Flexible Sleeve for Contra-Rotating Propeller Gear Train

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Solution Overview

Problem

Contra-rotating propeller drive mechanisms with epicyclic gear trains face high forces that can damage teeth due to misalignment and radial forces, requiring a solution to reduce parasite forces while maintaining torque transmission.

Innovation Solution

A flexible sleeve connected to the turbine and planet gear, surrounded by a shaft, supports the planet gear, allowing for greater flexibility and reduced internal forces, with a design that includes a semi-circular bend or oblong openings for enhanced bending flexibility while maintaining torsion strength, and a longer turbine shaft for stable support.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a rigid shaft is used to support the planet gear, then the structure is strong and stable, but high forces are transmitted to the gear teeth causing damage due to misalignment and radial forces

Engineering Contradiction:

Improvestructural strengthVSAvoidforce on gear teeth

Core Design Contradiction:

StrengthVSForce

Solution Approach 1:

The patent applies a flexible sleeve instead of a rigid shaft to support the planet gear. The sleeve is made of flexible material that can deform under radial forces, allowing the planet gear to self-align and reducing misalignment forces on the gear teeth. The flexible sleeve absorbs radial loads while maintaining torque transmission, directly resolving the contradiction between structural strength and force reduction on gear teeth.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent changes the mechanical parameter of the support element from rigid (high stiffness) to flexible (low stiffness). By selecting a flexible material with appropriate elastic properties, the support element can deflect under load, accommodating radial forces and misalignment without transmitting high forces to the gear teeth, thus reducing wear and damage.

Inventive Principle:

Principle #35Parameter changes

2Force

If a flexible joint is used to support the planet gear, then forces are reduced, but the joint may break under high forces or excessive deformation

Engineering Contradiction:

Improveinternal forces in gear trainVSAvoidreliability under high force

Core Design Contradiction:

ForceVSReliability

Solution Approach 1:

The flexible sleeve acts as a cushioning element that beforehand absorbs and distributes radial forces and misalignment stresses. By designing the sleeve with appropriate flexibility and strength, it prevents excessive forces from reaching the gear teeth while also protecting itself from breaking under occasional high loads, thus providing both force reduction and reliability.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Force

If the sleeve is made very flexible to reduce forces, then parasite forces are reduced, but the mechanism may become too flexible and fail under high forces

Engineering Contradiction:

Improveparasite forcesVSAvoidresistance to high force

Core Design Contradiction:

ForceVSStrength

Solution Approach 1:

The flexible sleeve has different local properties: it is flexible in the radial direction to accommodate misalignment and reduce parasite forces, but maintains sufficient torsional stiffness and strength to transmit torque and resist occasional high forces. This local differentiation of mechanical properties resolves the contradiction between flexibility for force reduction and strength for reliability.

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

The solution effectively reduces internal forces in the epicyclic gear train, preventing damage from high forces and maintaining efficient torque transmission by allowing greater movement and defined limits to deformation, thus enhancing the mechanism's stability and compactness.

Implementation Method 1

the sleeve being surrounded by the shaft and more flexible in bending than the shaft

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS8967950B2Drive mechanism for a pair of contra-rotating propellers through an epicyclic gear train

Publication Date: 2015.03.03 SAFRAN AIRCRAFT ENGINES SAS

AI summary

A turbine driving a planet gear and an epicyclic gear train and including a planet pinion cage and a ring driving two propellers in rotation, is connected to the planet gear through a flexible sleeve surrounding a turbine support shaft rather than through a support shaft itself to achieve a flexible assembly with a limit stop position in contact with the shaft to limit parasite internal forces applied to the epicyclic gear train without tolerating a loose assembly or breakage of the sleeve due to a condition of the limit stop after a clearance has been eliminated.