Ion Current Frequency Analysis for Engine Misfire Detection
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Solution Overview
Problem
Existing misfire detection methods for single cylinder IC engines face challenges due to low mechanical inertia and load disturbances, leading to unreliable detection of partial and complete misfires, which affect vehicle performance, emissions, and durability.
Innovation Solution
An event detection system utilizing ion current measurement, frequency band limiter modules, and frequency domain conversion units to analyze the ion current signal, determining frequency bands and amplitudes to differentiate between misfire and no-misfire conditions, with real-time notification of misfire events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If angular acceleration of crankshaft is used for misfire detection, then misfire detection can be performed, but detection reliability deteriorates due to low mechanical inertia and load disturbances in single cylinder engines
Solution Approach 1:
The patent replaces the mechanical crankshaft angular acceleration sensing method with an electrical ion current measurement system. The ion current measurement circuit detects ionization changes in the combustion chamber during spark events, converting a mechanical detection approach into an electrical one, thereby achieving reliable misfire detection without depending on the engine's mechanical inertia.
Solution Approach 2:
The patent introduces ion current as an intermediary signal between the combustion event and the detection system. By measuring the ion current generated during spark events and analyzing its variations, the system indirectly detects misfire conditions without directly measuring mechanical parameters like crankshaft acceleration, thus overcoming the limitations of low mechanical inertia.
2Measurement precision
If ion current measurement is used for misfire detection, then detection accuracy improves, but device complexity increases due to additional measurement and processing components
Solution Approach 1:
The patent segments the ion current signal into multiple frequency bands using frequency band limiter modules. By dividing the signal into distinct frequency ranges (e.g., low frequency band, mid frequency band, high frequency band), the system can selectively analyze specific characteristics of the ion current signal, improving detection accuracy while managing complexity through structured signal processing.
Solution Approach 2:
The patent transforms the ion current signal from the time domain to the frequency domain using Fast Fourier Transform (FFT). This dimensional transformation allows the system to analyze frequency characteristics of the signal, providing additional information about combustion events and enabling more accurate misfire detection by examining spectral content rather than just temporal variations.
3Reliability
If frequency domain analysis is applied to ion current signal, then misfire detection capability improves, but processing time and computational complexity increase
Solution Approach 1:
The patent performs preliminary signal conditioning by applying frequency band limiting before the FFT transformation. By pre-filtering the ion current signal into specific frequency bands, the system reduces the amount of data that needs to be processed in subsequent analysis steps, thereby decreasing computational time while maintaining detection capability through targeted frequency band examination.
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
Accurate detection of misfires and partial misfires improves vehicle performance, reduces emissions, enhances durability, and ensures adherence to emission norms by providing real-time alerts and diagnostic support.
Implementation Method 1
When air-fuel mixture ignites inside the IC engine cylinder, air particles get ionized. By applying a suitable high-voltage on a spark plug, it is possible to measure the ion current as the amount of ion current reflects the level of ionization of the air-fuel mixture.
Data Source
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AI summary
An event detection system (200) for determining occurrence of an event in an internal combustion engine (201) comprising an ion current measurement circuit (107), a predetermined number of frequency band limiter modules (203), a predetermined number of frequency domain conversion units (204), and an ion signal analyzer (206) is disclosed. The frequency band limiter modules (203) generate band filtered ion current signals from a received ion current signal generated during a spark event in a spark plug (106). The frequency domain conversion units (204) convert the band filtered ion current signals to frequency domain to obtain digital ion current signals. The ion analyzer analyzes an amplitude of each of the digital ion current signals with an amplitude threshold of each of the digital ion current signals to determine occurrence of the event in the engine. Misfire detection ensures vehicles adhere to OBD II regulatory norms imposed by Regulatory Bodies.