Downstream Air-Fuel Ratio Sensor Dead Time Diagnosis
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Solution Overview
Problem
Existing abnormality diagnosis systems for downstream air-fuel ratio sensors cannot differentiate between dead time and primary delay abnormalities, leading to inaccurate diagnosis and potential deterioration in exhaust emission control.
Innovation Solution
An abnormality diagnosis system that alternates the air-fuel ratio between rich and lean settings to calculate the time it takes for the downstream air-fuel ratio sensor to change towards the stoichiometric ratio, using differential values to determine abnormal dead time, and optionally corrects this time based on intake air amount to precisely diagnose dead time abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the time from target air-fuel ratio switching to sensor output reaching a threshold is used for diagnosis, then response delay abnormality can be detected, but dead time and primary delay abnormalities cannot be differentiated
Solution Approach 1:
The patent segments the response delay measurement into two distinct phases: dead time measurement (from target air-fuel ratio switching to sensor output starting to change) and primary delay measurement (from sensor output starting to change to reaching threshold). This segmentation allows independent diagnosis of each delay component, resolving the contradiction between detecting response delay abnormality and differentiating its causes.
2Measurement precision
If the target air-fuel ratio is switched between rich and lean settings, then dead time can be measured, but the measurement is affected by both dead time and primary delay
Solution Approach 1:
The patent uses preliminary action by first detecting when the sensor output starts to change (indicating dead time has passed) before measuring the time to reach the threshold (primary delay). This sequential measurement approach allows the system to separately identify and measure dead time and primary delay, preventing the mixing of these two delay components in a single measurement.
3Reliability
If the response delay of the downstream side air-fuel ratio sensor excessively increases, then the air-fuel ratio change cannot be quickly detected, but the cause of delay cannot be identified
Solution Approach 1:
The patent implements feedback by continuously monitoring the sensor output and comparing it against expected values based on target air-fuel ratio switching. The system uses this feedback to calculate both dead time and primary delay, and can identify which component is abnormally increased, thereby providing precise diagnostic information about the source of response delay while maintaining reliable air-fuel ratio detection.
Data Source
AI summary
The abnormality diagnosis system comprises an air-fuel ratio control means which sets the target air-fuel ratio of exhaust gas to a first set air-fuel ratio set to a first side of a rich side or a lean side, then, when a downstream side output air-fuel ratio is at the first side, switches the target air-fuel ratio to a second set air-fuel ratio set to a second side at the opposite side from the first side. The abnormality diagnosis system calculates the time from when the target air-fuel ratio is switched to when the downstream side output air-fuel ratio starts to change toward the stoichiometric air-fuel ratio based on a differential value of the downstream side output air-fuel ratio and, when the calculated time is a predetermined time or more, judges that a dead time at the downstream side air-fuel ratio sensor is abnormal.