Abstract:
The invention relates to a radial antifriction bearing which substantially consists of an outer bearing ring and of an inner bearing ring as well as of a multitude of rollers, arranged between the bearing rings and held by a bearing cage. The rollers are configured in the form of spherical disks that each have two parallel lateral surfaces which are symmetrically flattened from a basic spherical shape. The bearing cage according to the invention is characterized by having cage pockets in which the rollers are axially guided between the bearing rings via two low-friction point contacts between the center areas of their lateral surfaces and the longitudinal webs of the cage pockets. The rollers are configured to have a defined degree of freedom for tilt movements exerted at an angle to the running direction and a defined degree of freedom for self-adjustment to the pressure angle of the radial antifriction bearing.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a radial rolling bearing according to the features of patent claim  1  which form the preamble, and it can be implemented particularly advantageously on single-row grooved rolling bearings in motor vehicle transmissions, within the secondary drive of internal combustion engines or in electric brakes. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is generally known to a person skilled in the art of rolling bearings that single-row grooved ball bearings are rigid radial rolling bearings which cannot be dismantled and which are distinguished, above all, in that their radial and axial carrying capacity are equally high, and in that, because of their low friction, they have the highest rotational speed limits of all types of bearings. These grooved ball bearings have been known for a long time and consist essentially of an outer bearing ring and of an inner bearing ring and also of a number of balls which are arranged as rolling bodies between the bearing rings and which are guided at uniform distances from one another in each case in groove-shaped ball raceways in the inside of the outer bearing ring and in the outside of the inner bearing ring by means of a bearing cage. Radial ball bearings are filled with the balls in this case by means of the eccentric mounting method which became known from DE 168 499 and in which the two bearing rings are arranged eccentrically to one another, and the free space thereby occurring between the bearing rings is filled with the balls which are finally distributed at a uniform distance from one another on the pitch circle of the two ball raceways. 
         [0003]    In practice, however, it has been shown that grooved ball bearings of this type nevertheless have limits in terms of the carrying capacity of the bearing on account of the small maximum installable number of balls which depends on the dimensions of the inner and of the outer bearing ring and on the ball diameter. In the past, therefore, a multiplicity of solutions were proposed, by means of which an increase in the carrying capacity of grooved ball bearings was to be achieved by means of an increase in the number of balls. 
         [0004]    Such a possibility for increasing the number of rolling bodies on a radial rolling bearing became known, for example, from DE 43 34 195 A1. However, in this radial rolling bearing, designed per se as a single-row grooved ball bearing, the rolling bodies are not formed by balls, but by what are known as spherical disks which are formed with two side faces flattened symmetrically from a basic spherical shape and arranged parallel to one another. The width of these spherical disks between their side faces is in this case designed to be smaller than the distance between the inside of the outer bearing ring and the outside of the inner bearing ring, so that, when the bearing is being filled, the spherical disks can be introduced axially with respect to the bearing through the distance between the inner ring and outer ring into the bearing and can then be rotated through 90° into the raceways of the bearing rings. Since smaller distances between the individual rolling bodies can be achieved by means of this mounting method, therefore, overall, a higher number of rolling bodies can be introduced into the radial rolling bearing. In order, however, to avoid mutual contact and an automatic twisting of the rolling bodies transversely with respect to the running direction when the bearing is in operation, these rolling bodies, too, are held at uniform distances from one another and guided axially in a bearing cage. One of the proposed cage versions is in this case a bearing cage which is assembled from two ring halves and in which each of the ring halves has incorporated into it depressions which each correspond to the number of spherical disks and which engage into complementary centric depressions in the side faces of the spherical disks. The depressions in the side faces of the spherical disks are in this case connected to one another by means of a centric through bore through which the two ring halves are connected to one another by means of rivets, so that the spherical disks are fixed firmly with respect to one another in the circumferential direction. Between the depressions, the two ring halves of the bearing cage have in each case portions which run straight along the side faces of the spherical disks and by means of which in combination with the rivets serving as rolling axes of the spherical disks, an automatic twisting of the rolling bodies transversely with respect to their running direction is also avoided. 
         [0005]    It has proved, however, to be a disadvantage that a bearing cage designed in this way has not taken into account the overall kinematic behavior, occurring under different bearing loads, of the rolling bodies designed as spherical disks, and therefore this bearing cage seems to be unsuitable for such special rolling bodies. Thus, for example, it was found that spherical disks, as rolling bodies in radial rolling bearings, run in a stable manner in their rolling body raceways, without wrenching movements, at higher rotational speeds and under uniform load, because of the gyroscopic effect which occurs, and do not require any axial guidance by the bearing cage. If, however, the bearing rotational speed falls below a permissible minimum rotational speed, a wobble effect, as it is known, occurs, in which the spherical disks tend to roll in a wavy manner in their raceways transversely with respect to the running direction. In this case, contact occurs between the raceway edges of the spherical disks and the straight portions of the two ring halves of the bearing cage, which generates frictional heat and causes a rise in the operating temperature in the radial rolling bearing. The friction between the spherical disks and the bearing cage may in this case become so high that, due to the frictional heat occurring, the permissible operating temperature of the bearing is overshot and the required lubricating film between the spherical disks, the bearing cage and the bearing rings breaks away locally or the lubricant is partially burnt, thus resulting in the destruction of the bearing cage and in the premature failure of the bearing. It was likewise possible to ascertain that, in such a bearing cage, a similar effect likewise leading to the destruction of the bearing cage and to the failure of the bearing occurs in that the spherical disks, by being clamped between the two ring halves on the rivets of the bearing cage, have no possibility of not being able to orientate themselves with the respective pressure angle of the radial rolling bearing in the event of a mixed radial and axial load on the radial rolling bearing. In the endeavor of the spherical disks to orientate themselves automatically with the pressure angle of the radial rolling bearing under such loads on the radial rolling bearing, there is likewise contact of the side faces of the spherical disks with the straight portions of the ring halves of the bearing cage and also contact of the centric through bore in the spherical disks with the rivets of the bearing cage, so that under such conditions, too, excessive frictional heat has been generated in the radial rolling bearing. Finally, a bearing cage of this type for spherical disks has also proved to be a disadvantage in terms of the production costs of radial rolling bearings equipped with such bearing cages, since its manufacture and, in particular, by means of rivets, its mounting which is to take place in the equipped bearing, are relatively complicated. 
       OBJECT OF THE INVENTION 
       [0006]    Proceeding from the expounded disadvantages of the known prior art, therefore, the object on which the invention is based is to conceive a radial rolling bearing, in particular a grooved rolling bearing, which is designed with a bearing cage which can be produced simply and cost-effectively and, on the one hand, which ensures an axial guidance of the rolling bodies designed as spherical disks and, on the other hand, by means of which, even at low bearing rotational speeds and/or in the case of a mixed axial and radial bearing load, a contact generating frictional heat can be avoided between the spherical disks and the bearing cage. 
       DESCRIPTION OF THE INVENTION 
       [0007]    According to the invention, in a radial rolling bearing according to the preamble of claim  1 , this object is achieved in that the bearing cage has for each rolling body individual cage pockets which surround these along a pitch circle line and in which the rolling bodies, via two low-friction point contacts between the center region of their side faces and the longitudinal webs of the cage pockets, on the one hand, have axial guidance between the bearing rings and, on the other hand, are designed both with a defined degree of freedom for tilting movements occurring transversely with respect to the running direction and with a defined degree of freedom for automatic orientation with respect to the pressure angle of the radial rolling bearing. 
         [0008]    Preferred refinements and advantageous developments of the radial rolling bearing designed according to the invention are described in the subclaims. 
         [0009]    Thus, according to claim  2 , in the radial rolling bearing according to the invention there is provision for the center region of the side faces of the rolling bodies to be formed either by centric depressions incorporated into these side faces or by concentric recesses incorporated into these side faces. If the rolling bodies are designed with centric depressions, these are preferably designed in the form of circular shallow troughs, whereas, if the rolling bodies are designed with concentric recesses, these are preferably formed by shallow annular grooves which run around the rolling body axis. These depressions or recesses in this case have, above all, the advantage that the mass center of gravity of the rolling bodies is displaced radially outward toward their running surfaces and therefore the running properties of the rolling bodies are substantially improved. 
         [0010]    If the rolling bodies are designed in their side faces with centric depressions designed as circular troughs, then, as claimed in claim  3 , a further feature of the radial rolling bearing designed according to the invention is that the point contacts provided for the axial guidance of the rolling bodies, between the center region of the side faces and the longitudinal webs of the cage pockets can be produced via two cone apices incorporated along the longitudinal center into the longitudinal webs. These cone apices projecting axially into the centric depressions in the side faces of the rolling bodies are operatively connected to the planar bottom of the depressions in the case of guidance, but, when the bearing is in operation, have no permanent contact with the bottom of the depressions. Furthermore, it has proved advantageous to design the cone apices to be rounded at their ends, in order to prevent a premature wear of these cone apices. 
         [0011]    If, by contrast, the rolling bodies are designed with concentric recesses designed as annular grooves in their side faces, in the radial rolling bearing designed according to the invention it is alternately also possible, as claimed in claim  4 , to produce the point contacts, provided for the axial guidance of the rolling bodies, between the center region of the side faces and the longitudinal webs of the cage pockets via two cone apices integrally formed onto the rolling bodies. These cone apices in each case projecting axially out of the concentric recesses in the side faces of the rolling bodies are operatively connected to a planar longitudinally central region of the longitudinal webs of the cage pockets in a guidance situation, but likewise have no permanent contact with the longitudinal webs and are likewise designed to be rounded at their ends in order to avoid wear. 
         [0012]    According to claims  5  to  7 , furthermore, the radial rolling bearing designed according to the invention is also distinguished in that the transverse webs of the cage pockets, said transverse webs being designed to be curved according to the longitudinal and transverse radii of the running surfaces of the rolling bodies, extend beyond these running surfaces on both sides in such a way that the longitudinal webs of the cage pockets, said longitudinal webs being connected to the transverse webs between these via rounded transitional regions, are arranged at a distance from the side faces of the rolling bodies. The design of the transverse webs of the cage pockets in which the transverse webs extend beyond the running surfaces of the rolling bodies has in this case the effect that the rolling bodies have in the running direction, on both sides, a degree of freedom of an angle of about 3° to 7° which is limited by the transitional regions to the longitudinal webs of the cage pockets and by means of which, in the event of tilting movements of the rolling bodies occurring transversely with respect to the running direction below a permissible minimum rotational speed, a contact generating frictional heat is avoided between the spherical disks and the bearing cage. By contrast, the longitudinal webs of the cage pockets being arranged at a distance from the side faces has the advantage that the rolling bodies at the same time have, on both sides, an axial degree of freedom of an angle of about 12° to 18° which is limited by the upper and lower edges of the longitudinal webs and by means of which the rolling bodies can orient themselves automatically with respect to the pressure angle of the radial bearing under radial and axial bearing load. 
         [0013]    As further preconditions for implementing the two above-mentioned degrees of freedom for the rolling bodies, in an expedient development of the radial rolling bearing designed according to the invention, it is also proposed, furthermore, by claim  8  that the pitch circle of the bearing cage is smaller than the pitch circle of the radial rolling bearing and that the longitudinal webs of the cage pockets have a maximum height of 35% of the diameter of the rolling bodies. Since the pitch circle of the bearing cage is smaller than the bearing pitch circle, the rolling bodies are therefore surrounded below their longitudinal axes by the cage pockets, so that the rolling bodies, in conjunction with the low height of the longitudinal webs of the cage pockets and the above-described design of the cage pockets, have sufficient latitude of movement available to be able to adapt themselves, without contact with the bearing cage, to the bearing load prevailing in each case. The rolling body width limited by the side faces of the rolling bodies in this case amounts to at least 70% of the diameter of the basic spherical shape of the rolling bodies, since such a width has proved appropriate in practice in terms of the radial and axial carrying capacity of the bearing and corresponds approximately to the contact surface which the balls of conventional grooved ball bearings also have with their raceways in the bearing rings. 
         [0014]    Finally, the features of the radial bearing designed according to the invention, as claimed in claims  9  and  10 , also contribute to achieving the said object, according to which features the bearing cage either is formed as a stamped/drawn/embossed part, capable of being produced in a non-cutting manner, from a metal material or as an injection molding from an industrial or high-temperature plastic or alternatively is produced from a composite fiber plastic consisting of a fabric reinforcement and resin matrix. As regards the metal materials, in this case, above all, steel, brass or aluminum have proved to be suitable, by means of which the bearing cage can additionally be coated completely or to a limited extent at its contact points with the rolling bodies with functional layers consisting of hard material, chrome iron, oxide ceramics or molybdenum or can be injection-molded around with an industrial plastic. By contrast, appropriate industrial plastics for the bearing cage are PA 66 or PA 46 with or without inlays of glass fiber, while, for example, PAEK, PEEK, TPI or PAI with suitable additives or inlays of glass fiber can be used as high-temperature plastics. Said materials have in this case proved to be particularly cost-effective in terms of their procurement and, furthermore, make it possible to use cost-effective manufacturing methods for the bearing cage, so that radial bearings designed with bearing cages of this type can, overall, be produced at low production costs. 
         [0015]    The radial rolling bearing designed according to the invention thus has the advantage, as compared with the radial rolling bearings known from the prior art, that, by the bearing cage being designed with cage pockets in which the rolling bodies are axially guided solely by two point contacts, it takes into account the kinematic conditions in such a radial bearing to an extent such that it has a first degree of freedom, by means of which the wobbling movements, occurring below a permissible minimum rotational speed, or tilting movements, occurring transversely with respect to the running direction, of the rolling bodies no longer lead to a contact of the rolling bodies with the bearing cage and therefore no longer to frictional heat or to an inadmissible rise in the operating temperature of the radial rolling bearing. At the same time, by virtue of their point contact guidance in the cage pockets, the rolling bodies have a sufficient second degree of freedom in the axial direction, by means of which they can orientate themselves automatically with respect to the pressure angle of the radial rolling bearing present in each case under radial and axial bearing load, without likewise coming into contact with the bearing cage. Furthermore, such a bearing cage has also proved to be advantageous in terms of low production costs, since it is set up in a structurally simple way and can be produced from cost-effective materials and also by means of cost-effective manufacturing methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    A preferred embodiment of the radial rolling bearing designed according to the invention is explained in more detail below with reference to the accompanying drawings in which: 
           [0017]      FIG. 1  shows a three-dimensional exploded illustration of a radial rolling bearing designed according to the invention; 
           [0018]      FIG. 2  shows an enlarged three-dimensional illustration of a cross section through a radial rolling bearing designed according to the invention; 
           [0019]      FIG. 3  shows a three-dimensional individual part illustration of the bearing cage of a radial rolling bearing designed according to the invention; 
           [0020]      FIG. 4  shows an individual part illustration of a cage pocket of the bearing cage of a radial rolling bearing designed according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       [0021]    It may be gathered clearly from the exploded illustration according to  FIG. 1  that a radial rolling bearing  1  designed as a single-row grooved rolling bearing consists essentially, in a similar way to known grooved ball bearings, of an outer bearing ring  2  and of an inner bearing ring  3  and also of a multiplicity of rolling bodies  4  arranged between these bearing rings  2 ,  3 . The rolling bodies  4  are in this case formed, as can be seen clearly, by what are known as spherical disks which each have two side faces  8 ,  9  flattened symmetrically from a basic spherical shape and arranged parallel to one another and roll with their running surfaces  10  in two groove-shaped raceways  11 ,  12  which are in each case incorporated into the inside  13  of the outer bearing ring  2  and into the outside  14  of the inner bearing ring  3 . Furthermore, the rolling bodies  4  are held at uniform distances from one another in the circumferential direction by a bearing cage  5  which is assembled from two ring halves  6 ,  7  and the design of which is the subject of the following description. 
         [0022]    A comparison of  FIGS. 2 and 3  makes it clear that, according to the invention, the bearing cage  5  has for each rolling body  4  individual cage pockets  15  which surround these along a pitch circle line and in which the rolling bodies  4  are guided axially between the bearing rings  2 ,  3  via two low-friction point contacts between the center regions  16 ,  17  of their side faces  8 ,  9  and the longitudinal webs  18 ,  19  of the cage pockets  15 . As is also clear from  FIG. 4 , the center regions  16 ,  17  of the side faces  8 ,  9  of the rolling bodies  4  are in this case formed by centric depressions  20 ,  21  which are incorporated into these side faces  8 ,  9  and form part of the axial guidance of the rolling bodies and by means of which, at the same time, the mass center of gravity of the rolling bodies  4  is displaced radially outward toward their running surfaces  10 . 
         [0023]    Furthermore, it can be seen in  FIG. 4  that the point contacts between the center regions  16 ,  17  of the side faces  8 ,  9  and the longitudinal webs  18 ,  19  of the cage pockets  15  are produced via two axial cone apices  22 ,  23  which are incorporated along the longitudinal center into the longitudinal webs  18 ,  19  and project in each case into centric depressions  20 ,  21  in the side faces  8 ,  9  of the rolling bodies  4  and which are operatively connected to the planar bottom  24 ,  25  of the depressions  20 ,  21 . The transverse webs  26 ,  27  of the cage pockets  15 , said transverse webs being designed to be curved according to the longitudinal and transverse radii of the running surfaces  10  of the rolling bodies  4 , in this case, as can be seen clearly, extend beyond these running surfaces  10  on both sides in such a way that the longitudinal webs  18 ,  19  of the cage pockets  15 , said longitudinal webs being connected between the transverse webs  26 ,  27  to these via rounded transitional regions  28 ,  28 ′,  29 ,  29 ′, are arranged at a distance from the side faces  8 ,  9  of the rolling bodies  4 . 
         [0024]    The design of the transverse webs  26 ,  27  of the cage pockets  15  in which said transverse webs extend beyond the running surfaces  10  of the rolling bodies  4  in this case has the effect, on the one hand, that the rolling bodies  4  have on both sides a degree of freedom of about 3° to 7°, limited by the transitional regions  28 ,  28 ′,  29 ,  29 ′ to the longitudinal webs  18 ,  19  of the cage pockets  15  and indicated in  FIG. 4  by dashed lines, for tilting movements which occur transversely with respect to the running direction. On the other hand, what is achieved by the longitudinal webs  18 ,  19  of the cage pockets  15  being arranged at a distance from the side faces  8 ,  9  of the rolling bodies  4  is that the rolling bodies  4  at the same time have on both sides a degree of freedom of about 12° to 18°, limited by the upper and lower edges of the longitudinal webs  18 ,  19  and indicated in  FIG. 2  by dashed lines, for automatic orientation with respect to the pressure angle of the radial bearing  1  under radial and axial bearing load. 
         [0025]    Furthermore, it is also illustrated in  FIG. 2  that, as a further precondition for the two degrees of freedom mentioned, the pitch circle Tk cage  of the bearing cage  5  is smaller than the pitch circle Tk bearing  of the radial rolling bearing  1 , so that the rolling bodies  4  are surrounded below their longitudinal axes by the cage pockets  15 . The longitudinal webs  17 ,  18  of the cage pockets  15  in this case have a maximum height h of 35% of the diameter d w  of the rolling bodies  4 , and the rolling body width b w  limited by the side faces  8 ,  9  of the rolling bodies  4  amounts to at least 70% of the diameter d w  of the rolling bodies  4 . 
         [0026]    It may also be gathered, merely in passing, from the drawings that the bearing cage  5  is formed as a stamped/drawn/embossed part, produced in a non-cutting manner, from a steel sheet which is coated, limited to its contact points with the rolling bodies  4  with a wear-reducing functional layer consisting of chrome iron. 
         [0027]    List of Reference Numerals
     1  Radial rolling bearing     2  Outer bearing ring     3  Inner bearing ring     4  Rolling body     5  Bearing cage     6  Ring half of  5       7  Ring half of  5       8  Side face of  4       9  Side face of  4       10  Running surfaces of  4       11  Raceway of  2       12  Raceway of  3       13  Inside of  2       14  Outside of  3       15  Cage pockets     16  Center region of  8       17  Center region of  9       18  Longitudinal web of  15       19  Longitudinal web of  15       20  Depression in  8       21  Depression in  8       22  Cone apex on  18       23  Cone apex on  19       24  Bottom of  20       25  Bottom of  21       26  Transverse web of  15       27  Transverse web of  15       28  Transitional region     28 ′ Transitional region     29  Transitional region     29 ′ Transitional region   Tk cage  Pitch circle of  5     Tk bearing  Pitch circle of  1     h Height of  18 ,  19     d w  Diameter of  4     b w  Width of  4