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Hybrid power served 5 ways
By By Peter Valdes-Dapena, CNNMoney.com staff writer
"Hybrid" doesn't mean just one thing. Cars and SUVs can be set up in different ways to meet different needs. Here's a look at the various systems.
August 6, 2007
Choices
The hybrid menu
Hybrid gasoline/electric vehicles are often lumped into one, all-inclusive catagory. People will say "I'm thinking of buying a hybrid" without thinking about which model or type.
The fact is, hybrid vehicles vary enormously. It's not just that some are SUVs and some are cars. Their hybrid powertrains, themselves, can differ greatly in their design and programming. (Computer software has a lot to do with how a hybrid works.)
Right now, Toyota is the unchallenged hybrid leader. The Toyota Prius is the best selling hybrid by far, accounting for more than half of all the vehicles sold.
Toyota's "full hybrid" system is also used in Nissan's Altima Hybrid, and it's the same technology used in the Ford Escape and Mercury Mariner Hybrid SUVs.
General Motors, long seen as a laggard in hybrid technology, now has three types of hybrid systems on tap.
One, commonly called a "mild hybrid" system, is on the market now. Another, the "two-mode" hybrid system, will be introduced in the fall. A third "series hybrid" plug-in electric vehicle, is on the path to production, but no specific timetable is set.
Full Hybrid
Toyota Prius
The vehicle that most readily comes to mind when someone says "hybrid" is the Prius. It's a good car in many respects: The Prius has the interior space of a midsized Camry in a smaller package.
It's a "full hybrid:" in that it can run on its electric motor alone for short distances at low speeds.
The Prius was designed, from the outset, to be a gasoline/electric hybrid vehicle. That enabled designers to create the body around the hybrid system rather than cramming batteries and an electric motor into a body designed to house just a gas tank and an engine. For that reason, the Prius has plenty of usable storage space.
With its unique body design, it's also instantly recognizable as a high-tech hybrid car, which only increases its appeal.
Mild hybrid
Saturn Aura Green Line
The Saturn Green Line vehicles, the Aura sedan and Vue SUV, are "mild hybrids," in which the electric motor provides assistance to the gasoline engine but lacks the power to drive the vehicle on its own.
Fuel is saved by shutting the gasoline engine down altogether whenever the vehicle comes to a full stop.
Also, since the electric is there to provide additional thrust, the gasoline engine doesn't need to be as large. (The Aura Green Line, for instance, has a 4-cylinder engine where non-hybrid versions have V6's.)
The advantages of a system like this are cost and size. The system requires little alteration to the basic engine and transmission layout so that it costs much less to manufacture than a complex "full hybrid" system.
Also, since electricity needs are lower, the system requires only a small battery pack which, again, saves on costs, but also saves weight and space. Other hybrid sedans, such as the Nissan Maxima and Toyota Camry Hybrids, lose trunk space to make room for batteries.
The downsides are that the system's impact on fuel economy is relatively small while the drag on driving performance is sizable.
When not boosting performance, the Green Line electric motor/generator remains fully engaged, acting like an anchor bogging the car down whenever the gas pedal isn't being pressed.
Performance hybrid
Lexus LS600h
The LS600h offers the performance of a V12 with the fuel economy of a V8, Toyota boasts.
Compared to those cars, the Lexus looks downright thrifty. Not only does it get better fuel economy - it even costs a lot less. The V12-powered BMW 760li gets 15 mpg and costs about $20,000 more. The Lexus gets 21 mpg.
And the LS's performance really is impressive. Step on the gas the combined engine and motor, together producing a maximum of about 600 horsepower, push you back in your seat with an easy whisper, barely straining as the needle on the electric boost gauge moves into "performance" territory.
Toyota doesn't expect to sell very many of these cars. Market experience shows that hybrid shoppers are mostly interested in one thing: burning as little fuel as possible. High-end luxury hybrid buyers represent a market that has not yet shown itself. One can make a case for a performance-oriented six-figure hybrid car, but for now the jury is still out.
Two-mode hybrid
GMC Yukon Hybrid
This fall, General Motors will be coming out with hybrid versions of the company's most popular full-sized SUVs, the Chevrolet Tahoe and GMC Yukon.
It might seem silly to make hybrid versions of these big vehicles, but if you consider the amount of fuel ultimately saved, it actually makes a lot of sense. Even a modest improvement in the efficiency of a vehicle that uses a lot of fuel will save more gallons than a large improvement in an already-efficient small car.
There are performance challenges in creating a large hybrid SUV, though. If the hybrid version can't tow or haul just like the non-hybrid, consumers won't buy it. Instead they'll just go back to non-hybrid SUVs. So the hybrid SUVs have the same big V8 engines as their non-hybrid counterparts, ready to pull a trailer when needed.
When not needed, however, GM's "dual mode" hybrid system employs a variety of fuel-saving tricks when the vehicle is traveling at highway speeds.
Four of the eight cylinders will shut down when their power is not needed. (The hybrid uses a large engine - 6.0 liters - so that half will still provide adequate pull and the SUV can spend more time in 4-cylinder mode.)
The SUV's electric motor also connects to the wheels one way at low speeds and another at high speeds, allowing it to provide maximum assistance at any speed.
As with many other hybrid vehicles, the GM hybrid SUVs can travel under electric power alone for short distances at low speeds, and the gasoline engine shuts down altogether whenever the vehicle stops.
Plug-in Hybrid
Chevrolet Volt
Even though it has a gasoline engine and an electric motor, GM is careful not to call the Chevrolet Volt a hybrid car. We've included it here, though, because it's commonly referred to as a "plug-in hybrid." GM calls it a plug-in electric vehicle with on-board power generation.
The point is that, while the Volt has a gasoline engine, the engine does not power the car's wheels. The wheels are powered by an electric motor. Batteries for the electric motor can be charged by plugging the Volt into an ordinary electrical outlet.
After the batteries are fully charged, the car can be driven for up to 40 miles without needing additional charging. If batteries do run low, the gasoline engine will run to generate electricity as needed.
The only difference then between the Volt and what you would ordinarily call "an electric car" is that it can charge its own batteries - whenever that may be needed - in addition to using power supplied by your local electric utility.GM has no official on-sale date for the Volt. More research is still needed on the battery, and there's no way to put a timetable on the needed breakthroughs, the company has said.
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