Offset-Tab Lock Washer Structure for Aircraft Engine Fatigue Relief
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Solution Overview
Problem
Lock washers in aircraft engines experience fatigue and potential fractures due to high centrifugal stresses, leading to loose fragments in rotating components, as existing designs with circumferentially overlapping tabs are prone to stress concentration points.
Innovation Solution
A lock washer design with radially-inward and radially-outward protruding tabs that are circumferentially offset, eliminating overlap and featuring fillets and cutouts to distribute stress, and a retaining feature like a wire to axially secure the washer, preventing relative rotation between the shaft and nut.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circumferentially overlapping tabs are used in the lock washer, then the locking function is improved, but stress concentration occurs leading to fatigue and fractures
Solution Approach 1:
The lock washer is segmented into distinct radially-inward protruding tabs and radially-outward protruding tabs that are circumferentially offset from each other. This segmentation eliminates the overlapping structure, separating the engagement points with the shaft and nut into non-overlapping zones, thereby distributing stress more evenly across the washer body and preventing stress concentration at overlap regions.
Solution Approach 2:
The invention transitions from a conventional single-plane tab structure to a multi-dimensional arrangement where tabs protrude in different radial directions (inward and outward) and are offset circumferentially. This dimensional reconfiguration allows the tabs to engage with shaft and nut slots at different circumferential positions, eliminating overlap while maintaining effective locking across multiple engagement planes.
2Reliability
If circumferentially overlapping tabs are used in the lock washer, then the locking function is improved, but loose fragments are generated due to fractures
Solution Approach 1:
By segmenting the lock washer into non-overlapping radially-inward and radially-outward protruding tabs, the structure eliminates the weak overlap regions that are prone to fracture. Each tab is independently supported and engaged, preventing the propagation of cracks that would otherwise occur at overlapping joints, thereby avoiding generation of loose fragments.
Solution Approach 2:
The invention converts the potential harm of tab overlap (stress concentration and fracture) into a beneficial non-overlapping configuration. The circumferential offset arrangement transforms the overlapping hazard into a distributed stress pattern where each tab engages separately, converting a failure-prone structure into a reliable fragment-free design.
3Strength
If non-overlapping tabs are used in the lock washer, then stress is minimized, but the locking effectiveness may be reduced
Solution Approach 1:
The invention maintains locking effectiveness despite non-overlapping tabs by utilizing multiple radial dimensions and circumferential offset positions. The radially-inward tabs engage with shaft slots while radially-outward tabs engage with nut slots at different circumferential locations, creating a multi-point distributed locking system that achieves both stress minimization and effective locking.
Solution Approach 2:
The lock washer design achieves multi-functionality by having both radially-inward and radially-outward protruding tabs perform simultaneous locking functions. The inward tabs prevent relative rotation with the shaft while outward tabs secure the nut, creating a universal locking mechanism that maintains effectiveness across different engagement points without requiring overlapping structures.
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
A lock washer (60) for preventing relative rotation between an inner component and an outer component in an aircraft engine. The lock washer comprises an annular body (61) having an inner circumferential surface (62) and an outer circumferential surface (63) radially spaced apart to define a radial thickness (T) of the annular body. Radially-inward protruding tabs (65) extend radially inwardly from the inner circumferential surface (62) of the annular body (61) and are operable for engagement with slots in the inner component. Radially-outward protruding tabs (66) extend radially outwardly from the outer circumferential surface of the annular body (61) and are operable for engagement with slots in the outer component. The radially-outward protruding tabs (66) are circumferentially offset from the radially-inward protruding tabs (65) such that the radially-outward protruding tabs (66) and the radially-inward protruding tabs (65) are all free of circumferential overlap.