Toyota Develops Engines with Improved Thermal, Fuel Efficiency

Toyota City, Japan, April 10, 2014―Toyota Motor Corporation aims to further increase the environmental performance of its vehicles with a series of newly-developed, highly fuel-efficient engines that achieve outstanding thermal efficiency¹. The new engines leverage combustion and loss-reduction technologies Toyota has refined in its dedicated hybrid engines, and will achieve fuel efficiency improvements of at least 10 percent² over current vehicles. The engines will be used in models scheduled for partial redesign in the near future, and a total of 14 new engine variations will be introduced globally by 2015.

One of the engines is a 1.3-liter gasoline engine in which Toyota is employing the Atkinson cycle³―normally used in dedicated hybrid engines. Use of the Atkinson cycle provides an increased expansion ratio and reduces waste heat through a high compression ratio (13.5), resulting in superior thermal efficiency. Toyota aims to further improve the fuel efficiency of the engine by utilizing other innovations including an intake port with a new shape that generates a strong tumble flow (whereby the air-fuel mixture flows in a vertical swirl) inside the cylinder, and a cooled exhaust gas recirculation (EGR) system paired with Variable Valve Timing-intelligent Electric (VVT-iE) technology to improve combustion and reduce loss. As a result, the new engine will have a maximum thermal efficiency of 38 percent⁴―top-level among mass-produced engines. The new features, combined with idling stop and other functions, will lead to fuel efficiency gains of approximately 15 percent² by comparison with current vehicles.

Meanwhile, a 1.0-liter engine jointly developed with Daihatsu Motor Co., Ltd. has achieved maximum thermal efficiency of 37 percent⁴ due to a similar tumble flow-generating intake port, a cooled EGR system, and a high compression ratio. Combination with the idling-stop function and various other fuel consumption reduction technologies allows vehicles to achieve a maximum fuel efficiency improvement of approximately 30 percent² over current vehicles.

¹Numerical expression showing how much of the thermal energy generated by burning fuel is converted into effective power. The higher the thermal efficiency, the lower the fuel consumption.
²Under the Japanese Ministry of Land, Infrastructure, Transport and Tourism's (MLIT) JC08 test cycle
³Combustion cycle in which thermal efficiency is improved by making the expansion ratio larger than the compression ratio, thereby improving fuel efficiency
⁴Based on in-house calculations