Engine Misfire Diagnosis Using Dynamic Thresholds
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Solution Overview
Problem
Existing engine misfire diagnostic systems are prone to erroneous misfire determinations due to external disturbances affecting the engine output shaft, causing distortions in the misfire parameter waveform, which leads to inappropriate threshold values and incorrect diagnosis.
Innovation Solution
An engine misfire diagnostic apparatus that calculates a first misfire parameter based on differences between time measurement values of a designated cylinder and opposing cylinders, a second misfire parameter using reference cylinders, and a third misfire parameter as a derivative of the first, with determination thresholds adjusted based on mathematical relationships between these parameters to accurately determine cylinder misfires even under external disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single misfire determination threshold value is used, then the diagnostic system is simple to operate, but the measurement precision deteriorates when external disturbances are present
Solution Approach 1:
The patent implements dynamic threshold adjustment by calculating multiple misfire parameters (first misfire parameter from opposing cylinders, second misfire parameter from reference cylinders, third misfire parameter as derivative) and setting determination thresholds based on mathematical relationships between these parameters. This allows the threshold to adapt dynamically to different operating conditions and external disturbances, resolving the contradiction between operational simplicity and measurement precision.
2Measurement precision
If the misfire determination threshold is adjusted for external disturbances, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent segments the misfire detection process into multiple independent parameter calculations: first misfire parameter based on opposing cylinders, second misfire parameter based on reference cylinders, and third misfire parameter as a derivative. Each parameter has its own calculation methodology and contributes to the final determination. This segmentation allows complex adaptive thresholding to be achieved through modular, manageable components, reducing overall system complexity while maintaining high measurement precision.
3Reliability
If multiple misfire parameters are calculated, then the reliability of misfire determination improves, but the loss of time increases
Solution Approach 1:
The patent performs preliminary calculations of the first and second misfire parameters using readily available time measurement values from opposing and reference cylinders. The third misfire parameter (derivative) is then calculated based on these preliminary results. This preliminary action approach allows the system to prepare calculation components in advance and use mathematical relationships to efficiently derive the final determination threshold, reducing the time penalty associated with multiple parameter calculations while maintaining high reliability.
Data Source
AI summary
An engine misfire diagnostic apparatus measures an amount of time required for a crankshaft to pass through a prescribed crank angle range corresponding to a combustion stroke to obtain time measurement values on a per cylinder basis. A first misfire parameter is obtained based on stored time measurement values from a designated cylinder, an opposing cylinder corresponding to one crankshaft rotation prior and the opposing cylinder corresponding to one crankshaft rotation later. A second misfire parameter is obtained based on stored time measurement values from the designated cylinder, a first reference cylinder whose ignition occurs one ignition prior to the designated cylinder's ignition and a second reference cylinder whose ignition occurs later than the designated cylinder's ignition, the differences weighted according to a prescribed ratio. A determination of whether the designated cylinder has misfired is based on the second misfire parameter and a derivative value of the first misfire parameter.