Shielded Spark Plug Ion Sensor for Cleaner Combustion Signals
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Solution Overview
Problem
Conventional spark plug-based ionization sensors suffer from masking or imperfect ion current signals due to interference from the high voltage generated by ignition coils, which complicates accurate combustion sensing in internal combustion engines.
Innovation Solution
A spark plug combustion ionization sensor featuring dedicated ion current sensing electrodes, which are shielded and grounded to reduce electromagnetic interference, allowing for more accurate measurement of ion current during combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional spark plug-based ionization sensors are used, then the structure is simple and easy to manufacture, but the ion current signals are masked or imperfect due to electromagnetic interference from ignition coils
Solution Approach 1:
The patent divides the electrode system into separate functional components: a sparking electrode for ignition and a dedicated sensing electrode for ion current detection. This segmentation allows each electrode to perform its specific function without interference, resolving the contradiction by physically separating the ignition function from the sensing function while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent introduces an electrically conductive shield as an intermediary element between the sparking electrode and the sensing electrode. This shield, connected to ground, acts as a mediator that blocks electromagnetic interference from the ignition system from reaching the sensing electrode, thereby improving signal accuracy without significantly complicating the device structure.
2Measurement precision
If the sparking electrode is used to detect ionization, then no additional sensing electrode is needed, but the high voltage from ignition coils interferes with the ion current measurement
Solution Approach 1:
The patent extracts the sensing function from the sparking electrode by introducing a dedicated sensing electrode that is electrically isolated from the ignition system. This extraction removes the harmful electromagnetic interference from the measurement path while maintaining the original sparking electrode's ignition function, directly addressing the contradiction between signal quality and interference.
Solution Approach 2:
The electrically conductive shield serves as an intermediary that blocks the harmful electromagnetic fields from the ignition coils from reaching the sensing electrode. By placing this grounded shield between the source of interference and the sensing element, the patent effectively protects the measurement from electromagnetic interference without affecting the ignition process.
3Reliability
If a dedicated sensing electrode with shielding is implemented, then electromagnetic interference is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The electrically conductive shield serves multiple functions simultaneously: it acts as electromagnetic shielding, provides a ground reference for the sensing electrode, and can serve as part of the structural housing. This multi-functionality reduces the need for additional separate components, thereby improving reliability while minimizing the increase in manufacturing complexity.
Solution Approach 2:
The patent employs a nested structure where the sensing electrode is positioned within the housing, and the electrically conductive shield is integrated around the sensing electrode. This nesting approach allows multiple functional elements to be compactly arranged within the spark plug structure, reducing overall complexity while maintaining the benefits of shielding and dedicated sensing.
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 minimizes electromagnetic interference, resulting in more accurate and reliable ionization current signals that can be used for improved combustion control and emission management in internal combustion engines.
Implementation Method 1
an electrically conductive shield substantially surrounding the insulating material along its length, the electrically-conductive shield being electrically isolated from the sensing electrode and the sparking electrode, wherein the electrically-conductive shield substantially reduces electromagnetic interference in the sensing electrode
Implementation Method 2
a sensing circuit can then be connected to the sensing electrode to monitor ion current in an engine's cylinder during combustion
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3C
AI summary
A spark plug combustion ionization sensor for measuring ion current inside the cylinder of an internal combustion engine. The sensor measures ion current which flows when the energy released during combustion ionizes the air inside the cylinder, and thus can detect combustion and emission parameters. The spark plug combustion ionization sensor generally includes an insulated, dedicated sensing electrode, separate from the sparking electrode of a spark plug. The sensing electrode may also be shielded to further reduce interference such as electromagnetic interference (EMI). The use of a dedicated electrode allows for ion current measurement with less electromagnetic noise from the ignition process, and also eliminates the need for circuitry that is typically necessary when the sparking electrode is also used to sense ion current.