Hydraulic Hybrid School Bus Gets ?A? For Effort

Students at Georgia Tech are converting a conventional school bus into a hydraulic hybrid, with a unique energy-saving drivetrain that may help school districts realize fuel and maintenance savings.

The project, financed with a $50,000 grant from Ford, will also hopefully shed light on one of the least well-known alternative vehicle powertrains. Hydraulic hybrids use a vehicle?s conventional gas or diesel engine to power a pump that ?charges? an accumulator. Under acceleration, the accumulator can power hydraulic motors with the built-up pressure. Hit the brakes and the pump motors reverse, recapturing braking energy.

UPS rolled out a hydraulic hybrid demonstrator fleet back in 2008, and earlier this year Chrysler announced they?d be developing the technology in partnership with the EPA. Traditionally, the technology has worked best on large vehicles used in stop-and-go drive cycles, such as buses and delivery vans.?As installed on a school bus, the conversion is expected to offer a 20 percent fuel savings that eventually pays for the conversion and saves money over a traditional bus ? just what cash-strapped school districts need.

Led by mechanical engineering professor Dr. Michael Leamy, the team of three grad students and five undergrads have been designing the new drivetrain, fabricating parts and installing the conversion for the past eight months. According to Leamy, the team is about 85 percent done. ?At present, the transfer case is?mounted with one accumulator,? he said. ?The microcontroller is fully programmed and?the sensors are installed.?

When it?s complete, the bus will be painted by students at Atlanta?s Mary Lin Elementary and reenter the fleet of the Atlanta Public School system, fueled by biodiesel made from waste cooking oil donated by local restaurants.

With the exception of the paintjob, the bus itself has remained mostly intact. Leamy?s team split the driveshaft to provide power to a transfer case, which then was connected to the hydraulic pump and motor. ?The conventional powertrain is kept, outside of the driveshaft,? Leamy said.

At this point, any savings are strictly long-term. While Leamy estimated the cost of the single conversion at $20,000, he said that the additional savings of converting an entire fleet of buses could bring the per-unit cost down to between $8,000 and $10,000.??With diesel prices rising, we think the recuperation cost could reasonably get down to five years or so in the not too distant future,? he said.

Photos: Michael Leamy

Source: http://www.wired.com/autopia/2011/05/hydraulic-hybrid-school-bus/

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