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

ENGINE 642.8 in MODEL 207 as of 6/1/13 

ENGINE 642.8 in MODEL 212, 218 as of model year 2014 

Function requirements for thermal management, general points 

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

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. This has the following advantages:

• Rapid reaching of the optimal operating temperature
• Reduction of the exhaust emissions
• Fuel savings
• Improved heating comfort

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

• Left hot film mass air flow sensor (B26), engine load
• Left intake air temperature sensor (B2/6b1)
• Right hot film mass air flow sensor (B2/7)
• Right intake air temperature sensor (B27b1)
• Boost pressure sensor (B51), engine load
• Coolant temperature sensor (B11/4) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
• 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)
• Fuel temperature sensor (B50)
• Crankshaft Hall sensor (B70), engine rpm
• Temperature sensor in CDI control unit
• Fully integrated transmission controller unit (Y38) (with code 427 (7-speed A/T) or code 421 (9-speed automatic transmission), gear range via the drive train CAN (CAN C))
• Front SAM control unit with fuse and relay module (N10/1), outside temperature via chassis CAN 1 (CAN E1)
• Automatic air conditioning control and operating unit (N22/7), outside temperature and air conditioning system status via the interior CAN (CAN B) and chassis CAN 1
• Electronic Stability Program control unit (N30/4) (except code 233 (DISTRONIC PLUS) or Electronic Stability Program Premium control unit (N30/7) (for code 233 (DISTRONIC PLUS), vehicle speed signal via chassis CAN 1

Function sequence for thermal management 

The thermal management system is described in the following steps:

• Function sequence for post-start phase 
• Function sequence for 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 (for model 207, 212, 218) 
• Function sequence for overheating protection 

Function sequence for post-start phase 

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). The engine is warmed up quicker and this 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 quantities are still not reached.
• No "heating" was requested by the automatic air conditioning control and operating unit.
• The engine speed or injection quantity has not exceeded its established limit value.

Function sequence for coolant thermostat 

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 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
• Reduction of emissions and improved heating comfort

Schematic diagram 

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 requirements must be met at the same time:

• 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 below 7°C (renewed cut-in takes place at 4°C via the front SAM control unit with fuse and relay module)
• Coolant temperature lies below 82°C (new cut-in occurs again at 74°C)

During maximum heating combustion, a higher exhaust temperature is generated by means of 2 preinjections by the fuel injectors (Y76), for which a significantly greater quantity of fuel is used, followed by a late main injection. This process, in combination with exhaust gas recirculation actuator (Y27/9) 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 regulation 
• 2-control concept regulation 
• Quantity control valve regulation 

Pressure regulating valve regulation 

The fuel pressure is regulated by the pressure regulating valve (Y74) during the starting procedure and for fuel heating. The quantity control valve (Y94) is controlled to open.

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 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 fuel tank protection 

Increasing the fuel pressure via the high-pressure pump from 4.5 bar up to 1600 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 internal combustion engine and air conditioning fan motor with integrated control (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 "OFF"
• 10% fan motor "ON", minimum rpm
• 90% fan motor "ON", maximum rpm

A fault in the internal combustion engine and air conditioning fan motor with integrated control is transmitted to the CDI control unit by means of a PWM signal.

If there is a malfunction in the signal line (loss of frequency) from the CDI control unit, the internal combustion engine and air conditioning fan motor with integrated control switches automatically to the maximum rotational speed (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 

If the coolant temperature or engine oil temperature (calculated from the temperature model) has exceeded the specified maximum values with "ignition OFF", the fan motor runs on for up to 5 min.

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 (for model 207, 212, 218) 

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 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 are 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, the oil temperature sensor (B1) and the temperature sensor upstream of turbocharger (B19/11) (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 units sends an appropriate message via the CAN bus to the IC.

The messages for emitting warning messages are received by the IC from CDI control unit via the chassis CAN 2 (CAN E2) are routed from the front SAM control unit with fuse and relay module, which receives the message via the chassis CAN 1 by the CDI control unit.

	Electrical function schematic for Thermal management	ENGINE 642.8 in MODEL 207 as of 6/1/13	PE07.10-P-2712-97EAJ
		ENGINE 642.8 in MODEL 212 as of model year 2014	PE07.10-P-2712-97DAM
		ENGINE 642.8 in MODEL 218 as of model year 2014	PE07.10-P-2712-97XAE
	Overview of system components for common rail diesel injection (CDI)		GF07.16-P-9997OG