Gas Sensor Element Water Penetration Reduction

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Solution Overview

Problem

Sensor elements used to detect specific gas concentrations, such as NOx in exhaust gases, face issues with moisture penetration through porous protection layers, leading to corrosion and short circuits at connector electrodes due to capillary action.

Innovation Solution

Incorporating a water-penetration reduction portion with a dense layer and a gap region on the sensor element's side surface, which reduces capillarity and prevents moisture from reaching the connector electrodes, by positioning it closer to the front end than the connector electrodes and dividing the porous layer in the longitudinal direction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a porous protection layer is used to cover the sensor element, then the sensor element is protected from chemical corrosion, but moisture can penetrate through the porous layer via capillarity and cause rusting and short circuits at the connector electrodes

Engineering Contradiction:

Improvechemical corrosion protectionVSAvoidelectrical connection reliability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The protection layer is segmented into two distinct functional zones: a porous protection layer for chemical corrosion protection and a water-penetration reduction portion (dense layer) for moisture blocking. This segmentation allows each layer to perform its specialized function without compromising the other, resolving the contradiction between chemical protection and electrical reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The water-penetration reduction portion acts as an intermediary barrier between the porous protection layer and the connector electrodes. It intercepts moisture that has penetrated the porous layer through capillarity, preventing further migration to the electrical connections, thus protecting reliability while maintaining chemical protection.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the porous layer is made more dense to reduce moisture penetration, then moisture resistance improves, but the porosity decreases below 10% which compromises its protective function and increases warpage during baking

Engineering Contradiction:

Improvemoisture resistanceVSAvoidprotection layer effectiveness

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Different regions of the protection structure are assigned different porosity characteristics: the porous protection layer maintains high porosity (≥10%) for chemical protection, while the water-penetration reduction portion has low porosity (<10%) for moisture blocking. This local differentiation resolves the contradiction by applying the appropriate density characteristic to each specific functional requirement.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The protection system is divided into two segments with distinct porosity levels: a highly porous section for chemical resistance and a dense section for moisture resistance. This segmentation allows the overall system to achieve both chemical protection and moisture resistance without compromising either function.

Inventive Principle:

Principle #1Segmentation

3Reliability

If a dense layer is added to reduce water penetration, then moisture resistance improves, but the device complexity and structural complexity increase

Engineering Contradiction:

Improvemoisture resistanceVSAvoidprotection layer structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The water-penetration reduction portion is integrated into the existing porous protection layer structure rather than being added as a completely separate component. This merging approach reduces device complexity by combining multiple functions within a unified protection layer structure, while still achieving improved moisture resistance.

Inventive Principle:

Principle #5Merging (Combining)

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

Effectively prevents moisture from passing through to the connector electrodes, reducing the likelihood of corrosion and short circuits, while also minimizing warpage during baking by controlling the length and porosity of the dense layer.

Implementation Method 1

the moisture contained in an exhaust gas may move inside the porous layer by capillarity

Methodology Applied

Scientific EffectCapillary action: Capillary Action

Implementation Method 2

the water-penetration reduction portion reducing the capillarity of water in the longitudinal direction

Methodology Applied

Scientific EffectCapillarity reduction: Capillary Action

Data Source

PatentUS11692986B2Sensor element and gas sensor

Publication Date: 2023.07.04 NGK INSULATORS LTD

AI summary

A sensor element includes element main body including side surfaces, a detection unit, connector electrodes disposed on the rear end-side part of the side surfaces, a porous layer that covers at least front end-side part of the side surface, the porous layer having a porosity of 10% or more, and a water-penetration reduction portion. The water-penetration reduction portion is disposed on the side surface so as to divide the porous layer or to be located closer to the rear end than the porous layer. The length L of the water-penetration reduction portion is 0.5 mm or more. The water-penetration reduction portion includes, among a dense layer covering the side surface and having a porosity of less than 10% and a gap region in which the porous layer is absent, at least the dense layer. The water-penetration reduction portion reduces the capillarity of water.