Turbine Engine Free Shaft Overspeed Control

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Solution Overview

Problem

Existing turbomachines face challenges in preventing dangerous over-speeding of the free turbine due to power transmission breaks without requiring excessive oversizing or compromising performance, especially in aircraft applications where transient speed peaks are necessary.

Innovation Solution

The method dynamically adjusts the maximum speed threshold of the second rotary shaft based on indicative physical parameters such as torque, speed of the first rotary shaft, and ambient conditions, allowing for early fuel cutoff in case of power transmission failures while accommodating transient overspeeds without excessive oversizing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the maximum speed threshold of the second rotary shaft is set high to allow transient overspeeds during severe maneuvers, then the adaptability of the turbomachine is improved, but the free turbine becomes vulnerable to dangerous runaway in case of power transmission break

Engineering Contradiction:

Improveability to achieve transient overspeedsVSAvoidsafety against dangerous runaway

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The maximum speed threshold is made dynamic rather than fixed. It varies according to the indicative physical parameter (torque, power, or speed of first rotary shaft), being high when these parameters indicate normal operation to allow transient overspeeds, and low when they indicate abnormal conditions to prevent dangerous runaway

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control parameter (maximum speed threshold) is changed based on the state of the system. The threshold is adjusted according to the indicative physical parameter to differentiate between acceptable transient overspeeds and dangerous runaway conditions, resolving the contradiction between adaptability and reliability

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the maximum speed threshold is set low to prevent dangerous runaway, then the reliability is improved, but the turbomachine cannot achieve necessary transient speed peaks during severe maneuvers

Engineering Contradiction:

Improvesafety against dangerous runawayVSAvoidability to achieve transient overspeeds

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The control system dynamically adjusts the maximum speed threshold based on real-time monitoring of indicative physical parameters, allowing the threshold to be high during normal operation for adaptability and low during abnormal conditions for reliability

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control system uses feedback from indicative physical parameters (torque, power, or speed of first rotary shaft) to continuously adjust the maximum speed threshold, enabling the system to distinguish between intentional transient overspeeds and dangerous runaway conditions

Inventive Principle:

Principle #23Feedback

3Reliability

If the second turbine and second rotary shaft are oversized to withstand maximum torque at high speed thresholds, then the reliability is improved, but the mass of the turbomachine increases significantly

Engineering Contradiction:

Improveability to withstand maximum torqueVSAvoidmass of the turbomachine

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

By changing the maximum speed threshold parameter based on operative conditions, the system allows the second turbine and rotary shaft to be sized for normal operating torques rather than maximum emergency torques, significantly reducing mass while maintaining reliability through dynamic control

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The dynamic threshold adjustment acts as a preventive measure, reducing the speed threshold before dangerous runaway can occur, which allows the use of lighter turbine and shaft components that would not be sufficient to withstand unlimited overspeeds

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentEP3071798B1Turbine engine and control method

Publication Date: 2019.06.19 SAFRAN HELICOPTER ENGINES

Figure 1~2
Figure 3

AI summary

The invention relates to a method for controlling a turbine engine (5) which includes a compressor (8), a combustion chamber (9), first and second turbines (10, 12), a first rotary shaft (11) rotatably secured to said compressor and to said first turbine, a second rotary shaft (13) to which the second turbine is rotatably secured, said second rotary shaft being freely rotatable relative to the first rotary shaft, and a controller (15) for controlling the fuel supply to the combustion chamber. Said controller interrupts the fuel supply to the combustion chamber if a speed of rotation (N2) of said second rotary shaft exceeds a maximum threshold (N2imax) which varies according to at least one indicative physical parameter associated with a mechanical power extracted from combustion gases in the second turbine.