BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
       [0001]    The present invention relates to a thermal overload relay for change-over of a contact upon detection of an overcurrent. 
         [0002]    Patent Document 1, for example, discloses a thermal overload relay operated by detecting an overcurrent running in the main circuit. 
         [0003]    The thermal overload relay of Patent Document 1 is described referring to  FIG. 4 . 
         [0004]    This thermal overload relay comprises, in an insulator case  1  made of a resin mould, main bimetals  2  inserted in three phase electric circuit and wound with heaters  2   a , a shifter  3  linked to free ends of the main bimetals  2  and movably supported on the insulator case  1 , a switching mechanism  4  disposed in the insulator case  1  allowing linking to an end of the shifter  3 , and a contact reversing mechanism  5  to changeover contacts by operation of the switching mechanism  4 . 
         [0005]    The switching mechanism  4  comprises a temperature compensation bimetal  7  linked to one end of the shifter  3 , a release lever  8  fixed to the other end of the temperature compensation bimetal  7 , and an adjusting cam  12  connected to the release lever  8  through a swinging pin  9  projecting at the lower end of the adjusting mechanism and abutting on the circumferential surface of an eccentric cam  11   a  of an adjusting dial  11 , disposed rotatably in the insulator case  1  at the upper end of the adjusting cam  12 . A rotation angle of the release lever  8  is set by varying an abutting position of the adjusting cam  12  on the circumferential surface of the eccentric cam  11   a  of the adjusting dial  11  through adjustment of the adjusting dial  11 , thereby slightly rotating the adjusting cam  12  around a support shaft  13 . 
         [0006]    The contact reversing mechanism  5  comprises a reversing spring  14  fixed at its lower end to the release lever  8  and extending upwards, a slider  17  linking to the tip of the reversing spring  14  and moving a normally opened side movable contact piece  15   b  and a normally closed side movable contact piece  16   a , and a reset bar  18  to manually move the slider  17  to a normal position. The reversing spring  14  is a member having a punched window (not shown in the figure) formed by punching a thin spring material, and a curved surface with a disc spring shape around the punched window. The reversing spring  14  is convexly curved towards right hand side in a normal state shown in  FIG. 4 . 
         [0007]    When the bimetal  2  bends with the heat generated by the heater  2   a  due to an overcurrent in the above-described structure, the shifter  3  shifts to the direction indicated by the arrow P in  FIG. 4  caused by displacement of the free end of the main bimetal  2 . The Shift of the shifter  3  pushes a free end of the temperature compensation bimetal  7  and rotates the release lever  8  counterclockwise around the swinging pin  9 . 
         [0008]    With progression of the counterclockwise rotation of the release lever  8 , the reversing spring  14  deforms bending convexly towards the left hand side. The deformation of the reversing spring  14  moves the slider  17 , which is linked to the tip of the reversing spring  14 , so as to change the normally opened side movable contact piece  15   b  and the normally opened side fixed contact piece  15   a  into a closed state and to change the normally closed side movable contact piece  16   a  and the normally closed side fixed contact piece  16   b  into an opened state. 
         [0009]    Based on the information of the closed state of the normally opened side movable contact piece  15   b  and the normally opened side fixed contact piece  15   a , and the information of the opened state of the normally closed side movable contact piece  16   a  and the normally closed side fixed contact piece  16   b  conducted by the reversing action of the switching mechanism  4 , an electromagnetic contactor (not shown in the figures), for example, connected in the main circuit is opened to interrupt the overcurrent. 
       [Patent Document 1] 
       [0010]    Japanese Examined Patent Publication No. H7-001665 
         [0011]    Meanwhile, in the contact reversing mechanism  5  of the conventional thermal overload relay described above, the slider  17  for change over of the normally opened contact (the normally opened side movable contact piece  15   b  and the normally opened side fixed contact piece  15   a ) and the normally closed contact (normally closed side movable contact piece  16   a  and the normally closed side fixed contact piece  16   b ) is placed flatly in the region over the main bimetals  2  in the insulator case  1 . Moreover, the reversing spring  14  for moving the slider  17  is placed in a region different from the region for placing the slider  17 . Therefore, a large space is required in, the insulator case  1 , which is a problem in that it hinders a size reduction of a thermal overload relay. 
         [0012]    In view of the above-described unsolved problems in the conventional technology examples, it is an object of the present invention to provide a thermal overload relay in which a space for placing a normally opened contact and a normally closed contact is reduced in the case, thereby minimizing the size of a thermal overload relay. 
         [0013]    Further objects and advantages of the invention will be apparent from the following description of the invention. 
       SUMMARY OF THE INVENTION 
       [0014]    In order to accomplish the above object, a thermal overload relay according to the present invention comprises a case; main bimetals which bend upon detection of an overload current; a release lever working according to displacement of a shifter that is displaced with the bending of the main bimetals; and a contact reversing mechanism for changing-over contacts by rotation of the release lever, wherein the all three latter members are disposed in the case. The contact reversing mechanism includes a movable plate supported at a support point at one end thereof and swingably at the other end; a reversing spring stretched between the other end of the movable plate and a spring support, the other end of the movable plate and the spring support being positioned opposite each other with respect to the support point, and reversing the movable plate by coupling with a rotated release lever; and an interlock plate rotating around a support shaft together with movement of the movable plate. The contacts each have a normally opened contact piece and normally closed contact piece and are respectively disposed in the vicinity of a front surface and in a vicinity of a back surface of the interlock plate. 
         [0015]    According to the above-stated invention, the normally opened contact and the normally closed contact are changed-over by rotation of the interlock plate. These contacts are disposed in the vicinity of the front surface and the back surface of the interlock plate. Therefore, a space for placing the contacts in this case is significantly reduced as compared with the conventional device, thereby minimizing a size of the thermal overload relay. 
         [0016]    According to the above-stated invention, even if external disturbances such as vibration and shock occur, the movable contact piece of the contacts in a closed state effectively never separates from the fixed contact piece, thereby avoiding an improper operation of the contacts. 
         [0017]    In the thermal overload relay according to the invention, one of the normally opened contact and the normally closed contact has the movable contact piece on the other side of the movable plate, and the change-over of the movable contact piece and the fixed contact piece is carried out by transmitting rotation of the interlock plate on the movable plate as a load for the reversing action. 
         [0018]    According to this invention, the number of parts of the thermal overload relay is reduced, and a space for disposition of the contacts is further reduced in this case. 
         [0019]    In a thermal overload relay according to the present invention, the normally opened contact and the normally closed contact are changed-over by rotation of the interlock plate and are disposed in the vicinity of the front surface and the back surface of the interlock plate. Therefore, a space for placing the contacts in the case is significantly reduced as compared with the conventional device, thereby minimizing the size of the thermal overload relay. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a drawing showing basic parts of a thermal overload relay according to the present invention in a normal state; 
           [0021]      FIG. 2(   a ) is a drawing showing a contact reversing mechanism including a normally opened contact (a-contact) in the normal state; 
           [0022]      FIG. 2(   b ) is a drawing showing the contact reversing mechanism including the normally opened contact (a-contact) in a tripped state; 
           [0023]      FIG. 3(   a ) is a drawing showing the contact reversing mechanism including a normally closed contact (b-contact) in the normal state; and 
           [0024]      FIG. 3(   b ) is a drawing showing the contact reversing mechanism including the normally closed contact (b-contact) in a tripped state; 
           [0025]      FIG. 4  is a drawing showing essential parts of a conventional thermal overload relay in a normal state. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    The following describes the best mode of preferred examples of embodiments of the invention in detail with reference to the accompanying drawings. The parts of the embodiment of the invention similar to the parts in  FIG. 4  are denoted by the same symbols and their description is omitted. 
         [0027]      FIGS. 1 through 3  show an embodiment of a thermal overload relay according to the invention.  FIG. 1  is a drawing showing essential parts in a normal state of a thermal overload relay according to the present invention;  FIG. 2(   a ) is a drawing showing the contact reversing mechanism including a normally opened contact (a-contact) in the normal state;  FIG. 2(   b ) is a drawing showing the contact reversing mechanism including the normally opened contact (a-contact) in a tripped state;  FIG. 3(   a ) is a drawing showing the contact reversing mechanism including a normally closed contact (b-contact) in the normal state; and  FIG. 3(   b ) is a drawing showing the contact reversing mechanism including the normally closed contact (b-contact) in a tripped state. 
         [0028]    In the thermal overload relay of this embodiment, as shown in  FIG. 1 , in the insulator case  1  disposed are an adjusting mechanism  20  that works according to displacement of a shifter  3  linked to a free end of the main bimetals  2 , a contact reversing mechanism  21  that changes-over contacts by an action of the adjusting mechanism  20 , and a reset bar  43  for resetting the contact reversing mechanism  21 . 
         [0029]    The adjusting mechanism  20  comprises an adjusting link  22 , a release lever  23  rotatably supported by the adjusting link  22 , and a temperature compensation bimetal  24  fixed to the release lever  23  and linked to the shifter  3 . 
         [0030]    The adjusting link  22  is composed of a link support  25  supporting the release lever  23  and a leg part  26  extending downwards from one side of the link support  25 . 
         [0031]    A support shaft  27  is provided protruding from the inner wall at the lower part of the insulator case  1  into inside of the insulator case  1 . A tip of the support shaft  27  having a reduced diameter is inserted into the bearing hole  26   a  of the leg part  26  and the whole adjusting link  22  is supported rotatably around the support shaft  27  of the insulator case  1 . 
         [0032]    The release lever  23  is provided with a rotating shaft  23   e  rotatably supported by a link support  25  of the adjusting link  22 , and a reversing spring pushing part  23   f  formed in the portion of the release lever lower than the rotating shaft  23   e , and a cam contacting part  23   g  is formed in the upper portion. The top end of a temperature compensation bimetal  24 , a free end of which is located in a lower position, is fixed to the release lever  23 . 
         [0033]    The contact reversing mechanism  21  comprises, as shown in  FIG. 2(   a ), a reversing mechanism support  32  disposed in the insulator case  1 , an interlock plate  34  disposed in the vicinity of the reversing mechanism support  32  and rotatably supported on a support shaft  33  formed on the inner wall of the insulator case  1 , a movable plate  35  with the upper portion  35   b  thereof disposed swingably around the lower portion  35   a  of the movable plate abutting on the reversing mechanism support  32 . Further, a reversing spring  36  in the form of a tension coil spring is stretched between a coupling hole (not shown in the figure) formed in the side of the upper portion  35   b  of the movable plate  35  and a spring support  32   a  formed in the part of the reversing mechanism support  32  lower than the lower portion  35   a  of the movable plate  35 . 
         [0034]    The interlock plate  34  has a first linking pin  39   a  and a second linking pin  39   b  capable of linking with the movable plate  35  in the side of front surface  34   a  of the interlock plate  34 . The first and second linking pins  39   a  and  39   b  induce the interlock plate  34  to rotate around the support shaft  33  in the reversing operation and the returning operation of the movable plate  35 . 
         [0035]    A normally opened contact (a-contact) side leaf spring  37  is provided on the reversing mechanism support  32  so that the free end of the normally opened contact (a-contact) side leaf spring  37  extends upwards. A fixed contact piece  38   a  of the a-contact  38  is fixed on the free end side of this leaf spring  37 . A movable contact piece  38   b , which is arranged to contact the fixed contact piece  38   a , of the a-contact  38 , is fixed on the upper portion  35   b  of the movable plate  35 . 
         [0036]    As shown in  FIG. 3(   a ), on the back surface side  34   b  with respect to the intervening interlock plate  34 , a normally closed contact (b-contact) side leaf spring  40  is disposed so that the free end thereof extends upwards. A contact support plate  41  is disposed facing this leaf spring  40 . The movable contact piece  42   b  of the b-contact  42  is fixed on the free end side of the leaf spring  40 , and the fixed contact piece  42   a  of the b-contact  42  to be connected to the movable contact piece  42   b  is fixed on the contact supporting plate  41 . 
         [0037]    The reset bar  43  comprises, as shown in  FIG. 1 , a reset button  43   a  that is manually pressed into the insulator case  1  and an angled surface  43   b  for returning the movable plate  35  that is in contact with the a-contact side leaf spring  37  and in a tripped state as shown in  FIG. 2(   b ) to the initial position (normal state). 
         [0038]    Now, operation of the thermal overload relay of the embodiment will be described. 
         [0039]    When the main bimetal  2  is bent with the heat generated in the heater  2   a  by an overcurrent, displacement of the free end of the main bimetal  2  displaces the shifter  3  in the direction of arrow Q indicated in  FIG. 1 . When the free end of the temperature compensation bimetal  24  is pushed by the displaced shifter  3 , the release lever  23  joined to the temperature compensation bimetal  24  rotates clockwise around the rotating shafts  23   d ,  23   e  supported by the adjusting link  22  and the reversing spring pushing part  23   f  of the release lever  23  pushes the reversing spring  36 . 
         [0040]    Due to the rotation of the release lever  23  in the clockwise direction, at the moment the pushing force of the reversing spring biasing part  23   f  exceeds the spring force of the reversing spring  36 , the movable plate  35  starts to perform a reversing action around the lower part  35   a . Accompanying the reversing action of the movable plate  35 , the interlock plate  34 , receiving the reversing action of the movable plate  35  transmitted through the first linking pin  39   a , rotates around the support shaft  33  (see  FIG. 2(   b ) and  FIG. 3(   b )). 
         [0041]    As a result, the fixed contact piece  38   a  and the movable contact piece  38   b  of the a-contact  38  in the opened state shown in  FIG. 2(   a ) are connected together, and the fixed contact piece  42   a  and the movable contact piece  42   b  of the b-contact  42  in the closed state as shown in  FIG. 3(   a ) are separated away. Based on the information of the a-contact  38  and the b-contact  42 , the electromagnetic contactor (not illustrated) is opened to interrupt the overcurrent in the main circuit. 
         [0042]    Then, in the situation when the main bimetal  2  returns to the original configuration from the bent state after interruption of the main circuit current, the reset button  43   a  is pushed-in. With this manual reset operation of the reset bar  43 , the angled surface  43   b  of the reset bar  43  exerts a resetting force through the a-contact side leaf spring  37  on the movable plate  35  in the tripped state shown in  FIG. 2(   b ), thereby returning the movable plate  35  to the position of the initial state and at the same time, returning the interlock plate  34  to the position of the initial state (normal state) through the second linking pin  39   b . Thus, the thermal overload relay is reset. 
         [0043]    Now, effects of the thermal overload relay of the embodiment will be described. 
         [0044]    In the contact reversing mechanism  21  of the embodiment, the a-contact  38  and the b-contact  42  are changed-over by rotation of the interlock plate  34  and the movable plate  35 , and disposed in the vicinity of the front surface  34   a  side and the back surface  34   b  side of the interlock plate  34 . Therefore, the space for placing the a-contact  38  and the b-contact  42  in the insulator case  1  is significantly reduced as compared with a conventional device, achieving size reduction of a thermal overload relay. 
         [0045]    In addition, even if external disturbances such as vibration and shock come into the thermal overload relay, the movable contact piece  42   b  of the b-contact  42  in the closed state in the normal state shown in  FIG. 3(   a ) is effectively never separated from the fixed contact piece  42   a , preventing the contact from malfunctioning. 
         [0046]    The movable contact piece  38   b  of the a-contact  38  is provided on the upper portion  35   b  of the movable plate  35  and change-over operation of the a-contact  38  is conducted with the reversing action of the movable plate  35 . Consequently, the number of parts of the thermal overload relay is reduced, and in addition, the space for disposition of the a-contact  38  is decreased, thereby further reducing the size of the thermal overload relay. 
         [0047]    In the embodiment described thus far, the a-contact  38  is changed-over by the reversing action of the movable plate  35 . The reversing action of the movable plate  35 , however, can change-over the b-contact. 
         [0048]    The disclosure of Japanese Patent Application No. 2009-079396 filed on Mar. 27, 2009 is incorporated as a reference. 
         [0049]    While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.
A thermal overload relay includes main bimetals which bend upon detection of an overload current; a release lever displaced via movement of a shifter moved in response to the bending of the main bimetals; and a contact reversing mechanism for changing-over contacts responsive to a rotation of the release lever. The main bimetals, the release lever and the contact reversing mechanism are all disposed in a case. The contact reversing mechanism includes a pivotable movable plate; a reversing spring reversing the movable plate by coupling with a rotated release lever; and an interlock plate rotating around a support shaft together with the movable plate. Each contact has a normally opened contact piece and a normally closed contact piece and is disposed respectively in the vicinity of a front surface and in the vicinity of a back surface of the interlock plate.