Lubrication for a planetary gearset

The invention concerns an epicycloidal gear train comprising a central pinion (26), an outer crown (28) and satellite pinions (32) in engagement with the central pinion (26) and the outer crown (28) and each mounted freely rotatable on a satellite carrier (36), the gear train (10) comprising means for lubricating the teeth and axes (34) of the satellite pinions (32), these means including an annular cup (56) integral with the satellite carrier (36) opened radially inward. According to the invention, an annular bailer (64) is arranged radially inside the cup (56) and applied annularly sealingly to it, the annular bailer (64) being fixed in rotation to the central pinion (26).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 filing of International Application No. PCT/FR2018/050657 filed Mar. 19, 2018, which claims the benefit of priority to French Patent Application No. 1753294 filed Apr. 14, 2017, each of which is incorporated herein by reference in its entirety.

The field of the present invention is that of turbomachinery and more particularly epicycloidal gear trains and among epicycloidal gear trains more specifically epicycloidal reducers and differential transmissions.

Typically, an epicycloidal gear train reducer consists of a planetary or central pinion, a planetary crown or outer crown and satellite pinions that are in engagement with the planetary pinion and the crown, the support of one of these three components being locked in rotation for the operation of the gear train. When the satellite carrier is fixed in rotation, the central pinion and crown are driving and driven, respectively, or vice versa. The lubrication and cooling of the gears and axes of the satellite pinions are then not a problem and are ensured by nozzles that are fixed in rotation and can project oil permanently on the meshing areas of the satellite pinions with the central pinion and with the crown and on the satellite pinion axes.

However, in the most frequent case, the outer crown is fixed in rotation and the central pinion and the satellite carrier are driving and driven, respectively. This type of set-up is preferred in cases where a reduction ratio of more than three is desired since it is less cumbersome. Lubrication of the meshing zones and satellite pinion axes is then a problem that is solved in current technology by complex networks of pressurized oil routing pipes, using dynamic seals or rotating joints that are subject to wear and which must be checked and replaced regularly.

To avoid the use of rotary joints, the applicant proposed in her application WOA12010092263 a lubrication device in which a fixed injector sprays oil into an annular cup fixed to a satellite carrier, the oil being thus recovered by centrifugation and then directed to means for lubricating the pinions.

This device greatly improves the reliability of the reducer lubrication system, as well as its maintenance. However, this device induces a dependence of the supply pressure of the lubrication means of the satellite carrier pinions on the compression that can be created between the annular cup and the lubrication means, because the spray oil supply causes a pressure failure in the lubrication circuit. In a known manner, the oil supply means are configured to provide an oil flow proportional to the rotational speed of a turbomachine shaft, for example the high-pressure compressor shaft that does not drive the central pinion of the gear train. Thus, at high rotational speeds, the oil flow is high and can be sent by centrifugation to the gears and axes of the satellite carrier. However, at low speed, the lower oil flow rate cannot be properly centrifuged by the cup due to its low rotational speed. As a result, there is insufficient oil supply during idling phases, which can lead to damage to the teeth of the satellites, outer crown and central pinion due to lack of lubrication and cooling. The oil supply failure is more critical for the satellite pinions, the outer crown and the central pinion than for the satellite axes since the outputs of the satellite gear oil supply lines, outer crown and central pinion are located at a smaller radius than the outputs of the satellite axis oil supply lines, resulting in a lower supply pressure. Finally, the lack of oil centrifugation at low rpm can lead to an accumulation of oil in the annular cup inducing an oil overflow from the cup into the enclosure that houses it.

Similarly, in another known configuration, the nozzle can be carried by the shaft carrying the central pinion so that its oil jet is directed towards the cup. This assembly suffers from the same difficulties as mentioned with a fixed nozzle assembly.

The purpose of the invention is in particular to provide a simple, effective and economical solution to the problems of the prior art described above.

To this end, it offers an epicycloidal gear train comprising a central pinion, an outer crown and satellite pinions in engagement with the central pinion and the outer crown and each mounted to be freely rotatable on a satellite carrier, the gear train comprising gear and satellite pinion axis lubrication means, these means comprising an annular cup fixed to the satellite carrier which is open radially towards the inside, characterised in that an annular bailer is arranged radially inside the cup and applied annularly sealed to it, the annular bailer being fixed in rotation to the central pinion.

The integration of an annular bailer attached to the central pinion allows the oil recovered by the bailer to be centrifuged at a higher speed than that of the satellite carrier, which increases the oil pressure of the cup supply compared to the previous technique and thus ensures a better oil supply to the teeth and axes of the satellites when operating at low satellite carrier rotation speed.

According to another characteristic of the invention, the annular bailer comprises two annular flanks connected radially outwards by a radially outer bottom wall with oil passage openings to the cup. In addition, the sides can converge towards each other towards the back wall.

The cup can include two radial annular walls whose radially inner ends are supported on annular seals mounted in annular grooves in the annular bailer.

Ring seals are, for example, split annular seals mounted circumferentially prestressed in the ring grooves. These annular seals are usually called segments. This circumferential compression assembly of the seals in the grooves makes it possible to make them integral when rotating the cup.

When the central pinion is driven in rotation by the shaft of a low-pressure compressor, it is possible to distinguish two situations, a first one corresponding to a low rotational speed of the low-pressure compressor shaft and a second one corresponding to a high rotational speed of the low-pressure compressor shaft.

In the first situation, the low rotational speed of the shaft induces a low rotation of the satellite carrier so that oil accumulates in the annular cup and in the annular bailer, which induces a pressurization of the seals on the sides of the annular grooves of the annular bailer. In the second situation, the high rotational speed of the compressor shaft induces a high rotation of the satellite carrier, as the oil no longer accumulates in the annular bailer, and avoids pressurizing the seals on the sides of the grooves of the annular bailer. Thus, the sealing provided for with the assembly according to the invention allows to limit the wear of the seals only to phases with low rotational speed corresponding to phases of idling, which is not the case with the previous technique in which the seals are subjected to permanent wear.

The annular bailer can comprise a plurality of circumferentially spaced axial partitions and delimiting a plurality of independent circumferential cavities. This allows to increase the mechanical strength of the bailer during operation. In addition, these partitions also allow a better drive in rotation of the oil.

The bailer can still include a plurality of circumferentially spaced blade pairs, the blades of a given torque extending axially opposite each other from a flank of the annular bailer. In this embodiment, the axial extent of the fins is limited and they do not touch each other so that the oil projections outside the bailer are reduced compared to the embodiment with partitions.

The invention also concerns a turbomachine comprising a gear train reducer whose central pinion surrounds and is rotationally fixed to a shaft of the turbomachine, and first fixed oil spraying means arranged radially outside the shaft and having at least one oil jet projecting oil towards the shaft in the annular space between the annular bailer and the shaft.

The oil is sprayed directly onto the shaft, then flows into the bailer and then into the cup to feed the teeth and axes of the satellite pinions.

In a particular configuration of the invention, the shaft carries an annular oil deflection wall protruding radially outwardly on the shaft and positioned axially opposite the annular bailer, the oil nozzle being oriented so as to project oil towards said deflection wall.

When the gear train reducer is mounted in a turbomachine, it is arranged in an annular chamber formed radially inside a low-pressure compressor, the satellite carrier being connected to an upstream fan wheel and the shaft being a shaft of the low-pressure compressor.

Preferably, the gear train reducer is inserted axially between an upstream and a downstream bearing supported by a stator structure of the low-pressure compressor, the upstream bearing guiding in rotation a connecting shaft from the fan wheel to the satellite carrier and the downstream bearing guiding in rotation the shaft of the low-pressure compressor.

According to another characteristic of the invention, the first fixed oil spraying means are integrated into an oil circuit further comprising second oil spraying means on the upstream and downstream bearing and a pump for simultaneous feeding of the first and second oil spraying means.

The invention is, for example, applicable to a gear train, such as a gear train in which the outer crown is fixed. In this case, the gear train can be qualified as a reducer since the output speed, i. e. that of the satellite carrier, is lower than the input speed, i. e. that of the rotating drive shaft of the central pinion. The invention also concerns a differential transmission gear train, in which the satellite carrier and the outer crown are movable in rotation in opposite directions, the satellite carrier preferably driving a first upstream fan wheel and the outer crown preferably driving a second downstream fan wheel. With such an arrangement, a double counter rotative fan assembly is obtained.

First of all, we refer toFIG. 1A, which schematically represents a reducer10according to the invention, with epicycloidal gear trains mounted in a turbomachine such as an aircraft turbojet. Specifically, the gear train10is mounted in a radially formed annular chamber12inside a low-pressure compressor14arranged downstream of a fan wheel16and upstream of a high-pressure compressor (not shown). The low-pressure compressor14comprises a plurality of rows of fixed vanes18and annular rows of moving vanes20arranged axially, along the A axis, alternately. The rows of moving vanes20are connected by an annular wall22to a low-pressure shaft24, which also rotates the vanes of a downstream low-pressure turbine (not shown).

The gear train reducer10comprises a central pinion26or planetary pinion surrounding the upstream end of the shaft24of the low-pressure compressor and integral with it, an outer crown28or planetary crown surrounding the central pinion26and fixedly connected to an annular wall30defining internally the annular flow vein of the primary air flow (arrow B) flowing in the low-pressure compressor14. The reducer10also includes satellite pinions32which are engaged by their teeth with gears of the central pinion26and the outer crown28. These satellite pinions32are mounted freely rotating on axes34of a satellite carrier36whose upstream end is connected by a connecting shaft38to the fan wheel16.

The shaft24of the low-pressure compressor14is supported and guided in rotation by a downstream ball bearing40whose outer crown40ais fixed to a first stator part42of the low-pressure compressor14connected externally to the inner annular wall30of the primary air vein. The connecting shaft38is supported and guided in rotation by two bearings44,46arranged upstream of the gear train reducer10, a first bearing44of which is arranged upstream of a second bearing46is a roller bearing, the second bearing46being a ball bearing. The outer crowns44a,46aof the first and second bearings are supported by a second stator part48of the low-pressure compressor connected externally to the inner annular wall30of the primary air vein.

The annular enclosure12of the epicycloidal gear train reducer10is thus delimited radially inwardly by the shaft24of the low-pressure compressor14, radially outwardly by the first42and second48stator parts and the inner annular wall30of the primary air vein, upstream by the first upstream bearing44and downstream by the downstream bearing40. It should be noted that the connecting shaft38also includes an annular wall50that cooperates sealingly with the upstream end52of the shaft24of the low-pressure compressor14to prevent lubricating oil leaks at this point. Similarly, to limit oil leaks, the outer ring44aof the first upstream bearing44and the outer crown40aof the downstream bearing40each have an annular portion44b,40bsealingly cooperating with the connecting shaft38and the shaft24of the low-pressure compressor10, respectively.

The rotation of the satellite pinions32in the axes34of the satellite carrier is carried out by means of plain bearings.

The epicycloidal gear train reducer10includes means for lubrication by oil spraying on the gear teeth of satellite pinions32and their axes34, these means essentially comprising an oil receiving impeller54having an annular cup56, more particularly circular in shape. The cup56has a U-shaped section here, the opening of which faces radially inwards, i. e. in the direction of the axis of rotation A. The cup56of the impeller54has a bottom wall58with holes, some of which are connected to oil supply lines60of the axes34of the satellite pinions32and others of which are connected to oil supply lines62of the contact areas between the teeth of the satellite pinions32and the teeth of the central pinion26(FIG. 1B).

According to the invention, an annular oil recovery bailer64is applied annularly sealingly to the radially inner periphery of the cup56(the annular bailer is not shown inFIG. 1B). More precisely and with reference toFIGS. 2 to 5, the cup56comprises two upstream radial annular walls56aand downstream56bwhose radially inner ring edges56c,56dare sealingly connected to radially outer ring edges64c,64dof two upstream and downstream annular walls64a,64bdefining axially an oil recovery passage of the ring bailer64. The wall64bis connected radially inward to the shaft24so as to form an annular shoulder. To achieve a watertight joint, the radially outer edges64c,64dof the annular walls64a,64bof the bailer64each include an annular groove66receiving a split annular seal68. Each split annular seal68is mounted circumferentially prestressed in an annular groove66of bailer64so that in operation the annular seals68are integral with the radially inner ends56c,56dof the radial annular walls56a,56bof the cup56and rubs on a lateral flank of a groove66of the ring bailer64when the speed of rotation is low and the bailer is filled with oil. The friction of the upstream joint occurs on the upstream flank of the upstream groove formed in the annular wall64b. The friction of the downstream joint occurs on the downstream flank of the downstream groove formed in the annular wall64a.

According to the invention, the turbomachine includes first fixed oil spraying means70comprising a plurality of oil nozzles72distributed around the A axis which are connected to a pump and an oil tank (FIG. 1A). According to an embodiment of the invention, oil nozzles72are orifices arranged on a ring surrounding the shaft24of the low-pressure compressor14.

The diameter of the nozzle72must be greater than the maximum diameter of the particles likely to block the nozzles. The diameter must also be large enough to ensure a flow of oil to the cup56and energetic enough to be straight over a distance of about 5 cm. In a practical embodiment of the invention, the oil spraying means are configured to have an outlet pressure of about 1 bar in the least favourable regimes such as idling. If you want to move the nozzle66away from the shaft24, then the oil pressure must be increased.

These nozzles72are oriented so that their oil jets (arrow C inFIGS. 1A and 2) project oil into the annular space between the shaft24and the bailer64so that the oil is recovered by the bailer64and precentrifuged in the bailer64before passing into the cup56. This ensures a good oil supply to the impeller54even when the shaft speed24is low and the oil flow is low. Indeed, in the assembly described above, the central pinion26is connected to the shaft24of the low-pressure turbine and rotates faster than the satellite carrier36carrying the cup56. The oil spray on shaft24allows an initial centrifugation of the oil on shaft24and in the bailer64, inducing an increase in the oil pressure before its introduction into the cup56of the satellite carrier36compared to the oil pressure achievable if the oil was projected directly into the cup56.

As it is better visible inFIG. 2and following, the bailer64includes an annular oil receiving cavity which is delimited by two annular flanks64e,64fforming respectively the inner faces of the radial annular walls64a,64bof the annular bailer64. These annular flanks64e,64fconverge radially outwards towards each other towards an outer annular bottom wall64gwhich includes oil passage orifices64hto the annular cup56. The annular flanks64e,64fare inclined obliquely to a radial plane separating the two annular flanks64e,64f. The annular flanks64e,64fcan be substantially symmetrical to each other with respect to this radial plane. In all configurations, the upstream flank64fis truncated with an increasing cross-section downstream and the downstream flank64eis truncated with an increasing cross-section upstream. The upstream flank64fextends radially inwards by a substantially radial annular surface64i, so as to allow the oil flowing on the shaft24to be recovered and guided towards the upstream flank64fof the bailer64.

In a second embodiment of the annular bailer64shown inFIG. 3, sides64e,64fof the bailer64are connected by axial partitions74spaced circumferentially from each other so as to delimit independent circumferential cavities or troughs.

In a third embodiment of the annular bailer64shown inFIG. 4, fin pairs76a,76bare formed in the cavity of the bailer64. Each fin pair76a,76bincludes a first fin76aextending downstream from the upstream flank64fof the annular bailer64and a second fin76bextending upstream from the downstream flank64eof the annular bailer64. Fins76a,76bextend axially opposite each other without the free ends of the fins touching each other. The axial extent of the fins76a,76bis limited so as to reduce parasitic oil projections outside the annular bailer64.

The fourth embodiment, shown inFIG. 5, corresponds to a bailer64integrating both fins76a,76band partitions74. This embodiment improves the mechanical strength of the bailer while limiting splashes.

It should be noted that the embodiment ofFIG. 2offers reduced mechanical strength compared to the embodiments inFIGS. 3, 4 and 5but does not include any obstacle to the entry of oil into the bailer at low operating speed, as is the case in the embodiments inFIGS. 4 and 5. The embodiment ofFIG. 3offers better mechanical resistance than the other embodiments as well as good centrifugation at high speed but hinders the flow of oil at high operating speed, which can lead to oil splashes at the inlet of the bailer.

In other possible embodiments, the fins could be U-shaped or V-shaped.

To ensure an optimal oil supply to the annular cup56, the oil jets of the nozzles72should preferably aim at an impact point on the shaft24which is located axially between the two annular walls64b,64aof the bailer, preferably between the annular rib78and the downstream annular wall64aof the bailer64. The direction of an oil jet from a nozzle72therefore includes a non-zero axial component directed from the nozzle72to the bailer56and a non-zero radial component directed from the nozzle72to the shaft24.

According to an embodiment, the direction of each of the jets of the nozzles72can be entirely included in a plane containing the axis of rotation A of the shaft24. The direction of the oil jets may preferably include a non-zero tangential component directed in a direction of rotation of the shaft24in order to facilitate the rotational drive of the oil. The oil impacting the shaft24has thus a non-zero tangential speed, which reduces the tangential speed difference between the oil and the shaft24, thus limiting splashes.

As shown inFIGS. 3, 4 and 5, the shaft24can carry an annular wall78deflecting the oil to the annular bailer64. This annular wall78is arranged axially in line with the annular bailer64. The face of the deflection wall78impacted by the oil could have a concave curved shape, optimized to allow a good redirection of the oil towards the annular bailer64while limiting parasitic oil projections.

Finally, with reference toFIG. 1, the turbomachine also includes second oil spraying means80on the upstream rolling bearings44,46and downstream bearing40. These first70and second80oil spraying means are integrated into the same oil circuit82which also includes a pump84.

This pump84simultaneously supplies the first oil spraying means70supplying the epicycloidal gear train reducer10and the second bearing means40,44,46.

Thus, the assembly according to the invention of an annular bailer fixed to the shaft allows to ensure a centrifugation of the oil at low speed and it is possible to have a feed pump whose operating speed does not need to be a function of the rotational speed of the shaft24driving the central pinion. In a particular configuration, the operating speed of the pump can also be chosen to be dependent on the speed of a high-pressure shaft of the turbomachine such as the high-pressure compressor shaft.