Unison Ring Bush Segmentation for Gas Turbine Vane Positioning
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Solution Overview
Problem
The migration of bushes in unison ring assemblies used to actuate variable vanes in gas turbine engines can lead to inaccuracies in vane positioning due to cross-binding and reduced effectiveness in locating lever pins, causing bush migration and loss of hoop strength.
Innovation Solution
The bush is formed as separate first and second parts with stop features that prevent excessive insertion and a snap-fit configuration to maintain correct positioning, ensuring the joint is away from high-stress areas and preventing bush migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-piece bush is used to connect the lever pin to the unison ring, then the assembly is simple, but the bush migrates out of the unison ring due to cross-binding and lever rotation, causing vane positioning inaccuracies
Solution Approach 1:
The bush is divided into a first part and a second part that are inserted from opposite sides of the unison ring. Each part has a stop feature that prevents excessive insertion and migration. The two parts join together in the middle to form the complete bush, with the joint positioned away from high-stress areas. This segmentation prevents the bush from migrating while maintaining structural integrity and positioning accuracy.
2Ease of manufacture
If the bush is made as a single piece, then manufacturing is easier, but the bush cannot prevent migration under cross-binding forces, leading to loss of hoop strength
Solution Approach 1:
The bush is segmented into two parts that are inserted from opposite sides, each with stop features preventing migration. This design maintains hoop strength by distributing forces and positioning the joint away from high-stress areas, while still allowing for relatively simple manufacturing of each individual part.
Solution Approach 2:
The joint between the two bush parts is specifically positioned away from high-stress areas of the unison ring. This local placement strategy ensures that the weakest point (the joint) is located where stresses are minimal, thereby maintaining overall hoop strength despite the segmented construction.
3Ease of operation
If the bush allows the lever pin to rotate freely, then the lever can rotate smoothly, but the bush migrates out of the unison ring during operation
Solution Approach 1:
The bush is divided into two parts with stop features that prevent migration while allowing the lever pin to rotate freely within the bore. The stops constrain axial movement but do not interfere with rotational motion, thus maintaining smooth lever operation while preventing bush migration.
4Strength
If the bush is pushed fully into the unison ring, then the connection is secure, but the pin slides out during lever rotation, causing the bush to migrate
Solution Approach 1:
The bush is segmented into two parts inserted from opposite sides, each with a stop feature. The stops prevent the parts from being pushed in too far and also prevent them from sliding out during lever rotation. This maintains secure connection while ensuring accurate positioning throughout the operational cycle.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A unison ring assembly (100) for a gas turbine engine has a unison ring and a plurality of levers extending from the unison ring. Each lever (104) has a pin (108) at one end that inserts through a bore of a respective bush (109) mounted in the unison ring. Each bush is formed as separate first and second parts which are mounted to their through-hole by inserting the first part into the through-hole from one side of the unison ring and the second part into the through-hole from the opposing side of the unison ring. Each part has a respective stop which prevents that part from inserting into the through-hole by more than a predetermined amount. When both parts are inserted by their predetermined amounts, their ends join together to form the bush and prevent the parts being retracted from the through-hole.