FR2818691A1 - Hydro mechanical over speed limiter for aircraft gas turbine has limiter to restrict fuel flow when engine speed exceeds set value - Google Patents

Abstract

The hydro mechanical over speed limiter for an aircraft gas turbine limits the fuel feed (Wps) to the engine when the speed exceeds a maximum preset value. The limiter provides fuel feed at a fixed rate as the turbine returns to below threshold speed. It provides fuel feed at a set value (Wr) corresponding to a throttle down regime when the fuel feed valve (16) feeds a throttle back signal to the engine via an electronic control circuit.

Description

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Field of the Invention The present invention relates to the field of fuel injection in turbomachinery and more particularly relates to a device for protection against overspeeding.

PRIOR ART In turbomachinery, the best performances are obtained for rotational speeds of the rotating members close to the maximum admissible limits beyond which a loss of compressor or turbine blades can occur. However, such a loss is likely to cause a perforation of the crankcase, the consequences of which can go as far as complete destruction of the turbomachine.

Also, and as recommended by international regulations relating to civil aviation, the use of an overspeed protection device is essential to prevent the speed of these moving organs from exceeding these maximum authorized speeds. .

Until recently, these protection devices used regulators of the watt-balance regulator type, as illustrated by international application WO89 / 02980. However, today, these mechanical regulators are gradually being replaced by electronic regulators which act directly on the engine by cutting the fuel supply to the combustion chamber of the turbomachine. An example of such a current architecture is described in international application W099 / 00585.

Unfortunately, this solution has the serious drawback of involving the initiation of a subsequent restart procedure which, under certain special flight conditions (for take-off for example), may prove to be impossible to implement and cause irreparable loss of the aircraft.

OBJECT AND DEFINITION OF THE INVENTION The present invention therefore proposes to overcome these drawbacks with an electronic device for protection against overspeeding which does not cause the engine to stop completely and furthermore guarantees a minimum operating speed.

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assurant l'ensemble des servitudes de l'aéronef. Un but de l'invention est aussi de permettre au pilote d'agir directement sur le dispositif pour le déverrouiller et ainsi retrouver l'opérabilité du moteur.

ensuring all the servitudes of the aircraft. An object of the invention is also to allow the pilot to act directly on the device to unlock it and thus regain the operability of the engine.

These aims are achieved by a device for protection against overspeeding in a turbomachine whose speed of rotation is controlled, through an electronic control circuit, by a throttle control lever. characterized in that it comprises means for limiting the supply of fuel to said turbomachine to a predetermined fixed flow rate Wps when said speed of rotation exceeds a maximum authorized speed, means for maintaining this supply of fuel to said predetermined fixed flow rate when said rotational speed becomes again lower than said maximum authorized speed, and means for bringing this fuel supply to a flow Wr corresponding to an idle speed when said throttle control lever sends an idle command to said turbomachine via said electronic control circuit.

With the present invention, in the event of an overspeed, the fuel supply to the engine is reduced to a predetermined fixed fuel flow rate Wps and maintained at this flow rate value as long as the rotation speed of the engine does not drop below a speed predetermined, the protection then being erased by the pilot of the aircraft by returning the throttle control lever to an idle position Wr of the engine speed.

Preferably, the means for limiting the fuel supply to a predetermined fixed flow rate Wps comprise an electronic overspeed detection circuit producing an electrical signal (I) when a speed of rotation of the turbomachine (N) exceeds a maximum speed authorized (LIMIT), an overspeed solenoid valve connected to said electronic overspeed detection circuit and delivering a first hydraulic signal (Pxl) from said electrical signal, and an overspeed valve whose position is controlled by said first hydraulic signal so as to decreasing the flow of fuel injected into said turbomachine, by a metering device to which it is connected, up to said predetermined fixed flow Wps.

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The first hydraulic signal corresponds to a low pressure Pb when said speed of rotation of the turbomachine is lower than said maximum authorized speed and to a higher pressure Psf when this speed of rotation (N) exceeds said maximum authorized speed (N - LIMIT). Preferably, said upper pressure Psf is equal to a high pressure P1 at the outlet of a high pressure fuel injection pump.

According to an advantageous embodiment, the maintenance of said predetermined fixed flow rate when said speed of rotation of the turbomachine becomes lower than said maximum authorized speed is obtained by a second hydraulic signal (Px2) set to said higher pressure Psf and which is added at said first hydraulic signal for moving against a spring a hydraulic slide of said overspeed valve. This second hydraulic signal is obtained from a hydraulic control signal (PxO) generated through said metering device from said upper pressure Psf.

The present invention also relates to the method implemented in the above-mentioned protection device against overspeeding.

Brief description of the drawings The characteristics and advantages of the present invention will emerge more clearly from the following description, given by way of non-limiting illustration, with reference to the appended drawings in which: - Figure 1 is a partial schematic view of a system of fuel injection of a turbomachine provided with an overspeed protection device according to the invention, - Figure 2 is a view similar to that of Figure 1 in an overspeed detection position, - Figure 3 is a view similar to that of Figure 1 in a protection locking position, and - Figure 4 is a view similar to that of Figure 1 in a protection unlocking position.

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Detailed description of a preferred embodiment
A schematic view of part of a fuel injection system of an aircraft turbomachine is shown in FIG. 1.

 Such a fuel injection system is generally organized around a fuel metering unit (FMU) 10 intended to control the flow of fuel which flows between a high pressure pump 12 ensuring pressurization of this fuel withdrawn from a fuel tank (not shown) and a plurality of fuel injectors 13 from the combustion chamber of this turbomachine at the inlet of which is a shutoff valve 15 controlled by an electro- shut-off valve (not shown). PI will call the high pressure HP at the outlet of the high pressure pump and P2 the pressure at the inlet of the injectors. Continuous control of the flow of fuel supplied by the metering device (engine regulation) is ensured by an electronic control circuit 14 to which this device is connected as a function of the engine parameters P and of the position of a lever 16 for controlling the gases. operated by the pilot of the aircraft.

 The metering device essentially comprises a hydraulic metering element (fuel metering valve FMV) 20 of which a first fuel supply inlet 200 is connected at the outlet of the high pressure pump 12, an electro-overspeed valve 22 including a first inlet 220 is connected to a low pressure Pb and a second inlet 222 is connected to the upper pressure Psf, and an overspeed valve 24, a pilot outlet 240 of which is connected to the injectors, a first end inlet 242 of this valve being connected to a first use outlet 202 of the metering element 20 and a second end inlet 244, opposite the first end inlet, being connected to an outlet 224 of the overspeed solenoid valve. The hydraulic metering element 20 further comprises a second use outlet 204 directly connected to the pilot outlet 240 of the overspeed valve 24 at the inlet of the injectors and intended to deliver to these injectors a stabilized flow known as overspeed protection, predetermined fixed value Wps and corresponding to a flow rate close (preferably slightly higher) to an idle speed.

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The hydraulic metering element 20 includes a hydraulic drawer 210 which can move linearly under the control of the electronic control circuit 14. This drawer has two annular slots 212, 214. The first 212 is intended for metering the fuel which is received by the first supply inlet 200 and is discharged by the first and second use outputs 202, 204. The second light 214 provides communication between a second supply inlet 206 connected to the high pressure Psf (which advantageously corresponds to the pressure high pressure pump outlet) and a third use outlet 208 connected to a first supply orifice 246 of the overspeed valve 24 which by an annular opening 252 of a hydraulic slide 250 of this valve can be brought into communication with a second supply orifice 248 looped over the second end inlet 244 and therefore also connected to the outlet 224 of the electro- overspeed valve 22. The position of the overspeed valve 24 is controlled by referencing a spring 254 to a hydraulic signal. Thus, the overspeed valve is closed by applying a hydraulic signal equal to Psf to its second end inlet 244, which is then added to the action of spring 254. When the hydraulic signal disappears, its value becomes Pb and the action of the pressure P2 downstream of the metering device 20 becomes greater than the force exerted by the spring when it is referenced to Pb and the overspeed valve opens.

 The overspeed solenoid valve 22 is controlled by an electronic overspeed detection circuit 18 which has the function of detecting, in particular from the information of a speed sensor (N) of the high pressure body of the turbomachine, the speed limit of this HP body (LIMIT). Thus, if the speed of the body HP is greater than this limit and remains so, the electronic overspeed detection circuit 18 must produce an electrical control signal (I) which, through the electric tap 22 by generating a first hydraulic signal (Px 1), will command the closing of the overspeed valve 24.

 For the sake of simplification, the elements of the injection system which do not directly contribute to the invention have been deliberately omitted although they obviously appear in any injection system. This is for example the bypass type valve looped on the HP pump to recycle the fuel

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délivré en excès ou d'éventuelles soupapes classiques de pressurisation ou encore l'électro-robinet d'arrêt mentionné précédemment.

delivered in excess or any conventional pressurization valves or the electro-stop valve mentioned previously.

 The injection system modified according to the invention is built on the principle that, in normal operation, there is correspondence between the position of the pilot lever (TLA) and the position of the hydraulic element which performs the metering ( FMV) of the fuel flow supplying the injectors. Thus, if after an overspeed detection, the metering element responds as expected to the pilot lever setpoint (manual action), it can then be considered that the engine control chain (and in particular the electronic control circuit) which is between the joystick and the metering device is not the cause of the overspeed.

 The overspeed protection device according to the invention proposes to memorize the overspeed protection state hydraulically and also to erase it hydraulically once the metering element has returned to a position controlled manually by the pilot by means of his joystick. flight. The hydraulic control signal (PxO) which ensures both this locking and this unlocking of the overspeed valve 24 is constructed from the position of the second groove 214 of the metering slide 210 relative to the second supply inlet 206 and the third use outlet 208, this groove putting them into commumcation when the position of the metering device is greater than or equal to the predetermined speed of overspeed protection Wps. In this case, the hydraulic control signal (PxO) is equal to (Pst). If, on the contrary, the position of the metering device is lower than this predetermined overspeed protection flow, the communication is interrupted and the hydraulic control signal (PxO) then becomes zero (Pnull).

 The operation of the overspeed protection device according to the invention will now be described with reference to FIGS. 2 to 6.

 However, let us first return to FIG. 1 which shows the device in a normal operating state.

 The turbomachine is then at a speed greater than idle corresponding to a position of the slide 210 of the metering hydraulic element which therefore ensures communication between its first supply inlet 200 and its first and second use outputs 202, 204 (its third power input 206 which

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est à la pression Psf communique également par la seconde gorge annulaire 214 avec la seconde sortie d'utilisation 208 mettant le signal hydraulique de commande PxO à Pst). La vitesse (N) du corps HP est inférieure au seuil de déclenchement de protection de survitesse (LIMIT) et le circuit électronique de détection 18 n'envoie donc pas de signal électrique déclenchant l'action de protection (I = 1-null). Le premier signal hydraulique (Pxl) de sortie de l'électrorobinet de survitesse est dans une position de repos à la pression basse (Pb) correspondant à une ouverture du clapet de survitesse 24. L'état des pressions est donc le suivant : (Pxl) = (Px2) = (Pb) et (PxO) = (Pst).

is at the pressure Psf also communicates by the second annular groove 214 with the second use outlet 208 putting the hydraulic control signal PxO to Pst). The speed (N) of the HP body is lower than the overspeed protection triggering threshold (LIMIT) and the electronic detection circuit 18 therefore does not send an electrical signal triggering the protection action (I = 1-null). The first hydraulic signal (Pxl) from the overspeed solenoid valve is in a rest position at low pressure (Pb) corresponding to an opening of the overspeed valve 24. The state of the pressures is therefore as follows: (Pxl ) = (Px2) = (Pb) and (PxO) = (Pst).

The overspeed valve 24 is kept open by the action of pressure forces (P2) downstream of the metering device 20. The fuel flow going to the injectors is greater than the predetermined fixed speed Wps of overspeed protection.

FIG. 2 illustrates the state of the injection system at the end of the detection of an overspeed.

From the previous normal state, the HP body goes into overspeed for unknown reasons. The electronic overspeed detection circuit 18 observes that the speed of the body HP becomes greater than its predefined limit (LIMIT) and then generates an electric current (1) different from the previous state of rest (I ~ null). This electrical signal acts as a closing signal on the electric valve 22, the first hydraulic output signal (Pxl) of which is then brought to high pressure (Psf). The action of the spring (K) added to this pressure (Pst) has the effect of closing the overspeed valve 24. The fuel flow will then decrease to its minimum value Wps predetermined by the second use outlet 204 of the metering device 20. When the overspeed valve reaches its closed position (the first use outlet 202 then being completely closed), the third use outlet 208 of the metering device 20 and the first feed orifice 246 of this valve are placed in communication via the annular groove 252 generating a complementary hydraulic signal (Px2) which, by applying to the overspeed valve on the spring side, is added to the first hydraulic signal (Pxl). The state of the pressures therefore becomes: (Pxl) - (Psf) and (PxO) = (Px2) = (Pst),

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La figure 3 illustre l'état du système d'injection dans une position suivante de verrouillage de l'action de protection.

FIG. 3 illustrates the state of the injection system in a following position for locking the protective action.

signal (Pxl) de (Pst) à (Pb) mais (Px2) demeurant toujours égal à (Psf) (le ressort Ui 254 référencé à Psf permet de garder le clapet en position fermée) tant que la position de l'élément doseur reste supérieure à la valeur de ralenti fixée, le clapet de survitesse 24 est verrouillé en position fermeture et la turbomachine est

toujours dans l'état de protection de survitesse avec un débit égal à Wps. Dans Ui cette position de verrouillage, l'état des pressions est le suivant : (Pxl) = (Pb) et (PxO) = (Px2) = (Pst). The overspeed valve 24 is now closed and the metered flow rate is saturated with the predetermined fixed value of Wps, the speed of the body HP decreases to become again lower than the predefined limit of (LIMIT). At this moment the current (I) becomes again equal to its initial null value (null). The solenoid valve 22 switches the

signal (Pxl) from (Pst) to (Pb) but (Px2) always remaining equal to (Psf) (the spring Ui 254 referenced to Psf keeps the valve in the closed position) as long as the position of the metering element remains greater than the set idle value, the overspeed valve 24 is locked in the closed position and the turbomachine is

always in the overspeed protection state with a speed equal to Wps. In Ui this locking position, the state of the pressures is as follows: (Pxl) = (Pb) and (PxO) = (Px2) = (Pst).

 FIG. 4 illustrates the state of the injection system in a following position for unlocking the protective action.

 If the pilot returns the lever 16 to an engine idle position and the entire control loop between the lever and the metering device operates normally (that is to say in particular the electronic engine regulation circuit 14), the element metering unit returns to a corresponding idling position in which the communication between the third use outlet 208 of the metering unit 20 and the first supply port 246 of the overspeed valve 24 is interrupted (the fuel metering is then carried out through 'only part of the second use output 204). The signal (PxO) then drops to (Pnull) and the signal (Pxl) being equal to (Pb), the summation of (Pxl) and (P ~ null) is therefore equal to (Pb) thus causing the valve to open overspeed. We thus obtain its unlocking and the turbomachine then finds itself in an idle speed Wr <Wps with the following pressure state: (Pxl) = (Px2) = (Pb) and (PxO) = (P ~ null).

 Thus, in the event of overspeed, the pilot is no longer obliged as before to cut the engine of the aircraft in order to cancel the overspeed protection. He just needs to bring this engine back to idle. The

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dangers potentiels considérables résultant d'un arrêt en vol peuvent être ainsi évités.

considerable potential hazards resulting from a flight stop can be avoided.

 It will also be noted that the proposed configuration of the overspeed protection device lends itself well to tests of the proper functioning of the overspeed valve both at start-up and at engine stop.

 Thus, during the start-up sequence, the electronic overspeed detection circuit 18 can send an order to close the valve (I) * (I ~ null) on command of the control circuit 14. The first hydraulic signal from the electro- tap (Pxl) then becomes (Psf) and the overspeed valve 24 closes. The metering element 20 is then at an ignition flow position which is less than or equal to the idle flow. The lock signal (Px2) is zero. When this start-up test is finished, the current becomes zero (I) = (null), (Pxl) becomes equal to (Pb) and the valve opens.

 Similarly, when the pilot controls the engine stop by acting on the lever 16, the metering device 20 goes towards its closing stopper closing the communication by the second groove 214 and (PxO) = (Pnull). During the decrease in the HP speed, the electronic overspeed detection circuit 18 sends a current to test the closing of the overspeed valve and there is then a sequencing of the states identical to the case of test at start-up.

Claims (7)

1. Device for protection against overspeeding in a turbomachine, the speed of rotation of which is controlled, through an electronic control circuit (14), by a gas control lever (16), characterized in that it comprises means (20, 22, 24) for limiting the supply of fuel to said turbomachine to a predetermined fixed flow rate Wps when said speed of rotation exceeds a maximum authorized speed, means (20, 22, 24) for maintaining this supply of fuel at said predetermined fixed flow rate when said rotation speed becomes lower than said maximum authorized speed, and means (20, 22, 24) for reducing this supply of fuel to a flow rate Wr corresponding to an idle speed when said control lever for gas sends an idle command to said turbomachine via said electronic control circuit.  2. Protection device according to claim 1, characterized in that said means for limiting the supply of fuel to a predetermined fixed flow rate Wps comprise an electronic overspeed detection circuit (18) producing an electrical signal (I) when a rotation speed of the

 turbomachine (N) exceeds a maximum authorized speed (N ~ LIMIT), an overspeed solenoid valve (22) connected to said electronic overspeed detection circuit and delivering a first hydraulic signal (Px1) from said electrical signal, and a valve overspeed (24) whose position is controlled by said first hydraulic signal so as to decrease the fuel flow injected into said turbomachine, by a metering device (20) to which it is connected, up to said predetermined fixed flow Wps.  3. Protection device according to claim 2, characterized in that said first hydraulic signal corresponds to a low pressure Pb when said speed of rotation of the turbomachine is lower than said maximum authorized speed and to a higher pressure Psf when this speed of rotation (N) exceeds said maximum authorized speed (N ~ LIMIT). <Desc / Clms Page number 11>

 4. Protection device according to claim 3, characterized in that said upper pressure Psf is equal to a high pressure Pl available at the outlet of a high pressure fuel injection pump (12).  5. Protection device according to claim 1, characterized in that the maintenance of said predetermined fixed flow rate when said speed of rotation of the turbomachine becomes lower than said maximum authorized speed is obtained by a second hydraulic signal (Px2) set to said higher pressure Psf and which is added to said first hydraulic signal to move against a spring (254) a hydraulic slide (250) of said overspeed valve.  6. Protection device according to claim 5, characterized in that said second hydraulic signal is obtained from a hydraulic control signal (PxO) generated through said metering device (20) from said upper pressure Psf.  7. Method for protection against overspeeding in an aircraft engine whose speed of rotation is controlled, through an electronic control circuit (14), by a throttle control lever (16), method in which limits to a predetermined fixed flow rate Wps the supply of fuel to said engine when said speed of rotation exceeds a maximum authorized speed, then this predetermined fixed flow is maintained when said speed of rotation again becomes lower than said maximum authorized speed, and finally this supplying fuel at a rate Wr corresponding to an idle speed when said throttle control lever sends an idle command to said engine via said electronic control circuit.