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Stealth -> GM Cadillac OIL monitor algorithm - alghorythm (3/12/2007 11:27:14 PM)
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i will not try to re-write this, it is best for you and anyone else to interpret it as you will.
i hope this answers all your questions. it is a long response, but a fairly complete one.
btw, the gent mentioned there below (***** & ****) are names well known in the Cadillac circles
and by the members of the old ACA - Allante Appreciation Group. i wil just leave it at that in
respect of the old days and protect the identity of the gent.
to "elaborate", no?
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alghorythm / algorithm:
"Many computer programs deal with a substantial amount of data. In such applications, it is important to organize data in appropriate structures to make it easier or faster to process the data. In computer programming, the development of an algorithm and the choice of appropriate data structures are closely intertwined, and a decision regarding one often depends on knowledge of the other. Thus, the study of data structures in computer science usually goes hand in hand with the study of related algorithms. Commonly used elementary data structures include records, arrays, linked lists, stacks, queues, trees, and graphs."
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Posted: Apr 19 2005, 08:34 PM
GM Oil Life Monitor
From *********
The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.
You would obviously like to get the oil out of the engine before the ZDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.
The other things that determine oil life such a acid build up, oxidation, petane insuluables such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDP depletion line.
The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life montitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.
The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.
One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don''t believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.
Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.
There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDP depletion curve....in other words, zero percent oil life per the ZDP depletion is not zero ZDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDP is catostrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.
Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn''t work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.
There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car.
http://www.clubavalanche.com/forums/index.php?showtopic=7301&
http://www.bobistheoilguy.com/
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Oil Monitors Revisited
by Ed Newman
AMSOIL Marketing & Advertising Manager
This article appeared in National Oil & Lube News, February 2003
I just got this e-mail from a friend. It was his first oil change on a new 2003 Chevrolet Tahoe. He wondered how the vehicle could go so far without the oil monitor light going on.
He wrote, "I''ve never gone this far on an initial oil change before. Usually changed that oil out at 1500-2000 miles in the past. I had 5500 miles on the truck and it still had 23% of its life left in the oil." That calculates out to 7142 miles before it would have told him to change the oil, and 4.25 months (or 17 weeks) to reach the 7142 miles. He was curious about whether GM was lengthening the algorithm without telling consumers what they were doing.
Naturally I was curious to learn more and thought it a good opportunity to revisit an issue which five years ago seemed to put shudders into a lot of quick lube owners and operators. Did GM change the algorithm?
THE ISSUE
The matter came to his attention because the oil change light in his 2002 Chevrolet Tahoe came on much more often, even though it was the same engine, same drive train, and same travel route to work each day.
"Driving the same route, during spring and summer weather, my oil change light came on once at 3800 miles, and once at 4200 miles on my 2002 Tahoe. All things being equal, one would have thought that the severity of my driving during the colder months in the newer truck would have resulted in even shorter drain intervals as compared to my old one," he wrote.
I told him I''d be going to the SEMA Show in Las Vegas and would make it a point to find someone from GM who could address this issue. I also did some Internet research to see what else was out there.
INTERNET SIGHTINGS
A DejaNews word search on "oil monitor GM algorithm" yields a small number of search results. At the alt.autos.gm newsgroup, a writer notes that the "Oil Life System compensates for different driving styles and conditions.
The math model involves computerized monitoring of engine revolutions, operating temperature, coolant temperature, oil temperature, and other factors to calculate the rate of engine oil degradation and predict when it should be changed." It is an alternative to "fixed oil change schedules that may not be suitable for all situations."
THE INSIDE STORY
As luck would have it, on my last day at the Specialty Equipment Manufacturers Association (SEMA) show in November, I was able to locate a representative from General Motors who could assist in clarifying some of these issues for us. For nearly half an hour I spoke with Al Cline, who works in the GM Powertrain, High Performance Vehicle Operations division. My speculation is that Mr. Cline knew more about these sensors than nearly anyone at the show.
By the end of the conversation he said I should fly to Detroit and talk with the woman who developed the GM oil sensor logarithm, Dr. Shirley Schwartz.
Here are highlights from my discussion with Mr. Cline.
1. The first cars with the oil sensor were the pushrod Cadillacs and Buicks in 1986, followed by the Alante. As noted above, the sensor does not actually assess oil quality. Instead, it uses an algorithm to model oil life.
2. Mr. Cline does not believe in oil change intervals without monitoring the driving style. He said that some people, based on the way they drive, should change oil every 2,000 miles, others 12,000. There are too many variables, he said, therefore the entire industry is skewed because there is no such thing as a routine oil change interval.
3. GM believes the algorithm monitor is the most accurate way to measure when oil should be changed. It is adjusted for each engine because engines operate differently.
SUMMING UP
One thing is clear from this discussion: General Motors has a different philosophy about oil change intervals than the oil industry. While oil companies rally round the 3,000-mile-oil-change-flag, the auto industry is marching to the beat of a different drum altogether.
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Shirley E. Schwartz
outstanding contributions to lubrication
technology, development of environmentally friendly products,
conservation of non-renewable natural resources, and significant
achievements in promoting awareness of technical professions.
Achievements:
Developed a patented device that notifies a car’s driver
when the engine oil should be changed. Her area of expertise is the
conservation of engine oils for engines fueled with gasoline and
alternative fuels.
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