Two-Stroke Air Cleaner Pivotable Choke Valve Design
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Solution Overview
Problem
Conventional two-stroke engines with separate choke valves for air and air/fuel mixture passages face complexity and size issues due to increased number of valves, and achieving high airtightness with rotary valve members is difficult due to large sealing surfaces.
Innovation Solution
A pivotable choke valve with a flattened inlet opening closer to the pivot axis allows simultaneous opening and closing of both passages within a small angle range, reducing the size and work range of the valve, and ensuring high airtightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If separate choke valves are provided for the air passage and air/fuel mixture passage, then the air supply control is improved, but the device complexity and size increase
Solution Approach 1:
The patent combines two separate choke valves into a single choke valve that controls both the air passage and air/fuel mixture passage. The valve member is designed with a specific shape that allows it to simultaneously seal both passages when closed, reducing the number of components while maintaining independent control capability over air supply to each passage.
Solution Approach 2:
The single choke valve is designed to perform multiple functions: it controls air supply to both the air passage and air/fuel mixture passage, and can selectively close either passage or both passages based on operating conditions. This multi-functional design eliminates the need for separate valves while maintaining operational flexibility.
2Volume of stationary object
If a rotary valve member is used to close both passages simultaneously, then the device size is reduced, but the sealing surface area increases making manufacturing difficult
Solution Approach 1:
The valve member is designed with a segmented or distributed sealing structure where multiple smaller sealing points are arranged along the pivot axis, rather than requiring a single large sealing surface. This segmentation allows the valve to effectively close both passages while keeping the sealing surface area small and manageable for manufacturing.
Solution Approach 2:
The sealing approach transitions from requiring a large two-dimensional sealing surface to using a one-dimensional arrangement of sealing points along the pivot axis. This dimensional change allows simultaneous closure of both passages with minimal sealing surface area, making manufacturing feasible while maintaining compact device size.
3Volume of stationary object
If the pivot axis is positioned to reduce valve size, then the device compactness is improved, but achieving high airtightness becomes more difficult
Solution Approach 1:
The valve member is designed with an asymmetric shape that is optimized for the specific pivot axis position. The asymmetric geometry allows the valve to achieve effective sealing in both passages despite the constrained pivot location, maintaining compact valve size while ensuring high airtightness through carefully positioned sealing edges that conform to the passage inlet shapes.
Data Source
Figure 1~2
Figure 3~4(b)
AI summary
An air cleaner in a two-stroke engine having an air supply passage that is connected midway of a scavenging passage communicating a scavenging port provided in a side portion of a cylinder with a crank chamber and that supplies leading air from the air cleaner to the scavenging passage, and an air/fuel mixture supply passage supplying air/fuel mixture created in a carburetor to the crank chamber. The air cleaner includes: a first air passage and a second air passage arranged in parallel, the first air passage being communicated with the air supply passage and the second air passage being communicated with the air/fuel mixture supply passage; and a choke valve opening and closing both of the first air passage and the second air passage of the air cleaner. The choke valve has a pivot axis and a pivotable valve member pivoting about the pivot axis to open and close respective inlet openings of the first air passage and the second air passage. One of the first air passage and the second air passage that is located closer to the pivot axis has an inlet opening flattened along a pivoting edge of the valve member.