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 commercially available, because they are very simple in theory and manufacturing.

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.

Heavy vehicles

Hybrid power trains are used for diesel-electric or turbo-electric railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery, and ships. Typically some form of heat engine (usually diesel) drives an electric generator or hydraulic pump which powers 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. With the exception of non nuclear submarines, presently there is no or relatively little energy storage capacity on most heavy vehicles, e.g. auxiliary batteries and hydraulic accumulators—this is changing.

There are three main options for series hybrid electric motors: Permanent Magnet, 3-Phase AC Induction, Multi-Phase AC Induction. Permament Magnet motors, like those found in the Prius, degrade in performance at higher temperatures and require a cooling system in the design. They allow for regenerative braking, and this comes with a safety trade off as any time there is motion by the magnets, they produce voltage. Permanent magnets also require rare earth which are expensive and difficult to source.

In contrast, 3-Phase AC Induction motors can be air cooled and therefore have better stamina, but have less power density which means that the weight saved from removing the cooling system is replaced with heavier and more complex gearing for the drivetrain. This more complex transmission gearing is also needed to compensate for the fact that a standard 3-Phase AC Induction motor can be either low-speed high-torque (like a standrd vehicles starter) or a high-speed low-torque (like a standrd vehicles alternator) but not both.

A Multi-Phase AC Induction motor (called a Chorus Motor) co-opts the harmonics that limit motor performance, which means a that it can smoothly change from behaving like a high-torque low-speed motor to behaving like a low-torque high-speed motor, without the need for efficiency robbing physical gearing that would be required to compensate for a 3-Phase AC Induction motors lower power density. The January 2009 issue of Motor Trend magazine discusses this third choice and its use in planes and vehicles.