The diagram shows the two-module system. On the single-module system the IDM is integrated in the PCM.
1 Pilot injection and main injection fuel quantity
2 IDM
3 PCM
4 Fuel injector
With the common rail injection system, a small injected fuel quantity for pilot injection is injected into the combustion chamber prior to the main injection. In this system the PCM calculates the overall injected fuel quantity and the injection timing.
Before the signal for the overall injected fuel quantity and the injection timing is sent to the IDM, the PCM determines the angle for the start of the pilot injection and the main injection as well as the injected fuel quantity for pilot injection.
Injection signal to the solenoid valve of the fuel injector
a Interval between start of pilot injection and start of main injection
b Interval between pilot injection and main injection
c Injected fuel quantity for pilot injection
d Injected fuel quantity for main injection
1 Pilot injection timing (degrees crank angle)
2 Main injection timing (degrees crank angle)
Example
โข Overall injected fuel quantity 40 mm3,
โข of which injected fuel quantity for pilot injection = 2 mm3.
โข Start of main injection = 8 degrees before TDC,
โข Start of pilot injection = + 9 degrees before TDC.
The IDM, based on the stipulations of the PCM, generates the following signals for the fuel injector:
โข Injected fuel quantity for main injection = 38 mm3,
โข Injected fuel quantity for pilot injection = 2 mm3,
โข Main injection timing = 12 degrees before TDC,
โข Pilot injection timing = 17 degrees before TDC.
The timing of the pilot injection and main injection is designed here to be variable. This means that the timing and the duration of the pilot injection and main injection can be optimally adapted to the operating conditions.