Clapper armature with curved pole face

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.

BACKGROUND

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.

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.

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.

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.

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.

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.

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

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.

DETAILED DESCRIPTION

Turning now to the drawings, and referring toFIG. 1, a circuit interrupting device is illustrated in the form of a three-pole contactor10for controlling electrical current carrying paths for three separate circuits. The contactor10includes an upper housing12and a lower housing14. Upper housing12hosts one or more sets of electrically isolated contacts contained within the assembly. Line terminals22are used to connect line input wires16to each contact set. Load terminals24are used to connect contact outputs to the load output wires18. Also included are coil terminals26for the connection of the wires20that provide the electrical connection for the application of the control voltage to the stator coil32illustrated inFIG. 2.

An exploded perspective view of the contactor10is provided inFIG. 2. Upper housing12comprises a cover44, a set of line terminals with fixed contacts50and associated line terminal block screws46, a set of load terminals with fixed contacts52and associated load terminal block screws48, a set of auxiliary terminals and fixed contacts56and associated auxiliary terminal block screws54all of which are contained within the contact housing42. Contact housing42provides electrical isolation between individual terminals and contacts. Crossbar assembly34is transversely oriented on an axis perpendicular to that of the axis formed by the line terminals with fixed contacts50, the load terminals with fixed contacts52, and the auxiliary terminals with fixed contacts56such that lateral movement of crossbar assembly34will complete electrical circuits by the movement of moveable line contacts72, moveable load contacts, and moveable auxiliary contacts74into contact with their associated fixed contacts. Return spring36will return contact assembly34and associated moveable contacts to the open state in turn opening the associated electrical circuits.

Continuing in reference toFIG. 2, lower housing14comprises middle plate40which is positioned below contact housing42and crossbar assembly34and provides arc containment and electrical isolation to stator coil32and stator core30. Stator core30is inserted into stator coil slot68of stator coil32and in turn lower housing14. Armature62is positioned in lower housing14in free supported relation to the lower stator core face58and upper stator core face60. Stator coil32comprises a set of electrical windings whose ends are connected to coil terminals26such that the connection of an electrical current to coil terminals26energizes stator coil32and causes the formation of an electromagnetic field which is concentrated by stator core30. The electromagnetic attraction of the stator core30results in a rolling movement having a shifting center point of armature62towards stator core30. Movement of armature62causes movement of crossbar assembly34by the engagement of crossbar engagement arm64with actuator slot38of crossbar assembly34completing electrical circuits by the movement of moveable line contacts72, moveable load contacts70, and moveable auxiliary contacts74into contact with their associated fixed contacts. The removal of electrical current from coil terminals26de-energizes stator coil32causing the collapse of the electromagnetic field in stator coil32and stator core30and with the loss of the electromagnetic field, the loss of the associated attraction of armature62, and thus crossbar assembly34is returned to its de-energized state by return spring36. Lower housing14has a generally rectangular base providing a slot28therein for receiving a standard DIN rail along the transverse axis generally within the plane of the base. Upon assembly, upper housing12and lower housing14and associated elements are fastened together by closure ring76which is positioned between upper catch78and lower catch80.

Turning toFIG. 3AandFIG. 3B, bottom views of the upper housing12of the contactor ofFIG. 1are shown depicting the contactor in a de-energized state inFIG. 3Aand an energized state inFIG. 3B. As described inFIG. 2, energizing stator coil32and the associated electromagnetic field formed by stator core30results in the movement of armature62and crossbar engagement arm64which is engaged with actuator slot38of crossbar assembly34causing its subsequent motion and the completion of electrical circuits by the movement of moveable line contacts72, moveable load contacts70, and moveable auxiliary contacts74into contact with their associated fixed contacts, line terminal block and contact50, load terminal block and contact52, and auxiliary terminal block and contact56. Upon removal of the electrical current from coil terminals26and the loss of the electromagnetic field of stator coil32and stator core30, return spring36returns crossbar assembly34and armature62to a de-energized state.

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. 4AthroughFIG. 4Ddepict various views of an embodiment of the invention in which, armature62A has a radius pole face82. Adding a radius to the pole face82has the effect of reducing the volume of air at the point of engagement between the radius pole face82and the lower stator core face58as illustrated inFIG. 5Awith additional detail inFIG. 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 coil32is energized. In the closed or energized state, the effect of the radius pole face82is to increase the volume of air at the joint between the radius pole face82and the lower stator core face58as illustrated inFIG. 5Bwith additional detail inFIG. 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 face82with its associated rolling movement having a shifting center point changes the lever arm of the armature pole face82resulting in decreased closing force which in turn increases the service life of circuit interrupting device10. A similar result can be achieved by adding a radius to the lower stator core face58, or in a combination with radius pole face82wherein both surfaces have a radius.

Various views of an alternate embodiment are depicted inFIG. 6A-6D. In this embodiment armature62B has an involute pole face88as detailed inFIG. 6D. The involute pole face88provides improvement in an increased drop-out voltage, decreased pull-in voltage, and further decreased closing force over that of the radius pole face82. As in the case of the radius pole face82, improved results can be achieved by adding an involute curve to the lower stator core face58, or in a combination with involute pole face88wherein 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.