Spark Plug Ground Electrode Flexed Tip Design
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Solution Overview
Problem
Existing spark plugs with straight ground electrodes suffer from reduced ignitability due to the ground electrode's proximity to the center electrode and inadequate stress distribution, leading to potential breakage under engine vibrations.
Innovation Solution
A spark plug design featuring a ground electrode with a flexed portion, a tip projecting from the front end face and inner circumference-side surface, and an inner layer with higher thermal conductivity than the outer layer, ensuring a controlled spark discharge gap and reduced stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ground electrode is made straight to eliminate flexed portions, then breakage resistance is improved, but the ground electrode comes closer to the center electrode reducing spark growth space and ignitability
Solution Approach 1:
The ground electrode is designed with a flexed portion that curves toward the axis side, creating a specific spatial relationship with the center electrode. This curvature allows the front end portion to maintain adequate distance from the center electrode for spark growth, while the flexed portion position is optimized to minimize stress concentration and prevent breakage during engine operation.
2Reliability
If the ground electrode is bent to maintain distance from center electrode, then ignitability is improved, but stress concentration at flexed portion increases leading to breakage
Solution Approach 1:
The ground electrode structure is optimized with specific geometric parameters: the flexed portion is positioned at a specific location along the electrode length, and the ratio L/X is controlled to be 1.28 or less. This local geometric optimization ensures that stress concentration at the flexed portion is minimized while maintaining adequate spacing from the center electrode for proper spark discharge and ignitability.
3Manufacturing precision
If the tip projects more from the ground electrode, then spark discharge gap control is improved, but stress on the ground electrode increases under vibration
Solution Approach 1:
The design optimizes the projection length X of the tip from the ground electrode front end face and controls the L/X ratio to be 1.28 or less. This parameter optimization balances two requirements: sufficient tip projection for precise spark discharge gap control and minimal stress concentration under vibrational loads during engine operation, thereby preventing breakage.
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 enhances ignitability by maintaining a suitable spark discharge gap while reducing stress and overheating, thereby preventing breakage and improving the ground electrode's breakage resistance.
Implementation Method 1
the ground electrode further includes an outer layer and an inner layer. The inner layer is disposed inside of the outer layer, and is made of a metal with higher thermal conductivity than a thermal conductivity of the outer layer.
Data Source
Figure 1
Figure 2~3
Figure 4(a)~5
AI summary
Provided is a spark plug that achieves superior ignitability and further reliably prevents breakage of a ground electrode or the like. A spark plug 1 includes a center electrode 5, a ground electrode 27, and a ground electrode side tip 32. The tip 32 partially projects from a front end face 27F and an inner circumference-side side surface 27S of the ground electrode 27. The ground electrode 27 has a center CE of the front end face 27F. The center CE is located at a front end side in a direction of the axis CL1 with respect to a front end of the center electrode 5. L/X ≤ 1.28 is satisfied, where L (mm) represents a length of the ground electrode 27 along a central axis CL2 of the ground electrode 27 and X (mm) represents a projection length of the ground electrode 27 relative to a metallic shell 3. 8.4 ≤ (S1/S2)/A is satisfied, where S1 (mm2) represents a cross section area of a portion at a base end side with respect to a portion where the tip 32 is joined to the ground electrode 27 in cross section perpendicular to a central axis CL2, S2 (mm2) represents a cross section area of the tip 32 in cross section perpendicular to a projection direction of the tip 32, and A (mm) represents a projection length of the tip 32 relative to the front end face 27F.