Patent ID: 12234772

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

DESCRIPTION OF AN EMBODIMENT

In a turbomachine, for example a dual flow turbomachine shown inFIG.3, the outlet air flow at fan20is 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 compressors21and high-pressure compressors22, the combustion chamber3supplied by the fuel circuit mentioned previously, and then high-pressure turbines24and low-pressure turbines25. Generally, all the high-pressure compressors22and high-pressure turbines24rotate as a unit on a common axis26and form the engine part of the turbomachine with the combustion chamber.

Generally, the drive shaft26drives the accessory relay box5which 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 device6′, the volumetric pump1which supplies the hydromechanical group2injecting the fuel into the combustion chamber3. Generally also, the accessory relay box makes the connection between the drive shaft26and 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.

The turbomachine may also have variable geometries10, mentioned above, which can be activated under certain conditions of use. This variable geometries10are, for example, variable-pitch vanes at the inlet of a low-pressure compressor.

Here, with reference toFIG.6or7, the fuel supply system includes a drive device6′ between the accessory relay box5and the pump1different from that of the system inFIG.1. The pump1can 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 ω1, able to provide the flow rate necessary for the injection into the combustion chamber3and to pressurize the fuel circuit. Preferably, it has a linear characteristic Cyl relating the outlet flow rate to the rotational speed ω1.

First of all, we will show that there is at least one solution to make a drive device6′ capable of varying the ratio between the rotational speed of the shaft of the accessory relay box5and the rotational speed of the shaft of the pump1, in order to be able to adapt the speed of the pump1to the different operating points of the turbomachine.

The drive system6′ shown has an epicyclic gear reducer whose properties are used to adapt the rotational speed of pump1to the need for fuel flow rate according to the different operating speeds of the turbomachine.

With reference toFIG.4, the epicyclic gear reducer11comprises:a central sun gear11A, arranged to be able to rotate about the axis of the epicyclic gear at a speed ωA;planets11S meshing with the central sun gear11A and carried by a planet carrier11U, the planet carrier11U being arranged to be able to rotate about the axis of the epicyclic gear at a speed ωU;an external ring gear11B with which the planets11S also mesh, the ring gear11B being arranged to be able to rotate about the axis of the epicyclic gear at a speed ωB.

A characteristic of the epicyclic gear reducer11is therefore that its three elements, the central sun gear11A, the planet carrier11U and the ring gear11B, are able to rotate. Here, for example, the ring gear11B is free to rotate inside a fixed casing11C protecting the reducer11.

The operation of the epicyclic gear of the reducer11is 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 gear11A, the planet carrier11U and the ring gear11B, allows the calculation of the rotational speed of the third.

Rotation of the central sun gear11A: ωA

Rotation of the planet carrier11U: ωU

Rotation of the ring gear11B: ωB
(ωA−ωU)/(ωB−ωU)=kor ωA−k*ωB+(k−1)*ωU=0  WILLIS Equation:

In Willis equation, the factor k, also called the epicyclic gear reason, is a constant determined by the geometry of the gears. For the reducer11inFIG.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.

It is therefore understood that, if the outlet shaft of the accessory relay box5is coupled to one of the three elements and the shaft of the pump1is coupled to a second element, the rotational speed of the pump1can be varied for a given speed of the shaft of the box5by varying the rotational speed of the third element.

A first electric motor12is coupled to said third element to control the rotational speed of the latter.

Six combinations are possible to position the three equipment units, accessory relay box5, pump1and electric motor12, with respect to the three elements of the epicyclic gear reducer11.

A second motor13is also coupled to one of the elements of the reducer11which is not connected to the first motor12. The position of the second motor13doubles the number of possible combinations for the device6′. This results in twelve combinations listed in the table below.

This table also indicates the function giving the speed ω1of the pump1from the speed ω5of the shaft of the box5and the speed ω12of the first motor12. The rotational speed ω13of the second motor13is determined by the rotational speed of the equipment with which it is coupled in series on the reducer11, either the shaft of the pump1or the outlet shaft of the box5. In this table, option 1 corresponds to the cases where the second motor13is coupled in series with the pump1on the same element of the reducer11, and option 2 corresponds to cases where the second motor13is coupled in series with the outlet shaft of the accessory relay box5on the same element of the reducer11.

TABLE 1Connection box/pump/first motorPump speedConnection second motorBox 5 connected to the planet carrier 11UMotor 12Pump 1Option 1Option 21ring gear 11Bsun gear 11Aω1 = (1 − k)*ω5 +sun gear AplanetAk*ω12carrier 11U1sun gear 11Aring gear 11Bω1 = −ω5*(1 − k)/k +ring gear BplanetBω12/kcarrier 11UBox 5 connected to the ring gear 11BMotor 12Pump 1Option 1Option 22planet carrier 11Usun gear 11Aω1 = k*ω5 +sun gear Aring gear BA(1 − k)*ω122sun gear 11Aplanet carrier 11Uω1 = −ω5*k/(1 − k) +planet carrier 11Uring gear BBω12/(1 − k)Box 5 connected to the sun gear 11AMotor 12Pump 1Option 1Option 23ring gear 11Bplanet carrier 11Uω1 = ω5/(1 − k) −planet carrier 11Usun gear AAω12*k/(1 − k)3planet carrier 11Uring gear 11Bω1 = ω5/k −ring gear Bsun gear ABω12*(1 − k)/k

In the example shown inFIG.5, corresponding to the configuration “3A—Option 1”, the box5is connected to the central sun gear11A, the pump to the planet carrier11U, the first electric motor12is connected to the ring gear11B, so that it can drive in rotation the latter, and the second motor13is connected to the planet carrier11U.

The first motor12and the second motor13each have a stator and a rotor. Said motors12,13are controllable in terms of torque applied to their rotor and rotational speed ω12, ω13of their rotor. These are, for example, alternative current asynchronous motors. The torque and speed of each motor12,13are then controlled by the electrical power and the frequency of the current sent by a converter14,15dedicated to each.

In addition, the second motor13is electrically connected to the first motor12through said reversible voltage converters14,15, in order to pass power from one to the other.

In addition, with reference toFIG.6or7, the fuel supply system also differs from that inFIG.1in that the control box4′ is connected to the converter14, to control the speed ω12and the torque of the first motor12in order to adapt the speed ω1of the pump1, and to the converter15, to control the torque of the second motor13to manage the power transfer between the two motors.

The dynamic study of the reducer11shows that the torque CA acting on the sun gear11A, the torque CB acting on ring gear11B and the torque CU acting on planet carrier11U are related by two relationships:
CA+CB+CU=0  (epicyclic gear equilibrium)
ωA*CA+ωB*CB+ωU*CU=0  (dynamic equilibrium)

Considering the relationships relating the rotational speeds of these elements, it is possible to calculate the torques acting on two elements of the reducer11knowing the third one.

The second motor13, being connected in series with the pump1or the box5, has its rotational speed determined as being equal to that of this equipment unit.

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 pump1or the box on the corresponding element of the reducer11.

This additional degree of freedom can be used to ensure power transfer with the first motor: either providing power when the first motor12intervenes to accelerate the pump1with respect to the drive of the box5, or absorbing power when the first motor12intervenes to brake the pump1.

It is possible to use other configurations than that illustrated inFIG.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 reducer11, the ratio of the rotational speed ω5at the outlet of the box5with respect to the rotational speed of the axle of the turbine, the linear characteristic Cyl of the pump1, and the choice among the configurations1A to3B, must be made to achieve in particular the following objectives:allowing the pump1to rotate at a speed ω1that adjusts to provide a flow rate Cyl.ω1that corresponds to the need F1, as shown for example inFIG.2, when the rotational speed of the axle of the turbine varies between its minimum value ωmin and maximum value ωmax;minimizing the power spent in the motor12to adjust the speed w1of the pump1to the operating range of the turbomachine.

In addition, technological constraints on the equipment units used generally imply that:the speed ω1of the pump1must be lower than that ω5of the outlet shaft of the accessory relay box5; andthe speed ω12of the electric motor12must be limited to a maximum value.

This concept with two auxiliary electric motors for the drive system between the accessory relay box5and the pump1is very innovative because it offers the following advantages:taking from the accessory relay box5only 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),reduction of the displacement of the pump1,drastic reduction in the dimensioning of the recirculation loop9′ of the pump flow rate,simplification of the architecture of the hydromechanical group2for fuel regulation,no need for external power during the controlling of the pump speed by a motor12thanks to the power transfer between this motor and the second motor13.

In the system described above, the first motor12and the second motor13are especially dedicated equipment units, added to operate the drive device6′. In a variant, the starter of the turbomachine can be used as the first or second motor of the device.

The fuel supply system concept developed in the following allows optimal use of such a drive device6′.

With reference toFIG.6, a fuel supply system, according to the invention, includes:a drive device6′ between the accessory relay box5and the pump1as described above, allowing to adapt the speed of the pump1;a pump1dimensioned to be adapted to the flow rate supplied with the system according to the invention;a means7for supplying the circuit from fuel tanks8;a hydromechanical block2′ according to the invention;a control electronics4′.

Here, the fuel supply system is also connected to actuators of variable geometries10.

The hydromechanical block2′ according to the invention includes the following elements:a fuel flow rate sensor201between the pump1and the injection to the combustion chamber3;a pressurization valve202at the injection to the combustion chamber3;a return valve203branched between the flow rate sensor201and the pressurization valve202, and connected to a recirculation loop9′;a servo valve204essentially controlling the pressurization valve202and the return valve203.

When the fuel circuit is used to operate variable geometries10, the fuel circuit advantageously includes a derivation205to power a control loop for actuators of the variable geometries10. This derivation205is placed here between the pump1and the flow rate sensor201of the hydromechanical block2′.

The flow rate sensor201is realized by a modified metering unit.

A metering unit usually used in a conventional circuit includes a sliding drawer211whose position controls the flow rate through a metering unit section. In addition, a sensor212of the position of the drawer211allows to slave the metering unit, usually by a servo valve.

Here, the position of the drawer211is not controlled by a servo valve, but directly by the pressure difference across the flow rate sensor201which compensates the force applied by a return mean206, for example a spring, on the drawer211, 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 sensor212of position of the drawer211provides information on the actual flow rate really injected by the fuel circuit into the combustion chamber.

For example, flow rate information can be transmitted to the control electronics box4′ for action on the drive device6′ and so that the latter adjusts the speed of the pump1to ensure the correct fuel flow rate adapted to the need.

The hydromechanical block2′ 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 valve202.

The pressurization valve202ensures the minimum pressure for the correct operation of the variable geometries, as well as the cut-off of the injected flow rate.

The return valve203, allows ensuring the exhaust of the flow rate delivered by the pump1in order not to increase pressure in the circuit, when this cut-off is activated by the servo valve204.

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 pump1. The recirculation loop9′ is therefore much less important than for a conventional circuit.

At ignition, the pump1is driven at a minimum rotational speed. A part of the flow rate passes through the sensor201and is recirculated by the return valve203.

The speed of the pump1is then adjusted to reach the correct ignition flow rate setpoint value. The servo valve204is then activated, which cause the pressurization valve202to open, the return valve203to close and thus allows the ignition flow rate to be injected into combustion chamber3.

Finally, the return valve203provides protection in the event of overspeed due to a failure of the pump1speed control.

In the event of a flow rate call related to the actuation of variable geometries10, for a given rotational speed of the pump1, the flow rate passing through the sensor201tends to decrease due to the derivation205towards the variable geometries10, which is placed upstream. The information of a decrease in flow rate requires the drive system6′ to accelerate the speed of the pump1in order to maintain the correct injected flow rate required.

A control loop based on the flow rate information of the sensor201, installed in the control box4′, therefore allows the pump speed to be adjusted for any operating point of the turbomachine, whether the variable geometries10are active or not.

This hydromechanical block2′ concept therefore allows to take advantage of a drive system6′ capable of adapting the pump's rotation speed if necessary.

There is therefore no longer any need to size a recirculation loop9′ to dissipate a large flow rate surplus and this allows to gain power drawn from the accessory relay box5for fuel supply. This also allows to eliminate the regulating valve that exists in a conventional circuit.

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

The hydromechanical block2′ therefore allows to take full advantage of the potential power gain offered by the drive system6′.

It should be noted that this concept also works without powering variable geometries, for example if they are driven by electrical means17, as shown inFIG.7. In a configuration without variable geometries, the solution will only be easier to implement, and more efficient in terms of power gain.

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 box5, injected flow rate, cooling flow rate of the variable geometries10, 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.

This concept also has other positive impacts.

Regarding the volumetric pump1, 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.

Regarding the hydromechanical block2′, 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.

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

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

To do this, it is enough to add a speed sensor, not shown, to the volumetric pump1.

Indeed, the sensor201indicates the fuel flow rate. Since the volumetric pump1has 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 pump1: 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.