Unidirectional Clutch Wheel Assembly With Point-Contact Pawls
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Solution Overview
Problem
Existing unidirectional clutch wheel assemblies are sensitive to manufacturing and assembly tolerances, and wear, due to uncontrolled contacts between pawls, inner toothing, and rigid drive parts, which affects torque transmission and resistance, limiting their operational precision and efficiency.
Innovation Solution
A unidirectional clutch wheel assembly with a rigid pawl connected by a C-shaped elastic strip to a rigid drive member, featuring asymmetric inner toothing and point contacts for precise operation, allowing high torque transmission while minimizing friction and sensitivity to assembly tolerances, with the elastic strip being non-operational during coupling and disengaging easily during uncoupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If pawls are connected by U-shaped elastic strips to a rigid drive part with direct locking in inner toothing, then torque transmission in coupling direction is achieved, but contacts cannot be effectively controlled and the system becomes sensitive to manufacturing and assembly tolerances
Solution Approach 1:
The patent changes the geometric parameters of the pawls and inner toothing to achieve point contacts instead of line or surface contacts. The pawls are designed with specific curvature radii and the inner toothing has asymmetric teeth with controlled dimensions, transforming the contact regime to reduce sensitivity to tolerances while maintaining torque transmission capability
Solution Approach 2:
The patent introduces an intermediary elastic element (the elastic strip) that connects the pawl to the drive part, but designs it to be non-operational during coupling. This intermediary allows controlled disengagement while maintaining precise point contacts during engagement, mediating between the rigid torque transmission requirement and the need for tolerance compensation
2Loss of energy
If C-shaped elastic pawls are used with free end located on a larger circumference, then resistance torque is reduced during uncoupling, but torque transmission is limited by the risk of buckling
Solution Approach 1:
The patent makes the elastic strip operational only during disengagement, not during coupling. The pawl transitions from a static elastic element to a dynamic one that engages rigidly during torque transmission and becomes flexible only when needed for disengagement, optimizing both torque transmission and resistance reduction
Solution Approach 2:
The patent employs asymmetric inner toothing where the teeth have different geometries on different sides. This asymmetry allows the pawl to make point contacts with specific tooth surfaces during coupling for high torque transmission, while enabling easy disengagement by allowing the pawl to pass between asymmetric tooth profiles with minimal resistance
3Manufacturing precision
If point contacts are implemented with rigid pawl and asymmetric inner toothing, then manufacturing and assembly tolerance sensitivity is reduced, but device complexity increases
Solution Approach 1:
The patent merges the pawl, elastic strip, and drive part into a integrated assembly where the elastic strip is directly connected to the drive part. This consolidation reduces the number of separate components and assembly steps while achieving the complex point contact geometry through the integrated structure rather than through multiple separate elements
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 precise and robust clutch mechanism with high torque transmission, reduced friction, and improved resistance to wear and manufacturing tolerances, ensuring reliable operation in timepiece mechanisms.
Implementation Method 1
a rigid pawl (6) connected by a C-shaped elastic strip (7) to a rigid drive member (5)
Data Source
AI summary
Disclosed is a unidirectional clutch wheel assembly that includes a first wheel, a second wheel coaxial with the first wheel and including an inner toothing, a rigid drive member rotationally fixed with respect to the first wheel and at least one rigid pawl connected to the rigid drive member by an elastic strip. The rigid pawl is locked against the inner toothing by the rigid drive member to rotationally fix the first and second wheels to each other when the first wheel or the second wheel is rotationally driven in a direction corresponding to coupling. The inner toothing has asymmetrical teeth. The rigid pawl is arranged, in its position locked against the inner toothing, to be in point contact, in top plan view, with two consecutive teeth of the inner toothing and with the rigid drive member.