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Hybrid Vehicles

UCD-ITS-RP-95-06

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Electric vehicles have a number of important and well recognized advantages compared to conventional engine powered, liquid-fueled internal combustion engine (ICE) vehicles. These advantages include zero exhaust emissions, very quiet operation, home refueling, a relatively simple, highly efficient driveline, and the possible use of nonfossil, renewable energy as the primary energy source for commercial and personal transportation. The main disadvantage of electric vehicles in the minds of many consumers and the auto companies is their limited range before it is necessary to recharge the batteries, which in most instances takes a number of hours. Even though the daily travel of most vehicle owners on the vast majority of days is much less than the present range of electric vehicles, most consumers are reluctant to purchase a limited range vehicle, which could not be used to meet all their needs. This is especially true if, as is likely when electric vehicles are first marketed, their price is higher than that of conventional ICE vehicles. The limited range of the electric vehicle can be overcome by incorporating into the driveline of the vehicle the capability to generate electricity on-board the vehicle, when needed, from a chemical fuel. Such a vehicle is termed a hybrid-electric vehicle. It has the characteristics of both an electric vehicle and a conventional ICE vehicle and can be operated either on wall-plug electricity stored in a battery or from a liquid fuel (eg, gasoline) obtained at a service station. Hybrid-electric vehicles can be designed that will operate only on wall-plug electricity on most days for city commuting and yet offer the owner unlimited range without recharging the battery on those days when long distance travel (hundreds of miles) is needed. This type of hybrid-electric vehicle has all the advantages previously cited for the electric vehicle in city use for daily travel less than its battery range and could be marketed as a direct substitute for the conventional ICE vehicle to those consumers who feel they need an all-purpose vehicle. On those days that the hybrid-electric vehicle is operated on the battery alone, it is a zero emission vehicle and makes the maximum contribution to reducing air pollution in the urban area. On those days when the engine is operated to extend the range of the vehicle, the vehicle's exhaust emissions are not zero, but on an annual basis, as discussed later in the chapter, the average emissions of the vehicle can be very low, much below that for ICE vehicles meeting the California Ultra Low Emissions Vehicle (ULEV) standards. Present hybrid-electric vehicle designs utilize a heat engine driven generator to convert a chemical fuel to electricity on-board the vehicle. Future designs can use a fuel cell rather than an engine to convert the chemical fuel to electricity. The fuel cell-powered vehicle would have much lower emissions than the hybrid-electric vehicle with an engine.
Published in the Encyclopedia of Energy Technology and the Environment, ed. Attilio Bisio and Sharon Boots, W.J. Wiley & Sons.