Spark Plug Ground Electrode Weld Region Geometry

Solution Overview

Problem

The existing spark plugs with multilayer ground electrodes face challenges in achieving both high heat resistance and strong joint strength between the ground electrode and the metal shell, as the thickness of the surface layer decreases with increased core material, leading to reduced durability due to differences in melting points and strengths during resistance welding.

Innovation Solution

A spark plug design with a ground electrode having a surface layer and a core of higher thermal conductivity, where the surface layer thickness is maintained between 0.2 mm to 0.4 mm, and the core is structured with a first and second core member to enhance joint strength, with specific geometric configurations such as undulating weld regions and balanced thicknesses to prevent deformation and improve resistance welding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the amount of core material is increased to improve heat resistance, then heat resistance is improved, but joint strength between ground electrode and metal shell decreases

Engineering Contradiction:

Improveheat resistanceVSAvoidjoint strength

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The ground electrode is designed with non-uniform surface layer thickness, where the thickness varies along the longitudinal direction. Specifically, the surface layer is thicker at positions farther from the welding surface and thinner near the welding surface, creating local quality variations that optimize both heat resistance and welding performance in different regions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the thickness parameter of the surface layer from a constant value to a variable value that depends on the position along the longitudinal direction. This parameter change allows the surface layer to provide sufficient heat resistance while maintaining adequate thickness at the welding surface for strong joint formation.

Inventive Principle:

Principle #35Parameter changes

2Strength

If the surface layer thickness is increased to improve joint strength, then joint strength is improved, but heat resistance decreases

Engineering Contradiction:

Improvejoint strengthVSAvoidheat resistance

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The ground electrode is designed with non-uniform surface layer thickness, where the thickness varies along the longitudinal direction. Specifically, the surface layer is thicker at positions farther from the welding surface and thinner near the welding surface, creating local quality variations that optimize both heat resistance and welding performance in different regions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the thickness parameter of the surface layer from a constant value to a variable value that depends on the position along the longitudinal direction. This parameter change allows the surface layer to provide sufficient heat resistance while maintaining adequate thickness at the welding surface for strong joint formation.

Inventive Principle:

Principle #35Parameter changes

3Temperature

If resistance welding is performed on multilayer ground electrode, then heat resistance is improved, but surface layer spreads outwardly causing reduced joint strength

Engineering Contradiction:

Improveheat resistanceVSAvoidjoint strength

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The ground electrode is designed with non-uniform surface layer thickness, where the thickness varies along the longitudinal direction. Specifically, the surface layer is thicker at positions farther from the welding surface and thinner near the welding surface, creating local quality variations that optimize both heat resistance and welding performance in different regions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the thickness parameter of the surface layer from a constant value to a variable value that depends on the position along the longitudinal direction. This parameter change allows the surface layer to provide sufficient heat resistance while maintaining adequate thickness at the welding surface for strong joint formation.

Inventive Principle:

Principle #35Parameter changes

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 design enhances heat resistance and secures favorable joint strength between the ground electrode and the metal shell, preventing deformation during heating/cooling cycles and improving the durability of the spark plug.

Implementation Method 1

a core located inside the surface layer and having a higher thermal conductivity than that of the surface layer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

the ground electrode having a base end portion welded to the metal shell

Methodology Applied

Scientific EffectResistive heating: Joule Heating

Data Source

PatentUS9270087B2Spark plug with improved ground electrode joined to metal shell

Publication Date: 2016.02.23 NITERRA CO LTD

AI summary

A spark plug has a metal shell and a ground electrode joined at a base end portion thereof to the metal shell and includes a surface layer and a core higher in thermal conductivity than the surface layer. The core includes a first core member and a second core member. A weld region, where the ground electrode is joined to the metal shell, has an undulating shape. A distance between frontmost and rearmost ends of a part of the weld region in contact with the first core member in the axis direction is 0.15 mm or more.