Hybrid vehicles use two types of power sources; a petrol engine and an electric motor - which maximises the benefits of both and opens up possibilities for the future.
Hybrid vehicles typically use one of two types of hybrid systems; the series hybrid and the parallel hybrid.
Series hybrid system
As the name suggests, the power flow in a series hybrid system moves in a direct line.
Vehicles employing a series hybrid system use the engine to power a generator, producing electricity for the motor to drive the wheels.
The low-output gasoline engine operates almost constantly in its high-efficiency range, charging the battery while it runs.
While this method allows the engine to operate at peak efficiency, it requires a motor that is larger and heavier than in a parallel hybrid system.
Parallel hybrid system
The power flow in a parallel hybrid system uses both the engine and the motor to drive the wheels, and allocates the power of either according to driving conditions.
With a parallel hybrid system, the engine can power the wheels and charge the battery simultaneously.
Toyota Hybrid System (THS)
The Toyota Hybrid System (THS) combines the best features of series and parallel hybrid systems.
The electric motor drives the wheels on start-up and at low speeds. During normal driving, the engine provides most of the power to the wheels (a portion of the engine's output is converted to electricity) while the battery supplies additional power to the motor when required. Allocation of the engine and battery power is computer controlled according to driving conditions, ensuring smooth, responsive performance.
With THS, the engine operates constantly in its peak efficiency range. This means that in stop-and-go city driving, where the motor provides much of the power to the drive wheels, the THS offers twice the fuel efficiency of a conventional vehicle, with only half the C02 emissions. C02, HC and NOx emissions are 1/10 the level set by Japanese regulations.
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