Abstract:
A system for cooling a transmission of a hover-capable aircraft, the system having: a stator; a heat exchanger connectable thermally to the transmission; a fan for creating a current of a first heat-carrying fluid from the heat exchanger to the fan itself, to remove heat from the heat exchanger; a rotary member, which rotates about an axis to rotate an impeller of the fan about the axis; and a bearing supporting the rotary member for rotation about the axis; the system also having cooling means for cooling the bearing, and in turn having conducting means for conducting a current of a second heat-carrying fluid along a path from an outside environment, external to the bearing, to and to cool the bearing itself.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to European Patent Application. No. 12425158.8, filed Sep. 28, 2012, which is hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a system for cooling a hover-capable aircraft transmission. 
         [0003]    The present invention also relates to a method of cooling a hover-capable aircraft, e.g. helicopter, transmission. 
       BACKGROUND OF THE INVENTION 
       [0004]    As is known, helicopters are normally equipped with a number of transmissions for transmitting power from one or more turbines to the main and/or tail rotor, and/or to various accessory devices, e.g. for powering operation of on-board instruments. 
         [0005]    Lubricating fluid, typically oil, is circulated in known manner inside the transmission to both lubricate and cool the moving parts. 
         [0006]    For effective lubrication and cooling, the lubricating fluid circulating inside the transmissions must be cooled. 
         [0007]    So, helicopters are equipped with cooling systems substantially comprising:
       a heat exchanger for exchanging heat between the transmission oil and the air circulating inside the cooling system; and   a fan for creating airflow from the heat exchanger to the fan itself.       
 
         [0010]    More specifically, the airflow draws heat from the heat exchanger, and hence the transmission, and flows over the fan at a temperature of about 125° C. 
         [0011]    The cooling systems also comprise:
       a casing;   a shaft connected to a drive member to rotate the fan; and   one or more bearings supporting the shaft with respect to the casing.       
 
         [0015]    The hot airflow from the heat exchanger to the fan heats the area around the bearings, thus reducing their working life and dependability. 
         [0016]    A need is therefore felt within the industry for a system of cooling helicopter transmissions without impairing the working life and dependability of the fan shaft bearings. 
         [0017]    Known helicopter transmission cooling systems are described in GB 591,982 and KR-A-20100109717. 
         [0018]    EP-A-2409919 discloses a system for cooling a transmission of an aircraft, comprising a stator, a fan for creating a current of a heat-carrying fluid towards the heat-exchanger, a shaft rotating about an axis to rotate an impeller of the fan, and a bearing supporting the shaft in rotation about the axis and with respect to the stator. 
         [0019]    Due to the fact that the fan creates a current of the heat-carrying fluid directed towards the heat-exchanger, the bearing of EP-A-2409919 does not run a substantial risk of overheating. 
       SUMMARY OF THE INVENTION 
       [0020]    It is an object of the present invention to provide a helicopter transmission cooling system designed to meet the above demand in a straightforward, low-cost manner. 
         [0021]    According to the present invention, there is provided a system for cooling a transmission of a hover-capable aircraft, according to claim  1 . 
         [0022]    The present invention also relates to a method of cooling a transmission of a hover-capable aircraft, according to claim  10 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
           [0024]      FIG. 1  shows a view in perspective of a helicopter comprising a cooling system in accordance with the present invention; 
           [0025]      FIG. 2  shows an axial section of the  FIG. 1  cooling system; 
           [0026]      FIG. 3  shows the  FIG. 1  cooling system with parts removed for clarity. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Number  1  in  FIG. 1  indicates a helicopter comprising two turbines  2 , a main rotor  4 , and a tail rotor  5 . 
         [0028]    Helicopter  1  also comprises a number of secondary transmissions  6  for transmitting power from one of turbines  2  to respective known accessory devices (not shown), e.g. for powering respective on-board equipment. 
         [0029]    One of transmissions  6  is of the type described in Patent Application 05425470.1. 
         [0030]    Helicopter  1  also comprises a cooling system  7  for cooling the lubricating fluid circulating inside transmission  6 . 
         [0031]    System  7  ( FIGS. 2 and 3 ) substantially comprises:
       a stator  3 ;   a heat exchanger, e.g. a radiator,  8  connected thermally and adjacent to transmission  6 ;   a fan  9 ; and   a shaft  10  rotating about an axis A.       
 
         [0036]    Fan  9  is located downstream from heat exchanger  8 , and substantially comprises an impeller  20   a  rotated by shaft  10  about axis A; and a diffuser  20   b  fixed with respect to axis A and located downstream from impeller  20   a.    
         [0037]    Fan  9  circulates a current P (indicated by the pale arrow in  FIG. 2 ) of a heat-carrying fluid—in the example shown, the hot air inside stator  3 —from heat exchanger  8  to diffuser  20   b  to draw heat from, and cool the lubricating oil of, transmission  6 . 
         [0038]    In the flow direction of current P, stator  3  substantially comprises:
       a casing  11  fixed by a flange  35  to the fixed part of transmission  6 ;   a tubular body  23  fixed to casing  11  and forming part of diffuser  20   b ; and   an outlet pipe  13  (only shown schematically in  FIGS. 2 and 3 ) connected to tubular body  23  and located on the opposite side of fan  9  to heat exchanger  8 .       
 
         [0042]    More specifically, casing  11  comprises:
       a curved portion  33 , which defines an inlet  12  facing heat exchanger  8 , and houses fan  9 ; and   an axial portion  34  projecting from portion  33  and connected by flange  35  to the fixed part of transmission  6 .       
 
         [0045]    More specifically, portion  33  is interposed between heat exchanger  8  and tubular body  23  of diffuser  20   b.    
         [0046]    In the example shown, casing  11  is curved and/or made of aluminium. 
         [0047]    Shaft  10  is housed partly in portion  33  and partly in portion  34 . 
         [0048]    Impeller  20   a  substantially comprises:
       a predominantly radial wall  14  fixed to shaft  10 ;   a wall  15  sloping with respect to axis A and extending from both sides of wall  14 ; and   a number of blades  19 , which are spaced angularly about axis A, project radially from wall  15 , on the opposite side to wall  14 , and are separated by an annular gap from a wall of portion  33 , adjacent to diffuser  20   b  and opposite heat exchanger  8 .       
 
         [0052]    Blades  19  interact with the hot air inside casing  11  to create a low pressure at inlet  12  and, hence, current P. 
         [0053]    Inside, impeller  20   a  defines a cavity  29  housing bearing  16 . 
         [0054]    Being swept by current P, impeller  20   a  heats up during operation of system  7 , and transmits heat to bearing  16 , which thus operates at a temperature of roughly 125° C. 
         [0055]    In the direction of current P from heat exchanger  8  to diffuser  20   b , impeller  20   a  also comprises:
       an annular inlet section  37  upstream from blades  19  and extending radially between the portion of wall  15  upstream from blades  19 , and the inner wall of portion  33  of casing  11 ; and   an annular outlet section  38  downstream from blades  19  and extending radially between the portion of wall  15  downstream from wall  14 , and the inner wall of portion  33  of casing  11 .       
 
         [0058]    In the example shown, the reaction of impeller  20   a  is such that outlet section  38  is at a lower pressure than the outside environment  50 . 
         [0059]    Fan  9  distributes pressure radially inside cavity  29 . 
         [0060]    More specifically, when fan  9  is running, the radially innermost area, close to shaft  10 , of cavity  29  is at a lower pressure than inlet section  37  of fan  9 . 
         [0061]    Diffuser  20   b  substantially comprises:
       an ogival body  21  tapering radially from fan  9 , in the direction away from heat exchanger  8 ;   a number of ribs  22  projecting towards axis A from ogival body  21 ;   tubular body  23  surrounding ogival body  21 ; and   a number of blades  26  spaced angularly about axis A and extending between tubular body  23  and ogival body  21 .       
 
         [0066]    Tubular body  23  and ogival body  21  define an inlet section  24  and an outlet section  25  for current P. 
         [0067]    Inlet section  24  and outlet section  25  are annular with respect to axis A. 
         [0068]    Inlet section  24  of diffuser  20   b  is defined radially between an axial end  27  of tubular body  23  facing fan  9 , and an end  28  of ogival body  21  facing fan  9 . 
         [0069]    Outlet section  25  of diffuser  20   b  is defined radially between an end  31 , opposite end  27 , of tubular body  23 , and a corresponding portion  32  of ogival body  21 . 
         [0070]    In the example shown, tubular body  23  is truncated-cone-shaped, of axis A, and tapers from end  27  to end  31 . 
         [0071]    Inside, ogival body  21  defines a cavity  30  tapering radially from end  28  in the direction away from impeller  20   a.    
         [0072]    Cavity  30  is open on the impeller  20   a  side and communicates fluidically with cavity  29 , and is closed on the opposite side to impeller  20   a.    
         [0073]    Bearing  16  is housed in a portion of cavity  29  radially inwards of wall  15  of impeller  20   a.    
         [0074]    Bearing  16  is interposed radially between a bushing  17  fitted to shaft  10  and to fan  9 , and a flange  18  fixed to ribs  22  of diffuser  20   b.    
         [0075]    Bushing  17  is located radially inwards of flange  18  with respect to axis A. 
         [0076]    More specifically, bearing  16  is located radially inwards of end  28  of ogival body  21 , and is interposed axially between wall  14  of impeller  20   a  and ribs  22 , so the action of fan  9  and diffuser  20   b  places bearing  16  at a lower pressure than the outside environment  50 . 
         [0077]    System  7  advantageously comprises cooling means for cooling bearing  16 , and which comprise conducting means  40  for conducting a current Q (shown by the bold arrows in  FIG. 2 ) of a second heat-carrying fluid—in particular, ambient-temperature air—along a path from outside environment  50  to bearing  16 , so as to cool bearing  16 . 
         [0078]    It is important to note that conducting means  40  conduct current Q using only the pressure gradient between outside environment  50  and cavity  30 , i.e. with no need for any powered devices, such as pumps, in addition to impeller  20   a.    
         [0079]    More specifically, conducting means  40  comprise a cavity  41  formed in shaft  10  and coaxial with axis A; cavity  30  defined by ogival body  21 ; and cavity  29  defined by impeller  20   a.    
         [0080]    Cavity  41  communicates fluidically with the outside environment through a number of holes  42  in the lateral surface  43  of shaft  10 , and communicates fluidically with cavity  30  defined by diffuser  20   b.    
         [0081]    More specifically, shaft  10  comprises:
       an open axial end  44  located on the diffuser  20   b  side to fluidically connect cavity  41  to cavity  30 ; and   a closed axial end  47  opposite end  44  and outside stator  3 .       
 
         [0084]    Holes  42  are formed through a portion of surface  43  opposite end  44  and housed inside portion  34  of casing  11 . 
         [0085]    More specifically, holes  42  are equally spaced angularly, and connect outside environment  50  fluidically to cavity  41 . 
         [0086]    More specifically, holes  42  are located, radially with respect to axis A, over a slot  36  formed through portion  34  of casing  11 , and which connects outside environment  50  fluidically to the inside of portion  34 . 
         [0087]    For any position of shaft  10  about axis A, current Q therefore flows from outside environment  50  through slot  36  into portion  34 , and from the inside of portion  34  through holes  42  into cavity  41 . 
         [0088]    Impeller  20   a  and diffuser  20   b  define between them an annular passage  45  for current Q. 
         [0089]    Passage  45  communicates fluidically with outlet pipe  13  to expel current Q together with current P along outlet pipe  13 . 
         [0090]    More specifically, passage  45  extends between an annular end  46  of wall  15 , and end  28  of ogival body  21 . 
         [0091]    More specifically, end  46  defines cavity  30  radially outwards. 
         [0092]    Passage  45  also fluidically connects cavity  30  and inlet section  24  of diffuser  20   b.    
         [0093]    The Applicant has observed that, when fan  9  is run, passage  45  is at a lower static pressure than cavities  29  and  30 . 
         [0094]    When transmission  6  is running, the lubricating oil inside overheats. 
         [0095]    By virtue of heat exchanger  8 , the air in stator  3  reaches a temperature of about 125° C. 
         [0096]    Rotation of shaft  10  about axis A rotates impeller  20   a.    
         [0097]    Rotation of impeller  20   a  creates hot-air current P, which flows from heat exchanger  8  to outlet pipe  13 , and draws heat from heat exchanger  8  and, therefore, from transmission  6 . 
         [0098]    More specifically, current P flows through inlet section  37  of impeller  20   a , interacts with blades  19 , and flows away from impeller  20   a  along outlet section  38 . 
         [0099]    Impeller  20   a  is thus immersed in hot-air current P. 
         [0100]    The reaction of fan  9  lowers the pressure inside inlet section  37  with respect to that of outside environment  50 . 
         [0101]    The Applicant has observed a pressure difference of roughly a few KPa between outside environment  50  and the area of cavity  29  housing bearing  16 . 
         [0102]    Fan  9  generates ambient-temperature air current Q. 
         [0103]    More specifically, the pressure difference draws current Q through slot  36  in portion  34 , and through holes  42  in shaft  10  into cavity  41  inside shaft  10 . 
         [0104]    From there, the pressure difference draws current Q through end  44  into cavity  30  of diffuser  20   b.    
         [0105]    The difference in pressure produced by impeller  20   a  first directs current Q (along the path shown in  FIG. 2 ) onto the radially outermost areas of cavity  30  in diffuser  20   b , i.e. in a spinning direction with respect to axis A. 
         [0106]    Current Q then flows into, and produces a vortex field inside, cavity  29 , and so reaches and cools bearing  16 . 
         [0107]    Passage  45  being the low static pressure point of cavities  29  and  30 , current Q then flows through passage  45  to inlet section  24  of diffuser  20   b , where it mixes with current P. 
         [0108]    Finally, currents P and Q interact with fixed blades  26  of diffuser  20   b , and flow through outlet section  25  of diffuser  20   b  into outlet pipe  13 . 
         [0109]    The advantages of system  7  and the method according to the present invention will be clear from the above description. 
         [0110]    In particular, current Q cools bearing  16 , thus improving its dependability by preventing it from operating at high temperature, e.g. of about 120° C. 
         [0111]    Current Q being generated by the static pressure difference between outside environment  50  and cavities  29  and  30 , bearing  16  is cooled using the static pressure difference produced by fan  9 , i.e. with no need for any further drive devices. 
         [0112]    Current Q flows into cavity  41  in shaft  10 , cavity  30  in diffuser  20   b , and cavity  29  in impeller  20   a , which means it is produced with no need for any additional component parts, over and above the normally existing parts of known cooling systems. 
         [0113]    Clearly, changes may be made to system  7  and the method as described and illustrated herein without, however, departing from the protective scope of the accompanying Claims.