Abstract:
There is described a transmission for a helicopter, the transmission having a movable transmission member; a casing housing the movable member; lubricated supporting means for supporting the movable member inside the casing and for rotation about an axis; and feed means for feeding a lubricating fluid to the supporting means; the transmission also has storage means permitting gradual release of the lubricating fluid, and which are connected fluidically to the feed means and to the supporting means to permit lubrication of the supporting means in the event of breakdown of the feed means; and the storage means are angularly integral with the movable member and located radially inwards of the supporting means to feed the lubricating fluid centrifugally to the supporting means.

Description:
The present invention relates to an improved helicopter transmission. 
     BACKGROUND OF THE INVENTION 
     As is known, helicopters are normally equipped with a number of transmissions for transmitting motion from one or more turbines to the main and/or tail rotor, and/or from the turbine to a number of accessory devices, i.e. for powering on-board equipment, for example. 
     The transmissions normally comprise one or more rotary members rotating about respective axes; a casing housing the rotary members; a number of bearings supporting the rotary members in rotary and axially-fixed manner inside the casing; and a feed device for supplying and lubricating the bearings with lubricating oil contained inside special tanks. 
     In the event of damage to the tank or breakdown of the feed device, the oil pressure falls, thus preventing operation of the transmission. 
     In the industry, a need is felt to ensure, in such cases, correct operation of the transmission for a predetermined length of time, e.g. thirty minutes, to allow the helicopter to land. 
     Moreover, for missions of a given duration, helicopter certification regulations require that the helicopter be able to maintain level flight for said predetermined length of time. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a helicopter transmission designed to meet the aforementioned requirements in a straightforward, low-cost manner. 
     According to the present invention, there is provided a helicopter transmission as claimed in the attached Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a view in perspective of a helicopter comprising a transmission in accordance with the present invention; 
         FIG. 2  shows a larger-scale axial section of the  FIG. 1  transmission. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in  FIG. 1  indicates a helicopter comprising two turbines  2 ; a main rotor  4 ; a tail rotor  5 ; and a primary transmission  3  (shown schematically) for transmitting motion from turbines  2  to main rotor  4  and tail rotor  5 . 
     Helicopter  1  also comprises a number of secondary transmissions  6  for transmitting motion from primary transmission  3  to respective known accessory devices (not shown), i.e. for powering respective on-board equipment, for example. 
     For the sake of simplicity, and purely by way of example, the following description refers to only one transmission  6 . 
     With reference to  FIG. 2 , transmission  6  comprises a transmission shaft  7  rotating about an axis A to transmit motion from primary transmission  3  to the respective accessory device; a casing  8  secured to a fixed structure of helicopter  1  and housing shaft  7  coaxially; a number of bearings  9 ,  10  interposed radially between shaft  7  and casing  8  to support shaft  7  in rotary, axially-fixed manner inside casing  8 ; and a feed device  11  for receiving oil from a known tank (not shown) and feeding it to, and for lubricating, bearings  9 ,  10 . 
     More specifically, shaft  7  supports a flange  14  and a gear  15  connected functionally to primary transmission  3  and the accessory device respectively, and fixed to shaft  7  adjacent to respective opposite axial ends  18 ,  17  of shaft  7 . 
     Flange  14  projects axially from casing  8  for easy connection to transmission  3 . 
     Shaft  7  is axially hollow and open at opposite axial ends  17 ,  18 . 
     Bearings  9 ,  10  are rolling bearings, and are located with respect to shaft  7  as follows: three bearings  9  are interposed axially between flange  14  and gear  15 , and a fourth bearing  10  is interposed axially between end  17  of shaft  7  and gear  15 . 
     More specifically, each bearing  9  comprises an inner race and an outer race fixed to the outer surface of shaft  7  and the circumferential surface of casing  8  respectively; and bearing  10  comprises a radially outer race defined by a ring  12  fixed to casing  8 , and a radially inner race defined by a portion  13  of the outer circumferential surface of shaft  7  adjacent to end  17 . 
     In normal operating conditions, feed device  11  feeds the oil to lubricate bearings  9  into shaft  7  through end  17 , and the oil flows from shaft  7  to bearings  9  as described in detail below. 
     Feed device  11  also feeds the oil to lubricate bearing  10  onto portion  13  of shaft  7 . 
     More specifically, feed device  11  comprises a tubular member  21  defining a coaxial conduit  22  connected fluidically to the tank; and a number of nozzles  23  supplied by conduit  22  and for ejecting oil from feed device  11  to lubricate bearings  9 ,  10 . 
     More specifically, member  21  projects radially from casing  8  inside a cavity defined between casing  8  and shaft  7  at end  17 , and comprises opposite radial ends  38 ,  39  fixed to casing  8  and facing end  17  of shaft  7  respectively. 
     Nozzles  23  are located adjacent to end  39 . More specifically, in the example shown, two nozzles  23  eject oil into shaft  7  through end  17  to lubricate bearings  9 ; and one nozzle  23 , further outwards radially with respect to axis A, ejects oil onto portion  13  of shaft  7  to lubricate bearing  10 . 
     According to an important aspect of the present invention, transmission  6  also comprises a gradual-release oil storage device  25  connected fluidically to feed device  11  and bearings  9  to permit oil feed to bearings  9  in the event of breakdown of feed device  11  and/or damage to the tank. Storage device  25  is located radially inwards of bearings  9  with respect to axis A, to feed oil to bearings  9  centrifugally. 
     More specifically, storage device  25  is housed inside an axially hollow body  26  fitted coaxially inside shaft  7  and preferably made of aluminum. 
     In normal operating conditions, body  26  defines an oil flow path from feed device  11  to bearings  9  to permit lubrication of bearings  9 , and an oil flow path from feed device  11  to storage device  25  to collect oil inside storage device  25 . In the event of breakdown of feed device  11  and/or damage to the tank, body  26  also defines an oil flow path from storage device  25  to bearings  9  to still permit, albeit temporary, lubrication of bearings  9 . 
     More specifically, body  26  is fixed in fluidtight manner inside shaft  7  at opposite axial ends  27 ,  28  close to ends  17 ,  18  of shaft  7  respectively, and at a section  29  perpendicular to axis A and interposed axially between ends  27 ,  28 . 
     A radial clearance is therefore defined between the other portions of the body  26  and the shaft  7 . More specifically, between the section  29  and the end  28 , the body  26  and the shaft  7  define a radial gap, or first chamber,  30  for the purpose explained below. 
     More specifically, the body  26  and shaft  7  define the first chamber  30  bounded axially between the section  29  and the end  28 . 
     The first chamber  30  is connected fluidically to the bearings  9  by a number of—in the example shown, three—conduits  24  formed radially through the shaft  7 , and permits oil feed from the body  26  to the bearings  9 . 
     Working from the end  27  to the end  28 , the body  26  defines a succession of chambers:
         a second chamber  31  open at opposite axial ends to receive oil from feed device  11  at end  27 ;   an annular fourth chamber  32  connected fluidically at opposite axial ends to gap  30  and chamber  31 ; and   a third chamber  33  housing storage device  25 .       

     More specifically, the third chamber  33 , fluidically isolated from the fourth chamber  32  and closed axially at the end  28 , is of an axial extension within the axial extension of the first chamber  30 , and is connected to the second chamber  31  by a more radially inner conduit  34  extending coaxially through the fourth chamber  32 . 
     In normal operating conditions, oil therefore flows from feed device  11  to storage device  25  along the flow path defined, in order of flow, by chamber  31 , conduit  34 , and chamber  33 . 
     Chamber  32  is connected to chamber  31  by a number of spaced circumferential openings  35 , each having a respective axis sloping with respect to axis A and converging towards end  27 . 
     Chamber  32  is also connected to gap  30  by a number of spaced circumferential openings  36  interposed axially between section  29  and chamber  33 , and each having a respective axis sloping with respect to axis A and converging towards end  27 . 
     In normal operating conditions, oil therefore flows from feed device  11  to bearings  9  along the flow path defined, on order of flow, by chamber  31 , openings  35 , chamber  32 , openings  36 , gap  30 , and conduits  24 . 
     Storage device  25  is housed entirely inside chamber  33 , and comprises a cylinder  50  coaxial with axis A and communicating with chamber  31  via conduit  34 ; and an annular member  41  cooperating radially, on one side, with cylinder  50 , and, on the opposite side, with the inner surface of the portion of body  26  facing gap  30 . 
     Cylinder  50  is fixed at opposite axial ends to body  26 , is filled with oil, in normal operating conditions, by feed device  11  via conduit  34 , and has a number of holes (not shown) crosswise to axis A to permit oil flow from the inside volume of cylinder  50  to member  41 . 
     Member  41  is preferably made of porous sintered material to allow the lubricating oil through, and is connected to gap  30  by a number of radial holes  42  formed through body  26 . In the event of breakdown of feed device  11  and/or damage to the tank, the holes in cylinder  50 , together with the pores in member  41  and holes  42  in body  26 , feed oil centrifugally from chamber  33  to gap  30  to permit lubrication of bearings  9 . 
     The pores in member  41  are sized to resist centrifugal flow of the oil and so delay oil supply to bearings  9  in the event of breakdown of feed device  11  and/or damage to the tank. 
     In actual use, shaft  7  is supported in rotary and axially-fixed manner by bearings  9 ,  10 , which must be oiled to function correctly. 
     In normal operating conditions, nozzles  23  of feed device  11  feed oil from the tank onto portion  13  of shaft  7  to lubricate bearing  10 , and into chamber  31  of body  26  to lubricate bearings  9 . 
     A major portion of the oil fed into chamber  31  lubricates bearings  9  directly, while a residual portion is collected in storage device  25 . 
     More specifically, the major portion of the oil flows from chamber  31  through openings  35 , chamber  32 , and openings  36  into gap  30 , and then from gap  30  through conduits  24  to bearings  9  to lubricate the bearings. 
     The residual portion of the oil, on the other hand, flows from chamber  31  along conduit  34  to member  41 , where it accumulates, and from where, by virtue of centrifugal force and the porous material of member  41 , it is directed centrifugally to holes  42 . 
     In normal operating conditions, oil outflow from member  41  into gap  30  through holes  42  is prevented by the pressure of the oil already inside gap  30  and coming from chamber  32 . 
     In the event of breakdown of feed device  11  and/or damage to the tank, no oil is fed by nozzles  23  into chamber  31 , thus emptying chamber  32  and gap  30 . 
     In which case, the oil collected in storage device  25  is released gradually to temporarily lubricate bearings  9 . 
     That is, gap  30  being partly empty, the oil collected in member  41  is allowed to flow out through holes  42  into gap  30 . 
     More specifically, oil flows gradually out of member  41  by virtue of the porosity of member  41 . 
     The oil flow from member  41  into gap  30  through conduits  24  reaches bearings  9  to keep bearings  9  lubricated for a predetermined length of time, even in the event of breakdown of feed device  11  and/or damage to the tank. 
     In which case, helicopter  1  has a predetermined length of time, e.g. about thirty minutes, in which transmissions  6  continue to function until an appropriate landing site is located. 
     More specifically, helicopter  1  is able to maintain level flight for said predetermined length of time, thus conforming with certification requirements governing missions of predetermined duration. 
     Clearly, changes may be made to transmission  6  as described and illustrated herein without, however, departing from the protective scope defined in the accompanying Claims.