Variable Geometry Hysteresis Control for Gas Turbine Engine Vanes

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Solution Overview

Problem

Variable geometry mechanisms in gas turbine engines exhibit mechanical hysteresis due to positional variations caused by movement direction, leading to inefficiencies and potential performance limits, as the position of vanes differs based on whether approached from an open or closed position, resulting in a hysteresis band.

Innovation Solution

A control method is implemented where the desired position of the variable geometry vanes is consistently approached from the same direction, either closing or opening, to mitigate hysteresis by adjusting the vane positions within the hysteresis band, ensuring accurate positioning and reducing transient performance issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If variable geometry mechanisms are used to adjust vane positions, then engine efficiency and performance can be improved, but mechanical hysteresis causes positional variations that reduce control precision and create a hysteresis band

Engineering Contradiction:

Improveengine efficiencyVSAvoidvane position accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The control system performs preliminary action by anticipating the hysteresis effect and adjusting the commanded vane position in advance to compensate for the expected positional variation. When a position change is requested, the system calculates the hysteresis band based on the current vane state and applies a corrective offset before actuating the mechanism, ensuring the vane reaches the desired effective position despite mechanical hysteresis.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements feedback by continuously monitoring the actual vane position and using this information to adjust future control commands. The controller receives feedback on vane position and uses this data to dynamically adjust the commanded position, compensating for hysteresis effects in real-time and maintaining accurate control throughout operation.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If the vane position is changed rapidly to respond to operating conditions, then engine adaptability is improved, but mechanical hysteresis causes transient performance issues and delays in reaching the target position

Engineering Contradiction:

Improveengine adaptabilityVSAvoidtransient response time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system applies dynamics by making the hysteresis compensation adaptive rather than fixed. The controller dynamically adjusts the compensation strategy based on the current operating state and direction of travel, allowing optimal response for both opening and closing movements. This dynamic approach enables rapid adaptation while accounting for the direction-dependent nature of hysteresis.

Inventive Principle:

Principle #15Dynamics

3Measurement precision

If the hysteresis band is reduced through mechanical means, then vane position accuracy is improved, but the complexity of the variable geometry mechanism increases

Engineering Contradiction:

Improvevane position accuracyVSAvoidmechanism complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system replaces mechanical solutions with a control system approach. Rather than modifying the mechanical mechanism to reduce hysteresis (which would increase complexity), the invention uses electronic control to measure, calculate, and compensate for hysteresis effects. The controller digitally models the hysteresis behavior and applies software-based corrections, substituting complex mechanical adjustments with a more manageable electronic control strategy.

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 approach stabilizes the vane positions within the hysteresis band, enhancing engine efficiency and preventing performance limits, thereby maintaining desired efficiency and reducing the risk of exceeding operational limits.

Implementation Method 1

one or more mechanical components can display hysteresis. In some cases, it is desirable to account for such characteristics during engine operation

Methodology Applied

Scientific EffectMechanical hysteresis: Hysteresis

Data Source

PatentUS7866159B2Variable geometry hysteresis control for a gas turbine engine

Publication Date: 2011.01.11 ROLLS ROYCE CORP

AI summary

One embodiment of the present application is a gas turbine engine with a compressor that includes a variable geometry mechanism to vary working fluid flow area. A desired state of this mechanism is selected different than a current state to change the amount of flow area. The mechanism has a hysteresis band corresponding to a difference between increasing the flow area to reach the desired state and decreasing the flow area to reach the desired state. To control operation of the mechanism within this hysteresis band, a determination is made whether the desired state corresponds to a greater flow area or a lesser flow area relative to the current state.