Abstract:
The invention is aimed, in a rolling bearing device, to improve its durability by appropriately attenuating vibration of a rotating shaft by means of a high level of dumping performance, and thereby to reduce the load imposed on the rolling bearing and/or the overall system. A rolling bearing device of the present invention comprises a rolling bearing ( 13 ) including: an inner ring ( 24 ) and an outer ring ( 23 ) that are disposed so as to be relatively rotatable; and a plurality of rolling elements ( 25 ) disposed between the inner ring ( 24 ) and the outer ring ( 23 ), in which the rolling bearing ( 13 ) supports relative rotation between a shaft ( 14 ) and a housing ( 12 ). Besides, the rolling bearing device comprises, between the rolling bearing ( 13 ) and the housing ( 12 ), a damper member ( 60 ) formed by one or more metal wires ( 64 ) that are knitted.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a rolling bearing device and an electric generator. 
       BACKGROUND ART 
       [0002]    In an automobile, an alternator (electric generator) is equipped with a housing to which a stator is fixed, and a rotating shaft to which a rotor is fixed. The rotating shaft is supported by the housing through a rolling bearing. Because the power of an engine is transmitted to the rotating shaft through a drive belt, a high level of vibration caused by a high-speed revolution acts on the rotating shaft through the drive belt, thus inflicting a heavy load upon the rolling bearing device and its overall system. In particular, in a rolling bearing, there is a problem that white layer flaking occurs at the outer ring as ring roller and thus causes a shorter service life. 
         [0003]    For example, in Japanese Patent Application Publication No. 2005-308032, there is disclosed a technique regarding a bearing in possession of vibration damping function. The technique uses a vibration damping member intervening between an outer ring and a bearing housing of a rolling bearing in order to attenuate the vibration from a rotating shaft by the vibration damping member. However, because the vibration damping member is formed of elastic material such as synthetic resin material and rubber, it is insufficient for repressing the vibration of an apparatus like alternator used under a severe condition such as high temperature, high-speed revolution and heavy load, so it is not sort of a bearing that is durable for a long-term application. Especially, it is difficult that an elastic material such as synthetic resin materials and rubber sustains vibration depression effect under high temperature environments. Therefore, it is substantially difficult to adopt the technique as described in Japanese Patent Application Publication No. 2005-308032 for the reduction of vibration of a device such as alternator. 
         [0004]    The present invention was contrived in view of the aforementioned circumstances, and is aimed to provide a rolling bearing device and an electric generator that are adapted to improve their durability by appropriately attenuating vibration of a shaft by means of an excellent dumping performance and thereby reducing the load imposed on the overall system including the rolling bearing device and its housing. 
       DISCLOSURE OF INVENTION 
       [0005]    A rolling bearing device of the present invention comprises a rolling bearing including: an inner ring and an outer ring disposed so as to be rotatable relatively; and a plurality of rolling elements disposed between the inner ring and the outer ring; the rolling bearing device supports, through the rolling bearing, a shaft rotatable relative to a housing, wherein the rolling bearing device comprises a damper member disposed between the rolling bearing and the housing; and the damper member is formed of metal wire(s) that is(are) knitted. 
         [0006]    Besides, an electric generator of the present invention comprises: a stator and a rotor; a housing to which the stator is fixed; a rotating shaft to which the rotor is fixed and an rotational power is transmitted from external; and a rolling bearing that is fixed to the housing and supports the rotating shaft in such a manner that the shaft can rotate unrestrictedly, wherein the electric generator comprises a damper member disposed between the rolling bearing and the housing; and the damper member is formed of metal wire(s) that is(are) knitted. 
         [0007]    According to the above-mentioned inventions, since the damper member disposed between the rolling bearing and the housing is formed of metal wire(s) that is(are) knitted, it is capable of performing elastic deformation (contraction) over its entire dimensions, attenuating three-dimensionally omnidirectional vibrations, thereby providing high level of dumping performance. Thus, it is possible to reduce the load to the rolling bearing and the overall system, and thus to improve their durability. As for the rolling bearing, this especially helps repress white layer peeling. Additionally, because the damper member is formed of one or more metal wires, it has high strength and high heat resistance; therefore, even a device with heavy-duty working conditions like an electric generator such as an alternator and the like is capable of serving for a long-term application. 
         [0008]    Gaps are formed between the wire(s), and it is preferable that the gaps are filled with a lubricant. Thereby it is possible to prevent the wire from being worn out by rubbing each other in the course of its elastic deformation. 
         [0009]    Gaps are formed between the wire(s), and it is preferable that the porosity as defined by the ratio of overall volume of the gaps to overall volume of the damper member is set within a range exceeding 50% and under 70%. This can result not only in reducing omnidirectional vibrations in a well balanced manner, but also in securing rigidity required to support the rolling bearing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a sectional view of an electric generator to which a rolling bearing device according to an embodiment of the present invention is applied. 
           [0011]      FIG. 2  is a perspective view of a damper member. 
           [0012]      FIG. 3  is an enlarged view of the portion III of  FIG. 2 . 
           [0013]      FIG. 4  shows a performance test result of an electric generator comprising a damper member of 60% porosity, in which a graph (a) depicts a relationship between time and number of revolutions of a rotating shaft, and a graph (b) depicts a relationship between time and vibration value, respectively. 
           [0014]      FIG. 5  shows a performance test result of an electric generator comprising a damper member of 50% porosity, in which a graph depicts a relationship between time and vibration value. 
           [0015]      FIG. 6  shows a performance test result of an electric generator according to a comparative example, in which a graph(a) depicts a relationship between time and number of revolutions of a rotating shaft, and graph(b) depicts a relationship between time and vibration value, respectively. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]      FIG. 1  is a sectional view of an alternator (electric generator)  9  employing a rolling bearing device according to an embodiment of the present invention. The alternator  9  comprises a housing  12  and a rotating shaft  14 . The housing  12  comprises a front housing  10  and a rear housing  11  conjoined by bolts. The rotating shaft  14  is rotatably supported through two rolling bearings  13 ,  13  inside the housing  12 . In the housing  12  is disposed a stator  16  comprising a wound coil  15 . To the rotating shaft  14  is provided a rotor  18  comprising a wound coil  17 . To an end of the rotating shaft protruding from the housing  12  is attached a pulley  19  with a built-in fan. To the pulley  19  is transmitted a motive power from an engine through a drive belt which is not illustrated. 
         [0017]    The rolling bearing  13  is mounted inside a support tube member  20  formed in the housing  12  at each end of the axial direction. To be concrete, the rolling bearing  13  comprises an outer ring  23 ; an inner ring  24  disposed diametrically inside the outer ring  23 ; and a number of balls (rolling elements)  25  disposed between the outer ring  23  and the inner ring  24 , and it is made such that the outer ring  23  and the inner ring  24  are relatively rotatable. On the inner circumferential surface of the inner ring of the rolling bearing  13  is fitted the rotating shaft  14 , and between the outer circumferential surface of the outer ring and the inner circumferential surface of the support tube member  20  of the rolling bearing  13   a  is disposed a damper member  60  to attenuate the vibration occurring with revolution of the rotating shaft  14 . Then, the rolling bearing device of the present invention is composed of the rolling bearing  13  and the damper member  60 . 
         [0018]      FIG. 2  is a perspective view of the damper member  60 , and the damper member  60  is formed in a ring-shape of a generally rectangular cross section having a width  w  and a thickness  t . The inner circumferential surface of the damper member  60  is engaged with the outer circumferential surface of the outer ring of the rolling bearing  13 , and the outer circumferential surface of the damper member  60  abuts against the inner circumferential surface of the support tube member  20 . 
         [0019]      FIG. 3  is an enlarged view of the portion III of  FIG. 2 . The damper member  60  is formed of metal wire(s)  64  such as stainless steel as its material. Concretely, one or more metal wires  64  are three-dimensionally knitted while intricately flexed (i.e., one or more wires  64  are gathered, twisted, interlaced and/or intertwined with each other), thereby forming the dumper member  60  in a ring-shape as a whole with a generally rectangular cross section. 
         [0020]    Between metal wires  64  composing the damper member  60  are formed gaps (voids) generally or partially. The damper member  60  is capable of performing elastic deformation (contraction) generally in a diametrical direction (X-direction (page penetration direction), Y-direction, etc. in  FIG. 1 ), and shaft center Z-direction, by means of the wire  64  performing elastic deformation within the range of the gaps, the wires next to each other displacing longitudinally, and so on. Then, the damper member  60  is formed with an external diameter slightly greater than the inside diameter of the support tube member  20 , and disposed, as shown in  FIG. 1 , between the rolling bearing  13  and the support tube member  20  in a diametrically compressed state by a predetermined interference. 
         [0021]    As shown in  FIG. 3 , gaps between wires  64  in the damper member  60  are filled with a lubricant. For a lubricant, lubricating oil or grease can be used. For lubricating oil, for example, either of those from ester, ether, silicon, fluorine and synthetic hydrocarbon type is used. For grease, for example, either of those in which a thickener of lithium-type or urea-type is added to a base oil of those from ester oil, ether oil, silicone oil, fluorine oil or synthetic hydrocarbon oil is used. For a metal wire  64 , for example, one of those having 0.4 mm external diameter is used. The ratio (porosity) of the total volume occupied by the gaps to the total volume of the damper member  60  can be made as e.g. 60%. 
         [0022]    The damper member  60  is produced as follows. First, a ring-shaped intermediate article is formed having external diameter, thickness t and width w slightly greater than, and inside diameter smaller than, those of a finally shaped article. The intermediate article is formed by moderately knitting the metal wire  64  in order to have porosity greater than the porosity (e.g., 60%) of a finally shaped article. Then the gaps between wires  64  are decreased by compressing the intermediate article using a metallic mold, thus forming a finally shaped article with desired dimensions and porosity. 
         [0023]    In the above-mentioned constitution, the vibration transmitted through the rotating shaft  14  from the drive belt to the rolling bearing  13  is attenuated by the damper member  60 , and then transmitted to the housing  12 . In this event, because the damper member  60  is capable of performing elastic deformation in diametrical (X-, Y-) and shaft center (Z-) directions, it is capable of attenuating vibrations three dimensionally and omnidirectionally, thereby providing a high level of dumping performance. 
         [0024]    Moreover, not only through elastic deformation of metal wire  64  itself, but also through friction that is brought by knitted structure of the wire  64  as well as the state in which the wire  64  is intertwined and so forth, vibrational energy of all directions is sustained and can be alleviated by its performance that surpasses simple viscoelasticity. 
         [0025]    Therefore, vibration propagating from the rotating shaft  14  to the housing  12  through the rolling bearing  13  is reduced, so that durability of the rolling bearing  13 , the housing  12  and, in turn, the alternator  9  as a whole, can be improved. Particularly, in the rolling bearing  13 , white layer flaking can be suppressed. Besides, noise can be reduced as a result of decrease of vibration. 
         [0026]    Because the damper member  60  is formed using metal wire(s)  64 , it can provide robust strength and heat resistance. Accordingly, it does not deteriorate at an early stage even in high vibration (high load), high temperature working conditions, so that its long-term use is enabled. 
         [0027]    Also, since the gaps between the wires  64  in the damper member  60  are filled with grease, there is little chance of the wires&#39;  64  rubbing each other to be worn out in the course of elastic deformation. 
         [0028]    The elastic modulus (constant of spring) of the damper member  60  can be changed freely by appropriately selecting its porosity, direction of knitting, and external diameter of the wire  64 , etc. Further, the elastic modulus can be made different depending on the direction (diametrical direction, axial direction) of elastic deformation. Thus, a damper member  60  according to the required dumping characteristics can be produced easily. Moreover, because the geometry of the damper member  60  (outside diameter, inside diameter, width w, thickness t, cross-sectional geometry) can be designed freely, degree of freedom in designing an alternator  9  increases, which allows one to produce optimal alternators  9 . 
         [0029]    Shown below as a reference is a performance test result of an alternator  9  equipped with the damper member  60 . 
         [0030]    The test was performed on the alternator  9  equipped with the damper member  60  by measuring the vibration value of the housing  12  occurring with the revolutions while the rotational motive powers were transmitted to the rotating shaft  14  through the pulley,  FIG. 4  and  FIG. 5  are graphs showing the test result.  FIG. 4(   a ) shows a change in number of revolutions with passage of time, whereas  FIG. 4(   b ) and  FIG. 5  show changes in the vibration values of Y-direction and Z-direction that resulted from the change in number of revolutions expressed in  FIG. 4(   a ). 
         [0031]    In the test shown in  FIG. 4(   b ), the damper member  60  of 60% porosity was used, whereas the damper member  60  of 50% porosity was used in the test shown in  FIG. 5 . Then, the gaps between wires  64  were filled with fluorine type grease. 
         [0032]    Additionally,  FIG. 6  shows, as a comparative example, the vibration values measured in a test under the same condition as performed in  FIG. 4  and  FIG. 5 , however on an alternator  9  without a damper member (i.e. in which the rolling bearing  13  was mounted directly to the support tube member  20 ). 
         [0033]    In the comparative example of  FIG. 6 , when number of revolutions of the rotating shaft  14  was assumed at some 160,000 r/min level, maximum vibration values of X-, Y- and Z-directions fell within the range of about 1.4-1.9 m/sec 2 . Besides, the vibration values increased sharply after staring, and irregular fluctuations were also found. In contrast, when the damper member  60  of 60% porosity was used, as shown in  FIG. 4 , the vibration value had a maximum of about 1.6 m/sec 2  in X-direction; whereas in Y- and Z-directions, the vibration values remained within the range of about 1.0-1.3 m/sec 2 , showing substantial reductions. Besides, build-up of the vibration values from staring was moderate, and the vibration values stabilized at an earlier stage than those of the comparative example. 
         [0034]    Accordingly, it is understood that vibration can be reduced effectively by disposing a damper member  60  of the present embodiment. 
         [0035]    Further, when the damper member  60  of 50% porosity was used, although the vibration values in X- and Y-directions slightly rose compared with the comparative example (see  FIG. 6(   b )) as shown in  FIG. 5 , the vibration value became not more than 1 m/sec 2  in Z-direction, showing a considerable reduction. However, taking into consideration of reducing the vibration values in a well balanced manner omnidirectionally in X-, Y- and Z-directions, it may be said that using the damper member  60  of 60% porosity is preferred to using the damper member  60  of 50% porosity. Moreover, although it is not illustrated, strength of the damper member  60  decreases when porosity becomes not less than 70%, so that the rigidity to support the rolling bearing  13  becomes lowered; so, in this respect also, it is thought that using the damper member  60  of 60% porosity is preferred. 
         [0036]    Based upon the foregoing, in order to reduce the vibration values in a well balanced manner omnidirectionally in X-, Y- and Z-directions, and in order to retain the rigidity enough to support the rolling bearing  13 , it is preferred to set a porosity of the damper member  60  to fall within the range of over 50% and under 70%, and more preferred to fall within 55%-65%. 
         [0037]    Because the damper member  60  of the present invention consists of one or more metal wires, vibration suppression effect is sustained even at a high temperature. Consequently, it is superior to conventional damper members that are made from rubbers and/or synthetic resin materials whose vibration suppression effect deteriorates due to change of their physical properties at high temperatures. 
         [0038]    The present invention is adapted for any appropriate design change without being limited to the above-mentioned embodiments. For example, material and/or external diameter of the metal wire forming the damper member  60 , porosity of the damper member  60 , etc. can be changed accordingly. Further, in the above-mentioned embodiments, the damper member  60  is formed in the shape of a ring; however, it may otherwise be made to have circular arc geometry or block geometry divided in circumferential direction. The cross-sectional shape of the damper member  60  may be circular, or polygonal other than quadrangular. The rolling bearing  13  may be a roller bearing, not limited to a ball bearing. Further, an electric generator may be a DC generator, not limited to an AC electric generator (an alternator). Moreover, the present invention can be applied to other apparatus using a rolling bearing, not limited to an electric generator.