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Hybrid electric vehicle

Vehicle that operates on a combination of petrol and electricity

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Through Electric motor, Acceleration and Petroleum

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.

As of April 2020, 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 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 December 2020, the U.S. ranked second with cumulative sales of 5.8 million units since 1999, and, as of July 2020, 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 as of January 2020, followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1.35 million hybrids as of June 2014; As of September 2022, 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. 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.

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. As of 2013, 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.

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

Type of hybridization

  • Full hybrid, sometimes also called a strong hybrid, is a vehicle that can run entirely on its electric motor for a period of time. Ford's hybrid system, Toyota's Hybrid Synergy Drive, Peugeot-Citroën's HYbrid4 and General Motors/Chrysler's Two-Mode Hybrid technologies are full hybrid systems. The Toyota Prius, Peugeot 508 RXH HYbrid4, Ford Escape Hybrid, and Ford Fusion Hybrid are examples of full hybrids, as these cars can be moved forward on battery power alone. A large, high-capacity battery pack is needed for battery-only operation. These vehicles have a split power path allowing greater flexibility in the drivetrain by interconverting mechanical and electrical power, at some cost in complexity.
  • A mild hybrid is a vehicle that cannot be driven solely on its electric motor, because the electric motor does not have enough power to propel the vehicle on its own. Mild hybrids include only some of the features found in hybrid technology, and usually achieve limited fuel consumption savings, up to 15 percent in urban driving and 8 to 10 percent overall cycle. A mild hybrid is essentially a conventional vehicle with an oversized starter motor, allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly and cleanly. The motor is often mounted between the engine and transmission, taking the place of the torque converter, and is used to supply additional propulsion energy when accelerating. Accessories can continue to run on electrical power while the petrol engine is off, and as in other hybrid designs, the motor is used for regenerative braking to recapture energy. As compared to full hybrids, mild hybrids have smaller batteries and a smaller, weaker motor/generator, which allows manufacturers to reduce cost and weight. Honda's early hybrids including the first generation Insight used this design, leveraging their reputation for design of small, efficient petrol engines; their system is dubbed Integrated Motor Assist (IMA). Starting with the 2006 Civic Hybrid, the IMA system now can propel the vehicle solely on electric power during medium speed cruising. Another example is the 2005–2007 Chevrolet Silverado Hybrid, a full-size pickup truck. Chevrolet was able to get a 10% improvement on the Silverado's fuel efficiency by shutting down and restarting the engine on demand and using regenerative braking. General Motors has also used its mild BAS Hybrid technology in other models such as the Saturn Vue Green Line, the Saturn Aura Greenline, the 2008-2009 Chevrolet Malibu Hybrid and the 2013–2014 Chevrolet Malibu Eco.

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.

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.

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