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Thermal management, function - GF07.10-P-1012MRA

Engine 274.9 in model 205 (except 205.047/147/247), 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 [ME] control unit (N3/10). The following advantages arise from this:

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

Coolant circuit, shown schematically on M274 (175 kW) 

Function sequence for thermal management 

The thermal management is described in the following points:

Function sequence for the post-start phase (valid for M274 (175 kW)) 

In the post-start phase the coolant circulation is interrupted through cutting out of the coolant pump with the aid of the coolant pump switchover valve (Y133). To do this the coolant pump switchover valve is actuated by the ME-SFI [ME] control unit and apply a vacuum to the vacuum unit on the coolant pump. A linkage is actuated for the coolant pump which blocks off a ball rotary slide located in the coolant stream in the direction of flow and therefore the volumetric flow rate to the engine is blocked. Due to missing cooling the engine warms quicker and the exhaust emission are reduced.

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

View of coolant pump (valid for M274 (175 kW)) 

Fig 2: Identifying Coolant Pump Components
G10132465Courtesy of MERCEDES-BENZ USA

If the conditions for shutoff of the coolant pump are no longer fulfilled, the ME-SFI [ME] control unit stops actuation of the coolant pump switchover valve. The coolant pump switchover valve is ventilated over the aeration connection and the vacuum unit opens the ball rotary slide through spring support. The coolant pump is therefore switched on and the coolant circulation is achieved again.

Function sequence for post-start phase with electric coolant pump (not valid for M274 (175 kW)) 

In the post-start phase the coolant circulation has an open circuit through cutout of the electric coolant pump. Here the electric coolant pump is not actuated by the ME-SFI [ME] control unit. 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:

Through the request "Heating" the electric coolant pump and the shutoff valve electric coolant pump (Y67/3) is switched on. The shutoff valve for the electric coolant pump is actuated by the ME-SFI [ME] control unit. The shutoff valve for the electric coolant pump is actuated a vacuum unit over vacuum, which adjusts a valve and therefore the coolant circulation is controlled in the cooling circuit. In this way the FIR is heated quickly.

View of electric coolant pump (Not valid for M274 (175 kW)) 

Fig 3: Locating Electric Coolant Pump Inlet And Outlet
G10132466Courtesy of MERCEDES-BENZ USA

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 electric coolant pump is therefore switched on and the coolant circulation is achieved again. The coolant circulation the electric coolant pump is regulated by the shutoff valve.

Function sequence for coolant thermostat regulation 

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 98°C up to 108°C.

Additionally opening and closing of the coolant thermostat is performed variably and dependent on the motor requests dependent on actuation of the coolant thermostat heating element (R48).

To do this the ME-SFI [ME] control unit actuates coolant thermostat heating element by means of a ground signal dependent on the operating conditions. The power supply takers place over "circuit 87 M2".

The coolant thermostat can take on the following positions:

Closed 

The ball rotary slide 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 as required. 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 and emissions.

Open (mixed-fuel mode) 

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

In a temperature range of the coolant of about 98°C to 108°C or according to the flowing through of the coolant thermostat heating element the expanding wax element begins to expand and actuates the ball rotary slide. This releases the connection tr the engine radiator. The opening cross-section of the ball rotary slide is adapted according to the temperature of the expanding wax element or the coolant temperature. In this way the volumetric flow rate of coolant to the engine radiator can be varied.

View of coolant thermostat closed 

Fig 4: Closed Coolant Thermostat Flow Diagram
G10132467Courtesy of MERCEDES-BENZ USA

Open (radiator operation) 

For exceeding of a coolant temperature of about 108°C the ball rotary slide is opened completely and the coolant can flow unheeded over the engine radiator.

For a coolant temperature > 85°C and an open circuit request the ball rotary slide also opens through heating of the expanding wax element fully.

The coolant temperature is lowered under the following conditions to prevent a critical temperature range arising:

The coolant temperature is lowered dependent on the outside temperature through heating of the expanding wax element (for an outside temperature < 12°C to about 90°C and for an outside temperature > 12°C to about 80°C).

View of the coolant thermostat opened 

Fig 5: Opened Coolant Thermostat Flow Diagram
G10132468Courtesy of MERCEDES-BENZ USA

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 is shown in the instrument cluster for an excessively high coolant temperature. To do this the CDI control unit transmits a corresponding signal via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and via the user interface CAN to the instrument cluster.

The powertrain control unit reads in the temperature in the low-temperature circuit over the low-temperature circuit temperature sensor (B10/13) (valid for M274.9 with 155 kW or 175 kW). In this way the coolant temperature in the low-temperature circuit is detected.

Function sequence for fan control 

The powertrain control unit actuates the fan motor (M4/7). Here the actuation occurs via the drivetrain-LIN (LIN C3) and all rotational speeds between 0 and 100% can be adjusted. For faulty actuation the fan motor rotates at its maximum rotational speed (fan emergency mode).

The climate control unit transmits the status of the A/C to the interior CAN over the electronic ignition lock control unit, 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 

The fan motor runs on for "ignition OFF" for up to 6 minutes if the coolant temperature or the engine oil temperature has exceeded the prescribed maximum values. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.

Function sequence for radiator shutters (for code 2U1 (Radiator shutters)) 

The radiator shutters is closed 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 shutters actuator motor (M87) is actuated by the powertrain control unit after engine start via the drivetrain-LIN. Upon reaching a coolant temperature of 111°C the radiator shutters is opened and closed again at 99°C.

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.

IMPORTANT There is a Hall sensor for opening angle measurement integrated in the radiator trim flap actuator motor. Thus a malfunction can be diagnosed at any time.

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

IMPORTANT Cleaning position

Turn the key in the ignition lock to position 2 (engine not have started). The radiator trim flap opens itself after about 120 s.

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