PWM fuel pump

[rauscher at icst.com]

Dave wrote:

> All of the FI systems I've looked at so far use a fuel pressure
>regulator referenced to manifold pressure.  The regulator normally
>bypasses excess fuel back to the main tank or surge tank.
>
> Some newer cars use a resistor switched into the fuel pump power >wire
>to adjust fuel pressure for hot start.
>
>Some newer cars use deadhead or "returnless" fuel rails.
>
>
> On an add-on EFI conversion, running a fuel return line back to the
>tank is a hassle, at least if you're paranoid like I am.  What >problems
>would be involved in controlling an in-tank pump by pulsewidth
>modulation, to keep the fuel rail pressure constant and to not have >to run a
return line?
                                                  
There are some here who are now working on a PWM fuel pump system.
I've provided a PWM controller that takes an analog input to
control the duty cycle of a PM DC motor.

I'm now working on a feedback control system to close the 'loop',
and maintain a consistent fuel pressure.

But, I think that you will still need a return line of some sort
in order to bleed vapors out of the system. Any vapors or air
bubbles will cause hesitation and possibly stalling. A carb vents
vapors and air bubbles to the atmosphere. Don't have that luxury
with a 'closed' EFI system.

Even the lowly GM TBI has several bleeds in it to purge vapors out
and back to the tank.

A possible better use of the PWM system will be to provide a rising
rate fuel pressure. This will allow the pump to relax at idle, and
to run harder as required by the right foot.


Just my thoughts (IMHO)...

BobR

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