Patent Publication Number: US-9834303-B2

Title: Method and apparatus of connecting a fixed drive system to a rotating drive system for a tiltrotor aircraft

Description:
BACKGROUND 
     Technical Field: 
     The present disclosure relates to a fixed engine and rotating proprotor arrangement for a tiltrotor aircraft. The present disclosure also relates to a method and apparatus of connecting a fixed drive system to a rotating drive system for a tiltrotor aircraft. 
     Description of Related Art: 
     A conventional tiltrotor aircraft configuration can include a fixed engine with a rotating proprotor; however, conventional packaging arrangements of the fixed engine and the rotating proprotor can have significant shortcomings. Further, the location of the fixed engine and the rotating proprotor in relation to each other, as well as to the wing structure, can have significant influence upon the size and weight of the supporting structure, as well as the complexity of servicing procedures. For example, a rotating proprotor that is cantilevered outboard of the tip end of the wing can require significant structure to adequately support and prevent operationally induced deflection. Further, a rotating proprotor embedded in the wing structure can be difficult and time-consuming to perform maintenance thereon. 
     Hence, there is a need for a fixed engine and rotating proprotor arrangement that can be adequately supported with minimal structural mass, while also providing efficient maintainability. 
     Furthermore, a tiltrotor aircraft may have a fixed engine and a rotating proprotor with a gear and shaft to transfer torque therebetween. During operation, the fixed engine and the rotating proprotor may each endure a different operational loading which can induce operational misalignment therebetween. Also, misalignment can result from manufacturing and assembly tolerances. Designing the aircraft with structure with sufficient strength to resist the operational and tolerance misalignment therebetween can be undesirable due to the weight thereof. Further, conventional tiltrotor aircraft may have a torque transferring shaft between the fixed engine and the rotating proprotor that is burdensome to remove for maintenance and/or inspection, thus increasing the operational costs associated with operating the aircraft and performing maintenance and/or inspection thereof. 
     Hence, there is a need for a torque transferring device between a fixed engine system and a rotating proprotor of a tiltrotor aircraft that can allow for misalignment between the two. Further, there is a need for a torque transferring shaft that can be easily removed during a maintenance and/or inspection procedure. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the method and apparatus of the present disclosure are set forth in the appended claims. However, the method and apparatus itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a tiltrotor aircraft in helicopter mode, according to one example embodiment; 
         FIG. 2  is a perspective view of a tiltrotor aircraft in airplane mode, according to one example embodiment; 
         FIG. 3  is a perspective view of a tiltrotor aircraft in airplane mode, according to one example embodiment; 
         FIG. 4  is a partial perspective view of a propulsion system portion of the tiltrotor aircraft, according to one example embodiment; 
         FIG. 5  is a cross-sectional view of a prop rotor of the propulsion system, according to one example embodiment; 
         FIG. 6  is a partial perspective view of a propulsion system portion of the tiltrotor aircraft, according to one example embodiment; 
         FIG. 7  is a partial top view of the tiltrotor aircraft, according to one example embodiment; 
         FIG. 8  is a partial perspective view of the tiltrotor aircraft, according to one example embodiment; 
         FIG. 9  is a partial perspective view of the tiltrotor aircraft, according to one example embodiment; 
         FIG. 10  is a cross-sectional view of the propulsion system, according to one example embodiment; 
         FIG. 11  is a cross-sectional view of the propulsion system, according to one example embodiment; 
         FIG. 12  is a perspective view of a quill shaft, according to one example embodiment; 
         FIG. 13  is a perspective view of the propulsion system in a partially disassembled state, according to one example embodiment; and 
         FIG. 14  is a perspective view of the propulsion system in a partially disassembled state, according to one example embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the method and apparatus of the present disclosure are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such 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. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. 
     Referring to  FIGS. 1 and 2  in the drawings, a tiltrotor aircraft  101  is illustrated. Tiltrotor aircraft  101  can include a fuselage  103 , a landing gear  105 , a tail member  107 , a wing  109 , a propulsion system  111 , and a propulsion system  113 . Each propulsion system  111  and  113  includes a fixed engine and a rotatable proprotor  115  and  117 , respectively. Each rotatable proprotor  115  and  117  have a plurality of rotor blades  119  and  121 , respectively, associated therewith. The position of proprotors  115  and  117 , as well as the pitch of rotor blades  119  and  121 , can be selectively controlled in order to selectively control direction, thrust, and lift of tiltrotor aircraft  101 . 
       FIG. 1  illustrates tiltrotor aircraft  101  in helicopter mode, in which proprotors  115  and  117  are positioned substantially vertical to provide a lifting thrust.  FIG. 2  illustrates tiltrotor aircraft  101  in an airplane mode, in which proprotors  115  and  117  are positioned substantially horizontal to provide a forward thrust in which a lifting force is supplied by wing  109 . It should be appreciated that tiltrotor aircraft can be operated such that proprotors  115  and  117  are selectively positioned between airplane mode and helicopter mode, which can be referred to as a conversion mode. 
     The propulsion system  113  is substantially symmetric to the propulsion system  111 ; therefore, for sake of efficiency certain features will be disclosed only with regard to propulsion system  111 . However, one of ordinary skill in the art would fully appreciate an understanding of propulsion system  113  based upon the disclosure herein of propulsion system  111 . 
     Further, propulsion systems  111  and  113  are illustrated in the context of tiltrotor aircraft  101 ; however, propulsion systems  111  and  113  can be implemented on other tiltrotor aircraft. For example, an alternative embodiment may include a quad tiltrotor that has an additional wing member aft of wing  109 , the additional wing member can have additional propulsion systems similar to propulsion systems  111  and  113 . In another embodiment, propulsion systems  111  and  113  can be used with an unmanned version of tiltrotor aircraft  101 . Further, propulsion systems  111  and  113  can be integrated into a variety of tiltrotor aircraft configurations. 
     Referring now also to  FIGS. 3-11 , propulsion system  111  is disclosed in further detail. Propulsion system  111  includes an engine  123  that is fixed relative to wing  109 . An engine output shaft  125  transfers power from engine  123  to a spiral bevel gearbox  127  that includes spiral bevel gears to change torque direction by 90 degrees from engine  123  to a fixed gearbox  129  via a clutch. Fixed gearbox  129  includes a plurality of gears, such as helical gears, in a gear train that are coupled to an interconnect drive shaft  131 , and a quill shaft  203 . Torque is transferred to an input  167  in spindle gearbox  133  of proprotor gearbox  147  through the quill shaft  203 . 
     The interconnect drive shaft  131  provides a torque path that enables a single engine to provide torque to both proprotors  111  and  113  in the event of a failure of the other engine. In the illustrated embodiment, interconnect drive shaft  131  has a rotational axis  135  that is vertically lower and horizontally aft of the conversion axis  137  of the spindle gearbox  133 . Conversion axis  137  is parallel to a lengthwise axis  225  of wing  109 . Referring in particular to  FIG. 8 , interconnect drive shaft  131  includes a plurality of segments that share a common rotational axis  135 . Location of interconnect drive shaft  131  aft of the aft wing spar  197  provides for optimal integration with fixed gearbox  129  without interfering with the primary torque transfer in the quill shaft  203  between fixed gearbox  129  and spindle gearbox  133 ; as such, the conversion axis  137  of spindle gearbox  133  is parallel to the rotational axis  135  and interconnect drive shaft  131 , but located forward and above rotational axis  135 . 
     Engine  123  can be housed and supported in an engine nacelle  139 . Engine nacelle  139  can include an inlet  141 , aerodynamic fairings, and exhaust, as well as other structures and systems to support and facilitate the operation of engine  123 . 
     The proprotor  115  of propulsion system  111  can include a plurality of rotor blades  119  coupled to a yoke  143 . The yoke  143  can be coupled to a mast  145 . Mast  145  is coupled to a proprotor gearbox  147 . It should be appreciated that proprotor  115  can include other components, such as a swashplate  149  that is selectively actuated by a plurality of actuators  151  to selectively control the pitch of rotor blades  119  via pitch links  153 . 
     Proprotor gearbox  147  is configured to transfer power and reduce speed to mast  145 . Further, proprotor gearbox  147  provides operational support of proprotor  115 . Referring in particular to  FIG. 5 , proprotor gearbox  147  can include a top case  155  portion and spindle gearbox  133 . Speed reduction is accomplished by a low speed planetary gear assembly  159  and a high speed planetary gear assembly  161 . A spiral bevel gear assembly  163  includes a spiral bevel gear input  167  and a spiral bevel gear output  171 . Spiral bevel gear assembly  163  changes power direction from along a centerline axis  165  of spiral bevel gear input  167  to a centerline axis  169  of spiral bevel gear output  171 . An accessory drive  173  can be coupled to spiral bevel gear output  171 . It should be appreciated that proprotor gearbox  147  can include any bearings, lubrication systems, and other gearbox related components that may be beneficial for operation. 
     During operation, a conversion actuator  175  (shown at least in  FIG. 4 ) can be actuated so as to selectively rotate proprotor gearbox  147  about a conversion axis  137  that corresponds with axis  165 , which in turn selectively positions proprotor  115  between helicopter mode (shown in  FIG. 1 ) and airplane mode (shown in  FIG. 2 ). The operational loads, such as thrust loads, are transmitted through rotor mast  145  and into the spindle gearbox  133  of proprotor gearbox  147 , and thus the structural support of spindle gearbox  133  is critical. 
     In the illustrated embodiment, the spindle gearbox  133  of proprotor gearbox  117  is mounted to an inboard pillow block  181  with an inboard bearing assembly  177 . Similarly, spindle gearbox  133  of proprotor gearbox  147  is mounted to an outboard pillow block  183  with an outboard bearing assembly  179 . Thus, spindle gearbox  133  is structurally supported but rotatable about conversion axis  137  by conversion actuator  175 . Inboard pillow block  181  is structurally coupled to an inboard rib  185 . Similarly, outboard pillow block  183  is structurally coupled to an outboard rib  187 . In one embodiment, an inboard intermediate support  189  is utilized as a structural element between inboard pillow block  181  and inboard rib  185 , and an outboard intermediate support  191  is similarly utilized as a structural element between outboard pillow block  183  and outboard rib  187 . It should be appreciated that the exact structural configuration is implementation specific, and that structural components can be combined and/or separated to meet implementation specific requirements. 
     Spindle gearbox  133  of proprotor gearbox  117  is located above a surface of an upper wing skin  193  at a distance D 1  (shown in  FIG. 11 ), while also being approximately centered between inboard rib  185  and outboard rib  187 . One advantage of locating the proprotor gearbox  147  above the surface of upper wing skin  193  is that the fore/aft location of proprotor gearbox  147  can be easily tailored to align the aircraft center of gravity (CG) with the conversion axis  137  while the propulsion system  111  is in helicopter mode, while also aligning the aircraft center of gravity (CG) with the wing aerodynamic center of lift while the propulsion system  111  is in airplane mode. Because the aircraft center of gravity (CG) shifts as the proprotor  115  rotates between helicopter mode and airplane mode, the distance from the location of proprotor  115  in helicopter mode and airplane mode center of lift must correspond. As such, locating proprotor gearbox  147  above the wing allows the exact fore/aft location to be optimized accordingly, while also structurally attaching the proprotor gearbox  147  with in a zone of the torque box formed by forward wing spar  195 , aft wing spar  197 , inboard rib  185 , and outboard rib  187 . 
     The location of the spindle gearbox  133  portion of proprotor gearbox  147  provides an efficient structural support for enduring operational loads by being mounted to inboard rib  185  and outboard rib  187 , which together with a forward wing spar  195  and an aft wing spar  197 , form a structural torque box. For example, when aircraft  101  is in helicopter mode, torque about mast axis  169  is reacted by the torque box collectively formed by inboard rib  185 , outboard rib  187 , forward wing spar  195 , and aft wing spar  197 . It should be noted that location of spindle gearbox  133  of proprotor gearbox  147  also positions the mast axis  169 , while in helicopter mode, inboard of outboard rib  187 , outboard of inboard rib  185 , forward of aft spar  197 , and aft of forward spar  195 , which allows the axis of the torque to be inside of the torque box structure, rather than cantilevered outside of the torque box structure. In contrast, a spindle gearbox location outside (such as outboard, forward, or aft) would cause a moment that would increase operational loading, thus requiring heavier and less efficient structural support. 
     Fixed gearbox  129  is secured to outboard pillow block  183  with a housing  199 . Housing  199  is a conical structure with one or more flanges configured for coupling to gearbox  129  and outboard pillow block  183 . An additional support may be utilized to provide additional support between gearbox  129  and the wing structure, such as supplemental support  201  (shown in  FIG. 9 ); however, housing  199  is the primary support structure therebetween. In one embodiment, supplemental support  201  is strong in the inboard/outboard and vertical directions, but weak in the fore/aft direction. Housing  199  is significant because it is configured to minimize misalignment between fixed gearbox  129  and spindle gearbox  133 . If the primary attachment structure was not common with the attachment structure of proprotor gearbox  147 , then operation loading, such as load deflection and/or thermal growth, would dramatically increase the misalignment therebetween. 
     Power is transferred from fixed gearbox  129  to spindle gearbox  133  of proprotor gearbox  147  through the quill shaft  203 . Quill shaft  203  is a floating shaft configured to accept any misalignment due to manufacturing tolerances and operational effects between the fixed system (fixed gearbox  129 ) and the rotating system (proprotor gearbox  147 ). Quill shaft  203  is configured to be assembled and disassembled independently from the fixed and rotating systems. As such, quill shaft  203  can be removed without removing either of the fixed and rotating systems. 
     Referring also to  FIGS. 12-14 , quill shaft  203  can have a first splined portion  205  and a second splined portion  207 . In the illustrated embodiment, the first splined portion  205  has a smaller diameter than the second splined portion  207 , thus the first splined portion  205  is located inboard and the second splined portion  207  is located outboard so that the quill shaft  203  can be removed to the outboard direction for inspection/maintenance thereof. Quill shaft  203  can include one or more inboard lubrication ports  209  and outboard lubrication ports  211 . Quill shaft  203  can also include a first sect of o-ring glands  213  and a second set of o-ring glands  215 . 
     During operation, second splined portion  207  is in torque engagement with an output gear  217  of fixed gearbox  129  while first splined portion  205  is in torque engagement with a splined portion of the input  167  to spindle gearbox  133 . The first splined portion  205  and second splined portion  207  are crowned to promote teeth engagement in the event of non-axial misalignment between spindle gearbox  133  and fixed gearbox  129 . Lubrication oil is circulated to the mating surfaces of the first splined portion  205  through outboard lubrication ports  211 , the seals associated with the second set of o-ring glands forcing the lubrication fluid to flow to the first splined portion  205  instead of flowing toward the center of quill shaft  203 . Similarly, lubrication oil is circulated to the mating surfaces of the second splined portion  207  through inboard lubrication ports  209 , the seals associated with the first set of o-ring glands forcing the lubrication fluid to flow to the second splined portion  207  instead of flowing toward the center of quill shaft  203 . 
     One unique aspect of the configuration of quill shaft  203  in conjunction with spindle gearbox  133  and fixed gearbox  129  is that quill shaft  203  can be removed without removing either of the spindle gearbox  133  and fixed gearbox  129 . An access cover  219  can be removed thereby accessing the second splined portion  207  of quill shaft  203 . An interior portion  221  includes a feature, such as threads, for which a removal tool  223  can attach thereto. In one embodiment, interior portion  221  has female threads, while removal tool  223  has male threads that mate thereto. Upon attachment of removal tool  223  to quill shaft  203 , the quill shaft  203  can be removed by pulling out in an outboard direction along the centerline axis of the quill shaft  203 . Quill shaft  203  is critical for the operation of aircraft  101 , as such, safety and efficiency of operation is improved by increasing the ease for which quill shaft  203  can be inspected. 
     The embodiments disclosed herein provide one or more of the following advantages. For example, the location and orientation of proprotor in relation to the wing structure enables the proprotor to be adequately supported with minimal structural mass, while also providing efficient maintainability. Location of the proprotor above the wing allows the proprotor to be removed in an upward direction upon removing the quill shaft, as such, the fixed gearbox and engine don&#39;t have to be removed or disassembled when a maintenance action only requires servicing of the proprotor. 
     Further advantages include a quill shaft located between the fixed gearbox and a rotating spindle gearbox of the proprotor that allows for misalignment between the two. For example, the splined portions of the quill shaft allow for axial translation or floating in relation to the mating features on the fixed gearbox and the spindle gearbox, such as when operation of the tiltrotor causes misalignment in the axial direction of the quill shaft. Further, the splined portions on the quill shaft can be crowned to further allow for non-axial misalignment, such as fore/aft misalignment. Further, quill shaft is configured to be easily removed during a maintenance and/or inspection procedure. 
     The particular embodiments disclosed herein are illustrative only, as the system and method may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Modifications, additions, or omissions may be made to the system described herein without departing from the scope of the invention. The components of the system may be integrated or separated. Moreover, the operations of the system may be performed by more, fewer, or other components. 
     Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosure. Accordingly, the protection sought herein is as set forth in the claims below. 
     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 paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.