Air Flow Sensor Thermal Stress Isolation Mechanism

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Solution Overview

Problem

Conventional air flow rate measuring devices in engine intake passages face errors due to stress caused by linear expansion differences between the sensor assembly and the housing, leading to inaccurate electrical signals.

Innovation Solution

An air flow rate measuring device with an urging mechanism that presses the sensor assembly's contact surface onto the housing's contact surface, preventing linear expansion transmission and reducing stress on the sensor chip and circuit chip, while maintaining airtightness with an elastic adhesive.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the sensor assembly is fixed to the housing by bonding with adhesive to allow easy linear expansion transmission, then the fixation is simple, but stress is applied to the sensor chip or circuit chip causing measurement errors

Engineering Contradiction:

Improvefixation methodVSAvoidair flow rate measurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The contact surface is divided into a fixed portion and an elastic portion, creating distinct functional zones. The fixed portion provides stable mechanical support while the elastic portion absorbs thermal expansion stresses, preventing stress transmission to the sensor chip and circuit chip.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the contact surface have different properties: the fixed portion is rigid for stable positioning, while the elastic portion is compliant for stress absorption. This local differentiation allows the contact surface to simultaneously provide mechanical support and stress isolation.

Inventive Principle:

Principle #3Local quality

2Stability of the object's composition

If the sensor assembly is fixed rigidly to the housing, then the position is stable, but linear expansion differences cause stress on the sensor chip

Engineering Contradiction:

Improvesensor assembly positionVSAvoidelectrical signal accuracy

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The contact surface is segmented into fixed and elastic portions, allowing the system to simultaneously achieve positional stability through the fixed portion and stress relief through the elastic portion, preventing piezo resistive effects that would compromise signal reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The elastic portion acts as an intermediary between the rigid housing and the sensitive sensor assembly, absorbing thermal expansion stresses before they can reach the sensor chip or circuit chip, thereby maintaining both stability and reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If adhesive bonding is used to fix the sensor assembly, then the assembly is simple, but the linear expansion stress cannot be blocked

Engineering Contradiction:

Improveassembly processVSAvoidlinear expansion stress

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The contact surface is divided into fixed and elastic portions, providing a built-in stress absorption mechanism that eliminates the need for complex adhesive bonding processes while effectively blocking linear expansion stress from reaching the sensor components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The elastic portion of the contact surface converts the harmful linear expansion stress into beneficial elastic deformation, absorbing the stress energy and preventing it from reaching the sensor chip and circuit chip, thereby maintaining measurement accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 improves the accuracy of air flow rate measurements by blocking linear expansion stress, stabilizing the sensor assembly's position and reducing resistance value fluctuations, thereby enhancing the reliability of the electrical signals produced.

Implementation Method 1

generating a heat transfer phenomenon between the device and the air taken in thereby to measure a flow rate of air suctioned into the engine

Methodology Applied

Scientific EffectHeat transfer phenomenon: Conduction (thermal)

Implementation Method 2

due to a linear expansion difference between the sensor assembly and the housing, stress may be applied to the sensor chip or the circuit chip

Methodology Applied

Scientific EffectLinear expansion: Thermal Expansion

Data Source

PatentUS8677811B2Air flow rate measuring device

Publication Date: 2014.03.25 DENSO CORP

AI summary

An air flow rate measuring device includes a housing, a sensor assembly, and an urging mechanism. The housing defines an internal flow passage, through which air taken in by the device passes, and the housing includes a contact surface. The sensor assembly includes a sensor chip and a contact surface. The sensor chip is configured to generate an electrical signal through a heat transfer phenomenon. The sensor assembly is inserted and fixed in the housing such that the sensor chip is exposed to the internal flow passage. The contact surface of the sensor assembly is in surface contact with the contact surface of the housing. The urging mechanism is configured to press the contact surface of the sensor assembly on the contact surface of the housing, so that the sensor assembly is fixed to the housing by the urging mechanism.