TECH ARTICLE: how MAFs work

[trinydex]

http://www.autoshop101.com/forms/h34.pdf#search=%22karman%20vortex%20sensor%20%22

or

http://www.socalevo.net/gallery/albums/userpics/10991/mURI_temp_7aec5a48.pdf

[RhYZiN]

the article doesn't describe the mitsubishi's MAF system, just the fundamentals to a karmen vortex sensor. from what i've gathered, although it's been awhile, there are two pressure sensors behind the wedge that detect the alternating vortices. under idle/low load operation, the ecu activates another pair of sensors before the wedge to more accurately detect vortices. the MAF also integrates a barometric pressure sensor and an air temp sensor.

i think i read somewhere they were exclusively just pressure sensors. probably my mistake.

[trinydex]

and it all doesn't matter unless you can explain how it actually detects vortices and what qualifies as a vortex in the digitization.

everything else is just glitz that basically gives a calculation for estimated air flow.

[RhYZiN]

found it.
http://www.geocities.com/rhyzer149/mitsukarmanfaq.pdf



Page 3
Mitsubishi Applications
... In 1991, Mitsubishi changed to a redesigned Karman-Vortex sensor with an eight-pin connector that replaces the ultrasonic generator with a pressure sensor that measures fluctuations in air pressure directly...


also noted in the service manual diagrams is a diode instead of a phototransistor in the MAS. this doesn't mean there aren't phototransistors in the sensor though since the circuit is further connected to a tilde possibly hiding patented tech.

[RhYZiN]

true true. i just find it interesting to know what's exactly in the MAS as there's different types of Karman-Vortex sensors out there.

[trinydex]

hope someone tells us how the mitsu ones or any of them characterize vortices...

[Mike W]

Early (1G era) Karman MAFs used ultrasonics to detect the vorticies. Starting with the 2G Eclipses here they switched to a little piezo pressure sensors to detect the pressure pulses.

http://www.roadraceengineering.com/eclipsetech/2gmas/2Gmas-descriptions.jpg

http://www.roadraceengineering.com/eclipsetech/2gmas/2Gmas-ports.jpg

http://www.roadraceengineering.com/eclipsetech/2gmas/2Gmas-holethrough.jpg

http://www.roadraceengineering.com/eclipsetech/2gmas/2Gmas-pulsegeneration.jpg


http://www.roadraceengineering.com/eclipsetech/2gmas/2Gmas-piezopanel-enhanced.jpg

This was all of great interest back in 95 when they changed the design so much from the Battlestar Galactica MAF

http://www.roadraceengineering.com/eclipsetech/1gmas/1gmas-hcin.jpg


The 3G Eclipses got the more advanced vortex sensors with the round shaped sensor that the EVO uses. The RalliArt Prancer got the first hotwire current type sensor and the GS and GT 4G Eclipse has that now.

Here is a cool gif of the vorticies building and sheding as the air speed increases:

http://www.roadraceengineering.com/eclipsetech/karman.gif


With the small 1G MAF we were always concerned about exceeding the possible air speed that is was capable of reading. This led to all kinds of hacking to bypass the air flow that the measuring chamber could see. The larger 2G MAF moved that point up from around 275 hp to over 400 hp.

Mike W
(been doing this for a LONG time)

[RhYZiN]

Wow. I've been looking for this kind of info out of curiousity for forever. never came across anything like this. thanks Mike!

[EnginEar]

wow, very interesting, thanks for the info. hopefully i can solve my problem.

[ganma]

hmm....interesting...i broke some of my fin on my MAF....wonder if it will cause a problem.