Converting transfer box speedo drive to digital

[rcx132]

I've wired up the ECU on my buggy and the engine starts, yepee Got to say that was quite a challenge, reverse engineering the original loom, and all those sensors and plugs to solder up, but very happy with the result.

There's still one more ECU sensor to go, and that's the most challenging one, the vehicle speed sensor (VSS). The engine starts without it but won't run well under load. On the donor car there was a magnetic reed switch behind the mechanical speedometer that fed a signal to the ECU. I won't have that.

I'm thinking of making a digital sensor that will spin off the original transfer box mechanical speedo output. I have a lathe and it looks like I can turn a slotted shaft to run inside a cylinder that will fit the transfer box hole.

Question is about lubrication. Will a smear of grease be enough between the shaft and cylinder it will run inside of? I'm guessing it will seeing as mechanical speedo cables use grease.

Also open to any simpler ideas for making this sensor.

The ECU expects 100 Hz at 87 mph, so I have to do some maths, and may need multiple magnets on the shaft.

 

[Anguz]

I made one for a ford box.. sorry no photos but it hasnt failed yet... has a magnet on the speedo drive and a bracket made from an old drive cable outer

 

[jeremy]

I don't know if this will be of any help, but when fitting the SJ transfer box you have pictured to the later Jimny model you can buy a speedo conversion kit, that puts a relucter ring on the output shaft and uses the jimny speed sensor. Last photo showing my convertion with the ring under the handbrake caliper bracket.

 

[Bullet2012]

Not sure I understand why a vehicle speed signal input affects the running.
the Speed input is generally to provide data for calculating mpg, range etc for the in car display, or a speed limiting function or warning.

 

[rcx132]

I don't know if this will be of any help, but when fitting the SJ transfer box you have pictured to the later Jimny model you can buy a speedo conversion kit, that puts a relucter ring on the output shaft and uses the jimny speed sensor. Last photo showing my convertion with the ring under the handbrake caliper bracket.

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That looks like the Jimny needs a lot of pulses per rotation, which is why you need a big wheel for the sensor. The Vitara ECU I'm using was looking for only 6 pulses per rotation, So I can get away with using the speedo output. I may need to adjust for the gearing, so maybe I'll need 5 pulses, maybe 7, haven't done the maths yet.

Not sure I understand why a vehicle speed signal input affects the running.
the Speed input is generally to provide data for calculating mpg, range etc for the in car display, or a speed limiting function or warning.

Who knows. But others who've done conversions to this engine have said it doesn't run right without it.

 

[rcx132]

Any thoughts on my lubrication question? Is it ok to make a simple brass mechanism lubricated with grease? Attaching my idea, open to alternatives and critism.

 

[Agroshield]

I may need to adjust for the gearing, so maybe I'll need 5 pulses, maybe 7, haven't done the maths yet.

Doing it mechanically might be difficult to do by trial and error. You have to have an integer number of magnets, and what happens if the calculations show you need 3 1/2 for the output to be correct?

It is always easier to divide a high pulse train. If you put, say, a 200 pulse per revolution encoder on it, an Arduino or similar could convert that into the required number of pulses. It would count the pulses coming into it and release an output pulse at the correct interval. You can track the error if the input and output do not divide without a remainder and correct for it regularly so it does not accumulate (all possible with integer maths, which is fast). Having a microprocessor in there makes tuning it as simple as altering a number in the code rather than adding or subtracting a magnet and you can (in effect) add half a magnet if required.

On the lubrication, could you use a bearing on the shaft with an outer sleeve to make up the size difference and give a place for the locating screw to sit? Outer sleeve to have a thin wall at the base so it bottoms out on the lip around the speedo drive. You know a bearing will work. Steel shaft and oilite bearing is also a possibility.

 

[jsf55]

How about the way they do the dizzy conversion for the Megasquirt units? you can turn up a suitable housing with the sensor on the outside and as many magnets you need on the inside being rotatated on a suitable disc?

 

[rcx132]

Doing it mechanically might be difficult to do by trial and error. You have to have an integer number of magnets, and what happens if the calculations show you need 3 1/2 for the output to be correct?

It is always easier to divide a high pulse train. If you put, say, a 200 pulse per revolution encoder on it, an Arduino or similar could convert that into the required number of pulses. It would count the pulses coming into it and release an output pulse at the correct interval. You can track the error if the input and output do not divide without a remainder and correct for it regularly so it does not accumulate (all possible with integer maths, which is fast). Having a microprocessor in there makes tuning it as simple as altering a number in the code rather than adding or subtracting a magnet and you can (in effect) add half a magnet if required.

On the lubrication, could you use a bearing on the shaft with an outer sleeve to make up the size difference and give a place for the locating screw to sit? Outer sleeve to have a thin wall at the base so it bottoms out on the lip around the speedo drive. You know a bearing will work. Steel shaft and oilite bearing is also a possibility.

Thanks. I did think of an Arduino, but I'd need to justify it. Maybe if I have more use cases for it, then I can put one behind the dashboard to control the various idiot lights. The other option is to have a pair of gears at the transfer box speedo out put that correct for the error caused by using components from a mix of donor cars.

I'll see if I can fit a bearing into the mech. I briefly measured the speedo hole last night and it was an odd size so a bearing won't fit nicely.

 

[Agroshield]

I'll see if I can fit a bearing into the mech. I briefly measured the speedo hole last night and it was an odd size so a bearing won't fit nicely.

The bearing OD needs to be less than the speedo hole, that is all. The speedo hole size is immaterial. Then you can put a sleeve around it, into which you drill a divot for the retaining screw you show in your diagram. If space is tight, a thin section bearing would do:

Thin Section Bearings

Thin Section - Deep groove ball bearings Thin Section Ball Bearings were developed for applications where space limitations are of the utmost importance. As the name implies, the difference between the inside and outside diameters of the rings has been minimised or thinned out. Of course this...

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