EGR Control Switching to Mitigate Exhaust Pulsation Errors
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Solution Overview
Problem
At high engine load conditions, exhaust pulsations cause differential pressure sensors to overestimate EGR mass flow, leading to potential spark knock and reduced fuel economy and performance due to incorrect spark timing adjustments.
Innovation Solution
Implementing a method that switches between open loop and closed loop control of the EGR system based on engine load and intake manifold pressure, using intake carbon dioxide sensor data to estimate EGR mass flow independently of differential pressure sensor output at high loads and relying on DP sensor feedback at low loads to adjust spark timing accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential pressure sensor is used to estimate EGR mass flow at high load conditions, then EGR flow measurement is obtained, but exhaust pulsations cause overestimation of EGR mass flow leading to inaccurate spark timing
Solution Approach 1:
The patent changes the measurement parameter from differential pressure (which is affected by pulsations) to intake manifold pressure and lambda values. By using alternative parameters that are not influenced by exhaust pulsations, the system achieves accurate EGR flow estimation without the harmful effects of pulsation-induced measurement errors.
Solution Approach 2:
The patent introduces an intermediary calculation method that uses intake manifold pressure and lambda values as intermediate variables to estimate EGR flow. Instead of directly measuring EGR flow with a pulsation-sensitive sensor, the system uses these intermediary parameters that can be accurately measured and calculated to derive the EGR mass flow.
2Reliability
If spark timing is advanced based on overestimated EGR mass flow, then emission regulation is improved, but spark knock occurs due to excessive spark advance
Solution Approach 1:
The patent implements a feedback mechanism where the estimated EGR mass flow (derived from intake manifold pressure and lambda) is continuously used to adjust spark timing. The system monitors actual engine conditions and adjusts spark advance accordingly, preventing excessive spark advance that would cause knock while maintaining effective emission control.
Solution Approach 2:
The patent makes the spark timing dynamically adjustable based on real-time EGR flow estimation. Instead of using fixed spark timing or timing based on inaccurate pulsation-affected measurements, the system continuously adapts spark timing to actual EGR conditions, optimizing the balance between emission control and knock prevention.
3Object-affected harmful factors
If spark timing is retarded to prevent knock from overestimated EGR flow, then spark knock is reduced, but fuel economy and performance decrease
Solution Approach 1:
The patent performs preliminary accurate estimation of EGR mass flow using intake manifold pressure and lambda values before adjusting spark timing. By having accurate EGR flow information available in advance, the system can set optimal spark timing that prevents knock without requiring excessive retardation, thereby maintaining fuel economy and performance.
Data Source
AI summary
Methods and systems are provided for estimating exhaust gas recirculation (EGR) flow in an engine including an EGR system. In one example, a method may include operating the EGR system in an open loop feed forward mode based on an intake carbon di oxide sensor output above a threshold engine load and/or when a manifold absolute pressure (MAP) is above a threshold pressure, and operating the EGR system in a closed loop feedback mode based on a differential pressure sensor output when the engine load decreases below the threshold load and/or when the MAP decreases below the threshold pressure.