[Diy_efi] Speed-density vs. MAF/MAP...

[Bernd Felsche]

On Fri, Jan 31, 2003 at 09:44:37AM -0800, Klaus Allmendinger wrote:
> 1. MAF sensors would be the best way to measure mass air flow. The
> disadvantage is that MAF sensors are flow-direction insensitive
> (the output signal is essentially proportional to the full-wave
> rectified flow).

Not all the sensors. Some of the newer hot-film sensors have a
"front" sampling port that vents 90 degrees to the nominal flow
direction. Flow oscillations can still be a problem unless either
the film filters high-frequency oscillations, or the ECU
over-samples and filters based on engine speed.

> Therefore a low-pass filter (plenum) has to be inserted between
> the AC input signal (oscillating air mass in intake stream) and
> the sensor to filter out the AC component of the signal and allow
> to measure the DC component (the actual flow). Like all filters it
> creates a delay which is a problem for fast flow changes.

Indeed.


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