Patent Publication Number: US-11396371-B2

Title: Rotor hub assembly with universal joint

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of application Ser. No. 15/658,190, which was filed on 24 Jul. 2017 and entitled “Rotor Hub Assembly with Universal Joint,” the entire content of which is hereby expressly incorporated by reference. 
    
    
     BACKGROUND 
     Rotorcraft often utilize a gimbaled drive joint to allow the axis of rotation of the rotor hub to vary relative to the mast axis. These gimbaled drive joints may utilize universal joints (also known as a Hooke&#39;s joint or a Cardin joint) to accomplish the variable axis of rotation. However, the universal joints produce an undesirable two per revolution (“2/rev”) torsional drive force. In the past, two-bladed helicopters dealt with these torsional 2/rev forces that originate in the gimbaled hub flapping joint by tuning the drive train to avoid 2/rev resonances by using long slender masts that were torsionally soft. These long, thin, torsionally soft masts would attenuate the vibration. The long torsionally soft mast and careful tuning of all the drive elements of the rotor drive train have been used to produce helicopters that can run for thousands of hours with no issues from the torsional 2/rev forces and motions that are inherent in two-bladed rotor systems. However, tiltrotor aircraft require very stiff hubs in the chord wise direction and very stiff masts, pylons, and wings to prevent whirl flutter instability problems in the rotor system during high speed airplane flight. As such, the ability to attenuate the 2/rev vibration via long torsionally soft masts is not possible in tiltrotor aircraft. In a prior tiltrotor aircraft, it was attempted to solve the 2/rev dilemma by utilizing a true constant velocity joint instead of a simpler universal joint. However, even the true constant velocity joint produced unwanted 2/rev vibrations. In order to reduce the overall rotor hub 2/rev vibrations to a tolerable level, a pair of very heavy pendulum assemblies and additional vibration treatment were required. As such, there is a need to develop a simple, lightweight, gimbaled rotor hub assembly that will attenuate the 2/rev vibrations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of a rotor hub assembly according to this disclosure. 
         FIG. 2  is an oblique view of the rotor hub assembly of  FIG. 1 . 
         FIG. 3  is an oblique view of a portion of the rotor hub assembly of  FIGS. 1 and 2 . 
         FIG. 4  is an oblique view of a portion of the rotor hub assembly of  FIGS. 1-3 . 
         FIG. 5  is an exploded view of a portion of the rotor hub assembly of  FIGS. 1-4 . 
         FIG. 6  is an oblique view of an elastomeric member of the rotor hub assembly of  FIGS. 1-5 . 
         FIG. 7  is an oblique view of another rotor hub assembly according to this disclosure. 
         FIG. 8  is an exploded view of the rotor hub assembly of  FIG. 7 . 
         FIG. 9  is an oblique view of a portion of the rotor mast assembly of  FIGS. 7 and 8 . 
     
    
    
     DETAILED DESCRIPTION 
     In this disclosure, 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 this 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. 
     The solution presented in this disclosure solves the dilemma of 2/rev vibrations in a gimbaled rotor hub by using a rotor hub assembly with a universal joint and an elastomeric mast joint that may be used to tune the natural frequency away from the 2/rev torsional oscillatory drive forces that are generated by the universal joint. This simplified solution will not only save money but will also save a substantial amount of weight. While the disclosed rotor hub assembly may be used on any rotorcraft, it is particularly well-suited for use on tiltrotor aircraft. 
     As shown in  FIGS. 1 and 2 , a rotor hub assembly  101  is illustrated. Rotor hub assembly  101  is shown optionally disposed within a shroud  103  (shown cut-away). Rotor hub assembly  101  is attached to a rotor mast  105  to facilitate the transmission of torque from a powerplant to cause the rotation of blades  107 , thereby generating lift and/or thrust. Rotor hub assembly  101  includes a universal joint  109  attached to a yoke  111 . Universal joint  109  permits yoke  111  to rotate about an axis of rotation that is free to move relative to the axis of rotation of rotor mast  105 . Yoke  111  includes four arms  113  extending therefrom to support blades  107 . As shown, arms  113  may include structure to facilitate the attachment of outboard shear/CF bearings  115  as well as inboard pitch bearings  117 . 
       FIG. 3  illustrates universal joint  109  attached to rotor mast  105 . Universal joint  109  includes a pair of yoke brackets  119 A,  119 B. While yoke brackets  119 A,  119 B are shown as a pair, it should be understood that yoke brackets  119 A,  119 B could be one unitary yoke bracket. Each yoke bracket  119 A,  119 B includes a base  121 A,  121 B for providing a stable connection with yoke  111 . Bases  121 A,  121 B include a plurality of openings  123 A,  123 B extending therethrough to accept hardware for attaching yoke brackets  119 A,  119 B to yoke  111 . Extending from bases  121 A,  121 B are tabs  125 A,  125 B. Tabs  125 A,  125 B define openings  127 A,  127 B extending therethrough. Opening  127 A and opening  127 B are coaxial along a central longitudinal axis  129 . Each opening  127 A,  127 B is configured to receive a hinge pin  131 A,  131 B and a radial bearing  133 A,  133 B therein. Hinge pins  131 A,  131 B connect yoke brackets  119 A,  119 B to a cross member  135  via a first aperture  137  and a second aperture  139 . First aperture  137  and second aperture  139  are also coaxial about central longitudinal axis  129 . Hinge pin  131 A extends from opening  127 A to first aperture  137 . First aperture  137  may also include a radial bearing  141  configured to facilitate rotation of hinge pin  131 A therein. Similarly, second aperture  139  may include a radial bearing  143  configured to facilitate rotation of hinge pin  131 B therein. Universal joint  109  also includes a drive member  145  configured to transfer torque from rotor mast  105  to cross member  135 . 
     Referring to  FIGS. 4 and 5 , drive member  145  is shown in more detail. Drive member  145  includes an inner member  147  having an inner surface  149  configured to engage rotor mast  105 . This engagement may be accomplished via the use of splines  151  on inner surface  149  and complementary splines  153  on rotor mast  105 . Inner member  147  has an outer surface  155  that includes a plurality of projections  157  extending therefrom. Drive member  145  also includes an outer member  159  surrounding inner member  147 . Outer member  159  includes an inner surface  161  that includes a plurality of projections  163  extending therefrom, such that projections  163  interlace with projections  157 . A plurality of elastomeric members  165  are disposed between the interlaced projections  157  and  163 . Outer member  159  also includes an outer surface  167  with a pair of trunnions  169 A,  169 B extending therefrom. As shown in  FIG. 3 , trunnion  169 A extends into a third aperture  171  of cross member  135 , and trunnion  169 B extends in a fourth aperture  173  of cross member  135 , wherein third aperture  171  and fourth aperture  173  are coaxial about central longitudinal axis  175 . Accordingly, cross member  135  is pivotally attached to drive member  145  about central longitudinal axis  175 . 
     As shown in  FIG. 6 , elastomeric members  165  may be made of alternating layers of elastomeric material  177  and rigid material  179 . Elastomeric material  177  may comprise natural or synthetic rubber, or any other elastomeric material suitable for such application. Rigid material  179  may be formed of metal, plastic, composite, or any other material suitable for such application. 
     In operation, torque is transmitted through rotor mast  105  to drive member  145 , cross member  135 , yoke brackets  119 A,  119 B, and yoke  111 , which rotates blades  107 . When yoke  111  rotates about an axis that is not coincident with the axis of rotation of rotor mast  105 , 2/rev oscillations are generated by universal joint  109 . These 2/rev oscillations are attenuated by tuning elastomeric members  165  to absorb them in compression, rather than allowing the oscillations to be transmitted down rotor mast  105  to the drivetrain. 
     Referring to  FIGS. 7 and 8 , a rotor hub assembly  201  is illustrated. Rotor hub assembly  201  is attached to a rotor mast  205  to facilitate the transmission of torque from a powerplant to cause the rotation of blades (not shown), thereby generating lift and/or thrust. Rotor hub assembly  201  includes a universal joint  209  attached to a yoke  211 . Universal joint  209  permits yoke  211  to rotate about an axis of rotation that is free to move relative to the axis of rotation of rotor mast  205 . Yoke  211  includes three arms  213  extending therefrom to support the blades. Universal joint  209  includes a yoke bracket  219 . Yoke bracket  219  includes a base  221  for providing a stable connection with yoke  211 . Base  221  includes a plurality of openings  223  extending therethrough to accept hardware for attaching yoke bracket  219  to yoke  211 . Extending from base  221  are tabs  225 A,  225 B,  225 C,  225 D. Tabs  225 A,  225 B,  225 C,  225 D define openings  227 A,  227 B,  227 C,  227 D extending therethrough, respectively. Openings  227 A,  227 B,  227 C,  227 D are coaxial along a central longitudinal axis  229 . Openings  227 A and  227 B are configured to receive a hinge pin  231 A and a radial bearing  233 A therein. And openings  227 C and  227 D are configured to receive a hinge pin  231 B and a radial bearing  233 B therein. Hinge pins  231 A,  231 B connect yoke bracket  219  to a cross member  235  via a first aperture  237  and a second aperture  239 . First aperture  237  and second aperture  239  are also coaxial about central longitudinal axis  229 . Hinge pin  231 A extends from opening  227 A through first aperture  237  to opening  227 B. Hinge pin  231 B extends from opening  227 C through second aperture  239  to opening  227 D. Universal joint  209  also includes a drive member  245  configured to transfer torque from rotor mast  205  to cross member  235 . 
     Referring to  FIGS. 8 and 9 , drive member  245  includes an inner member  247  having an inner surface  249  configured to engage rotor mast  205 . Inner member  247  has a substantially cylindrical outer surface  255 . Inner member  247  also includes a flange  256  extending radially therefrom. Flange  256  defines a plurality of openings  258  extending therethrough. Drive member  245  also includes an outer member  259  surrounding inner member  247 . Outer member  259  includes a substantially cylindrical inner surface  261 . Outer member  259  also includes a flange  262  extending radially therefrom. Flange  262  includes a plurality of openings  264  extending therethrough. An elastomeric member  265  is located between inner member  247  and outer member  259 . The elastomeric member  265  includes a hollow cylindrical portion  266  configured to fit between substantially cylindrical outer surface  255  of inner member  247  and substantially cylindrical inner surface  261  of outer member  259 . Elastomeric member  265  includes a flange  268  extending therefrom. Flange  268  includes a plurality of openings  270  extending therethrough. Outer member  259  also includes an outer surface  267  with a pair of trunnions  269 A,  269 B extending therefrom. Trunnion  269 A extends into a third aperture  271  of cross member  235 , and trunnion  269 B extends in a fourth aperture  273  of cross member  235 , wherein third aperture  271  and fourth aperture  273  are coaxial about a central longitudinal axis  275 . Accordingly, cross member  235  is pivotally attached to drive member  245  about central longitudinal axis  275 . 
     Drive member  245  may also include an elastomeric ring  281  and an inelastic ring  283 . Elastomeric ring  281  and inelastic ring  283  each include a plurality of openings extending therethrough,  285  and  287 , respectively. When assembled, flange  262  of outer member  259  has flange  268  of elastomeric member  265  on top thereof, followed by flange  256  of inner member  247 , then elastomeric ring  281 , and finally inelastic ring  283  on the top. Flanges  262 ,  268 ,  256  and rings  281 ,  283  are aligned such that openings  264 ,  270 ,  258 ,  285 ,  287  are aligned and receive connection bolts  289  therethrough. 
     In operation, torque is transmitted through rotor mast  205 , drive member  245 , cross member  235 , yoke bracket  219 , and yoke  211 , to rotate the blades. When yoke  211  rotates about an axis that is not coincident with the axis of rotation of rotor mast  205 , 2/rev oscillations are generated by universal joint  209 . These 2/rev oscillations are attenuated by tuning elastomeric member  265  and elastomeric ring  281  to absorb them in shear, rather than allowing the oscillations to be transmitted down rotor mast  205  to the drivetrain. Additional elastomeric rings  281  and inelastic rings  283  may be added as required. 
     In the embodiments shown, the drive members and cross members show the masts passing through the centers thereof. It should be understood that the drive member could be mounted to a distal end of the mast. In addition, axis about which the cross member is pivotally attached to the yoke bracket could be above or below the drive member. 
     At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, RI, and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R l +k*(R u −R l ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.