Unison Ring Centralizer with Rolling Bearing
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Solution Overview
Problem
In gas turbine engines with variable stator vanes, unison rings often decentralize due to gravity, assembly loads, warpage, and thermal expansion, leading to vane angle errors and variations in the gap between the unison ring and engine casing, which existing centering devices fail to adequately address, particularly in maintaining accuracy and minimizing stresses and hysteresis.
Innovation Solution
A unison ring assembly with centralizer apparatuses featuring a rub button and a rolling bearing at the distal end of a stud, where the rolling bearing is trapped within a bearing chamber and spring-loaded, allowing for free rotation and secure attachment to the engine casing while accommodating thermal expansion and manufacturing tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed rub tips mounted on radially extending studs are used to center the unison ring, then the unison ring can be centered on the engine casing, but the device creates high lever arm stresses, ring and clevis stresses, and deflections due to rigid contact
Solution Approach 1:
The patent replaces the rigid mechanical contact system (fixed rub tips on studs) with a rolling bearing system. The rolling bearing at the distal end of the stud transforms the sliding friction contact into rolling contact, significantly reducing friction and stress concentrations. This substitution eliminates the high lever arm stresses and ring/clevis stresses while maintaining centering accuracy through the bearing's precise rolling elements.
Solution Approach 2:
The patent changes the contact interface parameters by introducing a rolling bearing with specific bore diameter, outer diameter, and width dimensions. The bearing's internal geometry and rolling elements alter the stress distribution parameters, converting concentrated point contacts into distributed line contacts, thereby reducing peak stresses in the lever arm, unison ring, and clevises while maintaining the centering function.
2Measurement precision
If fixed rub tips are used to center the unison ring, then centering is achieved, but the rigid contact creates hysteresis and prevents free rotation of the unison ring
Solution Approach 1:
The patent substitutes the sliding friction mechanism of fixed rub tips with a rolling bearing system. The rolling bearing's internal structure with rolling elements allows the unison ring to rotate freely with minimal resistance. The rolling contact mechanism eliminates the stick-slip hysteresis characteristic of sliding contacts, enabling smooth rotation while maintaining precise centering through the bearing's geometric constraints.
3Measurement precision
If fixed rub tips mounted on studs are used for centering, then the unison ring is centered, but the device does not accommodate thermal expansion and manufacturing tolerances effectively
Solution Approach 1:
The patent transforms the static, rigid centering system into a dynamic one by incorporating rolling bearings. The rolling bearing system can dynamically adjust to dimensional changes caused by thermal expansion and manufacturing tolerances. The rolling elements accommodate minor misalignments and dimensional variations through elastic deformation and rolling motion, maintaining centering accuracy across varying operating conditions without requiring rigid precision.
Solution Approach 2:
The patent accounts for thermal expansion by designing the rolling bearing system with appropriate clearance and tolerance ranges. The rolling bearing's internal geometry and material properties allow it to accommodate thermal growth of the unison ring and engine casing. The system maintains effective centering despite dimensional changes by allowing the rolling elements to adjust their position within the bearing's tolerance envelope as temperature varies.
4Measurement precision
If fixed rub tips on studs are used to center the unison ring, then centering is achieved, but the rigid contact increases friction and wear
Solution Approach 1:
The patent replaces the sliding friction contact system with a rolling bearing system that utilizes rolling contact mechanics. The rolling elements (balls or rollers) transform the high-friction sliding interface into a low-friction rolling interface. This substitution dramatically reduces friction forces and wear at the contact points between the centering device and the unison ring, while the bearing's precision-machined races maintain accurate centering positioning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes vane angle errors, reduces circumferential variation, and maintains accurate positioning of the unison ring, reducing stresses and hysteresis, while allowing for easy maintenance and repair, and ensuring precise alignment of the unison ring with the engine casing.
Implementation Method 1
rub button being spaced apart from the unison ring and including a rolling bearing
Implementation Method 2
allowing for free rotation of the unison ring
Implementation Method 3
spring loading the rolling bearing within the chamber with a spring between the bearing receptacle and the rolling bearing
Implementation Method 4
accommodate the varying tolerances caused by such thermal expansion
Data Source
AI summary
Centralizer apparatuses attached around a unison ring include rub buttons at inner ends of stud attached to and spaced apart from the unison ring and include rolling bearings. Each rolling bearing rotatably trapped within bearing chamber in bearing receptacle at inner end of stud.Tip cap includes bearing aperture trapping rolling bearing within bearing chamber. Rolling bearing extends partially through bearing aperture. Rolling bearing may be spring loaded within chamber by spring between the bearing receptacle and the rolling bearing. Stud may extend through and may be threaded into mounting aperture in unison ring and nut may be threaded onto outer end of stud. Variable stator vanes rotatably mounted to a casing and connected to vane crank arms connected to the unison ring mounted exterior to casing.