Air Flow Measuring Device Guiding Means Upstream
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Solution Overview
Problem
Conventional air flow measuring devices face variations in output due to gaps, projecting, or recessed step differences between the passage forming housing and sensor housing, leading to turbulence and inaccurate flow rate measurements.
Innovation Solution
Incorporating a guiding means within the passage forming housing to direct air flow along the inner wall surface towards the center of the passage, either by forming a bulged part or narrowing the passage upstream of the sensor attaching part, which helps air flow bypass these discrepancies and stabilize the measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor housing is attached to a passage forming housing, then the device can measure air flow rate, but gaps and step differences are formed between the housings causing turbulence and measurement variation
Solution Approach 1:
The guiding means is positioned upstream of the sensor attaching part to pre-guide the air flow along the inner wall surface before it reaches the sensor area. This preliminary action ensures that the air flow is already stabilized and directed toward the center of the passage when it encounters the sensor housing, preventing turbulence generation at the interface between the passage forming housing and sensor housing.
Solution Approach 2:
The guiding means acts as an intermediary structure between the passage forming housing and the sensor housing. It mediates the air flow transition by providing a controlled path that connects the main passage to the sensor attaching area, eliminating the harmful direct interface between the two housings that would otherwise create gaps and step differences.
2Measurement precision
If the inner wall forming part of the sensor housing is made coplanar with the passage forming housing, then measurement accuracy improves, but manufacturing precision becomes extremely difficult to achieve
Solution Approach 1:
The guiding means is extracted as a separate functional element from the sensor housing structure. Instead of attempting to make the sensor housing inner wall coplanar with the passage forming housing, the guiding means is positioned in the passage forming housing upstream of the sensor attaching part. This extraction allows the sensor housing to be manufactured independently without requiring high-precision coplanarity with the passage forming housing.
Solution Approach 2:
The guiding means serves as an intermediary that compensates for the lack of coplanarity between the passage forming housing and sensor housing. It provides the necessary flow guidance and stabilization function that would otherwise require precise coplanar alignment, thereby decoupling the manufacturing precision requirements.
3Measurement precision
If the measured passage cross-sectional area is reduced upstream of the sensor, then air flow velocity increases and measurement sensitivity improves, but the passage becomes more susceptible to turbulence from gaps and step differences
Solution Approach 1:
The guiding means performs the preliminary action of guiding and stabilizing the air flow before it enters the narrowed passage section upstream of the sensor. By pre-establishing a controlled flow path along the inner wall surface, it ensures that even though the passage is narrowed (which increases velocity and sensitivity), the flow remains laminar and free from turbulence caused by gaps and step differences.
Data Source
AI summary
An air flow measuring device includes a passage forming housing, a sensor housing, and a sensor part. An inner wall surface of the passage forming housing defines a measured passage. The passage forming housing includes a sensor attaching part. Measured air flows through the measured passage. The sensor housing is attached to the sensor attaching part. The sensor part is disposed on the sensor housing and measures a flow rate of the measured air flowing through the passage. The passage forming housing includes a guiding device for guiding the measured air, which flows along the inner wall surface of the passage forming housing on an upstream side of the sensor attaching part in a measured air flow direction, further toward a center of the passage than the inner wall surface of the passage forming housing on a downstream side of the sensor attaching part in the flow direction.