DIY_EFI Digest             Saturday, 26 July 1997       Volume 02 : Number 250

In this issue:

	knock sensing
	RE: Ignition Controllers
	Re: knock sensing
	Knock sensors, was Re: Ignitition Controllers
	SV: Ignition Controllers
	RE: Ignition Controllers
	EEC-IV knock sensing
	Re: SV: Ignition Controllers
	MAP SENSOR
	Re: MAP SENSOR

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----------------------------------------------------------------------

From: mcosta@xxx.com
Date: Fri, 25 Jul 97 09:26:19 EST
Subject: knock sensing

     The harris semi part number is hip9010 for the knock signal processor.

------------------------------

From: Tim Drury <tim.drury@xxx.edu>
Date: Fri, 25 Jul 1997 10:28:14 -0400
Subject: RE: Ignition Controllers

>Does anyone out there have any advice as to the best method to implement
>this ? Ideally what I would like to do is advance the timing to the onset
>of knock and then retard it slightly back into the safe zone. The
>controller will be used on a fuel injected 12A turbo rotary engine.

The first thing I would do (and I already did this), is find out what a knock
sensor really is.  Here's a starting point: a knock sensor is simply an
accelerometer tuned to high frequencies.  Knocking causes the engine
block to vibrate at high frequencies.  Which frequencies?  Where in the
block is the best place to measure?  Good questions.  

As far as where, I've heard the rule of thumb is to locate it fairly centrally.
In the case of large motors with lots of pistons, sometimes 2 knock sensors
are used.

At what frequencies?  It depends on the engine, which is why I didn't include
this feature in my system.  Engines knock and resonate at different frequencies.
You can look at all the technical papers you want (and this is a good idea
to learn how knock detection works) but unless you see one for your application,
the frequencies may be a little off.

Someone mentioned the Harris knock detection chip.  I've seen this (it was years
ago) and believe it could be tuned to detect knock in a narrow band.  It probably
is nothing more than a switched-capacitor bandpass filter, but this would be a
good start.

Without previous knowledge of what frequency to tune to, you'll have to experiment.
We've tried hooking a knock sensor up to a graphic equalizer with 10 bands.  We
didn't have any luck; I believe the bands were too broad.  If cost were no object,
I would install a knock sensor, hook its output to a spectrum analyzer tuned for
narrow bands between 5kHz and 20kHz.  Then advance the timing on the motor
_very_ slowly and look for spikes to occur.  This is _probably_ knock.  Be very 
careful though, too much knock for too long and you'll blow a hole through Mr. Piston.

The cheaper method would be to install the Harris chip or a narrow bandpass filter
to the output of the accelerometer and run the same test as above without the
spectrum analyzer.  Manually tune across the band using the filter and look for
higher voltages coming out of the filter (use an envelope detector).  This method
requires more time and more knocking from the motor.

And to be honest, I really don't have a clue what frequencies knocking occurs at.
5-20kHz is just a guess.  Read some SAE papers to get an idea.

- -tim





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------------------------------

From: garfield@xxx.com (Garfield)
Date: Fri, 25 Jul 1997 15:01:48 GMT
Subject: Re: knock sensing

On Fri, 25 Jul 97 09:26:19 EST, mcosta@xxx.com wrote:

>     The harris semi part number is hip9010 for the knock signal =
processor.

Yeah, I had a look. I couldn't tell from the data sheet if this device
could be operated in a mode that didn't require the processor?

Garfield

------------------------------

From: Brian Knowles <briankk@xxx.com>
Date: Fri, 25 Jul 97 08:33:01 -0700
Subject: Knock sensors, was Re: Ignitition Controllers

On Fri, 25 Jul 1997, Bruno Marzano wroto:
>
>On Fri, 25 Jul 1997, Rob Skala wrote:
>
>[snippity-snip]
>
>> incorporate a few additional features one of which in knock control. 
>> 
>> Does anyone out there have any advice as to the best method to implement
>> this ? Ideally what I would like to do is advance the timing to the onset
>> of knock and then retard it slightly back into the safe zone. The
>> controller will be used on a fuel injected 12A turbo rotary engine.
>
>If your engine needs to be run with the ddis before you implement knock,
>you could have the controller emulate a distributor initially, and (dons
>the asbestos underwear) gradually tweak the timing so that you might be
>able to get the engine to ping. If not, you may be able to set the dizzy
>to do so. You could record the engine sounds by bolting a microphone to
>the engine somewhere (or maybe even 3 or 4, near the valves :)) to find
>the best point where to "listen" for this condition. I've read that this
>should not continue for very long, if you want the engine to survive. 
>
>The signal could then be filtered out and cleaned up to give a knock
>sensor "switch". Make sure that other egine noises do not make the sensor 
>think it's knocking when it isn't.

It's my understanding (means I don't remember where I heard it) that the 
manufactures of knock sensors make them in only 4 frequencies, and you 
make your choice of one that comes closest to working on your engine, and 
that a lot (not all) aluminum OHC and DOHC engines, 'specially those with 
chain driven cams, make so much general thrashing noise as to prevent use 
of any of the available knock sensors.  4 cylinder Alfas, for instance.

Its my further understanding that because there are only four to choose 
from, many available implementations don't catch ALL detonation, 
especially under high boost, and that an engine with factory knock 
sensing can still detonate and damage itself because of this. Buick turbo 
V6s for instance.

I guess this explains why manufacturers put knock sensors in unlikely 
places.  4 cylinder turbo-ford engines have 'em low on the side of the 
inlet manifold.  I speculate that they got a sensor of the frequency that 
comes closest, and then optimised the location of the sensor to best 
detect that frequency.

Brian

------------------------------

From: "Stefan Olsson" <stefan.olsson@xxx.se>
Date: Fri, 25 Jul 1997 21:09:38 +0200
Subject: SV: Ignition Controllers

- ----------
> Fr=E5n: Tim Drury <tim.drury@xxx.edu>
> Till: 'diy_efi@xxx.edu'
> =C4mne: RE: Ignition Controllers
> Datum:  den 25 juli 1997 16:28
>=20
> >Does anyone out there have any advice as to the best method to impleme=
nt
> >this ? Ideally what I would like to do is advance the timing to the
onset
> >of knock and then retard it slightly back into the safe zone. The
> >controller will be used on a fuel injected 12A turbo rotary engine.
>=20
> The first thing I would do (and I already did this), is find out what a
knock
> sensor really is.  Here's a starting point: a knock sensor is simply an
> accelerometer tuned to high frequencies.  Knocking causes the engine
> block to vibrate at high frequencies.  Which frequencies?  Where in the
> block is the best place to measure?  Good questions. =20
>=20
> As far as where, I've heard the rule of thumb is to locate it fairly
centrally.
> In the case of large motors with lots of pistons, sometimes 2 knock
sensors
> are used.
>=20
> At what frequencies?  It depends on the engine, which is why I didn't
include
> this feature in my system.  Engines knock and resonate at different
frequencies.
> You can look at all the technical papers you want (and this is a good
idea
> to learn how knock detection works) but unless you see one for your
application,
> the frequencies may be a little off.
>=20
> Someone mentioned the Harris knock detection chip.  I've seen this (it
was years
> ago) and believe it could be tuned to detect knock in a narrow band.  I=
t
probably
> is nothing more than a switched-capacitor bandpass filter, but this wou=
ld
be a
> good start.
>=20
> Without previous knowledge of what frequency to tune to, you'll have to
experiment.
> We've tried hooking a knock sensor up to a graphic equalizer with 10
bands.  We
> didn't have any luck; I believe the bands were too broad.  If cost were
no object,
> I would install a knock sensor, hook its output to a spectrum analyzer
tuned for
> narrow bands between 5kHz and 20kHz.  Then advance the timing on the
motor
> _very_ slowly and look for spikes to occur.  This is _probably_ knock.=20
Be very=20
> careful though, too much knock for too long and you'll blow a hole
through Mr. Piston.
>=20
> The cheaper method would be to install the Harris chip or a narrow
bandpass filter
> to the output of the accelerometer and run the same test as above witho=
ut
the
> spectrum analyzer.  Manually tune across the band using the filter and
look for
> higher voltages coming out of the filter (use an envelope detector).=20
This method
> requires more time and more knocking from the motor.
>=20
> And to be honest, I really don't have a clue what frequencies knocking
occurs at.
> 5-20kHz is just a guess.  Read some SAE papers to get an idea.
>=20
> -tim
>=20

Have any one seen the instrument that Link is offering ? Its called
Knocklink.
Its made so You can tune it to hear pinging from different engines and it=
s
cheap to ($100,)


Stefan

------------------------------

From: <donleycott@xxx.COM>
Date: 25 Jul 1997 18:12:23 EDT
Subject: RE: Ignition Controllers

.ddn coulomb.eng.ohio-state.edu(diy_efi)
The shop manual for my Ford identifies the frequency of the knock sensor,
I would expect many of them do.

Pat
PDONLEYCOTT @xxx.COM

------------------------------

From: James Weiler <james@xxx.ca>
Date: Fri, 25 Jul 1997 17:05:10 -0700 (PDT)
Subject: EEC-IV knock sensing

The probst book on EEC-IV has a refrence in the back for a place that 
sells a knock sensing/retard device for any EEC-IV engine.  I forget the 
name of the place but I was wondering if anybody else has anything like it.

cheers
jw

------------------------------

From: James Weiler <james@xxx.ca>
Date: Fri, 25 Jul 1997 17:01:58 -0700 (PDT)
Subject: Re: SV: Ignition Controllers

On Fri, 25 Jul 1997, Stefan Olsson wrote:

> Have any one seen the instrument that Link is offering ? Its called
> Knocklink.
> Its made so You can tune it to hear pinging from different engines and its
> cheap to ($100,)

wow tell us more!  Got a 1-800 number ?
thanks
jw

------------------------------

From: clsnyde@xxx.net (Clare Snyder)
Date: Sat, 26 Jul 1997 00:18:07 GMT
Subject: MAP SENSOR

Just looking for some clarificarion:

Is MAP sensor output a linear analog signal? In other words, is it a
variable DC output voltage proportionate to manifold pressure? Something
like supply voltage (5VDC +/-) at atmospheric, and 1.0 +/- at full manifold
vacuum ( closed throttle decel?)or is it a frequency type signal?

Mabee there are both kinds?

------------------------------

From: Seth <n9540517@xxx.edu>
Date: Fri, 25 Jul 1997 21:00:17 -0700 (PDT)
Subject: Re: MAP SENSOR

On Sat, 26 Jul 1997, Clare Snyder wrote:

> 
> Just looking for some clarificarion:
> 
> Is MAP sensor output a linear analog signal? In other words, is it a
> variable DC output voltage proportionate to manifold pressure? Something
> like supply voltage (5VDC +/-) at atmospheric, and 1.0 +/- at full manifold
> vacuum ( closed throttle decel?)or is it a frequency type signal?
> 
> Mabee there are both kinds?
> 
> 
> 
The MAP sensor that I purchased, the motorola MPX4250AP, is absolute 
pressure withoutput 0-5 volts at pressures 20 to 250 kpa, or ~ 0-2.5 bar.
Similar sensors can be ordered form motorola, but if I seem to remember 
the resolution isnt much better than the MXP 4250AP. 

Seth Allen

------------------------------

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