Planet Gear Journal Bearing Geometry for Lower Gearbox Loss
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Solution Overview
Problem
Gas turbine engine gearboxes with larger diameter fans require optimized journal bearings to minimize weight and maximize efficiency, as existing bearings contribute to efficiency losses and weight increase due to the gearbox's additional weight and efficiency losses.
Innovation Solution
The gearbox design incorporates a sun gear, planet gears, and a ring gear with journal bearings featuring a surface coating of an alloy with aluminum or copper as a primary constituent, optimized for specific operating conditions including maximum operating specific load and sliding speed, and a ratio of internal to external sliding surface lengths to diameter, to reduce inefficiency and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If journal bearings with conventional materials and designs are used in aircraft gas turbine engine gearboxes, then the gearbox can be manufactured with standard components, but the gearbox weight increases and efficiency decreases due to higher bearing losses
Solution Approach 1:
The patent applies parameter changes by optimizing the journal bearing geometry through the L/D ratio (length to diameter ratio) and selecting specific operating conditions (PV values) to minimize bearing losses. By changing these parameters, the bearing efficiency is improved, reducing energy loss and allowing for lighter gearbox design while maintaining performance requirements.
Solution Approach 2:
The patent employs composite materials by specifying surface coatings on the journal bearing sliding surfaces. These coatings are applied to enhance the bearing properties, reducing friction and wear while maintaining structural integrity. This allows the bearing to operate more efficiently with lower losses, contributing to overall gearbox efficiency improvement without excessive weight increase.
2Productivity
If the fan diameter is increased to improve engine efficiency, then the fan can move more air, but the gearbox weight increases and efficiency decreases due to the need for speed reduction
Solution Approach 1:
The patent optimizes the journal bearing parameters (L/D ratio and operating PV conditions) to minimize the efficiency losses in the gearbox. This allows the gearbox to operate with higher efficiency, reducing the penalty associated with the speed reduction necessary for larger diameter fans, thereby preserving more of the fan's air movement capacity benefits.
Solution Approach 2:
The patent converts the potentially harmful effect of gearbox efficiency losses into a benefit by carefully selecting operating conditions and bearing geometry. The optimized bearings operate at specific PV values that minimize losses, effectively turning the necessary speed reduction (which normally causes efficiency losses) into a more efficient process that better preserves the overall engine performance benefits from larger fans.
3Power
If journal bearings are optimized for maximum efficiency, then power loss is reduced, but the manufacturing complexity increases due to surface coating requirements
Solution Approach 1:
The patent specifies particular L/D ratio ranges and operating PV conditions that optimize bearing efficiency while remaining compatible with standard manufacturing processes. By defining these specific parameter ranges, the patent achieves power loss reduction without requiring exotic or overly complex manufacturing techniques, balancing performance improvement with manufacturability.
Solution Approach 2:
The patent applies surface coatings to the journal bearing sliding surfaces to enhance efficiency and reduce power loss. These coatings are specified as practical industrial applications that can be applied using conventional coating technologies, thus achieving power reduction benefits while maintaining reasonable ease of manufacture through established industrial processes.
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 enhances the efficiency and reduces the power loss of the gearbox by optimizing the journal bearings' surface coating and geometric ratios, leading to improved performance and reduced weight, thereby maintaining engine efficiency.
Implementation Method 1
a surface coating comprising a layer of an alloy having aluminium or copper as a primary constituent
Implementation Method 2
journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin
Data Source
AI summary
Gearboxes for aircraft gas turbine engines, in particular to arrangements for journal bearings such gearboxes, and to related methods of operating such gearboxes and gas turbine engines. Example embodiments include a gearbox for an aircraft gas turbine engine, the gearbox including: a sun gear; a plurality of planet gears surrounding and engaged with the sun gear; and a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin.