Air flow meter

Claim 1

An air flow meter in an internal combustion engine, the air flow meter comprising: a main passageway having an air inlet portion; an air flow rate measuring tube mounted in said main passageway and extending over a predetermined axial length thereof; a bypass passageway formed in the air flow rate measuring tube and including an air inlet portion located substantially in a central portion of a cross-sectional area of said main passageway and an outlet portion disposed downstream of the air inlet portion of said main passageway, said bypass passageway including at least one substantially straight portion having a constant cross-sectional area, and at least one further portion extending substantially at a right angle to said substantially straight portion, said bypass passageway having an axial length greater than said predetermined axial length of said air flow rate measuring tube; a hot wire type air flow sensor mounted in the at least one substantially straight portion of the bypass passageway; a control means including a control circuit means for controlling an operation of said hot wire type air flow sensor; wherein said hot wire type air flow sensor and said control means are formed as an integral unit forming a sensor assembly insertable in said air flow rate measuring tube, said sensor assembly in said air flow rate measuring tube and said air flow rate measuring tube form a unit insertable in said air inlet portion, and wherein the air flow rate measuring tube including the bypass passageway and the hot wire type air flow sensor is exposed to the main air flow so that a temperature of the air in the bypass passageway becomes substantially equal to a temperature of the air in the main passageway.