Variable Valve Lift Misfire Reduction via Intake Timing Retard
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Solution Overview
Problem
Internal combustion engines with variable valve lift profile systems experience misfires when switching from a low lift profile mode to a high lift profile mode, especially at cold start conditions due to a lean peak in the air-fuel mixture.
Innovation Solution
The method involves controlling the variable valve timing system to reduce the amount of air captured in the cylinder during a mode change by retarding the intake valve timing, thereby preventing a lean peak and reducing the risk of misfire. This is achieved by adjusting the valve timing to push back air into the intake manifold during the high lift profile mode, ensuring the air-fuel ratio remains rich enough to prevent engine misfires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the valve lift profile mode is switched from low lift to high lift profile mode, then the valve lift is increased to improve engine performance, but the air-fuel mixture becomes lean causing misfire
Solution Approach 1:
The control unit retards the intake valve timing before the actual mode switch occurs. This preliminary timing adjustment ensures that when the high lift profile is activated, the valve closes earlier in the compression stroke, preventing excessive air intake and maintaining a rich enough air-fuel mixture to avoid misfire while still benefiting from the higher valve lift performance
2Reliability
If the intake valve timing is retarded to reduce air capture during mode change, then the air-fuel ratio is maintained to prevent misfire, but the valve timing control complexity increases
Solution Approach 1:
The control unit monitors the current valve lift profile mode and automatically adjusts the intake valve timing based on the detected mode. When a mode change from low lift to high lift is detected, the system automatically retards the timing by a predetermined amount, creating a closed-loop feedback mechanism that simplifies control complexity while maintaining reliable air-fuel ratio management
Data Source
AI summary
A method for an internal combustion engine that reduces the possibility of misfire during transitions between a lower valve lift mode and a higher valve lift mode.