crank triggers?

[ericjon262]

is there any particular reason other then packaging why crank triggers are sized the way they are?


example:


two crank triggers, one 80mm diameter, one 140mm diameter. the notches on both wheels are the same size in degrees


I could see where going smaller might cause problems, with the sensor not being able to pick up the gaps, but is there any reason a larger trigger would be a problem? seems to me like a larger sensor would be desirable, as the larger gaps would be easier for the sensor to pick up.

[robertisaar]

for a given sensor, size will largely be determined by how many teeth there are. essentially, density will be the limiting factor.

most crank sensors, in the 60V6 world anyways, are magnetic, variable reluctance units. when teeth pass near the sensor, it makes an A/C pulse which the ICM can interpret. some other applications use hall effect sensors though, they just create a DC square wave, usually these will be tied directly to the PCM instead of an ICM.

the LT1 actually has 180 "notches" on one of it's reluctors(and is a normal 4X on the other), but it's also optical, which can get away with some stupid-high speed decoding at the disadvantage of needing to be more or less sealed from the outside world. IIRC, that wheel is also TINY, like 4".

[ericjon262]

ahhh, the opti spark what a thing of beauty...

thanks, that answers my question!