Spark Plug Electrode Segmentation for Low Voltage and Self-Cleaning

Solution Overview

Problem

Spark plugs for internal combustion engines face challenges in inducing spark discharges with low discharge voltage while maintaining excellent self-cleaning capabilities, particularly in direct injection and high compression ratio engines, where carbon deposition is prevalent, leading to increased discharge voltage and potential dielectric breakdown.

Innovation Solution

A spark plug design with specific dimensional relationships between the center and ground electrodes, including a thin member and a protruding member of the ground electrode, allows for efficient spark discharge with low voltage and effective self-cleaning, where the inner edge of the protruding member is close to the thin member when clean and the outer edge is close to the insulator when fouled, ensuring reliable operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the end edge of the protruding member of the ground electrode is arranged close to the inner surface of the insulator to enhance self-cleaning capability, then the self-cleaning capability is improved, but the discharge voltage increases

Engineering Contradiction:

Improveself-cleaning capabilityVSAvoiddischarge voltage

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The ground electrode is divided into two distinct edges: an inner edge that faces the thin member of the center electrode for spark discharge, and an outer edge that faces the inner surface of the insulator for self-cleaning. This segmentation allows the two functions (ignition and cleaning) to be performed at different locations of the same electrode, resolving the contradiction between low discharge voltage and high self-cleaning capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the ground electrode are assigned different functional qualities: the inner edge is positioned to create a small discharge gap for low-voltage spark ignition, while the outer edge is positioned close to the insulator surface to enable effective self-cleaning through surface sparks when carbon deposits are present

Inventive Principle:

Principle #3Local quality

2Use of energy by moving object

If the end edge of the protruding member of the ground electrode is arranged close to the end edge of the thin member of the center electrode to reduce discharge voltage, then the discharge voltage is reduced, but the self-cleaning capability deteriorates

Engineering Contradiction:

Improvedischarge voltageVSAvoidself-cleaning capability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The ground electrode is divided into two distinct edges: an inner edge that faces the thin member of the center electrode for spark discharge, and an outer edge that faces the inner surface of the insulator for self-cleaning. This segmentation allows the two functions (ignition and cleaning) to be performed at different locations of the same electrode, resolving the contradiction between low discharge voltage and high self-cleaning capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the ground electrode are assigned different functional qualities: the inner edge is positioned to create a small discharge gap for low-voltage spark ignition, while the outer edge is positioned close to the insulator surface to enable effective self-cleaning through surface sparks when carbon deposits are present

Inventive Principle:

Principle #3Local quality

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 enables spark plugs to induce spark discharges with a low discharge voltage while maintaining excellent self-cleaning capabilities, preventing carbon deposition and ensuring reliable ignition and durability.

Implementation Method 1

sparks can be discharged across the spark gap 91 by applying a discharge voltage (i.e., the voltage required to induce spark discharges) between the center and ground electrodes 93 and 95

Methodology Applied

Scientific EffectSpark discharge: Electric Spark

Implementation Method 2

The spark discharges B pass the inner surface 924 of the insulator 92 defining the central bore 923, thereby burning off the carbon that has deposited on the inner surface 924

Methodology Applied

Scientific EffectCombustion: Combustion

Data Source

PatentUS7541724B2Spark plug requiring low discharge voltage and having high self-cleaning capability

Publication Date: 2009.06.02 DENSO CORP

AI summary

A spark plug according to the present invention includes a metal shell, an insulator retained in the metal shell, a center electrode secured in the insulator, and a ground electrode. The center electrode includes a base member and a thin member thinner the base member. The ground electrode includes a base member fixed to the metal shell and a protruding member that protrudes from the base member and has an end face with an inner and an outer edge. When the insulator is clean, sparks can be discharged between the thin member and the inner edge. When the insulator is fouled with carbon, sparks can be discharged between the base member and the outer edge to self-clean the insulator. Dimensional parameters and relationships are specified in the spark plug, so that the spark plug can induce spark discharges with a low discharge voltage while securing an excellent self-cleaning capability thereof.