Abstract:
This invention provides a roller bearing that can provide sufficient lubrication. A needle roller bearing has a plurality of rollers each having a first and second end portion and disposed circumferentially around a shaft, a cylindrical first retainer member having a plurality of first notches each adapted to rotatably support the first end portion of each roller, and a cylindrical second retainer member located away from and opposite the first retainer member and having a plurality of second notches each adapted to rotatably support the second end portion of each roller. A plurality of voids are provided to form grease containing spaces between the adjacent rollers between the first and second retainer members.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a roller bearing, and more particularly, a roller bearing having a plurality of rollers circumferentially disposed and each rotatably supported by a retainer.  
           [0002]    Generally, a roller bearing includes a plurality of circumferentially located rollers and a retainer with a plurality of supporting holes adapted to support the rollers rotatably. The retainer typically has an outer race and/or an inner race. As a lubricating method of such a roller bearing, applying grease on the retainer, forming a recess as a grease container on the retainer, or oil drip or splash is conducted.  
           [0003]    However, in a roller bearing with smaller rollers, especially, in a needle roller bearing, since a thickness of a retainer is thinner and a distance between adjacent supporting holes of the retainer is narrower, it is difficult to form a recess as a grease container between adjacent supporting holes on a retainer. Particularly, in a needle roller bearing with a smaller outer diameter, since a distance between adjacent supporting holes of the retainer is much narrower, it is very difficult to form a recess as a grease container between adjacent supporting holes on a retainer.  
           [0004]    Therefore, a prior art roller bearing, especially with smaller rollers and a smaller outer diameter, could not be fully lubricated.  
           [0005]    The present invention has been made to eliminate these problems and its object is to provide a roller bearing having an adequate lubricating function even in the case where the bearing is composed of smaller rollers or the bearing has a smaller outer diameter.  
         SUMMARY OF THE INVENTION  
         [0006]    A roller bearing of the present invention includes N pieces of rollers disposed circumferentially and parallel to each other, and a retainer adapted to support the rollers rotatably. Each roller has a first and second end portion located axially away from each other. The retainer includes a first, generally cylindrical retainer member having N pieces of first notches adapted to rotatably support the first end portion of each roller and a second, generally cylindrical retainer member that is located axially away from and opposite the first retainer member and that has N pieces of second notches adapted to rotatably support the second end portion of each roller. A plurality of voids are provided to form grease containing spaces between the oppositely disposed first and second notches and the circumferentially adjacent, oppositely disposed first and second notches between the first and second retainer members.  
           [0007]    According to the present invention, since the retainer is formed of the first and second retainer members contraposed and located away from each other, and voids for grease are formed between circumferentially adjacent notches of these retainer members, even in the case of a needle roller bearing having rollers of smaller diameters and a retainer of a thinner thickness, or a needle roller bearing with a smaller outer diameter and narrower spaces between the adjacent supporting holes, a grease containing space can be secured and thus, adequate lubricating function can be achieved.  
           [0008]    Moreover, in this case, because a grease container is not formed concavely on the surface of the retainer but formed at a void where no other members exist between the first and second retainer members, grease can be directly applied to a rolling contact surface between an inner and outer race member and each roller. Thus, the rolling contact surface can be fully and securely lubricated.  
           [0009]    When the first and second retainer members are formed separately, N pieces of voids are provided between the first and second retainer members. In this case, since the same number of grease containers as rollers is formed, each roller can be securely lubricated with adequate amount of grease. Also, in this case, not an elongated aperture but a notch is formed in the first and second retainer member to receive each roller. Thus, in injection molding each retainer member, it can be formed using an axially movable mold. Therefore, a multiple mold can be deployed on the same plane in a molding unit of a forming machine, thereby reducing the cost of a mold and manufacturing cost.  
           [0010]    To the contrary, in forming a prior art retainer having a plurality of apertures to hold rollers, an inner mold disposed on an inner circumferential side and a plurality of outer molds disposed on an outer circumferential side and divided in a normal direction are required to compose a mold, and each outer mold needs to be translatable in a normal direction. Thus, the structure of a mold becomes complicated and the only one mold can be disposed at a mold unit of a forming machine to secure a travel space of the outer mold, thereby increasing the cost of a mold and a manufacturing cost.  
           [0011]    When the first and second retainer members are connected to each other by n (&lt;N) pieces of connections provided at voids and (N−n) pieces of voids are formed between the first and second retainer members, the first and second retainer members can be formed integrally with each other through connections, thus facilitating assembly of a roller bearing. In addition, the first and second retainer members and connections are preferably welded or fused by ultrasonic wave or the like, and alternatively, they may be integrated with each other by plastics molding.  
           [0012]    When a cylindrical outer race is further provided and opposite ends of the outer race are supported by the first and second retainer member, the outer race is located on an outer circumferential side of each void formed at adjacent rollers, thereby preventing grease from flying out of the void through centrifugal force. Also, an axial distance between the first and second retainer member can be maintained by the outer race, and the first and second retainer member and the outer race can be integrated with each other, thus facilitating assembly of a roller bearing.  
           [0013]    A lip portion of tapered cross section contacting the inner circumference of the outer race may be formed on the first and second retainer member. In this case, by providing such a lip portion, grease which is housed in a void between the first and second retainer members can be prevented from leaking out from the inner circumference of the outer race through a clearance between the opposite ends of the outer race and the first and second retainer members.  
           [0014]    An oil groove may be formed at a portion of the first and second retainer member contacting the outer race. Thus, especially in an application where a shaft is fixed and an outer race is rotatable, wear to the retainers due to the difference of the rotational speeds between the retainer and the outer race can be prevented. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. In the drawings, which are not to scale:  
         [0016]    [0016]FIG. 1 is a cross sectional view of a needle roller bearing according to an embodiment of the present invention, showing a cross section of FIG. 2 taken along line I-I.  
         [0017]    [0017]FIG. 2 is a longitudinal sectional view of FIG. 1 taken along line II-II.  
         [0018]    [0018]FIG. 3 is a side view of a portion of a needle roller bearing of the present invention, as viewed from line III-III of FIG. 1.  
         [0019]    [0019]FIG. 4 is a side view of a portion of a needle roller bearing according to another embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is a sectional view of a column guide employing a needle roller bearing of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Referring now to the drawings, FIGS. 1 and 2 show a needle bearing according to an embodiment of the present invention. FIG. 1 is a cross sectional view of FIG. 2 taken along line I-I and FIG. 2 is a longitudinal sectional view of FIG. 1 taken along line II-II.  
         [0022]    As shown in FIGS. 1 and 2, a needle roller bearing  1  includes a plurality of needle-shaped rollers  10  disposed along a circumference and parallel to each other, and a first and second retainer member  2 ,  3  having a generally cylindrical shape and located axially away from and opposite each other.  
         [0023]    [0023]FIG. 3 is a side view of a portion of the needle roller bearing  1 . The first retainer member  2  has a plurality of first notches  20  each rotatably supporting an end portion  10   a  of the roller  10 . Similarly, the second retainer member  3  has a plurality of second notches  30  each rotatably supporting the other end portion  10   b  of the roller  10 . These notches  20 ,  30  are disposed opposite each other.  
         [0024]    There is provided a void  4  that forms a grease containing portion between adjacent rollers  10 . In other words, a protrusion  22  is formed between adjacent notches  20  of the first retainer member  2 , and similarly, a protrusion  32  is formed between adjacent notches  30  of the second retainer member  3 . And a void  4  is formed between these protrusions  22  and  32  oppositely disposed in an axial direction. The number of the voids  4  is the same as that of each of the notches  20 ,  30 .  
         [0025]    Turning back to FIGS. 1 and 2, a cylindrical outer race  5  is provided between the first and second retainer members  2 ,  3 . The first and second retainer members  2 ,  3  are respectively formed with bosses  2   a ,  3   a  each supporting an end portion  50 ,  51  of the outer race  5 . Lip portions  24 ,  34  each having a tapered cross section and contacting an inner circumferential surface  5   a  of the outer race  5  are formed at the bosses  2   a ,  3   a.  Also, the outer circumferential surface  5   b  or cylindrical surface of the outer race  5  is formed straight. That is, a generating line of the cylindrical surface  5   b  is straight.  
         [0026]    The first and second retainer members  2 ,  3  respectively have central holes  2   b ,  3   b  into which a shaft  6  is inserted. An oil groove  26  is formed on a side surface of the first retainer member  2  and an oil groove  28  is formed on an end surface  2   c  of the first retainer member  2 . Similarly, an oil groove  36  is formed on a side surface of the second retainer member  3  and an oil groove  38  is formed on an end surface  3   c  of the second retainer member  3 .  
         [0027]    Additionally, side walls  15 ,  16  are respectively provided beside the first and second retainer members  2 ,  3 . These side walls  15 ,  16  restrain axial movements of the first and second retainer members  2 ,  3 , thereby preventing the needle roller bearing  1  from falling off the shaft  6 .  
         [0028]    In this case, as above-mentioned, since a retainer is formed of the oppositely disposed, first and second retainer members  2 ,  3  and a plurality of voids  4  are formed between the adjacent rollers  10  to provide grease containers, especially in the case of a needle roller bearing with a thinner retainer, or with a very narrower space between the adjacent needle rollers and a smaller outer diameter, grease reservoir or container can be secured, and thus, an adequate lubricating function can be achieved.  
         [0029]    Also, because a grease container is formed not on the surface of the retainer but in the voids  4  where no other members exist between the retainer members  2  and  3 , more grease can be directly applied on a rolling contact surface between the shaft  6  and each needle  10 , thereby lubricating the rolling contact surface more adequately and securely.  
         [0030]    Moreover, in this case, since the same number of voids  4  or grease containers as that of the rollers  10  is formed between the first and second retainer members  2 ,  3 , an adequate amount of grease is maintained to lubricate each needle roller  10 .  
         [0031]    Furthermore, in operation, the outer race  5  positioned outside the voids  4  prevents grease in each void  4  from flying out of the void  4  through centrifugal force. Also, the first and second retainer members  2 ,  3  are integrated with each other through the outer race  5 , thus facilitating assembly of the needle roller bearing. Additionally, since the outer race  5  has a straight cylindrical face, working process of the outer race  5  becomes easier.  
         [0032]    Also, leakage of grease in the void  4  to the outside of the roller bearing  1  through a clearance between the bosses  2   a ,  3   a  of the retainer members  2 ,  3  and the inner circumference  5   a  of the outer race  5  is prevented by lip portions  24 ,  34  of the first and second retainer members  2 ,  3 .  
         [0033]    Moreover, in this case, not holes but notches  20 ,  30  are provided to receive needle rollers  10  in the first and second retainer members  2 ,  3 . Thus, in injection molding each retainer member  2 ,  3 , it can be formed using an axially movable mold. Therefore, a multiple mold can be deployed on the same plane in a molding unit of a forming machine, thereby reducing manufacturing cost.  
         [0034]    In contrast, when forming a retainer of prior art with a plurality of apertures to receive the whole lengths of rollers, an inner mold disposed on an inner circumferential side and a plurality of outer molds disposed on an outer circumferential side and divided in a normal direction are required to compose a mold, and each outer mold needs to be translatable in a normal direction. Thus, the structure of a mold becomes complicated and the only one mold can be disposed at a mold unit of a forming machine to secure a travel space of the outer mold, thereby increasing manufacturing cost.  
         [0035]    Also, especially in an application where a shaft  6  is fixed and the outer race  5  is rotatable, oil grooves  26 ,  36  formed on the side faces of the retainer members  2 ,  3  prevent wear to the side faces of the retainer members  2 ,  3  due to the difference of the rotational speed between the retainer members  2 ,  3  and the outer race  5 . Similarly, oil grooves  28 ,  38  formed on the end faces  2   c ,  3   c  of the retainer members  2 ,  3  prevent wear to the end faces  2   c ,  3   c.    
         [0036]    In the above-mentioned embodiment, the first and second retainer members  2 ,  3  are completely separated and located away from each other, but the application of the present invention is not limited to this embodiment. The present invention also applies to another embodiment shown in FIG. 4.  
         [0037]    In FIG. 4, the same reference numerals indicate the same or corresponding portions of FIG. 3. As shown in FIG. 4, the first retainer member  2  is partly connected to the second retainer member  3 . That is, between the first and second retainer members  2 ,  3 , voids  4  and connections  7  to connect the corresponding projections  22 ,  32  coexist.  
         [0038]    Here, when the number of needles  10  is N and the number of connections  7  is n (n is smaller than N), the number of voids  4  is (N−n). In this case, the first and second retainer members  2 ,  3  can be integrated with each other through connections  7 , thereby facilitating assembly of a needle roller bearing.  
         [0039]    A connection  7  is preferably formed by fusing or welding a connecting portion  29  of the first retainer member  2  to a corresponding connecting portion  39  of the second retainer member  3  through supersonic wave or the like. Alternatively, these connections  29 ,  39  may be formed integrally with each other through plastics molding.  
         [0040]    Next, FIG. 5 shows a column guide employing the needle roller bearing  1  of the present invention. As shown in FIG. 5, a column guide  100  includes an axially extending ram  8  of a solid cylindrical shape and a column  9  of a hollow cylindrical shape that receives the ram  8  and that is axially translatable relative to the ram  8 .  
         [0041]    The column  9  is composed of a plurality of ring-shaped members  90  that are stacked axially and fixed to each other in a known manner such as bolts. On contact faces of the adjacent ring-shaped members  90 , a plurality of recesses  90   a  disposed around the ram  8  are formed. The above-mentioned needle roller bearing  1  is housed in a space formed by the oppositely disposed recesses  90   a  of the adjacent ring-shaped members  90 . In FIG. 5, the needle roller bearing  1  is shown in a simplified manner.  
         [0042]    Each shaft  6  of the needle roller bearing  1  extends in a direction perpendicular to the axis of the ram  8  and is supported by the ring-shaped member  90 . The outer circumferential surface  5   b  of the outer race  5  is in contact with the outer circumferential surface  8   a  of the ram  8 . Thus, by rotation of the outer race  5  around the shaft  6  and axial rolling movement of the outer race  5  on the outer circumferential surface  8   a  of the ram  8 , the column  9  is axially translatable relative to the ram  8 .  
         [0043]    In an application to such a column guide, the outer race  5  of the needle roller bearing  1  may have a cylindrical surface  5   b  of a concavely curved generating line. When the outer circumferential surface  8   a  of the ram  8  is formed by a convexly curved surface with a smaller radius of curvature than a cylindrical surface  5   b  of the outer race  8 , a contact area between the cylindrical surface  5   b  of the outer race  5  and the outer circumferential surface  8   a  of the ram  8  increases and surface pressure on the contact surface can be decreased, thereby improving wear resistance. To the contrary, when the outer race  5  has a cylindrical surface  5   b  of a convexly curved generating line and the outer circumferential surface  8   a  of the ram  8  is formed by a concavely curved surface with a greater radius of curvature than a cylindrical surface  5   b  of the outer race  5 , a contact area between the cylindrical surface  5   b  of the outer race  5  and the outer circumferential surface  8   a  of the ram  8  increases and surface pressure on the contact surface can be decreased, thereby improving wear resistance.  
         [0044]    Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention without departing from its spirit or essential characteristics particularly upon considering the foregoing teachings. The described embodiments and examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments and examples, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art, yet fall within the scope of the invention.