[Diy_efi] Flap-type Airflow Meters

[Bernd Felsche]

On Wednesday 24 January 2007 14:21, Adam Wade wrote:
> --- "Steven P. Donegan" <steve at donegan.org> wrote:
> > I am adding an RS-232 port to the MAF interceptor so
> > folks can customize this mapping any way they wish.

> I was actually hoping for separate tables, one for the
> actual conversion numbers and one for "trimming"; that
> way you can set the device back to "zero" (same
> response as the stock flapper) without needing to
> re-load the calibration.

With the flap-type sensor, and to a lesser extent with others, the
dynamic response to a rapid change in airflow needs to be
compensated.

The flap-type sensor is "supported" against the airflow by a single
spring; and the flap has mass. The air in the system, as well as the
deliberate damping volume typically on the opposite side of the
pivot make for an "interesting" mass-spring-damper system.

The air flow itself, especially by being compressible, add other
dynamic components that have to be allowed for in a full model of
the device. Some of the contribution may be small enough not to
warrant being coded in the engine management system.

The flap dynamics of inertia and the spring response are definitely
not insignificant. If a sample device is handy and you can do a
rapid data capture, then hooking up either suction at the outlet,
or a pressure source at the inlet and "bursting" the airflow through
the meter can be used to ascertain the dynamic response curve, and
therefore the characteristic mass and spring constants of the flap
as well as a measure of the damping.

-- 
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