SYSTEM FOR SUPPLYING FUEL TO A TURBOMACHINE

Abstract

The present disclosure relates to a system for supplying fuel to a turbomachine. In some embodiments, a fuel circuit includes a pressurisation valve at an outlet of the system and a pump. The circuit may include a flow rate sensor arranged between the outlet of the pump and the pressurisation valve. In some embodiments, the flow rate sensor may include a sliding drawer, a restoring spring, and a sensor for detecting the position of said drawer in order to indicate the flow passing through the flow rate sensor. The system may include a device arranged to drive the pump with a controllable rotational speed and a control configured to control the device on the basis of a measurement supplied by the flow rate sensor, in such a way as to adapt the rotational speed of the pump shaft.

Claims

1. Fuel supply system of a turbomachine, comprising: a fuel circuit including a pressurization valve at an outlet of said circuit, a pump arranged to send fuel into said circuit at a fuel flow rate, the fuel flow rate an increasing function of a rotational speed of a shaft of said pump, wherein the circuit includes a flow rate sensor placed between the outlet of the pump and a pressurization valve, the flow rate sensor comprising a sliding drawer, a return spring and a sensor for detecting the position of said drawer, the position of said drawer controlled by a pressure difference across the flow rate sensor shaped to compensate for a force applied by the return spring to said drawer, wherein the position of said drawer indicates the flow rate passing through the flow rate sensor, a device arranged to drive the pump with a controllable rotational speed, and a control that controls the device based on a measurement provided by the flow rate sensor, wherein the rotational speed of the shaft of the pump adapts to a flow rate setpoint value at the outlet of the fuel circuit.

2. Fuel supply system according to claim 1, wherein the fuel circuit includes a control loop to actuate variable geometries of the turbomachine, said control loop starting with a branch connection on a derivation located between the outlet of the pump and the flow rate sensor.

3. Fuel supply system of a turbomachine according to claim 1, wherein the drive device drives the pump from a drive shaft of said turbomachine and is arranged to vary a ratio between the rotational speed of the shaft of the pump and a rotational speed of the drive shaft.

4. Fuel supply system according to claim 3, wherein the drive device comprises an epicyclic gear reducer comprising three elements, a central sun gear, an outer ring gear, and a planet carrier, whose planets mesh with the sun gear and the ring gear, a first of the three elements connected to the drive shaft and a second of the three elements coupled to a shaft of the pump, wherein said three elements are movable in rotation about an axis of the reducer, wherein said drive device further comprises at least first electrical motor arranged to rotatably drive a third of said elements of the reducer, to modify a rotational speed ratio between the first and second of said elements.

5. Fuel supply system according to claim 4, wherein the drive device comprises a second electrical motor coupled to the first or second of said elements of the reducer, the first and second electrical motors configured to transfer electrical power reversibly from one to the other.

6. Turbomachine comprising a system according to claim 1.

7. Method for regulating a fuel pump for a turbomachine according to claim 6 in an aircraft, wherein the method implements control laws of the rotational speed of the shaft of the pump, which increase or respectively decrease the rotational speed when the flow rate indicated by the sensor decreases or increases, causing the flow rate and pressure at the outlet of the circuit are adapted to flight conditions of the aircraft.

8. Method according to claim 7, wherein said control laws are arranged to also adapt the flow rate provided by the pump and the pressure in the circuit to conditions of use of variable geometries.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0038] This invention shall be better understood, and other details, characteristics and advantages of this invention shall appear more clearly when reading the description of the following non-limiting example, with reference to the annexed drawings on which:

[0039] FIG. 1 very schematically shows a fuel circuit according to the state of the art;

[0040] FIG. 2 shows a speed and flow rate diagram showing the difference between the flow rate provided by the fuel pump and the requirement for a circuit as shown in FIG. 1;

[0041] FIG. 3 very schematically shows a half section of a turbomachine that can use the invention;

[0042] FIG. 4 shows exploded views and a diagram for an epicyclic gear reducer that can be used by the invention;

[0043] FIG. 5 shows the diagram of an example of a drive device of the pump using a reducer from FIG. 4;

[0044] FIG. 6 very schematically shows a first fuel system configuration using the device from FIG. 5; and

[0045] FIG. 7 very schematically shows a second fuel system configuration using the device from FIG. 5.

[0046] The elements having the same functions in the different embodiments have the same references in the figures.

DESCRIPTION OF AN EMBODIMENT

[0047] In a turbomachine, for example a dual flow turbomachine shown in FIG. 3, the outlet air flow at fan 20 is divided into a primary flow P entering the engine and a secondary flow S surrounding the latter. The primary flow then passes through low-pressure compressors 21 and high-pressure compressors 22, the combustion chamber 3 supplied by the fuel circuit mentioned previously, and then high-pressure turbines 24 and low-pressure turbines 25. Generally, all the high-pressure compressors 22 and high-pressure turbines 24 rotate as a unit on a common axis 26 and form the engine part of the turbomachine with the combustion chamber.

[0048] Generally, the drive shaft 26 drives the accessory relay box 5 which can include several gear trains connected to outlet shafts to drive various equipment units. Here one of the outlet shafts of the gearbox drives, by a drive device 6, the volumetric pump 1 which supplies the hydromechanical group 2 injecting the fuel into the combustion chamber 3. Generally also, the accessory relay box makes the connection between the drive shaft 26 and a starter/generator, not shown in this figure, which can be used to drive the turbomachine during the start-up phases or generate an electric current when the turbomachine is on.

[0049] The turbomachine may also have variable geometries 10, mentioned above, which can be activated under certain conditions of use. This variable geometries 10 are, for example, variable-pitch vanes at the inlet of a low-pressure compressor.

[0050] Here, with reference to FIG. 6 or 7, the fuel supply system includes a drive device 6 between the accessory relay box 5 and the pump 1 different from that of the system in FIG. 1. The pump 1 can be of the same nature as the conventional solution. It is a rotary volumetric pump, whose flow rate is an increasing function of the rotational speed 1, able to provide the flow rate necessary for the injection into the combustion chamber 3 and to pressurize the fuel circuit. Preferably, it has a linear characteristic Cyl relating the outlet flow rate to the rotational speed 1.

[0051] First of all, we will show that there is at least one solution to make a drive device 6 capable of varying the ratio between the rotational speed of the shaft of the accessory relay box 5 and the rotational speed of the shaft of the pump 1, in order to be able to adapt the speed of the pump 1 to the different operating points of the turbomachine.

[0052] The drive system 6 shown has an epicyclic gear reducer whose properties are used to adapt the rotational speed of pump 1 to the need for fuel flow rate according to the different operating speeds of the turbomachine.

[0053] With reference to FIG. 4, the epicyclic gear reducer 11 comprises: [0054] a central sun gear 11A, arranged to be able to rotate about the axis of the epicyclic gear at a speed WA; [0055] planets 11S meshing with the central sun gear 11A and carried by a planet carrier 11U, the planet carrier 11U being arranged to be able to rotate about the axis of the epicyclic gear at a speed U; [0056] an external ring gear 11B with which the planets 11S also mesh, the ring gear 11B being arranged to be able to rotate about the axis of the epicyclic gear at a speed B.

[0057] A characteristic of the epicyclic gear reducer 11 is therefore that its three elements, the central sun gear 11A, the planet carrier 11U and the ring gear 11B, are able to rotate. Here, for example, the ring gear 11B is free to rotate inside a fixed casing 11C protecting the reducer 11.

[0058] The operation of the epicyclic gear of the reducer 11 is governed by Willis equation, which shows that it is a two degrees of freedom mechanism and that the knowledge of the rotational speeds of two elements among the central sun gear 11A, the planet carrier 11U and the ring gear 11B, allows the calculation of the rotational speed of the third.

[0059] Rotation of the central sun gear 11A: A

[0060] Rotation of the planet carrier 11U: U

[0061] Rotation of the ring gear 11B: B

(AU)/(BU)=k or Ak*B+(k1)*U=0WILLIS Equation:

[0062] In Willis equation, the factor k, also called the epicyclic gear reason, is a constant determined by the geometry of the gears. For the reducer 11 in FIG. 4, k=ZB/ZA, where ZA is the number of teeth of the central sun gear A and ZB the number of teeth of the ring gear B. The factor k is therefore negative with a modulus lower than 1.

[0063] It is therefore understood that, if the outlet shaft of the accessory relay box 5 is coupled to one of the three elements and the shaft of the pump 1 is coupled to a second element, the rotational speed of the pump 1 can be varied for a given speed of the shaft of the box 5 by varying the rotational speed of the third element.

[0064] A first electric motor 12 is coupled to said third element to control the rotational speed of the latter.

[0065] Six combinations are possible to position the three equipment units, accessory relay box 5, pump 1 and electric motor 12, with respect to the three elements of the epicyclic gear reducer 11.

[0066] A second motor 13 is also coupled to one of the elements of the reducer 11 which is not connected to the first motor 12. The position of the second motor 13 doubles the number of possible combinations for the device 6. This results in twelve combinations listed in the table below.

[0067] This table also indicates the function giving the speed 1 of the pump 1 from the speed 5 of the shaft of the box 5 and the speed 12 of the first motor 12. The rotational speed 13 of the second motor 13 is determined by the rotational speed of the equipment with which it is coupled in series on the reducer 11, either the shaft of the pump 1 or the outlet shaft of the box 5. In this table, option 1 corresponds to the cases where the second motor 13 is coupled in series with the pump 1 on the same element of the reducer 11, and option 2 corresponds to cases where the second motor 13 is coupled in series with the outlet shaft of the accessory relay box 5 on the same element of the reducer 11.

TABLE-US-00001 TABLE 1 Connection box/pump/first motor Pump speed Connection second motor Box 5 connected to the planet carrier 11U Motor 12 Pump 1 Option 1 Option 2 1 ring gear 11B sun gear 11A 1 = (1 k)*5 + sun gear A planet A k*12 carrier 11U 1 sun gear 11A ring gear 11B 1 = 5*(1 k)/k + ring gear B planet B 12/k carrier 11U Box 5 connected to the ring gear 11B Motor 12 Pump 1 Option 1 Option 2 2 planet carrier 11U sun gear 11A 1 = k*5 + sun gear A ring gear B A (1 k)*12 2 sun gear 11A planet carrier 11U 1 = 5*k/(1 k) + planet carrier 11U ring gear B B 12/(1 k) Box 5 connected to the sun gear 11A Motor 12 Pump 1 Option 1 Option 2 3 ring gear 11B planet carrier 11U 1 = 5/(1 k) planet carrier 11U sun gear A A 12*k/(1 k) 3 planet carrier 11U ring gear 11B 1 = 5/k ring gear B sun gear A B 12*(1 k)/k

[0068] In the example shown in FIG. 5, corresponding to the configuration 3AOption 1, the box 5 is connected to the central sun gear 11A, the pump to the planet carrier 11U, the first electric motor 12 is connected to the ring gear 11B, so that it can drive in rotation the latter, and the second motor 13 is connected to the planet carrier 11U.

[0069] The first motor 12 and the second motor 13 each have a stator and a rotor. Said motors 12, 13 are controllable in terms of torque applied to their rotor and rotational speed 12, 13 of their rotor. These are, for example, alternative current asynchronous motors. The torque and speed of each motor 12, 13 are then controlled by the electrical power and the frequency of the current sent by a converter 14, 15 dedicated to each.

[0070] In addition, the second motor 13 is electrically connected to the first motor 12 through said reversible voltage converters 14, 15, in order to pass power from one to the other.

[0071] In addition, with reference to FIG. 6 or 7, the fuel supply system also differs from that in FIG. 1 in that the control box 4 is connected to the converter 14, to control the speed 12 and the torque of the first motor 12 in order to adapt the speed 1 of the pump 1, and to the converter 15, to control the torque of the second motor 13 to manage the power transfer between the two motors.

[0072] The dynamic study of the reducer 11 shows that the torque CA acting on the sun gear 11A, the torque CB acting on ring gear 11B and the torque CU acting on planet carrier 11U are related by two relationships:

CA+CB+CU=0(epicyclic gear equilibrium)

A*CA+B*CB+U*CU=0(dynamic equilibrium)

[0073] Considering the relationships relating the rotational speeds of these elements, it is possible to calculate the torques acting on two elements of the reducer 11 knowing the third one.

[0074] The second motor 13, being connected in series with the pump 1 or the box 5, has its rotational speed determined as being equal to that of this equipment unit.

[0075] It is however understood that it provides an additional degree of freedom to the system according to the torque it exerts, which is added to that of the pump 1 or the box on the corresponding element of the reducer 11.

[0076] This additional degree of freedom can be used to ensure power transfer with the first motor: either providing power when the first motor 12 intervenes to accelerate the pump 1 with respect to the drive of the box 5, or absorbing power when the first motor 12 intervenes to brake the pump 1.

[0077] It is possible to use other configurations than that illustrated in FIG. 5. The choice depends on the operating characteristics of the turbomachine. The choice of parameters of the device such as the factor k of the epicyclic gear reducer 11, the ratio of the rotational speed 5 at the outlet of the box 5 with respect to the rotational speed of the axle of the turbine, the linear characteristic Cyl of the pump 1, and the choice among the configurations 1A to 3B, must be made to achieve in particular the following objectives: [0078] allowing the pump 1 to rotate at a speed 1 that adjusts to provide a flow rate Cyl.1 that corresponds to the need F1, as shown for example in FIG. 2, when the rotational speed of the axle of the turbine varies between its minimum value cumin and maximum value wax; [0079] minimizing the power spent in the motor 12 to adjust the speed 1 of the pump 1 to the operating range of the turbomachine.

[0080] In addition, technological constraints on the equipment units used generally imply that: [0081] the speed 1 of the pump 1 must be lower than that 5 of the outlet shaft of the accessory relay box 5; and [0082] the speed 12 of the electric motor 12 must be limited to a maximum value.

[0083] This concept with two auxiliary electric motors for the drive system between the accessory relay box 5 and the pump 1 is very innovative because it offers the following advantages: [0084] taking from the accessory relay box 5 only the mechanical power corresponding to the power requirement for supplying the variable geometries (pressure requirement) and for supplying the fuel flow rate (fuel flow rate requirement), [0085] reduction of the displacement of the pump 1, [0086] drastic reduction in the dimensioning of the recirculation loop 9 of the pump flow rate, [0087] simplification of the architecture of the hydromechanical group 2 for fuel regulation, [0088] no need for external power during the controlling of the pump speed by a motor 12 thanks to the power transfer between this motor and the second motor 13.

[0089] In the system described above, the first motor 12 and the second motor 13 are especially dedicated equipment units, added to operate the drive device 6. In a variant, the starter of the turbomachine can be used as the first or second motor of the device.

[0090] The fuel supply system concept developed in the following allows optimal use of such a drive device 6.

[0091] With reference to FIG. 6, a fuel supply system, according to the invention, includes: [0092] a drive device 6 between the accessory relay box 5 and the pump 1 as described above, allowing to adapt the speed of the pump 1; [0093] a pump 1 dimensioned to be adapted to the flow rate supplied with the system according to the invention; [0094] a means 7 for supplying the circuit from fuel tanks 8; [0095] a hydromechanical block 2 according to the invention; [0096] a control electronics 4.

[0097] Here, the fuel supply system is also connected to actuators of variable geometries 10.

[0098] The hydromechanical block 2 according to the invention includes the following elements: [0099] a fuel flow rate sensor 201 between the pump 1 and the injection to the combustion chamber 3; [0100] a pressurization valve 202 at the injection to the combustion chamber 3; [0101] a return valve 203 branched between the flow rate sensor 201 and the pressurization valve 202, and connected to a recirculation loop 9; [0102] a servo valve 204 essentially controlling the pressurization valve 202 and the return valve 203.

[0103] When the fuel circuit is used to operate variable geometries 10, the fuel circuit advantageously includes a derivation 205 to power a control loop for actuators of the variable geometries 10. This derivation 205 is placed here between the pump 1 and the flow rate sensor 201 of the hydromechanical block 2.

[0104] The flow rate sensor 201 is realized by a modified metering unit.

[0105] A metering unit usually used in a conventional circuit includes a sliding drawer 211 whose position controls the flow rate through a metering unit section. In addition, a sensor 212 of the position of the drawer 211 allows to slave the metering unit, usually by a servo valve.

[0106] Here, the position of the drawer 211 is not controlled by a servo valve, but directly by the pressure difference across the flow rate sensor 201 which compensates the force applied by a return mean 206, for example a spring, on the drawer 211, similar to the control of the regulating valve of the conventional solution. Knowing the characteristics of the metering unit section and the spring, the position read by the sensor 212 of position of the drawer 211 provides information on the actual flow rate really injected by the fuel circuit into the combustion chamber.

[0107] For example, flow rate information can be transmitted to the control electronics box 4 for action on the drive device 6 and so that the latter adjusts the speed of the pump 1 to ensure the correct fuel flow rate adapted to the need.

[0108] The hydromechanical block 2 therefore loses its function of regulating the flow rate but ensures a function of flow rate sensor. It keeps the functions of cutting off the fuel and pressurization of the system through the pressurization valve 202.

[0109] The pressurization valve 202 ensures the minimum pressure for the correct operation of the variable geometries, as well as the cut-off of the injected flow rate.

[0110] The return valve 203, allows ensuring the exhaust of the flow rate delivered by the pump 1 in order not to increase pressure in the circuit, when this cut-off is activated by the servo valve 204.

[0111] However, this recirculation only exists during the stop phase, or during preparation for ignition, the duration of the decreasing of the rotation speed of the pump 1. The recirculation loop 9 is therefore much less important than for a conventional circuit.

[0112] At ignition, the pump 1 is driven at a minimum rotational speed. A part of the flow rate passes through the sensor 201 and is recirculated by the return valve 203.

[0113] The speed of the pump 1 is then adjusted to reach the correct ignition flow rate setpoint value. The servo valve 204 is then activated, which cause the pressurization valve 202 to open, the return valve 203 to close and thus allows the ignition flow rate to be injected into combustion chamber 3.

[0114] Finally, the return valve 203 provides protection in the event of overspeed due to a failure of the pump 1 speed control.

[0115] In the event of a flow rate call related to the actuation of variable geometries 10, for a given rotational speed of the pump 1, the flow rate passing through the sensor 201 tends to decrease due to the derivation 205 towards the variable geometries 10, which is placed upstream. The information of a decrease in flow rate requires the drive system 6 to accelerate the speed of the pump 1 in order to maintain the correct injected flow rate required.

[0116] A control loop based on the flow rate information of the sensor 201, installed in the control box 4, therefore allows the pump speed to be adjusted for any operating point of the turbomachine, whether the variable geometries 10 are active or not.

[0117] This hydromechanical block 2 concept therefore allows to take advantage of a drive system 6 capable of adapting the pump's rotation speed if necessary.

[0118] There is therefore no longer any need to size a recirculation loop 9 to dissipate a large flow rate surplus and this allows to gain power drawn from the accessory relay box 5 for fuel supply. This also allows to eliminate the regulating valve that exists in a conventional circuit.

[0119] In addition, since the metering unit function has been removed, no flow rate surplus is required to operate it.

[0120] The hydromechanical block 2 therefore allows to take full advantage of the potential power gain offered by the drive system 6.

[0121] It should be noted that this concept also works without powering variable geometries, for example if they are driven by electrical means 17, as shown in FIG. 7. In a configuration without variable geometries, the solution will only be easier to implement, and more efficient in terms of power gain.

[0122] In a preliminary study that was carried out based on a particular type of application, where each operating point is described in terms of speed of the box 5, injected flow rate, cooling flow rate of the variable geometries 10, internal leaks, flow rate required to move the variable geometries and injection pressure, the inventors thus found a significant gain in power required to carry out the injection, whether with or without hydraulic power to the variable geometries.

[0123] This concept also has other positive impacts.

[0124] Regarding the volumetric pump 1, its displacement can be reduced by at least one third compared to a conventional solution. There is also a gain in the overall dimensions due to the reduction in the diameter of the pinions and a mass gain.

[0125] Regarding the hydromechanical block 2, there is a simplification and mass gains in relation to the disappearance of a servo valve, the replacement of a regulating valve by a return valve and the possibility of eliminating an electro-valve.

[0126] The concept allows also to reduce the size of heat exchangers.

[0127] In addition, with the proposed solution, it is possible to carry out an equipment monitoring action.

[0128] To do this, it is enough to add a speed sensor, not shown, to the volumetric pump 1.

[0129] Indeed, the sensor 201 indicates the fuel flow rate. Since the volumetric pump 1 has a characteristic linking the rotational speed and the injected flow rate, it is possible, on a stabilized point, or during a fixed motor point in dry ventilation, to control the wear of the pump 1: a too high drift of the flow rate reading at a given pump speed would indicate an increase in leakage in the system, whether at the pump or internal leaks in the fuel system.