NEW ELECTRIC POWER TRAIN PROMISES 160-KM ALL-ELECTRIC RANGE ON A BUS
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. 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.
Adura reaches this effect by breaking 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 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 slashing 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 just 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 is the system’s flexibility, according to the designers. 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. It could even accommodate a mix of batteries and supercapacitors, to better handle a 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.
