Free Turbine Overspeed Detection via Torque Measurement
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Solution Overview
Problem
Existing overspeed detection systems for free turbines in turboshaft engines face challenges such as unreliable sensors in high-temperature environments and slow reaction times, which can lead to inadequate protection against shaft breakage and subsequent engine damage.
Innovation Solution
A torque measurement device with a signal processing unit that rapidly detects a drop in torque during a fraction of a turn, triggering a reduction in fuel flow to prevent overspeed, utilizing a tone wheel torque meter for simultaneous speed and torque measurement with extremely fast reaction times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retention ring is mounted around the turbine to absorb blade energy, then the protection against overspeed is improved, but the mass of the engine increases significantly
Solution Approach 1:
The patent replaces the mechanical retention ring system with an electrical/electronic detection and control system. A torque meter measures torque on the output shaft, and a microprocessor compares the measured torque against expected values to detect shaft breakage and trigger fuel cutoff, eliminating the need for a heavy mechanical retention ring.
Solution Approach 2:
The patent introduces a torque meter as an intermediary measurement device that indirectly detects shaft integrity through torque measurement. Instead of directly containing blades with a retention ring, the system uses torque measurement as a mediator to detect anomalies and trigger protective action through fuel flow control.
2Measurement precision
If speed sensors are positioned in the hot enclosure near the free turbine to detect shaft breakage, then the detection capability is improved, but the reliability and lifetime of the sensors deteriorate due to unfavorable environmental conditions
Solution Approach 1:
The patent extracts the measurement function from the hot enclosure environment. Instead of placing sensors directly near the free turbine in the hot section, the torque meter is positioned on the output shaft in a cooler area, and the detection logic is moved to a microprocessor that can be located in a temperature-controlled electronics bay, separating the measurement function from the harsh thermal environment.
Solution Approach 2:
The patent replaces traditional speed sensors with a torque measurement system. The torque meter provides indirect measurement of shaft rotation and integrity through torque measurement, eliminating the need for direct speed sensing in the hot enclosure and allowing measurement in more favorable environmental conditions.
3Measurement precision
If traditional torque measurement devices are used, then the measurement capability is provided, but the reaction time is too long to prevent explosive overspeed
Solution Approach 1:
The patent changes the measurement parameter from indirect mechanical torque measurement to direct electrical torque sensing. The electrical torque meter provides instantaneous torque data that is immediately processed by the microprocessor, reducing the reaction time from seconds or hundreds of milliseconds to milliseconds, enabling rapid detection and response to shaft breakage.
Solution Approach 2:
The patent replaces mechanical torque measurement devices with an electrical torque meter and digital processing system. This substitution eliminates the mechanical inertia and response delays of traditional devices, providing near-instantaneous torque measurement and enabling the microprocessor to detect anomalies and trigger fuel cutoff within milliseconds.
Data Source
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Figure 3~4
AI summary
The invention relates to a device for protecting against the overspeed of a free turbine (6) of a turbine engine which comprises a gas generator including at least one compressor (1), a combustion chamber (3), at least one linked turbine (4) and a system for controlling the fuel injected into said combustion chamber, the gases produced by said generator being sent to said free turbine (6), said device including at least one torque-measuring means (12) supported by an output shaft (8, 11) mechanically coupled to said free turbine, and a signal-processing unit capable of transmitting an order to the control system of the turbine engine to reduce the flow rate of injected fuel in the event it is detected that the torque drops below a set value, wherein the measurement of the torque used for triggering said reduction is carried out during a rotation corresponding to a fraction of a revolution of said output shaft (8, 11).