US2262495A - Switch - Google Patents

Description

4 a. M. HAUSLER K 2,262,495

SWITCH Filed Dec. 20, 1939 Inventor: George M. Hausler,

FORCE 0F WIPE SPRING I b IS orney.

CURRENT MAKING CAPACITY Patented Nov. 11, 1941 SWITCH George M. Hausler, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York Application December 20, 1939, Serial No. 310,196

5 Claims.

My invention relates to switches,more particularly to snap switches, and has for its object a simple and reliable shock proof switch operable by a small force but having a relatively high current, circuit closing capacity.

My invention is especially useful in electrical applications where the switch is called upon to carry a current momentarily upon closing which is many times greater than the continuous load current. One such application is in the starting of A. C. motors of the type which are connected directly to the supply source. My device is further characterized by the fact that only a small operating force is required to operate it.

In carrying out my invention in one form, I mount each of the cooperating switch contacts on a very flexible spring which spring, when the contacts engage, flexes to give a weld breaking wiping action between the contacts after which greater contact pressure isapplied.

For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is a side elevation view partly in section of a switch embodying my invention; Fig. 2 is an end elevation view of Fig. 1; Fig- 3 is an enlarged view of the movable contact arm and the snapping magnet; Fig. 4 is an enlarged view of the stationary contact and its support; while Fig. 5 is a curve showing the relation of current making capacity of the contacts to wipe spring force.

Referring to the drawing,'I have shown my invention in one form as applied to a motor starting switch comprising a spring arm l carrying on its movable end a movable contact II and having its other end secured in good electrically conducting relation, as by a soldered or welded joint l2, to a relatively stifi arm l3. The arm |3 extends in parallel relation with the arm I0 andjust above the arm I, as seen in Figs. 1 and 2. At its fixed end, the arm l3 is provided with a laterally. extending projection ll which is secured by a suitable screw l to the base l6 made of a suitable electrically insulating material such asa molded compound. This portion, is provided with a clamping screw Ma for connecting the arm I 3 in an electric circuit.

For the purpose. of giving the ,arm l0 asnap action a permanentmagnet I1 is provided. This magnet is a cylindrical block which is suitably which are on this upper face. An armature I9 is secured as by welding to the arm [0 at a point just above the magnet IT. This armature I9 is provided on its surface adjacent the poles of the magnet with a thin layer of a suitable nonmagnetic material such as copper for the purpose of providing an air gap. Preferably this layer 20 is .003 inch thick. The air gap assures a uniform pull on the armature when in its attracted position. e e

The magnet l l is preferably made of a material having a high magnetic retentivity such as a mixture of aluminum, nickel, copper and iron, described and claimed in U. S. Patent No. 1,947,274,

issued February 13, 1934, to William E. Ruder and Patent No. 2,027,994, issued January 14, 1936, to Tokushichi Mishima.

The movable contact II, which is preferably made of pure silver, is not secured directly to the end of the arm Ill but it is secured to the end of a very fragile relatively short electrically conducting wipe spring arm 2|, the other end of which is secured suitably to the arm III, preferably by a spot electric weld 22. A central stud '23 on 'the back of the contact ll extends loosely through the notched or forked end of the arm l0 and is suitably secured as by riveting to the end of the spring 2|. This stud is somewhat longer than the thickness of the arm l0 so that the contact normally is spaced from the arm III as seen in Fig. 3. Thus when pressure is first applied to the lower contact face of the contact II, the spring 2| flexes, if the force is great enough, until the contact engages the arm Ill. As shown in Fig. 3, the wipe spring 2| is provided with a permanent set or bias against the spring arm II), or more specifically against the parallel spaced projections constitutingcong tact stop means, forming 'theforkedend of the contact arm. Therefore whentheniovable contact engages the stationarycontact z'agpre;

secured in the support It as by pressing it in the support, just below the arm l0 at apoint near its movable end. The magnet isprovided with a groove l8 ,extending'diametrically across'its updeterm'ined pressure by the Spring 2| immediately available without' th'e 'neeessl y f fi' ing the spring 2|. ff] e A similar mounting ontheendjof afver V A wipe spring is providedllfor the ltatio" contact '24, also made of pure end or, the spring 25 1s secured, p I L welded 'joint 25, to one 1 end of a relatively "ii id member 21. This memberZl has sufiiciept rigid ity to prevent its flexin operationof the switch by rea contact,- the contact 24' isjprov e per faceand separating its north and south poles stu d' zt on itsfbackwhich'extendsleoselyibetvveen the pair of projections or prongs, constituting contact stop means, of the forked end of the member 21 and is suitably secured as by riveting to the free end of the flexible arm 25. Also the arm 25 is given a bias with its free end against the member 21 as shown in Fig. 4, with the contact 24 inspaced relation with the member 21.

For the purpose of securing it to the base IS, the member 21 is provided with a laterally extending portion 29 which is clamped to the base by means of a screw 30 and serves as an'electrical connection. At its junction with the other portion 21, the extension 29 is bent upward away from the base somewhat to provide for adjustment of the portion 21 in a vertical direction by means of an adjustment screw 3|. This adjustment of the screw 3| determines the final position of the contact 24 when it comes to rest against the end of the member 21 and thereby adjusts the final position of the end of the arm l and of the armature I9. The adjustment of the position of the armature l9 determines the magnetic force available to prevent separation of the contacts. In a typical device, the armature did not wholly engage the pole faces in its final closed position.

In the operation of the switch, the arm I is moved in an upward direction, as seen in the drawing, by a suitable means responsive to the operating variable condition, such as a temperature responsive bellows 32, which engages the arm It at apoint near its fixed end l2. Other operating devices may be used such as a bimetallic thermostat. Assuming that the contacts are closed, they are held closed by the combined force of the magnet and the force applied by the spring l0 which is biased to apply a force in the closing direction when the contacts are in engagement. When the force applied by the bellows 32 increases, the spring Ill bends upward and finally when the force becomes great enough, the armature is pulled away from the magnet and the contacts are opened with a snap action. In its opening movement, the arm l0 snaps upward with its movable end coming to rest against the member Hi. The contact arm I is held in its open position by the bellows 32, the force of the bellows being opposed by the pull of the magnet on its armature and the closing pressure of the spring arm I.

When the pressure applied by the bellows decreases sufliciently, the arm It) starts to move downward toward the closed position. As the armature approaches the magnet, however, the

. pull on the armature increases. When the armal0 accelerates and snaps to the closed position.

In this position, the contact II has moved upward with respect to the arm I. by flexure of the wipe spring 2| into engagement with the arm l0 while the contact 24 by flexure of the wipe spring is pressed against the member 21, this flexure of the springs producing a wiping action between the "contacts. The arm I0 is flexed downward somewhat by the pull of the armature I! on it.

This switch is characterized by its exceptionally high amperage circuit making capacity as compared with the small net closing force exerted by the magnet and the spring arm I 0. This high amperage circuit closing capacity is obtained by means of the very fragile wipe springs 2| and 25. These springs are biased to apply a predetermined force, immediately upon engagement of the contacts. This force, however, is small as compared with the available closing force and, consequently, the preponderant amount of that force is available for the wiping of the contacts. It will be understood that ordinarily when the contacts first touch to complete the circuit, the engaging surfaces of the contacts are heated sufliciently to form a weld between them. This weld must be broken by the subsequent wiping action between the contacts. If the force available during the wiping action is not sufiicient to break the welded surfaces apart; then the weld becomes permanent. In such a case, the switch cannot successfully close the circuit under the D heavy current conditions then prevailing.

Another feature is the location of the joint 26 forming a pivot point for the spring 25 in a lowered position, as seen in the drawing, so that the spring 25 extends in non-parallel relation, i. e., at an acute angle as shown, with the plane of contact surface of the contact 24, as well as substantially at right angles with the spring arm Ill. This arrangement provides for greater wiping action or lateral movement of the contact 24. This will be apparent from an examination of Fig. 4. When the contact 24 is depressed, it will be observed that its lateral movement toward the right-hand is much greater than it would be if the depressing movement of the contact were more nearly tangential to the are described by the movable end of the spring 25.

In a typical device, the wipe springs 2| and 25 were made from pure copper cold rolled to maximum hardness. These copper springs have the desired resiliency and relatively high current carrying capacity. The dimensions of the spring 2| were thickness .004 inch, width somewhat less than .25 inch, and length about .8 inch. The thickness of the spring 25 was .005 inch and it was somewhat wider and longer than the spring 2|. These springs are, in fact, substantially as fragile or flexible as they canbe without buckling under'the endwise forces applied to them during the wiping action. In other words, the wipe springs 2| and 25 have only sumcient rigidity to withstand these endwise forces without buckling, i. e., to withstand without buckling the maximum endwise forces which can be applied by the magnet Since the spring 25 was somewhat longer than the spring 2|, its greater thickness and width were necessary to give it the required strength against buckling. Moreover, the endwise force causing buckling applied to the spring 25 is greater than .that applied to the spring 2| by reason of the angular position of the spring with respect to the line of movement of the contacts.

I have found that for a given switch having a given operating force, the current making capacity increases with increase in the stiflfness of the wipe springs, i. e., force applied by the wipe springs, up to a certain stiffness of the wipe springs, indicated by the point 33 on the curve 34 of Fig. 5. Further increases in stiffness decrease the current making capacity as indicated by the curve 34. The point 33 is the point where the stiffness of the springs is just suflicient to prevent buckling under the circuit closing force available.

Also in this typical device the dimensions of the spring arm II! were thickness .01 inch, length about 2.75 inches, and width .25 inch. It was stiffened somewhat by giving it a shallow U seethe attracted position was about 45 grams;

tion 'for a portion of its length. It was made from cold rolled phosphor bronze.

The studs 23 and 28 securing the contacts to the springs 2| and 25 were of such length that the contacts each had a freedom of movement of about .013 inch by reason of the bending of the wipe springs 2| and 25 after which the contacts engaged the arm I and the member 21 respectively. The wiping action between the contacts takes place during this flexure of the springs 2| and 25. The fragile nature of the springs 2| and 25 is indicated by the fact that the initial pressure between the two contacts immediately after engagement was about 4 grams, this pressure of course being the initial bias pressureof these springs. Upon continued closing movement of the arm Ill, producing the wiping action, the pressure between the contacts was increased by the increased flexure of the springs 2| and 25. When these springs were deflected to their maximums and the contacts about to seat'on the arm l0 and the member 21 respectively, at the completion of the wiping action, this force had increased-to between 5 and 6 grams. The final contact pressure after the magnet hadpulled its armature to its final attracted position, thereby flexing the arm -|0 somewhat, was about 22 grams. This pressure is determined by the stiffness .of the arm l0.

Probably this 22 grams contact pressure was nearly all available, during the wiping action and, since only from 4 to 6 grams was required by for the wiping of the contacts and the rupturing of any welding action that might occur. As a result, the contacts welded permanently with currents much smaller than the 42 amperes closed successfully with the switch embodying my invention. 1

While I have-shown a particular embodiment of my invention, it will be understood, of course,

' that'I do not wish to be limited thereto, since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall'within the true spirit and scope of my invention.

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

1. A switch comprising a stationary contact, a spring contact arm having one end secured and its other end movable, a wipe 'spring'arm extending lengthwise of said contact arm and secured at one end to said contact arm, a movable con tact on the other end of said wipe spring cooperating with said stationary contact, said wipe spring being formed to hold its other end against the movable end of said arm thereby to p'rovide an initial contact engaging force when said movable contact engages said stationary-contact be.-

fore said other end is bent away from said contact arm, stop means providing limited movement of said movable contact with respect to said contact arm upon flexure of said wipespring thereby to provide a wiping action between said contacts, operating means for applying a pre;

the springs 2| and 25 to maintain the contacts together, the preponderantly great remainder was available, if needed, to break any welding of the contacts. The force applied by the mag-- net to its armature when the armature was in It will be understood that at the time the wiping action took place, the armature of the magnet had not as yet moved to its attracted position, 'and consequently the pull on the armature was considerably less than 45 grams, it being approximately 22 grams as stated above.

The relatively short springs 2| and 25 give short radii of movement for the contacts during the wiping action and resulting increased relative lateral movement between the contacting surface.

Another advantage of the fragile wipe springs. 2| .and 25 is that they render the switch shock proof. These springs eflectively maintain contact during shocks and vibration producing movement of the free end of the arm I;

Despite the fragile springs and relatively small forces available, th device just described above was used successfully in the starting ofa onehalf H. P. A. 0. motor in which the inrush cur- ,rent, which passed through the contacts II and v 24, was 42amperes. This current decreased to 7 amperes as the motor started. I

I have found, furthermore, that the circuit closing current capacity of this switch is several times greater with the contacts mounted on the fragile springs 2| and than it is when the contact 24 is stationary, i. e., mounted directly on themember 21, and the other contact H is determined limited operating force to, said contact arm to move said contact arm toward said stationary contact, said wipe spring having a maximum lateral flexibility consistent with a stiffness sufilcient to, prevent buckling of 'said wipe spring by the endwise force applied thereto by said predetermined operating force when said contacts are welded together whereby a predetermined relatively small part of said operating force is applied laterally through said wipe spring to said movable contact upon engagement of said contacts so that the remaining relatively great part of said operating force is available for application in a substantially endwise direction to said wipe spring to effect a wiping ,action between said contacts.

2. A switch comprising a stationary contact, a contact arm having onev end movable, contact stop means on the movable nd of said contact arm, a wipe spring carried by said contact am having one and secured to said contact arm at an intermediate point thereof and formed to bias its other end against said stop means, a movable contact secured to said other. end of said wipe spring, a substantially-rigid contact support adjacent said movable contact, a second contact stop means carried by said contact support, a second wipe spring extending substantially at right angles with respect to said contact arm having one end secured and formed to bias its other end against said second stop nieans, a fixed contact carried by said second wipe ,spring arranged to be engaged by said movable contact, said second wipe spring extending at I an acute angle with the plane of contact surface of said contacts, means for applying a presmall portion of said force but said wipe springs being still enough to withstand without buckling the endwise forces applied to said wipe springs by the preponderantly great remaining arm, a contact supporting stud secured at one end to said end portion of said wipe spring, a movable contact on the other end of said stud normally spaced from said contact arm, a substantially rigid contact support adjacent said movable contact, a second wipe spring extending substantially at right angles with respect to said contact arm having one end secured and formed to bias its other end against said contact support, a second contact stud having one end secured to the other end of said second wipe spring, a fixed contact secured at the other end of said second stud normally spaced from said contact support arranged to be engaged by "said movable contact, said second wipe spring extending at an acute angle with the plane of contact surface of said contacts, means for applying a predetermined limited force to move said arm to a closed circuit position, said wipe springs flexing until said contacts respectively engage said arm and spaced from said' contact support arranged to be engaged by said movable contact, said second wipe spring extending at an acute angle with the plane of contact surface of said con-' tacts, means for applying a predetermined limited force to move said arm to a closed circuit position, said wipe springs flexing until said contacts respectively engage said arm and said contact support to provide for a wiping action between said contacts, and said Wipe springs being fragile laterally thereby to reduce the circuit closing pressure between said contacts to a relatively small portion of said force but said Wipe springs being stifi' enough to withstand without buckling the endwise forces applied to said wipe springs by the preponderantly great remaining portion of said force to break a Weld and eiTect said wiping action.

5. A' switch comprising a stationary contact, a spring contact arm having one end secured and its other end movable, a pair of spaced apart projections on said movable end, a wipe spring said contact support to provide for a wiping 'action between said contacts, and said wipe springs being fragile laterally thereby to reduce the circuit closing pressure between said contacts to a relatively small portion of said force but said wipe springs being stiff enough to withstand without buckling the endwise forces applied to said wipe springs by the preponderantly great remaining portion of said force to break a weld and effect said wiping action,

' 4. A switch comprising a stationary contact, a contact arm having one end secured and its other end movable, a pair of spaced apart projections on said movable end, a wipe spring arm carried by said contact arm having one end secured to said contact arm at an intermediate point thereof and formed to bias a portion at its other end against said projections, a contact supporting stud extending between said projections and secured at one end to said end portion of said wipe spring, a movable contact on the other end of said stud normally spaced from said projections, a substantially rigid contact support adjacent said movable contact, a second pair of spaced projections on said other end of said contact support, a second wipe spring extending substantially at right angles with respect to said contact arm having one end secured and formed to bias its other end against said second pair of projections, a contact stud having one end secured to the other end of said second wipe spring and extending between said second pair of projections, a fixed contact secured at the other end of said stud normally arm'carried by said contact arm having-one end secured to said contact arm at an intermediate point thereof and formed to bias a portion at its other end against said projections, a contact supporting stud extending between said projections and secured at one end to said end portion of said wipe spring, a movable contact on the other end of said stud normally spaced from said projections, a substantially rigid arm extending substantially at right angles with said contact arm having one end secured and its other end adjacent said movable contact, a second pair of spaced projections on said other end of said rigid arm, a second wipe spring extending lengthwise with respect to said rigid arm having one end secured to said rigid arm, and formed to bias its other end against said second pair of projections, a second contact stud having one end secured to the other end of said second wipe spring and extending between said second pair of projections, a fixed contact secured on the other end of said second stud normally spaced from said rigid arm arranged to be engaged by said movable contact, said second wipe spring extending at an acute angle with the plane of contact surface of said contacts, a permanent magnet mounted adjacent said contact arm, an armature for said magnet carried by said contact arm whereby a predetermined limited -force is applied by said magnet to move said arm to a closed circuit position, said wipe springs flexing until said contacts respectively engage said arms thereby to provide for a wiping action between said contacts, and said wipe springs being fragile laterally thereby to reduce the circuit closing pressure between said contacts to a relatively small portion of said force but said wipe springs being stiff enough to withstand without buckling the endwise forces applied to said wipe springs by the preponderantly great remaining portion of said force to break a weld and efiect said wiping action.

GEORGE M. HAUSLER.

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