Engine Control Device Combustion Stability via Compression Ratio Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional internal combustion engine control devices experience transient instability in combustion when stopping exhaust recirculation, due to residual exhaust gases in the EGR passage being introduced into cylinders after the EGR valve is fully closed.
Innovation Solution
A control device that adjusts the mechanical compression ratio using a variable compression ratio mechanism, setting a lower target compression ratio during exhaust recirculation at low engine loads and a higher target compression ratio when exhaust is not recirculated, to stabilize combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the EGR valve is fully closed to stop exhaust recirculation, then exhaust recirculation is stopped, but residual exhaust gases in the EGR passage are introduced into cylinders causing transient combustion instability
Solution Approach 1:
The control device performs preliminary action by fully opening the EGR valve before the engine operating conditions change to low load, ensuring that any residual exhaust gases in the EGR passage are minimized or flushed out before the transition occurs. This prevents the introduction of exhaust gases into cylinders during the subsequent shutdown phase, eliminating transient combustion instability.
Solution Approach 2:
The control device provides beforehand cushioning by anticipating the potential combustion instability issue and preemptively adjusting the EGR valve position. By fully opening the valve before the operating condition change, the system creates a buffer condition that prevents the harmful effect of residual exhaust gases from causing combustion instability during the transition period.
2Reliability
If exhaust recirculation is stopped at low engine load, then combustion instability is prevented, but engine performance optimization is reduced
Solution Approach 1:
The control device applies dynamics by making the EGR valve opening degree variable rather than fixed. The valve opening degree is dynamically adjusted based on real-time engine operating conditions, being fully opened when transitioning to low load to prevent combustion instability, and optimized for recirculation when operating conditions are favorable, thus balancing reliability and performance.
Solution Approach 2:
The control device implements parameter changes by varying the EGR valve opening degree according to engine operating parameters. The opening degree is changed from a closed or partially closed position during normal operation to a fully open position when transitioning to low load conditions, thereby adapting the exhaust recirculation level to maintain combustion stability while optimizing engine performance across different operating ranges.
Data Source
AI summary
A control device for controlling an internal combustion engine equipped with an engine body, a variable compression ratio mechanism A configured to be able to change a mechanical compression ratio of the engine body, and an intake system configured to be able to make exhaust discharged from combustion chambers of the engine body be recirculated to an intake passage of the engine body. The control device is provided with a compression ratio control part controlling the variable compression ratio mechanism A so that the mechanical compression ratio becomes the target compression ratio. The compression ratio control part sets the target compression ratio at a lower value when exhaust is being recirculated at a predetermined operating region at an engine low load side than when exhaust is not being recirculated.