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

Engine 264.9 in model 213, 238, 257 

up to model year 2021 

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:

Crankshaft Hall sensor

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

The ME-SFI [ME] control unit reads in the electric coolant pump signals via the engine LIN (LIN C2).

G13770189Courtesy of MERCEDES-BENZ USA

The thermal management is described in the following points:

Display of coolant thermostat connections 

G13770190Courtesy of MERCEDES-BENZ USA

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. 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:

View of coolant thermostat closed 

G13770191Courtesy of MERCEDES-BENZ USA

Closed 

The coolant thermostat's annular slide valve (12) is closed when the following conditions are met:

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 

G13770192Courtesy of MERCEDES-BENZ USA

Open (mixed-fuel mode) 

The annular slide valve (12) starts to open when one of the following conditions is met:

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

In a coolant temperature range from approx. 102°C to 118°C or depending on energization of the coolant thermostat heating element (R48), the expanding wax element (13) begins to expand and actuates the annular slide valve (12). This opens the connection to the engine radiator. The orifice area of the annular slide valve (12) is proportional to the temperature of the expanding wax element (13) or the coolant temperature. In this way the volumetric flow rate of coolant to the engine radiator can be varied as required.

Open (radiator operation) 

On reaching a coolant temperature of approx. 118°C, the annular slide valve (12) is completely open, and the coolant can flow through the radiator without restriction.

Electronic regulation 

Complete opening can also occur at lower temperatures if the coolant thermostat heating element (R48) is actuated by the ME-SFI [ME] control unit depending on operating conditions.

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

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

For a high specified coolant temperature (approx. 105°C), manual regulation is supported by additional heating of the expanding wax element (13) as of 106°C. At 110°C, the coolant thermostat heating element (R48) is fully energized, which results in full opening of the rotary ball valve. 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. In this case, the coolant thermostat heating element (R48) is subject to pilot control, which is variably adapted to the ambient conditions. In the 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.

Starter-alternator cooling (with code B01 (48V technology)) 

The starter-alternator is connected, together with the transmission oil heat exchanger, for cooling to the high temperature circuit. To prevent a heat buildup in the high temperature circuit, the coolant is also circulated by the starter-alternator coolant pump.

The ME-SFI [ME] control unit actuates the starter-alternator coolant pump in a demand-dependent manner from 0 to 100 % via the engine LIN based on the following signals:

The control unit for the fully integrated transmission control electric controller unit transmits the information via the drive CAN to the ME-SFI [ME] control unit.

Low-temperature circuit 1 (charge air cooling) 

The liquid-cooled charge air cooler is connected to the low-temperature circuit 1.

The coolant in low-temperature circuit 1 is circulated to prevent overheating at specific points in the circuit. To do this, low-temperature circuit circulation pump 1 is regulated by the powertrain control unit in a demand-dependent manner via the drivetrain LIN (LIN C3).

The regulation depends on the following variables:

The powertrain control unit reads the low-temperature circuit temperature sensor signals in directly.

Low-temperature circuit 2 (with code B01 (48V technology)) 

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 low-temperature circuit circulation pump 2 in a demand-dependent manner via the drivetrain LIN depending on the coolant temperature in low-temperature circuit 2. To do this, the powertrain control unit reads the low-temperature circuit 2 temperature sensor signals in directly.

G13770193Courtesy of MERCEDES-BENZ USA

Overview of low-temperature circuit 2 component parts, shown on model 238.3 with code B01 (48V technology) 

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 upper radiator trim flap actuator motor (M2/38) and the lower radiator trim flap actuator motor (M2/39) 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:

In the event of a malfunction, the radiator trim flaps are opened abruptly with a noticeable noise through the actuator motors' spring preload.

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.

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