FR3035155A1 - TURBOMACHINE FUEL DISTRIBUTION CIRCUIT WITH REDUCED SIZE - Google Patents

Abstract

The invention proposes a fuel distribution circuit (1) of a turbomachine comprising a fuel combustion chamber (C), and a set (E) of servovalves and actuators of variable geometry parts, the distribution circuit fuel system (1) comprising: - a pump (10), - a supply line (11a) of the combustion chamber, and - a supply line (11b) of the set of servovalves and actuators, characterized in that it further comprises a device (30) for shutting off the flow rate in the supply line of the set of servovalves and actuators when a engine speed of the turbomachine is below a determined threshold speed.

Description

FIELD OF THE INVENTION The invention relates to a fuel distribution circuit of a turbomachine, and a turbomachine comprising such a circuit.

STATE OF THE ART A turbomachine conventionally comprises a combustion chamber, and a set of parts with variable geometry (for example cylinders, variable pitch blades, thermal control valves, etc.) as well as fuel regulators, which in order to operate require to be fueled.

In this regard, a turbomachine also comprises a fuel distribution circuit, in particular comprising a volumetric-type pump as well as feed lines for the components to supply fuel. In all the operating conditions of the turbomachine, to ensure proper operation thereof, the flow rate supplied by the pump must be greater than the fuel requirement of the turbomachine. The pump is therefore sized to deliver a flow always greater than or equal to the maximum flow required by the operation of the turbomachine. With reference to FIG. 1, the flow rate provided by a pump is represented as a function of the engine speed of the turbomachine, expressed as a percentage of the maximum speed. The flow required for the operation of the turbomachine is represented by the hatched area while the actual flow delivered by the pump is represented by the line in solid lines. As can be seen in the figure, the flow rate supplied by a positive displacement pump is generally linear with its rotational speed corresponding to that of the turbomachine. The graph of Figure 1 shows the two points A and B sizing the pump, it is the points for which the difference between the flow delivered by the pump and the motor need is the lowest, namely: - The point A, at low revs, in so-called motor or reel self-rotation condition (also known as windmilling), that is to say when it is the relative speed of the air which drives the engine in rotation, and - Point B, in high speed, in take-off condition. The graph of Figure 1 also shows that the pump is oversized for most engine speeds, excluding A and B points, since 3035155 2 the flow it delivers is largely in excess of the needs of the turbomachine. This oversizing is manifested in terms of weight and bulk. The pump occupies a large volume, typically of the order of 50 to 100% of the volume occupied by an accessory box of the turbomachine, and weighs in the range of 20 to 40 kg. In order to lighten the aircraft carrying the turbomachine and to limit its fuel consumption, it is important that the pump is better sized in relation to the consumption needs of the turbomachine.

DESCRIPTION OF THE INVENTION The purpose of the invention is to overcome the drawbacks of the prior art, by proposing a solution for limiting the oversizing of the pump of a turbomachine with respect to the fuel requirements. The invention also aims to provide a reliable solution, avoiding the addition of additional valves or valves to those already required for the operation of a turbomachine. In this regard, the subject of the invention is a fuel distribution circuit of a turbomachine comprising a fuel combustion chamber, and a set of servo valves and variable geometry part actuators, the fuel distribution circuit. comprising: - a pump, - a supply line of the combustion chamber, and - a supply line of the set of servovalves and actuators, characterized in that it further comprises a device for breaking the flow rate in the supply line of the set of servovalves and actuators when a engine speed of the turbomachine is below a determined threshold speed. Advantageously, but optionally, the circuit according to the invention may further comprise at least one of the following characteristics: the circuit may further comprise a return line of the set of servovalves and actuators, in which the device flow cutoff is configured to cut the flow of the return line when the engine speed of the turbomachine is below a certain speed. The circuit may further comprise a fuel control valve, adapted to return an excess flow of fuel to the pump, and wherein the valve is further configured to cut the flow of the return line when the engine speed the turbomachine is less than a determined regime. the control valve may comprise: a cylinder and a piston movable in the cylinder, an inlet orifice, arranged in the cylinder, connected to the return line of the set of servovalves and actuators, an outlet port, arranged in the cylinder, connected to a low pressure return line to the pump, the piston being adapted to move between a first position in which the inlet port is in fluid communication with the orifice outlet, and a second position in which one of the inlet and outlet ports is closed. The regulating valve may further comprise: an orifice connected to a high-pressure line of the fuel circuit, and a second orifice connected to a low-pressure return line to the pump, and the valve is shaped so that the displacement of the piston towards the second position causes a gradual closing of the orifice connected to the high-pressure line so as to reduce a quantity of fuel flow flowing from the orifice connected to the high-pressure line and the second port connected to the low-pressure line. - The piston may comprise a base and a head comprising two sections 25 each closing a cross section of the cylinder, the base and the head defining two internal cavities of the cylinder, the first cavity extending between the base and the head connecting them together. orifice connected to the high-pressure line and the second orifice connected to the low-pressure line in at least one position of the piston, and the second cavity extending between the sections of the head connecting the orifice of input connected to the return line and the outlet port when the piston is in the first position. - The threshold engine speed may be less than 50% of the maximum engine speed, preferably equal to 40% of the maximum engine speed.

The invention also relates to a turbomachine, comprising a fuel combustion chamber and a set of servo valves and actuators of variable geometry parts, characterized in that it further comprises a fuel distribution circuit according to the invention. the above description.

Another object of the invention is a method of dispensing fuel in a turbomachine, implemented by a fuel distribution circuit, the preceding description, characterized in that it comprises cutting off the fuel supply to the engine. set of servovalves and actuators when the engine speed of the turbomachine is below a threshold regime. Advantageously, but optionally, the threshold speed is less than 50% of a maximum speed of the turbomachine, preferably equal to 40% of the maximum speed.

The fuel distribution circuit according to the invention makes it possible to better dimension the pump supplying the fuel flow for the operation of the turbomachine. Indeed, the supply of variable geometries being superfluous at low speed, the cut-off of the flow in the supply line makes it possible to eliminate a substantial part, of the order of one-half, of the required flow rate of the low-speed pump. engine. As the flow rate of the pump is linear with the engine speed, the degree of oversizing at higher engine speeds is decreased. In addition, the integration of the power cut-off function into a pre-existing control valve avoids adding additional components to the circuit, which would decrease its overall reliability and furthermore would significantly increase the overall mass of the assembly. . DESCRIPTION OF THE FIGURES Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the accompanying drawings, in which: FIG. 1, already described, the evolution of the flow rate provided by a pump in a fuel distribution circuit relative to the engine speed of the turbomachine. - Figure 2 schematically shows a fuel distribution circuit according to one embodiment of the invention. - Figure 3 shows the evolution of the flow rate provided by a pump distributed between the feed rate of a combustion chamber and the feed rate of actuators of variable geometries and fuel regulators. FIGS. 4a and 4b show the fuel flow delivered by the pump which is not operated and which must be recirculated to the pump. - Figures 5a and 5b show a control valve in two positions.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION With reference to FIG. 2, there is shown schematically a fuel distribution circuit 1 of a turbomachine T. The turbine engine T comprises at least one combustion chamber C and an assembly E of other fuel consuming components, comprising servo valves of fuel regulators as well as actuators of variable geometry parts such as, but not limited to, cylinders, variable pitch blades, temperature control valves, etc. . The fuel distribution circuit 1 comprises a positive displacement pump 25 10, a high-pressure line 11 supplying a first branch 11a to the combustion chamber C, this branch delivering the fuel to be injected into the chamber and a second branch 11b the set E servovalves and actuators. The fuel distribution circuit 1 further comprises a reservoir 12 in which the pump draws fuel and a low-pressure line 13 back to the pump. The return line to the pump comprises in particular a fuel return branch 13a extending from the set E servo valves and actuators.

With reference to FIG. 3, the evolution of the flow rate delivered by the pump as a function of the engine speed of the turbomachine is shown for low speeds, in this case for engine speeds of between 0 and 35.degree. % of the maximum engine speed, as well as the distribution of the flow rate consumed for the needs of the turbomachine, between: an injection rate in the combustion chamber (branch 11a), and a control flow rate of the servovalves and actuators of the engine; the set E (branch 11b). It can be seen that for the engine speeds represented, the distribution of the flow rate consumed is generally balanced between the two branches, that is to say that about 50% of the total flow rate is injected into the combustion chamber (part not shown). and about 50% (hatched portion) feeds the assembly E. However, the servo valves of the fuel regulators as well as the actuators of variable geometries are not operated for low-revs, particularly for regimes below a threshold regime less than 50% of the maximum speed of the turbomachine, typically of the order of 40% of the maximum speed of the turbomachine. Consequently, the part of the flow that supplies the set E is in fact superfluous for the engine speeds below this threshold.

As shown in FIG. 3, the elimination of the feed rate of the set E makes it possible to move the design dimension A of the pump by decreasing the maximum flow rate of the pump for the engine speed corresponding to this sizing point ( dashed curve). The sizing of the pump is therefore made from the new point A 'and the other sizing point corresponding to the take-off condition. As a result, the pump has a reduced mass and bulk. It is also less oversized compared to other engine speeds. Returning to FIG. 2, the fuel distribution circuit 1 thus advantageously comprises a device 30 for shutting down the flow in the branch 11b of the supply line 11 serving the set E of the servovalves and actuators, when the speed motor is higher than the speed for which this set is not operated. This speed is less than 50% of the maximum engine speed, and preferably equal to 40% of the maximum engine speed.

This device 30 may be configured to cut the flow in the branch 11b, but it is advantageously configured to cut the flow of the return line 13a common to the servovalves and actuators of the assembly E. In fact, the cutoff the flow in the return line causes the cutoff of the flow flowing in the elements of the set E and thus of all the flow supplying this set. According to a particularly preferred embodiment of the invention, the cut-off device 30 is integrated with a pre-existing fuel control valve of the fuel distribution circuit 1. The fuel control valve (known as English Bypass Valve) ) makes it possible to re-circulate a flow rate of the pump in excess of the need of the turbomachine to the pump 10. In FIG. 4a, which shows the diagram of FIG. 1, as well as in FIG. 3b, there is shown ( by arrows in Figure 4a, in points in Figure 4b) the excess fuel flow to be recirculated by the control valve.

This is the difference in flow rate between the total flow rate supplied by the pump and the actual flow rate required by the turbomachine for its operation. It can be seen in FIG. 4b, by the solid line, that over a certain engine speed range, typically for a lower engine speed at a speed of the order of 50% of the maximum engine speed, for example of the order 45% of the maximum speed, the flow 20 of the control valve is proportional to the engine speed. Referring to Figures 5a and 5b, there is shown an example of a control valve 30 exerting the power cut function of the set E indicated above. The regulating valve 30 comprises a cylinder 31 and a piston 32 mounted in translation in the cylinder. The piston comprises a base 320 and a head 321 interconnected by a rod 322. The base 320 and the head 321 occupy a whole cross section of the cylinder and define between them a first chamber 310. The cylinder 31 further comprises an orifice 311 connected to the high-pressure line 11 of the circuit 1, and an orifice 312 connected to the low-pressure line 13 of the circuit. The orifices 311, 312 may be more or less obstructed respectively by the base and by the piston head as a function of a displacement thereof.

On the side opposite the cavity 310 with respect to the head and the base of the piston, cavities 313, 313 'of the cylinder are connected to control pressure lines through inlet-outlet orifices 314, 314'. . In order to modulate the recirculated flow rate as a function of the engine speed, the valve control pressures are modulated so as to cause the piston to move in the cylinder, to selectively seal at least one of the ports 311 and of the orifice 312. In the example of FIGS. 4a and 4b, the higher the engine speed, the more the piston is moved downwards, that is to say towards its base, and less a large section 10 of the orifice 311 connected to the high-pressure line is closed, which increases the flow re-circulated to the pump. The cut-off function of the feed rate of the set E of the actuators and servo valves is advantageously integrated with the regulation valve 30. To do this, the regulation cylinder 30 is interposed between the assembly E and the pump 10 The cylinder 31 comprises an orifice 315 connected to the return line 13a of the servovalves and actuators of the assembly E, and a second orifice 316 connected to the low pressure line 13 leading to the pump 10. In addition, the piston comprises in addition, a slide formed in the piston head, namely that the piston head comprises two transverse sections 323, 324 occupying the cross section of the cylinder, the sections being integral in translation (for example by means of a rod connecting the sections) and being separated by a cavity 325. The piston can move between a first position, shown in FIG. 4a, in which the cavity 325 is opposite the orifices 315 and 316 and a 25 uxième position, shown in Figure 4b, wherein a section of the piston head closes one or other of the orifices 315, 316. In the first position, the line 13a is in fluid communication with the line 13 of back to the pump. This first position is reached for engine speeds above the threshold speed, for example for speeds greater than 50% of the maximum engine speed. In the second position of the piston, the flow of the return line 13a of the assembly E is cut. This position is reached for engine speeds below the threshold speed, for example for speeds below 50% of the engine speed.

In order for the fuel control function to be compatible with the power cutoff function of the set E, the valve is advantageously shaped so that the displacement of the piston towards the first position, for high engine speeds, corresponds to the displacement 5 increasing the amount of flow re-circulated to the pump. This is the case in FIGS. 4a and 4b, in which a displacement of the piston towards its base causes: - that the base 320 of the piston progressively releases the orifice 311 connected to the high-pressure line to increase the re-circulated flow rate towards the pump, and that the head 321 of the piston releases the orifice 316 connected to the low-pressure line 13, and in which a displacement of the piston towards its head, when the engine speed decreases, causes: - that the base 320 of the piston at least partially closes the orifice 311, 15 decreasing the flow recirculated to the pump, and - the section 324 of the piston closes gradually (to the second position or it closes completely) the orifice 316 and cut the flow in the return line 13a of the set E.

The embodiment described above makes it possible to adapt a control valve 30 which is already used in fuel distribution circuits to the flow-cutoff function of the return line of the assembly E. As a result, it is not necessary to add additional components whose weight or bulk would decrease the gain on the weight and bulk of the resized pump, and which would decrease the reliability of the entire circuit.

Claims (10)

REVENDICATIONS1. Fuel distribution circuit (1) of a turbomachine comprising a fuel combustion chamber (C), and an assembly (E) of servovalves and variable geometry part actuators, the fuel distribution circuit (1) comprising: - a pump (10), - a supply line (11a) of the combustion chamber, and - a supply line (11b) of the set of servovalves and actuators, characterized in that it further comprises a device (30) for shutting off the flow rate in the supply line of the set of servovalves and actuators when a engine speed of the turbomachine is below a determined threshold speed. The fuel distribution circuit (1) according to claim 1, further comprising a return line (13a) of the set (E) of servovalves and actuators, wherein the flow cutoff device (30) is configured to cut the flow of the return line (13a) when the engine speed of the turbomachine is below a certain speed. The fuel distribution circuit (1) according to claim 2, further comprising a fuel control valve (30) adapted to return an excess fuel flow to the pump, and wherein the valve (30) is in position. further configured to cut the flow of the return line (13a) when the engine speed of the turbomachine is below a certain speed. The fuel distribution circuit (1) according to claim 3, wherein the regulating valve (30) comprises: - a cylinder (31) and a piston (32) movable in the cylinder, - an inlet port ( 315), arranged in the cylinder, connected to the return line (13a) of the set of servovalves and actuators, - an outlet orifice (316), arranged in the cylinder, connected to a low pressure line (13). ) back to the pump, the piston (32) being adapted to move between a first position in which the inlet port (315) is in fluid communication with the outlet port 3035155 (316), and a second position in which one of the inlet and outlet ports (315, 316) is closed. The fuel distribution circuit (1) according to claim 4, wherein the regulating valve (30) further comprises: - an orifice (311) connected to a high-pressure line (11) of the fuel circuit, and a second port (312) connected to a low-pressure line (13) back to the pump, and the valve is shaped such that the displacement of the piston (32) towards the second position causes a gradual closure of the pump. orifice (311) connected to the high-pressure line (11) so as to reduce a quantity of fuel flow flowing from the orifice (311) connected to the high-pressure line and the second orifice (312) connected to the high-pressure line (311) low-pressure line (13). 15 A fuel distribution circuit according to claim 5, wherein the piston comprises a base (320) and a head (321) comprising two sections (323, 324) each closing a cross section of the cylinder (31), the base and the head defining two internal cavities (310, 325) of the cylinder, the first cavity (310) extending between the base (320) and the head (321) interconnecting the orifice (311) connected to the high line. -pressure and the second port (312) connected to the low-pressure line in at least one position of the piston, and the second cavity (325) extending between the sections (323, 324) of the head interconnecting the inlet port (315) connected to the return line and the outlet port (316) when the piston is in the first position. 7. Fuel distribution circuit (1) according to one of the preceding claims, wherein the threshold engine speed is less than 50% of the maximum engine speed, preferably equal to 40% of the maximum engine speed. 30 8. Turbomachine (T), comprising a fuel combustion chamber (C) and a set (E) of servovalves and actuators of variable geometry parts, characterized in that it further comprises a fuel distribution circuit (1) according to one of the preceding claims. 3035155 12 9. A method of dispensing fuel in a turbomachine, implemented by a fuel distribution circuit (1) according to one of claims 1 to 7, characterized in that it comprises cutting the supply of the fuel. together (E) of 5 servovalves and actuators when the engine speed of the turbomachine is below a threshold regime. 10. Fuel distribution method according to claim 9, wherein the threshold speed is less than 50% of a maximum speed of the turbomachine, preferably equal to 40% of the maximum speed.