Abstract:
An adjustable magnetic trip device for a molded case circuit breaker is provided where the trip device includes a plunger and a stationary core as well as a plunger support structure with a movable plunger carriage. The position of the plunger assembly and carriage relative to the stationary core is determined by a cam assembly having a body with a plurality of sections, each section having a different radius. The plunger carriage is responsive to rotation of said cam assembly and may be adjusted by rotating the cam. The over-current condition for the trip device is a function of the distance between the plunger assembly and the stationary core. Accordingly, the over-current condition may be changed by rotating the cam. As each section of the cam has a constant radius, the over-current condition remains the same no matter where the carriage contacts a certain section of the cam.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a circuit breaker with an adjustable magnetic trip device having a movable core and a stationary core and, more specifically, to a cam and axle which maintains each moveable core of a multi-core trip device at a consistent gap from an associated stationary core. 
     2. Description of the Prior Art 
     Molded case circuit breakers are well known in the art as exemplified by 5,927,484 issued Jul. 27, 1999 to Malingowski et al., U.S. Pat. No. 5,831,501 issued Nov. 3, 1998 to Kolberg et al., and by U.S. Pat. No. 4,503,408 issued Mar. 5,1985 to Mrenna et. al., entitled “Molded Case of Circuit Apparatus Having Trip Bar With Flexible Armature Interconnection” assigned to the assignee of the present application. The foregoing are incorporated herein by reference. 
     In molded case circuit breakers in which the power contacts, operating mechanism, and trip unit are mounted inside of a molded plastic insulative housing, a common type of magnetic trip device is a solenoid which includes a stationary core through which the current in the protected circuit is passed. The current passing through the stationary core creates a magnetic field. When there a very high instantaneous currents, such as those associated with a short circuit, the magnetic field intensifies. A plunger assembly, having a moveable core and a plunger tab which engages the trip latch on the operating mechanism, is partially disposed within the stationary core. Typically, a spring provides a limited force biasing the movable core away from the stationary core and preventing the plunger from engaging the trip latch. The force of the spring is overcome by the magnetic field generated by the stationary core during a short circuit. That is, when a short circuit occurs, the current in the stationary core creates a magnetic field strong enough to overcome the moveable core spring thereby allowing the moveable core to move toward the stationary core and causing the plunger to engage the trip latch. 
     The amount of current required to trip the device can be controlled by adjusting the amount of separation between the plunger assembly and stationary core. When the plunger assembly is located closer to the stationary core, a weaker magnetic field, and therefore a lower current, is required to draw the plunger assembly toward the stationary core to trip the device. In order to adjust the trip condition, the plunger assembly is mounted in a plunger assembly support structure having a base and a moveable plunger carriage. The carriage allows the plunger assembly, including the moveable core, to be moved relative to the stationary core. A carriage is used so that adjusting the gap between the moveable core and the stationary core does not impact on the compression of the moveable core biasing spring. The moveable plunger carriage is coupled to an adjustment device to address the initial gap between the plunger assembly and the stationary core. 
     As disclosed in Malingowski and Kolberg, prior art adjustment devices included adjustment means such as a cam or a rotatable disk having an angled surface. As these adjustment means are rotated, the trip condition is constantly changed, not unlike an analog device. That is, for every point for which the adjustment means is rotated, the moveable carriage and plunger assembly are moved toward or away from the stationary core, changing the amount of separation between the stationary and moveable cores. This is a disadvantage as users typically want the trip condition set to coincide with a discrete over-current condition. Because the adjustment means of the prior art change the trip condition for each point of rotation, it is difficult to set the trip device to trip at a precise over-current condition. For example, if the adjustment means is coupled to a wheel having a visual indication of various trip conditions and a pointer on the housing of the molded case circuit breaker where the user adjusts the wheel to adjust the trip condition, a user would have to set the wheel to be precisely aligned with, not slightly above or below, the visual indication in order for the trip device to be set at the indicated trip condition. 
     In a circuit breaker, such as a three phase breaker, having multiple main contacts, and therefore multiple adjustment means, an adjustment device having a smooth transition between various trip conditions is unlikely to place each movable core at the same degree of separation from the associated stationary core. Thus, if each adjustment means of a multiple main contact device is set slightly differently, the breaker will not be set to trip at a precise over-current condition. Additionally, such multiple unit trip devices are typically connected by an extended camshaft. Such a camshaft is subject to flexing which allows each cam to be set at a slightly different angle, and therefore, at a slightly different trip condition. Additionally, variations in the components during manufacture may result in a misalignment between the various trip units. 
     There is a need, therefore, for a molded case circuit breaker magnetic trip mechanism which sets the trip condition at a precise trip condition regardless of slight variation of the adjustment means. 
     There is a further need for a molded case circuit breaker magnetic trip mechanism which consistently sets the over-current condition for multiple main contacts within the circuit breaker. 
     There is a further need for a molded case circuit breaker magnetic trip mechanism which accommodates variations within the manufacturing tolerances of the trip mechanism components. 
     SUMMARY OF THE INVENTION 
     These needs and others are satisfied by the invention which provides magnetic trip adjustment scheme having a plunger assembly carriage coupled to a cam with a plurality of sections, each section having a constant radius. Thus, the plunger assembly carriage is maintained at a specific location so long as it is contacting the cam anywhere on a certain section. Where the circuit breaker has multiple main contacts, alignment of the magnetic trip units are maintained by a camshaft having an elongated coupling and crush ribs. 
     A molded case circuit breaker includes at least one pair of separable main contacts. The main contacts are disposed in the circuit breaker housing. The circuit breaker may be tripped manually by a handle or by a magnetic trip device. The magnetic trip device includes a rotating trip bar, a plunger assembly which includes a moveable core, and a stationary core. The stationary core is in electrical communication with the load side of the breaker. As electricity flows through the stationary core, a magnetic field is created. When an over-current condition occurs, the magnetic field intensifies, attracting the movable core of the plunger assembly. The plunger assembly includes a tab which contacts the rotating trip bar. When an over-current condition occurs and draws the moveable core towards the stationary core, the plunger tab causes the trip bar to rotate which in turn trips the breaker. 
     The plunger assembly is mounted in a moveable carriage which is responsive to a cam. By moving the carriage, the plunger assembly can be positioned closer to or further from the stationary core. When the plunger is closer to the stationary core, the magnetic force has a greater attracting effect. Thus, the over-current condition can be changed by moving the position of the plunger assembly relative to the stationary core. The cam, which positions the plunger carriage, is shaped to have a plurality of sections each with a specific constant radius. Each section positions the plunger assembly a specific distance from the stationary core. Each distance is associated with a specific and discrete over-current condition. The cam is coupled to a control mechanism, such as a wheel having a visual indication of the trip condition. Because the cam sections have a constant radius, a user does not have to set the control mechanism precisely. So long as the contact point between the moveable carriage and the cam is on the appropriate section of the cam, the carriage will be set to the indicated trip condition. 
     Additionally, when a circuit breaker has multiple main contacts, and therefore, multiple trip mechanisms, alignment between the trip mechanisms is more easily achieved by virtue of the cams with constant radius sections. This is because, even if the cams were at slightly different angles, the constant radius sections will maintain each carriage at the same distance from the stationary core. Thus, each unit will be set to trip at the same over-current condition. Additionally, when a trip mechanism has multiple units connected by an extended camshaft, this invention provides a camshaft which resists flexing so that each cam is angularly aligned. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a partial cut away view of a circuit breaker housing incorporating the plunger carriage according to the present invention. 
     FIG. 2 is an isometric view of a circuit breaker with the top covers and plunger carriages removed. 
     FIG. 3 is an isometric view of the circuit breaker mechanism without the circuit breaker housing. 
     FIG. 4 is a perspective view of a plurality of plunger carriage support structure according to the present invention. 
     FIG. 5 is a cross sectional view of a cam assembly according to the present invention. 
     FIG. 6 is an isometric view of a two-part camshaft. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, FIG. 1 shows a molded case circuit breaker  10  according to a preferred embodiment of the present invention. The molded case circuit breaker has a housing  11 , which includes a base portion  12  which is coupled to a primary cover  14 . Base portion  12  includes a plurality of cavities  13  which support the circuit breaker components (described below). Disposed on top of primary cover  14  is a secondary cover  16 . An operating handle  18  protrudes through secondary cover  16 . As shown in FIGS. 2 and 3, at least one pair of main contacts  2  are disposed within housing  11 . The contacts include a moveable contact  2 , and a stationary contact  4 . The movable contact  2  is coupled to and is in electrical communication with the load side of the circuit breaker  10 . The stationary contact  4  is coupled to and is in electrical communication with an electrical line (not shown). Handle  18  is coupled to a moveable contact  2  within the circuit breaker housing  11 . Handle  18  may be used to reset the circuit breaker  10  after it has been tripped or may be used to manually open and close the circuit breaker  10 . 
     As shown in FIG. 1, the circuit breaker  10  may be tripped by a separate magnetic trip assembly  20 . The magnetic trip assembly  20  cooperates with a rotating trip bar  21 , which is coupled to a latchable operating mechanism  24 . As is known in the prior art, rotation of trip bar  21  will release the latchable operating mechanism  24  (FIGS. 2 and 3) allowing the circuit breaker  10  to trip. The trip bar  21  includes at least one actuating arm  26 , which is adjacent to the magnetic trip assembly  20 . 
     The magnetic trip assembly  20  includes a stationary core  22  (FIGS.  2  and  3 ), a plunger assembly  28  (FIG. 1) and a plunger assembly support structure  50 . Stationary core  22  is disposed within a cavity  13  in the bottom housing  12 . The stationary core  22  is preferably shaped as a coil. The stationary core  22  includes a medial aperture  25 , preferably having a circular cross-section. The stationary core  22  is disposed between the moveable main contact  2  and a load-side collar (not shown). The load-side collar is in electrical communication with the electricity consuming load. When electricity flows through the stationary core  22  a magnetic field generating a magnetic force is created. 
     FIG. 4 shows a plurality of plunger assembly support structures  50  linked to each other by cam shaft  200 . For ease of identification, certain components are identified in the figure on separate units, however, it is understood each unit includes each identified component. Plunger assembly  28  includes a moveable core  30 , a coil spring  34  and a plunger tab  36 . The moveable core includes a flattened end  31 . As shown on FIGS. 2 and 3, the plunger assembly  28  is disposed within cavity  88  of plunger assembly support structure  50  (described below). One end of coil spring  34  contacts flattened end  31  while the other end contacts the support structure  50 . Plunger tab  36  is positioned adjacent to actuating arm  26  of the trip bar  21  (FIG.  2 ). 
     The strength of the magnetic force, which changes in relation to the amount of current through stationary core  22 , necessary acting on the plunger assembly  28  is a function the distance between the stationary core  22  and the moveable core  30 . Accordingly, the over-current situation for breaker  10  may be adjusted by moving the moveable core  30  closer or further from the stationary core  22 . When the moveable core  30  is closer to stationary core  22 , the strength of the magnetic force, and therefore the amount of current through stationary core  22 , required to overcome the bias of coil spring  34  is reduced as compared to the magnetic force, and therefore current through stationary core  22 , required to overcome the bias of coil spring  34  when moveable core  30  is further from stationary core  22 . The plunger carriage assembly  54 , which supports the plunger assembly  28  and moveable core  30 , is slidably disposed adjacent to base member assembly  52  to accomplish this adjustment. 
     In operation, plunger assembly support structure  50  may be coupled to the circuit breaker housing  11  in a base portion cavity  13 . Tab  60  cooperates with cavity  13  to position plunger assembly support structure  50  so that the end of moveable core  30  opposite flattened end  31  is partially disposed in stationary core aperture  25 . When so disposed, the magnetic force generated by electric current through stationary core  22  acts on moveable core  30  of plunger assembly  28 , as explained above. Additionally, when plunger assembly support structure  50  is coupled to cavity  13 , plunger tab  36  is positioned adjacent to trip bar actuating arm  26 . Under normal operating conditions, coil spring  34  overcomes the magnetic force created by the electric current through stationary core  22  and biases flattened end  31  of moveable core away from plunger carriage bottom member  86  and stationary coil  22 . The biasing force of coil spring  34  also prevents plunger tab  36  from engaging trip bar actuating arm  26 . 
     When an over-current situation occurs, however, the magnetic force created by the current through stationary core  22  increases in strength. When the magnetic force becomes strong enough to overcome the bias of coil spring  34 , the plunger assembly  28  is drawn towards stationary core  22 . As the plunger assembly  28  is drawn towards stationary core  22 , plunger tab  36  engages trip bar actuating arm  26  causing the trip bar  21  to rotate. When trip bar  21  rotates, latchable operating mechanism  24  is released allowing the circuit breaker  10  to trip. 
     The distance of separation between the plunger assembly  28  and the stationary core  22  is controlled by cam assembly  150 . As shown in FIG. 5, cam assembly  150  includes a central axis  151  and a generally circular body  152  having a medial opening  153  and plurality of sections  154 . Each section  154  has an arcuate outer surface  156 . Each arcuate outer surface  156  has a constant radius which is centered about axis  151 . Each arcuate outer surface  156  has a different radius from the adjacent arcuate outer surfaces  156 . Between each constant radius section is a transition area  155 . In a preferred embodiment, cam assembly  150  includes a minimum radius section  160 , having a first side  162  and a second side  164 , and a maximum radius section  170 , having a first side  172  and a second side  174 . The minimum radius section first side  162  is adjacent to the maximum radius section second side  174 . The remaining plurality of sections  154  are disposed about generally circular body  152  between the minimum radius section second side  164  and the maximum radius section first side  172 . In a more preferred embodiment, each section  154  increases in radius between the minimum radius section second side  164  and the maximum radius section first side  172 . Minimum radius section  160  may be integral to a camshaft  200  passing through medial opening  153 . 
     As shown in FIG. 4, the plunger assembly support assembly  50  includes a base member assembly  52  and a plunger carriage assembly  54 . The plunger assembly  28  is disposed within the plunger carriage assembly  54 . The plunger carriage assembly  54  is slidably disposed adjacent to the base member assembly  52 . The plunger carriage assembly  54  is slidable so that the distance between the moveable core  30  and the stationary core  22 , and therefore the trip condition of the circuit breaker  10 , may be selectively adjusted. 
     Base member assembly  52  includes a mounting tab  60 , a body  62  having a front face  64  and a camshaft nest  74 . Cam shaft nest  74  includes two spaced apart tabs  78 ,  79 . Each tab  78 ,  79  includes a rounded cutout shaped to engage camshaft  200 . The base member  52  further includes a plurality of guides  70  extending from the body front face  64 . The guides  70  are spaced to fit on either side of the plunger carriage assembly  54  (described below). The guides  70  are positioned so that at least two guides  70  are on one side of plunger carriage assembly  54 , and at least one guide  70  is on the opposite side of plunger carriage assembly  54 . Body  62  further includes a spring housing  72  extending from the body front face  64 . Any of the guides  70  or spring housing  72  may include guide grooves  76  shaped to cooperate with an alignment ridge  102  (described below). The body  62  also includes a camshaft nest  74 . 
     The plunger carriage assembly  54  includes a first side member  80  and a second side member  82 . The first side member  80  and the second side member  82  are held in spaced relation by a top member  84  and a bottom member  86 . An open-faced cavity  88  is formed between the first side member  80  and the second side member  82 . Both the first side member  80  and the second side member  82  each have an interior side  90 ,  92  and an exterior side  94 ,  96  respectively. The first side member exterior side  94  includes a spring tab  100  extending therefrom. The first side member exterior side  94  has an alignment ridge  102 . The second side member exterior side  96  also has an alignment ridge (not shown). Top member  84  includes a cam follower  85 . 
     As noted above, the plunger carriage assembly  54  is slidably disposed adjacent to base member assembly  52 . The plunger carriage assembly  54  is slidable between a first and second position. The carriage assembly  54  is movable in response to an over-current condition or in response to rotation of the cam assembly  150 . When assembled, as shown in FIG. 4, with plunger carriage  54  between guides  70  on base member  52 , cam nest  74  and top member  84  are adjacent to each other with cam follower  85  aligned with the space between tabs  78 ,  79 . A spring member  110  may be disposed between the spring housing  72  and spring tab  100 . Cam assembly  150  is rotatably disposed between tabs  78 ,  79  with camshaft  200  resting in cutouts  77 . Spring member  110  acts on carriage  54  so that cam follower  85  is biased against cam assembly  150  and, more specifically, outer surface  156 . Thus, because each cam section  154  has a different constant radius, plunger carriage assembly  54  may move specific distances relative to base member  52  as cam assembly  150  is rotated. 
     As noted above, the plunger carriage assembly  54  is slidably disposed adjacent to base member assembly  52 . The carriage assembly  54  is movable in response to an over-current condition and in response to rotation of the cam assembly  150 . When assembled, as shown in FIG. 2, with plunger carriage assembly  54  between guides  70  on base member assembly  52 , cam nest  74  and top member  84  are adjacent to each other with cam follower  85  aligned with the space between tabs  78 ,  79 . Cam assembly  150  is rotatably disposed between tabs  78 ,  79  with camshaft  200  resting in cutouts  77 . Spring  110  biases plunger carriage  54  so that cam follower  85  contacts cam assembly  150 . Thus, when cam assembly  150  rotates, cam follower  85  contacts the outer surface  156  of the various cam sections  154 . Because each cam section  154  has a different radius, the plunger carriage assembly  54  moves relative to the base member assembly  52  as cam assembly  150  is rotated. Thus, the trip condition may be selectively controlled by rotating cam assembly  150  to adjust the separation between the stationary core  22  and the plunger assembly  28 . 
     As shown in FIG. 4 cam assembly  150  may be coupled to an adjusting gear  210 . Adjusting gear  210  may be mounted on camshaft  200 . Adjusting gear  210  includes a plurality of teeth  211 . As shown in FIGS. 1 and 3, adjusting gear  210  is coupled to an adjusting means such as wheel  214 . Wheel  214  includes teeth  215  which may be coupled with adjusting gear teeth  211 . Wheel  214  is mounted in housing  11  with a portion of wheel  214  visible through secondary cover  16 . Wheel  214  may also include indicia, such as numbering or lettering. When circuit breaker  10  is assembled, wheel teeth  215  mesh with adjusting gear teeth  211  so that rotating wheel  214  causes cam assembly  150  to rotate. In this configuration, the adjusting means can be structured so that an indicia on wheel  214  is associated with cam assembly  150  being in a certain position and plunger assembly  54  being a certain distance from stationary core  22 . Thus, the indicia on wheel  214  can be associated with various trip conditions. 
     A plurality of plunger assembly support structures  50  may be assembled in series to cooperate with a circuit breaker which has more than one set of main contacts. As shown in FIG. 6, in such a multiple unit configuration, the plunger assembly support structures  50  are coupled by an extended camshaft  201 . Such an extended camshaft  201  may be formed integrally, however, in the preferred embodiment, the extended camshaft  201  is formed of two pieces, a base unit  202  and an extension  203 . The base unit  202  preferably includes one cam assembly  150 , a camshaft  200 , an adjusting gear  210 , and an elongated recess  204 . Elongated recess  204  is preferably a semi-circular recess, however, any shape may be used. Extension  203  includes a camshaft  200 , a plurality of cams  150  and a mating end  205 . Mating end  205  includes an extended tab  206  shaped to fit in elongated recess. A plurality of crush ribs  207  are disposed about extended tab  206 . The crush ribs  207  are raised ridges extending axially along tab  206 . The crush ribs ensure that tab  206  will be frictionally held in elongated recess  204 . 
     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 a disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.