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

ENGINE 651.9 as of 3/1/13 in MODEL 166 up to model year 2016 

Function requirements for thermal management, general points 

• Circuit 87M ON (Engine management ON) 
• Engine runs 

Thermal management, general 

The thermal management as controlled by the CDI control unit (N3/9) regulates the engine's coolant temperature, exhaust temperature and the fuel pressure. This has the following advantages:

• Rapid reaching of the optimal operating temperature
• Reduction of the exhaust emissions
• Fuel saving (up to about 4%)
• Improved heating comfort

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

• Hot film MAF sensor (B25), engine load
• Intake air temperature sensor (B2/5b1)
• Boost pressure sensor (B51), engine load
• Low-pressure turbocharger boost pressure sensor (B5/4), engine load
• Coolant temperature sensor (B11/4)
• Charge air temperature sensor (B17/8)
• Temperature sensor upstream of diesel particulate filter (B19/9) (with code 474 (Particulate filter))
• DPF differential pressure sensor (B28/8) (with code 474 (Particulate filter))
• Accelerator pedal sensor (B37), accelerator pedal actuation (how quickly and how far → vehicle type quiet or sporty)
• Coolant pump temperature sensor (B107) (with code 494 (USA version) ((as of 01.09.2013)
• Automatic air conditioning control and operating unit (N22/7), outside temperature via the interior CAN (CAN B) to the electronic ignition lock control unit (N73) and via chassis CAN 1 (CAN E1)
• Automatic air conditioning control and operating unit, status of the A/C via the interior CAN to electronic ignition lock control unit and via chassis CAN 1
• Crankshaft Hall sensor (B70), engine rpm
• Fuel temperature sensor (B50)
• Temperature sensor in CDI control unit
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN 1
• Fully integrated transmission control unit (Y3/8n4), gear range via drive train CAN (CAN C)

Function sequence for thermal management 

The thermal management system is described in the following steps:

• Function sequence for post-start phase 
• Function sequence for heating the coolant thermostat 
• Function sequence for maximum heating combustion 
• Function sequence for fuel preheating system 
• Function sequence for tank protection 
• Function sequence for fan control 
• Function sequence for radiator shutters 
• Function sequence for overheating protection 
• Function sequence for oil cooling system 

Function sequence for post-start phase 

In the post-start phase, the following measures are employed to warm up the engine rapidly, thereby reducing exhaust emissions:

• Interruption of coolant circulation by switching off the coolant pump using the coolant pump switchover valve (Y133)
• Interruption of piston cooling by cutting off the engine oil supply to the oil spray nozzles by means of the oil spray nozzle shutoff valve (Y131)

The coolant pump switchover valve is actuated in the process by an output stage switching to the ground connection in the CDI control unit and controls a bypass in the coolant pump using vacuum. The engine is warmed up quicker in the process and the exhaust emissions are reduced.

The coolant pump is switched off for a cold start for a maximum of 500 s if the following conditions are fulfilled:

• The limits stored in the CDI control unit for the intake air and coolant temperature as well as for the injected total fuel quantity are still not reached.
• The engine speed or injection quantity has not exceeded its established limit value
• No "heating" was requested by the automatic air conditioning control and operating unit.

If the conditions for shutoff of the coolant pump are no longer fulfilled the maximum switching time of 500 s is reached and the CDI control unit ends actuation of the coolant pump switchover valve.

The switchover valve is ventilated over the ventilation connection and the bypass in the coolant pump is closed again. Therefore the coolant pump is switched on and the coolant circulation is re-established.

At high engine oil temperatures, activation of the oil spray nozzles can be interrupted depending on the engine speed.

The oil spray nozzles are switched off in the post-start phase if one of the following conditions is met:

• Engine oil temperature > -10°C
• The max. shutoff time (depending on the engine performance, intake air and engine oil temperature) is not yet reached
• The engine speed or injection quantity has not reached an established limit value

Function sequence for heating the coolant thermostat 

The CDI control unit actuates the coolant thermostat heating element (R48) (except code (494) USA version with a ground signal dependent on the operating conditions (dependent on the characteristics map).

The power supply is over "circuit 87" from the CDI control unit.

The heating causes the two-disk thermostat in the coolant thermostat to open which leads to a lowering of the coolant temperature.

The orifice area of the two-disk thermostat is determined by the duty cycle of the electrical current. The coolant thermostat heating element (except code (494) USA version) regulates the coolant temperature within the range from approx. 55°C to 106°C.

The limp-home function ensures that the two-disk thermostat is completely opened above around 106°C, irrespective of actuation.

The two-disk thermostat can take the following positions:

• Short-circuit mode position; t < 55°C; coolant flow in engine only, flow through the passenger compartment heater is possible
• Mixed-fuel mode position; 55°C < t < 106°C; the coolant thermostat opens, radiator throughflow begins
• Radiator operation position; t > 106°C; the coolant thermostat is opened, full radiator throughflow

The following benefits result from regulating the coolant temperature of the engine:

• Operating temperature is reached faster
• Emissions reduced
• Improved heating comfort

Schematic diagram 

Courtesy of MERCEDES-BENZ USA

Function sequence for maximum heating combustion 

With the maximum heating combustion more heat is introduced into the coolant by a new combustion strategy on the engine side.

The following function conditions must be met simultaneously:

• Accelerator pedal position reported by the accelerator pedal sensor is below 80% (partial throttle)
• No regeneration mode for the diesel particulate filter (DPF) (with code 474 (Particulate filter))
• At least 90% heat output is requested by the automatic air conditioning control and operating unit
• Outside temperature below 7°C (it is actuated again at 4°C by the automatic air conditioning control and operating unit)
• Coolant temperature from coolant temperature sensor is below 82°C (renewed cut-in takes place at 74°C)

During maximum heating combustion, a higher exhaust temperature is generated by means of two preinjections by the fuel injectors (Y76) for which a significantly greater amount of fuel is used, followed by a late main injection. This process, in combination with exhaust gas recirculation (EGR), causes more heat to be transferred to the coolant inside the engine, allowing for more rapid attainment of the optimum operating temperature and improved warming of the vehicle interior.

The CDI control unit regulates, stabilizes and increases the idle speed depending on operating conditions and engine loads if the accelerator pedal is not actuated.

Function sequence for fuel preheating system 

Fuel preheating is achieved using the following regulation strategies:

• Pressure regulating valve (Y74) regulation 
• 2-control concept regulation 
• Quantity control valve (Y94) regulation 

Pressure regulating valve (Y74) regulation 

The fuel pressure is regulated by the pressure regulating valve during the starting procedure and for fuel heating. The quantity control valve is opened in a controlled manner.

Pressure regulating valve regulation takes place under one of the following conditions:

• Up to 30 s after the engine starts in idle
• Up to a fuel temperature of 20°C

Pressure regulating valve regulation causes the cold fuel to be heated rapidly by the fuel being forced at high pressure through a narrow gap in the pressure regulating valve.

2-control concept regulation 

The fuel pressure is jointly regulated in idle and in deceleration mode by the pressure regulating valve and quantity control valve.

Quantity control valve (Y94) regulation 

Fuel pressure regulation over the quantity control valve takes place from 30 s following engine start and from a fuel temperature of 20°C.

With the 2-regulator design and with regulation by the quantity control valve, the fuel is heated less than is the case with pressure regulating valve regulation.

Function sequence for tank protection 

Increasing the fuel pressure via the high-pressure pump from 4.5 bar up to 1800 bar also increases the temperature of the fuel. To protect the fuel tank from overheating, the CDI control unit reads in the fuel temperature sensor and thus monitors the temperature of the fuel delivered to the high-pressure pump.

If the temperature of the fuel delivered to the high-pressure pump rises above 90°C, the CDI control unit reduces the injection quantity and the fuel pressure using the pressure regulating valve. This causes less fuel to be compressed.

The CDI control unit causes the excess fuel to return to the fuel tank via the quantity control valve. When the temperature of the fuel delivered to the high-pressure pump drops below 90°C, the container protection function is deactivated by the CDI control unit.

Function sequence for fan control 

The CDI control unit actuates the fan motor (M4/7). The nominal fan speed is specified via a pulse width modulated signal by the CDI control unit.

The duty cycle of the pulse width modulated signal is 10 to 90%.

Here for example the following mean.:

• 10% fan motor "OFF"
• 20% fan motor "ON", minimum rotational speed
• 90% fan motor "ON", maximum rotational speed

A fault in the fan motor is sent to the CDI control unit via a PWM signal. In the case of a fault in the signal line (loss of frequency) by the CDI control unit the fan motor switches itself to the maximum rpm (fan emergency mode). The automatic air conditioning control and operating unit transfers the status of the air conditioning via the interior and chassis CAN 1 to the CDI control unit.

Delayed fan switch off 

With "ignition OFF", the fan motor runs on for up to 5 min. if the coolant temperature or engine oil temperature (calculated from the temperature model) has exceeded the specified maximum values. The duty cycle of the pulse width modulated signal for delayed fan switch off is a maximum of 40%. If the battery voltage drops too much during this time, delayed fan switch off is stopped.

Function sequence for radiator shutters 

The radiator shutters are closed in order to lower the fuel consumption (by producing 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 (Y84) is actuated by the CDI control unit after engine start by means of a ground signal. In this way the vacuum in the vacuum unit is built up and the radiator shutters closed by means of a linkage.

The radiator shutters are opened when the coolant temperature reaches 106°C and closed again at 94°C.

Function sequence for overheating protection 

The overheating protection protects against engine damage if there is a thermal overload. At a coolant temperature above 106°C the injection quantity is reduced based on the characteristics maps stored in the CDI control unit. Reduction occurs depending on the coolant temperature and oil temperature. To do this the CDI control unit reads in signals from the coolant temperature sensor, engine oil temperature sensor (B1) and the temperature sensor upstream of the turbocharger (B19/11) (ATL protection).

After evaluating the input signals, the CDI control unit regulates the fuel pressure in the rail via the quantity control valve and the pressure regulating valve and the injection period by actuating the fuel injectors. If engine oil or coolant temperature is too high, a warning message is shown in the multifunction display (A1p13) on the instrument cluster (A1). To do this the CDI control unit sends an appropriate signal via the chassis CAN 1, the electronic ignition lock control unit and the chassis CAN 2 (CAN E2) to the IC.

Function sequence for oil cooling system 

To lower the transmission oil temperature the transmission oil is routed through the transmission oil heat exchanger which is designed as a stacked plate cooler and integrated into the coolant circuit. The design of the plates seals them circumferentially from one plate to the next; this applies to the oil side as well as the coolant side. Through actuation of the oil cooler by the CDI control unit the cooling output of the heat exchanger is reduced, in which the coolant is passed by as required at the gear oil heat exchanger.

In addition to limiting the maximum temperature, feeding warm coolant into the transmission oil heat exchanger quickly heats up the transmission oil to operating temperature minimizing friction losses.

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