Abstract:
An electromagnetic relay includes a relay coil assembly, an armature, and a contact system. The contact system includes a stationary contact assembly stationary contacts and moveable contact springs adjacent to the stationary contacts. The moveable contact springs have a projecting portion. The armature is pivotably actuated in response to an electromagnetic force generated by the relay coil to move the at least one contact spring linearly between a first position and a second position. The stationary contact assembly includes an overmold portion attached to the at least one stationary contact. The overmold portion includes a dielectric material and is bonded to the at least one stationary contact to maintain a predetermined configuration of the stationary contact relative to the at least one moveable contact spring.

Description:
[0001]    The present invention is directed to an electromagnetic relay, and more particularly to an electromagnetic latching relay for motor protection. 
       BACKGROUND 
       [0002]    A relay is an electromagnetically actuated, electrical switch. Conventional relays include stationary contacts and moving contacts corresponding with the stationary contacts. When the relay is electromagnetically actuated, the moving contacts engage or disengage with the stationary contacts, to respectively close or open an electrical circuit. We modified the numbering scheme here. 
         [0003]    A latching relay can have one or two coils. Latching relays have no FCOILdefault position, so they maintain their last position or state when magnetizing current is interrupted. While the relays themselves may be latching, their reset position in a module is based on the control circuitry and software Latching relays may be used to reduce power consumption and dissipation because once actuated, latching relays require no current to maintain their position. In one-coil latching, the direction of current determines the relay position. In two-coil latching, the coil which is energized determines the position of the armature. 
         [0004]    A latching magnetic relay assembly typically includes a relay motor assembly that is magnetically coupled to an actuation assembly. The actuation assembly is then operatively coupled to a contact spring that is positioned opposite a pair of conductively isolated contact points. The relay motor typically drives the actuation assembly, which in turn drives the contact spring into contact with a pair of contact points positioned directly across from the spring. The conductive springs ensure good contact with the contact points, and they form a conductive pathway between the contact points. Conductive springs are typically made of copper or a copper alloy. 
         [0005]    Other latching relays may include electromagnets for generating a magnetic field that intermittently opposes a field generated by a permanent magnet. Although this is a bi-stable type of latching relay, such a relay requires consumption of power in the electromagnet to maintain at least one of the output states. Moreover, the power required to generate the opposing field may be significant, thus making the relay unsuitable for use in space, portable electronics, and other applications that demand low power consumption. 
         [0006]    Another bi-stable, latching type relay operates using a magnet to generate a magnetic field to induce a magnetization in a cantilever. The magnetization suitably creates a torque on the cantilever that forces cantilever toward or away from contacts, depending upon the direction of the magnetization, thus placing the relay into an open or closed state. The direction of magnetization in the cantilever may be adjusted by a second magnetic field. The second magnetic field may be generated through an electromagnet, or by passing a current through conductor. The second magnetic field may be applied in “pulses” or otherwise intermittently as required to switch the relay. 
         [0007]    Other concerns with existing latching or non-latching relays include stationary terminals that are inserted manually into a plastic frame during assembly of the relay. The stationary terminals may not be placed uniformly, making a manual adjustment necessary during assembly, and the terminals may eventually move out of position later. In others, there may be inconsistent and variable contact force and ampere levels due to uneven adjustment of the contact springs. Finally, long contact fingers for stationary relay contacts are difficult to insert into a small space and must be manually interlaced between many parts, in a tedious and time consuming manner. 
         [0008]    What is needed is a relay that includes a stationary contact frame assembly that provides shortened relay contacts that do not require interlacing between parts or manual adjustment during manufacturing. 
       SUMMARY OF THE INVENTION 
       [0009]    In one embodiment, the invention is directed to an electromagnetic latching relay. The latching relay includes a relay coil assembly, an armature, and a contact system. The contact system includes a stationary contact assembly stationary contacts and moveable contact springs adjacent to the stationary contacts. The moveable contact springs have a projecting portion. The armature is pivotably actuated in response to an electromagnetic force generated by the relay coil to move the at least one contact spring linearly between a first position and a second position. The at least one stationary contact assembly includes an overmold portion attached to the at least one stationary contact. The overmold portion includes a dielectric material and is bonded to the at least one stationary contact to maintain a predetermined configuration of the stationary contact relative to the at least one moveable contact spring. 
         [0010]    In another embodiment, the invention is directed to a stationary contact assembly for a relay. The contact assembly includes one or more stationary contacts, and an overmold portion attached to the stationary contacts. The overmold portion includes a dielectric material and is bonded to the at least one stationary contact to maintain a predetermined configuration of the stationary contact relative to at least one moveable contact spring. 
         [0011]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a latching relay in accordance with the present invention. 
           [0013]      FIG. 2  is a cross-sectional view of the latching relay taken along lines A-A in  FIG. 1 . 
           [0014]      FIG. 3  is an exploded view of the latching relay. 
           [0015]      FIG. 4  is an exploded view of the latching relay and cover components. 
           [0016]      FIG. 5  is a perspective view of the lead frame and stationary contact subassembly. 
           [0017]      FIG. 6  is a perspective view of a plurality of stationary contacts in a subassembly form before being separated for individual assembly. 
           [0018]      FIG. 7  is a top perspective view of an alternate embodiment of a latching relay. 
           [0019]      FIG. 8  is a side perspective view of the latching relay of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring to  FIGS. 1-3 , one embodiment of a latching relay  10  is shown in accordance with the present invention. The latching relay  10  includes a coil bobbin subassembly  12 , a contact arrangement  14  with one or more moveable contacts  18  and a contact lead frame  16 . A manual trip element  20  is disposed on the contact arrangement to permit manual override of the relay  10  position. 
         [0021]    The coil bobbin subassembly includes two or more separate electromagnetic coils  24  of electrically conductive wire that are concurrently wound around a bobbin  26  with an axial aperture  28 . Each of the electromagnetic coils  24  has one or more pairs of terminals  29  extending from the bobbin assembly  26  for connecting the electromagnetic coils  24  to external circuits. A pair of magnetically permeable yoke portions  30 ,  32  that include leg portions  30   a,    32   a,  which are disposed within axial aperture  28 . Leg portions  30   a,    32   a  are inserted from opposite ends of aperture  28  and have an abutting interface to form a magnetic circuit with an airgap  34  in which a magnetic pivot armature or actuator  36  is pivotably supported in a main frame  55 . The main frame  55  includes an aperture  35  for receiving and supporting a hub portion  37 . The hub portion  37  is freely rotatable within the aperture  35 . 
         [0022]    The pivot armature  36  has a magnet  38  disposed between a pair of magnetically permeable plates  40 ,  42 . A first winding, referred to as the reset coil (not shown) of coil  24  rotates the pivot armature  36  clockwise until the pivot armature plate  40  comes into contact with yoke cross-arms  30   b,    32   b,  and causes the movable contact springs  50  to return to their normally open or normally closed position, respectively. The second winding, referred to as the trip coil (not shown) of coil  24  rotates the pivot armature counterclockwise until the opposite pivot armature plate  42  comes into contact with the yoke arms  30   b,    32   b.  The counterclockwise rotation of the pivot armature  36  actuates or trips the moveable contact springs  50 . In an alternate embodiment, the pivot arm  36  may be arranged so that the clockwise rotation actuates the relay and the counterclockwise rotation resets the relay. 
         [0023]    Actuation of the latching relay  12  occurs when a first cam portion  44  contacts an angular projecting portion  52  of the moveable contact spring  50 . A second pair of moveable contact springs  54  is actuated by a second cam portion  46  on the opposite side of the latching relay  10  in a similar manner to that described above, wherein the second cam portion  46  and the corresponding angular projection portion  52  are offset from the moveable contact springs  50  and angular projection portion  52 . In the exemplary embodiment moveable contact springs  50  are normally open and moveable contact springs  54  are normally closed, although those skilled in the art will appreciate that the configuration of the contact springs may be reversed or otherwise altered within the scope of the invention. 
         [0024]    The moveable contact springs  50  include contact portions  56  that physically engage with contact portions  56  of stationary contacts  60  when the latching relay  10  is actuated for normally open contact springs  50 , and when the latching relay  10  is reset for normally closed contact springs  54 , as will be explained in greater detail below. 
         [0025]    Manual trip element  20  is biased against a return spring and provides a manual override of the relay  10 . A cam  23  extends radially from trip element  20  through a slot  25 . When the element  20  is rotated, e.g., by a screw driver, cam  23  rotates against a pivot arm  27  on the pivot armature  36 , to force the cam portion  44   
         [0026]    Referring next to  FIG. 4 , the latching relay  10  may include a cover portion  70  to enclose the operating parts of the relay  10 , and to shield electrically conductive relay components that may present a shock hazard. The cover portion  70  includes an aperture  62  that provides access to the trip element  20  for a tool, e.g., a screwdriver, wrench, knife blade or other tool that is capable of operating the trip element  20 . A second aperture  64  is provided in cover portion  70  for receiving a test button  66  with a plunger  68  and return spring  72  for returning the test button  66  to an inactive or normal position. The test button  66  manually trips the relay  10  by urging the pivot arm cams  44  or  46  into the moveable contact springs  50 ,  54 . Also included on the cover portion  70  are a window  74  disposed in aperture  76  for viewing a trip indicator (not shown) located on the pivot armature  36 , and a reset button  80 , which includes a return spring  78  and is supported in a circular rim  82 . The reset button  80 , when depressed, acts upon an arm  84  that resets the position of the contact springs  50 ,  54  to their normally open or normally closed state, respectively. Spring  85  maintains tension on arm  84 . 
         [0027]    Referring next to  FIG. 5 , the lead frame  16  is shown as a separate component of the latching relay  10 . Stationary contacts  60  are overmolded with a dielectric material, e.g., by an injection molding process. The dielectric material may be any suitable elastomeric resin, polymeric or plastic material having the desired combination of properties, e.g., dielectric coefficient, durometer, chemical and mechanical bonding, melting point, and flow characteristics. The overmold portion  90  encapsulates contacts  60  after the contacts  60  are bent into a final configuration to form separate conductive paths  94 ,  96  (indicated by broken lines) along contacts  60  that extend between contact portions  56  and external posts  92 . Conductive paths  94  and  96  are embedded in overmold portion  90 . The overmold portion  90  supports the contacts  60 , conductive paths  94 ,  96  and posts  92  in the lead frame  16 , to provide consistent minimum spacing and accurate location of the stationary contacts  60  relative to the moveable contact springs  50 ,  54 , and of the external posts relative to a relay socket (not shown). The lead frame  16  includes clip portions  98  spaced about the periphery which correspond with apertures  97  ( FIG. 4 ) of the cover portion  70  to retain the cover portion  70  in position. In one embodiment the lead frame  16  may be attached to the main frame  55  by ultrasonically welding the overmold portion  90  to the main frame  55 . Referring to  FIG. 6 , a pair of contact assemblies  100  is shown with the carrier webbing  102  attached. Carrier webbing  102  is removed prior to overmolding the overmold portion  90  around the stationary contacts  60 . The contact assemblies  100  are normally separable at a perforation line  104  to create individual pairs of stationary contacts  60 . The perforation lines  104  may be formed by scoring or stamping the assembly  100 . Alternately the individual pairs of stationary contacts  60  may be separated from the assembly  100  by laser or by machine cutting methods. It will be appreciated by those skilled in the art that the stationary contacts  60  may be used in a conventional relay, within the scope of the present invention. A conventional relay would simply include a single winding coil on the coil bobbin subassembly  24 . 
         [0028]    Referring to  FIGS. 7 and 8 , in an alternate embodiment the latching relay  10  may include a pusher portion  106  that provides a mechanical linkage between the pivot armature  36  and the moveable contact springs  50 ,  54 . The pusher portion  106  provides consistent overtravel adjustment of the moveable contact springs  50 ,  54 . The operation of the pusher portion  106  in an electromagnetic relay is described in greater detail in commonly owned U.S. patent application Ser. No. 12/115,638 filed May 6, 2008 entitled Relay With Automated Overtravel Adjustment, which patent application is incorporated by reference herein. 
         [0029]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.