EPA Innovates Hydraulic Hybrid System

The Environmental Protection Agency is testing a cheaper, simpler hybrid technology it hopes can greatly increase the mpg of American vehicles. The agency has 20 patents on the system and has already begun testing it this year. EPA's new hydraulic hybrid technology could improve fuel economy up to 55 percent—better than the 30 to 40 percent fuel economy of gas-electric hybrids. The system uses hydraulic pressure to recapture energy lost through braking, and then releases the pressure during acceleration.

The System
The basic technology was originally developed and patented by EPA's National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, over 10 years ago under a Clinton Administration's program to research cleaner energy technology. The technology is being refined under a cooperative agreement with Ford, UPS and Eaton Corporation, and the U.S. Army. The powertrain features a high-efficiency diesel engine teamed with a hydraulic hybrid propulsion system that uses hydraulic pumps and hydraulic storage tanks to store energy, in the place of electric motors and batteries used in electrical hybrid vehicles.


The EPA says the hydraulic system would cost an estimated $600 to install on a mass-production basis compared to $3,000 to $6,000 for an electric hybrid system. That cost, they say, could be recouped in the first year of driving. The system is less complicated than the gas-electric hybrids, and the simpler components could mean longer life and less maintenance. However, it adds about 190 pounds to a vehicle and, like other hybrid systems, does not spectacularly increase highway mileage figures.

Real World Testing
UPS recently unveiled its first delivery truck using EPA's hydraulic hybrid system and plans to test the technology in real world situations. Because of the added weight of the tanks used to store pressurized fluid in the system, the best application may be in heavy-duty trucks that inch their way through urban stop-and-go driving. UPS says its 88,000 delivery vans now average about 8.5 mpg costing $1.4 billion in fuel every year. EPA estimates that the UPS project truck could get a 70 percent increase in fuel efficiency driving on city routes, and the additional cost of the hybrid truck would be recouped in 2.5 years.


Ford is working with the EPA on developing a hydraulic hybrid Expedition prototype. It could get 32 mpg in city driving and 22 mpg on the highway. The conventional gas Expedition gets only 13 mpg in the city and 20 mpg on the highway. The EPA is working on other pilot projects with the U.S. Army, and Eaton Corporation, a waste management company. Eaton will test a fleet of 20 hydraulic hybrid garbage trucks in the last half of 2006.