Patent Publication Number: US-2002009247-A1

Title: High-speed rolling bearing, in particular, angular ball bearing

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a high-speed rolling bearing, in particular, an angular ball bearing, comprising an outer ring and an inner ring and rolling bodies which contact the outer ring and the inner ring.  
       [0003] 2. Description of the Related Art  
       [0004] It is conventional to employ angular ball bearings as rolling bearings for shafts and spindles which rotate at high-speeds. Such angular ball bearings are illustrated in FIGS. 1 a,    1   b  and  2   a,    2   b . The angular ball bearings are adjusted in an O or X arrangement axially relative to one another. The contact angle of these angular ball bearings are between 15° and 25°. The angular ball bearings have an outer ring  1  and an inner ring  2 . Between them, the rolling bodies  3  in the form of balls are positioned which are secured in a cage  4 .  
       [0005]FIG. 1 a  shows the force interrelationships for the rolling contact of the known angular ball bearing for a low rotational speed of the shaft or spindle. The oppositely directed axial preload forces F v  act onto the outer ring  1  and the inner ring  2 . The resultant force F n     —     nl  acts on the rolling bodies  3  in the contact area of the outer ring  1 , while at the oppositely positioned contact point of the inner ring  2  the normal force F n  acts on the rolling bodies  3  which is oriented opposite to the resultant normal force F n     —     nl . With increasing rotational speed of the shaft or spindle, the following effects disadvantageously affect the inner load and thus the service life of the rolling bearing. Since the centrifugal forces acting on the roller bodies  3  as well as the expansion forces acting on the inner ring  2  increase by a quadratic function, the rolling balls  3  are deflected in the direction toward the apex  5  of the outer ring  1  (FIG. 1 b ). The same effect is caused by the increasing preload forces F v , which increase more than proportionally with increasing rotational speed of the shaft or spindle, as a result of the increasing temperature gradient between the shaft, i.e., the inner ring  2  seated fixedly thereon, and the housing, i.e., the outer ring  1  fastened thereto. The result of these inter-relationships is a drastic reduction of the contact angle or pressure angle and, going hand-in-hand therewith, a dramatic increase of the contact loading as a result of the preload forces F v  and the outer loading. As is illustrated in FIG. 1 b , the radial force F radial     —     nll  increases greatly which results in a very strong increase of the resulting normal force F n     —     nll . Moreover, the expansion force F f  is also effective.  
       [0006] Also, with increasing rotational speed of the shafts and spindles, the kinematic conditions of the rolling contact of the balls  3  between the outer ring  1  and the inner ring  2  deteriorate. In FIG. 2 a  the spinning/rolling ratios of the inner ring  2  and the outer ring  1  are illustrated for low rotational speed of the shaft or spindle of the known angular ball bearing. FIG. 2 b  shows these ratios for high rotational speed of the shaft or spindle. It can be clearly seen that at a high rotational speed the spinning/rolling ratio at the inner ring  2  in comparison to the low rotational speed of the shaft or spindle (FIG. 2 a ) has increased greatly. The proportion of the spinning friction ω spin, i , of the inner ring  2 , which also increases wear and which determines the frictional loss and thus the temperature, also increases.  
       SUMMARY OF THE INVENTION  
       [0007] It is an object of the present invention to develop a high-speed rolling bearing of the aforementioned kind such that the increasing rotational speed of the rotary part supported in the rolling bearing has no disadvantageous effects on the rolling bearing.  
       [0008] In accordance with the present invention, this is achieved in that, for the purpose of achieving a contact or pressure angle that is at least approximately independent of the rotational speed of a rotary part supported in the rolling bearing, the rolling bodies are supported on two oppositely positioned contact points of the outer ring, respectively.  
       [0009] In the high-speed rolling bearing according to the invention, the rolling bodies are supported on two oppositely positioned contact points of the outer ring. This has the result that the contact or pressure angles are at least approximately independent from the rotational speed and the inner preload forces, i.e., remain at least substantially constant. Since the rolling bodies are supported on the oppositely positioned contact points of the outer ring, a position of the ball races relative to the outer ring that is virtually rotational speed-independent and force-independent is obtained. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0010] In the drawing:  
     [0011]FIG. 1 a  shows the force interrelationships of a prior art angular ball bearing for a low rotational speed of a supported shaft;  
     [0012]FIG. 1 b  shows the force interrelationships of the prior art angular ball bearing of FIG. 1 a  at high rotational speed of the supported shaft;  
     [0013]FIG. 2 a  shows the spinning/rolling ratios of the inner ring  2  and the outer ring  1  of the prior art angular ball bearing of FIG. 1 a  for low rotational speed of the shaft;  
     [0014]FIG. 2 b  shows the spinning/rolling ratios of the inner ring  2  and the outer ring  1  of the prior art angular ball bearing of FIG. 1 a  for high rotational speed of the shaft;  
     [0015]FIG. 3 illustrates the kinematic relations of a first embodiment of a high-speed rolling bearing according to the invention;  
     [0016]FIG. 4 shows in axial section a second embodiment of a high-speed rolling bearing according to the invention;  
     [0017]FIG. 5 is a perspective illustration and axial section of a portion of the high-speed rolling bearing according to FIG. 4  
     [0018]FIG. 6 shows in a representation corresponding to FIG. 5 the high-speed rolling bearing according to FIG. 3.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0019] The high-speed rolling bearing according to FIGS. 3 and 6 comprises the outer ring  1 , the inner ring  2 , as well as the rolling bodies  3  in the form of rolling balls which are secured in the cage  4 . The inner ring  2  is adjusted against the rolling bodies with one-sided contact. The outer ring  1  has at its inner surface a ball race  6  which is formed such that the rolling balls  3  are supported on two oppositely positioned contact points  7 ,  8  of the outer ring  1  wherein the contact or pressure angles at the inner and outer rings  2 ,  1  must not be identical. These spinning/rolling ratios at the outer ring will not change when the shaft or the spindle is driven at high rotational speed. In this way, an almost rotational speed-independent and force-independent position of the rolling bodies  3  relative to the outer ring  1  is obtained. The contact or engagement angles are designed according to the described geometry of the rolling bearing such that the contact or engagement angles are largely independent of the rotational speed and the preload forces, i.e., they remain constant.  
     [0020] Since the inner ring  2  is adjusted against the rolling bodies  3  with one-sided contact, the rolling bodies  3  are provided with a 3-point contact. In FIG. 3, the rotational speed ω shaft  of the shaft or spindle to be supported, the rotational speed ω ball  of the rolling bodies  3  as well as the rotational speeds ω a  (outer ring  1 ) and ω i  (inner ring  2 ) resulting at the contact points of the rolling bodies  3  with the outer ring  1  and the inner ring  2  are illustrated.  
     [0021] The inner ring  2  can also be configured such (FIGS. 4 and 5) that it also contacts the rolling bodies  3  at two oppositely positioned contact locations  9 ,  10 . The rolling bodies  3  are thus supported on four contact points/locations  7  through  10  so that this rolling bearing is a so-called “ball-4-spot” bearing. The two-point support of the rolling bodies  3  on the inner ring  2  is achieved in that the inner ring  2  is of a two-part configuration. This separation into two parts can be configured differently, for example, in the form of two symmetrical halves  11 ,  12  as illustrated in FIG. 4. The contact locations  9 ,  10  are provided accordingly on the inner ring half  11  and the inner ring half  12 , respectively. This configuration of the rolling bearing provides for an axial force introduction in both axial directions. In other respects, this rolling bearing is of the same configuration as the embodiment according to FIGS. 3 and 6.  
     [0022] The described rolling bearings are excellently suitable as high-speed rolling bearings as a result of the described favorable kinematic conditions and load conditions.  
     [0023] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.