Gas Sensor Thermal Expansion Compensation for Sealing Reliability

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Solution Overview

Problem

Gas sensors face breakage and deterioration in sealing performance at high temperatures due to thermal expansion of metallic shells, which increases the crimping force and reduces the pressing force on talc powder, leading to inadequate sealing.

Innovation Solution

A gas sensor design featuring a tubular metallic shell with a powder filler member of higher thermal expansion coefficient than ceramic holders, where the ceramic holders are fixed with a force application mechanism that maintains pressing force, ensuring the ratio of effective axial length of ceramic holders to overall pressing length is between 0.40 and 0.58, preventing excessive pressure on the sensor element.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the crimping force is increased to maintain pressing force on the powder filler member, then sealing performance is improved, but the sensor element may break due to excessive pressing force

Engineering Contradiction:

Improvesealing performanceVSAvoidsensor element withstanding pressure

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent changes the material parameter (thermal expansion coefficient) of the powder filler member to be higher than that of the ceramic holders. This parameter change allows the powder filler member to compensate for thermal expansion effects at high temperatures, maintaining pressing force without requiring increased crimping force, thereby preventing sensor element breakage while ensuring sealing performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent utilizes differential thermal expansion between the powder filler member and ceramic holders. The powder filler member's higher thermal expansion coefficient causes it to expand more than the ceramic holders when heated, which compensates for the reduction in pressing force due to thermal effects, thereby maintaining sealing performance at high temperatures without increasing crimping force.

Inventive Principle:

Principle #37Thermal expansion

2Volume of moving object

If the sensor element size is reduced, then the gas sensor is miniaturized, but the withstanding pressure of the sensor element decreases

Engineering Contradiction:

Improvesensor sizeVSAvoidwithstanding pressure

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The patent changes the material parameter (thermal expansion coefficient) of the powder filler member to compensate for the reduced withstanding pressure of miniaturized sensor elements. This allows the use of smaller sensor elements while maintaining adequate pressing force through thermal expansion compensation, preventing breakage despite the size reduction.

Inventive Principle:

Principle #35Parameter changes

3Temperature

If the metallic shell thermally expands at high temperature, then the pressing force from crimping decreases, but increasing crimping force may break the sensor element

Engineering Contradiction:

Improveoperating temperatureVSAvoidpressing force

Core Design Contradiction:

TemperatureVSForce

Solution Approach 1:

The patent utilizes the thermal expansion of the powder filler member, which has a higher thermal expansion coefficient than the ceramic holders. When the gas sensor is heated to high temperature, the powder filler member expands more than the ceramic holders, compensating for the reduction in pressing force caused by metallic shell expansion and maintaining adequate sealing pressure without requiring increased crimping force.

Inventive Principle:

Principle #37Thermal expansion

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 maintains sealing performance at high temperatures while preventing sensor element breakage by reducing the rate of reduction in pressing force, without the need for increased crimping force, thus enhancing reliability and durability.

Implementation Method 1

the powder filler member has a higher thermal expansion coefficient than that of the first ceramic holder and the second ceramic holder

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the first ceramic holder, the powder filler member, and the second ceramic holder are fixed while being pressed by force application means from a rear end side of the metallic shell toward a forward end side of the metallic shell

Methodology Applied

Scientific EffectMechanical force: Mechanical Force

Data Source

PatentUS10732142B2Gas sensor

Publication Date: 2020.08.04 NITERRA CO LTD

AI summary

A gas sensor (100) includes a sensor element (120), a metallic shell (110), a powder filler member (133), a first ceramic holder (135) in contact with the rear end of the powder filler member and from which the sensor element protrudes, and a second ceramic holder (131) in contact with the forward end of the powder filler member and from which the sensor element protrudes. The powder filler member has a higher thermal expansion coefficient than that of the first and second ceramic holders. The first ceramic holder, powder filler member, and second ceramic holder are pressed by force application means (118). A relation 0.40<(L−M)/L<0.58 holds, where L is the axial distance between the rearward-facing surface of the first ceramic holder and the forward end of the second ceramic holder, and M is the axial length of the powder filler member.