Emissions regulations for small motorcycles are becoming increasingly stringent every year in various countries throughout the world. Therefore, we conducted research on high-precision control of the air-fuel ratio with an emissions reduction system for small, fuel-injection motorcycles, in particular, for motorcycles equipped with a 100cm3 four-stroke engine. Fuel injection is controlled by two injection amount maps applied according to throttle opening, engine speed and intake pressure. The control index used in this control system maintains the engine intake pressure peak when the intake valve is open in order to eliminate the major impact of intake pressure fluctuation exhibited by single-cylinder engines. Moreover, O2 feedback control and three-way catalyst systems were applied for exhaust emissions purification, and a small, power-saving fuel pump was developed to improve fuel economy.In addition, a control system to obtain excellent starting ability with a kick starter was also developed. By adopting these systems, hydrocarbons were decreased to about 1/30 of the regulation value provided in the European motorcycle emissions regulation “Directive 97/24/EC chapter 5” (EURO-1), and the fuel economy was improved by approximately 20% compared to the base engine.
Article of Honda R&D Technical Review Vol.12 No.2 (17 - 22)