Air-Fuel Ratio Sensor Diagnosis Using Catalyst State Segmentation
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Solution Overview
Problem
The existing diagnosis systems for internal combustion engines struggle to accurately diagnose the deterioration of downstream air-fuel ratio sensors due to the influence of the exhaust purification catalyst's state, leading to inaccurate results even after fuel cut control.
Innovation Solution
A diagnosis system that controls the air-fuel ratio to a rich stoichiometric ratio after fuel cut control, using first and second change characteristics to calculate and correct the air-fuel ratio changes, allowing for precise diagnosis of sensor abnormalities by isolating the catalyst's state effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the air-fuel ratio of exhaust gas is made to change greatly in steps for high precision diagnosis, then the precision of deterioration diagnosis is improved, but the influence of the exhaust purification catalyst's state on the sensor output increases
Solution Approach 1:
The patent segments the air-fuel ratio change process into two distinct phases: a first period with a first air-fuel ratio (rich condition) and a second period with a second air-fuel ratio (lean condition). By dividing the diagnosis process into these segments, the system can separately evaluate sensor response characteristics under different operating conditions, thereby improving measurement precision while accounting for catalyst state influences through comparative analysis.
Solution Approach 2:
The patent changes the air-fuel ratio parameter between two distinct values (first air-fuel ratio and second air-fuel ratio) during the diagnosis process. This parameter change allows the system to observe sensor response characteristics under varying conditions, enabling accurate deterioration diagnosis while the dual-period approach helps isolate catalyst state effects from sensor degradation effects.
2Measurement precision
If fuel cut control is performed to create large air-fuel ratio changes, then the precision of response deterioration diagnosis is improved, but the oxygen storage ability of the exhaust purification catalyst affects the sensor output
Solution Approach 1:
The patent performs a preliminary fuel cut control action before the actual diagnosis measurement. This preliminary action allows the exhaust purification catalyst to reach a known oxygen storage state, providing a consistent starting condition for the subsequent dual-period diagnosis. By preparing the catalyst state in advance, the system reduces the variability introduced by oxygen storage effects and improves the reliability of sensor deterioration diagnosis.
Solution Approach 2:
The patent uses feedback from the sensor output during both the first and second periods to evaluate sensor response characteristics. By comparing the sensor's response to the known air-fuel ratio changes in both periods, the system can distinguish between sensor deterioration and catalyst state effects, thereby improving the reliability of the diagnosis while maintaining high precision through the large air-fuel ratio changes achieved by fuel cut control.
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
This approach enables accurate diagnosis of air-fuel ratio sensor deterioration while minimizing the impact of the exhaust purification catalyst's state, improving the precision of sensor health assessment.
Implementation Method 1
an exhaust purification catalyst arranged in an exhaust passage of the internal combustion engine and being able to store oxygen in inflowing exhaust gas
Data Source
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AI summary
An internal combustion engine comprises an exhaust purification catalyst (20) and an air-fuel ratio sensor (41) arranged at a downstream side of the exhaust purification catalyst, stops or decreases a feed of fuel as fuel cut control, and controls an air-fuel ratio of exhaust gas to a rich air-fuel ratio after the end of the fuel cut control as post reset rich control. The diagnosis system calculates a first characteristic of change of air-fuel ratio at the time when the output air-fuel ratio first passes a first air-fuel ratio region X leaner than a stoichiometric air-fuel ratio and a second characteristic of change of air-fuel ratio at the time when the output air-fuel ratio first passes a second air-fuel ratio region Y including a stoichiometric air-fuel ratio. The diagnosis system diagnoses the abnormality of the air-fuel ratio sensor based on the first characteristic of change of air-fuel ratio and the second characteristic of change of air-fuel ratio. As a result, it is possible to suppress the effects of the change of state of the exhaust purification catalyst while accurately diagnosing the abnormality of deterioration of response of a downstream side air-fuel ratio sensor.