Crank position sensors

[robert joseph dingli]

Hi everyone,

I'm hoping that my first semi technical post will clear a few misunderstandings
that I personally went through about two years ago.  

The computer I've made for my Daimler has been tested and will operate
from the following distributor/crank pickups :

a) neg side of coil  (as for a tacho)
b) optical pickup in dizzy
c) OEM inductive pickup in dizzy
d) hall effect pickup on crank
e) digital output inductive pickup on crank
f) analogue output inductive pickup on crank

Firstly, fuelling control is MUCH simpler than ignition control since
the user cannot normally tell if the fuelling misses a beat while
a missed ignition event is very noticable.  For any beginners, I'd
recommend toying with fuel only control initially (and prefferably
on a cheap four cylinder that you don't mind destroying at some stage).

Secondly, sequential injection only benefits over parallel injection
for idle and low load conditions where the injector duty cycle is
relatively low.  A typical high performance system will be operating
near 100% duty cycle at full load at high revs.  I have opted for
a twin bank system as a comprimise, mainly to minimise the fuel rail
pressure drops as the injectors open.  Sequential injection also
requires much more programming and hardware given that the HC11 only
has 4 OC outputs.  Sequential injection also require a half crank
speed sensor from the cams or distributor and thus another input.

For a fuel only system, it's hard to beat a tacho like coil trigger
as these can be made to be very immune to noise.  One must be careful
to fully protect the digital electronics from the 400V spikes that will
enter the ECU and to carefully lay the PCB to minimise noise problems
internally.

The optical pickup in the dizzy works well for fuelling and ignition
control.  The OEM inductive pickup in the distributor, as used in many 
Japanese systems (made by Nippondenso), uses a 24 tooth wheel spinning
in front of an inductive pickup.  With some careful grinding this wheel
can be modified to any configuration required.

The hall effect sensors I've encountered require a magnetised thingy
spinning past them and have thus been dumped as a useful choice.
Inductive pickups just require some ferrous metal to whiz past to get
them all excited.  They do tend to pickup noise and can be over
sensitive if used incorrectly but are my final choice for cars which
don't have OEM inductive dizzy distributor pickups to modify.
One important point is that the spinning disk should have the trigger
points sticking out rather than holes (which I know are easier to
machine).  This make them much more immune to noise.

Forget digital output inductive pickups as you will want to have
control over the input filtering and sensitivity of the input signal
before it enters the digital phase of the circuit.  They tend to 
be hyper sensitive to noise and minor irregularities in the toothed
disk (esp. runout).  The bigger the analogue sensor the better.  I
recommend a Bosch, Delco or similar unit as OEM sensors tend to be
much tougher than the stuff sold through convential elecrtronic 
suppliers.

Oh yes, and don't forget to through out those solid core ignition 
leads.

I hope this helps.

Since my unit is now in commercial production I can't download code
or schematics but will be very happy to answer any questions.  :-)

There are about 10 aftermarket systems available here, mostly made in
Australia with one from the US that I know of and one from New Zealand.
I'd like to find out what's available in other parts of the world.

Robert

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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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