MAP Questions...

[robert dingli]

> > Jim, have you considered a simple speed throttle system using throttle 
> > position
> > and rpm to index a map? 
> 
>   Robert,
>      The problem I have requires that it operate over very wide range of 
> temperatures and altitudes. A TPS system would be very simple and I could do it 
> with the scrap parts on my desk but it wouldn't be the best I could make it. 
> Also I would have to have a butload of calibration curves for it based on the 
> temp and altitude. I can check the temp no problem, I've got a small integrated 
> 0¡C to 100¡C National Semiconductor temp sensor. But I need some type of 
> correction for the pressure. 

Jim, you can simply map the injection duration per cycle as a function of rpm
and throttle position and then correct for ambient air temperature and pressure.
The air pressure would be measured in free air or, if you used some sort of ram 
air intake, inside the air box before the throttle.

>      This is what I know. The MAP sensor will give me a reading on the manifold 
> vacume. I can correct this with a temp sensor to give the amount of air that the
> engine desires. I was wondering how I would go about using this sensor to 
> determine how much air I need. 
>      Is a MAP system just mapped out? Like an array. Where temp is one 
> demension, Vac is the second dimesnion and the array value is the fuel. Take 
> this data for several points on the RPM curve then when the engine is running 
> have it integrate the curve data and find the appropriate value for fuel? With 
> an O2 sensor taking up the rear with corrections with are stored in some sort of
> temp table?    Just a thought----- After all I'm using a PC (286 w/ 287) So I 
> have all the horse power I need.

As above, you can simply map the injection duration as a function of rpm and
MAP value, and then correct for air temperature using the ideal gas law or
whatever is most appropriate for your intake system.  Thus, rpm is one 
dimension, MAP the other, and the array value the fuel injected per revolution
(or cycle).  Initially, you could meter the fuel as a linear function of MAP
only.  From my experiences with single cylinder engines, there generally
isn't a suitable MAP value to work from.  You could try mechanically filtering
the MAP value with a restriction in the pressure line.

I doubt your B&G will run well anywhere near stoiciometric, so unless you have
a wide range UEGO (Universal Exhaust Gas Oxygen) sensor, you will have to run
open loop.

A 286 may be good as communicating with a screen or other computer peripherals
but communicating with the real world is another matter.  While the processor
will have sufficient grunt, you will probably be restricted by the input and 
output systems.

regards,
Robert

-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **