Inclined Heating Resistor for Airflow Sensor
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Solution Overview
Problem
Conventional thermal flow measuring devices for internal combustion engines face challenges in accurately measuring airflow due to adhesion of suspended particulates, which impairs the heat radiation characteristics and output response, as existing protection mechanisms do not effectively prevent contamination of the heating resistor and lead members.
Innovation Solution
The airflow measuring device incorporates a bypass passage that deflects airflow perpendicularly, featuring a heating resistor inclined toward the downstream of the outer streamline in the bypass passage, combined with support members aligned with the airflow, to reduce stagnation and adhesion of particulates through an inertia separation effect and enhanced Brownian motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the heating resistor is positioned perpendicular to the flow direction for maximum heat transfer, then the heat transfer characteristic is enhanced, but suspended particulates adhere to the heating resistor and lead members, impairing measurement accuracy
Solution Approach 1:
The heating resistor is positioned at an asymmetric angle (inclined position) relative to the flow direction rather than perpendicular, creating an oblique arrangement that reduces particulate adhesion while maintaining adequate heat transfer performance
Solution Approach 2:
Instead of positioning the heating resistor perpendicular to maximize heat transfer, the patent inverts the approach by positioning it at an inclined angle to prioritize preventing contamination, accepting a trade-off in heat transfer efficiency
2Reliability
If the heating resistor is inclined toward the downstream of the outer streamline, then adhesion of suspended particulates is suppressed, but the heat transfer efficiency may be reduced
Solution Approach 1:
The patent optimizes the inclination angle parameter of the heating resistor to achieve a balance between suppressing particulate adhesion and maintaining heat transfer efficiency, finding the optimal angular parameter that satisfies both requirements
3Measurement precision
If protection mechanisms are added to prevent particulate adhesion, then measurement accuracy is maintained, but device complexity increases
Solution Approach 1:
The patent extracts the protection function from separate protection mechanisms and integrates it into the basic positioning structure of the heating resistor itself, eliminating the need for additional protection components
Solution Approach 2:
The inclined positioning structure serves dual functions: it maintains measurement accuracy by preventing particulate adhesion while also serving as the basic mounting structure, eliminating the need for separate protection mechanisms
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 configuration effectively suppresses the adhesion of suspended particulates, maintaining the accuracy and durability of the airflow measurement while optimizing the heat transfer characteristics, with a suitable inclination angle and controlled temperature range ensuring reduced contamination and improved output characteristics.
Implementation Method 1
measures airflow in accordance with heat radiation from the heating resistor to the airflow
Implementation Method 2
Heat dissipated from the heating resistor to airflow is substantially in proportion to the square root of velocity of the airflow
Implementation Method 3
The heating resistor is constructed by winding a metallic resistive element... An electric current is supplied to the resistance bridged circuit
Implementation Method 4
enhanced Brownian motion
Implementation Method 5
reduce stagnation and adhesion of particulates through an inertia separation effect
Data Source
AI summary
An airflow measuring device includes a sensing portion provided in a bypass passage, which perpendicularly deflects part of air from a main passage to therethrough bypass the part of air. The sensing portion includes a heating resistor energized and dissipate heat to airflow. The sensing portion is configured to measure airflow in the bypass passage based on the heat radiation. The sensing portion further includes a pair of support members erected in the bypass passage to support the heating resistor. The heating resistor of the sensing portion is inclined at a first inclination angle with respect to a direction, which is perpendicular to a flow direction of air in the bypass passage. The heating resistor is inclined toward downstream at an outer streamline of the airflow in the bypass passage.