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Thanks to high fuel prices, hybrid gasoline-electric vehicles such as the Toyota Prius are constantly in the limelight. But far away from that glow, government scientists, auto parts engineers, and garage inventors are toiling on a distinctly less glamorous way to save fuel. It's a hybrid vehicle that pairs a gas engine with a hydraulic transmission. You may associate hydraulics with ancient, oily gear lifting heavy loads on farms and construction sites. But like everything old, this is new again.
Whenever gas prices shoot up, inventors and tech companies come out of the woodwork, trumpeting the next mileage-boosting miracle. And certainly there is room for fresh thinking, since gas savings on hybrids and clean-diesel vehicles can take four years or more to make up for the difference in cost to the buyer. Maybe that's why parts makers such as Eaton Corp. and BorgWarner Inc. and a lonely inventor named Tom Kasmer are suddenly pushing hybrid hydraulic systems for everything from delivery trucks and garbage haulers to small cars and bicycles. The sales pitch: The hydraulic approach is relatively inexpensive. "This could be a better option than the hybrids on the road today," says Kasmer.
Hydraulic hybrids have been ignored because they present big engineering challenges, noise being one. Even so, Eaton and the Environmental Protection Agency teamed up with United Parcel Service to put hydraulic delivery trucks on the road. In tests, the prototypes get upwards of 50% better fuel economy. Kasmer himself has failed to connect with a big carmaker so far, but his hybrid approach, known as a hydristor, has attracted interest from Bobcat Co., a construction equipment maker. "The technology will start with large commercial vehicles," says Sohan Uppal, vice-president for research for Eaton's fluid systems group.
All hydraulic transmission systems have some basic features in common. They begin with a low-pressure tank filled with fluid, most often oil. When the driver hits the brakes, the liquid is pumped into a high-pressure tank. The pent-up fluid naturally wants to escape. But since it can't, pressure builds and energy is stored. Then, when the driver releases the brake and hits the accelerator, the liquid flows back to the low-pressure tank. Along the way, the rushing fluid turns vanes that rotate an axle, and the vehicle takes off. Only later does the gas engine take over.
Gas-electric hybrids also achieve efficiency by capturing energy from braking. But Kasmer claims his hydristor would be cheaper than the computer controllers and batteries in Prius-like hybrids. Working independently of Kasmer, the EPA, Eaton, and BorgWarner reached the same conclusion. BorgWarner put a prototype system in a Chinese-made subcompact car, raising its mileage from 33 mpg to 40 in tests, says Bill Kelly, vice-president for drive train development.PEDAL POWER
It's in trucks, however, that the technology may really prove its value. Eaton's Uppal says the company has developed a system for garbage haulers that could reap terrific fuel savings because the vehicles could make up to nine stops in a row running on stored hydraulic power alone. EPA project manager John Kargul says that for a variety of trucks, the fuel savings from hydraulics could offset higher sticker prices in less than three years -- a tall order for today's pricier gas-electric hybrid designs.
Truly exotic applications may be at hand. Stymied in Detroit, Kasmer is working with a major bicycle maker that hopes to adapt his design to replace conventional chains and gears. Such a bike might prove easier to build and pedal because the hydristor would make seamless, gear-like adjustments as the rider pumped up and down hills.
Detroit's carmakers say that they have good reasons for keeping their distance. Thomas G. Stephens, group vice-president for power train operations at General Motors Corp. (GM
), wrote in an e-mail that plenty of inventors have tinkered with hydraulics or related ideas. Yet he doesn't see how any could come close to doubling fuel economy, as Kasmer has claimed. And no matter how big their benefits, hydraulic systems are prone to leaks.
Then there's the noise issue. "[They] groan like the landing gear on an airplane," admits Kelly of BorgWarner. Considering their shaky financial situation, U.S. automakers aren't likely to spend the research money needed to iron out these kinks. They're even less likely to bet the $1 billion it takes to scale up production of a new transmission, Kelly says.
Kasmer still dreams of getting his hydristors into passenger cars. But he has to work on his presentation. When he spoke to a group of engineers at Munro & Associates Inc., a Troy (Mich.) engineering consulting firm with clients such as DaimlerChrysler (DCX
) and Boeing Co., the demo impressed some of the engineers. But when they asked him for technical details, he balked at giving away design secrets. Instead, says Sandy Munro, principal of the firm and one of Kasmer's financial backers, Kasmer lectured listeners about cleaning up the air for tomorrow's children. The techies wanted more info, and when it wasn't forthcoming, a few headed for the door. By David Welch