Mass air flow sensor structure with bi-directional airflow incident on a sensing device at an angle

A method of sensing mass air flow through a duct comprising the steps of:

• suspending a substrate in the duct, wherein the substrate contains a heater, a first sensing element on a first side of the heater and a second sensing element on a second side of the heater opposite the first side and wherein the substrate is oriented so that air flow passes one of the sensing elements, the heater and then the other sensing element, or vice versa, wherein the heater and first and second sensing elements are located on a substantially flat portion of the substrate, and wherein the sensing elements are responsive to heat generated by the heater that propagates upstream in the flow path towards one of the sensing elements and downstream in the flow path towards the other of the sensing elements;
• using an air foil having a convex surface continuously curved in a direction parallel to the flow path facing the substantially flat portion of the substrate, deflecting flow from a first direction through the duct at an angle toward the substrate so that air flow past the sensing element is substantially free of turbulence in a region of the sensing elements;
• and
• using the air foil, deflecting flow from a second direction opposite the first direction at an angle against the sensing device so that the air flow is substantially free of turbulence in the region of the sensing elements.

A mass air flow sensor comprising:

• a sensing device with a substantially flat surface from a first point to a second point in a flow path, a heating element substantially centrally located between the first and second points, a first sensing element located between the first and second points on a first side of the heating element in a flow path direction, a second sensing element located between the first and second points on a second side of the heating element opposite the first side in the flow path direction, and wherein the sensing elements are responsive to heat generated by the heater that propagates upstream in the flow path towards one of the sensing elements and downstream in the flow path towards the other of the sensing elements;
• and
• an air foil mounted a predetermined distance apart from the sensing device having an air foil surface that is convex and continuously curved along a direction parallel to the flow path between the first point and the second point facing the heating element and the first and second sensors, wherein the air foil surface deflects air flow past the sensing device to be incident on the sensing device at an angle, wherein the air foil is symmetrical with respect to a line perpendicular to the flat surface and intersecting a center of the heating element and wherein bi-directional air flow past the sensing device is substantially free of turbulence between the first and second points.