Patent Publication Number: US-7210974-B1

Title: Slip-on linkage

Description:
BACKGROUND 
   1. Technical Field 
   The disclosure contained in this document relates to a linkage for rotating mechanisms, and particularly to a linkage for coupling the rotating shafts of a high voltage circuit breaker or recloser in end-to-end relationship. 
   2. Description of the Related Art 
   High voltage circuit breakers are used in the distribution of three phase electrical energy to prevent the flow of current in a circuit when a fault or other disturbance is detected. When a sensor or protective relay detects a fault or disturbance in the circuit, current-carrying contacts in each of the three phases are physically separated to prevent current flow until the circuit is clear. A recloser is similar to a circuit breaker, except that a circuit breaker opens a circuit and keeps it in the open position indefinitely, but a recloser may open and reclose the circuit several times in quick succession to allow a temporary fault to clear. A circuit breaker or recloser includes interrupters for physically separating the current-carrying contacts and an operating or switching mechanism for providing the energy necessary to accomplish separation of the contacts. 
   A linkage is provided for mechanically coupling the operating mechanism to each of the interrupters. In general, the linkages or mechanical couplings may be one of several types. For example, in a “push/pull” type coupling, conductive elements are moved into engagement when a rigid rod is moved in one direction, and the coupling elements are disengaged when the rod is moved in the opposite direction. In a rotational coupling, one of the conductive elements moves in response to the rotation of a bell crank as a link element between the three phases of the breaker rotates. 
   An example of such a mechanical coupling is illustrated in U.S. Pat. No. 5,569,891.  FIG. 3  of this patent, which is reproduced herein as  FIG. 1 , shows a prior art example of a dependent pole mechanism for opening and closing all three phases of a circuit breaker simultaneously. In  FIG. 1 , a single connecting rod  22  connects operating mechanism  20  to two rotatable linking elements  25  and  26  by lever  24 . The linking elements are coupled to bell cranks in the terminal portion of the interrupters (not shown).  FIG. 4  of the patent, which is reproduced herein as  FIG. 2 , shows an example of a linkage for independent pole operation of the circuit breaker. In  FIG. 2  herein, three independently operated connecting rods,  32 ,  33  and  34 , are provided. Two of the connecting rods  32  and  33  are connected to lever assemblies  40  and  41  which couple the connecting rods to rotatable linking elements  37  and  39 , respectively. Lever assemblies  40  and  41  also provide a mechanical bearing for decoupling connecting rods  32  and  33  from rotatable linking elements  38  and  36 , respectively. The third connecting rod  34  is connected to a lever assembly that does not have a bearing for decoupling from a linking element.  FIG. 6  of the patent, which is reproduced herein as  FIG. 3 , shows a lever assembly  40  having aperture  62  for mechanically coupling to one linking element and a hollow opening  63  with bearings  67  for decoupling from a second linking element. The lever assemblies are coupled to the one linking element by splining, pinning or bolting. 
   Rotating linkages that need to carry high energy loads without severe flexing or looseness have typically been made using multiple components with special splines and heavy bolted joints used to carry the loads. Typically these linkages allow for little axial alignment variation, have high stresses, and can become loose after many high load operations. These characteristics result in a high cost, dimensionally unforgiving, and failure prone design that requires careful manufacturing and detailed assembly procedures. There is a need for a linkage that overcomes the shortcomings of prior linkage designs. 
   SUMMARY 
   In one embodiment, a linkage is provided for coupling to at least one rotatable shaft having a square or rectangular end. The linkage comprises an elongated body having a central body portion and opposed end portions. At least one of the end portions comprises a pair of parallel side walls and a bottom wall extending longitudinally from the central body portion along the end portion. The parallel side walls and bottom wall form a slot having an upper longitudinal opening between an upper edge of the side walls and an open end between an outer end of the side walls and bottom wall. The slot is adapted to receive a square or rectangular end of a rotatable shaft. A plurality of connectors is provided for clamping the parallel side walls against the end of the rotatable shaft to secure the rotatable shaft in the slot. The connectors extend transversely across the upper longitudinal opening of the slot at spaced locations along the length and adjacent an upper surface of the side walls. In some embodiments, each of the connectors may extend through mateably aligned holes in the upper portion of the side walls and a body portion of each connector may abut an upper surface of the end of the rotatable shaft. In other embodiments the linkage may be cylindrical. And in still further embodiments the central portion of the linkage may be hollow. 
   In another embodiment, the linkage comprises an elongated body having a central body portion and opposed end portions. At least one of the end portions of the linkage comprises a pair of parallel side walls and a bottom wall extending longitudinally from the central body portion along the end portion. In this embodiment, each of the parallel side walls comprises an outer side wall portion and an inner side wall portion. Each outer side wall portion extends longitudinally beyond an outer end of each inner said side wall portion and an outer end of the bottom wall. The parallel side walls and bottom wall form a slot having an open end adapted to receive a square or rectangular end of a rotatable shaft in the slot. The slot has an upper longitudinal opening between the upper edges of the side walls and a lower longitudinal opening between adjacent lower edges of the outer side wall portions that extend beyond the bottom wall. A plurality of connectors is provided for clamping the parallel side walls against the end of the rotatable shaft to secure the rotatable shaft in the slot. In some embodiments, each of the connectors may extend through mateably aligned holes in the upper portion of the side walls and a body portion of each connector may abut an upper surface of the end of the rotatable shaft. In other embodiments the linkage may be cylindrical. And in still further embodiments the central body portion of the linkage may be hollow. 

   
     DESCRIPTION OF THE DRAWINGS 
     Before explaining at least one embodiment in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. For example, all singular forms and the words “a,” “an,” and “the” include the plural reference unless expressly stated otherwise. 
       FIG. 1  illustrates an exemplary prior art rotating linkage with a single connecting rod for a three-phase circuit breaker. 
       FIG. 2  illustrates an alternate embodiment of  FIG. 1  in which three connecting rods are used. 
       FIG. 3  illustrates a prior art lever assembly for connecting a connecting rod to a rotating link member. 
       FIG. 4  is a perspective view of a coupling for connecting two rotatable shafts of a high voltage circuit breaker in end-to-end relationship. 
       FIG. 5  is a perspective view of the coupling of  FIG. 4  showing a rotatable shaft having a square end inserted in the coupling with bolts and nuts securing the end of the shaft in the coupling. 
       FIG. 6  is a top view of the coupling of  FIG. 4 . 
       FIG. 7  is an end view of the coupling in  FIG. 4 . 
       FIG. 8  is a half cross sectional view taken at VIII–VVII of  FIG. 7 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 4 and 5 , a linkage  70  for a high voltage circuit breaker comprises a central body portion  72  and opposed end portions  74  and  76 . Typically, a lever  78  is provided on central body portion  72  for connection to a connecting rod or other mechanical power output from an operating mechanism of the circuit breaker. The lever may be integral with the central body portion or separately attached. The lever may be centrally located along the length of the linkage or offset toward one end.  FIG. 5  shows a rotatable shaft  80  having a square end secured in end portion  74  of the linkage. Referring again to  FIG. 4 , each end portion of the linkage may have a pair of spaced side walls  84  and  86  and a bottom wall  88 . Each of the side walls may have a flange  90  and  92  extending outwardly for additional strength. A plurality of pairs of mateable holes  94 ,  96  and  98  are provided in the side walls for receiving connectors such as bolts, screws or other fastening devices.  FIG. 5  shows a plurality of high strength bolts  100  extending through the holes with each bolt having a nut  102  threaded on one end for securing the bolt. In some embodiments, a central body portion  104  of the bolts contacts an upper surface of the end of the shaft so as to act as a fourth wall of the joint to fully retain the shaft end in the linkage. 
   Referring to  FIG. 6 , an outer portion  106  of each side wall extends longitudinally beyond an outer end  108  of bottom wall  88  so that the outer portions of the side walls can be clamped together in spring-like fashion against the end of the rotatable shaft more easily than the inner portions  110  of the sidewalls. In this regard, at least one pair of mateable holes as described above is provided in the outer portion  106  of the sidewalls so that a connector can be inserted through the holes and secured so as to draw the outer portion of the sidewalls together against the end of the rotatable shaft. This spring-like connection acts to dampen and limit any harmful impacting in the cavity when rotational forces are reversed during high speed operation. It also keeps the joint tight and helps to prevent the bolts from loosening through many flexing cycles. 
   In some embodiments, the distance or lateral spacing between the outer portions  106  of the sidewalls is greater than the distance or lateral spacing between inner portions  110  of the sidewalls. For example, the distance between the outer portions  106  may be a first distance and the distance between the inner portions  110  may be a second distance so that the distance or spacing between the outer and inner portions decreases in step-like fashion. In other embodiments the distance between the sidewalls may be tapered from a distance greater at the outer end  112  of the sidewalls to a smaller distance between the inner end  114 . The step-like spacing may be easier and cheaper to manufacture than the tapered pacing. In both cases, the difference in spacing between the outer and inner ends of the sidewalls provides leeway for significant axial misalignment of the linkage and rotatable shaft which can change during shaft rotation. Also the stepped or tapered cavity forces the major loading to be in the inner portion of the linkage where it is the strongest and most rigid. 
   Referring to  FIGS. 6 ,  7  and  8 , a possible example of a linkage for a high voltage circuit breaker may be provided as follows: A cylindrical body of precipitation hardenable stainless steel, such as 17-4PH steel, is cast, heat treated and then machined. In  FIG. 8 , the central body portion  72  has an outer diameter  116  of about 5.75 inches and a hollow interior  118  so that the overall weight of the linkage may be reduced. In  FIG. 6 , outer portions  120  and  122  of the central body portion are machined to a diameter  124  of about 5.494 to about 5.497 inches in order to provide a smooth surface and a stop edge  126  for locating a reaction force control arm which is disclosed in a separate patent application of assignee filed on the same date as the present application. Referring to  FIGS. 6 and 8 , end portions  74  and  76  are machined to a diameter  128  of about 5.37 inches and have a length  130  of about 3 inches. Additional metal is removed by machining to form a slot between sidewalls  84  and  86  and bottom wall  88 . Referring to  FIG. 8 , the bottom wall  88  and the inner portions  110  of the sidewalls have a length  132  of about 1.40 inches. The outer portions  106  of the sidewalls have a length  134  of about 1.60 inches. The sidewalls have a thickness  136  of from about 0.592 to about 0.590 inches. The flanges  90  and  92  have a thickness  138  of about 0.5 inches. The outer portions of the sidewalls have a height  140  of about 2–4 inches. The tab created by  140  serves as a flexible member that bends around the end of  80  to form a tight but flexible end connection to adjust for size tolerances and to allow soft reversal loading of the shaft  80  in the linkage pocket. The depth  142  of the slot from the upper edge of the inner portion of the sidewalls to the upper or inner surface of the bottom wall is about 3.7 inches. The width  144  of the slot between outer portions  106  of the sidewalls is about 2.396 to about 2.4 inches and the width  145  of the slot between the inner portions  114  of the sidewalls is about 2.383 to about 2.386 inches in order to form a step-like shape in the slot. Three pairs of mateable holes  94 ,  96  and  98  ( FIG. 8 ) are drilled in each sidewall with the center of each hole spaced a distance  146  of about 1 inch from the center of each adjacent hole. The center of holes  94  and  96  are spaced a distance  148  of about 0.5 inches from each end of the sidewall. Connecting hardware (such as bolts) assembled through these holes may form a fourth wall to completely encompass the ends of the rotatable shaft  80 . Finally the center of each hole is spaced a distance  150  of about 1.420 to 1.425 inches from the lower edge of each sidewall. A hole  152  ( FIG. 7 ) of about 2.3 inches diameter is drilled or otherwise formed in each end of central body portion  72 . Opposed end surfaces  154  and  156  of central body portion  72  serve as a stop surfaces for properly locating the end of the rotatable shafts in the linkage. The overall length  158  of the linkage is about 15.75 inches. All sizes listed in this paragraph are merely exemplary. Other sizes and dimension ratios are possible depending on the desired application. 
   It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which are also intended to be encompassed by the following claims.