Stratified Scavenging Two-Stroke Engine Blow-by Suppression
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Solution Overview
Problem
The existing stratified scavenging two-stroke engines with a throttle near the scavenging port fail to ensure a sufficient amount of leading air, leading to inadequate suppression of blow-by of the air-fuel mixture.
Innovation Solution
The engine design includes a scavenging passage with a main passage near the exhaust port and a sub passage near the intake port, where the sub passage has an air-fuel mixture inlet acting as a flow rate adjuster, and the outer piston circumference has recesses to communicate with the scavenging passages, allowing a large amount of leading air to be fed through the entire scavenging passage, ensuring reliable blow-by suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a throttle is provided near the scavenging port to reduce inflow energy of air-fuel mixture, then blow-by suppression is improved, but the amount of leading air fed into the scavenging passage is insufficient
Solution Approach 1:
The scavenging passage is divided into a main passage near the exhaust port and a sub passage near the intake port, with the throttle positioned only in the sub passage. This segmentation allows the main passage to receive sufficient leading air from the crankcase while the sub passage with the throttle controls the air-fuel mixture flow, resolving the contradiction between leading air quantity and blow-by suppression.
Solution Approach 2:
Different sections of the scavenging passage are given different functions: the main passage is optimized for leading air flow with larger cross-section, while the sub passage contains the throttle for localized flow rate adjustment of air-fuel mixture. This local differentiation allows each section to optimize its specific function without compromising the other.
2Device complexity
If the scavenging passage is extended from the opening end of the cylinder bore to the scavenging port, then the structure is simplified, but the amount of leading air may be insufficient without a flow rate adjustor
Solution Approach 1:
The extended scavenging passage is segmented into main and sub passages, with the throttle positioned only in the sub passage. This allows the overall passage to be long and simple in structure while ensuring that the main passage remains open for sufficient leading air flow, and the throttle in the sub passage provides necessary flow control without restricting overall leading air quantity.
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 ensures a sufficient amount of leading air is supplied to the combustion chamber, effectively scavenging exhaust gas and reliably suppressing blow-by of the air-fuel mixture, while maintaining a simplified structure and reduced production costs.
Implementation Method 1
the outer circumference of the piston is provided with a pair of recesses for communicating the leading-air passage and the scavenging passages in conjunction with the upward movement of the piston
Implementation Method 2
the sub passage includes an air-fuel mixture inlet provided at a position corresponding to an opening end of the cylinder bore that faces the crankcase, and the inlet functions as a flow rate adjustor
Implementation Method 3
leading air is fed into a scavenging passage through a scavenging port, and the leading air is initially supplied to the combustion chamber through the scavenging passage prior to air-fuel mixture for scavenging, thereby suppressing blow-by of the air-fuel mixture
Data Source
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AI summary
A stratified scavenging two-stroke engine includes: a crankcase (2); a cylinder (3) being provided with a cylinder bore (31); an intake passage (4) supplying air-fuel mixture into the crankcase (2) via an intake port (4A); a scavenging passage (5) supplying the air-fuel mixture from the crankcase (2) into the cylinder bore (31) via a scavenging port (5A); a leading-air passage (6) supplying leading air into the scavenging passage (5); and an exhaust passage (7) being disposed on an opposite side of the intake passage (4) with the cylinder bore (31) interposed therebetween, the exhaust passage (7) discharging exhaust gas via an exhaust port, in which the scavenging passage (5) includes a main passage (51) provided near the exhaust port and a sub passage (52) provided near the intake port (4A), the main passage (51) and the sub passage (52) are isolated from each other by a partition (25, 34) that extends over substantially an entire length of the main passage (51) and the sub passage (52), the sub passage (52) includes an air-fuel mixture inlet (55) provided at a position corresponding to an opening end (35) of the cylinder bore (31) that faces the crankcase (2), and the inlet (55) functions as a flow rate adjuster having a throttle effect.