Choke Lever Guide Hole Structure for Backlash-Free Positioning
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Solution Overview
Problem
The existing opening/closing mechanisms for intake members in general-purpose engines, such as those in weed trimmers, experience backlash and imperfect positioning due to gaps between the choke lever and guide hole, leading to rattling and wear during engine operation.
Innovation Solution
An opening/closing mechanism with a guide hole that includes first and second fixing portions with widths equal to or less than the arm portion's width, and a wide portion with a length greater than the arm portion, allowing for stable fixation and smooth movement of the choke lever, reducing backlash and improving assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin slit-shaped guide hole is used to guide the choke lever movement, then positioning precision is improved, but assembly difficulty increases due to the need for precise width matching
Solution Approach 1:
The guide hole is segmented into three functional portions: a first fixing portion at one end, a second fixing portion at the other end, and a wide portion connecting them. This segmentation allows each portion to serve a specific function - the fixing portions provide precise positioning with widths equal to or less than the arm portion width, while the wide portion facilitates easy assembly by allowing the arm portion to be inserted without precision alignment.
2Ease of manufacture
If the guide hole width is made larger than the arm portion width for easy assembly, then assembly ease is improved, but backlash increases due to gaps between the choke lever and guide hole
Solution Approach 1:
The guide hole exhibits local quality variations along its length. The wide portion has a larger width that exceeds the arm portion width, providing assembly clearance and ease of insertion. In contrast, the first and second fixing portions have widths equal to or less than the arm portion width, creating interference-fit conditions that eliminate gaps and prevent backlash during operation. This localized variation in dimensional tolerance resolves the contradiction between assembly ease and operational reliability.
Data Source
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AI summary
Provided is an opening/closing mechanism for an intake member which enables backlash suppression a working member and positioning of a choke lever. The opening/closing mechanism includes the intake member that accommodates a filter part and has an opening leading to a carburetor at an end wall portion facing the filter part; an opening/closing member that is disposed between the filter part and the end wall portion, and opens and closes the opening; and a working member that is disposed on a side opposite to the opening/closing member with the end wall portion interposed therebetween. The working member includes an arm portion that extends along the end wall portion and is coupled with the opening/closing member at one end by sandwiching the end wall portion therebetween, and a holding portion that is provided at the other end of the arm portion, the intake member has a guide hole into which the arm portion is inserted to guide movement of the arm portion, the guide hole has a first fixing portion that fixes the arm portion on one side in a movement direction of the arm portion, and a second fixing portion that fixes the arm portion on the other side in the movement direction of the arm portion, and widths of the first fixing portion and the second fixing portion of the guide hole are respectively equal to or less than a width of the arm portion.