Gear Shift Pawl Locking Structure for Durable Ratio Selection
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Solution Overview
Problem
Existing gear change devices for mobility machines, such as bicycles, are fragile due to the high force required to maintain clips in place, leading to potential deterioration and reliability issues.
Innovation Solution
A gear change device featuring a selection shaft with a shuttle and endless screw for speed changes, utilizing a ratchet system with a blocking mechanism comprising a single part with tabs and a groove to maintain the ratchet in place, reducing the force needed and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional locking system with multiple separate components is used to hold pawls in place, then the structural strength and reliability are improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The locking system merges multiple separate locking components into a single integrated locking element that simultaneously engages with multiple pawls. This single piece structure eliminates the need for multiple separate clips or retainers, reducing assembly complexity while maintaining the reliability of holding all pawls securely in place during operation.
Solution Approach 2:
The single-piece locking system is designed to perform multiple functions simultaneously: it holds multiple different-sized pawls (for various gear ratios) in place, provides structural support for the selection shaft assembly, and enables easy release when gear changing is required. This multi-functional design reduces the overall number of components needed in the gear changing device.
2Strength
If a robust locking system with multiple components is used to hold pawls, then the strength and durability are improved, but the ease of manufacture and assembly deteriorate
Solution Approach 1:
By combining multiple locking components into a single molded or machined piece, the manufacturing process is simplified from assembling multiple precision parts to producing one integrated component. This single-piece locking system can be manufactured using standard injection molding or CNC machining processes, reducing both manufacturing steps and quality control requirements while maintaining sufficient strength to hold pawls under operational loads.
3Reliability
If a traditional multi-component locking system is used, then the reliability is improved, but the cost of manufacturing and assembly increases
Solution Approach 1:
The consolidation of multiple locking components into one integrated piece eliminates the need for purchasing, inventory management, and assembly of several separate parts. This single-component approach reduces material costs, manufacturing overhead, and assembly labor, resulting in lower overall production costs while maintaining the reliability needed for durable gear changing operation.
4Reliability
If high force is applied to hold pawls in place, then the reliability is improved, but the fragility and risk of deterioration increase
Solution Approach 1:
The locking system distributes the holding force across multiple engagement points through a single integrated structure, rather than concentrating high force on individual clips or retainers. Each pawl is engaged by a dedicated section of the locking element, distributing mechanical stress and preventing localized fatigue or failure that would occur with high-force single-point locking mechanisms.
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
The solution provides a robust and efficient gear change system that reduces the risk of deterioration while allowing easy assembly and manufacturing, offering improved reliability and reduced costs by minimizing the force required to maintain the ratchet in position.
Implementation Method 1
a selection shaft in which a shuttle and a worm screw are arranged, a gear change actuator arranged to move the shuttle along the worm screw between at least two positions
Implementation Method 2
at least two pawls arranged at the selection shaft, the shuttle allowing the lifting of a pawl to engage the selected gear
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
The invention relates to a gear change device (20) for a mobility device (1) comprising: - a selection shaft (40) in which a shuttle (41) and a worm gear (21) are disposed, - a gear change actuator (70) arranged to move the shuttle (41) along the worm gear (21) between at least two positions, and engage a selected ratio, - at least two pawls (42) disposed at the level of the selection shaft (40). the shuttle allowing the lifting of a pawl to engage the selected ratio, each pawl having a first part (421) inserted in the shaft (40) and a second part (422), - a radial locking system (44), formed of a single piece, to hold all the pawls (42) in place on the selection shaft (40), characterized in that the locking system is arranged at the level of the first part (421) of the pawl (42).