Patent ID: 7530267

Claim:
A flow rate measuring apparatus comprising: a main body portion projecting into a main passage, said main body portion having a circuit housing portion disposed internally; a measuring passage formed on said main body portion at a projecting end of said circuit housing portion, a portion of a measured fluid flowing through said main passage being induced to flow through said measuring passage; a flow rate detecting element disposed inside said measuring passage; a control circuit housed inside said circuit housing portion, said control circuit driving said flow rate detecting element and processing a signal therefrom; and a plate including a wall surface that constitutes said measuring passage, wherein the plate holds the flow rate detecting element and the control circuit, wherein: said measuring passage comprises: an inflow aperture positioned in a vicinity of an end portion of said main body portion in a direction of projection and opening onto a surface of said main body portion that is perpendicular to a direction of flow of a main flow of said measured fluid so as to be facing upstream relative to said direction of flow of said main flow; an outflow aperture positioned in a vicinity of an end portion of said main body portion in said direction of projection and opening onto a surface of said main body portion that is parallel to said direction of flow of said main flow; a first passage extending from said inflow aperture in said direction of flow of said main flow to a first bend portion; a second passage extending from said first bend portion in a direction that is perpendicular to said direction of flow of said main flow toward said circuit housing portion to a second bend portion; a third passage extending from said second bend portion in said direction of flow of said main flow to a third bend portion; and a fourth passage extending from said third bend portion in a direction that is perpendicular to said direction of flow of said main flow in a direction away from said circuit housing portion; said fourth passage is connected to said outflow aperture directly or by means of an additional passage; and said flow rate detecting element is disposed in said third passage, and wherein: said flow rate detecting element and said control circuit are installed so as to be positioned substantially in a common plane with the wall surface of the plate constituting said measuring passage.