Air/Fuel Ratio Sensor Correction for Catalyst Monitoring
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Solution Overview
Problem
Existing air/fuel ratio sensors, particularly those downstream of a catalyst in an internal combustion engine, face challenges in accurately detecting low-concentration exhaust gases and maintaining control accuracy due to output delays and potential shifts caused by deterioration, making it difficult to accurately determine catalyst deterioration.
Innovation Solution
A correction device that includes air/fuel ratio control means to switch between rich and lean air/fuel ratios, an air/fuel ratio sensor for downstream output, and correction coefficient calculating means to adjust the sensor output based on differences during predetermined periods, stabilizing the output to a stoichiometric reference and accounting for sensor deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electromotive force-type oxygen sensor is installed downstream of the catalyst to detect air/fuel ratio changes, then catalyst deterioration can be detected, but the sensor cannot accurately detect low-concentration exhaust gases and has delayed output response
Solution Approach 1:
The patent changes the operating parameters of the oxygen sensor by controlling the upstream air/fuel ratio to fluctuate between rich and lean conditions. This creates varying exhaust gas concentrations that stimulate the sensor output, enabling accurate detection despite low average concentrations. The correction coefficient is calculated based on these parameter variations to compensate for sensor deterioration.
Solution Approach 2:
The system implements feedback control by using the oxygen sensor output to calculate a correction coefficient, which is then applied to adjust the upstream air/fuel ratio control. This closed-loop feedback mechanism continuously compensates for sensor drift and deterioration, maintaining reliable detection accuracy over time despite changing sensor characteristics.
2Object-generated harmful factors
If the exhaust gas concentration becomes lower due to stricter regulations, then emissions are reduced, but the oxygen sensor cannot accurately detect air/fuel ratio changes
Solution Approach 1:
The patent applies periodic action by forcing the upstream air/fuel ratio to oscillate between rich and lean conditions at predetermined intervals. This periodic variation creates corresponding fluctuations in downstream exhaust gas composition, generating sufficient signal amplitude for accurate sensor detection even when average concentrations are low due to strict emissions control.
Solution Approach 2:
The system performs preliminary action by pre-controlling the upstream air/fuel ratio to specific rich or lean states before measurement. This proactive manipulation ensures that the exhaust gas composition entering the sensor zone has sufficient variability and concentration contrasts to enable accurate detection, rather than relying on passive natural variations.
3Measurement precision
If a limiting-current type air/fuel ratio sensor is used downstream to detect low-concentration gases, then detection accuracy improves, but output shifts occur due to sensor deterioration over time
Solution Approach 1:
The patent applies dynamics by making the sensor operating conditions variable rather than static. The upstream air/fuel ratio is dynamically adjusted between rich and lean states, creating a dynamic test environment that reveals sensor deterioration trends. The correction coefficient is continuously updated based on these dynamic responses, compensating for drift over time.
Solution Approach 2:
A feedback mechanism is implemented where the sensor output under controlled rich/lean cycling is used to calculate a correction coefficient that compensates for deterioration. This feedback loop continuously adjusts for output shifts, maintaining reliable measurements despite aging effects on the limiting-current type sensor.
Data Source
AI summary
A correction device for an air/fuel ratio sensor in the present invention, the sensor issuing an output according to an air/fuel ratio and installed on the downstream from catalyst of the exhaust passage, has air/fuel ratio control means for controlling an air/fuel ratio of an exhaust gas on the upstream side from a catalyst to switch between a rich air/fuel ratio which is richer and a lean air/fuel ratio which is leaner than a stoichiometric air/fuel ratio. Moreover, correction means for correcting an output of the sensor in accordance with a difference between the output of the sensor during a predetermined period during air/fuel ratio control by the air/fuel ratio control means, and a reference output corresponding to a stoichiometric air/fuel ratio, is provided.