Hybrid and Electric Types of Powertrain

Electric and Hybrid Powertrains

A battery electric vehicle runs entirely on electric energy, typically a large electric motor/generator and a large battery pack. Based on the number of battery packs, converters, and generators, there can be many variations on the basic design. A hybrid electric vehicle relies on two power sources, an internal combustion gas engine and an battery with an electric generator. Combined gas and electric power improve fuel efficiency and emit less carbon dioxide compared to conventional cars, saving money at the pump and reducing the carbon footprint.

A mild hybrid is the least electrified, a conventional internal-combustion car with an oversized starter motor that can double as a generator and an oversized battery that powers the motor/generator, which can recharge it. The gas engine must be always on while the vehicle moves; however, the electric generator can idle with the engine off when the vehicle stops. The electric generator can assist the engine at high loads to improve vehicle performance.

A power-split hybrid, a two-mode vehicle with hybrid synergy drive, perhaps the most popular hybrid electric system in use today, allows propulsion on gas alone, battery alone, or a combination. The car has a large battery charged by the gasoline engine, ideal for commuters often in stop-and-go traffic as the power-split hybrid can run solely on electric power at low speeds with greatly improved fuel efficiency.

In a series hybrid there is a single path to power the vehicle from two energy sources. The fuel tank feeds a gas engine that charges the battery that sends electrical energy to the electric generator that drives the wheels. The electric generator also recharges the battery during deceleration and braking. This power train runs entirely on an electric generator but has a gas engine to recharge the battery as needed. Series hybrids are unique in that they can be charged from any electrical outlet as well as by the gas engine. As most of these vehicles have a range of less than 100 miles on battery power alone, they are better for daily commuting than for long-distance driving.

The parallel hybrid combines gas and electric energy simultaneously. There are parallel paths to power the vehicle from the engine and from the electric generator, allowing either or both to drive the wheels. Control of a parallel is more complex than that for a series hybrid because of the need to couple the electric generator and engine to maintain performance. The electric generator assists acceleration and allows the gas engine to shut down when the car coasts, brakes, or stops. Parallel hybrid electric vehicles use regenerative braking to capture energy from application of brakes. This power train improves both city and highway fuel efficiency driving as the electric generator constantly assists the gas engine. Parallel hybrids can operate in engine-only traction, electric-only traction, hybrid- traction, regenerative-braking, and battery-charging modes.

A series-parallel hybrid has both series and parallel energy paths. Variations on this configuration can be complex or simple depending on the number of electric generators and their mode of use. Series-parallel hybrids can operate in engine-only traction, electric-only traction, hybrid-traction, engine-traction and battery-charging, regenerative-braking, and hybrid battery-charging modes.