Open-Loop Characterization - Delphi Multec 3.5 Applications Manual

Multec 3.5 Fuel Injector Application Manual
Note
5.2.3

Open-Loop Characterization

Delphi Energy and Chassis Systems
flow deviates significantly from the predicted linear flow through either
non-linearity or excessive variation.
• For control software that has low pulse width correction (see section
5.2.2.3), compensation can be made for the non-linearity, so the
injector population variation is the determining criteria for minimum
pulse-width. Injector to injector flow variation increases as pulse
widths decrease from the set point (2.0 ms PW.) The working flow
range calculation quantifies the 3-sigma variation vs. pulse width (see
section 3.10.2.) SAE J1832 defines the 5% variation value as the
criteria to calculate the working flow rage value. For use in the
vehicle calibration, the variation limit should be determined in
conjunction with the system calibrator. Injector to injector flow
variation will result in cylinder-to-cylinder A/F deviation. (For
example, at 14.7 A/F nominal a +/- 7 % flow variation will result in a
+/- 1 A/F variation cylinder to cylinder.)
• For control software that does not have low pulse width correction,
both the non-linearity of the injector (LFR) resulting in a mean shift,
and the part-to-part variation (WFR) resulting in cylinder-to-cylinder
A/F variation should be taken into account when determining the
minimum pulse width to use for the application.
The minimum BPW is typically a 2-byte variable referred to in software
for synchronous and asynchronous operation.
Minimum PW is expressed in terms of BPW and does not include the
injector offset term.
If the system requires operation below the minimum operating pulse-
width, the following is recommended:
• A double-fire system may switch to single-fire or asynchronous
operation.
• Deliver minimum pulse width calibration value.
Open-loop characterizations are based on fixed, predetermined engine and
fuel system characteristics. Error driven feedback loops do not exist in
open-loop characterizations; instead, characterizations are based on what
happens in an average engine and vehicle with average components during
expected operating ranges. The goals of optimum open-loop
characterization are to: attain the required air/fuel ratio with the least
amount of closed-loop correction, and to provide best driveability and
minimum emissions during warm up before closed-loop feedback is
possible. When air/fuel ratios need to be rich or lean of stoichiometric,
Software
Revision: 11/05-1 5-9