Asymmetric Pivot Pin Grooves for Epicyclic Gear Alignment
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Solution Overview
Problem
In aircraft gas turbine engines, epicyclic planetary gear trains experience misalignments between upstream and downstream bearing seatings of pivot pins due to applied torques and centrifugal forces, leading to reliability and efficiency issues.
Innovation Solution
A pivot pin design with asymmetrical axial distances between circumferential grooves provides differential flexibility to balance bearing seating displacements, maintaining the pivot pin parallel to its axis and reducing misalignment by optimizing the ratio of these distances (D1/D2 between 0.9 and 0.99) to enhance alignment and heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If symmetrical circumferential grooves are provided on the pivot pin, then the structure is simple and manufacturing is easy, but misalignment occurs between upstream and downstream bearing seatings due to applied torques and centrifugal forces
Solution Approach 1:
The patent applies asymmetry by providing circumferential grooves with different axial depths on opposite sides of the pivot pin. Specifically, one circumferential groove has a first axial depth while the opposite circumferential groove has a second axial depth that differs from the first. This asymmetrical design creates differential flexibility that compensates for the non-symmetrical loading conditions (applied torques and centrifugal forces) experienced by the pivot pin during operation, thereby preventing misalignment between bearing seatings while maintaining manufacturing simplicity.
Solution Approach 2:
The patent applies local quality by creating different structural properties at different locations of the pivot pin. The circumferential grooves are designed with different axial depths at opposite locations, providing localized flexibility variations. This allows the pivot pin to have different compliance characteristics in different directions, enabling it to adapt to the specific loading patterns and maintain proper alignment under operational conditions.
2Manufacturing precision
If the pivot pin is made rigid to maintain alignment, then misalignment is reduced, but the bearing seating displacements cannot be balanced under applied loads
Solution Approach 1:
The patent applies dynamics by designing the pivot pin with circumferential grooves that provide controlled flexibility. The grooves allow the pivot pin to deform dynamically in response to applied torques and centrifugal forces, enabling the bearing seatings to displace and balance under operational loads. This dynamic adaptability maintains alignment precision while accommodating the varying stress conditions during gear train operation.
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 reduces radial and tangential misalignments by more than 5% and 1.5%, respectively, while maintaining the pivot pin parallel to its axis, thereby improving the reliability and efficiency of the gear train operation.
Implementation Method 1
Displacements, whether tangential, due to applied torques, and/or radial due to centrifugal force, and not symmetrical between upstream and downstream along the axis of rotation X, were observed on pivot pins.
Implementation Method 2
The axial distance (hereinafter D1) between said plane and the bottom end of one of the circumferential grooves is smaller than the axial distance (hereinafter D2) between said plane and the bottom end of the axially opposite circumferential groove
Data Source
AI summary
The invention relates to a pivot pin (5) for an epicyclic gear train sliding bearing, the pivot pin having a portion (23) forming a central shank, extending around an axial passage (15), and axially opposed, axially open circumferential grooves (25a,25b) which radially separate two axially opposed lateral end portions (230a,230b) of the central shank from two cantilevered lateral portions (27a,27b). With respect to a plane (33) perpendicular to said axis of the axial passage (15) and passing through the axial middle 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 opposed circumferential groove (25b).