Spark Plug Insulator Crack Detection Using Capacitive Coupling
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Solution Overview
Problem
Current spark plug testers are unreliable in detecting cracked ceramic insulators and out-of-specification spark plug gaps after assembly in internal combustion engines, leading to suboptimal engine performance.
Innovation Solution
A high voltage test probe with a non-electrically conductive part and an electrically conductive ring, connected to a high voltage control box containing an insulator crack detection circuit and a spark plug firing circuit, which generates signals to indicate cracks in the insulator and the specification of the spark plug gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an inductive sensor is used to monitor electromagnetic field changes around the ignition coil, then the testing can be performed after spark plug assembly in the engine, but the detection of cracked ceramic insulators and out-of-specification gaps becomes unreliable
Solution Approach 1:
The patent introduces a conductive ring as an intermediary element that couples to the ceramic insulator through capacitance. This ring serves as a mediator between the testing system and the spark plug, allowing direct electrical field interaction with the insulator to detect cracks, thereby improving detection reliability while maintaining post-assembly testing capability
Solution Approach 2:
The patent replaces the indirect electromagnetic field monitoring method with a direct capacitive coupling approach. Instead of using an inductive sensor to monitor general electromagnetic field changes, the system uses a conductive ring that forms a capacitive sensor directly coupled to the insulator, substituting the mechanical/inductive sensing method with an electrical/capacitive sensing method for more reliable crack detection
2Reliability
If a high voltage test probe with conductive ring is used for direct capacitive coupling to detect cracks, then detection reliability improves, but the device complexity increases
Solution Approach 1:
The high voltage test probe is designed to perform multiple functions: it applies high voltage for spark plug firing tests, provides capacitive coupling for crack detection through the conductive ring, and serves as a mechanical probe for positioning. This multi-functionality reduces the need for separate testing devices, thereby limiting the increase in overall device complexity while improving reliability
3Device complexity
If current spark plug testers are used, then the testing process is simple, but out-of-specification spark plug gaps and cracked insulators cannot be reliably detected
Solution Approach 1:
The patent replaces simple electromagnetic field monitoring with a capacitive sensing system that directly couples to the spark plug components. The conductive ring forms a capacitive sensor that can detect changes in electrical field caused by gap variations and insulator cracks, substituting the simple inductive sensing method with a more precise electrical sensing approach
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 solution effectively detects cracked ceramic insulators and verifies the spark plug gap specification, ensuring optimal engine performance by providing reliable testing of assembled spark plugs.
Implementation Method 1
an insulator crack detection circuit for connecting the high voltage contactor to the electrical ground and the electrically conductive ring to the high voltage source to generate an insulator crack detection signal indicating if an insulator is cracked
Implementation Method 2
a spark plug firing circuit for connecting the high voltage contactor to the high voltage source to fire the spark plug in a firing test
Data Source
AI summary
An apparatus and method is provided for testing a spark plug after the spark plug is assembled in an internal combustion engine. The apparatus includes a high voltage test probe to mechanically probe the spark plug. The high voltage test probe includes a non-electrically conductive part, an electrically conductive ring substantially shielded by the non-electrically conductive part, and a high voltage contactor for electrically connecting to a terminal end of the spark plug. The apparatus also includes a high voltage control box having a high voltage source and an electrical ground, and including at least one of an insulator crack detection circuit and a spark plug firing circuit. The method includes using the apparatus to test assembled spark plugs.