SHUTTER-ENGINE WITH SIMPLIFIED BEARING LUBRICATION UNIT

Description

DOMAINE DE L'INVENTION

[0001] The invention relates to the general field of dual-flow turbomachines, and more particularly to turbomachines having a high bypass ratio. ARRIERE-PLAN TECHNOLOGIQUE

[0002] A turbofan engine generally comprises, from upstream to downstream in the direction of gas flow, a ducted fan housed in a fan casing, an annular primary flow space and an annular secondary flow space. The air mass drawn in by the fan is therefore divided into a primary flow, which circulates in the primary flow space, and a secondary flow, which is concentric with the primary flow and circulates in the secondary flow space.

[0003] The primary flow space passes through a primary body comprising one or more compressor stages, for example a low pressure compressor and a high pressure compressor, a combustion chamber, one or more turbine stages, for example a high pressure turbine and a low pressure turbine, and a gas exhaust nozzle.

[0004] Typically, the high-pressure turbine rotates the high-pressure compressor via a first shaft, called the high-pressure shaft, while the low-pressure turbine rotates the low-pressure compressor and the fan via a second shaft, called the low-pressure shaft. The low-pressure shaft is generally housed in the high-pressure shaft, said shafts being fixed to the structural parts of the turbojet engine via bearings.

[0005] In order to improve the propulsive efficiency of the turbojet and reduce its specific consumption as well as the noise emitted by the fan, turbojets have been proposed with a high dilution ratio (bypass ratio in English, which corresponds to the ratio between the flow rate of the secondary flow (cold) and the flow rate of the primary flow (hot, which passes through the primary body)).

[0006] To achieve such bypass ratios, the fan is decoupled from the low-pressure turbine, thus enabling their respective rotational speeds to be optimized independently. For example, decoupling can be achieved using a reduction gear such as a planetary gear reduction mechanism or a star gear reduction mechanism, placed between the upstream end (relative to the direction of gas flow in the turbojet) of the low-pressure shaft and the fan. The fan is then driven by the low-pressure shaft via the reduction mechanism and an additional shaft, called the fan shaft, which is fixed between the reduction mechanism and the fan disc.

[0007] This decoupling thus makes it possible to reduce the rotational speed and the pressure ratio of the fan (fan pressure ratio in English), and to increase the power extracted by the low-pressure turbine. Thanks to the reduction mechanism, the low-pressure shaft can rotate at higher rotational speeds than in conventional turbojets.

[0008] The high-pressure shaft is attached to the engine's structural parts by means of a front bearing HP#1 and a rear bearing HP#2. The front bearing HP#1 is usually mounted on the high-pressure shaft and on the casing that connects the low-pressure compressor and the high-pressure compressor (inter-compressor casing). The rear bearing HP#2 is mounted on the high-pressure shaft and on the inter-turbine casing (i.e., on the casing extending between the casing housing the high-pressure turbine and the casing housing the low-pressure turbine).

[0009] A third HP#3 bearing can, if necessary, be provided between the front HP#1 bearing and the rear HP#2 bearing.

[0010] The low pressure shaft is generally supported by three bearings BP#1, BP#2 and BP#3. The first bearing BP#1 is located furthest upstream of the low pressure shaft and can be mounted on the one hand on the low pressure shaft and on the other hand between the reduction mechanism and the booster (on the "inlet" casing). The third bearing BP#3, which is located furthest downstream of the low pressure shaft, can be mounted on the low pressure shaft and on the exhaust casing of the turbojet. The position of the bearings BP#1 and BP#3 being conventional, it will not be detailed further in what follows.

[0011] The second bearing BP#2, which is adjacent to the third bearing BP#3, may be mounted on the low pressure shaft and on the inter-turbine casing, upstream of the low pressure turbine or on the exhaust casing like the bearing BP#3. In one embodiment, the second bearing BP#2 extends downstream of the rear bearing HP#2.

[0012] The blower shaft, which is mounted between the output of the reduction mechanism and the blower rotor, is further supported by an upstream bearing S#1 arranged below the blower and a downstream bearing S#2 arranged at the inlet of the secondary flow space, upstream of the reduction mechanism.

[0013] The turbojet engine further includes a gear configured to take power from the high-pressure shaft. This gear is usually placed upstream (and close to) the HP#1 front bearing.

[0014] These various bearings, the reduction mechanism and the gearing must be lubricated and cooled. For this purpose, the turbojet engine generally comprises a lubrication unit supplying a closed oil circuit, enclosures in which the bearings, the reduction mechanism and the gearing are housed, nozzles configured to inject oil into the enclosures and recovery pumps configured to recycle the oil that has been injected into the enclosures.

[0015] In practice, each piece of equipment (i.e. each bearing and the reduction mechanism) is housed in a respective enclosure with which one or more nozzles and at least one oil recovery pump are associated. Each enclosure comprises for this purpose bearings interposed between an inner ring and an outer ring coaxial with the X axis of the turbojet engine and substantially annular. The outer ring may be fixed relative to the structural elements of the turbojet engine while the inner ring is fixed to rotating parts of the turbojet engine and therefore mobile in rotation about its axis. Alternatively, both rings are rotating. The equipment housed in the enclosures is lubricated and cooled by oil which is sprayed into the enclosure by nozzles in order to form a mist of suspended droplets.Sealing means are provided in the areas where the rings meet to allow the passage of an air flow in order to pressurize the enclosure and retain as much oil as possible inside it. An oil recovery pump is also provided per enclosure to evacuate a volume of oil equivalent to that injected into the enclosure via the nozzles.

[0016] When the enclosure houses a bearing, the support of said bearing is for example fixed to the external ring of the enclosure.

[0017] This configuration allows for efficient lubrication and cooling of these devices. However, the enclosures and recovery pumps have a significant impact on the size and weight of the engine, thus increasing the specific consumption of the turbojet.

[0018] Document WO 2013 / 141926 describes a turbojet engine, and more particularly a system for cooling the bearing housings and shafts of the turbojet engine. Documents US 2016 / 0003142 A1 and US 2009 / 0218006 A1 describe other turbojet engines. RESUME DE L'INVENTION

[0019] An objective of the invention is therefore to propose a dual-flow turbojet engine which has a reduced mass in comparison with conventional dual-flow turbojet engines while ensuring optimal lubrication and cooling of its equipment such as its bearings and, where appropriate, its reduction mechanism.

[0020] For this, the invention provides a bypass turbojet according to claim 1. Preferred features are defined in the dependent claims. BREVE DESCRIPTION DES DESSINS

[0021] Other characteristics, aims and advantages of the present invention will appear more clearly on reading the detailed description which follows, and with regard to the appended drawings given as non-limiting examples and in which the Figures 1a à 3l are schematic and sectional views of different embodiments of a turbojet engine according to the invention, on which only a part of the turbojet engine has been shown. The examples of figures 1b , 1d , 1f, 1g And 3e-3l are not covered by the claims. DESCRIPTION DETAILLEE D'UN MODE DE REALISATION

[0022] In the following, a turbojet engine 1 will now be described with reference to the attached figures.

[0023] The turbojet engine 1 conventionally comprises a fan 2 and a primary body. The primary body comprises, in the direction of gas flow, a low-pressure compressor 3a, a high-pressure compressor 3b, a combustion chamber 4, a high-pressure turbine 5a, a low-pressure turbine 5b, and a gas exhaust nozzle.

[0024] The fan 2 comprises a fan disc provided with fan blades at its periphery which, when rotated, drive the airflow into the primary and secondary flow spaces of the turbojet engine 1. The fan disc is rotated by a low-pressure shaft 6 of the low-pressure turbine 5b.

[0025] The turbojet engine 1 has a high bypass ratio. By high bypass ratio, we mean here a bypass ratio greater than 10, for example between 12 and 18. For this, the fan 2 is decoupled from the low pressure turbine 5b to independently optimize their respective rotation speed, for example using a reduction mechanism 10 of the epicyclic or planetary type, placed between the upstream end (relative to the direction of flow of the gases in the turbojet engine 1) of the low pressure shaft 6 and the fan 2.

[0026] The blower 2 is then driven by the low pressure shaft 6 via the reduction mechanism 10 and a blower shaft 7, which is fixed between the reduction mechanism 10 and the disc of the blower 2.

[0027] To calculate the bypass ratio, the secondary flow rate and the primary flow rate are measured when the turbojet engine 1 is stationary in a standard atmosphere (as defined by the International Civil Aviation Organization (ICAO) manual, Doc 7488 / 3, 3rd edition) and at sea level.

[0028] In one embodiment, the reduction mechanism 10 comprises an epicyclic reduction mechanism 10.

[0029] The reduction ratio of the reduction mechanism 10 is preferably between 2.6 and 5.

[0030] The diameter of the blower 2 may be between eighty inches (203.2 centimeters) and one hundred and ten inches (279.4 centimeters), preferably between eighty inches (203.2 centimeters) and ninety inches (228.6 centimeters).

[0031] The fan shaft 7, the high pressure shaft 8 and the low pressure shaft 6 are centered on the X axis of the turbojet engine 1 by a series of bearings.

[0032] In this case, the fan shaft 7 is supported by the upstream bearing S#1 and the downstream bearing S#2, the high pressure shaft 8 is supported by the front bearing HP#1, the rear bearing HP#2 and, if applicable, a third bearing HP#3, while the low pressure shaft 6 is supported by the three bearings BP#1, BP#2 and BP#3. These seven or even eight bearings being conventional, they will not be described further here.

[0033] In one embodiment illustrated in the figures 1a à 2h , the low pressure shaft 6 can also be supported by a fourth bearing BP#4, placed between the first bearing BP#1, which is the most upstream bearing of the low pressure shaft 6, and the front bearing HP#1 of the high pressure shaft 8. This fourth bearing BP#4 can in particular be mounted on the low pressure shaft 6 and on the inter-compressor casing, i.e. between the booster 3a and the high pressure compressor 3b.

[0034] The mounting of the low pressure shaft 6 on four bearings BP#1-BP#4 makes it possible to efficiently move the bending modes of the low pressure shaft 6, which is supercritical (i.e. with a bending mode in the operating range), in order to position these modes in the transient regime of the turbojet engine 1 with safety margins compared to the stabilized regimes. By stabilized regime, we will understand here a regime defined by a spectrum of rotational speeds of the low pressure shaft 6 in which the turbojet engine 1 can be placed and maintained for a relatively long time (between a few minutes and several hours). Examples of stabilized regimes include in particular ground idle, flight idle, cruise or takeoff.By transient regime, we will understand here a regime corresponding to the passage from one stabilized regime to another in which the rotation speed of the low pressure shaft 6 varies rapidly. Indeed, the stabilized regimes do not cover the entire spectrum between idle and the redline (English term designating the absolute maximum speed encountered by the low pressure shaft 6 during the entire flight), so that it may be necessary, depending on the stabilized regime to be reached, to go through a transient regime to reach this stabilized regime.

[0035] Thus, thanks to the addition of the low pressure bearing BP#4, the first deformation mode of the low pressure shaft 6 is moved to approximately 8000 rpm, i.e. between the ground idle speed (which corresponds to a rotation speed of the low pressure shaft of 2000 to 4500 revolutions per minute (rpm)) and the cruising speed (which corresponds to a rotation speed of the low pressure shaft of 8500 to 9500 rpm), for a turbojet 1 having a redline between 10,000 rpm and 12,000 rpm.

[0036] It also becomes possible to reduce the diameter of the low pressure shaft 6 and therefore the size of the primary body to achieve, with the reduction mechanism 10 and the large diameter of the fan 2, a high bypass ratio for the turbojet 1. Typically, the low pressure shaft 6 may have an external diameter of less than fifty millimeters, for example less than forty-five millimeters.

[0037] This positioning of the BP#1 and BP#4 bearings also makes it possible to reduce the play consumption (radial displacement) of the 3a booster, the latter now being placed between two BP#1 and BP#4 bearings.

[0038] The turbojet 1 further comprises a gear 12 configured to take power from the high pressure shaft 8. Here, it is a bevel gear connected to a radial shaft. This gear 12 is here placed upstream of the front bearing HP#1.

[0039] The turbojet engine 1 comprises at most six AF enclosures, configured to contain the oil introduced by the nozzles in order to lubricate and cool the assembly of bearings S#1, S#2, HP#1, HP#2, BP#1-BP#4 and the reduction mechanism 10. More precisely, the turbojet engine 1 may comprise exactly three (AC), four (AD), five (AE) enclosures or six (AF) enclosures. These enclosures are illustrated schematically in the figures.

[0040] Similarly, the turbojet engine 1 comprises at most six recovery pumps (not visible in the figures), configured to recycle the oil that has been injected into the enclosures. More precisely, the turbojet engine 1 comprises at most one recovery pump per enclosure.

[0041] For this purpose, the two fan bearings S#1 and S#2 and the reduction mechanism 10, and optionally the low pressure bearing BP#1, can be housed in the same enclosure A. A recovery pump is then associated with this enclosure A. The other bearings can be housed in dedicated enclosures or, on the contrary, in several common enclosures, in order to reduce the number of enclosures required. It should be noted that for these other bearings, a maximum of one oil recovery pump per enclosure is required. Typically, the same recovery pump can be used for two enclosures, or even three enclosures.

[0042] The number of enclosures is therefore greatly reduced in comparison with the prior art, which places each piece of equipment (bearing #1, S#2, HP#1, HP#2, BP#1-BP#4 or reduction mechanism 10) in an enclosure. This reduction in the number of enclosures also makes it possible to reduce the number of recovery pumps at least as much, since such a pump was systematically associated with an enclosure in the prior art. This greatly reduces the mass of the turbojet 1, the radial and axial dimensions resulting from the presence of the AF enclosures. The lubrication circuit is also greatly simplified, due to the reduction in the number of recovery pumps.

[0043] In the examples of realization illustrated on the figures 1a à 2h , the turbojet 1 comprises two fan bearings S#1 and S#2, a reduction mechanism 10, two high pressure bearings HP#1 and HP#2 and four low pressure bearings BP#1, BP#2, BP#3 and BP#4.

[0044] The turbojet 1 can then comprise exactly three, four or five enclosures, the bearings and the reduction mechanism 10 being distributed as follows in these enclosures.

[0045] In the example embodiment illustrated on the figure 1a , the turbojet 1 comprises four AD enclosures, each enclosure comprising at most one recovery pump: an enclosure A housing the two fan bearings S#1 and S#2, the reduction mechanism 10 and the low pressure bearing BP#1, an enclosure B housing the low pressure bearing BP#4 and the front high pressure bearing HP#1. an enclosure C housing the rear high pressure bearing HP#2. an enclosure D housing the low pressure bearings BP#2 and BP#3.

[0046] In this exemplary embodiment, the turbojet engine 1 therefore comprises at most four recovery pumps, namely one recovery pump per enclosure A to D. Alternatively, the turbojet engine 1 may comprise exactly three recovery pumps, namely one pump for enclosure A, one pump for enclosure B and one pump configured to recover the oil in enclosures C and D.

[0047] The second and third low pressure bearings BP#2 and BP#3 are connected to the exhaust casing and the low pressure shaft is connected to the low pressure turbine casing.

[0048] It should be noted that, in general, when the second and third low pressure bearings BP#2 and BP#3 are housed in the same enclosure (as illustrated for example in the figure 1a , but also in the embodiments of the figures 1c , 2a , 2e , 3a , 3e And 3i), the second bearing BP#2 is preferably fixed on the exhaust casing. Furthermore, when the second low pressure bearing BP#2 and the high pressure rear bearing HP#2 are housed in the same enclosure (as illustrated for example on the figure 1e , 1f , 2b , 2f , 3b , 3f And 3j ), the second bearing BP#2 is preferably fixed on the inter-turbine casing. On the other hand, when the second low pressure bearing BP#2, the third low pressure bearing BP#3 and the rear bearing HP#2 of the high pressure shaft are housed in the same enclosure or in three separate enclosures, the second bearing BP#2 can be fixed either on the exhaust casing (as illustrated in particular on the figures 2c et 2d ) or on the inter-turbine casing (as illustrated in particular on the figures 3c et 3d ).

[0049] Optionally, the low pressure shaft is further connected to the low pressure turbine by a connection 14, between the rear bearing HP#2 and the second low pressure bearing BP#2.

[0050] In one embodiment, the turbojet engine 1 may comprise exactly three recovery pumps, namely a pump for enclosure A, a pump for enclosure B and a pump configured to recover oil in enclosures C and D.

[0051] The example of realization illustrated in figure 1b is identical to the one illustrated in figure 1a , except that the turbojet engine does not include a second low-pressure bearing BP#2. The low-pressure shaft is therefore only supported by a bearing (BP#3) in the downstream part. It is also connected to the low-pressure turbine by a connection 14, between the rear bearing HP#2 and the third low-pressure bearing BP#3. In this exemplary embodiment, the turbojet engine 1 therefore includes at most four recovery pumps, namely one recovery pump per enclosure A to D. Alternatively, the turbojet engine 1 may include exactly three recovery pumps, namely a pump for enclosure A, a pump for enclosure B and a pump configured to recover the oil in enclosures C and D.

[0052] The examples of realization illustrated in figure 1c And 1d are identical to those illustrated in figure 1a et 1b , respectively, except that the low pressure bearing BP#4 and the front high pressure bearing HP#1 are housed in separate enclosures E and B. In this exemplary embodiment, the turbojet 1 may comprise a recovery pump per enclosure E, B or alternatively a single recovery pump for these two enclosures E, B.

[0053] The example of realization illustrated in figure 1e is identical to the one illustrated in figure 1a , except that the low pressure bearing BP#2 is placed in enclosure C (with the rear bearing HP#2) and is connected to the interturbine casing. In this exemplary embodiment, the turbojet engine 1 therefore comprises at most four recovery pumps, namely one recovery pump per enclosure A to D. In one embodiment, the turbojet engine 1 may comprise exactly three recovery pumps, namely one pump for enclosure A, one pump for enclosure B and a pump configured to recover the oil in enclosures C and D.

[0054] The example of realization illustrated in figure 1f is identical to the one illustrated in figure 1e , except that the turbojet engine does not include a third low pressure bearing BP#3. In this embodiment, the turbojet engine 1 therefore includes at most three recovery pumps, namely one recovery pump per enclosure A to C.

[0055] The example of realization illustrated in figure 1g is identical to the one illustrated in figure 1f , except that the rear high pressure bearing HP#2 and the second low pressure bearing BP#2 are each placed in a respective enclosure C and D. In this exemplary embodiment, the turbojet engine 1 therefore comprises four enclosures AD, each enclosure comprising at most one recovery pump. In one embodiment, the turbojet engine 1 may comprise exactly three recovery pumps, namely a pump for enclosure A, a pump for enclosure B and a pump configured to recover the oil in enclosures C and D.

[0056] Alternatively, an exemplary embodiment (not shown) identical to that illustrated in figure 1e is also possible with the only modification compared to the figure 1e the fact that the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3 are placed in a single enclosure. If necessary, the second low pressure bearing BP#2 can be connected either to the inter-turbine casing or to the exhaust casing. In this exemplary embodiment, the turbojet 1 therefore comprises three enclosures AC, each enclosure comprising at most one recovery pump.

[0057] Alternatively, another exemplary embodiment (not shown) identical to that illustrated in figure 1e is also possible with the only modification compared to the figure 1e the fact that the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3 are each placed in a dedicated enclosure. If necessary, the second low pressure bearing BP#2 can be connected either to the inter-turbine casing or to the exhaust casing. In this exemplary embodiment, the turbojet engine 1 therefore comprises five enclosures AE, each enclosure comprising at most one scavenge pump. Alternatively, the turbojet engine could comprise exactly 3 or 4 scavenge pumps, using a single scavenge pump to recover the oil from enclosures C and D, or D and E, or C, D and E.

[0058] It should be noted that, whatever the embodiment, the low pressure bearing BP#4 and the front high pressure bearing HP#1 can be housed either in the same enclosure B, or in separate enclosures (as illustrated in the figures 1c And 1d). Thus, it is possible to obtain a turbojet engine comprising up to six AF enclosures (i.e. a turbojet engine 1 comprising three enclosures A, B and F upstream of the combustion chamber, as illustrated in the figure 1c , and three enclosures C, D and E downstream, as illustrated in particular on the figures 2c And 3c ).

[0059] In the example embodiment illustrated on the figure 2a , the turbojet 1 comprises four AD enclosures, each enclosure comprising at most one recovery pump: an enclosure A housing the two fan bearings S#1 and S#2, the reduction mechanism 10 and the low pressure bearings BP#1 and BP#4. an enclosure B housing the front high pressure bearing HP#1. an enclosure C housing the rear high pressure bearing HP#2. an enclosure D housing the low pressure bearings BP#2 and BP#3.

[0060] The second and third low pressure bearings BP#2 and BP#3 are connected to the exhaust casing. In addition, the low pressure shaft is connected to the low pressure turbine casing, between the rear high pressure bearing HP#2 and the second low pressure bearing BP#2.

[0061] In one embodiment, the turbojet engine 1 may comprise exactly three recovery pumps, namely a pump for enclosure A, a pump for enclosure B and a pump configured to recover oil in enclosures C and D.

[0062] This example of realization is therefore identical to that illustrated in figure 1e , except that the low pressure bearing BP#4 is placed in enclosure A rather than in enclosure B.

[0063] The example of realization illustrated in figure 2b is identical to the one illustrated in figure 2a , except that the low pressure bearing BP#2 is placed in enclosure C, that the second low pressure bearing BP#2 is connected to the inter-turbine casing and that the connection 14 optionally extends between the second BP#2 and the third low pressure bearing BP#3. The turbojet 1 can therefore comprise at most four recovery pumps, namely one recovery pump per enclosure A to D, or alternatively exactly three recovery pumps, using a single pump to recover the oil in enclosures C and D.

[0064] The example of realization illustrated in figure 2c is identical to the one illustrated in figure 2a , except that the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3 are each placed in a respective enclosure C, D, E. Alternatively, the second low pressure bearing BP#2 could be connected to the inter-turbine casing. In this exemplary embodiment, the turbojet engine 1 therefore comprises five enclosures AE, each enclosure comprising at most one scavenge pump. Alternatively, the turbojet engine could comprise exactly 3 or 4 scavenge pumps, using a single scavenge pump to recover the oil from enclosures C and D, or D and E, or C, D and E.

[0065] The example of realization illustrated in figure 2d is identical to the one illustrated in figure 2a , except that the turbojet 1 only comprises enclosures A, B and C, enclosure C housing the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3. Alternatively, the second low pressure bearing BP#2 could be connected to the inter-turbine casing. In this exemplary embodiment, the turbojet 1 therefore comprises at most three recovery pumps, namely one recovery pump per enclosure A to C.

[0066] The examples of realization illustrated in figure 2e à 2h are identical to those illustrated in figures 2a à 2d respectively, except that the low pressure bearing BP#4 is supported by the inlet casing (just like the low pressure bearing BP#1), i.e. by the casing which extends between the fan 2 and the booster 3a.

[0067] Optionally, the turbojet 1 may not include a second low pressure bearing BP#2 or a third low pressure bearing BP#3, in a manner similar to what has been described and illustrated with reference to figures 1b , 1d , 1f et 1g .

[0068] In the example embodiment illustrated on the figures 3a à 3c , the turbojet 1 comprises two fan bearings S#1 and S#2, a reduction mechanism 10, two high pressure bearings HP#1 and HP#2 and exactly three low pressure bearings BP#1, BP#2 and BP#3.

[0069] In the example embodiment illustrated on the figure 3a , turbojet 1 includes four AD enclosures: an enclosure A housing the two fan bearings S#1 and S#2, the reduction mechanism 10 and the low pressure bearing BP#1, an enclosure B housing the front high pressure bearing HP#1. an enclosure C housing the rear high pressure bearing HP#2. an enclosure D housing the low pressure bearings BP#2 and BP#3.

[0070] In this exemplary embodiment, the turbojet engine 1 comprises at most four recovery pumps, namely one recovery pump per enclosure A to D. Alternatively, the turbojet engine 1 could comprise exactly 3 pumps, using a single recovery pump to recover the oil from enclosures C and D.

[0071] The second and third low pressure bearings BP#2 and BP#3 are connected to the exhaust casing. In addition, the low pressure shaft is connected to the low pressure turbine casing, between the rear high pressure bearing HP#2 and the second low pressure bearing BP#2.

[0072] The example of realization illustrated in figure 3b is identical to the one illustrated in figure 1a , except that the low pressure bearing BP#2 is placed in enclosure C (with the high pressure rear bearing HP#2) and that the second low pressure bearing BP#2 is connected to the inter-turbine casing and that the connection 14 optionally extends between the second BP#2 and the third low pressure bearing BP#3. In this exemplary embodiment, the turbojet engine 1 comprises at most four recovery pumps, namely one recovery pump per enclosure A to D. Alternatively, the turbojet engine 1 could comprise exactly three pumps, using a single recovery pump to recover the oil from enclosures C and D.

[0073] The example of realization illustrated in figure 3c is identical to the one illustrated in figure 3b , except that the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3 are each placed in a respective enclosure C, D, E. Alternatively, the second low pressure bearing BP#2 could be connected to the exhaust casing, in which case the connection 14 optionally extends between the rear high pressure bearing HP#2 and the second low pressure bearing BP#2. In this exemplary embodiment, the turbojet engine 1 comprises at most five enclosures AE, each enclosure comprising at most one scavenge pump. Alternatively, the turbojet engine could comprise exactly three or four scavenge pumps, using a single scavenge pump to recover oil from enclosures C and D, or D and E, or C, D and E.

[0074] The example of realization illustrated in figure 3d is identical to the one illustrated in figure 3b , except that turbojet 1 only comprises enclosures A, B and C, enclosure C housing the rear high pressure bearing HP#2 and the low pressure bearings BP#2 and BP#3. In this embodiment, turbojet 1 comprises exactly three recovery pumps.

[0075] The examples of realization illustrated in figure 3e à 3h are identical to those illustrated in figure 3a à 3d , respectively, except that the low pressure bearing BP#1 is not placed in enclosure A, but in a separate enclosure F, upstream of enclosure B of the high pressure front bearing HP#1.

[0076] The examples of realization illustrated in figure 3i à 3l are identical to those illustrated in figure 3a à 3d , respectively, except that the low pressure bearing BP#1 is this time placed in the same enclosure B as the front high pressure bearing HP#1, and no longer in the front enclosure A or in the enclosure F.

[0077] In one embodiment, the high pressure shaft 8 may further comprise a third high pressure bearing (not visible in the figures), placed between the front bearing HP#1 and the rear bearing HP#2. In this case, whatever the embodiment, the bearing HP#3 is placed in the vicinity of the front high pressure bearing HP#1, or even housed in the enclosure B with the front high pressure bearing HP#1.

[0078] Optionally, whatever the embodiment, the enclosure which houses the front bearing HP#1 (generally, enclosure B) also houses the gear 12 configured to take the power from the high pressure shaft 8. This configuration thus makes it possible to share the lubrication of the gear in question and the front bearing HP#1.

[0079] In an exemplary embodiment, the front bearing HP#1 of the high pressure shaft 8 comprises a ball bearing while the rear bearings HP#2 and HP#3 comprise roller bearings.

[0080] Also optionally, regardless of the embodiment, the second low pressure bearing BP#2 can be omitted. In this case, the low pressure shaft is supported by a single rear bearing (BP#3) and one or two front bearings (BP#1 and BP#4).

[0081] The S#1 fan front bearing may be of the roller bearing type and comprise a coaxial inner ring and outer ring between which rollers are mounted.

[0082] The rear fan bearing S#2 may be of the ball bearing type and comprise a coaxial inner ring and outer ring between which balls are mounted.

[0083] For comparison, in the prior art, the front fan bearing S#1 and the rear fan bearing S#2 each comprise a tapered roller bearing, which are dynamically comparable to a single bearing. In contrast, the implementation of a roller bearing and a ball bearing for the front fan bearing and the rear fan bearing respectively thus allows for two "real" bearings, thus allowing for more precise rotational guidance.

[0084] The low pressure bearing BP#1 may be of the ball bearing type and comprise a coaxial inner ring and outer ring between which balls are mounted.

[0085] The low pressure bearings BP#2, BP#3 and where applicable BP#4 can be of the roller bearing type.

[0086] Enclosures A to C (and where applicable enclosures D and E) can be ventilated or non-ventilated.

[0087] By non-vented enclosure, we mean here an enclosure that is not directly in fluid communication with the open air and that does not include a degassing tube. For this purpose, an oil recovery pump connected to a recovery port can be placed at the low point of the engine in order to recover the oil and air from the non-vented enclosure and thus create an air suction through the seals of the enclosure. The pump advantageously has a pumping flow rate greater than that of the oil inlet in the enclosure allowing the lubrication of the bearing(s) and where applicable the reduction mechanism 10. In this case, it is preferable to have an air flow through the two upstream and downstream seals, in order to retain the oil at the two seals.Furthermore, in order for there to be air flows through both seals of the oil chamber, it is preferable that the pressure upstream of the two seals is substantially equal in order to avoid the formation of a preferential path of the air flow which would compromise the sealing performance of one of the seals.

[0088] A vented enclosure is understood here to mean an enclosure capable of being in communication with the open air while being maintained at a pressure close to atmospheric pressure. The bearings inside such enclosures are bathed in an oil mist which is continuously extracted from the enclosure by a degassing tube, the air and oil then being separated in an oil separator. In such an enclosure, the recovery pump has a pumping flow rate substantially equal to that of the oil supply to the enclosure (via the nozzles). Furthermore, it is possible to have air flows passing through the upstream and downstream seals of the enclosure, said air flows having a pressure greater than or equal to that prevailing in the enclosure.

[0089] In one embodiment, when the enclosure comprises at most two seals, the enclosure is preferably non-ventilated. Similarly, when the enclosure comprises more than two seals, the enclosure is ventilated.

[0090] Typically, regardless of the embodiment, enclosure A is preferably ventilated to the extent that it systematically comprises a first seal corresponding to the interface between the rotor of the blower 2 and the blower casing 2 (enclosure A housing the blower bearings S#1 and S#2), a second interface between the blower shaft 7 and the low pressure shaft 6 (enclosure A housing the reduction mechanism 10) and a third interface between the low pressure shaft 6 and the inter-compressor casing (enclosure A housing the low pressure bearing BP#1). This enclosure A therefore necessarily comprises a dedicated recovery pump.

[0091] In the examples of realization illustrated in figures 1c ,2c , 2g , 3c , 3g And 3k , the rear bearings HP#2, BP#2 and BP#3 are each housed in a respective enclosure C, D and E. These enclosures C, D and E can therefore be non-ventilated. Furthermore, for these enclosures and as described with reference to the figures above, the recovery pumps can (optionally) be shared, that is to say that the lubrication group comprises at most three recovery pumps to recover the oil in these three enclosures C, D and E, preferably exactly two recovery pumps, or even a single recovery pump.

[0092] On the other hand, in the examples of realization illustrated in figures 2d , 2h , 3d , 3h And 3l , the rear bearings HP#2, BP#2 and BP#3 are all three housed in the same enclosure C, which is therefore preferably ventilated. In this case, a recovery pump is associated with this enclosure C.

[0093] In the examples of realization illustrated on the figures 1c , 1d , 2a-2h And 3a-3h , enclosures B can be non-ventilated, these only including the high pressure front bearing HP#1. In this case, a recovery pump is associated with this enclosure B.

[0094] In the examples illustrated on the figures 1a-1d , 1g , 2a , 2e , 3a , 3e and (respectively 1b , 1d , 1e , 2b , 2f , 3b , 3f And 3j) enclosure C (respectively enclosure D) houses only the high pressure rear bearing HP#2 (respectively only the rear bearing BP#3) and can therefore be unventilated, while enclosure D (respectively enclosure C) houses two bearings and can therefore be ventilated or unventilated. Recovery pumps can therefore be shared for these enclosures, in which case the lubrication group includes fewer recovery pumps than there are enclosures.

[0095] Optionally, in the examples of embodiment illustrated in figures 1a-1d , enclosures B can be ventilated as long as they house the two bearings (BP#1 and HP#1).

[0096] The use of non-ventilated enclosures has the advantage of reducing the consumption of air taken from the high-pressure compressor 3b, and therefore of increasing the quantity of air entering the combustion chamber 4, thus improving the performance of the turbojet 1. However, non-ventilated enclosures cannot be used everywhere because, beyond two seals, it is difficult to maintain pressure balance upstream of the seals.

Claims

1. A dual-flow turbojet engine (1) comprising : - a low-pressure shaft (6) supported by at least two low-pressure bearings (BP#1-BP#4), - a high-pressure shaft (8) supported by at least one front high-pressure bearing (HP#1) and one rear high-pressure bearing (HP#2), - a fan shaft (7) supported by at least two fan bearings (S#1, S#2), and - a reduction mechanism (10), coupling the low-pressure shaft (6) and the fan shaft (7), the turbojet engine (1) further comprising at most six enclosures (A-F) housing the low-pressure bearings (BP#1-BP#4), the high-pressure bearings (HP#1, HP#2), the fan bearings (S#1, S#2) and the reduction mechanism (10), the low-pressure shaft (6) being supported by at least three low-pressure bearings (BP#1-BP#4), the fan bearings (S#1, S#2), the reduction mechanism (10) and at least one low-pressure bearing (BP#1) being housed in a same enclosure (A), which is ventilated, and the rear high-pressure bearing (HP#2) and two further low-pressure bearings (BP#2, BP#3), which are rear low-pressure bearings, being housed in non-ventilated enclosures (C, D, E).

2. A turbojet engine (1) according to claim 1, comprising at most five enclosures (A-F).

3. A turbojet engine (1) according to any one of claims 1 or 2, wherein each enclosure comprises at most one scavenge pump.

4. A turbojet engine (1) according to any one of claims 1 to 3, wherein the low-pressure shaft (6), the high-pressure shaft (8) and the fan shaft (7) are supported by eight or nine bearings (S#1, S#2, HP#1, HP#2, BP#1-BP#4) in all.

5. A turbojet engine (1) according to any one of claims 1 to 4, wherein the low-pressure bearings (BP#1-BP#4) comprise a front low-pressure bearing (BP#1, BP#4) and a rear low-pressure bearing (BP#2, BP#3), the rear high-pressure bearing (HP#2) and the rear low-pressure bearing (BP#2, BP#3) each being housed in separate enclosures (C, D).

6. A turbojet engine (1) according to any one of claims 1 to 4, wherein the low-pressure bearings (BP#1-BP#4) comprise a front low-pressure bearing (BP#1, BP#4) and a rear low-pressure bearing (BP#2, BP#3), the rear high-pressure bearing (HP#2) and the rear low-pressure bearing (BP#2, BP#3) being housed in the same enclosure (C).

7. A turbojet engine (1) according to any one of claims 1 to 6, wherein a first and a second of said low-pressure bearings (BP#1, BP#4) are positioned between the fan bearings (S#1, S#2) and the high-pressure bearings (HP#1, HP#2).

8. A turbojet engine (1) according to any one of claims 1 to 7, wherein the low-pressure shaft (6) is supported by four low-pressure bearings (BP#1-BP#4), a first and a second of the low-pressure bearings (BP#1, BP#4) being positioned between the fan bearings (S#1, S#2) and the high-pressure bearings (HP#1, HP#2), while a third and a fourth of the low-pressure bearings (BP#2, BP#3) are positioned downstream of the high-pressure bearings (HP#1, HP#2), upstream and downstream being defined along a direction of gas flow in the turbojet engine (1).

9. A turbojet engine (1) according to any one of claims 1 to 8, having a bypass ratio greater than or equal to 10, preferably greater than or equal to 18, for example between 12 and 18.

10. A turbojet engine (1) according to any one of claims 1 to 9, wherein the reduction mechanism (10) comprises a planetary reduction mechanism (10) having a reduction ratio between 2.6 and 5.

11. A turbojet engine (1) according to any one of claims 1 to 10, wherein the fan bearings comprise a front bearing (S#1) and a rear bearing (S#2), the front bearing (S#1) comprising a roller bearing comprising an inner ring and a coaxial outer ring between which rollers are mounted while the rear bearing (S#2) comprises a ball bearing comprising an inner ring and a coaxial outer ring between which balls are mounted.

12. A turbojet engine according to any one of claims 1 to 11, wherein the fan bearings (S#1, S#2) and the reduction mechanism are housed in one and the same enclosure (A) associated with a scavenge pump.