Spark Plug Shell Geometry for Pre-Ignition Heat Control
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Solution Overview
Problem
Existing spark plugs are prone to pre-ignition due to overheating of the insulator, which acts as an ignition source.
Innovation Solution
A spark plug design that includes a specific relationship between the capacity of a space within the metal shell, the outer diameter of the threaded portion, and the distance from the front end of the metal shell to the seating surface, ensuring V/(R²·L) ≤ 0.0170, with a rounded outer corner radius of 1 mm or less and a contact area ratio of 1.90 ≤ S/V, to manage heat transfer effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the space volume between the metal shell and insulator is increased, then the insulator is better protected from overheating, but the heat dissipation capability is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the space volume V between the metal shell and insulator, and adjusting the ratio V/(R²·L) to satisfy V/(R²·L)≤0.0170. This optimization balances the protective effect (reducing insulator temperature) and heat dissipation capability, resolving the technical contradiction between temperature protection and energy loss.
2Reliability
If the insulator volume is increased to reduce pre-ignition, then the heat absorption capacity increases, but the spark plug size and complexity increase
Solution Approach 1:
The patent applies local quality by creating a specific space structure between the metal shell and insulator, concentrating the heat management function in this localized region. The space volume V and its ratio V/(R²·L) are optimized to provide pre-ignition resistance without requiring overall insulator volume increase, thus maintaining simple spark plug structure while improving reliability.
3Use of energy by moving object
If the metal shell contact area with combustion gas is increased, then heat transfer efficiency improves, but the risk of heat-induced pre-ignition increases
Solution Approach 1:
The patent applies parameter changes by optimizing the ratio V/(R²·L) where V is the space volume between metal shell and insulator, R is the metal shell outer diameter, and L is the distance from front end to seating surface. By controlling this ratio to satisfy V/(R²·L)≤0.0170, the patent balances heat transfer efficiency (through adequate metal shell contact area) with pre-ignition risk reduction (through controlled space volume for heat isolation).
Solution Approach 2:
The patent uses the space between the metal shell and insulator as an intermediary element. This space acts as a thermal buffer that mediates between the heat transfer function of the metal shell and the heat protection function of the insulator, allowing efficient heat transfer while preventing heat-induced pre-ignition.
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
Reduces the occurrence of pre-ignition by effectively managing heat transfer from combustion gases, preventing overheating and ignition.
Implementation Method 1
By focusing on the relationship between the capacity of the space that the combustion gas enters and the volume of a portion that transmits the heat of the combustion gas to the engine, the relationship between the heat received by the spark plug from the combustion gas and the heat released from the spark plug can be appropriately set
Data Source
AI summary
A spark plug includes an insulator including a step portion; a center electrode, and a metal shell being disposed around an outer periphery of the insulator and including an inner peripheral surface. The metal shell includes a threaded portion; a seating portion including a seating surface provided on the rear-end side of the threaded portion; and a retaining portion provided on the inner peripheral surface, the retaining portion retaining the step portion. The spark plug satisfies V/(R2·L)≤0.0170, where V (mm3) is a capacity of a space that is located on the front-end side of the retaining portion and inside the inner peripheral surface including the retaining portion and that excludes the center electrode and the insulator, R (mm) is an outer diameter of the threaded portion, and L (mm) is a distance from a front end of the metal shell to the seating surface.