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How Idle-stop Systems Work

Cars with Idle-stop Systems
Some predict that a third of all new cars will use some kind of idle-stop system by 2012.
Some predict that a third of all new cars will use some kind of idle-stop system by 2012.
AP Photo/Shuji Kajiyama

Although the savings you'll get on fuel in a mild hybrid won't really compare to those of a full hybrid car, stop-start technology is still a promising step forward in making conventional cars much more fuel-efficient. This is an especially important step, since most fuel economy problems stem from idling and the constant stop and go nature of city driving. The technology has actually been around for a while, but we'll a look at some notable newer cars using idle-stop systems and the improvements that are underway for the existing technology.

Several recent car models will use (or have used) some kind of stop-start technology, with most examples coming from Europe or Japan. Some people might not know that the MINI Cooper, built under the BMW Group, has actually used idle-stop technology since 2007. And German automaker Audi started using an idle-stop system in the second quarter of 2009 in its A3, A4 and A5 models, with more to follow.

The most recent, and perhaps the most significant, example of a vehicle receiving an idle-stop system is the Madza3, which will begin using a new and improved type of stop-start technology by the end of 2009. While some systems tend to suffer due to the use of a conventional electric starter, which can cause slow and sluggish restarts, the new Mazda system will use combustion for the restart. Direct injection plays an integral part in the function of the system that Mazda calls the Smart Idle Stop System, or SISS. When a vehicle slows down and stops, sensors position the engine's pistons in specific locations within each of the cylinders. This allows the system to determine which of the cylinders is fully pressurized and ready to fire. At restart, fuel is injected into the appropriate cylinder, the fuel and air mix is ignited and the engine continues to operate as it normally would.

With these slight improvements, Mazda claims that their engines can restart in 350 milliseconds, about half the time it takes for other conventional systems to restart, and it results in a 10 percent reduction in fuel use, too.

For lots more information about hybrid cars and fuel-efficient technology, follow the links on the next page.