Abstract:
A sealed contact device includes an electromagnet block  2  including a coil bobbin  21 , a movable iron core  25 , a yoke  26 , and a return spring  27 ; a contact block  3  including a sealing container  31 , fixed contact points  32 , a movable contact member  35  arranged within the sealing container  31  and composed of a rectangular body portion  35   a , first and second protrusions  35   b   , 35   c  formed in longitudinal sides of the body portion  35   a  and movable contact points  34 , and a shaft  37 ; and a case  4 . The first and second protrusions  35   b   , 35   c  of the movable contact member  35  are formed in non-point symmetry with respect to a connection portion of the movable contact member  35  and the shaft  37  so that, when the movable contact member  35  is rotated, only one of the first and second protrusions  35   b   , 35   c  makes contact with the sealing container  31.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sealed contact device. 
     BACKGROUND OF THE INVENTION 
     There is conventionally available a sealed contact device B which includes, as shown in  FIGS. 8A ,  8 B,  9 A,  9 B and  10 A through  10 C, a hollow box-shaped case  4  and an inner block  1  arranged within the case  4 , the inner block  1  having an electromagnet block  2  and a contact block  3  combined together (see, e.g., Japanese Patent Application Publication No. H11-238443). In the description given below, an up-down direction, a left-right direction and a front-rear direction orthogonal to the up-down direction and the left-right direction will be defined on the basis of the directions shown in  FIG. 8A . 
     The electromagnet block  2  includes a hollow cylindrical coil bobbin  21  made of an insulating material and wound with an exciting coil  22 , a pair of coil terminals  23  connected to the opposite end portions of the exciting coil  22 , a stationary iron core  24  fixed to the inside of the coil bobbin  21  and magnetized by the energized exciting coil  22 , a movable iron core  25  arranged within the coil bobbin  21  in an axially opposing relationship with the stationary iron core  24  so that, upon energizing and de-energizing the exciting coil  22 , the movable iron core  25  can be attracted by the stationary iron core  24  and axially moved within the coil bobbin  21 , a yoke  26  made of a magnetic material and arranged to surround the coil bobbin  21 , and a return spring  27  arranged within the coil bobbin  21  to bias the movable iron core  25  downwards. 
     The contact block  3  includes a sealing container  31  formed of an insulating material and having a hollow box-shape with an open lower surface, a pair of substantially cylindrical columnar fixed terminals  33  arranged to extend through an upper surface of the sealing container  31  and provided with fixed contact points  32  on its lower surface, a movable contact member  135  arranged within the sealing container  31  and provided with movable contact points  34  for moving toward and away from the fixed contact points  32 , a pressure contact spring  36  kept in contact with a lower surface of the movable contact member  135  to bias the movable contact member  135  toward the fixed contact points  32 , and a shaft  37  coupled with the movable contact member  135  at its upper end and connected to the movable iron core  25  at its lower end to move together with the movable iron core  25 . 
     The coil bobbin  21  is formed of a resin material and has a hollow cylindrical shape. The coil bobbin  21  includes upper and lower flange portions  21   a  and  21   b  and a cylinder portion  21   c . The exciting coil  22  is wound around the outer circumference of the cylinder portion  21   c . The inner diameter of a lower extension of the cylinder portion  21   c  is greater than the inner diameter of an upper extension thereof. 
     As shown in  FIGS. 10B and 10C , the exciting coil  22  is connected at its opposite ends to a pair of terminal portions  121  provided in the upper flange portion  21   a  of the coil bobbin  21 . Then, the exciting coil  22  is connected to the coil terminals  23  through lead lines  122  extending from the terminal portions  121 , respectively. 
     Each of the coil terminals  23  includes a base portion  23   a  made of an electrically conductive material such as copper and connected to the lead lines  122  by soldering or other methods, and a terminal portion  23   b  arranged to extend substantially vertically from the base portion  23   a.    
     As shown in  FIG. 10B , the yoke  26  includes a substantially rectangular first yoke plate  26 A arranged at the upper end side of the coil bobbin  21 , a substantially rectangular second yoke plate  26 B arranged at the lower end side of the coil bobbin  21  and a pair of third yoke plates  26 C arranged to extend upwards from the left and right end portions of the second yoke plate  26 B and connected to the first yoke plate  26 A. 
     A recessed portion  26   a  is formed substantially at the center of an upper surface of the first yoke plate  26 A. An insertion hole  26   c  is defined substantially at the center of the recessed portion  26   a . A closed-bottom cylinder member  28  with an upper flange portion  28   a  is inserted into the insertion hole  26   c . The upper flange portion  28   a  is jointed to the recessed portion  26   a . The movable iron core  25  is formed from a magnetic material into a substantially cylindrical columnar shape and is arranged within the lower extension of the cylinder portion  28   b  of the cylinder member  28 . The stationary iron core  24  is formed from a magnetic material into a substantially cylindrical columnar shape and is inserted into the cylinder portion  28   b  in an opposing relationship with the movable iron core  25 . 
     A metal-made cap member  45  is arranged on the upper surface of the first yoke plate  26 A. The cap member  45  includes a peripheral edge portion fixed to the first yoke plate  26 A and a raised portion  45   a  formed substantially at the center thereof to define a space for accommodating the upper flange portion  24   a  of the stationary iron core  24 . Removal of the stationary iron core  24  is prevented by the cap member  45 . 
     A cylindrical bush  26 D made of a magnetic material is fitted to a gap portion between the lower inner circumferential surface of the coil bobbin  21  and the outer circumferential surface of the cylinder member  28 . The bush  26 D makes up a magnetic circuit in cooperation with the yoke  26 , the stationary iron core  24  and the movable iron core  25 . 
     The return spring  27  extends through an axial insertion hole  24   b  of the stationary iron core  24 . The return spring  27  makes contact with the upper surface of the movable iron core  25  at its lower end and with the lower surface of the cap member  45  at its upper end. The return spring  27  is kept compressed between the movable iron core  25  and the cap member  45 , thereby resiliently biasing the movable iron core  25  downwards. 
     The shaft  37  is formed of a non-magnetic material to have a vertically elongated bar shape. The shaft  37  extends through an insertion hole  45   b  of the cap member  45  defined substantially at the center of the raised portion  45   a  and then through the return spring  27 . The shaft  37  includes a thread portion  37   b  formed in the lower extension thereof. The thread portion  37   b  is threadedly coupled with, and connected to, an axial thread hole  25   a  of the movable iron core  25 . 
     The movable contact member  135  includes a substantially rectangular body portion  135   a  having an insertion hole  135   d  defined substantially at the center thereof. The shaft  37  is inserted into the insertion hole  135   d . Movement of the movable contact member  135  toward the fixed contact points  32  is restrained by a flange-shaped restraint portion  37   a  formed at the upper end of the shaft  37 . As can be seen in  FIG. 11A , the movable contact points  34  are fixed to the left and right end portions of the body portion  135   a . Substantially rectangular protrusions  135   b  and  135   c  protrude from the longitudinal sides of the body portion  135   a . The protrusions  135   b  and  135   c  are substantially in point symmetry with respect to the insertion hole  135   d . The protrusions  135   b  and  135   c  are formed to have the same width a 5  and the same protruding length b 5 . 
     The fixed terminals  33  are formed from an electrically conductive material such as copper into a substantially cylindrical columnar shape. Each of the fixed terminals  33  includes a flange portion  33   a  formed at the upper end thereof. The fixed contact points  32  are fixed to the lower surfaces of the fixed terminals  33  in an opposing relationship with the movable contact points  34 . Each of the fixed terminals  33  has a thread hole  33   b  axially extending from the upper surface thereof. Thread portions of an external load device (not shown) are threadedly coupled to the thread holes  33   b  of the fixed terminals  33 . 
     The sealing container  31  is formed from a heat-resistant material such as ceramics into a hollow box shape with an open lower surface. Two through-holes  31   a  through which the fixed terminals  33  pass are formed side by side on the upper surface of the sealing container  31 . The fixed terminals  33  are inserted into the through-holes  31   a  with the flange portions  33   a  thereof positioned above the upper surface of the sealing container  31  and are jointed to the sealing container  31  by soldering. As shown in  FIG. 10A , one end of a flange member  38  is jointed to the peripheral edge of an opening of the sealing container  31  by soldering. The other end of the flange member  38  is jointed to the first yoke plate  26 A by soldering, whereby the sealing container  31  is sealed. 
     In the opening of the sealing container  31 , there is provided an insulating member  39  for isolating an arc generated between the fixed contact points  32  and the movable contact points  34  from the joint portion of the sealing container  31  and the flange member  38 . 
     The insulating member  39  is formed from an insulating material such as ceramics or a synthetic resin into a substantially hollow cuboid shape with an open upper surface. The insulating member  39  includes a rectangular rim  39   a  formed substantially at the center of the lower surface thereof. The raised portion  45   a  of the cap member  45  is fitted to a recessed portion defined within the rectangular rim  39   a . The upper end of a peripheral wall of the insulating member  39  makes contact with the inner surface of a peripheral wall of the sealing container  31 , thereby isolating the joint portion of the sealing container  31  and the flange member  38  from the contact portions including the fixed contact points  32  and the movable contact points  34 . 
     The insulating member  39  includes a circular rim  39   c  formed substantially at the center of the inner bottom surface thereof. The inner diameter of the circular rim  39   c  is substantially equal to the inner diameter of the pressure contact spring  36 . An insertion hole  39   b  through which the shaft  37  extends is formed substantially at the center of the circular rim  39   c . The lower end of the pressure contact spring  36  through which the shaft  37  extends is fitted to a recessed portion defined within the circular rim  39   c , thereby preventing misalignment of the pressure contact spring  36 . 
     The pressure contact spring  36  makes contact with the lower surface of the movable contact member  135  at its upper end and remains compressed between the insulating member  39  and the movable contact member  135 . Thus, the pressure contact spring  36  resiliently biases the movable contact member  135  toward the fixed contact points  32 . 
     The case  4  is formed from a resin material into a substantially rectangular box shape. The case  4  includes a hollow box-shaped case body  41  with an open upper surface and a hollow box-shaped cover  42  arranged to cover an opening of the case body  41 . 
     As shown in  FIG. 10C , the case body  41  includes ear portions  141  formed at the front ends of the left and right side walls thereof. The ear portions  141  have insertion holes  141   a  used in attaching the sealed contact device B to an installation surface with screws. The case body  41  has a stepped portion  41   a  formed in the peripheral edge of the upper opening thereof. The outer dimension of the upper end extension of the case body  41  is smaller than the outer dimension of the lower extension thereof. A pair of slits  41   b  for insertion of the terminal portions  23   b  of the coil terminals  23  is formed in the front wall of the case body  41  above the stepped portion  41   a . In the rear wall of the case body  41  above the stepped portion  41   a , a pair of recessed portions  41   c  is arranged side by side along the left-right direction. 
     The cover  42  is formed into a hollow box shape with an open lower surface. A pair of protrusions  42   a  is formed on the rear surface of the cover  42 . The protrusions  42   a  are fitted to the recessed portions  41   c  of the case body  41  when the cover  42  is mounted to the case body  41 . A partition portion  42   c  for substantially bisecting the upper surface of the cover  42  into left and right areas is formed on the upper surface of the cover  42 . A pair of insertion holes  42   b  for insertion of the fixed terminals  33  is formed on the upper portion of the cover  42  bisected by the partition portion  42   c.    
     When the inner block  1  including the electromagnet block  2  and the contact block  3  is put into the case  4 , a substantially rectangular lower cushion rubber  43  is interposed between the lower flange portion  21   b  of the coil bobbin  21  and the bottom surface of the case body  41  and an upper cushion rubber  44  having insertion holes  44   a  for insertion of the flange portions  33   a  of the fixed terminals  33  is interposed between the sealing container  31  and the cover  42 . 
     In the conventional sealed contact device B configured as above, the return spring  27  has a spring constant higher than that of the pressure contact spring  36 . Therefore, the movable iron core  25  is slid downwards by the biasing force of the return spring  27  and, concurrently, the shaft  37  is moved downwards. Since the movable contact member  135  is moved downwards together with the restraint portion  37   a  of the shaft  37 , the movable contact points  34  are initially kept spaced apart from the fixed contact points  32 . 
     If the exciting coil  22  is energized, the movable iron core  25  is attracted by the stationary iron core  24  and moved upwards. Thus, the shaft  37  connected to the movable iron core  25  is also moved upwards. As a result, the restraint portion  37   a  of the shaft  37  is moved toward the fixed contact points  32 , and the movable contact member  135  is also moved toward the fixed contact points  32  by the biasing force of the pressure contact spring  36 . Accordingly, the movable contact points  34  fixed to the movable contact member  135  are brought into contact with, and electrically connected to, the fixed contact points  32 . 
     If the exciting coil  22  is de-energized, the movable iron core  25  is slid downwards by the biasing force of the return spring  27 . Accordingly, the shaft  37  is also moved downwards. As a result, the restraint portion  37   a  is moved downwards together with the movable contact member  135 , whereby the fixed contact points  32  and the movable contact points  34  are spaced apart from each other and electrically interrupted. 
     In the conventional sealed contact device B described above, the pressure contact spring  36  is kept compressed. Therefore, if the pressure contact spring  36  is extended to cause the movable contact member  135  to slide toward the fixed contact points  32 , the movable contact member  135  is rotated clockwise as illustrated in  FIG. 11B  by the torque of the pressure contact spring  36  acting in the direction (clockwise direction) opposite to the winding direction (counterclockwise direction) thereof. If the pressure contact spring  36  is retracted to move the movable contact member  135  away from the fixed contact points  32 , the movable contact member  135  is rotated counterclockwise by the torque of the pressure contact spring  36  acting in the same direction as the winding direction thereof. 
     Consequently, the movable contact member  135  makes sliding movement in a state that two diagonal points of the protrusions  135   b  and  135   c  remaining in point symmetry with respect to the insertion hole  135   d  are brought into contact with, and pressed against, the inner surfaces of the sealing container  31 . This leads to an increased friction force and hinders smooth movement of the movable contact member  135 , which may possibly impair the reliability of a switching action between the contact points. 
     In general, if the contact points are electrically connected to each other, electric currents flow in the opposite directions on the surfaces of the fixed contact points  32  and on the surfaces of the movable contact points  34  opposing to the fixed contact points  32 . This generates an electromagnetic repulsion force acting to move the movable contact points  34  away from the fixed contact points  32 . 
     If the movable contact member  135  is tilted by, e.g., an unbalanced biasing force applied from one end of the pressure contact spring  36  and if the centers of the movable contact points  34  make contact with the off-centered areas of the fixed contact points  32 , the electromagnetic repulsion force mentioned above acts on the movable contact member  135  as rotation torque. When the contact points are electrically connected or when the intensity of an electric current flowing between the contact points is changed sharply, the movable contact member  135  is continuously affected by the variations of the rotation torque and is vibrated about the connection portion thereof connected to the shaft  37 . Abnormal noises may possibly be generated by the vibration of the movable contact member  135 . 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a sealed contact device capable of enabling a movable contact member to move smoothly and enhancing the reliability of a switching action between contact points. 
     In claim  1 , there is described a sealed contact device, including: an electromagnet block including a hollow cylindrical coil bobbin made of an insulating material and wound with an exciting coil, a movable iron core arranged inside the coil bobbin to axially move within the coil bobbin upon energization and de-energization of the exciting coil, a yoke arranged to form a magnetic circuit and including a first yoke plate having an insertion hole and facing one axial end of the coil bobbin, a second yoke plate facing the other axial end of the coil bobbin and a third yoke plate interconnecting the first yoke plate and the second yoke plate, and a return spring arranged inside the coil bobbin to bias the movable iron core toward the second yoke plate; 
     a contact block including a sealing container made of an insulating material and air-tightly jointed to the first yoke plate, fixed contact points arranged within the sealing container, a movable contact member arranged within the sealing container and including a substantially rectangular body portion, first and second protrusions formed in longitudinal sides of the body portion and movable contact points for making movement toward and away from the fixed contact points, a pressure contact spring interposed between the movable contact member and the first yoke plate to bias the movable contact member toward the fixed contact points, and a shaft movably extending through the first yoke plate, the shaft being connected to the movable contact member at one end and to the movable iron core at the other end to move the movable contact member toward the fixed contact points in accordance with the movement of the movable iron core; and a case made of an insulating material and arranged to accommodate an inner block including the electromagnet block and the contact block combined together, wherein the first and second protrusions of the movable contact member are formed in non-point symmetry with respect to a connection portion of the movable contact member and the shaft so that, when the movable contact member is rotated, only one of the first and second protrusions makes contact with the sealing container. 
     With such configuration, only one of the first and second protrusions of the movable contact member makes contact with the sealing container when the movable contact member is rotated and slid in contact with the sealing container. As compared with a case where both of the first and second protrusions would make contact with the sealing container, it is possible to reduce the friction force acting between the movable contact member and the sealing container, thereby enabling the movable contact member to move smoothly and enhancing the reliability of the switching action between the contact points. 
     In claim  2 , the movable contact member has a gravity center positioned below the connection portion of the movable contact member and the shaft in a gravitational force direction. 
     With such configuration, the gravity center of the movable contact member is positioned below the vibration center, i.e., the connection portion of the movable contact member and the shaft, in the gravitational force direction. This helps reduce the amplitude of vibration of the movable contact member and makes it possible to restrain generation of abnormal noises caused by the vibration. 
     In claim  3 , the first and second protrusions are shaped and sized so that only the first protrusion makes contact with the sealing container, the gravity center of the movable contact member being positioned in the first protrusion, the first protrusion being arranged below the connection portion of the movable contact member and the shaft in the gravitational force direction. 
     With such configuration, the amplitude of vibration of the movable contact member is reduced. This makes it possible to restrain generation of abnormal noises caused by the vibration. 
     In claim  4 , the first protrusion is greater in width than the second protrusion. 
     With such configuration, the width of the first protrusion is greater than the width of the second protrusion. Therefore, only one of the first and second protrusions of the movable contact member makes contact with the sealing container when the movable contact member is rotated and slid in contact with the sealing container. As compared with a case where both of the first and second protrusions would make contact with the sealing container, it is possible to reduce the friction force acting between the movable contact member and the sealing container, thereby enabling the movable contact member to move smoothly and enhancing the reliability of the switching action between the contact points. 
     In claim  5 , the width of the first protrusion is set to ensure that, when the movable contact member is rotated at a predetermined angle, the first protrusion makes contact with the sealing container. 
     With such configuration, the rotation angle of the movable contact member is reduced. This makes it possible to reduce the pressing force of the movable contact member acting against the sealing container, thereby enabling the movable contact member to move smoothly and further enhancing the reliability of the switching action between the contact points. 
     In claim  6 , the first protrusion is greater in protruding length than the second protrusion. 
     With such configuration, the protruding length of the first protrusion is greater than the protruding length of the second protrusion. Therefore, only one of the first and second protrusions of the movable contact member makes contact with the sealing container when the movable contact member is rotated and slid in contact with the sealing container. As compared with a case where both of the first and second protrusions would make contact with the sealing container, it is possible to reduce the friction force acting between the movable contact member and the sealing container, thereby enabling the movable contact member to move smoothly and enhancing the reliability of the switching action between the contact points. 
     In claim  7 , the protruding length of the first protrusion is set to ensure that, when the movable contact member is rotated at a predetermined angle, the first protrusion makes contact with the sealing container. 
     With such configuration, the rotation angle of the movable contact member is reduced. This makes it possible to reduce the pressing force of the movable contact member acting against the sealing container, thereby enabling the movable contact member to move smoothly and further enhancing the reliability of the switching action between the contact points. 
     As set forth above, the present invention has an effect of enabling the movable contact member to move smoothly and enhancing the reliability of the switching action between the contact points. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic section view showing a sealed contact device in accordance with one embodiment of the present invention. 
         FIG. 1B  is another schematic section view of the sealed contact device shown in  FIG. 1A . 
         FIG. 2A  is a plan view showing a movable contact member as one of major parts of the sealed contact device and  FIG. 2B  is a section view showing a sealing container as another major part of the sealed contact device. 
         FIG. 3A  is a plan view showing another example of the movable contact member and  FIG. 3B  is a section view showing the sealing container. 
         FIG. 4A  is a plan view showing a further example of the movable contact member and  FIG. 4B  is a section view showing the sealing container. 
         FIG. 5A  is a plan view showing a still further example of the movable contact member and  FIG. 5B  is a section view showing the sealing container. 
         FIG. 6A  is a plan view showing a yet still further example of the movable contact member and  FIG. 6B  is a section view showing the sealing container. 
         FIG. 7A  is a plan view showing an even yet still further example of the movable contact member and  FIG. 7B  is a section view showing the sealing container. 
         FIG. 8A  is a schematic section view showing a conventional sealed contact device. 
         FIG. 8B  is another schematic section view of the conventional sealed contact device shown in  FIG. 8A . 
         FIG. 9A  is a bottom view illustrating the outward appearance of a case of the conventional sealed contact device shown in  FIG. 8A . 
         FIG. 9B  is a side view illustrating the outward appearance of the case of the conventional sealed contact device shown in  FIG. 8A . 
         FIGS. 10A to 10C  are exploded perspective views of the conventional sealed contact device shown in  FIG. 8A . 
         FIG. 11A  is a plan view showing a movable contact member as one of major parts of the conventional sealed contact device and  FIG. 11B  is a section view showing a sealing container as another major part of the conventional sealed contact device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 
     A sealed contact device A according to the present embodiment will be described with reference to  FIGS. 1A ,  1 B,  2 A,  25 ,  3 A and  3 B. In the following description, the up-down direction and the left-right direction in  FIG. 1B  will be defined as an up-down direction and a front-rear direction, respectively. The direction orthogonal to the up-down direction and the front-rear direction will be defined as left-right direction. 
     The sealed contact device A of the present embodiment differs from the conventional sealed contact device shown in  FIGS. 8A and 8B  in that the sealed contact device A of the present embodiment includes a movable contact member  35  having protrusions  35   b  and  35   c  differing in shape from the protrusions  135   b  and  135   c  of the movable contact member  135  of the conventional sealed contact device. 
     Referring to  FIG. 2A , the sealed contact device A of the present embodiment includes a movable contact member  35  having a body portion  35   a , a substantially rectangular protrusion  35   b  formed in a lower longitudinal side of the body portion  35   a  and a substantially rectangular protrusion  35   c  formed in an upper longitudinal side of the body portion  35   a . The protrusions  35   b  and  35   c  differ in left-and-right dimension (width) from each other. In other words, the width a 1  of the protrusion  35   b  is greater than the width a 2  of the protrusion  35   c . The protruding length b 1  of the protrusion  35   b  is equal to the protruding length b 1  of the protrusion  35   c.    
     In the sealed contact device of the present embodiment configured as above, if the pressure contact spring  36  is extended, as shown in  FIG. 2B , the winding torque of the pressure contact spring  36  causes the movable contact member  35  to rotate by an angle of θ 1  within the sealing container  31  about the connection portion of the movable contact member  35  and the shaft  37  (the vibration center) in the direction (clockwise direction) opposite to the winding direction (counterclockwise direction) of the pressure contact spring  36 . At this time, only one (right) corner portion c 1  of the tip end of the protrusion  35   b  having an increased width makes contact with the inner surface of the sealing container  31 . Rotation of the movable contact member  35  is stopped just when the corner portion c 1  comes into contact with the sealing container  31 . Therefore, the corner portions of the tip end of the protrusion  35   c  do not make contact with the sealing container  31 . Only the corner portion c 1  of the protrusion  35   b  is kept in contact with the sealing container  31 . 
     Accordingly, when the movable contact member  35  is rotated, all the protrusions  35   b  and  35   c  do not make contact with the inner surface of the sealing container  31  and, instead, only one corner portion c 1  of the protrusion  35   b  having an increased width makes contact with the inner surface of the sealing container  31 . This reduces the frictional resistance acting between the movable contact member  35  and the sealing container  31 , thereby enabling the movable contact member  35  to move smoothly and enhancing the reliability of the switching action between the contact points. 
     Since the width of the protrusion  35   b  is greater than the width of the protrusion  35   c , the weight of the lower portion of the movable contact member  35  positioned below the connection portion of the movable contact member  35  and the shaft  37  (i.e., the insertion hole  35   d ) becomes greater than the weight of the upper portion of the movable contact member  35  positioned above the connection portion. In other words, the gravity center of the movable contact member  35  is positioned lower than the vibration center thereof. 
     Accordingly, when the movable contact member  35  vibrates in a state that the exciting coil  22  is energized with the contact points kept in contact with each other, the amplitude of vibration of the movable contact member  35  is reduced. This makes it possible to restrain generation of abnormal noises. 
     Referring to  FIG. 3A  which shows another example of the movable contact member  35 , the width of the protrusion  35   b  is set equal to a 1 +α which is greater than a 1  by α, This further increases the difference between the width of the protrusion  35   b  and the width a 2  of the protrusion  35   c . As shown in  FIG. 3B , the rotation angle of the movable contact member  35  when the movable contact member  35  makes contact with the sealing container  31  is set equal to a predetermined angle θ 2  which is smaller than θ 1 . Accordingly, it is possible to reduce the pressing force of the corner portion c 1  of the movable contact member  35  acting against the sealing container  31 . This further reduces the friction force generated between the protrusion  35   b  and the sealing container  31 , thereby enabling the movable contact member  35  to move smoothly and further enhancing the reliability of the switching action between the contact points. 
     In addition, the weight of the lower portion of the movable contact member  35  positioned below the connection portion of the movable contact member  35  and the shaft  37  becomes even greater than the weight of the upper portion of the movable contact member  35  positioned above the connection portion. Thus, the gravity center of the movable contact member  35  is shifted further downwards along the gravitational force direction. As a result, the amplitude of vibration of the movable contact member  35  is further reduced. This makes it possible to further restrain generation of abnormal noises. 
     Referring to  FIG. 4A  which shows a further example of the movable contact member  35 , the protrusions  35   b  and  35   c  have the same width a 1  but the protruding length b 1  of the protrusion  35   b  is greater than the protruding length b 2  of the protrusion  35   c . If the pressure contact spring  36  is extended, as shown in  FIG. 4B , the winding torque of the pressure contact spring  36  causes the movable contact member  35  to rotate by an angle of θ 3  within the sealing container  31  in the direction (clockwise direction) opposite to the winding direction (counterclockwise direction) of the pressure contact spring  36 . At this time, only one (right) corner portion c 2  of the tip end of the protrusion  35   b  having an increased protruding length makes contact with the inner surface of the sealing container  31 . Rotation of the movable contact member  35  is stopped just when the corner portion c 2  comes into contact with the sealing container  31 . Therefore, the corner portions of the tip end of the protrusion  35   c  do not make contact with the sealing container  31 . Only the corner portion c 2  of the protrusion  35   b  is kept in contact with the sealing container  31 . 
     Accordingly, when the movable contact member  35  is rotated, all the protrusions  35   b  and  35   c  do not make contact with the inner surface of the sealing container  31  and, instead, only one corner portion c 2  of the protrusion  35   b  having an increased protruding length makes contact with the inner surface of the sealing container  31 . This reduces the frictional resistance acting between the movable contact member  35  and the sealing container  31 , thereby enabling the movable contact member  35  to move smoothly and enhancing the reliability of the switching action between the contact points. 
     Since the protruding length of the protrusion  35   b  is greater than the protruding length of the protrusion  35   c , the weight of the lower portion of the movable contact member  35  positioned below the connection portion of the movable contact member  35  and the shaft  37  (i.e., the insertion hole  35   d ) becomes greater than the weight of the upper portion of the movable contact member  35  positioned above the connection portion. In other words, the gravity center of the movable contact member  35  is positioned lower than the vibration center thereof. 
     Accordingly, when the movable contact member  35  vibrates in a state that the exciting coil  22  is energized with the contact points kept in contact with each other, the amplitude of vibration of the movable contact member  35  is reduced. This makes it possible to restrain generation of abnormal noises. 
     Referring to  FIG. 5A  which shows a still further example of the movable contact member  35 , the protruding length of the protrusion  35   b  is set equal to b 1 +α which is greater than b 1  by α. This further increases the difference between the protruding length of the protrusion  35   b  and the protruding length b 2  of the protrusion  35   c . As shown in FIG.  5 B, the rotation angle of the movable contact member  35  when the movable contact member  35  makes contact with the sealing container  31  is set equal to a predetermined angle θ 4  which is smaller than θ 3 . Accordingly, it is possible to reduce the pressing force of the corner portion c 2  of the movable contact member  35  acting against the sealing container  31 . This further reduces the friction force generated between the protrusion  35   b  and the sealing container  31 , thereby enabling the movable contact member  35  to move smoothly and further enhancing the reliability of the switching action between the contact points. 
     In addition, the weight of the lower portion of the movable contact member  35  positioned below the connection portion of the movable contact member  35  and the shaft  37  becomes even greater than the weight of the upper portion of the movable contact member  35  positioned above the connection portion. Thus, the gravity center of the movable contact member  35  is shifted further downwards along the gravitational force direction. As a result, when the movable contact member  35  vibrates in a state that the contact points are kept in contact with each other, the amplitude of vibration of the movable contact member  35  is further reduced. This makes it possible to further restrain generation of abnormal noises. 
     By setting the width a 3  of the protrusion  35   b  greater than the width a 4  of the protrusion  35   c  as shown in  FIG. 6A  or by setting the protruding length b 3  of the protrusion  35   b  greater than the protruding length b 4  of the protrusion  35   c  as illustrated in  FIG. 7A , the gravity center of the movable contact member  35  may be shifted upwards along the gravitational force direction to a position higher than the connection portion of the movable contact member  35  and the shaft  37 . In this case, it is equally possible to reduce the pressing force of the corner portion c 4  or c 5  of the movable contact member  35  acting against the sealing container  31 . This further reduces the friction force generated between the protrusion  35   b  and the sealing container  31 , thereby enabling the movable contact member  35  to move smoothly and further enhancing the reliability of the switching action between the contact points. 
     In the present embodiment, there is illustrated an instance where the pressure contact spring  36  is extended. However, even if the pressure contact spring  36  is retracted so that the movable contact member  35  can be rotated counterclockwise under the winding torque of the pressure contact spring  36 , only the right corner portion c 3  of the protrusion  35   b  makes contact with the inner surface of the sealing container  31 . Therefore, it is possible to obtain the advantageous effects mentioned above. 
     In the present embodiment, the winding direction of the pressure contact spring  36  is counterclockwise. However, the winding direction is not limited thereto but may be clockwise. 
     In the present embodiment, there is illustrated an instance where the protrusions  35   b  and  35   c  differ from each other in only one of the width and the protruding length. Alternatively, the protrusions  35   b  and  35   c  may differ from each other in both of the width and the protruding length, as long as only the corner portion of one of the protrusions  35   b  and  35   c  makes contact with the inner surface of the sealing container  31 .