New Electric Power Train Promises 160-km All-Electric Range�on a Bus

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Scientists with an eye toward making the perfect battery for electric vehicles (EVs) and hybrids have been brewing an endless array of chemical potions. Their hope is that their voltaic alchemy might someday yield a golden storage device with high specific energy for long trips on a single charge, ample power density for quick acceleration and highway-speed cruising, and the durability to match a vehicle's life expectancy. But technologists at Adura Systems, a Menlo Park, Calif.�based power-train company, are convinced that the path to better EV travel lies in improved electronic design rather than more brilliant chemical or mechanical engineering.

Adura emerged from stealth mode this month to claim it has developed intelligent electronics that more efficiently manage the performance of batteries and the rest of the power train. The system could let a hybrid-electric bus travel as far as 160 kilometers in electric-only mode before its range-extending engine kicks in. The Modular Electric Scalable Architecture (MESA) power train will be featured in hybrid-electric buses operated by Chinese mass-transit systems as soon as next year, according to the company.

City buses traveling a total of 210 km per day will have an effective fuel economy of 4.7 liters per 100 km, or 50 miles per gallon. MESA should be an Olympic triple jump past the 47L/100 km (5 mpg) performance of traditional diesel buses. That translates to an estimated annual reduction in greenhouse-gas emissions of 4250 metric tons per bus, or 5.5 billion tons per year if all of China's 1.3 million diesel buses were replaced with MESA power trains.

How did Adura do it? CEO Marvin Bush was understandably reticent to describe the company's secret sauce in detail. But he did tout one important decision: to break the battery pack into small modules. Because the complexity of a battery's electricity and thermal management system increases exponentially rather than linearly with the addition of cells, breaking Adura's energy storage into smaller modules lessens their complexity, and therefore their weight and cost. Each of Adura's 160-kilogram power modules stores 22 kilowatt-hours; bus manufacturers may install as many as 10 modules to deliver a tailored amount of pure EV range.

The net effect, Bush says, is that Adura's modules have a much greater specific energy (energy per unit mass) than the 450-kg, 53-kWh battery pack in the Tesla Roadster, even when made up of the same battery cells.

Another big factor in MESA's ability to squeeze so much range out of its battery modules comes from the ruthlessness with which the Adura engineers slashed components that weigh a vehicle down. The power train that will propel the Chinese buses includes a 120-kilowatt electric motor and a 60-kW flex-fuel microturbine in a series hybrid system, in which an electric motor propels the bus and the internal combustion engine acts as an electricity generator. While the diesel engines on most passenger buses weigh more than 1300 kg, the microturbine weighs in at a svelte 230 kg. And because it burns fuel more completely than a diesel engine, such exhaust treatments as catalytic converters or urea spray devices, which add both bulk and expense, are unnecessary.

Just as important, says Bush, is the system's flexibility. It maintains continuous communication among the power modules and is capable of instantly reconfiguring the load if a module were to fail while a vehicle was cruising down the road. The battery-management system has also been designed to allow modules containing different battery chemistries to peacefully coexist. Bush says that it could even accommodate a mix of batteries and supercapacitors, as a trash-carting company is interested in doing with its garbage trucks to better handle the vehicles' frequent starts and stops.

Adura is rolling out the first MESA-based vehicles in China for several reasons. The automotive development cycle for buses there is much shorter than in the United States, so the company could get the power train on the road much faster, and because Adura outsources manufacturing to Chinese firms, it will save on shipping costs in the early stages.

Adura is in talks with U.S. automakers about developing a version for trucks. "The only thing that changes in the MESA power train between buses, trucks, and cars is the size of the battery modules, the motor, and the rack they're mounted on," Bush says.