Ignition Device Retainer Reduces Resin Stress
Solution Overview
Problem
Conventional ignition devices with resin cases experience stress concentration and cracking due to thermal expansion differences between the core and filling resin, leading to potential failures.
Innovation Solution
The ignition device features a retainer with a ring portion and leg portions extending along the corners of a polygonal columnar core, allowing the filling resin to be exposed around the ring portion, reducing stress concentration and using a nylon retainer for improved corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resin case is completely filled with filling resin, then the core is well-supported and positioned, but stress concentration occurs at the interface between the core and filling resin due to thermal expansion differences, causing cracks
Solution Approach 1:
The patent extracts the filling resin from the region around the ring portion, creating a resin-free zone. This removes the harmful stress concentration effect that would occur if filling resin contacted the core at the ring portion, while maintaining support in other areas through the leg portions and end portions.
Solution Approach 2:
The patent segments the filling resin coverage into different regions: the resin covers the core at the end portions and between leg portions, but is excluded from the ring portion region. This segmentation allows different stress management strategies in different areas, preventing cracks at the critical ring portion interface.
2Manufacturing precision
If the core is positioned directly in the resin case, then the structure is simple, but the position between the core and coil bobbin cannot be defined with high accuracy
Solution Approach 1:
The patent introduces the retainer as an intermediary component between the core and the resin case/coil bobbin. The retainer's ring portion and leg portions provide precise positioning surfaces that define the position of the core relative to the coil bobbin and case, achieving high manufacturing precision without direct contact between the core and case.
3Reliability
If conventional materials are used for the retainer, then the structure is simple, but corrosion resistance against alkali is insufficient
Solution Approach 1:
The patent specifies using nylon (a polyamide material) for the retainer, which provides superior corrosion resistance against alkali compared to conventional materials. This material selection enhances reliability in harsh chemical environments while remaining manufacturable through standard molding processes.
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 design stabilizes the position of the core and coil bobbin with high accuracy, prevents resin cracking, and enhances corrosion resistance against alkali, ensuring reliable high-voltage generation for internal combustion engines.
Implementation Method 1
stress may be concentrated in a part of the filling resin contacting the core due to a difference in coefficient of thermal expansion between the core and the filling resin
Data Source
AI summary
An ignition device includes a case having an opening and a bottom wall, a coil bobbin arranged in the case having a through hole, a first end and a second end, an ignition coil wound around the coil bobbin, a core made of magnetic material and projecting from the opening and from the bottom wall, and extending through the coil bobbin, a retainer having a ring portion and multiple leg portions extending from the ring, and a filling resin in the case. The core extends through the ring portion and the leg portions extend in between an inner surface of the coil bobbin and an outer peripheral surface of the core toward the bottom wall, and the case is filled with the filling resin in a manner that at least a part of the ring portion is not covered by the resin.