Spark Plug Center Electrode Sloping Insulator Flashover
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Solution Overview
Problem
Existing spark plugs face issues with flashover resistance and thermal resistance, leading to potential pre-ignition due to overheating, as conventional methods to extend the creeping distance often compromise thermal resistance.
Innovation Solution
A spark plug design featuring a center electrode with a multi-layer construction, including an outer layer and an inner layer with improved thermal conductivity, where the front end face of the insulator slopes towards the rear and the boundary between the shoulder and main body portions is configured to maximize creeping distance and thermal resistance, with specific geometric angles and clearances to prevent direct discharges and enhance ignitability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the creeping distance is extended by conventional methods (longer leg portion, larger outside diameter, annular grooves, or steps), then flashover resistance is improved, but thermal resistance becomes insufficient and the front end of the insulator becomes overheated
Solution Approach 1:
The invention introduces a new geometric dimension by forming a front end face that slopes towards the rear end side at a specific angle (30° to 60°). This angular configuration extends the creeping distance in a directional manner without increasing the overall length or diameter of the insulator, thereby improving flashover resistance while preserving thermal conduction pathways.
Solution Approach 2:
The invention applies different functional properties to different regions of the insulator. The front end portion is configured with a specific sloping angle to optimize flashover resistance, while the main body maintains its thermal conduction properties. This localized geometric modification allows the front end to provide enhanced flashover protection without compromising the overall thermal management of the spark plug.
2Reliability
If the front end of the insulator is made to project further forward to extend creeping distance, then flashover resistance is improved, but the volume of the front end portion is reduced and thermal resistance decreases
Solution Approach 1:
Instead of extending the insulator in the axial direction (which would reduce front end volume), the invention utilizes the radial-angular dimension by creating a sloping front end face. This angular configuration (30° to 60°) effectively increases the creeping path length without sacrificing the volumetric heat conduction capacity of the front end portion.
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 increases flashover resistance and thermal resistance, preventing abnormal discharges and pre-ignition by extending the creeping distance while maintaining sufficient thermal conductivity and structural integrity.
Implementation Method 1
an inner layer which is provided in an interior of the outer layer and which contains a material having better thermal conductivity than that of the outer layer
Implementation Method 2
a front end face, which is connected to an outer circumferential surface of the insulator and the axial hole and slopes towards the rear end side
Implementation Method 3
a ground electrode which is provided at a front end portion of the shell to form a spark discharge gap between the center electrode
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
An improvement in thermal resistance is attained while realizing the suppression of abnormal discharge by improving a flashover resistance. A sparkplug 1 includes an insulator 2 having an axial hole 4, a center electrode 5 of which a front end is placed further forwards than a front end of the insulator 2, and a shell 3. The center electrode 5 has a shoulder portion 52 and a main body portion 53 and is made up of an outer layer 5A and an inner layer 5B. A front end face 41, which is connected to an outer circumferential surface of the insulator 2 and the axial hole 4 and slopes towards the rear end side, is formed at a front end portion of the insulator 2, and the front end of the insulator 2 is placed further forwards than a boundary between the shoulder portion 52 and the main body portion 53. A front end portion of the inner layer 5A is placed further forwards than the boundary between the shoulder portion 52 and the main body portion 53. Predetermined angles A1, A2, A3, A4 and A5 on the insulator 2 and the center electrode 5 are set so as to satisfy A1>90°, A2<90°, A4>A5 andA3>Al.