Spark Plug Laser Weld Bead Protrusion Positioning
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Solution Overview
Problem
Abnormal discharge occurs frequently in spark plugs with a noble metal tip welded to a center electrode base metal, leading to deterioration in ignition performance due to irregularities in the weld bead and metal oxide films, causing electric field concentration and electron emission.
Innovation Solution
The spark plug design involves laser welding the noble metal tip to the center electrode base metal in excess of full circumference, ensuring the protrusion formed at the end of the weld bead is positioned circumferentially away from the straight line connecting the center of the noble metal tip and the ground electrode, reducing electric field concentration and abnormal discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If laser welding is performed to join the noble metal tip to the center electrode base metal, then welding strength is improved, but abnormal discharge occurs due to weld bead irregularities and metal oxide films
Solution Approach 1:
The patent removes the harmful weld bead protrusion from the critical discharge path by precisely controlling the welding parameters and bead geometry, extracting the harmful element while preserving the beneficial welding strength
Solution Approach 2:
The patent changes the welding parameters (laser power, welding speed, focal position) to control the weld bead morphology, specifically reducing the protrusion height and metal oxide film formation to prevent abnormal discharge while maintaining adequate welding strength
2Volume of moving object
If the spark plug diameter is reduced, then compactness is improved, but the lateral gap becomes insufficient leading to abnormal discharge
Solution Approach 1:
The patent changes the geometric parameters of the weld bead (protrusion height, lateral dimension) to optimize the lateral gap distribution, ensuring adequate clearance from the ground electrode even in compact spark plug designs
3Area of stationary object
If welding is performed in excess of full circumference, then welding coverage is improved, but weld bead protrusion increases causing electric field concentration
Solution Approach 1:
The patent precisely controls the welding parameters to achieve optimal weld bead geometry, maintaining adequate welding coverage while minimizing the protrusion height that causes electric field concentration and abnormal discharge
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 effectively reduces abnormal discharge and enhances regular spark gap ignition performance by positioning the weld bead protrusion away from the center of the ground electrode, improving fuel ignition efficiency.
Implementation Method 1
laser welding is performed in the circumferential direction along the circumference of a joint surface between the center electrode base metal and the noble metal tip
Implementation Method 2
the surface of the bead is irregular; thus, an electric field is apt to concentrate thereon
Data Source
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AI summary
[Objective] To reduce or prevent the generation of abnormal discharge across a gap other than the regular gap between a center electrode and a ground electrode in a spark plug which has the center electrode formed by performing laser welding along the circumference of a joint surface between a center electrode base metal and a noble metal tip in excess of full circumference. [Means for Solution] When G represents a spark gap and A represents a shortest gap between a laser weld bead and a line drawn in parallel with the axis X of a metallic shell along the inner surface of a proximal end portion of a ground electrode which faces a center electrode, G and A establish a dimensional relation A ≤ 3G. As viewed in the direction of the axis X from the front end of the noble metal tip 1, a straight line S1 which connects the center of the noble metal tip 1 and the circumferential center of a proximal end 52 of the ground electrode 51 and a straight line S2 which connects the center of the noble metal tip 1 and a vertex 8 of a protrusion 7 formed at a final end portion 6e of a bead 6 formed by circumferential laser welding form an angle θ of 45 degrees. Since the protrusion 7 of the bead is the angle θ away from the ground electrode 51, an abnormal discharge is unlikely to be generated.