OIL SUPPLY DEVICE FOR A MECHANICAL REDUCTION GEAR OF AN AIRCRAFT TURBOMACHINE

Abstract

Oil supply device (22) for a mechanical reducer (10) of an aircraft turbomachine (1), this device (22) comprising an impeller (24) which has a generally annular shape around an axis (X) and which comprises: - a first annular groove (26) opening radially inwards for supplying oil to the device (22) by spraying oil into the groove (26), - first internal channels (28) for connecting the first groove (26) to ports (30) for supplying oil to the reducer (10), - a second annular groove (32) opening radially inwards for supplying oil to the device (22) by spraying oil into the groove (32), and - second channels (40) for connecting the second groove (32) to the ports (30), these second channels (40) having a minimum oil passage section (S2) less than a minimum passage section oil (S1) of the first channels (28). Figure for abstract: Figure 2

Description

Title of the invention: OIL SUPPLY DEVICE FOR A MECHANICAL REDUCER OF AN AIRCRAFT TURBO-MACHINE Technical field of the invention

[0001] The present invention relates to an oil supply device for a mechanical reducer of an aircraft turbomachine, as well as a mechanical reducer comprising such a device. Technical background

[0002] The role of a mechanical reducer is to modify the speed ratio and the torque between the input axis and the output axis of a mechanism.

[0003] New generations of dual-flow turbomachines, particularly those with a high bypass ratio, include a mechanical reducer to drive the shaft of a fan (also called a "fan"). Usually, the reducer aims to transform the so-called fast rotation speed of the shaft of a power turbine into a slower rotation speed for the shaft driving the fan.

[0004] Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called satellites, which are engaged between the sun gear and the crown gear. The satellites are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planetary gears because their axes of revolution coincide with the longitudinal axis of the turbomachine. The satellites each have a different axis of revolution and are equally distributed over the same operating diameter around the axis of the planetary gears. These axes are parallel to the longitudinal axis of the turbomachine.

[0005] There are several gearbox architectures. In the state of the art of double-flow turbomachines, the gearboxes are of the planetary or epicyclic type. In other similar applications, there are so-called differential or compound architectures.

[0006] - On a planetary reducer, the planet carrier is fixed and the crown constitutes the output shaft of the device which rotates in the opposite direction of the solar.

[0007] - On an epicyclic reducer, the crown is fixed and the planet carrier constitutes the output shaft of the device which rotates in the same direction as the solar.

[0008] - On a differential reducer, no element is fixed in rotation. The crown rotates in the opposite direction of the solar and the satellite carrier.

[0009] The reducers can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, by friction or even by magnetic fields.

[0010] There are several types of contact meshing such as with straight teeth or chevron.

[0011] Epicyclic gear reducers, in particular, have the advantage of offering significant reduction rates of rotational speed in reduced dimensions. On the other hand, like differential reducers, they have the disadvantage of having satellites which move by rotating around the axis of rotation of the drive shaft of the reducer, which is coaxial with the sun gear. They therefore require devices for transferring the oil from a reservoir and a pump located in a fixed reference to lubrication means which follow the rotational movement of the axes of the satellites around the drive shaft. To solve this problem, commonly used devices include rotating joint systems.

[0012] These systems have the disadvantages of being very bulky and of wear which is not very compatible with the service lives required for aeronautical engines, which impacts the maintenance of the engines. Finally, these reducers are not very compatible with a flexible assembly of the structure of the turbomachine, recommended for example to overcome a problem of loss or breakage of a blade of the fan propeller, or with a modular type assembly, to facilitate the assembly of the engine.

[0013] In order to overcome these drawbacks, the applicant has already proposed, in applications WO-A1-2010 / 092263, FR-A1-2 987 416, WO-A1-2019 / 16463 and WO-A1-2019 / 16491, lubrication devices without rotating seals. These devices comprise oil nozzles which are connected to an oil circuit of the fixed reference and are intended to spray oil into an annular groove of an oil supply device (called a "wheel" or "distributor") of the rotating reference. The oil supply device is integral in rotation with the planet carrier and confines the oil sprayed by the nozzles and then directs it by centrifugation towards the lubrication means of the bearings of the planets in particular.

[0014] These devices thus significantly improve the reliability of the reducer lubrication system as well as its maintenance.

[0015] Furthermore, the technical solution described in application FR-A1-3 047 279 attempts to adjust the flow of oil going to different gears according to their lubrication needs. For this, the supply device comprises two annular grooves and axially offset nozzles which supply these grooves. These grooves supply different circuits and communicate with each other by overflow.

[0016] The technical solution described in application FR-A1-3 041 054 also attempts to adjust the flow of oil going to different lubrication stations such as gears according to their lubrication needs. For this, the oil supply device is segmented into a circumferential succession of bowls arranged around the axis of rotation and nozzles supply these sections. The oil recovered by each bowl is then directed to a circuit dedicated to a particular lubrication station.

[0017] Among the parts of the reducer that are lubricated by the oil supply device are the planetary bearings. The planetary bearings support the load exerted on the planetary gears. When the bearings are of the smooth or hydrodynamic type, these bearings must be supplied with a certain quantity of oil because without oil the bearings do not function properly.

[0018] When the oil supply is cut off, the pump does not draw oil from the oil reservoir and the device is therefore no longer supplied with oil. The planet gear bearings are then no longer supplied with oil, which risks damaging them and causing premature wear of the reducer. There is therefore a need to continue to supply oil to the planet gear bearings during the phases of cut-off of the oil supply to the device. It would indeed be useful for the planet gear bearings to remain supplied with oil, even with a small quantity of oil, to maintain a film of oil between the planet gears and their bearings and prevent the planet gears from rubbing against their bearings. This would avoid a phenomenon of overheating, wear or seizure by friction, which would be dangerous for the operation of the reducer.

[0019] The invention makes it possible to meet this need in a simple, efficient and economical manner. Summary of the invention

[0020] The invention relates to an oil supply device for a mechanical reducer of an aircraft turbomachine, this device comprising an impeller which has a generally annular shape around an axis and which comprises:

[0021] - a first annular groove opening radially inwards for the oil supply to the device by spraying oil into the groove,

[0022] - first internal channels extending at least partly radially relative to to the axis and comprising radially internal ends connected to the first groove and radially external ends connected to oil supply ports of the reducer, these ports opening in the axial direction,

[0023] characterized in that it further comprises:

[0024] - a second annular groove opening radially inwards for supplying oil to the device by spraying oil into the groove, the first and second grooves being adjacent,

[0025] the second groove being connected to said ports or to said first channels or to said first groove by second channels which have a minimum oil passage section less than a minimum oil passage section of the first channels.

[0026] It is therefore understood that the two grooves of the impeller have the function of supplying oil the same ports. The first groove of the impeller is connected to the ports by first channels which are capable of supplying oil to the ports in normal operation and with a normal flow rate, which depends in particular on the minimum oil passage section of these first channels and the speed of rotation of the device around its axis. The second groove of the impeller is connected to second channels which are themselves capable of supplying oil to the ports in degraded operation, and for example in the event of a cut-off of the oil supply to the device. The second channels have a minimum oil passage section which is lower than that of the first channels so as to deliver oil with a lower flow rate but which will allow the ports to continue to be supplied with oil as long as there is oil in the second groove.In normal operation, oil may also flow from the second groove to the second channels, but the flow rate provided by these second channels is not significant compared to that delivered by the first groove and the first channels. During an oil supply interruption, only the second groove and the second channels will deliver oil at a lower flow rate. According to the invention, the second channels may be connected to the first groove, to the first channels, or directly to the ports. The .

[0027] second annular groove thus constitutes an additional reserve of oil which empties less quickly than the first annular groove constituting a main reserve of oil.

[0028] The proposed solution is compatible with a single-stage or multi-stage reducer. It is also compatible with a so-called epicyclic or differential reducer. It is also compatible with straight, helical or chevron teeth. It is also compatible with any type of planet carrier, whether monobloc or cage and cage carrier type.

[0029] The device according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another: - the minimum oil passage section of the second channels is defined by the second channels themselves; - the minimum oil passage section of the second channels is defined by flow restrictors mounted in the second channels; - the minimum oil passage section of the first channels is defined by the first channels themselves; - the ratio between the minimum oil passage section of the first channels and the minimum oil passage section of the second channels is between 2 and 10, and preferably between 3 and 5; - the first channels have an L-shape, their radially external ends being bent at right angles; - the second channels extend at least partly radially relative to the axis and have radially inner ends connected to the second groove and radially outer ends connected to the ports or the first channels; - the second channels have an L-shape, their radially external ends being bent at right angles; - the second channels extend axially between the first and second grooves.

[0030] The present invention also relates to a mechanical reducer for an aircraft turbomachine, this reducer comprising:

[0031] - a solar centered on an axis,

[0032] - a fixed crown extending around the axis and the solar,

[0033] - satellites mounted between the sun and the crown and meshed with the sun and the crown,

[0034] - a satellite carrier which supports the satellites and which is mobile in rotation around the axis, and

[0035] - a device as described above which is centered on the axis and which is fixed to the carrier- satellites, the impeller ports opening into internal lubrication cavities of the satellite bearings.

[0036] The satellites are preferably guided in rotation by bearings, of the smooth or hydrodynamic type. The internal cavities of the bearings are supplied with oil by the device for the purpose of forming oil films between the bearings and the satellites.

[0037] The present invention also relates to an assembly comprising a reducer as described above and at least one oil jet capable of spraying oil into the first and second grooves of the impeller.

[0038] A single nozzle may be capable of spraying oil into the first and second grooves. Alternatively, two separate nozzles may be capable of spraying oil into the first and second grooves respectively. Brief description of the figures

[0039] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0040] [Fig.l] [Fig.l] is a half schematic view in axial section of an aircraft turbomachine,

[0041] [Fig.2] [Fig.2] is a half axial sectional view of an epicyclic reducer,

[0042] [Fig.3] [Fig.3] is a half schematic view in axial section of a device oil supply according to one embodiment of the invention,

[0043] [Fig.4] [Fig.4] is a schematic half-view in axial section of a variant of production of the oil supply device according to the invention,

[0044] [Fig.5] [Fig.5] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention,

[0045] [Fig.6] [Fig.6] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention,

[0046] [Fig.7] [Fig.7] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention,

[0047] [Fig.8] [Fig.8] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention,

[0048] [Fig.9] [Fig.9] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention,

[0049] [Fig. 10] [Fig. 10] is a schematic half-view in axial section of an alternative embodiment of the oil supply device according to the invention. Detailed description of the invention

[0050] [Fig.l] shows a turbomachine 1 which comprises, in a conventional manner, a fan propeller S, a low pressure compressor 1a, a high pressure compressor 1b, an annular combustion chamber 1c, a high pressure turbine 1d, a low pressure turbine 1c and an exhaust nozzle 1h.

[0051] The high-pressure compressor 1b and the high-pressure turbine 1d are connected by a high-pressure shaft 2 and form with it a high-pressure (HP) body. The low-pressure compressor 1a and the low-pressure turbine 1c are connected by a low-pressure shaft 3 and form with it a low-pressure (LP) body.

[0052] The fan propeller S is driven by a fan shaft 4 which is coupled to the LP shaft 3 by means of a reducer 10 with an epicyclic gear train shown here schematically.

[0053] The reducer 10 is positioned in the front part of the turbomachine 1. A fixed structure comprising schematically, here, an upstream part 5a and a downstream part 5b is arranged so as to form an enclosure E1 surrounding the reducer 10.

[0054] This enclosure E1 is here closed upstream by seals at the level of a bearing allowing the fan shaft 4 to pass through, and downstream by seals at the level of the passage of the LP shaft 3.

[0055] With reference to [Fig. 2], the reducer 10 comprises a crown 14 which is fixed by means of a crown carrier (not shown) to the fixed structure 5a, 5b with flexible means arranged to enable it to follow the possible movements of the fan shaft 4, in certain cases of degraded operation for example. In a planetary architecture, the crown carrier is composed of a more or less flexible part which drives the crown and a part held by bearings or bearings and on which the blower is mounted. These fixing means are known to those skilled in the art and are not detailed here. A brief description can be found for example in FR-A1-2 987 416.

[0056] The reducer 10 engages on the one hand on the LP shaft 3 via splines 7 which drive a planetary or sun gear pinion 11, and on the other hand on the fan shaft 4 which is attached to a planet carrier 13. Conventionally, the sun 11, whose axis of rotation X coincides with that of the turbomachine 1, drives a series of planet gears or planets 12, which are distributed regularly on the circumference of the reducer 10. The number of planets 12 is generally defined between three and seven.

[0057] The satellites 12 also rotate around the axis X of the turbomachine 1 except in the case of a planetary architecture where they rotate only around their axes of revolution, by meshing with internal teeth of the crown 14, which is fixed to a stator of the turbomachine 1 by means of flanges 20 in the case of an epicyclic architecture or fixed to a rotor of the turbomachine in the case of the planetary architecture.

[0058] Each of the satellites 12 rotates freely around a satellite axis / bearing 16 connected to the satellite carrier 13, using a bearing which can be smooth, as shown in [Fig.2], or a rolling element bearing (ball or roller bearings).

[0059] The rotation of the satellites 12 around their satellite axes 16, due to the cooperation of their pinions with the teeth of the crown 14, causes the rotation of the planet carrier 13 around the axis X, and consequently that of the fan shaft 4 which is connected to it, at a rotation speed which is lower than that of the LP shaft 3.

[0060] [Fig. 2] shows the routing of the oil to the reducer 10 and its path inside it. Arrows show in [Fig. 2] the path followed by the oil from, in this example, a buffer tank linked to the fixed structure of the turbomachine 1, to the pinions and bearings to be lubricated.

[0061] The lubrication device comprises in particular a first part linked to the fixed structure and delivering the oil to the rotating parts of the reducer 10, and a supply device 22 rotating with the planet carrier s 13 and receiving this oil in the case of a reducer qualified as “epicyclic” (epicyclic architecture commonly called “planetary” in the English-language literature).

[0062] The device 22 comprises a wheel 24 which has a generally annular shape around the axis X and which comprises:

[0063] - a first annular groove 26 opening radially inwards for the oil supply of the device 22 by spraying oil into the groove 26,

[0064] - first internal channels 28 extending at least partly radially by relative to the X axis and comprising radially internal ends 28a connected to the first groove 26 and radially external ends 28b connected to oil supply ports 30 of the reducer 10, these ports 30 opening in the axial direction, and

[0065] - a second annular groove 32 opening radially inwards for supplying oil to the device 22 by spraying oil into the groove 32, the first and second grooves 26, 32 being adjacent.

[0066] The oil is sprayed into the grooves 26, 32 by one or more nozzles 34. The same nozzle may be capable of spraying oil into the first and second grooves 26, 32, as in the example shown. Alternatively, two separate nozzles could be capable of spraying oil into the first and second grooves 26, 32 respectively.

[0067] The first groove 26 supplies oil to the first channels 28 by centrifugation, the oil circulating in these channels 28 to the ports 30 for the purpose of lubricating the bearings of the satellites 12 in the example shown.

[0068] The first groove 26 could also be connected to other channels 36 for supplying oil to nozzles 38 for example, these nozzles 38 being located in the reducer 10 and intended to spray oil onto gears.

[0069] According to the invention, the second groove 32 is connected to the ports 30, or to the first channels 28 or to the first groove 26 by second channels 40 which have a minimum oil passage section less than a minimum oil passage section of the first channels 28.

[0070] Figures 3 to 10 illustrate several embodiments of the power supply device 22.

[0071] It is important to note that these figures show one half of an axial section of this device 22, the device 22 and its impeller 24 having a generally annular shape around the axis X.

[0072] It is also important to note that the device 22 can be in the general form:

[0073] - of a disc centered on this X axis, and comprising at its internal periphery the grooves 26, 32, the channels 28, 40 extending inside the annular wall of the disc, or

[0074] - of a ring centered on the X axis and around which arms extend radially distributed around the X axis, the grooves 26, 32 being made in the ring and the channels 28, 40 being formed inside the arms.

[0075] In Figures 3 to 10, the elements already described in the above are designated by the same references. Furthermore, the minimum oil passage section of the first channels 28 is noted S1, and the minimum oil passage section of the second channels 40 is noted S2.

[0076] The ratio SI / S2 is between 2 and 10, and preferably between 3 and 5.

[0077] In all of these figures, the first groove 26 and the ports 30 are located on the same axial side of the device 22 although this aspect is not limiting.

[0078] As in the examples shown, the first channels 28 have an L shape, their radially external ends 28b being bent at right angles.

[0079] [Fig. 3] represents a first embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by flow restrictors 42 mounted in the second channels 40.

[0080] The second channels 40 extend radially relative to the X axis and have radially inner ends 40a connected to the second groove 32 and radially outer ends 40b connected to the ports 30.

[0081] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0082] A flow restrictor 42 is mounted in each of the channels 40, in particular in its radially internal end 40a.

[0083] [Fig.4] represents an alternative embodiment in which the minimum section of oil passage S2 of the second channels 40 is defined by flow restrictors 42 mounted in the second channels 40.

[0084] The second channels 40 extend radially relative to the axis X and have radially inner ends 40a connected to the second groove 32 and radially outer ends 40b connected to the ports 30.

[0085] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0086] A flow restrictor 42 is mounted in each of the channels 40, in particular in its radially external end 40b.

[0087] [Fig. 5] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by the second channels 40 themselves.

[0088] The second channels 40 extend radially relative to the axis X and have radially inner ends 40a connected to the second groove 32 and radially outer ends 40b connected to the ports 30.

[0089] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0090] The portion 40c of each conduit 40, which extends radially outward from the end 40a, defines the section S2 which is constant over all or part of the length of this portion 40c. The portion 40d of each conduit 40, which is part of the radially outer end 40b of the conduit and which extends axially to the port 30, has a section S3 which is greater than the section S2. This section S3 is constant over all or part of the length of this portion 40d and may be close to or equal to the section SL

[0091] [Fig.6] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by the second channels 40 themselves. same.

[0092] The second channels 40 extend radially relative to the axis X and have radially inner ends 40a connected to the second groove 32 and radially outer ends 40b connected to the ports 30.

[0093] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0094] The portion 40d of each conduit 40, which is part of the radially outer end 40b of the conduit and which extends axially to the port 30, defines the section S2 which is constant over all or part of the length of this portion 40d. The portion 40c of each conduit 40, which extends radially outward from the end 40a, has a section S3 which is greater than the section S2. This section S3 is constant over all or part of the length of this portion 40d. This section S3 may be close to or equal to the section SL

[0095] [Fig.7] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by flow restrictors 42 mounted in the second channels 40.

[0096] The second channels 40 extend radially relative to the axis X and comprise radially internal ends 40a connected to the second groove 32 and radially external ends 40b connected to the first channels 28 and in particular to their radially external ends 28b.

[0097] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0098] A flow restrictor 42 is mounted in each of the channels 40, in particular in its radially internal end 40a.

[0099] [Fig.8] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by the second channels 40 themselves.

[0100] The second channels 40 extend radially relative to the axis X and comprise radially internal ends 40a connected to the second groove 32 and radially external ends 40b connected to the first channels 28 and in particular to their radially external ends 28b.

[0101] The second channels 40 have an L shape in the example shown, their radially external ends 40b being bent at right angles.

[0102] The portion 40c of each conduit 40, which extends radially outward from the end 40a, defines the section S2 which is constant over all or part of the length of this portion 40c. The portion 40d of each conduit 40, which forms part of the radially outer end 40b of the conduit and which extends axially to the channel 28, has a section S3 which is greater than the section S2. This section S3 is constant over all or part of the length of this portion 40c. part of the length of this part 40d. This section S3 can be close to or equal to the section SI.

[0103] [Fig.9] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by the second channels 40 themselves.

[0104] The second channels 40 extend axially, therefore along the axis X, between the two grooves 26, 32.

[0105] The section S2 of each channel 40 is preferably constant over its entire length.

[0106] [Fig. 10] represents an alternative embodiment in which the minimum oil passage section S2 of the second channels 40 is defined by flow restrictors 42 mounted in the second channels 40.

[0107] The second channels 40 extend axially, therefore along the axis X, between the two grooves 26, 32.

Claims

Claims

1. Oil supply device (22) for a mechanical reducer (10) of an aircraft turbomachine (1), this device (22) comprising an impeller (24) which has a generally annular shape around an axis (X) and which comprises: - a first annular groove (26) opening radially inwards for supplying oil to the device (22) by spraying oil into the groove (26), - first internal channels (28) extending at least partly radially with respect to the axis (X) and comprising radially internal ends (28a) connected to the first groove (26) and radially external ends (28b) connected to ports (30) for supplying oil to the reducer (10), these ports (30) opening in the axial direction, characterized in that it further comprises: - a second annular groove (32) opening radially inwards for the oil supply to the device (22) by spraying oil into the groove (32),the first and second grooves (26, 32) being adjacent, the second groove (32) being connected to said ports (30) or to said first channels (28) or to said first groove (26) by second channels (40) which have a minimum oil passage section (S2) less than a minimum oil passage section (SI) of the first channels (28).,

2. Device (22) according to claim 1, characterized in that the minimum oil passage section (S2) of the second channels (40) is defined by the second channels (40) themselves.

3. Device (22) according to claim 1, characterized in that the minimum oil passage section (S2) of the second channels (40) is defined by flow restrictors (42) mounted in the second channels (40).

4. Device (22) according to one of the preceding claims, characterized in that the minimum oil passage section (SI) of the first channels (28) is defined by the first channels (28) themselves.

5. Device (22) according to one of the preceding claims, characterized in that the ratio between the minimum oil passage section (SI) of the first channels (28) and the minimum oil passage section (S2) of the second channels (40) is between 2 and 10, and preferably between 3 and 5.

6. Device (22) according to one of the preceding claims, characterized in that the first channels (28) have an L shape, their radially external ends (28b) being bent at right angles.

7. Device (22) according to one of claims 1 to 6, characterized in that the second channels (40) extend at least partly radially relative to the axis (X) and comprise radially internal ends (40a) connected to the second groove (32) and radially external ends (40b) connected to the ports (30) or to the first channels (28).

8. Device (22) according to the preceding claim, characterized in that the second channels (40) have an L shape, their radially external ends (40b) being bent at right angles.

9. Device (22) according to one of claims 1 to 6, characterized in that the second channels (40) extend axially between the first and second grooves (26, 32).

10. Mechanical reducer (10) for an aircraft turbomachine (1), this reducer comprising: - a sun gear (11) centered on an axis (X), - a fixed ring gear (14) extending around the axis (X) and the sun gear (H), - satellites (12) mounted between the sun gear (11) and the ring gear (14) and meshed with the sun gear (11) and the ring gear (14), - a planet carrier (13) which supports the satellites (12) and which is rotatable around the axis (X), and - a device (22) according to one of the preceding claims which is centered on the axis (X) and which is fixed to the planet carrier (13), the ports (30) of the impeller (24) opening into internal lubrication cavities of bearings of the satellites (12).

11. Assembly comprising a reducer (10) according to claim 10 and at least one oil jet (34) capable of spraying oil into the first and second grooves (26, 32) of the impeller (24).

12. An assembly according to claim 11, wherein the same nozzle (34) is capable of spraying oil into the first and second grooves (26, 32), or two separate nozzles (34) are capable of spraying oil respectively into the first and second grooves (26, 32).

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