Catalyst Efficiency Diagnosis via Downstream Oxygen Sensor Signal Analysis
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Solution Overview
Problem
Existing diagnostic methods for catalysts in exhaust gas treatment systems require changes in the air-fuel mixture richness during diagnosis, which affects emissions and customer satisfaction, and fail to non-intrusively discriminate between catalyst operating states without altering the richness setpoint.
Innovation Solution
A method that maintains a stoichiometric air-fuel mixture using a richness regulation setpoint with oscillations to keep the catalyst within its catalytic window, allowing for non-intrusive diagnosis by analyzing the downstream oxygen sensor signal, with low-pass filtering to isolate richness modulations and determine catalyst degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the air-fuel mixture richness is modified during diagnosis to evaluate catalyst efficiency, then the catalyst conversion efficiency can be assessed, but emissions increase and customer satisfaction decreases
Solution Approach 1:
The patent changes the observation parameters rather than the operating parameters. It analyzes the downstream oxygen sensor signal characteristics (voltage amplitude, frequency response) under normal stoichiometric operating conditions to diagnose catalyst efficiency, avoiding the need to modify air-fuel mixture richness during diagnosis.
Solution Approach 2:
The patent replaces the mechanical/chemical approach of modifying mixture richness to test catalyst performance with a signal processing approach. It uses digital analysis of the downstream sensor signal under normal operating conditions to infer catalyst state, substituting direct intervention with indirect measurement.
2Reliability
If the richness setpoint is changed during diagnosis to detect catalyst degradation, then catalyst state can be discriminated, but the diagnostic process becomes intrusive and affects normal engine operation
Solution Approach 1:
The patent enables the diagnostic system to use the existing downstream oxygen sensor signal under normal operating conditions to self-diagnose catalyst efficiency. The system extracts diagnostic information from the natural variations in the sensor signal without requiring external intervention or deviation from normal engine operation.
Solution Approach 2:
The patent utilizes the feedback signal from the downstream oxygen sensor under normal closed-loop control conditions to diagnose catalyst efficiency. By analyzing how the catalyst responds to normal richness variations around the stoichiometric setpoint, the system obtains diagnostic information without disrupting the feedback control loop.
3Measurement precision
If injection parameters are modified during diagnosis to evaluate catalyst performance, then catalyst conversion efficiency can be measured, but fuel consumption increases and engine efficiency decreases
Solution Approach 1:
The patent maintains continuous normal engine operation during the diagnostic process. The engine continues to operate at optimal fuel consumption with stoichiometric air-fuel mixture while the diagnostic system continuously analyzes the downstream sensor signal to assess catalyst efficiency, eliminating the need for interruptive rich/lean cycling.
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
Enables effective diagnosis of catalyst efficiency without impacting emissions, allowing for early detection of degradation by maintaining constant engine operating conditions and using digital processing to analyze the downstream probe signal, ensuring compliance with emission standards.
Implementation Method 1
a three-way catalyst 4, which performs a triple function: oxidation of unburned hydrocarbons (HC), oxidation of carbon monoxide (CO) to carbon dioxide (CO2), and reduction of nitrogen oxides (NOx) to nitrogen gas (N2)
Implementation Method 2
An oxygen (or lambda) sensor 5 is generally positioned upstream of the three-way catalytic converter 4... It outputs a voltage that corresponds to the air-fuel ratio
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for diagnosing a catalytic converter (4) of an exhaust gas treatment system (3), said system comprising a first (5) and a second (8) oxygen sensor these being installed upstream and downstream of said catalytic converter (4), in which method - a setpoint for regulating the richness of the engine is supplied on the basis of the signal supplied by the upstream sensor (5) to make it possible to maintain a stoichiometric mixture at the inlet to the catalytic converter (4), and - a setting fluctuation is applied to said setting setpoint in order alternately to impose a rich mixture and a lean mixture upstream of the catalytic converter, the amplitude of which fluctuation is calibrated so as to keep the mixture value within the range of values of the catalytic window for which the efficiency of the catalytic converter is at a maximum; - a variation in the signal supplied by the downstream sensor (8) while said setting fluctuation is being applied is analyzed so as to diagnose the catalytic converter.