The $50,000 project, led by Dr. Michael Leamy and his team of undergraduate and graduate engineering students, is yielding notable results. Not only is their work realizing the potential of new fuel efficiencies for school buses everywhere, but it has also engaged college and pre-college students in hands-on learning about eco-friendly fluid power.
In the past two years, Leamy and his students have designed, built and begun testing a hydraulic-hybrid propulsion system retrofit and biofuel conversion of a public school bus donated by the Atlanta (Ga.) Public Schools. Now that the hybrid retrofit has moved from the lab to the street, tests are under way to verify estimated gains of more than 20 percent in fuel economy. The project also includes a cost-benefit analysis of a large-scale conversion of a school bus fleet to hydraulic hybrid powertrains designed to recover lost braking energy.
"We expect our research will lead to cleaner, more efficient school buses that will help school districts like APS significantly reduce fuel costs and greenhouse gas emissions," Leamy said.
The project is helping students at Mary Lin Elementary learn about how to protect the environment. The students painted the 16-passenger bus green on May 13 and organized a drive to collect used cooking oil for processing into biodiesel.
"The Green Eco School Bus turns a theoretical concept into a fun and exciting reality that stimulates their learning," added Principal Brian Mitchell.
As first reported in the August 2011 edition of STN, school buses are considered ideal for hydraulic hybrid power because of their large mass and stop-and-go drive cycles. The hydraulic retrofit captures braking energy using a pump-motor that first pumps hydraulic fluid into a high-pressure accumulator and then releases the stored energy to the drivetrain via the pump-motor. A microcontroller-based system developed at Georgia Tech controls the mode of operation of the pump-motor, its displacement and various valve components.
Originally funded by a grant from the Ford Motor Company Fund, Georgia Tech's work has moved forward through component donations and direction from engineers at Eaton Corporation, Evonik RohMax, Linde Corporation and Poclain Hydraulics.
Eaton also works with IC Bus to specially design a charge-sustaining hybrid system, which combines the MaxxForce DT with MaxxForce Advanced EGR and an electric motor with a peak power output of 44 kilowatts.