From DIY_EFI-Digest-Owner@xxx.edu Wed Dec 13 12:34:59 1995 Date: Wed, 13 Dec 1995 10:00:08 GMT From: DIY_EFI-Digest-Owner@xxx.edu Reply to: diy_efi@xxx.edu To: DIY_EFI-Digest@xxx.edu Subject: DIY_EFI Digest V0 #2 DIY_EFI Digest Wednesday, 13 December 1995 Volume 00 : Number 002 In this issue: reading the crank Re: reading the crank Re[2]: reading the crank MAP sensors See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- From: pantera@xxx.com (David Doddek) Date: Tue, 12 Dec 1995 20:51:38 -0600 (CST) Subject: reading the crank Lets take a look at a typical example of reading the crank for degrees. Say that you have a crank trigger wheel with 4 teeth. One being longer than the rest for sync reasons. The leading edge of each trigger point is 90 degrees before TDC for some cylinder (4 or 8 cyl engine). Now lets say that you want a delay of 60 degrees so that you will have 90-60=30 deg BTDC timing. Lets also assume that you have a 16 bit counter with a resolution of 1 count per microsecond. Measure the time between the leading edges of the two triggers before the desired timing event = delta t in microseconds. You know that during this time, the crank rotated 90 degrees. Relating these two quantities gives : delta t / 90 = microseconds per degree (mpd) (1) Multiply (1) by the desired delay in degrees (60): delta t (uS) --------------- * 60 deg = delay time in microseconds 90 deg So thus if you were to start timing from the instant that the trigger pulse occured, you will have an event at 30 deg BTDC. This event would then be used to turn off the coil. To get RPM from this information, we know that one revolution takes four times our delta t ,the time it took for our 90 degree crank segment. Since we have one revolution in some amount of microseconds and we want some number of revolutions in one minute, we need to convert. Our only incorrect term is time, so remember that there are 1 million microseconds in a second and 60 seconds in a minute. This gives 60,000,000 uS / Min (2) Multiply (2) by our microseconds per rev and: 60,000,000 (us) 1 rev ------------- * -------------- = RPM Min delta t * 4 (us) Of course there is more to this such as calculating when to turn on the coil and determining the sync of the crankshaft from the given triggers. Also it is up to the individual to come up with a clever way of doing the math in the simplest form. (Especially when using assembler, 60,000,000 is not a fun number). I hope that this was of help and answered some questions and I was not just babling. By the way this is the way that the Yamaha FZR 600 reads the crank, 3 short pulses and 1 long. And this is a very dynamic engine, so dont flame on only having 4 triggers per rev please. David J. Doddek |pantera@xxx.com Owner SGD Electronics & Development Engr for Caterpillar |h 309 685-7965 Formula SAE Team Sidewinder 94-95 |w 309 578-2931 89 T-bird SC, 69 Fairlane w/SGD EFI |fx 217 428-4686 74 Pantera w/Electromitive Tec-II Twin turbos and Nitros | Hey, If you are going to go fast, go REEEAAL FAST. | ------------------------------ From: ricrain@xxx.net (Ric Rainbolt) Date: Tue, 12 Dec 1995 22:44:49 -0600 Subject: Re: reading the crank >By the way this is the way that the Yamaha FZR 600 reads the crank, 3 short >pulses and 1 long. And this is a very dynamic engine, so dont flame on only >having 4 triggers per rev please. > Wow. The system I'm working on has 144 teeth. Guess I'll be *REALLY* accurate. :-) By the way, the starter ring on the flywheel is an excellent place to pick this up, no cogs, gears or wheels to add, just mill a hole for a reluctive sensor and voila! Of course, you may run into a problem if your CPU of choice can't keep up (i.e. 8051, etc). ------------------------------ From: dzorde@xxx.au Date: Wed, 13 Dec 95 14:52:09 Subject: Re[2]: reading the crank How do you know where on the crank stroke you are when all the teeth on the flywheel are the same, you can't really make one longer since the starter motor will then have a winge. Dan ______________________________ Reply Separator _________________________________ Subject: Re: reading the crank Author: diy_efi@xxx.edu at INTERNET Date: 13/12/95 2:31 PM >By the way this is the way that the Yamaha FZR 600 reads the crank, 3 short >pulses and 1 long. And this is a very dynamic engine, so dont flame on only >having 4 triggers per rev please. > Wow. The system I'm working on has 144 teeth. Guess I'll be *REALLY* accurate. :-) By the way, the starter ring on the flywheel is an excellent place to pick this up, no cogs, gears or wheels to add, just mill a hole for a reluctive sensor and voila! Of course, you may run into a problem if your CPU of choice can't keep up (i.e. 8051, etc). ------------------------------ From: MTaylorfi@xxx.com Date: Wed, 13 Dec 1995 02:15:04 -0500 Subject: MAP sensors Hey there, Was wondering if anyone tried to use MAP sensors and Bernollies equation to determine Mass Airflow. I'm thinking if one had three MAP sensors (one for ambiant air pressure, one for static pressure within a tube and one for a Pitot tube) one could figure out Mass Airflow. Has anyone done this before, please respond. See ya, Mike ------------------------------ End of DIY_EFI Digest V0 #2 *************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. 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