Spark Plug Insulator Body Holder Prestress Design
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Solution Overview
Problem
Internal combustion engine spark plugs face issues with gas leakage due to peak pressures causing the insulator body to be pressed out, leading to premature failure and reduced service life, especially in gas engines where high torques are required for maintenance, which can result in spark plug breakage during replacement.
Innovation Solution
A spark plug design featuring an insulator body holder that applies prestress to the insulator body against the housing head, using materials with matched thermal expansion coefficients to maintain sealing at elevated temperatures, and incorporating vent holes in the tube housing to manage peak pressures, along with precise welding techniques like arc welding for enhanced sealing and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulator body is mounted between the housing head and tube housing with welding, then pressure resistance and sealing are improved, but the risk of breakage during maintenance increases due to high torques
Solution Approach 1:
The spark plug is divided into functionally independent parts: the tube housing for torque transfer and the insulator body holder for clamping and sealing. This segmentation allows each component to be optimized for its specific function, reducing stress concentration and breakage risk during maintenance.
Solution Approach 2:
The insulator body holder acts as an intermediary component between the tube housing and insulator body. It transfers the clamping force while allowing the tube housing to focus on torque transfer, thereby reducing the load on welding joints and preventing breakage during maintenance operations.
2Reliability
If the tube housing clamps the insulator body directly, then sealing is achieved, but the torque transfer capability is compromised
Solution Approach 1:
The clamping function is separated from the torque transfer function. The insulator body holder performs clamping to ensure sealing, while the tube housing with hexagon head performs torque transfer for screwing into the engine block. This functional separation allows both requirements to be met simultaneously.
Solution Approach 2:
Different parts of the spark plug are given different local qualities: the insulator body holder is designed for clamping and sealing with appropriate material properties, while the tube housing is designed for torque transfer with a hexagon head. Each component has optimized local properties for its specific function.
3Ease of manufacture
If conventional materials are used for the insulator body holder, then manufacturing is easier, but thermal expansion causes sealing failure at elevated temperatures
Solution Approach 1:
The thermal expansion coefficient is changed as a key parameter for the insulator body holder material. By selecting a material with a thermal expansion coefficient matched to the insulator body (αM−αK≤6×10⁻⁶/K), the design ensures that both components expand at similar rates during engine operation, maintaining sealing pressure and preventing gas leakage at elevated temperatures.
4Manufacturing precision
If high torques are applied during spark plug replacement, then thread engagement is improved, but the spark plug housing may break
Solution Approach 1:
The housing is segmented into the tube housing and insulator body holder, allowing the tube housing to bear the full torque load during installation and removal. This structural separation prevents stress concentration in the insulator body holder and reduces the risk of breakage during maintenance operations.
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
The design significantly increases the service life and operating reliability of spark plugs by preventing gas leakage and reducing the risk of breakage during maintenance, ensuring effective sealing and torque transfer without compromising structural integrity.
Implementation Method 1
an insulator body holder (7) that presses the insulator body (6) with a prestress against the housing head (2)
Implementation Method 2
the thermal expansion coefficient αM of the insulator body holder (7) is lower than the thermal expansion coefficient αK of the insulator body (6) or surpasses it by less than 1·10−6/K
Implementation Method 3
Precise welding techniques like arc welding for enhanced sealing and structural integrity
Data Source
AI summary
The invention relates to a spark plug for igniting a combustible gas mixture in an internal combustion engine, comprising an ignition electrode (4), an electrical supply line (5), to which the ignition electrode (4) is connected, an insulator body (6), through which the supply line (5) is passed, a housing head (2), which rests in sealing fashion on the insulator body (6) and bears an outer thread (3) for the purpose of screwing it into an internal combustion engine, a tube housing (9), which is fixed on the housing head (2), surrounds the insulator body (6) and has a hexagon head (13). The invention provides that the tube housing (9) surrounds an insulator body holder (7), which is welded to the housing head (2) and presses the insulator body (6) with a prestress against the housing head (2).