THROTTLE BODY

Efforts have been made in recent years to provide lightweight, low-cost throttle bodies by forming throttle bodies of resins. The bore of a throttle body must be formed so that the gap between the bore of the throttle body and a throttle valve placed in the bore is in the range of 80 to 100 mu m. Even if the bore and the throttle valve are made of the same resin, the bore and the throttle valve have different linear expansion coefficients, respectively, when the bore and the throttle valve differ from each other in the orientation of a filler contained in the resin and, consequently, the bore and the throttle valve differ from each other in thermal deformation. Roundness can be deteriorated by molding shrinkage. Therefore, there is the possibility that the bore and the throttle valve interfere with each other and an excessively large gap is formed. The present invention circumferentially orients filler contained in a resin forming a throttle valve to make the radial linear expansion coefficient of the throttle valve substantially equal to that of a bore 4. Grooves 17 are formed on concentric circles in the throttle valve to orient filler 2 circumferentially. A throttle valve provided with circumferentially oriented filler can be formed by impregnating an aggregate formed by circumferentially arranging the filler with a resin and curing the resin. A rib 28 is formed in a part near a throttle shaft to control molding shrinkage so that the roundness of the bore 4 is small.