Patent Publication Number: US-2022235708-A1

Title: Aircraft turbomachine comprising means for priming the lubricating pump

Description:
TECHNICAL FIELD 
     The invention relates to an aircraft turbomachine including a lubricating circuit and means for priming the pump. 
     More particularly, the invention relates to an aircraft turbomachine including a pneumatic pipe for priming the pump upon start-up of the turbomachine. 
     PRIOR ART 
     In particular, an aircraft turbomachine includes a lubricating circuit allowing supplying different components of the turbomachine with lubricating liquid. 
     In particular, this lubricating circuit includes a tank in which the lubricating liquid is stored and a pump drawing the lubricating liquid to send it towards the components to be lubricated. 
     In general, the tank is disposed in the FAN compartment, i.e. a compartment surrounding the fan of the turbomachine. 
     In turn, the pump is disposed proximate to an accessory drive box, in a central compartment of the turbomachine, commonly called “core” compartment. 
     To connect the pump to the tank, the lubricating circuit includes a suction pipe which is connected to the tank and to a suction orifice of the pump. 
     This suction pipe extends in the turbomachine while crossing a structural arm, whose main function is to support the central compartment of the turbomachine. 
     An aircraft turbomachine may essentially include two structural arms disposed at 6 O&#39;clock and at 12 O&#39;clock, i.e. vertically with respect to Terrestrial gravity below and above the central compartment, respectively. 
     According to a known embodiment, the suction pipe crosses a support arm located at 6 O&#39;clock, i.e. which is located vertically below the central compartment. 
     When the turbomachine is at stop, the lubricating liquid naturally lies in the suction pipe, by the effect of Terrestrial gravity. Thus, there is no problem in priming the pump on start-up. 
     However, in other configurations of turbomachines, it is not possible to use a support arm (also called bifurcation) located at 6 O&#39;clock for the passage of the suction pipe, in particular if the turbomachine does not comprise such a bifurcation. This is the case for example of a turbomachine whose nacelle comprises a thrust reverser of the so-called “O-Duct” technology which, by its mere design, does not comprise a bifurcation at 6 O&#39;clock. The suction pipe connecting the pump to the tank then should pass throughout the support arm located at 12 O&#39;clock. 
     As a result, at stop, the suction pipe is emptied off the lubricating liquid by the action of Terrestrial gravity, into the tank and/or into the pump. 
     During a restart of the turbomachine, the pump should provide a considerable suction effort to reprime the suction pipe because of the height to be covered by the liquid. For example, the level difference between the tank and the topmost point of the suction pipe is in the range of 2 m. 
     In general, the pump is not sized to provide this suction effort, since in the other operating phases of the turbomachine, the pump provides a lower effort. 
     The invention aims to provide an aircraft turbomachine including means for repriming the suction pipe during a start-up phase of the turbomachine, to allow lubricating the components of the turbomachine quickly. 
     DISCLOSURE OF THE INVENTION 
     The invention provides an aircraft turbomachine including a lubricating circuit comprising in particular a lubricating liquid tank, a pump drawing lubricating liquid from the tank to inject it onto several components of the turbomachine and a suction pipe connecting the tank to a suction orifice of the pump, 
     the turbomachine further including a start-up pneumatic circuit including a start-up tube in which a compressed air flow circulates intended to supply a pneumatic starter of the turbomachine, 
     characterised in that it includes a pneumatic pipe extending from the start-up tube up to the tank to supply the tank with compressed air, in order to make the lubricating liquid circulate throughout the suction pipe in the direction of the pump upon start-up of the turbomachine. 
     The compressed air circuit is a pressurised air source that is available very quickly. Thus, during the start-up phase, this pressurised air source is used to pressurise the tank, allows repriming the suction pipe quickly, thus, it allows feeding the pump in quickly. 
     Preferably, the turbomachine includes a start-up valve disposed on the start-up tube and including a tapping at which the pneumatic pipe is connected to the start-up tube, the tapping being located on the start-up tube upstream of the start-up valve. 
     Preferably, the turbomachine includes an additional valve disposed on the pneumatic pipe. 
     Preferably, the turbomachine includes a start-up valve disposed on the start-up tube and a tapping at which the pneumatic pipe is connected to the start-up tube, the tapping being located on the start-up tube downstream of the start-up valve. 
     Preferably, the turbomachine includes a pressure limiter located in the pneumatic pipe, in order to limit the air pressure in the tank on start-up. 
     Preferably, the turbomachine includes a central compartment coaxial with a main axis A of the turbomachine, a fan compartment extending around and at a distance from the central compartment and coaxially with the main axis A and structural arms, extending radially with respect to the main axis A and vertically according to the direction of Terrestrial gravity, the structural arms being distributed vertically on either side of the central compartment and mechanically linking the central compartment to the fan compartment, wherein the suction pipe extends throughout a structural arm located vertically above the central compartment. 
     Preferably, the pump is mounted on the central compartment and the tank is mounted on the fan compartment. 
     The invention also relates to a method for starting up a turbomachine according to the invention, including a lubricating liquid pump, a lubricating liquid tank connected to the pump through a suction pipe and including a pneumatic starter supplied with compressed air through a start-up pipe, characterised in that it includes a phase of supplying the pneumatic starter with compressed air and a phase of supplying the tank with a portion of the compressed air in the start-up tube to make lubricating liquid circulate in the suction pipe from the tank up to the pump. 
     Preferably, the start-up tube includes a start-up valve which is open during the phase of supplying the pneumatic starter, and the phase of supplying the tank is implemented upon opening of the start-up valve. 
     Preferably, the tank sis supplied with compressed air through a pneumatic pipe including a valve and connected to the start-up tube, and the phase of supplying the tank is implemented upon opening of the valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation in a view according to an axial direction of an aircraft turbomachine including a suction pipe crossing the support arm disposed at 12 O&#39;clock 
         FIG. 2  is a schematic representation of a portion of the turbomachine including the lubricating circuit combined with a compressed air circuit for the implementation of the invention 
         FIG. 3  is a schematic representation of a variant of the portion of the turbomachine represented in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , an aircraft turbomachine  10  is represented including a main axis A, a central compartment  12  coaxial with the main axis A, commonly called “core compartment” and in which the different compressor stages, the combustion chamber and the turbines are arranged, and a fan compartment  14  coaxial with the main axis A and with the central compartment  12  and extending around and at a distance from the central compartment  12 . 
     An annular space  16  is present between the central compartment  12  and the fan compartment  14  and enables the circulation of air in the turbomachine  10 . 
     The link between the central compartment  12  and the fan compartment  14  is done in particular by structural arms  18 ,  20  which extend according to a radial direction with respect to the main axis A. The structural arms  18 ,  20  are provided with a profiled fairing in order to limit the aerodynamic drag and thus disturb the air flow throughout the annular space  16  as low as possible. 
     Furthermore, the structural arms  18 ,  20  include hollow portions to enable the passage of non-structural components, such as pipes, throughout the annular space  16 , without interacting with the air flow flowing throughout the annular space  16 . 
     The two structural arms  18 ,  20  also extend according to the vertical direction, when the turbomachine  10  is mounted on an aircraft on a horizontal ground and they are distributed vertically on either side of the central compartment  12 . 
     A first structural arm  18  is located vertically below the central compartment  12 , at the commonly so-called “6 O&#39;clock” position, by analogy with a watch dial. The second structural arm  20  is located vertically above the central compartment  12 , at the commonly so-called “12 O&#39;clock” position. 
     The turbomachine  10  also includes a lubricating circuit  22  intended to supply lubricating liquid to a plurality of components (not represented) of the turbomachine  10 , such as rotational guide bearings of a shaft. In particular, this lubricating circuit  22  includes a lubricating liquid tank  24  which is carried by the fan compartment  14  and a pump  26  which is mounted at the central compartment  12 . 
     More particularly, the pump  26  is mounted in an accessory drive box  28  which is coupled to a shaft of the turbomachine and which includes a plurality of gears allowing providing different gear ratios for equipment of the turbomachine  10  rotatably driven by the accessory drive box  28 , including the pump  26 . 
     The lubricating circuit  22  also includes a suction pipe  30  which connects a suction orifice of the pump  26  to the tank  24  and through which the pump  26  draws the lubricating liquid contained in the tank  24 . 
     Since the tank  24  is mounted on the fan compartment  14  and the pump  26  is mounted on the central compartment  12 , the suction pipe  30  crosses the annular space  16 . Thus, the suction pipe  30  is mounted throughout the second structural arm  20  which is located at the 12 O&#39;clock position, i.e. above the central compartment  12 . 
     As said before, when the turbomachine  10  is at stop, the pump  26  does not suck in lubricating liquid from the tank  24 . Since the suction pipe passes throughout the second structural arm  20 , it includes a top point at the upper end of the second structural arm  20 . By the action of Terrestrial gravity, the lubricating liquid contained in the suction pipe  30  is then emptied in the tank  24 . 
     To reprime the suction pipe  30  during a start-up phase of the turbomachine, in order to quickly feed in the pump  26 , and as shown in  FIGS. 2 and 3 , the turbomachine  10  includes a pneumatic pipe  32  which supplies the tank  24  with compressed air during the start-up phase. 
     The compressed air forces the lubricating liquid contained in the tank  24  to circulate in the suction pipe  30 , crossing the top point of the suction pipe  30 , until reaching the pump  26 . Once the suction pipe  30  is filled with lubricating liquid, the pump  26  can then suck in alone the liquid contained in the tank  24 . 
     This repriming of the suction pipe  30  is necessary only during a start-up phase of the turbomachine  10  because, at that time, the tank  24  is still not pressurised. 
     Next, when the turbomachine is operating, the tank  24  is continuously pressurised, for example and in particular by air drawn from a high-pressure (HP) compressor stage of the turbomachine. 
     At the time of start-up of the turbomachine  10 , the high-pressure compressor does not operate at a speed high enough allowing producing a pressure for pressurising the tank  24  that would allow crossing the lubricating liquid vertical column between the tank  24  and the top point of the suction pipe  30 . 
     The compressed air supplying the tank  24  during the start-up phase is derived from a pneumatic start-up circuit  34  of the turbomachine  10  whose compressed air source (not represented) is outside the turbomachine  10 . For example, this air source consists of a compressor of an Auxiliary Power Unit APU of the aircraft or by a compressor air tank. This external compressed air source allows supplying an air pressure that is high enough to pressurise the tank  24 . 
     The start-up circuit  34  includes a pneumatic starter  36  which is mounted on an accessory drive box  28 , and a start-up tube  38  connecting the compressed air source to the starter. 
     To pressurise the tank  24  with compressed air from the start-up circuit  34 , the pneumatic pipe  32  is connected to the start-up tube  38  by a tapping  40  formed in the start-up tube  38 . 
     The pressure of air in the start-up tube, even outside the start-up phase, is generally in the range of 3 to 4 bars, which is largely enough to overcome the vertical column. 
     A pressure-relief valve  42  is arranged in the tank  24  to regulate the inner pressure of the tank  24  via a venting circuit  44 . 
     As a non-limiting example, for a vertical column value of 2.5 m, which could be considered as a reference, a pressure 0.25 bar is then necessary to overcome this column at −40° C. 
     According to the embodiment represented in  FIG. 2 , the tapping  40  is disposed downstream of a start-up valve  46 , i.e. between the start-up valve  46  and the starter  36 . 
     This disposition has the advantage of not pressuring the tank  24  outside a start-up phase. 
     According to the embodiment represented in  FIG. 3 , the tapping  40  is disposed upstream of the start-up valve  46 . For the pressurisation of the tank  24  to occur only during the start-up phase, an additional valve  48  is disposed in the pneumatic pipe  32 . 
     This disposition has the advantage of enabling the pressurisation of the tank  24  even outside the start-up phase, for example in the event of failure. 
     Regardless of the embodiment, the pressure in the start-up tube  38  may be excessively high and hinder the operation of the pump  26 . 
     To this end, the pneumatic pipe  32  includes a restriction  50  allowing limiting the air pressure supplying the tank  24 . 
     Also, check valve  52  are disposed in the suction pipe  30  and the pneumatic pipe  32  in order to avoid inadvertent circulations of air or lubricating liquid.