Engine Valve Timing Control for Cold-Start HC and Soot
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Solution Overview
Problem
Existing engine systems face challenges in achieving optimal exhaust performance immediately after a cold start due to insufficient catalyst activation and inefficient fuel evaporation, leading to increased discharge of unburnt HC and soot.
Innovation Solution
The engine control system adjusts the timing of the exhaust and intake valves to create negative or positive overlap periods, along with optimized fuel injection and ignition timing, to trap hot burnt gas and stimulate fuel evaporation, even at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exhaust valve phase is advanced at cold start to increase exhaust gas temperature and flow rate for early catalyst activation, then the catalyst device is activated earlier, but the exhaust performance remains insufficient until the catalyst device is activated
Solution Approach 1:
The patent applies preliminary action by creating positive valve overlap before the catalyst device is activated. During the cold start phase, the exhaust valve is closed before TDC and the intake valve is opened after TDC, creating an overlap period where both valves are closed. This traps hot burnt gas in the combustion chamber, raising the temperature to stimulate fuel evaporation and reduce unburnt HC and soot discharge before the catalyst becomes active.
Solution Approach 2:
The patent changes the valve timing parameters dynamically based on engine temperature. At cold start, the exhaust valve closing timing is advanced and intake valve opening timing is retarded to create positive overlap. As the engine warms up and the catalyst activates, the valve timing is adjusted to normal operation settings. This parameter change optimizes fuel evaporation at low temperatures while maintaining normal exhaust performance after catalyst activation.
2Temperature
If a large amount of burnt gas is trapped inside the combustion chamber to increase temperature and stimulate fuel evaporation, then fuel evaporation is improved, but combustion stability may become unstable when engine temperature is particularly low
Solution Approach 1:
The patent applies dynamics by making the valve timing adjustable rather than fixed. The control device varies the exhaust valve closing timing and intake valve opening timing based on real-time engine temperature conditions. When the engine is particularly cold, the overlap is optimized to provide sufficient heat for fuel evaporation. As the engine warms up, the timing is dynamically adjusted to prevent excessive burnt gas trapping that could destabilize combustion. This dynamic adjustment maintains both temperature and combustion stability across different operating conditions.
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 enhances combustion stability and reduces unburnt HC and soot discharge, improving exhaust performance and fuel efficiency during cold starts by increasing the temperature and air flow within the combustion chamber.
Implementation Method 1
a large amount of hot burnt gas can be trapped inside the combustion chamber to increase a temperature inside the combustion chamber, thereby stimulating the evaporation of fuel
Implementation Method 2
the combustion chamber is put under a high negative pressure condition in the intake stroke... intake air can flow vigorously into the combustion chamber when the intake valve is opened
Data Source
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AI summary
A control apparatus for an engine including intake and exhaust valve phase variable devices and a control device is provided. At an engine temperature below a first determination temperature, the control is performed so that an exhaust valve close timing is at or retarded from the exhaust top dead center, an intake valve open timing is retarded from the exhaust valve close timing, and the fuel supply to the combustion chamber starts in an intake stroke on a retarding side of the exhaust valve close timing. At the engine temperature above the first determination temperature and below a second determination temperature, the control is performed so that a negative overlap with both the exhaust and intake valves closed during a period including the exhaust top dead center, or a positive overlap with both the exhaust and intake valves opened during a period including the exhaust top dead center, occurs.