Abstract:
A split rolling element guide for a bearing assembly for a balance shaft of an internal combustion engine, having two axial support faces and a plurality of axial cross members defining rolling element pockets. A plurality of radial cutouts at each pocket increase flexibility of the cage and allow for greater opening of the cage at the split portion

Description:
TECHNICAL FIELD 
       [0001]    Example aspects described herein relate to bearing assemblies, particularly of bearing rolling element guides or cages, and more particularly, for balance shaft bearings for balance shafts in internal combustion engines. 
       BACKGROUND 
       [0002]    Bearing assemblies are typically circular in shape, and generally comprise rolling elements sandwiched between raceways in bearing rings. Rolling elements take many forms, including spherical balls, rollers or various other configurations, such as cone-shaped tapered rollers or barrel-shaped spherical rollers. Bearing rolling element guides, or cages, retain rolling elements within a bearing assembly, while typically allowing for free rotation of the rolling elements within the cages, and rotation of the cages within the bearing assembly. Cages can be used to separate rolling elements from each other, generally at equal intervals, and hold rolling elements in alignment with respect to the bearing rings. Depending on the structure of the bearing, or the bearing design, cages may be linear or circular and made from a variety of materials, including, but, not limited to brass, steel, and various types of plastic. 
         [0003]    In some applications, such as for balance shafts for internal combustion engines, a rolling element and cage assembly can be used without discrete bearing rings, with the balance shaft and surrounding engine housing or block acting as inner and outer raceways, respectively. In other words, rolling element raceways are integrally formed on the outer diameter of the balance shaft and the inner diameter of the balance shaft housing or block, respectively. In this form, the cage retains the rolling elements within the cage pockets during assembly and operation. 
         [0004]    Broadly, there are two main types of bearing cages; “crown” or “snap” cages; and “ribbon” or “riveted” cages. The “snap” type has an annular side member and axial partitions projecting from said member. These partitions are typically parallel to each other and have open rolling element pockets, allowing said rolling elements to seat or “snap” into position within these open pockets. The “riveted” type is comprised of two pieces or halves, each half with an open pocket to accommodate a rolling element. The halves are assembled on opposite sides of the rolling element, the pockets surrounding the rolling elements, and contact at land surfaces at intervals between rolling elements, then are joined together at the mating surface using various types or fastening elements, such as rivets. When rolling element bearings are used in balance shafts, typically cages of the “snap” type are used. 
         [0005]    Cages are guided by one of the available surfaces between the inner and outer rings. Cages may be guided by the inner land or surface, wherein, the cage&#39;s bore slides, or is guided by, the outer diameter of the inner ring. They may also be guided by the outer land, wherein, the cage&#39;s bore slides, or is guided by, the inner diameter of the outer ring. Finally, cage&#39;s may touch neither ring, and be guided by the rolling elements themselves. 
         [0006]    Some example bearing cages are shown in U.S. Pat. Nos. 6,247,847, 5,154,401 and 4,004,840. 
         [0007]    Different types and sizes of bearings require specifically designed bearing cages, taking into account bearing assembly size, operating conditions, and rolling element size, among other factors. It is understood that a particular design of bearing may incorporate a type of cage, but, may require variations in the cage to accommodate the specific bearing, for example choice of rolling element or material used. In balance shaft applications, the balance shaft has a number of diameter variations along its length as a result of balancing masses and mounting features on the balance shaft that prevent a bearing or cage and rolling element assembly from sliding along a length of the shaft during assembly. Therefore, the cage and rolling element assembly is typically wrapped around the shaft, which, in turn requires that the cage be separatable and flexible, in order to return to its required cylindrical form. A cage with increased flexibility is needed. 
       SUMMARY OF THE INVENTION 
       [0008]    A new design for a bearing cage is disclosed. In one example embodiment of the invention, the cage comprises cutout features around an internal circumference of the cage, on at least one axial end of the cage. 
         [0009]    In another example embodiment of the invention, the cage comprises cutout features at alternating positions along an inner and outer circumference of the cage, on at least one axial end of the cage. 
         [0010]    In a further embodiment of the invention, the cage comprises cutout features at alternating positions along an inner and outer circumference of the cage, on at least one axial end of the cage with the relative diameter of the cutout features decreasing as the distance from the separatable cage feature increases. 
         [0011]    In a further embodiment of the invention, the cage comprises cutout features around an external or internal circumference of the cage, with the diameter of the cutout features decreasing as the distance from the separatable cage feature increases. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The above mentioned and other features and advantages of the embodiments described herein, and the manner of attaining them, will become apparent and be better understood by reference to the following description of at least one example embodiment in conjunction with the accompanying drawings. A brief description of those drawings now follows. 
           [0013]      FIG. 1   a  is a perspective view of a cylindrical coordinate system demonstrating spatial terminology used in the present application; 
           [0014]      FIG. 1   b  is a perspective view of an object in the cylindrical coordinate system of  FIG. 1   a  demonstrating spatial terminology used in the present application; 
           [0015]      FIG. 2  is a cross sectional view of a prior art balance shaft system, with a cage and rolling element assembly thereon; 
           [0016]      FIG. 3  is a perspective view of a prior art cage and rolling element assembly; 
           [0017]      FIG. 4  is a front axial view of the prior art cage and rolling element assembly of  FIG. 3 ; 
           [0018]      FIG. 5  is a perspective view of a bearing cage according to an example embodiment of the invention; 
           [0019]      FIG. 6  is perspective view of a bearing cage according to another example embodiment of the invention; 
           [0020]      FIG. 7  is a front axial view of the bearing cage of  FIG. 6 ; 
           [0021]      FIG. 8  is a perspective view of a bearing cage according to a further example embodiment of the invention; 
           [0022]      FIG. 9  is a front axial view of the bearing cage of  FIG. 8 ; 
           [0023]      FIG. 10  is a perspective view of a bearing cage according to a further example embodiment of the invention; 
           [0024]      FIG. 11  is a front axial view of the bearing cage of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Identically labeled elements appearing in different ones of the figures refer to the same elements but may not be referenced in the description for all figures. The exemplification set out herein illustrates at least one embodiment, in at least one form, and such exemplification is not to be construed as limiting the scope of the claims in any manner. “Cage” and “rolling element guides” are used interchangeably. 
         [0026]      FIG. 1   a  is a perspective view of cylindrical coordinate system  80  demonstrating spatial terminology used in the present application. The present invention is at least partially described within the context of a cylindrical coordinate system. System  80  has a longitudinal axis  81 , used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis  81 , radius  82  (which is orthogonal to axis  81 ), and circumference  83 , respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects  84 ,  85 , and  86  are used. Surface  87  of object  84  forms an axial plane. That is, axis  81  forms a line along the surface. Surface  88  of object  85  forms a radial plane. That is, radius  82  forms a line along the surface. Surface  89  of object  86  forms a circumferential plane. That is, circumference  83  forms a line along the surface. As a further example, axial movement or disposition is parallel to axis  81 , radial movement or disposition is parallel to radius  82 , and circumferential movement or disposition is parallel to circumference  83 . Rotation is with respect to axis  81 . 
         [0027]    The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis  81 , radius  82 , or circumference  83 , respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes. 
         [0028]      FIG. 1   b  is a perspective view of object  90  in cylindrical coordinate system  80  of  FIG. 1A  demonstrating spatial terminology used in the present application. Cylindrical object  90  is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention in any manner. Object  90  includes axial surface  91 , radial surface  92 , and circumferential surface  93 . Surface  91  is part of an axial plane, surface  92  is part of a radial plane, and surface  93  is a circumferential surface. 
         [0029]      FIG. 2  is a cross sectional view of a prior art balance shaft system  50 , comprising balance shaft  52  supported by at least one bearing journal  54  in a housing or block  56  of the internal combustion engine  58 . The balance shaft  52  is supported via two bearing journals  54  in the housing  56  via rolling bearing assembly  5 , preferably in the form of needle bearings that have rolling elements  3 , such as rollers or needles, held in place via bearing cages  1 . The rollers or needles preferably contact the bearing journals  54  which form the inner bearing races directly on the inner side and may be supported on their radially outer sides by an outer race (not shown) or the housing  56  that supports the balance shafts  52 . 
         [0030]    The following description should be viewed with regard to  FIGS. 3 and 4 .  FIG. 3  is a perspective view of prior art bearing assembly  5  of  FIG. 2 , comprising cage  1  and rolling elements  3  held in place and separated from each other by cage  1 . Cage  1  comprises separable locking feature  7 , which may take several forms, including the “tongue and groove” embodiment shown, and rolling element pockets  9 . Pockets  9  are formed by parallel cross members  10  extending axially from one axial support face  11  to the opposite axial support face  12 . Shallow cutouts  20  are formed in axial support faces  11 ,  12  at axial opposed ends of rolling elements  3  and at each rolling element  3 , along an entire outer circumference of cage  1 . Cutouts  20  are shown as circular segments defined by a height h, no greater than 50% the thickness t of cage  1 . In the embodiment shown, height h is no more than 33% that of thickness t. 
         [0031]      FIG. 5  is a perspective view of a bearing cage  1 ′ according to an example embodiment of the invention, comprising cross members  10 ′, extending axially between support faces  11 ′, 12 ′ and defining pockets  9 ′, and cutouts  20 ′. Cutouts  20 ′ are at axial opposed ends of rolling elements  3  and at each rolling element  3 , along an entire inner circumference of cage  1 . Cutouts  20 ′ are shown as circular segments defined by a height h, no greater than 50% the thickness t of cage  1 . In the embodiment shown, height h is no more than 50% that of thickness t. It is understood that actual dimensions of the cage, rolling elements and cutouts will vary according to the requirements of any particular design. However, in an example cage design having axial length L of 30 mm, and an inner diameter d of 32 mm (see  FIG. 7 ), Table 1 shows the gap height f between ends of separable locking feature  7  resulting from a change in cutout location. 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Cutouts on outer circumference 
                 Cutouts on inner circumference 
               
               
                   
               
             
             
               
                 25 mm 
                 30.7 mm 
               
               
                   
               
             
          
         
       
     
         [0032]    As a result of the improved flexibility, a particular cage and rolling element assembly can be installed radially onto a larger diameter balance shaft than prior art cage and rolling element assemblies. 
         [0033]      FIGS. 6 and 7  are perspective and axial views, respectively, of another example embodiment of the invention. Cage  1 ″ comprises axial support faces  11 ″,  12 ″, cross members  10 ″ extending axially from one support face to the other and defining pockets  9 ″, and cutouts  20 ″. Cutouts  20 ″ are at axial opposed ends of rolling elements  3  (not shown) and at each rolling element  3  (not shown), and are alternated from an inner circumferential position to an outer circumferential position, such that no two adjacent pockets  9 ″ have cutouts  20 ″ at the same radial position. In addition, diameter D of cutouts  20 ″ vary as the distance from separable locking feature  7  increases. In particular, diameter D 2  of cutouts  20 ″ is less than diameter D 1  of cutouts  20 ″, such that the circumferential diameter gradually decreases as the distance from separable feature  7  increases. 
         [0034]      FIGS. 8 and 9  are a perspective view and front axial view, respectively, of a further embodiment of the invention. Cage  1 ′″ comprises axial support faces  11 ′″,  12 ′″, cross members  10 ′″ extending axially from one support face to the other and defining pockets  9 ′″, and cutouts  20 ″″. Cutouts  20 ′″ are at axial opposed ends of pockets  9 ′″ and at each pocket  9 ′″, along an entire inner circumference of cage  1 ′″. In addition, diameter D of cutouts  20 ′″ vary as the distance from separable locking feature  7  increases. In particular, diameter D 2  of cutouts  20 ′″ is less than diameter D 1  of cutouts  20 ′″, such that the diameter gradually decreases as the circumferential distance from separable feature  7  increases. 
         [0035]      FIGS. 10 and 11  are a perspective view and front axial view, respectively, of a further embodiment of the invention. Cage  1 ″″ comprises axial support faces  11 ″″,  12 ″″, cross members  10 ″″ extending axially from one support face to the other and defining pockets  9 ″″, and cutouts  20 ″″. Cutouts  20 ″″ are at axial opposed ends of pockets  9 ″″ and at each pocket  9 ″″, along an entire outer circumference of cage  1 ″″. In addition, diameter D of cutouts  20 ″″ vary as the distance from separable locking feature  7  increases. In particular, diameter D 2  of cutouts  20 ′″ is less than diameter D 1  of cutouts  20 ″″, such that the diameter gradually decreases as the circumferential distance from separable feature  7  increases. 
         [0036]    In the foregoing description, example embodiments are described. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense. It will, however, be evident that various modifications and changes may be made thereto, without departing from the broader spirit and scope of the present invention. 
         [0037]    In addition, it should be understood that the figures illustrated in the attachments, which highlight the functionality and advantages of the example embodiments, are presented for example purposes only. The architecture or construction of example embodiments described herein is sufficiently flexible and configurable, such that it may be utilized (and navigated) in ways other than that shown in the accompanying figures. 
         [0038]    Although example embodiments have been described herein, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present example embodiments should be considered in all respects as illustrative and not restrictive.