Abstract:
In a circuit breaker, fixed electrodes  14  in pair are secured in a male housing  13.  A female housing  21  which contains a moving electrode  30  is fitted into the male housing  13,  whereupon the moving electrode  30  contacts and straddles the fixed electrodes  14  to make a short circuit. The moving electrode  30  comprises in integral combination retainer pieces  32  that are retained in an electrode retainer tube  22  in the female housing  21,  a contact lug  31  that either contacts or detaches from the fixed electrodes  14,  and a narrow-width joint  33  that joints the retainer pieces  32  and the contact lug  31  to make an integral unit. The narrow-width joint  33  flexes to deform, thereby absorbing the positional offset that develops when the contact lug  31  comes into engagement with the fixed electrodes  14.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit breaker that may typically be provided halfway on power cables in an electric vehicle. 
     2. Description of the Related Art 
     Certain models of electric vehicles have a circuit breaker provided halfway on power cables so that they can be disconnected if necessary as in maintenance. A prior art example of such circuit breaker is described in Unexamined Published Japanese Patent Application (kokai) No. 223439/1997. As shown in FIG. 10, the circuit breaker which is generally indicated by a comprises a casing b and two cylindrical fixed electrodes c and d erected within the casing b to provide a bipolar structure. One fixed electrode c is connected to a terminal metal plate f pressed against an electric cable e whereas the other fixed electrode d is connected to an end of a fuse i via a bus bar h. The other end of the fuse i is connected to a terminal metal plate g pressed against an electric cable e. 
     A moving electrode j having a handle o can be brought into or out of engagement with the fixed electrodes c and d. The combination of these electrodes constitutes a breaker switch p which is connected in series with the fuse i between the electric cables. The moving electrode j of the breaker switch p has contacts k and m that establish communication via a communicating portion n. The contacts k and m are brought into or out of engagement with the fixed electrodes c and d to establish or break continuity between the electric cables e. 
     Electric vehicles today are required to use smaller and lighter parts, among which the circuit breaker a is by no means an exception. A problem with this circuit breaker is that its minimum size is determined by the bipolar structure of the fixed electrodes c and d and the demand for further reduction in size and weight cannot be met. 
     As another problem, in order to bring the moving electrode j into engagement with the fixed electrodes c and d, the two contacts k and m need have registry with the respective fixed electrodes c and d but this involves a cumbersome operation. If the contacts and the fixed electrodes are installed in positions offset from the exact correspondence, the pressure required to insert the moving electrode j increases, making it difficult to bring this electrode into or out of engagement with the fixed electrodes. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under these circumstances and has as an object providing a circuit breaker that is made smaller and lighter and which permits ease in bringing the moving electrode into or out of engagement with the fixed electrodes. 
     To achieve the above object, according to a first aspect of the invention, there is provided a circuit breaker comprising a pair of fixed electrodes, a moving electrode that is brought into or out of engagement with the fixed electrode pair to connect or disconnect the fixed electrodes, and a housing of the moving electrode that is made of an insulating resin, said moving electrode having in integral combination with retainer pieces that are retained in the housing, a contact lug that either contacts or detaches from the fixed electrodes, and a narrow-width joint that joins the retainer pieces and the contact lug. 
     According to a second aspect of the invention, the retainer pieces form a tubular shape that surrounds the contact lug. 
     According to a third aspect of the invention, the contact lug is split in the distal end portion by means of a slit extending from the distal end toward the basal end. 
     According to a fourth aspect of the invention, the fixed electrodes are each provided with an elastic lug formed by bending the free end in a U shape to be parallel with the direction in which said moving electrode is inserted. 
     In the first aspect of the invention, the pair of fixed electrodes have a unipolar structure that is created by arranging two electrodes to face each other. Compared to fixed electrodes arranged to have a bipolar structure, the unipolar structure requires a smaller space of installation and a smaller and lighter circuit breaker can be realized. The fixed electrodes of a unipolar structure have the additional advantage of reducing the likelihood for the occurrence of a positional offset between the fixed electrode pair and the moving electrode, thus providing ease in bringing the moving electrode into or out of engagement with the fixed electrodes. As a further advantage, the moving electrode is contained in a housing made of an insulating resin, so safety is assured when bringing it into or out engagement with the fixed electrodes. 
     Since the moving electrode is contained in the housing, one may suspect that the positioning action of the housing could introduce, rather than eliminate, a positional offset from the fixed electrodes. But this will not happen in the present invention; the contact lug of the moving electrode that contacts the fixed electrode pair and the retainer piece retained in the housing are joined via the narrow-width joint, and upon flexing to deform, the joint absorbs any positional offset to ensure that no galling force will be exerted upon the moving electrode or the fixed electrodes. This provides greater ease in the process of bringing the moving electrode into or out of engagement with the fixed electrodes. 
     In the second aspect of the invention, since the retainer pieces of the moving electrode are formed in a tubular shape that surrounds the contact lug, there is no possibility for the contact lug to deform by bumping against a foreign object or to be damaged in the manufacturing process at the step of installing the moving electrode on the housing. 
     In the third aspect of the invention, since the distal end portion of the contact lug of the moving electrode is split into two parts by means of a slit, the moving electrode, when brought into engagement with the fixed electrodes, has better fit to assure stable contact with the latter. 
     In the fourth aspect of the invention, since the fixed electrodes are each provided with the elastic lug, they can have more stable contact with the contact lug of the moving electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows in section the male and female units of a circuit breaker according to the first embodiment of the invention as they are disconnected from each other to open the circuit; 
     FIG. 2 shows in section the two basic units that are fitted (connected) together to close the circuit; 
     FIG. 3 is a perspective exploded view of the essential parts of the circuit breaker according to the first embodiment of the invention; 
     FIG. 4 is a plan view of the moving electrode in the circuit breaker according to the first embodiment of the invention; 
     FIG. 5 is a front view of same moving electrode; 
     FIG. 6 is a side view of the same moving electrode; 
     FIG. 7 is a perspective exploded view of the essential parts of a circuit breaker according to the second embodiment of the invention; 
     FIG. 8 is a sectional view of a circuit breaker according to the third embodiment of the invention; 
     FIG. 9 is a perspective view of one of the fixed electrodes in pair used in the circuit breaker according to the third embodiment of the invention; and 
     FIG. 10 is a perspective view of a prior art circuit breaker. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Several embodiments of the invention are described below with reference to accompanying drawings. 
     &lt;First Embodiment&gt; 
     The first embodiment of the invention is now described with reference to FIGS. 1-6. This embodiment relates to a circuit breaker provided halfway on power cables in an electric vehicle. The circuit breaker consists of a male unit  10  shown in the lower block of FIG. 1 and a female unit  20  shown in the upper block. We first describe the male unit  10 , which comprises an inner tube  11  and an outer tube  12  that are each in the form of a generally rectangular tube and which combine to form a bottomed male housing  13  that has a pair of fixed electrodes  14  secured in its interior. Each fixed electrode  14  is formed by bending a metal plate in a generally L shape. The bottom sides  14 A of the fixed electrodes  14  are secured to the bottom of the male housing  13  with bolts  15  and their rising sides  14 B are secured to opposite sides of an electrode retainer plate  16  erected as an integral part of the center of the inner tube  11 . Each rising side  14 B has a contact bead  14 C extending vertically. 
     Each bolt  15  also tightens a terminal metal plate  18  that is clamped to each cable  17  in the power line of an electric vehicle, so that the two cables  17  are interrupted by the two fixed electrodes  14 . The left side of the outer tube  12  of the male housing  13  has an engagement wall  19  projecting as an integral part and an engagement hole  19 A is formed in this wall. 
     The female unit  20  comprises a female housing  21  and a moving electrode  30  contained in it. The female housing  21  which is molded of an insulating synthetic resin consists of an electrode retainer tube  22  in the form of a rectangular tube that can be fitted into the inner tube  11  of the male housing  13  and an outer tube  23  that can be inserted between the inner tube  11  and the outer tube  12  of the male housing  13 . The female housing  21  is in the form of an inverted container, with the two tubes  22  and  23  connected together on the top, and it can be fitted into the male housing  13 . The outer tube  23  of the female housing  21  has an elastic engagement lug  24  as an integral part that extends upward from the lower end of the left side. When the two housings  13  and  21  are combined as shown in FIG. 2, an engaging projection  24 A of the elastic engagement lug  24  fits into the engagement hole  19 A in the male housing  13  so that the female housing  21  will not slip out of the male housing  13 . The outer tube  23  of the female housing  21  has an annular waterproof seal  25  fitted therein so that, when the two housings  13  and  21  are combined, the inner peripheral surface of the waterproof seal  25  makes intimate contact with the outer peripheral surface of the inner tube  11  of the male housing  13  to prevent the entrance of water into the inner tube  11 . 
     The electrode retainer tube  22  holds the moving electrode  30  that is prevented from slipping out by means of a retainer  26  which, in turn, is prevented from slipping out by means an engaging projection  22 A at the bottom end of the electrode retainer tube  22 . 
     We now describe the moving electrode  30  in detail. This electrode is formed by bending a single metal plate into the shape shown in FIGS. 3-6. As specifically shown in FIG. 5, the moving electrode  30  has a generally U-shaped contact lug  31  that has an upper U-shaped bend  31 A which extends downward with the decreasing distance between the two branches to form outwardly curved guides  31 B at the bottom ends. The distance between the curved guides  31 B is set to be smaller than the thickness of the electrode retainer plate  16  of the male unit  10 . The moving electrode  30  also has a pair of retainer pieces  32  in such a position that they cover the contact lug  31  from opposite sides. The retainer pieces  32  each have a U-shaped cross section and, when combined together, they form a rectangular tube that holds the contact lug  31  from opposite sides and which is accommodated within the electrode retainer tube  22  of the female housing  21 . The retainer pieces  32  as inserted into the electrode retainer tube  22  do not make intimate contact with the inner surfaces of the latter but leave a slight gap that is large enough to permit some rattling. 
     The top end of each retainer piece  32  and the U-shaped bend  31 A of the contact lug  31  are joined integrally by means of a narrow-width joint  33  such that the contact lug  31  is suspended from above to lie between the retainer pieces  32 . The narrow-width joint  33  as it keeps the contact lug  31  suspended is capable of flexing to deform so that the bottom ends of the contact lug  31  swing back and forth in the direction of the two-head arrow A in FIG.  1 . Each retainer piece  32  has at its bottom end a contact lug protector  34  that is bent inwardly. 
     Having the construction described above, the circuit breaker according to the first embodiment of the invention works in the following manner. When the female unit  20  is not fitted in the male unit  10  as shown in FIG. 1, the fixed electrodes  14  are not in contact with each other, so the electric cables  17  are electrically interrupted. 
     When the female unit  20  is pushed into the male unit  10 , the electrode retainer tube  22  of the female unit  20  is first inserted into the inner tube  11  of the male housing  13  and as it is guided by the inner peripheral surface of the inner tube  11 , the fitting of the female unit  20  proceeds until the contact lug  31  of the moving electrode  30  contacts and straddles the two fixed electrodes  14 , thereby establishing continuity between those fixed electrodes (see FIG.  2 ). 
     In the fitting process described above, the housing  13  of the male unit  10  and the housing  21  of the female unit  20  are fitted into each other to produce a positioning effect and the moving electrode  30  contacts and straddles the fixed electrodes  14  in the positions that are determined by this positioning effect. The fixed electrodes  14  are secured in the male housing  13  and the moving electrode  30  is provided in the female housing  21 , so theoretically the two groups of electrodes  14  and  30  should contact each other in appropriate relative positions. In practice, however, various errors such as electrode bending errors, housing molding errors and electrode installation errors are unavoidable and even if the positioning effect of the housings  13  and  21  enables themselves to be fitted in the normal positions, the two groups of electrodes  14  and  30  may occasionally be offset from each other. If this occurs, the electrodes  14  and  30  might begin to contact either obliquely or in an offset condition in the process of fitting of the housings  13  and  21 . 
     In the embodiment under consideration, the contact lug  31  of the moving electrode  30  is joined to each retainer piece  32  via the narrow-width joint  33 . Therefore, even if the retainer pieces  32  are positioned with respect to the male housing  13  as if they were an integral part of the female housing  21 , the narrow-width joint  33  flexes to deform as the contact lug  31  is fitted into the male housing  13  until it straddles the fixed electrodes  14 ; as a result, any offset between the two groups of electrodes  14  and  30  is effectively absorbed and those electrodes smoothly reach the final fitting positions without producing any unstrained galling forces. What is more, the retainer pieces  32  of the moving electrode  30  can rattle to some extent within the electrode retainer tube  22  of the female housing  21  and this rattling is also effective to absorb positioning errors. As a result, the female unit  20  (moving electrode  30 ) can be brought into and out of engagement with the male unit  10  (fixed electrodes  14 ) in a very simple manner. 
     Needless to say, the pair of fixed electrodes  14  have a unipolar structure that is created by arranging two electrodes to face each other. Compared to the prior art circuit breaker in which fixed electrodes are arranged to have a bipolar structure, the unipolar structure requires a smaller space of installation and a smaller and lighter circuit breaker can be accomplished. As a further advantage, the moving electrode  30  is contained in the female housing  21  made of an insulating resin, so safety is assured when bringing it into or out engagement with the fixed electrodes  14 . What is more, in the first embodiment under consideration, the retainer pieces  32  of the moving electrode  30  form a tubular shape that surrounds the contact lug  31 , so there is no possibility for the contact lug  31  to deform by bumping against a foreign object or to be damaged in the process of circuit breaker manufacture at the step of installing the moving electrode  30  on the female housing  21 . 
     &lt;Second Embodiment&gt; 
     FIG. 7 shows the second embodiment of the invention. It has two differences from the first embodiment: first, the contact lug  31  of the moving electrode  30  has a slit  35  that extends from the distal end toward the basal end to split the distal end portion into two parts; second, two contact beads  14 C are correspondingly formed on each fixed electrode  14 . The other features of the second embodiment are essentially the same as the first embodiment and need not be described in detail. 
     In this design, the split parts of the contact plug  31  respectively contact the two contact beads  14 C to provide more positive contact between the two groups of electrodes. 
     &lt;Third Embodiment&gt; 
     FIGS. 8 and 9 show the third embodiment of the invention. It also has two differences from the first embodiment: first, the rising side  14 A of each fixed electrode  14  has an elastic lug  14 D formed by bending its free end downward in a U shape; second, the rising side  14 A has an engaging lug  14 E that projects from its top end to come into engagement with the upper part of the electrode retainer plate  16  of the male housing  13 . The other features of the third embodiment are essentially the same as the first embodiment and need not be described in detail. 
     With this design, the elastic lug  14 D of each fixed electrode  14  also helps produce a resilient force at the point of contact with the moving electrode  30  and even if no contact beads are provided on the fixed electrodes  14 , they can have contact with the moving electrode across the entire surface of the contact lug  31 . As a result, the two groups of electrodes can have more reliable contact while reducing the contact resistance. 
     &lt;Other Embodiments&gt; 
     The present invention is by no means limited to the embodiments described with reference to the foregoing disclosure and attached drawings. The following embodiments are also feasible and included within the technical scope of the invention. 
     (1) In each of the embodiments described above, the fixed electrodes are of a bipolar type but they may be of a tripolar type in which they are provided within three regions of a circle that are spaced apart by an angle of 120 degrees, with one fixed electrode being in a face-to-face relationship with two adjacent fixed electrodes such that two fixed electrodes make a pair with respect to a common fixed electrode. 
     (2) In each of the embodiments described above, the circuit breaker is designed to have only a switching capability but it may be so designed that a fuse connected to the fixed electrodes is incorporated in the male unit. 
     (3) In each of the embodiments described above, the fixed electrode pair is on the male side and the moving electrode is on the female side which is fitted into the male side. The concept of the invention is also applicable if the fixed electrode pair is one the female side and the moving electrode is on the male side. 
     (4) If the fixed electrode pair is on the male side, the shape of the individual fixed electrodes is not limited to a cylinder and it may be a prism. Even non-columnar shapes are also included in the scope of the invention.