Geared Unison Ring With Harmonic Drive for Stable Vane Actuation

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Solution Overview

Problem

Existing gas turbine engine variable vane systems face challenges in efficiently managing significant stress loads and forces, particularly due to the mechanical linkage used to rotate variable vanes, which can result in substantial forces being transmitted through these linkages, leading to inefficiencies and potential instability.

Innovation Solution

The implementation of a variable vane system utilizing a harmonic drive with a strain wave gearing mechanism, including a fixed circular spline, a flex spline, and a wave generator, along with a geared unison ring that spans multiple variable vane stages, provides a high gear ratio (30:1 - 320:1) and minimizes axial motion through a flange interface with the engine case, allowing precise control and reduced backlash.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mechanical linkage is used to rotate variable vanes, then the vanes can be actuated, but significant forces are transmitted through the linkage leading to inefficiencies and potential instability

Engineering Contradiction:

Improvesystem stabilityVSAvoidforces transmitted through mechanical linkage

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The patent replaces the traditional mechanical linkage system with a harmonic drive system that uses strain wave gearing. This substitution eliminates the need for robust mechanical linkages by using a flexible spline and wave generator mechanism that achieves the same rotational actuation with significantly reduced force transmission and improved stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operational parameters of the actuation system by introducing a high gear ratio (30:1 to 320:1) through the harmonic drive mechanism. This parameter change allows the system to achieve the required vane rotation with much lower input forces, thereby reducing the forces transmitted through the mechanical components and improving overall system reliability.

Inventive Principle:

Principle #35Parameter changes

2Power

If a high gear ratio is achieved through harmonic drive, then torque capability is enhanced, but device complexity increases

Engineering Contradiction:

Improvetorque capabilityVSAvoidharmonic drive mechanism complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The patent merges multiple functions into the harmonic drive system, which simultaneously provides high gear ratio multiplication, torque amplification, and back-driving prevention in a single integrated mechanism. This consolidation achieves the desired torque capability while minimizing the number of separate components needed compared to traditional gear train approaches.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent utilizes a flexible spline (thin film component) as a core element of the harmonic drive system. This flexible component enables the strain wave gearing mechanism to function, providing high gear ratios and torque multiplication without requiring complex rigid gear trains. The flexibility of the spline allows for compact design while maintaining the necessary mechanical advantage.

Inventive Principle:

Principle #30Flexible shells and thin films

3Strength

If variable vanes are robustly designed to handle stress loads, then strength is improved, but weight and complexity increase

Engineering Contradiction:

Improvevane strengthVSAvoidvane weight

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

The patent replaces the robust mechanical linkage system with a harmonic drive system that inherently handles stress loads more efficiently. This substitution allows the variable vanes to be designed with reduced weight since they no longer need to accommodate the high forces transmitted through traditional mechanical linkages, while the harmonic drive mechanism itself handles the stress management.

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 torque capability and precision of vane rotation, preventing back driving by aerodynamic forces and ensuring stable operation across varying conditions, thereby improving the operational efficiency and reliability of the gas turbine engine.

Implementation Method 1

the harmonic drive includes a strain wave gearing mechanism including 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 EffectStrain wave gearing: Gear

Data Source

PatentEP3241997B1Geared unison ring for variable vane actuation

Publication Date: 2022.12.21 RTX CORP

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AI summary

An actuator system (118) including a harmonic drive (122) operable to drive a variable vane system (100) of a gas turbine engine (20).