FR3099203A1 - LUBRICATION CIRCUIT OF AN AIRCRAFT TURBOMACHINE - Google Patents

Abstract

An aircraft turbomachine lubrication circuit (10), comprising: a lubrication unit (12) equipped with at least one feed pump (14) comprising a rotor configured to be driven by an output shaft (26 ) of a gearbox (27), at least one oil reservoir (18) comprising an oil outlet (18a) connected to said at least one pump, characterized in that it further comprises: a mechanical differential (22) with planetary gear, this differential comprising: - a first input configured to be driven by said output shaft, - a second input driven in rotation by a first electric motor (30), and - an output which drives said rotor in rotation. Figure for the abstract: Figure 2

Description

LUBRICATION CIRCUIT OF AN AIRCRAFT TURBOMACHINE

Technical field of the invention

The present invention relates to the general field of lubrication in an aircraft turbomachine.

Technical background

Aircraft turbomachines are equipped with a lubrication unit whose function, via a distribution network, is to inject into the engine a flow of oil necessary for the lubrication of enclosures, certain equipment of a gearbox of the AGB type (acronym for Accessory Gear Box ), as well as the mechanical transmission between a mechanical reduction gear of the turbomachine and the AGB.

The lubrication unit is equipped with a volumetric feed pump and scavenge pumps which are coupled in rotation to the gearbox drive. Their flow rates are therefore linear with the rotation of the turbomachine.

The fuel pump is sized to provide the take-off flow which generally corresponds to the point of maximum heat output generated on the oil by the engine. This flow rate on takeoff is the result of thermal calculations making it possible to meet the oil temperature specifications and the available fluids recovering the calories from the oil. The flow rates at the other operating points are deduced from the characteristic and the speed of rotation of the pump.

To cool the oil, two fluids are available, namely the fuel and the air taken from the engine or the aircraft. Each heat exchanger, of the oil-fuel or air-oil type, has the function of transferring part of the calorific power collected by the oil to a cold source. The air-oil exchanger air circuit is an additional cold source to allow cooling of the oil when the oil-fuel exchanger is no longer sufficient.

The dimensioning point of the air-oil exchanger is most often located in cruise because this non-transitory point approaches a permanent state. Unfortunately, at this dimensioning point, the flow rate optimized for the transfer of heat flux does not correspond to the maximum flow rate that the feed pump is capable of delivering. The efficiency of the exchanger is optimized in relation to the real flow exchanged on the maximum exchangeable flow at this cruising point with the flow rate supplied by the pump. The optimization of the efficiency with this flow leads us to a size of exchanger not optimized but necessarily compatible with this flow and the temperatures of the fluids.

For the other points, the heat output dissipated by current turbomachines is a linear function of the speed of the turbomachine in most applications. As the flow rate characteristic of the feed pump is also a linear function with the speed of the turbomachine, the efficiency coefficient of the exchanger estimated at the dimensioning point in cruise will maintain an acceptable value at the other operating points at lower debit.

At present, we are confronted with turbomachine architectures where not only the thermal rejection is greater but where the thermal rejections and therefore the flow requirements are no longer linear with the speed of the turbomachine.

The size of the exchanger estimated at the sizing point therefore risks being strongly impacted by the value of the flow rate which does not correspond to the maximum flow rate delivered by the feed pump. In addition, this exchanger size will no longer allow the same efficiency value to be maintained at the other operating points. The need for flow to optimize heat transfer (i.e. efficiency) at other points is therefore no longer assured since the flow follows a linear law.

The present invention provides a solution to this problem, which is simple, efficient and economical.

The present invention proposes a lubrication circuit for an aircraft turbine engine, comprising:

• a lubrication unit equipped with at least one feed pump comprising a rotor configured to be driven by an output shaft of a gear box,
• at least one oil tank comprising an oil outlet connected to said at least one pump,

characterized in that it further comprises:

• a mechanical differential with planetary gear, this differential comprising:

-- a first input configured to be driven by said output shaft,

-- a second input driven in rotation by a first electric motor, and

-- An output which rotates said rotor.

The invention thus consists in modulating the drive speed of the rotor of the supply pump by not exceeding, for example, the maximum take-off speed and by not falling, for example, below a certain minimum threshold. This can in particular make it possible to reduce the size and pressure drops of the oil exchangers associated with this circuit.

A mechanical planetary gear differential comprises two inputs and one output chosen from among a ring gear, a sun gear, and a planet carrier carrying gears meshed respectively with the crown gear and the sun gear.

The circuit according to the invention may comprise one or more of the characteristics below, taken separately from each other or in combination with each other:

- a mechanical differential with planetary gear, this differential comprising:

-- a crown configured to be driven by said output shaft,

-- a solar powered in rotation by a first electric motor, and

-- satellites meshed respectively with the crown and the sun and carried by a planet carrier which rotates said rotor,

- said planet carrier is connected to said rotor by a second electric motor,

- said first and second electric motors are connected together by control units of the operating mode of each motor from motor and generator modes,

- said lubrication unit comprises several oil recovery pumps, the outlets of which are connected to an inlet of said tank,

- the outlets of the recovery pumps are connected to the tank inlet by an air-oil heat exchanger and/or by an air-fuel heat exchanger,

- said planet carrier is further configured to rotate a rotor of a permanent magnet alternator, for example via a first speed multiplier, and

- Said planet carrier is further configured to drive in rotation a rotor of a pump of a fuel circuit of the turbomachine, for example via a second speed multiplier.

The present invention also relates to an aircraft turbine engine, comprising at least at least one circuit as described above.

Brief description of figures

The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

Figure 1 is a schematic view of a lubrication circuit of an aircraft turbine engine, according to the prior art,

FIG. 2 is a schematic view of a lubrication circuit of an aircraft turbine engine, according to the invention,

FIG. 3 is a schematic view of an alternative embodiment of a lubrication circuit of an aircraft turbomachine, according to the invention.

Detailed description of the invention

Figure 1 shows a lubrication circuit 10 of an aircraft turbine engine according to the invention.

Circuit 10 includes a lubrication unit 12 comprising a supply pump 14 and several recovery pumps 16, as well as an oil tank 18.

The tank 18 comprises an outlet 18a connected to an inlet 14a of the pump 14 and an inlet 18b connected to the outlets 16a of the pumps 16. The outlet 14b of the pump 14 is connected to several pieces of equipment 20 of the turbomachine for the purpose of their lubrication. This equipment 20 includes, for example, enclosures for lubricating the bearings of the turbomachine, a gearbox, a mechanical reduction gear with an epicyclic gear train, etc. The oil that supplies this equipment is then recovered by pumps 16 for recycling and is therefore redirected to the inlets 16b of pumps 16.

The invention proposes an improvement to this technology, which consists in driving the rotor of the pump 14 by means of a mechanical differential with planetary gear train.

Figure 2 illustrates a first embodiment of this invention.

The mechanical planetary gear differential 22 comprises:

- a crown 24 configured to be driven by an output shaft 26, for example of an AGB type gearbox 27,

- a solar 28 driven in rotation by a first electric motor 30, and

- satellites 32 meshed respectively with crown 24 and solar 28 and carried by a planet carrier 34 which rotates the rotor of pump 14.

Advantageously and as shown in the drawing, the planet carrier 32 is connected to the rotor of the pump 14 by a second electric motor 36.

The electric motors 30, 36 are connected together by boxes 38 for controlling the mode of operation of each motor from motor and generator modes.

The rotor of pump 14 is thus no longer driven directly in rotation by the gearbox but by a differential transmission with two inputs and one output. This transmission makes it possible to connect the two inputs, the shaft of the box 27 and the axis of the electric motor 30, to the output formed by the rotor of the pump 14. The electric motor 30 is configured to adjust the speed of the group of lubrication 12 and in particular the rotor of the supply pump 14.

The additional motor 36 makes it possible to ensure the transfer of power with the motor 30. If the speed of the lubrication unit 12 must be increased, the electric motor 30 will operate in motor mode and its energy will be delivered by the motor 36 positioned on the rotor of the pump. If the speed of the lubrication unit 12 must be reduced, the electric motor 30 will operate in generator mode and its energy will be transferred to the motor 36. The two motors 30, 36 are controlled through so-called "inverter" control boxes which transfer the reciprocal power.

The planetary gear train has several kinematic configurations in terms of input and output combinations. The choice of configurations must be identified according to the constraints of the application in question.

In the example shown, the outlets 16a of the recovery pumps 16 are connected to the inlet 18b of the tank 18 by an air-oil heat exchanger 40 and/or by an air-fuel heat exchanger 42.

If, for example, the point sizing the exchanger 40 is the cruising speed, the architecture will make it possible to increase the drive speed of the pump 14 to that of take-off to increase the flow. This increase in flow without exceeding the maximum take-off flow should promote heat exchange.

With the surface of a heat exchanger that would have been determined without this speed modularity, the increase in flow will lower the maximum oil temperature thanks to the improvement in the efficiency of the heat exchanger. Indeed, the efficiency coefficient is a function of the heat capacities of the fluids but also of the Nusselt numbers of the fluids. These Nusselt numbers are dependent on the speed of the fluids passing through this exchanger through the Reynolds number. If the exchange surface is reduced, an increase in the flow rate will maintain the same maximum oil temperature value with an efficiency similar to that which would have been obtained without this speed modularity. The efficiency coefficient is also a function of geometric characteristics including the heat exchange surface. It is therefore possible to reduce the surface of the exchanger in proportion to the gain in efficiency.

The objective is therefore achieved by increasing the flow, improving the exchange coefficient and therefore the ability to exchange calories. This exchange being favoured, this results in a better coefficient of efficiency or in a reduction of the exchange surface either of the exchanger 42, or of the exchanger 40, or even the elimination of the exchanger 40.

For any operating point, the speed of the pump 14 will be adjusted by the motor 30 in order to guarantee the optimum flow rate. At low speeds, a minimum speed of the pump 14 will be maintained to guarantee a minimum flow rate at the point of operation when the fan of the turbomachine is freewheeling.

The present invention thus proposes:

- when the thermal rejections are linear with the speed of the turbomachine: an architecture which aims to reduce the size of the air-oil exchanger in cruise with similar efficiency while not impacting the dimensioning of the lubrication unit; the size of the air-oil exchanger positioned at the level of the vein is penalizing by its mass but also by the pressure drop it induces.

- when thermal rejections are no longer linear with the speed of the turbomachine: an architecture which also aims to improve efficiency at other operating points

This architecture therefore proposes to adapt the flow rate requirement by not exceeding the take-off flow rate to be at iso lubrication group. It is important to note that the oil consumption has an impact on the size of the tank, that the excess oil consumption of the engine has an impact on the sizing of the recovery pumps. It is therefore essential to optimize the oil flow in order to avoid oversizing of other components. This adaptation of the bit rate is obtained by an adaptation of the speed.

The present invention also proposes to ensure a minimum flow rate at low speed. Indeed, at low speed, when the turbomachine fan is freewheeling, the flow delivered by the feed pump is limited for the fire resistance of certain components coupled to the gearbox. To compensate for this low flow, some components are fitted with thermal protection. On the other hand, if we want to avoid the problem of coking during the operation of the engine at standstill, a minimum of oil flow should be ensured.

The present invention therefore proposes, in addition to the flexibility of the drive speed of the pump, a reduction in the variability of this drive speed in order to increase the speed at low speed of the gearbox. This flexibility and the restriction of the range of speed variability are the result of a mechanical differential transmission with power transfer.

The present invention proposes an architecture, which depending on the application and after analysis, could be very useful in the face of the problems cited. The main objective is to reduce the mass of the air-oil exchanger 40 and its pressure drop in the vein. The architecture consists in adjusting the drive speed of the feed pump in order to achieve an optimization flow rate of the exchanger.

An optimization flow rate at the exchangers for any flight point makes it possible either to reduce the size of the exchangers or to reduce the transfer of heat from the oil to the fuel or to the air. Any reduction in heat transfer to the fuel is of interest as it could lead to suppression of the fuel return valve (FRV). This fuel return valve has been designed to mix hot and cold fuel in order to reduce the temperature of the fluid returned to the tank to limit the impact on the temperature of the fuel contained in the tank (which will re-enter the engine).

In the variant embodiment of FIG. 3, the planet carrier 34 of the differential 22 is also configured to drive in rotation a rotor of a permanent magnet alternator 44, for example via a first speed multiplier 46.

In the example shown, the planet carrier 34 is also configured to drive in rotation a rotor of a pump 48 of a fuel circuit of the turbomachine, for example via a second speed multiplier 50 .

It is indeed possible to extend this architecture to the PMA ( permanent magnet alternator ) power generating source of the FADEC and to the fuel system by positioning them on the same drive axis of the lubrication unit if the sizing of this equipment allows it. . The choice of the differential output speed for each flight point must be compatible with the needs of the fuel system, the needs of the lubrication unit and the PMA through multipliers 46, 50.

For the PMA, the guarantee of a minimum speed at low speed would make it possible to reach higher torques, which leads to a reduction in the size of the PMA.

This architectural extension for the fuel system is particularly useful if the fuel circuit only incorporates a centrifugal pump with regulation of the flow injected by the engine 30 and no longer by regulation of a diaphragm in series with the pump.

Indeed, this flexibility and restriction of the range of speed variability would make it possible both to eliminate the recirculation loop of the fuel system but also to ensure, at low engine speeds, a sufficient drive speed for the centrifugal pump of the fuel system. The differential pressure required for the activation of the variable geometries at low speeds would therefore be ensured at the terminals of the centrifugal pump thanks to this minimum drive speed.

This differential drive principle of the lubrication unit is very innovative because it offers the following advantages:

- reduction in the size of the oil exchangers;

- potential removal of the FRV valve;

- simultaneous drive of the supply pump and the FDA; parallel drive of the PMA by the output shaft of the differential through the necessary multiplier; reduction in the size of the FDA, because training at higher speeds at low speeds and therefore an increase in torque at low speeds;

- no additional tapping of electrical power for driving the electric steering motor thanks to power transfer;

- simultaneous drive of the pump and the fuel system; parallel drive of the fuel system by the planet carrier of the differential through a multiplier; simplified architecture of the fuel system by centrifugal pump without recirculation loop because drive at higher speeds at low revs and therefore increase in the differential pressure required for the activation of the variable geometries.

Claims (9)

Circuit (10) for lubricating an aircraft turbine engine, comprising:

• a lubrication unit (12) equipped with at least one supply pump (14) comprising a rotor configured to be driven by an output shaft (26) of a gearbox (27),
• at least one oil tank (18) comprising an oil outlet (18a) connected to said at least one pump,

characterized in that it further comprises:

• a mechanical differential (22) with an epicyclic train, this differential comprising:

-- a first input configured to be driven by said output shaft,
-- a second input driven in rotation by a first electric motor (30), and
-- An output which rotates said rotor. A circuit (10) according to claim 1, wherein the mechanical differential (22) includes:
-- a crown (24) configured to be driven by said output shaft,
-- a solar (28) driven in rotation by a first electric motor (30), and
-- satellites (32) meshed respectively with the crown and the solar and carried by a planet carrier (34) which rotates said rotor. A circuit (10) according to claim 2, wherein said carrier (34) is connected to said rotor by a second electric motor (36). A circuit (10) according to claim 3, wherein said first and second electric motors (30, 36) are interconnected by control boxes (30, 36) of the mode of operation of each motor among motor and generator modes. Circuit (10) according to one of the preceding claims, in which said lubrication unit (12) comprises several oil recovery pumps (16) whose outlets (16a) are connected to an inlet of said reservoir (18). Circuit (10) according to claim 5, in which the outlets (16a) of the recovery pumps (16) are connected to the inlet (18b) of the tank (18) by an air-oil heat exchanger (40) and/ or by an air-fuel heat exchanger (42). Circuit (10) according to one of the preceding claims, in which said planet carrier (34) is further configured to rotate a rotor of a permanent magnet alternator (44), for example by means of a first speed multiplier (46). Circuit (10) according to one of the preceding claims, in which the said planet carrier (34) is further configured to drive in rotation a rotor of a pump (48) of a fuel circuit of the turbomachine, for example through a second speed multiplier (50). Aircraft turbomachine, comprising at least one circuit (10) according to one of the preceding claims.