| 摘要 |
A throttle valve is rotatably mounted to a throttle body through a throttle shaft. An internal bore shape of the throttle body is of a straight bore type having a shape in which the center of rotation of the throttle valve is placed on the central line of the throttle body. Spherically-shaped internal profile portions are provided in an idle control region lying in the neighborhood of a fully-closed angle of the throttle valve. Further, spherically-shaped internal profile portions are provided as regions following the spherically-shaped internal profile portions referred to above. Moreover, regions each formed by a spherical shape and a composite surface profile of a cylindrical surface substantially parallel to the flow of intake air or regions each formed by a conical surface profile are provided as regions following the spherically-shaped profiles. Incidentally, the center of each spherical profile is offset on the central line of the bore in upward and downward directions. As a result, a clearance defined between each spherical profile and the throttle valve increases as the degree of opening of the throttle valve increases. When the present invention is used in an electronically-controlled type throttle valve control device, the engine speed is set so as to be changed 20 rpm when the throttle valve is opened 0.1° in a low degree-of-opening region of the throttle valve. Therefore, idle control exercised by an ISC valve is unnecessary.
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