Eccentric Oscillation Gear Fastening for Stable Bearing Preload
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Solution Overview
Problem
Conventional eccentric oscillation gear devices experience instability in axial tension due to variations in frictional force among fasteners, leading to uneven preloading of main bearings and reduced rotational stability.
Innovation Solution
The eccentric oscillation gear device incorporates a fastening portion with an internally threaded portion and a fastener having an externally threaded portion with a Rockwell hardness of 44 or higher. This design allows the externally threaded portion to plastically deform the internally threaded portion, increasing the contact area and reducing variations in fastening force, thereby stabilizing the axial tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fasteners with uniform hardness are used to fasten the hold and shaft portion, then the fastening structure is simple, but the frictional force varies among fasteners causing instability in axial tension
Solution Approach 1:
The fastener is designed with non-uniform hardness distribution: the shaft portion has higher hardness (HRC 44 or higher) to maintain dimensional stability and reduce frictional force variation, while the head portion has lower hardness to allow plastic deformation and increase contact area. This local quality differentiation resolves the contradiction by improving axial tension stability through targeted hardness optimization in different regions of the fastener.
2Reliability
If the fastener has high hardness to reduce frictional force variation, then axial tension stability improves, but the fastener may not deform to increase contact area
Solution Approach 1:
The fastener employs differentiated hardness in its components: the shaft portion maintains high hardness (HRC 44 or higher) to minimize frictional force variation and stabilize fastening force, while the head portion uses lower hardness material that can plastically deform to increase contact area with the internally threaded portion. This local quality approach resolves the contradiction by assigning different hardness characteristics to different functional regions of the fastener.
3Reliability
If the internally threaded portion has the same hardness as the fastener, then manufacturing is simpler, but the contact area between threads remains small causing variation in fastening force
Solution Approach 1:
The internally threaded portion is designed with lower hardness compared to the fastener shaft portion. This parameter change in hardness allows the internally threaded portion to undergo plastic deformation during fastening, increasing the contact area between threads and reducing fastening force variation. The hardness parameter is specifically optimized to enable controlled deformation while maintaining structural integrity.
4Reliability
If conventional fastening methods are used, then the manufacturing process is straightforward, but the axial tension varies among fastening portions leading to uneven bearing preload
Solution Approach 1:
The fastener shaft portion is designed with high hardness (HRC 44 or higher) to minimize frictional force variation during fastening. This parameter change in hardness ensures that axial tension remains consistent across multiple fastening portions, enabling uniform bearing preload. The high hardness material maintains dimensional stability and reduces variation in fastening force, resolving the contradiction between reliability and manufacturing efficiency.
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 effectively stabilizes the axial tension between the hold and shaft portions, ensures even preloading of main bearings, and improves the rotational stability of the eccentric oscillation gear device, maintaining the upper limit of axial tension variation below the bolt yield point.
Implementation Method 1
the threads of the externally threaded portion having the above-mentioned hardness can plastically deform the rough surface or micro projections of the threads of the internally threaded portion when the first and second members are fastened
Data Source
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AI summary
An eccentric oscillation gear device includes a casing, a first member supported by the casing via a first bearing, a second member supported by the casing via a second bearing, and a fastening portion fastening the first and second members in an axial direction of the casing. The fastening portion includes an internally threaded portion formed in the first member, and a fastener having an externally threaded portion. The fastener has a Rockwell hardness (HRC) of 44 or higher, and the internally threaded portion has a lower hardness than the fastener.