faulty actuation the fan motor rotates at its maximum rotational speed (fan emergency mode).

The Climate Control control unit transmits the status of the A/C to the interior CAN over the electronic ignition lock control unit and the chassis-FlexRay to the powertrain control unit and via the drive train CAN to the ME-SFI [ME] control unit.

Delayed fan switch off

After "ignition OFF", the fan motor continues to run for up to 6min if the coolant temperature or engine oil temperature has exceeded the specified maximum value. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.

Function sequence for radiator trim flaps (for code 5U3 (AIRPANEL)) 

The radiator trim flaps are close in order to lower the fuel consumption (thorough having a lower aerodynamic drag). This also causes reduced engine compartment cooling off and a dampening of engine external noise emissions to the outside. The radiator trim flaps are opened under the following preconditions:

The radiator trim flap actuator motor (M2/37) is actuated by the powertrain control unit via the drivetrain-LIN. The radiator trim flaps are closed when the conditions are no longer fulfilled or the engine is off.

Through the spring preload of the actuator motor, the radiator trim flaps are opened suddenly with a noticeable noise if a malfunction occurs (emergency function).

Cleaning position

Turn the key in the ignition lock to position 2 (engine not have started).

The radiator trim flaps open automatically after approx. 120 seconds.

  Electrical function schematic for heat management   PE07.10-P-2712-97FBA
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