Spark Plug Melt Portion Geometry for Crack Suppression
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Solution Overview
Problem
The increased temperature and thermal stress in high compression and supercharged internal combustion engines lead to cracks and oxide scale growth at the interface between the electrode tip and the melt portion of spark plugs, reducing their service life.
Innovation Solution
A spark plug design where the electrode tip is joined to the electrode base material via a melt portion, with specific geometric constraints that increase the amount of tip material in the melt portion, reducing thermal expansion differences and suppressing crack and oxide scale growth, achieved by laser welding with controlled application of the laser beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the electrode tip is joined to the electrode base material via a melt portion formed by welding, then the electrical conductivity and structural integrity are improved, but the difference in thermal expansion coefficients between the tip and melt portion causes cracks to occur under high temperature conditions
Solution Approach 1:
The patent applies parameter changes by controlling the geometric parameters of the melt portion (specifically the ratios C1/D1 and C2/D2) to optimize the composition and distribution of tip material within the melt portion. This ensures the melt portion has thermal expansion properties intermediate between the tip and base material, reducing thermal stress and preventing cracks under high temperature conditions while maintaining structural integrity
Solution Approach 2:
The patent creates a composite structure where the melt portion contains a controlled mixture of tip material and base material. By ensuring the ratios C1/D1 < 1.0 and C2/D2 < 1.0, the melt portion becomes a composite with intermediate thermal expansion characteristics, effectively bridging the thermal expansion mismatch between the noble metal tip and the base material
2Reliability
If the amount of tip material in the melt portion is increased, then the thermal expansion matching is improved, but the welding process complexity increases
Solution Approach 1:
The patent simplifies the welding process control by establishing clear numerical criteria (C1/D1 < 1.0 and C2/D2 < 1.0) that define the desired melt portion geometry. These parameter thresholds provide straightforward guidance for controlling laser welding conditions, making it easier to achieve the optimal mix of tip material in the melt portion without excessive process complexity
3Duration of action of stationary object
If the service life of the spark plug is extended, then the durability is improved, but oxide scale growth occurs at the interface between the tip and melt portion due to thermal stress
Solution Approach 1:
The patent addresses oxide scale growth by controlling the geometric parameters of the melt portion to reduce thermal stress concentration at the tip-interface region. By ensuring C1/D1 < 1.0 and C2/D2 < 1.0, the melt portion geometry is optimized to distribute thermal stresses more uniformly, preventing the conditions that lead to oxide scale formation and extending service life
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 the thermal expansion matching between the tip and the melt portion, reducing the likelihood of cracks and oxide scale growth, thereby improving the service life and durability of the spark plug.
Implementation Method 1
the electrode tip is joined to an electrode base material via a melt portion which is formed by a portion of the electrode tip and a portion of the electrode base material being melted together in welding
Implementation Method 2
a melt portion which is formed by a portion of the electrode tip and a portion of the electrode base material being melted together
Implementation Method 3
due to the difference between the thermal expansion coefficient of the electrode tip and the thermal expansion coefficient of the melt portion, a crack is likely to occur
Data Source
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AI summary
[Objective] To suppress occurrence and growth of a crack and oxide scale between an electrode tip and a melt portion. [Means for Solution] Pa1: a point farthest from an end surface 453 in an axial direction, on a melt portion 455 at one side with respect to an axis CA. Pa2: a similar point at the other side. Pa3: a point farthest from the axis CA, on the melt portion 455 at the one side with respect to the axis CA. Pa4: a similar point at the other side. Pa5: a point closest to the end surface 453 in the axial direction, on the melt portion 455 at the one side with respect to the axis CA. Pa6: a similar point at the other side. RL: a reference line which is a straight line passing through the point Pa3 and the point Pa4. C1: a distance between the reference line RL and the point Pa5. D1: a distance between the reference line RL and the point Pa1. C2: a distance between the reference line RL and the point Pa6. D2: a distance between the reference line RL and the point Pa2. The spark plug (10) satisfies C1 ≥ D1 and C2 ≥ D2.