Spark Plug Weld Part Geometry for Joint Strength
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Solution Overview
Problem
The existing spark plug designs face issues with joint strength between the electrode tip and body due to laser welding, which can lead to welding drop, affecting ignition and durability.
Innovation Solution
A spark plug design featuring a weld part with orthogonal projections and specific directional arrangements, where the length of the second line segment perpendicular to the first line segment connecting peaks of projecting portions is greater than the first line segment, enhancing joint strength and preventing welding drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the entire contact surfaces of the electrode tip and electrode body are joined by laser welding, then the joint strength is enhanced, but the amount of melted material increases causing the electrode tip to tilt or sink and forming welding drop
Solution Approach 1:
The patent applies local quality by creating a weld part with non-uniform thickness distribution. The weld part has a first thickness in a first region and a second thickness in a second region, where the thickness ratio is controlled within 0.5-2.0. This localized thickness variation allows different regions of the weld to serve different functions: one region provides sufficient melting for strong bonding while the other region controls material flow to prevent welding drop, thus resolving the contradiction between joint strength and welding precision.
2Strength
If the entire contact surfaces are joined by laser welding, then the joint strength is enhanced, but welding drop occurs which causes failure of ignition and decay of durability
Solution Approach 1:
The controlled thickness distribution of the weld part creates local quality differences that prevent welding drop. By having a thickness ratio between 0.5-2.0 between the first and second regions, the weld structure locally manages material flow during laser welding, preventing excessive material accumulation that would form welding drop. This ensures ignition reliability while maintaining joint strength.
3Area of stationary object
If the weld part has large amount of melted material, then the contact area increases, but the electrode tip tilts or sinks during welding
Solution Approach 1:
The patent resolves this contradiction by creating local quality variation in the weld part thickness. The first region has sufficient thickness to provide large contact area for strong bonding, while the second region has controlled thickness to prevent excessive material accumulation. The thickness ratio control (0.5-2.0) ensures that one region can accommodate the melted material without causing electrode tip tilting or sinking, thus maintaining stability while achieving adequate contact area.
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 configuration increases the contact area and strength of the joint between the electrode tip and body, reducing the occurrence of welding drop and improving the durability and heat dissipation of the spark plug.
Implementation Method 1
a process for joining the electrode tip to an electrode body by laser welding, while forming a weld part between their contact surfaces
Data Source
AI summary
A spark plug includes a ground electrode and a center electrode, at least one of which includes an electrode body, an electrode tip, and a weld part formed therebetween. The weld part has an orthogonal projection on a virtual plane perpendicular to a layering direction of the electrode body and the electrode tip. The orthogonal projection includes projecting portions extending in a specific direction. The weld part satisfies a condition that a first line segment is shorter than a second line segment, wherein: the first line segment is a virtual line segment connecting peaks of adjacent two projecting portions; and the second line segment is a virtual line segment that is perpendicular to the first line segment and connects the first line segment to an outer periphery of the weld part at a point farthest from the first line segment.