Abstract:
An apparatus and system for supporting a planetary carrier within an aircraft gearbox includes a retainer for engaging a rotor mast and for supporting the planetary carrier.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional U.S. Patent Application Ser. No. 62/295,922, which was filed in the U.S. Patent and Trademark Office on Feb.  16 , 2016. Application Ser. No. 62/295,922 is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The application generally relates to rotorcraft drive systems and, more particularly, to a system and method of supporting a planetary carrier within rotorcraft gearbox. 
       BACKGROUND OF THE INVENTION 
       [0003]    Rotorcraft drive systems typically include one or more gearboxes. A rotorcraft gearbox—particularly a main rotor gearbox—will often include one or more planetary gear sets. The planetary gear set may include a central sun gear, an outer ring gear, and a plurality of planet gears rotatably coupled to a planetary carrier and configured to “orbit” the sun gear while engaging both the sun gear and the ring gear. Typically, the sun gear receives the torque input to the planetary gear set while the planetary carrier provides the torque output from the planetary gear set. The planetary carrier is often coupled to a rotor mast, such that the torque output from the planetary gear set is applied to the rotor mast. 
         [0004]    In some rotorcraft, the planetary carrier and the rotor mast are coupled together using a set of splines. For example, internal splines located on the planetary carrier may transmit the torque output from the planetary gear set to mating external splines located on the rotor mast. Because these splines are typically helical or aligned axially (i.e., substantially parallel to the longitudinal axis of the rotor mast), they provide no support for the planetary carrier in the axial direction. 
         [0005]    One solution is to provide carrier-support bearings that support the planetary carrier relative to some fixed structure within the gearbox. The carrier-support bearings are typically rolling-element bearings, such as a ball bearing. However, this solution has several drawbacks. The addition of the carrier-support bearings introduces one or more additional components, which may add complexity to the design, increase weight, and make assembly more difficult. Additionally, the carrier-support bearing will typically necessitate that the planetary carrier include a mating bearing surface, which adds to the cost and complexity of manufacturing the planetary carrier. For instance, the bearing surface will typically require one or more additional machining steps, which might need to be held to tight tolerances. Furthermore, the carrier-support bearing will typically require lubrication, which may require one or more dedicated lube jets to provide oil to the carrier-support bearing. Lubricating the carrier-support bearing may further necessitate additional core passages in the gearbox housing. The addition of lube jets and/or core passages may further negatively impact the gearbox&#39;s weight, cost, design complexity, and manufacture and assembly. The carrier-support bearing may require periodic inspection, maintenance, and/or replacement. And, the carrier-support bearing introduces an additional potential failure mode within the gearbox. Other drawbacks associated with such a design will be apparent to one skilled in the art. 
         [0006]    Other rotorcraft utilize a rotor mast with an integral planetary carrier. That is, the rotor mast and the planetary carrier are a single, unitary piece having a rotor mast portion and a planetary carrier portion. The planetary carrier is, therefore, supported in the axial direction by the rotor mast portion, which is, in turn, supported in the axial direction by mast bearings. This solution also has several drawbacks. For instance, the gearbox assembly may be more difficult to assemble, ship, and/or store, and it may require more space, because the rotor mast is permanently affixed to the planetary carrier. Manufacture of the rotor mast with integral planetary carrier may be significantly more expensive than the manufacture of two separate parts, particularly because a rotor mast alone might be manufactured from an appropriately sized pipe structure, while a rotor mast with integral planetary carrier might have to be machined from a large billet, casting, or forging, which will potentially result in more machining steps, a longer cycle time, and more material waste. Another disadvantage is that shipping, overhaul, and repair of the mast and/or gearbox becomes more difficult and expensive where the rotor mast and planetary carrier are a single, unitary piece. And, damage or wear to either the rotor mast or the planetary carrier will necessitate overhaul or replacement of the entire unitary piece—which is itself more expensive to repair, overhaul, or manufacture than a separate rotor mast and/or planetary carrier would be. 
         [0007]    Consequently, a need exists for a method and apparatus for supporting a planetary carrier in the axial direction, without permanently coupling the planetary carrier to the rotor mast, and without introducing an additional bearing dedicated solely to providing axial support for the planetary carrier. These and other advantages of the present invention will become apparent to one skilled in the art. The embodiments described below, and the inventions set forth in the appended claims, may provide all, some, or none of these advantages. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the invention includes an aircraft gearbox comprising: a gearbox housing; a planetary gear set disposed within the gearbox housing, the planetary gear set comprising: a sun gear; a ring gear; a planetary carrier; and a plurality of planet gears; and a retainer configured to be coupled to a mast, the retainer comprising a surface configured to support the planetary carrier. 
         [0009]    In another aspect, the invention includes a retainer for supporting a planetary carrier within a gearbox comprising: a coupling feature adapted for coupling the retainer to a mast; and a surface configured to support the planetary carrier. 
         [0010]    In a third aspect, the invention includes an aircraft gearbox comprising: a gearbox housing; a planetary gear set disposed within the gearbox housing, the planetary gear set comprising: a sun gear configured to receive rotational energy from an input; a stationary ring gear fixedly mounted within the gearbox housing; a planetary carrier configured to transmit rotational energy to a mast through a first set of splines provided on the planetary carrier and a second set of splines provided on the mast, the planetary carrier being an overhung planetary carrier comprising a plurality of downwardly-extending, cantilevered posts; and a plurality of planet gears, each of the plurality of planet gears being rotatably mounted on one of the posts of the planetary carrier, wherein the sun gear, the planetary carrier, and the mast are all configured to rotate about a substantially common axis of rotation, the axis of rotation defining an axial direction; and a retainer configured to be coupled to the mast, the retainer comprising a surface configured to support the planetary carrier in the axial direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Preferred features of certain embodiments of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein: 
           [0012]      FIG. 1  shows a rotorcraft according to one embodiment; 
           [0013]      FIG. 2  shows the power train system of the rotorcraft of  FIG. 1 ; 
           [0014]      FIG. 3A  shows an isometric view of a rotorcraft gearbox according to one embodiment; 
           [0015]      FIG. 3B  shows a top view of the rotorcraft gearbox of  FIG. 3A ; 
           [0016]      FIG. 4  shows the geartrain within the rotorcraft gearbox of  FIG. 3A ; 
           [0017]      FIG. 5  shows the planetary gearset according to the geartrain of  FIG. 4 ; 
           [0018]      FIG. 6  shows a partial cross-section of a rotorcraft gearbox, according to the viewpoint established by the  6 - 6  section lines shown in  FIG. 3B ; and 
           [0019]      FIG. 7  shows a partial cross-section of an alternative rotorcraft gearbox, according to the viewpoint established by the  6 - 6  section lines of  FIG. 3B . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The embodiments of the present invention will now be described more fully, with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, the illustrated embodiments are provided so that this disclosure will be thorough and complete and will convey the scope of the invention to those skilled in the art. 
         [0021]    In the interest of clarity and brevity, all features of an embodiment may not be described. In the development of any actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. While such a development effort might be complex and time-consuming, it would, nevertheless, be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0022]      FIG. 1  shows a rotorcraft  100  according to one example embodiment. Rotorcraft  100  features power train system  110 , main rotor blades  120 , tail rotor blades  120 ′, a fuselage  130 , a landing gear  140 , and an empennage  150 . Power train system  110  may rotate blades  120  and/or blades  120 ′.  FIG. 2  shows the power train system  110  of  FIG. 1 . 
         [0023]    In the example of  FIGS. 1 and 2 , power train system  110  includes an engine  112 , a gearbox  160 , a rotor mast  114 , and a tail rotor drive shaft  116 . Engine  112  supplies torque to mast  114 , via gearbox  160 , for rotating of blades  120 . Engine  112  also supplies torque to tail rotor drive shaft  116  for rotating blades  120 ′. In the examples of  FIGS. 1 and 2 , gearbox  160  is a main rotor transmission system. Teachings of certain embodiments recognize, however, that power train system  110  may include more or different gearboxes than gearbox  160  shown in  FIG. 1 . Power train system  110  may include a control system for selectively controlling the pitch of each blade  120  in order to selectively control direction, thrust, and lift of rotorcraft  100 . 
         [0024]    Fuselage  130  represents the body of rotorcraft  100  and may be coupled to power train system  110  such that power train system  110  and blades  120  may move fuselage  130  through the air. Landing gear  140  supports rotorcraft  100  when rotorcraft  100  is landing and/or when rotorcraft  100  is at rest on the ground. Empennage  150  represents the tail section of the aircraft and features blades  120 ′. Power train system  110  and blades  120 ′ may collectively provide thrust in the same direction as the rotation of blades  120  so as to counter the torque effect created by blades  120 . It should be appreciated that teachings from rotorcraft  100  may apply to aircraft other than rotorcraft, such as airplanes, tilt rotors, and unmanned aircraft, to name a few examples. In addition, teachings of certain embodiments relating to rotor systems described herein may apply to power train system  110  and/or other power train systems, including but not limited to non-rotorcraft power train systems. 
         [0025]    In the embodiment of  FIGS. 1 and 2 , gearbox  160  transmits power from a power source (e.g., engine  112 ) to an object or objects to be moved (e.g., blades  120 ). Gearbox  160  converts speed and torque between the power source and the object(s) to be moved. Gearbox  160  may be configured to reduce the speed of the rotational output of engine  112 , while increasing the torque applied to blades  120 . 
         [0026]      FIGS. 3A and 3B  show a gearbox  160  according to one example embodiment. According to the embodiment of  FIGS. 3A and 3B , gearbox  160  is a main rotor gearbox and includes a rotor mast  114 . Gearbox  160  also includes at least one gearbox housing  180  and various gears contained therein (see  FIGS. 4 and 5 ). A gear is a rotating part having teeth that mesh with another toothed part in order to transmit rotational energy. As one skilled in the art will readily appreciate, the gears within gearbox  160  accomplish speed and torque conversions that are desired for a given implementation. For instance, the gearbox  160  of  FIGS. 3A and 3B  reduces rotational speed while multiplying the torque output, which is applied to blades  120  of rotorcraft  100 . 
         [0027]      FIGS. 4 and 5  illustrate a gear train  161  contained within gearbox housing  180 . Referring to the embodiment of  FIG. 4 , gear train  161  includes an input pinion  162 . Input pinion  162  is in mechanical communication with, and receives rotational energy from, a power source (e.g., engine  112 ). Input pinion  162  includes a helical bevel gear portion  163 . The helical bevel gear portion  163  of input pinion  162  meshes with, and transmits rotational energy to, bevel gear  164 . Bevel gear  164  is a helical bevel gear. Bevel gear  164  meshes with and drives an accessory drive gear  190 , which is configured to provide rotational energy to an accessory gearbox (not shown) and/or various aircraft accessories, such as air blowers, cooling fans, lubrication pumps, hydraulic pumps, electrical generators, and similar components and systems (not shown). Bevel gear  164  is attached via a common shaft  165  to helical spur gear  166 . Thus, bevel gear  164 , common shaft  165 , and helical spur gear  166  rotate together about a common axis. Torque applied to bevel gear  164  is transmitted via common shaft  165  to helical spur gear  166 . Helical spur gear  166  meshes with, and transmits rotational energy to, bull gear  167 . Bull gear  167  is integral with sun gear  171  (see  FIG. 5 ) of planetary gear set  170 . Thus, torque applied to bull gear  167  is transmitted to sun gear  171 . 
         [0028]    The embodiment of  FIG. 4  is configured to receive rotational energy from two power sources. Specifically, gear train  161  includes a second input pinion  162 ′, which may be configured to receive rotational energy from a second power source (e.g., a second engine  112 ). Second input pinion  162 ′ includes a helical bevel gear portion  163 ′. The helical bevel gear portion  163 ′ of second input pinion  162 ′ meshes with, and transmits rotational energy to, a second bevel gear  164 ′. Like bevel gear  164 , second bevel gear  164 ′ is a helical bevel gear. Second bevel gear  164 ′ meshes with and drives a second accessory drive gear  190 ′, which is configured to provide rotational energy to an accessory gearbox (not shown) and/or various aircraft accessories, such as air blowers, cooling fans, lubrication pumps, hydraulic pumps, electrical generators, and similar components and systems (not shown). Second bevel gear  164 ′ is attached via a second common shaft  165 ′ to a second helical spur gear  166 ′. Thus, second bevel gear  164 ′, second common shaft  165 ′, and second helical spur gear  166 ′ rotate together about a common axis. Torque applied to second bevel gear  164 ′ is transmitted via second common shaft  165 ′ to second helical spur gear  166 ′. Second helical spur gear  166 ′ meshes with, and transmits rotational energy to, bull gear  167 , which is integral with sun gear  171  (see FIG.  5 ). Accordingly, rotational energy provided at either or both input pinions  162 ,  162 ′ is ultimately combined at bull gear  167  and transmitted to sun gear  171 . 
         [0029]      FIG. 5  depicts the planetary gear set  170  within gear train  161 . Specifically, sun gear  171  is a straight-cut spur gear that meshes with, and transmits rotational energy to, a plurality of planet gears  172 . Planet gears  172  are rotatably mounted to a planetary carrier  173 . The embodiment of  FIGS. 5 and 6  includes a total of six planetary gears  172 , but only one planetary gear  172  is shown in  FIG. 6  for clarity. According to the present embodiment, planetary carrier  173  includes a plurality of posts  174  configured to receive each of the plurality of planet gears  172 . Each post  174 , therefore, defines the rotational axis for a corresponding planet gear  172  rotatably mounted thereon. The planetary carrier  173  of  FIGS. 4 and 5  is an overhung planetary carrier, having a plurality of downwardly-extending, cantilevered posts  174 . However, one skilled in the art will appreciate that other configurations and orientations are possible for the planetary gear set  170 , including the planetary carrier  173 . For instance, in an alternative embodiment planetary carrier  173  might be a conventional planetary carrier, which one skilled in the art would appreciate as comprising a lower plate, an upper web, and planetary posts extending between the lower plate and upper web. 
         [0030]    Referring to  FIG. 4 , each planet gear  172  also meshes with ring gear  175 . Ring gear  175  is stationary. According to the present embodiment, ring gear  175  is fixedly mounted within gearbox housing  180  and does rotate with respect to the gearbox housing  180 . Planetary carrier  173  establishes the spatial relationship among the sun gear  171 , the planet gears  172 , and the ring gear  175 , such that each planet gear  172  meshes with both the sun gear  171  and the ring gear  175 . Because the sun gear  171  rotates while the ring gear  175  is fixed, the planet gears  172  travel on an orbiting path about sun gear  171  as they rotate on posts  174 . This orbiting action causes planetary carrier  173  to rotate. 
         [0031]    According to the embodiment depicted in  FIGS. 4 and 5 , the planetary carrier  173  includes internal splines  176 . Internal splines  176  mesh with mating external splines  118  on rotor mast  114  (see  FIG. 4 ). Thus, planetary carrier  173  serves as the main output for gearbox  160  by transmitting rotational energy to rotor mast  114 . In the embodiment of  FIGS. 4 and 5 , the bull gear  167 , sun gear  171 , planetary carrier  173 , and rotor mast  114  all rotate about a substantially common axis of rotation  195  (see  FIGS. 5-7 ). 
         [0032]      FIG. 6  depicts a partial cross-section of gearbox  160 , in the area of the planetary gear set  170 . The viewpoint of the cross-section of  FIG. 6  corresponds to the section lines ( 6 - 6 ) shown in  FIG. 3B . According to the embodiment of  FIG. 6 , a retainer  200  attached to the rotor mast  114  provides axial support for the planetary carrier  173 . Specifically, retainer  200  is a threaded ring having external threads  201  and a flange portion  202 . The external threads  201  mate with internal threads  119  located on the rotor mast  114 . This threaded connection attaches retainer  200  to the rotor mast  114 . The flange portion  202  of retainer  200  extends radially with respect to the axis of rotation  195 . Flange portion  202  includes a contact surface  203  that provides support in an axial direction to planetary carrier  173 . According to the embodiment of  FIG. 6 , the contact surface  203  is an upper surface of flange portion  202 . A corresponding contact surface  177  is provided on planetary carrier  173  and configured to mate with the contact surface  203  of the retainer  200 . The corresponding contact surface  177  is adjacent to the internal splines  176  of planetary carrier  173 . 
         [0033]      FIG. 7  depicts the partial cross-section of  FIG. 6  according to an alternative embodiment. The viewpoint of the cross-section of  FIG. 7  corresponds to the section lines ( 6 - 6 ) shown in  FIG. 3B . Similar to the embodiment of  FIG. 6 , a retainer  200  attached to the rotor mast  114  provides axial support for the planetary carrier  173 . However, in the embodiment of  FIG. 7 , retainer  200  is a threaded ring having internal threads  201 . The internal threads  201  mate with external threads  119  located on the rotor mast  114 . This threaded connection attaches retainer  200  to the rotor mast  114 . Retainer  200  also includes a contact surface  203  that provides support in an axial direction to planetary carrier  173 . According to the embodiment of  FIG. 7 , the contact surface  203  is an upper surface of retainer  200 . A corresponding contact surface  177  is provided on planetary carrier  173  and configured to mate with the contact surface  203  of the retainer  200 . The corresponding contact surface  177  is adjacent to the internal splines  176  of planetary carrier  173 . 
         [0034]    Thus, the embodiments of  FIGS. 6 and 7  eliminate the need for a carrier-support bearing, which would otherwise be necessary in order support the planetary carrier  173  relative to some other fixed or rotating structure within the gearbox (such as gearbox housing  180  or sun gear  171 ) while still allowing the planetary carrier  173  to rotate about axis of rotation  195 . Additionally, the embodiments of  FIGS. 6 and 7  do not utilize a unitary rotor mast with integral planetary carrier, and, therefore, the embodiments of  FIGS. 6 and 7  avoid the above-described disadvantages associated with such a gearbox design. 
         [0035]    One of ordinary skill will recognize that alternative retainer configurations may exist that—while not shown in  FIGS. 6 and 7 —are nevertheless enabled by this disclosure and may be within the scope of, or equivalent to, the claims that follow. For instance, a variety of mechanical interfaces might be utilized to engagably couple retainer  200  to rotor mast  114 . In one alternative embodiment, retainer  200  comprises a snap ring that is configured to engage a corresponding annular groove located in rotor mast  114 . In yet another embodiment, retainer  200  is attached to rotor mast  114  using one or more fasteners (e.g., bolts, studs, nuts, rivets, pins, etc.) to form the connection. In another embodiment, retainer  200  includes tabs or pins that engage a slotted pathway in rotor mast  114 . And in yet another exemplary embodiment, retainer  200  is equipped with tabs that engage into corresponding depressions or apertures in rotor mast  114 . The tabs of this embodiment may be spring-loaded such that they “click” into the depressions or apertures of rotor mast  114 . Alternatively, the tabs may be deformable such that they are bent or pressed into the depressions or apertures of rotor mast  114 . 
         [0036]    In the embodiment of  FIG. 6 , contact surface  203  is located on flange portion  202  and is a continuous circular surface that extends radially about the entire circumference of retainer  200 . In the embodiment of  FIG. 7 , contact surface  203  is a continuous circular surface located on an upper portion of retainer  200 . However, a variety of alternative mechanical interfaces might be utilized between retainer  200  and planetary carrier  173 . For example, in an alternative embodiment similar to  FIG. 6 , flange portion  202  is one or more tabs extending radially from retainer  200 , and contact surface  203  includes one or more surfaces located on the tabs. And in an alternative embodiment similar to  FIG. 7 , contact surface  203  may be located on one or more bosses provided on retainer  200 . 
         [0037]    Modifications, additions, or omissions may be made to the methods, systems, and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims. 
         [0038]    To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke 35 U.S.C. §112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.