Abstract:
The subject matter of the invention is an electrical apparatus ( 1 ) with a screw terminal ( 3 ) for connecting electrical conductors, comprising a housing ( 5 ) with a shaft ( 7 ), in which a screw ( 9 ) with a screwdriver opening ( 11 ) is provided, which screw is surrounded radially by the shaft ( 7 ) and can be rotated in a targeted manner only via the screwdriver opening ( 11 ) thereof, wherein the screw head ( 15 ) and the shaft ( 7 ) are matched to one another in such a way that, during a rotation of the screw ( 9 ), a minimum torque is passed through in a first rotary angle range and a maximum torque is passed through in a second rotary angle range, wherein the screw head ( 15 ) has a maximum screw head diameter (D 1 ) and a screw head diameter (D 2 ) which is reduced in comparison therewith, wherein the shaft ( 7 ) contains a first shaft diameter (DS 1 ) which corresponds to the maximum screw head diameter (D 1 ), and a smaller second shaft diameter (DS 2 ), wherein the lateral surface of the screw head ( 15 ) is curved in the region of the maximum screw head diameter (D 1 ) and is planar in the region of the reduced screw head diameter (D 2 ).

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German applications 10 2007 043 312.5 filed Sep. 12, 2007 and 10 2007 047 521.9 filed Oct. 4, 2007. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns an electrical apparatus with terminal screw. 
       BACKGROUND 
       [0003]    Such an electrical apparatus with terminal screw is generally known and disclosed in for example DE 30 28 958 C2. The known electrical apparatus is implemented as a terminal strip with a housing made of insulation material. The housing features a round shaft with a screw that is disposed therein. The shaft leads to an internal thread of a clamping sleeve by means of which electrical conductors can be connected. 
         [0004]    The screw head features a screw driver opening. A screw driver can, by means of its blade, be brought into engagement with the screw driver opening of the screw through the shaft opening, so that the screw can be turned with its threaded shank into the internal thread of the clamping sleeve. Thereby an electrical conductor is clamped that is inserted into the clamping sleeve. 
         [0005]    In order to secure the position of a screw that is only partially screwed into the internal thread, axially oriented ribs are provided on the internal side of the shaft. In these locations the internal diameter of the shaft is implemented smaller than the external diameter of the screw head. Consequently the screw head is held nonpositively by means of the ribs in a radial direction, whereby partly an unwanted twisting, caused for example through vibrations, or even the loss of the screw can be prevented. 
         [0006]    The users of electrical apparatus with terminal screws demand on the one hand that as part of delivery of the electrical apparatus the screw with its threaded shank is already brought into engagement with the internal thread of the clamping sleeve in order that damage to the threads due to inaccurate alignment of the screw on the internal thread of the clamping sleeve is precluded and an electrical conductor that has been inserted in the clamping sleeve can be clamped immediately without loss of time simply by turning the screw. 
         [0007]    On the other hand there is the demand that the screw is brought into engagement with the internal thread only to the degree that also electrical conductors with a maximally acceptable diameter can be inserted by means of the clamping opening into the clamping sleeve. This is however not the case if the threaded shank is brought into engagement with the internal thread beyond a certain depth because the clamping opening is reduced with increasing penetration depth. In this case, for the connection of a thick electrical conductor, the screw has to be turned upward to the extent and the clamping opening has to be opened that the electrical conductor can be inserted by means of the clamping opening into the clamping sleeve. Since however, as a rule, power screw drivers are utilized, the screw is frequently indeed loosened to the point that its threaded shank is no longer brought into engagement with the internal thread. In this case the threaded shank has to be initially aligned again on the internal thread in order to assure that the screw is not screwed in askew and the internal thread is damaged. 
         [0008]    Therefore it is of central importance that as part of delivery of the electrical apparatus the thread shank is screwed into the internal thread with such a predetermined engagement depth that also electrical conductors with a maximally acceptable diameter can be inserted into the clamping sleeve by means of the clamping opening. 
       SUMMARY OF THE INVENTION 
       [0009]    Based on the initially mentioned state of the art it is the purpose of the invention to assure that, in the context of an electrical apparatus with terminal screw, a twisting of the screw because of vibrations and/or oscillations is assuredly prevented. The object is met according to the characteristics of the electrical apparatus of claim  1 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawing are shown 
           [0011]      FIG. 1  an electrical apparatus, according to the invention with terminal screws, encompassing a shaft into which a screw is inserted, in a perspective view with view of the screw and the shaft in a cutaway, 
           [0012]      FIG. 2  in plan view the electrical apparatus from  FIG. 1  in a first rotational angle range, 
           [0013]      FIG. 3  the electrical apparatus from  FIG. 1  in perspective with view of its clamp openings for the insertion of electrical conductors, 
           [0014]      FIG. 4  the terminal screws of the electrical apparatus from  FIG. 1  in perspective with view of its clamp openings, 
           [0015]      FIG. 5  in plan view a section of the electrical apparatus from  FIG. 1 , wherein the screw head is positioned in the first rotational angle range in which the screw is smooth-turning, 
           [0016]      FIG. 6  in plan view a section of the electrical apparatus from  FIG. 1 , wherein the screw head is positioned at the end of the first rotational angle range, 
           [0017]      FIG. 7  in plan view a section of the electrical apparatus from  FIG. 1 , wherein the screw head is positioned in a second rotational angle range in which the screw is stiff-turning, 
           [0018]      FIG. 8  as a break-out the terminal screw is cut from an electrical apparatus and in plan view, wherein the screw head features a setback of the kind of a locking groove, wherein the shaft features a corresponding counter-locking element. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    This application claims priority to German applications 10 2007 043 312.5 filed Sep. 12, 2007 and 10 2007 047 521.9 filed Oct. 4, 2007, the entire disclosures of which are incorporated by reference. 
         [0020]    The electrical apparatus with terminal screw for the purpose of connection of electrical conductors, according to the invention, encompasses a housing with a shaft in which is provided a screw with an opening for a screw driver, said screw is radially enclosed by the shaft and specifically turnable only by means of its screw driver opening, whereby the screw head and the shaft are adjusted relative to one another in such a way that during a revolution of the screw in a first rotational angle range a minimal torsional moment and during a second rotational angle range a maximum torsional moment is traversed. If the screw is located within the first rotational angle range, vibrations and/or oscillations have the effect that the screw turns within the first rotational angle range alone in a clockwise and counterclockwise direction, but without reaching into the second rotational angle range. A prerequisite therefore is of course that the torsional moment in the second rotational angle range is correspondingly large. 
         [0021]    By means of the invention at issue it will also be accomplished that the screw driver opening can be aligned exactly to the housing if the first rotational angle range is selected to be particularly small. This offers the significant advantage that automatic screwdrivers can be utilized due to the position of the screw driver opening, which is always the same, relative to the housing and consequently the connecting and clamping of electrical conductors can be fully automated by simple means. This automization leads to significant cost savings in the context of the connection of electrical conductors. 
         [0022]    The previously mentioned rotational angle ranges can be particularly easily realized by providing a clearance fit between the screw head and the shaft in the first rotational angle range and a press fitting in the second rotational angle range. 
         [0023]    This type of implementation is particularly advantageous because a permanent distortion and deformation of the shaft is precluded by the clearance fit in the first rotational angle range. A permanent deformation is particularly disadvantageous because it is uncontrolled and due to the uncontrolled deformation the torsional moment therefore changes undeterminably during tightening or loosening of the screw. As the case may be the turning of the screw can even be completely blocked. The degree of deformation is dependent on the shaft material, the storage time of the electrical apparatus as well as the climate conditions. Therefore the electrical apparatus according to the invention offers the additional advantage that the influence of the storage time and the climatic storage conditions are largely of no relevance if the screw is positioned in the shaft in the clearance fit during storage of the electrical apparatus. Furthermore are the options greater for the selection of materials of the shaft. 
         [0024]    The different clearances can be implemented such that the screw head features a maximal screw head diameter and, relative to it, a reduced screw head diameter, wherein the shaft has a first shaft diameter, which corresponds to the maximal screw head diameter, and a smaller second shaft diameter. 
         [0025]    In addition provision is made that the surface area of the screw head is implemented curved in the range of the maximal screw head diameter and implemented level in the range of the reduced screw head diameter. 
         [0026]    Due to the fact that the surface area is curved in the range of the maximal screw head diameter it is assured that no mechanical damage of the shaft is caused by the turning of the screw that is inserted in the screw shaft. With this screw head geometry a level surface area follows necessarily a curved surface and vice versa. In the transition area between the curved and even surface area an edge is implemented. This edge is due to the previously mentioned sequence of the surface areas implemented less sharp-edged than commonly utilized polygonal screws. Because in the context of these polygonal screws the edges corresponding to the circumferentially arranged corners of the screw head are implemented through sequentially following level surfaces. This results in the sharp edges or corners on the screw head. 
         [0027]    Advantageously provision is made with this embodiment that the screw head features a maximal screw head diameter and, relative to it, a reduced screw head diameter, wherein the shaft has a first shaft diameter, which corresponds to the maximal screw head diameter, and a smaller second shaft diameter, wherein the second shaft diameter is implemented through the arrangement of ribs within the shaft. This embodiment is advantageous because the shaft with the two diameter ranges is already known and the invention can therefore be achieved by simple means by reducing the screw head diameter in one or several positions. 
         [0028]    In a further improvement of the invention it is provided that the screw driver opening is implemented as a slit that breaks the surface area of the screw head in at least one opening, whereby in the area of the opening the screw head diameter is reduced relative to other areas of the screw head. This improvement is preferred and particularly advantageous because by means of the reduction of the screw head diameter at the opening it is avoided that a radially projecting slug, which was formed during the manufacture of the slit, comes in contact with the shaft. A prerequisite therefore is of course that a clearance fit, which is larger than the radially projecting slug, is provided between the shaft and the screw head diameter at the opening. 
         [0029]    From the point of view of manufacturing technology it is particularly easy when the surface area of the screw head is level and flat at the opening. This can for example be easily achieved by swaging of the screw head. Furthermore the disposition of the reduced screw head diameter at the opening has the effect that during the course of the manufacturing process, in which initially the screw head with its reduced screw head diameter can be manufactured completely and subsequently the slit can be placed in the screw head diameter, a deburring is no longer necessary. If the slug is particularly long, a simple pushing-away of the slug tip would be already sufficient in order to avoid, during the turning of the screw that is provided in the shaft, a contact of the sharp slug with the shaft or the shaft&#39;s inner surface. Thereby the shaft&#39;s inner surface can be protected from mechanical damage by particularly simple means. 
         [0030]    The manufacture of an electrical apparatus with terminal screw for the purpose of connection of electrical conductors, encompassing a housing with a shaft in which is provided a screw with an opening for a screw driver, said screw is radially enclosed by the shaft and specifically turnable only by means of its screw driver opening, whereby the screw head and the shaft are adjusted relative to one another in such a way that during a revolution of the screw in a first rotational angle range a minimal torsional moment and during a second rotational angle range a maximum torsional moment is traversed, is particularly efficient if the following steps are implemented: 
         [0000]    a) Manufacture of the screw head with different screw head diameters
 
b) Placement of a screw driver opening
 
c) Insertion of the screw into the shaft of the electrical apparatus is implemented. It is advantageous during this separation of the processing steps that non-cutting and cutting processes (swaging of the screw head, sawing of the slit) are separated so that each process step can be executed on a manufacturing station in an automated manufacturing machine. Furthermore it is advantageous if these processing steps proceed in a set-up. Hereby therefore a high piece count per unit time can be realized.
 
         [0031]    For the particularly exact alignment of the screw driver opening it is proposed in the context of the process for the manufacture of the electrical apparatus described above, that the screw is screwed into a thread of the electrical apparatus to a predetermined engagement depth, wherein subsequently the screw is turned forward or backward to the extent that, in a first rotational angle range, a minimal torsional moment is achieved. Preferably the size of the first rotational angle range is thereby adapted to the precision requirements with respect to the alignment of the screw driver opening to the housing. It is advantageous in this context to also provide a snap-in connection. 
         [0032]    The electrical apparatus according to the invention, the process for the manufacture of the electrical apparatus as well as the utilization of a screw in the electrical apparatus are described and graphically represented in what follows in an embodiment example illustrated by a terminal screw. 
         [0033]    In the  FIGS. 1 to 3  an electrical apparatus  1  is shown with a terminal screw  3  for the connection of electrical conductors (not shown). It encompasses a housing  5  with a shaft  7  in which a screw  9  with a screw driver opening  11  is provided. 
         [0034]    The shaft  7  encompasses the screw  9 , according to  FIG. 1 , circumferentially entirely in the radial direction. The screw  9  itself is therefore circumferentially not accessible. It can therefore only be specifically turned and tightened by means of a screw driver (not shown) that is inserted into its screw driver opening  11 . The blade of the screw driver can be guided through the shaft opening  13  into the screw driver opening  11  and be inserted. The screw  9  is guided through the shaft  7  to the terminal screw  3  that is shown in  FIG. 4 . The terminal screw  3  encompasses an as such known and therefore not further described clamping housing  16  with a pressure piece  18 , a clamping opening  21  and an internal thread (not shown) as a counter piece for the threaded shank of the screw  9 . The screw engages the internal thread with its threaded shank in the present embodiments. 
         [0035]    In this case the screw head  15  and the shaft  7  are adjusted relative to one another in such a way that during a revolution of the screw  9  in a first rotational angle range a minimal torsional moment and during a second rotational angle range a maximum torsional moment is traversed. 
         [0036]    Preferably the distribution of the different torsional moments during a rotation of the screw  9  is implemented by providing between the screw head  15  and the shaft  7  in a first rotational angle range a clearance fit  17  and in the second rotational angle range a press fitting  19 . The implementation of the clearance fit  17  and the press fitting  19  can be achieved by the screw head  15  having different screw head diameters D 1 , D 2 , wherein the shaft  7  has a first shaft diameter DS 1 , which corresponds to the maximal screw head diameter D 1 , and a smaller second shaft diameter DS 2 . The first shaft diameter DS 1  should be a little bit larger than the maximal screw head diameter D 1 , wherein the second shaft diameter DS 2  is in any case implemented smaller than the maximal screw head diameter D 1 . The second shaft diameter D 2  is preferably implemented by means of the arrangement of ribs in the shaft  7 . 
         [0037]    The surface area of the screw head is, as can be seen from the figures particularly well, implemented curved in the range of the maximal screw head diameter D 1  and implemented level in the range of the reduced screw head diameter D 2 . 
         [0038]    The screw head  15  has, as indicated in  FIG. 6 , a first range with a maximal screw head diameter D 1  and a second range with a hereto reduced screw head diameter D 2 . According to the present embodiment according to  FIGS. 1 to 7  a flat and evenly implemented surface area is located in the second range. The corners labeled with  22  in  FIGS. 5 and 6  delimit the ranges with the reduced screw head diameter D 2  relative to the ranges with the maximal screw head diameter D 1 . 
         [0039]    Alternatively the second range with the reduced screw head diameter D 2  could, according to  FIG. 8 , also be implemented as a setback of a kind of a locking groove, in such a way that, during a rotation of the screw  9  the screw head  15  interlocks by means of its setback with a counter-locking element of the screw head  15 . A rib that is disposed in the shaft  7  is suitable as a counter-locking element. 
         [0040]    According to the  FIGS. 1 to 7  the screw driver opening  11  is implemented as a slit that breaks the surface area of the screw head  15  in at least one opening  23  (see  FIG. 4 ), whereby in the area of the opening  23  the reduced screw head diameter D 2  is provided. Preferably the surface area of the screw head  15  is implemented level and flat at the opening  23  according to  FIG. 4 . The surface area at the opening  23  is, as can be seen from  FIGS. 2  as well as  5  to  7  particularly well, aligned perpendicularly to the slit. This reduced screw head diameter D 2  is implemented across the entire height of the screw head  15 . Alternatively it could be implemented only at the opening  22 , or only there where a slug could be formed on the surface area as a result of the slit. 
         [0041]      FIG. 6  shows in plan view a section of the electrical apparatus from  FIG. 1 , wherein the screw head  15  is positioned at the end of the first rotational angle range. In this first rotational angle range the screw head  15  has clearance relative to the shaft  7 . That is to say between the screw head  15  and the shaft  7  exists, even if it is not clearly indicated in these statements, a gap. The gap is the reason for the smooth-turning property and the minimal torsional moment during the turning of the screw  9 . A gap should theoretically be present in this first rotational angle range also between the ribs and the screw head  15 . The ribs are disposed on the internal side of the shaft and form a part of shaft  7 . They reduce the first shaft diameter DS 1  to the shaft diameter DS 2 . 
         [0042]    The screw head  15  that is shown in  FIG. 6  abuts with its corner  22  against the rib of the shaft  7 . This is border line between the clearance fit  17  and the press fitting  19  in relation to the screw head  15  and the shaft  7 . If the screw  9  is turned out of the position shown in  FIG. 6  in a counterclockwise sense, the screw  9  then reaches the first rotational angle range in which it can be moved easily because the screw head  15  is in a clearance fit  17  with the shaft  7  according to  FIG. 5 . If the screw  9  is turned in a clockwise sense, it overruns the corner  22  and a torsional moment peak and reaches a second rotational angle range in which a maximal torsional moment is achieved because the screw head  15  is in a press fitting  19  with the shaft  7  according to  FIG. 7 . 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
         Electrical apparatus  1   
         Terminal screw  3  housing  5   
         Shaft  7   
         Screw  9   
         Screw driver opening  11   
         Shaft opening  13  screw head  15   
         Clamping housing  16   
         Clearance fit  17   
         Pressure piece  18   
         Press fitting  19  clamping opening  21   
         Corner  22   
         Opening  23   
         Maximal screw head diameter D 1  reduced screw head diameter D 2   
         First shaft diameter DS 1   
         Second shaft diameter DS 2