Hybrid vehicle

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For other types of hybrid transportation, see Hybrid vehicle (disambiguation).

Prius hybrid vehicle

A hybrid vehicle is a vehicle that uses two or more distinct power sources to propel the vehicle.^[1] Common power sources include:

On-board rechargeable energy storage system (RESS) and a fueled power source (internal combustion engine or fuel cell)
Air and internal combustion engines
Human powered bicycle with electric motor or gas engine assist
Human-powered or sail boat with electric power

The term most commonly refers to Hybrid-electric vehicle (HEV) which includes internal combustion engines and electric motors.

[edit] Hybrid types

[edit] Vehicle type

[edit] Single-wheeled vehicles

There were large Chinese wheelbarrows depicted with sails and masts.^[2] Likewise, there are the same Chinese wheelbarrows with sailing masts depicted in the Atlas of Gerardus Mercator (1512–1594 AD), as well as the 1626 AD book Kingdome of Chinay J. Speed.^[2] The English poet John Milton (1608–1674 AD) popularized the Chinese sailing carriage in Europe with a poem written in 1665.^[2]

[edit] Two-wheeled and cycle-type vehicles

Mopeds and electric bicycles are a simple form of a hybrid, as power is delivered both via an internal combustion engine or electric motor and the rider's muscles. Early prototypes of motorcycles in the late 1800s used the same principles.

In a parallel hybrid bicycle human and motor power are mechanically coupled at the pedal drive train or at the rear or the front wheel, e.g. using a hub motor, a roller pressing onto a tire, or a connection to a wheel using a transmission element. Human and motor torques are added together. Almost all manufactured models are of this type. See Motorized bicycles, Mopeds and^[3] for more information.

In a series hybrid bicycle (SH) the user powers a generator using the pedals. This is converted into electricity and can be fed directly to the motor giving a chainless bicycle but also to charge a battery. The motor draws power from the battery and must be able to deliver the full mechanical torque required because none is available from the pedals. SH bicycles are commercially available, because they are very simple in theory and manufacturing.^[4]

The first known prototype and publication of an SH bicycle is by Augustus Kinzel (US Patent 3'884'317) in 1975. In 1994 Bernie Macdonalds conceived the Electrilite SH lightweight vehicle which used power electronics allowing regenerative braking and pedaling while stationary. In 1995 Thomas Müller designed a "Fahrrad mit elektromagnetischem Antrieb" in his 1995 diploma thesis and built a functional vehicle. In 1996 Jürg Blatter and Andreas Fuchs of Berne University of Applied Sciences built an SH bicycle and in 1998 mounted the system onto a Leitra tricycle (European patent EP 1165188). In 1999 Harald Kutzke described his concept of the "active bicycle": the aim is to approach the ideal bicycle weighing nothing and having no drag by electronic compensation. Until 2005 Fuchs and colleagues built several prototype SH tricycles and quadricycles. [1]

[edit] Heavy vehicles

Hybrid power trains are used for diesel-electric or turbo-electric railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery, and ships. Ships with both sails and engines are an early form of hybrid which may return to more common use as costs of fuels rises. Typically some form of heat engine (usually diesel) drives an electric generator or hydraulic pump which power one or more electric or hydraulic motors. There are advantages in distributing power through wires or pipes rather than mechanical elements especially when multiple drives—e.g. driven wheels or propellers—are required. There is power lost in the double conversion from typically diesel fuel to electricity to power an electric or hydraulic motor. With large vehicles the advantages often outweigh the disadvantages especially as the conversion losses typically decrease with size. Presently there is no or relatively little energy storage capacity on most heavy vehicles, e.g. auxiliary batteries and hydraulic accumulators—this is changing.

[edit] Rail transport

An example of a typical "hybrid" is the new Canadian, Bombardier-built railroad engine called the AGC (Autorail à grande capacité, high-capacity railcar) which has dual mode (diesel and electric motors) and dual voltage capabilities (1500 and 25000 V) allowing it to be used on many different rail systems. [2]. The first operational prototype of a hybrid train engine with significant energy storage and energy regeneration capability has been introduced in Japan as the Kiha E200. It utilizes battery packs of lithium ion batteries mounted on the roof to store recovered energy.^[5] In the U.S., General Electric introduced a prototype railroad engine with their "Ecomagination" technology in 2007. They store energy in a large set of sodium nickel chloride (Na-NiCl2) batteries to capture and store energy normally dissipated during dynamic braking or coasting downhill. They expect at least a 10% reduction in fuel use with this system and are now spending about $2 billion/yr on hybrid research.^[6] Variants of typical diesel-electrical locomotives are like the Green Goat (GG) and Green Kid (GK) switching/yard engines built by Canada's Railpower Technologies. They utilize a large set of heavy duty long life (~10 yr) rechargeable lead acid (Pba) batteries and 1000 to 2000 HP electric motors as the primary motive sources and a new clean burning diesel generator (~160 Hp) for recharging the batteries that is used only as needed. No power or fuel are wasted for idling—typically 60–85% of the time for these type locomotives. Its unclear if dynamic braking (regenerative) power is recaptured for reuse; but in principle should be easily utilized. Since these engines typical need extra weight for traction purposes anyway the battery pack's weight is a negligible penalty. In addition the diesel generator and battery package are normally built on an existing "retired" "yard" locomotive's frame for significant additional cost savings. The existing motors and running gear are all rebuilt and reused. Diesel fuel savings of 40–60% and up to 80% pollution reductions are claimed over that of a "typical" older switching/yard engine. The same advantages that existing hybrid cars have for use with frequent starts and stops and idle periods apply to typical switching yard use.^[7] "Green Goats" locomotives have been purchased by Canadian Pacific Railway, BNSF Railway, Kansas City Southern Railway and Union Pacific Railroad among others.

Railpower Technologies Corp. engineers working with TSI Terminal Systems Inc. in Vancouver, British Columbia are testing a hybrid diesel electric power unit with battery storage for use in Rubber Tyred Gantry (RTG) cranes. RTG cranes are typically used for loading and unloading shipping containers onto trains or trucks in ports and container storage yards. The energy used to lift the containers can be partially regained when they are lowered. Diesel fuel and emission reductions of 50–70% are predicted by Railpower engineers.^[8] First systems are expected to be operational in 2007.^[9]

[edit] Road Transport, Commercial Vehicles

GM has launched hybrid versions of its full-size GMC Yukon (pictured) and Chevrolet Tahoe SUVs' for 2008

Early hybrid systems are being investigated for trucks and other heavy highway vehicles with some operational trucks and buses starting to come into use. The main obstacles seem to be smaller fleet sizes and the extra costs of a hybrid system are yet compensated for by fuel savings, but with the price of oil set to continue on its upward trend, the tipping point may be reached by the end of 2008. Advances in technology and lowered battery cost and higher capacity etc. developed in the hybrid car industry are already filtering into truck use as Toyota, Ford, GM and others introduce hybrid pickups and SUVs. Kenworth Truck Company recently introduced a hybrid-electric truck, called the Kenworth T270 Class 6 that for city usage seems to be competitive.^[10]^[11] FedEx and others are starting to invest in hybrid delivery type vehicles—particularly for city use where hybrid technology may pay off first.^[12] The U.S. military is investigating hybrid Humvees^[13] and other vehicles.

[edit] Engine type

[edit] Hybrid-electric petroleum vehicles

Hybrid New Flyer Metrobus

Hybrid Optare Solo

Main article: Hybrid electric vehicle

When the term hybrid vehicle is used, it most often refers to a Hybrid electric vehicle. These encompass such vehicles as the AHS2 (Chevrolet Tahoe, GMC Yukon, Chevrolet Silverado, Cadillac Escalade, and the Saturn Vue), Toyota Prius, Toyota Camry Hybrid, Ford Escape Hybrid, Toyota Highlander Hybrid, Honda Insight, Honda Civic Hybrid and others. A petroleum-electric hybrid most commonly uses internal combustion engines (generally gasoline or Diesel engines, powered by a variety of fuels) and electric batteries to power electric motors. There are many types of petroleum-electric hybrid drivetrains, from Full hybrid to Mild hybrid, which offer varying advantages and disadvantages.^[14]

While liquid fuel/electric hybrids date back to the late 1800s, the braking regenerative hybrid was invented by David Arthurs, an electrical engineer from Springdale, Arkansas in 1978-79. His home-converted Opel GT was reported to get as much as 75MPG and plans are still sold to this original design, and the "Mother Earth News" modified version on their website. ^[15]

[edit] Continuously recharged battery electric vehicle (BEV)

Given suitable infrastructure, permissions and vehicles, BEVs can be recharged while the user drives. The BEV establishes contact with an electrified rail, plate or overhead wires on the highway via an attached conducting wheel or other similar mechanism (see Conduit current collection). The BEV's batteries are recharged by this process—on the highway—and can then be used normally on other roads until the battery is discharged.

This provides the advantage, in principle, of virtually unrestricted highway range as long as you stay where you have BEV infrastructure access. Since many destinations are within 100 km of a major highway, this may reduce the need for expensive battery systems. Unfortunately private use of the existing electrical system is nearly universally prohibited.

The technology for such electrical infrastructure is old and, unfortunately outside of some cities, is not widely distributed (see Conduit current collection, trams, electric rail, trolleys, third rail). Updating the required electrical and infrastructure costs can be funded, in principle, by toll revenue, gasoline or other taxes.

[edit] Hybrid fuel (dual mode)

In addition to vehicles that use two or more different devices for propulsion, some also consider vehicles that use distinct energy sources or input types ("fuels") using the same engine to be hybrids, although to avoid confusion with hybrids as described above and to use correctly the terms, these are perhaps more correctly described as dual mode vehicles:

Some electric trolleybuses can switch between an on board diesel engine and overhead electrical power depending on conditions (see dual mode bus). In principle, this could be combined with a battery subsystem to create a true plug-in hybrid trolleybus, although as of 2006, no such design seems to have been announced.
Flexible-fuel vehicles can use a mixture of input fuels (petroleum and biofuels) in one tank — typically gasoline and bioethanol or biobutanol, though diesel-biodiesel vehicles would also qualify.
Dual mode:Liquified petroleum gas and natural gas are very different from petroleum or diesel and cannot be used in the same tanks, so it would be impossible to build an (LPG or NG) flexible fuel system. Instead vehicles are built with two, parallel, fuel systems feeding one engine. While the duplicated tanks cost space in some applications, the increased range and flexibilty where (LPG or NG) infrastructure is incomplete may be a significant incentive to purchase.
Some vehicles have been modified to use another fuel source if it is available, such as cars modified to run on autogas (LPG) and diesels modified to run on waste vegetable oil that has not been processed into biodiesel.
Power-assist mechanisms for bicycles and other human-powered vehicles are also included.

[edit] Fluid power hybrid

Hydraulic and pneumatic hybrid vehicles use an engine to charge a pressure accumulator to drive the wheels via hydraulic or pneumatic (i.e. compressed air) drive units. The energy recovery rate is higher and therefore the system is more efficient than battery charged hybrids, demonstrating a 60% to 70% increase in energy economy in EPA testing ^[16]. Under tests done by the EPA, a hydraulic hybrid Ford Expedition returned 32 mpg–U.S. (7.35 L/100 km / 38.4 mpg–imp) City, and 22 mpg–U.S. (10.69 L/100 km / 26.4 mpg–imp) highway. ^[17]

UPS currently has two trucks in service with this technology. ^[18]

While the system has faster and more efficient charge/discharge cycling and is cheaper than gaselectric hybrids, the accumulator size dictates total energy storage capacity and requires more space than a battery.

[edit] Plug-in Hybrid Electrical Vehicles (PHEV)

Main article: Plug-in hybrid

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The latest hybrid technology is the Plug-in Hybrid Electric Vehicle (PHEV). The PHEV consists of a gasoline-electric hybrid whose battery pack (usually Li-ion) is upgraded to a larger capacity, which can be recharged by either a battery charger hooked into the electrical grid or the gasoline engine (only if required). The car runs on battery power for the first 10 to 60 miles (16–100 km), with the gasoline engine available for faster acceleration, etc. After the battery is nearly discharged, the car reverts to the gasoline engine to recharge the battery and/or return the car to the charging station. This may get around the fundamental obstacle of battery range that has made nearly all pure electric cars impractical. Fuel costs (ignoring conversion costs), in principle, may be as low as 5 cents/mile. It's not clear yet whether converting an existing hybrid car will ever pay for itself in fuel savings. The biggest problem is finding a good, cheap, high-energy battery pack—the same problem that has plagued the pure electric car. If everyone plugged into the utility grid to charge up their car this would seem to be merely displacing the gasoline/diesel combustion problem to the typical coal powered electrical generating plant. But, if cars were recharged late at night this would allow the base load of the electrical system to be more efficient with a much more even base load and electrical power can also be generated by clean wind, hydro, tide power, etc. Since most travel is about 30 miles/day this may be the cleanest personal transportation system presently available. There is a "cottage" conversion industry for owners of existing hybrids, and several large auto industry groups (GM, Toyota, Mercedes etc.) as well as the US Department of Energy^[19] are investigating this system. No major car company (as of late 2007) offers PHEVs yet. The typical "cottage" industry conversion car is the Toyota Prius (cost of conversion $5k-$40k), since it is a full hybrid with enough power in its electrical system to maintain typical city speeds.^[20]^[21]

[edit] Environmental issues

[edit] Fuel consumption and emissions reductions

The hybrid vehicle typically achieves greater fuel economy and lower emissions than conventional internal combustion engine vehicles (ICEVs), resulting in fewer emissions being generated. These savings are primarily achieved by four elements of a typical hybrid design:

recapturing energy normally wasted during braking etc.;
having significant battery storage capacity to store and reuse recaptured energy;
shutting down the gasoline or diesel engine during traffic stops or while coasting or other idle periods;
relying on both the gasoline (or diesel engine) and the electric motors for peak power needs resulting in a smaller gasoline or diesel engine sized more for average usage rather than peak power usage.

These features make a hybrid vehicle particularly efficient for city traffic where there are frequent stops, coasting and idling periods. In addition noise emissions are reduced, particularly at idling and low operating speeds,^[22] in comparison to conventional gasoline or diesel powered engine vehicles. For continuous high speed highway use these features are much less useful in reducing emissions.

[edit] Environmental impact of hybrid car battery

Main article: Electric vehicle battery

Though hybrid cars take in substantially less petroleum than conventional cars, there is still an issue regarding the environmental damage of the Hybrid car battery. Today most Hybrid car batteries are one of two types: (1) nickel metal hydride, or (2) lithium ion; both are regarded as more environmentally friendly than lead-based batteries (which constitute the bulk of car batteries today). “Jim Kliesch, author of the ‘Green Book: The Environmental Guide to Cars and Trucks’ told HybridCars.com, ‘There are many types of batteries. Some are far more toxic than others. While batteries like lead acid or nickel cadmium are incredibly bad for the environment, the toxicity levels and environmental impact of nickel metal hydride batteries—the type currently used in hybrids—are much lower.’"[3].

Though substantially less toxic than conventional car batteries, nickel-based batteries are known carcinogens, as well as can lead to a wide array of other health problems (little testing has been done to show the effects of nickel on people but other possible side effects may include: “xencephaly, everted viscera, short and twisted neck, short and twisted limbs, microphthalmia, hemorrhage, and reduced body size” [4]).

[edit] Raw materials shortage

There is an impeding shortage of many rare materials used in the manufacture of hybrid cars ^[23].

For example, the rare earth element dysprosium is required to fabricate many of the advanced electric motors and battery systems in hybrid propulsion systems ^[24]^[23].

However, nearly all the rare earth elements in the world come from China^[25], and many analysts believe that an overall increase in Chinese electronics manufacturing will consume this entire supply by 2012.^[23] In addition, export quotas on Chinese Rare Earth exports have resulted in a generally shaky supply of those metals ^[26] ^[27].

A few non-Chinese sources such as the advanced Hoidas Lake project in northern Canada as well as Mt Weld in Australia are currently under development;^[28] however it is not known if these sources will be developed before the shortage hits.

[edit] Alternative green vehicles

Main article: Green vehicle#Types

Other types of green vehicles include other vehicles that go fully or partly on alternative energy sources than fossil fuel. Another alternative is to use alternative fuel composition in conventional fossil fuel-based vehicles, making them go partly on renewable energy sources.

Other approaches include personal rapid transit, a public transportation concept that offers automated on-demand non-stop transportation, on a network of specially-built guideways.