FR3062423A1 - DRIVE SYSTEM FOR A FUEL PUMP OF A TURBOMACHINE - Google Patents

Abstract

The invention relates to a drive system for a fuel pump of a turbomachine, the turbomachine comprising a motor shaft and a starter (16) also having a generator function, the system comprising an epicyclic gear reducer (11) comprising three elements, a sun gear (11 A) central, an outer ring (11 B) and a planet carrier (11 U) whose satellites (11 S) mesh with the sun gear and the ring gear, a first of the three elements being intended to be connected to the motor shaft 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 about an axis of the gearbox, in the system further comprises first electrical means (12) arranged to rotate the third of said gear elements (11) to change a rotational speed ratio between the first and second of said elements, and second electrical means (13) coupled to one of said first or second element of the reducer (11), the first and second electrical means being arranged to transfer reversibly electric power from one to the other. other, and in that the first means (12) or second electrical means (13) comprise the starter (16)

Description

@ Holder (s): SAFRAN AIRCRAFT ENGINES.

Agent (s):

GEVERS & ORES Public limited company.

® DRIVE SYSTEM OF A FUEL PUMP OF A TURBOMACHINE.

FR 3 062 423 - A1 (® The invention relates to a system for driving a fuel pump of a turbomachine, the turbomachine comprising an engine shaft and a starter (16) also serving as a 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 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 around an axis of the reducer, in that the system further comprises first electrical means (12) arranged to rotate the third of said elements of the reducer (11), so as to modify a rotational speed ratio between the first er and the second of said elements, and second electrical means (13) coupled to one of said first or second element of the reducer (11), the first and second electrical means being arranged to transfer electrical power reversibly from the 'to each other, and in that the first means (12) or the second means (13)

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 an axis of the primary body of the turbomachine, not shown in FIG. 1. A drive 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 engine axis of the turbomachine, the fuel requirement F1 varies non-linearly as a function of the speed 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 an engine shaft and a starter also having the function of 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 further comprises first electrical means arranged to rotate 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, and of the second s electrical means coupled to the first or second of said elements of the reducer, the first and second electrical means being arranged to transfer electrical power reversibly from one to the other, and in that the first means or the second electrical means include the starter.

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 operating point at takeoff and not on that at ignition

From an energy point of view, the power taken from the motor axis will always be strictly equal to the minimum need thanks to the power transfer. We therefore obtain a gain on the power drawn for the operation of the fuel system.

In addition, the reversible power transfer between the starter and the other motor makes it possible to operate the device without the need for external power when controlling the pump, one of the motors taking the power necessary for the operation of the other motor. , when the latter is operating as an engine. The power transfer allows the two motors to operate in both modes, both in motor mode and in generator mode. Depending on the operating point, the starter can either be in engine mode or in generator mode and the engine in generator mode or in engine mode.

In addition, the use of the starter makes it possible to use equipment already present.

In addition, the responsiveness of the drive device to adapt the speed of the pump simplifies the fuel system. This makes it possible to greatly reduce the size of the fuel recirculation loop, or even to eliminate it.

Advantageously, the second electrical means are coupled to the second of the three elements of the reducer and the first of said elements of the reducer may be the planetary.

In a first preferred embodiment, the starter forms the second electrical means and the second of said elements of the reduction gear can be the planet carrier.

This first embodiment simplifies the design of an accessory relay box at the input of the system.

In a second preferred embodiment, the starter forms the first electrical means and the second of said elements of the reducer can be the crown.

This second embodiment makes it possible to optimize the dimensioning of the starter by allowing it high rotation speeds and low torques.

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

The invention also relates to a method of regulating a fuel pump for a turbomachine in an aircraft, a shaft of the pump being driven by a motor axis of the turbomachine by means using a drive system as described above where the starter forms the first electrical means, 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 flow of fuel delivered by the pump is adapted to the flight conditions of the aircraft, and in that the second electrical means are piloted so as to supply electrical energy to the starter when it is a motor and / or to absorb the energy electric supplied by the starter when it is generator.

The invention also relates to a method of regulating a fuel pump for a turbomachine in an aircraft, a shaft of the pump being driven by a motor axis of the turbomachine by means using a drive system as described above where the starter forms the second electrical means, 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 first electrical means, so that the flow of fuel delivered by the pump is adapted to the flight conditions of the aircraft, and in that the starter is piloted so as to supply electrical energy to the first electrical means when they are motors and / or to absorb the electrical energy supplied by the first electrical means when they are generators.

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 rotation speed 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 first embodiment of a drive device according to the invention between the turbomachine and the pump using a reducer of Figure 4;

Figure 6 shows the diagram of a second embodiment of a drive device according to the invention between the turbomachine and the pump using a reducer of Figure 4; and FIG. 7 very schematically shows a fuel circuit using a driving device in FIG. 5 or in FIG. 6.

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 driving device 6 ', the positive displacement pump 1 which supplies the hydromechanical group 2 injecting the fuel into the combustion chamber 3. Generally also, the relay box d 'accessories makes the link between the motor axis 26 and a starter / generator, not shown in this figure, 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 FIG. 7, the fuel supply system comprises a drive 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, able to supply the flow rate required for injection into the combustion chamber 3 and to put the fuel circuit under pressure. Preferably, it has a linear characteristic Cyl connecting the output flow to the speed of rotation ω1.

The driving device 6 ’comprises 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: cüU

Rotation of the crown 11B: ωΒ

WILLIS formula: (ωΑ - uuU) / (ωΒ- uuU) = k or ωΑ - k * ωΒ + (k-1) * uuU = 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, a first electric motor 12 is coupled to said third element to control the speed of rotation of the latter.

Six combinations are possible for positioning the three pieces of equipment, accessory relay box 5, pump 1 and electric motor 12, relative to the three elements of the planetary gear reducer 11.

To illustrate this with examples of configurations, reference is made here to FIGS. 5 and 6 where the references 12 and 13 are taken into account in parentheses and not the reference 16. In FIG. 5, the housing 5 being connected to the planetary central 11A and the pump to the planet carrier 11 U, an electric motor 12 is connected to the crown 11 B, so as to be able to drive the latter in rotation. In FIG. 6, the housing 5 being connected to the central sun gear 11A and the pump to the crown 11 B, an electric motor 12 is connected to the planet carrier 11 U, so as to be able to drive the latter in rotation.

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.

For illustration, FIG. 5 illustrates the configuration “3A-Option1”, where the second motor 13 is connected to the planet carrier 11 U, and FIG. 6 illustrates the configuration “3B-Option1”, where the second motor 13 is connected to the planetary 11A.

The first motor 12 and the second motor 13 each comprise a stator and a rotor. Said motors 12, 13 can be controlled in torque applied to their rotor and in rotation speed ω12, ω13 of their rotor. These are, for example, asynchronous AC motors. The torque and speed of each motor 12, 13 are then controlled by the electric power and the frequency of the current sent by a converter 14, 15 dedicated to each.

Furthermore, the second motor 13 is electrically linked to the first motor 12 by means of said reversible voltage converters 14, 15, in order to pass power from one to the other.

The position of the second motor 13 doubles the number of possible combinations for the 6 ’device. Twelve combinations are thus obtained, listed in the table below.

This table also indicates the function giving the speed ω1 of the pump 1 from the speed ω5 of the shaft of the housing 5 and the speed ω12 of the first motor 12. The speed of rotation ω13 of the second motor 13 is determined by the speed of rotation of the equipment with which it is coupled in series on the reduction gear 11, either the pump shaft 1 or the output shaft of the housing 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 the cases where the second motor 13 is coupled in series with the output shaft of the relay relay box 5 accessories on the same element of the reducer 11.

Housing / Pump / First Motor Connection Pump speed Second motor connection Box 5 connected to the 11U planet carrier Option 1 Option 2 Motor 12 Pump 1 1 AT crown 11B planetary 11A ω1 = (1-k) * u) 5 + k * co12 planetary A planet carrier 11U 1 B planetary 11A crown 11B ω1 = -u) 5 * (1-k) / k + u) 12 / k crown B planet carrier 11U Box 5 connected to the crown 11B Option 1 Option 2 Motor 12 Pump 1 2 planet carrier planetary 11A ω1 = k * ω5 planetary A crown B

AT 11U + (1-k) * co12 2 B planetary 11A planet carrier 11U ω1 = -u) 5 * k / (1-k) + ω12 / (1 -k) planet carrier 11U crown B Box 5 connected to the planetary 11A Option 1 Option 2 Motor 12 Pump 1 3 AT crown 11B planet carrier 11U ω1 = u) 5 / (1-k) - u) 12 * k / (1-k) planet carrier 11U planetary A 3 B planet carrier 11U crown 11B ω1 = ωδ / k - u) 12 * (1-k) / k crown B planetary A

Table 1.

Furthermore, with reference to FIG. 7, the fuel supply system also differs from that of FIG. 1 in that the control unit 4 'is connected to the converter 14, to control the speed ω12 and the torque of the first motor 12 in order to adapt the speed ω1 of the pump 1, as well as to the converter 15, to control the torque of the second motor 13 in order to manage the transfer of power between the two motors.

The study of the reduction gear 11 shows that the couple CA acting on the planet gear 11 A, the couple CB acting on the crown 11B and the couple CU acting on the planet carrier 11U are connected by two relationships:

CA + CB + CU = 0 (train balance) ωΑ * CA + ωΒ * CB + cuU * CU = 0 (power balance)

Given the relationships between the rotational speeds of these elements, this makes it possible to calculate the torques exerted on two elements of the reducer 11 with the third.

The second motor 13, being placed in series with the pump 1 or the housing 5, has its speed of rotation determined to be equal to that of this equipment.

It is understood, however, that it brings an additional degree of freedom to the system according to the torque which it exerts and which is added to that of the pump 1 or of the housing on the corresponding element of the reducer 11.

This additional degree of freedom can be used to ensure a transfer of power with the first motor: either supply power when the first motor 12 intervenes to accelerate the pompel with respect to the drive of the housing 5, or absorb power when the first motor 12 intervenes to brake the pump.

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:

- Withdrawal from the accessory relay box 5 only of the mechanical power corresponding to the power requirement for supplying variable geometries (pressure requirement) and for fuel flow supply (fuel flow requirement),

- reduction in the displacement of pump 1,

- drastic reduction in the size of the 9 ’recirculation loop of the pump flow,

- simplification of the architecture of the hydromechanical group 2 for fuel regulation,

- no need for external power when controlling the speed of the pump by a motor 12 thanks to the transfer of power between this motor and the second motor 13.

In the system described above, the first motor 12 and the second motor 13 are specially dedicated equipment, added to operate the drive device 6 ’.

According to the invention, one of the two auxiliary motors 12, 13 is replaced by the electric starter 16 of the turbomachine. This again doubles the number of possible configurations. In Table 1, each option 1 or 2 splits into two options, 1 a / 1 b or 2a / 2b, depending on whether the starter 16 replaces the second engine 13 (version a) or replaces the first engine 12 (version b) .

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 carried out identifies the configurations meeting 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 input speed ω2 for the shaft of the accessory relay box 5,

the reason k of the planetary gear train of the reducer 11,

- the power transmitted between the starter 16 and the other motor, 12 or 13, (this power sizes the other motor and also corresponds to an excess of power taken from the shaft of the housing 5)

- the speed of rotation of the starter 16 (this sizes the starter, which must also provide the power to prepare the start of the turbomachine)

- Limiting the torque to be delivered by the second engine 13 if the starter 16 is positioned in place of the first engine 12 or limiting the torque to be delivered by the first engine 12 if the starter 16 is positioned in place of the second engine 13 .

The inventors carried out, for a given application, a systematic study on all of the configurations with an objective of a power limited to 3 kW for the transfer between the starter 16 and the other engine. This value of 3 kW advantageously makes it possible to limit the size of the auxiliary motor 12 or 13, depending on the place of the starter 16. They have found in particular that the two combinations described below have various advantages to be considered for integration into a turbomachine for the given application. Depending on the application, the studies will lead to other configurations. The two configurations presented are therefore not exhaustive.

We now refer to Figures 4 and 5 taking into account the reference 16 and not the reference in parenthesis, indicating the replaced auxiliary motor.

With reference to Figure 5, the "3A-Option 1a" configuration corresponds to the following connections:

- housing 5 coupled to the central planet 11A;

- pump 1 coupled to the planet carrier 11U;

- first motor 12 coupled to the crown 11B;

- starter 16 coupled to the planet carrier 11 U, in series with pump 1.

Here, with reference to FIG. 7, the control unit 4 ′ is connected to the converters 14, 15, to drive the auxiliary motor 12 and the starter 16 in the four quadrants, in terms of torque and speed, in order to adapt the speed ω1 of pump 1 and optimize the power transfer.

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

ω1 = u) 5 / (1-k) - u> 12 * k / (1 -k)

Depending on whether the motor 12 drives the crown B with a positive or negative ω12 value the pump 1 can be driven at a speed lower or higher than the speed cü5 / (1-k) that it would have for a train 11 with a fixed crown .

When the turbomachine is operating 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 engine 12.

Depending on whether the speed of rotation of the motor 12 is positive or negative, the motor 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 always strictly equal to the minimum need for useful power thanks to the transfer of power whatever the flight point.

The 4 ’control unit also controls the starter 16 so as to adapt its torque to transfer power with the first motor 12, in one direction or another depending on the operating point of the turbomachine. Referring to the case of FIG. 2 where it is the ignition operating point which is dimensioning for the pump 1, the starter 16 supplies power to the first engine 12 during ignition.

This configuration makes it possible to meet the following constraints:

- The power transmitted between the first motor 12 and the starter 16 is limited, advantageously it is less than 3 kW;

- the speed ω12 of the electric motor 12 is higher than that ω1 of the pump 1;

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

- the torque supplied by starter 16 is limited while using direct mounting on the shaft of pump 1.

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. This has two positive consequences.

First, the power taken directly from the output shaft of the accessory relay box 5 is always strictly equal to the need thanks to the transfer of power between the two motors 12, 13.

The absence of loss comes from this transfer of electric power, motor 12 either recovering energy through the transmission device and returning it to the motor 13, or recovering energy from the motor 13 and returning it in motor mode to transmission device. The power taken from the turbomachine is therefore less than that taken from an architecture such as that described in FIG. 1.

In addition, the size and mass of motors capable of absorbing or restoring the power transferred between them are less than that of a battery which acts as a reservoir of electrical energy. This configuration therefore achieves the objectives by minimizing the size and mass of the second engine.

12.

Secondly, the flow delivered by the pump 1 being adapted to the need, there is no longer any need for a recirculation loop leaving the hydromechanical regulating group 2 for the phases of stationary operation. 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. 7, the fuel circuit can keep 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 group hydromechanical regulation 2, pump 1 and the sensors not shown which are used for regulation.

In addition, the limitation of the transferred power, associated with reasonable torque values and high rotation speeds, makes it possible to limit the size and mass of the motors. This therefore makes it possible to achieve the objectives while minimizing the size and the mass of the driving device 6 ’between the accessory relay box 5 and the pump 1.

It will also be noted that using the starter 16 equipment which must necessarily exist for its main function, the addition of an auxiliary motor is therefore 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.

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

- the gear train for the starter 16 because the reducer 11 ensures the reduction ratio between housing 5 and the starter during the start-up and ignition preparation phases;

- the gear train for pump 1 because the reducer 11 ensures the reduction ratio between housing 5 and the pump.

This preferred embodiment however has the following drawbacks:

- the speed of starter 16 cannot exceed the maximum speed of pump 1 since it is connected to the same axis (to minimize the size of starter 16, it would be preferable to drive the pump at higher speed but this requirement is incompatible with the maximum output speed of the housing 5);

- It may be necessary to place a reducer between the first motor 12 and the ring gear 11B to achieve low torque values with reasonable sizing.

With reference to Figure 6, the "3B-Option 1b" configuration corresponds to the following connections:

- housing 5 coupled to the central planet 11A;

- pump 1 coupled to the crown 11 B;

- starter 6 coupled to the planet carrier 11U;

- second motor 13 coupled to the sun gear 11A, in series with the housing 5.

Similarly to the previous configuration, with reference to FIG. 7, the control unit 4 ′ is connected to the converters 14, 15, to drive the auxiliary motor 12 and the starter 16 in the four quadrants, in terms of torque and speed in order to adapt the speed ω1 of pump 1 and optimize the power transfer.

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

ω1 = ωδ / k -u) 12 * (1-k) / k

Here, it is the starter 16 which adjusts the speed ω1 of the pump 1 to the fuel requirement of the ignition chamber 3 varying its speed ω12. The second motor 13, in series with the pump, is used for power transfer with the starter 16.

We find for this second preferred embodiment all the advantages cited for the first with in addition, in particular:

- a speed ω12 of the starter 16 higher than that ω1 of the pump 1;

a limitation of the torque to be delivered by the starter 16 during the piloting phase of the pump 1.

These advantages make it possible to optimize the size of the starter 16 without the drive function of the fuel pump impacting its first starter function.

Claims (10)

Claims 1. Drive system for a fuel pump of a turbomachine, the turbomachine comprising a motor shaft (26) and a starter (16) also serving as a generator, the system comprising a reduction gear (11) with planetary gear comprising three elements, a central sun gear (11 A), an outer ring (11B) and a planet carrier (11U) whose satellites (11S) mesh with the sun gear and the ring, the 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 around an axis of the reduction gear, in that the system further comprises first electrical means (12) 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 é elements, and second electrical means (13) coupled to the first or second of said elements of the reducer (11), the first and second electrical means being arranged to transfer electrical power reversibly from one to the other, and in that the first means (12) or the second electrical means (13) comprise the starter (16). 2. System according to claim 1, characterized in that the second electrical means (13) are coupled to the second of the three elements of the reducer. 3. System according to the preceding claim, characterized in that the first of said elements of the reducer (11) is the planetary (11 A). 4. System according to the preceding claim, characterized in that the starter (16) forms the second electrical means. 5. System according to the preceding claim, characterized in that the second of said elements of the reducer (11) is the planet carrier (11 U). 6. System according to claim 3, characterized in that the starter (16) forms the first electrical means. 7. System according to the preceding claim, characterized in that the second of said elements of the reducer (11) is the crown (11 B). 8. Turbomachine comprising a system according to the preceding claim. 9. Method for regulating a fuel pump (1) for a turbomachine in an aircraft, a pump shaft being driven by a motor axis of the turbomachine by means using a drive system according to claim 6, characterized in changing the speed of rotation of the pump shaft by controlling the speed of rotation of the third element of the gearbox by the starter (16), so that the fuel flow delivered by the pump is adapted to flight conditions of the aircraft, and in that the second electrical means (13) are piloted so as to supply electrical energy to the starter when it is powered and / or to absorb the electrical energy supplied by the starter when it is generator. 10. Method for regulating a fuel pump (1) for a turbomachine in an aircraft, a pump shaft being driven by an engine axis of the turbomachine by means using a drive system according to claim 4, characterized in changing the speed of rotation of the pump shaft by controlling the speed of rotation of the third element of the reducer by the first electrical means (12), so that the flow of fuel delivered by the pump is adapted to the flight conditions of the aircraft, and in that the starter (16) is piloted so as to supply electrical energy to the first electrical means when they are driving and / or to absorb electrical energy provided by the first electrical means when they are generators. 1/4