Variable-Pitch Rotor Thread Assembly for Axial Load Distribution
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Solution Overview
Problem
Existing turbomachine rotor assemblies face challenges in efficiently transmitting large axial forces while managing high mechanical stresses, leading to rapid wear and short lifetime of threaded components due to uneven stress distribution.
Innovation Solution
A mechanical assembly with variable pitch threading and nut assembly, where the pitch varies along the axial dimension to distribute stress more evenly across multiple threads, reducing the load on the first thread and enhancing mechanical strength and lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional constant pitch threading is used, then the assembly structure is simple and easy to manufacture, but the stress concentrates on the first thread causing rapid wear and short lifetime
Solution Approach 1:
The patent applies local quality by varying the pitch of threads along the axial dimension of the threaded shaft. Different sections of the threading have different pitch values, with the pitch increasing from the first thread toward the last thread. This creates non-uniform stress distribution that reduces concentration on the first thread, thereby improving reliability and lifetime of the threaded components.
Solution Approach 2:
The patent changes the geometric parameter of the threading by varying the pitch along the axial dimension. Instead of using a constant pitch, the pitch parameter is modified progressively from one thread to the next, creating a gradient structure that optimizes stress distribution and prevents premature failure while maintaining manufacturability.
2Strength
If the first thread is overdimensioned to handle high stress, then the mechanical strength is improved, but the mass of the assembly increases
Solution Approach 1:
The variable pitch threading creates local quality variations where each thread section is optimized for its specific stress conditions. Threads experiencing higher stress have smaller pitch values providing stronger engagement, while threads in lower stress regions have larger pitch values reducing material requirements. This optimizes strength-to-weight ratio throughout the assembly.
Solution Approach 2:
Instead of overdimensioning the entire threading uniformly, the patent applies partial action by concentrating the enhanced strength characteristics only where needed - specifically in the first few threads that bear the highest stress. The pitch variation provides sufficient strength at critical locations without unnecessarily increasing the mass of the entire threaded assembly.
3Reliability
If constant pitch threading is used, then the manufacturing process is simple, but the stress distribution is uneven causing rapid wear
Solution Approach 1:
The patent modifies the pitch parameter along the axial dimension to improve wear resistance. By increasing the pitch from the first thread toward the last thread, the stress is more evenly distributed across all thread engagements, preventing rapid wear at the first thread while maintaining compatibility with conventional manufacturing processes.
Data Source
AI summary
The invention proposes a mechanical assembly for the transmission of axial forces between two secured parts, at least one of these parts having a portion with outer threading, said assembly further including a nut with inner threading able to cooperate with said outer threading to axially block by tightening the other part relative to the first part and to allow the transmission of axial forces between these two parts. The pitch of the outer threading and/or of the nut vary/varies along the axial dimension of the threading, the space gradually decreasing from the first thread to the rear thread in the expected direction for the axial force.The variable threading can be produced by chemical etching.