Harmonic Drive Actuation for Gas Turbine Variable Vanes

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Solution Overview

Problem

Legacy gas turbine engine variable vane systems face challenges in efficiently managing significant stress loads and forces, often relying on hydraulic actuation which can be cumbersome and inefficient, particularly in achieving precise control and high gear ratios.

Innovation Solution

The implementation of a geared unison ring system with a strain wave gearing mechanism, including a fixed circular spline, flex spline, and wave generator, along with electric motor actuation, provides a compact, high-torque, and backlash-free mechanism for rotating variable vanes, offering a gear ratio of 30:1 to 320:1 and allowing for precise control through a multi-planar drive gear system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If hydraulic actuation is used to rotate variable vanes, then significant stress loads can be handled, but the system becomes cumbersome and less efficient

Engineering Contradiction:

Improvestress load handlingVSAvoidactuation system complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent replaces the hydraulic actuation system with an electric motor-driven harmonic drive system. The electric motor (208) connects through a harmonic drive (204) to the geared unison ring (202), eliminating hydraulic fluid power transmission while maintaining the ability to handle significant stress loads through the high gear ratio (30:1 to 320:1) and compact mechanical design.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The harmonic drive acts as an intermediary mechanism between the electric motor and the geared unison ring. It provides the necessary torque multiplication and motion transmission while maintaining a compact, efficient design that avoids the complexity of hydraulic systems.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If a mechanical linkage is used to rotate variable vanes, then precise control can be achieved, but the forces transmitted through the linkage become significant

Engineering Contradiction:

Improvecontrol precisionVSAvoidtransmitted forces

Core Design Contradiction:

Measurement precisionVSForce

Solution Approach 1:

The patent replaces traditional mechanical linkages with a harmonic drive system that uses elastic deformation of the flex spline to transmit motion and force. This substitution reduces the peak forces transmitted through rigid linkages while maintaining precise control through the high gear ratio and direct connection to the geared unison ring.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If a high gear ratio is achieved through traditional gearing, then precise control is possible, but the mechanism becomes complex and large

Engineering Contradiction:

Improvecontrol precisionVSAvoidgearing mechanism volume

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent substitutes traditional multi-stage gear trains with a single-stage harmonic drive mechanism. The harmonic drive achieves the high gear ratio (30:1 to 320:1) through the interaction of the wave generator, flex spline, and circular spline, providing compact, lightweight gearing that eliminates the need for multiple gear stages and reduces overall mechanism volume.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The harmonic drive components are nested within each other - the flex spline is deformed by the wave generator and engages with the circular spline in a compact, space-efficient arrangement. This nested configuration achieves high gear ratios in a minimal volume, eliminating the need for large, multi-stage gear trains.

Inventive Principle:

Principle #7Nested doll (Nesting)

4Reliability

If robust variable vanes are designed to handle stress loads, then reliability is improved, but the actuation system becomes more complex

Engineering Contradiction:

Improvevane system reliabilityVSAvoidactuation system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex hydraulic actuation systems with a simpler electric motor-driven harmonic drive system. This substitution maintains the ability to reliably actuate robust variable vanes under stress loads while reducing actuation system complexity through the use of electric motors and compact harmonic gearing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enhances the operational efficiency of gas turbine engines by providing precise control over variable vanes, reducing the need for hydraulic actuation, and minimizing back-driving forces, leading to improved performance and reduced complexity in managing aerodynamic loads.

Implementation Method 1

the strain wave gearing mechanism includes a fixed circular spline, a flex spline attached to an output shaft, and a wave generator attached to an input shaft, the flex spline driven by the wave generator with respect to the circular spline

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentEP3228823B1Sliding gear actuation for variable vanes

Publication Date: 2020.11.25 RTX CORP

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AI summary

An actuator system includes a harmonic drive operable to drive a variable vane system of a gas turbine engine. A geared unison ring may be driven by the harmonic drive, and may be axially slidable.