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

ENGINE 642.8 in MODEL 166 up to model year 2016 

Function requirements for thermal management, general points 

• Circuit 87 (Engine management ON)
• Engine runs

Thermal management, general 

The thermal management as controlled by the CDI control unit (N3/9) regulates the coolant temperature, the exhaust temperature and the fuel pressure of the engine. The following advantages arise from this:

• Rapid reaching of the optimal operating temperature
• Reduction of the exhaust emissions
• Fuel savings (up to around 4%)
• Improved heating comfort
• Component protection for engine high load

The controlling of the thermal management is dependent on the following sensors and signals:

• Engine oil temperature sensor (B1)
• Left hot film mass air flow sensor (B26), engine load
• Left intake air temperature sensor (B2/6b1)
• Right hot film mass air flow sensor (B27), engine load
• Right intake air temperature sensor (B2/7b1)
• Boost pressure sensor (B51), 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))
• Differential pressure sensor DPF for OBD (B28/16) (with code U42 (BlueTEC (SCR) diesel exhaust treatment) and code 494 (USA version)
• Accelerator pedal sensor (B37), accelerator pedal actuation (how quickly and how far → vehicle type quiet or sporty)
• Fuel temperature sensor (B50)
• Crankshaft Hall sensor (B70), engine rpm
• Temperature sensor in CDI control unit
• SAM control unit (N10), outside temperature via the interior CAN (CAN B), electronic ignition lock control unit (N73) and chassis CAN 1 (CAN E1)
• Automatic air conditioning control and operating unit (N22/7), status of the A/C via the interior CAN, electronic ignition lock control unit and chassis CAN 1
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN 1
• Fully integrated transmission control controller unit (Y3/8), gear range over drive train CAN (CAN C)

Function sequence for thermal management 

The thermal management is described in the following points:

• 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 fuel tank protection 
• Function sequence for fan control 
• Function sequence for radiator shutters 
• Function sequence for overheating protection 

Function sequence for post-start phase 

In the post start phase, the coolant circulation can be interrupted by switching off the coolant pump with the aid of a coolant pump switchover valve (Y133).

The coolant pump switchover valve is actuated in the process by a switching output stage in the CDI control unit and controls a bypass in the coolant pump by way of a 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 300 s if the following conditions are fulfilled:

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

If the conditions for shutoff of the coolant pump are no longer fulfilled the maximum switching time of 300 s is reached and the CDI control unit ends actuation of the coolant pump switchover valve. The switchover valve is ventilated over the coolant pump switchover valve and the bypass in the coolant pump is closed again. The coolant pump is therefore switched on and the coolant circulation is achieved again.

If the coolant pump was activated once, it remains active in the entire ignition sequence.

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.

Through heating the two-disk thermostat in the coolant thermostat already opens at a low coolant temperature, which leads to lowering of the coolant temperature. The opening cross-section of the two-disk thermostat is determined over the duty cycle of the electrical power and over the coolant temperature.

The coolant thermostat heating element regulates the coolant temperature within the range of approx. 87°C to 102°C. The limp-home function ensures that the two-disk thermostat is completely opened above around 102°C, irrespective of actuation.

The two-disk thermostat can take the following positions:

• Short-circuit mode position; t < 87°C; coolant flow in engine only, a flow through the passenger compartment heater is possible
• Mixed-fuel mode position; 87°C < t < 102°C; the two-disk thermostat opens, the coolant throughflow begins
• Radiator mode position; t > 102°C; the two-disk thermostat is opened, full radiator throughflow

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

• Operating temperature is reached faster
• Emissions reduced
• Improved heating comfort
• Component protection for engine high load

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 air temperature under 7°C (renewed cut-in takes place at 4°C by the SAM control 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 achieved by means of 2 preinjections from the fuel injectors (Y76) using a much greater fuel quantity, plus a retarded 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. To do this the exhaust gas recirculation actuator (Y27/9) is actuated by the CDI control unit.

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 regulation 

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

Quantity control valve regulation 

Regulation of the fuel pressure in the rail via 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 fuel tank protection 

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 fuel system high pressure pump drops below 90°C, the tank 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.:

• 0% fan motor "OFF"
• 10% fan motor "ON", minimum rpm
• 90% fan motor "ON", maximum rotational speed

A fault in the fan motor is transferred to the CDI control unit via a pulse width modulated signal (ground sampling).

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 sends the air conditioning status via the interior CAN and chassis CAN 1 to the CDI control unit including a fan request. If the CDI control unit does not receive a valid fan request from the AAC control and operating unit, the fan motor is actuated at the maximum rpm.

Delayed fan switch off 

The fan motor runs on for up to 5 min. for "ignition OFF" if the coolant temperature, the temperature of the CDI control unit or a thermal input integral calculated based on an engine load, coolant temperature, vehicle speed and outside temperature (averaged over the last 6 min.) has exceeded a prescribed threshold value.

The duty cycle of the pulse width modulated signal for delayed fan switch off is a maximum of 40%. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.

The delayed fan switch off is not broken off by "ignition ON". When starting the engine in delayed fan switch off the fan regulation for normal operation is suppressed until the delayed fan switch off is completed.

Function sequence for 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 external noise of the engine. The radiator shutters actuator (Y84) (except code 550 (Trailer hitch)) is actuated by the CDI control unit after the 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.

Further opening conditions are:

• Request for delayed fan switch off
• Request for basic ventilation of the A/C
• Charge air temperature above the threshold value
• Request to lower the coolant temperature for component protection

Function sequence for overheating protection 

Increasing the fuel pressure via the fuel system high pressure pump from 4.5 bar up to 1, 600 bar also increases the temperature of the fuel itself.

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 fuel system high pressure pump rises above 90 °C, the CDI control unit reduces the injection quantity and the fuel pressure in the rail using the pressure regulating valve.

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 the coolant temperature sensor, engine oil temperature sensor and the temperature sensor upstream of the ATL (B19/11) (exhaust gas turbocharger protection).

After evaluating the input signals, the CDI control unit regulates the fuel pressure in the rails via the quantity control valve and the pressure regulating valve, and controls the injection duration 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.

	Electrical function schematic for heat management		PE07.10-P-2712-97NAC
	Overview of system components for common rail diesel injection (CDI)		GF07.16-P-9997OGR