Delphi Multec 3.5 Applications Manual page 103

Multec 3.5 Fuel Injector Application Manual
5.2.1.3 Alternating Simultaneous Double Fire (ASDF)
5.2.1.4 Sequential Fuel Injection (SFI)
Note
5.2.1.4.1 Make-up (Trim) Fuel Pulses
Note
Note
Delphi Energy and Chassis Systems
Injectors are pulsed in groups twice every combustion cycle, once every
crankshaft revolution (the amount of injectors in each group usually
equals 1/2 of the number of cylinders). One half the required fuel for each
combustion event is injected with each injector pulse. Compared to SFI,
ASDF has more variation in fuel delivery to the cylinder, because of
variations in when the fuel is injected relative to each cylinder event. It is
less costly; since each injector group shares an injector driver, only two
drivers are required. Also, a cam position sensor is not always required.
The injectors pulse in sequence to the engine's firing order, one time
every two crankshaft revolutions. This assures that each injector is pulsed
in the same relative position to the cylinder event and prevents the
spraying of fuel into an open intake valve. SFI does require a cam
position input to correctly pair respective injectors and cylinders. Fuel
injection is timed relative to the opening of the intake valve. This system
provides the best cylinder-to-cylinder consistency in fuel delivery.
System dynamic range is affected by the injector firing method.
When SFI is utilized, make-up fuel pulses may be added to the
commanded fuel pulse to more accurately fuel a cylinder for a given event
if sufficient time is available prior to the intake valve opening. The
benefit is better air/fuel control resulting in improved emissions.
The make-up fuel pulses are usually small in amount resulting in very low
pulse widths – increasing the performance requirements of the injector.
Software schemes using make up fuel pulses increase the durability
requirements of the injector. Normally injector cycles are directly related
to the number of engine revolutions. Make-up pulses increase the number
of injector cycles beyond this.
Software
Revision: 11/05-1 5-3