Two-Stroke Engine Crankcase Recess for Emission Reduction
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Solution Overview
Problem
Two-stroke engines face challenges in reducing exhaust gas values and optimizing the design for low emissions while maintaining structural stability and compact size.
Innovation Solution
The design incorporates a recess in the crankcase side wall around the crankshaft bearing, open to the crankcase interior over an angle of at least 45° to 320°, which increases the crankcase volume, reduces pressure, and slows the flow of the fresh mixture into the combustion chamber, while maintaining structural stability through end walls and stiffening ribs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the crankcase volume is increased to reduce pressure and slow mixture flow, then exhaust gas values are reduced, but the engine size increases
Solution Approach 1:
The crankcase volume is increased by creating a recess in the side wall that segments the crankcase interior into distinct regions. This recess is open to the crankcase interior over an angle of at least 45° and at most 320° around the axis of rotation, effectively adding volume without increasing the overall engine footprint, thereby reducing pressure and slowing mixture flow to reduce exhaust gas values.
Solution Approach 2:
Instead of increasing engine size in all dimensions, the solution adds volume in the radial direction by creating a recess in the side wall. This dimensional approach allows volume increase while maintaining compact overall engine dimensions, as the recess extends into the side wall rather than expanding the external envelope.
2Object-generated harmful factors
If a recess is created in the side wall to increase crankcase volume, then pressure is reduced and mixture flow is slowed, but structural stability may be compromised
Solution Approach 1:
The recess is designed with specific angular constraints (at least 45° and at most 320° around the axis of rotation) and is delimited at both ends by end walls. This localized geometry provides sufficient volume increase while maintaining structural integrity in critical areas, balancing the need for volume expansion with structural stability requirements.
Solution Approach 2:
The solution combines the recess structure with end walls that close the recess at both ends. This composite structural approach allows the recess to provide volume increase while the end walls maintain structural stability, creating a hybrid structure that achieves both objectives simultaneously.
3Volume of moving object
If the recess is open over a large angle to maximize volume, then crankcase volume is increased, but the risk of annular flow formation increases
Solution Approach 1:
The angular extent of the recess is precisely controlled within specific boundaries (at least 45° and at most 320° around the axis of rotation). By optimizing this angular parameter, the design achieves sufficient volume increase while preventing the formation of annular flow patterns that would occur with larger angular openings, thus simplifying the flow pattern.
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 design effectively reduces exhaust gas values by optimizing the flow of the fresh mixture and maintaining structural integrity, achieving a compact engine size with improved scavenging efficiency and reduced emissions.
Implementation Method 1
The volume of the crankcase interior can be increased via the recess, which is open to the crankcase interior over an angle of at least 45° and at most 320° around the axis of rotation of the crankshaft. As a result, the pressure in the interior of the crankcase is reduced during operation
Implementation Method 2
As a result, the speed at which the fresh mixture flows over into the combustion chamber can be reduced
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A two-stroke engine (9) comprises a cylinder (38) and a crankcase (39). A combustion chamber (25) is formed in the cylinder (38), which is bounded by a piston (19) mounted to reciprocate within the cylinder (38). The piston (19) drives a crankshaft (21) rotatably mounted in the crankcase (39). A crankcase interior (40) and the combustion chamber (25) are fluidically connected to each other via at least one transfer port (26) in at least one position of the piston (19). The crankcase interior (40) is bounded in the direction of the axis of rotation (22) of the crankshaft (21) by two opposing side walls (51, 52). The crankshaft (21) is supported by at least one crankshaft bearing (47, 48) arranged in one of the side walls (51, 52).In at least one side wall (51, 52) a recess (53, 53a, 53b, 54) extends around the crankshaft bearing (47, 48), around the axis of rotation (22) of the crankshaft (21), and is open to the crankcase interior (40) at an angle (a) of at least 45° and at most 320° around the axis of rotation (22) of the crankshaft (21). The recess (53, 53a, 53b, 54) is bounded at its ends (55, 56, 57, 58) by at least one end wall (65, 66, 67, 68).