Coaxial Split-Torque Gearbox Layout for Compact Load Sharing
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Solution Overview
Problem
Conventional coaxial rotary-wing aircraft gearboxes face challenges in packaging due to space constraints, leading to increased weight, height, and complexity, particularly with split-torque designs that require numerous gears and bearings, complicating the integration of flight control components.
Innovation Solution
A multi-pinion gearbox arrangement with a three-stage reduction system, utilizing torsionally compliant quill shafts for balanced load sharing and allowing variance in gear numbers, along with a compact design that places torque-splitting gears inwardly to accommodate flight controls, reducing overall height and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional coaxial gearbox with two large final reduction stages is used, then power can be transferred to both rotor assemblies, but the gearbox height and complexity increase significantly
Solution Approach 1:
The patent divides the single large final reduction stage into two separate smaller reduction stages, each handling a portion of the power transfer. This segmentation allows the gear train to be arranged in a more compact configuration, reducing the overall gearbox height while maintaining the capability to transfer power to both coaxial rotor assemblies
Solution Approach 2:
The patent rearranges the gear train configuration from a vertical stacking arrangement to a more distributed spatial arrangement. By changing the dimensional layout of the gear stages and utilizing radial positioning of gears, the design achieves compactness in the height dimension while preserving power transfer functionality
2Reliability
If numerous gears and bearings are used for split-torque design, then load distribution is improved, but device complexity and packaging difficulty increase
Solution Approach 1:
The patent combines multiple gear functions into integrated gear assemblies where gears serve both power transmission and load distribution functions simultaneously. By merging the load-splitting function with the power transmission function in the same gear stages, the design achieves balanced load distribution without requiring separate dedicated components for each function
Solution Approach 2:
The gear train components are designed to perform multiple functions: power transmission, torque splitting, and load distribution. Each gear stage is configured to handle multiple operational requirements, reducing the total number of specialized components needed while maintaining reliable load distribution across the dual rotor system
3Strength
If flight control components are integrated into the gearbox, then structural efficiency is improved, but space availability for controls is reduced
Solution Approach 1:
The patent positions the flight control components in the radial dimension rather than the vertical dimension, placing them between the gear train and the gearbox housing. This dimensional repositioning allows structural integration for efficiency while preserving adequate space for control component installation and access
Data Source
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Figure 2
AI summary
A coaxial split torque gearbox (26) comprises a first pinion (54) meshed with a first gear (70); a second pinion (74) attached to the first gear and meshed with a first bull gear (46), the first bull gear operable for transferring torque to cause a first rotor (32) to rotate; and a third pinion (76) attached to a second gear (72) and meshed with a second bull gear (48), the second bull gear operable for transferring torque to cause a second rotor (28) to rotate, the second gear being meshed with the first gear, and a number of teeth of the first gear being different than a number of teeth of the second gear.