Patent ID: 8191417

Claim:
A flow rate measuring apparatus comprising: a main body portion comprising: a circuit housing portion that projects into a main passage; and a bypass passage forming member that is disposed so as to extend from a projecting end of said circuit housing portion in a direction of projection of said circuit housing portion; a bypass passage that is formed on said bypass passage forming member and through which a portion of a measured fluid that flows through said main passage is allowed to flow; a flow rate detecting element that is disposed inside said bypass passage and that has a detecting portion on a surface; and a control circuit that is housed inside said circuit housing portion and that drives said flow rate detecting element and processes a signal therefrom, wherein: said bypass passage forming member has: a front surface that is oriented upstream with respect to a direction of a main flow of said measured fluid and that is perpendicular to said direction of said main flow, a bottom surface that is positioned at a leading end in a direction of extension from said circuit housing portion and that is parallel to said direction of said main flow; two side surfaces that intersect with said front surface and said bottom surface; and a flow direction-changing means, formed on said front surface of said bypass passage forming member, for making said measured fluid, that collides with said front surface of said bypass passage forming member, flow in a horizontal direction that is perpendicular with respect to both (i) said direction of said main flow and (ii) said direction of projection of said bypass passage forming member; said bypass passage has: an inflow port that has an opening in a vicinity of an end portion of said front surface of said bypass passage forming member in said direction of extension of said bypass passage forming member; and an outflow port that has an opening on said bottom surface of said bypass passage forming member; and the flow direction-changing means comprising a pair of curved surfaces formed by relieving intersecting portions between said front surface and said side surfaces of said bypass passage forming member, each of the curved surfaces being streamlined relative to said direction of said main flow or being arc shaped, the pair of curved surfaces intersecting each other at a position that is in a common plane with said front surface, extending in said direction of projection of said bypass passage forming member for a predetermined range and extending over an entire region of said front surface of said bypass passage forming member in the horizontal direction, the flow direction-changing means making the measured fluid that collides with the front surface of said bypass passage forming member within said pair of curved surfaces formed by the relieving intersecting portions to flow in the horizontal direction.