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Injection Regulation, Function - GF07.10-P-1004OLG

ENGINE 651.9 up to 2/28/13 in MODEL 166 

Function requirements for CDI injection regulation, general points 

CDI injection regulation, general 

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

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

Function sequence for CDI injection regulation 

The injection regulation is described in the following steps:

Function sequence for rail pressure regulation 

Rail pressure regulation is subdivided into the following regulation strategies:

Pressure regulating valve regulation 

The fuel pressure is regulated by the pressure regulating valve after each engine start. The quantity control valve is deenergized here 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:

IMPORTANT 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.

Quantity control valve regulation 

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

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

IMPORTANT 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. In this way the high-pressure pump is relieved and the fuel consumption reduced.

The fuel system high pressure fuel circuit is unpressurized after switching off the engine. For vehicles with code B03 (ECO start/stop function) a fuel pressure of about 250 bar is maintained in the fuel system high pressure circuit during the automatic engine stop.

Function sequence for preinjection 

The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by pre-injecting fuel up to 2 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 operating point dependent. In addition, the ambient condition and the engine temperature, the last beginning of actuation of the main injection and the on-board electrical system voltage determined by the on-board electrical system battery (G1) are taken into account. Preinjection is prevented by the CDI control unit if one of the following statuses exists:

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 prevent by the CDI control unit if one of the following conditions exist:

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 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 prevented by the CDI control unit if one of the following statuses exists:

Additional function requirements 

Injection quantity correction 

Function sequence for injection quantity correction 

Injection quantity correction is subdivided into 2 subareas:

Zero quantity calibration 

Due to friction and the associated wear during opening and closing of the fuel injectors a change in injection quantity takes place over time. This change in injection quantity can be corrected by adapting the actuation duration (zero quantity calibration). The zero quantity calibration is called "Accelerator Pilot Control" for engines with a Delphi injection system. It occurs with the aid of knock sensor 1 (A16/1) and knock sensor 2 (A16/2). During normal engine operation or in deceleration mode, a pilot injection quantity is calibrated at defined intervals selectively for each cylinder. To calibrate the injection quantity, the actuation time is increased until the CDI control unit receives a signal from knock sensors 1 and 2. This actuation duration corresponds to a defined injection quantity. The difference between the new and nominal actuation duration is used for injection quantity correction.

Main injection quantity correction 

For this function, the main injection quantity is corrected using the oxygen sensor upstream of the catalytic converter. Here the actuation time of the main injection is corrected in such a way that the lambda value calculated by the CDI control unit matches the lambda value measured by the oxygen sensor upstream of CAT. The correction values needed for this are taught in at certain operating points and stored in the CDI control unit.

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