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Custom 60-2 Wheel - suitable tooth dimensions?

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Hi guys,

I'm planning to machine a 60-2 trigger profile into the OD of my (cast iron) flywheel. I've modeled it so far based on a profile which generates a tooth which is 2mm high, 8.75 wide with a 6mm gap - does this sound suitable? Can anyone offer any experience as to tooth height & width to generate a strong, consistent signal for a Honeywell Hall sensor?

Cheers

Alex

The common Honeywell GT101 hall sensors don't work well with high tooth count trigger inputs and certainly they can be problematic at high engine speed with a 60 tooth input. I'd personally be inclined to use a reluctor sensor instead. I've attached MoTeC's data sheet for the GT101 sensor for interest sake too.

Attached Files

According to this document: http://www.mouser.com/ds/2/187/honeywell-sensing-speed-sensors-1gt-series-3231520-947405.pdf

You need to have a tooth height of 5.06mm, and a minimum gap of 10.16mm, with a minimum tooth width of 2.54mm.

I see Andre staged early and cut a much better light! Same trap speed (result) however.

The issue isn't so much the high tooth count, it is the missing teeth that cause the issues with the GT101 sensors. I have seen them generate an extra tooth in the gap in input captures at high speeds (6000rpm+), supposedly due to the operation of the capacitor in the circuitry. If it is just on a 60+ tooth wheel without the missing teeth, then they do not have issues.

Either use a magnetic sensor, or find an OEM supplied hall effect sensor that is used on a 60-2 crank wheel.

I will also add my 2 cents...

Cherry (now ZF) have a sensor that is very similar to the GT101, but works fine with high tooth counts, high RPM and missing teeth. Search GS1012.

Your teeth will need to be deeper/higher than 2mm for these types of hall sensors - more like 4mm minimum.

If you instead go for a VR/magnetic type sensor then be aware your teeth will need to be designed much smaller - They need to be about the same "length" as the pole piece diameter in the sensor (usually about 3mm). Also with a high tooth count missing tooth wheel designed for a VR sensor you dont want true "missing teeth", they will work better with a half depth like the picture below.

Thanks guys for the detailed info. My concern with the depth of the tooth is that I really can't make them much more than 3mm deep due to proximity to the pressure plate bolts, so perhaps a VR sensor is the way forward.

I've been successfully using a GT101 on a trigger wheel I made for vehicle speed sensor off a driveshaft, but this only has 8 teeth and obviously less rpm so I guess it's in its comfort zone.

I can easily get hold of an OEM Audi trigger sensor which is run with a factory 60-2 flywheel (different flywheel to mine of course), I'm not sure what type of sensor it is without testing it. I've attached a pic of the OEM flywheel that this sensor is design to work with. The teeth/gaps look pretty equally sized, of course I'm not sure of the depth.

Adam what is the theory behind the half sized "missing" tooth rather than a full missing tooth?

Attached Files

It floats the signal around 0 volts, rather than going to a negative value. By doing this, the signal should stay within the threshold and hysteresis values for the input, and not trigger a false signal.

Here as a cut and paste from the PCLink help file>G4+ ECU Tuning Functions > Triggers > Solving Triggering Issues >Incorrect Trigger Wheel Design.

Brilliant thanks again guys for the detailed info

Couple quick questions:

with GS1012 do you simply remove two tooth or do you need to include a raised section in the wheel as adam showed above?

can a GS1012 work as both the home trigger on cam (single tooth) as well as crank trigger sensor (36-2)?

finally with trigger wheels is the tooth completely square or is the top of the tooth radiused? radius would keep a constant air gap how ever i imagine a square OD would create a sharper edge?

with GS1012 do you simply remove two tooth or do you need to include a raised section in the wheel as adam showed above?

Yes, the "half depth missing teeth" is only relevant to VR type sensors. You want full depth gaps for hall sensors.

can a GS1012 work as both the home trigger on cam (single tooth) as well as crank trigger sensor (36-2)?

Yes, that will do it fine. Depending on which ECU you have you may need to fit a stronger external pullup on the crankl sensor. Check the data sheet against the ECU spec. The recommended pull-up varys depending on the supply voltage but it is stronger than most ecu's have internally and they get lazy with high tooth count wheels if the pull up is too weak.

finally with trigger wheels is the tooth completely square or is the top of the tooth radiused? radius would keep a constant air gap how ever i imagine a square OD would create a sharper edge?

Either will work perfectly fine, I highly doubt you would ever be able to measure the difference but I would stick to the norm and have a turned (round) OD.

Adam

appreciate the help final question is around the missing tooth and trigger location with regards to TDC.

i was told to put the missing teeth at 60 degrees before top dead centre, and there for you want the home trigger 180 crank deg later. so about 120 degrees after top dead centre.

this is all referenced to cylinder #1, i would have thought the position of trigger and home relative to the spark event is irrelevant?

all ears on the topic.

cheers

As for the position of the missing tooth gap - most modern ECU's are pretty flexible and can work with it anywhere, there are some older ECU's around that have more specific requirements such as it must be 60 or 90 deg BTDC. However even with a flexible ECU, there are still some general rules of thumb to give the best result.

1. It is best to keep the gap outside of your normal operating range of ignition advance - so say before 50 BTDC or after 20ATDC, this is becaus e in the missing tooth area the ECU gets less position/speed updates so there is potentially more error in commanded advance.

2. Some engines have very uneven cranking speed - for instance low inertia/high compression race engines. In these cases if you have the missing tooth gap pass the sensor near TDC (when the crank quickly slows down due to compression) the ECU can have trouble differentiating the gap from normal teeth. So generally for 1,2 & 4 cyl engines the best place for the missing tooth is about 90deg before or after TDC. For 6 cyl use 60deg before or after.

As for the position of the cam/home/sync tooth, again this is a bit ECU specific but there is one general rule that applies to most - Keep it well away from the missing tooth area (thats probably where the 180deg comment came from). Link ECU for example say it can be anywhere except in the gap or up to 30deg later (so you have about 300deg of freedom). Motec M*00 says it must occur 180 +/-70 deg from the gap (so you have 140deg of freedom).