Planetary Gearbox Bearing Ducts for Thermal Deformation Control
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Solution Overview
Problem
Plain bearings in gas turbine engine gearboxes experience high thermal deformations due to limited oil availability and high operating temperatures, leading to reduced service life and potential coating damage, especially in highly loaded regions where oil flow is insufficient.
Innovation Solution
Incorporating a duct with a closed cross-section within the plain bearing to direct gearbox oil through the highly loaded region, which extracts thermal energy and reduces thermal deformations, and using a stepped flow profile to enhance thermal transfer by transitioning from laminar to turbulent flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If plain bearings are used in highly loaded regions without additional cooling, then the structure remains simple, but thermal deformations increase and service life decreases
Solution Approach 1:
The bearing structure is segmented into multiple functional zones: a through-hole for oil supply, circumferential grooves for oil distribution, and a porous coating for oil retention. This segmentation allows oil to be delivered systematically to different regions of the bearing surface, ensuring adequate lubrication in highly loaded zones without requiring a completely redesigned bearing structure.
Solution Approach 2:
The patent implements a nested structure where the porous coating is applied on top of the bearing surface, which itself contains circumferential grooves, and the through-hole penetrates through the entire bearing structure. This nesting allows multiple lubrication functions to be integrated within the bearing component itself, providing effective cooling and lubrication without adding external complex systems.
2Temperature
If oil flow is increased to cool the bearing, then thermal energy dissipation improves, but oil availability becomes insufficient
Solution Approach 1:
Instead of uniformly distributing oil throughout the bearing, the patent applies local quality by concentrating oil supply at the through-hole in the highly loaded region, using circumferential grooves to channel oil along specific paths, and employing porous coating material only in areas where oil retention is most beneficial. This localized approach maximizes cooling efficiency in critical zones while minimizing overall oil consumption.
3Strength
If the bearing surface is hardened to resist wear, then load-bearing capability improves, but thermal deformations and coating damage increase
Solution Approach 1:
The patent employs composite materials by applying a porous coating (such as porous chromium or ceramic coating) onto the bearing surface. This composite structure combines the high strength and hardness of the base bearing material with the heat-resistant and low-friction properties of the porous coating layer. The porous structure also facilitates oil retention and heat dissipation, reducing thermal deformations while maintaining load-bearing capability.
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 increases the load-bearing capability and service life of the plain bearing by effectively dissipating thermal energy and reducing maximum operating temperatures, thereby improving thermal stability and coating durability.
Implementation Method 1
at least one duct carrying gearbox oil is provided in the circumferential region of a main load direction of the plain bearing... which extracts thermal energy and reduces thermal deformations
Implementation Method 2
using a stepped flow profile to enhance thermal transfer by transitioning from laminar to turbulent flow
Implementation Method 3
the two parts that move relative to one another in the plain bearing are in direct contact. Said two parts slide on one another counter to the resistance caused by dynamic friction. The sliding resistance has the effect that a proportion of the kinetic energy is converted into thermal energy
Data Source
AI summary
A planetary gearbox for a gas turbine engine has a planet gear rotatably mounted on a carrier element, which is connected in a rotationally fixed manner to a planet carrier. An oil feed pocket is in a region of an external side of the carrier element, via which oil is passed into a bearing gap between the carrier element and the planet gear. The carrier element has a duct carrying oil. The duct in is provided radially within an external side of the carrier element, having a cross section which is closed in relation to the bearing gap. The duct in the flow direction of the oil has at least two sequential duct portions. The flow cross section of the duct in a transition region between an upstream duct portion and a next downstream duct portion decreases in an at least approximately step-shaped manner.