Abstract:
The present disclosure describes an apparatus for increasing the initial closing force and reducing the final closing force in the actuating mechanism of electromechanical switching devices such as relays or contactors.

Description:
BACKGROUND 
       [0001]    The invention relates generally to electromechanical switching devices such as relays or contactors. More particularly the invention relates to the armature or stator that is a part of the actuating mechanism. 
         [0002]    Among the various mechanisms used to mechanically actuate electromechanical switching devices such as relays or contactors a commonly used form is the clapper mechanism. The clapper mechanism is named as it functions in a manner similar to that of clapping hands. One hand is movable and is called the armature. The armature is drawn by magnetic force to the second hand which is stationary and is referred to as the stator or core. An electromagnetic field is induced into the stator through the use of a coil that can be excited by either direct current (DC) or alternating current (AC). Application of a voltage to the coil will result in an electromagnetic field being induced in the stator which will attract the armature as the armature is comprised of a ferromagnetic material. As the armature is attracted to the stator it moves to the closed state for the device and actuates a mechanism which opens and closes electrical contacts in the electromechanical switching device. Removal of the voltage to the coil results in the loss of the electromagnetic field of the stator and the armature will move away from the stator under the influence of a return mechanism, usually comprised of a spring or other tension providing device, until it comes to rest in what is known as the open state. It is important to note that for the purposes of this disclosure the words “open” and “closed” refer to the state of the actuating mechanism for the device. Open being when the coil is de-energized and closed being when the coil is energized. Another usage for the terms “open” and “closed” is in relation to the electrical contacts that are operated by the clapper mechanism where the electrical contacts being controlled are commonly referred to as either Normally Open (NO) or Normally Closed (NC). For the purposes of this disclosure “open” and “closed” will refer to the state of the clapper mechanism, not the electrical contacts that may be controlled by the device. 
         [0003]    Clapper mechanisms are designed with planar armature plates and planar stator cores that move about a fixed fulcrum point on the bottom of the armature plate. Upon energizing the coil, an electromagnetic field is created in the stator, and the armature is attracted to the stator and moves toward it until it comes to rest upon contacting the face of the stator. The armature is held in this position by electromagnetic force until such time when the coil is de-energized at which point the electromagnetic field collapses and the armature returns to the open state under the influence of the return mechanism. 
         [0004]    In the art, the voltage at which the coil is energized is referred to as the “pull-in” voltage and the voltage at which the coil is de-energized is referred to as the “drop-out” voltage. Recall that the coil voltage induces an electromagnetic field in the coil and in turn the stator, thus below the pull-in voltage the electromagnetic field is insufficient to overcome the mass, friction, and return mechanism of the armature and move it into the closed position. At or above the pull-in voltage there will be sufficient electromagnetic field to overcome these elements and the clapper armature will be moved to the closed state. Conversely, in order to return the clapper mechanism to the open state the electromagnetic field must decrease to a point at which it can be overcome by the return mechanism and thus move the armature away from the stator pole face to the open position. 
         [0005]    In the open position the planar armature is positioned with an inclination of a few degrees in relation to the flat pole face of the stator or core. This relationship describes a triangular shaped volume of air and defines the amount of travel required to close the clapper mechanism. Due to the size of the volume of air in the case where both the armature and stator have a planar face, the pull-in voltage must be high enough to generate an electromagnetic field sufficient to initiate the closing of the mechanism. The magnetic field starts out relatively weak though sufficient to initiate movement so the initial closing force is relatively low. However, as the armature moves toward the flat pole face of the stator the magnetic field rapidly increases and in turn the closing force until the armature contacts the pole face of the stator in the closed position. A problem with typical planar faced armature and stator embodiments is that this rapid increase of closing force overshoots the level required to close the clapper mechanism resulting in undesired wear and a decrease in the mechanical life of the device. 
         [0006]    When the clapper mechanism is closed the magnetic field is at its strongest. Unfortunately the strength of the magnetic field in the closed state requires the drop-out voltage of the coil to fall to a very low level in order to allow the return mechanism to overcome the electromagnetic field and move the armature to the open state. The longer it takes for the coil to become de-energized the longer an electrical circuit that is being controlled by the contacts associated with the electromechanical switching device remain energized consequently presenting a potentially hazardous state to people or devices in addition to decreasing the service life of the device due to longer arcing times until the clapper mechanism moves to the open state and in turn de-energizes any circuits associated with the electromechanical switching device. 
         [0007]    Thus there remains a need to increase the drop-out voltage within the tolerance band given by the relevant product standards in order to increase the speed at which a controlled circuit is de-energized improving safety while simultaneously decreasing the pull-in voltage resulting in a longer service life for these devices. 
       BRIEF DESCRIPTION 
       [0008]    The embodiments in the present disclosure provide a novel technique for increasing the force between the armature and the core of an electromechanical switching device resulting in the reduction of the required pull-in voltage. Additionally the remnant or holding force of the closed armature is reduced which results in increased dropout voltage allowing the electromechanical switching device to open more quickly when the control voltage has been removed. 
     
    
     
       DRAWINGS 
         [0009]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0010]      FIG. 1  is a perspective view of an electromechanical switching device, in this case a contactor; 
           [0011]      FIG. 2  is an exploded perspective drawing of the contactor of  FIG. 1 ; 
           [0012]      FIG. 3A  is a bottom view of the upper housing of the contactor of  FIG. 1  showing the contactor in a de-energized state; 
           [0013]      FIG. 3B  is a bottom view of the upper housing of the contactor of  FIG. 1  showing the contactor in an energized state; 
           [0014]      FIG. 4A  is a front view of an armature with a radius embodiment of the pole face; 
           [0015]      FIG. 4B  is a side view of an armature with a radius embodiment of the pole face; 
           [0016]      FIG. 4C  is a perspective view of an armature with a radius embodiment of the pole face; 
           [0017]      FIG. 4D  is a detail view of the pole face of an armature with a radius embodiment of the pole face; 
           [0018]      FIG. 5A  is a sectional side view of the contactor of  FIG. 1  showing the armature of  FIG. 4A-4D  with a radius embodiment of the pole face in its location in the contactor oriented in the de-energized state; 
           [0019]      FIG. 5B  is a sectional side view of the contactor of  FIG. 1  showing the armature of  FIG. 4A-4D  with a radius embodiment of the pole face in its location in the contactor oriented in the energized state; 
           [0020]      FIG. 5C  is a detail of the sectional side view of  FIG. 6A  showing a radius embodiment of the pole face of the armature of  FIG. 4A-4D  in the de-energized state; 
           [0021]      FIG. 5D  is a detail of the sectional side view of  FIG. 6B  showing a radius embodiment of the pole face of the armature of  FIG. 4A-4D  in the energized state; 
           [0022]      FIG. 6A  is a front view of an armature with an involute embodiment of the pole face; 
           [0023]      FIG. 6B  is a side view of an armature with an involute embodiment of the pole face; 
           [0024]      FIG. 6C  is a perspective view of an armature with an involute embodiment of the pole face; 
           [0025]      FIG. 6D  is a detail view of the pole face of an armature with an involute embodiment of the pole face; 
           [0026]      FIG. 7A  is a sectional side view of the contactor of  FIG. 1  showing the armature of  FIG. 6A-6D  with an involute embodiment of the pole face in its location in the contactor oriented in the de-energized state; 
           [0027]      FIG. 7B  is a sectional side view of the contactor of  FIG. 1  showing the armature of  FIG. 6A-6D  with an involute embodiment of the pole face in its location in the contactor oriented in the energized state; 
           [0028]      FIG. 7C  is a detail of the sectional side view of  FIG. 7A  showing an involute pole face of the armature of  FIG. 6A-6D  in the de-energized state; and 
           [0029]      FIG. 7D  is a detail of the sectional side view of  FIG. 7A  showing an involute pole face of the armature of  FIG. 6A-6D  in the energized state. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Turning now to the drawings, and referring to  FIG. 1 , a circuit interrupting device is illustrated in the form of a three-pole contactor  10  for controlling electrical current carrying paths for three separate circuits. The contactor  10  includes an upper housing  12  and a lower housing  14 . Upper housing  12  hosts one or more sets of electrically isolated contacts contained within the assembly. Line terminals  22  are used to connect line input wires  16  to each contact set. Load terminals  24  are used to connect contact outputs to the load output wires  18 . Also included are coil terminals  26  for the connection of the wires  20  that provide the electrical connection for the application of the control voltage to the stator coil  32  illustrated in  FIG. 2 . 
         [0031]    An exploded perspective view of the contactor  10  is provided in  FIG. 2 . Upper housing  12  comprises a cover  44 , a set of line terminals with fixed contacts  50  and associated line terminal block screws  46 , a set of load terminals with fixed contacts  52  and associated load terminal block screws  48 , a set of auxiliary terminals and fixed contacts  56  and associated auxiliary terminal block screws  54  all of which are contained within the contact housing  42 . Contact housing  42  provides electrical isolation between individual terminals and contacts. Crossbar assembly  34  is transversely oriented on an axis perpendicular to that of the axis formed by the line terminals with fixed contacts  50 , the load terminals with fixed contacts  52 , and the auxiliary terminals with fixed contacts  56  such that lateral movement of crossbar assembly  34  will complete electrical circuits by the movement of moveable line contacts  72 , moveable load contacts, and moveable auxiliary contacts  74  into contact with their associated fixed contacts. Return spring  36  will return contact assembly  34  and associated moveable contacts to the open state in turn opening the associated electrical circuits. 
         [0032]    Continuing in reference to  FIG. 2 , lower housing  14  comprises middle plate  40  which is positioned below contact housing  42  and crossbar assembly  34  and provides arc containment and electrical isolation to stator coil  32  and stator core  30 . Stator core  30  is inserted into stator coil slot  68  of stator coil  32  and in turn lower housing  14 . Armature  62  is positioned in lower housing  14  in free supported relation to the lower stator core face  58  and upper stator core face  60 . Stator coil  32  comprises a set of electrical windings whose ends are connected to coil terminals  26  such that the connection of an electrical current to coil terminals  26  energizes stator coil  32  and causes the formation of an electromagnetic field which is concentrated by stator core  30 . The electromagnetic attraction of the stator core  30  results in a rolling movement having a shifting center point of armature  62  towards stator core  30 . Movement of armature  62  causes movement of crossbar assembly  34  by the engagement of crossbar engagement arm  64  with actuator slot  38  of crossbar assembly  34  completing electrical circuits by the movement of moveable line contacts  72 , moveable load contacts  70 , and moveable auxiliary contacts  74  into contact with their associated fixed contacts. The removal of electrical current from coil terminals  26  de-energizes stator coil  32  causing the collapse of the electromagnetic field in stator coil  32  and stator core  30  and with the loss of the electromagnetic field, the loss of the associated attraction of armature  62 , and thus crossbar assembly  34  is returned to its de-energized state by return spring  36 . Lower housing  14  has a generally rectangular base providing a slot  28  therein for receiving a standard DIN rail along the transverse axis generally within the plane of the base. Upon assembly, upper housing  12  and lower housing  14  and associated elements are fastened together by closure ring  76  which is positioned between upper catch  78  and lower catch  80 . 
         [0033]    Turning to  FIG. 3A  and  FIG. 3B , bottom views of the upper housing  12  of the contactor of  FIG. 1  are shown depicting the contactor in a de-energized state in  FIG. 3A  and an energized state in  FIG. 3B . As described in  FIG. 2 , energizing stator coil  32  and the associated electromagnetic field formed by stator core  30  results in the movement of armature  62  and crossbar engagement arm  64  which is engaged with actuator slot  38  of crossbar assembly  34  causing its subsequent motion and the completion of electrical circuits by the movement of moveable line contacts  72 , moveable load contacts  70 , and moveable auxiliary contacts  74  into contact with their associated fixed contacts, line terminal block and contact  50 , load terminal block and contact  52 , and auxiliary terminal block and contact  56 . Upon removal of the electrical current from coil terminals  26  and the loss of the electromagnetic field of stator coil  32  and stator core  30 , return spring  36  returns crossbar assembly  34  and armature  62  to a de-energized state. 
         [0034]    Given the interest in increasing the drop-out voltage in order to increase the speed at which a controlled circuit is de-energized in order to improve safety while simultaneously decreasing the pull-in voltage resulting in a longer service life for circuit interrupting devices,  FIG. 4A  through  FIG. 4D  depict various views of an embodiment of the invention in which, armature  62 A has a radius pole face  82 . Adding a radius to the pole face  82  has the effect of reducing the volume of air at the point of engagement between the radius pole face  82  and the lower stator core face  58  as illustrated in  FIG. 5A  with additional detail in  FIG. 5C . Reducing the volume of air in the open or de-energized state causes an increase in the magnetic flux and associated magnetic force resulting in a reduced pull-in voltage when stator coil  32  is energized. In the closed or energized state, the effect of the radius pole face  82  is to increase the volume of air at the joint between the radius pole face  82  and the lower stator core face  58  as illustrated in  FIG. 5B  with additional detail in  FIG. 5D . Therefore the magnetic flux and associated magnetic force is reduced which results in a higher dropout voltage with the additional benefit that the introduction of radius pole face  82  with its associated rolling movement having a shifting center point changes the lever arm of the armature pole face  82  resulting in decreased closing force which in turn increases the service life of circuit interrupting device  10 . A similar result can be achieved by adding a radius to the lower stator core face  58 , or in a combination with radius pole face  82  wherein both surfaces have a radius. 
         [0035]    Various views of an alternate embodiment are depicted in  FIG. 6A-6D . In this embodiment armature  62 B has an involute pole face  88  as detailed in  FIG. 6D . The involute pole face  88  provides improvement in an increased drop-out voltage, decreased pull-in voltage, and further decreased closing force over that of the radius pole face  82 . As in the case of the radius pole face  82 , improved results can be achieved by adding an involute curve to the lower stator core face  58 , or in a combination with involute pole face  88  wherein both surfaces have an involute curve. In other embodiments various curved surfaces may be modeled and developed by the iteration of numerous planar surfaces in an arrangement that approximates a curved surface providing similar benefits as described. 
         [0036]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.