GB2230822A

GB2230822A - Apparatus and method for control of gas turbine engine overspeed

Info

Publication number: GB2230822A
Application number: GB8927808A
Authority: GB
Inventors: Robert John Vandermolen; Frederick John Pineo; Douglas Paul Otis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1989-04-17
Filing date: 1989-12-08
Publication date: 1990-10-31
Also published as: GB8927808D0; DE3940248A1; FR2645908A1; JPH02275027A

Description

13LN-1913 APPARATUS AND METHOD FOR CONTROL OF GAS TURBINE ENGINE OVERSPEED

The U.S. Government has rights in this invention pursuant to Contract No. DAM51-83-C-0014 awarded by the Department of the Army.

The present invention relates to a control system for a gas turbine engine and, more particularly, to an apparatus and method for controlling overspeed of a gas turbine engine.

Gas turbine engines typically comprise a compressor for producing a downstream axial flow, a combustor downstream of the compressor and a turbine downstream of the combustor which drives the compressor by an interconnecting shaft. In these gas turbine engines it is important to insure that the turbine does not exceed acceptable speeds such that critical stresses occur on the disk. This is particularly important in engines which incorporate a free power turbine downstream of the compressor driving turbine. In these engines the power turbine rotates independently of the compressor driving turbine and is typically connected to a load through a gearbox such as in a turbo-shaft or turbo-prop engine. In these engines sudden changes in load, such as during a gearbox failure, may result in the power turbine being subjected to overspeed. If the power 13LN-1913 turbine overspeed is not controlled then not only the turbine but also the entire engine may be damaged when critical overstresses develop in the power turbine. Previously, various systems have sought to control overspeed by gradually or rapidly reducing fuel supplied to the engine. This reduction in fuel reduces the energy supplied to the power turbine and therefore gradually reduces turbine speed. However, since the reduction of energy supplied to the turbine is not immediate the power turbine is subjected to rapid overspeed and therefore the turbine must be designed to withstand these stresses by increasing the turbine's size and weight. Therefore, it would be desirable to have a control system and method of controlling a gas turbine engine to further reduce turbine stresses in a gas turbine engine during an overspeed situation.

In accordance with one aspect of the invention, a control system for gas turbine engine having a turbine comprises a means for receiving a signal representative of turbine overspeed, and a means for reducing airflow entering the turbine in response to said turbine overspeed signal.

Another aspect of the invention provides a control system for a gas turbine engine having a variable guide vane, a turbine and a port positioned upstream of said turbine for providing a means for air to exit the engine. comprising a means for receiving a signal representative of turbine overspeed and a means for producing a port adjustment signal for adjusting said port such that air exits the engine in response to said turbine overspeed signal.

A further aspect of the invention provides a method for controlling a gas turbine engine having-a variable guide vane, a turbine and a port positioned upstream of said turbine, comprising the steps of receiving a 1 1 13LN-1913 signal representative of turbine overspeed; and producing a port adjustment for adjusting said port such that air exits the engine in-response to said turbine overspeed signal.

In the drawings:

FIGURE 1 is a schematic diagram of an illustrative gas turbine engine which incorporates the present invention.

FIGURE 2 is a flow diagram of an alogorithm used in a control system embodying the present invention.

In Fig. 1, a gas turbine engine system 10 comprises a turbo-shaft gas turbine engine 12 having a supporting structure or casing 20. Disposed within the casing 20 is a first compressor 22 for producing a downstream axial flow. The first compressor 22 has an inlet guide vane 24 before a first stage 26 of the first compressor 22 and typically has variable guide vanes 28 positioned between other stages 30 of the first compressor 22. A bleed port 32 extending through the casing 20 is positioned downstream of the first compressor 22. A second compressor 34 is positioned downstream of the bleed port 32, and the second compressor 34 also typically has variable guide vanes 28 positioned between the compressor stages 30. An environmental port extending through the casing 20 is positioned downstream of the second compressor 34 and a combustor 40 is positioned downstream of the second compressor 34. A compressor driving turbine 44 is positioned downstream of the combustor 40 which is connected to the first and second compressors 22 and 34 respectively through a shaft. A free power turbine 50 is positioned downstream of the compressor driving turbine 44 and the free power turbine is coupled to an 1 13LN-1913 output drive shaft 52. The drive shaft 52 is coupled to a gearbox means 54 and the gearbox means 54 is coupled to at least one airfoil 60. In Fig. 1, the gearbox 54 is coupled to first and second airfoils, 60a and 60b, respectively. The first airfoil 60a represents the main airfoil and the second airfoil 60b represents a supplementary airfoil exemplary of helicopter-type systems. A control system 70 which in part controls turbine overspeed receives various lo inputs representative of-operator commands and-engine parameters which provide the signals upon which the control system 70 operates. For example, the control system 70 may receive an input relating to the speed of the free turbine 50 such as by a speed sensor 72. The control system 70 then provides various outputs which controls the engine such as at the bleed port 32, inlet guide vanes 24 and variable stator vanes 28.

The control system 70 typically comprises an overspeed detector 82 which detects whether the speed of the free turbine 50 is above an acceptable speed. The overspeed detector 82 is coupled to a fuel control 84 which limits fuel or preferably sends a signal to close a fuel control valve after an overspeed situation is detected. The overspeed detector 82 is also coupled to a port control 86 which control ports such as the bleed port 32 and the environmental port 38 such that after an overspeed situation is detected the port control sends a signal to open the ports.

The overspeed detector 82 is also coupled to a guide vane control 88 which controls the variable guide vanes 28 such that after overspeed is detected, the guide vane control 88 sends a signal to adjust the position of the inlet guide vane 24 and the variable guide vanes 28.

z -5 13LN-1913 In Fig. 2, is depicted an algorithm 200 which is implemented in the control system embodying the present invention. The algorithm 200 comprises an input block 210 which serves as a means for receiving inputs such as an input corresponding to a speed of the free turbine as in Fig. 1. Input block 210 is coupled to decision block 214 which compares whether the speed of the free turbine is above an acceptable level, thereby indicating a free turbine is in an overspeed situation.

If the speed of the freeturbine is not in an overspeed situation, then the algorithm switches back to input block 210 for receiving updated inputs. Alternatively, if decision block 214 indicates free turbine overspeed then the algoriith switches to output block 218 which is outputs a signal to a fuel control to limit fuel flow. output block 218 is coupled to output 222 which outputs a signal to a port control to open ports such as bleed port 32 or environment port 38 of Fig. 1. Output block 222 is coupled to output block 226 which outputs a signal to a variable guide vane control to close the inlet guide vane 24 and the variable guide vanes 28. output block 226 is coupled to input block 210.

The control system embodying the present invention may be any control means such as an analog or digital controller. Preferably, the control system implements the algorithm of Figure 2 in a full authority digital electronic control (FADEC) system.

The control system may receive inputs and process these signals to determine whether an overspeed situation exists by any suitable means. For example, the sensor 72 may count the passage of blades on the free power turbine 50 as the turbine rotates. This is then converted into acceptable units and compared with a maximum acceptable speed.

13LN-1913 In operation, when an overspeed is detected, the overspeed detector provides an overspeed signal to the fuel control 84, port control 38, and guide vane control 88. The fuel control 84 limits fuel supplied to the engine 12, therefore decreasing energy supplied to the free power turbine 50. The port control 86 opens ports in the engine. Typically, bleed ports 32 are opened which reduces the energy in the engine 12. Further, depending on the engine's application, it may also be feasible to open the environmental ports, or any other ports which may serve as means for releasing fluid such as air from the engine prior to the turbine and more particularly the power turbine. Typically, opening bleed valve ports will reduce turbine overspeed by approximately 10 percent.

During an overspeed situation, signals are also supplied to the guide vane control 88 which adjusts the guide vanes in response to the turbine overspeed signal. Preferably, the inlet guide vane is adjusted such that the amount of air introduced into the engine is reduced. Further, the variable guide vanes may be adjusted such as to reduce compressor efficiency and, therefore, reduce the energy of the fluid in the engine. Typically, adjusting the guide vanes to a fully closed position, to the extent possible, will reduce turbine speed by approximately four percent. For example, in a system having 151% overspeed in a system in which only fuel is shut off, closing guide vanes may result in a reduction to 147% overspeed.

Further, when bleed valve ports are opened in this system, turbine overspeed may be reduced to 137%. Therefore, peak overspeed may be reduced by 14% by using guide vane adjustment and bleed port adjustment in accordance with the present invention. Since stress on a turbine corresponds to the square of the turbine's speed, this system can greatly reduce 1 13LN-1913 turbine stress. Consequently, turbine disk weight may be reduced by about nine pounds in a representative system while maintaining or even increasing present safety margins. In a FADEC controlled engine, typically the bleed ports and variable guide vanes are controlled such as to maximize efficiency and to control airflow in the compressor. Therefore, the present system and method is also particularly advantageous since it can be employed in a gas turbine engine having a FADEC control without significant additional hardware which may result in 15 additional maintainability and reliability concepts corresponding to adding additional components to the engine. Rather, guide vane and ports are presently regulated on the engine to maximize efficiency and turbine overspeed is presently monitored thereby comprising the primary controlled components.

Although the principles of the invention have been described in relation to a particular control system it will be apparent to those skilled in the art that many changes and modifications may be made from the disclosed preferred embodiments. It is therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

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Claims

13LN-1913 1. A control system for a gas turbine engine having a turbine comprising: means for receiving a signal representative of turbine overspeed, and means for reducing airflow entering the turbine in response to said turbine overspeed signal.

2. The control system of claim 1 wherein said engine has a variable guide vane and said means for reducing airflow entering the turbine comprises a means for producing a variable guide vane adjustment signal for adjusting the guide vanes in response to said turbine overspeed signal.

3. The control system of claim 2 wherein said variable guide vane adjustment signal is a signal for closing an inlet guide vane of said engine.

4. The control system of claim 1 wherein said engine has a port positioned upstream of said turbine for providing a means for airflow to exit the engine and said means for reducing airflow entering the turbine comprises a means for producing a port adjustment- signal for adjusting said port such that air exits the engine in response to said turbine overspeed signal.

5. The system of claim 4 wherein said port is a bleed valve.

6. The system of claim 4 wherein said port is an environmental port.

1 v, 13LN-1913 -g-

7. A control system for a gas turbine engine having a variable guide vane, a turbine and a port positioned upstream of said turbine for providing a means for fluid to exit the engine, engine comprising means for receiving a signal representative of turbine overspeed, and means for producing a port adjustment signal for adjusting said port such that fluid exits the engine in response to said turbine overspeed signal.

8. The system of claim 7 wherein said port is a bleed valve.

9. The system of claim 7 wherein said port is an environmental port.

10. The system of claim 1 further comprising means for producing a variable guide vane adjustment signal for adjusting the guide vanes in response to said turbine overspeed signal.

11. The system of claim 10 wherein said variable guide vane adjustment signal is a signal for closing an inlet guide vane of said engine.

12. A method for controlling a gas turbine engine having a variable guide vane, a turbine and a port positioned upstream of said turbine, comprising the steps of: receiving a signal representative of turbine overspeed; and producing a port adjustment for adjusting said port such that air exits the engine in response to said turbine overspeed signal.

13LN-1913

13. The method of claim 12 further comprising the step of producing a variable guide vane adjustment signal for adjusting the guide vanes in response to said turbine overspeed signal.

14. The method of claim 13 wherein said step of an adjustment signal is a signal for closing an inlet guide vane of said engine.

15. A control system for a gas turbine engine substantially as hereinbefore described with reference to Figures 1 and 2.

16. A method of controlling a gas turbine engine substantially as hereinbefore described with reference to Figures 1 and 2.

Published 1990 atThe Patent Office, State HOUse.6671 High Holborn, LondonWC1R4TP. Further copies maybe obtained from The Patent Mce. Sales Branch. St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. V.7 11