Toyota introducing new series of gasoline engines with gain of at least 10% fuel efficiency; up to 38% maximum thermal efficiency
|New 1.3L Atkinson cycle engine can reach a thermal efficiency of 38%. Click to enlarge.|
Toyota Motor Corporation has developed a new series of fuel-efficient gasoline engines that achieve improved thermal efficiency. The new engines leverage combustion and loss-reduction technologies Toyota has refined in its dedicated hybrid engines (such as use of the Atkinson cycle) as well as in its conventional engines, and will deliver fuel efficiency improvements of at least 10% over current vehicles (based on the JC08 cycle).
In developing the new engines, Toyota focused on four key areas: rapid combustion; a higher compression ratio; reduced pumping losses (e.g., through using the Atkinson cycle and large-volume cooled EGR); and low friction.
|New intake port and strong tumble flow. Click to enlarge.|
Rapid combustion. Toyota is utilizing an intake port with a new shape that generates a strong tumble flow. (In a paper presented at the SAE 2014 World Congress, Toyota researchers described their work on an optimized combustion concept for turbocharged gasoline direct-injection engines that leverages optimized intake ports, dog dish-type curved pistons with a lip, and a fan injection spray to minimize flow disturbance and intensify in-cylinder flow.)
The system on the new engines achieves unprecedented efficiency and tumble, Toyota said. The higher tumble flow enables more rapid combustion.
Higher compression ratio. A higher compression ratio leads to greater efficiency; it also results in knock. To avoid knock, Toyota is increasing scavenging efficiency in the combustion chamber.
Further, Toyota is also preventing knocking by controlling the cylinder wall temperature.
Reduced pumping losses. ￼Variable valve technology enables adoption of the Atkinson cycle in a conventional vehicle engine. 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.
Low friction. Toyota has taken a number of measures to reduce friction, including a modified piston skirt surface; plastic-coated bearing; new structure water jacket spacer; reduced capacity oil pump; and auxiliary belt with reduced bending loss.
The engines will be used in models scheduled for partial redesign in the near future; a total of 14 new engine variations will be introduced globally by 2015.1.3-liter engine with max 38% thermal efficiency. One of the engines is a 1.3-liter gasoline engine in which Toyota is employing the Atkinson cycle—normally used in dedicated hybrid engines—and a compression ratio of 13.5:1. Toyota is further improving the fuel efficiency of the engine by utilizing its other innovations including the new shaped intake strong tumble flow 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%—top-level among gasoline-fueled mass-produced engines. The new features, combined with idling stop and other functions, will lead to fuel efficiency gains of approximately 15% by comparison with current vehicles, Toyota said.
|New 1.0-liter engine. Click to enlarge.|
1.0-liter with max 37% thermal efficiency. Meanwhile, a 1.0-liter engine jointly developed with Daihatsu Motor Co., Ltd. has achieved maximum thermal efficiency of 37% due to a similar tumble flow-generating intake port, a cooled EGR system, and a high compression ratio (11.5:1 in this case).
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% over current vehicles.
Mitani, S., Hashimoto, S., Nomura, H., Shimizu, R. et al. (2014) “New Combustion Concept for Turbocharged Gasoline Direct-Injection Engines,” SAE Int. J. Engines 7 (2) doi: 10.4271/2014-01-1210