Hybrid electric vehicle

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 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 and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy. (Natural gas and propane fuels produce fewer emissions.)


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. Types by degree of hybridization Full hybrid, sometimes also called a strong hybrid, is a vehicle that can run only on a combustion engine, only on an electric motor, or a combination of both. Ford's hybrid system, Toyota's Hybrid Synergy Drive and General Motors/Chrysler's Two-Mode Hybrid technologies are full hybrid systems. The Toyota Prius, 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. 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 oversize 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 gasoline 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 gasoline 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 and the Malibu Hybrid. 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 powersource. 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 gasoline-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. Chinese battery manufacturer and automaker BYD Auto released the F3DM PHEV-62 (PHEV-100 km) hatchback to the Chinese fleet market on December 15, 2008, for 149,800 yuan (US $22,000). General Motors launched the 2011 Chevrolet Volt series plug-in in December 2010. At the time, the Volt displaced the Toyota Prius as the most fuel-efficient car sold in the United States. As of December 2016, the Volt/Ampera family is the world's all-time best-selling plug-in hybrid car, with global sales totaling about 134,500 units since its inception, including over 10,000 Opel/Vauxhall Amperas sold in Europe. The Mitsubishi Outlander P-HEV ranks second with about 119,500 units delivered worldwide. Third is the Toyota Prius Plug-in Hybrid with cumulative global sales of 79,300 units at the end of January 2017. Efficiency advantages An internal combustion engine can be characterized as follows: The chemical energy of the fuel is first partially converted into heat. Part of the heat is converted into mechanical energy (rotation of the crankshaft) and used for propulsion. The majority of the primary energy is released to cooling water and exhaust gases. The efficiency of a gasoline engine is at maximum speed and capacity maximum about 37%. It is strongly load-dependent at a given speed - the highest at just under full load, falling to zero at zero. That means in part-load operation, when little gas is given, gasoline engines have a poor efficiency. In Marx are given for vehicles with internal combustion engine 20% efficiency. Part load and idling of the internal combustion engine is common in city traffic and can be largely avoided in hybrid electric vehicles. The burner can now be operated more frequently and longer at high load with favorable efficiency. The resulting excess energy is used by a generator for the battery charge. During acceleration, the combustion engine and the electric motor can work together. With the same acceleration, a smaller internal combustion engine can be used (downsizing). When braking and coasting, the greater part of the braking energy is returned to the accumulator (regenerative braking). In urban transport in particular, these recoveries reduce consumption by up to 60%. The combustion engine is switched off when little or no drive power is required. Noise reduction during overrun, at standstill or during slow driving (parking) with a charged battery is another benefit in urban areas. On a separate starter can be omitted, because the electric motor takes over the function. Electric motors have a comparatively high efficiency of over 90%. This remains high over a wide speed range. The efficiency drops at high torque, especially in case of overload. In the overall electrical balance is still the storage efficiency of the accumulator. Supercapacitors are rarely used. The latter, like the power electronics very efficient (> 90%), while the efficiency of the battery due to the Peukert effect may be less depending on battery chemistry and pollution. For electric drives an overall efficiency of 85% is specified.

Electric motors are also overloadable, meaning that they can deliver higher torque and, for a short time, more power than their rated output. This torque is also available when the engine is stopped, unlike the combustion engine, which can be charged only from a minimum speed. By combining the two engines, the vehicle can accelerate faster with the same system performance by about 10-20% (electric boosting). Due to the hybrid engine often small sized engine, they often have a slightly lower top speed and are louder at high power requirement, because they then have to work in higher speed ranges.

On the one hand, the driving management ensures a high degree of driving comfort and desired acceleration values, and on the other hand it optimizes the overall efficiency through the choice and distribution of the two drives. There are three possibilities:

Pure electric driving, combustion engine switched off, when parking
Electrical support of the internal combustion engine, For accelerating at high speed
Load point boost: internal combustion engine to the drive and the battery charging, thereby higher efficiency

As a result, the overall efficiency of the vehicle can be increased to over 38%. An econometer can be used to display the operating status.

Diesel engines have a slightly more favorable efficiency curve (small throttle losses), which is why they benefit less from the installation of an electric motor and accumulator.

A hybrid electric vehicle is slightly heavier than a vehicle of the same internal combustion engine series. With unrealistic assumed constant, fast driving on the highway, the additional weight can be reflected in a higher consumption. If accelerated and decelerated or peaks and troughs alternate, then caused by the additional weight increase in consumption may be more than offset by the possibility of regenerative braking. A predictive driving style can already save 10 to 20 percent of consumption in the normal car, while this value increases again in the hybrid, because any predictive braking can be used to generate energy. The internal combustion engine already operates at highway speed in a relatively low efficiency range.

Combustion Optimization
The hybrid drive makes it possible to design the internal combustion engine differently than in a vehicle in which it alone has to constantly drive the vehicle. For example, Toyota operates the Atkinson cycle engine to achieve fuel economy and volume reduction at low to medium horsepower. Honda implements a cylinder cut-off and operates the engine with the electric flywheel directly on the crankshaft as an active flywheel even in work areas that would lead to uncomfortable engine or engine running without electromotive assistance.


The varieties of hybrid electric designs can be differentiated by the structure of the hybrid vehicle drivetrain, the fuel type, and the mode of operation.

In 2007, several automobile manufacturers announced that future vehicles will use aspects of hybrid electric technology to reduce fuel consumption without the use of the hybrid drivetrain. Regenerative braking can be used to recapture energy and stored to power electrical accessories, such as air conditioning. Shutting down the engine at idle can also be used to reduce fuel consumption and reduce emissions without the addition of a hybrid drivetrain. In both cases, some of the advantages of hybrid electric technology are gained while additional cost and weight may be limited to the addition of larger batteries and starter motors. There is no standard terminology for such vehicles, although they may be termed mild hybrids.

Engines and fuel sources

Fossil fuels
Free-piston engines could be used to generate electricity as efficiently as, and less expensively than, fuel cells.

Gasoline engines are used in most hybrid electric designs and will likely remain dominant for the foreseeable future. While petroleum-derived gasoline is the primary fuel, it is possible to mix in varying levels of ethanol created from renewable energy sources. Like most modern ICE powered vehicles, HEVs can typically use up to about 15% bioethanol. Manufacturers may move to flexible fuel engines, which would increase allowable ratios, but no plans are in place at present.

Diesel-electric HEVs use a diesel engine for power generation. Diesels have advantages when delivering constant power for long periods of time, suffering less wear while operating at higher efficiency. The diesel engine’s high torque, combined with hybrid technology, may offer substantially improved mileage. Most diesel vehicles can use 100% pure biofuels (biodiesel), so they can use but do not need petroleum at all for fuel (although mixes of biofuel and petroleum are more common). If diesel-electric HEVs were in use, this benefit would likely also apply. Diesel-electric hybrid drivetrains have begun to appear in commercial vehicles (particularly buses); as of 2007, no light duty diesel-electric hybrid passenger cars are available, although prototypes exist. Peugeot is expected to produce a diesel-electric hybrid version of its 308 in late 2008 for the European market.

PSA Peugeot Citroën has unveiled two demonstrator vehicles featuring a diesel-electric hybrid drivetrain: the Peugeot 307, Citroën C4 Hybride HDi and Citroën C-Cactus. Volkswagen made a prototype diesel-electric hybrid car that achieved 2 L/100 km (140 mpg‑imp; 120 mpg‑US) fuel economy, but has yet to sell a hybrid vehicle. General Motors has been testing the Opel Astra Diesel Hybrid. There have been no concrete dates suggested for these vehicles, but press statements have suggested production vehicles would not appear before 2009.

At the Frankfurt Motor Show in September 2009 both Mercedes and BMW displayed diesel-electric hybrids.

Robert Bosch GmbH is supplying hybrid diesel-electric technology to diverse automakers and models, including the Peugeot 308.

So far, production diesel-electric engines have mostly[vague] appeared in mass transit buses.

FedEx, along with Eaton Corp. in the USA and Iveco in Europe, has begun deploying a small fleet of Hybrid diesel electric delivery trucks. As of October 2007, Fedex operates more than 100 diesel electric hybrids in North America, Asia and Europe.

Liquefied petroleum gas

Hyundai introduced in 2009 the Hyundai Elantra LPI Hybrid, which is the first mass production hybrid electric vehicle to run on liquefied petroleum gas (LPG).

Hydrogen can be used in cars in two ways: a source of combustible heat, or a source of electrons for an electric motor. The burning of hydrogen is not being developed in practical terms; it is the hydrogen fuel-cell electric vehicle (HFEV) which is garnering all the attention. Hydrogen fuel cells create electricity fed into an electric motor to drives the wheels. Hydrogen is not burned, but it is consumed. This means molecular hydrogen, H2, is combined with oxygen to form water. The molecular hydrogen and oxygen’s mutual affinity drives the fuel cell to separate the electrons from the hydrogen, to use them to power the electric motor, and to return them to the ionized water molecules that were formed when the electron-depleted hydrogen combined with the oxygen in the fuel cell. Recalling that a hydrogen atom is nothing more than a proton and an electron; in essence, the motor is driven by the proton’s atomic attraction to the oxygen nucleus, and the electron’s attraction to the ionized water molecule.

An HFEV is an all-electric car featuring an open-source battery in the form of a hydrogen tank and the atmosphere. HFEVs may also comprise closed-cell batteries for the purpose of power storage from regenerative braking, but this does not change the source of the motivation. It implies the HFEV is an electric car with two types of batteries. Since HFEVs are purely electric, and do not contain any type of heat engine, they are not hybrids.

Hybrid vehicles might use an internal combustion engine running on biofuels, such as a flexible-fuel engine running on ethanol or engines running on biodiesel. In 2007 Ford produced 20 demonstration Escape Hybrid E85s for real-world testing in fleets in the U.S. Also as a demonstration project, Ford delivered in 2008 the first flexible-fuel plug-in hybrid SUV to the U.S. Department of Energy (DOE), a Ford Escape Plug-in Hybrid, capable of running on gasoline or E85.

The Chevrolet Volt plug-in hybrid electric vehicle would be the first commercially available flex-fuel plug-in hybrid capable of adapting the propulsion to the biofuels used in several world markets such as the ethanol blend E85 in the U.S., or E100 in Brazil, or biodiesel in Sweden. The Volt will be E85 flex-fuel capable about a year after its introduction.

Electric machines
In split path vehicles (Toyota, Ford, GM, Chrysler) there are two electrical machines, one of which functions as a motor primarily, and the other functions as a generator primarily. One of the primary requirements of these machines is that they are very efficient, as the electrical portion of the energy must be converted from the engine to the generator, through two inverters, through the motor again and then to the wheels.

Most of the electric machines used in hybrid vehicles are brushless DC motors (BLDC). Specifically, they are of a type called an interior permanent magnet (IPM) machine (or motor). These machines are wound similarly to the induction motors found in a typical home, but (for high efficiency) use very strong rare-earth magnets in the rotor. These magnets contain neodymium, iron and boron, and are therefore called Neodymium magnets.

The price of Neodymium went through a price bubble due to Chinese export restriction in 2010–11, rising from $50/kg at the start of 2010 to $500/kg by the summer of 2011. This resulted in ‘demand destruction’ as many producers quickly turned to substituting induction motors in their cars to defend their production line. This was in spite of such motors inferior ‘power to weight’ ratio attributes significantly impacting all but the most powerful (energy guzzling) motor sizes, e.g. those used in the Tesla. As of April 2014 there are other non-Chinese producers of Neodymium and its price/kg is not much more than it was in 2010. Cutting edge U.K. motors that are now being produced are using Neodymium Permanent Magnet technology. As security of supply returns, it is certain that there will accordingly be a return to superior motor designs that NdFeB Permanent Magnets enable.

Design considerations
In some cases, manufacturers are producing HEVs that use the added energy provided by the hybrid systems to give vehicles a power boost, rather than significantly improved fuel efficiency compared to their traditional counterparts. The trade-off between added performance and improved fuel efficiency is partly controlled by the software within the hybrid system and partly the result of the engine, battery and motor size. In the future, manufacturers may provide HEV owners with the ability to partially control this balance (fuel efficiency vs. added performance) as they wish, through a user-controlled setting. Toyota announced in January, 2006 that it was considering a “high-efficiency” button.

Conversion kits
One can buy a stock hybrid or convert a stock petroleum car to a hybrid electric vehicle using an aftermarket hybrid kit.

Vehicle types

Companies such as Zero Motorcycles and Vectrix have market-ready all-electric motorcycles available now, but the pairing of electrical components and an internal combustion engine (ICE) has made packaging cumbersome, especially for niche brands.
Also, eCycle Inc produces series diesel-electric motorcycles, with a top speed of 80 mph (130 km/h) and a target retail price of $5500.

Peugeot HYmotion3 compressor, a hybrid scooter is a three-wheeler that uses two separate power sources to power the front and back wheels. The back wheel is powered by a single cylinder 125 cc, 20 bhp (15 kW) single cylinder motor while the front wheels are each driven by their own electric motor. When the bike is moving up to 10 km/h only the electric motors are used on a stop-start basis reducing the amount of carbon emissions.

SEMA has announced that Yamaha is going to launch one in 2010, with Honda following a year later, fueling a competition to reign in new customers and set new standards for mobility. Each company hopes to provide the capability to reach 60 miles (97 km) per charge by adopting advanced lithium-ion batteries to accomplish their claims. These proposed hybrid motorcycles could incorporate components from the upcoming Honda Insight car and its hybrid powertrain. The ability to mass-produce these items helps to overcome the investment hurdles faced by start-up brands and bring new engineering concepts into mainstream markets.

Automobiles and light trucks

High-performance cars
As emissions regulations become tougher for manufacturers to adhere to, a new generation of high-performance cars will be powered by hybrid technology (for example the Porsche GT3 hybrid racing car). Aside from the emissions benefits of a hybrid system, the immediately available torque which is produced from electric motor(s) can lead to performance benefits by addressing the power curve weaknesses of a traditional combustion engine. Hybrid racecars have been very successful, as is shown by the Audi R18 and Porsche 919, which have won the 24 hours of Le Mans using hybrid technology.

Formula 1
In 2014, Formula 1 has changed the cars from 2.4 L V8 engine to 1.6 L turbocharged V6 engine, limited to 15,000 rpm. These turbocharged V6 engines can propel a F1-racecar up to 360 km/h (220 mph).

In 2000, North America’s first hybrid electric taxi was put into service in Vancouver, British Columbia, operating a 2001 Toyota Prius which traveled over 332,000 km (206,000 mi) before being retired. In 2015, a taxi driver in Austria claimed to have covered 1,000,000 km (620,000 mi) in his Toyota Prius with the original battery pack.

Many of the major cities in the world are adding hybrid taxis to their taxicab fleets, led by San Francisco and New York City. By 2009 15% of New York’s 13,237 taxis in service are hybrids, the most in any city in North America, and also began retiring its original hybrid fleet after 300,000 and 350,000 miles (480,000 and 560,000 km) per vehicle. Other cities where taxi service is available with hybrid vehicles include Tokyo, London, Sydney, Melbourne, and Rome.

Hybrid technology for buses has seen increased attention since recent battery developments decreased battery weight significantly. Drivetrains consist of conventional diesel engines and gas turbines. Some designs concentrate on using car engines, recent designs have focused on using conventional diesel engines already used in bus designs, to save on engineering and training costs. As of 2007, several manufacturers were working on new hybrid designs, or hybrid drivetrains that fit into existing chassis offerings without major re-design. A challenge to hybrid buses may still come from cheaper lightweight imports from the former Eastern block countries or China, where national operators are looking at fuel consumption issues surrounding the weight of the bus, which has increased with recent bus technology innovations such as glazing, air conditioning and electrical systems. A hybrid bus can also deliver fuel economy though through the hybrid drivetrain. Hybrid technology is also being promoted by environmentally concerned transit authorities.

In 2003, GM introduced a hybrid diesel-electric military (light) truck, equipped with a diesel electric and a fuel cell auxiliary power unit. Hybrid electric light trucks were introduced in 2004 by Mercedes Benz (Sprinter) and Micro-Vett SPA (Daily Bimodale). International Truck and Engine Corp. and Eaton Corp. have been selected to manufacture diesel-electric hybrid trucks for a US pilot program serving the utility industry in 2004. In mid-2005 Isuzu introduced the Elf Diesel Hybrid Truck on the Japanese Market. They claim that approximately 300 vehicles, mostly route buses are using Hinos HIMR (Hybrid Inverter Controlled Motor & Retarder) system. In 2007, high petroleum price means a hard sell for hybrid trucks and appears the first U.S. production hybrid truck (International DuraStar Hybrid).

Other vehicles are:

Big mining machines like the Liebherr T 282B dump truck or Keaton Vandersteen LeTourneau L-2350 wheel loader are powered that way. Also there was several models of BelAZ (7530 and 7560 series) in USSR (now in Belarus) since the middle of 1970th.
NASA’s huge Crawler-Transporters are diesel-electric.
Mitsubishi Fuso Canter Eco Hybrid is a diesel-electric commercial truck.
Azure Dynamics Balance Hybrid Electric is a gasoline-hybrid electric medium dutry truck based on the Ford E-450 chassis.
Hino Motors (a Toyota subsidiary) has the world’s first production hybrid electric truck in Australia (110 kW or 150 hp diesel engine plus a 23 kW or 31 hp electric motor).

Other hybrid petroleum-electric truck makers are DAF Trucks, MAN with MAN TGL Series, Nissan Motors and Renault Trucks with Renault Puncher.

Hybrid electric truck technology and powertrain maker: ZF Friedrichshafen, EPower Engine Systems.

By a voice vote, the United States House of Representatives approved the Heavy Duty Hybrid Vehicle Research, Development, and Demonstration Act of 2009 (for heavy duty plug-in hybrid vehicles) authored by representative James Sensenbrenner.

Military vehicles
Some 70 years after Porsche’s pioneering efforts in hybrid-drivetrain armored fighting vehicles in World War II, the United States Army’s manned ground vehicles of the Future Combat System all use a hybrid electric drive consisting of a diesel engine to generate electrical power for mobility and all other vehicle subsystems. However, all FCS land vehicles were put on hold in the 2010 DOD budget. Other military hybrid prototypes include the Millenworks Light Utility Vehicle, the International FTTS, HEMTT model A3, and the Shadow RST-V.

In May 2003, JR East started test runs with the so-called NE (new energy) train and validated the system’s functionality (series hybrid with lithium-ion battery) in cold regions. In 2004, Railpower Technologies had been running pilots in the US with the so-called Green Goats, which led to orders by the Union Pacific and Canadian Pacific Railways starting in early 2005.

Railpower offers hybrid electric road switchers, as does GE. Diesel-electric locomotives may not always be considered HEVs, not having energy storage on board, unless they are fed with electricity via a collector for short distances (for example, in tunnels with emission limits), in which case they are better classified as dual-mode vehicles.

Marine and other aquatic
For large boats that are already diesel-electric, the upgrade to hybrid can be as straightforward as adding a large battery bank and control equipment; this configuration can provide fuel saving for the operators as well as being more environmentally sensitive.

Boeing has stated that for the subsonic concept, hybrid electric engine technology is a clear winner. Hybrid electric propulsion has the potential to shorten takeoff distance and reduce noise. The AgustaWestland Project Zero is one aircraft that is intended to be hybrid-electric.

The DA36 E-Star, an aircraft designed by Siemens, Diamond Aircraft and EADS, employs a series hybrid powertrain with the propeller being turned only by a Siemens 70 kW (94 hp) electric motor. The aim is to reduce fuel consumption and emissions by up to 25%. An onboard 40 hp (30 kW) Austro Engines Wankel rotary engine and generator provides the electricity because of the small size, light weight and high power-to-weight ratio of the engines. The electric motor also uses electricity stored in batteries to take off and climb reducing sound emissions by eliminating the engine. The series hybrid powertrain using the Wankel engine reduces the weight of the plane by 100 kilos to its predecessor. The DA36 E-Star first flew in June 2013, making this the first ever flight of a series hybrid powertrain. Diamond aircraft state that the technology using Wankel engines is scalable to a 100-seater aircraft.

Source from Wikipedia