Tuesday, May 18, 2010

Hybrid: Toyota vs Honda

It took 10 years for Toyota to sell its first 1 million hybrids globally. The Nikkei reported last month that Toyota plans to double its global production of hybrids vehicles from the 2009 level by 2011. Toyota expects US car sales to rise 10 percent this year to about 11.4 million vehicles.

(Picture left: Toyota FT-CH) Toyota currently makes the Camry Hybrid in the United States, at its Georgetown, Ky. plant. Honda, the second largest global hybrid producer, made less than 150,000 hybrids in 2009.

Toyota currently sells more than 10 hybrids, including dedicated models such as the Prius and Lexus HS 250h—as well as the Toyota Sai, a sister model to the HS 250h only sold in Japan. Toyota plans to boost production of these existing vehicles in addition to launching new hybrid minivans, subcompacts and luxury cars, according to the report.

No details are available yet on the Toyota hybrid minivan.

Toyota introduced its first-generation Prius hybrid in 1998 to the Japanese market. Honda's HEV features the company's innovative Integrated Motor Assist (IMA) hybrid system that was detailed in Green Car Journal's Fall 2004 issue.

Toyota uses its sophisticated Hybrid Synergy Drive system to power todays Prius, a follow-on to the first-generation Toyota Hybrid System. Both automakers are now offering their second generation hybrid vehicles. Both the Toyota and Honda hybrids are parallel configurations, with wheels driven by both their internal combustion engine and electric motor. The Honda IMA systems electric motor/generator supplies additional power to the gasoline engine when needed for acceleration or when driving demands are greater, such as when climbing grades, thus the designation motor assist. The Honda gasoline engine always provides propulsion.

Things are reversed with Toyotas Hybrid Synergy Drive, which finds the Prius starting out on battery electric power. The gasoline engine seamlessly starts up to provide additional power during acceleration, at higher speeds, or when driving up grades. Hondas hybrids cannot do this.
The Prius uses a four-cylinder, 1.5-liter Atkinson cycle engine. The four-stroke Atkinson cycle, invented by James Atkinson in 1882, is different than the Otto cycle engine were used to driving in very distinct ways. Restricting throttle opening results in large pumping losses and greatly reduced efficiency. Effectively, the use of the Atkinson cycle allows the Prius engine to operate quite efficiently at relatively low power levels while still having sufficient power for climbing hills at freeway speeds.

The Prius uses the same basic 1.5 liter engine as the Toyota Echo, where the engine is rated at 108 horsepower at 6000 rpm. Variable intake valve timing (VVT-I) reduces cylinder pressure to eliminate knocking, important because the engine has a 13:1 compression ratio. The aluminum, dual overhead camshaft (DOHC) 16-valve engine produces 76 horsepower at 5000 rpm and 82 lbs-ft of torque at 4200 rpm. The engine earns an Advanced Technology Partial Zero Emission Vehicle (AT-PZEV) rating, is a Super Ultra Low Emission Vehicle (SULEV), and has an EPA rating of 60 mpg city/51 mpg highway, for a combined estimated 55 mpg fuel economy rating.

The permanent magnet, AC (alternating current) synchronous motor produces 67 horsepower (50 kW) at 1200-1540 rpm. A built-in transformer converts some of the hybrid batterys power into 12 volts DC to operate vehicle accessories. In the latest generation Prius, the high voltage converter system increases battery voltage from 202 volts to 500 volts for driving the electric motor. This Power Split Device allows the engine to operate in its most efficient load and speed range most of the time. The planetary gear system connects the engine, generator, and motor together, allowing operation in a parallel hybrid mode with the electric motor and gasoline alone or together powering the car. It can also operate like a series hybrid when the gasoline engine operates independently of the vehicle speed to charge the battery or provide power to the wheels.

This advanced hybrid vehicle shares virtually nothing with other Toyota models. Hybrid Synergy Drive is quite scalable, so expect to see it used in other Toyota and Lexus models. Other Toyota hybrid models will be sure to follow.

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