Physical Quantity Detector Pin Positioning for Accurate Flow Measurement
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Solution Overview
Problem
Conventional physical quantity detection devices suffer from lower positioning accuracy due to increased tolerances during assembly, leading to variations in dimension and shape of auxiliary passages, which affect measurement accuracy.
Innovation Solution
The device incorporates a positioning portion with a pin extending in the thickness direction of the circuit board, featuring an engagement portion and a fitting portion, to restrict movement of the circuit board, enhancing the alignment between the housing and cover, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If multiple projections and recesses are used for positioning between the base and housing, then the assembly can be stabilized, but the tolerances during assembling increase, leading to lower positioning accuracy
Solution Approach 1:
The patent combines multiple positioning functions into a single pin structure. The pin includes both a positioning function (restricting movement in the thickness direction through the fitting portion) and a movement restriction function (restricting movement in the surface direction through the engagement portion). This merging of functions reduces the number of separate positioning elements needed, thereby reducing cumulative tolerances while maintaining assembly stability.
Solution Approach 2:
The pin serves multiple functions: it positions the circuit board in the thickness direction via the fitting portion, restricts movement in the surface direction via the engagement portion, and provides structural support. This multi-functionality eliminates the need for separate positioning projections and recesses, reducing the number of interfaces and associated tolerances.
2Stability of the object's composition
If the number of projections and recesses for positioning increases, then the assembly stability improves, but the variations in dimension and shape of auxiliary passages increase, affecting measurement accuracy
Solution Approach 1:
The pin integrates multiple positioning functions that were previously distributed across multiple projections and recesses. By consolidating these functions into a single pin structure, the number of interfaces between components is reduced, minimizing the sources of dimensional variation that affect auxiliary passage geometry and measurement accuracy.
3Device complexity
If a simple positioning structure is used, then the device complexity is reduced, but the positioning accuracy between housing and cover decreases
Solution Approach 1:
The pin combines multiple positioning functions (thickness direction positioning and surface direction movement restriction) into a single structural element. This merging approach maintains structural simplicity while achieving high positioning accuracy, as the pin's geometry can be precisely controlled during manufacturing without requiring multiple separate components.
Solution Approach 2:
The pin's geometry is optimized with specific parameters: the fitting portion has a diameter that restricts movement in the thickness direction, while the engagement portion has features that restrict movement in the surface direction. By carefully controlling these dimensional parameters, high positioning accuracy is achieved without increasing overall device complexity.
Data Source
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AI summary
Provided is a physical quantity detection device that can improve physical quantity measurement accuracy over a conventional device. A physical quantity detection device 20 includes a detector including a flow rate detection unit 205, a circuit board 207, a housing 201, and a cover 202. The detector detects a physical quantity and is mounted on the circuit board 207. The housing 201 houses the circuit board 207. The cover 202 is fixed to the housing 201 and defines an auxiliary passage 234 in which the flow rate detection unit 205 is disposed. The housing 201 and the cover 202 include a positioning portion P that includes a pin P1 extending in a thickness direction Dt of the circuit board 207 and a fitting portion P2 into which an end portion P11 of the pin P1 is fitted for positioning between the housing 201 and the cover 202. The pin P1 includes an engagement portion P12 that faces an engagement surface 207f of the circuit board 207 along the thickness direction Dt and restricts movement of the circuit board 207 in a surface direction Df along the front and rear surfaces thereof.