As the hybrid market heats up, the major automakers are jockeying for position as the technology leader. Each company trumpets its technology as the best approach to combining a gasoline engine and electric motor. Toyota currently dominates with its “Hybrid Synergy Drive.” Honda continues to evolve its “Integrated Motor Assist.” And General Motors makes big claims for its “two-mode” hybrid system. In 2007, we’ll see if G.M.’s system represents anything beyond a clever new name for what others already have. Is there a genuinely different approach out there? Yes. Hydraulic hybrids.
Hydraulic hybrids operate basically the same way as gasoline-electric hybrids, but they use a motor-pump instead of an electric motor-generator—and an accumulator rather than the battery pack. An accumulator is essentially a pressure tank that stores compressed gas or liquid. When the driver slows down or brakes, the pump forces the hydraulic fluid out of a low-pressure tank into a twin high-pressure tank. To accelerate, the fluid is forced back to the low-pressure tank past the pump/motor, which applies torque to the wheels. The hydraulic regenerative braking system, which can put as much as 80 percent of the braking energy back to the wheel, is more efficient than regen braking in current hybrid cars.
More Efficient than a Prius
Hydraulic hybrids caught the attention of the Environmental Protection Agency, because the system promises 25 – 45 percent improvements in fuel economy and emissions. The E.P.A. is working with Eaton Corporation to install hybrid hydraulics in a number of United Parcel Service trucks. Eaton and Peterbilt have also announced joint development of garbage trucks. While delivery trucks, and other vehicles which make frequent quick stops, could experience the greatest benefits from this technology, it’s possible that hydraulic hybrid technology could be applied to passenger vehicles one day.
Jim O’Brien, of Hybrid-Drive Systems, LLC, in Deerfield Michigan, has moved the technology one step closer to reality by converting a 1968 Volkswagen Beetle to a hydraulic hybrid. “We are not aware of anything else like it,” O’Brien said. “This new powertrain is more efficient than electric hybrid powertains being used in such cars as Toyota Prius and Ford Escape.”
The Beetle has a dented roof, patchwork paint job, and timeworn interior. But the innovation lies in the trunk. Two accumulator tanks, which resemble scuba tanks, protrude from the left side of the engine compartment. The engine is on the right side. The wheel pump motor is buried out of sight. Hydraulic fluid hoses connect the components. When the system is pressurized by the onboard 6.5 horsepower Briggs and Stratton lawnmower engine, the Beetle is ready to run. The car can reach speeds of 30 miles per hour.
Despite the proof-of-concept with the compact Beetle, O’Brien’s now plans to apply the technology to a larger vehicle. “Our next project is to scale up the hydraulics to power a van for city delivery,” said O’Brien. Hybra-Drive recently purchased a deliver van from Arrow Uniform in Taylor, Michigan. According to O’Brien, if the first one works out, Arrow intends to operate five hybrid hydraulic trucks.
Dr. Ram Chandran, associate professor of mechanical engineering at Kettering University, said, “It’s a simple design and will help keep the cost low. I believe it has a high potential for success.”