Everything you ever wanted to know about power steering
Since no ones biatchin about RtOS, I figure this forum could double as a forum on embedded apps and sensors. Here's a good article discussing [link|http://www.embedded.com/showArticle.jhtml?articleID=164904435|Power Steering] that might interest some hereabouts who like to tinker with their cars.
I don't know why, but they don't use Stepper motors. Stepper Motors are know for a good many things that are good in EPS. Even Fly-by-wire with Stepper Motors would be good. It is how many of the newer Military Aircraft work.
Why not for the average consumer... they would only have to have direct link to the steering column. Basically make it a manual rack with the stepper motor assist. The stepper motor could be a high-speed high-frequency, with Step down. You trade Rotational Speed for Rotational torque.
And on the subject of failure, you could *STILL* have a default failure mode with direct connection from column to rack. I don't see this much as a Problem, but as a Challenge to make the cheapest and safest auto-steer/steer-assist mechanism.
Stepper motors are exceptionally well know and how to use and measure them. Near that, Stepper motors are also very, very reliable. Not so cheap, but could be custom built for exacting locations. Or using OTS motors to do the work as well.
If the Car DC Voltage went to 42 Volts, That would make a huge change it the designs. Higher Voltage means less size to do the same work. Or keep the size and offer more head space.
Blah, Blah, Blah, blah, baalaahh.
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Interesting stuff on 42 volt
[link|http://www.assemblymag.com/CDA/ArticleInformation/coverstory/BNPCoverStoryItem/0,6490,98697,00.html|The 42-Volt Challenge]
Keim says 42 volts is the threshold\ufffdanything higher presents safety concerns. Because 50 volts can stop a human heart, anything higher than that requires special safety systems to prevent contact with wiring. In addition, any voltage above 60 needs more heavily insulated wires and connectors that would add weight.
Darrell Spice, Jr. [link|http://spiceware.org/gallery/ArtisticOverpass|Artistic Overpass]\n[link|http://www.spiceware.org/|SpiceWare] - We don't do Windows, it's too much of a chore
Actually, stepper motors are cheap and sucky
I've used both steppers and (especially) BLDC's (BPM) extensively. Maybe if you run a hybrid stepper with feedback [link|http://www.d3engineering.com/kruse.phtml?topic=imaging"|(e.g. Kruze control)] it's OK.
But the torque curves are sucky; stepper torque drops dramatically at higher speeds. They don't have the high peak torque of BLDC's, either. They don't handle high inertial loads well, and can stall. I doubt they're as smooth as the alternatives; definitely not very smooth if you don't microstep, and I've seen microstepping still be a lot rougher than I'd like.
I haven't used AC Induction or SR motors, but the article's analysis seems reasonable to me (and we try to avoid brush motors).