Up Time Magazine - February/March 2009 - (Page 38) motor testing upload Expanding Maintenance Technologies Electrical Motor Diagnostics in Hybrid and Electric Vehicles by Howard W. Penrose, PhD, CMRP M ost of the first automobiles produced in the 19th Century were all-electric. Among other advantages, the primary reason was the amount of instantaneous power and torque provided. However, the batteries limited the distance that the vehicles could travel, which opened the door for the dominance of the combustion engine, which had a much greater range due to the lighter fuel. For the greater part of a century the internal combustion engine (ICE) held on to its dominance, an intricate infrastructure was built around the use of gasoline, and the automotive industry focused on the customer requirements of size and power. Following the 1973 Oil Embargo on the USA, and the near-forgotten lines at gas stations, a hardy few realized that the flow of oil would not last forever. In addition to alternative fuels, battery and hybrid/electric research was initiated by governments, automotive companies, universities, independent research facilities and individuals in an effort to return to the original concept of an electric vehicle. The first modern production electric vehicle produced was the General Motors EV1, which was first released in 1996 and ran for three years on a lease-only, 3 year, 30,000 mile warranty. With a total population of 2,234 EV1’s built at the GM Lansing Craft Centre in Lansing, Michigan, the vehicle was an engineering and marketing evaluation in California and Arizona only. At the end of the run, the EV1 was pulled out of production and almost all vehicles recovered by GM due to problems with expected advancements in battery technology. Most automotive manufacturers made the decision to focus on hybrid technology while working towards allelectric powertrains, with the exception of Tesla Motors® who have focused, and released, all-electric sports cars in the $105,000+ range. One of the first hybrids to market was the Toyota Prius which instilled the concept that a fuel efficient vehicle must be small in order to obtain good mileage and fuel range. General Motors, Ford, and Chrysler focused their primary work related to hybrids on their better selling, more profitable larger vehicles with an assortment of SUVs and pickup trucks now being available and all-electric production vehicles being made available by 2010. General Motors and Chrysler partnered on the development of the ‘heavy hybrid’ two-mode transmission, which is the subject of the tests in this article. The transmission, as shown in Figure 1, is in direct line with the combustion engine and contains two powerful electric motors driven by two variable frequency drives under the hood which is supplied by a 300 volt battery pack under the rear passenger seats. In the two-mode Figure 1- GM 2Mode Hybrid Transmission full-sized SUVs and trucks, the ICE is: a GM Active Fuel Management® Vortec® engine; and, a displacement on demand Hemi® for Chrysler. The transmissions are 4-speed with the electric motors assisting. This provides for an infinite variation in speeds, resulting in an extremely versatile transmission which, combined with the ability to vary the ICE between 4 and 8 cylinders, increases the fuel efficiency of the vehicles by more than 50%. The 300 volt system operates in both motoring and regeneration mode, meaning that in addition to operating as an electric motor, the machines also act to generate power for the battery and are also used as part of the braking system. The result is an even and very fast braking through the transmission. The combination of increased power over an ICE-only SUV and braking capability that outperforms most passenger vehicles makes for an impressive performance. Because of the additional weight of the hybrid powertrain, many of the components, such as the rear hatch, are aluminum versus steel, which lowers the center of gravity and allows for exceptional handling in all weather conditions. The challenge at hand: can modern maintenance testing technologies be used to evaluate the electric motors in an electric or hybrid machine? What can they tell us? 38 february/march 2009
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