Flow measuring device measuring air flow through a bypass passage throttled by a throttle portion

A flow measuring device comprising:

• a housing including a bypass passage that introduces a part of an air flowing through a duct;
• and
• a flow sensing chip located in the bypass passage and including a sensing surface portion that generates an electrical signal in response to a flow volume of the air in the duct, wherein
• the bypass passage includes:
• a main-bypass passage introducing the air into the housing through an inlet and discharging the air from the housing through an outlet;
• and
• a sub-bypass passage branching off from the main-bypass passage, the sub-bypass passage introducing a part of the air flowing through the main-bypass passage through a sub-bypass inlet and discharging the air from the housing through a sub-bypass outlet,
• the sub-bypass passage is throttled by a throttle portion such that a cross-sectional area of the sub-bypass passage perpendicular to a flowing direction in which the air flows through the sub-bypass passage decreases in accordance with a decrease in distance from a gravity center of the sensing surface portion to a center of the cross-sectional area in a direction parallel to the flowing direction,
• the flow sensing chip is disposed in the sub-bypass passage and the throttle portion is a part of a flowing passage wall facing the sensing surface portion,
• a position where the throttle portion starts is referred to as a start point position, the start point position is located upstream of the sensing surface portion in the flowing direction, and
• the throttle portion includes a surface that is a planar surface, the surface of the throttle portion and the flowing direction define an angle that is in a range from 0 degrees to 20 degrees.

A flow measuring device comprising:

• a housing including a bypass passage that introduces a part of an air flowing through a duct along a main-flow direction;
• and
• a flow sensing chip located in the bypass passage and including a sensing surface portion that generates an electrical signal in response to a flow volume of the air in the duct by a heat transmission between the sensing surface portion and the air flowing through the bypass passage, wherein
• the bypass passage includes:
• a main-bypass passage introducing the air into the housing through an inlet and discharging the air from the housing through an outlet;
• and
• a sub-bypass passage branching off from the main-bypass passage, the sub-bypass passage introducing a part of the air flowing through the main-bypass passage through a sub-bypass inlet and discharging the air from the housing through a sub-bypass outlet,
• the flow sensing chip is disposed in the sub-bypass passage so that the sensing surface portion extends along a flowing direction in which the air flows through the sub-bypass passage,
• the sub-bypass passage is throttled by a throttle portion such that a cross-sectional area of the sub-bypass passage perpendicular to the flowing direction decreases in accordance with a decrease in distance from a gravity center of the sensing surface portion to a center of the cross-sectional area in a direction parallel to the flowing direction,
• the throttle portion is a part of a flowing passage wall that is included in the housing and faces the sensing surface portion, the throttle portion throttles the cross-sectional area of the sub-bypass passage such that a distance from the sensing surface portion to the flowing passage wall at the cross-sectional area in a direction perpendicular to the sensing surface portion decreases in accordance with a decrease in distance from the gravity center of the sensing surface portion to the center of the cross-sectional area in the direction parallel to the flowing direction,
• a position where the throttle portion starts is referred to as a start point position, and a position of the throttle portion where a distance between the gravity center of the sensing surface portion and the throttle portion is shortest is referred to as an end point position,
• the start point position and the end point position define an imagination line, and the imagination line and the flowing direction define an angle that is in a range from 0 degrees to 30 degrees,
• the sub-bypass outlet of the sub-bypass passage discharges the air that passed through the sensing surface portion into the duct from the sub-bypass passage, and
• the sub-bypass outlet opens along the main-flow direction.