A hybrid electric vehicle (HEV) is any vehicle that has two or more distinct sources of power connected to the drivetrain. HEVs have been under development for a long time, with the first mass-produced Toyota Prius sold in 1997 in Japan. Over 2.5 million have now been sold worldwide. Students have also participated in technology exploration by building experimental HEVs for competition. HEVs have increasingly gained attention in recent years because they are able to produce a higher than average range between fill-ups while greatly reducing emissions and still meeting expected performance standards.
How Hybrids Work. Most HEVs have an internal combustion engine powered by fuel (commonly gasoline) and an electric motor powered by electricity from a high voltage battery pack. The engine and motor may provide power to the drivetrain individually or together. The battery pack is automatically recharged by surplus engine energy (from burning fuel in the ICE) and regenerative braking. Anytime the engine is running and full power is not needed surplus energy is available. Surplus energy can be sent through the generator directly to power the electric motor or stored in the high voltage battery pack.
Internal Combustion Engine. The engine is a hybrid’s main power source, supplying power when driving conditions require more than the electric motor can provide efficiently. Gasoline is what provides the hybrid’s energy, either directly from the ICE to the drivetrain or through surplus engine energy. The engine is sized for average power needs (not peak performance) and is engineered to run at a more constant and efficient speed than conventional vehicles. Start-stop technology shuts down the engine when not under a load, saving fuel. A conventional starter is not needed because the motor/generator is also used as the starter.
Electric Motor. The electric motor is a hybrid’s alternative power source. The electric motor may be used independently during initial acceleration from a stop, traveling at low speeds, and stop and go traffic (city driving), when it is more efficient than the ICE. Power for the electric motor to propel the vehicle is provided by reusing otherwise wasted braking energy, surplus engine energy, and energy stored in the battery pack. The electric motor propels the vehicle when the ICE is least efficient and when additional or peak performance power is needed.