Dynamic Bidirectional Valve Overlap Control for Engine Misfire Prevention
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Solution Overview
Problem
Existing methods for controlling engine valve timing, which limit intake cam movement based on exhaust cam position, can lead to undesirable valve overlap and engine misfires, especially when exhaust cams move faster than intake cams, resulting in reduced engine power and increased emissions.
Innovation Solution
A method that adjusts the timing of both intake and exhaust valves dynamically, allowing for independent control of each cam's movement to optimize valve overlap, reducing the risk of misfires and improving fuel economy by restricting movement based on actual overlap conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the intake cam movement is limited based on exhaust cam position, then valve overlap can be controlled, but engine power is reduced and misfires occur when exhaust cam is retarded faster than intake cam can be adjusted
Solution Approach 1:
The patent implements dynamic, bidirectional control of valve timing where the intake cam and exhaust cam can independently adjust their timing based on real-time overlap conditions. The system transitions from static unidirectional control to dynamic bidirectional control, allowing the faster-moving cam to lead the other cam's adjustment, thereby maintaining combustion stability while preserving engine power output.
Solution Approach 2:
The patent employs feedback control by continuously monitoring valve overlap conditions and using this information to regulate both camshafts' movements. The system adjusts the timing of whichever cam would cause excessive overlap based on real-time feedback from overlap sensors, enabling precise control that prevents misfires while maintaining optimal power delivery.
2Reliability
If the intake cam is strictly constrained based on exhaust cam position, then overlap is regulated, but the system cannot respond adequately when exhaust cam moves faster than intake cam can adjust
Solution Approach 1:
The patent makes the control system dynamic by allowing either camshaft to lead the other's adjustment based on their respective movement rates. When the exhaust cam moves faster, it can lead the intake cam's adjustment, and vice versa. This dynamic adaptability ensures the system responds adequately to rapid cam movements while maintaining reliable overlap control.
Solution Approach 2:
The patent changes the control parameters from fixed unidirectional constraints to variable bidirectional control. The system adjusts which camshaft's timing is regulated based on real-time operating conditions and movement rates, enabling flexible adaptation to different scenarios while maintaining precise overlap control.
3Speed
If overlap is increased to allow faster cam adjustment, then response time improves, but uncombusted air-fuel charge passes through the engine (blow-through)
Solution Approach 1:
The patent uses feedback from overlap sensors to continuously monitor and control the actual overlap condition. This feedback mechanism allows the system to increase cam adjustment speed when safe while preventing blow-through by stopping or reversing adjustment when overlap approaches harmful levels, thus balancing speed and safety.
Solution Approach 2:
The patent applies preliminary anti-action by proactively preventing blow-through before it occurs. The system monitors overlap conditions and takes preemptive action to regulate cam adjustment when approaching the blow-through threshold, rather than reacting after blow-through begins. This prevents the harmful effect while allowing optimal adjustment speeds.
Data Source
AI summary
A method for controlling valve timing for and engine having adjustable valve timing is presented. In one embodiment, the method allows the intake valve timing to be controlled with respect to exhaust valve timing or the method allows the exhaust valve timing to be controlled with respect to intake valve timing. In addition, the method can bound valve overlap between upper and lower limits so that engine emissions and fuel economy may be improved.