Spark Plug Insulating Member Projection for Lateral Spark Suppression
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Solution Overview
Problem
Conventional spark plugs with smaller diameters experience issues with lateral and inside sparks due to reduced insulating distances, leading to decreased normal spark gap discharge frequency and ignition problems.
Innovation Solution
A spark plug design with a rod-shaped center electrode, a cylindrical insulating member, and a metal shell, where the insulating member projects 2 mm or more from the metal shell, and specific dimensions are defined to ensure effective suppression of lateral and inside sparks, including a parallel displacement of 0.75 mm or more, and a spark gap ratio between 0.8 to 1.3 times the insulating member and metal shell gap, maintaining ignition performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the spark plug is reduced to accommodate smaller engine spaces, then the spark plug can be installed in engines with increased output and larger water jackets, but the insulating distance between the insulating member and metal shell is narrowed, leading to lateral sparks and inside sparks
Solution Approach 1:
The insulating member is designed with non-uniform thickness, featuring a front end portion with greater thickness (2 mm or more projection) and a rear end portion with lesser thickness. This local quality variation ensures adequate insulating distance at the critical front end where lateral sparks occur, while maintaining overall compact dimensions for engine installation.
Solution Approach 2:
Instead of uniformly increasing the insulating distance in all directions, the invention focuses the insulating distance enhancement specifically at the front end portion along the axial direction, where the insulating member projects 2 mm or more from the metal shell. This dimensional focus resolves the contradiction by providing localized insulation where needed while maintaining compact overall size.
2Reliability
If the insulating distance is increased to prevent lateral sparks and inside sparks, then spark discharge reliability improves, but the spark plug diameter increases, reducing adaptability to engines with limited installation space
Solution Approach 1:
The insulating member features localized thickening at the front end portion with a projection of 2 mm or more, concentrating the insulating function where lateral sparks most frequently occur. This allows adequate insulating distance for reliable spark discharge while keeping the overall spark plug diameter compact for engine installation.
Solution Approach 2:
The insulating member is segmented into different thickness zones: a front end portion with greater thickness (2 mm or more projection) for lateral spark prevention, and a rear end portion with lesser thickness. This segmentation allows the spark plug to provide reliable insulation where needed while maintaining compact overall dimensions.
3Reliability
If the front end portion of the insulating member is enlarged to prevent lateral sparks, then insulation performance improves, but the complexity of manufacturing increases due to precise volume requirements
Solution Approach 1:
The invention specifies a clear quantitative parameter for the front end portion: a projection of 2 mm or more from the metal shell front end face. This parameter change provides a straightforward manufacturing target that ensures lateral spark suppression while maintaining ease of production through a well-defined geometric feature.
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 suppresses lateral and inside sparks, ensuring ignition performance comparable to standard-sized spark plugs while maintaining strength and preventing carbon deposits from causing preignition.
Implementation Method 1
an insulating distance between an insulating member and a metal shell is narrowed... a lateral spark in which a spark occurs from the center electrode to the metal shell via an insulator
Implementation Method 2
a ground electrode which is joined to a front end face of the metal shell and which forms a spark gap with a front end portion of the center electrode... The fuel mixture is ignited by a spark discharge occurring in the spark gap
Data Source
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AI summary
A spark plug is such that a front end portion of an insulating member projects 2 mm or larger from a front end face of a metal shell and a volume of a portion of the insulating member which lies within a range from a front end of the insulating member to a position lying 1 mm towards a rear end side from the front end is 11 mm3 or smaller. When assuming that a corner portion where a front end face of the insulating member intersects a side surface of an axial hole is referred to as a position PA, a position on a center electrode where a straight-line distance from the position PA to the center electrode within the axial hole is referred to as a position PB, a position where the insulating member first contacts the metal shell from the front end face of the insulating element along a surface of the insulating element is referred to as a position PC, and a position on the insulating element where a straight line BC which connects the position PB with the position PC contacts the surface of the insulating member when the straight line BC is displaced parallel towards an outside of an axis is referred to as a position PD, a parallel displacement amount E by which the straight line BC is displaced parallel until it contacts the position PD is 0.75 mm or larger. According to the spark plug configured in this way, even though the spark plug is shaped small, the occurrence of lateral spark and inside spark can be suppressed effectively.