Abstract:
A screw terminal and a terminal block incorporating the same provides a mechanically a screw terminal frame with a closed perimeter that resists deformation of the terminal frame when a captured nut is being clamped against a wire within the terminal frame, allowing the captured nut to be clamped more tightly against the wire. Sidewalls of the terminal frame may include tabs that engage ledges of a block housing to support the screw terminal and the captured nut may have surface irregularities upon the surface that engages the wire and to improve electrical contact therebetween and resist mechanical pull out of the wire.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This Non-Provisional Application claims benefit to U.S. Provisional 61/254,092 filed Oct. 22, 2009 and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to electrical terminals providing a releasable mechanical and electrical connection to a current-carrying wire and, in particular, to a screw terminal in which the connection is made by tightening a machine screw. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electrical screw terminals, normally as part of a terminal block, provide a versatile and reliable method of making electrical connections. The quality of the connection to a screw terminal, both in terms of providing low electrical resistance and high mechanical stability, is increased by increasing the clamping force of the nut on the wire. Increased clamping force may be obtained by applying greater torque to the machine screw. However, known screw terminals and terminal blocks are limited with respect to how much screw tightening torque they can accept and are correspondingly limited with respect to how much clamping force the screw terminals can apply to a wire. 
         [0004]    In a simple terminal block, each screw terminal includes an electrically conductive machine screw which is threadably received by the terminal body. The wire to be connected is captured under the head of the machine screw as the machine screw is tightened. 
         [0005]    In these simple terminal blocks, tightening the screw beyond a certain extent can squeeze the wire at least partially out from under the screw head. For multi-strand wires, this may reduce the number of strands that are mechanically held by the screw and compromise the electrical connection between the wire and screw terminal. For single-strand wires, this may completely remove the wire from its connection with the screw terminal, requiring an installer to loosen the screw and start over with connecting the wire to the terminal. 
         [0006]    More sophisticated screw terminals employ enclosed channels into which the wire may be inserted to be captured between one wall (a clamping wall) of the channel and a threaded nut within the channel. Multiple terminals of this type may be held in an electrically insulating housing having barrier walls between terminals to form a terminal block. The nut may be guided by flanking walls of the channel to prevent its rotation as the machine screw is loosened or tightened. The channel may provide a lip opposite the clamping wall to retain the nut on the machine screw when the nut is loosened. 
         [0007]    All such potential issues associated with existing screw terminals can compromise the clamping force that is applied to the wires and correspondingly compromise the integrity of the electrical connection. This can lead to device malfunction that may require field service calls by technicians to resolve and/or other downsides. 
       SUMMARY OF THE INVENTION 
       [0008]    The present inventor has recognized that in channel-type screw terminals, tightening the screw beyond a certain extent can force the nut to rotate within the channel and push out the channel walls, away from each other. This distorts the channel which may loosen the connection between the screw terminal and the terminal housing. When the nut rotates in the channel, it is turning in unison with the screw, whereby it is not further advancing along the screw and not increasing the clamping force on the wire. 
         [0009]    The inventor has also recognized that in such channel-type screw terminals, standard nuts are used which may be relatively thin in some screw terminals. Thin or short nuts have relatively few threads so that tightening the screw beyond a certain extent may strip the threads from the nut, rendering the screw terminal unusable. 
         [0010]    Furthermore, the inventor has recognized that terminal blocks having channel-type screw terminals which require the nuts to be pulled up toward the screw head can be difficult to visually differentiate from those having screw terminals that require the nuts to be pushed away from the screw head. That is because many terminal blocks have small windows through which the wires are inserted into the screw terminals, while the particular mechanical configurations of the nuts, screws, and channels of the screw terminals are mostly covered by terminal blocks. Correspondingly, at times, assemblers mistakenly place wires underneath nuts in channel-type screw terminals, so that the wires get pinched between the nuts and the window perimeter edges instead of the nuts and the respective clamping walls. 
         [0011]    The present inventor has developed screw terminals and corresponding terminal blocks that can apply larger clamping forces to wires while avoiding numerous problems that have previously been associated with trying to apply higher torques to the screws. The particular configuration(s) of the screw terminal and terminal block allow the machine screws to be tightened more than could previously be done, without compromising the interaction of the nut, the screw, and the clamping wall. 
         [0012]    Specifically, the present invention provides an electrical screw terminal that includes a blade for connecting the electrical screw terminal to a receptacle that is provided in an electrical circuit. A terminal frame is connected to the blade and has a closed perimeter with an inner space defined within the closed perimeter. The inner space of the terminal frame houses a captured nut that moves along a screw when the screw is rotated. The closed perimeter of the terminal frame defined, at least in part by an upper wall, a pair of side walls extending from the upper wall, and a base wall extending between and connecting the side walls to each other at their lower ends. 
         [0013]    It is thus one object of the invention to provide an electrical screw terminal of simple construction with a closed perimeter terminal frame that anchors its side walls together at their upper and lower ends, mitigating the extent to which a captured nut can within the terminal frame and push the side walls away from each other. This may increase how much clamping force the captured nut applies to a wire because rotation of the screw is substantially converted into linear movement of the captured nut along the screw. Therefore, the captured nut may move along the length of the screw in preference to rotating the captured nut and bending out the sidewalls of the terminal frame. 
         [0014]    The base wall may include (i) an upright base wall portion that extends generally parallel to the side walls, and (ii) an angled base wall portion that extends generally angularly with respect to the side walls. The terminal frame may include a pair of lips extending from the side walls toward each other and connecting the side walls to the upright and angled base wall portions of the terminal frame. 
         [0015]    It is thus another object of the invention to provide an electrical screw terminal with multiple base wall portions, at least one of which extends angularly with respect to the side walls. The angled base wall portion may serve as an angled gusset or brace that adds rigidity to the terminal frame. The pair of lips connects the side and base wall portions to each other, which may further add to the rigidity of the terminal frame. The rigidity of the terminal frame may help hold the side walls a constant distance from each other, ensuring that the sidewalls do not bend out to accommodate rotation of the captured nut, and resist folding, buckling over, or collapsing of the terminal frame. This may allow greater downward pressure and torque to be applied to the screw while installing a wire into the screw terminal, increasing the amount of clamping force applied to the wire. 
         [0016]    The terminal frame may also include a finger extending between and fixing the upright and angled base wall portions with respect to each other, anchoring the side walls at a constant distance with respect to each other. An aperture may extend through at least one of the blade and the upright base wall portion and the finger may extend through the aperture. An end of the finger may be bent to define a J-shaped profile with the bent end pointing upward toward the terminal frame. 
         [0017]    It is thus another object of the invention to provide an electrical screw terminal with upright and angled base wall portions that are mechanically attached to each other or to other components or portions of the screw terminal. This may prevent relative sliding movement and bending of portions of the screw terminal with respect to each other and may maintain the integrity of the terminal frame so that the side walls of the frame do not bend outwardly and thus may also mitigate tendencies of the captured nut to rotate between the side walls. 
         [0018]    The captured nut may include a top wall with an irregular surface. The irregular surface of the captured nut top wall may include multiple ridges. The ridges may extend in a direction that is generally orthogonal to the wire that is held in the screw terminal. 
         [0019]    It is thus another object of the invention to provide an electrical screw terminal with a capture nut that includes ridges, grooves, or other surface irregularities that can engage or bite into the wire. This configuration increases the surface area of the interface of the captured nut and wire and may supplement the holding ability of the screw terminal so that a greater pulling force would be required to withdraw the wire from the screw terminal. 
         [0020]    The electrical screw terminal may be provided within a terminal block that includes a housing which is made from an insulating material that at least partially covers the electrical screw terminal. The housing of the terminal block includes an opening that aligns with the inner space of the terminal frame. The captured nut is movable between (i) an open position in which a passage extends through the opening of the housing and into the inner space of the terminal frame, allowing the wire to insert through the housing and into the terminal frame, and (ii) a closed position in which the captured nut extends across substantially the entire opening of the housing, preventing the wire from inserting into the terminal frame. 
         [0021]    It is thus another object of the invention to provide a terminal block with a captured nut that is tall enough to substantially cover the opening through the housing when the captured nut is tightened without a wire in the screw terminal. This may ensure that the wire is inserted on the appropriate side of the nut and the relatively taller nut may have more threads that can accommodate greater forces in its thread engagement with the screw, allowing the nut to apply greater clamping forces to the wire. 
         [0022]    The housing may include a top wall that retains the screw from above. The housing may also include a ledge that supports the screw terminal by an engagement of a tab that extends from the terminal frame and the ledge. The screw terminal is vertically maintained within the housing, between the housing top wall, and the ledge. 
         [0023]    It is thus another object of the invention to provide a terminal block that can prevent the screw from being completely removed from the capture nut. It is another object of the invention to provide a terminal block with a robust support that can hold the screw terminal in a vertical direction, allowing move downward force to be applied to the screw when rotating it, which may result in more torque being applied to the screw without the tool slipping out of the screw. 
         [0024]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a perspective view of a terminal block of the present invention; 
           [0026]      FIG. 2  is an enlarged pictorial and exploded view of a portion of the terminal block of  FIG. 1  cross-section along line  2 - 2  in  FIG. 1 ; 
           [0027]      FIG. 3  is a sectional view of the terminal block of  FIG. 1  taken generally in the plane indicated by line  3 - 3  in  FIG. 1 ; and 
           [0028]      FIG. 4  is a perspective view of a captured nut of the terminal block of  FIG. 1 . 
       
    
    
       [0029]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]      FIGS. 1 and 2  each shows a terminal block  5  or portion thereof that is configured for electrically connecting wires  8  to a receptacle  6  in an electronic device or system. Terminal block  5  includes a housing  10  which holds at least one screw terminal  100 . As shown in  FIG. 2 , each screw terminal  100  includes a generally box-shaped frame  110  from which a conductive blade  130  extends and that has open ends and an inner space that holds a captured nut  160  that is movable along a screw  150 , explained in greater detail elsewhere herein. 
         [0031]    Referring now to  FIG. 1 , this particular embodiment of housing  10  holds three screw terminals  100 . The three illustrated screw terminals  100  are provided to connect wires  8  to the line “L”, neutral “N”, and ground “G” conductors of an electrical circuit(s). This configuration can be used with, for example, circuits carrying about 20 A at about 300V, or others, based on the particular end-use configuration of the electronic device or system. 
         [0032]    Still referring to  FIG. 1 , the housing  10  of block  5  is made from an insulating material and at least partially covers each of the electrical screw terminals  100 , which are made from a suitably electrically conductive metallic material(s). Only blades  130  and screws  150  are readily accessible from outside of the housing  10 . Blades  130  insert into conductive sockets of the receptacle  6  that are part of the corresponding electrical circuit(s) to connect the screw terminals  100  and thus also terminal block  5  to the end use device or system. 
         [0033]    Referring yet further to  FIG. 1 , the illustrated housing  10  includes cylindrical screw bosses at its ends. Mounting screws extend through to secure the block  5  to the receptacle  6 . The front of housing  10  includes flexible tabs that interlock with or snap-fit into corresponding structures of the receptacle  6 , which helps hold the block  5  to the receptacle  6 . A release lever is provided by one of the flexible tabs that facilitates removal of the block  5  from the receptacle  6 . Portions of the housing  10  that hold the screw terminals  100  are spaced from each other by parallel and upright support webs. 
         [0034]    Referring now to  FIG. 3 , the respective portions of the housing  10  that confine the screw terminals  100  each includes a top wall  12  that overlies the respective screw terminal  100 , so as to prevent removal of the screw terminal  100  from the top of the block  5 . In this embodiment, top wall  12  has a hole through which part of the head of screw  150  extends. A flange that radiates from the bottom of the screw  150  head nests inside of a curved undercut in the bottom of the top wall  12 .  FIG. 2  shows the undercut as a step at the bottom of the curved back edge of the opening in top wall  12 . Preferably, the top wall  12  retains the screw  150  within the housing  10  so that when the nut  160  is pushed all the way down toward the blade  130 , the screw  150  still extends into the nut  160 . In this configuration, the screw  150  cannot be fully removed from the nut  160  when the screw terminal  100  is mounted in the housing  10 . 
         [0035]    Still referring to  FIG. 3 , each portion of the housing  10  that confines a screw terminal  100  includes a pair of walls  14 ,  15  that extend down from the top wall  12 , covering most of the length of the screw terminal  100 . Ledges  16 ,  17  extend inwardly from the walls  14 , toward each other and into a void space of the housing  10  in which the screw terminal  100  sits. Ledges  16  and  17  have ramped lower surfaces that facilitate insertion of the screw terminal  100  through an opening at the bottom of the housing  10 . The ledges  16 ,  17  include flat top surfaces that serve as shoulders against which the screw terminal  100  is supported in a vertical direction, described in greater detail elsewhere herein. 
         [0036]    Referring again to  FIGS. 1 and 2 , openings  18  extend through a forward facing wall of the housing  10 . The openings  18  are aligned with corresponding openings that extend into the terminal frames  110  of the screw terminals  100 . This allows wires  8  to be inserted into and connected to the screw terminals  100  by way of the screws  150 , nuts  160 , and terminal frames  110 . 
         [0037]    Referring now to  FIGS. 2 and 3 , the terminal frame  110  of screw terminal  100  includes a flat upper wall  112  that abuts the bottom surface of top wall  12  of the housing. Upper wall  112  has a hole through which the treaded shaft of screw  150  extends. In this embodiment, the hole in upper wall  112  is slightly off-center, as is the longitudinal axis of screw  150 , with respect to the upper wall  112 . 
         [0038]    Still referring to  FIGS. 2 and 3 , a pair of side walls  114 ,  115  extends downwardly from opposing sides of the upper wall  112 . The side walls  114 ,  115  have tabs  116 ,  117  that extend outwardly to engage the ledges  16 ,  17  of the housing walls  14 ,  15  ( FIG. 3 ). In this embodiment, the tabs extend angularly out and down from upper portions of the side walls  114 ,  115 . This allows the tabs to deflect inwardly and slide over the lower surface ramps of the ledges  16 ,  17  when the screw terminal  100  is inserted into the housing  10  through the open bottom wall of the housing  10 . Tabs  116 ,  117  are sufficiently resilient to snap out against the housing walls  14 ,  15  after the tabs  116 ,  117  have slid past the ledges  16 ,  17  during insertion. Accordingly, once the screw terminal  100  is installed in the housing  10 , the screw terminal  100  is vertically captured between the housing upper wall  12  and the ledges  16 ,  17 . The ledges  16 ,  17  provide mechanical stops against which the tabs  116 ,  117  wedge and sit so that downward forces applied to the screw  150  are transferred through the tabs  116 ,  117  into and through the ledges  16 ,  17  and thus into the housing walls  14 ,  15  distributing such forces through the housing  10 . 
         [0039]    Still referring to  FIGS. 2 and 3 , the overall configuration of the terminal frame  110  helps ensure that the screw terminal  100  has sufficient structural integrity to transfer such loads. The generally box-shaped configuration that defines a closed perimeter of the terminal frame  110  holds the side walls  114 ,  115  in a constant position which prevents the nut  160  from rotating between them. In this way, the terminal frame  110  resists the input torque being to the screw  150  and nut  160 , which forces the nut  160  to move linearly along the screw  150  instead of rotating. Holding the side walls  114 ,  115  in constant positions also holds the tabs  116 ,  117  in their proper positions for engaging and being supported by ledges  16 ,  17 . 
         [0040]    Referring yet further to  FIGS. 2 and 3 , lips  120 ,  121  extend from the bottoms of side walls  114 ,  115 , respectively, toward each other. Lips  120 ,  121  support the nut  160  from below when the nut  160  is at its bottom position or at the downward travel limit, blocking further downward travel of the nut  160 , as shown in  FIG. 2 . In this embodiment, lip  121  extends about three times further or is about three times wider than lip  120 . The end of lip  121  that is furthest from side wall  115  sits under the threaded shaft of the screw  150 , whereas the end of lip  120  that is furthest from side wall  114  sits approximately under the flange of the screw  150  head. 
         [0041]    Shown best in  FIG. 3 , a bottom portion of the closed perimeter of terminal frame  110  is defined by a base wall  122  that extends between and connects the side walls  114 ,  115  to each other. In this embodiment, the base wall  122  has multiple segments or portions that are connected or joined together to cumulatively define the base wall  122 . Base wall  122  includes an angled base wall portion  124  that extends from the lip  120  and an upright base wall portion  125  that extends from the lip  121 . Angled base wall portion  124  extends at approximately a 45-degree downward angle with respect to a flat upper surface of lip  120 . Upright base wall portion  125  extends at approximately a 90-degree downward angle with respect to a flat upper surface of lip  121 . The angled and upright base wall portions  124 ,  125  define an approximately 45-degree angle therebetween and converge directly under the longitudinal axis of screw  150 . 
         [0042]    Referring again to  FIGS. 2 and 3 , in this embodiment, the blade  130  extends continuously from the end of angled base wall portion  124 . The top portion of blade  130  and the bottom portion of upright base wall portion  125  overlap each other or sit in face-to-face communication at such portions. An aperture  132  extends through the top portion of blade  130 . Finger  128  extends continuously from the end of upright base wall portion  125 , through the aperture  132 , and includes a bent end that engages an outwardly facing surface of the blade  130 . In this embodiment, the bent end of finger  128  bends upwardly, toward the terminal frame  110  so that the upright base wall portion  125  and the finger  128  define a J-shaped cross-section. In other embodiments, finger  128  has no discernable bent end or is bent toward some other direction, for example, downwardly, forward, rearward, or otherwise, depending on the particular end-use configuration of the screw terminal  100 . 
         [0043]    Shown best in  FIG. 2 , blade  130  extends as a planar strip of material from the terminal frame  110 . Blade  130  includes opposing rectangular projections that extend from front and back edges of the blade  130  and are received in corresponding grooves of frontward and rearward facing walls of the housing  10 . Regardless of the particular configuration of blade  130 , it is configured for receipt into a conductive socket or other electrical component of the end-use device to electrically couple the wire  8  to an electrical circuit of such device, the wire  8  being clamped in the screw terminal  100  with the nut  160 . Therefore, although blade  130  includes not only planar strips of conductive material, but also, for example, conductive pins, conductive posts, and/or other conductive hardware depending on the particular end use configuration of the block  5  and/or receptacle  6 . 
         [0044]    Referring again to  FIGS. 2 and 3 , preferably the entire screw terminal  100 , with the exception of screw  150  and nut  160 , is made from a single continuous piece of electrically conductive material. In such configuration, the screw terminal  100  may start from a single piece of material that is, for example, punched, blanked, and then braked or otherwise bent to form the entire assemblage of screw terminal  100 . Accordingly, screw terminal  100  may be formed from generally flat material blanks that have the blade  130  at one end and the finger  128  at the other end. The material that will form the angled base wall portion  124 , lip  120 , side wall  114  and tab  116 , upper wall  112 , side wall  115  and tab  117 , lip  121 , and base wall upright portion  125  extends between the blade  130  and finger  128 . Such material is then bent at respective locations along its length to create the corners defined between the various segments in order to arrive at the unitary screw terminal  100  as illustrated, with the bottom wall  122  joining the bottoms of the side walls  114  and  115  together to define the closed perimeter of terminal frame  110  that restricts rotation of nut  160  while allowing the nut  160  to travel vertically therethrough. 
         [0045]    Referring now to  FIGS. 1 and 4 , nut  160  has a generally rectangular perimeter shape and defines a tallness, thickness, or height dimension “H” which is shown in  FIG. 4 . In this embodiment, height “H” is greater than a height dimension of opening  18  of the block housing  10 . Best shown in  FIG. 1 , referring to the neutral “N” and ground “G” associated screw terminals  100 , such screw terminals  100  have nuts  160  that are in a closed position. The nuts  160  in the closed position are screwed all the way up against the upper wall  112  of the terminal frame  110 . In this position, since the height “H” of nut  160  is greater than the height of opening  18 , the opening  18  is completely blocked by the nut  160  from inside of the screw terminal  100 , fully preventing the wire  8  from being inserted into the screw terminal  100  in any way. Referring to the line “L” associated screw terminal  100 , in this screw terminal  100 , the nut  160  is in an open position in which it is spaced from the upper wall  112  of the terminal frame  110 . When the nut  160  is in such an open position, a passage is defined through the opening  18  of the housing  10 , above the nut  160 , and into the inner space of the terminal frame  110 . Wire  8  can be inserted into the screw terminal  100  when the nut  160  is in the open position, such as that associated with line “L”, as shown in  FIG. 1 . 
         [0046]    In other embodiments, the height “H” of nut  160  is not large enough to completely cover the opening  18 . However, in such embodiments, it is preferred that any gap which is defined between the edges of opening  18  and nut  160 , when the nut is in a closed position, is too small for the wire  8  to fit into. This may reduce the likelihood of the wire  8  being installed improperly into the screw terminal  100 , with the wire  8  being on the wrong side of the nut  160 . 
         [0047]    Referring now to  FIG. 4 , in this embodiment, nut  160  includes a top wall that has an irregular surface  162 . The irregular surface  162  of this top wall is in the form of multiple ridges  165  that extend parallel to each other. A direction of extension of the ridges  165  is orthogonal to the longitudinal axis of the wire  8 , so that the ridges  165  engage the outer circumferential surface of the wire  8  in a crosswise manner. 
         [0048]    Ridges  165  are configured to create transversely extending localized deformations in the wire  8 . This increases the surface area of the interface between the wire  8  and nut  160  and provides a wavy or toothed mechanical interlock therebetween. Although the ridges  165  can deform the wire  8 , the top surfaces of ridges  165  are blunt enough to prevent them from shearing through the wire  8  when clamping the wire  8  into the screw terminal  100 . 
         [0049]    Still referring to  FIG. 4 , in this embodiment, the ridges  165  have flat surfaces and are defined between pairs of adjacent grooves  172 . The grooves  172  of the illustrated embodiment have flat bottom walls. Each groove  172  includes a pair of slanted side walls that extend from the groove bottom wall, away from each other, and connect the bottom wall to the adjacent ridges  165  on opposing sides of the groove  172 . Ridges  165  of this embodiment are about half as wide as the bottom walls of the grooves  172 . In one embodiment, bottom walls  172  are about 0.010 inch to about 0.020 inch wide, preferably about 0.015 inch wide and ridges  165  are about 0.006 inch to about 0.012 inch wide, preferably about 0.008 inch wide. The depth of the grooves  172  can be about the same as the width of the flat bottom walls of the grooves  172 , optionally less deep, for example, about 0.006 inch in depth. Of course, irregular surface  162  in some embodiments has other configurations besides ridges  165  and grooves  172 . For example, the irregular surface  162  can be defined by knurling, bumps, and/or other surface irregularities which may enhance the ability of the screw terminal  100  to hold wire  8  without shearing it. 
         [0050]    Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
         [0051]    Various features of the invention are set forth in the following claims.