[YesAuto Engine Technology] Hybrid technology has been recognized as an important development direction for automobiles in the future, and Toyota, the pioneer of hybrid power, has gone through 18 years since the launch of the first-generation Prius in 1997. As the “two legs” of hybrid power, both the electric motor and the engine are indispensable, so Toyota is still sparing no effort to research engine technology. In the hybrid models Axio and FIELDER recently launched in Japan, Toyota is equipped with the newly developed 1.5L gasoline engine with a thermal efficiency of 38%. Although this “new weapon” will not be installed on domestic models soon, there are dreams. What if it comes true?
● Code 2NR-FKE
Toyota's 1.5L gasoline engine, code-named 2NR-FKE, uses the same structure and cylinder block components as the 1.3L engine launched last year. It increases the displacement to 1.5L by changing the stroke. The diameter of the intake manifold has been enlarged by 1mm, and the diameter of two of the exhaust manifolds has been enlarged by 2mm.
The maximum output power of this 1.5L engine is 81.6Ps (60kW), the maximum output torque is 136N·m, and the cylinder diameter×stroke is 72.5mm×90.6mm. It uses the Atkinson cycle technology, its compression ratio is as high as 13.5, and the thermal efficiency reaches 38%. It is necessary to know that the thermal efficiency of an ordinary gasoline engine is only about 30%. Why can it achieve such a high compression ratio and thermal efficiency? Let's briefly introduce it below.
● VVT-iE electric variable valve timing system
This engine uses electric VVT technology (which Toyota officially calls VVT-iE) and adds an intake valve timing adjustment motor. This is one of the important reasons for its compression ratio to reach 13.5. This is also similar to the Mazda 2.0L Chuangchi Blue Sky engine that we disassembled before. Compared with ordinary hydraulic VVT technology, this electric VVT has faster response and more precise control, and most importantly, it can be steplessly adjustable. At the same time, it also avoids the problem of low working efficiency of the intake valve timing mechanism when the oil pressure is insufficient at the beginning of the engine operation (for example, under cold conditions).
● Exhaust gas recirculation technology (EGR)
This engine also incorporates water-cooled exhaust gas recirculation technology (EGR), which not only reduces nitrogen oxide emissions, but also improves combustion heat efficiency. In order to reduce the temperature of the circulating exhaust gas, it adds a complicated cooling pipeline.
● New type spacer
The lower part of the cylinder water jacket of this new 1.5L engine has a new type of spacer, which is made of foamed rubber and stainless steel sheet. This foamed rubber will absorb the cooling water and block part of the flow path after expansion, thereby reducing the capacity of the water jacket, thus achieving the effect of shortening the engine warm-up time. This is the same as the structure and principle of the previous 1.3L engine.
In addition, the addition of this spacer block can also achieve the effect of optimizing the temperature of the upper and middle parts of the cylinder. Because of its blocking effect, the temperature of the upper part of the cylinder is reduced by about 20°C, which reduces the probability of knocking; it makes it difficult for cooling water to flow into the middle of the cylinder, and the temperature in the middle of the cylinder rises by about 20°C. As the temperature rises, the viscosity of the lubricating oil between the piston and the cylinder wall becomes smaller, which reduces the friction loss.
● 4-2-1 exhaust system
Its exhaust manifold has been changed from the original 4-1 form to the 4-2-1 form. Due to the large number of welded parts and longer manifolds for this type of exhaust, the manufacturing cost will increase. However, the 4-2-1 form makes the exhaust system smoother, and is more conducive to the compression ratio reaching a value as high as 13.5. At the same time, it also reduces a part of the pumping loss and improves the thermal efficiency.
This 1.5L gasoline engine can achieve such a high combustion heat efficiency, of course, thanks to Toyota's pursuit of fuel economy for so many years. The high thermal efficiency of this engine is very suitable for hybrid models, and it is believed that more Toyota hybrid vehicles will be equipped with this machine in the future. Although we have never known that the domestically produced hybrid Corolla will be equipped with this engine, the good technology will definitely be getting closer and closer to us in the near future. (Part of the information compiled by Car House Xia Zhimeng comes from Nikkei Technology Online)