Another injector question

[james.drysdale at utoronto.ca]

I'm far from an expert on the subject, but I can tell you the choices I made 
regarding my SAE SuperMileage EFI system:

> Right now, we are still debating MAP vs. MAF

I went with MAF because I was under the impression a MAF system had a lot more 
'play' in it than a speed/density system. That is, a MAF system is more 
adaptable to changes in your EFI hardware than a MAP system, the software 
tables of which are generated for a certain throttle size, engine displacement, 
etc. only.

Of course, a MAP system might be easier to implement and will probably give you 
more reliable airflow data due, to the relatively long response time inherent 
to MAFs.

Our smallish (42mm dia.) low-flow (3-250 kg/hr) MAF sensors were donated to us 
by Siemens Automobiltechnik in Germany. They like to sponsor teams like ours 
and have their stickers gratuitously plastered all over our vehicles.

> Right now I am leaning towards (mostly) software control, via either a
> 68 series Motorola processor or through a PC/parallel port. 

I'm using a Motorola 68HC812A4 microcontroller on a board with 128 kb of 
additional memory (which I need for the lookup tables). It's got over 40 
digital I/O ports and 8 A/D channels, which are enough to handle all of the 
sensors. There are inexpensive C compliers and freeware assemblers for this 
processor, so programming it is relatively easy. I'm driving the injector with 
a National Semiconductor LM1949 injector driver.

Sensor-wise, I'm using a shaft-mounted optical encoder to measure rpm (there 
are cheaper ways to do this, but we had an encoder sitting around) and some 
hall-effect sensors to determine crankshaft angle. Engine temp. is being 
measured with a thermocouple, and I've also got a throttle-position sensor to 
measure throttle angle and rate of change. 

I'm not worried about controlling the spark timing...I've got enough on my 
plate this year :) Next year's team can play with that.
 

james

"God help us. We're in the hands of engineers."
- from Jurassic Park
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