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

Engine 256.9 in model 213, 238, 257, 290 

up to model year 2021 

Engine 256.9 in model 222 

Function requirements, general 

IMPORTANT The ME-SFI [ME] control unit (N3/10) detects the engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Thermal management, general 

The ME-SFI [ME] control unit regulates the engine coolant temperature via the heat management.

The following advantages arise from this:

The ME-SFI [ME] control unit reads in the following signals to the control the heat management:

The ME-SFI [ME] control unit also evaluates the following variables:

Shown on high temperature circuit 

G14549100Courtesy of MERCEDES-BENZ USA

Shown on low-temperature circuits 1 and 2 

G14549101Courtesy of MERCEDES-BENZ USA

The thermal management is described in the following points:

Coolant thermostat closed-loop control 

Mechanically influenced opening and closing of the ball rotary slide in the coolant thermostat occurs through the temperature-influenced elongation or contraction of the expansion wax element in a temperature range of about 102°C to 118°C. The target temperature is about 105°C. For 118°C the ball rotary slide is fully opened.

The opening and closing of the coolant thermostat can also be electronically influenced by the actuation of the coolant thermostat heating element. This occurs fully variable and dependent on the motoric requests.

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

View of coolant thermostat closed 

G14549102Courtesy of MERCEDES-BENZ USA

Coolant thermostat closed 

The ball rotary slide (48b) of the coolant thermostat is closed if the following conditions are fulfilled:

In this position the coolant flows through the engine circuit and the heater heat exchanger and the ATL and, as required, the heater heat exchanger for the passenger compartment heater. The engine radiator is not integrated in the coolant circuit. The coolant is heated more quickly in this way.

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

View of the coolant thermostat opened 

G14549103Courtesy of MERCEDES-BENZ USA

Coolant thermostat opening (mixed-fuel mode) 

The ball rotary slide (48b) begins to open if one of the following conditions is fulfilled:

In a coolant temperature range between approx. 102°C and 118°C or depending on the energization of the coolant thermostat heating element (R48), the expanding wax element (48a) begins to expand and actuates the ball rotary slide (48b). This opens the connection to the engine radiator. The opening cross-section of the ball rotary slide (48b) is proportional to the temperature of the expanding wax element (48a) or the coolant temperature. In this way the volumetric flow rate of coolant to the engine radiator can be varied as required.

Coolant thermostat open (radiator operation) 

When a coolant temperature of approx. 118°C is reached, the ball rotary slide (48b) is fully open and the coolant can flow freely through the radiator.

Electronic regulation 

A complete opening is also possible at lower temperatures if the coolant thermostat heating element (R48) is actuated by the ME-SFI [ME] control unit depending 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.

To achieve a high specified coolant temperature (approx. 105°C), manual control is supported by additional heating of the expanding wax element (48a) as from 106°C. At 110°C, the coolant thermostat heating element (R48) is fully energized, which results in the full opening of the ball rotary slide (48b). An increased coolant temperature produces in partial-load range a favorable performance level, which works very positively on the fuel consumption.

The low coolant target temperature lies around 85°C. Here, the coolant thermostat heating element (R48) is subject to pilot control, which is adapted variably to the ambient conditions. In summer and at high outside temperatures, the coolant thermostat heating element (R48) can already be fully energized at 80°C in order to avoid critical temperature ranges. In the winter and at low outside temperatures, the coolant thermostat heating element (R48) 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.

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 engine from right 

G14549104Courtesy of MERCEDES-BENZ USA

Low-temperature circuit 1 

The integrated starter alternator and the starter-alternator control unit are connected to low-temperature circuit 1 together with the liquid-cooled charge air cooler for cooling.

The coolant in low-temperature circuit 1 is constantly circulated to prevent overheating at certain points in the circuit. To this end, the powertrain control unit regulates the low-temperature circuit circulation pump 1 via the drivetrain LIN (LIN C3) such that the requirements are met.

In low-temperature circuit 1, the flow volume is regulated via the low-temperature circuit switchover valve. The powertrain control unit actuates the low-temperature circuit switchover valve via the drivetrain LIN in a map-controlled way and such that the requirements are met.

The regulation depends on the following variables:

Low-temperature circuit 2 

The DC/DC converter control unit and the 48 V on-board electrical system battery are cooled via low-temperature circuit 2. The coolant in low-temperature circuit 2 is circulated by low-temperature circuit circulation pump 2.

The powertrain control unit regulates the low-temperature circuit circulation pump 2 via the drivetrain LIN such that the requirements are met and depending on the coolant temperature in low-temperature circuit 2. To do so, the powertrain control unit reads in the signals from the low-temperature circuit 2 temperature sensor directly.

Overheating protection 

The overheating protection protects the engine and catalytic converter against damage due to thermal overload.

In the case of an imminent thermal overload, the ME-SFI [ME] control unit initiates the following measures:

Fan control 

The powertrain control unit actuates the fan motor (M4/7) via the drivetrain LIN in an output-controlled manner between 0 and 100 %. For faulty actuation the fan motor rotates at its maximum rotational speed (fan emergency mode).

Delayed fan switch off 

After "ignition OFF", the fan motor continues to run for up to 6 min 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.

Radiator trim flaps (with code 2U1 (Radiator shutters)) 

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 powertrain control unit actuates the following actuator motors via the drivetrain LIN:

The radiator trim flaps are closed when the conditions are no longer fulfilled or the engine is off.

IMPORTANT Limp-home function:

Due to the spring preload of the actuator motors, the radiator trim flaps are opened suddenly and with an audible sound if a malfunction occurs.

IMPORTANT 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 Engine 256.9 in model 213, 238 up to model year 2021 PE07.10-P-2712-97DBA
    Engine 256.9 in model 222 PE07.10-P-2712-97SEM
    Engine 256.9 in model 257 up to model year 2021 PE07.10-P-2712-97XBB
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