Ref teeth and Sync Sensors

Discussion and support for MoTeC's earlier generation ECUs

Ref teeth and Sync Sensors

Postby majorcrimesracing on Thu Oct 01, 2009 5:52 am

I think I've gone through the entire documentation and every single drawing for this ECU and I can't seem to figure out how crank position is actually calculated. Is there a more technical manual on crank position sensing?

I'm running the M48 on a KTM 1 cylinder motor that poses a lot of issues, so I've got a few questions:

Are missing teeth required? At one point I read that the ref tooth is the one following the missing teeth, but in other documentation (multi-tooth) no mention of missing teeth is made. Is multi-tooth the differentiation between missing and non-missing tooth wheels?

I thought that the point of the sync pulse is to indicate when (after a gap in the teeth) is the reference tooth indicating compression stroke TDC on cylinder one.

If the teeth aren't required, is it possible for the ecu to simply count teeth from when the indicated sync pulse occurs?

How quick are the m48's calculations? We're currently running a ref with no missing teeth, either 8 or 12 positions (two motors) and I suspect this is too low a resolution for the ECU. It has compatibility with the Nissan 360 tooth optical cam sensors, so I wonder if the ecu throws out every second pulse or if it is actually capable of making calculations based on that sensor. 360 teeth per cycle at 8400 rpm is 25200 teeth per second!

Any help is greatly appreciated. We've had reliablity issues with these motors for YEARS and I'd like to solve these problems this year.

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Re: Ref teeth and Sync Sensors

Postby RossB on Thu Oct 01, 2009 9:41 am

The Ref teeth are the teeth on the crank trigger
The Sync tooth is the tooth on the cam (or distributor) that occurs once every 720 degrees
The index tooth is the Ref tooth used to calculate TDC position.
CRIP is the number of degrees of crankshaft rotation from the Index tooth to TDC.

The index tooth on a multi tooth trigger mode is the first Ref tooth (trigger edge) that occurs after the Sync tooth.

The Index tooth on a missing tooth trigger mode is the first tooth that occurs after the missing teeth following the sync tooth.

A missing tooth mode can be used without a sync sensor in which case the Index tooth is the tooth after the missing teeth. Using this mode the engine is synced for a 360 degree cycle and you will get asn injection event every 360 degrees.

Missing tooth modes can cause starting problems on a single cylinder engine because of the un-even cranking speed caused by the compression of the single cylinder. THis makes it difficult to distinguish the missing teeth from the increase in the time between the teeth occuring due to the slowing down of the engine when it comes up to the compression point.

You would probably be best to use multi tooth trigger with 12 teeth and a single sync tooth.

What sort of problems are you having with this setup?
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Re: Ref teeth and Sync Sensors

Postby majorcrimesracing on Fri Oct 02, 2009 7:22 am

So let me get this straight:

If we have 12 teeth on the sensor, that's one every 30 degrees. The index tooth should be (or so I read somewhere) 90 degrees BTDC (which makes CRIP 90 degrees) . In that case, the sync should occur on the compression stroke at about 115 BTDC? That sould put it between the index tooth and the one before it.

Also, during cranking, it said in the manual that the fuel during warm starts is calculated in the MAIN table at the 0 rpm sites (the leftmost column I assume). This I assume negates the fact that the trigger during startup flies around near 500 rpm, so long as the M48 knows you're cranking. Is this the same for the ignition table? Can I set the spark way retarded at the 0 rpm sites to improve starting? Or is there a way to adjust spark separately during cranking? Maybe with the clever use of an aux trim?

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Re: Ref teeth and Sync Sensors

Postby majorcrimesracing on Wed Oct 07, 2009 4:45 am


Really need some answers!


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Re: Ref teeth and Sync Sensors

Postby TunedByShaneT on Thu Oct 08, 2009 2:12 pm

You just about have the ref/sync thing sorted except the REFerence tooth (the one the CRIP is calculated from) does not have to be 90 before TDC. They want the missing teeth located there on a missing tooth wheel because this is where the speed is greatest and the acceleration is lowest giving the most reliable sensing of the missing teeth. On a multitooth mode (12 even on the crank) you can choose whichever one you want as the reference tooth by placing the sync in front of it.

For your starting issue assuming a 12 tooth wheel - try phasing the trigger wheel on the crank so that a tooth is aligned with the sensor at about 10-15 BTDC. At low RPM the ECU will trigger on the tooth edge not necessarily the table value. So having a tooth in about the right spot for cranking timing will be helpful.

So assuming you have a tooth at 45 before, 15 before, 15 after etc I would set the sync signal so that it is aligned at either 60 BTDC, 30 BTDC, TDC, or 30 ATDC etc.
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