Hybrid Electric Vehicle (HEV) is a general term for automobiles whose powertrain combines two sources of power: one electric and one internal combustion. The electric power is supplied to an electric motor from an energy storage device such as a flywheel, battery, or ultracapacitor. Hybrids can make use of regenerative braking, in which the electric motor captures energy that would normally be lost as heat during braking, acting as a generator to convert the energy to electric current.
Power sources in an HEV may be combined either in series or in parallel. In a series hybrid, the fuel engine produces energy that is stored in the energy storage device (in effect acting as a generator of electricity), and the electric motor takes energy from the storage device to power the vehicle. In this case, the electric motor is the main source of power for the vehicle. In comparison, a parallel hybrid vehicle is one that is capable of being powered by either source separately, or by both simultaneously. In a typical parallel hybrid, the fuel engine is the main source of power, and the electric motor is used selectively when extra power is needed, such as when accelerating or climbing hills.
Compared to an internal-combustion vehicle, an HEV is more efficient (and has lower emissions) because of its regenerative braking capability, and because the electric motor and the internal combustion engine complement each other. An HEV has a greater range than an electric vehicle, because the fuel engine and regenerative braking supply energy while the range of the latter is limited to what its batteries can provide.
A parallel hybrid has more power than a series hybrid, because both the fuel engine and the electric motor supply power simultaneously. The main advantage of a series hybrid is that the internal combustion engine always runs in its optimum range, which reduces its emissions and increases its performance. HEVs are currently expensive and are subsidized by the manufacturer. |
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