Patent ID: 7228734

Claim:
An air flow rate measuring device comprising: a bypass passage through which air flowing in an air passage is capable of partially flowing; and a heater element that is arranged in the bypass passage, the heater element measuring an air flow rate on the basis of a quantity of heat, which is radiated to air, wherein the bypass passage defines an inlet, an inflow passage, and an outflow passage, the inlet opens in a direction that is opposite to a flow direction of air flowing through the air passage such that air flowing through the inlet bends to be in a predetermined flow direction and flows into the inflow passage, the outflow passage connects to the inflow passage via a bent portion in which air flowing from the inflow passage further changes in flow direction, the heater element is arranged in the inflow passage, the heater element is arranged such that a lengthwise direction of the heater element is substantially in parallel with a flow direction of air flowing through the air passage, the heater element has an element length in a longitudinal direction of the heater element, air flowing through the inflow passage defines a flow velocity distribution having a peak, which is located in a range of the element length substantially throughout a measurement range of the air flow rate, the heater element has a center portion with respect to the longitudinal direction, and the center portion is in the vicinity of the peak of the flow velocity distribution when the air flow rate is low.