Engine Fuel Control During Positive Valve Overlap Start
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Solution Overview
Problem
During engine cold starting, positive valve overlap can lead to residual backflow stripping fuel from intake port surfaces, causing air-fuel combustion errors due to uncorrelated intake cam timing, manifold pressure, and cylinder air amount, which existing fuel injection control systems fail to adequately address.
Innovation Solution
The method involves starting the engine with a default variable valve timing position, increasing positive valve overlap before the engine warms, and adjusting fuel injection to account for increased fuel evaporation from intake valves and ports, using estimated manifold pressure and engine coolant temperature to maintain proper air-fuel ratios and reduce NOx formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If positive valve overlap is increased during cold starting to improve exhaust gas recirculation and fuel evaporation, then fuel evaporation and mixing are improved, but residual backflow strips fuel from intake port surfaces causing air-fuel combustion errors
Solution Approach 1:
The system performs preliminary fuel injection before the positive valve overlap period begins, so that fuel is already present on the intake port surfaces before residual backflow occurs. This preliminary action ensures that when the valve overlap strips fuel during cold starting, the critical fuel amount has already been delivered to the cylinder, preventing air-fuel combustion errors while still allowing the beneficial fuel evaporation and mixing during overlap
Solution Approach 2:
The control system monitors engine temperature, manifold pressure, and cam timing to dynamically adjust the fuel injection amount. During cold starting conditions with positive valve overlap, the system detects these parameters and automatically compensates for the fuel stripping effect by adjusting injection quantity, thereby maintaining precise air-fuel combustion ratio while preserving the improved fuel evaporation benefits
2Loss of energy
If variable valve timing is adjusted to increase positive valve overlap during cold start, then pumping losses are reduced and NOx formation is reduced, but fuel injection control becomes more complex to account for transient fuel effects
Solution Approach 1:
The system changes the timing parameter of fuel injection to occur before the valve overlap period rather than during or after it. This parameter change simplifies the control logic by decoupling the fuel injection event from the complex transient effects during overlap, while still achieving the energy loss reductions from improved pumping and reduced NOx formation through the variable valve timing adjustment
Solution Approach 2:
By performing fuel injection as a preliminary action before the variable valve timing induces positive overlap, the system avoids the need for complex real-time compensation calculations during the transient period. The fuel is delivered in advance when the intake port conditions are more stable, simplifying the overall control system while maintaining the energy efficiency benefits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables efficient exhaust gas recirculation, improves fuel evaporation and mixing, reduces pumping losses, and maintains stable combustion by compensating for transient fuel effects caused by valve overlap changes, even after valve movement decreases.
Implementation Method 1
adjusting a fuel injection amount in response to the increase in positive overlap, where the adjustment of fuel provides a decrease in injected fuel to account for an increase in fuel evaporating from the intake valve and/or the intake port
Implementation Method 2
This operation may be used as an intended form of exhaust gas recirculation that exploits positive valve overlap to improve pumping losses, reduce NOx formation, and increase fuel evaporation and mixing
Data Source
AI summary
An approach is provided for compensating engine fueling during starting conditions in which positive valve overlap is enabled early in the start. In one example, the valve timing is adjusted to increase positive overlap during cold starting conditions, and fuel adjustments are provided to compensate for the evaporation effects of the increased residual push-back.