The Prius is a power-split or series-parallel hybrid, a vehicle that can be propelled by gasoline (petrol) and/or electric power. Components of the system include:
1. Regenerative braking, using motor-generators, which converts kinetic energy of motion into electrical energy that is stored in the traction battery and reduces wear on the brake pads;
2. A 1NZ-FXE internal combustion engine (ICE) using Atkinson cycle which is more efficient than the more powerful Otto cycle. The gasoline engine normally shuts off during traffic stops and the accessories (including the air conditioning) are powered by the battery pack. The engine is used both to propel the vehicle and to recharge the batteries. Because of the availability of extra power from the electric motors for rapid acceleration the engine is sized smaller than usual for increased fuel efficiency and lowered emissions with acceptable acceleration; The penalty of the Atkinson cycle is low specific power, so the battery and generator is needed to give extra power when accelerating, whilst allowing the vehicle to cruise on the low powered engine,3. A Hybrid Synergy Drive (HSD) unit that combines a planetary gearset that behaves like a Continuously Variable Transmission (CVT) called the Power Split Device to increase efficiency. The computer controlled HSD transaxle adjusts and blends the amount of power from the gasoline engine and electric motor-generator(s) as needed by the front drive wheels and rechargeable batteries;
4. A sealed 38-module nickel metal hydride (NiMH) battery pack providing 273.6 volts, 6.5 A·h capacity and weighing 53.3 kg (118 lb) is supplied by Japan's Panasonic. They are normally charged to 40–60% of maximum capacity to prolong battery life as well as provide a reserve for regenerative braking;5. A vacuum flask for storing hot coolant when the vehicle is powered off for reuse so as to reduce warm-up time (US market);
6. An EV mode (or stealth mode) that allows drivers to operate on electric power only under low-power conditions for a limited duration of time . Advocates for the blind warn that
the Prius is silent, and that it could be hazardous to blind pedestrians and others accustomed to engine noise to warn of a nearby vehicle;7. Vehicle weight is reduced by the use of a flexible resin gasoline tank and by the use of aluminum instead of steel for the engine bay hood and hatchback.
8. Starting with the 2010 model year (3rd generation), the gasoline engine uses an electric water pump, permitting an engine design with no serpentine belts, improving efficiency.
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