Angle vs time ...

[Bernd Felsche]

John S. Gwynne writes:

>   In message <38BFE61A.EAA1C5B at cruzers.com>, you write:
>| > Nicholas Parker wrote:
>| > 
>| > 2.   Is it correct that the TPU can run the engine under static
>| > conditions.? Without any help from the cpu except to supply what
>| > ? coil load time, ign angle ,  pulse width, pulse start angle, &
>| > injector on delay compensation.

>| No angles.  The TPU will want those values expressed as time durations.

>That depends on which TPU code you are using. Nicholas is correct for
>the engine management TPU code on our web page. It does use
>angles... more specifically spark angle, dwell, inject pulse width, and
>either stop or stop injector angle (don't remember which). Once given
>these parameters, The TPU risk processor does the rest without the
>core CPU32 intervention.

I haven't been able to figure out why a spark angle is used. AFAIK
spark angles date back to mechanical distributors and their advance
mechanisms. That's not to say that this specific use of angle is
incorrect - if your timing base in angle, then that may be appropriate.

The spark timing is the critical condition - and oddly enough, this
is actually amenable to computer control with a constant clock
timing. The spark under static conditions is always a constant clock
offset before TDC because the _time_ to light the mixture is
constant, as is the required dwell.

Now, when you get to injection, you do have to be aware of the start
and end angles because of the camshaft imposing a mechanical
constraint - it's not generally a good idea to squirt as the valve
opens as the scavenging process during overlap might exhaust
precious fuel.  (Haven't yet figured out why squirting on a closing
valve is such a problem - valve seats maybe?)

The actual injection time is however determined by the fuel
requirements - which don't vary with crank or camshaft angle.
(Ignoring stratified charging!)

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
	http://www.perth.dialix.com.au/~bernie - Private HP
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