The system in the Toyota Prius incorporates elements of both the parallel and series hybrid. The engine, a fuel-efficient, low-revving (its power peak is at 4,000 rpm) 1.5 liter four-cylinder, delivers its output both to a generator and the wheels, through an electronic power-splitter. When the car is stopped, the engine shuts down automatically. This means it won't pollute when stuck in traffic jams. An engine management system decides how the power is divided, and if it makes the right decision the Prius (which also uses regenerative braking) can achieve 4.5 L/100 km of fuel consumption.
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| The Toyota Prius incorporates both parallel and series hybrid engine methods. (Photo: Toyota) |
Basically, when the car first starts up or is moving slowly, the engine is turned off and the batteries are in charge. At normal running speeds, the gas motor starts up and sends power to the generator and to the road. When the Prius accelerates abruptly, horsepower from the engine is aided by extra power extracted from the batteries. As the car slows down or brakes the motor becomes a generator, capturing the kinetic energy from the wheels and recharging the batteries.
While only parallel hybrids, or combinations of the two, have been produced for mass consumption thus far, serial hybrids aren't far away. Either way, hybrid gas/diesel-electric powertrains are here to stay, the forerunners to fuel cell vehicles.