Negative-Deflection Strain Wave Gearing with Passing-Type Meshing
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Solution Overview
Problem
Generic strain wave gearings lack a tooth profile that enables passing-type meshing with a concave tooth profile for the externally toothed gear, which is necessary for reducing rim bending stress and improving lubrication and transmission torque.
Innovation Solution
A strain wave gearing design featuring a rigid internally toothed gear and a flexible externally toothed gear with an ellipsoidal wave generator, where the externally toothed gear has a concave tooth profile and a negative deflection tooth profile, allowing for passing-type meshing and reduced rim bending stress, and employing a convex basic tooth profile for the internally toothed gear to ensure effective lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If countermovement-type meshing is used in strain wave gearing, then the tooth profile design is simplified, but the lubrication performance deteriorates and wear resistance decreases
Solution Approach 1:
The patent changes the meshing type parameter from countermovement-type to passing-type meshing. This is achieved by specifically designing the tooth profiles of the internally toothed gear and externally toothed gear to satisfy the passing-type meshing conditions, where the linear elements of the tooth profiles are positioned on the same side relative to the contact point. This parameter change improves lubrication performance and wear resistance while maintaining manufacturability.
2Strength
If the externally toothed gear uses a convex tooth profile, then the tooth strength is improved, but the rim bending stress increases
Solution Approach 1:
The patent inverts the conventional convex tooth profile to a concave tooth profile for the externally toothed gear. This inversion reduces the rim bending stress by changing the stress distribution pattern in the gear rim. The concave profile, combined with passing-type meshing, maintains adequate tooth strength while significantly reducing the bending stress concentrated at the tooth root and rim interface.
3Reliability
If passing-type meshing is implemented in generic strain wave gearing, then lubrication performance is improved, but the tooth profile design complexity increases
Solution Approach 1:
The patent changes the meshing type parameter from countermovement-type to passing-type meshing. This is achieved by specifically designing the tooth profiles of the internally toothed gear and externally toothed gear to satisfy the passing-type meshing conditions, where the linear elements of the tooth profiles are positioned on the same side relative to the contact point. This parameter change improves lubrication performance and wear resistance while maintaining manufacturability.
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 design enhances the service life and allowable transmission torque of the strain wave gearing by achieving passing-type meshing and reducing rim bending stress, while maintaining effective lubrication.
Implementation Method 1
The externally toothed gear is ellipsoidally flexed by the wave generator, and external teeth of the ellipsoidally flexed externally toothed gear mesh with internal teeth of the internally toothed gear
Data Source
AI summary
A strain wave gearing is a negative deflection strain wave gearing. The tooth profile shape for the internally toothed gear is defined by using a convex, basic tooth profile curve, which is a curve portion from an inflection point (A) to a bottom-part point (B) of a moving locus (Mc) of an externally toothed gear with regard to an internally toothed gear obtained by a rack meshing approximation. The tooth profile shape for the externally toothed gear at a principal cross section is defined by a concave, basic tooth profile curve, which is generated in the externally toothed gear by the convex, basic tooth profile curve of the internally toothed gear moving from an apex (C) to an inflection point (A) of the moving locus (Mc). Passing-type meshing that is effective in lubrication is established, and bending stress in the tooth-bottom rim of the externally toothed gear can be reduced.