Patent ID: 7665351

Claim:
An air flow measuring device for measuring a flow amount of air flowing in an interior of a duct, the air flow measuring device comprising: a tube body for defining a bypass passage configured to introduce therein a part of air flowing in the duct; a sub-bypass passage branched from the bypass passage and being configured to introduce therein a part of air flowing in the bypass passage; and a flow amount sensor located in the sub-bypass passage to measure a flow amount of air flowing in the sub-bypass passage, wherein: an upstream end surface of the tube body has an inlet of the bypass passage, open toward upstream in the duct, and a downstream end surface of the tube body has an outlet of the bypass passage, open toward downstream in the duct; the tube body has an outer peripheral surface extending from the upstream end surface to the downstream end surface; an outer diameter of the outer peripheral surface of the tube body has a smallest dimension at the upstream end surface, and a largest dimension at the downstream end surface; the outer peripheral surface of the tube body has a first portion extending downstream from the upstream end surface in a predetermined range; and the first portion of the outer peripheral surface is a convex curve surface in which the outer diameter is increased by a ratio from a position on the upstream end surface toward downstream; further comprising: a throttle portion provided in the tube body at a position adjacent the outlet of the bypass passage to gradually reduce a passage sectional area of the bypass passage approaching the outlet of the bypass passage, wherein: the sub-bypass passage has an outlet around an outer periphery of the outlet of the bypass passage.