Quote:
Originally Posted by Atlas1
...WTF is zero quantity adaptation anyway?...
|
The following text is from (page 61) of the BMW training document "ST810 Advanced Diesel Technology Workbook" - you can probably find the whole pdf document by Googling for st810. Basically, each injector is slightly different and the DDE has separate "adaptation" values for each injector so that it can properly inject a precise volume of fuel. There _appears_ to be a poorly designed driver circuit on the DDE board that sometimes fails a little bit and results in the adaptation value going out of range. (Or something like that.)
FYI, there are three BMW PDF training documents out there that are really cool and informative. ST810 is one, another is named "Advanced Diesel with Blue Performance", and the last is "Introduction to Diesel Technology". The "...Blue Performance" seems to subsume the other two to some degree.
----------------------------------
Fuel InjectorVolume Adjustment
Piezo-fuel injectors not only bear the hydraulic tolerances but also
information concerning the stroke characteristics of the injector.
This is a separate classification for the injector voltage calibration.
This information is necessary due to the individual voltage requirement
of each fuel injector. The fuel injector is assigned to a voltage
requirement class. This replaces the seventh digit of the numerical
combination on the injector for hydraulic adjustment.
A piezo-fuel injector therefore has only six characters for the
hydraulic adjustment (due to a more precise manufacture of the
piezo-fuel injectors) and a seventh character for the injector voltage
adjustment.
Volume Adjustment
If the digital diesel electronics detects engine speed fluctuations,
the actuation period of the fuel injectors is corrected based on
these engine speed fluctuations. The volume adjustment adapts
the injected volume of all cylinders with respect to each other.
Zero Volume Adaptation
The zero volume adaptation is a continual learning process.
This learning process is required to enable precise pre-injection for
each individual fuel injector. Accurate metering of the very low
pre-injection volume is necessary for the fulfilment of exhaust
emission regulations.
Zero volume adaptation must be carried out on a continual basis
due to the volume drift of the fuel injectors.
At each cylinder, a small amount of fuel is injected during overrun
mode. This volume continues to increase until a slight increase in
engine speed is detected by the digital diesel electronics.
The digital diesel electronic is thus able to detect when the respective
cylinder begins to work. The volume of fuel injected during
zero volume adaptation is used by the digital diesel electronics as a
value for the characteristic map of pre-injection.
Zero volume adaptation takes place alternately from one cylinder to
the next during the overrun phase at engine speeds from 1500 to
2500 rpm and with the engine at operating temperature.
Zero volume adaptation has no influence on fuel consumption as
only very small quantity of fuel (about 1mm3) is injected at one