Tri-tab Lock Washer Anti-rotation Design
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Solution Overview
Problem
Previous mid turbine frame assemblies experience reduced service life due to stress risers formed by grooves and slots in the inner and outer cases, which are necessary for anti-rotation features, and there is a risk of improper installation without clear orientation guidance.
Innovation Solution
A washer with a hub and three lobes, each with a hole, and anti-rotation tabs that can be bent against fastener heads, is used to prevent rotation and loosening of fasteners without requiring slots or grooves in the inner case, and its unique triangular outline ensures correct installation by allowing only one orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grooves and slots are formed in the inner case and outer case to prevent strut movement, then the anti-rotation and loosening of fasteners is improved, but stress risers are created that reduce the service life of the MTF assembly
Solution Approach 1:
The invention extracts the anti-rotation function from the inner case structure (by removing grooves and slots) and relocates it to the washer component. The washer includes tabs that extend into slots formed in the strut foot, thereby preventing fastener rotation without requiring modifications to the inner case that would create stress risers.
Solution Approach 2:
The washer acts as an intermediary component between the fastener and the inner case. Instead of directly forming grooves in the inner case to prevent rotation, the washer with its tabs engages with slots in the strut foot, serving as a mediator that provides anti-rotation functionality while preserving the integrity of the inner case structure.
2Stability of the object's composition
If the inner case and outer case are modified with grooves and slots to secure struts, then the mechanical connection stability is improved, but the structural integrity and stress distribution are worsened
Solution Approach 1:
The invention removes the need for grooves and slots in the inner case by extracting the anti-rotation functionality and placing it in the washer. This preserves the structural integrity of the inner case while still achieving stable mechanical connections through the washer tabs engaging with slots in the strut foot.
Solution Approach 2:
The invention applies the slot feature locally to the strut foot rather than extensively to the inner case structure. The slots are formed only in the strut foot where they are needed for tab engagement, while the inner case remains intact without stress-inducing modifications, thus maintaining local structural quality.
3Ease of manufacture
If a symmetric washer design is used, then manufacturing simplicity is improved, but installation orientation guidance is lost leading to potential improper installation
Solution Approach 1:
The invention introduces asymmetry to the otherwise symmetric triangular washer design by forming tabs of different lengths on different lobes. Specifically, one lobe has a first-length tab while another lobe has a second-length tab. This asymmetric feature provides clear orientation guidance during installation while maintaining the simple triangular overall shape that is easy to manufacture.
Data Source
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AI summary
A washer 46 includes a hub 78 and a first lobe 80 connected to the hub 78. The first lobe 80 includes a first hole 92. A second lobe 82 is also connected to the hub 78 and includes a second hole 96. A third lobe 84 is also connected to the hub 78 and includes a third hole 100. The first lobe 80 extends from the hub 78 at least partially in a first direction opposite the second lobe 82 and the third lobe 84.