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For the common automotive use of "hybrid vehicle", see Petroleum electric hybrid vehicle.
A hybrid vehicle (HV) is a vehicle that uses two or more distinct power sources such as:
- An on-board rechargeable energy storage system (RESS) and a fueled power source for vehicle propulsion
- Human powered bicycle with battery assist
- A sail boat with electric power
The term most commonly refers to a petroleum electric hybrid vehicle, also called Hybrid-electric vehicle (HEV) which use internal combustion engines and electric batteries to power electric motors. See also "Types of hybrid vehicles" and "List of hybrid vehicles".
One of the earliest hybrid vehicles were simply boats with both sails and oars, such as the Greek/Phoenician trireme warships. These used a sail for traveling with the wind, and the oars for when there was insufficient wind, or in circumstances that the sail was unfavorable (such as naval combat, in the case of the triremes).
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.
- 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  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 not yet commercially available. They will become feasible if extremely high-efficiency generators and motors are available at competitive prices, especially for recumbent bicycles and tandems, where problems associated with the complexity of a long chain drive can be avoided. .
- The first known prototype and publication of a 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 a 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. 
Hybrid power trains are used for diesel-electric or turbo-electric railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery, and ships. Some form of heat engine drives an electric generator or hydraulic pump which power one or several 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 are disadvantages due to the power lost in the double conversion. With large vehicles the advantages often outweigh especially as the relative conversion losses decrease with size. Generally there is no or relatively little energy storage capacity, e.g. auxiliary and emergency batteries and hydraulic accumulators.
When the term hybrid vehicle is used, it most often refers to a Petroleum electric hybrid vehicle. These encompass such vehicles as the Toyota Prius, Toyota Camry Hybrid, Ford Escape Hybrid, Honda Insight 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 .
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 input types ("fuels") using the same tank and engine to be hybrids, although to avoid confusion with hybrids as described above and to use correctly the terms, these are 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. Liquified petroleum gas and natural gas are very different from each other and cannot be used in the same tanks, so it would be impossible to build an (LPG-NG) flexible fuel system.
- 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 bio-diesel.
- Power-assist mechanisms for bicycles and other human-powered vehicles are also included.
Continuously Recharged BEVs
Given suitable infrastructure, 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.
This provides the advantage of virtually unrestricted highway range. Since most destinations are within 100 km of a major highway, this reduces the need for expensive battery systems.
The technology for such infrastructure is old and well established - (see Conduit current collection, trams, electric rail, trolleys, third rail). Electricity and infrastructure costs can be funded by toll revenue, gasoline taxes or other sources.
- ^ Das Powerbike (German), ISBN 3895951234. Retrieved on February 27, 2007.
- ^ Velomobile Seminar 1999, ISBN 3-9520694-1-8. Retrieved on January 11, 2006.
- ^ Fuel Saving Calculator
Man Motors On Hybrid Bicycle video - Sept 2006
Categories: Alternative propulsion | Hybrid vehicles | Engines | Electric vehicles