Thermal Flow Meter Bypass Passage Pollutant Separation

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Solution Overview

Problem

Thermal flow meters in internal combustion engines face challenges in maintaining high measurement accuracy due to pollutants like dust and liquid droplets adhering to the heat transfer surface, which can alter the thermal conductivity and cause measurement errors, especially when these pollutants are not easily centrifugally separated.

Innovation Solution

A thermal flow meter design featuring a bypass passage with an upstream curved path and a branching wall that directs pollutants to either the outer or inner circumference path, preventing them from reaching the heat transfer surface, and an air flow sensing portion arranged inside the outer circumference path parallel to the upstream curved path to minimize pollutant contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a bypass passage is used to measure intake air amount, then measurement capability is provided, but pollutants can adhere to the heat transfer surface causing measurement errors

Engineering Contradiction:

Improveintake air amount measurement accuracyVSAvoidpollutant adhesion to heat transfer surface

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The bypass passage is divided into two separate paths: an outer circumference path and an inner circumference path. The air flow sensing portion is arranged in the outer circumference path, while the inner circumference path serves as a pollutant collection zone. This segmentation allows the measurement function to be isolated from pollutant contamination zones.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inner circumference path acts as an intermediary zone that captures and contains pollutants before they can reach the heat transfer surface. By introducing this intermediate path, pollutants are diverted away from the sensitive measurement area, protecting the heat transfer surface from adhesion.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the bypass passage is curved to separate pollutants, then pollutant removal is improved, but the structure becomes more complex

Engineering Contradiction:

Improvepollutant separation effectivenessVSAvoidbypass passage structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The upstream curved path and the downstream straight path are merged into a single continuous bypass passage structure. The branching wall is integrated within this passage to divide the flow into two paths. This merging approach achieves pollutant separation functionality without requiring multiple separate components, thereby reducing overall structural complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The bypass passage utilizes the radial dimension of the cylindrical intake pipe by creating outer and inner circumference paths. Instead of adding complexity in the axial direction, the solution exploits the radial space available in the cylindrical structure, efficiently using the existing geometric dimensions to achieve pollutant separation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 effectively suppresses the impact of pollutants on measurement accuracy by guiding them away from the heat transfer surface, ensuring high and consistent measurement precision even in the presence of dust and liquid pollutants.

Implementation Method 1

an air flow sensing portion that measures a flow rate by performing heat transfer between a heat transfer surface and a measurement target gas

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

the bypass passage has an upstream side curved path formed in a curved shape along an unique plane at least in an upstream side from the air flow sensing portion

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Data Source

PatentUS9970800B2Thermal flow meter with bypass passage including an outer circumference path and an inner circumference path

Publication Date: 2018.05.15 ASTEMO LTD

AI summary

The present invention aims to provide a thermal flow meter capable of avoiding pollutants guided to an outer circumference side of the bypass passage by virtue of a centrifugal force or particle or liquid pollutants that are not centrifugally separated from reaching a heat transfer surface of an air flow sensing portion and obtaining high measurement accuracy. In the thermal flow meter of the present invention, the bypass passage has an upstream side curved path 390 formed in a curved shape along an unique plane at least in an upstream side from an air flow sensing portion 602 in a flow direction of the measurement target gas 30, and a branching wall 378 formed from a downstream side of the upstream side curved path 390 to a downstream side of the air flow sensing portion 602. The bypass passage of the downstream side of the upstream side curved path 390 is branched by the branching wall 378 into a main flow path 377 that fluidly communicates with an outer wall side of the upstream side curved path 390 and a branching path 388 that fluidly communicates with an inside wall side of the upstream side curved path 390. The air flow sensing portion 602 is arranged inside the main flow path 377 such that the heat transfer surface exposing portion 436 is in parallel with the unique plane of the upstream side curved path 390.