A hybrid electric vehicle (HEV) is a type of hybrid vehicle that couples a conventional internal combustion engine (ICE) with one or more electric engines into a combined propulsion system. The presence of the electric powertrain, which has inherently better energy conversion efficiency, is intended to achieve either better fuel economy or better acceleration performance than a conventional vehicle. 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 hybrid electric passenger cars, although hybrid electric trucks (pickups, tow trucks and tractors), buses, motorboats, and aircraft also exist.

Modern HEVs use energy recovery technologies such as motor–generator units and regenerative braking to recycle the vehicle's kinetic energy to electric energy via an alternator, which is stored in a battery pack or a supercapacitor. Some varieties of HEV use an internal combustion engine to directly drive an electrical generator, which either recharges the vehicle's batteries or directly powers the electric traction motors; this combination is known as a range extender. Many HEVs reduce idle emissions by temporarily shutting down the combustion engine at idle (such as when waiting at the traffic light) and restarting it when needed; this is known as a start-stop system. A hybrid-electric system produces less tailpipe emissions than a comparably sized petrol engine vehicle since the hybrid's petrol engine usually has smaller displacement and thus lower fuel consumption than that of a conventional petrol-powered vehicle. If the engine is not used to drive the car directly, it can be geared to run at maximum efficiency, further improving fuel economy.

Ferdinand Porsche developed the Lohner–Porsche in 1901. But 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. Initially, hybrid seemed unnecessary due to the low cost of petrol. 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.

, over 17 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 . Japan also has the world's highest hybrid market penetration with hybrids representing 19.0% of all passenger cars on the road , both figures excluding kei cars. , the U.S. ranked second with cumulative sales of 5.8 million units since 1999, See Table 6.2: Hybrid and Plug-In Vehicle Sales, 1999-2020 and, , Europe listed third with 3.0 million cars delivered since 2000.

Global sales are led by the Toyota Motor Corporation with more than 15 million Lexus and Toyota hybrids sold , followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1.35 million hybrids ; Honda sold 187,851 hybrids in 2013. Honda sold 158,696 hybrids during the first six months of 2014. , worldwide hybrid sales are led by the Toyota Prius liftback, with cumulative sales of 5 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. , 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.

Classification

Types of powertrain

Hybrid electric vehicles can be classified according to the way in which power is supplied to the drivetrain:

In parallel hybrids, the ICE and the electric motor are both connected to the mechanical transmission and can simultaneously transmit power to drive the wheels, usually through a conventional transmission. Honda's Integrated Motor Assist (IMA) system as found in the Insight, Civic, Accord, as well as the GM Belted Alternator/Starter (BAS Hybrid) system found in the Chevrolet Malibu hybrids are examples of production parallel hybrids. The internal combustion engine of many parallel hybrids can also act as a generator for supplemental recharging. , commercialized parallel hybrids use a full size combustion engine with a single, small (<20 kW) electric motor and small battery pack as the electric motor is designed to supplement the main engine, not to be the sole source of motive power from launch. But after 2015 parallel hybrids with over 50 kW are available, enabling electric driving at moderate acceleration. Parallel hybrids are more efficient than comparable non-hybrid vehicles especially during urban stop-and-go conditions where the electric motor is permitted to contribute, and during highway operation. In series hybrids, only the electric motor drives the drivetrain, and a smaller ICE (also called range extender) works as a generator to power the electric motor or to recharge the batteries. They also usually have a larger battery pack than parallel hybrids, making them more expensive. Once the batteries are low, the small combustion engine can generate power at its optimum settings at all times, making them more efficient in extensive city driving. Power-split hybrids have the benefits of a combination of series and parallel characteristics. As a result, they are more efficient overall, because series hybrids tend to be more efficient at lower speeds and parallel tend to be more efficient at high speeds; however, the cost of power-split hybrid is higher than a pure parallel. Examples of power-split (referred to by some as "series-parallel") hybrid powertrains include 2007 models of Ford, General Motors, Lexus, Nissan, and Toyota.Toyota Motor Corporation (2006) "Series Parallel Hybrid System" Hybrid Synergy Drive. Retrieved June 19, 2007.

In each of the hybrids above it is common to use regenerative braking to recharge the batteries.

Type of hybridization

Plug-in hybrids (PHEVs)

A plug-in hybrid electric vehicle (PHEV), also known as a plug-in hybrid, is a hybrid electric vehicle with rechargeable batteries that can be restored to full charge by connecting a plug to an external electric power source. A PHEV shares the characteristics of both a conventional hybrid electric vehicle, having an electric motor and an internal combustion engine; and of an all-electric vehicle, also having a plug to connect to the electrical grid. PHEVs have a much larger all-electric range as compared to conventional petrol-electric hybrids, and also eliminate the "range anxiety" associated with all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted. pp. 30–32 See reviewed by CalCars founder Felix Kramer (September 9, 2008) "T. Friedman's New Bestseller Hot, Flat & Crowded Touts Plug-Ins"

Flex-fuel hybrid

In December 2018, Toyota do Brasil announced the development of the world's first commercial hybrid electric car with flex-fuel engine capable of running with electricity and ethanol fuel or petrol. The flexible fuel hybrid technology was developed in partnership with several Brazilian federal universities, and a prototype was tested for six months using a Toyota Prius as development mule. Toyota announced plans to start series production of a flex hybrid electric car for the Brazilian market in the second half of 2019.

The twelfth generation of the Corolla line-up was launched in Brazil in September 2019, which included an Altis trim with the first version of a flex-fuel hybrid powered by a 1.8-litre Atkinson engine. By February 2020, sales of the Corolla Altis flex-fuel hybrid represented almost 25% of all Corolla sales in the country.

Energy Management Systems To take advantage of the emission reduction potential of hybrid electric vehicles (HEVs), appropriate design of their energy management systems (EMSs) to control the power flow between the engine and the battery is essential.

In a conventional (non-hybrid) vehicle, there is no need for an energy management strategy: the driver decides the instant power delivery using the brake and accelerator pedals and, in manual transmission vehicles, decides which gear is engaged at any time. In a hybrid vehicle, on the other hand, there is an additional decision that must be taken due to its ability to recover energy during braking or driving downhill: how much power is delivered by each of the energy sources on board the vehicle. The recovered energy can be stored in the battery and deployed at a later time to assist the prime mover to provide tractive power. This is why all hybrid vehicles include an energy management controller, interposed between the driver and the component controllers. As mentioned, the aim of the energy management system is to determine the optimal power split between the on-board energy sources. The decision regarding what to consider optimal depends on the specific application: in most cases, the strategies tend to minimize the fuel consumption, but optimization objectives could also include the minimization of pollutant emissions, maximization of battery life or—in general—a compromise among all the above goals.

History

Early days

William H. Patton filed a patent application for a petrol-electric hybrid rail-car propulsion system in early 1889, and for a similar hybrid boat propulsion system in mid-1889.W. H. Patton, Motor for Street Cars, , granted Aug. 13, 1889.Boat, , granted Apr. 1, 1890. He went on to test and market the Patton Motor Car, a gas-electric hybrid system used to drive tram cars and small locomotives. A petrol engine drove a generator that served to charge a lead acid battery in parallel with the traction motors. A conventional series-parallel controller was used for the traction motors. A prototype was built in 1889, an experimental tram car was run in Pullman, Illinois, in 1891, and a production locomotive was sold to a street railway company in Cedar Falls, Iowa, in 1897.The Patton Motor, The Street Railway Journal, Vol. VII, No. 10 (October, 1891); pages 513–514. Includes Photo.The Patton Motor Car, English Mechanic and World of Science, no. 1713 (Jan. 21, 1898); page 524.

In 1896, the Armstrong Phaeton was developed by Harry E. Dey and built by the Armstrong Company of Bridgeport, CT for the Roger Mechanical Carriage Company. Though there were steam, electric, and internal combustion vehicles introduced in the early days, the Armstrong Phaeton was innovative with many firsts. Not only did it have a petrol powered 6.5-litre, two-cylinder engine, but also a dynamo flywheel connected to an onboard battery. The dynamo and regenerative braking were used to charge the battery. Its electric starter was used 16 years before Cadillac's. The dynamo also provided ignition spark and powered the electric lamps. The Phaeton also had the first semi-automatic transmission (no manual clutch). The exhaust system was an integrated structural component of the vehicle. The Armstrong Phaeton's motor was too powerful; the torque damaged the carriage wheels repeatedly.