Temperature Sensor Thermal Stress Reduction via Segmented Welding

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Solution Overview

Problem

Temperature sensors used in exhaust gas purification devices face reliability issues due to the significant stress caused by the difference in axial thermal expansion between element electrode wires and lead wires made of materials with different linear expansion coefficients, particularly with increasing exhaust gas temperatures.

Innovation Solution

A temperature sensor design featuring element electrode wires made of noble metals or alloys, lead wires made of Ni-based or Fe-based alloys, and intermediate members of the same alloys, with a filler filling the gap between the wires to reduce thermal expansion stress and improve bonding strength, and the lead wire positioned closer to the temperature detector to enhance stiffness and durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If element electrode wires and lead wires are bonded together in a wide range along the axial direction, then electrical connection is improved, but thermal expansion stress increases due to large difference in linear expansion coefficients

Engineering Contradiction:

Improveconnection reliabilityVSAvoidthermal expansion stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent introduces an intermediate member (reference numeral 4) that segments the bonding structure into two parts: element-side weld (51) connecting element electrode wire (23) to intermediate member (4), and lead-side weld (52) connecting intermediate member (4) to lead wire (3). This segmentation reduces the bond part width in the axial direction, thereby reducing thermal expansion stress while maintaining electrical connection reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The intermediate member (4) acts as a mediator between the element electrode wire (23) and lead wire (3). It has a linear expansion coefficient that is intermediate between the noble metal wire and the stainless steel wire, helping to reduce thermal expansion stress. The intermediate member provides a transition zone that accommodates the differential thermal expansion between the two dissimilar metals.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stress or pressure

If element electrode wire and intermediate member are welded with abutting surfaces, then bond part width is reduced, but welding complexity increases

Engineering Contradiction:

Improvethermal expansion stressVSAvoidwelding ease

Core Design Contradiction:

Stress or pressureVSEase of manufacture

Solution Approach 1:

The patent changes the welding configuration from axial overlap (width-direction bonding) to end-to-end abutting (axial-direction bonding). The element electrode wire (23) and intermediate member (4) are welded such that their opposing surfaces abut against each other in the axial direction, reducing the bond part width in the radial direction while maintaining adequate weld strength.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Strength

If lead wire is positioned closer to temperature detector, then structural stiffness is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvestructural stiffnessVSAvoidpositioning precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent applies local quality by positioning the lead wire (3) specifically closer to the temperature detector (2) only in the radial direction, while maintaining adequate axial spacing through the intermediate member (4). This localized positioning adjustment provides structural stiffness where needed (near the detector) without compromising the overall assembly tolerances or manufacturing feasibility.

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 solution reduces thermal expansion stress, enhances the reliability of connections between the element electrode wires and lead wires, and improves the durability of the temperature sensor by minimizing bond area and using materials with matching expansion coefficients, thereby improving the overall performance and longevity of the sensor.

Implementation Method 1

the bond part may be subjected to significant stress due to their large difference in axial thermal expansion

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

A gap between the element electrode wire and the lead wire at least in the direction orthogonal to the extending direction is filled with filler, and the element electrode wire, the element-side weld, and the lead wire are fixed to one another by the filler

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10422701B2Temperature sensor

Publication Date: 2019.09.24 DENSO CORP

AI summary

A temperature sensor includes a temperature detector, an element electrode wire, a lead wire, and an intermediate member. Each of the lead wire and the intermediate member is made of a Ni-based alloy or an Fe-based alloy. The element electrode wire and the intermediate member are welded together in such a manner that opposing surfaces, facing each other abut against each other to constitute an element-side weld. The intermediate member and the lead wire are welded together such that they overlap each other in a longitudinal direction Z to constitute a lead-side weld. The lead wire is extended closer to the temperature detector than the element-side weld is located. A gap between the element electrode wire and the lead wire at least in the longitudinal direction Z is filled with a filler. The element electrode wire, the element-side weld, and the lead wire are fixed to one another by the filler.