Abstract:
A terminal connecting-and-fixing structure capable of ensuring the connection between the terminal and the bus bar even in the case of loose of the bolt and suppressing increase in the contact resistance, thereby preventing poorness of the conduction, is provided. A terminal connecting-and-fixing structure comprises a bus bar  10  having a plate-like shape, a bolt  30  penetrating the bus bar  10,  and a nut  40  tightened by the bolt  30,  and a terminal  20  mounted on the bolt  30,  wherein the terminal  20  and the bus bar  10  is connected and fixed by fastening the nut  40  to the bolt  30,  and wherein the bus bar  10  has a concave portion  12,  and the terminal  20  and the bus bar  10  is connected and fixed by fastening the nut  40  to the bolt  30  while an end portion of the terminal  20  is press-fitted in the concave portion  12.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a terminal connecting-and-fixing structure, particularly to a terminal connecting-and-fixing structure comprising a bus bar having a plate-like shape, a bolt penetrating the bus bar, and a nut tightened by the bolt, and a terminal mounted on the bolt, wherein the terminal and the bus bar is connected and fixed by fastening the nut to the bolt. 
       BACKGROUND 
       [0002]    Electric vehicle driven by a motor, such as a battery-powered forklift has an inverter mounted thereon to convert a DC voltage charged in a battery to an AC voltage, and the inverter has a terminal portion to which a cable connected to e.g. a motor is to be connected.  FIG. 10  is a schematic diagram illustrating a conventional terminal connecting-and-fixing structure. 
         [0003]    As illustrated in  FIG. 10 , a conventional terminal connecting-and-fixing structure  100  comprises a bus bar  110  having a plate-like shape, a bolt  130  penetrating the bus bar  110 , and a terminal  120  mounted on the bolt  130 . Further, the terminal  120  and the bus bar  110  is connected and fixed by fastening the nut  140  to the bolt  130 , whereby the terminal  120  and the bus bar  110  are electrically continued. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Document 1: JP2005-16355 A 
       SUMMARY 
     Technical Problem 
       [0005]    In general, the terminal  120  and the bolt  130  are composed of different materials and have different linear expansion coefficients. Thus, when the terminal connecting-and-fixing structure is kept in a high-temperature environment, the fastening of the bolt  130  may be loosened due to the difference in the amount of thermal expansion between the two. Further, the fastening of the bolt  130  may also be loosened by e.g. vibration. If the fastening of the bolt  130  is loosened as above, the contact resistance between the terminal  120  and the bus bar  110  may be increased, and the conduction therebetween may become poor. 
         [0006]    In particular, as a battery-powered forklift employs a high-output inverter in terms of easiness of vehicle installation and is placed in an enclosed space in terms of dust-proof property and waterproof property, the terminal connecting-and-fixing structure  100  is likely to be kept in a high-temperature environment. Further, as a forklift is started and stopped repeatedly in operation, vibration is likely to occur. Thus, there has been a problem such that poorness of conduction as described above is likely to arise. 
         [0007]    Patent document 1 discloses a stud bolt type terminal device having a structure where an O-ring is disposed at the boundary between a stud bolt and a resin mold cover in order to prevent entrance of foreign matters from an interspace resulting from a difference between the linear expansion coefficient of the stud bolt and the linear expansion coefficient of the resin mold cover. However, Patent Document 1 does not refer at all to preventing increase in the contact resistance due to the loose of the bolt. 
         [0008]    The present invention has been made in view of the above problems and is to provide a terminal connecting-and-fixing structure capable of ensuring the connection between the terminal and the bus bar even in the case of loose of the bolt and suppressing increase in the contact resistance, thereby preventing poorness of the conduction. 
       Solution to Problem 
       [0009]    The present invention has been made to accomplish an object as above and provides a terminal connecting-and-fixing structure comprising: 
         [0010]    a bus bar having a plate-like shape; 
         [0011]    a bolt penetrating the bus bar, and a nut tightened by the bolt; and 
         [0012]    a terminal mounted on the bolt; 
         [0013]    wherein the terminal and the bus bar is connected and fixed by fastening the nut to the bolt; and 
         [0014]    wherein the bus bar has a concave portion, and the terminal and the bus bar is connected and fixed by fastening the nut to the bolt while an end portion of the terminal is press-fitted in the concave portion. 
         [0015]    Accordingly in the present invention, the bus bar has a concave portion, and the terminal and the bus bar is connected and fixed by fastening the nut to the bolt while an end portion of the terminal is press-fitted in the concave portion. That is, the terminal and the bus bar is connected and fixed by press fitting, which provides a structure where the bus bar and the terminal are hard to be separated even if the bolt is loosened. Further, the terminal and the bus bar are in contact with each other not only at the end of the terminal and the bottom surface of the concave portion, but also at the outer peripheral surface of the terminal and the inner peripheral surface of the bus bar, whereby it is possible to ensure a large contact area relative to a conventional structure thereby to suppress the contact resistance. 
         [0016]    It is preferred that the terminal is made from a material having a linear expansion coefficient higher than a material of the bus bar. 
         [0017]    According to such a construction, when the terminal connecting-and-fixing structure is kept in a high-temperature environment and the terminal and the bus bar are thermally expanded, the press fit interference will not be decreased due to thermal expansion as the thermal expansion amount of the terminal is larger than the bus bar. Thus it is possible to connect and fix the terminal and the bus bar steadily even in a high-temperature environment. 
         [0018]    It may be that the end portion of the terminal and the concave portion have a pair of engagement means configured so that the end portion of the terminal is engaged with the concave portion by turning the terminal a prescribed degree around an axis of the bolt while the end portion of the terminal is press-fitted in the concave portion. 
         [0019]    When such an engagement means is formed in the end portion of the terminal and the concave portion of the bus bar, it is possible to connect and fix the terminal and the bus bar steadily without separation even if the bolt is loosened. 
         [0020]    The concave portion may have an opening end having a foldable collar portion projecting along a radial direction. 
         [0021]    When such a collar portion is formed, it is possible to ensure a connection at least between the collar portion and the outer peripheral surface of the terminal even when the bolt is loosened and moved in the axial direction. 
         [0022]    It may be that a brazing material is disposed on an edge portion of the opening end of the concave portion. 
         [0023]    When a brazing material is disposed on an edge portion of the opening end of the concave portion as above, the brazing material will be melted in a high-temperature environment, whereby it is possible to ensure a large contact area between the terminal and the bus bar. Further, a gap which is possibly formed between the end portion and the concave portion of the bus bar can be filled with the brazing material, whereby it is possible to improve the waterproof property and the dust-proof property in the connecting-and-fixing portion. 
         [0024]    In this case, it is preferred that at least one of an inner peripheral surface or a bottom surface of the concave portion has a groove in which the brazing material being melted is to be flown because it is thereby possible to allow the molten brazing material to conductively flow between the end portion and the concave portion of the bus bar. 
         [0025]    It is preferred that the bolt is made from the same material as the material of the terminal. 
         [0026]    By employing such a structure, it is possible to suppress loose of the bolt itself arising from the difference in the thermal expansion coefficient between the bolt and the terminal. 
       Advantageous Effects 
       [0027]    According to the present invention, it is possible to provide a terminal connecting-and-fixing structure capable of ensuring the connection between the terminal and the bus bar even in the case of loose of the bolt and suppressing increase in the contact resistance, thereby preventing poorness of the conduction. The terminal connecting-and-fixing structure according to the present invention may preferably be used for an inverter to be mounted on a battery-powered forklift. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]      FIGS. 1(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a first embodiment of the present invention. 
           [0029]      FIGS. 2(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a second embodiment of the present invention. 
           [0030]      FIGS. 3(   a ) to ( c ) are schematic perspective views illustrating a method of assembling the terminal connecting-and-fixing structure according to the second embodiment of the present invention. 
           [0031]      FIGS. 4(   a ) to ( c ) are schematic diagrams illustrating a method of assembling the terminal connecting-and-fixing structure according to the second embodiment of the present invention:  FIG. 4(   a ) is a plan view of a bus bar,  FIG. 4(   b ) is a cross-sectional view along the line A-A, and  FIG. 4(   c ) is a cross-sectional view along the line B-B. 
           [0032]      FIGS. 5(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a third embodiment of the present invention. 
           [0033]      FIGS. 6(   a ) and ( b ) are diagrams illustrating a bus bar according to the third embodiment of the present invention:  FIG. 6(   a ) is a schematic plan view, and  FIG. 6(   b ) is a schematic cross-sectional view. 
           [0034]      FIGS. 7(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a fourth embodiment of the present invention. 
           [0035]      FIGS. 8(   a ) and ( b ) are schematic diagrams of a variation of the terminal connecting-and-fixing structure of the fourth embodiment of the present invention. 
           [0036]      FIG. 9  is a schematic diagram of another variation of the terminal connecting-and-fixing structure of the fourth embodiment of the present invention. 
           [0037]      FIG. 10  is a schematic cross-sectional view illustrating a conventional terminal connecting-and-fixing structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not limitative of the scope of the present invention. In the following, an example where a terminal connecting-and-fixing structure according to the present invention is applied to an inverter which is to be mounted on a battery-powered forklift will be described; however, it should be understood that use of the terminal connecting-and-fixing structure according to the present invention is by no means limited thereto. 
       First Embodiment 
       [0039]      FIGS. 1(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a first embodiment of the present invention. As illustrated in  FIGS. 1(   a ) and ( b ), the terminal connecting-and-fixing structure  1  comprises a bus bar  10  having a plate-like shape, a bolt  30  penetrating the bus bar  10  and a nut  40  tightened by the bolt  30 , and a terminal  20  mounted on the bolt  30 . 
         [0040]    The bus bar  10  is a member made from cupper and having a plate-like shape and is a member through which an AC current converted from a DC current by an inverter (not shown) flows. The bus bar  10  has, as seen in  FIG. 1(   a ), a concave portion  12  thereon, which is depressed relative to its surrounding area in a concave shape. The shape of this concave portion  12  in a plan view is not particularly limited, and in this embodiment, it has a round shape having a diameter B. 
         [0041]    The terminal  20  is a member having, for example, a cylindrical shape made from brass, and it has an end portion  22  to be connected with the bus bar  10  to allow a flow therein of an AC current flowing through the bus bar  10 . The terminal  20  has a central hole  20   a,  of which shape is not particularly limited but is, for example, a cylindrical shape having a slightly larger diameter A than the diameter B of the concave portion  12 . 
         [0042]    The bolt  30  is, for example, a member made from iron and having a rod-like shape and has a spiral-shaped groove on a surface of its shaft portion  34 . The shaft portion  34  is inserted into the central hole  20   a  of the terminal  20 . On the opposite side of the terminal  20  across the bus bar  10 , a head portion  32  having a larger diameter than the shaft portion  34  is formed. The nut  40  is, for example, a ring-like member made from iron, which is screwable with the shaft portion  34  of the bolt  30 . 
         [0043]    In the terminal connecting-and-fixing structure  1  of the present invention having such a configuration, as seen in  FIG. 1(   b ), the end portion  22  and the concave portion  12  of the bus bar  10  are connected and fixed by fastening the nut  40  to the tip portion  36  of the bolt  30  while the end portion  22  of the terminal  20  is press-fitted in the concave portion  12  of the bus bar  10 . 
         [0044]    That is, in the terminal connecting-and-fixing structure  1  according to the present invention, the bus bar  10  and the terminal  20  are hard to be separated even when the bolt  30  is loosened as the terminal  20  and the bus bar  10  are connected and fixed by press fitting. Further, in the terminal connecting-and-fixing structure  1 , the terminal  20  and the bus bar  10  are in contact with each other not only at the end  22   b  and the bottom surface  12   b  but also at the outer peripheral surface  22   a  and the inner peripheral surface  12   a,  whereby it is possible to ensure a large contact area, thereby to suppress the contact resistance. 
         [0045]    Further, as described above, as the bus bar  10  is made from cupper and the terminal  20  is made from brass, the material of the terminal  20  has a linear expansion coefficient larger than the bus bar  10 . Accordingly, when the terminal connecting-and-fixing structure  1  is kept in a high-temperature environment and the terminal  20  and the bus bar  10  are thermally expanded, the press fit interference will not be decreased due to thermal expansion. Therefore, it is possible to connect and fix the terminal  20  and the bus bar  10  steadily even in a high-temperature environment. 
       Second Embodiment 
       [0046]    Now, a second embodiment of the present invention will be described with reference to  FIG. 2  to  FIG. 4 .  FIGS. 2(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to the second embodiment;  FIG. 3  and  FIG. 4  are diagrams each illustrating a method of assembling the terminal connecting-and-fixing structure according to the second embodiment, and  FIGS. 3(   a ) to ( c ) are schematic perspective views illustrating the assembling method.  FIG. 4(   a ) is a plan view of a bus bar  10 ,  FIG. 4(   b ) is a cross-sectional view along the line A-A in  FIG. 3(   b ) and  FIG. 4(   a ), and  FIG. 4(   c ) is a cross-sectional view along the line B-B in  FIG. 4(   a ). The terminal connecting-and-fixing structure according to the second embodiment fundamentally has the same structure as the above-described terminal connecting-and-fixing structure, and the same elements as those of the above embodiment are assigned with the same reference numerals as those of the above embodiment, and the same description thereof will be omitted. 
         [0047]    In the terminal connecting-and-fixing structure  1 , the end portion  22  of the terminal  20  has a terminal-side engagement means  25  comprising a concave part  25   a  and a convex part  25   b,  and the inner peripheral surface  12   a  of the concave portion  12  has a bus bar-side engagement means  25  comprising a convex part  15   a.  Further, as illustrated in  FIG. 2(   b ), the terminal-side engagement means  25  and the bus bar-side engagement means  15  are configured so that they are engageable with each other. That is, the pair of engagement means  50  in the present invention comprises the terminal-side engagement means  25  and the bus bar-side engagement means  15 . 
         [0048]    The concave part  25   a  of the terminal-side engagement means  25  is, as seen in  FIG. 3(   a ), formed all over the circumference of the outer surface of the end portion  22 . On the other hand, the convex part  25   b  of the terminal-side engagement means  25  is formed not all over the circumference but partially in the circumferential direction. In this embodiment, the convex part  25   b  is formed in two positions 180 degrees apart from each other. 
         [0049]    The convex part  15   a  of the bus bar-side engagement means  15  is, as seen in  FIG. 4(   a ), formed not all over the circumference but partially along the circumferential edge of the concave portion  12 . In the portion where the convex part  15   a  is not formed, an opening portion  15   b  is formed. In this embodiment, the opening portion  15   b  is formed in two positions 180 degrees apart from each other. 
         [0050]    As illustrated in  FIGS. 3(   a ) to ( c ), the convex part  25   b  of the terminal  20  is inserted to fit into the opening portion  15   b  to press fit the end portion  22  of the terminal  20  into the concave portion  12 .  FIG. 3(   b ) and  FIG. 4(   b ) illustrate such a condition. Then, by turning the terminal  20  a prescribed angle (e.g. 90 degrees) around an axis of the bolt  30 , the convex part  25   b  of the terminal  20  is held between the convex part  15   a  and the bottom surface  12   b  of the concave portion  12 , as seen in  FIG. 3(   c ) and  FIG. 4(   c ), whereby the terminal-side engagement means  25  are engaged with the bus bar-side engagement means  15 . In  FIG. 3  and  FIG. 4 , the head portion of the bolt  30  is omitted for the convenience of drawing. 
         [0051]    Accordingly, the terminal connecting-and-fixing structure  1  according to this embodiment has a pair of engagement means  50  configured so that the end portion  22  of the terminal  20  are engaged with the concave portion  12  by turning the terminal  20  a prescribed angle around an axis of the bolt  30  while the end portion  22  of the terminal  20  is press-fitted in the concave portion  12  of the concave portion  12 . Thus, it is thereby possible to connect and fix the terminal  20  and the bus bar  10  steadily without separation even if the bolt  30  is loosened. 
       Third Embodiment 
       [0052]    Now, a third embodiment of the present invention will be described with reference to  FIG. 5  and  FIG. 6 .  FIGS. 5(   a ) and ( b ) are schematic cross-sectional views illustrating the terminal connecting-and-fixing structure according to the third embodiment, and  FIGS. 6(   a ) and ( b ) are diagrams illustrating a bus bar according to the third embodiment. The terminal connecting-and-fixing structure according to the this embodiment fundamentally has the same structure as the terminal connecting-and-fixing structure according to the first embodiment, and the same elements as those of the first embodiment are assigned with the same reference numerals as those of the first embodiment, and the same description thereof will be omitted. 
         [0053]    The terminal connecting-and-fixing structure  1  according to this embodiment is different from the first embodiment in that the concave portion  12  has an opening end having a foldable collar portion  17 , as illustrated in  FIGS. 5(   a ) and ( b ). The collar portion  17  is formed so as to project along a radial direction in the opening end portion of the concave portion  12 , as illustrated in  FIG. 6(   b ). Further, as illustrated in  FIG. 6(   a ), the color portion  17  is foldable because of a plurality of cuts  17   a  formed at the portion projecting along the radial direction. 
         [0054]    Further, the terminal connecting-and-fixing structure  1  according to this embodiment is obtained by folding the collar portion  17  upward as indicated by the arrows in 
         [0055]      FIG. 6(   b ), and then press fitting the end portion  22  of the terminal  20  into the concave portion  12 . 
         [0056]    According to the terminal connecting-and-fixing structure  1  of this embodiment, the concave portion  12  has an opening end having a foldable collar portion  17  projecting along a radial direction, whereby it is possible to ensure the connection at least between the collar portion  17  and the outer peripheral surface  22   a  of the end portion  22  of the terminal  20  even when the bolt  30  is loosened and moved in the axial direction. 
       Fourth Embodiment 
       [0057]    Now, a fourth embodiment of the present invention will be described with reference to  FIG. 7  to  FIG. 9 .  FIGS. 7(   a ) and ( b ) are schematic cross-sectional views illustrating a terminal connecting-and-fixing structure according to a fourth embodiment, and  FIG. 8  and  FIG. 9  are each a schematic diagram of a variation of the terminal connecting-and-fixing structure of the fourth embodiment. The terminal connecting-and-fixing structure according to the this embodiment fundamentally has the same structure as the terminal connecting-and-fixing structure according to the first embodiment, and the same elements as those of the first embodiment are assigned with the same reference numerals as those of the first embodiment, and the same description thereof will be omitted. 
         [0058]    The terminal connecting-and-fixing structure  1  according to this embodiment is different from the first embodiment in that a brazing material  60  is disposed on an edge portion of the opening end of the concave portion  12 , as illustrated in  FIGS. 7(   a ) and ( b ). The brazing material  60  may, for example, be a ring-like member made from e.g. silver, copper or phosphor copper, and will be melted when the terminal connecting-and-fixing structure  1  is kept in a high-temperature environment. The molten brazing material  60  will flow into a tiny gap formed between the end portion  22  of the terminal  20  and the concave portion  12  of the bus bar  10 , whereby the terminal  20  and the bus bar  10  are connected without a gap. 
         [0059]    Accordingly, the terminal connecting-and-fixing structure  1  comprises a brazing material  60  disposed on an edge portion of the opening end of the concave portion  12 , and the brazing material  60  will be melted to fill a gap formed between the end portion  22  of the terminal  20  and the concave portion  12  of the bus bar  10 , whereby it is possible to ensure a large contact area between the terminal  20  and the bus bar  10 . Further, a gap which is possibly formed between the end portion  11  of the terminal  20  and the concave portion  12  of the bus bar  10  can be filled with the brazing material, whereby it is possible to improve the waterproof property and the dust-proof property in the connecting-and-fixing portion. 
         [0060]    Further, it is preferred that the inner peripheral surface  12   a  and the bottom surface  12   b  of the concave portion  12  has a groove  14  because it is thereby possible to allow the molten brazing material  60  to conductively flow between the end portion  22  of the terminal  20  and the concave portion  12  of the bus bar  10 , as illustrated in  FIGS. 8(   a ) and ( b ). Further, although not shown in the figure, it may be that only at least one of the inner peripheral surface  12   a  or the bottom surface  12   b  of the concave portion  12  has such a groove  14 . 
         [0061]    Further, the edge portion of the opening end of the concave portion  12  may have a step portion  16  having a height lower than the surface of the bus bar  10  by a step, as illustrated in  FIG. 9 . When such a step portion  16  is formed, it is possible to dispose the brazing material  60  on the step portion  16 , thereby to facilitate positioning of the brazing material  60  to be disposed. Further, it is also possible to prevent outflow of the molten brazing material  60  to the surface of the bus bar  10 . 
         [0062]    Some preferred embodiments of the present invention are described above; however, the present invention is by no means limited thereto and further modifications and variations may be made without departing from the scope of the invention. 
         [0063]    For example, in the above embodiments, an example where bolt  30  is made from iron and the terminal  20  to be mounted on the shaft portion  34  of the bolt  30  is made from brass, that is, an example where the bolt  30  and the terminal  20  are made from different materials, is described. However, the terminal connecting-and-fixing structure  1  is not limited thereto, and the bolt  30  may be made from the same material (e.g. brass) as the material of the terminal. When the bolt  30  is made from the same material as the material of the terminal  20  as above, they have the same linear expansion, and the thermal expansion amount will also be the same, whereby it is possible to suppress loose of the bolt  30  itself arising from the difference in the thermal expansion coefficient between the bolt  30  and the terminal  20 . 
       INDUSTRIAL APPLICABILITY 
       [0064]    The present invention can be used as, for example, a terminal connecting-and-fixing structure for and inverter, preferably as a terminal connecting-and-fixing structure for an inverter to be kept in a high-temperature environment, such as an inverter to be mounted on a battery-powered forklift.