Manifold Pressure Model for Skip Fire Engine Control
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Solution Overview
Problem
Existing methods for estimating mass air charge in internal combustion engines, particularly in dynamic skip fire applications, face challenges due to unpredictable manifold absolute pressure fluctuations caused by irregular firing and skipping of engine cylinders, leading to inaccurate fuel delivery and potential engine performance issues.
Innovation Solution
An engine controller with a mass air charge determining unit that estimates manifold absolute pressure using firing frequency and air flow data, allowing for accurate mass air charge estimation without relying on direct MAP sensor data, and adjusts fuel delivery based on these estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mass air flow sensor is used to measure mass air charge, then direct measurement of air flow is achieved, but time delay and lack of direct relation between measured mass air and cylinder air mass charge occurs
Solution Approach 1:
The system performs preliminary calculations using the measured mass air flow signal and firing frequency to estimate the manifold absolute pressure and cylinder air mass charge before fuel injection occurs. This allows the control system to have advance knowledge of the actual air charge that will be inducted into each cylinder, eliminating the time delay problem by computing the corrected value in advance rather than relying on direct sensor measurement at the moment of injection.
2Measurement precision
If manifold absolute pressure sensor data is used to calculate mass air charge, then direct measurement of manifold pressure is achieved, but inaccurate fuel delivery occurs in dynamic skip fire applications
Solution Approach 1:
The system uses feedback from the measured mass air flow signal and the actual firing frequency to continuously update and correct the estimate of manifold absolute pressure. By comparing the expected pressure based on direct MAP sensor readings with the pressure inferred from mass air flow measurements and firing patterns, the system adjusts its calculations to account for the irregular pressure fluctuations caused by skip fire operation, thereby maintaining accurate fuel delivery.
Solution Approach 2:
The system dynamically changes the parameters used for mass air charge calculation based on operating conditions. In dynamic skip fire mode, it transitions from relying primarily on direct MAP sensor data to using a corrected approach that incorporates firing frequency and mass air flow measurements, adapting the calculation methodology to match the varying engine operating state and maintain accuracy.
3Device complexity
If direct MAP sensor measurement is used, then simple measurement approach is maintained, but complex and rapidly varying pressure waves in skip fire mode cause estimation errors
Solution Approach 1:
The system introduces an intermediary calculation step that uses the measured mass air flow signal and firing frequency as mediators to estimate manifold absolute pressure indirectly. Rather than relying directly on the MAP sensor reading which is corrupted by pressure waves in skip fire mode, the system uses these intermediary parameters to compute a corrected pressure estimate that filters out the harmful pressure fluctuations while maintaining the simple measurement approach.
Data Source
AI summary
In one aspect, an engine controller for an engine including multiple working chambers is described. The engine controller includes a mass air charge determining unit that estimates a mass air charge or amount of air to be delivered to a working chamber. Firing decisions made for a firing window of one or more firing opportunities are used to help determine the mass air charge. The engine controller also includes a firing controller, which is arranged to direct firings to deliver a desired output. Fuel is delivered to a working chamber based on the estimated mass air charge.