Design optimization of 4-stroke engine and jet pump for personal watercraft

摘要

Personal watercrafts (PWC) equipped with a four-stroke engine are getting into the main stream in the market. Along with such movement, high-priced high-horsepower models have emerged to set the latest trend. On the opposite end, relatively low cost low-horsepower models using a two-stroke engine still keep high popularity because of their affordability. With these conditions in the background, a four-stroke engine and a jet pump for PWC application were developed, securing optimum and appropriate performance along with enhanced reliability and high economical efficiency, while reducing the cost significantly. In designing the new engine and the jet pump, the functions and structures of the base engine were re-examined to the details based on the comparative study. Approximately 30% of cost reduction was achieved through the comprehensive study in regard to the base engine (intake, exhaust, and cooling systems) and the jet pump. Also the fuel economy was improved by approximately 50% in comparison with two-stroke carburetor type model, and by approximately 35% in comparison with current four-stroke model. Electronically-controlled throttle body, a new feature for PWC's, was incorporated. This results in more stable, smooth control in Low-Rpm-Mode and when Off Throttle Steering System (OTS) is activated. In addition, the modification of the reverse system has enhanced the astern thrust almost three times as much as our benchmark model. The reverse operation performance was improved greatly with the new reverse system.