A project to develop a hydraulic hybrid retrofit of a school bus, led by Dr. Michael Leamy at the Georgia Institute of Technology and his team of undergraduate and graduate engineering students, is yielding impressive results. Not only is their work realizing the potential of new fuel efficiencies for school buses everywhere, but it also provides a model for effectively engaging college and pre-college students in hands-on learning about eco-friendly fluid power.
Over the last two years, Dr. Leamy and his students have designed, built and have begun testing a hydraulic hybrid propulsion system retrofit and biofuel conversion of a public school bus donated by the Atlanta Public Schools. Much of the design and fabrication work to date has been carried out by undergraduates in Georgia Tech’s mechanical engineering program; ME graduate students have taken on leadership roles in the project. Their work, originally funded by grant from the Ford Motor Company Fund, has been further enabled through donations of components as well as guidance from engineers at Eaton Corporation, Evonik RohMax, Linde Corp. and Poclain Hydraulics, all industry affiliate members of the Engineering Research Center for Compact and Efficient Fluid Power (CCEFP). The CCEFP will provide funding for work during the project’s third year. School buses are suitable for hydraulic hybrid power due to their large mass and typically stop-and-go drive cycles.
The hydraulic retrofit captures braking energy using a pump-motor which first pumps hydraulic fluid into a high pressure accumulator (thereby storing energy), and then releases this energy to the drivetrain through the motoring capability of 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. Next steps involve incorporating complementary technologies including a clean start technology in which the diesel engine is shut down at bus stops and restarted using a hydraulic motor, saving children’s lungs from harmful emissions.
The hybrid retrofit has moved from the lab to the street, and tests are underway aimed at verifying predicted gains of more than 20% in fuel economy. Considering that more than 700,000 gal of diesel fuel are used by school buses each year in Atlanta alone, a 20% gain in efficiency could significantly lower both fuel costs and emissions through widespread adoption.
The impact of the project’s education and outreach efforts grows, too, as more undergraduates and graduate students get involved, some even taking on the role of teacher as they use the bus to show precollege students not only how hydraulic systems operate but also why the work of engineers is so important. For further information, contact Dr. Leamy (Michael.leamy@me.gatech.edu) or Dr. Stelson, CCEFP Director (kstelson@umn.edu).
Engineering Research Center for Compact and Efficient Fluid Power (CCEFP)
