Variable Time Constant Filtering for Cylinder Imbalance Detection
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Solution Overview
Problem
Existing fuel injection systems for multi-cylinder internal combustion engines face challenges in maintaining uniform air-fuel ratios across cylinders, leading to imbalances that result in increased emissions and reduced efficiency of three-way catalysts, due to issues like selective diffusion of hydrogen and erroneous lean corrections.
Innovation Solution
A fuel injection amount control system that adjusts the time constant of a filtering operation to quickly respond to changes in air-fuel ratio imbalance index values, reducing noise interference and improving accuracy in detecting cylinder imbalances, thereby enabling more precise control of fuel injection amounts to maintain a stoichiometric air-fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed time constant filtering operation is used to reduce noise in imbalance index values, then noise interference is reduced, but the response time to detect actual cylinder imbalances increases
Solution Approach 1:
The patent applies dynamics by making the time constant variable rather than fixed. The ECU dynamically adjusts the time constant based on the operating condition and the magnitude of changes in the imbalance index value. When the imbalance index changes significantly, a smaller time constant is used for faster response; when changes are gradual, a larger time constant is used for better noise filtering.
Solution Approach 2:
The patent implements parameter changes by modifying the time constant parameter according to different conditions. The ECU changes the time constant value based on the rate of change of the imbalance index and the current operating state, allowing the system to adapt between noise reduction and rapid response requirements.
2Speed
If the time constant is reduced to respond quickly to imbalance changes, then response time is improved, but noise interference in the filtered values increases
Solution Approach 1:
The system dynamically adjusts the time constant based on the magnitude of changes in the imbalance index. When significant changes are detected, the time constant is reduced for faster response. When changes are minor, the time constant is increased to filter noise, thus adapting the response speed and precision requirements in real-time.
Solution Approach 2:
The ECU changes the time constant parameter value according to the detected imbalance characteristics. By adjusting this parameter, the system optimizes the balance between response speed and measurement accuracy under different operating conditions and imbalance scenarios.
3Quantity of substance
If common feedback control is applied to all cylinders, then the average air-fuel ratio is maintained, but individual cylinder imbalances are not corrected
Solution Approach 1:
The patent applies segmentation by dividing the control approach into two levels: common feedback control for all cylinders to maintain average air-fuel ratio, and individual cylinder imbalance detection and correction. The system segments the control strategy to address both overall and individual cylinder requirements simultaneously.
Solution Approach 2:
The system implements local quality by applying different control strategies to different cylinders based on their individual imbalance characteristics. While maintaining common feedback for the average ratio, the ECU applies specific correction amounts to individual cylinders based on their detected imbalance indices, ensuring uniformity across all cylinders.
Data Source
AI summary
A fuel injection amount control system acquires an air-fuel ratio imbalance index value that increases as the degree of ununiformity in the air-fuel ratio among cylinders increases, based on an output value of an upstream air-fuel ratio sensor, and acquires an imbalance index learned value by performing a first-order lag filtering operation for removing noise, on the air-fuel ratio imbalance index value. Also, the fuel injection amount is increased based on the imbalance index learned value. In the filtering operation, the time constant of the filter is set to a smaller value when a magnitude of a difference between the current value and the last value of the air-fuel ratio imbalance index value is equal to or larger than a threshold value.