Thermal Flow Sensor Sub-Passage Design for Unsteady Air Mass Measurement
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Solution Overview
Problem
Conventional flow rate measurement apparatuses experience accuracy deterioration during unsteady flow conditions due to the presence of a drain hole, which leads to increased air flow out of the sub-passage and reduced air flow to the heat-resistance element, especially during abrupt changes in flow rate.
Innovation Solution
The apparatus incorporates a sub-passage design with a stepped-like recess and a hole configuration that acts as a hood, allowing air to easily flow out even during abrupt changes in flow rate, preventing pressure buildup and maintaining accurate detection by ensuring air flow to the heat-resistance element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a drain hole is provided in the sub-passage to drain water, then water drainage function is improved, but air flow to the heat-resistance element is reduced during unsteady flow conditions, deteriorating measurement accuracy
Solution Approach 1:
The sub-passage is divided into multiple sections: a first sub-passage for water drainage and a second sub-passage for air flow measurement. The drain hole is provided only in the first sub-passage, while the second sub-passage remains sealed to maintain proper air flow to the heat-resistance element during unsteady flow conditions.
Solution Approach 2:
Different portions of the sub-passage are given different functions: the upstream portion (first sub-passage) is designed for water drainage with a drain hole, while the downstream portion (second sub-passage) is designed for air flow measurement without a drain hole, ensuring local optimization of both drainage and measurement functions.
2Speed
If the flow rate of intake air is abruptly changed, then vehicle acceleration response is improved, but pressure in the sub-passage becomes higher around the drain hole, causing air to flow out through the drain hole and reducing air flow to the detecting element
Solution Approach 1:
The sub-passage is segmented into a first sub-passage that handles water drainage and a second sub-passage that handles air flow measurement. By providing the drain hole only in the first sub-passage and keeping the second sub-passage sealed, the design prevents air from escaping through the drain hole during abrupt acceleration, maintaining detection accuracy.
Solution Approach 2:
The division of the sub-passage into two functional sections acts as an intermediary structure that separates the water drainage function from the air flow measurement function, allowing each to operate independently without interfering with the other during transient flow conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances air discharge and maintains accurate flow rate measurement during both steady and unsteady conditions, preventing output value degradation during transient flow periods.
Implementation Method 1
the amount of heat radiation would becomes excessive, resulting in occurrence of measurement error since the heat radiation to water is large in comparison with that to air
Implementation Method 2
the separation of the air is caused in the outlet part of the sub-passage so that the pressure is decreased therearound, and accordingly, the air is liable to flow out from the outlet part
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a thermal type flow rate measurement apparatus comprising a sub-passage having a detour passage and a hole just before a flow rate measuring part. A slit is formed downstream of a flow rate detecting element (3) located after the detour passage. The slit hole may be arranged between the flow rate detecting element (3) and the outlet port part (14), and may be opened between a wall surface side and a recess part (17). Thereby, it is possible to prevent the output value from falling in the negative side upon rise-up thereof.