Hybrid vehicle drivetrain

Hybrid vehicles are vehicles with two or more power duced at present, have both an internal combustion engine sources in the drivetrain. There are many different types (ICE) and an electric motor coupled. If they are joined at of hybrid vehicles, although only the gasoline-electric hy- an axis in parallel, the speeds at this axis must be identical brid is currently commercially available. and the supplied torques add together. Most electric bi- cycles are of this type. When only one of the two sources Hybrids are classified by the division of power between sources; both sources may operate in parallel to simul- is being used, the other must either also rotate in an idling manner, be connected by a one-way clutch, or freewheel. taneously provide acceleration, or they may operate in series with one source exclusively providing the accel- With cars, the two sources may be applied to the same eration and the second being used to augment the first’s shaft- for example with the electric motor lying between power reserve. The sources can also be used in both se- the engine and transmission. The speeds are thus equal ries and parallel as needed, the vehicle being primarily and the torques add up, with the electric motor adding or driven by one source but the second capable of providing subtracting torque to the system as necessary. The Honda direct additional acceleration if required. Insight uses this system. Current hybrids use both an internal combustion en- Parallel hybrids can be further categorized depending gine (ICE) and a battery/electric drive system (using upon how balanced the different portions are at provid- ultracapacitors) to improve fuel consumption, emission, ing motive power. In some cases, the combustion en- and performance. Electrically assisted pedal bicycles are gine is dominant (the electric motor turns on only when a a form of hybrid drive. Other combinations of energy boost is needed) and vice versa. Others can run with just storage and conversion are possible, although not yet in the electric system operating. But because current paral- commercial production. lel hybrids are unable to provide all-electric (ICE=OFF) propulsion, they are often categorized as mild hybrids Combustion-electric hybrids have larger battery sets (see below). than what a normal combustion engine only vehicle would have. Battery and supercapacitor technology is Because parallel hybrids can use a smaller battery pack advancing.[1] A potential advantage is that when these as they rely more on regenerative braking and the internal battery sets require renewing in the future, the newer bat- combustion engine can also act as a generator for supple- tery sets will be potentially superior having higher energy mental recharging, they are more efficient on urban stop storage giving greater range enhancing a vehicle. and go conditions or city driving compared to highway driving.[2] Honda's Insight, Civic, and Accord hybrids are examples of production parallel hybrids.[2] General Mo- tors Parallel Hybrid Truck (PHT) and BAS Hybrids such 1 Types by drive train structure as the Saturn VUE and Aura Greenline and Chevrolet Malibu hybrids are also considered as utilizing a paral- 1.1 Parallel hybrid lel architecture.

1.1.1 TTR hybrid Electric Battery Converter motor An alternative parallel hybrid layout is the 'through the road' type.[3][4] Here a conventional drivetrain powers one axle, with an electric motor or motors driving the other. The batteries can be recharged through regenerative brak- ing, or by loading the electrically driven wheels during cruise. Power is thus transferred from the engine to the Reservoir Engine batteries through the road surface. This layout also has the advantage of providing four-wheel-drive in some con- ditions. An example of this principle is a bicycle fitted Structure of a parallel hybrid electric vehicle. The gray squares with a front hub motor, which assists the cyclist’s pedal represent differential gears. power at the rear wheel. Other examples include the Audi 100 Duo II and Subaru VIZIV concept cars, the Peu- Parallel hybrid systems, which are most commonly pro- geot 3008 HYbrid4, the Volvo V60 plug-in hybrid and

1 2 1 TYPES BY DRIVE TRAIN STRUCTURE

the BMW i8. quite independently of each other. This has advantages. This arrangement allows for a smaller sized generator en- gine to be used compared to the size of a conventional 1.2 Series hybrid direct drive engine. The traction motors receive electric- ity from the battery or generator or both. The traction motors, depending on the size of the battery bank, will in Reservoir Battery many cases of operation have most of the power provided only by the electric battery, which may be charged from Electric Engine Generator Charger Converter external sources such as the electricity grid. The vehicle motor can move primarily using energy from only the battery Flywheel bank with the generator operating as a second stage only or Capacitor when needed to drive the vehicle or charge the batteries. A great advantage is that the vehicle can be driven in ur- Structure of a series-hybrid vehicle. The grey square represents ban areas with zero emissions with the generator cutting a differential gear. An alternative arrangement (not shown) is to in for longer journey’s when the battery bank is depleted. have electric motors at two or four wheels. In short, a series-hybrid is simple, the vehicle is driven only by electric traction motors with a generator set pro- Series hybrids have also been referred to as extended- [5] viding the electric power when needed. An electric bat- range electric vehicles (EREV) or range-extended elec- tery acts as buffer evening out demand and the stored en- tric vehicles (REEV). ergy may be use only as the prime source to propel the vehicle. When using the generator set to propel the ve- 1.2.1 Overview hicle the batteries reserve energy can be used to assist in acceleration or pulling heavy loads. Firstly, look at an electric transmission, which dates The choice of electric traction motors has great advan- from 1903. Conventional mechanical transmissions add tages. Unlike piston internal combustion engines, electric weight, bulk and saps power from the engine with auto- motors are highly efficient with exceptionally high power- matic shifting being complex when used. Unlike combus- to-weight ratios providing adequate torque when running tion engines, with electric motors matched to the vehicle over a wide speed range. Internal combustion engines run a multiple-speed transmission is not essential. The me- at their most efficient when turning at a constant speed. chanical transmission between the engine and the wheels An engine turning a generator can be designed to run at is removed and replaced by electric driving traction mo- its maximum efficiency constant speed, or a series of con- tors which are powered by an electric generator turned stant speeds. Combining the two, which can operate quite by an internal combustion engine. The driving electric independently of each other, gives maximum efficiency traction motors are the only form of propulsion. and performance overall. In certain operational situations it is economical and flex- The arrangement was difficult for early production cars ible as the driving internal combustion engine is discon- as synchronization of power generation and demand was nected from the demand. This is a series-hybrid arrange- inefficient, resulting in higher fuel consumption. This is ment and is common in diesel-electric locomotives and no longer an issue with modern computer engine man- ships. The river ship the Russian Vandal launched in agement systems optimizing when the generator runs to 1903, was the world’s first diesel-powered and diesel- match the power needed. Since Ferdinand Porsche’s electric powered ship. Ferdinand Porsche successfully series-hybrid car, electric motors have become substan- used this arrangement in the early 20th century in rac- tially smaller, lighter and efficient over the years. One of ing cars. Porsche named the system, System Mixt. A the advantages of a series-hybrid system is the smoother wheel hub motor arrangement, with a motor in each of progressive ride with no stepped gear ratio changes. the two front wheels, setting speed records. Ferdinand The electric transmission is currently viable in replac- Porsche’s system was even used, with much less success, ing the mechanical transmission. However, the modern to power his competitor for the “Tiger” tank contract, and series-hybrid vehicles takes the electric transmission to a the heaviest armored fighting vehicle design ever built, higher plane adding greater value. Modern series-hybrids both during World War II. incorporate: However greater flexibility, higher efficiencies and less emissions are achieved in a series-hybrid system for road • Electric traction only - using only one or more elec- vehicles when an intermediate electric battery, acting as tric motors to turn the wheels. an energy buffer, is between the electric generator and the • Combustion engine - that turns only a generator. electric traction motors. The internal combustion engine is mechanically disconnected from the driving wheels, in • A generator - turned by the combustion engine to effect disconnecting the engine from the demand. The make up a generator set that also acts as an engine electric traction motors and the generator may operate starter. 1.2 Series hybrid 3

• A battery bank - which acts as an energy buffer. more efficient or alternative engine designs, such as a microturbine,[8] rotary Atkinson cycle engine or a linear • Regenerative braking - The driving motor be- combustion engine.[9] comes a generator and recovers potential and kinetic (inertial) energies through its conversion to electri- General Motors in 1999 made the experimental EV1 se- cal energy, a process which in turn is able to slow the ries hybrid using a turbine generator set. The turbine vehicle and thus preventing wasteful transfer of this weighed 220 lb (99.8 kg), measured 20 inches (50.8 cm) energy as thermal losses within the friction brakes. in diameter by 22 inches (55.9 cm) long and ran be- tween 100,000 and 140,000 rpm. Fuel consumption was In addition: 60 mpg-US (3.9 L/100 km; 72 mpg-ᵢ) to 100 mpg-US (2.4 L/100 km; 120 mpg-ᵢ) in hybrid mode. Depend- • May be plugged into the electric mains system to ing on the driving conditions, a highway range of more recharge the battery bank. than 390 miles (627.6 km) was achieved. The results were highly successful, and would have promised to be • May have supercapacitors to assist the battery bank more successful if a smaller microturbine was used, yet and claw back most energy from braking - only fitted the EV1 project was dropped. in proven prototypes currently. The use of an electric motor driving a wheel directly eliminates the conventional mechanical transmission ele- 1.2.2 In detail ments: gearbox, transmission shafts and differential, and can sometimes eliminate flexible couplings. This offers The electric driving motor may run entirely fed by elec- great simplicity. If the motors are integrated into the tricity from a large battery bank or via the generator wheels a disadvantage is that the unsprung mass increases turned by the internal combustion engine, or both. The and suspension responsiveness decreases which impacts battery bank may be charged by mains electricity reduc- ride performance and potentially safety. However the im- ing running costs, as the range running under the electric pact should be minimal if at all as electric motors in wheel motors only is extended. The vehicle conceptually re- hubs such as Hi-Pa Drive, may be very small and light sembles a Diesel-electric locomotive with the addition of having exceptionally high power-to-weight ratios. The a large battery bank that may power the vehicle without braking mechanisms can be lighter as the wheel motors the internal combustion engine running and acting as an brake the vehicle. Light aluminum wheels may be used energy buffer. The energy buffer is used to accelerate and reducing the unsprung mass of the wheel assembly. Ve- a greater top speed. The generator may simultaneously hicle designs may be optimized to lower the center of charge the battery bank and power the driving electric gravity having the heavy mechanics and battery banks motor that moves the vehicle. An advantage is that when at floor level. If the motors are attached to the vehicle the vehicle is stopped the combustion engine is switched body, flexible couplings are still required. Advantages of off. When the vehicle moves it does so using the energy in individual wheel motors include simplified traction con- the batteries. This reduces kerbside emissions greatly in trol and all wheel drive if required, allowing lower floors, cities and towns. Vehicles at traffic lights, or in slow mov- which is useful for buses. Some 8x8 all-wheel drive mili- ing stop-start traffic need not be polluting when stationary tary vehicles use individual wheel motors. Diesel-electric or moving very slowly. Series-hybrids can also be fitted locomotives have used this concept (albeit with the indi- with a supercapacitor or a flywheel to store regenerative vidual motors driving axles connecting pairs of wheels) braking energy, which can improve efficiency by clawing for 70 years.[10] back energy that otherwise would be lost being dissipated In a typical road vehicle the whole series-hybrid power- via heat through the braking system. transmission setup may be smaller and lighter than the Because a series-hybrid omits a mechanical link between equivalent conventional mechanical power-transmission the combustion engine and the wheels, the engine can be setup liberating space. As the combustion generator set run at a constant and efficient rate even as the vehicle only requires cables to the driving electric motors, there changes speed. The vehicle speed and engine speed are is greater flexibility in major component layout spread not necessarily in synchronization. The engine can thus across a vehicle giving superior weight distribution and maintain an efficiency closer to the theoretical limit of maximizing vehicle cabin space. This flexibility may lead 37%, rather than the current average of 20%.[6] At low to superior vehicle designs. or mixed speeds this could result in ~50% increase in In 1997, Toyota released the first series-hybrid bus sold overall efficiency (19% vs 29%). The Lotus company in Japan.[11] Designline International of Ashburton, New has introduced an engine/generator set design that runs Zealand produces city buses with a microturbine pow- at two speeds, giving 15 kW of electrical power at 1,500 ered series-hybrid system. Supercapacitors combined rpm and 35 kW at 3,500 rpm via the integrated electrical with a lithium ion battery bank have been used by AFS generator,[7] used in the Nissan concept Infiniti Emerg-e. Trinity in a converted Saturn Vue SUV vehicle. Using As the requirements for the engine are not directly supercapacitors they claim up to 150 mpg in a series- linked to vehicle speed, this gives greater scope for 4 1 TYPES BY DRIVE TRAIN STRUCTURE

hybrid arrangement.[12] steady speed cruising. An electric motor, on the other Series-hybrids have been taken up by the aircraft indus- hand, exhibits maximum torque at standstill and is well- try. The DA36 E-Star, an aircraft designed by Siemens, suited to complement the engine’s torque deficiency at Diamond Aircraft and EADS, employs a series hybrid low RPMs. In a power-split hybrid, a smaller, less flexi- powertrain with the propeller turned by a Siemens 70 kW ble, and highly efficient engine can be used. The conven- (94 hp) electric motor. A power sapping propeller speed tional Otto cycle (higher power density, more low-rpm reduction unit is eliminated. The aim is to reduce fuel torque, lower fuel efficiency) is often also modified to a consumption and emissions by up to 25 percent. An on- Miller cycle or Atkinson cycle (lower power density, less low-rpm torque, higher fuel efficiency). The smaller en- board 40 hp (30 kW) Austro Engine Wankel rotary en- gine and generator provides the electricity. A Wankel en- gine, using a more efficient cycle and often operating in the favorable region of the brake specific fuel consump- gine was chosen because of the very small size, low weight and great power to weight ratio offered, which are as- tion map, contributes significantly to the higher overall efficiency of the vehicle. sets suited to aircraft. Wankel engines also run efficiently at a constants speed of approximately 2,000rpm which Interesting variations of the simple design (pictured at is highly suited to generator turning operation. Keeping right) found, for example, in the well-known Toyota Prius to a near constant, or narrow band, of revolutions elimi- are the: nates, or vastly reduces, many of the disadvantages of the Wankel engine.[13] The electric propeller motor uses elec- • addition of a fixed gear second planetary gearset as tricity stored in batteries, with the engines not operating, used in the Lexus RX400h and Toyota Highlander to take off and climb reducing sound emissions. The se- Hybrid. This allows for a motor with less torque but ries hybrid powertrain using the Wankel engine reduces higher power (and higher maximum rotary speed), the weight of the plane by 100 kilos to its predecessor. i.e. higher power density The DA36 E-Star first flew in June 2013, making this the • addition of a Ravigneaux[16]-type planetary gear first ever flight of a series hybrid powertrain. Diamond (planetary gear with 4 shafts instead of 3) and two aircraft state that the technology using Wankel engines is clutches as used in the Lexus GS450h. By switching scalable to a 100 seater aircraft.[14][15] the clutches, the gear ratio from MG2 (the “drive” An example of series-hybrid car was the Fisker Karma, motor) to the wheel shaft is switched, either for which had a sizable battery bank that could also be higher torque or higher speed (up to 250 km/h / charged by the electricity mains to give a longer range on 155 mph) while sustaining better transmission ef- battery operation only. The car was propelled by electric ficiency. motor traction only.

1.3 Power-split or series-parallel hybrid

Battery

Electric Reservoir Generator Charger Converter motor

Engine

Structure of a combined hybrid electric vehicle Power-splitter series-hybrid Toyota Prius.

Power-split hybrid or series-parallel hybrid are paral- • addition of two additional planetary gear sets in lel hybrids. They incorporate power-split devices allow- combination with four clutches to create a Two- ing for power paths from the engine to the wheels that can Mode Hybrid configuration able to operate in all- be either mechanical or electrical. The main principle be- electric, blended electric and ICE, or ICE alone hind this system is the decoupling of the power supplied with four fixed gears. Examples of Two-Mode Hy- by the engine (or other primary source) from the power brids include the General Motors Two-Mode Hybrid demanded by the driver. full-size trucks and SUVs, the BMW X6 ActiveHy- A combustion engine’s torque output is minimal at lower brid[17] and the Mercedes ML 450 hybrid.[17] RPMs and, in a conventional vehicle, a larger engine is necessary for acceptable acceleration from standstill. The The Toyota Hybrid System THS / Hybrid Synergy Drive larger engine, however, has more power than needed for has a single power-split device (incorporated as a single 5

three-shaft planetary gearset) and can be classified as an smaller motors to do the job of larger motors when com- Input-Split, since the power of the engine is split at the in- pared to single-mode systems, because the derived elec- put to the transmission. This in turn makes this setup very trical peak power is proportional to the width of the con- simple in mechanical terms, but does have some draw- tinuous variation range. The four fixed gears enable the backs of its own. For example, the maximum speed is Two-Mode Hybrid to function like a conventional parallel mainly limited by the speed of the smaller electric motor hybrid under high continuous power regions such as sus- (usually functioning as a generator). Also, the efficiency tained high speed cruising or trailer towing. Full electric of the transmission is heavily dependent on the amount boost is available in fixed gear modes.[23] of power being transmitted over the electrical path, as multiple conversions, each with their own, less than per- fect efficiency, lead to a low efficiency of that path (~0.7) 2 Types by degree of hybridization compared with the purely mechanical path (~0.98). Es- pecially in higher speed regimes (>120 km/h or 70 mph) the efficiency (of the transmission alone) therefore drops 2.1 Micro hybrids below that of a generic automatic transmission with hy- drodynamic coupler. Micro hybrid is a general term given to vehicles that use some type of start-stop system to automatically shut off the engine when idling. Strictly speaking, micro hybrids are not real hybrid vehicles, because they do not rely on two different soures of power.[24]

2.2 Mild hybrids

Main article: Mild hybrid Mild hybrids are essentially conventional vehicles with

Hybrid Synergy Drive engine with electric motor and generator.

General Motors, BMW, and DaimlerChrysler have devel- oped in collaboration a system named “Two-Mode Hy- brid” as part of the Global Hybrid Cooperation. The tech- nology was released in the fall of 2007 on the Chevrolet Tahoe Hybrid. The system was also featured on the GMC Graphite SUV concept vehicle at the 2005 North American International Auto Show in Detroit.[18] BYD Auto's F3DM sedan is a series-parallel plug-in hybrid au- tomobile, which went on sale in China on December 15, Engine compartment of a 2006 GMC Sierra Hybrid. 2008.[19][20][21] The Two-Mode Hybrid name is intended to emphasize some degree of hybrid hardware, but with limited hybrid the drive-train’s ability to operate in all-electric (Mode 1, feature utilization. Typically, they are a parallel system or Input-Split) as well as hybrid (Mode 2, or Compound- with start-stop only or possibly in combination with mod- Split) modes. The design, however, allows for operation est levels of engine assist or regenerative braking features. in more than two modes; two power-split modes are avail- Unlike full hybrids, Mild hybrids generally cannot pro- able along with several fixed gear (essentially parallel hy- vide ICE-OFF all-electric (EV) propulsion. brid) regimes. For this reason, the design can be referred Mild hybrids like the General Motors 2004-07 Parallel to as a multi-regime design.[22] The Two-Mode Hybrid Hybrid Truck (PHT) and the Honda Eco-Assist hybrids powertrain design can be classified as a compound-split are equipped with a three-phase electric motor mounted design, since the addition of four clutches within the within the bell-housing between the engine and transmis- transmission allows for multiple configurations of engine sion, allowing the engine to be turned off whenever the power-splitting. In addition to the clutches, this transmis- truck is coasting, braking, or stopped, yet restart quickly sion also has a second planetary gearset. The objective when required. Accessories can continue to run on elec- of the design is to vary the percentage of mechanically trical power while the engine is off, and as in other hybrid vs. electrically transmitted power to cope both with low- designs, the motor is used for regenerative braking to re- speed and high-speed operating conditions. This enables capture energy. The large electric motor is used to spin 6 2 TYPES BY DEGREE OF HYBRIDIZATION

up the engine to operating rpm speeds before injecting electrical power needed is much smaller, the size of the any fuel. system is reduced. The 2004–07 Chevrolet Silverado PHT, was a full-size A variation on this type of hybrid is the Saturn Vue Green pickup truck. Chevrolet was able to get a 10% improve- Line BAS Hybrid system that uses a smaller electric mo- ment on the Silverado’s fuel efficiency by shutting down tor (mounted to the side of the engine), and battery pack and restarting the engine on demand and using regenera- than the Honda IMA, but functions similarly. tive braking. However the electrical motor was not used Another variation on this type is Mazda's e-4WD system, to provide propulsion or assist, rather the electrical en- offered on the Mazda Demio sold in Japan. This front- ergy was used to drive accessories like the A/C and power wheel drive vehicle has an electric motor which can drive steering.The GM PHT used a 42 volt systems via a pack the rear wheels when extra traction is needed. The system comprising three 12 V vented lead acid batteries con- is entirely disengaged in all other driving conditions, so it nected in series (36V total) to supply the power needed does not directly enhance performance or economy but for the startup motor, as well as to compensate for the allows the use of a smaller and more economical engine increasing number of electronic accessories on modern relative to total performance. vehicles. Ford has dubbed Honda’s hybrids “mild” in their advertis- General Motors followed the parallel hybrid truck with ing for the Escape Hybrid, arguing that the Escape’s full their BAS Hybrid system, another mild hybrid implemen- hybrid design is more efficient. tation officially released on the 2007 Saturn Vue Green Line. For its “start-stop” functionality, it operates simi- larly to the system in the Silverado, although via a belted 2.3 Full hybrids connection to the motor/generator unit. However the GM BAS Hybridsystem has broader hybrid functionality as the electric motor can also provide modest assist under acceleration and during steady driving, and captures en- ergy during regenerative (blended) braking. The BAS Hybrid can result in as much as a 27% improvement in combined fuel efficiency as noted by the EPA in testing of the 2009 Saturn VUE.[25] The BAS Hybrid system can also be found on the 2008-09 Saturn Aura and the 2008- 2010 Chevrolet Malibu hybrids. Another way to provide for shutting off a car’s engine when it is stopped, then immediately restarting it when it’s time to go, is by employing a static start engine. Such an engine requires no starter motor, but employs sensors to determine the exact position of each piston, then pre- cisely timing the injection and ignition of fuel to turn over the engine.[26] Engine compartment of a 2006 Mercury Mariner Hybrid. Mild hybrids are sometimes called Power assist hybrids’ A full hybrid, sometimes also called a strong hybrid, as they use the engine for primary power, with a torque- is a vehicle that can run on just the engine, just the boosting electric motor also connected to a largely con- batteries, or a combination of both. The Toyota Prius, ventional power train. The electric motor, mounted be- Toyota Camry Hybrid, Ford Escape Hybrid/Mercury tween the engine and transmission, is essentially a very Mariner Hybrid, Ford Fusion Hybrid/Lincoln MKZ Hy- large starter motor, which operates not only when the en- brid/Mercury Milan Hybrid, Ford C-Max Hybrid, Kia gine needs to be turned over, but also when the driver Optima Hybrid, as well as the General Motors 2-mode “steps on the gas” and requires extra power. The elec- hybrid trucks and SUVs, are examples of this type of tric motor may also be used to restart the combustion en- hybridization as they are able to be propelled on bat- gine, deriving the same benefits from shutting down the tery power alone. A large, high-capacity battery pack is main engine at idle, while the enhanced battery system is needed for battery-only operation. These vehicles have a used to power accessories.GM is going to produce Buick split power path that allows more flexibility in the drive- LaCrosse and Buick Regal mild hybrids dubbed Eassist. train by inter-converting mechanical and electrical power, Honda's hybrids including the Insight use this design, at some cost in complexity. To balance the forces from leveraging their reputation for design of small, efficient each portion, the vehicles use a differential-style linkage gasoline engines; their system is dubbed Integrated Motor between the engine and motor connected to the head end Assist (IMA). Assist hybrids differ fundamentally from of the transmission. full hybrids in that propulsion cannot be accomplished The Toyota brand name for this technology is Hybrid on electric power alone. However, since the amount of Synergy Drive, which is being used in the Prius, the 2.4 Plug-in hybrid 7

Highlander Hybrid SUV, and the Camry Hybrid. A com- 2.4 Plug-in hybrid puter oversees operation of the entire system, determin- ing which half should be running, or if both should be in use. The operation of the Prius can be divided into six distinct regimes.

Electric vehicle mode: The engine is off, and the battery provides electrical energy to power the motor (or the reverse when regenerative braking is engaged). Used for idling as well when the battery State Of Charge (SOC) is high.

Cruise mode: The vehicle is cruising (i.e. not accelerating), and the engine can meet the road load demand. The power from the engine is split between the mechanical path and the gen- erator. The battery provides electrical energy to power the motor, whose power is summed mechanically with the engine. If the battery state-of-charge is low, part of the power from the generator is directed towards charging the battery.

Overdrive mode: A portion of the rotational energy is siphoned off by the main electric mo- tor, operating as a generator, to produce elec- tricity. This electrical energy is used to drive Chevrolet Volt charging the sun gear in the direction opposite its usual rotation. The end result has the ring gear ro- Main article: Plug-in hybrid tating faster than the engine, albeit at lower See also: Vehicle-to-grid and Plug-in electric vehicles torque. A plug-in hybrid electric vehicle (PHEV) has two defin- Battery charge mode: Also used for idling, ing characteristics: except that in this case the battery state-of- charge is low and requires charging, which is 1. It can be plugged into an electrical outlet to be provided by the engine and generator. charged.

Power boost mode: Employed in situations 2. It has some range that can be traveled on the energy where the engine cannot meet the road load de- it stored while plugged in. mand. The battery is then used to power the motor to provide a boost to the engine power. They are full hybrids, able to run in electric-only mode, with larger batteries and the ability to recharge from the Negative split mode: The vehicle is cruising electric power grid. And can be parallel or series hybrid and the battery state-of-charge is high. The designs. They are also called gas-optional, or griddable battery provides power to both the motor (to hybrids. Their main benefit is that they can be gasoline- provide mechanical power) and to the genera- independent for daily commuting, but also have the ex- tor. The generator converts this to mechanical tended range of a hybrid for long trips. They can also energy that it directs towards the engine shaft, be multi-fuel, with the electric power supplemented by slowing it down (although not altering its torque diesel, biodiesel, or hydrogen. The Electric Power Re- output). The purpose of this engine “lugging” search Institute’s research indicates a lower total cost of is to increase the fuel economy of the vehicle. ownership for PHEVs due to reduced service costs and gradually improving batteries. The "well-to-wheel" effi- The hybrid drivetrain of the Prius, in combination with ciency and emissions of PHEVs compared to gasoline hy- aerodynamics and optimizations in the engine itself to brids depends on the energy sources of the grid (the US reduce drag, results in 80%–100% gains in fuel econ- grid is 50% coal; California’s grid is primarily natural gas, omy compared to four-door conventional cars of similar hydroelectric power, and wind power). Particular interest weight and size. in PHEVs is in California where a “million solar homes” 8 3 TYPES BY NATURE OF THE POWER SOURCE initiative is under way, and global warming legislation has 3 Types by nature of the power been enacted. source

3.1 Electric-internal combustion engine hybrid

There are many ways to create an electric-Internal Com- bustion Engine (ICE) hybrid. The variety of electric- ICE designs can be differentiated by how the electric and combustion portions of the powertrain connect, at what times each portion is in operation, and what percent of the power is provided by each hybrid component. Two ma- jor categories are series hybrids and parallel hybrids, though parallel designs are most common today. Most hybrids, no matter the specific type, use Engine compartment of a BYD F3DM plug-in hybrid. regenerative braking to recover energy when slow- ing down the vehicle. This simply involves driving a Prototypes of PHEVs, with larger battery packs that can motor so it acts as a generator. be recharged from the power grid, have been built in the U.S., notably at Prof. Andy Frank's Hybrid Center[27] Many designs also shut off the internal combustion en- at University of California, Davis and one production gine when it is not needed in order to save energy. That PHEV, the Renault Kangoo, went on sale in France concept is not unique to hybrids; Subaru pioneered this in 2003. DaimlerChrysler is currently building PHEVs feature in the early 1980s, and the Volkswagen Lupo based on the Mercedes-Benz Sprinter van. Light Trucks 3L is one example of a conventional vehicle that shuts are also offered by Micro-Vett SPA[28] the so-called Daily off its engine when at a stop. Some provision must be Bimodale. made, however, for accessories such as air conditioning which are normally driven by the engine. Furthermore, The California Cars Initiative has converted the 2004 and the lubrication systems of internal combustion engines newer Toyota Prius to become a prototype of what it calls are inherently least effective immediately after the engine the PRIUS+. With the addition of 140 kg (300 lb) of starts; since it is upon startup that the majority of engine lead-acid batteries, the PRIUS+ achieves roughly double wear occurs, the frequent starting and stopping of such the gasoline mileage of a standard Prius and can make systems reduce the lifespan of the engine considerably. trips of up to 16 km (10 mi) miles using only electric Also, start and stop cycles may reduce the engine’s abil- power.[29] ity to operate at its optimum temperature, thus reducing Chinese battery manufacturer and automaker BYD Auto the engine’s efficiency. released the F3DM compact sedan to the Chinese fleet market on December 15, 2008.[30][31] Due to low sales, BYD announced in April 2010 that the F3DM will be Reservoir Battery replaced by the BYD Qin plug-in hybrid.[32][33] General Motors began deliveries of the Chevrolet Volt in Power Electric Fuel Cell Conditioner Converter the United States in December 2010,[5] and its sibling, the motor Opel Ampera, was released for retail customers in Europe by early 2012.[34][35] As of November 2012, other plug-in hybrids available in several markets are the Fisker Karma, Toyota Prius Plug-in Hybrid, and Ford C-Max Energi. Structure of a fuel cell hybrid electric vehicle As of October 2012, the best selling plug-in hybrid is the Chevrolet Volt, with more than 33,000 units of the Volt/Ampera family sold worldwide since De- cember 2010, with sales led by the U.S. with 27,306 Volts sold through October 2012,[36][37] followed by the 3.2 Electric-fuel cell hybrid Netherlands with 2,175 Amperas sold through October 2012.[38][39] The second top selling PHEV is the Prius Fuel cell vehicles are often fitted with a battery or super- Plug-in Hybrid, with 21,600 units sold worldwide through capacitor to deliver peak acceleration power and to re- October 2012, with sales led by the United States with duce the size and power constraints on the fuel cell (and 9,623 units through October 2012, followed by Japan thus its cost); this is effectively also a series hybrid con- with 9,500 units through October 2012.[37][40] figuration. 3.3 Internal combustion engine-hydraulic hybrid 9

3.3 Internal combustion engine-hydraulic sized accumulators entails downsizing an engine to aver- hybrid age power usage, not peak power usage. Peak power is provided by the energy stored in the accumulator.[42] The kinetic braking energy recovery rate is higher and therefore the system is more efficient than current battery charged hybrids, demonstrating a 60% to 70% increase in economy in EPA testing.[43] Under tests undertaken by the EPA, a hydraulic hybrid Ford Expedition returned 32 mpg-US (7.4 L/100 km) in urban driving, and 22 mpg- US (11 L/100 km) on the highway.[44] UPS currently has two trucks in service with this technology.[45] While the system has faster and more efficient charge/discharge cy- cling, the accumulator size and pressure dictates total en- ergy capacity, and requires more space than a battery. However for the energy stored the accumulator is smaller in physical size than a current battery pack. Chrysler are adapting a minvan to a gasoline-hydraulic hybrid setup. One research company’s goal is to create a blank paper design new car, to maximize the packaging of gasoline- A hydraulic hybrid vehicle uses hydraulic and mechan- hydraulic hybrid components in the vehicle. All bulky ical components instead of electrical. A variable dis- hydraulic components are integrated into the chassis of placement pump replaces the electric motor/generator. A the car. One design has claimed to return 130mpg in tests hydraulic accumulator, is a vessel which stores energy. by using a large hydraulic accumulator which is also the The vessel typically has a flexible bladder of pre-charged structural chassis of the car. The small hydraulic driv- pressurized nitrogen gas inside. Pumped hydraulic fluid ing motors are incorporated within the wheel hubs driv- is compressed against the bladder storing the energy in ing the wheels and reversing to claw-back kinetic brak- the highly compressed nitrogen gas. Some versions have ing energy. The aim is 170mpg in average driving con- a piston in a cylinder rather than pressurized bladder of ditions. Energy created by shock absorbers and kinetic nitrogen gas. The accumulator replaces the batteries on braking energy that normally would be wasted assists in petro-electric hybrid. The hydraulic accumulator is po- charging the accumulator. A small fossil fuelled piston tentially cheaper and more durable than batteries. Hy- engine sized for average power use charges the accumu- draulic hybrid technology was originally implemented in lator. The accumulator is sized at running the car for 15 Germany in the 1930s. Volvo Flygmotor used petro- minutes when fully charged. The aim is a fully charged hydraulic hybrids experimentally in buses from the early accumulator with an energy storage potential of 670 HP, 1980s and is still an active area. which will produce a 0-60 mph acceleration speed of un- [46][47][48] Initial concept involved a giant flywheel (see Gyrobus) for der 5 seconds using four wheel drive. storage connected to a hydrostatic transmission, however In January 2011, industry giant Chrysler announced later changed to a simpler system using a hydraulic accu- a partnership with the U.S. Environmental Protec- mulator connected to a hydraulic pump/motor. The sys- tion Agency (EPA) to design and develop an exper- tem is also being actively developed by Eaton and several imental gasoline-hydraulic hybrid powertrain suitable other companies, primarily in heavy vehicles like buses, for use in large passenger cars. Chrysler adapted trucks and military vehicles. An example is the Ford F- an existing production minvan to the new hydraulic 350 Mighty Tonka concept truck shown in 2002. It fea- powertrain.[49][50][51][52] Research is ongoing in this tures an Eaton system that can accelerate the truck up to field.[53] highway speeds. NRG Dynamix of the U.S.A. claims its approach reduces The system components were expensive which precluded cost one-third compared with electric hybrids and adds installation in smaller trucks and cars. A drawback was only 300 lbs (136 kg) to vehicle weight vs. 1,000 lbs (454 that the power driving motors were not efficient enough at kg) for electric hybrids. Under tests the company claim a part load. Focus has now switched to smaller vehicles. A standard pickup vehicle powered by a 2.3 litre 4 cylinder British company has made a breakthrough by introduc- engine returns 14 mpg (16.8 l/100 km) in city driving. ing an electronically controlled hydraulic motor/pump, Using the petro-hydraulic setup fuel economy climbs to the Digital Displacement® motor/pump, that is highly ef- “the mid 20s”.[54] ficient at all ranges and loads making small applications of petro-hydraulic hybrids feasible.[41] The company con- verted a BMW car as a test bed to prove viability. The BMW 530i, gave double the MPG in city driving com- pared to the standard car. This was tested using the stan- dard 3,000cc engine. Petro-hydraulic hybrids using well 10 7 REFERENCES

3.4 Internal combustion engine-pneumatic (electric or hybrid) powertrain can be added to a glider[55] hybrid by a third party aftermarket installer. A University of Central Florida senior design team, On Compressed air can also power a hybrid car with a gaso- the Green, is currently developing a bolt-on hybrid con- line compressor to provide the power. Motor Devel- version kit to transform an older model vehicle into a gas- opment International in France is developing such air- electric hybrid.[56] powered cars. A team led by Tsu-Chin Tsao, a UCLA mechanical and aerospace engineering professor, is col- An example of a conversion using a 1966 Mustang was laborating with engineers from Ford to get Pneumatic hy- demonstrated by an engineer in California. The sys- brid technology up and running. The system is similar to tem replaces the alternator with a 12 kW (30 kW peak) that of a hybrid-electric vehicle in that braking energy is brushless electric motor. Gas mileage and power were [57] harnessed and stored to assist the engine as needed during improved. acceleration. 6 See also 3.5 Human power and environmental power hybrids • Battery electric vehicle

Many land and water vehicles use human power com- • Electric vehicle bined with a further power source. Common are parallel • hybrids, e.g. a boat being rowed and also having a sail Engine control unit set, or motorized bicycles, or a human-electric hybrid ve- • Hybrid electric vehicle hicle such as the Twike. Also some series hybrids exist, see in hybrid vehicle. Such vehicles can be tribrid ve- hicles, combining at the same time three power sources e.g. from on-board solar cells, from grid-charged batter- 7 References ies, and from pedals. [1] “DOE to Award Up to $2.4B for Advanced Batteries, Electric Drive Components, and Electric Drive Vehi- cle Demonstration/Deployment Projects”. Green Car 4 Hybrid vehicle operation modes Congress. March 19, 2009.

Hybrid vehicles can be used in different modes. The fig- [2] “Hybrids Under the Hood (Part 2): Drivetrains”. Hybrid ure shows some typical modes for a parallel hybrid con- Center (Union of Concerned Scientists). Retrieved 2010- figuration. 03-18. [3] {cite web |title=What do you mean when you say Through-The-Road-Hybrid (TTRH)? |publisher=Protean Electric |url=http://www.proteanelectric.com/en/faqs/ what-do-you-mean-when-you-say-through-the-road-hybrid-ttrh/ |accessdate= July 2014}

[4] {cite web |title=Through-The-Road (TTR) Hybrid - Through-The-Roof Potential - 598 |publisher=Argonne National Laboratory |url=http://www.transportation.anl. gov/pdfs/HV/598.PDF |accessdate= July 2014}

[5] Matthe, Roland; Eberle, Ulrich (2014-01-01). “The Voltec System - Energy Storage and Electric Propulsion”. Retrieved 2014-05-04. 5 Adding powertrains and after- [6] “Improving IC Engine Efficiency”. University of Wash- ington: Energy & Environment – Autumn 2001. Re- market kits trieved April 18, 2013.

[7] “Lotus to Introduce Range Extender Engine”. Green Car One can install conmarket or aftermarket powertrain to a Congress. September 7, 2009. vehicle to hybridise it. [8] Neuman, William (October 11, 2007). “The turbine on The conmarket solution is used when the user buys the the bus goes purr purr purr”. New York Times. glider (rolling chassis) and the hybrid (two engines) or all-electric (only an electric motor) powertrain kit to the [9] Linear Combustion Engine Project. Retrieved April 18, automaker and receives it installed in the car. Also an 2013. 11

[10] Churella, 28-30 [30] Crippen, Alex (December 15, 2008). “Warren Buffett’s Electric Car Hits the Chinese Market, But Rollout De- [11] “Toyota debuts power-hybrid bus”. The Japan Times. Au- layed For U.S. & Europe”. CNBC. gust 22, 1997. [31] Balfour, Frederik (December 15, 2008). “China’s First [12] “AFS Trinity urgees Congress and candidates to support Plug-In Hybrid Car Rolls Out”. Business Week. proposed auto stimulus package”. AFS Trinity. Septem- ber 24, 2008. [32] Voelcker, John (April 20, 2012). “BYD Chin: World’s First Plug-In Hybrid, Updated And Renamed”. Green [13] “Mazda stays loyal to rotary engines”. The Daily Tele- Car Reports. graph (London). September 18, 2012. [33] Blanco, Sebastian (April 20, 2012). “BYD’s Beijing [14] “Siemens, Diamond Aircraft, EADS unveil world’s first Motor Show line-up includes Chin Dual Mode, remote- serial hybrid aircraft”. Autoblog. 2011-07-03. Retrieved controlled F3”. Autoblog Green. 2011-07-03. [34] Chambers, Nick (December 16, 2010). “First Chevy [15] http://www.greencarcongress.com/2013/06/ Volts Reach Customers, Will Out-Deliver Nissan in De- eads-21030618.html cember”. plugincars.com.

[16] “Ravigneaux planetary gear set of carrier, sun, planet, and [35] “Opel Ampera: First Customers Take Delivery”. Opel ring wheels with adjustable gear ratios and friction losses Europe. February 21, 2012. - Simulink”. Mathworks.com. Retrieved 2012-08-01. [36] Voelcker, John (August 1, 2012). “July Plug-In Electric [17] Krust, Matthias (July 14, 2009). “BMW, Daimler, GM Car Sales: Volt Steady, Leaf Lethargic (Again)". Green hybrid alliance nears end”. Automotive News. Car Reports.

[18] “The GMC Graphyte — A hybrid SUV concept vehicle”. [37] Cole, Jay (November 1, 2012). “October 2012 Plug-In GM - GMability Education 9-12: Fuel Cells & Energy. Electric Vehicle Sales Report Card”. Inside EVs. Archived from the original on January 16, 2006. [38] RAI (2012-06-04). “Autoverkopen mei 2012 dalen met [19] “New BYD Hybrid Gets Jump in Electric Car Wars in 4,4 procent” [Car sales in May 2012 decreased by 4.4 China”. China Stakes. December 1, 2008. percent] (in Dutch). RAI Vereniging. Retrieved 2012- 08-05. Download pdf file for detailed sales in 2011 and [20] Yoney, Domenick (April 13, 2009). “Chinese plug-in hy- 2012 CYTD. brid, BYD F3DM, has sold just 80 copies in four months”. Autoblog Green. [39] RAI (October 2012). “Verkoopcijfers oktober 2012 - Modellenoverzicht” [Sales October 2012 - Models [21] Shirouzu, Norihko (October 13, 2008). “BYD to Launch overview] (in Dutch). Auto Week Netherlands. Retrieved Electric Car Sales in China Next Month”. The Wall Street 2012-11-01. Table shows September and October 2012 Journal. (subscription required) sales.

[22] Wishart, J.; Zhou, Y.; Dong, Z. (2008). “Review of multi- [40] “Cumulative Sales of TMC Hybrids Top 2 Million Units regime hybrid vehicle powertrain architecture”. Interna- in Japan”. Toyota. November 8, 2012. tional Journal of Electric and Hybrid Vehicles 1 (3): 248– [41] “Our Technology”. Artemis Intelligent Power. Retrieved 275. doi:10.1504/IJEHV.2008.019900. April 18, 2013.

[23] “Powerfully Efficient: GM Two-Mode Hybrid”. General [42] “Applications – On-road”. Artemis Intelligent Power. Motors. Archived from the original on February 25, 2009. Retrieved April 18, 2013.

[24] . KFZ-tech.de http://www.kfz-tech.de/Engl/ [43] “EPA Announces Partnership to Demonstrate World’s HybridBegriffe.htm. Retrieved 13 April 2015. First Full Hydraulic Hybrid Urban Delivery Vehicle”. Missing or empty |title= (help) EPA. February 2005. Retrieved April 18, 2013.

[25] “Compare Cars Side-by-Side”. Fueleconomy.gov. Re- [44] Vanzieleghem, Bruno (June 15, 2006). “Capturing the trieved 2012-08-01. power of hydraulics”. Autoblog Green.

[26] Kassakian, J.G (1996). “Automotive electrical sys- [45] Nunez, Alex (June 26, 2006). “EPA unveils hydraulic hy- tems circa 2005”. Spectrum, IEEE 33 (8): 22–27. brid UPS delivery truck”. Autoblog. doi:10.1109/6.511737. [46] Proefrock, Philip (March 25, 2010). “Hybrid Hydraulic [27] “Team Fate”. UC-Davis Hybrid Electric Vehicles Group. Drive Vehicle Promises 170 MPG”. Inhabitat. Archived from the original on January 12, 2006. [47] Turpen, Aaron (February 15, 2012). “INGOCAR from [28] “Hybrid Daily: Technical Data”. Micro-Vett. Archived Valentin Tech shatters the way we think about cars”. from the original on January 10, 2006. Torque News.

[29] “How We Green-Tuned an '04 Prius into a PRIUS+ Plug- [48] “170 MPG Ingocar”. Valentin Technologies, Inc. Re- In Hybrid!". CalCars. Retrieved April 18, 2013. trieved April 18, 2013. 12 8 EXTERNAL LINKS

[49] Hanlon, Mike (January 26, 2011). “Chrysler announces development of hydraulic hybrid technology for cars”. Gizmag.

[50] “EPA and Chrysler to Take Latest Hybrid Technology from Lab to Street/Partnership to adapt fuel efficient tech- nology”. EPA. January 19, 2011.

[51] “Hydraulic Hybrid Research”. EPA. Retrieved April 18, 2013.

[52] “Demonstration Vehicles”. EPA. Retrieved April 18, 2013.

[53] http://www.greencarcongress.com/2013/09/ 20130924-chrysler.html

[54] http://wardsauto.com/vehicles-amp-technology/ new-hydraulic-hybrid-system-claims-big-mpg-boost

[55] “Energy Storage Fuel Cell Vehicle Analysis: Preprint”. National Renewable Energy Laboratory. April 2005.

[56] On the Green. Retrieved April 18, 2013.

[57] How To Build A Hybrid. Retrieved April 18, 2013.

8 External links

• Hybrid Cars Need Special Mechanics at HowStuffWorks • The Rise of the REEV

• Serial Hybrids Are Here - Ecoworld.com • Air Car video

• Zeroshift hybrid and electric vehicle Transmission (EV transmission) Systems 13

9 Text and image sources, contributors, and licenses

9.1 Text • Hybrid vehicle drivetrain Source: http://en.wikipedia.org/wiki/Hybrid%20vehicle%20drivetrain?oldid=656276778 Contributors: Mac, Mulad, Leonard G., Rchandra, Beland, LHOON, Brianhe, Rich Farmbrough, Vsmith, Kbyrd, Deicas, Chizu, Hadlock, Wtshymanski, RJFJR, Mattbrundage, Dan100, Stemonitis, Bobrayner, Woohookitty, Plek, Vegaswikian, Lonestarnot, Grs1969, Skierpage, Wingchi, RedGreenInBlue, Wavelength, Jzylstra, StuffOfInterest, RussBot, Arado, D0li0, Casey56, Hydrargyrum, Ospalh, MaxDZ8, Ageekgal, SmackBot, Ariedartin, Sam8, By78, Chris the speller, Improbcat, Thumperward, DeFacto, Mhrogers, JanCeuleers, Derek R Bullam- ore, The PIPE, DMacks, Daniel.Cardenas, FlyHigh, Gerben1974, Zero10one, Smenjas, CmdrObot, Tomcha, Ken Gallager, Cydebot, ANTIcarrot, Ssilvers, IJB TA, Jeffwishart, JustAGal, Gregalton, IanOsgood, Igodard, Mwarren us, Magioladitis, KJRehberg, Zojj, Kyli- eTastic, Funandtrvl, Joeinwap, Theosch, Aznshark4, Rich Janis, Takeitupalevel, Ng.j, Tri400, Typ932, Caltas, Brucedp, Sfan00 IMG, ClueBot, Mariordo, Numindast, Fatsamsgrandslam, Lkruijsw, DumZiBoT, XLinkBot, Jovianeye, Greasywheel, Andromon58, Download, Dude1024, Yobot, ClockwerkMao, Fraggle81, Pineapple fez, AnomieBOT, LilHelpa, WopOnTour, Honza.havlicek, RightCowLeftCoast, Rudimae, FrescoBot, Atarivideomusic, Torotrak, Lotje, Whgs09, RjwilmsiBot, Zilyuki, Liverpool-8-boy, John of Reading, GoingBatty, Rayukk, H3llBot, Pepsi132, Widr, Dougmcdonell, Nbrewton, Dhirukapur, Newuser06081958, Fnevt24p, Begonia Brandbygeana, Doc- torKubla, Khazar2, VX1NG, NCWA1, CsDix, Comp.arch, Monkbot, B4qpcGKd0fedr and Anonymous: 98

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