Captain Hybrid

Steer-By-Wire to Reach Production Vehicles

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William K.
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Re: Steer by wire??? I don't think so.
William K.   12/21/2012 8:46:50 PM
If you want to experience just how difficult anti-intuitive steering can be, try this experiment on a bicycle. After you get rolling along a straight clear path, grb the right-hand grip with your left hand and try to kep going straight. BUt be certain that your helmet is on correctly before doing this experiment.

Going to a non-intuitive steering method could be a real disaster.

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Re: Steer by wire??? I don't think so.
tekochip   12/23/2012 10:59:39 AM
You know that was a popular challenge around our office and one ME, let's call her Christine, failed  the experiment with grand results.

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Examine failure modes
dstroz   1/29/2014 9:18:59 AM
Having experenced a failure of ABS the dealer told me could never happen, drive by wire scares the hell out of me. My ABS on a GM product would wait untill travling more than 32 mph before totaly disabling all brakes. I don't believe the automakers are willing to dedicate the necessary resources to developing the same safty protocals the aviation industry has. Besides, if anything goes wrong just pull over to the side of the road, oh! wait maybe that won't work.

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steer by wire
Stirwelder   1/29/2014 11:20:36 AM
I first saw an electric power steering system implemented in an advanced prototype my employer was asked to simulate in 1978 or 79. The design had a hollow armature servomotor driving a ballnut on a ballscrew rack that went thru the center of the motor to assist in steering and sensed the need for assist just as a hydraulic system does, by sensing the windup of a torsion rod at the pinion. It was an electric servo instead of a hydraulic servo. It seemed to work just fine, although if you turned the wheel rapidly you could feel the inertia of the servomotor.

My concern then was that the mechanical backup mode operation required backdriving the servomotor thru the ball screw-nut. That is fine when it is new, lubricated and smooth, but if the screw or nut has fatigue damage, corrosion and or contamination it would still probably work OK under power but it might not manually backdrive at all. To my knowledge, the hydraulic system doesn't have a failure mode that locks up the rack and pinion precluding manual operation.

That concept was a very compact affair, but it seemed to have a fatal flaw. I wouldn't want it in my life. How does this system deliver power assist from servomotor to the rack? Not much engineering detail given. Not in fashion.


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Re: Mechanical Backup
patb2009   2/2/2014 6:42:27 PM
You could look at going to a centerstick, side stick system like the X-15 used.

Have the center stick be the computer driven controller but you can reach over and yank on the side stick to get some steering inputs, and if it's over on the side it may package up nicely especially if it only needs a relatively small movement.

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resale value
ragtoplvr   2/4/2014 10:46:50 AM
We are reaching the point where when a car gets a few years on it, what is a relatively minor failure now, like a power steering rack or a brake booster, will be so expensive to repair it effectively makes the car a total loss.  This will adversly affect resale value.  As an example, take a  common 2002 to 2005 Buick LeSabre.  The Limited with all the bells and whistles, often can be had for the same or less than the much simpler custom trim version.


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