Eccentric Spark Plug Insulator Prevents Lateral Discharge
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Solution Overview
Problem
Conventional spark plugs experience lateral sparking due to increased electric field strength and reduced clearance between the insulator and metal shell, especially in miniaturized designs, leading to smoldering and carbon adherence issues.
Innovation Solution
The spark plug design features an eccentric arrangement of the metal shell and insulator axial lines, with a relationship A>B between specific distances, and a nominal diameter of the screw portion ≤ M12, to prevent lateral sparking by increasing the distance between the ground electrode and the insulator, and incorporating chamfered portions to reduce electric field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the clearance between the insulator and metal shell is decreased to miniaturize the spark plug, then the size of the spark plug is reduced, but lateral sparking occurs more easily due to increased electric field strength
Solution Approach 1:
The patent applies asymmetry by positioning the insulator eccentrically within the metal shell, creating an asymmetric clearance distribution. The minimum clearance is specifically increased on the ground electrode side where lateral sparking is most likely to occur, while maintaining smaller clearances in other areas to minimize overall size. This asymmetric design allows the spark plug to be miniaturized while preventing lateral sparking at the critical location.
2Volume of moving object
If the dimensions of individual parts are scaled down, then the spark plug is miniaturized, but the electric field strength around the ground electrode increases causing spark discharge from the insulator surface
Solution Approach 1:
The patent applies local quality by differentiating the clearance characteristics in different regions around the insulator. Specifically, the minimum clearance is increased in the region near the ground electrode where the electric field strength is highest and lateral sparking is most problematic. Other regions can maintain smaller clearances, allowing overall miniaturization while locally addressing the harmful electric field effect where it matters most.
3Reliability
If the clearance between insulator and metal shell is increased to prevent lateral sparking, then lateral sparking is prevented, but the spark plug size increases reducing design freedom
Solution Approach 1:
The patent resolves this contradiction by using asymmetric clearance distribution rather than uniformly increasing clearance in all directions. The insulator is positioned eccentrically so that the minimum clearance is specifically increased on the ground electrode side to prevent lateral sparking, while clearances in other directions remain smaller. This allows reliable prevention of lateral sparking without proportionally increasing the overall spark plug size, thereby maintaining design freedom.
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 prevents lateral sparking by maintaining a sufficient distance between the insulator and ground electrode, even in smoldered states, while reducing electric field concentration and enhancing manufacturing yield.
Implementation Method 1
an insulator (10) which has an axial hole (12) extending in an axial direction (O) of the center electrode (20) and holding the center electrode (20) in the axial hole (12)
Implementation Method 2
When a spark discharge is caused between the center electrode and the ground electrode, an air-fuel mixture between the two electrodes is ignited and a flame nucleus is formed
Data Source
AI summary
A spark plug including: a center electrode (20); an insulator (10) having an axial hole (12) extending in an axial direction of the center electrode (20) and holding the center electrode (20) in the axial hole (12); a cylindrical metal shell (50) surrounding the insulator (10) and holding the insulator (10); and a ground electrode (30) having first and second end portions, an end face (35) of one end portion (32) being joined to a tip face (57) of the metal shell (50) and which is bent so that the other end portion (31) is opposed to the center electrode (20). An axial line (P) of the metal shell (50) and an axial line (O) of the insulator (10) deviate from one another so that a relationship A>B is satisfied for distances A and B as defined herein.