Voltage Comp

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Subj:   FW: pulse width correction
From:   BZUBLIN at po2.gi.com (Zublin, Bryan (SD-MS))

  RE: Injector voltage compensation

  > I have wondered about this myself.  I assume that this is done mainly
  > to handle the low voltage when the engine is not running (12V vs.  14
  > V), and during starting (< 12 V).  Also, if the alternator dies, the
  > voltage will slowly drop.

  > One could measure the change in injector flow rate at a fixed duty
  > cycle with changes in voltage to come up with a correction curve.  I
  > would guess that the "peak/hold" type of injector drivers would be less
  > sensitive to voltage changes since they regulate the current to the
  > injector, regardless of supply voltage.  Comments?

  > Bryan Zublin
  > bzublin at gi.com

    I would guess that the manufacturers would have to be ready for all
    contingencies.....  In code I have looked at, all of the regular
    saturated injectors use a voltage compensation adder table, similar to
    the idea expressed in the original append.  There is also a table that
    appears to compensate for injector nonlinearity at low pulse widths.

    In the one ECM that I have that uses peak and hold injectors, the
    voltage compensation is a multiplier factor.  The voltage compensation
    is not merely added, but multiplied by the Sync and Async pulsewidths.

    In Bryans' idea above, how would duty cycle and pulsewidth affect the
    voltage compensation?  It would seem that it would only affect the
    turn-on/turn-off times, with full-open injector flow not affected by
    voltage. Anyone with hands-on experience?

    Scot Sealander    FIScot at aol.com