US2362855A - Electric switch - Google Patents

Description

NOV. 14, v STIMSQN 2,352,855

ELECTRIC SWITCH Filed Nov; 22, 1941 Inventor: Allen GStimson,

His ttorney.

j UNITED, STATES PATENT OFFICE 2,362,855 npnc'rmc swrron Allen G; Stimson,

General Electric Company,

New York Marblehead, Masa, assignor to a corporation of Application November 22, 1941, Serial No. 420,107

Claims. (Cl. 260-166) My invention relates to electric switches, par ticularly electric switches provided with a contact which is subject to rebound with consequent damaging arcing upon engagement with the other contact, and has for its object simple and effective means for preventing rebound of a switch contact upon engagement with another contact.

It is generally understood that failure of electric contacts is due to arcing and welding of the contacts. Furthermore, since the heat required for noticeable welding can be produced only by arcing, and since arcing will take place only if, the contacts rebound after initial en-= gagement, it follows that contact failures maybe eliminated or reduced 'by preventing rebound of the contacts after their initial engagement. Rebound of contacts is a common impact phenomenon and is due to the conversion of'the kinetic energy of the moving parts into potential energy having a tendency to simply reverse the direction of motion of the moving parts if the impact is direct. Since the rebound velocity is a fixed percentage ofthe speed of approach, the percentage depending only upon the materials involved and not upon the mass of moving parts, the rebound is particularly vioj small snap with the fixed contact zero. By of the weight is permitted forces by building up a certain amount of potential energy by elastic strain in a direction having little tendency to reopen the contacts. Ultimate dissipation of the potential energy into internal friction or the like permits the weight to come to rest without causing the contacts to rebound.

For a more complete understanding of my invention reference should now be had to the following detailed description taken in conjunction with the accompanying drawing in which Fig. 1 is aside view of \an electrical contact element embodying my invention in oneform; and Fig. 2 is a similar view of the essential parts of an electrical cotact device embodying my invention in another form.

Referring now to Fig. 1, the embodiment of my invention illustrated therein comprises a fixed contact l0 mounted upon a support I l adjacent a action magnet l2. For cooperation I0 I provide a movable" contact arm comprising a pivotally mounted end portion l3 carrying at its end an elongated spring strip It. The member I3 is shown pivotally mounted upon a fixed knife-edge sup.-

lent where the speed of apporach is relatively p 1f A Su a m n y be Provided high. Thus, while the impact forces and confor actuating the contact arm l3, I4 between sequent rebound may be reduced by reducing open and closed circuit positions. In the form the speed of approach and hence the kinetic enshown the pivoted member I3 is of magnetic material and forms a movable armature for comergy, this is impractical in certain applications, for example, in snap acting devices or in elecpleting the magnetic circuit of an actuating tromagnetically actuated switches; In such apelectromagnet IS. The contact arm l3, M is plications it becomes necessary to devise means tor converting the kinetic energy of the moving parts to some other form of energy having little or no tendency to reopen the contacts. In general, the kinetic energy may be converted into either heat or other forms of work, potential energy such as elastic strain, electric energy, or kinetic energy in another direction. I

In carrying out my invention I provide. means for converting the kinetic energy of movin contact parts into elastic strain in a direction having little or no tendency to reopen the contacts and then dissipating such potential energy into heat of internal friction or the like.

In one 'form' of my invention I resiliently mount a substantial 'weight'uppn the movin contact member in such a way thatafter the contacts come into engagementthe weight continues to move but the-direction of motion of the weight is changed. Thus the kinetic energy of the movingparts is not immediately reduced to light tension spring 11. spring strip ll biased into open circuit position by means of a At its free end the carries a movable contact l8 for cooperation with the fixed contact l0 and a magnetizable armature IQ for cooperation with the snap action magnet l2.

Mounted upon the spring strip l4 intermediate its ends I provide an inertia member or weight 20 having a substantial mass relative'to the mass of the contact arm itself. In the form shown the weight 20 is mounted upon a resilient, angle bracket 2| which is in turn attached as by welding to approximately the center of the spring strip l4. Due to the inertia of the weight 20 the effective length of the contact spring I4 is reduced to that distance between the movable contact and the pointof attachmentof the bracket 2| to the spring ll. This distance is indicated by the reference numeral 22,

In operation, when the actuating electromagnet It is energized to attract the armature l3 this means the continued movement to cushion the impact merely tends and move the contact spring H into contact engaging position all the moving parts move substantially in unison until the contacts and 18 are engaged. Upon engagement of the contacts the kinetic energy of the moving parts is not immediately reduced to zero but the weight 28 continues to move against the bias of the springs l4 and 2|. Such continued movement of the weight 20, however, is a substantially free rotary movement with respect to the point of attachment of the bracket 2! to the spring II. This rotation is due to the fact that the bracket 2| is equally or less resilient. than the spring i4 and supports the weight 20 in cantilever fashion. Thus the kinetic energy in the weight 20 is Q changed in direction and permitted to build up a certain amount of potential energy by twisting of the spring strip l4. Twisting of the spring l4 at its center caused by the rotary movement of the weight 20 tends to slide the contact 18 longitudinally to a small degree, but not to reopen the contacts. When the weight 20 is brought to rest by elastic strain in the spring strip the potential energy in the spring strip 14 and the bracket 2| will reverse the movement of the weight 20 and twist the spring I 4 in the opposite direction, and oscillation of the weight 20 about the point of connection of the bracket I 2i to the spring strip M will continue until all the energy of the weight is dissipated in friction. However, the elastic strain in the spring strip i4 is in such a direction that the spring strip I l to straighten longitudinally rather than to rebound laterally and reopen the contacts. It is not contemplated that the weight 26 will engage the arm H above the contact 18.

At Fig. 2.1 have shown another embodiment of my invention in which the contact arm comprisesa rigid lever 25 pivoted at a fixed point and a rigid weighted contact lever 23 pivotally mounted upon the end of the lever 25. The rigid lever 25, or part of it, may be composed of magnetizable material to serve as a movable armature completing the magnetic circuit of an actuating electromagnet 2?. The lever 25 is pivotally mounted upon a fixed knife-edge pivot formed upon the magnetic frame 28 of the magnet and is biased to a circuit opening position by means of a light tension spring 23. Preferably the free end of the rigid pivoted member 25 is formed to provide a knife-edge pivot 33 engaging the contact lever 26 intermediate its ends. The contact lever 28 carries at one end a movable contact 31 arranged to engage a fixed contact 32. At the opposite end of the contact lever 26 is disposed a substantial mass or weight 33. The contact lever 36 is disposed on the side of the rigid lever 25 adjacent the fixed contact 32 in such a way that the movable contact 31 extends beyond the end of the lever 25. The members 25 and 25 are connected together and biased into engagement by means of a rivet or bolt 34 and a compression spring 35. The contact lever .23 and the weight 33 are so designed that their integrated center of gravity is located between the pin 34 and the weight 33, that; is, the center of gravity of the contact lever assembly is located on the opposite side of the pin 34 from the movable contact 3 I In operation, when the electromagnet 21 is energized the armature lever 25 is drawn toward the magnet in a'direction to close the contacts 3| and 32. Initially the entire contact arm, including the levers 25 and 23 and the weight 33, are moved as a unit. However, as soon as the contacts come into engagement, the contactcarrying 'end of the. contact lever 26 is brought to rest while the weight 33 and the armature lever 25 continue to move. During this latter phase of the movement the armature lever 26 and the weight 33 rotate about the point of engagement of the contacts 3i and 32, thereby causing the weight 33 to move away from the armature lever 25 and to compress the spring 35. Thus, the weight 33, initially rotating about the knife-edge pivot on the frame 28, is forced to change its point of rotation after the contacts come into engagement so that the kinetic energy of the moving parts is not immediately reduced to zero but is changed in direction and gradually converted into elastic strain in the spring 35. When recovery of the potential energy stored in the spring 35 takes place the contact lever 26 and the weight 33 ar forced to rotate in the opposite direction about the point of. engagement of the contacts so that there is no substantial tendency to reopen the contacts. Since the point of engagement of the contacts is the center of rotation for the lever 26 and the weight 33, there is no tendency to open or to slide the contacts.

While I have shown only certain embodiments of my invention by way of illustration, many further modifications will occur to those skilled in the art, and I therefore wish to have it understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention. i

What I claim as new and desire to secure'by Letters Patent oi the United States is:

1. An electric contact making and breaking device comprising cooperating switch contacts, a

movable contact arm pivotally mounted at one end and carrying one of said contacts at its other end, a relatively movable weight carried by said contact arm, said weight having a mass sub stantial with respect to the mass of said arm, means including a resilient member for connecting said weight to said arm, and means for moving said arm to engage and disengage said contacts, said connecting means being arranged to permit appreciable free arcuate movement of said weight after engagement of said contacts and about said contacts as a center after engagement of said contacts thereby to convert the kinetic energy or said weight arm into elastic strain having no-substantial tendency to disengage said contacts or produce relative sliding movement thereof.

2. An electric contact making and, breaking device comprising cooperating switch contacts, a

movable contact arm pivotally mounted at one end and carrying one of said contacts at the other end thereof, a weight movable with said arm and having a mass substantial with respect to the mass of said arm, resilient means for pivotally mounting said weight upon said arm, meam for I moving said contact arm to engage said con tents, and means for constraining said weight to rotate freely about the point of engagement of said contacts after their engagement thereby to stress'said resilient means and to convert the kinetic energy of said contact arm into elastic strain in said resilient means, said strain being so directed that it has no substantial tendency to reopen said contacts.

3. An electric contact making and breaking device comprising a fixed contact, a movable switch arm including a rigid member pivotally mounted at one end and a weighted contactlever resiliently connected to the other end of ed to said rigid arm at a point intermediate said movable contact and the center of gravity of said contact lever, and means for moving said rigid member to engage said contacts, whereby when said contacts engage said contact leverpivots about the point of engagement of said contacts thereby to change the path of' travel of said lever and to convert the kinetic energy of said switch arm into elastic strain having no substantial tendency to disengage said contacts and having no tendency to produce relative sliding movement of said contacts.

4. An electric contact making and breaking device comprising a fixed contact, a movable switch arm including a movably mounted rigid member and a weighted contact lever pivotally connected to said rigid member, said contact 1ever carrying at one end thereof a movable contact arranged to engage said fixed contact and being pivotally connected to said rigid member at a point intermediate said movable contact and the center of gravity of said contact lever, resilient means connected between said contact lever and said rigid member for biasing said members to a predetermined relative position, stop means for determining said predetermined position, and, means for moving said switch arm to engage said contacts, whereby when said contacts engage said contact lever rotates relative to said rigid member and against the bias of said resilient means thereby to change the path of travel of said lever and to convert the kinetic energy of said switch arm into elastic strain having no substantial tendency to disengage said contacts. I I

5. An electric contact making and breaking device comprising a fixed contact, a. movable switch member, a contact lever pivotally connected to said movable switch member, said con-- tact lever having a substantial mass and carrying at one end thereof a movable contact arranged to engage said fixed contact, said pivotal connections being positioned intermediate said movable contact and the center of gravity of said contact lever, resilient means for biasing said contactv lever to a predetermined fixed position with respect to said switch member, and means for moving said switch member to engage said contacts, whereby said contact lever ,moves with said switch member until said contacts engage and thereafter .rotate relativ to said switch member against the bias of said resilient means thereby to convert the kinetic energy of said switch member and contact lever into elastic strain having no substantial tendency to disengage said contacts. 6. An electric contact, making and breaking device comprising cooperating'switch contacts,

a resilient contact arm carrying on of said contacts at one end thereof, said arm being mounted for lateral movement between contact breaking and contact making positions, an inertia member of substantial mass in relation to the mass of said contact arm, and resilient cantilever supporting means for mounting said inertia member intermediate the ends of said contact arm in spacedv relation thereto for appreciable free overtravel with respect to said arm after engagement of said contacts, said overtravel being a substantially arcuate movement about the fixed end of said cantilever supporting means thereby to convert the kinetic energy of said contact arm into elastic strain in a direction having no substantial tendency to reopen said contacts.

'7. An electric contact making and breaking device comprising cooperating switch contacts, a resilient contact arm carrying one of said contacts at one end and being pivotally mounted at the other end for movement between circuit breaking and circuit making positions, an inertia member of substantial mass in relaton to the mass of sad contact arm, offset resilient cantilever supporting means having a portion extending in substantially parallel spaced relation with respect to said contact arm for mounting said inertia member intermediate the ends of said contact arm for appreciable fre .overtravel with respect to said contact arm after engagement of said contacts, and means for moving said contact arm and said inertia member in unison from a contact breaking to a contact making position, said resilient cantilever supporting means permitting free'overtravel of said inertia member wth respect to said arm after engagement of said contacts thereby to twist an intermediate section of said contact arm and to dissipate the kinetic energy of the moving parts in relative sliding movement of said contacts and in elastic strain of said contact arm in a direction having no substantial tendenc to reopen said contacts.

tact arm and said inertia member in unison, and

means for moving said contact arm and said inertia member together from a contact breaking to a contact making position, said resilient mounting means for said inertia'member being arranged to permit appreciable free overtravel of said inertia member with respect to said contact arm after engagement of said contacts therebyto cushion the impact of said contacts by converting the kinetic energy of said contact arm and inertia member into elastic strain having no substantial tendency to reopen said contacts.

9. An electric contact making and, breaking device comprising cooperating switch contacts, a contact arm movably mounted at one end to control one of said contacts, an inertia member having a substantial mass in relation to the mass of said arm, means including resilient means between said inertia member' and said arm for mounting said inertia member upon said arm for appreciable free arcuate movement with respect to said arm, and means for simultaneously moving said contact arm and said inertia member from contact breaking to contact making positions, said resilient means permitting continued movement of said inertia member relative to said arm after said contacts are engaged thereby to convert the kineticenergy of said member and said am into elastic strain having no substantial tendency to reopen said contacts.

10. An electric contact making and breakin device comprising cooperating switch contacts. a contact arm movably mounted at one end to control one of said contacts, an inertia member of substantial mass in relation to the mass oi said contact arm, means including a resilient member for mounting said inertia member upon said arm for appreciable tree arcuate movemen of said member with respect to said arm, and means for simultaneously moving said contact arm and saidinertia member about. said one end of said-arm from a contact breaking position to a contact making position, said resilient mountin: means being arranged to permit appreciable said contacts.

overtravel of said inertia member but to change its path of travel atter engagement of said con-- tact: thereby to cushion the impact of said con tact: by converting the kinetic energy of said contact arm and inertia member into elastic strain having no substantial tendency to reopen ALLEN G. STIMSON.

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