Understanding layouts
A hybrid vehicle is powered by a conventional internal combustion engine (ICE) and/or a high-voltage battery, with the power source selected automatically. The battery is charged by regenerative braking and/or the ICE. Just as we see transverse, longitudinal, mid- and rear-engined layouts with two- and four-wheel drive in conventional vehicles, hybrid layouts vary as well.
Parallel hybrid is the simplest layout, where an electric motor is sandwiched between the engine and transmission to provide assistance. Many Honda, Hyundai and Kia vehicles have this arrangement.
Series hybrids have no mechanical connection between the engine and wheels; all drive is provided by the vehicle’s electric motor. The Mitsubishi Outlander PHEV, Vauxhall Ampera/chevrolet Volt and BMW i3 Range Extender are typical examples of this layout.
Power split hybrid is the most common system that you’ll encounter, but is also the most complicated. The wheels are powered by either the motor, or engine, or both. It employs two motor/generators, meaning that one of them can recharge the battery, while the other powers the wheels, or assists the engine. The heart of the system is a complex gearset. Examples include the Toyota Prius, Auris and Yaris.
Dual hybrids separate the power sources between axles. For example, a conventional transverse engine/transmission can power the front axle, with a battery, electric motor and a differential powering the rear wheels. Peugeot/citroën’s Hybrid4 and BMW’S i8 employ this layout.
Pure electric vehicles (EV) lack any alternative power. With no ICE installed, EVS have very simple mechanical layouts, although the individual components can be sited almost anywhere. Being the only source of power, the battery must have an extremely large capacity and, therefore, tends to be very bulky.
Plug-in hybrids allow mains charging. All forms of hybrid can be adapted to mains charging by the manufacturer, although the main downsides involve fitting a larger, or more expensive high-voltage battery, as well as access points for the appropriate socket and storage for the electrical cabling.
Mild hybrids employ a less expensive high-voltage battery and motor to assist the engine, but the components are smaller and do not deliver the fuel economy benefits of full hybrids. A typical example is the Suzuki SHVS system, which incorporates a belt-driven starter/alternator to charge the battery and assist the engine – a high-voltage lithium-ion battery is installed beneath the passenger seat.