Abstract:
Method and apparatus are provided for reducing vibration in bearings. There are provided first and second bearing rings with races, rotating members rollingly engaging both first and second bearing races, a cage for aligning the rotating members between the first and second bearing races, and vibration reduction means coupled to the cage. The vibration reduction means preferably comprises one or more resonant spring-mass combinations mounted in or on the cage. Damping means is preferably included with the resonant spring-mass combinations. The resonant frequencies of the unmodified bearing cage are first determined and then the spring-mass combinations tuned so that the spring-mass combinations when attached to the cage absorb vibrational energy that would otherwise excite cage vibrations. By selecting the type of spring-mass combination different vibrational modes can be suppressed and/or controlled.

Description:
TECHNICAL FIELD 
   The present invention generally relates to vibration damping, and more particularly to vibration damping in bearing cages. 
   BACKGROUND 
   Ball bearings typically use a ball separator or cage to space the balls in the annulus between the inner and outer races, which are part of the inner and outer rings.  FIG. 1A  is a plan view and  FIG. 1B  is a cross-sectional view through a typical prior art bearing  20  having inner ring  22  with inner race  23 , outer ring  24  with outer race  25 , balls  26  and ball cage  28 .  FIG. 2  is a perspective view of ball cage  28  of bearing  20  with rings  22 ,  24  and balls  26  omitted. The cage is positioned through contacts with the balls and either the inner or outer race. The cage keeps the balls approximately evenly spaced around the bearing and reduces friction and wear by preventing contact between adjacent balls. However, the cage is an additional dynamic element in the system. It is free to move in all degrees of freedom, that is, rotationally, torsionally and translationally, within limits constrained by ball and race contacts. Because of this freedom of motion, the cage can experience unwanted oscillations known as instabilities. These instabilities can occur as linear oscillations, as torsional oscillations and/or elliptical oscillations known as whirl modes. When a cage becomes unstable it dissipates energy which increases the drag torque of the bearing, increases cage wear at the contact points and increases bearing operating temperatures, all of which can have a negative impact on bearing life. Bearing vibrations can also be transmitted to the equipment being supported by the bearing and the base supporting the bearing, thereby having a negative impact on the overall system performance. 
   Several approaches have been used to minimize cage or other bearing instabilities. For example, judicious selection of race and ball pocket clearances and proper lubrication can reduce some cage instabilities. Improvement can also be had by using more complex bearing structures such as are described, for example, in U.S. Pat. No. 3,918,778 to Jacobson et al, and U.S. Pat. No. 6,196,721 B1 to Farkaly. Other approaches external to the bearings have also been used to reduce overall vibrations such as for example are described in U.S. Pat. No. 6,682,219 B2 to Alam et al; U.S. Pat. No. 5,247,855 to Alten et al; U.S. Pat. No. 6,358,153 B1 to Carlson et al; U.S. Pat. No. 6,422,083 B1 to Hobbs; U.S. Pat. No. 6,641,119 B2 to Kato; U.S. Pat. No. 5,816,373 to Osterberg et al; U.S. Pat. No. 5,873,438 to Osterberg et al; and U.S. Pat. No. 5,522,815 to Schierling et al. Nevertheless, such approaches are only partially successful in controlling bearing cage instabilities and can be unduly complex and more expensive than is desired. Thus, there continues to be a need for effectively and inexpensively reducing cage instabilities in bearings 
   Accordingly, it is desirable to provide an improved bearing cage structure that can damp unwanted cage oscillations. In addition, it is desirable that the improved cage structure be simple, rugged and reliable and involve minimal modification of the overall bearing structure and size. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
   BRIEF SUMMARY 
   An apparatus is provided for reducing vibration in bearings. The apparatus comprises first and second bearing rings, rotating members rollingly engaging races on both first and second bearing rings, a cage for aligning the rotating members between the first and second bearing rings, and vibration reduction means coupled to the cage. The vibration reduction means preferably comprises one or more resonant spring-mass combinations mounted in or on the cage. Damping means is preferably included with the resonant spring-mass combinations. 
   A method is provided for providing reduced vibration bearings. The method comprises determining resonant frequencies of an unmodified bearing cage, selecting resonant spring-mass combinations tuned so that when attached to the cage the spring-mass combinations absorb vibrational energy that would otherwise excite cage vibrations, then forming a complete bearing by assembling the bearing rings, rolling members and the modified cage with the selected spring-mass combinations coupled thereto. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
       FIG. 1A  is a plan view of a typical prior art bearing having a ball cage and  FIG. 1B  is a cross-sectional view through the bearing of  FIG. 1A ; 
       FIG. 2  is a perspective view of the prior art ball cage of the bearing of  FIGS. 1A–B  with the balls and races omitted 
       FIG. 3  is a plan view of a ball bearing cage according to a first embodiment of the present invention; 
       FIGS. 4–5  are first and second side views of the ball bearing cage of  FIG. 3  showing further details; 
       FIG. 6  is a perspective view of the ball bearing cage of  FIGS. 3–5 ; 
       FIG. 7  is a cross-sectional view through a portion of the ball bearing cage of  FIG. 4 ; 
       FIGS. 8–10  are enlarged side views of a segment of a ball cage according to other embodiments of the present invention; 
       FIG. 11  is a cross-sectional view similar to  FIG. 7  but according to another embodiment of the present invention; 
       FIG. 12  is a perspective view of a ball bearing cage incorporating features illustrated in  FIGS. 10–11 ; 
       FIG. 13  is side view and  FIG. 14  is a simplified cross-sectional view of a self-contained tuned mass damper suitable for use with a bearing cage; and 
       FIGS. 15–16  are partial cross-sectional views of a bearing cage of the present invention with the tuned mass dampers of  FIGS. 13–4  inserted at various angles into the cage wall, according to a still further embodiment of the present invention; and 
       FIG. 17  is a side view of a ball cage according to a yet further embodiment of the present inventions utilizing the tuned mass dampers of  FIGS. 13–14 . 
   

   DETAILED DESCRIPTION 
   The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     FIG. 3  is a plan view of ball bearing cage assembly  40  according to a first embodiment of the present invention,  FIGS. 4–5  are first and second side views of ball bearing cage assembly  40  of  FIG. 3  showing further details,  FIG. 6  is an isometric view of assembly  40  and  FIG. 7  is a partial cross-section through assembly  40  as indicated in  FIG. 4 . Assembly  40  comprises bearing cage  42  with holes  44  to accommodate the balls of the ball bearing. The bearing balls and rings are not shown. Mounted above rim  45  of bearing cage  42  is segmented annular ring  46 . In the example of  FIGS. 3–5 , ring  46  has  4  segments  46 - 1 ,  46 - 2 ,  46 - 3 ,  46 - 4  with angular sizes  47 - 1 ,  47 - 2 ,  47 - 3 ,  47 - 4 , respectfully, but this is merely for convenience of description. Any number of ring segments from  1  to N could be used and of various sizes and mass, depending upon the frequencies intended to be resonated. Ring  46  is coupled to rim  45  of cage  42  by one or more springs  48 . For example, ring segment  46 - 1  is coupled to rim  45  by three springs  48 - 1 A,  48 - 1 B,  48 - 1 C, but this is merely for convenience of explanation and not intended to be limiting. Different segments are coupled to rim  45  by different numbers of springs  48 , e.g., segment  46 - 2  by springs  48 - 2 A and  48 - 2 B, segment  46 - 3  by springs  48 - 3 A and  48 - 3 B and segment  46 - 4  by single spring  48 - 4 A. The number of springs and the spring characteristics will depend upon the cage vibration modes desired to be resonated. Springs  48  and ring segments  46  form spring-mass combinations. Ring segments  46  form a distributed mass. As will be explained in more detail later, by suitable choices of segment masses and spring characteristics, these spring-mass combinations can be designed to resonate at specific bearing cage frequencies, thereby transferring the cage vibrations to the suspended masses of ring segments  46 . By use of suitable energy absorbers  50  these oscillations can also be rapidly damped. This reduces the oscillations of cage  42 , thereby improving bearing performance. 
   In addition to the springs  48  and ring segment masses  46 , assembly  40  also desirably but not essentially includes damper pads  50  located between ring segments  46  and rim  45 . Pads  50  are desirably of a compressible elastomeric material such that, as ring segments  46  begin to vibrate in resonance or anti-resonance with ring  42 , pads  50  absorb vibrational energy, thereby damping the cage vibrations. The number, size and material properties of pads  50  will depend upon the cage vibration frequencies intended to be damped. An example of a suitable pad material is Type 242F04 manufactured by the 3M Corporation of St. Paul, Minn. Pads  50  can also act to bias springs  48 . 
   Springs  48  in  FIGS. 3–7  are illustrated as being small coil springs or the like, but this is merely for convenience of description and not intended to be limiting. As will be subsequently explained different types of springs can be used to control the degrees of vibrational freedom in which a given spring-mass segment may vibrate. For example, where springs  48  are coil springs, then ring segments  46  may vibrate (see  FIG. 3 ) in X and Y directions as shown by arrows  53 ,  55  respectively and rotationally or torsionally in angular direction Φ as shown by arrows  57 , and also (see  FIG. 7 ) in the Z-direction as shown by arrows  59 . Thus the arrangement of  FIGS. 3–7  maybe said to have unlimited vibrational degrees of freedom, that is, X, Y, Z and Φ. 
     FIGS. 8–9  are enlarged side views of segment  52  of ball cage  42  according to other embodiments of the present invention illustrating the use of different types of springs. In  FIG. 8 , one or more ring segments  46  are suspended from rim  45  by substantially straight spring(s)  54  coupling ring segments  46  to rim  45 . If spring  54  has a round cross-section like a wire, then ring segments  46  may move in X, Y and Φ directions  53 ,  55 ,  57  but not in Z direction  59 . If spring(s)  54  have a rectangular cross section, that is, like a flat leaf-spring and the principal faces of multiple leaf spring(s)  54  disposed around rim  45  of cage  42  are oriented in the same direction, e.g., parallel to the X-axis, then such ring segments can move in X direction  53  generally perpendicular to the broad face of leaf spring(s)  54 , but not in the Y, Φ or Z directions. By orienting the leaf springs of different ring segments in different directions, some segments can be free to move in X direction  53 , and some in Y direction  55  (or any other 2-D translational direction) but not in Z direction  59  or Φ direction  57 . In  FIG. 9 , one or more ring segments  46  are suspended from rim  45  by bent or angled spring(s)  58 . Depending upon whether spring(s)  58  are wire-like or flat blade-like, the same discussion applies as for spring(s)  54  of  FIG. 8 , except that segments  46  with springs  58  may now also move in Z direction  59 . Thus, cage assembly  40  allows the degrees of vibrational freedom of various mass-spring combinations provided by ring segments  46  and springs  48 ,  54 ,  58  to be tailored to the specific needs of the designer for resonating and damping undesirable vibrations of cage  42 . 
     FIGS. 10–12  illustrate arrangements for resonating and damping cage vibrations according to further embodiments of the present invention.  FIG. 10  is an enlarged side view of segment  60  of ball cage  42 ′ (similar to cage  42  but without segments  46 ),  FIG. 11  is a cross-sectional view similar to  FIG. 7  of segment  64  of cage  42 ′ and  FIG. 12  is a perspective view of cage  42 ′.  FIG. 10  illustrates a situation where the distributed mass provided by segmented ring  46  is replaced by one or more discrete mass elements  62 . In this example, discrete mass elements  62  are shown as being disk-shaped, e.g., like hockey pucks, but this is merely for convenience of description and not intended to be limiting. Mass elements  62  may have any convenient shape. Further, while mass elements  62  are illustrated as each being suspended by single spring  48 ,  54  any number of springs and any desired combination of different spring types may also be used, depending upon the needs of the user and the desired degrees of vibrational freedom. For example, the combination of spring  48  and mass  62  (hereafter spring-mass combination  48 ,  62 ) is capable of vibration in X, Y, Z and Φ directions. Spring-mass combination  54 ,  62  is capable of vibration in X, Y and Φ directions if spring  54  has a circular cross-section and one translational direction (X or Y) if spring  54  is a flat leaf-type spring, but not in the Z direction (perpendicular to the surface of cage  42 ′ on which spring  54  is mounted). While spring mass combinations  48 ,  62  and  54 ,  62  are shown in  FIG. 10  as being adjacent, this is merely for convenience of illustration and not intended to be limiting or imply that such proximity is necessarily desirable. The spacing and location of such spring-mass combinations will be chosen by the designer depending upon the vibration modes to be resonated.  FIG. 11  is a view similar to  FIG. 7  but for an alterative placement of spring-mass combination  54 ,  62  (or  48 ,  62 ). In  FIG. 11 , spring-mass combination  54 ,  62  extends from side face  65  of cage  42 . This allows further control over the vibrational degrees of freedom and direction of vibration of resonant elements  54 ,  62  (or  48 ,  62 ).  FIG. 12  is a perspective view of ball bearing cage  42 ′ incorporating spring-mass elements  54 ,  62  (or  48 ,  62 ) illustrated in  FIGS. 10–11 . 
     FIG. 13  is side view and  FIG. 14  is a simplified cross-sectional view of self-contained tuned mass damper (TMD)  80  suitable for use with a bearing cage of the present invention to damp out the vibrations thereof. Tuned mass dampers (TMDs) are known in the art and described in commonly assigned U.S. Pat. No. 5,816,373 and 5,873,438 to Osterberg et al, which are incorporated herein by reference. The illustrations in  FIGS. 13–14  and the description thereof that follows here are simplified and reference should be had to the above-noted patents for further internal design features. TMD  80  has outer shell  84  closed by end caps  86 ,  88 . Threads  90  are conveniently provided for attaching TMD  80  to a bearing cage. However, threads  90  are not essential and illustration thereof is not intended to be limiting. Any suitable means of attaching tuned mass dampers  80  to bearing cages may be used. TMD  80  has therein mass  81  suspended between springs  94 ,  96  that are retained by end caps  88 ,  86  respectively. Mass  81  is free to move in the direction of arrows  95 . Spaces  97 ,  99  within outer shell  84  and in and around mass  81  are filled with damping fluid  93 . Either liquids or gases may be used for damping fluid  93 . 
     FIGS. 15–16  are partial cross-sectional views of bearing cage  82  according to a further embodiment of the present invention. Cage  82  is analogous to cage  42 ,  42 ′ but without segmented ring  46 . TMDs  80  of  FIGS. 13–14  are inserted at various angles into the walls of cage  82 . In  FIG. 15 , TMD  80 - 1  is inserted approximately normal to face  100  of cage  82  and TMD  80 - 2  is inserted in face  102  substantially at right angles to TMD  80 - 1 . Face  100  of cage  82  is analogous to face  45  of cage  42  (see  FIGS. 4–7 ) and face  102  is analogous to face  65  of cage  42 ′ (see  FIG. 11 ). In  FIG. 16 , TMDs  80 - 3  and  80 - 4  oriented at approximately 45 degrees with respect to TMDs  80 - 1 ,  80 - 2 . While  FIGS. 15–16  illustrate TMDs  80  as being inserted in bearing cage  82  at particular angles, this is not intended to be limiting and TMDs  80  may be inserted at whatever angle is needed to damp particular vibrational modes of the cage. Because the harmonic motion of each TMD  80  is essentially linear as illustrated by arrows  95  in  FIG. 14 , each TMD  80  damps vibrations in a single degree of freedom. The particular direction in which it is effective with respect to bearing cage  82  can therefore be selected by choosing the orientation of TMDs  80  with respect to bearing cage  82 .  FIGS. 15–16  illustrate non-limiting examples of the various choices that can be used by a designer to suppress different vibrational modes in bearing cage  82 . 
     FIG. 17  is a view of bearing cage  82 , similar to  FIG. 4  but illustrating a still further embodiment of the present invention in which several TMD&#39;s  80  are mounted externally on surfaces  100  and/or  102  of cage  80  rather than internally within the walls of cage  82 . Any convenient means of attaching TMDs  80  to surfaces  100 ,  102  or other cage surfaces may be used. TMDs  80  of  FIG. 17  are shown as being attached at different angles on different surfaces to illustrate how additional vibrational modes may be suppressed. For example, TMDs  80 - 6 ,  80 - 7  and  80 - 8  are mounted so that their vibrational vectors  95  (see  FIG. 14 ) are tangentially oriented with respect to cage  82 , thus allowing them to assist in suppressing rotational or torsional vibrations, in addition to particular translational vibrations parallel to their individual motion vectors  95 . TMD  80 - 8  is illustrated as being mounted at an angle with respect to the circumferential or tangential direction of cage  82 , thus providing additional flexibility, for example, in suppressing swirl modes.  FIGS. 15–17  have illustrated the use of TMDs  80  in different orientations and attachments. Persons of skill in the art will understand based on the description herein that multiple TMDs may be mounted in different orientations and locations on the same bearing cage, some internally, some externally or a combination thereof, according to the vibrational modes desired to be suppressed. 
   The mass, spring and damping constants needed to damp bearing cage vibrations may be determined using means well known in the art. See for example, Chapter 6, “Dynamic Vibration Absorbers and Auxiliary Mass Dampers” in Harris&#39;  Shock and Vibration Handbook  (5 th Edition ), Edited by C. M. Harris and A. G. Piersol, McGraw-Hill, N.Y. 2002. A convenient rule of thumb is that a mass ratio of 5% will yield a damping ratio of about 5%, however, larger or smaller mass ratios may also be used. The mass ratio is the ratio of the damping mass to the mass being damped. In general, the vibrational modes of a bearing cage can be complex and an iterative design approach is sometimes required. That is, do a preliminary design according to the methods described for example, in Harris (ibid), build and test the results, refine the design and test again. Such iterative design approaches are well understood by persons of skill in the art. 
   While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, while the present invention has been illustrated for ball bearings, this is not intended to be limiting. The present invention applies to all types of bearings in which a cage is used to align the rolling elements or members. Balls as rolling elements or members are merely one example of many different types of rolling elements or rolling members that exist and are used in various types of bearings. Non-limiting examples of other types of bearings to which the present invention applies are roller bearings, thrust bearings, sleeve bearings and so forth that contain cages for aligning the rolling elements or members. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.