Abstract:
An electromagnetic contactor is provided an electromagnetic contactor including an upper frame having a fixed contact point and a guide rail; a cross bar comprising a sliding portion engaged with the guide rail, a movable contact point contacting and separating with respect to the fixed contact point while sliding along the guide rail, and a movable core; and a lower frame comprising a fixed core disposed adjacent to the movable core, an excitation coil magnetizing the fixed core by an electromotive force, and a return spring exerting an elastic force to the cross bar, wherein the sliding portion is configured separately from the cross bar, and a material forming the sliding portion has a friction coefficient against the guide rail less than that of the cross bar.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2008-0122118 filed on Dec. 3, 2008, the contents of which are incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electromagnetic contactor having an abrasion preventing means, and more particularly, to an electromagnetic contactor having a means for preventing an sliding portion of a cross bar within the electromagnetic contactor, which is mainly used for opening or closing a motor circuit, from being abraded. 
     2. Description of the Related Art 
     In general, an electromagnetic contactor or electromagnetic switch is most generally used when electrically connecting or disconnecting between a power source and a load. The contactor connects or disconnects between two fixed electrodes spatially separated from each other through a moving electrode, in which the force of an electromagnet is used when connecting to each other and the elastic force of a spring or the like is used when disconnecting from each other. 
     For such a conventional electromagnetic contactor, a cross bar is slidably provided within an upper frame and a lower frame thereof, and an electromotive force is applied to an excitation coil adjacent to a fixed core to magnetize the fixed core, and then a magnetic force generated by the magnetization is applied to pull a movable core mounted on the cross bar to a side of the fixed core, thereby sliding the cross bar. Due to that, it is configured in such a manner that a fixed contact point being fixed and provided at the upper frame is contacted or separated with respect to a movable contact point provided at the cross bar based on a sliding movement of the cross bar, thereby opening or closing a circuit connected to the fixed contact point. 
     On the other hand, the electromagnetic contactor should have a predetermined insulation as well as should withstand high-temperature heat generated therewithin during the operation. Accordingly, the cross bar and upper/lower frames are formed by using a thermosetting resin. 
     However, such a thermosetting resin has a relatively high rigidity, thereby easily causing an abrasion when continuously rubbing against each other as described above. In other words, in the electromagnetic contactor, the cross bar continuously repeats to make a sliding movement during the operation and thus a sliding portion of the cross bar may be gradually worn out due to friction during the process. If the abrasion is accumulated, then the sliding movement of the cross bar may be deteriorated, and therefore a contact between the fixed contact point and the movable contact point may be deteriorated, thereby decreasing the reliability of the equipment. Moreover, due to abrasion, dust is generated within the upper and lower frames and it may be a cause of the contact failure and burning damage, thereby reducing the life of the equipment. 
     SUMMARY OF THE INVENTION 
     The present invention is contrived to overcome the foregoing disadvantage in the related art, and it is a technical subject of the present invention to provide an electromagnetic contactor having a means for preventing a sliding portion from being abraded by minimizing the friction of a sliding portion of a cross bar even when used for a long period of time. 
     In order to accomplish the foregoing technical subject, the present invention may provide an electromagnetic contactor including an upper frame having a fixed contact point and a guide rail; a cross bar including a sliding portion sliding on the guide rail, a movable contact point contacting and separating with respect to the fixed contact point while sliding along the guide rail, and a movable core; and a lower frame including a fixed core disposed adjacent to the movable core, an excitation coil magnetizing the fixed core by an electromotive force, and a return spring exerting an elastic force to the cross bar, wherein the sliding portion is configured separately from the cross bar, and a material forming the sliding portion has a friction coefficient against the guide rail less than that of the cross bar. In other words, according to the present invention, a slide portion corresponding to a portion contacting the cross bar and guide rail is configured with a material having a lower friction coefficient than that of the cross bar body to reduce friction therebetween, thereby preventing abrasion thereof. Through this, the cross bar is configured with a material most suitable for operating the electromagnetic contactor, and the sliding portion is configured with a material suitable for preventing abrasion, thereby maintaining the performance of an electromagnetic contactor as well as minimizing abrasion due to the sliding movement. 
     Preferably, the sliding portion may have a block form extending from a side of the cross bar in a sliding direction. At this time, both ends of the contact surface of the sliding portion adjoining the guide rail may be rounded in order to prevent a front end of the contact surface from being stuck on a surface of the guide rail. In addition, the sliding portion may be formed in an oval or round shape, or the like. Furthermore, the sliding portion may be formed of a plate, which surrounds part of the cross bar. In this case, the sliding portion may be positioned between the cross bar and the guide rail. 
     Here, the sliding portion may be formed of any material having a lower friction coefficient than that of the cross bar, for example, a stainless material. 
     On the other hand, the sliding portion may include a body portion and a contact portion protruded to a side of the guide rail from the body portion. In other words, the body portion has a width smaller than that of the guide rail, and the contact portion is only brought into contact with the guide rail, thereby reducing an amount of material consumed in producing the sliding portion and facilitating dimensional control thereof during the production. 
     Here, the body portion may include two or more contact portions with respect to a side of the guide rail. 
     Furthermore, the present invention may provide an electromagnetic contactor including a frame having a guide rail thereinside; a cross bar having a movable contact point, which slides along the guide rail; a fixed contact point contacting or separating with respect to the movable contact point; and an actuator moving the cross bar to a side of the fixed contact point, wherein the cross bar additionally comprises a sliding portion adjoining the guide rail, and a friction coefficient between the sliding portion and the guide rail is less than a friction coefficient between the cross bar and the guide rail. 
     Here, the actuator may include a movable core mounted at the cross bar; a fixed core mounted at the frame; and an excitation coil magnetizing the fixed core by an electromotive force. 
     Furthermore, the present invention may provide an electromagnetic contactor including an upper frame having a fixed contact point and a holder; a cross bar comprising a guide portion slidably fixed at an inner side of the holder, a movable contact point contacting and separating with respect to the fixed contact point while sliding, and a movable core; and a lower frame comprising a fixed core disposed adjacent to the movable core, an excitation coil magnetizing the fixed core by an electromotive force, and a return spring exerting an elastic force to the cross bar, wherein a friction coefficient between the guide portion and the holder is less than a friction coefficient between the cross bar and the upper frame. 
     Here, the holder may be provided to replace a conventional guide rail, and it may be configured with a material having a low friction coefficient, thereby preventing abrasion thereof. 
     Preferably, a through hole may be formed at an inner side of the holder, and the guide portion may be inserted and fixed within the through hole. 
     Here, the holder may be made of a stainless material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a cross-sectional view illustrating a first embodiment of an electromagnetic contactor having an abrasion preventing means according to the present invention; 
         FIG. 2  is a perspective view illustrating an enlarged cross bar in an embodiment as illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating an enlarged upper housing in an embodiment as illustrated in  FIG. 1 ; 
         FIG. 4  is a plan view schematically illustrating a coupling state of the cross bar and the guide rail in an embodiment as illustrated in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along the line A-A′ of  FIG. 4 ; 
         FIG. 6  is a view equivalent to  FIG. 4  schematically illustrating a second embodiment of an electromagnetic contactor having an abrasion preventing means according to the present invention; 
         FIG. 7  is a view equivalent to  FIG. 4  schematically illustrating a third embodiment of an electromagnetic contactor having an abrasion preventing means according to the present invention; and 
         FIG. 8  is a cross-sectional view taken along the line B-B′ of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of an electromagnetic contactor having an abrasion preventing means according to the present invention will be described in detail with reference to the accompanying drawings. 
     Referring to  FIG. 1 , an embodiment of an electromagnetic contactor according to the present invention is illustrated. The electromagnetic contactor include a lower frame  10 , an upper frame  20  covering an upper portion of the lower frame  10 , and a cross bar  30  slidably provided in a vertical direction of the upper frame within a predetermined range inside the upper frame. 
     Furthermore, a fixed contact point  22  for opening or closing the circuit is provided inside the upper frame  20 , and a movable contact point  32  is disposed in a state of being fixed to the cross bar  30  at a position facing the fixed contact point  22 . A return spring  34  is provided at a rear surface of the cross bar  30 , thereby exerting an elastic force for returning the cross bar  30  to an original position when the cross bar  30  is retreated out of a predetermined range. 
     On the other hand, a fixed core  12  and an excitation core  14  for magnetizing the fixed core  12  are provided within the lower frame  10 . Furthermore, a movable core  36  is disposed in a state of being fixed to the cross bar  30  at a position facing the fixed core  12 . For the electromagnetic contactor, an external electromotive force is applied to the excitation core  14 , and it magnetizes the fixed core  12 . The magnetic force of the magnetized fixed core  12  pulls the movable core  36  to a side of the fixed core  12 , and due to this the cross bar  30  is slidably moved to the right side of  FIG. 1  while contracting the return spring  34 , thereby the movable contact point  32  adjoining the fixed contact point  22  to connect the circuit. 
     Then, if the electromotive force is removed, then the cross bar  30  that has been moved to a side of the fixed core  12  by the magnetic force returns to an initial position by an elastic force of the return spring  34  and the movable contact point  32  is separated from the fixed contact point  22  to block the circuit. 
       FIG. 2  is an enlarged view illustrating the cross bar  30 . 
     The cross bar  30  is formed to be protruded to both sides of the central portion thereof, and it may include a movable core fixed portion  35  to which the movable core  36  is fixed on the rear surface thereof. Furthermore, it may include a movable contact point fixed portion  37  protruded from the movable core fixed portion  35  to the front surface thereof, and further include a pair of guide portions  100  formed to be extended to a rear side of the movable core fixed portion  35 . 
     The guide portion  100  is positioned within guide rails  25 , which will be described later to play a role of guiding a sliding movement of the cross bar  30 . A cylindrically-shaped end portion  102  is formed at an end of the guide portion  100 , and a pair of fixed protrusions  104  are protruded at the lateral surface thereof adjacent to the end portion  102 . Furthermore, a slide portion  110  is inserted and fixed in the vicinity of the end portion  102  of the guide portion  100 . The coupling relation of the guide portion  100  and the slide portion  110  will be described later. 
       FIG. 3  is a view illustrating an inside of the upper frame  20  provided with the cross bar  30 . The upper frame  20  has a substantially rectangular box-shaped form as a whole, and the bottom surface thereof is open to accommodate the lower frame  10 . On the other hand, guide rails  25  extended in parallel to each other are formed at a pair of inner surfaces  27  facing each other on an inner surface of the upper frame  20 . The guide rails  25  are extended in a sliding direction of the cross bar  30  as described above to guide a movement of the cross bar  30  in a state of the guide portion  100  being inserted thereinside. 
     Referring to  FIG. 4 , the operation of the foregoing embodiment will be described. 
       FIG. 4  is a plan view schematically illustrating a state in which the guide portion  100  is coupled to the guide rails  25 . Here, a width between the guide rails  25  is set to slightly larger than that of the guide portion  100 , thereby minimizing a contact with the guide rails  25  of the guide portion  100  during the operation. The slide portion  110  has a cap shape covering an end of the guide portion  100 , and the end portion  102  penetrates an end thereof to be protruded outward. 
     Furthermore, as illustrated in  FIG. 5 , two fixed holes  112  are formed on a surface of the slide portion  110  to prevent the slide portion  110  from being leaving out of the guide portion  100  during the sliding process, and fixed protrusions  104  are inserted through the fixed holes  112 . 
     Here, the fixed protrusions  104  are not necessarily two, and also the shape thereof should not be limited to a rectangular shape, and therefore, it will be apparent to those skilled in the art that the fixed protrusions  104  can be modified in various suitable forms. For example, the fixed protrusions  104  may be in a round shape. 
     The slide portion  110  moves, namely, slides while adjoining an inner surface of the guide rails  25  in a state of being fixed to an end of the guide portion  100 . Here, the slide portion  110  is made of a material different from the guide portion  100  made of a heat-curing resin, specifically, a material having a lower friction coefficient against the guide rails  25  than that of the guide portion  100 . In the illustrated embodiment, the slide portion  110  is formed of a stainless material. 
     The slide portion  110  formed of the stainless material has a lower friction coefficient than that of the guide portion  100  made of a heat-curing resin, and frictional resistance is drastically reduced, thereby reducing abrasion thereof. Furthermore, stainless material is advantageous over heat-curing resin from the standpoint of rigidity, and thus has a high abrasion resistance, thereby minimizing abrasion thereof. Moreover, the slide portion  110  is rounded in the vicinity of each vertex thereof, thereby preventing the vertex from being stuck to the guide rails  25  to obstruct the movement thereof during the sliding process. 
     Here, the slide portion  110  is not required to be configured in a box form in which it is vacant, and may be also configured in a block form that is fixed to the guide portion  100 . In this case, the slide portion  110  may be insert-molded together with the guide portion  100 . 
     A second embodiment of the sliding portion is illustrated in  FIG. 6 . The remaining configuration excluding the guide portion and sliding portion in the second embodiment is similar to the first embodiment that has been described with reference to  FIGS. 1 through 3 , and the redundant description thereof will be omitted. 
     In a second embodiment as illustrated in  FIG. 6 , the guide portion  100  has a cylindrically-shaped end portion  102  and a fixed protrusions  104  similarly to the first embodiment. On the other hand, a sliding portion having a stainless material is inserted and fixed at an end of the guide portion  100 , and has four contact portions  212  being protruded toward the guide rails  25  at both sides of the body  210  having a smaller width than that of the guide rails  25 . Accordingly, in the second embodiment, a front end of the contact portion  212  guides a movement of the cross bar while sliding on a surface of the guide rails  25 . Here, the contact portion is not necessarily four, and may be modified to any suitable number. 
     According to the second embodiment, the contact portion is only brought into contact with the guide rail, and thus strict dimensional control of the remaining parts not being brought into contact is not necessarily required, thereby facilitating the production. In addition, an amount of material is less consumed compared to a case when the whole width of the guide rail is filled, thereby reducing the cost thereof. 
     A third embodiment of an electromagnetic contactor according to the present invention is illustrated in  FIGS. 7 and 8 . The remaining configuration excluding the guide portion and sliding portion in the third embodiment is similar to the first embodiment that has been described with reference to  FIGS. 1 through 3 , and the redundant description thereof will be omitted. 
     In the third embodiment, a guide portion  300  has two cylindrically-shaped end portions  302  at the end thereof, and the end portions  302  are extended in a sliding direction of the cross bar and disposed in parallel to each other. Moreover, a holder  310  having a stainless material is fixed and provided in the guide rails  25 , and the two end portions  302  are slidably inserted within a through hole  312  formed inside the holder  310 . 
     In the third embodiment, the holder  310  maintains in a state of being fixed to the guide rail without movement, and the through hole  312  guides a sliding movement of the cross bar. In other words, the size of the holder  312  is not required to be precisely formed at a width of the guide rail, thereby facilitating the production. 
     Here, an example may be also considered in which the guide rail is omitted and the holder  310  is directly fixed to an inner surface of the upper frame  20 . In addition, another example may be also considered in which a plate having a low friction coefficient and high rigidity such as a stainless material is adhered to an inner side of the guide rail without forming a separate sliding portion on the guide portion to prevent abrasion thereof.