Injection-molded gear for engine and manufacturing method therefor

Abstract

An injection-molded gear for an utility engine has a high reliability, tenacity, and accuracy, capable of being manufactured at low cost without requiring cutting, and ensuring a substantial reduction in noise. An inner part of a cam crankshaft gear is formed of an insert ring of a sintered iron alloy. An outside portion and a toothed crest portion of the gear are formed by injection-molding a polyamide resin such as nylon 66 and heat-treating the resulting molded product so that its relative viscosity is equal to or larger than 3.5. The relative viscosity is defined as .eta./.eta..sub.0 where .eta..sub.0 is a viscosity of sulfuric acid of 98% concentration and .eta. is a viscosity of a solution of the 98% sulfuric acid in which the polyamide resin is dissolved at a concentration of 1.0%.

Dependencies are inferred from the claim text.