Abstract:
A planetary gear assembly includes a sun gear, planetary gears engaging the sun gear, a ring gear arranged about the planetary gears, the ring gear engaging the planetary gears, and a carrier frame including one or more pairs of bearing containment bands, a plurality of connecting segments, a plurality of spoke portions, and a hub portion, wherein each pair of bearing containment bands is connected to an adjacent pair of bearing containment bands with a connecting segment of the plurality of connecting segments and a spoke portion of the plurality of spoke portions connects each connecting segment to the hub portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention is related to reduction gears and, in particular, to a carrier frame used in a planetary gear system. 
         [0002]    Gear reductions are often used in mechanical systems to provide a differential in the rates of rotation of an input shaft and an output shaft. Planetary gear assemblies are one example of such a reduction gear system. 
         [0003]    Planetary gear assemblies may include, for example, an input shaft having a sun gear arranged coaxially with an axis of rotation of the input shaft. Planetary gears engage the sun gear in a radial arrangement about the sun gear, and engage a fixed ring gear that is concentrically arranged about the sun gear. The planetary gears are arranged between the sun gear and the ring gear. The planetary gears are supported by bearings (generally two per gear, or two bearing sets) that are mounted in a carrier frame. These bearings are arranged in two planes with a bearing supporting each end of the planetary gear at each of these two planes. These planes are commonly arranged such that one is on either side of the gear so that the gear is straddle mounted (where gear face load occurs between bearings). The bearing centers are closely aligned between the two planes to establish an axis of rotation about their center that is parallel to the axis of rotation of the sun gear. 
         [0004]    In operation, a torsional force applied to the input shaft rotates the sun gear, which in turn, rotates the planetary gears that are coupled to the carrier frame resulting in the rotation of the carrier frame, and an output shaft connected to the carrier frame. The tooth count of each of the gears used collectively establishes the specific reduction ratio of the planetary gear assembly. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to an exemplary embodiment of the present invention, a planetary gear assembly includes a sun gear, planetary gears engaging the sun gear, a ring gear arranged about the planetary gears, the ring gear engaging the planetary gears, and a carrier frame including one or more pairs of bearing containment bands, a plurality of connecting segments, a plurality of spoke portions, and a hub portion, wherein each pair of bearing containment bands is connected to an adjacent pair of bearing containment bands with a connecting segment of the plurality of connecting segments and a spoke portion of the plurality of spoke portions connects each connecting segment to the hub portion. 
         [0006]    According to yet another exemplary embodiment of the present invention, a carrier frame of a planetary gear assembly, the carrier frame including one or more pairs of bearing containment bands, a plurality of connecting segments, a plurality of spoke portions, and a hub portion, wherein each pair of bearing containment bands is connected to an adjacent pair of bearing containment bands with a connecting segment of the plurality of connecting segments and a spoke portion of the plurality of spoke portions connects each connecting segment to the hub portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  illustrates a perspective view of an exemplary embodiment of a planetary gear assembly. 
           [0009]      FIG. 2  illustrates a perspective view of the carrier frame, the planetary gears, and the supporting bearings of the gear assembly of  FIG. 1 . 
           [0010]      FIG. 3  illustrates a perspective view of an exemplary embodiment of the carrier frame of  FIGS. 1 and 2 . 
           [0011]      FIG. 4  illustrates another perspective view of the carrier frame of  FIG. 3 . 
           [0012]      FIG. 5  illustrates a section view (side partially cut away) of the planetary gear frame arranged within an exemplary embodiment of a housing portion and gear train. 
           [0013]      FIG. 6  illustrates a perspective partially cut-away view of the carrier frame. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  illustrates a perspective view of an exemplary embodiment of a planetary gear assembly  100 . The planetary gear assembly  100  includes a sun gear portion  102  coupled to an input shaft  104 . Planetary gears  106  engage the sun gear  102 , and are arranged radially about the sun gear  102 . The planetary gears  106  are coupled to bearings  108  that engage bearing containment bands  110  of a carrier frame  112 . The carrier frame  112  is connected to an output shaft  114 . An outer ring gear  116  engages the planetary gears  106  and is arranged concentrically about the sun gear  102 . 
         [0015]    In operation, the outer ring gear  116  may be fixed in position to, for example a housing portion (not shown). The input shaft  104  may be coupled to a device that provides a torque force such as, for example, an engine. When torque is applied to the input shaft  104 , the sun gear  102  rotates about the axis of rotation indicated by the arrow  101 . The rotation of the sun gear  102  in turn, drives the engaged planetary gears  106  such that the planetary gears  106  rotate about their respective axes of rotation indicated by the arrows  103 . The axes of rotation  103  of the planetary gears  106  are arranged substantially in parallel with the axis of rotation  101  of the sun gear  102 . The fixed arrangement of the outer ring gear  116  in engagement with the rotating planetary gears  106  results in the rotation of the carrier frame  112 , the output shaft  114 , and the collectively supported planetary gears  106  about an axis of rotation (indicated by the arrow  105 ) that is substantially coaxial with the axis of rotation indicated by the arrow  101 . 
         [0016]    In previous examples of carrier frames, a torque was applied to the input shaft, the resulting applied force is transmitted from the sun gear, to the planet gears, thru the bearing pairs, and onto the carrier frames. One plane of the bearings was coincident with the principle supporting plate, but the opposing plane of bearings were effectively moment loads (loads applied at a distance), which resulted in non-uniform torsional deflection of the carrier frame, creating misalignment of one bearing on a shaft relative to the other bearing. The illustrated exemplary embodiments of the carrier frame  112  described herein provide a carrier frame  112  that results in symmetric moment loading from bearings onto the carrier, which then exhibits uniform torsional deflection between bearing pairs when a torque is applied to the input shaft  104 . This outcome preserves suitable alignments between the bearing pairs supporting the planet gears, and thereby improving bearing life. The illustrated exemplary embodiments also requires less structural material and may be lighter than previous examples, thus providing additional benefits by reducing the amount of material resources used, and minimizing the total weight of the carrier frame. 
         [0017]      FIG. 2  illustrates a perspective view of the carrier frame  112 , the bearings  108  and the planetary gears  106 . The bearings  108  engage bearing containment bands  110  of the carrier frame  112 . The bearing containment bands  110  of the illustrated embodiment define an inner surface  201  and an outer surface  203 . The inner surface  201  defines an inner diameter that corresponds to an outer diameter of the bearings  108 . The outer surface  203  of each of the bearing containment bands  110  is connected to an adjacent outer surface  203  of a bearing wrap portion  110  by connecting segments  202 . A hub portion  204  having a conical profile includes connecting spokes  206  that extend radially from a portion  208  that connects to the output shaft  114  to connect to an inner surface  205  of the connecting segments  202 . The curved profile of the conical hub portion  204  facilitates clearance for the sun gear  102  (of  FIG. 1 ) such that the hub portion  204  and spokes  206  do not interfere with the rotation of the sun gear  102  or the engagement of the sun gear  102  with the planetary gears  106 . In the illustrated embodiment, the carrier frame  112  is fabricated from a single piece of material such as, for example, steel, titanium, or aluminum. However, in alternate embodiments the carrier frame  112  may be fabricated from any number of separate components. The output shaft  114  is presented in this embodiment as being integrally formed with the carrier frame  112 , however alternate embodiments may provide a carrier frame  112  having a coupling or fastening portion operative to engage the output shaft  114 . The terms input shaft  104  and output shaft  114  are used for illustrative purposes. One of ordinary skill in the art would understand that an input force may be applied to either the input shaft  104  or output shaft  114  and, thus, the function of the respective shafts are interchangeable, and the terms input shaft  104  or output shaft  114  do not limit the functions of the shafts. 
         [0018]      FIG. 3  illustrates a perspective view of an exemplary embodiment of the carrier frame  112  of  FIGS. 1 and 2 .  FIG. 4  illustrates another perspective view of the carrier frame  112  of  FIG. 3 . Referring to  FIG. 4 , the bearing containment bands  110  are arranged in pairs that are spaced a distance d along a line that is substantially parallel to the axis of rotation indicated by the arrow  105 . The connecting segments  202  define a dimension x that is substantially parallel to the axis of rotation indicated by the arrow  105 . In the illustrated embodiment the distal ends  401  of the spokes  206  intersect and are connected to the inner surface  205  of corresponding connecting segments  202  at approximately the mid point of the dimension x. The positions of the intersections of the distal ends  401  of the spokes  206  with the connecting arc segment  202  affects the torsional deflection of the carrier frame  112  when a bearing reaction force is applied to the bearing containment bands  110  via the planetary gears  106  and bearings  108  (of  FIG. 1 ). Though in the illustrated embodiment, the intersections of the distal ends  401  of the spokes  206  with the connecting segment  202  is arranged at approximately the mid point of the dimension x, alternate embodiments may arrange the intersections of the distal ends  401  of the spokes  206  with the connecting segment  202  in any position relative to the dimension x to optimize the reduction of torsional deflection of the carrier frame  112  when a force is applied to the bearing containment bands  110  via the planetary gears  106 . For example, it may be desirable to locate the intersections of the distal ends  401  of the spokes  206  with the connecting arc segment  202  in line, or substantially coplanar with the gear mesh plane (or center of the gear faces). In this regard, the intersection point may be determined based on system geometry, applied loads, and design goals for the carrier frame  112 . 
         [0019]      FIG. 5  illustrates a side partially cut away view of the presented planetary gear assembly  100  arranged in an exemplary embodiment of a housing portion  502 . In this regard, the outer ring gear  116  is secured to the housing portion  502 . The spokes  206  define an angle θ relative to the axis of rotation of the carrier frame  112  as indicated by the arrow  105 . The spokes  206  also define an angle θ′ relative to the inner surface of the  205  of the connecting segments  202 . In this illustrated embodiment, these angles are approximately supplements, though curvature of the connecting conical surface subtly influences the relationship between the angles. However, the connecting segments  202  may facilitate at any angle θ′ based on system packaging, production methods, operating loads, and tolerable deflection levels. 
         [0020]      FIG. 6  illustrates a perspective partially cut-away view of the carrier frame  102 . When a load is applied to the carrier frame  114  via the planetary gears  106  (of  FIG. 1 ), the bearing reaction force is directed as indicated by the arrows  601  into the bearing containment bands  110 . The arrows  603  illustrate the structural path of the forces toward the output shaft  114  via the connecting segments  202  and the spokes  206  of the hub portion  204 . The arrangement of the intersections of the distal ends  401  of the spokes  206  with the connecting segment  202  at approximately the mid point of the dimension x provides equalized torsional deflection of the carrier frame  112  and improved planet bearing alignments when the force is applied as indicated by the arrows  601 . As discussed above, the intersections of the distal ends  401  of the spokes  206  with the connecting segment  202  may be arranged at any point along the dimension x (relative to the spacing of the bearing containment bands  110  in each of the pairs of bearing containment bands  110 ) to optimize the reduction of the torsional deflection of the carrier frame  112 . Thus, the relative torsional deflection of the carrier frame  112  can be influenced (e.g., balanced or equalized) if the intersections of the distal ends  401  of the spokes  206  with the connecting segment  202  are arranged, for example, in another position that is not equidistant from the planes defined by the surfaces  605  of the bearing containment bands  110 . 
         [0021]    Though the illustrated embodiments include a planetary gear assembly having five planetary gears, alternate embodiments may include a plurality of planetary gears having any number of planetary gears. 
         [0022]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.