Reduced-Shank Gearbox Fasteners for Deeper Low-Friction Assembly
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Solution Overview
Problem
Conventional fasteners with uniform shank diameters face challenges in clearance and friction when used with imperfect threads, limiting their installation depth and increasing the risk of bending or shear loading, especially in applications like rotorcraft gearboxes where high tolerance and reduced lubrication are critical.
Innovation Solution
A fastener design featuring a shaft with first and second threaded portions separated by a central portion of reduced diameter, chamfered to reduce friction, made from high-strength steel alloys like nickel chromium or chromium molybdenum steel, allowing deeper installation and maximizing tensile strength along the longitudinal axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fasteners with uniform shank diameters are used, then the fastener structure is simple and easy to manufacture, but the fastener experiences increased friction and limited installation depth, increasing the risk of bending or shear loading
Solution Approach 1:
The fastener shank is segmented into multiple portions with different diameters: a first shank portion with a first diameter for engagement with the first threaded hole, and a second shank portion with a second diameter for engagement with the second threaded hole. This segmentation allows each portion to be optimized for its specific function, reducing friction and bending moments in the second portion while maintaining structural integrity.
Solution Approach 2:
Different portions of the fastener shank are given different local qualities (diameters) to optimize performance in specific locations. The reduced diameter of the second shank portion provides clearance to surrounding material and reduces friction on leading threads in the second threaded hole, while the first shank portion maintains a larger diameter for structural support and engagement with the first threaded hole.
2Length of moving object
If the fastener shank diameter is reduced to provide clearance, then installation depth increases and friction is reduced, but the fastener tensile strength decreases
Solution Approach 1:
The shank is divided into segments with different diameters, allowing the second shank portion to be reduced for deeper installation and reduced friction, while the first shank portion maintains a larger diameter to preserve overall tensile strength and structural integrity of the fastener.
Solution Approach 2:
The fastener employs local quality by providing different diameters at different locations along the shank. The reduced diameter is applied locally to the second shank portion where clearance and reduced friction are needed, while other portions maintain larger diameters to preserve strength, achieving both deeper installation and maintained tensile strength.
3Reliability
If the fastener is installed deeper into the structure, then clearance is improved and friction is reduced, but the fastener becomes more susceptible to bending and shear loading
Solution Approach 1:
The segmented shank design allows the second shank portion to extend deeper into the second threaded hole with reduced diameter, improving clearance and reducing friction. Simultaneously, the first shank portion with larger diameter provides structural support that resists bending and shear loading, maintaining stability despite the deeper installation.
Solution Approach 2:
By applying reduced diameter locally to the second shank portion rather than uniformly across the entire shank, the fastener achieves improved clearance and reduced friction in the critical engagement zone while maintaining larger diameter sections that provide resistance to bending and shear loading.
Data Source
AI summary
A method of fastening gearbox housing components together, comprising: selecting a gearbox housing fastener comprising a straight shaft having a longitudinal axis, a first threaded portion, a single cylindrical central portion, and a second threaded portion, wherein the first and second threaded portions are separated by the cylindrical portion, wherein the cylindrical portion comprises a single reduced diameter that is less than first and second minor diameters of the first and second threaded portions, the first and second threaded portions are chamfered, and the fastener comprises a material having a tensile strength along the longitudinal axis that is greater than a sheer strength at the cylindrical portion; and fastening the gearbox housing components together with the fastener, wherein the first and third gearbox housing components are fastened with the first and second threaded portions, and the second gearbox housing component is positioned around the single cylindrical central portion.