Quote:
Originally Posted by 97 SL320
Variable reluctance sensors need a clean sharp edge to make a clean sine wave. With your tone ring design I'd expect the " zero crossing " voltage to rise with increased speed and eventually be higher than the trigger point of the speedo. RE: I'm expecting the sides of the open window area to still have an effect on a VR sensor, a sprocket design would be better.
Early Sprinters supposedly used a sensor in the rear of the trans for road speed. The casting hole is there however you would have to dissemble the trans to drill the case and I don't know what the tooth count is.
Making the ring from 4140 is probably overkill, measure the hardness of the output flange and adjust accordingly. I'd expect mild steel to be just fine.
Powder coat is just plastic so over time I'd expect it to cold flow and bolts lose some tension. Depending on the sensing range of you hall effect, a layer of power coat might take you out of range. A VR sensor needs tight clearance so I'd expect that to be even worse.
Regardless, I tend not to like power coat in a corrosive environment and prefer paint because paint tends to have better adhesion. Paint will slowly peel as the base metal rusts where as powder coat comes off in sheets due to rapidly advancing corrosion.
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VR sensors need to be about 3 times the width of the probe to eliminate what you speak of. The widows at 9mm wide and the VR probes I have are I believe 2.5 mm in a 12 mm body. It all worked fine until I bolted it up. These sensors were tested on the lathe and worked very well with the VR sensors, but When I put them on the car I found that the presence of the nuts was enough to piss off the signal and cause issues. I installed it with the installation nuts on the lathe and was able to replicate the problem.
So I tried the Hall Effect sensor and that worked well up to about 80 MPH but using it with the VR wheel was too much the slots need to be shorter. I was able to simulate the Hall effect signal with 50% slot/material and drive the speedometer all the way up to 450Hz (~ 210MPH). Which is the max the speedometer will do.
So the second picture shows the installation with nuts and the old long slots. The first picture shows the latest rev that is threaded to avoid the nut problem. Unfortunately that drove the requirement for the 4140 Steel with heat treat.
I believe this new wheel will work with either VR or hall effect. But I do like hall effect better. Its just a constant 12 square wave output. Compared to the VR's spikes running well over 100V at higher speeds.
As far as the coating I am still up in the air with that. I have considered having the mounting area masked for the coating process, be it paint or powder. But I really would prefer cad plating.