Spark Plug Insulator Geometry for Thermal Shock Resistance
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Solution Overview
Problem
High compression and supercharging engines require higher discharge voltages, leading to potential spark penetration through the insulator, and thickening the insulator tip to improve dielectric strength results in thermal shock issues, particularly in direct injection engines where the insulator is prone to breakage due to rapid cooling.
Innovation Solution
A spark plug design with a cylindrical insulator having a thickness of 1.07 mm or more at the tip to prevent spark penetration and a volume of 3.9 mm^3 or less to reduce thermal shock stress, along with a gap configuration and curved tip design to enhance thermal shock resistance and prevent abnormal discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tip of the insulator is thickened to improve dielectric strength and prevent spark penetration, then the prevention of spark penetration is improved, but the insulator is more likely to breakage due to thermal shock
Solution Approach 1:
The insulator is designed with different thickness characteristics in different regions: the tip portion has a controlled thickness to reduce thermal shock, while the side surface thickness is optimized to prevent spark penetration. This local differentiation allows each region to perform its specific function optimally without compromising the other.
Solution Approach 2:
The invention specifies precise parameter ranges for the insulator geometry: the distance L from the metal shell tip to insulator tip is 0.5mm or more, the side surface thickness C is 1.07mm or more, and the volume V of the tip portion is 3.9mm³ or less. These parameter changes optimize both dielectric strength and thermal shock resistance.
2Temperature
If the insulator is rapidly cooled by direct fuel injection to improve cooling efficiency, then the cooling efficiency is improved, but the breakage of the insulator due to thermal shock is increased
Solution Approach 1:
The insulator tip portion is designed with a specific volume (3.9mm³ or less) to minimize thermal stress concentration in the region most susceptible to rapid cooling from direct fuel injection, while maintaining sufficient overall insulator thickness for dielectric strength.
Solution Approach 2:
The insulator geometry is pre-designed to withstand thermal shock before it occurs. By optimizing the tip portion volume and side surface thickness beforehand, the insulator is prepared to resist the thermal shock that will result from rapid fuel injection cooling, preventing breakage before it happens.
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 effectively prevents spark penetration and reduces the risk of insulator breakage due to thermal shock, ensuring stable ignition and prolonged lifespan of the spark plug.
Implementation Method 1
the thickness C of a tip portion of the insulator 2 is 1.07 mm or more... ensure the prevention of the spark penetration in the insulator
Implementation Method 2
a large thermal shock occurs at the tip portion of the insulator at a heating and cooling, which is likely to cause a breakage of the insulator
Data Source
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AI summary
A spark plug 1 that suppresses a breakage of an insulator due to the thermal shock while ensuring the prevention of a spark penetration in the insulator has a metal shell 3 and a cylindrical ceramic insulator 2 disposed in an inner circumference of the metal shell 3, having an axial hole 4 extending in an axial line CL direction, and having a tip located in more tip side than a tip of the metal shell 3, and a distance along the axial line CL1 from the tip of the metal shell 3 to the tip of the ceramic insulator 2 is 0.5 mm or more. It satisfies C ≥ 1.07 mm and V ≤ 3.9 mm3, where C is a thickness of the ceramic insulator in a cross section passing an inner circumference surface tip 3A of the metal shell 3 and orthogonal to the axial line CL1 and V is a volume of the ceramic insulator 2 within a range of 0.5 mm from the tip of the ceramic insulator 2 to a rear end side in the axial line CL1 direction.