Rebuilding toward the future: California city purchases rebuilt buses incorporating hybrid drive system

Diesel Progress North American Edition, June, 2005 by Bill Siuru

Many transit agencies wanting to upgrade their bus fleets to attract more riders, add more routes or meet more stringent air quality standards frequently run into budgetary roadblocks. Yet while it's hard for many communities to justify the expense of new vehicles, many are opting for remanufactured buses.

Not only can a bus chassis be recycled to like-new condition, but the recycling can also incorporate the latest drivetrain and other system technologies to improve fuel economy, reduce emissions and offer riders the latest amenities. Besides being less costly compared to new buses, they can be delivered in significantly less time.

As an example, the city of Elk Grove, Calif., recently put 17 hybrid electric buses into service, becoming California's first 100% hybrid electric commuter bus fleet. While these e-tran buses feature the latest fuel-saving, clean propulsion system technologies and many upscale creature comforts, the basic buses were far from new. The city purchased remanufactured Gillig 40 ft. transit buses rebuilt by Complete Coach Works, Riverside, Calif. The buses, which were purchased from the San Diego MTB at the end of their 12-year lifetime, were put into operation in January and have been operating at better than 96% availability since then, according to Elk Grove transit officials.

The heart of the recycled buses is the ThunderVolt hybrid-electric drive system supplied by ISE Corp., San Diego, Calif. The ThunderVolt system incorporates a standard 6.8 L, Ford Triton V10 engine rated 305 hp and 405 lb.ft, of torque. Modifications to the engine included replacing the intake throttle with a Bosch electric throttle actuator and the flex plate flywheel is replaced by a coupling on the Siemens ELFA, 140 kW generator. The crankshaft pulley is replaced by a heavy-duty spider-mounted pulley and belt tensioner that drives a heavy-duty Niehoff alternator on a custom mount system. The alternator supplies electricity to the low voltage batteries.

In this series hybrid configuration, the gasoline engine drives the Siemens generator that in turn supplies electricity to two 85 kW, 146 lb.ft, continuous (150 kW, 299 lb.ft, peak) output electric motors, also supplied by Siemens. The wheel motors drive the rear wheels through a 4:1 reduction Flender gearbox.

Excess energy and energy from regenerative braking is stored in two ThunderPack Ultracapacitor packs developed by ISE and Maxwell Technologies, San Diego. An electrically driven hydraulic pump, high efficiency electric fan cooling system, scroll air compressor and air conditioner are run on 230 Vac power supplied by the 600 Vdc bus through a Siemens DUO-Inverter. The inverter also controls the generator, drive motors, braking resistors and ultracapacitor energy storage. The system control software was a joint ISE-Siemens development.

An onboard ISE Remote Diagnostic Unit (RDU) stores operating history, which is available through a remote Internet site. All of the components, except for the two ultracapacitor packs and the electronics cooling radiator with fans, are mounted on a support cradle that slides in and out of the rear of the bus and attaches to the frame rails.

The engine, operating on 87 octane gasoline, produces virtually zero particulate matter and already meets the 2007 California Air Resources Board (CARB) and EPA standards for emissions of N[O.sub.x] and PM, resulting in an ultra-low emission vehicle (ULEV) rating. With its 0.4 g/bhp-hr of N[O.sub.x] and zero PM emissions, it was the first hybrid system certified by CARB as a ULEV, ISE said. According to the company, the ThunderVolt system can also improve fuel economy by 50% and requires no special refueling infrastructure such as that needed to operate natural gas vehicles.

During the remanufacturing process, Complete Coach Works took the buses down to bare frame, made necessary structural repairs and rebuilt the buses from the ground up. Elk Grove City Manager John Danielson said one of the goals of the new bus purchase was "to take our commuters out of their cars and on to the bus." To do that, the buses had to not only provide the positive air quality benefits, but also provide a comfortable ride and "an onboard environment that is conducive to both productivity and relaxation."

To meet these objectives, the recycled buses are fitted with airline style high-back reclining seats with parcel racks and individual reading lamps. Eight television screens provide real-time satellite programming and news broadcasts. Eventually, there is a plan for Internet access for riders.

Other upgrades on the freeway-capable e-tran buses include LED destination signs, Talking Bus automatic stop annunciation and Transit Care 3-Minute Windows. The 17 e-tran buses were delivered and in revenue service in a relatively short six months after contract award.