Abstract:
A transfer gear assembly includes a transfer gear rotatably supported directly by a tapered roller bearing and thrust bearing. A tapered snap ring is positioned in a circumferential groove on a hub to provide a preload on the tapered roller bearing and thrust bearing. The tapered roller bearing and thrust bearing each may include only a single race.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a transfer gear assembly for a transmission in which a needle roller thrust bearing and tapered roller bearing are preloaded against each other as they support a transfer gear.  
         BACKGROUND OF THE INVENTION  
         [0002]    Vehicle transmissions with multiple axles include a transfer gear to transmit torque and speed from one axis to another. These transfer gears are typically supported by multiple bearings, each having races, so that the bearings can handle significant radial as well as fore-and-aft loads originating from the helical gears. The bearing preloaded positions are held either by a large nut or a tapered snap ring.  
           [0003]    It is desirable to improve upon the above-described transfer gear arrangement by reducing part count, reducing space usage, improving serviceability and reducing allowable axial play for the transfer gear.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a transfer gear assembly in which the transfer gear is supported directly by a thrust bearing and tapered roller bearing, and a preload is applied to the bearings by a tapered snap ring on a stationary hub.  
           [0005]    More specifically, the present invention provides a transfer gear assembly for a transmission including a stationary hub having a cylindrical hub surface and a radial hub surface. The cylindrical hub surface has a circumferential groove formed therein. A tapered inner race is positioned on the cylindrical hub surface. A complement of tapered rollers is positioned on the tapered inner race. A radially extending race is positioned against the radial hub surface. A thrust bearing is positioned against the radially extending race. A transfer gear is positioned around the hub and in direct contact with the tapered roller bearing and with the thrust bearing. A tapered snap ring is positioned in the circumferential groove in contact with the tapered inner race to provide a preload on the tapered roller bearing and thrust bearing. The tapered snap ring may be replaced by a different preload member, such as a nut.  
           [0006]    The invention also provides a method of assembling a transfer gear assembly as described above wherein the tapered inner race, tapered rollers, radially extending race, thrust bearing and transfer gear are positioned around the hub and preloaded so that the tapered snap ring drops into the circumferential groove in the hub.  
           [0007]    Accordingly, an object of the invention is to provide a transfer gear assembly which reduces space usage, reduces part count and improves serviceabilty.  
           [0008]    The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a longitudinal cross-sectional view of a transmission in accordance with the present invention;  
         [0010]    [0010]FIG. 2 shows an enlarged cross-sectional view of a transfer gear assembly taken from FIG. 1;  
         [0011]    [0011]FIG. 3 shows a flow chart of a transmission assembly process in accordance with the present invention; and  
         [0012]    [0012]FIG. 4 shows a partial longitudinal cross-sectional view of a transfer gear assembly in accordance with an alternative embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 1 shows a longitudinal cross-sectional view of a five-speed transmission  10  which receives power from an engine  12  and transfers this power through a differential  14  to left and right axles  16 , 18  of a vehicle.  
         [0014]    By way of example, with the transmission in the first forward speed setting, the engine  12  drives the torque converter  20  which drives the input shaft  22 . The input shaft is welded to the third clutch housing  24 , which is splined to the third clutch backing plate  26 , which rotates the input sun gear  28 . The input sun gear  28  rotates input planetary gear  30 , which rotates the input ring gear  32 . The input ring gear  32  is splined to the second clutch hub  34 . The second clutch hub  34  drives the output sun gear  36 , which is welded to the second clutch hub  34 . This structure is more readily seen in FIG. 2. The output sun gear  36  drives the output pinion gears  38 , which drive the output ring gear  40 . The output ring gear  40  is connected to the transfer gear  42 , which transfers torque and speed to the second shaft  44  via the second transfer gear  46 . The term “transfer gear” may be used interchangeably with “transfer pinion” or “transfer pinion gear.” 
         [0015]    Still referring to FIG. 2, a snap ring  48  secures the output ring gear  40  to the transfer gear  42 .  
         [0016]    The present invention is particularly characterized by the structure which rotationally supports and preloads the transfer gear  42  and is most clearly shown in FIG. 2. As shown, a stationary pump cover  50  acts as a stationary hub having a cylindrical hub surface  52  and a radial hub surface  54 .  
         [0017]    A tapered inner race  56  is positioned against the cylindrical hub surface  52 , and a complement of tapered rollers  58  is positioned on the tapered inner race  56 . A radially extending race  60  is positioned against the radial hub surface  54 , and a thrust bearing  62  is positioned against the radially extending race  60 .  
         [0018]    The transfer gear  42  has a conical interior surface  64  which is in direct contact with the tapered rollers  58 , and a side face  66  which is in direct contact with thrust bearing  62 .  
         [0019]    A tapered snap ring  68  is positioned in a circumferential groove  70  which is formed in the cylindrical hub surface  52 . The snap ring  68  has a flat surface  72  facing the tapered inner race  56 , and an oppositely facing tapered surface  74  which engages a corresponding tapered surface  76  in the groove  70 . The tapered snap ring takes up axial play and holds the components in place because of the locking angle provided by the tapered surfaces  74 , 76 . The tapered snap ring  68  also has a narrow inner tip  78  facing the bottom of the groove  70 .  
         [0020]    The transfer gear  42  has approximately the same hardness as the hardness of the rollers of tapered roller bearing  58  and thrust bearing  62  so that these components are compatible and additional races are not required. The hardness of each such component is approximately 58-64 Rockwell C. The core of the transfer gear  42  is low carbon steel and the surface is carburized to enable the desired hardness, and the tapered roller bearing  58  and thrust bearing  62  are alloy steel components.  
         [0021]    In this configuration, the transfer gear  42  forms the outer race for the tapered bearing  58 , and the transfer gear  42  also forms the side race for the thrust bearing  62 , thereby eliminating components and reducing packaging space.  
         [0022]    Turning to FIG. 3, a flow diagram of an assembly process is illustrated. As shown, in step  100  a stationary hub  50  is provided as described above. In step  102 , the axial race  60  and thrust bearing  62  are positioned against the radial hub surface  54 . In step  104 , the transfer gear  42  is positioned against the thrust bearing  62 . In step  106 , the tapered race  56  and tapered roller bearing  58  are positioned against the conical interior surface  64  of the transfer gear  42 . In step  108 , the tapered snap ring  68  is positioned in the circumferential groove  70  of the hub  50 . A preload force is applied against the tapered race  56  in step  110  toward the right as viewed in FIG. 1, so that the narrow inner tip  78  of the tapered snap ring  68  drops further into the cylindrical groove  70 . When the preload force is removed, the tapered snap ring  68  maintains the preload.  
         [0023]    Of course, the races  56 , 60 , bearings  58 , 62  and transfer gear  42  could be pre-assembled and then installed onto the stationary hub  56  as a sub-assembly. Also, the tapered snap ring could be installed after the preload force has been applied against the tapered race  56 .  
         [0024]    The transfer gear assembly is serviceable by removing the snap ring  68  from the circumferential groove  70 . This design also reduces or eliminates axial play for the transfer gear and provides a stiffer transfer gear.  
         [0025]    The alternative arrangement is shown in FIG. 4. Transfer gear  142  receives the torque from output shaft  122  through flange  177 . Preload on tapered inner rate  156  is applied by means of nut  168  threaded to radial hub  150 . Once the desired preload is achieved, nut  168  gets locked by swaging the nut material into slot  170  extended radially on a face of hub  150 .  
         [0026]    While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.