Frangible Bushing for Compressor Vane Overload Detection
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Solution Overview
Problem
Gas turbine engine variable stator vane actuation systems face challenges in detecting mechanical overloads, as existing designs may not visibly indicate lever arm buckling or separation, potentially leading to off-schedule compressor operation and hidden failure risks, necessitating a low-cost, on-wing inspection method to assess the need for detailed inspection or refurbishment.
Innovation Solution
A bushing with a polygonal flange, cylindrical barrel, and frangible overload indicators, including spring indicator tabs and coupons with distinctive marks visible under visible or ultraviolet light, designed to break off and indicate overload conditions, facilitating easy detection during inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a weak link is designed to indicate overload, then overload detection capability is improved, but the connection between vane and actuation ring may be compromised
Solution Approach 1:
The bushing is segmented into a main body and a separate frangible indicator component. The indicator is a distinct element that can fracture independently to signal overload, while the main bushing body maintains the structural connection between the lever arm and unison ring. This segmentation allows the indicator to fail safely without compromising the primary load-bearing connection.
Solution Approach 2:
The frangible indicator acts as an intermediary element between the load path and the observation system. It translates the mechanical overload condition into a visible signal (fractured indicator) without being part of the primary load-bearing connection. The indicator mediates between the hidden mechanical stress and the external inspection capability.
2Reliability
If lever arms are made less stiff to enable buckling at lower loads, then overload indication is improved, but lever arm strength and dynamic response are reduced
Solution Approach 1:
The buckling indication function is separated from the lever arm structure itself and placed in the bushing indicator. This allows the lever arm to maintain its optimal stiffness and strength for dynamic response, while the separate bushing indicator provides the overload indication function that would otherwise require compromising the lever arm design.
3Reliability
If clamping load at the vane-lever joint interface is increased to prevent sliding, then connection reliability is improved, but the small size of mating elements limits the increase
Solution Approach 1:
The frangible indicator in the bushing serves as an intermediary that provides overload detection without requiring increased clamping load. This allows the mating elements to maintain their small size for weight and compactness while still achieving reliable operation through the indicator-mediated overload protection.
4Reliability
If a frangible indicator is added to the bushing, then overload detection capability is improved, but device complexity increases
Solution Approach 1:
The frangible indicator is designed as a simple, inexpensive, single-use component. Once it fractures to indicate overload, it is discarded and replaced. This disposable nature keeps the complexity low while providing effective overload detection, as the indicator does not need to be durable or complex, only sufficiently reliable to fracture at the designated overload threshold.
Solution Approach 2:
The indicator uses visual changes (fracture appearance, potential color-coded markings) to communicate overload status. This simple visual signaling mechanism provides effective overload detection without requiring complex sensors, electronics, or sophisticated indication systems, thereby minimizing the increase in device complexity.
Data Source
AI summary
A bushing includes cylindrical body depending from preferably annular polygonal flange, bore extending through flange and body, and at least one overload indicator. Overload indicator may be frangible such as frangible tab at distal end of indicator tab depending from body or frangible coupons extending between forward and aft sections of polygonal flange. Frangible tab and coupons may include distinctive mark discernible or visible under visible or ultraviolet light. Bushing may be used in unison ring of high pressure compressor assembly to connect lever arms, coupled to variable vanes, to unison ring. Pins disposed in bore of bushing couple arm to unison ring. Forward and aft overhangs may depend from forward and aft sections of polygonal flange and overhang forward and aft annular sides of unison ring.