Thermal Flow Sensor Recessed Resistor Design
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Solution Overview
Problem
Thermal type flow sensors for internal combustion engines face measurement errors due to fluid disturbances and dust impingement, leading to increased manufacturing costs and sensor element damage, particularly when the sensor element is protruded or depressed from the passage surface.
Innovation Solution
A thermal type flow sensor design featuring a semiconductor sensor element with an exothermic resistor positioned away from the step portion, utilizing a constricted passage configuration to minimize fluid disturbance and dust impact, with the exothermic resistor placed at the narrowest portion of the constricted passage to enhance measurement accuracy without increasing sensor size or manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the sensor element surface is made flush with the passage surface, then manufacturing precision is improved, but the sensor element is vulnerable to dust impingement and fluid disturbance
Solution Approach 1:
The patent applies preliminary action by forming a recessed portion in the base portion before mounting the sensor element. This pre-prepared recessed structure allows the sensor element to be positioned at an optimal distance from the passage surface, preventing dust impingement and fluid disturbance before these harmful factors can affect the sensor. The recessed portion is designed with specific dimensional relationships (depth, width, length) to ensure the sensor element is protected while maintaining measurement accuracy.
2Measurement precision
If the exothermic resistor is disposed away from the edge portion to minimize measurement error, then measurement precision is improved, but the sensor element area must be increased
Solution Approach 1:
The patent applies local quality by creating a non-uniform spatial distribution of the exothermic resistor within the sensor element. The exothermic resistor is positioned at a specific location that is determined by the local geometry of the recessed portion and passage configuration. This localized positioning optimizes the balance between measurement precision (by being away from edge effects) and compactness (by utilizing the specific recessed geometry to minimize required area).
Solution Approach 2:
The patent resolves the area contradiction by transitioning from a two-dimensional surface placement problem to a three-dimensional spatial arrangement. By utilizing the depth dimension of the recessed portion, the exothermic resistor can be positioned optimally in space without requiring increased sensor element area. The recessed portion provides vertical clearance that allows the exothermic resistor to be disposed at an optimal distance from the passage surface while maintaining a compact overall sensor footprint.
3Ease of manufacture
If the sensor element is protruded from the passage surface, then ease of manufacture is improved, but fluid disturbance and measurement error increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the recessed portion in the base portion during the manufacturing process. This preliminary structural preparation simplifies the subsequent sensor element mounting operation, as the recessed portion automatically provides mechanical support and positioning features. The sensor element can be easily mounted by fitting it into the pre-formed recessed portion, eliminating the need for complex alignment procedures while simultaneously preventing fluid disturbance and measurement error.
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
The design effectively reduces measurement errors and sensor damage by stabilizing fluid flow over the exothermic resistor, maintaining accuracy and minimizing manufacturing costs, while ensuring the sensor element is protected from dust and fluid impingement.
Implementation Method 1
an exothermic resistor and a temperature-sensing resistor are formed on a thin film portion
Implementation Method 2
a temperature-sensing resistor are formed on a thin film portion having a thickness of several microns formed on a semiconductor substrate
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
The present invention relates to a thermal type flow sensor (1A) comprising: a base portion (4) provided along the flowing direction of a fluid passing through a main passage (10); and a sensor element (2) mounted on the base portion (4) and equipped with an exothermic resistor (3) formed on a substrate for detecting the flow rate of fluid passing through main passage (10). This flow sensor (1A) is featured in that a rectangular recessed portion (5) is formed in the base portion (4), that the sensor element (2) is fixedly fitted in the recessed portion (5) in a manner that the surface of detecting portion of sensor element (2) is positioned lower than an upper edge of recessed portion (5), that a wall portion of measuring passage which is located to face the sensor element (2) is constricted, and that the exothermic resistor (3) is disposed along a passage of fluid and spaced away from the upstream side upper edge of recessed portion (5) and cannot be substantially affected by a disturbance of flow of fluid that may be caused to generate due to a step portion formed between the upper edge (5a) of recessed portion (5) and the surface of detecting portion of sensor element (2).