Thermal Flow Meter Resin Fixing Stress Reduction
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Solution Overview
Problem
The existing thermal flow meters face challenges in maintaining high measurement accuracy due to positional changes caused by elastic deformation of the adhesive used in the gap between the bypass passage and the flow rate detection circuit, leading to inaccurate gas flow rate measurements.
Innovation Solution
A thermal flow meter design featuring a resin-molded circuit package with a bypass passage trench and a cover, where the circuit package is fixed using a fixing portion with both thick and thin portions to maintain accurate positional relationships and enhance airtightness, reducing stress and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If elastic adhesive is filled in the gap between the bypass passage and the flow rate detection circuit, then the mutual linear expansion difference is absorbed, but the positional relationship between the bypass passage and the flow rate detection circuit cannot be maintained with high accuracy
Solution Approach 1:
The patent removes the elastic adhesive from the gap between the bypass passage and the flow rate detection circuit, eliminating the source of positional drift. Instead, it uses a rigid resin-molded housing with integrated fixing portions to maintain precise positioning without relying on deformable adhesive materials.
Solution Approach 2:
The patent integrates the bypass passage and flow rate detection circuit into a single rigid resin-molded housing structure. The fixing portions are formed as an integral part of the housing, combining the functions of structural support and precise positioning into one unified component, eliminating the need for separate adhesive bonding.
2Adaptability or versatility
If elastic adhesive is used to fill gaps, then thermal expansion differences are accommodated, but the positional relationship changes due to elastic deformation
Solution Approach 1:
The patent changes the material parameter from elastic adhesive to rigid resin, fundamentally altering the mechanical properties of the bonding medium. The rigid resin-molded housing maintains dimensional stability across temperature variations, preventing the elastic deformation that causes positional drift while still accommodating thermal expansion through the overall structure design.
3Reliability
If the circuit package is firmly fixed to the housing, then reliability is improved, but stress concentration may occur in the resin molding
Solution Approach 1:
The patent implements local quality by creating fixing portions with varying thickness - thicker regions provide strong fixation and reliability, while thinner regions reduce stress concentration in the resin molding. This spatial variation in structural properties allows the same component to simultaneously achieve both firm fixation and stress resistance.
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 achieves high measurement accuracy and reliability by maintaining precise positional relationships and reducing stress on the circuit package, while also improving airtightness and suppressing warpage in the resin molding process.
Implementation Method 1
a flow rate detection circuit which is used for detecting the flow rate of a gas by performing heat transfer with the measurement target gas flowing through the bypass passage
Data Source
AI summary
The present invention provides a thermal flow meter 300 which reduces a stress applied from a fixing portion 3721, which is used to hold and fix a circuit package 400 with respect to a housing 302, to the circuit package 400 and has high reliability. In the thermal flow meter of the invention, the circuit package 400 embedded with a flow rate measurement circuit is formed through a first resin molding process, the fixing portion 3721 is formed along with the housing 302 through a second resin molding process, and the circuit package 400 is enveloped by the fixing portion 3721, whereby the circuit package 400 is held by and fixed to the housing 302. In order to reduce the influence of a stress, generated based on a temperature change of the fixing portion 3721, on the circuit package 400, the fixing portion 3721 is constituted of a thick portion 4714 and a thin portion 4710. Since thickness of a resin of the thin portion 4710 is small, the stress to be generated is small, and a force applied to the circuit package 400 can be reduced.