Strain Wave Gear Tooth Layout for Tooth-Root Fatigue Relief
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Solution Overview
Problem
The tooth root of an externally toothed gear in strain wave gearing experiences stress concentration due to meshing with an internally toothed gear and bending, leading to reduced fatigue strength.
Innovation Solution
A strain wave gearing design that includes a non-meshing region along the tooth trace direction of the externally toothed gear, supported by a wave bearing, which mitigates stress concentration by removing teeth at the center portion where the radial force from the wave bearing is maximum, thereby increasing the tooth-root fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If teeth are formed continuously along the tooth trace direction of the externally toothed gear, then the torque transmission capability is improved, but stress concentration occurs at the tooth root leading to reduced fatigue strength
Solution Approach 1:
The patent divides the tooth trace direction into multiple segments: meshing regions with teeth for torque transmission and non-meshing regions without teeth for stress relief. This segmentation allows the gear to maintain torque transmission capability while eliminating stress concentration at the tooth root by creating tooth-free zones where bending stresses are highest during flexing.
Solution Approach 2:
The patent applies different structural qualities to different regions along the tooth trace direction. In meshing regions, full teeth are provided for effective torque transmission. In non-meshing regions, teeth are removed or reduced to create stress-free zones. This local differentiation optimizes both power transmission and fatigue resistance by matching structural properties to functional requirements in each region.
2Ease of operation
If the externally toothed gear is flexed into an elliptical shape by the wave generator, then the meshing with the internally toothed gear is enabled, but stress concentration occurs at the center portion along the tooth trace direction
Solution Approach 1:
The patent extracts or removes teeth from the center portion along the tooth trace direction where the wave generator applies radial forces and where bending stresses are maximized during elliptical flexing. By taking out teeth from this critical stress zone, the design eliminates the source of stress concentration while preserving teeth in regions where meshing forces are more favorable.
Solution Approach 2:
The patent preemptively removes teeth from the center portion before stress concentration can occur during operation. This preliminary structural modification prevents the harmful stress concentration effect from developing, rather than attempting to mitigate it after the gear is assembled and operating.
Data Source
AI summary
A strain wave gearing has a wave generator which flexes an externally toothed gear in a radial direction to form meshing portions thereof with an internally toothed gear in positions that are separated along a circumferential direction of the externally toothed gear. When the wave generator rotates, the meshing portions move in the circumferential direction. Non-meshing regions are formed in part of the meshing portions along the tooth trace direction thereof. The non-meshing regions are those of a prescribed width including the support center of a wave bearing in the tooth trace direction. The concentration of stress in the tooth root of the externally toothed gear can be alleviated, and the tooth-root fatigue strength of the externally toothed gear can be increased.