Cylinder Air-Fuel Imbalance Detection via Normalized Lambda Differential Counting
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Solution Overview
Problem
Existing methods for detecting cylinder combustion imbalance in engines, such as air-fuel ratio dither control and differential summation methods, are intrusive, lead to inconsistent results, and are limited by sensor noise and vehicle load, failing to accurately monitor cylinder-to-cylinder variations which can cause increased emissions and decreased fuel economy.
Innovation Solution
A method that monitors cylinder air-fuel imbalance by counting instances where peak-to-peak exhaust lambda differentials are below a threshold, normalized to total peak-to-peak oscillations, allowing for non-invasive monitoring during normal engine operation and improving fault separation by analyzing differentials below a noise threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If air-fuel ratio dither control is used to differentiate individual cylinder air-fuel ratios, then cylinder air-fuel ratio imbalance can be detected, but emissions are degraded and over-fueling events occur
Solution Approach 1:
The patent converts the harmful sensor noise band into a beneficial resource by utilizing differential signal lengths that fall within the noise floor. Instead of filtering out these signals as unwanted noise, the invention counts instances where peak-to-peak differential signal lengths are below a threshold, transforming the previously useless noise region into a valuable data source for detecting cylinder air-fuel ratio imbalance without intrusive control actions
2Measurement precision
If noise floor threshold is increased to compensate for signal noise, then fault separation between small and large deviations from stoichiometric air-fuel ratio is improved, but sample size is diminished and results become unreliable
Solution Approach 1:
The patent applies partial action by counting only the instances where differential signal lengths fall below a threshold (the partial subset of data within the noise band) rather than requiring all signals to exceed a high threshold. This approach maintains a large sample size by utilizing the entire noise band region, thereby ensuring reliable and consistent results while still achieving fault separation
3Measurement precision
If differential summation method is used to detect cylinder air-fuel imbalance, then imbalance detection is achieved, but sampling variation leads to inconsistent results
Solution Approach 1:
The patent inverts the traditional differential summation approach by counting instances where differential signal lengths are below a threshold rather than summing only the large deviations. This inversion transforms the detection methodology to produce more consistent results by reducing sampling variation, while still effectively detecting cylinder air-fuel imbalance through the normalized count of sub-threshold differentials
4Measurement precision
If summation method is used for air-fuel ratio imbalance determination, then imbalance detection is provided, but the method is constrained to higher vehicle loads
Solution Approach 1:
The patent creates a universal detection method that functions across all vehicle load conditions by utilizing the normalized count of differential signal lengths below a threshold. This approach is adaptable to varying engine operating conditions because it relies on the statistical distribution of differential signals rather than absolute magnitude thresholds, enabling reliable imbalance detection whether the vehicle is under light or heavy load
Data Source
AI summary
Air/fuel imbalance monitoring systems and methods for monitoring air/fuel ratio imbalance of an internal combustion engine are disclosed. In one embodiment, adjusting engine operation responsive to cylinder air/fuel imbalance based on a determined total number of instances where sensed peak-to-peak exhaust air-fuel ratios differentials are less than a threshold normalized to a total number of peak-to-peak oscillations. The approach can be used to indicate air/fuel ratio imbalances between engine cylinders.