Abstract:
There is described a drive for a helicopter, the drive having at least one rotary member; a casing housing the rotary member and defining a compartment containing a lubricating fluid and air; and separating means for separating the lubricating fluid from the air and retaining the lubricating fluid inside the casing in the presence of airflow outwards of the casing and produced by pressure gradients between the compartment and the outside; the separating means are angularly integral with the rotary member to centrifugally separate the lubricating fluid from the air radially with respect to the axis.

Description:
[0001]     The present invention relates to a perfected helicopter drive.  
       BACKGROUND OF THE INVENTION  
       [0002]     As is known, helicopters are normally equipped with a number of drives 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, e.g. for powering on-board instruments.  
         [0003]     The drives normally comprise a number of gears; and a casing housing the gears and defining a compartment containing air and a lubricating oil bath, which is retained inside the drive by a number of seals fixed to the casing and operating in contact with air.  
         [0004]     When the drive is running, the temperature and therefore pressure of the air inside the casing increases; and the increase in air pressure overloads the seals, thus resulting in oil leakage and impaired lubrication.  
         [0005]     To reduce the pressure inside the casing in such conditions, relief devices are known to be used comprising a filter permeable to air but not to oil.  
         [0006]     Such devices are located along a peripheral edge of the casing, and allow air to escape from the casing to restore the pressure inside the casing to practically atmospheric pressure.  
         [0007]     Known relief devices are inefficient alongside high local pressures and particular attitudes of the helicopter, thus resulting anyway in oil leakage and impaired lubrication of the drive.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to provide a helicopter drive designed to eliminate the aforementioned drawback typically associated with known drives.  
         [0009]     According to the present invention, there is provided a helicopter drive as claimed in the attached Claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0011]      FIG. 1  shows a view in perspective of a helicopter comprising a drive in accordance with the present invention;  
         [0012]      FIG. 2  shows a larger-scale axial section of the  FIG. 1  drive. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Number  1  in  FIG. 1  indicates a helicopter comprising two turbines  2 ; a main rotor  4 ; a tail rotor  5 ; and a primary drive  3 , only shown schematically, for transmitting motion from turbines  2  to main rotor  4  and tail rotor  5 .  
         [0014]     Helicopter  1  also comprises a number of secondary drives  6  for transmitting motion from primary drive  3  to respective known accessory devices (not shown), e.g. for powering respective on-board instruments.  
         [0015]     In the following description, reference is made to only one drive  6  for the sake of simplicity and purely by way of example.  
         [0016]     With reference to  FIG. 2 , drive  6  comprises a gear train  7  rotating about an axis A and for transmitting motion from primary drive  3  to the respective accessory device; and a casing  8  secured to a fixed structure of helicopter  1  and defining a compartment  9  housing gear train  7 .  
         [0017]     More specifically, gear train  7  is partly immersed in an oil bath, so that compartment  9  contains part oil and part air.  
         [0018]     Compartment  9  communicates externally through an axial opening  20  located at one axial end of casing  8 .  
         [0019]     Oil leakage from casing  8  through opening  20  is prevented by a seal  14 , of axis A, interposed radially between gear train  7  and casing  8  and facing opening  20 .  
         [0020]     Gear train  7  is secured in axially-fixed, rotary manner to casing  8 , is housed partly inside casing  8 , and projects partly from casing  8  outside opening  20 .  
         [0021]     More specifically, gear train  7  comprises a gear  10  rotated by drive  3 ; and a splined gear  11  rotated by gear  10  and connected operatively to the respective accessory device.  
         [0022]     More specifically, gear  10  comprises a tubular body  12  secured coaxially and in axially-fixed, rotary manner to casing  8 ; external teeth  13  connected operatively to drive  3 ; and internal teeth  15  which mesh with gear  11 .  
         [0023]     More specifically, body  12  is secured to casing  8  by a number of bearings, of which only one is shown in detail and indicated  22 .  
         [0024]     Teeth  13  are carried on a portion projecting radially from body  12 , and are located on the opposite side of bearing  22  to opening  20 .  
         [0025]     Gear  11  comprises a tubular body  16  housed partly inside body  12  and projecting partly from body  12  outside opening  20 ; external teeth  17  meshing with teeth  15  of gear  10 ; and a radial flange  21  which fits to the respective accessory device.  
         [0026]     More specifically, flange  21  is carried by a radially larger portion of body  16 , extends outwards with respect to casing  8 , and is located on the opposite side of bearing  22  to teeth  13 .  
         [0027]     Body  16  houses a separator  23 , for separating air from oil in the event of airflow caused by pressure gradients between the air inside compartment  9  and the outside air, and comprises a number of radial holes  18  formed in a portion of body  16  inside casing  8  and outside body  12 , and which allow air to escape outwards to reduce the pressure in compartment  9  in said condition.  
         [0028]     In the presence of said airflow, the air inside compartment  9  is separated from the oil by separator  23 , and flows out through holes  18  into an annular chamber  40  defined between seals  14  and opening  20 . The air therefore escapes from casing  8  through opening  20  to reduce the air pressure inside compartment  9 , thus reducing the risk of damage to seals  14  and consequent oil leakage.  
         [0029]     Separator  23  advantageously rotates about axis A to centrifugally separate the oil from the air radially with respect to axis A.  
         [0030]     More specifically, separator  23  is fitted rigidly inside body  16 , and is designed to prevent air flowing axially out of the open axial end of body  16  at flange  21 .  
         [0031]     Separator  23  comprises a case  27 , of axis A, defining a path for airflow from compartment  9  to holes  18 ; and an oil-resistant filter  32  permeable to air and housed inside case  27 .  
         [0032]     Case  27  is hollow and comprises, at the axial end facing away from opening  20  in use, an air and oil inlet  28 , and, on the axially opposite side of filter  32  to inlet  28 , a number of radial outlets  29  directed towards holes  18  and through which air with substantially no oil flows out into chamber  40 . More specifically, case  27  is open axially at the inlet  28  end and closed axially at the opposite end.  
         [0033]     Filter  32  is therefore fitted inside case  27  in a position interposed axially between inlet  28  on one side and outlets  29  on the other, and occupies the whole cross section of case  27  in a plane perpendicular to axis A, so as to interfere completely with the oil-entraining airflow.  
         [0034]     Case  27 , filter  32 , and body  16  thus define a cavity  19  inside body  16 .  
         [0035]     Cavity  19  is bounded axially at one axial end by filter  32 , is connected fluidically to compartment  9  at the opposite end to filter  32  in a manner not shown, and therefore contains oil and air at substantially the same pressure as in compartment  9 .  
         [0036]     When the pressure in compartment  9  is higher than the outside pressure, separator  23  receives a stream of air entraining atomized oil, centrifugally retains the oil separated from the air inside cavity  19 , and directs the air to holes  18 .  
         [0037]     More specifically, a sleeve  34  is fitted inside case  27  in a position interposed axially between inlet  28  and filter  32  to hold filter  32  in position and guide the air and oil between inlet  28  and filter  32 .  
         [0038]     In axial section, sleeve  34  comprises a truncated-cone-shaped portion  30  close to inlet  28 ; and a cylindrical portion  31  fixed to case  27  in a position interposed axially between portion  30  and filter  32 . Portion  30  and portion  31  collect the oil separated from the air by filter  32  and spun onto the wall of sleeve  34  facing axis A.  
         [0039]     More specifically, portion  30  diverges with respect to axis A towards inlet  28  of case  27  to withdraw the oil from separator  23  while still keeping it inside cavity  19 . Portion  31  has different radial dimensions to decelerate the oil-rich radially outer regions and accelerate the oil-poor radially inner regions of the fluid flowing towards filter  32 .  
         [0040]     Case  27  is fixed at its axial ends to body  16 , and is preferably formed in one piece to avoid using separate component parts requiring precise angular connection to prevent abnormal rotation.  
         [0041]     Drive  6  also comprises a drain conduit  35 , shown only partly, for draining any oil droplets escaping separator  23  into a sump not shown in the accompanying drawings.  
         [0042]     More specifically, drain conduit  35 , shown only partly, originates radially from chamber  40 .  
         [0043]     Finally, as shown in  FIG. 2 , chamber  40  is bounded axially by a radial constriction at the portion of opening  20  extending radially between body  16  and the lateral edge of opening  20 . The purpose of the constriction is to assist in drawing and collecting inside chamber  40  any oil droplets escaping filter  32 .  
         [0044]     In actual use, secondary drive  6  is operated to transmit motion via gear train  7  from drive  3  to the respective accessory device.  
         [0045]     Operation of gear train  7  heats, and so increases the pressure of, the air inside compartment  9 , and also rotates gears  10  and  11  about axis A to rotate the air and oil inside cavity  19  connected fluidically to compartment  9 .  
         [0046]     The pressure gradient between the air inside compartment  9  and the air outside drive  6  produces an air stream, which guides the oil into case  27  of separator  23  through inlet  28 .  
         [0047]     Inside case  27 , the air and oil flow helically with a component of motion parallel to axis A, caused by the pressure gradient, and a component of motion rotating about axis A, caused by rotation of separator  23  integral with gear  11 .  
         [0048]     The component of motion parallel to axis A causes the air and oil to interact with filter  32 , which lets the air through and retains the oil inside cavity  19 .  
         [0049]     The component of motion rotating about axis A causes the oil separated from the air by filter  32  to collect on the inner wall of sleeve  34 .  
         [0050]     By virtue of the pressure gradient, the air then flows out of separator  23  through outlets  29 , out of gear  11  through holes  18 , into chamber  40 , and then to the outside. Conversely, by virtue of the shape of portion  31 , the oil collected on the inner wall of sleeve  34  moves, in the opposite direction to the airflow, inwards of cavity  19  and away from separator  23 .  
         [0051]     After a given transient period, the airflow from compartment  9  to the outside balances the air pressure inside compartment  9  and the outside air pressure, thus preventing overloading of seals  14 .  
         [0052]     Any oil droplets escaping separator  23 , and drawn out of body  16  by the pressure gradient together with the air, are collected in chamber  40  and drained into the sump by drain conduit  35 .  
         [0053]     When the outside air pressure is higher than the air pressure in cavity  19  and compartment  9 , airflow is generated from the outside into cavity  19 .  
         [0054]     In which case, the airflow path is the opposite of that described when pressure is higher in cavity  19  than outside, and filter  32  prevents any particulate in the air from reaching cavity  19  and so polluting the oil.  
         [0055]     The advantages of drive  6  according to the present invention will be clear from the foregoing description.  
         [0056]     In particular, separator  23  provides for effectively separating oil from the incoming. air from cavity  19  and compartment  9  in the presence of particularly high air pressures and in numerous attitudes of helicopter  1 .  
         [0057]     The risk of damage to seals  14  and poor lubrication is therefore greatly reduced.  
         [0058]     Clearly, changes may be made to drive  6  as described and illustrated herein without, however, departing from the protective scope defined in the accompanying Claims.  
         [0059]     In particular, case  27  may be defined by two separate, angularly connected members, each fixed inside cavity  19 .