Engine Misfire Detection via O2 Sensor Rich Lean Analysis
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Solution Overview
Problem
Conventional misfire detection in general purpose engines is challenging due to large rotational inertia and varied load conditions, making it difficult to accurately distinguish between misfire and load changes, and requiring extensive manual adaptation, which can lead to incorrect determinations and damage to three-way catalysts.
Innovation Solution
A control apparatus equipped with sensors for load and rotational speed, an O2 sensor, and units for air fuel ratio determination and feedback correction, which calculates a rich lean period to determine misfires and stops fuel injection when a misfire is detected, preventing catalyst damage and harmful emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional angular velocity fluctuation-based misfire detection is used in general purpose engines, then misfire detection can be attempted, but detection accuracy deteriorates due to large rotational inertia and varied load conditions
Solution Approach 1:
The patent replaces the mechanical/physical detection method (angular velocity fluctuation measurement) with an electrical/sensor-based method (O2 sensor signal analysis). By using the O2 sensor to detect air-fuel ratio variations and analyzing the rich-lean cycle characteristics, the system achieves misfire detection without relying on mechanical angular velocity measurements, thereby overcoming the limitations imposed by large rotational inertia and varied load conditions.
Solution Approach 2:
The patent introduces the O2 sensor as an intermediary measurement device between the combustion process and the detection system. Instead of directly measuring angular velocity fluctuations, the system uses the O2 sensor signal as an intermediate indicator to infer misfire conditions. The analysis of rich-lean cycle patterns in the O2 sensor output provides a reliable indirect measurement that overcomes the direct measurement difficulties.
2Measurement precision
If extensive manual adaptation is performed for each engine model, then detection precision can be improved, but device complexity and time consumption increase
Solution Approach 1:
The patent employs parameter changes by dynamically adjusting the rich-lean cycle determination criteria based on engine operating conditions such as rotational speed and load. Instead of requiring manual adaptation for each model, the system automatically modifies detection parameters according to real-time operational data, enabling universal application across different engine models while maintaining high detection precision.
Solution Approach 2:
The patent achieves universality by developing a misfire detection method that can be applied across multiple engine models and types. The O2 sensor-based rich-lean cycle analysis provides a universal detection approach that does not require model-specific calibration, allowing the same basic system to function effectively in various engine configurations without extensive manual adaptation.
3Object-affected harmful factors
If misfire is not detected in general purpose engines, then three-way catalyst damage can be prevented, but harmful emissions increase due to unburnt gas discharge
Solution Approach 1:
The patent implements feedback control by continuously monitoring the O2 sensor signal and analyzing rich-lean cycle patterns to detect misfire conditions. When a misfire is detected, the system provides feedback to the control unit, which then adjusts fuel injection or ignition timing to prevent further misfires. This continuous feedback mechanism protects the three-way catalyst from temperature damage while minimizing harmful emissions by addressing misfire conditions promptly.
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
Accurately detects misfires in general purpose engines with high rotational inertia and varied models, preventing three-way catalyst damage and harmful emissions by stopping fuel injection, while reducing the need for extensive manual adaptation.
Implementation Method 1
an O2 sensor that is arranged at the upstream side of the three-way catalyst
Implementation Method 2
a three-way catalyst that is arranged in an exhaust passage of the general purpose engine
Implementation Method 3
a fuel injection control unit that supplies fuel to the general purpose engine
Implementation Method 4
a general purpose engine which serves to control the amount of fuel injection
Data Source
AI summary
A general purpose engine control apparatus can detect misfire occurrence with high accuracy, while reducing adaptation man hours of misfire determination. The apparatus includes a first air/fuel ratio determiner to make a rich/lean determination, an injection amount corrector to calculate a corrected injection amount corresponding to a stoichiometric air/fuel ratio, an injection controller to supply fuel to the engine so as to match the corrected injection amount, a second air/fuel ratio determiner to make a rich/lean determination based on a comparison of the O2 sensor output with a rich and a lean determination voltage, a rich/lean period calculator to calculate a rich/lean period according to the determination of the second air/fuel ratio determiner, and a misfire determiner to determine the presence or absence of a misfire based on the rich/lean period. The injection controller stops fuel injection to the engine in the presence of a misfire.