Spark Plug Ground Electrode Positioning for Combustion Chamber Ignition
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Solution Overview
Problem
Conventional spark plugs face challenges in achieving both excellent ignitability and anti-fouling characteristics, particularly in direct-injection engines where carbon accumulation on the insulator surface leads to misfires due to insufficient carbon burn-off and varied physical relationships between the center and ground electrodes.
Innovation Solution
A spark plug design with a ground electrode positioned such that its front end is outside the virtual outer circumferential face of the center electrode, with a specific distance ratio (1.1 <= b/a <= 1.6) to ensure spark discharge near the center of the combustion chamber, and featuring a noble metal portion on the electrodes for improved ignitability and anti-fouling, along with additional configurations like a tapered bore and multiple ground electrodes for enhanced carbon burn-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ground electrode is disposed to face the center electrode for spark discharge near the combustion chamber center, then ignitability is improved, but carbon accumulation on the insulator surface increases leading to insufficient anti-fouling characteristics
Solution Approach 1:
The insulator is designed with different surface characteristics in different regions: the front end surface (first surface) maintains high electrical insulation to prevent carbon-induced leakage, while the side surface (second surface) is positioned to receive spark discharge for carbon burn-off. This local differentiation allows the insulator to simultaneously protect against carbon accumulation while enabling effective spark discharge near the combustion chamber center.
Solution Approach 2:
The patent introduces the insulator's side surface as an intermediary medium that facilitates spark discharge to burn off carbon from the combustion chamber center region. By positioning the ground electrode to discharge through the insulator's side surface rather than directly through the front end surface, the system enables effective carbon removal while maintaining the front end surface's insulation integrity.
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 achieves improved ignitability and anti-fouling characteristics by ensuring spark discharge occurs near the center of the combustion chamber, effectively burning off carbon from the insulator surface, thereby preventing misfires and maintaining engine performance.
Implementation Method 1
the current applied to the center electrode is transmitted and leaks to the metal shell through the carbon adhered to the front end of the insulator. As a result, a normal spark discharge is less likely conducted (i.e., misfire). Therefore, it is disclosed that the front end portion of the ground electrode is disposed so as to face a side surface of the center electrode, thereby generating the spark discharge between two electrodes through the front end face of the insulator
Implementation Method 2
The conventional art can burn off the carbon adhering to the front end of the insulator at the time of the spark discharge, and excellent anti-fouling characteristics are materialized
Data Source
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AI summary
An object of the present invention is to offer a spark plug for internal-combustion engines, which has excellent ignitability and sufficient anti-fouling characteristics. A spark plug 1 is comprised of a ceramic insulator 2 having an axial bore 4 extending in an axis CL1 direction, a metal shell 3 provided on an circumference of the ceramic insulator 2, a center electrode 5 inserted in the axial bore 4, and a ground electrode 27 provided in a front end portion 26 of the metal shell 3. A spark discharge gap 33 is formed between the ground electrode 27 and the center electrode 5. The ground electrode 27 is positioned such that the front end portion thereof is outside of a virtual outer circumferential face KG and is positioned on the front end side with respect to a virtual face KS in the axis CL1 direction. The virtual outer circumferential face KG is defined by extending a front end outer circumferential face 5G of the center electrode 5 in the axis CL1 direction, and the virtual face KS includes the front end of the center electrode 5. The present invention satisfies an equation of: 1.1<=b/a<=1.6, where "a" (mm) represents a first minimal distance between the front end portion of the center electrode 5 and the front end portion of the ground electrode 27, where "b" (mm) represents a second minimal distance between the front end portion of the ceramic insulator 2 and the front end portion of the ground electrode.