Pencil Ignition Coil Boot Compression Loading
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Solution Overview
Problem
Pencil ignition coils in spark ignition systems suffer from premature failure due to stress fractures in the boot wall caused by repeated cycles, leading to electrical punch-through and ignition failure.
Innovation Solution
A pencil ignition coil and boot design featuring an annular male protrusion and a correspondingly configured female cavity, which creates a friction fit with the spark plug head, altering the loading condition from shear to compression, increasing the path length for electrical tension and enhancing the durability of the apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the male protrusion is spaced from the neck portion of the plug receiving cavity, then the assembly is easier to manufacture, but the boot is subjected to shear load causing stress fractures and premature failure
Solution Approach 1:
The invention inverts the loading condition from shear to compression by repositioning the male protrusion to project past the engaging portion of the plug receiving cavity. This causes the boot material to be compressed between the male protrusion and the enlarged end portion of the spark plug head, rather than subjected to shear loads at the base of the female cavity. Compression loading significantly improves boot durability and prevents stress fractures while maintaining manufacturing simplicity.
2Duration of action of stationary object
If the male protrusion projects past the engaging portion of the plug receiving cavity, then the boot is loaded in compression increasing lifetime, but the device complexity increases
Solution Approach 1:
The invention changes the geometric parameters of the boot structure, specifically the depth of the female cavity and the length of the male protrusion. By increasing the female cavity depth and male protrusion length, the male protrusion projects past the engaging portion of the plug receiving cavity. This parameter change transforms the loading condition to compression, significantly extending boot lifetime without adding complex components or mechanisms.
3Reliability
If the path length for electrical tension is increased, then electrical punch-through is prevented, but the boot wall must be thicker increasing device complexity
Solution Approach 1:
The invention extends the electrical path length by utilizing the axial dimension through the boot wall. The male protrusion projects past the engaging portion of the plug receiving cavity, creating an extended path that electrical tension must traverse. This axial extension in another dimension effectively increases insulation path length and prevents electrical punch-through without requiring increased radial wall thickness, thereby avoiding additional structural complexity.
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 significantly increases the lifespan of the pencil ignition coil and boot by reducing the likelihood of cracking and ensuring a secure, compression-loaded interface, preventing electrical punch-through and enhancing system reliability.
Implementation Method 1
defining a spark plug receiving cavity having a profiled inner surface including an engaging portion so configured as to effect in use a friction fit with an enlarged diameter portion of a head of a spark plug
Implementation Method 2
the material of the boot is compressed, at least in one point, between the male protrusion and the enlarged end portion of the spark plug head
Data Source
Figure 1~2
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AI summary
The invention relates to a pencil ignition coil and boot for ignition of an internal combustion engine's spark plug and an assembly of the same with a spark plug. The coil has an ignition terminal which is provided with an annular male protrusion (12) and a boot (15) for housing the spark plug (18). The boot (15) has an annular side wall which forms a female cavity which can receive the annular male protrusion (12) of the pencil coil. The female cavity and the male protrusions are dimensioned to allow the male protrusion of the terminal (12) to project past a spark plug engaging portion (21) of the boot that receives an enlarged portion (18a) of the spark plug (18) head. This provides an overlap which ensures that the boot is locally loaded under compression rather than shear during the ignition cycle.