Car reviews - Toyota - Prius - i-Tech 5-dr hatch
9 Jul 2004
The Prius has a constantly variable (CVT) transmission with a difference: instead of the normal tapered pulleys and belts used by other car-makers, the Prius achieves its constantly varying ratios via the planetary gearset that also apportions power between the electric engine, the petrol engine and the electric generator. It achieves this simply by controlling the speed of the central "sun" gear via the electric generator-motor so that the petrol engine (which is connected to the central "planetary" gear carrier) can spin at varying speeds while sending drive through to the main, outer "ring" gear (which is directly connected to the main electric motor and the final drive).
Toyota says the "use of one set of planetary gears to achieve two roles provides a significant saving in weight and space under the bonnet - compared with either a traditional automatic transmission or a belt and pulley type CVT".
The new Prius uses higher revs for both petrol and electric powerplants, as well as a lower (higher revving) final drive ratio.
Did you know?Conventionally, there are two kinds of hybrid systems. Series hybrids use a petrol engine to generate electricity for the electric motor (and sometimes batteries) to propel the vehicle. Parallel hybrids use both petrol engines and electric motors for motive power, and switch back and forth between them as driving conditions demand
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