Monday, December 22, 2008

Want to Save at the Pump? Try Stopping Smart by Mike Trudel, Freelance Writer

According to several reputable studies, up to thirty percent of a typical gasoline car engine's output is lost during braking in everyday city driving situations. Believe it or not, this simple principle is one of the primary reasons gas mileage on the highway is so much higher: less braking.

Most cars' braking systems depend on friction, applied on metal drums or disks, to stop the rotation of the wheels. All the kinetic energy built up during driving, then, is abruptly halted through this friction and converted to useless heat, as the vehicle cannot employ that energy for forward propulsion. One important advantage of hybrid-electric vehicles (HEVs) is that they use regenerative braking. This, in turn, helps to provide better fuel economy. Waiting lists are getting longer and longer for the most popular HEV models as gas prices rise. Such high demand surpassing customarily high supply is a feat for the automotive industry, which usually has a standard 100-day reserve of any given vehicle, according to a popular news magazine.

Regenerative braking is the process of reducing a vehicle's speed by converting some of its kinetic energy into another useful form. In many HEVs, the electric motor is used to create torque to drive the wheels and may often be designed to closely resemble electric generators. The HEV engine, then, can either use electricity to create torque or vice versa. Rather than creating friction and useless heat to slow the vehicle, it reverses the electric motor -- essentially turning it into an electric generator. This process generates electricity, which is then fed and stored into a battery to be used once the car starts moving. Every time an HEV slows down, reduces acceleration or uses its brakes, energy can be stored.

The shift from losing energy during braking to packing it away may seem minor to the average consumer, but it is an essential element in creating the hybrid engine's ability for better fuel economy. So is its ability to actually turn itself off at idle and then quickly -- smoothly -- restart once the accelerator is pressed.

Stop/start technology conserves energy by shutting off the gasoline engine when the vehicle is at idle. This is difficult to imagine for those who, for their entire driving lives, have been accustomed to a vehicle only starting through the use of a key. This, however, is precisely what happens. The engine automatically re-starts when the driver pushes the gas pedal to go forward and continues on just as smoothly as a traditional gasoline engine would. This, too, saves on fuel.

Of course, specialized equipment is needed to incorporate such technology. An integrated starter generator system, which includes more than just a smart braking system, is a good beginning. The best will have a crankshaft-mounted starter generator, traction inverter, DC/DC converter, controllers and a battery pack. It will also provide quick, quiet stop/start, regenerative braking, torque smoothing, high power generation, launch-assist to reduce fuel consumption and emissions, and battery management to increase battery life.

There's more, of course, for the savvy. Such systems can also provide on-board electrical power generation, which will create a smoother ride and efficient on-board power production. Integrated power electronics and controllers will give the consumer a traction inverter, DC/DC converter motor, an energy controller, Control Area Network (CAN) communications and 5 to 10 kilowatts of on-board electrical power, enabling customer features. The engine on such models can also start five times faster than its conventional counterparts, and a liquid cooling element allows the elimination of a second coolant loop in some applications.

Pretty fancy, eh?

So you thought fuel economy was all about smaller cars, the latest and greatest engines and race car technology? While these all help, fuel economy is also about using brake energy more efficiently. Using "stop smart" technology just might save the impact on your wallet.

About the Author

Mike Trudel, Freelance Writer. Delphi Corporation is committed to contributing state-of-the-art technologies and automotive innovation to help achieve greener roadways. For more information, please visit

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