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Vehicles that utilize more than one energy source for propulsion are usually termed hybrid vehicles. Although the onboard energy storage system (ESS) may be a flywheel or a hydraulic accumulator, most hybrid vehicles use chemical batteries or capacitors and are termed hybrid-electric vehicles. Fuel cells (FCs) may be used in hybrid-electric vehicles as primary power sources instead of conventional internal combustion engines (ICEs). In this article, ICE–battery hybrid transit buses are discussed specifically and contrasted with conventional drive buses. . | Buses ICE Battery Hybrids NN Clark and F Zhen West Virginia University Morgantown WV USA 2009 Elsevier B.V. All rights reserved. Introduction Vehicles that utilize more than one energy source for propulsion are usually termed hybrid vehicles. Although the onboard energy storage system ESS may be a flywheel or a hydraulic accumulator most hybrid vehicles use chemical batteries or capacitors and are termed hybrid-electric vehicles. Fuel cells FCs may be used in hybrid-electric vehicles as primary power sources instead of conventional internal combustion engines ICEs . In this article ICE-battery hybrid transit buses are discussed specifically and contrasted with conventional drive buses. Transit buses most typically are equipped with two axles and have a nominal length of 12 m 40 ft although they may range in size from large vans to articulated units of 18 m 60 ft nominal length. Conventional buses may be equipped with manual or automatically shifted transmissions but most typically have conventional automatic transmissions with a torque converter. Modern automatic transmissions have improved bus powertrain efficiency by employing four or more speeds gear ratios with a lockup capability on the torque converter. Over-the-road coaches are similar to transit buses but are typically 14 m 45 ft in length and may have three axles instead of two. Hybrid-electric buses typically have better fuel economy and lower emissions than comparable conventional buses. Instead of employing aerodynamic body design or weight reduction to improve vehicle fuel efficiency the hybrid system focuses on recovering energy loss during braking and deceleration and increasing powertrain efficiency over a cycle. Consider the road-load equation used to describe the power demand at the drive wheels of a vehicle vehicle power demand 1pC Av3 Crrmgv m - mgv sina 1 The road-load equation is composed of terms representing aerodynamic drag rolling resistance and power required for changing inertia and .
