Patent Publication Number: US-2003231096-A1

Title: Adjustable thermal trip assembly for a circuit breaker

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to circuit breakers with a thermal trip assembly, and more particularly to an arrangement for adjustment of the current/time characteristic value at which the assembly responds.  
       [0003] 2. Background Information  
       [0004] It is common in the small circuit breakers used for residential and light commercial or industrial applications to utilize a bimetal to provide a delayed trip in response to persistent overload conditions. The heat generated by the overload condition causes the bimetal to deflect until it actuates a trip mechanism to interrupt the current. Thus, it is also known as a thermal trip. In some applications, it is desirable to allow the user to adjust the thermal trip function. Thus, it is known, for instance, to provide a slide which adjusts a gap between the deflecting bimetal and the trip mechanism. Such an arrangement is not always possible, as where the available location for the adjustment mechanism is substantially spaced from the bimetal within the molded housing of the circuit breaker.  
       [0005] There is need, therefore, for an improved adjustable thermal trip assembly for circuit breakers.  
       SUMMARY OF THE INVENTION  
       [0006] This need and others are satisfied by the invention, which is directed to an adjustable thermal trip assembly for a circuit breaker comprising a coupler that is adjustable to select the overload current/time characteristic value at which deflection of the free end of a bimetal actuates the trip mechanism of the circuit breaker. This adjustable coupler includes a first pivoted member, a second pivoted member and a coupling member adjustably positioned between the first and second pivoted members to convert pivoting of the first pivoted member by the free end of the bimetal into rotation of the second pivotal member to actuate the trip mechanism after a selected deflection of the free end of the bimetal and therefore in response to a selected current/time characteristic value. The first and second pivoted members can be pivoted about parallel pivot axes with the adjustable coupler including a positioner moving the coupling member selectively toward and away from the parallel pivot axes of the first and second pivot members. The parallel pivot axes of the first and second pivot members can comprise a common pivot axis with the first and second pivot members axially spaced along this common pivot axis. In this case, the coupling member extends axially parallel to the common pivot axis.  
       [0007] The positioner can comprise a rotatable member rotatable about a positioner axis parallel to but laterally displaced from the common pivot axis. In this case, the coupling member can have a mounting arm eccentrically engaging the rotatable member, whereby rotation of the rotatable member effects the movement of the coupling member toward and away from the common pivot axis of the first and second pivot members. This rotatable member can comprise a driven bevel gear in which case the positioner further includes a driving bevel gear meshing with the driven bevel gear and an adjustment knob coupled to the driving bevel gear. The adjustment knob can have an indexer setting discrete rotatable positions of the driving bevel gear and therefore the discrete current/time characteristic values at which the trip mechanism is actuated.  
       [0008] The invention is applicable to single-pole and multipole circuit breakers. In the latter case, where each of the plurality of poles has a bimetal, a first pivoted member mounted on the common pivot axis is associated with each bimetal and the coupling member couples the selected rotation of any of the first pivoted members by the associated bimetal into rotation of the second pivoted member, and therefore actuation of the trip mechanism at the selected current/time characteristic value.  
       [0009] In another embodiment of the invention adapted for use with a multipole circuit breaker each pole has an adjustable coupler with the rotatable member of the positioner of the adjustable coupler of all of the poles mounted on a common shaft rotatable about the positioner axis parallel to but laterally displaced from the common pivot axis. In this arrangement, the rotating member of the positioner of one of the poles can be a driven bevel gear which is engaged by a driving bevel gear that is rotated by an adjustment knob to effect rotation, and therefore, simultaneous adjustment of the current/time characteristic value at which the trip mechanism of each pole is actuated. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:  
     [0011]FIG. 1 is an elevation view of an adjustable thermal trip assembly for a circuit breaker in accordance with the invention.  
     [0012]FIG. 2 is an isometric view of a portion of the assembly shown in FIG. 1.  
     [0013]FIG. 3 is a fragmentary horizontal section through a portion of the circuit breaker casing.  
     [0014]FIG. 4 is a side elevation view of a multipole embodiment of the invention.  
     [0015]FIG. 5 is a side elevation view of another multipole embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0016]FIG. 1 illustrates an adjustable thermal trip assembly  1  of the invention mounted in the partially shown molded casing  3  of a circuit breaker. The adjustable thermal trip assembly  1  includes a bimetal  5  having a fixed end  7  and a free end  9 . As is well known in the art, current in the circuit being protected by the circuit breaker is either passed through the bimetal  5  or through a heater adjacent the bimetal  5 . In either case, the bimetal is heated by the load current, which in effect, provides an integration of the load current over time. This heating of the bimetal  5  causes the free end  7  to deflect, to the right as viewed in FIG. 1.  
     [0017] The adjustable thermal trip assembly  1  also includes a trip mechanism  11  which in this case has a trip bar  13 . In this known type of trip mechanism  11 , the free end  9  of the bimetal  5  couples directly to the trip bar  13  to actuate the trip mechanism  11  when the current/time characteristics of the load current is at a specified value. It is an object of the present invention to make the value of this current/time characteristic at which the trip mechanism  11  actuates adjustable, especially where the bimetal  5  and trip bar  13  are located in the circuit breaker at a distance from where an adjustment mechanism accessible from outside of the molded housing can be located. Thus, the invention includes an adjustable coupler  15  between the free end  9  of the bimetal  5  and the trip bar  13  of the trip mechanism  11 . This adjustable coupler  15  includes a first pivoted member  17  rotatably mounted on a shaft  19 . A second pivoted member  21  is mounted for separate rotation upon the shaft  19  which forms a common pivot axis  23  for the two pivoted members  17  and  21 . The pivoted members  17  and  21  each have a pair of arms  25  and  27  which form obtuse angles α and β, respectively, such that the arms of each of the pivoted members remains on the same side of the vertical as seen in FIG. 1.  
     [0018] The adjustable coupler  15  also includes a coupling member  29 . As can be appreciated by reference also to FIG. 2, this coupling member  29  extends axially parallel to but offset laterally from the common pivot axis  23  within the angle γ formed by the upper arms  25  and  27  of the pivoted members  17  and  21 . With this arrangement, when the bimetal  5  detects a persistent overload condition and the free end  9  deflects clockwise in FIG. 1, it engages a foot  31  on the lower arm  25  and rotates the first pivoted member  17  in the counterclockwise direction as seen in FIG. 1. This brings the upper arm  25  of the pivoted member  17  into contact with the coupling member  29  which is carried with the pivoted member  17  counterclockwise until it contacts the upper arm  27  to in turn rotate the second pivoted member  21  counterclockwise. A foot  33  on the lower arm  27  of the second pivoted member  21  engages a hook  35  on the trip bar  13 , thereby pulling the trip bar to the right and actuating the trip mechanism  11 .  
     [0019] The adjustable coupler  15  further includes a positioner  37  which moves the coupling member  29  toward and away from the common pivot axis  11  within the angle γ between the upper arms  25  and  27  of the first and second pivoted members  17  and  21 . As the lateral distance between these arms increases with distance from the common pivot axis  23 , it can be appreciated that increased deflection of the free end  9  of the bimetal  5  is required to actuate the trip mechanism as the coupling member  29  is moved further from the common pivot axis  23 . Thus, the current/time characteristic value at which the trip mechanism is actuated can be selectively varied by raising and lowering the coupling member  29 .  
     [0020] The positioner  37  includes a rotatable member in the form of a first bevel gear  39  which is mounted for rotation on a positioner shaft  41  which is parallel to but laterally separated from the common pivot axis  23 . The coupling member  29  has a mounting arm  43  having a terminal section  45  which is parallel to the coupling member  29 . This terminal section  45  of the mounting arm is rotatably received in an opening  47  in the bevel gear  39  which is eccentric to the gear shaft  41 . Thus, rotation of the first bevel gear in the clockwise direction moves the coupling member  29  toward the common axis  23  to reduce the amount of bimetal deflection, and therefore lowers the current/time characteristic value, required to actuate the trip mechanism. Conversely, counterclockwise rotation of the first bevel gear  39  raises the coupling member  29  and increases the current/time characteristic value for trip mechanism actuation.  
     [0021] The positioner  37  further includes a driving bevel gear  49  which meshes with the first or driven bevel gear  39  and is mounted for rotation about a vertical axis in a slot  51  in the molded casing  3 . An adjustment knob  53  has a shaft  55  which is keyed to and is axially slidable within a bore  57  in the driving bevel gear  49 . An indexer  59  on the adjustment knob  53  has a number of peripheral flats  61 . A locking spring  63  bearing against the driving bevel gear  49  biases the indexer  59  upward toward a slot  65 . However, as shown in FIG. 3, the slot  65  is sized such that the indexer  59  can only enter the slot  65  when the flats  61  are aligned with the sides of the slot  65 . This locks the adjustment knob  53  and, in turn, the position of the coupling member  29  relative to the common axis  23  in one of a plurality of discrete positions. In order to select between these discrete positions, the adjustment knob  53  is pushed downward against the bias of the locking spring  63  until the indexer  59  is aligned with a wider slot  67  in which it can be rotated between the discrete positions, as shown in phantom in FIG. 3. When the indexer is aligned with another discrete position, release of the adjustment knob  53  allows the locking spring  63  to seat the indexer in the slot  65 .  
     [0022] The adjustable thermal trip assembly  1  of the invention can be applied to multipole circuit breakers as shown in FIG. 4. This circuit breaker has three poles  69   1 - 69   3 , each with a bimetal  5   1 - 5   3 . In this arrangement, a separate first pivoted member  17   1 - 17   3  associated with one of the three bimetals  5   1 - 5   3 , respectively, is separately pivotally mounted on the shaft  19  for rotation about the common axis  23 . A single second pivoted member  21  is also mounted on the shaft  19  for rotation about the common pivot axis  23 . The coupling member  29 ′ is lengthened so that it is engageable by each of the first pivoted members  17   1 - 17   3  and also engages the single second pivoted member  21 . Thus, an overload in any one of the poles will rotate the associated first pivot member  17   1 - 17   3  to engage the coupling member  29 ′, which couples the bimetal deflection to rotation of the single second pivoted member  21  to actuate the trip mechanism. A common positioner  37  adjusts the current/time characteristic value for actuation of the trip mechanism for all three poles simultaneously by raising and lowering the coupling member  29 ′.  
     [0023]FIG. 5 illustrates another multipole embodiment of the invention. Each pole  69   1 ,  69   2  and  69   3  has its own adjustable coupler  15   1 ,  15   2  and  15   3 . Each of these adjustable couplers  15   1 ,  15   2  and  15   3  has its own first pivoted member  17   1 ,  17   2 , and  17   3 , and its own second pivoted member  21   1 ,  21   2  and  21   3  mounted on a common shaft  19   1 ,  19   2  and  19   3 . Each also has its own coupling member  29   1 ,  29   2  and  29   3  with a mounting arm  41   1 ,  41   2  and  41   3  eccentrically mounted on a rotating member  39   1 ,  39   2  and  39   3 . The rotating members  39   1 ,  39   2  and  39   3  are all mounted for simultaneous rotation on common positioner shaft  41  which is parallel to but also laterally spaced from the shafts  19   1 ,  19   2  and  19   3 . One of the rotating members, for instance,  39   1  is a driven bevel gear which meshes with the driving bevel gear  49 . As described in connection with FIG. 1, the driving bevel gear  49  can be rotated by the adjustment knob  53 . The rotating members  39   2  and  39   3  do not have to be bevel gears, although the number of different parts is reduced when they are bevel gears as shown in FIG. 5. With the arrangement of FIG. 5, rotation of the adjustment knob  53 , effects adjustment of the positions of the coupling members  29   1 ,  29   2  and  29   3  to adjust the current/time characteristics at which the trip mechanism for each of the poles is actuated.  
     [0024] While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.