The U.S. Environmental Protection Agency and Chrysler Group have partnered to test a hydraulic hybrid system for minivans that could be cheaper than conventional hybrid systems and could save more gasoline. EPA and Chrysler are each spending $2 million (for a total of $4 million) on the project, and they expect to begin road testing next year.
Conventional hybrids save gas in part by using energy from braking to charge a battery. A hydraulic hybrid captures energy by using a hydraulic pump instead of conventional friction brakes to slow the vehicle. The pump forces fluid into a tank, compressing air that can then be used to help propel the vehicle.
Hydraulic systems are bulky and loud, which has limited their use to large vehicles such as garbage trucks. But they're attractive because pumps and air storage tanks are cheap compared to batteries. Also, hydraulic hybrids have the potential for larger fuel economy improvements than battery hybrids because hydraulic systems can store energy very quickly, allowing them to capture more energy from braking. While conventional battery hybrid systems for minivans might improve fuel economy by 25 percent compared to gas-powered cars, hydraulic systems could improve fuel economy by 30 percent to 35 percent under most conditions, says David Haugen, manager of the technology development group at EPA's National Vehicle and Fuel Emissions Laboratory. In city driving, the improvement could be as much as 60 percent. Chris Cowland, Chrysler's director responsible for advanced powertrains, says the 60 percent improvement is "way more significant than any other technology that we know of today."