Asymmetric Flap Valve Two-Stroke Engine Port Timing
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Solution Overview
Problem
Prior two-stroke internal combustion engine configurations face challenges in maximizing pre-combustion cycle pressurization, as conventional designs restrict the ability to maintain high pressures or loads due to fixed and symmetrical port timing.
Innovation Solution
An asymmetric exhaust port/transfer port inversion device with a hollow flap valve that pivots about a hollow pivot shaft, allowing air or air/fuel mix to continue transferring after the piston closes the exhaust port, thereby advancing the exhaust port closing timing and extending the pressurization duration, facilitated by a cam, electromagnetic, or pneumatic actuation for variable timing control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional fixed port timing design is used, then the engine structure is simple, but the pre-combustion cycle pressurization cannot be maximized
Solution Approach 1:
The patent applies the dynamics principle by replacing the fixed port timing with a movable flap valve that can dynamically adjust its position. The flap valve is actuated by a cam mechanism that varies the port opening and closing timing according to the engine cycle, allowing optimization of pre-combustion pressurization while maintaining reasonable structural complexity through standardized cam mechanisms.
Solution Approach 2:
The patent implements parameter changes by modifying the port timing parameters through the cam-driven flap valve system. The cam profile can be designed to provide specific timing variations, changing when the exhaust and transfer ports open and close relative to the piston position, thereby optimizing the pressurization process without requiring complete redesign of the engine architecture.
2Productivity
If an asymmetric port timing system is implemented, then the pre-combustion pressurization is improved, but the device complexity increases
Solution Approach 1:
The flap valve serves multiple functions: it acts as both the exhaust port closure and the transfer port opening mechanism. By positioning the flap valve at the exhaust port location, it simultaneously controls exhaust gas evacuation and fresh charge admission, reducing the need for separate components and simplifying the overall mechanism despite the asymmetric timing requirements.
Solution Approach 2:
The cam mechanism acts as an intermediary that translates the rotational motion of the crankshaft into the desired asymmetric port timing. The cam profile encapsulates the complex timing requirements, providing a simple mechanical interface that automatically achieves the optimized pressurization timing without requiring complex control systems or multiple actuators.
3Duration of action of moving object
If the exhaust port closes early, then the pressurization duration is extended, but the exhaust evacuation may be incomplete
Solution Approach 1:
The asymmetric port timing is designed so that the transfer port opens before the exhaust port closes, creating an overlapping period where fresh charge begins to enter the combustion chamber while exhaust is still being evacuated. This preliminary action of the transfer port ensures that the pressurization process can begin earlier without compromising exhaust evacuation, as the two processes occur in sequence with proper timing coordination.
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 solution enables the engine to operate at high pressures and loads by allowing continued charge transfer into the combustion chamber after the exhaust port has closed, overcoming the limitations of fixed port timing in conventional designs.
Implementation Method 1
the hollow pivot shaft is adapted to receive a supply of air or air/fuel mix; and wherein pivoting the device to the open position as a piston begins the compression stroke allows the transfer of air or air/fuel mix to continue
Implementation Method 2
a hollow flap valve adapted to pivot about a hollow pivot shaft between a closed position and an open position
Implementation Method 3
the leading edge of the flap valve of the asymmetric exhaust port/transfer port inversion device is shaped to seal against the cylinder wall in the case of a conventional, round sliding two stroke piston engine or, alternatively, to seal against the sealing surfaces of the piston
Implementation Method 4
The piston further includes an arrangement to allow liquid coolant to pass through the pivot shaft, through liquid cooling galleries in the piston and out of the pivot shaft
Implementation Method 5
The piston is connected adjacent the end of the piston remote from the pivot point to a connecting rod which drives a crankshaft
Data Source
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AI summary
A two stroke internal combustion engine (1) incorporating an asymmetric exhaust port/transfer port inversion device (2) characterised in that the device includes a hollow flap valve (100) adapted to pivot about a hollow pivot shaft (101) between a closed position and an open position wherein pivoting the device (2) to the open position as the piston (3) begins the compression stroke allows the transfer of air to continue after the leading edge of the piston has closed off the exhaust port (105) thereby advancing the timing of the exhaust port closing and extending the duration of air transfer from the crankcase primary compression chamber (103).