FR3062424A1 - DRIVE SYSTEM FOR A FUEL PUMP OF A TURBOMACHINE - Google Patents

Abstract

The invention relates to a drive system for a fuel pump (1) of a turbomachine, the turbomachine comprising a motor shaft and a starter (16) also having a generator function, the system comprising a gearbox (11) for epicyclic gear train comprising three elements, a central sun gear (11 A), an outer ring gear (11 B) and a planet carrier (11 U) whose satellites (11 S) mesh with the sun gear and the ring gear, a first of three elements being intended to be connected to the motor shaft (26) and a second of the three elements being intended to be coupled to a shaft of the pump (1), characterized in that said three elements are rotatable around an axis of the gearbox, in that the system further comprises the starter (12), the latter being arranged to drive in rotation the third of said elements of the gear (11), so as to modify a speed ratio of rotation between the first and the second said elements. It also relates to the turbomachine equipped with the system and the method of regulating the pump.

Description

@ Holder (s): SAFRAN AIRCRAFT ENGINES.

O Extension request (s):

Agent (s):

GEVERS & ORES Public limited company.

® DRIVE SYSTEM OF A FUEL PUMP OF A TURBOMACHINE.

FR 3,062,424 - A1 (57) The invention relates to a drive system for a fuel pump (1) of a turbomachine, the turbomachine comprising a motor shaft and a starter (16) also having the function of generator, the system comprising a planetary gear reducer (11) comprising three elements, a central sun gear (11 A), an outer ring (11 B) and a planet carrier (11 U) whose satellites (11 S) mesh with the sun gear and the crown, a first of the three elements being intended to be connected to the motor axis (26) and a second of the three elements being intended to be coupled to a pump shaft (1), characterized in that said three elements are movable in rotation about an axis of the reduction gear, in that the system further comprises the starter (12), the latter being arranged to rotate the third of said elements of the reduction gear (11), so as to modify a rotational speed ratio between l e first and second of said elements. It also relates to the turbomachine equipped with the system and to the pump regulation method.

6 '

i

Fuel pump drive system for a turbomachine

Field of the invention:

The present invention relates to the field of turbomachinery. It relates more particularly to the fuel supply circuit and the regulation of the fuel flow in this circuit.

State of the art:

The turbomachines installed on an aircraft are equipped with a fuel supply circuit, delivering the fuel to the combustion chamber, which must be regulated as required according to the flight conditions. Referring to FIG. 1, the fuel circuit generally comprises a main high-pressure pump 1 of volumetric type which sends the fuel to a hydromechanical group 2 before injection to the combustion chamber 3. The assembly is arranged to ensure, at the outlet to the combustion chamber, a fuel flow rate adapted to the need. A control unit 4 generally controls the hydromechanical group 2 so that it adapts the flow rate sent by the pump 1 to the needs of the combustion chamber 3.

In general, the pump 1 is driven by an output shaft of the accessory box 5 of the turbomachine, itself driven by a motor axis of the primary body of the turbomachine, not shown in FIG. 1. A transmission device 6 is generally installed between the shaft of the accessory relay box 5 and the pump 1 to adapt the rotation regimes between these two pieces of equipment. This device determines a ratio K between the speed of the pump 1 and the speed of rotation ω of the engine axis of the turbomachine. This device generally also drives a supply means 7 for the circuit from the fuel tanks 8.

The linear characteristic Cyl of pump 1 between the fuel flow rate and its drive speed depends in particular on its displacement. The pump 1 must be dimensioned in such a way that this displacement makes it possible to deliver the flow rates required for all the operating regimes of the turbomachine, therefore of the speed of the output shaft of the accessory relay box 5, both at low speed than high speed.

As can be seen in FIG. 2, representing the variations in flow rate F as a function of the speed of rotation ω of the shaft of the engine axis of the turbomachine, the fuel requirement F1 varies non-linearly as a function of the regime of the turbomachine. The speed of rotation ω of the engine axis of the turbomachine varies between a minimum value cumin, for the ignition of the turbomachine, and a maximum value œmax for takeoff. The regime corresponding to a cruise flight falls between these two extremes.

Depending on the application, the crucial point is located either at low speed ignition or at takeoff at high speed. In Figure 2, this crucial point is at the ignition level, the displacement of the pump must be chosen in such a way that its linear characteristic is equal to the value Cyl1, to ensure sufficient flow during all the conditions of flight. This Cyl1 value can be significantly higher than the minimum Cylmin value required under certain flight conditions, or even that Cyl2 required during takeoff.

According to this design, the flow rate supplied by the pump therefore follows the line L1 on the flow rate / rotation speed diagram in FIG. 2. During a large phase of drive speed, in particular in cruising flight, the pump therefore delivers a flow rate greater than the fuel flow requirement, therefore an excess F2 of fuel.

The hydromechanical group 2 must therefore return to the pump, by a recirculation loop 9, the excess fuel F2 compared to the need.

This problem of regulating the fuel flow is further accentuated when the fuel circuit is used, as indicated in FIG. 1, to actuate variable geometries 10 of the turbomachine. The actuation of the variable geometries 10 creates variations in the fuel requirement in the circuit which must be taken into account in the dimensioning of the pump 1, in the operation of the hydromechanical group 2 and in the characteristics of the recirculation loop 9.

This architecture of the fuel supply system has several drawbacks. The excess flow injected by the pump 1 induces a surplus of power draw on the accessory relay box 5 compared to the need, detrimental to the performance of the turbomachine. The excess mechanical power is transformed into thermal power dissipated in the recirculation loop 9 which must be evacuated. This has a negative influence on the size and the mass of the fuel circuit, in particular for heat exchangers, not shown, placed to evacuate the heat in this circuit.

The object of the invention is to remedy at least some of these drawbacks.

Statement of the invention:

To this end, the invention relates to a system for driving a fuel pump of a turbomachine, the turbomachine comprising a motor shaft and a starter also serving as a generator, the system comprising a planetary gear reduction unit comprising three elements , a central sun gear, an outer ring and a planet carrier of which the satellites mesh with the sun gear and the ring, a first of the three elements being intended to be connected to the motor axis and a second of the three elements being intended to be coupled to a pump shaft, characterized in that said three elements are movable in rotation about an axis of the reduction gear, in that the system also comprises the starter, the latter being arranged to drive the third of said elements of the reducer, so as to modify a rotational speed ratio between the first and the second of said elements.

The drive system thus arranged makes it possible to modify the speed of the pump for a given engine speed of the turbomachine. Thus, the speed of the pump can be adapted so that it delivers the correct fuel flow rate to the various operating points of the turbomachine. By setting a maximum permissible speed of the pump, the displacement of the pump only depends on the take-off operating point and not on ignition. The displacement of the pump can therefore be reduced compared to that of the state of the art.

From an energy point of view, the power taken from the engine axis will be in certain flight phases lower than the hydraulic power requirement of the pump and in certain flight phases higher than the flight phase need but the overall energy during the entire flight phase will be close to the minimum requirement. We therefore obtain a gain on the power drawn for the operation of the fuel system.

The use of the starter / generator to adapt the speed of the pump makes it possible to take advantage of its existence to avoid adding an element, on the other hand to use its generator function in most conditions of use of the pump. , except that close to the ignition of the turbomachine.

This also makes it possible to greatly reduce the dimensioning of the fuel recirculation loop, as well as the thermal rejection.

Preferably, the first of said elements of the reducer is the planetary, the second of said elements is the crown and the third of said elements is the planet carrier.

This configuration makes it possible to comply with technical constraints such as that of turning the starter at high speeds to optimize its dimensioning. It also makes it possible, during integration into the turbomachine, to directly ensure the appropriate reduction ratio between an output shaft of an accessory relay box and the starter / generator.

The starter can be thermally coupled to a dissipative resistor.

The invention also relates to a turbomachine comprising a fuel pump drive system as described above.

Preferably, an accessory relay box connected to the motor axis is coupled to the first of the three elements of the reducer.

Advantageously, the accessory relay box has a unique coupling with the starter produced by the reducer.

The turbomachine can have variable geometries hydraulically connected to the pump.

The turbomachine may, on the contrary, have variable geometries hydraulically decoupled from the pump and connected to independent actuation means.

The invention also relates to a method of regulating a fuel pump for such a turbomachine in an aircraft, characterized in that the speed of rotation of the pump shaft is modified by controlling the speed of rotation of the third element. of the reducer by the starter, so that the fuel flow delivered by the pump is adapted to the flight conditions of the aircraft.

Brief description of the figures:

The present invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description of a nonlimiting example which follows, with reference to the appended drawings in which:

Figure 1 very schematically shows a fuel system according to the state of the art;

FIG. 2 presents a diagram in speed of rotation of the turbomachine and flow rate showing the difference between the flow rate supplied by the fuel pump and the requirement, for a circuit according to FIG. 1;

Figure 3 very schematically shows a half section of a turbomachine that can use the invention;

Figure 4 shows exploded views and a diagram for a planetary gear reducer which can be used by the invention;

Figure 5 shows the diagram of a transmission device according to the invention between the turbomachine and the pump using a reducer of Figure 4; and Figure 6 very schematically shows a first variant of a fuel system using the device of Figure 5; and FIG. 7 very schematically shows a second variant of a fuel circuit using the device of FIG. 5.

The elements having the same functions in the different implementations have the same references in the figures.

Description of an embodiment:

In a turbomachine, for example a double-flow turbomachine shown in FIG. 3, the air flow at the outlet of the 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 22, the combustion chamber 3 supplied by the fuel circuit previously mentioned, then high pressure turbines 24 and low pressure 25. Generally, all of the high pressure compressors 22 and high pressure turbines 24 rotates in one block on a common axis 26 and forms the engine part of the turbomachine with the combustion chamber.

Generally, the motor axis 26 drives the accessory relay box 5 which can include several gear trains connected to output shafts to drive various pieces of equipment. Here one of the output shafts of the gearbox drives, by a transmission device 6 ', the positive displacement pump 1 which feeds the hydromechanical group 2 injecting the fuel into the combustion chamber 3. Generally also, the relay box of accessories makes the link between the motor axis 26 and a starter / generator, not shown in FIG. 3, which can be used to drive the turbomachine during start-up phases or generate an electric current when the turbomachine is switched on.

The turbomachine can also include variable geometries 10, previously mentioned, which can be activated under certain conditions of use. These variable geometries 10 are, for example, vanes with variable setting at the inlet of the low pressure compressor.

Here, with reference to FIGS. 6 or 7, the fuel supply system comprises a transmission device 6 'between the accessory relay box 5 and the pump 1 different from the system of FIG. 1. The pump 1 can be of the same nature as for the conventional solution. It is a rotary positive displacement pump, the flow rate of which is an increasing function of the rotation speed ω1 of its shaft, capable of supplying the flow rate necessary for injection into the combustion chamber 3 and putting the fuel circuit under pressure. Preferably, it has a linear characteristic Cyl, depending on its displacement, which connects the output flow to the speed of rotation ω1.

The 6 ’transmission device includes a planetary gear reducer, the properties of which are used to adapt the speed of rotation of the pump 1 to the fuel flow requirement according to the different operating modes of the turbomachine.

With reference to FIG. 4, the planetary gear reducer 11 comprises:

- a central sun gear 11 A, arranged to be able to rotate around the axis of the train at a speed ωΑ;

- satellites 11S meshing with the central planet 11A and carried by a planet carrier 11 U, the planet carrier 11U being arranged to be able to rotate around the axis of the train at a speed ωυ;

- An outer ring 11B with which the satellites 11S also mesh, the ring 11B being arranged to be able to rotate around the axis of the train at a speed ωΒ.

A characteristic of the planetary gear reducer 11 is therefore that its three elements, the central sun gear 11 A, the planet carrier 11U and the ring gear 11 B, are capable of turning. Here, for example, the crown 11B is free to rotate inside a fixed casing 11C protecting the reduction gear 11.

The operation of the gear train 11 is governed by the formula of Willis which shows that it is a mechanism with two degrees of freedom and that the knowledge of the speeds of rotation of two elements among the central planet 11 A, the planet carrier 11U and the crown 11 B, allows the calculation of the speed of rotation of the third.

11A central planetary rotation: ωΑ

11U planet carrier rotation: ωΙΙ

Rotation of the crown 11B: ωΒ

WILLIS formula: (ωΑ - ωΙ_Ι) / (ωΒ- ωΙ_Ι) = k or ωΑ - k * ωΒ + (k-1) * ωΙΙ = 0

In Willis' formula, the factor k, also called reason of the train, 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 planet A and ZB the number of teeth of the crown B. The factor k is therefore negative with a modulus less than 1 .

It is therefore understood that, if the output shaft of the accessory relay box 5 is coupled to one of the three elements and the pump shaft 1 is coupled to a second element, the speed of rotation of the pump 1 for a given speed of the shaft of the housing 5 by varying the speed of rotation of the third element.

According to the invention, with reference to FIG. 5 showing a preferred embodiment of the system corresponding to the configuration 3B in the table below, the starter / generator 12 is connected to said third element to control the speed of rotation of the latter.

Six combinations are possible for positioning the accessory relay box 5, the pump 1 and the starter / generator 12 with respect to the three elements of the planetary gear reducer 11. They are listed in the table below. This table 1 also indicates the function giving the speed ω1 of the pump from the speed ω5 of the shaft of the housing 5 and the speed ω12 of the motor 12, by associating them with the rotation speeds ωΑ, ωΒ, coU, corresponding elements of the reducer 11 in the configuration.

Box 5 connected to the 11U planet carrier Pump speed 1A Starter 12 connected to the crown 11B and Pump 1 connected to the planetary 11A ω1 = (1-k) * ω5 + k * ω12 1B Starter 12 connected to planetary 11A and Pump 1 connected to the crown 11B ω1 = -ω5 * (1 -k) / k + ω12 / k Box 5 connected to the crown 11B Pump speed 2A Starter 12 connected to the planet carrier 11U and Pump 1 connected to the planetary 11A ω1 = k * ω5 + (1-k) * cu12 2B Starter 12 connected to planetary 11A and Pump 1 connected to planet carrier 11U ω1 = -üù5 * k / (1-k) + ω12 / (1 -k) Box 5 connected to the planetary 11A Pump speed 3A Starter 12 connected to the crown 11B and Pump 1 connected to the 11U planet carrier ω1 = co5 / (1-k) - üù12 * k / (1-k) 3B Starter 12 connected to the planet carrier 11U and Pump 1 connected to the crown 11B ω1 = ωδ / k - ω12 * (1 -k) / k

Table 1.

FIG. 5 illustrates the configuration 3B where the box 5 is connected to the central sun gear 11 A, the pump 1 to the crown 11B and the starter / generator 12 to the 5 planet carrier 11 U.

Advantageously, the starter / generator 12 is supplied with current by a reversible voltage converter 13.

The starter / generator 12 comprises a stator and a rotor. It can be controlled by the torque applied to the rotor and by the speed of rotation ω2 of the rotor. The torque and the speed of the starter / generator 12 are then controlled by the electric power and the frequency of the current sent by the converter 13.

When the starter / generator 12 is driven by the motor shaft 26 and operates as a generator, the converter 13 makes it possible to return the current to an electrical circuit of the turbomachine or of the aircraft.

A dissipative resistor 14 can be connected to the starter / generator 12 in cases where it must dissipate too much energy which cannot be recovered in the electrical circuit.

Furthermore, with reference to Figures 6 and 7, the fuel supply system also differs from that of Figure 1 in that the control unit 4 'is connected to the converter 13, to control the speed ω12 and the torque of the motor 12 in order to adapt the speed ω1 of pump 1.

The technical feasibility of this fuel system concept has been verified based on the needs of a particular type of turbomachine by considering four operating points:

- The take-off point with the actuation of variable geometries of the turbojet,

- The take-off point without actuation of variable geometries of the turbojet,

- The cruise flight point,

- The ignition point.

The study was carried out to verify certain constraints with the estimation of the following parameters for the four operating points:

- the speed range ω1 of pump 1, in particular the maximum value,

- the speed of rotation ω2 of the output shaft of the accessory relay box 5,

- the reason k of the planetary gear train 11,

- the gain on the power taken from the shaft of the housing 5 compared to other solutions, in particular the state of the art as mentioned in the introduction,

- the speed of rotation ω12 of the starter 12 (this sizes the starter, which must also provide the power to prepare the start of the turbomachine).

Furthermore, the technological constraints on the equipment used generally imply that:

- the speed ω1 of the pump 1 must be greater than that ω5 of the output shaft of the accessory relay box 5; and

- the speed ω12 of the starter / generator 12 must be higher than that ω1 of the pump 1.

It has been found that the configuration 3B of table 1, shown in FIG. 5, makes it possible to meet these constraints.

In this configuration, the speed ω1 of pump 1 is given by the formula in Table 1:

ω1 = ωδ / k - ω12 * (1 -k) / k

Depending on whether the starter / generator 12 drives the planet carrier 11A with a positive or negative ω12 value, the pump can be driven at a speed lower or higher than the speed ωδ / k it would have for a train 11 with a planet carrier fixed.

During the operation of the turbomachine on the aircraft, the control unit 4 ’adjusts the speed ω1 of the pump 1 to the fuel requirement of the ignition chamber 3 varying the speed ω12 of the starter / generator 12.

Depending on whether the speed of rotation of the starter / generator 12 is positive or negative, the starter / generator 12 provides power to increase the speed of the pump 1 or recovers it to decrease this speed. The power taken from the output shaft of the accessory relay box 5 is, in certain flight phases, less than the hydraulic power requirement of the pump 1 and, in certain flight phases, greater than the flight phase need .

When designing pump 1, it is therefore no longer necessary to size it with a displacement corresponding to the maximum value of K but, for example, for an intermediate value. If we refer to the case of Figure 2, for example, by setting a maximum allowable speed for pump 1, we can size pump 1 for the take-off point and no longer for the ignition point, more restrictive. This reduces the displacement of the pump compared to the state of the art.

In addition, the system makes it possible to always supply pump 1 with the minimum power to meet the need for fuel flow.

Referring to FIG. 2, in the case where the pump 1 is dimensioned for the take-off point, when the motor shaft 26 rotates at its maximum speed cumax, it is understood that the starter / generator 12 brakes the pump 1 in most operating points other than those close to ignition and therefore operates as a generator. So, in particular in cruising flight conditions, it acts as a generator and sends electrical power back to the aircraft's on-board circuit.

This has several positive consequences.

First, the flow delivered by the pump 1 being adapted to the need, there is no longer any need for a recirculation loop leaving the electromechanical control unit 2 for the stationary operating phases. There is therefore no longer any need to evacuate the excess thermal energy created by the excess flow. This therefore simplifies the fuel system and minimizes the size of the heat exchangers on the fuel system.

With reference to FIG. 6, the fuel circuit can retain a recirculation loop 9 ′, but the latter is only dimensioned to allow the circuit to adapt during transients, taking into account the reaction times of equipment such as the housing. electromechanical control, pump 1 and the sensors not shown which are used for regulation.

Second, the power taken directly from the output shaft of the accessory relay box 5 is always strictly equal to the need and the power taken from the turbomachine is less than that which is taken in an architecture such as that described in the figure. 1.

It will also be noted, that equipment which must necessarily exist for its main function is used with the starter 12, therefore the addition of an auxiliary motor is avoided. The starter performs the starting function of the turbomachine. The architecture of the fuel circuit 2 in FIG. 7 will include a return valve which will be piloted during opening during this start-up preparation phase. In fact, during this start-up preparation phase, the pump will be driven by the transmission device 6 and the latter will deliver a flow which is not required at the injection level. This flow will therefore be recirculated. This recirculation will only exist during the shutdown phase or during preparation for ignition.

The choice of configuration depends on the application considered. The configurations shown in the figures are therefore given for information only.

It has been found that the configuration illustrated in FIG. 6 makes it possible to meet the following constraints for the application considered:

- a speed ω12 of the starter / generator 12 higher than that ω1 of the pump 1, which makes it possible to minimize its size;

a limitation of the torque to be delivered by the starter 12 during the piloting phase of the pump 1,

- an optimization of the power gain taken from the box 5 compared to the state of the art;

- the maximum value of the speed ω1 of the pump 1 limited to a traditional maximum value for the maximum speed of the shaft of the accessory relay box 5.

Furthermore, this configuration makes it possible to simplify the accessory relay box 5, in fact it is possible to delete there:

- a reduction gear train for the starter / generator 12, because the reducer 11 ensures the reduction ratio between housing 5 and the starter / generator 12 during the start-up and ignition preparation phases;

- a reduction gear train for pump 1, because the reduction gear 11 provides the reduction ratio between the housing 5 and the pump 1.

The overall configuration of the circuit presented in FIG. 6 seems optimal in the case where the constraints imposed by the fuel circuit on the operation of the pump 1 do not have too much impact on the gain in power taken from the housing 5 to actuate the pump.

It appeared that the actuation of the variable geometries 10 which imposes strong constraints in terms of the pressure required in the fuel circuit can have negative consequences on the power gain for controlling the pump 1, in particular during takeoff.

An alternative embodiment of the turbomachine with variable geometries 10, shown in FIG. 7, makes it possible to overcome this drawback. In this case, the fuel system is decoupled from the variable geometries. The latter are actuated by independent electrical means. The operation of the pump 1 is then no longer affected by the stresses of variable geometries 10, which makes it possible to adjust the configuration of the transmission device 6 to optimize the energy gain taken from the accessory relay box 5. A dissipative resistor 14 can be installed on the starter / generator 12 to dissipate in thermal form an excess of energy which could not be returned to the on-board electrical circuit.

Claims (9)

Claims 1. Drive system for a fuel pump (1) of a turbomachine, the turbomachine comprising a motor shaft (26) and a starter (12) also serving as a generator, the system comprising a reduction gear (11) to planetary gear train comprising three elements, a central sun gear (11 A), an outer crown (11 B) and a planet carrier (11 U) whose satellites (11 S) mesh with the sun gear and the crown, a first of three elements being intended to be connected to the motor axis (26) and a second of the three elements being intended to be coupled to a shaft of the pump (1), characterized in that said three elements are movable in rotation around an axis of the reducer, in that the system further comprises the starter (12), the latter being arranged to rotate the third of said elements of the reducer (11), so as to modify a rotational speed ratio between the first and the second of said elements. 2. System according to claim 1, in which the first of said elements of the reducer (11) is the planetary (11 A), the second of said elements is the crown (11B) and the third of said elements is the planet carrier (11U) . 3. System according to one of the preceding claims, characterized in that the starter (12) is thermally coupled to a dissipative resistance (14). 4. Turbomachine comprising a fuel pump drive system (1) according to one of the preceding claims. 5. Turbomachine according to the preceding claim, in which an accessory relay box (5) connected to the motor shaft (26) is coupled to the first of the three elements of the reducer (11). 6. Turbomachine according to the preceding claim, in which the accessory relay box (5) has a single coupling with the starter (12) produced by the reducer (11). 7. Turbomachine according to one of claims 4 to 6, comprising variable geometries (10) hydraulically connected to the pump (1). 8. Turbomachine according to one of claims 4 to 6, comprising variable geometries (10) hydraulically decoupled from the pump (1) and connected to independent actuation means (15). 9. Method for regulating a fuel pump (1) for a turbomachine according to one of claims 4 to 8 in an aircraft, characterized in that the speed of rotation of the pump shaft (1) is modified ) by controlling the speed of rotation of the third element of the reducer (11) by the starter (12), so that the fuel flow delivered by the pump is adapted to the flight conditions of the aircraft. 1/4