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

ENGINE 651.9 in MODEL 204 (except 204.9), 204.9 up to 5/31/12, 207, 212.0 (except 212.098), 212.2 (except 212.298), 218 

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 performance map, the CDI control unit calculates the fuel quantity and rail 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 (Y74) regulation 

The rail pressure is regulated by the pressure regulating valve after each engine start. At this time the quantity control valve is 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:

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

Quantity control valve (Y94) regulation 

The rail 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 compress the fuel which the quantity control valve lets through to it as required by the current situation. The high-pressure pump therefore does not have to work as hard which reduces fuel consumption.

IMPORTANT After switching off the engine, there is a residual pressure of about 50 to 80 bar in the high-pressure control circuit. The high-pressure system may only be opened on safety grounds after successful pressure reduction 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 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 according to the load. Furthermore, the position of the throttle valve actuator (M16/6), the actuation start time of the last main injection and the 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:

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:

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. To do this, the load condition of the DPF is detected by the DPF differential pressure sensor.

The 2nd post injection further increases the exhaust temperature and the regeneration process is triggered. The soot particles in the exhaust gas are then burnt.

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

Additional function requirements for injection quantity correction 

Function sequence for injection quantity correction 

Injection quantity correction is subdivided into 3 subareas:

Zero quantity calibration 

The possible friction caused when the fuel injectors are opened and closed results in a change in injection quantity over time. This change in injection quantity can be corrected by adaptation the actuation duration (zero quantity calibration). The zero quantity calibration for engines with Delphi injection system is called "Accelerator Pilot Control" and takes place with the aid of the knock sensor for cylinders 3+4 (A16/1) and the knock sensor for cylinders 1+2 (A16/4) (model 212 up to 31.08.2013 except code (494) USA version) or with the aid of the combustion chamber pressure sensors for cylinders 1 to 4 (model 212 as of 01.09.2013 (except code (494) USA version). During normal engine operation or in deceleration mode, a pilot injection quantity is calibrated at defined intervals selectively for each cylinder. The actuation period is increased for calibration of the injection quantity until the CDI control unit receives a signal over the knock sensor for cylinders 3+4 and the knock sensor for cylinders 1+2 (model 212 up to 31.08.2013 except code (494) USA version) or over the combustion chamber pressure sensors for cylinders 1 to 4 (model 212 as of 01.09.2013 (except code (494) USA version). 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 (model 212 as of 01.09.2013) (with code (494) USA version)

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 altering 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.

Main injection quantity correction 

With this function, the main injection quantity is corrected using the oxygen sensor upstream of the catalytic converter.

Here the injection quantity is adjusted until the specified lambda value stored in the CDI control unit is reached.

The CDI control unit changes the exhaust gas recirculation rate (AGR rate) over the exhaust gas recirculation actuator (Y27/9) to prevent an increase in the emission values resulting from tolerances in the fuel injectors and the hot film mass air flow sensor. The residual oxygen content is monitored by the oxygen sensor upstream of catalytic converter (G3/2).

  Electrical function schematic for injection regulation function MODEL 204 PE07.10-P-2704-97FAE
MODEL 207 PE07.10-P-2704-97EAE
MODEL 212 PE07.10-P-2704-97DAE
MODEL 218 PE07.10-P-2704-97XAD
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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