Hydraulic hybrid engines

Dec 1, 2006

Hydraulic hybrid engines may be on the road and saving millions in the near future. A Kettering professor is helping with the EPA research to make it happen.

When the testing is finalized and the matrix is complete, a new hydraulic hybrid technology for use in large commercial trucks could represent billions of dollars in fuel savings.

Dr. Ram S. Chandran, professor of Mechanical Engineering at Kettering University, is part of a research team at the Environmental Protection Agency (EPA) working on perfecting the hydraulic hybrid technology that stores energy more efficiently and cuts down on fuel consumption.

Chandran got involved in the hydraulic hybrid research after responding to an EPA Request for Proposals in the area of hydraulics. He submitted a proposal for a high-speed flywheel combined with a hydraulic motor and was turned down. The EPA liked what they saw, however, and Dr. Charles Gray, of the National Vehicle and Fuel Emissions Laboratory (NVFEL) of the EPA in Ann Arbor, Mich., contacted Chandran about joining his research team testing hydraulic motors that run the truck.

Not a lot of research is done on hydraulic vehicles in this country, according to Chandran, so the 10-year-plus project is relatively unique in the U.S.

Chandran agreed to work at the NVFEL lab two days a week running tests to analyze the impact that surface friction, temperature and various loads (stresses) have on the motor and its performance and how they reduce or increase engine efficiency. He has been making the bi-weekly commute to Ann Arbor for the past five months.

His work involves putting a prototype motor on a dynamometer, an instrument used to measure force and power, and exposing it to conditions such as the heat of Arizona and the cold of North Dakota mornings in January. "We have to expose the test motor to everything a real UPS truck would experience on the road," he said. UPS is working with the EPA on the prototype testing and currently has one vehicle on the road for field testing in Michigan.

"We have a huge matrix to finish testing," he said, "we're making more changes in the design all the time. It is seemingly mundane work but I enjoy it," he added, "sometimes I think I should thank the EPA for letting me come and use their big equipment." Chandran is not being paid for his work on the project other than mileage to drive to Ann Arbor.

The hydraulic hybrid is like an electric hybrid except that instead of an electrical system working with the engine there is a hydraulic system. The EPA research project involves a large truck engine that runs a pump, according to Chandran. The pump drives a hydraulic motor connected to a differential that turns the wheels (there is no gear box). FEV, an independent engine and powertrain systems research, design and development company, has developed the prototype for testing, Chandran said.

"It is very energy efficient to run a pump and motor together," said Chandran, "it runs at about 90-95 percent efficiency. This is because the transmission can select any position based on speed and torque."

"Typically a vehicle loses energy when the brakes are applied. In this hydraulic system, when the brakes are applied the motor becomes a pump that converts low pressure fluid into high pressure fluid and stores it in big bottles under the truck," he said. These bottles compress nitrogen and store the energy which can be given back to the engine when the brake is released and the truck accelerates, he added.

The bottles of high pressure gas enable faster storage and release of energy than that provided by the traditional model of braking systems and batteries used to store energy, according to Chandran.

The prototype hydraulic hybrid system weighs about 300 pounds more than a traditional engine gear box-powertrain combination, but still provides a 50 to 60 percent increase in fuel efficiency over a traditional engine powertrain combination," Chandran said.

"The UPS truck currently being road tested is getting 65 percent better fuel economy than a regular UPS truck," said Chandran. "UPS spends about $800,000,000 on fuel each year. Even a 20 percent improvement represents a large savings both in dollars and in fuel."

In addition to the increased fuel efficiency, one of the more attractive features of the system is that it is possible to convert existing vehicles to hydraulic hybrid, so manufacturers do not have to re-tool entire production lines.

Companies other than UPS that are interested in the hydraulic hybrid technology range from manufacturers of component systems to automakers. Eaton Corporation, a diversified industrial manufacturer of hydraulic systems, press brakes and hydraulic components, is collaborating with EPA to develop a production version of the final design, according to Chandran.

And, the Ford Motor Company is also interested in the hydraulic hybrid technology for two of its larger heavy-duty vehicles slated for the consumer market.

Written by Dawn Hibbard
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