Development of the Resin Throttle Body Valve for FI System of Small-motorcycle Single Cylinder Engine

The throttle body valve used on FI systems, to control the amount of air intake to an engine, is normally made of metallic material such as aluminum. This requires considerable amount of processing manpower in the manufacturing process, as well as many different parts needed to configure the engine, which makes it a relatively expensive part of the system. The authors of this paper focused on resin as a material to significantly reduce manpower requirements and number of parts used. They considered using dies to produce the body and valve as a single piece by precision molding. A characteristic of the developed plastic throttle is that it secures sealability by having a double molded structure enveloping the valve with an elastic body of elastomer which makes it possible to ease the dimensional accuracy requirements between the body and valve. At the same time, a 2 split bush made of plastic was installed to the rotating shaft of the valve which makes it a construction that holds down the cap to the body via a spring thereby making it a construction that is easily adaptable to automatic assembly. We were able to develop a cheaper throttle body valve by securing dimensional accuracy of component parts, being able to eliminate processing steps and simplifying assembly. In addition, we tested the controllability of air intake amount and durability under each type of “use condition” on the actual vehicle. As a result of these tests we were able to verify that this system is sufficiently suited to an actual vehicle as an FI system for small motorcycles and that it can be taken to mass production.