Toyota Prius Hybrid

Under the United States Environmental Protection Agency's (EPA) recently revised testing procedures, the 2007 Toyota Prius is the most fuel efficient car sold in the U.S., with a combined city and highway fuel economy of 46 mpg–U.S.

Under the UK Department for Transport's "Best on CO2 rankings" scheme, the Toyota Prius is ranked as equal second, alongside the diesel MINI Cooper D Hatchback, and behind the diesel Volkswagen Polo.

The Prius is a parallel configuration hybrid, a vehicle that can run on just the combustion engine, just the electric motor, or a combination of both. Toyota's design goals are to reduce the amount of pollution and to maximize fuel efficiency. To do this, it uses a gasoline/electric hybrid power train, incorporating large batteries that are charged by the gas (petrol) engine directly or by regenerative braking. Either the engine or the battery (or both) can power the vehicle, depending on conditions. This gives it the acceleration and power of a standard car having a much larger internal combustion engine.

One reason that the Toyota Prius gets such good fuel consumption is that the ICE is smaller than in most cars this size. The ICE usually shuts off at stop lights and when backing up and descending long hills. The Prius performance remains very good because the battery/electric motor booster automatically provides adequate extra power for moderate acceleration and hill climbing. This means it drives like a traditional ICE automobile, with the on-board computer taking care of shifting power to and from the engine and motors, and automatically determining when to charge the battery, as well as the most efficient use of the engine or the electric motors (or both) based on driving conditions. This also means that one cannot use electricity from external sources. Advocates of "plug-in" hybrids consider this to be a missed opportunity. The Toyota Prius also uses its electric motor to recharge the battery during braking, with kinetic energy normally wasted as heat being recaptured. This also significantly reduces brake wear.

The engine can shut down once it has warmed up and the catalytic converter in the exhaust system has reached operating temperature. The Toyota Prius can then operate solely on electric power under low energy loads. This is sometimes referred to as "stealth mode" due to the lack of engine noise. While this further reduces fuel consumption and engine wear, advocates for the blind warn that the Toyota Prius is so quiet it could be hazardous to blind pedestrians and others accustomed to engine noise to warn of a nearby vehicle. When driving conditions demand additional power, the engine starts up automatically.

The on-board computer ensures that the engine runs under the most efficient conditions. Typically, a petrol/gasoline engine runs inefficiently at half-throttle, creating a choking condition. This effect, called pumping loss, is a major reason for the inefficiency of gasoline engines compared to diesels. The Toyota Prius minimizes pumping loss by running the gasoline engine at a high torque range with the throttle fully open. Drive-by-wire throttle control technology and Toyota's Hybrid Synergy Drive (a torque combiner, electric drive, and computer control) are essential to this engine control.

In addition the Toyota Prius benefits from reducing fuel consumption and emissions, stopping the combustion engine also improves the performance of the catalytic converter. In a non-hybrid vehicle the exhaust gases from an idling engine tend to cool the catalysts below their optimal temperature.

Toyota Prius Hybrid