Electronic power steering help

[Dromas]

I purchased a eps unit out of a Saturn vue and the fancy control unit off eBay. When it all arrived I tested it and it worked good. For my application I removed the input shaft and added a 3/4 48 spline. Now with the unit assembled when hooking it to power you hear a relay click on and then off and obviously there is no steering assistance. If I split the unit and add power the relay clicks on and the unit is functional as far as I can tell. Inserting the a shaft from outside causes it to spin one way and from the inside it spins the opposite. Any ideas?


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[K-fab]

Disclaimer right off the bat here - I know absolutely nothing about these systems Never even held one in my hand (will be soon, though).

But here's my thinking:

If you put the shaft in one way it'll turn one direction. Flip it over and it does the opposite. That says, at least to me, that there's got to be some sort of magnetic actuation.

Is there any chance that during reassembly that you put something on backwards or flipped over? Like maybe the collar with the teeth in it?

Looking at the disassembled pieces, it appears that the toothed collar slides into the area that has the ring and the plastic bushing looking things. Is this some sort of sensor that tells the system what's going on?

If (using my theory above which may be totally wrong) the sensing ring is magnetic or has some sort of field it generates and is inserted incorrectly the system tries to read what's going on but isn't getting the correct response. Hence the relay click but no action/response.

Like I said, this is all speculation just from reading what you posted and looking at the pic.

[Dromas]

As far as I've figured you are correct in your thinking. What happened is when I disassembled it to weld the new spline on the distance between the lower sets of "teeth" changed and to top it of if you zoom into the picture you can see at some point I damaged a few of the lower teeth. This distance is critical and could probably just be reset if I had not damaged it. When torsion is applied to the input shaft and there is a resistance on the output shaft it causes a deflection between the teeth the larger the deflection the more steering assistance you get. As of now I will be buying another unit, I attempted many times to change the distance between the teeth with varying results...now it turns on and stays on while assembled but won't stop turning left lol. As for the upper most set of teeth think it is a speed sensor so it knows how fast you are turning the steering wheel.


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[CARLRIDDLE]

I thought the lower teeth looked messed a bit. Google wasn't much help on a inside pic. You can but the right splined joint for the unit, if ya don't get it with unit when ya buy. I also wondered how it knew which way you turned, magnets makes sense with teeth, just like a crank sensor. Keep up up on what ya do. Looking to add to mine as well.

[plkracer]

There has to be a physical connection from input to output. They usually use some sort of compliant elastomer or ramps to allow small misalignments between input and output (which is how the unit knows which direction to apply force) yet still allow you to steer in case of failure.

The sensors should measure some sort of encoder on both the input and output to tell the difference between the two angles. I'm not sure on the exact methodology here, but it shouldn't be too difficult to tell what it is measuring.

The unit should self calibrate when turned on. It will behave erratic if you change the setup after turning it on.

[Dromas]

So one last update. I picked up a new power steering unit tested it to be sure it was working before I took it apart and all good. I then removed the input shaft re-assembled and tested and once again it's turns constantly one direction.... Removed the cover from the brain box and started playing with the potentiometers inside adjusting these cured my problem. Then when I installed the new modified shaft I had to adjust once again as it was turning by itself once again. It appears any changes to the shaft confuse it.


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[deaner]

A GM mechanic told me they are very finicky. In the OEM car they need to be"centered" before adjusting them.