Product Description
Multec 3.5 Fuel Injector Application Manual
3-30
Delphi Energy and Chassis Systems
Revision: 11/05-1
3.9.2 Tailbiting
Refer to Figure 3-16. The trace for driver logic represents the commanded
signal to the injector. The trace for injector valve stroke is an example of
the actual response of the injector to this input. This trace represents the
result of commanding the injector to open before the injector has fully
closed from the previous input signal. This phenomenon is often referred
to as "tailbiting", and will occur when the injector is operated at a pulse
width just below the static (fully open) operating point of the injector.
The following are characteristics of tailbiting:
• Α
rich shift occurs at high pulse-widths approaching static flow (100%
duty cycle)
•
Flow rates in the tailbiting portion of the fuel flow curve have a large
part-to-part variation
While this does not cause any damage to the injector, it will have an
impact on fuel system performance, especially emissions. The maximum
useable pulse width can be estimated as:
Engine injection period – injector closing response time
Thus the maximum useable pulse width is a function of injection
frequency. The engine injection period is determined by the injection
scheme (see Section 5.2.1) and the engine rpm.
See Section 3.6.4
Note
: It is important to consider the impact of tailbiting when sizing the
injector flow rate for a vehicle application. It is desirable to have
approximately 5% more injector flow than is required for maximum
fueling conditions on the vehicle.