Variable Stator Vane Backlash Reduction via Spring Biasing

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Solution Overview

Problem

Variable stator vanes in gas turbine engines experience wear due to backlash and hysteresis caused by gear teeth tolerances, leading to reduced accuracy and performance.

Innovation Solution

A variable stator guide vane system with a ring gear and pinion gears, where biasing members, such as springs, are used to maintain meshing engagement and reduce clearance between the gears, allowing for precise control of vane angle and accommodating manufacturing tolerances and thermal changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If gear teeth tolerances are used in the variable stator vane system, then manufacturing cost is reduced and ease of manufacture is improved, but backlash and hysteresis occur causing wear and reduced accuracy

Engineering Contradiction:

Improveease of manufactureVSAvoidvane angle accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

A biasing member (spring) is introduced as an intermediary element between the pinion gear and the drive mechanism. This spring applies continuous force to eliminate backlash between gear teeth while accommodating manufacturing tolerances. The biasing member acts as a mediator that transforms the rigid gear connection into a controlled, backlash-free connection that maintains both ease of manufacture and angular accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the mechanical state of the gear connection by introducing a variable force through the biasing member. The spring force dynamically adjusts the engagement between gear teeth, eliminating the clearance parameter that causes backlash while maintaining the ability to accommodate manufacturing tolerances in the gear teeth dimensions.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If gear teeth tolerances are used in the variable stator vane system, then manufacturing cost is reduced, but wear due to chatter and backlash increases

Engineering Contradiction:

Improvemanufacturing costVSAvoidcomponent wear

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The biasing member applies a preliminary counteracting force to prevent the harmful chatter and backlash that would otherwise occur during operation. By pre-loading the gear engagement in the opposite direction of the expected backlash, the system eliminates the relative motion between gear teeth that causes wear, while still allowing standard manufacturing tolerances.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The spring biasing member provides beforehand cushioning by maintaining continuous contact between gear teeth. This pre-compression prevents the sudden impacts and chatter that occur when gears engage with clearances, thereby protecting the gear teeth from wear while accommodating economical manufacturing tolerances.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Manufacturing precision

If biasing members are added to eliminate backlash, then vane angle accuracy is improved, but device complexity increases

Engineering Contradiction:

Improvevane angle accuracyVSAvoidsystem complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The biasing member is designed to be self-regulating, automatically maintaining the optimal engagement force between gear teeth throughout the range of motion. The spring self-adjusts to accommodate thermal expansion, manufacturing variations, and operational wear without requiring external control systems, thereby achieving high accuracy without proportionally increasing system complexity.

Inventive Principle:

Principle #25Self-service

4Reliability

If biasing members are added to reduce clearance, then wear is reduced and accuracy is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvecomponent wearVSAvoidassembly complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The biasing member system is segmented into modular components that can be independently manufactured and assembled. The spring element is a separate, standardized component that can be installed independently of the gear assembly, allowing for simplified manufacturing and assembly processes while achieving the benefit of reduced backlash and wear.

Inventive Principle:

Principle #1Segmentation

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 system reduces wear and improves vane accuracy and performance by minimizing backlash and accommodating manufacturing and thermal variations, leading to enhanced operational reliability and reduced manufacturing costs.

Implementation Method 1

biasing members biasing the pinion gears in meshing engagement with the ring gear

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS10450890B2Variable stator guide vane system

Publication Date: 2019.10.22 PRATT & WHITNEY CANADA CORP

AI summary

A variable stator guide vane system for a gas turbine engine comprises a set of vanes circumferentially distributed around a central axis and rotatably mounted for rotation about respective spanwise axes. A ring gear is rotatably mounted about the central axis. Pinion gears are operatively coupled to respective ones of the vanes and in driving engagement with the ring gear. Biasing members individually bias the pinion gears in meshing engagement with the ring gear.