A hybrid electric vehicle (HEV) is a type of hybrid vehicle that combines a conventional internal combustion engine (ICE) system with an electric propulsion system (hybrid vehicle drivetrain). The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle or better performance. There is a variety of HEV types, and the degree to which each functions as an electric vehicle (EV) also varies. 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 brakes which convert the vehicle's kinetic energy to electric energy, which is stored in a battery or supercapacitor. Some varieties of HEV use their internal combustion engine to generate electricity by spinning an electrical generator to either recharge their batteries or to directly power the electric drive motors; this combination is known as a motor–generator. Many HEVs reduce idle emissions by shutting down the engine at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less tailpipe emissions than a comparably sized gasoline car, since the hybrid gasoline engine is usually smaller than a comparably sized, pure gasoline-powered vehicle and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy.
Although Ferdinand Porsche developed the Lohner-Porsche in 1901, hybrid electric vehicles 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.As of January 2017, over 12 million hybrid electric vehicles have been sold worldwide since their inception in 1997. Japan has the world's largest hybrid electric vehicle fleet with 7.5 million hybrids registered as of March 2018. Japan also has the world's highest hybrid market penetration with hybrids representing 19.0% of all passenger cars on the road as of March 2018, both figures excluding kei cars. As of April 2016, the U.S. ranked second with cumulative sales of over 4 million units since 1999, and Europe with about 1.5 million hybrids delivered since 2000.Global sales are led by the Toyota Motor Company with more than 10 million Lexus and Toyota hybrids sold as of January 2017, followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1.35 million hybrids as of June 2014; As of January 2017, worldwide hybrid sales are led by the Toyota Prius liftback, with cumulative sales of almost 4 million units. The Prius nameplate had sold more than 6 million hybrids up to January 2017. Global Lexus hybrid sales achieved the 1 million unit milestone in March 2016. As of January 2017, the conventional Prius is the all-time best-selling hybrid car in both Japan and the U.S., with sales of over 1.8 million in Japan and 1.75 million in the U.S.