Thermal Flow Meter Cover Bypass Passage Positioning
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Solution Overview
Problem
The existing thermal flow meters face challenges in accurately setting and fixing the positional and angular relationships between the air flow sensing portion and the bypass passage, leading to difficulties in achieving high measurement accuracy due to the variability of adhesives used in the assembly process, especially in large-quantity production.
Innovation Solution
The thermal flow meter design incorporates a circuit package with an integrated air flow sensing portion and connection terminal, a housing with a bypass passage trench, and a cover that forms the bypass passage through resin molding processes, ensuring precise positioning and fixation of the circuit package within the housing, thereby maintaining high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive bonding is used to fix the sensor assembly to the casing, then assembly ease is improved, but measurement precision deteriorates due to variability in adhesive conditions affecting positional and angular relationships
Solution Approach 1:
The invention divides the housing into two separate parts: a housing body and a cover. The air flow sensing portion is integrated into the cover, which is then assembled to the housing body. This segmentation allows the sensing portion to be precisely positioned relative to the bypass passage through the cover structure itself, rather than relying on adhesive bonding of a separate sensor assembly, thereby maintaining measurement precision while preserving assembly ease.
Solution Approach 2:
The invention merges the air flow sensing portion with the cover structure through integrated molding. This combination ensures that the sensing portion and the cover form a unified structure with fixed positional and angular relationships, eliminating the variability introduced by adhesive bonding while maintaining ease of assembly as a single unit.
2Adaptability or versatility
If separate sensor assembly and casing are used with adhesive bonding, then manufacturing flexibility is improved, but manufacturing precision deteriorates in large-quantity production due to difficulty in defining positional and angular relationships during adhesive solidification
Solution Approach 1:
The housing is segmented into a housing body and a cover that can be manufactured separately and then assembled. The air flow sensing portion is integrated into the cover, which is molded as a single piece with the bypass passage. This segmentation enables flexible manufacturing while ensuring precise positional relationships are built into the mold design, eliminating variability during assembly.
Solution Approach 2:
The positional and angular relationships between the air flow sensing portion and the bypass passage are predetermined in the mold design during the molding process. This preliminary action ensures that when the cover is assembled to the housing body, the sensing portion is automatically positioned with high precision relative to the bypass passage, without requiring complex adhesive bonding processes.
3Reliability
If elastic adhesive is used to absorb linear expansion difference, then reliability is improved, but measurement precision deteriorates due to inability to accurately maintain positional and angular relationships
Solution Approach 1:
The housing is divided into a housing body and a cover that can expand and contract independently. The air flow sensing portion is integrated into the cover, so both the sensing portion and the bypass passage (in the cover) move together during thermal expansion. This eliminates differential expansion issues that would otherwise affect measurement precision, while the modular design maintains assembly reliability.
Solution Approach 2:
The cover structure provides a rigid local framework that maintains the positional and angular relationships between the air flow sensing portion and the bypass passage. This local rigidity ensures measurement precision is maintained even when the overall housing undergoes thermal expansion, as the critical measurement geometry is preserved within the cover structure.
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 the measurement accuracy of the thermal flow meter by stabilizing the positional and angular relationships between the air flow sensing portion and the bypass passage, improving the overall detection precision and reliability.
Implementation Method 1
a flow rate of the gas is measured by performing heat transfer between the air flow sensing portion and the gas as a measurement target
Data Source
AI summary
The present invention has been made to improve measurement accuracy of a thermal flow meter. In the thermal flow meter according to the invention, a circuit package (400) that measures a flow rate is molded in a first resin molding process. In a second resin molding process, a housing (302) having an inlet trench (351), a bypass passage trench on frontside (332), an outlet trench (353), and the like are formed through resin molding, and an outer circumferential surface of the circuit package (400) produced in the first resin molding process is enveloped by a resin in the second resin molding process to fix the circuit package (400) to the housing (302).