Spark Plug Terminal Fixing Strength via Hardness Control
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Solution Overview
Problem
Conventional spark plugs with reduced insulator diameters face challenges in maintaining load life performance and fixing strength of the metallic terminal, often resulting in insulator breakage during manufacturing, leading to defective products.
Innovation Solution
A spark plug design featuring a metallic terminal with specific diameter and hardness ranges, along with an intermediate diameter portion and connecting portion configurations, to enhance adhesion and prevent deformation, ensuring effective press-insertion and reduced defective incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the insulator is decreased to reduce the size of the spark plug, then the size of the spark plug is reduced, but the load life performance and fixing strength of the metallic terminal deteriorate
Solution Approach 1:
The metallic terminal is divided into two constituent portions: a first constituent portion exposed from the axial hole and a second constituent portion accommodated in the axial hole. This segmentation allows the second portion to be press-fit into the insulator with optimized dimensions, providing sufficient fixing strength even when the insulator diameter is reduced.
Solution Approach 2:
The second constituent portion of the metallic terminal is given specific local properties: a diameter within 0.8 to 1.2 times the insulator diameter, and Vickers hardness of 100-430 Hv. These localized quality specifications ensure optimal press-fit strength and adhesion to the insulator while maintaining overall compactness.
2Volume of moving object
If the diameter of the insulator is decreased to reduce the size of the spark plug, then the size of the spark plug is reduced, but the insulator breaks during insertion of the metallic terminal, increasing defective incidence
Solution Approach 1:
The Vickers hardness of the second constituent portion is controlled within 100-430 Hv, and its diameter is set to 0.8-1.2 times the insulator diameter. These parameter optimizations ensure the terminal is hard enough to maintain structural integrity but not so hard as to cause insulator breakage during press-fit insertion, thereby reducing defective incidence.
3Volume of moving object
If the diameter of the insulator is decreased to reduce the size of the spark plug, then the size of the spark plug is reduced, but the load life performance deteriorates
Solution Approach 1:
The second constituent portion of the metallic terminal is pre-designed with optimized dimensions and hardness properties before assembly. This preliminary preparation ensures that when the terminal is press-fit into the insulator, it achieves optimal adhesion and mechanical strength, resulting in excellent load life performance even in compact spark plugs.
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3~4
AI summary
An object of the present invention is to provide a spark plug which is excellent in load life performance and fixing strength of a metallic terminal to an insulator, and which reduces the incidence of defectives produced as a result of breakage of the insulator when the metallic terminal is inserted into the axial hole of the insulator. The spark plug of the present invention is characterized in that the distance ((B-A)/2) between the forward end portion of the metallic terminal and the wall surface of an intermediate diameter portion of the axial hole of the insulator falls within a range of 0.0 2 mm to 0.2 mm, the shrinkage amount (D-C) of a connecting portion falls within a range of 6 mm to 27 mm, and the Vickers hardness of the metallic terminal at ordinary temperature falls within a range of 100 Hv to 430 Hv.