Planetary Gear Pivot Structure for Misalignment Compensation
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Solution Overview
Problem
In gas turbine engines for aircraft, misalignments between upstream and downstream spans of pivots in planetary gear trains lead to reliability and efficiency issues due to tangential and radial displacements caused by applied torques and centrifugal forces, which existing plain bearings with symmetrical flexibility zones fail to adequately address.
Innovation Solution
A pivot design with asymmetrical axial distances between circumferential grooves on a central shaft, allowing for differential flexibility upstream and downstream, and a one-piece construction to enhance heat transfer and alignment, with a D1/D2 ratio between 0.9 and 0.99 for optimal balance and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If symmetrical circumferential grooves are provided on the pivot, then the pivot structure is simple and manufacturing is easy, but misalignment occurs between upstream and downstream spans due to non-identical deformations under torque and centrifugal force
Solution Approach 1:
The patent applies asymmetry by providing circumferential grooves at different axial positions on upstream and downstream sides of the pivot. Specifically, the first circumferential groove is positioned at a first axial position while the second circumferential groove is positioned at a second axial position that is offset from the first. This asymmetric arrangement compensates for the non-identical deformation patterns experienced by upstream and downstream spans under torque and centrifugal force, thereby maintaining proper alignment of the satellite pinion teeth with the ring gear teeth while preserving manufacturing simplicity.
2Manufacturing precision
If the pivot is made more flexible to accommodate deformations, then misalignment is reduced, but the structural strength and stability of the pivot decreases
Solution Approach 1:
The patent applies local quality by providing circumferential grooves only in specific axial zones where flexibility is needed, rather than making the entire pivot uniformly flexible or rigid. The grooves are positioned at optimized axial locations that allow localized deformation in the upstream and downstream spans to accommodate misalignment, while the central portion of the pivot maintains sufficient structural strength. This creates a gradient of stiffness properties along the axial direction, with softer zones at the ends and a stiffer central region.
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
This design reduces misalignment by more than 5% radially and 1.5% tangentially, maintaining pivot alignment and improving heat transfer efficiency, thereby enhancing the reliability and efficiency of the gear train.
Implementation Method 1
axially opposed circumferential grooves, open axially (therefore laterally, thereby providing flexibility to the pivot) which radially separate, from two cantilevered side parts of the pivot, two axially opposite lateral end parts of the central shaft
Implementation Method 2
a one-piece construction to enhance heat transfer and alignment
Data Source
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AI summary
The invention relates to a pivot (5) for a sliding bearing of a planetary geartrain, the pivot having a portion (23) forming a central shaft, extending around an axial passage (15), and axially opposed, axially open circumferential grooves (25a,25b) that radially separate two projecting side portions (27a,27b) from two axially opposite side end portions (230a,230b) of the central shaft. With respect to a plane (33) extending perpendicular to said axis of the axial passage (15) and through the axial center of the axial passage, the axial distance between said plane (33) and the bottom end of one of the circumferential grooves (25a) is smaller than the axial distance between said plane and the bottom end of the axially opposite circumferential groove (25b).