Introduction of Hybrid Electric VehicleAbstract: As the environmental pollution and energy crises are getting more and more remarkable, hybrid electric vehicles (HEVs) have taken on an accelerated pace in the world、In this paper, we will see the types of HEV, and introduce some famous HEVs in China and all around the world、Key words: HEV, automobile, Classification, development、In 1997, Toyota Motor Corporation released the hybrid electric vehicle(HEV) in the world, which was named "Prius"、Firstly, what is a hybrid electric vehicle? Broadly speaking, a hybrid electric vehicle has two power sources at least, no matter fossil fuel, nuclear energy, solar energy or electric energy and so on, but in real life, most hybrid cars use the traditional internal combustion engine and electric motor as a power source、Why hybrid electric vehicle feel valued by many countries recent years? As we know that, oil is not in resources,a lot of information indicate that if mining speed remain at current level, proved oil reserves could merely use fifty to sixty years, so, energy supply becomes a tough question、And also by the reason of more and more serious environmental pollution, hybrid electric vehicles have to be pushed onto the stage of history、And what is the advantage of hybrid electric vehicles when compared to blade electric vehicles(BEV) or conventional vehicles? The characteristic of the electric motor is, when compared to internal combustion engine, more quiet, efficiency and cleaner, in the same time, speed-torque control features is more flexible、When at low rotate speed, electric motor has a constant torque, when at high rotate speed, it has a constant power、Hybrid electric vehicles combine electric drive with traditional internal combustion engine drive, give full play to the advantages of both、Meanwhile, it can effect a permanent cure to the problem of blade electric vehicles(BEV)'s weak dynamic performance and short cruising distance、In summary, as a appropriate transitional product, hybrid electric vehicle is a good choice in this time that energy crises are getting more and more remarkable and the development of new energy automobile is still in a primary、Compare to conventional vehicle, HEV can save fuel for the following reasons、(1)HEV can store part of the vehicle’s kinetic energy in battery while braking or downslope in which otherwise is burnt in the brake drums in the form of heat in conventional vehicle、(2)The ICE in an HEV can be designed with a smaller displacement without compromising the performance of vehicle、[1](3)HEV can make ICE operate at maximum efficiency point or optimal operating line by regulating the output power of battery to satisfy the required power of vehicle、(4)HEV is a multiple energy system; the main issue of HEV is how to optimize the power flow to obtain best fuel economy or low emission at lower cost, which is often referred to as the energy management (EM) problem、The issue will be discussed in next section in detail、[2]ClassificationHybrid electric vehicles can be classified according to the way in which power issupplied to the drivetrain、So, it has three types、The first one is called the series hybrid, picture 1、1[3] shows the simple structure of this type、Series hybrid is the simplest of three types、The mechanical energy made by internal combustion engine transformmed into electricity through generator, then one part of the electricity is used to propel the wheels through electric motor and transmission, and the other part of the electricity is used to recharge the storage battery, when the vehicle is accelerating or on other working condition, this part can be used、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、Compared to conventional internal combustion engine vehicle, it is a electrombile with a assistant engine, in order to increase the trip distance of a vehicle、There is no clutch in the mechanical connection device of engine and electric motor, so it has Some flexibility、Although the transmission structure is simple, it still need three drive parts,engine, generator and electric motor、If in consideration of large climbing gradient and frequent acceleration, the maximum power should be supplied, the three drive parts need higher quality、This type of structure is widely used on urban buses, rarely used on saloon cars、[4]The second one is called the parallel hybrid, picture 1、2[3] shows the simple structure of this type、What this type different from the series hybrid is that it propels the vehicle by two independent drive system of engine and electric motor、Engine and electric motor usually drive wheels through different clutches, it can adapts three different work pattern:single engine drive, single electric drive and hybrid drive, this system is suitable for a wide variety of driving conditions, especially for complex road、On the contrary, it is a engine with a electric motor, in order to reduce emissions and fuel consumption、When the power provided by engine exceed what the vehicle need or on regenerative braking, electric motor working at a stage of a generator, charge the excess energy into the storage battery、Compared to the series hybrid, the patten of parallel hybrid only need two drive part of engine and electric motor, in addition, before the storage battery is discharged, its power requirement of engine and electric is lower、[4]The third one is called the power-split hybrids, picture 1、3[3] shows the simple structure of this type、This type combines the features of the parallel hybrid and the series hybrid、Compared to the series hybrid, it has added the transmission line of power machinery; When compared to the parallel hybrid, it has added the transmitting way of electric energy、Thus, power-split hybrids have the benefits of a combination of series and parallel characteristics But on the other hand, it also causes the shortage of structural complexity and high cost、[4]According to the motor output power accounted for the percentage of total output power in the whole system, hybrid systems can be divided into the following four categories, it also can be described as the degree of hybridization、The first one is called the micro hybrid、In this hybrid electric system, a belt-alternator starter generator is mounted at the start motor of conventional internal combustion engine、This electric motor controls the start and shutoff of the engine in the same time, thus, it has cancelled idling working condition and cut down the fuel consumption and exhaust emission、From the strict sense, micro hybrid is not really a hybrid electric system, because its electric motor by no means provides the vehicle a continuous power、The second one is the light hybrid、This hybrid system adopts a integrated starter generator(ISG),in comparison with the previous one, it can start or stop the engine by a dynamo, it also can achieve some other functions, for instant, when at the operation condition of decelerating or braking, it can absorb a portion of the energy, and when driving the vehicle, engine operates at a constant speed, the energy produced by engine can be divided to driving the wheels or to charge the battery reasonably、The mixedness degree of this system usually below twenty percents、General Motors Corporation's hybrid electric pickup trucks use this the hybrid system、The third one is namely the mild hybrid、It also has a integrated starter generator, whilst what different from the light hybrid system is that it adopts a high tension dynamo、In addition, when vehicle is accelerating or at high load condition, the electric motor gives a assist to the engine to propel the vehicle, in order to make up the lack of power of the engine, consequently improving the property of the vehicle、The mixedness of this system is considerable high, reaching a value of 30% about, the mature technologies make it widely used、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,[26] 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、[5][6]The last one is called the full hybrid, sometimes also called a strong hybrid, is a vehicle that can run on just the engine, just the batteries, or a combination of both、This system adopts a high tension electric motor from 272 to 650V、Compared to the mild hybrid system, the mixedness even reach at a value of 50%、Ford's hybrid system, Toyota's Hybrid Synergy Drive and General Motors/Chrysler's Two-Mode Hybridtechnologies are full hybrid systems、Ford's hybrid system, Toyota's Hybrid Synergy Drive and General Motors/Chrysler's Two-Mode Hybridtechnologies are full hybrid systems、[26] The T oyota 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、The full hybrid system will gradually become the main development direction with the technology developing、[5][6]A new type HEV is called 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、[6][7][8]Development in the worldIn HEV's domain, Japan, Germany and America are the main countries, they grasp many technologies of hybrid, and they also own many famous HEV products、[9][10] Buick Regal EcoHybrid made by General Motors Corporation, it adopts the BSG hybrid pattern, fuel consumption per hundred kilometers has lifted from 9、8 to 8、3 litersBMW X5 HEV is the first vehicle that adopts BMW ActiveHybrid system, its hybrid pattern is ISG with AT、[11]Civic Hybrid made by Honda Motor Corporation adopts a hybrid pattern of ISG with CVT, it is a new generation、Some other hybrid electric vehicles such as S400 BlueHybrid made by Daimler-Benz Motors Company, Cadillac Escalade, Chevrolet Volt etc, are some outstanding hybrid electric vehicles、Around the world, Japan is one of the few countries in the fastest rate of development of electric vehicle technology, especially in terms of the development of hybrid vehicles, Japan is a world leader、Only two Japanese car companies have the capacity of bulk sales of hybrid vehicles in the world、Recent years, China has put a high value to the research and development of hybrid electric vehicle, colleges, scientific research institutions and companies have be encouraged by government to exploit the way of HEV developing、under such circumstances, significant developments have been made on HEV、Changan Jiexun HEV is the first mild hybrid motorcycle type with independent research in China, and it is mass produced, thereout, Changan Motor Corporation has set up the China's first production line of HEV by totally independent research and development、Benteng B70 made by First Auto Work is another HEV, it has two electric motor, and is the type of full hybrid、However the manufacturing costs is even triple to the same vehicle type of internal combustion engine、Some other hybrid electric vehicles such as Rongwei 750 HEV made by Shanghai Motor Corporation, A3ISG and A5BSG made by Chery Automobile Co, EQ7200 HEV made by Dongfeng Motor Corporation, F6DM made by BYD Motor Corporation etc, also playing a role in a China's HEV market、Particularly worth mentioning is the BYD Motor Corporation, its "Two-Mode Hybrid" is much more advanced than other companies's、At the Beijing Auto Show in 2012, BYD Motor Corporation launched their brand new HEV vehicle type which is namely "Qing", with the 0-100km/h sprint completed in 5、9s seconds it stunned many car enthusiasts、Qing adopts BYD's second generation two-mode hybrid, and it is a parallel hybrid, it came into existence marked that China's hybrid technologies has reached at a new stage、Just also at the Beijing Auto Show in 2014 a few days ago, BYD gave us anther surprise, BYD Tang appeared, it's a SUV, the 0-100km/h sprint completed in 4、9s seconds stunned us once again、However, comprehensively, hybrid technologies in China is mainly focus on light and mild hybrid, lags behind developed countries、summaryHEVs have many advantages ,however, PEV is not widely used currently、Expensive price keeps people from it、But we can believe that with the technology developing, the cost of HEV will be much lower, and the reliability will be more better by that moment, HEVs will become mainstream of automobile market, and be loved by people、[1]A、Sciarretta and L、Guzzella, “Control of hybrid electric vehicles,”IEEE Control Systems Magazine, vol、27, no、2, pp、60–70, 2007、View at Publisher ·View at Google Scholar[2]International Journal of Vehicular T echnology Volume 2011 (2011), Article ID 571683, 7 pages[3][4] Hybridcenter、org、"Hybrids Under the Hood (Part 2): Drivetrains"、Union of Concerned Scientists、Retrieved 2010-03-17、[5]Sam Abuelsamid (2009-04-03)、"What is a mild hybrid?"、AutoblogGreen、Retrieved 2010-03-22、[6]Sherry Boschert (2006)、Plug-in Hybrids: The Cars that will Recharge America、Gabriola Island, Canada: New Society Publishers、ISBN 978-0-86571-571-4、[7]Archer, David 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