Hybrid vehicle drivetrain

Hybrid vehicle drivetrains transmit power to the driving wheels for hybrid vehicles. A hybrid vehicle has multiple forms of motive power.

Hybrids come in many configurations. For example, a hybrid may receive its energy by burning gasoline, but switch between an electric motor and a combustion engine.

Electrical vehicles have a long history combining internal combustion and electrical transmission – as in a diesel–electric power-train – although they have mostly been used for rail locomotives. A diesel–electric powertrain fails the definition of hybrid because the electric drive transmission directly replaces the mechanical transmission rather than being a supplementary source of motive power. One of the earliest forms of hybrid land vehicle was the 'trackless' trolleybus experiment in The United States (New Jersey) that ran from 1935 to 1948, which normally used traction current delivered by wire. The trolleybus was fitted with an internal combustion engine (ICE) to power the mechanical drivetrain directly, not to generate electricity for the traction motor. This enabled the vehicle to be used for revenue service where there was no contact wire. Since the 1990s trolleybus hybrids have been introduced with small power plants to provide a low speed capability for emergency and maintenance but not to support general revenue service.

The powertrain includes all of the components used to transform stored potential energy. Powertrains may either use chemical, solar, nuclear or kinetic and make them useful for propulsion. The oldest example is the steam locomotive. A common modern example is the electric bicycle. Hybrid electric vehicles combine a battery or supercapacitor supplemented by an ICE that can recharge the batteries or power the vehicle. Other hybrid powertrains use flywheels to store energy.

Among the different types of hybrid vehicles, only the electric/ICE type was commercially available as of 2017. One variety operated in parallel to provide power from both motors simultaneously. Another operated in series with one source exclusively providing the power and the second providing electricity. Either source may provide the primary motive force, with the other augmenting the primary.

Other combinations offer efficiency gains from superior energy management and regeneration that are offset by expense, complexity and the battery limitations. Combustion-electric (CE) hybrids have battery packs with far larger capacity than a combustion-only vehicle. A combustion-electric hybrid has batteries that are light that offer higher energy density that are far more costly. ICEs require only a battery large enough to operate the electrical system and ignite the engine.^[1]