Spark Plug Shell Opening Geometry to Prevent Thread Biting
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Solution Overview
Problem
Existing spark plugs tend to have screw threads that incline forward when attached to internal combustion engines, leading to potential biting into the threaded holes during attachment or removal, which can cause installation and removal issues.
Innovation Solution
A spark plug design featuring a metallic shell with a sloping opening in the attachment screw portion, where the angle between the sloping portion and the tangent to the outer surface is 90 degrees or greater, preventing the screw thread from inclining forward and reducing the likelihood of biting into the engine's threaded hole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the opening is formed with a machined surface orthogonal to the center axis of the metallic shell, then the manufacturing process is simple, but the screw thread inclines forward and may bite into the threaded hole of the internal combustion engine
Solution Approach 1:
The patent changes the geometric parameter of the opening from an orthogonal configuration to a sloping configuration. Specifically, the machined surface of the opening is inclined relative to the center axis of the metallic shell, with the slope angle being greater than or equal to the lead angle of the screw thread. This parameter change ensures that the screw thread does not incline forward during attachment, preventing biting into the threaded hole of the internal combustion engine while maintaining manufacturing simplicity.
2Ease of operation
If the screw thread is provided on the outer circumferential surface of the tubular portion, then the spark plug can be attached to the internal combustion engine, but the screw thread may bite into the threaded hole during attachment or removal
Solution Approach 1:
The patent modifies the geometric parameter of the opening's machined surface to create a sloping configuration. The slope angle of the opening is designed to be greater than or equal to the lead angle of the screw thread. This ensures that during attachment and removal operations, the screw thread does not incline forward and bite into the threaded hole of the internal combustion engine, thereby eliminating the harmful biting effect while maintaining ease of operation.
Data Source
AI summary
A spark plug includes a metallic shell member having a tubular portion extending along an axial line of the metallic shell, a center electrode disposed inside the tubular portion and extending along the axial line, and a ground electrode which is inserted into an opening 5 provided in the tubular portion and forms a gap between the center electrode and a forward end portion of the round electrode in a direction in which the round electrode extends. A screw thread is provided on an outer circumferential surface of the tubular portion. The opening has a sloping portion which tapers from the outer circumferential surface of the tubular portion toward an inner circumferential surface side. An angle formed between the 10 sloping portion of the opening and a tangent line to the outer circumferential surface is 90 degrees or greater.