Development of a 4-Stroke Small-Displacement Scooter with Discharge Pump Type Fuel Injection System

This paper describes the development of a new fuel supply system for small-displacement motorcycles which achieved better functions for environmental protection such as reduced exhaust emissions and improved fuel economy and was installed on a new 4-stroke 50 cm³ model scooter. The new fuel supply system, in which the fuel injection is controlled electronically, is called the discharge pump (DCP) system. Previously, electronically-controlled fuel injection systems were normally used for large-displacement models due to high cost, but the newly developed. DCP system makes it practical to use electronically-controlled fuel injection systems for small-displacement models whose production cost must be kept low. In addition to the same ECM and sensors as used in the conventional electronically-controlled fuel injection systems, the DCP system has the fuel pump, regulator, and injector combined in a single unit as the DCP, and the gravity-flow normal-pressure fuel piping system (with the fuel tank installed above the DCP). This new arrangement enables the system to be manufactured at lower cost while maintaining the same high mechanical performance as the conventional electronically-controlled fuel injection systems. Furthermore, compared with conventional systems, the new system demonstrates excellent performance such as improved startability, all-weather adaptability, and fuel economy, all of which can be achieved by monitoring engine conditions with various sensors and controlling fuel injection with high accuracy.