http://www.technewsw...tory/69571.html
This post has been edited by Emax: 18 March 2010 - 05:44 PM
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Toyota Recall
Started by Emax, Jan 22 2010 08:47 AM
43 replies to this topic
#41
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- Industry II
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Posted 18 March 2010 - 05:31 PM
The industry finally raises an eyebrow...
http://www.technewsw...tory/69571.html
http://www.technewsw...tory/69571.html
There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians. Georges Pompidou
#42
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- Administrator II
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lift mechanic
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Posted 19 March 2010 - 04:44 AM
Perhaps we'll see some good come out of this, in that regard. I've heard of problems with airplanes with regard to the 'fly-by-wire' system they use for controlling flaps, elevators, the rudder, et cetera. I think the automotive issue is bigger in the media simply because more people own cars than planes. I like my fully-mechanical brakes and throttle more every day, and I don't mind replacing a worn accelerator cable every once in a while :)
Member, Department of Ancient Technology, Colorado chapter.
#43
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Posted 21 March 2010 - 08:22 PM
I was planning to call what follows a bet - but I'll back off a bit and call it a passionate proposal.
This whole issue with misperforming throttles and braking systems smells exactly like a feedback loss - not a software glitch. When the incidents occur, all happens in a far too well controlled (smooth) manner to be a digital issue. Those of you who cut their teeth in the DC drive world about the same time that I did will know exactly what I mean.
When a system is designed to be regulated, its output is determined by a comparison made between a command input and at least one - system generated - feedback (usually more). The feedback is used as evidence of the system's output having had an effect on the controlled device. Prior to "regulation", the system operator sensed feedback and changed his input command accordingly. Remove just one of those feedback signals and the regulator (digital, analog - it doesn't matter) will continue to increase its output - regardless of command input - in search of some evidence of a change in the driven device.
Modern automobiles are full of such systems that require feedback. A favorite "position sensor" today is the Hall Effect sensor - an electronic chip that changes its output in reaction to a magnetic field. A magnet that moves with the changing mechanical position of a device affects the Hall chip to create a position feedback signal. No doubt, this is what is used on the servo-driven throttle bodies. In the real world, unwanted magnetic fields aren't hard to find. But this is only one of the many feedback loops - what about road speed? How is that being sensed? When a driver changes his accelerator position, it is an attempt to change the speed of the vehicle - upward or downward. He continues to make small changes until he senses the result he is looking for. In the so-called "fly-by-wire" scheme, his throttle position is transduced and used as an electronic input to a decision-making network that depends on a system feedback to evidence a correct speed change. At this point, it would be appropriate to mention that assisted, anti-lock braking systems also require this same road-speed feedback. It just could be that a production run of faulty - or misapplied sensors is at the bottom of this whole problem.
A topic parallel to this one has been opened in the "combustion engine" section of the electrical forum. Please direct all serious technical comment to that thread.
This whole issue with misperforming throttles and braking systems smells exactly like a feedback loss - not a software glitch. When the incidents occur, all happens in a far too well controlled (smooth) manner to be a digital issue. Those of you who cut their teeth in the DC drive world about the same time that I did will know exactly what I mean.
When a system is designed to be regulated, its output is determined by a comparison made between a command input and at least one - system generated - feedback (usually more). The feedback is used as evidence of the system's output having had an effect on the controlled device. Prior to "regulation", the system operator sensed feedback and changed his input command accordingly. Remove just one of those feedback signals and the regulator (digital, analog - it doesn't matter) will continue to increase its output - regardless of command input - in search of some evidence of a change in the driven device.
Modern automobiles are full of such systems that require feedback. A favorite "position sensor" today is the Hall Effect sensor - an electronic chip that changes its output in reaction to a magnetic field. A magnet that moves with the changing mechanical position of a device affects the Hall chip to create a position feedback signal. No doubt, this is what is used on the servo-driven throttle bodies. In the real world, unwanted magnetic fields aren't hard to find. But this is only one of the many feedback loops - what about road speed? How is that being sensed? When a driver changes his accelerator position, it is an attempt to change the speed of the vehicle - upward or downward. He continues to make small changes until he senses the result he is looking for. In the so-called "fly-by-wire" scheme, his throttle position is transduced and used as an electronic input to a decision-making network that depends on a system feedback to evidence a correct speed change. At this point, it would be appropriate to mention that assisted, anti-lock braking systems also require this same road-speed feedback. It just could be that a production run of faulty - or misapplied sensors is at the bottom of this whole problem.
A topic parallel to this one has been opened in the "combustion engine" section of the electrical forum. Please direct all serious technical comment to that thread.
This post has been edited by Emax: 21 March 2010 - 08:45 PM
There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians. Georges Pompidou
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