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Old 03-24-2005, 07:36 PM   #1
Jon [in CT]
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Default Subaru Investigating Cylinder Pressure Sensors

It appears that Subaru is looking deeply into installing individual cylinder pressure sensors in its engines. Take a look at a Subaru patent application, 20050061296, which the US patent office published today. If you want to view the IMAGES, you'll need a .tiff browser plugin, like the free one at www.alternatiff.com.
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Old 03-27-2005, 10:23 PM   #2
Steppin Razor
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Well, that certainly sounds interesting. Great find, Jon. I only got about half way through the application before I couldn't take it any more, but I think at this point it's more important to understand the concept than exactly how the readings are generated, processed, and sent to the ECU.

What ramifications might this have on:
- The performance and emissions of future Subaru engines?
- The aftermarket's ability to generate effective engine management products?
- Those of us who enjoy tuning our own cars?

First of all, what exactly can combustion pressure tell a person who is trying to tune an engine? The first and most obvious answer is that detonation and/or pre-ignition should become very easy to spot, with the added advantage of knowing what cylinder(s) it's happening in. This in itself would be a massively helpful tool especially for tuning a highly modified engine for high output.

Although I can't explain how cylinder pressure data can be used by the ECU to affect the amounts of CO2 and other harmful emissions generated by an engine, this ability is mentioned in the patent application. I'm sure it's not too complicated, so hopefully some of the more knowledgeable members can chime in.

Tim
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Old 03-27-2005, 10:54 PM   #3
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Jon....I didn't read all of that, but what I did read leads me to believe that there may be mischief afoot in Subaruville's engine management house.....
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Old 03-28-2005, 12:16 AM   #4
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Subaru is behind the times. It could get all the pressure readings (including a knock sensing ability with well over twice the resolution of a microphone knock sensor), EGT readings, A/F ratio readings, and cam-timing readings through the existing spark-plugs with just an ECU change. Mass-fraction-burned profile and all burn angles can be extrapolated from the ion-current across a polarized plug-gap.

But I'm glad Subaru is working on it at least. The Ion-sensing ignition system is currently patented by Saab/GM.

Here's a PDF of just SOME of the things you can do with only your spark plug: http://www.fs.isy.liu.se/Publication...PhD_580_LE.pdf

Behiiiiind the times.

Adrian~
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Old 03-28-2005, 08:08 AM   #5
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Quote:
Originally Posted by SaabTuner
Subaru is behind the times. It could get all the pressure readings (including a knock sensing ability with well over twice the resolution of a microphone knock sensor), EGT readings, A/F ratio readings, and cam-timing readings through the existing spark-plugs with just an ECU change. Mass-fraction-burned profile and all burn angles can be extrapolated from the ion-current across a polarized plug-gap.

But I'm glad Subaru is working on it at least. The Ion-sensing ignition system is currently patented by Saab/GM.

Here's a PDF of just SOME of the things you can do with only your spark plug: http://www.fs.isy.liu.se/Publication...PhD_580_LE.pdf

Behiiiiind the times.

Adrian~
good read.

as you know, GM has some shares of subaru...and saab is getting subaru hand-me-downs. maybe the ion sensing ignition is something they can hand down to subaru?

in that publication, they did use a pressure sensor as verification, though...so maybe subaru is heading down that path.
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Old 03-28-2005, 08:29 AM   #6
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Quote:
Originally Posted by happasaiyan
good read.

as you know, GM has some shares of subaru...and saab is getting subaru hand-me-downs. maybe the ion sensing ignition is something they can hand down to subaru?

in that publication, they did use a pressure sensor as verification, though...so maybe subaru is heading down that path.
Dude, that would be AWESOME!! I've been saying they should do that for over a year now.

Now if they could just hand down the Nimonic alloy exhaust valves ... jk :P

Adrian~

edit: Going over that patent application. I'm not sure how it differentiates from existing piezeolectric pressure sensors already used for multi-cylinder pressure measurement dating as far back as the 1940's. Oh well ... haven't finished reading. Maybe it will come to me.

Last edited by SaabTuner; 03-28-2005 at 08:34 AM.
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Old 03-28-2005, 03:08 PM   #7
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Quote:
Originally Posted by SaabTuner
Subaru is behind the times. It could get all the pressure readings (including a knock sensing ability with well over twice the resolution of a microphone knock sensor), EGT readings, A/F ratio readings, and cam-timing readings through the existing spark-plugs with just an ECU change. Mass-fraction-burned profile and all burn angles can be extrapolated from the ion-current across a polarized plug-gap.

But I'm glad Subaru is working on it at least. The Ion-sensing ignition system is currently patented by Saab/GM.

Here's a PDF of just SOME of the things you can do with only your spark plug: http://www.fs.isy.liu.se/Publication...PhD_580_LE.pdf

Behiiiiind the times.

Adrian~
Yea there are cars that use that technology right now. The new M5 comes to mind. It doesn't seem cheap tho so I dont know if we will see it in the same level of sophistication.
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Old 03-28-2005, 07:55 PM   #8
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Quote:
Originally Posted by cdvma
Yea there are cars that use that technology right now. The new M5 comes to mind. It doesn't seem cheap tho so I dont know if we will see it in the same level of sophistication.
Saab has been using that technology since 1990. Heck, they patented it in 1985. Then when GM bought them out, it spread a bit. The patent may have run out since then, allowing BMW to use it, and a few others. Mostly Saab just uses it for knock, misfire, and cam-phase detection. Knock detection is the most usefull.

How it works is really wild, but strikingly simple; just apply a charge-bias to the plug when combustion is taking place, and then carefully analyze the current flow due to combustion ions. The first flame peak is ionized negative ions contacting the positive center electrode, and the second peak is caused by the actual combustion flame-wave impacting the walls of the combustion chamber, which are all, of course, connected to the negative side of your electrical system. When you look at an ion trace, you're physically seeing the number of charged particles impacting the chamber-walls. It's directly linked to the pressure in the cyllinder.

Very cool.

It's not that expensive; if you have a coil-on-plug ignition system, you just need a small change to the hardware, and a big change to the software.

Adrian~
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Old 03-30-2005, 11:18 PM   #9
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Patent applications are filed for many reasons including to block competitors from having any economical alternative and to make yearly patent quotas. It does seem somewhat strange that Subaru is doing research in an area where GM already owns a superior, or at least cheaper to implement technology.
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