PWM injector driver

[BamaInstrument]

Any source of current flow will cause the injector (solenoid) to break more
slowly.  When a diode is added in parallel (with a resistor in series with
the diode, hopefully) it is to reduce the voltage spike generated by the
coils di/dt.  An open circuit is the quickest method to close a solenoid.
dh

----- Original Message -----
From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
To: <diy_efi at diy-efi.org>
Sent: Saturday, April 07, 2001 8:21 PM
Subject: Re: PWM injector driver


> Brian Michalk tapped away at the keyboard with:
>
> > When you guys talk about a PWM injector driver, are you referring
> > to SEFI, or just EFI?  If you are referring to EFI, then what is
> > so special about the peak and hold features?  I thought it was a
> > digital on off thing, and not an analog thing.
>
> There are two types of pulsed injectors: peak-and-hold (P&H) and
> saturation (SAT). The former are much more common; resistance is an
> indicator of the injector type; about 2 Ohms for P&H and 8 Ohms for
> SAT.
>
> The peak current in P&H arises when the injector has been "fully
> opened". A subsequent, reduced holding current is required to keep
> the injector open for the required time. Maintaining the peak
> current is likely to burn out the injector with long and/or high
> duty cycles.
>
> A SAT injector OTOH will happily operate as a "switch" with full,
> nominal battery voltage applied for the entire cycle as long as
> there's a flow of fuel.
>
> The high, peak current in a P&H when opening provides a greater
> magnetic flux for faster-acting injectors. The hold current
> maintains sufficient flux to hold the injector open against the
> closing spring - not enough to open the injector quickly.
> Rapid opening provides for more predictable injected quantities and
> better control.
>
> Which begs the question of whether anybody uses a reverse current to
> assist in closing the injector. One would probably not want to give
> it much more than a "nudge" due to the needle valve seat accelerated
> wear under excessive closing force. Hydraulic damping just before
> contact *may* cushion the impact but I've not read of that as a
> feature in the literature.
>
> I'll leave that one to the experts.
>
> --
> Bernd Felsche - Innovative Reckoning, Perth, Western Australia
> --------------------------------------------------------------------------
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