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Oil Changes by the DASH

2012-06-08   來源:潤滑油情報網 網友評論 0

摘要:In

In \

In 1984, Donald Smolenski and his GM colleague Shirley Schwartz (now retired) had the idea of using an algorithm to calculate engine oil life, rather than mileage.

     "How often should I change my oil? Is it every 3,000 miles or 7,500 miles?” “Is my driving pattern ‘severe’ or ‘normal’?” “Does the drain interval differ if I’m driving a gasoline-fueled car or a dieselpowered light truck?”  

   Automobile owners ask all of these questions, and usually hear the answer from quick lubes, car dealers and garages. Is there a better way to determine the right oil change interval, one that is more definitive?

   Back in 1968, the recommended oil change for vehicles operating in severe service was 3,000 miles. That number has remained basically unchanged in most drivers’ minds, even though improvements in engine design and oil quality have made it a very conservative recommendation. (The adage which   often accompanies the 3,000-mile recommendation is “It’s good insurance.”) At the same time, the push for a cleaner environment has resulted in increased oil recycling and pressure to dispose of used oil properly. The logical extension of these forces has been a shift to longer oil drains.

   Beginning in 1984, Donald Smolenski and Shirley Schwartz of General Motors Research started tinkering with an idea that would allow the engine to tell the motorist when the oil needed to be changed. They reasoned that engine operations could be equated with oil change intervals and went to work to identify what parameters should be followed.

   The two enlisted Ann Wisehart at Delco and Tina Traylor from Buick,   along with many others, to help develop the means of measuring engine parameters that relate to oil condition. The on-board computer was the natural choice and needed only minor modifications to handle the additional work. Schwartz was the math wiz who worked out the algorithm used to make the oil change decisions.

  

Finding the Sweet Spot

   For the next two years, Schwartz and Smolenski worked on proving their theories through field testing of various engines. First, they ran field tests on vehicles (mostly Buicks) operating in various driving cycles and conditions, with regular used engine oil analysis measuring a number of oil properties. They evaluated key properties including   viscosity, total acid number (TAN), total base number (TBN), fuel dilution, water, metals and oil oxidation. They collected and analyzed data to develop a pattern of useful oil life. It turned out that an algorithm could be based on the engine’s operating temperature and the total number of engine revolutions.

   The key to the algorithm’s accuracy proved to be essentially counting engine revolutions and applying socalled “penalty factors” based on engine oil temperature; as revolutions and temperature effects mounted, more penalties were deducted from the oil’s expected life. Engine oil operating temperatures between 185 to 265 degrees F were considered to be in the optimum temperature range. When oil temperatures fell below or above this   range, they were assigned a penalty factor, with successively colder or hotter oil temperatures earning larger penalty factors.

   Basically, the more the engine oil temperature deviates from the optimum operating range, the shorter the oil change interval becomes. An additional and important factor in engine oil life is the vehicle’s environment. Many factors such as the type of road (level or mountainous), the air quality (dust), and how the vehicle is being used (heavy loads, towing) can have a big impact on oil life.

 

Installing the Prototype

   After two years of data gathering and massaging, Delco created two prototype Oil Life Monitor devices. The first     one was mis-installed on a Corvette and promptly failed. After repairs, it was installed and wired properly. When the second unit was installed in a Buick, technicians were warned not to wire it directly to the high-voltage distributor lead — which they inadvertently did anyway, so that unit failed as well. It too was repaired and wired properly. From there, the real data gathering began.

   For the next two years GM gathered over 2 million miles of vehicle, engine dynamometer and chassis rolls test results. Federal emissions test cycles as well as a number of other cycles were run to confirm that the OLM unit would give the kind of results required. In order to cross check the device, used oil analyses were also run. Everything checked out.  

   GM marketing got wind of the OLM and thought it would be an excellent addition to some of their highend automobiles. The first vehicles to have the system were the 1988 Corvette, Buick and Cadillac models. For the next 12 years, only high-end vehicles offered the OLM system. It wasn’t until 2000 that the system became available in most GM products.

   The Oil Life Monitor system has undergone some minor adjustments to take into account engine design changes and oil specification changes.   The introduction of GM’s new proprietary Dexos 1 engine oils this year will result in yet more adjustments to the system. However, since the system only looks at engine oil   temperature and engine revolutions, it cannot take into account such things as the use of alternate fuels, low oil levels due to oil consumption, or synthetic engine oils.

   Alternate fuels can lead to some unusual side effects. For instance, ethanol based fuels could result in fuel dilution that lowers engine oil viscosity or creates emulsions in the crankcase which could lead to problems. If biodiesel is used in a light-duty diesel engine, here too fuel dilution can impact the oil’s low-temperature properties.

 

Hitches and Glitches

   Oil consumption can also be a problem. If the oil level drops below the onequart-low mark, the oil will be subject to more stress. Since the OLM only   tracks oil temperature and engine revolutions, it might not detect any change. The dashboard lights (sometimes known as “idiot lights”) will indicate low oil level — but that is really too late. Vehicle owners still need to check that their oil level is correct, a task that is easy to perform but often overlooked.

   Then there is the use of synthetic engine oil. Typically, synthetics have more resistance to oxidation which is related to engine oil temperature. The OLM system is based on conventional engine oil, so it may be too conservative on oil change intervals if synthetics are used. At present there is no adjustment that can be made for the use of synthetic engine oils.

   The GM OLM system is not the only game in town. Mercedes-Benz also has a system which it calls the Flexible Service System (FSS). In addition to engine revolutions and oil temperature, the FSS system evaluates clock time, coolant temperature, vehicle speed, engine load and oil level. These additional data points are useful, but if they require additional sensors, Smolenski pointed out, it would have a big negative impact on the OLM system’s cost, while adding   only incremental (“about 5 percent”) improvements in precision.

   An interesting sidelight to the onboard oil monitor story is that Mercedes-Benz developed its oil drain algorithm based on the use of synthetic oil. However, many Mercedes dealers and owners in the United States used conventional oils in their vehicles. This resulted in some engine failures and a class-action lawsuit with over 350,000 plaintiffs, which cost Mercedes about $32 million dollars to settle in 2003.

   Meanwhile, GM is not standing pat on its invention. The OLM is nearing its 20th birthday, and its patents are also winding down. To extend GM’s commercial advantage, its researchers are hard at work to create a next-generation OLM.

   OLM is also strongly promoted in GM’s OnStar Vehicle Diagnostics program. Since 2005, OnStar has remotely collected data from participating vehi-     cles’ onboard computers, and e-mailed drivers with maintenance reminders, including the status of their oil life and an estimate of when their next oil change may be due.

   By following these alerts rather than an arbitrary 3,000-mile interval, OnStar said its subscribers can save an aggregate $12.5 million a month and more than $150 million annually on oil changes. One adherent boasted of needing only four oil changes in 52,000 miles, for an average interval of 12,000 miles between drains, thanks to the OnStar e-mails. “If we were doing the traditional 3,000-mile intervals, we would have had 17 oil changes instead!” Saturn owner Elijah Scott posted on Facebook last year.  

 

Next Steps

   For many, the question regarding the OLM and similar systems is how reliable they are. Based on GM’s experience and increasing comfort in using OLM data to extend drain intervals, the answer is very trustworthy. U.S. drivers appear happy to have systems that tell them when something needs to be done (reactive), versus remembering to schedule and carry out regular maintenance (proactive). The OLM system gives these drivers a light on the control panel that reminds to change the oil. It fits with the other lighted warnings found there such as low oil pressure, overheated engine, fuel level, and newer alerts such as low tire pressure.

   Oil maintenance gurus point out that there still are three things to remember with regard to the OLM system. First, as GM recommends, make sure to change the oil within 600 miles of when the “Change Oil Soon” light comes on.   Second, make sure the OLM is reset after each oil change — the system cannot detect fresh oil, so the driver or the oil change technician must do it. Third, make sure to use the proper engine oil category and viscosity grade recommended for the vehicle. The OLM system is designed to be most precise with the proper oil quality and viscosity for each vehicle make and model year.   Following these steps guarantees the accuracy of the system.

   The OLM system has yet to have a huge effect on the oil-change marketplace, but it’s among the reasons why consumption is waning. National Oil & Lube News last year found the average oil change interval with onboard monitors was about 4,800 miles, versus 4,300 for those without — and most vehicles still are without.

   Quick lubes, dealers and garages still promote the 3,000-mile/three-month oil change interval. Oil marketers are also supporting the same regime. The reason for this is obvious: More oil changes equal more sales volumes and revenues for all concerned. Given that OEMs are seeking longer oil drains and the oil marketers are for the status quo, the question arises: What potential impact will the OLM have on future oil sales?  

   In December, Smolenski told the ICIS Pan American Base Oils & Lubricants Conference that the 3,000-mile interval is not “cheap insurance” — it’s sheer waste. Especially with the OLM, oil change intervals of between 6,000 and 15,000 miles are achievable. “If all U.S. GM vehicle owners used the GM Oil Life System as intended, more than 100 million gallons of engine oil could be saved annually,” he urged.

   In a market that has been steady at around 1 billion gallons per year since 1980, that would be a noticeable dent.  

 

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