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Mydesign
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Platinum
Wrong interpretation from hall Effect Sensor
Mydesign   11/1/2012 7:25:31 AM
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1 saves
"It appeared the steel gear and shaft were becoming magnetized by the wiping action from the camshaft and caused the Hall Effect sensor to get false readings"

Bob, these problems occurs with Hall Effect sensors. When I had done some experiments with Hall Effect sensors, I found that any magnetic field near to the Sensor will be interpreted as signal. This will lead to the malfunction of system, where sensor o/p is served as the input to the system. I had faced similar problem in Brushless DC motor drive, where Hall Effect sensors are using to drive the circuits.

btlbcc
User Rank
Gold
Re: Wrong interpretation from hall Effect Sensor
btlbcc   11/2/2012 10:17:44 PM
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Hall effect sensors incorporate a magent in the design (that's how they work - the Hall sensor senses changes in the magnetic field due to the motion of a distributor cam, "gear"  or interruptor wheel).  Presumably it's possible for this small magnet to eventually magnetize the distributor shaft, etc.

Another possibility might be a short circuit (or partial short circuit) from the battery to the distributor shaft.  Since automobiles use DC, such leakage could cause the shaft to become magnetized over time. 

Demagnetization would solve the problem in either scenario, but only temporarily.

 

naperlou
User Rank
Blogger
thing we do
naperlou   11/1/2012 12:03:40 PM
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Bob, I am impressed with your ability to track down and resolve this problem.  I was especially amused at your early solution, though.  The idea of using a hand vacuum pump to keep the truck going at idle was great.  The things we will do to keep moving. 

bob from maine
User Rank
Platinum
Re: thing we do
bob from maine   11/2/2012 9:51:20 AM
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naperlou I also had a seemingly endless supply of British motorcars and as a result, learned a great deal about bad design, poor materials, bad luck and how to 'make do'.

tekochip
User Rank
Platinum
Excellent Job
tekochip   11/1/2012 1:26:20 PM
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I really don't think I would have been able to figure that out.

OLD_CURMUDGEON
User Rank
Platinum
GREAT Detective work ...
OLD_CURMUDGEON   11/1/2012 3:26:31 PM
This IS an excellent example of how INTERDISCIPLINARY knowledge is essential in any technical endeavor.  Even though his main thrust was / is electronic troubleshooting, he had / has sufficient understanding of the principles of ignition in an internal combustion engine and the Kettering Ignition system, so was able to dig deeply into the problem.

What's really a total bummer is that his "discovery" went unacknowledged & unrewarded by the DODGE factory geniuses.  It would be interesting to determine IF Dodge prepared a TSB (Technical Service Bulletin) for distribution throughout their dealer network, OR if it fell by the wayside, so the customers affected by this malady continue to pay through the nose at the dealers' incompetence!

 

Stuart21
User Rank
Gold
Re: GREAT Detective work ...
Stuart21   12/4/2012 9:24:14 PM
"What's really a total bummer is that his "discovery" went unacknowledged & unrewarded"

Absolutely. This is the penalty for offending the wage slave geniuses 'inside'. Have a wealth of experience in this area.

Solution might be to copyright your solution (& maybe a patent application) (DIY ONLY) - don't waste money on patent attorneys!!!!

Then advise Co you have a solution, cost is $xxxx, disclosure available for $xxx, (or free disclosure with NDA / NCA (Non disclosure agreement / non compete agreement) & 7 days to accept. 

Your solution is a very valuable asset & many cos would try to obtain by any means. Many have no qualms about stealing even IP, often advised by their IP counsel to do so - said counsel cognisant that lawyers always win, clients only average 50% win - & that is before costs.

Right now I would like to share some ideas with Fedex - been a customer of theirs for 20 odd years - asked them if I were to disclose it, would they agree to not use ideas without further agreement - reply is (before disclosure ;-) ) 'We do not wish to employ you'.

Stuart Saunders.

IPROAG Intellectual Property Rightful Owners Action Goup.

 

 

Hop
User Rank
Iron
Magnetized distibutor shaft faults Hall-effect sensor
Hop   11/1/2012 4:22:37 PM
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This was an excellent example of real troubleshooting versus the dealer's "shotgun maintenance" approach of changing everything in sight. Good work!

Larry M
User Rank
Platinum
Who'd a thunk it?
Larry M   11/1/2012 4:37:19 PM
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Bob, thanks for the excellent insight. I have been fiddling with Hall effect sensors on my 1992 Mitsubishi Expo (250 K miles) for some time. In hot weather I get misfires and diagnostic codes from the one in the distributor, and I periodically also get them from the sensor in the air-inlet servo--a valve controlled by a DC servo motor.

It never occurred to me that magnetization could be the source of either problem. I have a degaussing coil from an old color TV and I think it's going to get a workout.

William K.
User Rank
Platinum
GREAT Detective work ...
William K.   11/1/2012 7:31:20 PM
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Definitely some good reasoning as well as the detective work. Changing to cheaper materials is something that Chrysler purchasing has quite a reputation for. So even if the design started out good, purchasing may cut costs without any clue as to why it had been designed differently, and often without contacting the design engineer. Of course many of the managers were devoid of any clue, so the problem would not be discovered until it would damage the designers career.

I am not sure just how steel parts self magnetize, but we often had to demagnetize production fixture parts. So I guess that it does happen.

Larry M
User Rank
Platinum
Re: GREAT Detective work ...
Larry M   11/2/2012 9:38:26 AM
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William, you can magnetize any piece of steel by stroking it in one direction with a magnet. E.g., if you have a bar magnet and an unmagnetized steel rod or bar or horseshoe, you can magnetize the unmagnetized component by repeatedly stroking it in one direction with one end of the bar magnet.

Think about it. Magnetization is simply alignment of all the molecules in the same direction. If each stroke aligns a few more molecules due to the influence of the passing field, ultimately a significant proportion will be aligned.

No piece of steel is pefectly unmagnetized. There has got to be a bit of residual magnetism there someplace, even if it's only a couple of molecules. If the pieces are stroked in a repeated manner, the pieces will ultimately become magnetized.

When two gears are in contact, a wiping (stroking) action takes place as the teeth pairs com in contact. transfer motion, and leave contact. Check out this animation of the contact point motion:

http://science.howstuffworks.com/transport/engines-equipment/gear8.htm

William K.
User Rank
Platinum
Re: GREAT Detective work ...
William K.   11/2/2012 9:42:41 PM
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Yes, I have magnetized things by rubbing them with a magnet. BUT WHERE did the original magnetism come from? Engine parts are NOT supposed to be magnetic especially gears. And I don't believe that rubbing non magnetic parts with non magnetic parts would cause them to be come megnetized. That was the point. 

Where did the initial magnetization come from??

Larry M
User Rank
Platinum
Re: GREAT Detective work ...
Larry M   11/3/2012 11:45:04 AM
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William,

As I stated previously, no steel is PERFECTLY unmagnetized. By virtue of entropy, there must be a couple more molecules aligned than exactly 50% in each direction. With the two gears (cam and distributor shaft) rubbing egainst one another, each becomes more and more magnetized over time.

Tool_maker
User Rank
Platinum
Re: GREAT Detective work ...
Tool_maker   11/5/2012 12:49:33 PM
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  To back up your remark about no steel being completely without magnitism I remember compass reading when in the Army. You put the compass up to your eye so you could see both the compass needle and the sight wire attached. You lined the needle with the desired azmuth and picked your target with the sight wire. If you did it without removing your steel pot, or laying your weapon aside, the readings were very unreliable. In fact some times the steel pot could pull the needle to which ever direction you looked and if I remember correctly, you might be 10 or 15 degrees off.

  I never really questioned from where the original magnetism came, but was well aware of it being there.

bob from maine
User Rank
Platinum
Re: GREAT Detective work ...
bob from maine   11/2/2012 9:44:04 AM
I always remember high-school shop class, our teacher wanted us to learn SOMETHING so he frequently repeated; "you magnetize steel by stroking and direct current; you demagnetize steel by heating and alternating current." The cam gear is helical so each turn of the distributor represents 10 or so strokes by one steel gear wiping against another steel gear. The old TV degausser was part of my ever growing pile of things I'm sure I'll never need, but in this case I was wrong. It still hangs on the wall of my garage right over the sign "Danger, HIGH Resistance".

Rob Spiegel
User Rank
Blogger
Question about design
Rob Spiegel   11/2/2012 12:25:15 PM
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Here's a question from Mike Krysiak:

Would replacing the steel drive gear with a bronze gear(as in the older design) eliminate or reduce the chance of the distributor shaft from being magnetized?

 

bob from maine
User Rank
Platinum
Re: Question about design
bob from maine   11/2/2012 2:44:18 PM
Rob, yes, replacing the steel gear with bronze would prevent the issue but create another; the government requires 100K mile emission warranty, the wear characteristics of the bronze gear would require replacement before 100K miles. Most old distributers (using ignition contact points, not Hall-effect sensors) taken from high-mileage engines of old had bronze gears with severe wear. This could be seen using Sun test stands or a good dwell tach which showed the dwell and timing jumping back and forth. Replacement gears were readily available through parts distributors. I don't think individual parts are stilll available for distributors or alternators or starters. Your choice is buy new from the dealer or remanufactured from the parts distributors. Considering a mechanic at a good garage bills between $50 and $85/hour, it just isn't worth it to pay them to rebuild anything.

Tool_maker
User Rank
Platinum
Re: Question about design
Tool_maker   11/5/2012 1:02:12 PM
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  I think this is more an issue of cost rather than the desirable wear feature of steel. It has been my unfortunate experience to machine some different types of bronze that machined as hard as any steel I have come up against. But it is not a cheap substitute and in many cases is hard to justify the expense involved.

   One such application involved the weapons industry and the final product had to be Non-sparking, as it was used in a cartridge loading application that involved gun powder. Sparks and gun powder do not mix, so any ferrous material on ferrous material was forbidden, but we still needed the wear characteristics of tool steel. I had to learn more about metallurgy than I ever thought I would need, but in the end the product worked well and the customer was satisfied. Always a good thing.

Rob Spiegel
User Rank
Blogger
Re: Question about design
Rob Spiegel   11/5/2012 1:55:34 PM
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Thanks for the explanation, Bob. But it makes me wonder why this problem is not more widespread. Do most cars have a different type of setup.

bob from maine
User Rank
Platinum
Re: Question about design
bob from maine   11/5/2012 3:17:25 PM
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Newer vehicles have crankshaft position sensors and multiple coils. Not many even have distributors, instead having coils that fire multiple cylinders. Some still use distributors and Hall-effect sensors but not many. Considering the number of trucks, vans and SUV's that had V8 engines with a similar set-up from Chrysler, GM and Ford, there were relatively few that exhibited this problem. The only "unique" aspect of this truck was a 200A alternator, 2 large batteries and a 2000W inverter to power the occasional 115VAC power tool. There may have been eddy-currents drifting around but I was never able to measure anything unusual. This same set-up has run on thousands of marine applications with no ill-effects.

Rigby5
User Rank
Platinum
Car makers don't offer enough support
Rigby5   11/2/2012 12:58:52 PM
It is clear car makers are at fault, not for trying a steel gear that will cause failure eventually, but for not giving the dealer mechanics the tools to diagnose it.

Clearly mechanics used to use oscilloscopes a lot in the past, to diagnose alternators, condensers, point bounce, advance curves, etc.

Oscilloscopes are still important for things like this Hall effects failure, and the diagnostic procedure should have been covered.  In fact, the ODBII standard should already have caught this.  All fuel injected cars should also come with a dash display for fuel pressure as well.  Current cars are not being supported properly by the maker, and they are ignoring maintenance.  It is getting worse.  I stick to buying the older cars because they are far more reliable.  New cars these days are junk because they are becoming impossible to maintain.

Amclaussen
User Rank
Platinum
Re: Car makers don't offer enough support
Amclaussen   12/5/2012 2:29:37 PM
EXACTLY!  Newer cars are a nightmare to maintain.  Maybe they are somewhat maintenance-free for some 3-5 years, but eventually, a belt, belt tensioner, hose, filter, water pump, or spark-plugs WILL need to be changed... THEN the terrible design job of the factory "geniuses" will be immediately apparent!

I've just finished a "revamp" project on my old 1991 Dodge Spirit R/T, consisting of upgrading the original smallish turbo Intercooler and engine radiator with newer, larger units. These units were less expensive than the original replacements, so I decided to go to as large possible sizes, meant for other makes and models of cars.  Taking advantage of the disassembly already done to modify the car, I decided to replace the timing belt and tensioner, the water pump and all the accessories belts.  Even when I had to remove a lot of brackets, belt covers, the Air Conditioner Compressor, the Alternator and one engine mount, I had just enough space and clearance to perform all the tasks without too much knuckle chafing and bruising...

But looking at the task of water-pump and timing belt replacement on a 2006 Dodge Stratus is ANOTHER matter! Not only is insufficient space to use any hand tool, but component location and disassembly requirements make that otherwise simple task a complete nightmare, probably requiring the whole engine to be dropped from the car.

What overly optimistic (and dumb) ideas were inside the brain (if any) of the "automotive designers" that create present day automobiles? Can anybody assure that not a single component will fail before warranty ends and needs a difficult and lenghty disassembly before the vehicle is close to its true useful life?

marcopolo
User Rank
Iron
But...
marcopolo   2/12/2013 1:35:58 PM
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  The small block Dodge/Chrysler/Plymouth does not *have* any

gear on the bottom of the distributor!  Unlike a Ford/Chevrolet, the gear

is on the oil pump driveshaft and the distributor shaft has only a tang on

the bottom of it's shaft that engages a slot on top of the oil pump shaft. Makes it really easy to remove/replace them as you can only install it one of two ways!  Could the author be mis-remembering the manufacturer?  No one takes out the oil pump drive shaft when replacing a distributor...



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