PWM injector driver
Bernd Felsche
bernie at innovative.iinet.net.au
Sun Apr 8 08:52:08 GMT 2001
Brian Michalk tapped away at the keyboard with:
> For regular EFI:
>
> The Bosch books I have states that the injectors fire once per
> crank revolution, therefore twice per power stroke.
> Does the injector require synchronization with the crank? It seems
> like it would be much easier to just set up at a certain frequency
> and then modulate the duty cycle.
The timing is to avoid squirting on an open valve as this usually
causes high HC emissions. Not of much importance in an off-road
application, but worth keeping in mind in a road car.
> I understand that at low RPMs, the injector might be to slow to
> open for a very short duration, and it would cause the engine to run
> rich, so at low RPMs, keep the duty cycle fixed, and vary the
> frequency. At higher RPMs, go up to a certain frequency, and then
> modulate the squirt time with duty cycle.
Some systems only squirt once every two RPM (some Digifants) with
batch firing at low engine loads. That gets around the slow
opening/closing of the injectors (1 to 1.5ms each) and the poor
control around that sort of opening time.
> So my question is: do I really need a crank signal to synchronize
> TDC with my injector firing?
Synchronize on the camshaft so that the injector closes before the
inlet valve opens.
--
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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