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Engines for Hybrids Take a Supporting Role |
That is a change of direction from recent developments in engine design aimed at improving power and performance. Conventional methods of raising power output — adding camshafts and valves to let the engine breathe easier, for example — have been employed alongside refinements in electronic control systems. |
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| Modern engines develop more power, over a wider range of speeds, with little sacrifice of drivability or fuel economy. But eventually, all the power and flexibility so carefully engineered into today's engines will not be needed. Instead, tomorrow's engines will wait patiently until their services are required to extend an electric car's range. After starting, they will hum quietly while assisting the new heroes of hybrid propulsion, electric motors powered by lithium-ion batteries. Automakers have already begun previewing the engine of this electric-car future. The 2010 Toyota Prius has no rubber belts under its hood to drive external accessories. All of the accessory equipment, including the air-conditioning compressor and the power steering, is powered by electric motors. One engine strategy used by the Prius and other hybrids is the Atkinson combustion cycle, which sacrifices some power to gain efficiency. The electric motor's torque more than makes up for the slight reduction in engine output. While General Motors won't reveal the details of the 1.4-liter 4-cylinder planned for use as a range-extender in the 2011 Volt, John Bereisa, whose many roles at G.M. include directing advanced engineering and technology development strategy, did offer an overview of the engine that will power this car's generator. “All we need is 67 horsepower, enough to maintain the batteries' charge when the car is cruising at highway speed,” he said. “Since there wasn't time to design an engine from scratch, we looked for the smallest existing engine capable of supplying 67 horsepower, which turned out to be G.M.'s Family Zero design used in Europe, Asia, Africa and the Middle East.” Mr. Bereisa continued: “When you map an engine's power versus r.p.m. versus fuel consumption, the resulting chart looks like the Rocky Mountains. In conventional cars, you're driving all over that map. But in the Volt, we're able to keep the engine operating in what I call its happy valley, where it delivers the power that's required while consuming minimal fuel.” The borders of that valley, Mr. Bereisa said, are still under development, but they may range from a low of 2,000 r.p.m. to a high of 3,000 r.p.m, enough to maintain the battery pack's charge. Pressed to speculate about how electric car engines will further evolve, Mr. Bereisa acknowledged that G.M. engineers are already considering a clean-sheet design for the car he calls Volt II. “We'd select a smaller displacement engine for the future, probably less than 1 liter,” he said. “We'd position the catalytic converter and route the coolant lines to minimize heat losses.” “The engine for the next Volt will definitely be as simple and as light as possible.” |
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