TOKYO -- Toyota Motor Corp. will unleash a blitz of 14 new gasoline engines through 2015 in a long-awaited powertrain overhaul that aims to boost fuel efficiency by at least 10 percent.
The push deploys clean-burning Atkinson cycle engines, once reserved for electric-gasoline hybrids, across the lineup to nonhybrid vehicles in segments from compact to premium.
The usual downside of Atkinson cycle engines is low power, but Toyota says it has boosted performance by increasing combustion ratios.
"There is always the challenge of lower performance in torque," said Shouji Adachi, project general manager of powertrain planning. "For the new engines, we were able to resolve these issues."
When the 14 new engines come to market over the next two years, they will cover 30 percent of Toyota's lineup. The new technology also will underpin engines using direct injection and turbocharging, Adachi said. He gave no details.
Toyota did not say what vehicles will get the engines. The first two small-displacement power plants, a 1.0- and a 1.3-liter engine, are expected to be deployed in nonhybrid compact cars for the Japanese market.
They mark a couple of firsts for the world's biggest automaker. The new engines will be Toyota's first Atkinson cycle power deployed in a nonhybrid. They are also the first engines developed at the company's new Powertrain Joint Development Building, a massive 12-story r&d center that opened last year.
Toyota's more efficient powerplants come as rivals such as Honda Motor Co. and Mazda Motor Corp. overhaul their own engine lineups to meet more stringent fuel economy regulations. Honda's Earth Dreams engines use direct injection technology and turbocharging. Mazda's updated Skyactiv engines pair fuel injection with high combustion ratios.
Toyota aims for its new engines to deliver fuel economy gains of at least 10 percent over the engines they replace. "Unless a 10 percent increase is achieved, customers would not able to feel the improvement," Adachi said.
The new 1.3-liter, four-cylinder engine will achieve thermal efficiency rates of 38 percent, while the 1.0-liter, three-cylinder one delivers 37 percent, compared with 35 percent for the engines they replace. Higher efficiency means more energy from internal combustion is captured to power the wheels and less is lost through heat. The new efficiency rates are on a par with the 38.5 percent ratio achieved in the current engine of the Prius hybrid.
The Atkinson cycle improves fuel efficiency by keeping the intake valves open briefly during the compression stroke.
Atkinson's lackluster horsepower is not a problem in Toyota's hybrids because the company can augment performance with output from the battery-powered electric motor.
The new approach aims to boost power other ways.
Raising the combustion ratio is critical. The 1.3-liter engine achieves a compression ratio of 13.5 while the 1.0-liter engine reaches 11.5. Mazda, by contrast, has achieved a 14.0 ratio and is targeting ratios of 18.0 in its next-generation engines.
Toyota's new offerings are powerful for Atkinson engines but still not high performance, Adachi conceded. For customers demanding high-torque, he said, Toyota will need turbocharging.