News / Motoring
Tuesday, January 29, 2008
2008 Toyota Prius Hybrid
Image: courtesy of Toyota (

Toyota's Very Capable Hybrid

Toyota's 2008 Prius has the best fuel economy of all manufacturers in the hybrid category with a 48 city and 45 highway mpg fuel economy rating. For the 2008 model year, the Prius continues as Toyota's flagship hybrid. The company first started selling hybrids in Japan in 1997 and then launched the Prius model in the United States in 2001. Toyota's second generation Prius model was introduced in 2004.

The EPA rates the Toyota Prius Hybrid as an Advanced Technology Partial Zero Emissions Vehicle (AT-PZEV). Whenever the Prius is stopped, the engine switches off and reverts to battery power to run the accessories, and so the term partial zero emissions vehicle. A Toyota Prius can accelerate from a stop on just battery power alone and reach speeds of up to 25 mph (40kph) before the engine starts. Under heavy acceleration, both the gasoline engine and the electric motor deliver power together to the wheels. The only limiting factor is when the battery runs out of charge, at which point all power is delivered by the gasoline engine.

Toyota has given the Prius a combined hybrid net power of 110 hp (82 kW), with a peak 34 hp (25.5 kW) provided by the electric motor and 76 hp (57 kW) provided by the DOHC 16-valve WT-i 4 cylinder gasoline engine. The high output electric motor is a permanent magnet AC synchronous type and is rated at 67 hp (50 kW). There is also a smaller electric motor that acts as a starter motor for power delivery and for regenerative braking in conjunction with the high output motor.

For battery power Toyota uses a 201.6 volt sealed Nickel Metal Hydride (NiMH) battery to store energy from the regenerative braking, created during all braking manoeuvres. Regeneration charging is provided by the Prius's small and large power delivery motors.

The transmission on the Prius is an ECVT type, standing for electronically controlled continuously variable transmission, that uses a Toyota engineered planetary gear power split device (PSD) coupled to a steel drive belt that transfers power to the front wheels. The PSD balances the power delivery between the larger high output electric motor and the gasoline engine. The transmission performs similar to a conventional automatic, but without any gear changes.

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