Abstract:
An electromagnetic switch includes: a stationary contact; a movable contact movably provided with respect to the stationary contact; a coil configured to move the movable contact to a side of the stationary contact by means of current conduction; and a shaft provided inside the coil such that the movable contact is provided at an end portion thereof, wherein a snap-fit portion having a pair of hooks disposed to face each other is provided at an end portion of the shaft, and the movable contact is fixed between the end portion of the shaft and the hook.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2010-0100772, filed on Oct. 15, 2010, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a movable contact assembly employed in an electromagnetic switch. 
     2. Description of the Related Art 
     In general, an electromagnetic switch may be provided between a storage battery and a power converting device in an electric vehicle such as a hybrid vehicle, a fuel cell vehicle, a golf cart, and an electric forklift to perform the function of supplying and cutting off power provided from the storage battery to the power converting device. 
     The electromagnetic switch may include a stationary contact, a movable contact brought into contact with or separated from the stationary contact, and an electronic actuator for driving the movable contact. The electronic actuator in the related art may include a coil, a stationary core, a movable core, a shaft, and a return string. The coil may generate an electromagnetic force when a current is supplied. The stationary core may be fixed and disposed at the center of the coil. The movable core may be disposed to be approached to or separated from the stationary core. 
     The shaft may be provided in a slidably movable manner with respect to the stationary core through the stationary core. Furthermore, an end portion of the shaft may be combined with the movable core so as to be moved together with the movable core, and the other end portion thereof may be connected to the movable contact. The return spring may exert an elastic force to the movable core in a direction such that the movable core is separated from the stationary core. 
     According to the related art, the movable contact and the shaft may be connected to each other in the following structure. A through hole into which an end portion of the shaft can be inserted may be formed at the center of the movable contact. The movable contact may be inserted into an end portion of the shaft through the through hole. In this state, a corking member may be combined with a corking groove formed at an end portion of the shaft from the outside of the movable contact using a punch not to allow the movable contact to be released from the shaft. 
     However, in the foregoing case, in order to assemble the shaft with the movable contact, the corking member may be combined with the corking groove using a punch in a state that the movable contact is inserted into an end portion of the shaft and then the movable contact and the shaft are fixed to each other by a jig. Accordingly, it may have a drawback that the overall assembly process is complicated and inconvenient. 
     Furthermore, the movable contact may be supported in a movable manner along an axial direction of the shaft in the state of being inserted into an end portion of the shaft, and a push spring may be provided between the shaft and the movable contact. The push spring may exert an elastic force in a direction such that the movable contact is to be approached to the stationary contact, thereby allowing the movable contact to maintain the state of being in contact with the stationary contact under a predetermined or higher pressure. 
     In this case, subsequent to inserting the push spring to an end portion of the shaft, the movable contact should be fixed by a jig to disallow the movable contact to be released from the end portion of the shaft by an elastic force of the push spring. In this state, the corking member may be combined with the corking groove from the outside of the movable contact using a punch. As a result, it may have a drawback that the assembly process is further complicated. 
     SUMMARY OF THE INVENTION 
     A task of the present invention is to solve the foregoing problem, and there is provided an electromagnetic switch capable of enhancing the assembly performance to simplify the process. 
     In order to accomplish the foregoing task, according to an aspect of the present invention, there is provided an electromagnetic switch including a stationary contact; a movable contact movably provided with respect to the stationary contact; a coil configured to move the movable contact to a side of the stationary contact by means of current conduction; and a shaft provided inside the coil such that the movable contact is provided at an end portion thereof, wherein a snap-fit portion having a pair of hooks disposed to face each other is provided at an end portion of the shaft, and the movable contact is fixed between the end portion of the shaft and the hook. 
     According to the foregoing aspect of the present invention, the movable contact may be fixed in a snap-fit manner by a hook other than a corking manner in the related art, thereby further facilitating the assembly process. 
     Here, a distance between the hook and the end portion of the shaft may be set to be greater than a thickness of the movable contact such that the movable contact is fixed in a movable manner within the snap-fit portion, and a push spring disposed between the end portion of the shaft and a rear surface of the movable contact to exert an elastic force in a direction such that the movable contact is to be approached to the stationary contact may be additionally provided. 
     Furthermore, the push spring may be a helical compressive spring, and a spring support groove for accommodating and supporting part of the helical compressive spring may be formed at an end portion of the shaft. 
     Furthermore, a head having a pair of rib portions protruded in parallel to each other may be provided at the shaft, and both lateral surfaces of the movable contact may be supported between the pair of the rib portions to prevent rotation using the shaft as a rotational axis. 
     Furthermore, the snap-fit portion may be made of a different material from that of the head. 
     Furthermore, the snap-fit portion may be fixed between the pair of rib portions. 
     According to the present invention, a movable contact assembly may be assembled in a snap-fit manner. Accordingly, a movable contact, or even a push spring if necessary, may be easily and conveniently assembled with respect to a shaft without fixing the movable contact by a jig as well as without using a punch. As a result, the assembly can be easily and conveniently carried out, and the assembly process may be also simplified compared to the existing corking method. 
    
    
     
       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 an example of an electromagnetic switch to which a movable contact assembly according to an embodiment of the present invention is applied; 
         FIG. 2  is a cross-sectional view illustrating a configuration in which a movable contact is moved to be brought into contact with a stationary contact in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view illustrating a movable contact assembly in  FIG. 1 ; and 
         FIG. 4  is a perspective view illustrating a configuration in which the movable contact assembly of  FIG. 3  is assembled. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an electromagnetic switch according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view illustrating an example of an electromagnetic switch to which a movable contact assembly according to an embodiment of the present invention is applied, and  FIG. 2  is a cross-sectional view illustrating a configuration in which a movable contact is moved to be brought into contact with a stationary contact in  FIG. 1 , and  FIG. 3  is an exploded perspective view illustrating a movable contact assembly in  FIG. 1 , and  FIG. 4  is a perspective view illustrating a configuration in which the movable contact assembly of  FIG. 3  is assembled. 
     Referring to  FIGS. 1 through 4 , an electromagnetic switch may include a cover portion  11 , a plate  12 , a stationary contact  13 , a coil assembly  14 , a stationary core  15 , a movable core  16 , and a return spring  17 . 
     The cover portion  11  may be fixed on the plate  12  to form an arc extinguishing space between the plate  12  and itself. The stationary contact  13  may be accommodated into the cover portion  11 , and supported by the cover portion  11 . A stationary terminal  21  may be connected to the stationary contact  13 . The stationary contact may include a plurality of contact terminals. 
     The coil assembly  14  may be provided on the plate  12 , and include a coil  14   a  for generating a magnetic force when a current is supplied. The coil  14   a  may be wound around a bobbin  14   b . An end portion of the stationary core  15  may be inserted and fixed into the plate  12 . The movable core  16  may be operated to be approached to or separated from the stationary core  15  while slidably moving along an inner wall of the cylinder  22 . 
     The return spring  17  may be provided between the movable core  16  and the stationary core  15 . The return spring  17  may exert an elastic force to the movable core  16  in a direction such that the movable core  16  is separated from the stationary core  15 . Accordingly, when a current supplied to the coil  14   a  is cut off in a state that the movable core  16  has been moved to the stationary core  15  by a magnetic field generated by the current supplied to the coil  14   a  as illustrated in  FIG. 2 , the movable core  16  may be returned to the original position by an elastic force of the return spring  17  as illustrated in  FIG. 1 . The return spring  17  may be made of a helical compressive spring. 
     A movable contact assembly  100  according to an embodiment of the present invention may be moved by a magnetic field of the coil  14   a  to be brought into contact with the stationary contact  13  when a current is supplied to the coil  14   a , and moved by an elastic force of the return spring  17  to be separated from the stationary contact  13  when a current is cut off from the coil  14   a . The movable contact assembly  100  may include a movable contact  110 , a shaft  120 , and a snap-fit portion  130 . 
     The movable contact  110  may be disposed to face the stationary contact  13  and operated to be brought into contact with or separated from the stationary contact  13 . In case that the stationary contact  13  has two contact terminals, the movable contact  110  may have the corresponding number of contact terminals  111 . The contact terminals  111  of the movable contact  110  may be formed to be separated from each other on the movable contact plate  112 . 
     The shaft  120  may move back and forth through the center of the coil  14   a , and may include a shaft body  121 , a head  122 , and a pair of rib portions  123 . The shaft body  121  may be formed in a cylindrical shape. An end portion of the shaft body  121  may be combined with the movable core  16 . Accordingly, the shaft body  121  may be moved together with the movement of the movable core  16 , thereby allowing the movable contact  110  to be brought into contact with or separated from the stationary contact  13 . 
     The head  122  may be formed at an end portion of the shaft body  121 . The head  122  may be formed in a shape such that the diameter of the upper surface thereof is greater than that of the shaft body  121 . A pair of rib portions  123  may be protruded from both sides of the head  122 , respectively, and separated from each other to allow the movable contact  110  to be inserted from the upper portion of the head  122  and support both sides of the movable contact  110 . Since the rib portions  123  are separated from each other, the movable contact  110  may be disposed to be placed between the separated rib portions  123 . 
     The snap-fit portion  130  may include a pair of hooks  131 . The hooks  131  may be disposed on the rib portions  123 , respectively. The hooks  131  may be pushed by the movable contact  110  and deformed to be spaced apart from each other while the movable contact  110  is being inserted between the rib portions  123 , and then elastically restored to cross both sides of the movable contact  110  when the movable contact  110  has been inserted between the rib portions  123 . As a result, the movable contact  110  may not be released from a space between the rib portions  123  because the movable contact  110  is fastened by the hooks  131  in the state of being inserted between the rib portions  123 . 
     The hooks  131  may be formed of a material having elasticity, for example, plastic and the like. The hooks  131  may be disposed at a position higher than an upper end of the rib portions  123 . The snap-fit portion  130  may be formed in a structure that the hooks  131  are connected to each other by a hook connecting portion  132 . The hook connecting portions  132  may be combined with each other in a caved-in shape over an inner wall of the rib portions  123  and an upper surface of the head  122 . When the snap-fit portion  130  is made of a plastic material and the shaft  120  is made of a metallic material, the snap-fit portion  130  and the shaft  120  may be fabricated with an insert molding process. 
     Since the movable contact assembly  100  has the foregoing structure, the process of putting the movable contact  110  and the shaft  120  together may be carried out in the following manner. The movable contact  110  may be pushed between the hooks  131  of the snap-fit portion  130  from an upper portion of the head  122 . Then, the hooks  131  may be pushed by the movable contact  110  to be spaced apart from each other, and therefore the movable contact  110  may pass through between the hooks  131 . Then, the hooks  131  may be elastically restored and moved over an upper surface of the movable contact  110 , respectively, to lock both ends of the movable contact  110 . Consequently, the process of putting the movable contact  110  into the shaft  120  will be completed. 
     The assembly process of the movable contact assembly  100  may be carried out in a snap-fit manner as described above. Accordingly, the movable contact  110  may be easily and conveniently assembled with respect to the shaft  120  without fixing the movable contact  110  and the shaft  120  by a jig as well as without using a punch. As a result, the assembly can be easily and conveniently carried out, and the assembly process may be also simplified compared to the existing corking method. 
     Meanwhile, the rib portions  123  may be formed in such a manner that the movable contact  110  can be moved along an axial direction of the shaft  120 . In addition, a push spring  140  may be provided between the head  122  and the movable contact  110 . The push spring  140  may exert an elastic force in a direction such that movable contact  110  is to be approached to the stationary contact  13 . As a result, when the movable contact  110  is brought into contact with the stationary contact  13 , the movable contact  110  can maintain the state of being in contact with the stationary contact  13  under a predetermined or higher pressure. The push spring  140  may be made of a helical compressive spring. 
     The push spring  140  may be made of a helical compressive spring. In this case, the helical compressive spring may be provided in a compressed state between the head  122  and the movable contact  110 . A spring support groove  124  for accommodating and supporting part of the helical compressive spring may be formed on the head  122 . 
     When the push spring  140  is provided in the movable contact assembly  100 , referring to  FIGS. 3 and 4 , the movable contact assembly  100  may be assembled as follows. First, the push spring  140  may be inserted into the spring support groove  124  of the head  122 . Subsequently, the movable contact  110  may be pushed between the hooks  131  in the snap-fit portion  130  from an upper portion of the head  122 . Then, the hooks  131  may be pushed by the movable contact  110  to be spaced apart from each other, and therefore the movable contact  110  may pass through between the hooks  131 . 
     At this time, the push spring  140  may be pushed by the movable contact  110 . If the movable contact  110  has passed between the hooks  131 , then the hooks  131  may be elastically restored to move over an upper surface of the movable contact  110 , respectively, to lock both sides of the movable contact  110 . Consequently, the process of putting the push spring  140  and the movable contact  110  into the shaft  120  will be completed. As described above, the push spring  140  and the movable contact  110  may be easily and conveniently assembled with respect to the shaft  120  without fixing the movable contact  110  by a jig, and therefore the assembly can be easily and conveniently carried out, and the assembly process may be also simplified compared to the existing corking method. 
     Meanwhile, movement prevention grooves  113  fit into the rib portions  123 , respectively, to prevent a horizontal movement of the movable contact  110  may be formed at both sides of the movable contact  110 , respectively. The movable contact  110  may be disposed to be placed between the rib portions  123  separated from each other, and thus can be freely moved horizontally. The movement prevention grooves  113  may be fit into the rib portions  123 , respectively, to prevent the movable contact  110  from being freely moved horizontally.