Epicyclic Gear Carrier Structure for Bearing Alignment Under Torque
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Solution Overview
Problem
In epicyclic gearing of gas turbine engines, maintaining the parallelism of planet gear axes with the sun gear axis is challenging, especially under high torque conditions, leading to axial torsion and undesirable bearing axis inclination, which complicates lubrication oil supply and affects structural integrity, weight, and manufacturability.
Innovation Solution
The design incorporates a carrier with two annular structural members and connecting members with radial protrusions and connecting arms to balance torque loads and limit axial torsion, while a lubricant network is provided through circumferentially interspaced oil paths to ensure effective lubrication, using plain journal bearings and separate torque transfer and carrier components for optimal weight and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If cylindrical bearings are used to carry planet gears, then the structure is simpler and lighter than spherical bearings, but the bearings wear quickly when the axes of the planet gears are inclined off parallel relative to the axis of the sun gear
Solution Approach 1:
The carrier structure is designed with torque transfer portions and connecting members that preemptively counteract axial torsion forces before they can cause bearing axis inclination. The balanced torque transfer mechanism prevents the development of torsional moments that would otherwise incline the bearing axes, thereby protecting the cylindrical bearings from premature wear while maintaining their lightweight advantage.
2Manufacturing precision
If the carrier structure is made more robust to resist axial torsion, then bearing axis parallelism is maintained, but the weight and structural complexity increase
Solution Approach 1:
The carrier is segmented into distinct functional portions: a bearing support portion that carries the planet gears and a torque transfer portion that handles torque transmission. These portions are connected by connecting members that provide the necessary structural reinforcement against axial torsion only where needed, rather than making the entire carrier more robust. This segmentation allows the carrier to maintain bearing axis parallelism while minimizing unnecessary weight.
Solution Approach 2:
The carrier structure implements local quality by providing enhanced structural properties specifically in the torque transfer portions and connecting members where axial torsion resistance is needed, while keeping the bearing support portions lighter and simpler. The connecting members with radial protrusions and connecting arms provide localized reinforcement without increasing the overall weight of the entire carrier structure.
3Reliability
If oil supply channels are integrated within gas turbine engine components, then lubrication is provided, but the presence of channels impacts structural integrity
Solution Approach 1:
The patent introduces an intermediary lubrication system where a lubrication oil supply device provides oil to the epicyclic gear stage through an external oil supply line rather than integrating channels within the carrier structure. This intermediary approach maintains structural integrity by avoiding holes and channels in the carrier while still providing effective lubrication to the gear interfaces and bearings through a dedicated lubrication system.
4Adaptability or versatility
If flexible joints are used to connect shafts to epicyclic gear stages, then relative movement is accommodated, but integrated oil supply channels cannot be provided
Solution Approach 1:
The flexible joint connection between the shaft and epicyclic gear stage is accommodated by using an external lubrication oil supply line that acts as an intermediary, delivering oil to the gear stage without requiring integrated channels within the flexible joint or carrier structure. This approach maintains the adaptability of flexible joints for accommodating relative movement while providing lubrication through a separate, flexible supply path.
Data Source
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AI summary
The epicyclic gear stage (30) has a carrier body (40) receiving planet gears (24) via corresponding planet bearings (38), a first bearing plane (52) where a first axial end (53) of the planet bearings (38) are received by the carrier body (40), a second bearing plane (54) where a second axial end (55) of the planet bearings (38) are received by the carrier body (40), a torque transfer body (50) made integral to the carrier body (40) externally to the sun gear (36), at a balanced torque transfer plane (70) located between the first bearing plane (52) and the second bearing plane (34), and extending away therefrom to a shaft coupler (42), for transferring torque between the carrier body (40) and a shaft (32), and an oil network extending within the carrier (40), the oil network having an inlet in the torque transfer body (50), extending within the torque transfer body (50) and into the carrier body (40), and extending within the carrier body (40) and into the planet bearings (38).