| abstract | - A hybrid electric vehicle (HEV) is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle, or better performance. A variety of types of HEV exist, and the degree to which they function as EVs varies as well. The most common form of HEV is the hybrid electric car, although hybrid electric trucks (pickups and tractors) and buses also exist. Modern HEVs make use of efficiency-improving technologies such as regenerative braking, which converts the vehicle's kinetic energy into electric energy to charge the battery, rather than wasting it as heat energy as conventional brakes do. Some varieties of HEVs use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor-generator), to either recharge their batteries or to directly power the electric drive motors. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its ICE than a comparably-sized gasoline car, since an HEV's gasoline engine is usually smaller than a comparably-sized pure gasoline-burning vehicle (natural gas and propane fuels produce lower emissions) and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy. Ferdinand Porsche in 1900 developed the Lohner-Porsche Mixte Hybrid, the first gasoline-electric hybrid automobile in the world. The hybrid-electric vehicle did not become widely available until the release of the Toyota Prius in Japan in 1997, followed by the Honda Insight in 1999. While initially perceived as unnecessary due to the low cost of gasoline, worldwide increases in the price of petroleum caused many automakers to release hybrids in the late 2000s; they are now perceived as a core segment of the automotive market of the future. Worldwide sales of hybrid vehicles produced by Toyota, the market leader, reached 1.0 million vehicles by May 31, 2007; the 2.0 million mark was reached by August 31, 2009; and 3.0 million units by February 2011, with hybrids sold in 80 countries and regions. Worldwide sales are led by the Toyota Prius, with cumulative sales of 2.36 million by August 2011, and sold in 70 countries and regions. The United States is the largest hybrid market in the world, with 2 million hybrid automobiles and SUVs sold through May 2011, and California is the biggest regional American market. The Prius is the top selling hybrid car in the U.S. market with 1 million units sold by April 2011, and cumulative sales of the Prii in Japan reached the 1 million mark in August 2011.
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