Switchable Crankcase Overflow in Two-Stroke Engines
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Solution Overview
Problem
Internal combustion engines face challenges in achieving improved exhaust gas values, particularly in efficiently scavenging the combustion chamber and reducing scavenging losses, especially at varying engine speeds and loads.
Innovation Solution
The engine design incorporates a switching element that controls the connection between the crankcase interior and the combustion chamber via a first overflow channel, allowing for precise fuel metering and air supply, with the switching element adjusting based on engine speed and throttle position to optimize fuel delivery and scavenging efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the overflow channel is always open to the crankcase interior, then fuel can be supplied into the crankcase for lubrication, but fuel/air mixture may enter the crankcase causing incomplete combustion and higher exhaust gas values
Solution Approach 1:
The connection opening in the overflow channel is made switchable between open and closed states. The switching element dynamically controls whether the overflow channel connects to the crankcase interior, allowing the system to adapt between fuel supply mode (open) and scavenging mode (closed), thereby preventing harmful fuel/air mixture entry while maintaining lubrication capability when needed
Solution Approach 2:
The system changes the flow path parameter by switching the connection opening state. When closed, the overflow channel directs fuel/air mixture exclusively to the combustion chamber; when open, it allows crankcase lubrication. This parameter change controls whether harmful factors are generated or avoided
2Object-generated harmful factors
If the connection opening is closed to prevent fuel/air mixture entry, then exhaust gas values improve, but the system loses adaptability to different operating conditions
Solution Approach 1:
The switching element provides dynamic adaptability by allowing the system to change states based on operating conditions. The connection opening can be opened for crankcase lubrication needs and closed for optimal scavenging, giving the system versatility to handle different operational requirements while maintaining low exhaust gas values as the default state
Solution Approach 2:
The system can self-adjust between modes by using the switching element to control whether the overflow channel serves fuel delivery or crankcase lubrication functions, adapting to different operating conditions without external intervention while maintaining improved exhaust gas values
3Productivity
If fuel is supplied into the overflow channel, then combustion chamber scavenging improves, but unburned fuel may transfer to the outlet increasing losses
Solution Approach 1:
The switching element extracts or removes the harmful effect by closing the connection opening to prevent fuel/air mixture from taking an unintended path through the crankcase to the outlet. This ensures fuel is delivered only where needed (combustion chamber via overflow channel) and not lost to the crankcase, maintaining both scavenging efficiency and fuel economy
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 improved exhaust gas values by ensuring precise fuel metering and scavenging, reducing unburned fuel transfer to the outlet and minimizing scavenging losses across different engine operating conditions.
Implementation Method 1
the overflow channel establishes a fluidic connection between a crankcase interior and a combustion chamber formed in the cylinder
Implementation Method 2
The first transfer channel is connected to the crankcase interior via a first orifice opening
Data Source
Figure 1
Figure 2a~2e
Figure 3~4
AI summary
An internal combustion engine (1) has a cylinder (2) in which a combustion chamber (3) is formed and a piston (5) that delimits the combustion chamber (3). The internal combustion engine (1) has at least one first transfer port (14) which, in the region of the bottom dead center of the piston (5), establishes a fluidic connection between a crankcase interior (24) of a crankcase (4) and the combustion chamber (3). The internal combustion engine (1) has a fuel supply device that supplies fuel between a first transfer port (15) of the first transfer port (14) and a first outlet (25) of the first transfer port (14) into the first transfer port (14).To enable the operation of the internal combustion engine (1) with low emissions, the first transfer port (14) is provided with a connecting opening (26) to the crankcase interior (24), and a switching element (22, 22') is provided for switching the connecting opening (26). A method for operating the internal combustion engine (1) provides that the switching element (22, 22') is adjusted, depending on the rotational speed of the internal combustion engine (1), between a first switching position (27), in which the flow cross-section of the connecting opening (26) is open, and a second switching position (28), in which the flow cross-section of the connecting opening (26) is at least partially closed.