Abstract:
A lubricating and cooling system for a mechanical assembly includes a first path having a reservoir of lubricating and cooling liquid and a second path having a source of pressurized gas. A feed mechanism receives the lubricating and cooling liquid from the first path and the pressurized gas from the second path and outputs the pressurized gas and liquid. First and second spray nozzles spray the pressurized gas and liquid onto the mechanical assembly. The first path has a pressure and flow limiter arranged between the reservoir and the first and second spray nozzles so that the first and second spray nozzles are fed with the lubricating and cooling liquid at a pressure no greater than 2 bar (2×105 Pascal).

Description:
This is a divisional of application Ser. No. 10/170,405 filed Jun. 14, 2002 now U.S. Pat. No. 6,817,448. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a system for lubricating and cooling a mechanical assembly. Although not exclusively, it is particularly well suited to lubricating and cooling a transmission gearbox, particularly a main transmission gearbox, usually used on board helicopters. Thus, the present invention will be described more particularly hereinafter in relation to this application. 
   It is known that, for correct operation, such a transmission gearbox is lubricated and cooled, generally by a device which circulates a lubricating and cooling liquid, such as oil. In addition, to prevent said transmission gearbox from being able to be damaged or even destroyed through lack of lubrication and cooling in the event of this device failing during flight, a backup device is provided whose purpose is to, at least partially, lubricate and cool said transmission gearbox to allow the helicopter to continue to fly for a predetermined survival time. 
   DESCRIPTION OF THE PRIOR ART 
   For example, American patent U.S. Pat. No. 4,717,000 has already disclosed a system for lubricating and cooling helicopter transmission gearboxes comprising a main device which circulates a stream of oil under pressure through said transmission gearboxes and a backup device which is set in operation automatically or manually when said main device becomes defective. This backup device comprises:
         a reservoir connected to said main device so as to fill with lubricating and cooling liquid from said main device;   a source of pressurized air, consisting of a compressor stage of the engine of said helicopter; and   spray nozzles fed, on the one hand, with pressurized lubricating and cooling liquid from said reservoir and, on the other hand, with pressurized gas from said compressor stage, said spray nozzles being able to spray a mist of lubricating and cooling liquid onto certain components of said transmission gearboxes so as temporarily to supplement the defective main device.       

   In that known system, the lubricating and cooling liquid is contained in said reservoir at the relatively high pressure (at least 10 bar=10 6  pascal) of the main device and, should the latter fail, is expelled therefrom by the action of the compressed air produced by said compressor stage, the pressure of which has to overcome that of the liquid in the reservoir. The result of this is that the lubricating and cooling liquid sent to said nozzles is at a high pressure, itself equal to at least 10 bar (10 6  pascal). In consequence, the backup device consumes a significant amount of lubricating and cooling liquid and the reservoir of the backup device needs to be of large capacity, thus causing its mass and bulk to be high. 
   The object of the present invention is to overcome these disadvantages and to make it possible to produce a lubricating and cooling system which, for a backup device with the same predetermined survival time, requires only a reservoir with a capacity much lower than that of the known system described hereinabove. 
   SUMMARY OF THE INVENTION 
   To this end, according to the invention, the system for lubricating and cooling a mechanical assembly such as a helicopter transmission gearbox, said system comprising:
         a main lubricating and cooling device circulating a stream of lubricating and cooling liquid through said mechanical assembly at a relatively high pressure; and   an auxiliary backup device set in operation automatically or manually when said main device becomes defective, said backup device comprising:
           at least one reservoir of lubricating and cooling liquid;   at least one source of pressurized gas;   at least one spray nozzle which is fed, on the one hand, with pressurized lubricating and cooling liquid from said reservoir and, on the other hand, with pressurized gas from said source, which is able to spray onto a mist of lubricating and cooling liquid said mechanical assembly so as temporarily to supplement the defective main device, is notable in that:   
           said reservoir of the auxiliary backup device is independent of said main device; and   said spray nozzle is fed with lubricating and cooling liquid from said reservoir at a pressure at most equal to 2 bar (2.10 5  pascal).       

   What happens, according to the invention, because the reservoir of the auxiliary backup device is independent of the main device, that is to say because it has no hydraulic communication therewith, is that the lubricating and cooling liquid sent to the spray nozzles can be at a pressure far lower than that of the liquid of the main device, at most equal to 2 bar (2.10 5  pascal) and, preferably, roughly equal to 1 bar (10 5  pascal). The result of this is that, for the same predetermined survival time, the consumption of the backup device according to the present invention is far lower than that of the known system, which means that the amount of lubricating and cooling liquid needed for backup purposes is also far lower. As a result, the capacity, the mass and the bulk of the reservoir are considerably reduced. 
   Such a low pressure of the lubricating and cooling liquid used for backup purposes may be obtained in various ways. For example:
         the lubricating and cooling liquid contained in said reservoir is pressurized by said source of pressurized gas feeding said spray nozzle, for example a compressor stage of the helicopter engine, and a pressure and flow limiter is arranged between said reservoir and said spray nozzle; or alternatively   the lubricating and cooling liquid contained in said reservoir is pressurized by an auxiliary gas source, for example a pressurized gas cylinder, independent of said pressurized gas source feeding said spray nozzle, and a pressure and flow limiter is arranged between said reservoir and said spray nozzle; or alternatively still   the lubricating and cooling liquid contained in said reservoir is pressurized by a pump the outlet of which is connected to said reservoir by a bypass comprising a calibrated valve that opens as soon as the outlet pressure of said pump becomes higher than said feed pressure of the spray nozzle.       

   It is also noted that, because the reservoir of the auxiliary backup device is independent of the main device, it is easy and advantageous for said reservoir to be arranged some distance away from said mechanical assembly so that said lubricating and cooling liquid it contains does not experience the effect of the heat given off by said mechanical assembly. 
   Thermal degradation of the liquid contained in said reservoir is thus avoided. 
   When the system according to the present invention comprises a number of spray nozzles, these may be fed with pressurized gas and with lubricating and cooling liquid through a splitter. 
   In addition, these nozzles may be split into groups and all the nozzles in one group may be fed with pressurized gas and with lubricating and cooling liquid by a common feed device, all said common feed devices themselves being fed with pressurized gas and with lubricating and cooling liquid by said splitter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The figures of the appended drawing will make it easy to understand how the invention may be achieved. In these figures, identical references denote similar elements. 
       FIG. 1  schematically illustrates a lubricating and cooling system according to the present invention. 
       FIGS. 2 and 3  depict, in views similar to  FIG. 1 , alternative forms of embodiment of the lubricating and cooling system according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically depicts the main transmission gearbox  1  of a helicopter (not depicted) and its lubricating and cooling system  2 ,  3 . 
   This lubricating and cooling system comprises a main device  2  circulating through said main transmission gearbox  1  a stream of main lubricating and cooling liquid, essentially oil or some similar liquid. This main device comprises a closed-loop circuit  4  through which said main liquid circulates under the action of a pump  5 . The circuit  4  introduces said main liquid at  6  into the main transmission gearbox  1  and, having lubricated and cooled the internal components of said main transmission gearbox (these components are not depicted), this main liquid is collected at  7  by said circuit  4 . After filtering at  8 , the main liquid thus collected is returned to a tank  9 , from which it is once again circulated through the circuit  4  by the pump  5 . The latter imparts to said main liquid a pressure generally of the order of around 10 bar. 
   The lubricating and cooling system additionally comprises an auxiliary backup device  3  set in operation when said main device  2  becomes defective, so as temporarily to maintain lubrication and cooling of the internal components of the main transmission gearbox  1  and thus prevent the latter from becoming damaged or even destroyed. 
   The auxiliary backup device  3  comprises a reservoir  10  of backup lubricating and cooling liquid, completely independent of the main device  2 , that is to say that the reservoir  10  has no hydraulic connection with the circuit  4 . The backup liquid (oil or similar product) contained in the reservoir  10  is pressurized by compressed air from a compressor stage  11  of the engine (not depicted) of the helicopter. This compressed air is sent to the reservoir  10  through a filter  12 , a control valve  13  which is normally closed, for example of the electrically operated valve type, a cooler  14  and a connection  10 A between the outlet of the latter and said reservoir  10 . The cooler  14  may be of the heat exchanger type. 
   In addition, the reservoir  10  is preferably arranged some distance away from the main transmission gearbox  1  so that the backup lubricating and cooling liquid it contains does not experience the effect of the heat given off by said main transmission gearbox. 
   Furthermore, the auxiliary backup device  3  comprises groups  15 ,  16  of spray nozzles  17 ,  18 , for example mounted on the housing  19  of the main transmission gearbox  1 . The spray nozzles  17 ,  18  of the groups  15 ,  16  are of a known type which, fed with pressurized gas and with liquid that is to be sprayed, are able to spray said liquid in the form of a mist. In consequence, each spray nozzle  17  of the group  15  is connected, by a double connection (pressurized gas/liquid for spraying), to a feed device  20  able to deliver pressurized gas and liquid for spraying. Likewise, each spray nozzle  18  of the group  16  is connected, by a double connection (pressurized gas/liquid for spraying), to a feed device  21  able to deliver pressurized gas and liquid for spraying. In addition, the feed devices  20 ,  21  may themselves be fed with pressurized gas and with liquid for spraying from a splitter  22 . 
   This splitter  22  may receive compressed air from the compressor stage  11 , by virtue of a connection with the outlet of the cooler  14 , via a nonreturn valve  23  and a filter  24 . Likewise, the splitter  22  may receive backup lubricating and cooling liquid by virtue of a connection with the reservoir  10 , via a pressure and flow limiter  25 , a nonreturn valve  26  and a filter  27 . Such a pressure and flow limiter  25  may consist of a calibrated pressure relief valve. 
   The control valve  13  may be opened manually using a member  28 , for example available to the helicopter pilot, or via a pressure sensor  29  arranged in the circuit  4 . 
   Thus, when the main circuit  2  becomes defective, for example following a breakdown of the pump  5  or a leak from the circuit  4 , the pressure of the main lubricating and cooling liquid in said circuit  4  decreases very rapidly. The drop in pressure is detected by the sensor  29 , which either is connected to an alarm (not depicted) alerting the pilot who can then act on the member  28 , or directly opens the valve  13 . Whatever the mode of operation (manual using the member  28  or automatic via the sensor  29 ), the valve  13  allows fluid through, which means that the compressed air from the compressor stage  11  is sent to the cooler  14 , possibly after filtering at  12 . The cooler  14  therefore feeds compressed air to both the splitter  22  (through the nonreturn valve  23  and the filter  24 ) and the reservoir  10  containing the backup lubricating and cooling liquid (via the connection  10 A). The latter liquid is therefore also sent under pressure to the splitter  22 , through the pressure and flow limiter  25 , the nonreturn valve  26  and the filter  27 . By virtue of the limiter  25 , which may be of any known type, the pressure of the backup lubricating and cooling liquid at the splitter  22  is at most equal to 2 bar (2.10 5  pascal) and preferably equal to 1 bar (10 5  pascal). 
   The splitter  22  therefore feeds the feed devices  20  and  21  and the nozzles  17  and  18  with backup liquid (at this low pressure) and with compressed gas. These nozzles  17  and  18  are therefore able to spray a mist of said backup liquid onto the internal components (or some of them) of the gearbox  1 , to lubricate and cool them so as to allow the gearbox (and therefore the helicopter) to survive in spite of the failure of the main device  2 . 
   It will be noted that, because the pressure with which the backup lubricating and cooling liquid is sent to the nozzles  17  and  18  is low, the consumption of these nozzles is also low, which means that, for a predetermined survival time, the amount of backup liquid needed, and therefore also the volume of the reservoir  10 , can be small. Thus the applicant company has been able to discover that, on one of its helicopters, the amount of backup lubricating and cooling liquid could, for the same survival time, be reduced from  35  liters to  10  liters by implementing the present invention. 
   In the alternative form of embodiment depicted in  FIG. 2 , there can be found all the elements  1  to  29  described hereinabove, arranged in the same way except as regards the connection  10 A between the cooler  14  and the reservoir  10 , which connection has been omitted. 
   By contrast, the system of  FIG. 2  has, in addition by comparison with that of  FIG. 1 , a capsule  13  of pressurized gas and another valve  31 , normally closed and in parallel with the valve  13 . This valve  31  may also be of the electrically operated valve type. It can be opened by the member  28  and/or the pressure sensor  29 , in the same way as was described hereinabove in respect of the valve  13 , the valves  13  and  31  being operated jointly and simultaneously. 
   In the light of the foregoing explanations, it will therefore be readily understood that, in the event of the main device  2  becoming defective, the valves  13  and  31  are opened together so that the splitter  22 , and therefore the spray nozzles  17  and  18 , are fed with compressed air, as above, through the valve  13 , the cooler  14 , the nonreturn valve  23  and the filter  24 , and with backup lubricating and cooling liquid by the action of the compressed gas capsule  30 , through the pressure and flow limiter  25 , the nonreturn valve  26  and the filter  27 . As before, the pressure of the backup liquid at the nozzles  17  and  18  is at most equal to 2 bar (2.10 5  pascal) and preferably equal to 1 bar (10 5  pascal). 
   In the other alternative form of embodiment depicted in  FIG. 3 , there can again be found all the elements  1  to  24  and  26  to  29  described hereinabove with reference to  FIG. 1  and arranged in the same way, the connection  10 A between the cooler  14  and the reservoir  10  however being omitted. In addition, the pressure and flow limiter  25  is also omitted. The connection  10 A and the limiter  25  are replaced by a device  32  comprising, on the one hand, a pump  33  which can be operated in parallel with the valve  13  by the member  28  and/or the sensor  29  and, on the other hand, a bypass comprising a nonreturn valve  34 , which is mounted in parallel with the pump  33 , between the outlet thereof and the reservoir  10 . The opening of the nonreturn valve  34  is set to be just higher than the pressure desired for the nozzles  17  and  18 . The pump  33  is, for example, of the positive-displacement type and performs regulation. It may be of variable output and adjustable pressure type. 
   Thus, when the main device  2  becomes defective, the member  28  and/or the pressure sensor  29  simultaneously open the valve  13  (as was the case for the systems in  FIGS. 1 and 2 ) and actuate the pump  33  which sends the backup liquid contained in the reservoir  10  to the splitter  20  and to the nozzles  17  and  18 . If the pressure of this backup liquid exceeds the desired low value (at most equal to 2 bar), then the nonreturn valve  34  opens and the liquid is returned to the reservoir  10 . The nonreturn valve  34  therefore acts as a pressure limiter.