Automotive manufacturers have been increasing the ratio of electric powertrains in recent years in order to reduce CO2 emissions from vehicles. Honda has a lineup of plug-in hybrid electric vehicles (PHEV) equipped with a two-motor hybrid system. Vehicles equipped with the newly developed PHEV system will be going on sale gradually in Europe and China starting this autumn. The PHEV is positioned as the highest grade of vehicle so it is required to provide an exhilarating driving feeling, high environmental performance, and high-quality quietness. In the European market, in particular, a powertrain that is capable of handling a variety of driving scenarios, including towing, is necessary. In order to satisfy the requirements for PHEV products and to comply with the emissions regulations of each region, a 2.0-L four-cylinder engine has been adopted that has commonalities with the engine for the FHEV system launched in 2022. This PHEV system has driving modes of three patterns. They are the EV drive mode, hybrid drive mode, and engine drive mode. Performance such as exhilarating driving feeling, high environmental performance, and high-quality quietness are achieved by making effective use of each mode and by adding expanding the lock-up operating range, lowering the engine operation speed, and using linear shift control, which is a new operating control. In order to achieve the above objectives, it is necessary to have an engine with a wider stoichiometric range, higher torque, a wider high-efficiency range, and improved NV performance. This paper will report in detail on the key technologies adopted for the newly developed engine and the results achieved by those technologies. In order to expand the high thermal efficiency range, the Atkinson cycle and cooled EGR system from the previous model were adopted. In addition, a high-flow intake port and combustion chamber shape that maintains high-flow were newly designed. High-speed combustion was achieved by combining it with a high-pressure in-cylinder direct fuel injection system and optimizing injection control. In addition to them, newly designed exhaust port and two-piece water jacket reduced the exhaust gas temperature when the engine is operating under high load. This achieved stoichiometric combustion across a broad operating range. It is generally known that high-speed combustion leads to greater vibration and noise. Therefore, the crankshaft, cylinder block, and chain case were newly designed to increase the engine stiffness, reducing vibration and noise. Adopting the high-pressure in-cylinder direct fuel injection system also increased the operating noise. Therefore, the placement of insulators on parts that contribute to noise radiation was optimized, reducing the engine radiation noise. By means of these technologies for combustion, exhaust temperature reduction, and vibration and noise reduction, following results have been achieved compared to the previous model. Engine power and torque are increased while emissions are reduced. Stoichiometric operating range is expanded to the engine high-load operating range, and the high-efficiency range of 230 g/kWh or less of brake specific fuel consumption rate (BSFC) has been greatly expanded. However, the contradictory noise and vibration performance equal to previous model generations is realized.
Mr. Nobuhiko Sasaki, Assistant Chief Engineer, Honda Moter Co.,Ltd.