MAF and SD (was re: Re: New member intro)

[Steve=Ravet%Prj=Eng%PCPD=Hou at bangate.compaq.com]

tsakiris at ed8200.ped.pto.ford.com Wrote:
| 
| I'm sorry I can't elaborate in full detail. I'm working on these types of
| issues for a large company and must maintain an appropriate degree of 
| confidentiality.  I can however discuss what is already public information
| (e.g. SAE papers, ASME Journals).

Hmmmmm..... that large company wouldn't be ford, now would it?

| 
| The intake manifold is a dynamic system.  It can be analyzed as a simple 
| control volume, with inflows and outflows of air.  The air that flows out is
|not the same as the air that flows in.  The inflow is measured by the sensor.
| The outflow can be approximated from the conditions of the air inside the 
| manifold.  The difference is flows is what accounts for changes in manifold
| pressure.

Duh, that makes sense.  But it still seems like you'd have more problems with 
SD.  Simply driving to a different altitude would change the density of the 
air, and throw off the calculation.  Or would it?  Maybe I'm missing something 
wrt SD.

| 
| In the simplest of models, the dynamics can be approximated as a first-order
| lag (i.e. a differential equation for pressure can be written which is 
| first-order).  The time constant in such an equation may include a term 
| representing volumetric efficiency.

Geez, I hate differential equations :-).  I assume what you mean is that if 
you suddenly accelerate or decelerate the engine, the change in airflow won't 
be seen immediately at the MAF sensor due to the fact that the manifold takes 
some time to respond.  I can see that, but can you elaborate on how 
significant that really is?  Since manifolds are designed to have little 
restriction it would seem that their time constant would also be small, 
especially when compared to the max delta rpm you are likely to see.

Anyone else care to comment and/or straighten me out?

--steve