Spark Plug Ground Electrode Flat Region Design
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Solution Overview
Problem
High-compression-ratio engines with direct fuel injection are prone to grain defect formation in ground electrodes due to thermal shock, leading to variations in engine ignition performance and potential preignition issues.
Innovation Solution
A spark plug design featuring a ground electrode with a flat region on its outer peripheral surface and a convex curved region, satisfying specific dimensional conditions, to prevent grain defects and ensure consistent ignition performance by distributing thermal shock vectors evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cylindrical ground electrode is used to allow air-fuel mixture to flow easily around it, then ignition performance is improved, but the electrode becomes susceptible to grain defect formation under direct fuel injection
Solution Approach 1:
The ground electrode is designed with different surface characteristics at different locations: the front end portion has a flat outer peripheral surface to prevent grain defects when fuel directly impacts, while other portions maintain convex curved surfaces to facilitate air-fuel mixture flow. This local differentiation allows each region to perform its specific function optimally.
Solution Approach 2:
The ground electrode's outer peripheral surface is segmented into distinct regions: a flat region at the front end and convex curved regions in other areas. This segmentation allows the electrode to simultaneously achieve flow facilitation in most areas while providing protection at the vulnerable front end where fuel direct injection occurs.
2Productivity
If the ground electrode is positioned to face the incoming air-fuel mixture, then ignition efficiency is improved, but the electrode is exposed to thermal shock from direct fuel contact
Solution Approach 1:
The front end portion of the ground electrode is specifically designed with a flat outer peripheral surface that is resistant to grain defect formation, allowing the electrode to maintain its optimal position for ignition efficiency while protecting the critical front end area from thermal shock caused by direct fuel contact.
3Ease of manufacture
If the ground electrode has a simple cylindrical shape, then manufacturing is easier, but it cannot prevent grain defects under direct fuel injection conditions
Solution Approach 1:
Rather than changing the overall cylindrical shape, the invention applies a localized flat surface treatment only to the front end portion's outer peripheral surface. This maintains the simplicity of the overall electrode structure for easy manufacturing while adding the necessary flat region to prevent grain defects in the critical area exposed to direct fuel injection.
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 effectively prevents grain defect formation and maintains engine ignition performance across varying fuel injection angles and engine conditions, ensuring reliable operation and reduced preignition risks.
Implementation Method 1
the ground electrode gets suddenly cooled by the fuel and thus may suffer a grain defect formation phenomenon (also called a 'wormhole phenomenon') in which some crystal grains fall out of their grain boundaries
Data Source
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AI summary
A spark plug includes a ground electrode formed with a flat region and a convex curved region on an outer peripheral surface thereof. The flat region is located on a front end of the ground electrode and has a length of 0.2 mm or more from a front end face of the ground electrode in a longitudinal direction of the ground electrode. The ground electrode satisfies the following dimensional condition (1) with respect to first and second cross sections of the ground electrode taken through the convex curved region and the flat region in directions perpendicular to the longitudinal direction of the ground electrode, 0.950≤S2/L2/S1/L1≤0.995 where S 1 is the area of the first cross section; L 1 is the perimeter of the first cross section; S2 is the area of the second cross section; and L2 is the perimeter of the second cross section.