Engine Misfire Detection Using Crank Angle Fluctuation Differences
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Solution Overview
Problem
Existing engine misfire detection systems fail to accurately detect misfires during the warm-up phase of internal combustion engines, especially in hybrid vehicles where delayed ignition timing is used to accelerate catalyst warm-up, leading to inadequate detection due to slower combustion and lower criterion levels.
Innovation Solution
An engine misfire detection apparatus that calculates rotational fluctuations at different crank angles and computes first and second rotational fluctuation differences to detect misfires based on preset values and proportions, ensuring accurate detection from engine start to catalyst warm-up completion, even with delayed ignition timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the criterion level is lowered during catalyst warm-up to improve misfire detection sensitivity, then detection sensitivity is improved, but detection accuracy deteriorates due to slower combustion from delayed ignition timing
Solution Approach 1:
The patent segments the misfire detection process into two distinct phases: warm-up phase detection and normal operation phase detection. During warm-up, the system uses a lower criterion level (first criterion level) to maintain sensitivity, while during normal operation, it switches to a higher criterion level (second criterion level) to ensure accuracy. This segmentation allows the system to optimize detection parameters for each specific operating condition, resolving the contradiction between sensitivity and accuracy.
Solution Approach 2:
The patent implements dynamic adjustment of the criterion level based on engine operating conditions. The ECU dynamically switches between the first criterion level (lower, for warm-up) and the second criterion level (higher, for normal operation) based on whether the catalyst warm-up is complete. This dynamic parameter adjustment enables the system to adapt to changing combustion characteristics, maintaining both sensitivity during warm-up and accuracy during normal operation.
2Speed
If delayed ignition timing is used to accelerate catalyst warm-up, then catalyst warm-up speed is improved, but misfire detection accuracy deteriorates due to slower combustion
Solution Approach 1:
The patent changes the detection parameter (criterion level) based on the engine operating phase. During the warm-up phase with delayed ignition timing, the system uses a lower criterion level that is suitable for slower combustion. Once warm-up is complete and ignition timing returns to normal, the system switches to a higher criterion level. This parameter change allows the system to maintain accurate misfire detection despite the temporary change in combustion characteristics during warm-up.
3Device complexity
If a single criterion level is used for misfire detection throughout engine operation, then system complexity is reduced, but detection adequacy deteriorates during warm-up phase
Solution Approach 1:
The patent implements a dynamic criterion level adjustment mechanism that automatically switches between two preset levels based on engine operating phase. The ECU monitors catalyst warm-up status and dynamically selects the appropriate criterion level: the first (lower) level during warm-up and the second (higher) level during normal operation. This dynamic approach ensures adequate detection across all phases while maintaining relatively simple system architecture through the use of preset levels and automated switching.
Data Source
AI summary
The engine misfire detection apparatus of the invention successively determines whether a rotational fluctuation difference Nxd360 as a difference between a rotational fluctuation Nxd at a certain crank angle CA of an engine and a rotational fluctuation Nxd at a 360 degree-prior crank angle CA exceeds a predetermined reference value A1 (step S150) and whether a rotational fluctuation difference Nxd720 as a difference between the rotational fluctuation Nxd at the certain crank angle CA and a rotational fluctuation Nxd at a 720 degree-prior crank angle CA exceeds a predetermined reference value B1 (step S160). The engine misfire detection apparatus detects a misfire of the engine upon satisfaction of all conditions regarding rotational fluctuation difference proportions Nja2, Nja3, and Nja4 on the basis of the rotational fluctuation difference Nxd360 (step S200) and all conditions regarding rotational fluctuation difference proportions Njb2, Njb3, and Njb4 on the basis of the rotational fluctuation difference Nxd720 (step S210), when both the rotational fluctuation differences Nxd360 and Nxd720 exceed the respective reference values A1 and B1 (steps S150 and S160). This arrangement ensures adequate and accurate detection of an engine misfire during warm-up of a catalyst included in an exhaust emission control unit with a significant delay of the ignition timing in the engine.