The US Environmental Protection Agency says it has developed a hydraulic hybrid powertrain capable of delivering fuel consumption of 30km per liter in a full-sized sedan.
Ford Motor Co. was sufficiently impressed with the hydraulic hybrid to sign a deal with the EPA last October to continue research. But Ford says the technology is a long way from dealer showrooms.
The car uses a conventional internal-combustion engine attached to a pump that compresses gaseous nitrogen in high-pressure tanks. Releasing the pressure pushes hydraulic fluid through a hydraulic motor, which turns the wheels.
The test car, admittedly a crude prototype, is noisy. Its tanks, motors and pumps would be difficult to package under the hood, particularly in a small car.
'Ford certainly is serious' about the technology, said John Brevick, a project leader at Ford Research Laboratory. But he acknowledged significant problems: 'The cost, the package, making it totally transparent to the customer, plus reliability, durability - are all issues that have to be worked out.'
The hybrid's efficient regenerative braking gives it a major advantage over gasoline-electric hybrids, says the car's inventor, Charles Gray, 55, the top researcher at the EPA lab in Ann Arbor, Michigan.
The car captures 98 percent of the energy available from braking, compared with 30 percent for a gasoline-electric hybrid, he said. When the brakes are applied, the flow of hydraulic fluid that provides forward motion is altered in a way that returns pressure to the tank, making that energy available for use in acceleration.
A gasoline-electric hybrid stores the braking energy in a battery, which is inherently less capable than a pressurized tank of quickly absorbing and releasing energy.
Both Honda and Toyota are selling gasoline-electric hybrids in the USA. Honda last month started selling a gasoline-electric Civic that gets about 20 km per liter.
Gray developed the engine on a modest budget, about $20 (E22 million) million over seven years, at the EPA lab. He used US government funds from the Partnership for a New Generation of Vehicles, a project set up by the administraton of former US President Bill Clinton to encourage research into fuel-efficient vehicles by government scientists and General Motors, Ford and then-Chrysler Corp.
The US government required the EPA to keep quiet about the vehicle because the partnership was designed to help US domestic automakers develop an advantage over foreign competitors. But the partnership expired, freeing the EPA to talk about the hydraulic hybrid.
Hydraulic equipment is used widely in factories, construction equipment and on airplanes. So Gray had a supply of ready-made equipment to assemble his car. But the resulting diverse mix of parts in the EPA's concept car is noisy.
Gray said the car was built to prove the concept. He is busy on a second-generation car that he said will be far more efficient and quiet.
The first-generation powertrain would achieve 26.5km per liter on a car the size of the Ford Focus. Improved versions are capable of 30km per liter on a heavier model, he said.
Gray is convinced his invention will wind up in showrooms.
'From a technical perspective, I truly believe it has a chance to be the prominent drivetrain in new vehicles in 10 years,' he said. 'I know that's a bold statement.'
He said hydraulic hybrids would be more expensive than conventional autos. He declined to be specific. But he said gasoline savings would recoup the extra cost to the consumer in less than three years, assuming an automaker produced at least 50,000 units a year to achieve sufficient economies of scale.
Eaton of Cleveland, Ohio, USA, an auto supplier that manufactures hydraulic equipment for construction, factories and other uses, also signed an agreement with the EPA to develop hydraulic hybrids.
Eaton is concentrating at first on only one portion of the powertrain, which it calls hydraulic launch assist. The device captures braking energy in a pressurized tank. A hydraulic motor uses the pressure to help launch a vehicle from a stop. Eaton installed it on the Ford Mighty F-350 Tonka concept truck, shown at the Detroit auto show in January.
The technology is 'not a dry hole,' said Brad Bohlmann, business development coordinator at Eaton. 'Hydraulic launch assist is proven. It will be commercialized.'