Segmented Journal Bearing Geometry for Planetary Gear Lubrication
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Solution Overview
Problem
Turbine engine manufacturers face challenges in supporting and lubricating planetary gears, which can affect the engine's thermal, transfer, and propulsive efficiencies.
Innovation Solution
A fan drive gear system is introduced, featuring a sun gear, compound intermediate gears, a ring gear assembly, a rotatable carrier, and journal bearing assemblies with specific geometries and lubricant supply mechanisms to support the planetary gears effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional journal bearing is used to support planetary gears, then the bearing structure is simple, but the bearing cannot adequately support and lubricate the gears under high load conditions, affecting thermal and transfer efficiencies
Solution Approach 1:
The journal bearing is divided into multiple segments (typically three or four) that can be assembled together to form a complete bearing structure. Each segment can be independently manufactured and positioned, allowing for better adaptation to the gear geometry and improved lubrication distribution. The segments are held in place by a retaining structure that prevents them from moving during operation.
Solution Approach 2:
The bearing design transitions from a simple radial support to a multi-dimensional solution by incorporating axial length optimization (L/D ratio between 1.5 and 6) and segmented construction. This allows the bearing to handle both radial and axial loads more effectively, and provides multiple surfaces for lubricant film formation, thereby improving the lubrication regime under high load conditions.
2Force
If the journal bearing has a high L/D ratio to improve load capacity, then the bearing can support higher loads, but the bearing becomes longer and occupies more space in the limited design envelope
Solution Approach 1:
The optimal L/D ratio is specified within the range of 1.5 to 6, which represents a parameter optimization to balance load capacity with spatial constraints. This parameter range is derived from analyzing the relationship between bearing geometry and performance, identifying the optimal zone where sufficient load support is achieved without excessive length that would encroach on the limited design envelope of the planetary gear system.
3Adaptability or versatility
If the bearing is designed to accommodate compound intermediate gears with multiple gear portions, then the gear system can achieve high gear ratios, but the bearing must support multiple gear interfaces increasing complexity
Solution Approach 1:
The journal bearing is designed as a universal support structure that can accommodate multiple gear portions (forward gear portion and aft gear portion) of compound intermediate gears. The bearing's segmented construction and optimized geometry allow it to serve multiple functions: supporting radial loads from different gear meshes, providing lubrication interfaces for multiple gear contacts, and accommodating the rotational motion of the carrier. This multi-functional design enables the bearing system to support complex high gear ratio configurations without proportionally increasing complexity.
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 system enhances gear support and lubrication, leading to improved thermal, transfer, and propulsive efficiencies in turbine engines, while operating within a limited design space.
Implementation Method 1
a plurality of journal bearing assemblies that correspond with the plurality of intermediate gears, each of the plurality of journal bearing assemblies includes a ratio of a journal length to a journal diameter that is between 1.5 and 6
Data Source
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AI summary
A fan drive gear system (48) for a turbine engine includes a gear system with a plurality of compound intermediate gears (66) that each include a first gear portion (74) and a second gear portion (76). The second gear portion (76) includes a forward gear portion (78) and an aft gear portion (80). A ring gear assembly (68) of the fan drive gear system (48) includes a forward ring gear (82) that is engaged to the forward gear portion (78) and an aft ring gear (84) that is engaged to the aft gear portion (80). A carrier (70) supports rotation of the plurality of compound intermediate gears (66) with a plurality of corresponding journal bearings.