US2040405A - Switch structure with means to prevent arcing upon circuit closure - Google Patents

Description

y 1936' 1.. M. PERSONS 2,040,405

SWITCH STRUCTURE WITH MEANS TO PREVENT ARCING UPON CIRCUIT CLOSURE Filed April 29, 1935 M X/2m ET/1W0 Vim AQQWW afw-mys Patented May 12, 1936 UNITED STATES PATENT OFFICE SWITCH STRUCTURE WITH MEANS TO PREVENT ARCING UPON CIRCUIT CLO- SURE a corporation of Iowa Application April 29, 1935, Serial No. 18,742

8 Claims.

An object of my invention is to provide a switch structure with simple, durable and inexpensive means for preventing arcing at the contacts when they are brought into engagement with each other. In a control switch, especially switches for alternating current adapted for controlling motors, arcing at the contacts is always experienced, and sometimes such arcing is more excessive than at other times. This is due to the fact that an alternating current of volts, for instance, is actually at a value of approximately volts at the peak of the alternating current wave, and if contacts are engaged at this particular point, any rebounding of the movable contact from the stationary contact will cause an excessive arcing and thereafter a current flow which welds the melted metal on the contact faces together without giving the fused metal a chance to harden, so that the next switch operation can be effected without any difficulty.

Upon separation of the switch contacts, arcing also occurs, but such arcing is not of a degree of arcing caused upon closing of the circuit, because in closing a motor circuit about five times as much current flows as when the circuit is opened, because the starting current is much heavier than the running current. Also upon separation of the contacts any arcing will cause the surfaces of the contacts to be melted. Since such arcing occurs upon separation, the contacts are then in a spaced position so that the melted metal does not fuse together and has a chance to harden before the next switch operation. It is evident, therefore, that any structure which will eliminate arcing upon closure of the switch will provide a switch which will operate satisfactorily over an indefinite period of time.

The mainobject of my present invention is to overcome such arcing upon closure of the circuit through the switch.

More particularly it is my object to provide electromagnetic means affecting an armature, which is connected with the movable contact of the switch, the electro-magnetic means tending to open the switch when the means is energized, this means being automatically energized, however, only when the contacts are separated so that it thereupon jerks the contacts apart, thus minimizing arcing upon separation of the contacts.

A further object is to provide the electromagnetic means operable to urge the movable contact in the separating direction and responsive to the alternations of the current, so as to cause the armature and thereby the movable contact to vibrate in synchronism with the current variations, so that the contacts are closest at the zero point of the alternating current wave, and consequently the switch is closed at this point when there is a minimum of current to cause arcing, the electro-magnet thereupon being immediately de-energized so as not to exert further separating tendency on the contacts until they are separated by a controlling element, thus preventing chattering of the contacts when in closed position.

With these and other objects in view my invention consists in the construction, arrangement and combination of the various parts of my device, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a front elevation of a switch casing showing therein a switch structure embodying my invention, the contacts being shown in opened position.

Figures 2, 3 and 4 are views of the contact arrangement in fully opened, partially closed and fully closed positions illustrating the action of the movable contact under the influence of my are preventing means; and

Figure 5 is an electro diagrammatical view of an alternating current wave, shown for the purpose of illustrating the action of my are preventing means.

On the accompanying drawing I have used the reference character A to indicate generally a switch housing. The switch housing A includes a base In from which projects a stationary projection I2, having mounted thereon a relatively stationary contact l4. Secured to a projection I6 is a leaf spring l8 (preferably non-magnetic responsive), on which is mounted a relatively movable contact 20 for engagement with the stationary contact M. The leaf spring I8 is so mounted that it normally retains the contact 20 engaged with the contact l4.

An armature 2,2 in the form of a magnetic responsive pin extends from the leaf spring l8. Mounted on a projection 24 from the base It] is a c-shaped pole element C, having therein an insulating sleeve 26 and a solenoid winding 28. The poles of the pole element C are indicated at 30 and 32. The flux lines for the pole element are indicated by the dotted lines a" and a'.

Circuit wires 34 and 36 connect with the stationary and movable contacts respectively, the wire 36 being connected with the leaf spring I 8. The solenoid coil 28 shunts the contacts I4 and 20, wires 38 and 48 being provided for this purpose. The coil 28 is of very low capacity. For instance when the switch is used to control a one horse power motor, I have found that one watt of current is sufficient for the coil. The vibration period of the leaf spring I8 and the armature 22 is preferably close to twice the cycle period of the alternating current controlled. This is so that it will vibrate in synchronism with the pulsations of the current, there being, for instance, 120 pulsations per second for a sixty cycle alternating current.

Any type of control element can be used for moving the leaf spring 18. By way of example I have shown a "wire motor B for this purpose. The wire motor 13 comprises a stationary projection 42, a movable element 44, a plate 46, insulating end members 48 on the ends thereof, and a resistance wire 58 wound around the elements 42, 44 and 48. The element 44 is then connected by a link 52 and a leaf spring 54 with the leaf spring l8, the leaf spring tending to stretch the resistance wire 50 to the diamond shape illustrated. Accordingly when an electric current flows through the circuit wires 56 and 58 for energizing the resistance wire 50, the temperature thereof will be raised and the wire can stretch, permitting the spring l8 to close the contacts I4 and 20. When the wire 50 is deenergized, it will contract to its original position, thus separating the contacts I! and 20. In this manner the switch structure acts as a relay, although, of course, a temperature or other responsive element, such as shown in the Henning Patent No. 1,962,505, of June 12, 1934, may be directly connected with the spring [8 for direct rather than relay operation of the switch.

Practical operation Considering Figure 1, it will be noted that the bulk of the current is broken across the contacts H and 20, current flowing through the wires 34 and 36, however, because the coil 28 shunts the contacts [4 and 20. This current, of course, can be no more than can pass through the coil, and if the switch were used to control a furnace burner, for instance, a room thermostat circuit being connected with the wires and 58, this current flow through the motor and ignition transformer is so slight that it has no operating effect thereon. During the entire period that the contacts l4 and 20 are separated, vibration will occur when the circuit is of alternating current character.

Referring to Figure 5, the line 0 indicates zero voltage, the line I I0 indicates volts, and the line Ill. indicates 141.4 volts. 110 volts is the effective voltage in an alternating current circuit, 141.4 volts being the maximum voltage at the peak of the wave. Due to the current flow through the solenoid 28, the leaf spring l8 will assume the full line position shown in Figures 2 and 3 at the peak of the wave referred to in Figure 5 as 1). It will assume the dotted position at the base of the wave indicated at b. As the resistance wire 50 heats up, the spring I8 will assume successively the positions of Figures 2 and 3, vibrating in synchronism with the alternating current all during this period of time.

Finally, at the case of the wave the contacts will engage as in Figure 4, whereupon the coil 28 is immediately de-energized and the contacts will therefore remain in engagement without any chattering or rebounding normally caused by but slight pressure being effective at the time of contact engagement because of the slow movement of the actuating element, such as the wire motor B, but which, however, is eliminated with my construction, because as soon as the contacts are engaged the force of the magnet, which has been holding the contacts separated, is released so that whatever energy was stored up in the wire motor by trying to close the contacts, and whatever resiliency in the spring i8 was working against the magnet, are then free to keep the contacts engaged.

Subsequently when the contacts are opened by deenergizing of the resistance wire 50, the contacts will be separated in the ordinary manner but the instant they are separated the solenoid 28 is thrown into operation, so as to quickly jerk them apart. Thus arcing is prevented upon the closure of the contacts when arcing is most destructive, and is minimized upon opening of the contacts by my construction.

I have provided the core element C in the particular shape shown so that the change in position of the armature 22 does not change the magnetic pull to any great degree. The flux lines (1" enter the armature 22 intermediate its ends, and the flux lines a extend between the inner end of the armature and the pole 30. Accordingly the magnetic pull is approximately the same regardless of the distance the armature is extended into the solenoid, which is not true of an ordinary poleless solenoid, wherein the strength of the magnetic pull is in proportion to the distance the armature extends into the solenoid.

I have designed my switch especially for alternating current, although for direct current it is also useful. On direct current, of course, it does not cause vibration of the leaf spring 18 unless the current is of pulsating character, whereupon it would operate in the same fashion as it does for alternating current. It is helpful, however, on non-pulsating direct current for preventing arcing upon switch closure, because as soon as the contacts are closed, the magnetic effect is no longer present, and as soon as they are separated, it comes into operation for jerking the contacts apart.

Some changes may be made in the construction and arrangement of the parts of my device without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims, any modified forms of structure or use of mechanical equivalents, which may be reasonably included within their scope.

I claim as my invention:

1. In a switch structure, a pair of contacts for controlling an alternating current circuit, means for separating and engaging said contacts, and means in addition to said first means for exerting a separating force thereon, said last means being operable while said contacts are separated and inoperable while they are engaged, said last said means being electro-magnetic and one of said contacts being responsive thereto, movable thereby and responsive to the pulsations thereof.

2. In a switch structure, a pair of contacts for controlling an alternating current circuit, means for separating and engaging said contacts, and means in addition to said fi st means for exerting a separating force th:.'a:0n, said last means being operable while said contacts are separated and inoperable while they are engaged, said last said means being electro-magnetic and one of said contacts being responsive thereto, movable thereby and responsive to the pulsations thereof, said means being shunt connected with said contact to thereby receive current only while they are separated.

3. In a switch structure for controlling an alternating current circuit, a relatively fixed contact, a relatively movable contact, means for separating and engaging said contacts and electro responsive means for vibrating said movable contact while it is separated from said fixed contact in synchronism with the alternations of'said alternating current.

4. In a switch structure for controlling an alternating current circuit, a relatively fixed contact, a carrier therefor including magnetic responsive material, a relatively movable contact, means for separating and engagin said contacts, electro responsive means for vibrating said movable contact while it is separated from said fixed contact, in synchronism with the alternations of said alternating current.

5. In a switch structure for controlling an alternating current circuit, a relatively fixed contact, a relatively movable contact, means ior separating and engaging said contacts and electro responsive means for vibrating said movable contact in synchronism. with the altemations of said alternating current, said electro responsive means being operable while said contacts are separated and inoperable while they are engaged.

6. In a switch structure for controlling an alable contact in synchronism with the alternations of said alternating current, said electro magnetic means being in operation only while said contacts are separated.

I. In a switch structure for controlling an alternating current circuit, a relatively fixed contact, a relatively movable contact, means for separating and engaging said contacts .and electro responsive means for vibrating said movable contact in synchronism with the alternations of said alternating current, said electro responsive means being shunt connected with said contacts.

8. In a switch structure for controlling an alternating current circuit, a relatively fixed contact, a carrier therefor including magnetic responsive material, a relatively movable contact,

.means for separating and engaging said contacts and electro responsive means adjacent said magnetic responsive material for vibrating said movable contact in synchronism with the alternations of said alternating current, said electro-magnetic means being shunt connected with said contacts.

LAWRENCE M. PERSONS.

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