Toyota Prius

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The Toyota Prius is a hybrid electric vehicle developed and manufactured by the Toyota Motor Corporation, and one of the first such vehicles to be mass-produced and marketed.

The Prius first went on sale in Japan in 1997, and worldwide in 2001. By the end of 2003, nearly 160,000 units had been produced for sale in Japan, Europe, and North America. The Prius has won several awards, including the Car of the Year Japan (1997-98), the North American Car of the Year (2004), and the European Car of the Year (2005).

Under the United States Environmental Protection Agency's (EPA) recently revised testing procedures, the 2007 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. (5.11 L/100 km / 55.2 mpg–imp).

Under the UK Department for Transport's "Best on CO2 rankings" scheme, the Prius is ranked as equal second, alongside the diesel MINI Cooper D Hatchback, and behind the diesel Volkswagen Polo 1.4 TDI 80PS, out of all the cars ranked.

The Prius is a series-parallel configuration hybrid, a vehicle that can run on just the engine, just the batteries, 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 powertrain, 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 gasoline-burning engine. Specifically, the Prius incorporates:

1. More efficient use of the internal combustion engine (ICE), reducing gasoline/petrol consumption. The 1NZ-FXE engine uses the more efficient Atkinson cycle instead of the more common Otto cycle;

2. Two electric motor/generators, MG1 and MG2 are in the transaxle. The MG2 provides 50 kW (67 hp) @ 1,200 to 1,540 rpm and 400 N·m (295 ft·lbf) torque from 0 to 1,200 rpm, which significantly contributes to performance and economy. The MG1, with rpm from -10,000 to +10,000 rpm, provides the engine starter and counter torque for the electronic Continuously Variable Transmission;

3. 50 kW IGBT inverter controlled by a 32-bit microprocessor, which efficiently converts power between the batteries and the motor/generators.

4. Lower coefficient of drag at 0.26 (0.29 for 2000 model), with a Kammback design reducing air resistance, especially at higher speeds;

5. Lower rolling-resistance tires on the 2000 model, reducing road friction;

6. Regenerative braking, a process for recovering kinetic energy when braking or travelling down a slope and storing it as chemical potential energy in the traction battery for later use while reducing wear and tear on the brake pads;

7. Sealed 168-cell nickel metal hydride (NiMH) battery providing 201.6 volts; supplied by Panasonic EV Energy Co

8. Continuously variable transmission — the Prius uses a computer-managed (rather than a mechanical) CVT; Toyota calls it the Power Split Device[4]. The electric motors and gasoline engine are connected to a planetary gear set which is always engaged, and there is no shifting.

9. Flexible resin gasoline tank, reducing the amount of hydrocarbon emissions in the form of escaped gasoline vapor; (US model only)

10. Vacuum flask coolant storage system that stores hot engine coolant when the vehicle is powered off, then reuses it to reduce warm-up time. (US model only)

11. EV mode (Europe and Asian markets only, aftermarket option in the U.S.) allows the driver to select electric-only mode in low-power conditions. The vehicle can only be driven a couple of kilometers (depending on conditions) on battery power alone before the gas engine is needed.

12. Weight reduction — for example the hatch and hood/bonnet are made of aluminium instead of steel.

One reason that the 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 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 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 gasoline consumption and engine wear, the Prius is so quiet it can 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.

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