Patent ID: 7685874

Claim:
A thermal type flow sensor comprising: a measuring passage which is disposed in a main passage; a base portion provided along a flowing direction of a fluid passing through the measuring passage; and a sensor element mounted on the base portion and equipped with an exothermic resistor formed on a substrate; the thermal type flow sensor being featured in that a recessed portion is formed in the base portion, that the sensor element is fixedly fitted in the recessed portion in a manner that the surface of a detecting portion of the sensor element is positioned lower than an upper edge of the recessed portion, and that a wall portion of the measuring passage which is located to face the sensor element is constricted, wherein the constricted wall portion is configured to provide a constricted passage in the measuring passage such that a cross-sectional area of the measuring passage is gradually reduced to a narrowest portion of the constricted passage from an upstream side upper edge of the recessed portion to a downstream side thereof, and the exothermic resistor of the sensor element is mounted downstream of an upstream end of the narrowest portion of the constricted passage.