Injection regulation, function - GF07.10-P-1004OG

ENGINE 642.8 in MODEL 204, 207, 212, 218 

Function requirements for CDI injection regulation, general points 

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

CDI injection regulation, general 

The CDI control unit (N3/9) allocates the required fuel quantities to the engine.

Based on a characteristics map, the CDI control unit calculates the injection period and fuel pressure on the basis of the following sensors and signals:

• Oil temperature sensor (B1)
• Left hot film mass air flow sensor (B2/6), for the intake air mass
• Left intake air temperature sensor (B2/6b1) (model 212), left intake air temperature sensor (B2/6b1) (model 204, model 207, model 218)
• Right hot film mass air flow sensor (B2/7), for the intake air mass
• Right intake air temperature sensor (B2/7b1) (model 212), right intake air temperature sensor (model 204, 207, 218))
• Rail pressure sensor (B4/6)
• Cylinder 1 combustion chamber pressure sensor (B4/34)
• Cylinder 2 combustion chamber pressure sensor (B4/35)
• Cylinder 3 combustion chamber pressure sensor (B4/36)
• Cylinder 4 combustion chamber pressure sensor (B4/37)
• Cylinder 5 combustion chamber pressure sensor (B4/38)
• Cylinder 6 combustion chamber pressure sensor (B4/39)
• Boost pressure sensor (B5/1)
• Camshaft Hall sensor (B6/1)
• Coolant temperature sensor (B11/4) (model 204, model 207, model 212), coolant temperature sensor (B11/4) (model 218)
• Charge air temperature sensor (B17/8)
• Temperature sensor upstream of diesel particulate filter (B19/9), for regulation of the exhaust aftertreatment (with code 474 (Particulate filter))
• Temperature sensor upstream of turbocharger (B19/11)
• Pressure sensor downstream of air filter (B28/5)
• DPF differential pressure sensor (B28/8) (with code 474 (Particulate filter))
• Accelerator pedal sensor (B37), driver engine load request
• Accelerator pedal sensor, fast or slow accelerator pedal application
• Fuel temperature sensor (B50)
• Crankshaft Hall sensor (B70), engine RPM
• Oxygen sensor upstream of catalytic converter (G3/2)
• Atmospheric pressure sensor (integrated into CDI control unit), atmospheric pressure for altitude adaptation

Function sequence for CDI injection regulation 

The injection regulation is described in the following steps:

• Function sequence for rail pressure regulation 
• Function sequence for preinjection 
• Function sequence for main injection 
• Function sequence for post injection 
• Function sequence for injection quantity correction 

Function sequence for rail pressure regulation 

Rail pressure regulation is subdivided into 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 is regulated by the pressure regulating valve after each engine start. At this time the quantity control valve is de-energized and therefore fully open so that the maximum fuel quantity is delivered to the high-pressure pump.

Pressure regulating valve regulation takes place under the following conditions:

• After each engine start at idle up to a fuel temperature of 10°C (if fuel temperature is rising)
• After each engine start at idle down to a fuel temperature of 5°C (if fuel temperature is falling)

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. In extreme driving conditions, the fuel temperature can be up to 150°C.

2-control concept regulation 

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

Quantity control valve regulation 

The fuel pressure is regulated by the quantity control valve as soon as the following conditions exist:

• Fuel temperature > 10°C
• One-off rail pressure request > 310 bar (e.g. abrupt acceleration or when starting off)

The pressure regulating valve is closed in a controlled manner and thus performs a retention function.

The advantage of quantity control valve regulation is that the high-pressure pump only needs to compact the fuel which the quantity control valve lets through to the high-pressure pump as required by the current situation. The high-pressure pump therefore relieved which reduces fuel consumption.

After switching off the engine, there is a residual pressure of about 50 to 80 bar in the high-pressure control circuit. The fuel high-pressure circuit may only be opened on safety grounds after the pressure has been reduced by the CDI control unit.

Function sequence for preinjection 

The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by injecting fuel one or two times before the main injection starts to make the combustion run smoother. The start of actuation of the fuel injectors (Y76) for preinjection is calculated by the CDI control unit load-dependent. Furthermore, the position of the throttle valve actuator (M16/6), the last actuation start time of the main injection and the on-board electrical system voltage produced by the on-board electrical system battery (G1) are taken into account.

Preinjection is not initiated by the CDI control unit if one of the following statuses is present:

• Preinjection timing point exceeded
• Calculated preinjection quantity is too low.
• Detected engine speed too high
• Main injection quantity too low
• Fuel pressure too low.
• The engine is switched off

Function sequence for main injection 

The main injection is performed immediately after preinjection and generates power and torque. Main injection is controlled by the start of actuation (injection timing point) and the actuation duration (injection period).

Main injection for the fuel injectors is not initiated by the CDI control unit if one of the following statuses is present:

• Fuel temperature range exceeded
• Wide open throttle injection quantity limitation is active (engine speed > 4500 RPM)
• Fuel pressure too low.
• Engine is in the deceleration mode
• An external quantity intervention occurs, for example by the ESP®
• The engine is switched off

Function sequence for post injection 

Post injection serves to increase the exhaust temperature as well as to support the conversion of the exhaust gas components in the oxidation catalytic converter and to support diesel particulate filter (DPF) regeneration.

For this purpose, the load condition of the DPF is recorded by the differential pressure sensor (DPF). A second post injection increases the exhaust temperature and the regeneration process is triggered. The soot particles in the exhaust gas are then burnt subsequently. Post injection is not initiated by the CDI control unit if one of the following statuses is present:

• Preinjection timing point exceeded
• Detected engine speed too high
• Calculated post-injection quantity is too low.
• Main injection quantity too low
• Fuel pressure too low.
• The engine is switched off

Additional function requirements 

Injection quantity correction 

• Engine speed between 1200 RPM and 3000 RPM (deceleration mode or normal driving mode)
• Engine oil temperature >80°C
• Fuel temperature 30 to 50°C

Function sequence for injection quantity correction 

Injection quantity correction is subdivided into 2 subareas:

• Zero quantity calibration 
• Quantity mean value adaptation 

Zero quantity calibration 

The possible friction caused when the fuel injectors are opened and closed results in a change in injection quantity over runtime. This change in injection quantity can be corrected by adapting the actuation duration (zero quantity calibration).

This actuation duration corresponds to a defined injection quantity. The difference between the new and nominal actuation duration is used for injection quantity correction.

Zero quantity calibration is conducted for various prescribed injection pressures in deceleration mode. The fuel injectors are actuated one after the other in this phase using a calibration value and the respective engine speed evaluated. If the respective engine speed deviates from the stored specified value then the calibration value is adapted and stored in the CDI control unit.

Quantity mean value adaptation 

The quantity mean value adaptation is a teach-in function of the CDI control unit with the help of which the exhaust gas recirculation rate (EGR rate) is adjusted so that emission levels are not degraded by the tolerances of the fuel injectors and the hot film MAF sensor.

To do this, the CDI control unit reads in the following signals:

• Left hot film mass air flow sensor
• Right hot film mass air flow sensor
• Oxygen sensor upstream of catalytic converter

The CDI control unit alters the EGR rate via the exhaust gas recirculation actuator (Y27/9) and the throttle valve actuator. The residual oxygen content is monitored by the oxygen sensor upstream of catalytic converter.

	Electrical function schematic for injection control	ENGINE 642.8 in MODEL 204	PE07.10-P-2704-97FAH
		ENGINE 642.8 in MODEL 207	PE07.10-P-2704-97EAF
		ENGINE 642.8 in MODEL 212	PE07.10-P-2704-97DAF
		ENGINE 642.8 in MODEL 218	PE07.10-P-2704-97XAA
	Overview of system components for common rail diesel injection (CDI)		GF07.16-P-9997OG