Misfire Detection Using NOx Concentration Changes
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Solution Overview
Problem
Existing misfire detection methods for internal combustion engines face challenges in accurately detecting misfires when the rotational frequency of the crankshaft deviates from the resonance frequency band, as the rotational fluctuation amounts may not significantly differ between misfire and non-misfire conditions.
Innovation Solution
A misfire detection device that includes a selective reduction type catalyst, an addition valve for adding a reducing agent, and a NOx concentration sensor, which determines a misfire based on a decrease in downstream NOx concentration and NOx removal rate, with variable settings for exhaust gas flow rate, adsorption amount, and catalyst temperature to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotational fluctuation amount is used for misfire detection, then misfire can be detected when rotational frequency is within resonance frequency band, but detection accuracy deteriorates when rotational frequency deviates from resonance frequency band
Solution Approach 1:
The patent changes the detection parameter from rotational fluctuation amount to NOx concentration. By monitoring the downstream NOx concentration during reducing agent addition, the system can detect misfires regardless of the engine's rotational frequency, thus resolving the contradiction between detection accuracy at resonance frequencies and adaptability across different rotational frequencies.
Solution Approach 2:
The patent replaces the mechanical vibration-based detection method (rotational fluctuation measurement) with a chemical-based detection method (NOx concentration measurement). This substitution eliminates the dependency on resonance frequency conditions, allowing reliable misfire detection across all rotational frequencies.
2Measurement precision
If reducing agent addition is performed continuously, then NOx concentration decreases downstream of catalyst, but false positives increase when no misfire occurs
Solution Approach 1:
The patent uses feedback by monitoring the downstream NOx concentration and comparing it with the upstream concentration to calculate the removal rate. The system adjusts the reducing agent addition amount based on this feedback, adding reducing agent only when the removal rate exceeds a threshold, thereby preventing false positives while maintaining detection sensitivity.
Solution Approach 2:
The patent implements dynamic control of the reducing agent addition process. Instead of continuous addition, the system dynamically adjusts the addition amount based on real-time NOx concentration measurements and calculated removal rates, optimizing both detection accuracy and reliability.
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
The solution accurately detects misfires even in situations where rotational fluctuation-based methods fail, by utilizing NOx concentration and removal rate changes, improving detection accuracy and reducing false positives.
Implementation Method 1
a selective reduction type catalyst arranged in an exhaust gas passage and configured to remove NOx from an exhaust gas
Implementation Method 2
a selective reduction type catalyst arranged in an exhaust gas passage and configured to remove NOx from an exhaust gas
Implementation Method 3
a NOx concentration sensor arranged in the exhaust gas passage at a downstream side of the selective reduction type catalyst and configured to detect a downstream concentration
Data Source
AI summary
A misfire detection device for an internal combustion engine includes processing circuitry. The internal combustion engine includes a selective reduction type catalyst configured to remove NOx from an exhaust gas, an addition valve arranged upstream of the catalyst to add a reducing agent into the exhaust gas, and a NOx concentration sensor arranged downstream of the catalyst to detect a downstream concentration, that is, a NOx concentration in the exhaust gas downstream of the catalyst. The processing circuitry is configured to execute an addition process adding the reducing agent into the exhaust gas with operation of the addition valve and a determination process determining that a misfire has occurred in the internal combustion engine when a detection value of the downstream concentration is decreased on condition that the addition process is being executed.