Coaxial Split-Torque Gearbox with Sequential Load Sharing

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Solution Overview

Problem

Conventional coaxial rotary-wing aircraft gearboxes face challenges in compact packaging due to space constraints, leading to increased weight, height, and complexity, particularly in split-torque designs that require multiple gears and bearings, complicating flight control systems and limiting reduction ratios.

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, with torque-splitting gears arranged inwardly to accommodate flight controls and reduce overall diameter, weight, and height.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a conventional coaxial gearbox uses multiple gears and bearings for split-torque design, then torque transmission capability is improved, but device complexity and packaging space increase

Engineering Contradiction:

Improvetorque transmission capabilityVSAvoidnumber of gears and bearings

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The patent merges multiple gear stages into a compact multi-pinion arrangement where pinions share common shafts and mesh with bull gears. This consolidation reduces the total number of discrete gears and bearings while maintaining the split-torque functionality needed for coaxial rotor systems.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The gearbox employs a nested arrangement where pinions are positioned within the radial space of larger bull gears, and multiple pinions share common shafts. This nesting allows multiple torque transmission paths to coexist in a compact volume, reducing overall device complexity while preserving power transmission capability.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Speed

If a conventional coaxial gearbox increases reduction ratio, then rotor velocity control is improved, but gearbox height and weight increase

Engineering Contradiction:

Improverotor velocity controlVSAvoidgearbox height

Core Design Contradiction:

SpeedVSLength of stationary object

Solution Approach 1:

The patent transitions from a vertical stacking arrangement (increasing height) to a radial expansion arrangement (increasing diameter). The multi-pinion configuration allows reduction gears to be arranged side-by-side in the radial direction, achieving high reduction ratios without proportionally increasing gearbox height.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Power

If a conventional coaxial gearbox uses large diameter gears for high reduction ratios, then torque transmission is improved, but available space for flight controls and rotor swashplates decreases

Engineering Contradiction:

Improvetorque transmission efficiencyVSAvoidspace for flight controls

Core Design Contradiction:

PowerVSArea of stationary object

Solution Approach 1:

The patent segments the torque transmission function across multiple smaller pinions that share common shafts, rather than using a single large gear. This segmentation allows the gear train to be distributed more efficiently in space, reducing the overall envelope and creating clearance for flight control systems and rotor swashplates.

Inventive Principle:

Principle #1Segmentation

4Ease of manufacture

If a conventional coaxial gearbox uses symmetric gear arrangement, then manufacturing is simplified, but load distribution balance deteriorates

Engineering Contradiction:

Improvegear arrangement symmetryVSAvoidload distribution balance

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The patent applies different gear ratios and tooth configurations to pinions at different locations within the same gear train. This local differentiation allows each pinion-bull gear pair to be optimized for its specific load conditions, achieving balanced load distribution across all torque paths while maintaining manufacturing feasibility through modular design.

Inventive Principle:

Principle #3Local quality

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 a lightweight, compact gearbox with balanced load sharing, reducing the number of parts and weight, allowing for more space for rotor swashplates and structural load paths, while maintaining efficient torque transmission and counter-rotating capabilities.

Implementation Method 1

utilizing torsionally compliant quill shafts for balanced load sharing

Methodology Applied

Scientific EffectTorsion: Torque

Implementation Method 2

a first pinion meshed with a first gear; a second pinion attached to the first gear and meshed with a first bull gear

Methodology Applied

Scientific EffectMechanical Advantage: Gear

Data Source

PatentUS11702197B2Coaxial split torque gearbox with sequential load distribution

Publication Date: 2023.07.18 LOCKHEED MARTIN CORP

AI summary

A coaxial split torque gearbox comprises a first pinion meshed with a first gear; a second pinion attached to the first gear and meshed with a first bull gear, the first bull gear operable for transferring torque to cause a first rotor to rotate; and a third pinion attached to a second gear and meshed with a second bull gear, the second bull gear operable for transferring torque to cause a second rotor 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.