トヨタにおけるガソリンエンジン燃焼開発の取り組みと今後の展望

抄録

Toyota has been developing high thermal efficiency gasoline engines for the past twenty years for energy security and preventing global warming. Various combustion technologies were adopted to increase thermal efficiency at every launch of hybrid vehicles. Then, Toyota has developed new engines with common architecture concept, which is called as Toyota New Global Architecture (TNGA), based on the philosophy of developing ever-better vehicles. The target of new TNGA gasoline naturally aspirated engines was to achieve over 40% thermal efficiency and a high engine specific power simultaneously. In order to reach these targets, increasing the combustion speed was required. To realize this, stroke-bore ratio, intake port, and piston cavity shape were optimized. Additionally, injection spray shape and combustion strategy for catalyst heating was modified to meet upcoming PN regulations. Applying the common stroke-bore ratio realized similar combustion quality in the series of TNGA engines. On the other hand, reduction of CO₂ emission has to be achieved on a “Well to Wheel” basis, considering the electrification of powertrain and the variety of fuel in the near future. For that purpose, an extensive approach is required incorporating not only auto-mobile industries, but also oil companies, governments and academic societies.