Spark Plug Cylindrical Part Mitigates Thermal Stress
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Solution Overview
Problem
The reduction in size and thickness of internal combustion engine components leads to increased thermal stress and mechanical load on spark plug mounting holes, potentially causing damage and reducing heat conduction efficiency, as smaller spark plugs with reduced thread diameters are used to accommodate design changes.
Innovation Solution
A spark plug design featuring a cylindrical part with no threads on the leading end, a tapered connection to the mounting part, and a flange part, which reduces close contact with the mounting hole, allowing for improved heat conduction and thermal stress mitigation by directing heat through the mounting part and tapered sections to the engine head.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the mounting hole diameter is reduced to increase design freedom, then design flexibility is improved, but thermal stress resistance deteriorates
Solution Approach 1:
The metal housing is segmented into multiple functional parts: a mounting part with threads for secure attachment, a cylindrical part that extends into the mounting hole without threads to reduce thermal stress concentration, and a flange part for sealing and structural support. This segmentation allows each part to perform its specific function optimally while resolving the contradiction between reduced mounting hole diameter and thermal stress resistance.
2Object-affected harmful factors
If no threads are formed on the leading end side to eliminate close contact, then thermal stress effects are mitigated, but heat conduction efficiency deteriorates
Solution Approach 1:
The cylindrical part acts as an intermediary element between the threaded mounting part and the combustion chamber environment. It provides a smooth, thread-free surface that reduces thermal stress concentration while still allowing effective heat conduction from the grounding electrode and metal housing to the engine head through its direct contact with the mounting hole walls.
3Volume of moving object
If thread diameter is reduced for smaller spark plugs, then compactness is improved, but mechanical strength deteriorates
Solution Approach 1:
Different parts of the metal housing are given different qualities and functions: the mounting part has threads for mechanical attachment, the cylindrical part has a smooth surface for stress reduction and heat conduction, and the flange part provides sealing and structural reinforcement. This local differentiation allows the spark plug to maintain compact size while ensuring adequate mechanical strength and thermal management.
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 enhances heat resistance and ignition performance by ensuring effective heat conduction while minimizing thermal stress on the engine head, thereby increasing the lifespan of the engine head and maintaining efficient combustion.
Implementation Method 1
the heat accompanying combustion of the air-fuel mixture in the combustion chamber that is taken up by the grounding electrode and metal housing mainly escapes via the threads
Data Source
AI summary
To provide a spark plug with improved heat resistance and an internal combustion engine in which that spark plug is mounted where there is good conduction of the heat near the opening on the combustion chamber side of the mounting hole for the spark plug provided in the engine and the effects of thermal stress occurring near that opening are mitigated. A cylindrical part without threads formed thereon is provided on the leading end side of a metal housing of a spark plug and the thermal stress applied to a mounting hole is mitigated by avoiding close contact with the mounting hole of an engine head. Furthermore, the spark plug has a mounting structure in which the leading end surface of the cylindrical part is disposed 1.55 mm or more to the base end side in a mounting hole in the direction of the axial line O with respect to the wall surface inside the combustion chamber. By this means, the metal housing does not easily take up the heat that accompanies combustion of the air-fuel mixture inside the combustion chamber at the cylindrical, part so there may be good heat conduction.