Misfire Detection Using Relative Torque Index
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Solution Overview
Problem
Existing misfire detection devices for internal combustion engines face accuracy issues due to unstable crankshaft rotation behavior, which can lead to incorrect determination of misfires, especially when noise is superimposed on rotational fluctuation values.
Innovation Solution
A misfire detecting device that calculates a torque index value using a crank angle sensor output and determines misfires by comparing the relative magnitude of the current torque index value to an average of past values, minimizing the influence of tolerances and unstable rotation behavior, and further uses a low frequency component extracting process to quantify rotation speed changes over longer periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rotational fluctuation Nxd is compared with a determination value to detect misfire, then misfire detection can be performed, but accuracy deteriorates when crankshaft rotation behavior is unstable due to superimposed noise
Solution Approach 1:
The patent uses feedback by comparing the current rotational fluctuation Nxd with a reference value derived from past rotational fluctuations (specifically, the rotational fluctuation 360°CA prior to the current one). This feedback mechanism allows the system to adapt to changing operating conditions and maintain detection accuracy despite unstable crankshaft rotation behavior.
Solution Approach 2:
The patent performs preliminary action by pre-calculating and storing reference rotational fluctuation values from past cycles before the current misfire detection is needed. This allows the system to have ready-made comparison values that account for historical operating conditions, enabling accurate misfire detection even when current rotation behavior is unstable.
2Device complexity
If the same crank rotor tooth is used to calculate current and past rotational fluctuations, then calculation simplicity is maintained, but measurement precision deteriorates due to similar tolerance effects on both values
Solution Approach 1:
The patent applies local quality by using different reference values for different detection scenarios. Specifically, it uses the rotational fluctuation from 360°CA prior as a reference, which provides a localized comparison point that is both simple to calculate and effective at detecting misfires. This localized reference approach maintains calculation simplicity while improving measurement precision by accounting for local operating conditions.
3Reliability
If rotational fluctuation difference is compared with determination value, then misfire detection is enabled, but reliability deteriorates when noise is superimposed on past rotational fluctuation values
Solution Approach 1:
The patent converts the harmful effect of noise from unstable rotation behavior into a beneficial comparison mechanism. By using the rotational fluctuation from 360°CA prior as a reference, the system can distinguish between normal variation and actual misfire conditions. The noise that would normally degrade accuracy actually provides a baseline for comparison, allowing the system to detect deviations that indicate misfire.
Data Source
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AI summary
A CPU determines that there is a misfire when a relative magnitude of a rotation fluctuation amount ΔT30[0] related to a cylinder subject to the determination in relation to a rotation fluctuation amounts ΔT30[4] of the previous combustion cycle is greater than or equal to the determination value Δth. However, during the execution of a catalyst warm-up process, the CPU uses, in the comparison, the relative magnitude of the rotation fluctuation amount ΔT30[0] in relation to the average ΔT30ave[0] of the smallest five of the rotation fluctuation amounts ΔT30[4] to ΔT30[40] from the past ten combustion cycles.