Dual circuit lubrication method and device with increased reliability for a main power transmission gearbox of an aircraft

Abstract

A dual circuit lubrication device for lubricating a mechanical system, the lubrication device being provided with two independent lubrication circuits and a tank that is common to both lubrication circuits and that contains a lubrication liquid. A first lubrication circuit has two first suction points for sucking in the lubrication liquid and situated inside the tank, and a second lubrication circuit includes a second suction point for sucking in the lubrication liquid and situated inside the tank. The dual circuit lubrication device has means for detecting the lubrication liquid passing below a limit depth in the tank, which means are formed by a high first suction point situated at the level of the limit depth, the second suction point being situated below the limit depth, and a low first suction point being below the second suction point.

Claims

1. A dual circuit method of lubricating a mechanical system that includes a tank containing a lubrication liquid, the method comprising: using the lubrication liquid to lubricate the mechanical system simultaneously via a first lubrication circuit and a second lubrication circuit, the second lubrication circuit having a second suction point situated below a limit depth in the tank, the first lubrication circuit including at least one first suction point that can be situated below the second suction point; detecting a drop in the level of the lubrication liquid in the tank to below the limit depth; stopping the flow of the lubrication liquid in the first lubrication circuit; measuring the pressure of the lubrication liquid in the second lubrication circuit; detecting a drop of the pressure of the lubrication liquid in the second lubrication circuit; reestablishing the flow of the lubrication liquid in the first lubrication circuit; and stopping the flow of the lubrication liquid in the second lubrication circuit.

2. A lubrication method according to claim 1, wherein the first lubrication circuit includes a first valve, the first valve is operated as a result of the drop of the level of the lubrication liquid in the tank below the limit depth, and the flow of the lubrication liquid in the first lubrication circuit is stopped by means of the first valve.

3. A lubrication method according to claim 1, wherein the first lubrication circuit includes a first valve, the first valve is operated on detecting a drop in the pressure of the lubrication liquid in the second lubrication circuit, and the flow of the lubrication liquid in the first lubrication circuit is reestablished by means of the first valve.

4. A lubrication method according to claim 1, wherein the first lubrication circuit includes a first pump, the flow of the lubrication liquid in the first lubrication circuit is stopped by stopping the pump, and the flow of the lubrication liquid in the first lubrication circuit is reestablished by restarting the first pump.

5. A lubrication method according to claim 1, wherein the second lubrication circuit includes a second pump and the flow of the lubrication liquid in the second lubrication circuit is stopped by stopping the second pump.

6. A lubrication method according to claim 1, wherein the second lubrication circuit includes a second valve, the second valve is operated on detecting a drop in the pressure of the lubrication liquid in the second lubrication circuit, and the flow of the lubrication liquid in the second lubrication circuit is stopped by means of the valve.

7. A lubrication method according to claim 1, wherein the drop in the level of the lubrication liquid to below the limit depth in the tank is detected by detecting a drop of the pressure of the lubrication liquid in the first lubrication circuit.

8. A lubrication method according to claim 1, wherein the drop of the level of the lubrication liquid to below the limit depth in the tank is detected by means of a liquid presence sensor situated in the tank at the level of the limit depth.

9. A lubrication method according to claim 1, wherein after detecting the drop of the pressure of the lubrication liquid in the second lubrication circuit, the lubrication liquid is delivered into the first lubrication circuit via a first suction point situated in the tank below the limit depth.

10. A lubrication method according to claim 1, wherein, after reestablishing the flow of the lubrication liquid in the first lubrication circuit, the pressure of the lubrication liquid in the first lubrication circuit is measured.

11. A dual circuit lubrication device for lubricating a mechanical system, the lubrication device having a tank and two lubrication circuits, the tank containing a lubrication liquid, a first lubrication circuit comprising a first pump, first pipes, a first pressure sensor, first nozzles, and at least one first suction point for sucking the lubrication liquid, each first suction point being situated in the tank, a second lubrication circuit comprising a second pump, second pipes, a second pressure sensor, second nozzles, and a second suction point for sucking the lubrication liquid, the second suction point being situated in the tank, each pump acting via the first and second suction points to deliver the lubrication liquid respectively into the first and second pipes, and then into the first and second nozzles in order to lubricate the mechanical system, wherein the dual circuit lubrication device includes detector means for detecting the lubrication liquid passing below the limit depth in the tank, the second suction point being situated below the limit depth, the lubrication device implementing the lubrication method according to claim 1.

12. A lubrication device according to claim 11, wherein the first lubrication circuit has two first suction points and a first valve connecting the first pump to the two first suction points, the detector means being formed by a high first suction point and the first pressure sensor, the high first suction point being situated at the level of the limit depth, and a low first suction point being situated at a low position situated below the second suction point.

13. A lubrication device according to claim 12, wherein the first valve is a two-position valve putting the first pump into communication with one or the other of the first suction points, the first valve being operated by the second pressure sensor.

14. A lubrication device according to claim 12, wherein the first valve is a three-position valve enabling the lubrication liquid to flow between the first pump and one or the other of the first suction points in order to enable the lubrication liquid to flow in the first lubrication circuit, or else interrupting the flow of the lubrication liquid in the first lubrication circuit, the first valve being operated by the first pressure sensor and the second pressure sensor.

15. A lubrication device according to claim 11, wherein the first lubrication circuit includes a single first suction point that is movable, the detector means being formed by the first suction point and the first pressure sensor, the first suction point being movable in the tank between the limit depth and a low position situated below the second suction point.

16. A lubrication device according to claim 11, wherein the first lubrication circuit includes a single first suction point and a liquid presence sensor, the detector means being formed by the liquid presence sensor positioned in the tank at the level of the limit depth, the first suction point being situated at the level of a low position below the second suction point.

17. A lubrication device according to claim 16, wherein the first lubrication circuit includes a two-position first valve enabling the lubrication liquid to flow between the first pump and the first suction point and then in the first lubrication circuit, or else interrupting the flow of the lubrication liquid in the first lubrication circuit, the first valve being operated by the liquid presence sensor.

18. A lubrication device according to claim 11, wherein the second lubrication circuit includes a two-position second valve enabling the lubrication liquid to flow between the second pump and the second suction point and then into the second lubrication circuit or else interrupting the flow of the lubrication liquid in the second lubrication circuit, the second valve being operated by the second pressure sensor.

19. A lubrication device according to claim 11, wherein the mechanical system is a main power transmission gearbox of a rotary wing aircraft.

20. A main power transmission gearbox for a rotary wing aircraft, wherein the main power transmission gearbox is provided with a lubrication device according to claim 19, the tank being constituted by a casing of the main power transmission gearbox.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the context of the following description of examples given by way of illustration with reference to the accompanying figures, in which:

(2) FIGS. 1 to 3 show variants of a first embodiment of the dual circuit lubrication device;

(3) FIG. 4 shows a second embodiment of the dual circuit lubrication device; and

(4) FIG. 5 is a diagram summarizing a dual circuit lubrication method.

DETAILED DESCRIPTION OF THE INVENTION

(5) Elements that are present in more than one of the figures are given the same references in each of them.

(6) The purpose of dual circuit lubrication devices 1 as shown in FIGS. 1 to 4 is to lubricate a mechanical system 3 including in particular rotary elements 5, such as shafts and bearings, together with elements for transmitting power and for reducing or increasing speed, such as gearing. By way of example, the mechanical system 3 may be a main power transmission gearbox of a rotary wing aircraft.

(7) Each dual circuit lubrication 1 has a tank 2 and two lubrication circuits 10, 20 serving simultaneously to lubricate the mechanical system 3. The tank 2 is formed by a casing of the mechanical system 3 and it contains a lubrication liquid such as oil. Each lubrication circuit 10, 20 includes a pump 11, 21, a pressure sensor 12, 22, a heat exchanger 13, 23, a filter 15, 25, spray nozzles 14, 24, at least one suction point 16, 17, 27, and pipes respectively connecting together the components in each lubrication circuit 10, 20. The second lubrication circuit 20 has a single second suction point 27, where the first lubrication circuit 10 may have one or else two first suction points 16, 17. The suction points 16, 17, 27 are situated inside the tank 2, with the second suction point 27 being positioned in an intermediate position B in the tank 2.

(8) Each pump 11, 21 serves to draw lubrication liquid from the tank 2 via a suction point 16, 17, 27 and to deliver the lubrication liquid into the corresponding lubrication circuit 10, 20. Each heat exchanger 13, 23 serves to cool the lubrication liquid before it reaches the nozzles 14, 24 after passing through the filters 15, 25. The nozzles 14, 24 are specific and distinct for each lubrication circuit 10, 20, however they could nevertheless coincide and be common to both lubrication circuits 10, 20.

(9) In a first variant of a first embodiment of the dual circuit lubrication device 1 as shown in FIG. 1, the first lubrication circuit 10 has two first suction points 16, 17 and a two-position first valve 19. This first valve 19 serves to connect the first pump 11 to one or the other of the two first suction points 16, 17 in order to deliver the lubrication liquid into the first lubrication circuit 10. A high first suction point 16 and a low first suction point 17 are situated respectively in a high position A and in a low position C inside the tank 2. The low position C is at the bottom of the tank 2 and the intermediate position B is situated between the high position A and the low position C.

(10) A second variant of the first embodiment of the dual circuit lubrication device 1, as shown in FIG. 2, differs from the first variant in two respects. The two-position first valve 19 is replaced by a three-position first valve 19 serving to connect the first pump 11 with one or the other of the first suction points 16, 17 so that lubrication liquid flows into the first lubrication circuit 10, or else interrupting this flow of lubrication liquid into the first lubrication circuit 10. This first valve 19 controls both the suction and the delivery of the first pump 11, a first secondary valve 19′ connected to the first valve 19 being on the delivery side of the first pump 11. This first valve 19 thus serves either, when in a first position, to deliver the lubrication liquid into the first lubrication circuit 10 via the high first suction point 16, or, when in a closed second position, to prevent any flow of lubrication liquid into the first lubrication circuit 10, or else, when in a third position, to deliver the lubrication liquid into the first lubrication circuit 10 via the low first suction point 17.

(11) In the secondary first valve 19′, the first and third positions put the delivery from the first pump 11 into communication with the first lubrication circuit 10, thus enabling the lubrication liquid leaving the first pump 11 to reach the first nozzle 14. In contrast, in the second position, the secondary first valve 19′ puts the delivery from the first pump 11 into communication with a first return pipe 31, enabling the lubrication liquid leaving the first pump 11 to return to the tank 2. Furthermore, the second and third positions of the first valve 19 proper are connected to the low first suction point 17, whereas the first position is connected to the high first suction point 16.

(12) These first and third positions of the first valve 19 in this second variant correspond likewise to the two positions of the first valve 19 in the first variant. By default, the first valve 19 is in the first position in both the first and second variants.

(13) Furthermore, the second lubrication circuit 20 has a two-position second valve 29 serving to connect the second pump 21 to the second suction point 27 so that the lubrication liquid flows into the second lubrication circuit 20 or else so that this flow of lubrication liquid into the second lubrication circuit 20 is cut off. By default, the second valve 29 is in an open position connecting the delivery from the second pump 21 to the second lubrication circuit 20, thus enabling the lubrication liquid leaving the second pump 21 to reach the second nozzles 24. A closed position of this second valve 29 connects the delivery from the second pump 21 to a second return pipe 32, enabling the lubrication liquid leaving the second pump 21 to return to the tank 2.

(14) A third variant of the first embodiment of the dual circuit lubrication device 1 is shown in FIG. 3. This third variant differs from the first variant by the presence of a single first suction point 16 and the absence of a first valve 19. This first suction point 16 is movable inside the tank 2 between the high position A and the low position C.

(15) In addition, the first and second pumps 11, 21 are situated inside the mechanical system 3 and above the tank 2. As a result, if there is a leak from a pump 11, 21, the lubrication liquid returns into the tank 2, thus avoiding discharging some of the lubrication liquid from the tank 2.

(16) In a second embodiment of the dual circuit lubrication device, as shown in FIG. 4, the first lubrication circuit 10 has a single first suction point 16, a liquid presence sensor 18, and a two-position first valve 19. This first valve 19 serves to connect the first pump 11 to the first suction point 16 so that the lubrication liquid flows into the first lubrication circuit 10 or else to interrupt this flow of lubrication liquid into the first lubrication circuit 10. The open position of this first valve 19 puts the delivery from the first pump 11 into communication with the first lubrication circuit 10, thereby enabling the lubrication liquid leaving the first pump 11 to reach the first nozzle 14. The closed position of this first valve 19 puts the delivery from the first pump 11 into communication with a first return pipe 31 enabling the lubrication liquid leaving the first pump 11 to return to the tank 2. The first suction point 16 is positioned in the tank 2 in the low position C. The liquid presence sensor 18 is situated in the tank 2 at the high position A.

(17) In addition, the second lubrication circuit 20 has a two-position second valve 29, this second valve 29 being identical to the valve in the second variant of the first embodiment of the dual circuit lubrication device 1.

(18) The dual circuit lubrication devices 1 shown in FIGS. 1 to 4 are capable of performing the lubrication method of the invention as summarized in the diagram shown in FIG. 5. The lubrication method comprises a plurality of steps.

(19) During a first step 51, the lubrication liquid is used to lubrify the mechanical system 3 simultaneously via the first lubrication circuit 10 and via the second lubrication circuit 20. The lubrication liquid is drawn by the first and second pumps 11, 21 from the tank 2 and is distributed respectively to the first and second lubrication circuits 10, 20. The nozzles 14, 24 can then spray this lubrication liquid onto the mechanical system 3.

(20) During a second step 52, the level of the lubrication liquid in the tank 2 dropping below a limit depth is detected by detector means for detecting that the level of the lubrication liquid in the tank 2 has passed under this limit depth.

(21) In the first embodiment of the dual circuit lubrication device 1, the detector means are formed by the high first suction point 16 and the first pressure sensor 12. In the third variant, the movable first suction point 16 should then be located in the high position A.

(22) In the second embodiment of the dual circuit lubrication device 1, the detector means are formed by the liquid presence sensor 18.

(23) The high position A corresponds to the limit depth in the tank 2 and the detector means serve to determine that the level of the lubrication liquid has dropped below this limit depth. This drop in the level of the lubrication liquid in the tank 2 to below a limit depth means that the tank 2 is becoming progressively emptied of the lubrication liquid, and consequently that a leak has occurred in one of the lubrication circuits 10, 20.

(24) In the first embodiment of the dual circuit lubrication device 1, as a result of this level of the lubrication liquid in the tank 2 dropping below the limit depth, the high first suction point 16 that is situated in the high position A is to be found above the level of the lubrication liquid. As a result, the first pump 11 can no longer deliver the lubrication liquid into the first lubrication circuit 10. The pressure of the lubrication liquid thus drops in this first lubrication circuit 10, with this pressure drop being detected by the first pressure sensor 12.

(25) In the second embodiment of the dual circuit lubrication device 1, this drop in the level of the lubrication liquid in the tank 2 to below the limit depth is detected directly by the liquid presence sensor 18.

(26) During a third step 53, the flow of lubrication liquid in the first lubrication circuit 10 is stopped in order to test the operation of the second lubrication circuit 20. The detector means serve to determine the presence of a leak in one of the lubrication circuits 10, 20 without identifying the particular lubrication circuit 10, 20 that actually has the leak. Consequently, by stopping the flow of lubrication liquid in the first lubrication circuit 10, lubrication liquid flows only in the second lubrication circuit 20.

(27) Since the lubrication liquid is below the limit depth in the tank 2, the first pump 11 can no longer feed the first lubrication circuit 10 in the first embodiment of the dual circuit lubrication device 1. Consequently, the flow of lubrication liquid in this first lubrication circuit 10 is stopped.

(28) However, in the second embodiment of the dual circuit lubrication device 1, the sole first suction point 16 is in the low position C, i.e. below the limit depth. It is therefore appropriate to stop the lubrication liquid flowing into the first lubrication circuit 10, either directly by stopping the first pump 11, or else by using the first valve 19. This first valve 19 must then be put into the closed position in order to interrupt the flow of the lubrication liquid in the first lubrication circuit 10. The first valve 19 is put into the closed position as a result of detecting that the level of the lubrication liquid in the tank 2 has dropped below the limit depth, and this is performed automatically. Nevertheless, it is also possible for the first valve 19 to be put into this closed position manually by an operator as a result of a visible or audible alarm being issued following detection of the level of the lubrication liquid dropping below the limit depth.

(29) The first pump 11 can be stopped by switching off its electrical power supply if the first pump 11 is an electric pump. The first pump can also be stopped by using clutch means when the first pump 11 is a mechanical pump driven by a transmission unit which may be the mechanical system 3.

(30) It is also possible in a specific first stopping mode for the first embodiment of the dual circuit lubrication device 1 to stop the flow of the lubrication liquid in the first lubrication circuit 10 by directly stopping the first pump 11. In a second specific stopping mode that is suitable solely for the second variant of this first embodiment, it is also possible to put the first valve 19 into its closed second position. These specific stopping modes serve to avoid the flow of the lubrication liquid into the first lubrication circuit 10 being reestablished and stopped in untimely manner, e.g. as a result of the lubrication liquid sloshing in the tank 2, e.g. as a result of changes in the attitude of an aircraft fitted with the mechanical system 3.

(31) During a fourth step 54, the pressure of the lubrication liquid in the second lubrication circuit 20 is measured by the second pressure sensor 22.

(32) During a fifth step 55, the presence or absence of a drop in the pressure of the lubrication liquid in the second lubrication circuit 20 is detected. The pressure of the lubrication liquid in the second lubrication circuit 20 may drop either as a result of a major leak directly from the second lubrication circuit 20, or else as a result of the level of the lubrication liquid in the tank 2 dropping below the second suction point 27.

(33) If no drop is detected in the pressure of the lubrication liquid in the second lubrication circuit 20, then the method switches to a sixth step 56. It can then be concluded that the failure of the lubrication device stems probably from the first lubrication circuit 10 which must have a leak. This sixth step 56 thus brings the method to an end, and it is then possible to issue a first alarm in the form of a first luminous and/or audible signal to inform an operator that the first lubrication circuit 10 probably includes a leak.

(34) If a drop in the pressure of the lubrication liquid in the second lubrication circuit 20 is detected, then the method continues with additional steps. This drop of pressure in the lubrication liquid in the second lubrication circuit 20 probably confirms the presence of a leak in the second lubrication circuit 20.

(35) During a seventh step 57, the flow of lubrication liquid is reestablished in the first lubrication circuit 10 in order to enable the mechanical system 3 to be lubricated.

(36) In the first and second variants that have two first suction points 16, 17, the first valve 19 needs to be switched to the third position enabling the first pump 11 to be connected to the low first suction point 17. This placing of the first valve 19 in the third position is controlled by detecting the drop in the pressure of the lubrication liquid in the second lubrication circuit 20.

(37) For the third variant, the movable first suction point 16 needs to be lowered to below the level of the lubrication liquid in order to enable the first pump to draw the lubrication liquid from the tank 2 and thus feed the first lubrication circuit 10. This movable first suction point 16 needs to be lowered at least to below the intermediate position B, and preferably to the low position C.

(38) Furthermore, in these three variants, if the first pump 11 has been stopped during the third step 53, it is necessary to put this first pump 11 back into operation.

(39) During an eighth step 58, the flow of the lubrication liquid in the second lubrication circuit 20 is stopped. Since the lubrication liquid is below the second suction point 27 in the tank 2, the second pump 21 can no longer feed the second lubrication circuit 20. Consequently, the flow of lubrication liquid is stopped in the second lubrication circuit 20.

(40) In contrast, it is also possible in the first specific mode of stopping to stop the flow of the lubrication liquid in the second lubrication circuit 20 by directly stopping the second pump 21. It is also possible in the second specific mode of stopping to put the second valve 19 into the closed position so as to interrupt the flow of the lubrication liquid in the second lubrication circuit 20. The second valve 29 is put into its closed position as a result of detecting the drop in the pressure of the lubrication liquid in the second lubrication circuit 20.

(41) The seventh and eighth steps may be performed sequentially or else simultaneously. Nevertheless, the seventh step is preferably performed before the eighth step in order to minimize the duration during which the mechanical system 3 is not being lubricated.

(42) During a ninth step 59, the pressure of the lubrication liquid in the first lubrication circuit 10 is measured by using the first pressure sensor 12 in order to verify that a leak is not also present in the first lubrication circuit 10.

(43) During a tenth step 60, the presence or absence of a drop of pressure in the lubrication liquid in the first lubrication circuit 10 is detected. The pressure of the lubrication liquid in the first lubrication circuit 10 can drop either as a result of a major leak directly from the first lubrication circuit 10, or else as a result of the level of the lubrication liquid in the tank 2 dropping below the low first suction point 17.

(44) If no drop is detected in the pressure of the lubrication liquid in the first lubrication circuit 10, then the method switches to an eleventh step 61. It can then be concluded that the failure of the lubrication device does indeed stem from the second lubrication circuit 20 which must contain a leak. This eleventh step 61 then brings the method to an end, with it being possible for a second alarm to be issued in the form of a second luminous and/or audible signal informing an operator that the second lubrication circuit 20 probably includes a leak.

(45) If a drop is detected in the pressure of the lubrication liquid in the first lubrication circuit 10, then the method switches to a twelfth step 62. This drop of the pressure of the lubrication liquid in the first lubrication circuit 10 reveals the presence of a leak also in the first lubrication circuit 10, or more probably that the leak is directly from the tank 2. This twelfth step 62 also brings the method to the end, with it then being possible to issue a third alarm in the form of a third luminous and/or audible signal informing an operator that the entire dual circuit lubrication device 1 has failed.

(46) Under such circumstances, the lubrication circuits 10 and 20 do not provide the mechanical system 3 with any lubrication.

(47) This dual circuit lubrication device 1 thus makes it possible to propose a lubrication system for a mechanical system 3 that presents increased reliability, without using an emergency circuit, and without using a plurality of lubrication liquid tanks. In addition, this dual circuit lubrication device 1 makes it possible to ensure that the lubrication liquid is cooled continuously and that there is no limit on the duration of lubrication once a leak has been detected.

(48) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described above, it will readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.