Abstract:
The double row, tandem, angular contact ball bearing assembly uses snap cages for both rows of ball bearings. The use of snap cages reduces straddle between the rows and allows for improvements in spacing and increased load carrying capacity without increased outer dimensions of the bearing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present Invention relates to double row, tandem, angular contact ball bearing assemblies and, especially, tandem ball bearing assemblies construed for use within differential gearings and other applications where high radial and high unidirectional axial rigidity is a requirement. 
       BACKGROUND OF THE INVENTION 
       [0002]    Depending on the inclination and orientation of the contact angles between the rolling elements and the bearing rings, angular contact ball bearing assemblies are generally grouped into three species which are O-arrangements, X-arrangements, and tandem-arrangements. Each one of these arrangements has its specific purpose and unique design characteristics to solve a particular set of tasks enabling respective specific applications. 
         [0003]    Tandem ball bearings are usually designed in a manner wherein the contact angles for the adjacent rows of ball bearings are quite similar. The balls as received within the raceways are guided within respective windows formed by two separate annular window-cages. The distance between both raceways is designed such that the inner rings of the window-cages may not abut against each other. The axial distance between the both raceways is designed to secure a sufficient safety clearance between the inner annular ribs of the cages of both rows. Due to this fact, there exists a design restriction in respect to the selection of ball size for the tandem ball bearing in order to maintain the straddle distance between the cages to avoid the interference of the cages of both the rows. This results in designing the bearing with lower load carrying capacity and large overall bearing width. 
         [0004]    Currently, all tandem ball bearing designs use window type cages. A typical cross section of a tandem ball bearing using the window-style cages is illustrated in  FIG. 1 . As shown in  FIG. 1 , tandem ball bearing assembly  10  has an outer ring  12 , an inner ring  14 , two adjacent sets of rolling elements  16  in bearings  10  with contact angles  17 , illustrated as 25°. Each set of the rolling elements  16  are housed in a window-type cage  18 . The inner rib of window-type cages restricts the size of the bearing assembly due to straddle illustrated in circle  19 . As can be seen in  FIG. 1 , the inner rib of each cage requires safety gap (or clearance to prevent interference) with the other thereby restricting the size of the overall assembly; therefore, limiting the load carrying capacity and envelope size of bearing. 
       OBJECT OF THE PRESENT INVENTION 
       [0005]    It is an object of the present Invention to create a dual row, tandem, angular contact ball bearing assembly wherein there is enhanced load carrying capacity within the same dimensions. 
         [0006]    It is also an object of the present Invention to provide a compact bearing design. 
         [0007]    It is a further object of the present Invention, to create a double row, tandem, angular contact ball bearing assembly which provides a high axial and radial load carrying capacity at improved relation to its outer dimensions. 
         [0008]    It is a further object of the present Invention to enhance the bearing performance by increasing the load carrying capacity of the bearing and lowering the production related costs. 
         [0009]    It is just a further object of the present Invention to reduce the limitations in the selection of ball size within a given bearing envelope size. 
         [0010]    These and other objects and advantages of the Invention will become more readily apparent by the following description. 
       SUMMARY OF THE INVENTION 
       [0011]    The objects of the present Invention are obtained by a particular internal design of the bearing, which allows to axially adhere the balls of the two rows, wherein the saved space may be used to increase the diameter of the balls, or to reduce the overall dimensions of width of the bearing without reducing its load carrying characteristic. The cages are designed so as to open inwardly which allows to design the cages as snap-in cages with balls as the rolling elements. More specifically, the Invention may be defined as a double row, tandem, angular contact, ball bearing assembly comprising: 
         [0012]    a one piece outer bearing ring having two adjacent outer races, each of the outer races having a single shoulder, the shoulder of one of the outer races is located adjacent an axial edge of the outer ring and the shoulder of the other of the outer races is located axially inward on the outer ring; 
         [0013]    a one piece inner bearing ring having two adjacent inner races, each of the inner races having a single shoulder, the shoulder of one of the inner races is located axially inward on the inner ring and the shoulder of the other of the inner races is located axially adjacent a front edge of the inner ring; 
         [0014]    one raceway formed by the one of the outer races opposing the one of the inner races; 
         [0015]    another raceway formed by the other of the outer races opposing the other one of the inner races; 
         [0016]    one set of balls located in the one raceway; 
         [0017]    another set of balls located in the other raceway; 
         [0018]    one snap cage housing the one set of balls and another snap cage housing the other set of balls, each of the one and other snap cage having a plurality of thin-walled, cup shaped pockets connected to one another by a single rib, each of the pockets housing one of the balls, the rib of the one cage is mounted adjacent one axial edge of the assembly and the other cage is mounted adjacent the other axial edge of the assembly, and each of the pockets open axially inward of the assembly. 
         [0019]    The balls of the two rows thus may adhere each other to just leave a minimum axial space and without being separated or shielded from each other by an annular rib-structure of any of the cages. This minimum axial space may be dimensioned to come close to 0.5 mm. 
         [0020]    Preferably, the balls in one set do have the same diameter as the balls in the other set. Alternatively, the balls in one set may have a diameter different from the diameter of the balls in the other set. 
         [0021]    The pockets of the cages are such that the balls may snap-fit into the pockets from an axial side entry. Suitably, the cages encircle the ball in an amount of about 240°. Although the cages are open towards the inner shoulders of the bearing rings, the cages may be designed such that the balls are fitted into the pocket from a radial direction without requiring significant elastic deformation of the free inner end sections of the sidewalls of the pockets. 
         [0022]    The tandem ball bearing design according to the present Invention is suited as replacement to taper roller bearings in a broad field of applications, especially for differential gearings and pinion axle support. By comparison, tandem ball bearings according to the Invention come at least close to the load carrying capacity of taper roller bearings of similar outer dimension while providing less friction and thus improved mechanical efficiency. A particular achievement of the technical concept for tandem ball bearings according to the present Invention is the enhancement of the bearing load carrying capacity using the same or similar envelop dimensions, or to compact the bearing size (overall width) providing the same load carrying capacity. 
         [0023]    In contrast to the conventional constructions, the balls of the two rows are no longer separated by a pair of annular ribs of the so far employed window type cage design. The concept according to the present Invention allows to no longer provide axial space for a pair of independent cage ribs and also does no longer require an axial gap between these ribs of the cages. The construction of both cages of the tandem ball bearings according to the Invention is no longer subject of a restriction of the space requirement of the inner ribs of the conventional cages. The tandem ball bearing according to the present Invention provides a higher load carrying capacity compared to conventional taper roller bearings, it requires less space as conventional bearings of same load carrying capacity and also allows to reduce the ring weight and material related costs. 
         [0024]    One of the main advantages of the construction according to the present Invention is to enhance the design and capacity of tandem ball bearing by using cages similar to the so called TVH-type cages. Using those cages similar to TVH-type cages avoids the restriction to maintain a quite considerable distance between two rows. The advantages using the TVH-type cages are: 
         [0025]    almost no restriction for the distance between the two rows within the same envelop dimensions; 
         [0026]    broadening of the option to select larger ball size; 
         [0027]    achieving higher load carrying capacity of the bearing within the same envelope dimensions; 
         [0028]    higher bearing life; 
         [0029]    with higher load carrying capacity design the overall width of the bearing can be reduced (This is due to reducing the distance between the two rows. Assuming 0.5 mm of minimum gap maintained between two balls extreme ends) 
         [0030]    more compact bearing design; 
         [0031]    overall bearing cost will be reduced since the use of larger balls in the design will reduce the wall thickness of the outer ring and inner ring races and ultimately the cost of the tubes or forgings used for the outer ring and inner ring; 
         [0032]    cost savings due to reduced material consumption of cages. 
         [0033]    By adopting a cage design similar to the TVH-type cage design it will be possible to select a larger ball size since there is no restriction to keep an axial gap between the inner annular ribs of the cages (The only restriction is, that the balls of both the rows do not interfere each other, while a minimum gap of 0.5 mm between the axial face sections of balls between the two rows is assumed as sufficient). This extremely narrow gab is sufficient, as the balls are stably guided in their races and thus do not have that much axial play as window-type cages would take. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    These and other aspects of the present Invention may be become further and even more readily apparent by reference to one or more of the following drawings presented herein for purpose of illustration, wherein: 
           [0035]      FIG. 1  illustrates a conventional tandem ball bearing assembly; 
           [0036]      FIG. 2  illustrates a tandem ball bearing similar to the present Invention with increased load capacity; 
           [0037]      FIG. 3  illustrates the tandem ball bearing assembly according to the present Invention having compact design; 
           [0038]      FIG. 4  illustrates a snap-in cage for use in the present Invention; 
           [0039]      FIG. 5  shows a cross section of the cage of  FIG. 4  taken along lines V V; 
           [0040]      FIG. 6  shows a perspective view of the snap-in cage; and 
           [0041]      FIG. 7  shows an exploded view of a bearing assembly according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]      FIG. 2  illustrates a tandem ball bearing assembly  20  for the present Invention having an outer ring  22  with adjacent outer races  24  and  26 . Each outer race  24 ,  26  is limited in axial direction by a respective shoulder  28  and  30 . 
         [0043]    The outer ring  22  has a first shoulder  30  located axially adjacent the side edge of outer ring  22  and a second shoulder  28  located axially inward on the inner circumferential wall of the outer ring  22 . 
         [0044]    The outer circumferential wall of the inner ring  32  is shaped to provide inner races  34  and  36 . Each inner race  34 ,  36  is limited by a first shoulder  38  and a second shoulder  40 , respectively. Shoulder  38  is located axially adjacent the side edge of inner ring  32  while shoulder  40  is located axially inward on the inner ring  32 . 
         [0045]    Outer race  24  and inner race  34  define a raceway  42  with a contact angle  43 . Outer race  26  and inner race  36  do define a raceway  44  with contact angle  45 . A first set of balls  46  is located in raceway  42  while another, i.e. a second set of balls  48  is located in raceway  44 . One snap cage  50  holds balls  46  and another snap cage  52  holds balls  48 . 
         [0046]      FIGS. 4 and 5  illustrate snap cages  50  and  52 . Snap cages  50  and  52  each have pockets  54  connected by an annular rib  56 . Each of the pockets  54  has side walls  58  which are separated by a free space  60 . Balls  46 ,  48  are illustrated as snapped into snap cage  50 ,  52  in  FIG. 5 . As shown in  FIG. 4 , each of the pockets  54  has sidewalls  58  which are rounded concave as shown by edges A, B, C and D in order to snap fit balls  46 ,  48  into the respective pocket  54 . Side walls  58  encircle balls  46 ,  48  by about 240°. 
         [0047]      FIG. 3  illustrates one of the improvements achieved according to the present Invention in that adjacent raceways  42  and  44  adhere to each other closer together, i.e. are spaced less, such that the overall axial dimension of tandem ball bearing assembly  20  can be less than within conventional tandem roller bearings. 
         [0048]    That allows for larger sized balls without diminishing the axial dimension of the bearing assembly thereby allowing for a higher bad carrying capacity and longer bearing life. 
         [0049]    Additionally, by eliminating the cages stick out (or eliminating inner ribs) of the cages between the two rows from the window style cage, the axial width of the bearing assembly can be decreased and a more compact bearing design obtained. 
         [0050]    Additionally, overall bearing costs can be reduced since the use of larger balls in the design will reduce the wall thickness of the outer ring and inner ring races and ultimately the cost of tubes and the forging used in the outer rings and the inner rings. 
         [0051]      FIG. 7  illustrates a particular embodiment of the bearing according to the present invention as axial crossection and as a kind of exploded view. The bearing according to  FIG. 7  is a double row, tandem, angular contact, ball bearing. This bearing includes a one piece outer bearing ring  22  having two adjacent outer races  26 ,  24  each of the outer races  26 ,  24  having a shoulder  28 ,  30 , the shoulder  30  of one of the outer races  26  adjacent an axial edge E 1  of the outer ring  22  and the shoulder  28  of the other  24  of the outer races  24 ,  26  is located axially inward on the outer ring  22 . 
         [0052]    The bearing further includes a one piece inner bearing ring having two adjacent inner races  36 ,  34 , each of the inner races  36 ,  34  having a shoulder  40 ,  38 , the shoulder  40  of one of the inner races  36  is located axially inward on the inner ring and the shoulder  38  of the other of the inner races  34  is located axially adjacent an edge E 3  of the inner ring  32 . 
         [0053]    Upon mounting the bearing by axially fitting the shown components, one raceway  44  will be defined and formed by the one of the outer races  26  opposing the one  36  of the inner races. Another  42  raceway is formed by the other  24  of the outer races opposing the other  34  of the inner races. One set  48  of balls located in the one raceway  44 , and another set  46  of balls is located in the other raceway  42 . 
         [0054]    The particular bearing assembly further includes a first cage  52  which accommodates and guides the one set  48  of balls and a second cage  50  housing the other set  46  of balls. According to the present invention, at least one of the cages  52 ,  50  being construed as snap cage having a plurality of thin-walled, cup shaped pockets  54  connected to one another by a rib  56 , each of the pockets  54  housing one of the balls, the rib  56  of the at least one snap cage  52  is arranged adjacent one axial edge E 1  of the assembly and each of the pockets  54  of the snap cage  52  open axially inward of the assembly. 
         [0055]    In this particular embodiment, the axial distance d between the centers C 1 , C 2  of the balls in both rows is less than 1.2 the average diameter of the balls. In this embodiment, the balls of one set  48  and the other set  46  have the same diameter. 
         [0056]    This particular assembly is further construed in such a manner, that the minimum axial distance CA between the outer surfaces of the balls in both rows is less than 0.5 mm. Further, the axial width B of the outer ring  22  measures less than 2.2 the average diameter D of the balls. 
         [0057]    The ratio between the overall axial width and the radial height of the bearing (B/H) is less than 1.36. 
         [0058]    The bearing assembly as shown here may be mounted in that the balls are fitted into the pockets  54  of the cages  50 ,  52 . Although the cages  50 ,  52  have a design as ball snap fitting cages, the balls may be inserted just from a radial direction, preferably from the inner side. The pockets  54  may be formed to provide a complementary spherical geometry, so as to quite stably guide the balls with merely little clearance. The inner surface of the pockets as facing the balls may have a micro-structure such as small groves or channels, designed to build up a particular lubricant film, in particular to concentrate lubricant on those areas of the balls which likely come in load carrying contact with the races upon rotation. 
         [0059]    The completed cages  50 ,  52  are fitted on the inner ring  32 , while the balls of the first set  48  of the balls may snugly walk into the inner race  36  after walking above a narrow front shoulder as shown in this embodiment. The thus formed subassembly may now be axially fitted into the outer ring  32 . 
         [0060]    In this mounted stage, the balls of the sets  48 ,  46  adhere to each other close in axial direction, and leave just a minimum axial gap of about 0.5 mm. The thus achieved bearing assembly has a considerable axial and radial load bearing capacity but requires less axial and radial space than a conventional bearing with similar load bearing capacity. 
         [0061]    Although the present invention was illustrated in connection with an embodiment were both sets of balls are first fitted with their cages onto the inner ring and than axially fitted into the outer ring, the invention also covers those embodiments were at least one of the sets of balls is first fitted into the outer ring  22  and the inner ring is axially fitted into the preassembly either with the other set of balls sitting on the inner ring or while the other set of balls is also already seated in the outer ring. 
       REFERENCE CHARACTERS 
       [0000]    
       
           10 . tandem ball bearing assembly 
           12 . outer ring 
           14 . inner ring 
           16 . set of rolling elements 
           17 . contact angles 
           18 . cages 
           19 . straddle window 
           20 . tandem ball bearing assembly 
           22 . outer ring 
           24 . outer race 
           26 . outer race 
           28 . shoulder 
           30 . shoulder 
           32 . inner ring 
           34 . inner race 
           36 . inner race 
           38 . shoulder 
           40 . shoulder 
           42 . raceway 
           43 . contact angle 
           44 . raceway 
           45 . contact angle 
           46 . set of balls 
           48 . set of balls 
           50 . snap cage 
           52 . snap cage 
           54 . pockets 
           56 . rib 
           58 . sidewalls of pocket 
           60 . Free space 
         B. width of outer ring 
         H. radial height 
         C 1 . ball center 
         C 2 . ball center 
         CA. axial clearance 
         d. distance between ball centers 
         E 1 . axial face of outer ring 
         E 3 . axial face of inner ring 
         D. diameter ball