Patent ID: 7661405

Claim:
A throttle valve device for an internal combustion engine, comprising: a throttle valve body defining a throttle bore extending substantially in a horizontal direction from an inlet on an upstream end of the throttle bore to an outlet on a downstream end of the throttle bore, the throttle bore extending along an axis that is substantially in the horizontal direction; a throttle valve member comprising a butterfly valve rotatably supported by the throttle valve body for selectively opening and closing the throttle bore at an axially intermediate point of the throttle bore, the throttle valve having a default position defined by a small opening angle with respect to a fully closed position thereof; an upstream recess formed in an inner wall of the throttle valve body and extending laterally, substantially in a lower part of the throttle bore, and extending axially for a prescribed distance in an upstream direction starting from a point upstream from a lower edge of the throttle valve member at the default position; and a downstream recess formed in an inner wall of the throttle valve body and extending laterally, substantially in a lower part of the throttle bore, and extending axially for a prescribed distance in a downstream direction starting from a point downstream from the lower edge of the throttle valve member at the default position wherein the throttle bore has a reference cross sectional area at a point corresponding to the lower edge of the throttle valve member at the default position, each recess enlarging the cross sectional area of the throttle bore in comparison to the reference cross sectional area, and a cross sectional area of one of the recesses over which the lower edge of the throttle valve member sweeps as the throttle valve member opens from the fully closed position is smaller than the cross sectional area of the other recess.