Spark Plug Sub-Chamber Pre-Ignition Suppression
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Solution Overview
Problem
The existing spark plug designs suffer from pre-ignition issues due to the fused portions having lower thermal conductivity than the cap member and metal shell, which overheats and ignites the combustible air-fuel mixture in the sub-chamber.
Innovation Solution
The spark plug design features a first and second fused portion located on the front-end side relative to the spark gap, with a facing portion configuration that reduces overheating by providing a sufficient distance and joint strength, and an inner peripheral surface conformity between the cap member and metal shell to minimize the effect of heat on the sub-chamber, preventing pre-ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the fused portion joins the metal shell and cap member, then joint strength is improved, but the fused portion becomes overheated and causes pre-ignition
Solution Approach 1:
The harmful fused portion is extracted from the inner peripheral surface region and relocated to the outer peripheral surface of the cap member. This separation removes the low thermal conductivity fused portion from the heat-sensitive sub-chamber environment, preventing pre-ignition while maintaining joint strength through proper positioning on the outer surface.
Solution Approach 2:
The cap member acts as an intermediary structure that provides a dedicated outer peripheral surface for the fused portion. This intermediary location serves as a thermal buffer, allowing the fused portion to maintain joint strength without directly exposing low thermal conductivity material to the high-temperature sub-chamber environment.
2Ease of manufacture
If the fused portion is exposed in the sub-chamber, then manufacturing is simplified, but pre-ignition occurs due to overheating
Solution Approach 1:
The fused portion is extracted from the sub-chamber environment and positioned on the outer peripheral surface of the cap member. This extraction maintains manufacturing simplicity by using a straightforward fusion process while eliminating the reliability issue of pre-ignition by removing the fused portion from the high-temperature combustion zone.
Solution Approach 2:
The low thermal conductivity of the fused portion, which causes harm when exposed in the sub-chamber, is converted into a benefit by positioning it on the outer peripheral surface where it can dissipate heat to the external environment rather than allowing heat accumulation that would cause pre-ignition.
3Strength
If the first facing portion is located on the sub-chamber side relative to the first fused portion, then joint strength is enhanced, but heat transfer to the sub-chamber increases
Solution Approach 1:
The first facing portion is extracted from the sub-chamber side and repositioned on the outer peripheral surface of the cap member. This extraction breaks the direct heat transfer path from the fused portion to the sub-chamber, reducing thermal energy loss to the combustion chamber while maintaining joint strength through the structural configuration.
Solution Approach 2:
The outer peripheral surface of the cap member serves as an intermediary location for the first facing portion, mediating between the joint strength requirement and heat transfer prevention. This intermediary position allows the facing portion to provide structural support without directly conducting heat into the sub-chamber environment.
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
This configuration effectively suppresses pre-ignition by reducing the thermal impact of the fused portions on the sub-chamber, enhancing joint strength, and optimizing gas flow velocity and turbulence, thereby improving combustion efficiency.
Implementation Method 1
A first fused portion that joins the metal shell and the cap member is located on the front-end side relative to the spark gap
Implementation Method 2
The ground electrode is joined to the metal shell via a second fused portion
Implementation Method 3
a ground electrode that has one end portion joined to the metal shell and the other end portion forming a spark gap between the other end portion and a front end portion of the center electrode
Data Source
AI summary
A spark plug that can suppress pre-ignition of a combustible air-fuel mixture that has flowed into the sub-chamber. The spark plug includes a ground electrode that joins to a metal shell and forms a spark gap; and a cap member that covers a center electrode and the ground electrode and forms a sub-chamber. A first fused portion that joins the metal shell and the cap member is located on the front-end side relative to the spark gap. At least a part of a first facing portion at which the metal shell and the cap member face each other is located on the sub-chamber side relative to the first fused portion. The first fused portion is not formed in an inner peripheral surface of the metal shell and an inner peripheral surface of the cap member.