Rotor Hub Universal Joint with Elastomeric Vibration Attenuation

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Solution Overview

Problem

Tiltrotor aircraft face challenges in attenuating two-per-revolution (2/rev) torsional vibrations due to the need for stiff hubs and masts, which cannot accommodate the vibration attenuation achieved by long, torsionally soft masts used in two-bladed helicopters, and previous solutions like true constant velocity joints have introduced additional unwanted vibrations.

Innovation Solution

A rotor hub assembly incorporating a universal joint and an elastomeric mast joint to tune the natural frequency away from 2/rev torsional oscillatory drive forces, allowing the elastomeric members to absorb these vibrations in compression or shear, thereby reducing their transmission to the drivetrain.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a universal joint is used in the gimbaled rotor hub, then the axis of rotation can vary relative to the mast axis, but 2/rev torsional vibrations are generated

Engineering Contradiction:

Improvevariable axis of rotationVSAvoid2/rev torsional vibrations

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

An elastomeric member is introduced as an intermediary between the universal joint and the mast. This elastomeric member absorbs the 2/rev torsional vibrations generated by the universal joint through its compliant properties, preventing the vibrations from being transmitted to the mast and drivetrain while allowing the universal joint to maintain its variable axis of rotation capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The natural frequency of the mast-joint system is tuned by modifying the elastomeric member properties so that it does not resonate at the 2/rev frequency. This parameter tuning allows the system to operate with the universal joint without amplifying the harmful vibrations through resonance

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If long torsionally soft masts are used to attenuate 2/rev vibrations, then vibration attenuation is achieved, but the mast cannot provide sufficient stiffness for tiltrotor aircraft

Engineering Contradiction:

Improve2/rev vibration attenuationVSAvoidmast stiffness

Core Design Contradiction:

Object-generated harmful factorsVSStrength

Solution Approach 1:

The vibration attenuation function is separated from the mast structure itself and assigned to a dedicated elastomeric member in the rotor hub assembly. This segmentation allows the mast to be designed for maximum stiffness and strength while the elastomeric member handles the vibration attenuation, eliminating the need for a long torsionally soft mast

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The elastomeric member serves as an intermediary that provides vibration attenuation without requiring the mast itself to be torsionally soft. This mediator absorbs the 2/rev vibrations locally at the rotor hub, allowing the mast to maintain its stiff structure necessary for tiltrotor aircraft

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-generated harmful factors

If a true constant velocity joint is used instead of a universal joint, then 2/rev vibrations are reduced, but additional unwanted vibrations are introduced and the assembly becomes heavier

Engineering Contradiction:

Improve2/rev vibrationsVSAvoidrotor hub assembly weight

Core Design Contradiction:

Object-generated harmful factorsVSWeight of moving object

Solution Approach 1:

The patent uses a simple universal joint combined with a lightweight elastomeric vibration absorber rather than a complex constant velocity joint. This approach achieves acceptable vibration levels with significantly reduced weight and complexity, trading perfect vibration elimination for a practical, lightweight solution

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Instead of trying to eliminate the 2/rev vibrations completely through a complex constant velocity joint, the patent accepts the vibrations from the simple universal joint and converts them into a manageable problem by using the elastomeric member to absorb them. This turns the harmful vibrations into a localized issue that can be solved with a simple, lightweight component

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution effectively attenuates 2/rev vibrations, reducing the weight and cost of the rotor hub assembly while maintaining operational stability, particularly suited for tiltrotor aircraft.

Implementation Method 1

an elastomeric mast joint to tune the natural frequency away from 2/rev torsional oscillatory drive forces, allowing the elastomeric members to absorb these vibrations in compression or shear

Methodology Applied

Scientific EffectVibration absorption: Damping

Implementation Method 2

an elastomeric member made of a material having a shear modulus between 0.01 and 0.5 million psi

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS11396371B2Rotor hub assembly with universal joint

Publication Date: 2022.07.26 TEXTRON INNOVATIONS INC

AI summary

A rotor hub assembly that includes a yoke configured to attach blades thereto, a universal joint configured to attach to, and transmit forces between, a mast and the yoke, and an elastomeric member configured to attenuate vibrations transmitted from the universal joint to the mast.