Spark Plug Cap Sealing via Inner Surface Inversion
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Solution Overview
Problem
The existing plug cap designs for spark plugs suffer from water ingress due to gaps between the terminal body and the rubber member, leading to current leakage, especially with increased voltage requirements in modern internal combustion engines.
Innovation Solution
The design incorporates a cylindrical rubber member with annular protrusions that come into press contact with the terminal body's smooth inner surface, reducing clearance and preventing water ingress, along with a longer inner cylindrical portion to enhance sealing and a reduced-diameter portion at the leading end to minimize water accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a terminal body is formed by molding using a plurality of split molds, then the terminal body can be formed with complex outer shapes, but a parting line is formed on the outer peripheral surface causing gaps between the terminal body and rubber member
Solution Approach 1:
Instead of trying to eliminate the parting line from the outer surface, the invention inverts the approach by making the inner peripheral surface smooth and free of parting lines, while allowing the outer surface to have the parting line from split mold molding. The sealing function is achieved through the smooth inner surface that prevents water ingress, rather than relying on the outer surface appearance.
Solution Approach 2:
The invention applies different surface quality requirements to different locations: the outer peripheral surface can have parting lines from split mold molding, but the inner peripheral surface is specifically designed to be smooth without parting lines. This local differentiation allows the inner surface to provide reliable sealing while the outer surface maintains manufacturing feasibility.
2Ease of manufacture
If the inner peripheral surface of the terminal body is a smooth surface formed by split mold molding, then molding is simplified, but gaps occur between the terminal body and rubber member allowing water to enter
Solution Approach 1:
The invention applies different surface quality requirements to different locations: the outer peripheral surface can have parting lines from split mold molding, but the inner peripheral surface is specifically designed to be smooth without parting lines. This local differentiation allows the inner surface to provide reliable sealing while the outer surface maintains manufacturing feasibility.
Solution Approach 2:
Instead of trying to eliminate the parting line from the outer surface, the invention inverts the approach by making the inner peripheral surface smooth and free of parting lines, while allowing the outer surface to have the parting line from split mold molding. The sealing function is achieved through the smooth inner surface that prevents water ingress, rather than relying on the outer surface appearance.
3Ease of operation
If the gap between the terminal body and rubber member is not sufficiently sealed, then assembly is easier, but water enters and causes current leakage
Solution Approach 1:
The invention applies different surface quality requirements to different locations: the outer peripheral surface can have parting lines from split mold molding, but the inner peripheral surface is specifically designed to be smooth without parting lines. This local differentiation allows the inner surface to provide reliable sealing while the outer surface maintains manufacturing feasibility.
Solution Approach 2:
Instead of trying to eliminate the parting line from the outer surface, the invention inverts the approach by making the inner peripheral surface smooth and free of parting lines, while allowing the outer surface to have the parting line from split mold molding. The sealing function is achieved through the smooth inner surface that prevents water ingress, rather than relying on the outer surface appearance.
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 configuration effectively prevents water from entering the spark plug or plug cord, ensuring reliable electrical connection and preventing current leakage, even under high voltage conditions.
Implementation Method 1
the inner cylindrical portion includes an annular protrusion that comes into contact with the inner peripheral surface of the terminal body
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
One object of the invention is to provide a plug cap that more reliably prevents the leakage of current by suppressing the ingress of water from a gap between a terminal body and a rubber member. A plug cap 1 includes an electrical connection portion 5 that electrically connects a spark plug to a plug cord, a terminal body 2 that is provided on the outer periphery of the electrical connection portion 5, and a cylindrical rubber member 3 which is mounted on at least one of one end portion and the other end portion of the terminal body 2 and into which the spark plug or the like is inserted. The terminal body 2 includes a one end-side insertion portion 41 which is formed at one end of the terminal body and into which the spark plug is inserted and the other end-side insertion portion 42 which is formed at the other end of the terminal body and into which the plug cord is inserted. The rubber member 3 includes an inner cylindrical portion 31 that is inserted into the one end-side insertion portion 41 or the other end-side insertion portion 42, and a cylindrical outer cylindrical portion 32 that is positioned close to the outer periphery of the inner cylindrical portion 31. The inner cylindrical portion 31 includes annular protrusions 35 that come into contact with the inner peripheral surface of the terminal body 2.