Intake Oxygen Sensor PCV Flow Estimation for EGR Control
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Solution Overview
Problem
The accuracy of exhaust gas recirculation (EGR) estimation in engine systems is compromised due to the sensitivity of intake oxygen sensors to fuel vapor and oil mist, leading to incorrect interpretation of oxygen concentration changes, which affects EGR control and emission levels.
Innovation Solution
A method is implemented to adjust the EGR valve based on the output of the intake oxygen sensor, using a correction factor learned from the difference in oxygen concentration between non-boosted and boosted engine operations, to account for the impact of positive crankcase ventilation (PCV) flow, thereby isolating the effect of EGR on the sensor readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an intake oxygen sensor is used to estimate EGR flow rate, then EGR control can be achieved, but the measurement accuracy is reduced due to sensor sensitivity to fuel vapor and oil mist from PCV flow
Solution Approach 1:
The system performs preliminary identification of PCV flow during a specific operating condition (engine running with EGR valve closed and purge valve closed) before using the sensor for EGR estimation. This preliminary action establishes a baseline correction factor that accounts for the harmful PCV effects, allowing subsequent EGR measurements to be corrected and accurate despite the sensor's sensitivity to fuel vapor and oil mist.
2Reliability
If the oxygen sensor output is used directly for EGR estimation, then the control system is simple, but the EGR control accuracy is degraded due to confounding effects of PCV flow
Solution Approach 1:
The system uses feedback by continuously monitoring the oxygen sensor output and comparing it against the previously identified PCV correction factor. The controller adjusts the EGR valve position based on the difference between the expected sensor output (corrected for PCV) and the actual sensor output, creating a closed-loop control system that maintains accurate EGR control despite the presence of confounding PCV flow effects.
3Productivity
If PCV flow is present during EGR operation, then engine ventilation is achieved, but the oxygen sensor measurements are confounded leading to incorrect EGR interpretation
Solution Approach 1:
The system extracts and isolates the PCV flow effect from the oxygen sensor measurements by performing identification during a condition where EGR is disabled. This separates the PCV contribution from the EGR signal, allowing the control system to remove the PCV-related information loss and use the corrected sensor output for accurate EGR estimation while maintaining normal PCV ventilation functionality.
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 improves the accuracy of EGR flow rate estimation and control, maintaining engine emissions at target levels by correcting for the confounding effects of PCV flow on the intake oxygen sensor measurements.
Implementation Method 1
an intake oxygen sensor which may be employed during non-EGR conditions to determine the oxygen content of fresh intake air
Implementation Method 2
Hydrocarbons ingested from purge air, the positive crankcase ventilation (PCV), and/or rich EGR can consume oxygen on the sensor catalytic surface and reduce the oxygen concentration detected by the sensor
Implementation Method 3
Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system (intake passage), a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions and improve fuel economy
Data Source
AI summary
Methods and systems are provided for estimating a positive crankcase ventilation (PCV) flow based on outputs of an intake manifold oxygen sensor. For example, during engine operation when exhaust gas recirculation (EGR) and fuel canister purge are disabled, PCV flow may be estimated based on a difference between a first output of the sensor with boost enabled and a second output of the sensor with boost disabled. Then, during subsequent operation wherein EGR is enabled, PCV flow is enabled, and purge is disabled, a third output of the sensor may be adjusted based on the estimated PCV flow.