In the early morning hours across America, five days a week, an army of big-dog garbage trucks sets out to pick up our trash. They pull up, stop, idle, load and take off for the next stop, often only 100 feet or less away. This happens 300 to 1,200 times per day, per vehicle.

On a good day, a diesel garbage hauler will eke out 4 to 5 mpg. Then there are all those icky, nasty pollutants pouring out of the exhaust pipe.

But thanks to the United States Environmental Protection Agency (EPA), yes, those government folks who monitor environmental laws and fuel mileage testing, a system called “hydraulic hybrid” increases fuel economy up to 30 percent and reduces carbon dioxide emissions by 40 percent or more in heavy-duty truck applications.

Developed at EPA’s National Vehicle and Fuel Emissions Laboratory (NVFEL) in Ann Arbor, Michigan, the government agency partnered with Cleveland, Ohio-based Eaton Corporation, a global diversified power management company. The technology, called the Hydraulic Launch Assist (HLA) system essentially operates in the same manner as a gasoline-electric hybrid. Like gasoline-electric hybrid versions, HLA works by recovering a portion of the energy normally lost as heat by the vehicle’s brakes. But instead of a battery pack, a hydraulic system uses pistons to capture the wasted energy by compressing nitrogen gas stored in a tank, called an accumulator. When the driver lets off the accelerator pedal, the wheels drive a hydraulic pump that pumps hydraulic fluid to compress the nitrogen gas and slows the truck down. When the driver accelerates, the nitrogen is allowed to expand and pushes a piston in a cylinder filled with hydraulic fluid. This action assists the diesel engine in turning the rear wheels.

An added advantage to the HLA system is reduced brake wear because Eaton’s technology hydraulically stops the truck. Typically, refuse haulers require several brake replacements each year, costing around $2,000 each time. The hydraulic regenerative braking system cuts this to less than once a year.

Several cities are testing the HLA equipped garbage trucks. The latest is, appropriately, Ann Arbor with four Peterbilt equipped trucks. The city is one of the first to obtain funding for them through the U.S. Department of Energy’s Clean Cities Program. The $156,000 grant offsets the nearly $40,000 cost difference over a conventional diesel hauler. UPS hydraulic hybrid

UPS has been testing Navistar delivery trucks with an Eaton hydraulic system that does not use the diesel engine to power the wheels.

An aggressive variation of the HLA design is being tested in UPS Navistar parcel delivery trucks. Using an Eaton series-type hybrid design, the V6 diesel engines do not power the vehicles, but serve solely to actuate the hydraulic systems’ pumps. It’s estimated that these vehicles could see fuel economy improvements of as much as 60 percent and a reduction of greenhouse emissions of 40 percent.

Using hydraulic technology to increase fuel economy and lower emission isn’t an exclusive for the United States. Hydraulic hybrid buses are being tested on the streets of Beijing, China with the hope of introducing them to other parts of the country.

The hydraulic hybrid appears to offer huge benefits when applied to heavy vehicles that operate in stop-and-go driving conditions, but what about passenger cars and trucks? The engineers at the EPA’s Michigan laboratory have built and tested many prototypes over the years, including a diesel-hydraulic Ford Taurus that chalked up more than 80 miles per gallon. In 2004, the EPA displayed a hydraulic hybrid Ford Expedition SUV with a small diesel engine replacing the large displacement gasoline V8. It delivered an 82 percent improvement in combined city and highway gas mileage. Ford was an early partner with the EPA in developing the system, but later dropped out.

Reprinted with permission from Hybrid Cars