Variable Ratio Choke Linkage for Handheld Engine Start
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Solution Overview
Problem
Handheld work apparatuses with combustion engines face challenges in providing a simple and ergonomic operating configuration for switching between warm and cold start positions, affecting the choke element's pivot angles and transmission ratios, which impact starting behavior and user comfort.
Innovation Solution
The design incorporates a pivotable operating-mode selector with specific pivot angles and contact points that adjust the choke element differently between warm and cold start positions, ensuring ergonomic operation and improved starting behavior by varying the pivot angles and transmission ratios, allowing for precise choke element positioning in warm start and quick closure in cold start.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the operating mode selector is pivoted by the same angle between operating position, warm start position and cold start position, then ergonomic operation is achieved, but the choke element cannot be pivoted by different angles to achieve good starting behavior
Solution Approach 1:
The transmission ratio between the operating mode selector and the choke element is made variable rather than fixed. The adjusting element is designed with different contact points (first contact point for warm start, second contact point for cold start) that engage with the actuating element at different positions, causing the transmission ratio to change dynamically based on the operating mode. This allows the choke element to be pivoted by a smaller angle during warm start and a larger angle during cold start, while the operator always pivots the selector by the same ergonomic angle.
Solution Approach 2:
The transmission ratio parameter is changed by selecting different contact points on the adjusting element. When the operating mode selector is in the warm start position, the first contact point engages with the actuating element, providing a first transmission ratio. When in the cold start position, the second contact point engages, providing a second, different transmission ratio. This parameter change enables different choke element pivot angles for different operating conditions while maintaining constant operator input angle.
2Manufacturing precision
If the choke element is pivoted by a small angle between operating position and warm start position, then precise positioning is achieved, but the transmission ratio becomes too high for quick closure in cold start position
Solution Approach 1:
The transmission ratio is dynamically adjusted based on the operating mode. During warm start, the first contact point engagement provides a higher transmission ratio for precise positioning of the choke element. During cold start, the second contact point engagement provides a lower transmission ratio, allowing the choke element to be pivoted by a larger angle and close more quickly. The system automatically selects the appropriate transmission ratio based on the operating mode selector position.
Solution Approach 2:
The transmission ratio parameter is changed by engaging different contact points on the adjusting element. The first contact point is positioned to provide a higher transmission ratio for warm start positioning accuracy. The second contact point is positioned to provide a lower transmission ratio for cold start quick closure. This parameter change resolves the contradiction between precision and speed by selecting the appropriate transmission ratio for each operating condition.
3Device complexity
If the adjusting element and actuating element engage at the same contact location for both warm and cold start positions, then the configuration is simple, but the choke element cannot be actuated by different pivot angles
Solution Approach 1:
The adjusting element is segmented with distinct first and second contact points positioned at different locations. The first contact point is positioned to engage with the actuating element at a first position that provides a first transmission ratio for warm start. The second contact point is positioned to engage at a second position that provides a second transmission ratio for cold start. This segmentation allows different pivot angles to be achieved while maintaining a relatively simple overall configuration using standard mechanical linkages.
Solution Approach 2:
The adjusting element acts as an intermediary between the operating mode selector and the actuating element. By providing multiple contact points (first and second contact points) at different positions, it mediates the transmission of motion with different transmission ratios depending on which contact point is engaged. This intermediary mechanism enables different pivot angles for different operating modes without requiring complex separate mechanisms for each mode.
Data Source
AI summary
A work apparatus has an engine with a carburetor. An actuating element is connected to the choke shaft of the choke element of the carburetor. An operating mode selector has operating, warm start and cold start positions and is connected fixedly in terms of rotation to an adjusting element. The actuating element is pivoted through a pivot angle (α1) from the operating position into the warm start position and through a pivot angle (α2) from the warm start position into the cold start position. The selector is pivoted through a pivot angle (γ1) from the operating position into the warm start position and through a pivot angle (γ2) from the warm start position into the cold start position. The ratio of the pivot angle (α2) to the pivot angle (α1) is at least approximately 1.5 times the ratio of the pivot angle (γ2) to the pivot angle (γ1).