ERC's Innovative Research and Educational Outreach Program Leads to Breakthroughs in Applying Hydraulic Hybrid Technology

Achievement date: 

Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, have developed a hydraulic hybrid retrofit of a school bus.


The team, led by Dr. Michael Leamy at CCEFP partner institution the Georgia Institute of Technology, is yielding impressive results. The work is realizing the potential of new fuel efficiencies for school buses everywhere; it also provides a model for effectively engaging college and pre-college students in hands-on learning about eco-friendly fluid power. The impact of the project’s education and outreach efforts also grows as more undergraduate and graduate students get involved, some even taking on the role of teacher as they use the bus to show pre-college students how hydraulic systems operate and why the work of engineers is so important.


School buses are ideal for hydraulic hybrid power due to their large mass and 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 drive train 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 associated valve components.

Over the past two years, the team has designed, built, and begun testing a hydraulic hybrid propulsion system retrofit and bio-fuel conversion of a public school bus donated by Atlanta (GA) Public Schools (see accompanying figure). Much of the design and fabrication work has been carried out by undergraduates in Georgia Tech’s mechanical engineering program. Mechanical engineering graduate students have taken on leadership roles in the project. The hybrid retrofit has moved from the laboratory to the street, and tests are underway to verify predicted gains of over 20% in fuel economy. Considering that more than 700,000 gallons of diesel fuel are used by school buses each year in Atlanta, a 20% gain in efficiency could significantly lower both fuel costs and emissions through widespread adoption.