Gas Sensor Protective Layers With Porous Thermal Stress Buffer

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Solution Overview

Problem

Existing gas sensors face challenges in preventing damage to the surface protective layer due to thermal expansion differences, particularly when exposed to high temperatures and increased exhaust gas flow rates.

Innovation Solution

A gas sensor design featuring a sensor element with an element body, a surface protective layer, and an internal protective layer, where the internal protective layer has a lower thermal conductivity or higher porosity than the surface protective layer, and is positioned between the element body and the surface protective layer to mitigate thermal stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the surface protective layer is made dense and thick to protect the element body from water and deleterious substances, then the protection capability is improved, but the thermal expansion difference between the insulator and protective layer increases, causing damage to the protective layer under high temperature conditions

Engineering Contradiction:

Improveprotection capabilityVSAvoidresistance to thermal expansion damage

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The protective layer is divided into two distinct segments: a surface protective layer for chemical protection and an internal protective layer for thermal management. This segmentation allows each layer to be optimized for its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the protective structure have different properties: the surface protective layer has high density for chemical resistance, while the internal protective layer has high porosity for thermal expansion accommodation. Each region's properties are locally optimized for its specific role.

Inventive Principle:

Principle #3Local quality

2Productivity

If the exhaust gas flow rate is increased to improve detection responsiveness, then the detection speed is improved, but the thermal stress on the protective layer increases, causing damage

Engineering Contradiction:

Improvedetection responsivenessVSAvoidthermal stress

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The internal protective layer acts as an intermediary between the insulator and the surface protective layer. It mediates the thermal stress by accommodating expansion differences, thereby protecting the surface protective layer from damage while allowing high exhaust gas flow rates for responsive detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Temperature

If the thermal conductivity of the protective layer is increased to improve heat dissipation, then the temperature control is improved, but the thermal expansion difference increases, causing protective layer damage

Engineering Contradiction:

Improveheat dissipationVSAvoidresistance to thermal expansion damage

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The internal protective layer has high porosity that allows it to accommodate thermal expansion without transmitting excessive stress to the surface protective layer, while still permitting adequate heat dissipation from the insulator to the environment.

Inventive Principle:

Principle #3Local quality

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 proposed design effectively reduces the likelihood of damage to the surface protective layer by minimizing temperature differences and thermal expansion disparities between the insulator and the protective layers, thereby enhancing the sensor's durability and responsiveness.

Implementation Method 1

the internal protective layer having a lower thermal conductivity or a higher average porosity than the surface protective layer

Methodology Applied

Scientific EffectThermal conductivity: Conduction (thermal)

Implementation Method 2

minimizing temperature differences and thermal expansion disparities between the insulator and the protective layers

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

the protective layer is formed of a porous ceramic material

Methodology Applied

Scientific EffectPorosity: Porosity

Data Source

PatentUS12345674B2Gas sensor and method of manufacture thereof

Publication Date: 2025.07.01 DENSO CORP

AI summary

The sensor element of a gas sensor includes an element body, a surface protective layer provided at the outermost surface position of a tip portion of the element body, in the longitudinal direction of the element body, and an internal protective layer provided between the surface protective layer and the element body. The internal protective layer has a lower thermal conductivity and a higher average porosity than the surface protective layer, and is disposed between the surface protective layer and the element body. In the internal protective layer, a first protective layer portion of the internal protective layer is located on a side that faces the heater, and at least the base position is positioned closer in the longitudinal direction to the tip end of the element body than is the maximum temperature position on the element body.