Compound Planetary Gearbox Layout for Low Turbomachine Gear Ratios
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Solution Overview
Problem
Conventional gear assemblies in gas turbine engines face limitations in achieving low gear ratios due to mechanical demands, complexity, and efficiency, particularly with high part counts and size constraints, which affect durability and maintenance costs.
Innovation Solution
The development of multistage epicyclic gear assemblies with a compound planet gear design, featuring a first and second stage gear configuration, allowing for smaller input shafts, larger planet gears, and reduced part counts, enabling lower gear ratios with improved durability and efficiency, and the use of helical gears for smoother operation and increased load capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional single-stage planet gear assemblies are used, then the design is simpler, but the gear ratio cannot be sufficiently reduced and the assembly size becomes larger
Solution Approach 1:
The gear assembly is divided into two independent stages: a first stage planet gear assembly and a second stage planet gear assembly. Each stage performs a portion of the total gear ratio reduction, allowing the system to achieve low overall gear ratios while keeping each individual stage mechanically simple and manageable in size.
Solution Approach 2:
The patent transitions from a single-stage to a two-stage epicyclic gear configuration, adding an axial dimension to the design. This multi-stage arrangement enables compounded gear ratio reduction by multiplying the ratios of individual stages, achieving much lower overall ratios without increasing the radial footprint of individual gears.
2Productivity
If larger planet gears are used to reduce gear ratio, then the gear ratio decreases, but the assembly size increases
Solution Approach 1:
By segmenting the gear reduction into two stages, each stage uses moderately sized planet gears rather than one extremely large gear. The first stage reduces speed by a moderate ratio, and the second stage further reduces it, achieving a compounded low gear ratio while keeping individual gear sizes manageable and the overall assembly compact.
Solution Approach 2:
The second stage planet gear assembly is nested within the structure of the first stage, with the second stage sun gear positioned at the center and its planet gears arranged radially outward. This nested configuration allows both stages to occupy overlapping spatial volumes, reducing the overall assembly footprint while maintaining the compounded gear ratio reduction capability.
3Productivity
If more gears are added to achieve low gear ratio, then the gear ratio reduces, but the part count and complexity increase
Solution Approach 1:
Each planet gear in both stages serves multiple functions: it acts as a gear element for speed reduction, a structural support element, and a load-distributing component. The carrier structures in both stages are designed to simultaneously support multiple planet gears and provide mounting interfaces, reducing the number of separate components needed compared to a single-stage design with equivalent gear ratio reduction.
4Device complexity
If conventional gear assemblies are used, then the design is straightforward, but efficiency and durability are limited
Solution Approach 1:
Dividing the gear reduction into two stages allows each stage to operate at more favorable mechanical conditions, with smaller tooth contact stresses and lower individual gear ratios. This segmentation improves durability by reducing stress concentrations and enhances efficiency by minimizing slippage and heat generation in each stage, while the overall design remains straightforward through modular repetition of the planet gear concept.
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 achieves low gear ratios with reduced complexity and size, enhancing durability, efficiency, and maintenance efficiency by utilizing larger planet gears and helical gears, resulting in lower maintenance needs and improved engine performance.
Implementation Method 1
the use of helical gears for smoother operation and increased load capacity
Data Source
AI summary
A gear assembly for use with a turbomachine engine comprises a sun gear, a plurality of planet gears, and a ring gear. The gear assembly is connected to an input shaft and an output shaft. The sun gear is configured to rotate about a longitudinal centerline of the gear assembly and is driven by the input shaft. A component of the gear assembly drives the output shaft. The planet gears can be compound planet gears having a first stage and a second stage.