AFM measurement/backpressure (was Turbo speed sensor)

[Mike (Perth, WA)]

At 08:15 PM 7/03/2000 +0100, you wrote:
>Hi !
>What I tryed to say was that the AFM cant give info for the retard of
>ignition advance that the backpressure is indicating.

OK - I understand now, the backpressure affects ignition timing but the
AFM still manages to report actual air flow - over time as it were.

I suppose in those conditions a simple pressure sensor off the exhaust
before the turbo would be OK.

ie Short (cooled) piece of pipe to carefully mounted sensor.

The speed wouldn't be much of an issue for this reason. Once its installed
and calibrated then the conditions which lead to a immediate ignition
retard can be 'pre-emptive' ie. a differentiator off the pressure sensor
could initiate an interrupt for immediate retard by a set number of
degrees - or even better, the differentiator sets the interrupt pulse
width depending on rate of 'upward' change of pressure in exh before turbo.

Once this is done a few times the s/w can 'learn' the pre-emptive point
combination of AFM, engine speed, turbo estimate speed (if no turbo
speed sensor) and thereby not advance the timing by the same amount if
such a pre-emptive condition was detected - naturally the pressure sensor
provides the final OK such that when pressure drops (turbo spooled up)
and combination of AFM, speed etc then the advance can go up again.

Of course it would help heaps to have a turbo speed sensor as well which
had a short gate time - like 10mS - it could report an output from 0
to 25 for range idle to 150,000 rpm at blade... I think 100 samples per
second would be fine given the rate of change of turbine wheel (i think)
might be a little less then that...

Would this be a fair algorithisation of backpressure pressure sense for
ignition retard on changing boost condition ?


Rgds ~`:o)

Mike Massen         Trading as "Network Power Systems" and "Network Computers"
Perth, Western Australia  Ph +61 8 9444 8961  Fx +618 9264 8229 (fax -> email)
Products/Personal/Client web area at http://www.wantree.com.au/~erazmus
 (Current pics - trip to Malaysia to install equipment in jungle power site)

Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.

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