Abstract:
A bushing structure includes an outer shell and an inner shell. The outer shell shaped as a thin ring with a predetermined length further has at least a locating aperture. The inner shell shaped as another thin ring to be double layered firmly inside the outer shell has at least a locating protrusion with respect to the locating aperture. When the inner shell is mounted inside the outer shell, the locating protrusion is anchored inside the respective locating aperture so as to prevent possible relative movement in between. By providing the thin outer shell and the thin inner shell to form a complete bushing structure, an inherent material-shrinkage problem of plastic bushing can then be avoided.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The invention relates to a bushing structure, and more particularly to a two-piece bushing which includes a hard body and a separable soft lining for absorbing possible deformation formed during the application of the bushing.  
         [0003]     (2) Description of the Prior Art  
         [0004]     Bushings or bearings in the art are usually utilized on shafts or shaft-like elements for providing lubrication, offset or wear compensation. Generally speaking, in the case that the bushings are designed for lubricating shafts, ductile materials such as coppers are usually used. On the other hand, in the case that the bushings are used as compensations for offsets and wears, material selection can be more versatile. However, in consideration of material cost and its performance, it is obvious that the plastic material become much and much popular in making the bushings.  
         [0005]     While the plastic material is used to replace the metals for producing the bushings, two of obvious advantages are cost down and ease in manufacturing. On the other hand, disadvantages of utilizing the plastics may include less-precision control, ill environmental resistance, and short service life. The latter two can be acceptable trade-offs with respect to the low-cost merit. Yet, the problem in less-precision control while in producing the plastic bushings is really concerned and is a topic to be overcome.  
         [0006]     It is well known that the dimension distortion in production is an inherent feature to the plastic material. In the art, plastic bushings are generally produced by inject-molding which usually present a shrinkage problem in the plastic products. Empirically, the shrinkage problem is highly related to the thickness of the product. In the case that a bushing is thick, a high degree of shrinkage is usually seen. On the other hand, in the case that a bushing is thin, the shrinkage problem would be dim and usually show no harm to the operation of the bushing.  
         [0007]     Referring to  FIG. 1 , a cross-sectional view of a traditional plastic bushing  3  applied to carry a shaft  2  on a work piece  1  is shown. The bushing  3  firstly sleeves the shaft  2  and then the combination is mounted to a hole of the work piece  1 . Ideally, by providing the bushing  3  to interface rotations of the shaft  2  on the work piece  1 , better lubrication can be achieved and also possible dimension bias in between can be compensated.  
         [0008]     Nevertheless, if a shrinkage cavity  30  as shown in  FIG. 1  exists whatever in the bushing  3 , a severe eccentric rotation would happen to the combination of the shaft  2  and the bushing  3 . As a consequence, notorious vibrations or some other ill-rotation problems would occur and severely may even degrade dynamic performance of the combination which has a high possibility to make worse the wears of the bushing  3 .  
         [0009]     Therefore, an improvement upon the plastic bushing structure for overcoming foregoing shrinkage problem so as to avoid unexpected consequence in rotating a biased shaft is definite a topic to the art.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, it is a primary object of the present invention to provide a two-piece bushing structure which has less shrinkage in production by separately forming a sleeve body and a lining element.  
         [0011]     The bushing structure of the present invention includes a sleeve body and a lining element to be mounted firmly inside the sleeve body. The sleeve body, formed as a cylindrical shell, has a first end and an opposing second end. The first end can further include at least a locating aperture. The lining element, formed as another cylindrical shell to be fixedly telescoped inside the sleeve body, has a first lining end and an opposing second lining end. The first lining end can further include at least a locating anchor. While the bushing structure of the present invention in an assembly state, the lining element fits inside the sleeve body with the first lining end adjacent to the first end, the second lining end adjacent to the second end, and the locating anchor nesting in the respective locating aperture so as to form a stop pair for preventing relative motion between the sleeve body and the lining element.  
         [0012]     In one embodiment of the present invention, the lining element can further include at least an elastic arm formed as a cantilever beam extended to the first lining end by cutting axially the lining element. In this embodiment, the locating anchor to pair with the locating aperture of the sleeve body can be now located at a free end of the elastic arm. Preferably, the locating anchor can further include an out-facing lead surface for facilitating assembling of the lining element into the sleeve body.  
         [0013]     In one embodiment of the present invention, the second end of the sleeve body can further include at least a positioning part, while the second lining end includes at least a positioning counter part. While the bushing structure in the assembly state, the positioning part can match with the respective positioning counter part so as to form another stop pair for preventing relative motion between the sleeve body and the lining element.  
         [0014]     In this embodiment, the positioning part can be formed as a protrusion while the positioning counter part is formed as an aperture for receiving the protrusion.  
         [0015]     Alternative, in this embodiment, the counter positioning part can be formed as a protrusion while the positioning part is formed as an aperture for receiving the protrusion.  
         [0016]     In one embodiment of the present invention, the second lining end of the lining element can further include a flange. While the bushing structure in the assembly state, the flange is located exterior to the second end so as to form another stop pair for preventing relative motion between the sleeve body and the lining element.  
         [0017]     In the embodiment including the flange, the second end of the sleeve body can further include at least a positioning part while the flange includes at least a positioning counter part for matching with the respective positioning part so as to form a further stop pair for preventing relative motion between the sleeve body and the lining element. Similarly, in this embodiment, the positioning part can be formed as a protrusion while the positioning counter part is formed as an aperture for receiving the protrusion. Also, alternative, in this embodiment, the counter positioning part can be formed as a protrusion while the positioning part is formed as an aperture for receiving the protrusion.  
         [0018]     In the present invention, the sleeve body is preferably made of a material harder than that for making the lining element, such that the lining element can be easily mounted into the sleeve body.  
         [0019]     All these objects are achieved by the bushing structure described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which  
         [0021]      FIG. 1  is a cross-sectional view of a conventional plastic bushing used in mounting a shaft into a work piece;  
         [0022]      FIG. 2  is a perspective exploded view of a first embodiment of the bushing structure in accordance with the present invention;  
         [0023]      FIG. 3  is a cross-sectional view of the bushing structure of  FIG. 2  used in mounting a shaft into a work piece;  
         [0024]      FIG. 4  is a perspective view of a preferred lining element of a second embodiment of the bushing structure in accordance with the present invention;  
         [0025]      FIG. 5  is a cross-sectional view of a third embodiment of the bushing structure in accordance with the present invention;  
         [0026]      FIG. 6  is a perspective exploded view of a fourth embodiment of the bushing structure in accordance with the present invention; and  
         [0027]      FIG. 7  is a perspective exploded view of a fifth embodiment of the bushing structure in accordance with the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     The invention disclosed herein is directed to a bushing structure. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention.  
         [0029]     In the following description, those components having the same function but different profiles or locations are named and labeled by the same so as to achieve consistency in presenting the present invention.  
         [0030]     In order to resolve the aforesaid shrinkage problem of the plastic bushings, it is noted that producing the cylindrical bushing with a relative thin wall is obvious a resort. Based on this understanding, the present invention presents a two-piece bushing structure to give the designer a better control upon the thickness selection of each single piece.  
         [0031]     Referring now to  FIG. 2  and  FIG. 3 , a perspective exploded view of a first embodiment of the bushing structure in accordance with present invention and a cross-sectional view of the first embodiment in application are shown, respectively. In the first embodiment, the bushing structure  5  can include a sleeve body  51  and a lining element  53  to be mounted firmly inside the sleeve body  51 .  
         [0032]     The sleeve body  51 , preferably formed as a cylindrical shell, has a first end  510  and an opposing second end  514 . The first end  510  can further include at least a locating aperture  511  (four shown in this embodiment).  
         [0033]     The lining element  53 , shaped as another cylindrical shell to be fixedly telescoped inside the sleeve body  51  so as to form the bushing structure  5  as a double-eccentric-layer shell structure, has a first lining end  530  and an opposing second lining end  534 . The first lining end  530  can further include at least a locating anchor  5311  (four shown in this embodiment). The second lining end  534  can further include a flange  532 . As shown, the lining element  53  can further include at least an elastic arm  531  (four shown in this embodiment) formed as a cantilever beam extended to the first lining end  530  by cutting axially the lining element  53 .  
         [0034]     In this embodiment, the locating anchor  5311  to pair with the locating aperture  511  of the sleeve body  51  can be located at a free end of the elastic arm  531 . By providing elasticity of the cantilever-shape elastic arms  531 , the locating anchor  5311  can be easily pushed inward radially during the lining element  53  telescoping or plugging into the sleeve body  51 .  
         [0035]     As shown in  FIG. 2 , the locating anchor  5311  can further include an out-facing lead surface  5310  for easing the elastic arm  531  to deflect while encountering the pushing of the sleeve body  51  during the assembling and thus for facilitating assembling of the lining element  53  into the sleeve body  51 .  
         [0036]     Also, in this embodiment, the flange  532  is formed as a collar at the second lining end  534  of the lining element  53 . While the lining element  53  is mounted inside to the sleeve body  51 , the flange  532  can act as a position stop for the second end  514  of the sleeve body.  
         [0037]     As shown in  FIG. 3 , while the bushing structure  5  of the present invention in an assembly state, the lining element  53  just fits inside the sleeve body  51  with the first lining end  530  adjacent to the first end  510 , the second lining end  534  adjacent to the second end  514 , and the locating anchor  5311  nesting in the respective locating aperture  511  so as to form the bushing structure  5  as a double-layer shell. In this embodiment, the pair of the locating anchor  5311  and the locating aperture  511  forms a stop pair to prevent relative motion between the sleeve body  51  and the lining element  53 , while the pair of the flange  532  of the second lining end  534  and the second end  514  forms another stop. Since the two-piece structure  5  is formed, the bushing structure  5  can be sleeved onto a shaft  2 , and then the combination of the shaft  2  and the bushing structure  5  can be mounted into a hole or a bore of a work piece  1 .  
         [0038]     In the present invention, the sleeve body  51  is preferably made of a material harder than that for making the lining element  53 . Upon such an arrangement, the soft lining element  53  can be easily mounted into the sleeve body  51  and can have a better contribution in compensating possible offset or wear of the shaft  2 . On the other hand, the harder sleeve body  51  can achieve a better shield effect so as to steadily rotate in or engage with the work piece  1 . Also, the rotation center of the shaft  2  can be thus effectively ensured by the hard sleeve body  51 .  
         [0039]     In the first embodiment, the lining element  53  can be easily assembled inside to the sleeve body  31  with the help from the elastic arms  531  which can deflect inward radially to allow the sleeve body  51  to pass the locating anchor  5311  easily during the assembling. Also, the flange  532  of the lining element  53  can perform as an end stop for the sleeve body  51  while in assembling.  
         [0040]     Nevertheless, inclusions of the elastic arms  531  and the flange  532  are not requirements in the present invention. The reason is that both the sleeve body  51  and the lining element  53  are made of plastics which present substantial elasticity. Under proper managements of dimensions and materials for the sleeve body  51  and the lining element  53 , the assembling of the busing structure of the present invention would not cause any problem. In particular, in the case that the lining element  53  is made of a softer material, the elastic arms  532  of the lining element  53  can be retractable. Similarly, with substantial engagement between the locating aperture  511  and the locating anchor  5311 , the flange  532  can be omitted.  
         [0041]     Referring now to  FIG. 4 , a lining element  53  of a second embodiment of the bushing structure in accordance with the present invention is perspective shown. In this embodiment, the bushing structure can include the sleeve body  51  shown in  FIG. 2  and the lining element  53  shown in  FIG. 4 . The lining element  53  of  FIG. 4  obviously cancel the design of the flange and the elastic arms as described in the first embodiment. As stated, such cancellation wouldn&#39;t affect the engagement of the sleeve body  51  and the lining element  53 .  
         [0042]     Referring now to  FIG. 5 , a cross-sectional view a third embodiment of the bushing structure in accordance with the present invention is shown. Compared with the foregoing first embodiment of  FIG. 3 , this third embodiment adopts the lining element  53  as the same as the first embodiment does. On the other hand, a difference in sleeve body  51  exists in the structure of the locating aperture  511 . In the first embodiment as shown in  FIG. 2  or  FIG. 3 , the locating aperture  511  is open through the exterior surface of the sleeve body  51 . Contrarily, in this third embodiment of  FIG. 5 , the locating aperture  511  is a blind aperture with respect to the exterior surface of the sleeve body  51 .  
         [0043]     Referring now to  FIG. 6 , an exploded perspective view of a fourth embodiment of the bushing structure in accordance with the present invention is shown. Compared with the first embodiment of  FIG. 2 , the second end  513  of the sleeve body  51  of this fourth embodiment can further include at least a positioning part  512  (shown as an aperture), while the second lining end  534  of the lining element  53  includes at least a positioning counter part  5321  (shown as a protrusion of the flange  532  toward the first lining end  530 . While the bushing structure  5  in the assembly state, the positioning part  512  can match with the respective positioning counter part  5321  so as to form another stop pair for preventing relative motion, mainly distortion, between the sleeve body  51  and the lining element  53 .  
         [0044]     In  FIG. 6 , the pair of the positioning part  512  and the positioning counter part  5321  is embodied as a pair of an aperture and a counter protrusion on the flange  532 , respectively. Yet, in the present invention, the protrusion as the positioning counter part  5321  needn&#39;t co-exist with the flange  532 . In an embodiment not shown here, the lining element  53  can exclude the flange  532  but include the protrusion type of the positioning counter part  5321 .  
         [0045]     Referring now to  FIG. 7 , a perspective exploded view of a fifth embodiment of the bushing structure in accordance with the present invention is shown. Compared with the foregoing fourth embodiment of  FIG. 6 , the positioning part  512  of the sleeve body  51  in the fifth embodiment is embodied as a protrusion while the positioning counter part  5321  of the lining element  53  is embodied as a counter aperture formed in the flange  531 . While the fifth embodiment  5  is in the assembly state, the protrusion  512  of the sleeve body  51  can engage with the counter aperture  5321  of the lining element  53  so as to define a predetermined stop or engagement relation for avoiding further motions between the lining element  53  and the sleeve body  51 .  
         [0046]     By providing the two-piece bushing structure of the present invention, the prior shrinkage problem in producing the conventional one-piece bushing can be avoided and also a better control on applying the bushing can be achieved.  
         [0047]     While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.