Air flow meter

An air flow meter comprising:

• a housing, which has an inlet portion and an outlet portion, forming a main passage through which air flows;
• a bypass passage forming member, provided substantially in a center of said main passage of said housing, which has an inlet and an outlet opened at an outer periphery of said bypass passage forming member, at a location opposing an inner surface of said housing, for forming a bypass passage therein which is communicated with said main passage and extends long enough to equalize a flow of air introduced from said main passage through said inlet into said bypass passage;
• flow rate detecting means, provided in said bypass passage, for detecting a flow rate of air flowing through said bypass passage;
• downstream throttling means formed between said inner surface of said housing and an outer surface of said bypass passage forming member, for throttling a flow of air in said main passage at a first throttling area near said outlet of said bypass passage so as to cause air in said main passage to be introduced into an inlet of said bypass passage;
• and
• upstream throttling means, which is provided between said inner surface of said housing and said outer surface of said bypass passage forming member and surrounding said outer surface of said bypass passage forming member at a first location upstream of said downstream throttling means to form a second throttling area which is smaller than said first throttling area of said downstream throttling means, for limiting a flow of air in each cross-sectional segment of said first location of said main passage so that the flow of air in said main passage is equalized.

An air flow meter for a vehicle comprising:

• a cylindrical housing which has an inlet portion, an outlet portion, and a main passage therein through which intake air flows;
• an egg-shaped member, provided in said main passage of said housing, which has an inlet, an outlet, and a bypass passage therein which is communicated with said main passage;
• a plurality of supporting members for supporting said egg-shaped member substantially in a center of said main passage of said cylindrical housing;
• flow rate detecting means, provided in said bypass passage, for detecting a flow rate of intake air flowing through said bypass passage;
• downstream throttling means, which is provided near said outlet of said bypass passage, for throttling a flow of air in said main passage near said outlet of said bypass passage so as to cause a pressure difference which causes air in said main passage to be introduced into said inlet of said bypass passage;
• and
• upstream throttling means, which is provided at a first location upstream of said downstream throttling means, having a throttling area which is smaller than that of said downstream throttling means, for limiting a flow of air in each portion of said first location of said main passage so that the flow of air in said main passage is equalized.