Electric Power Steering solution

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Dale
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Joined: Wed Dec 23, 2009 1:02 pm
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Electric Power Steering solution

Post by Dale »

Hi, I built a project vehicle ( picture a Kawasaki Mule ect.) I am upgrading the steering to a 2004 Saturn Vue (KOYO) electric power steering unit. It is a niece compact unit. Problem: I was going to use a 555 (not ready for PIC's yet) and send a dummy VSS signal. Well it use's 2 class 2 serial data lines + ign power. It would turn on if it recieved an "ign" on signal and the vss is not even really needed. However. I cannot find the actual values for the signals anywhere. For instance the "ign on" signal value is listed as yes or no on the mechanics scan tool chart. Bottom line is that I do not have the skills to replicate the serial data. So, I would like to make my own simple controller as follows. The critical torque sensing wires are right on the side. With ign power (not to be confused with the i"gnition switch on position" serial signal), the circuit draws 6 mA and sends a 0.572 volt AC signal that rides on a 3.5 volt DC. It has 2 coils, one for temp compensation. I would only use one. Turning the torque arm gives a AC swing of 12 mV each way. I would like to start simple and take the AC to a simple comparator. the out put to an adjustable 555 acting as a pulse width. Then the 555 output to an opto isolator that would drive FET's or a relay. I would use 2 comparators as well as 555's. One for each direction. This gives a fixed amount of assist which is fine. I would make a better variable circuit later if this works well. Questions: What is the best way to bring that mV ac signal into the comparator - (a 741 - less sensitive or a 339). Because coil inputs will be in parallel with the original circuit, is this a consideration? Do I need to research the DC motors kickback when it changes direction. The uint is rated for 65 Amps. My vehicle weighs 1/4 of the Saturn Vue. They have thermal controls and I could make my own. Lastly, how do you know you are not heating up a dc motor with pulse width controll by not giving it enough current hurting it over the long run? To opperate at the lowest assistance can I monitor slowest motor speed that turns the wheels but maintains the highest voltage reading? Sorry for the ramble but I won't sleep until I blow something up or arrive at power steering. Any suggestions are welcome. Thanks
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