Exhaust Catalyst Degradation Diagnosis via Dynamic Air-Fuel Switching
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Solution Overview
Problem
Existing degradation diagnosis methods for exhaust gas control catalysts in internal combustion engines allow nitrogen oxides (NOx) to potentially flow out during the diagnosis process, which is undesirable.
Innovation Solution
A degradation diagnosis device that alternately and repeatedly performs rich and lean air-fuel ratio processes, with specific switching conditions based on oxygen storage and release amounts, to diagnose catalyst degradation while minimizing NOx emission, using a control device and air-fuel ratio sensors to manage the air-fuel ratio control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lean process is executed until the output air-fuel ratio of the downstream air-fuel ratio sensor is equal to a lean air-fuel ratio, then the oxygen storage capability diagnosis is improved, but nitrogen oxides (NOx) flow out of the exhaust gas control catalyst
Solution Approach 1:
The patent applies dynamics by making the oxygen storage amount a dynamic switching parameter. The control device dynamically adjusts the switching timing between rich and lean processes based on the real-time oxygen storage amount of the catalyst, rather than using a fixed switching criterion. This dynamic adjustment allows the system to maintain diagnostic accuracy while preventing NOx emissions by switching to rich process before the catalyst becomes fully depleted of oxygen.
Solution Approach 2:
The patent implements feedback control by using the oxygen storage amount (calculated from air-fuel ratio sensor data) as a feedback parameter to control the switching between rich and lean processes. The control device continuously monitors the oxygen storage amount and uses this feedback information to determine the optimal switching timing, thereby resolving the contradiction between maintaining diagnostic accuracy and preventing NOx emissions.
2Measurement precision
If active air-fuel ratio control is performed to diagnose degradation, then the degradation detection accuracy is improved, but the complexity of the control process increases
Solution Approach 1:
The patent applies universality by making the control device perform multiple functions: it controls air-fuel ratio for normal engine operation, monitors oxygen storage amount, determines switching timing for rich/lean processes, and diagnoses catalyst degradation. By integrating these functions into a single control device that uses oxygen storage amount as a universal parameter, the patent reduces overall system complexity while maintaining diagnostic accuracy.
Solution Approach 2:
The patent uses parameter changes by transitioning from fixed air-fuel ratio switching criteria to dynamic oxygen storage amount-based switching. This parameter change simplifies the control logic by using a single critical parameter (oxygen storage amount) to govern both the rich/lean switching and degradation diagnosis, rather than requiring separate complex control algorithms for each function.
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
Effectively suppresses NOx from flowing out of the exhaust gas control catalyst during diagnosis, allowing for accurate degradation assessment without compromising emission control.
Implementation Method 1
The exhaust gas control catalyst that can store oxygen stores oxygen in an exhaust gas when the air-fuel ratio of the exhaust gas which flows in is leaner (hereinafter referred to as a 'lean air-fuel ratio') than the stoichiometric air-fuel ratio, and releases the stored oxygen when the air-fuel ratio of the exhaust gas which flows in is richer (hereinafter referred to as a 'rich air-fuel ratio') than the stoichiometric air-fuel ratio
Data Source
AI summary
A degradation diagnosis device includes a downstream air-fuel ratio sensor and a control device. The control device is configured to perform a rich process and a lean process alternately and repeatedly in a degradation diagnosis process for diagnosing degradation of the exhaust gas control catalyst. The control device is configured to, in the degradation diagnosis process, determine that the exhaust gas control catalyst has been degraded when the lean process is executed and the frequency with which an output air-fuel ratio of the downstream air-fuel ratio sensor is equal to the lean air-fuel ratio is equal to or more than a predetermined frequency.