Cylinder Air Charge Estimation for Engine Starting
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Solution Overview
Problem
Existing methods for determining air charge in internal combustion engines with direct fuel injectors face challenges in accurately estimating air-fuel ratios, especially during engine starting, due to rapid changes in intake manifold pressure, leading to deviations in air-fuel ratios and spark timing.
Innovation Solution
The method involves using an open-loop estimate of cylinder air charge based on the first cylinder to fire since the most recent engine stop and the actual total number of combustion events, adjusting this estimate with cylinder pressure data to improve accuracy, allowing for earlier fuel injection and maintaining a desired air-fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intake manifold pressure is sampled long before the cylinder's intake valve closes, then the sampling time is early enough to avoid interference, but the pressure may not be indicative of air charge in the cylinder during engine starting
Solution Approach 1:
The system performs preliminary actions by sampling intake manifold pressure at multiple predetermined times before intake valve closing, including a first sample time and a second sample time. This allows the system to have advance knowledge of pressure trends and use them to calculate air charge estimates that remain accurate even when sampled before the valve closes, resolving the contradiction between early sampling and measurement accuracy.
Solution Approach 2:
The system uses feedback from multiple pressure samples taken at different times before intake valve closing to calculate a more accurate air charge estimate. By comparing pressure changes between the first and second sample times, the system can compensate for the timing discrepancy and maintain measurement precision without requiring sampling at the optimal moment.
2Manufacturing precision
If direct fuel injectors are sized to provide accurate small or large amounts of fuel, then fuel delivery precision is improved, but the injectors must begin injecting before intake valves close to meet driver demand torque
Solution Approach 1:
The system performs preliminary air charge estimation using intake manifold pressure samples taken before intake valve closing. This preliminary estimate allows the fuel injection system to begin injecting fuel earlier in the cycle while still maintaining the ability to deliver the precise amount of fuel required, as the air charge estimate provides a head start for calculating the needed fuel quantity.
3Device complexity
If fuel injection is based solely on intake manifold pressure before intake valve closing, then the control system is simple, but the air-fuel ratio deviates from the desired air-fuel ratio
Solution Approach 1:
The system implements feedback by taking multiple pressure samples at different times before intake valve closing and using the pressure change information to calculate a more accurate air charge estimate. This feedback mechanism allows the control system to maintain relatively simple hardware while significantly improving air-fuel ratio control accuracy by compensating for the timing discrepancy through calculated corrections.
Data Source
AI summary
Systems and methods for operating an internal combustion engine based on output of an intake manifold pressure sensor and output of an in cylinder pressure sensor are described. The systems and methods provide a way of determining cylinder air charge so that a fuel injector has sufficient time to provide a desired amount of fuel to a cylinder during a cycle of the cylinder.