Thermal Flowmeter Bypass Passage Protrusion for Backflow Suppression
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Solution Overview
Problem
Thermal flowmeters face challenges in accurately measuring low intake air flow rates due to pressure fluctuations from blow-by gas pipes, leading to air pulsation and erroneous backflow detection, especially under low idle conditions, where flow path resistance differences cause circulation of air flow between the flow detection unit and the bypass passage.
Innovation Solution
The thermal flowmeter design incorporates a bypass passage with a protrusion that throttles air flow and divides the passage into sections with varying sectional areas to minimize pressure differences, reducing air flow circulation and preventing backflow detection by optimizing the sectional area ratio between the flow detection unit side and the bypass passage side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the bypass passage is split between the flow detection unit side and the back side, then contamination to the flow detection unit is reduced, but air flow circulation occurs due to flow path resistance difference
Solution Approach 1:
The patent changes the geometric parameters of the bypass passage by introducing a protrusion that divides the passage into first and second bypass passages with different sectional areas. This parameter change creates different flow path resistances that counterbalance the pressure differences caused by pulsation, preventing air flow circulation while maintaining contamination protection.
Solution Approach 2:
The bypass passage is segmented into multiple sections (first bypass passage and second bypass passage) by a protrusion. This segmentation allows independent control of flow characteristics in each section, enabling the design to simultaneously achieve contamination protection and prevent circulation by optimizing the sectional area ratio between the segments.
2Speed
If the flow rate resistance on the flow detection unit side is significantly larger than the back side, then flow velocity difference occurs, but air circulation from back side to flow detection element side occurs causing erroneous backflow detection
Solution Approach 1:
The patent introduces a protrusion with a specific sectional area ratio between the first and second bypass passages. This parameter change creates an optimized flow path resistance distribution that maintains appropriate flow velocity differences for measurement while preventing the pressure difference from causing reverse flow circulation.
3Productivity
If the intake air flow rate decreases under low idle condition, then fuel economy is improved, but the influence of pressure from blow-by gas pipe becomes relatively great causing air pulsation
Solution Approach 1:
The patent modifies the bypass passage geometry by adding a protrusion that creates different sectional areas in the first and second bypass passages. This parameter change optimizes the flow path resistance to counterbalance pulsation pressure effects, maintaining air flow stability even at low idle conditions where fuel economy is improved.
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 effectively suppresses air flow circulation and enhances the accuracy of intake air flow rate measurement under low flow pulsation conditions, preventing erroneous backflow detection and improving detection precision.
Implementation Method 1
The thermal flowmeter is configured to measure the intake air flow rate by performing heat transfer between a flow detection unit formed in a flow detection element and the intake air flow rate to be measured.
Implementation Method 2
The thermal flowmeter design incorporates a bypass passage with a protrusion that throttles air flow and divides the passage into sections with varying sectional areas to minimize pressure differences
Data Source
AI summary
The present invention is directed to a thermal flowmeter that prevents erroneous detection of backflow by suppressing circulation of air flow from a flow detection unit side to a back side or from the back side to the flow detection unit side and measures a gas flow rate with high accuracy. A thermal flowmeter of the present invention includes a bypass passage through which a gas to be measured passes; a dividing portion which divides the inside of the bypass passage into a first passage portion and a second passage portion; and a flow detection unit which is provided on a surface of the dividing portion on the first passage portion side and detects a flow rate of the gas to be measured. Further, the first passage portion has a detection surface on which the flow detection unit is exposed, an opposing surface which opposes the flow detection unit on the detection surface, and non-opposing surfaces and which are disposed at positions deviating from the opposing surface in a bypass passage width direction of the first passage portion and do not oppose the flow detection unit, and the non-opposing surface is separated from the detection surface farther than the opposing surface.