US3340372A - Pressure switch with non-welding contact structure - Google Patents

Description

P 1967 c. A. SCHAEFER 3,340,372

' PRESSURE SWITCH WITH NON W-ELDING CONTACT STRUCTURE Filed March 1, 1965 J4, J5 J3 4.

' Q/ZZ Z/ZZE" Qw Q. 62M227 United States Patent 3,340,372 PRESSURE SWITCH WITH NON-WELDING CONTACT STRUCTURE Carl A. Schaefer, Asheville, NC, assignor to Square D Company, Park Ridge, 111., a corporation of Michigan Filed Mar. 1, 1965, Ser. No. 435,815 3 Claims. (Cl. 200-83) This invention relates to electrical switches operated by fluid pressure, and more particularly to a pressure switch having an improved operating mechanism for insuring positive engagement of its separable contacts thereby to prevent the contacts from welding together.

Contact welding is a problem sometimes encountered in the use of electrical pressure switches of the type having a pair of double-break contacts. Such switches have two pairs of fixed contacts, the pairs of fixed contacts being bridged by respective movable contact bridges each of which includes a pair of movable contacts or contact portions. The contact bridges are pivotally and sli'dably supported on a movable contact arm or carrier and are biased outwardly away from the carrier by respective springs. Contact welding can occur when a relatively high current flows upon initial closure of the switch. If one of the movable contacts on one of the contact bridges makes a relatively light initial contact with its complementary or associated fixed contact, the high current level and light contact pressure can combine to cause the two contacts to become welded together in a position preventing the other contact on the bridge from engaging its complementary or associated one of the fixed contacts. Electrical continuity may be initially established between the load and the line circuit by momentary contact between the other contacts of the switch followed by rebound or by arcs drawn between the contacts not making actual contact. Such arcs, however, become extinguished during a zero point in the alternating current cycle thereby leaving an uncompleted current path between the load and the line.

An object of the present invention is to provide a multicontact pressure switch having an improved operating mechanism which reduces contact bounce and insures positive electrical continuity between all contacts thereof upon a closing operation by preventing welding of any two of the mating contacts.

Another object is to provide a pressure switch having an improved operating mechanism effecting two separate and distinct hammer blows on the movable contact carrier thereof upon closure of the switch.

Still another object is to provide an improved pressure switch having means to effect non-resilient and positive engagement of resiliently mounted movable-contacts with associated fixed contacts. 7

Other objects and advantages of the invention will become apparent from the following specification wherein reference is made to the drawings, in which:

FIGURE 1 is a plan view of a presure switch embodying the present invention with a portion of the cover broken away;

FIGURE 2 is a cross-sectional view taken generally along the line 2-2 of FIGURE 1;

FIGURE 3 is a cross-sectional view taken along the line 33 of FIGURE 2;

FIGURE 4 is a view from the left of FIGURE 1 with portions shown in section; and

FIGURES 5 and 6 are fragmental views of the switch generally ture in an open and in a welded position, respectively.

Referring to the drawings, a pressure switch 10 embodying the present invention comprises a base or frame 11 having a pair of upstanding brackets 12 and 13 at op- 3,340,372 Patented Sept.j5, 1967 minal and contact member 19 by means of an associated.

screw 20. As shown best in FIGURE 4, each of the members 19 is generally L-shaped and has a terminal screw 21 threaded into one leg portion and a fixed contact 22 suitably secured to the other leg portion.

The frame 11 supports a pair of upwardly-extending posts 24 and 25. A range spring 26 disposed about the post 24 has its upper end bearing against a cup washer 27 captivated by a nut 28 threaded on the post 24. The lower end of the range spring 26 abuts against, and applies a force to, a free end portion of a generally channel-shaped operating lever 29 provided with relatively large openings through which the posts 24 and 25 respectively extend. The amount of force applied by the spring 26 to the lever 29 is determined by adjustment of the nut 28. The other end portion of the operating lever 29 is pivotally received (FIGURE 2) in the arm portions 14,

in suitable slots 31 and 15, respectively.

As shown in FIGURE 3, one hooked end portion of a helical toggle spring 33 29 by means of a small aperture provided therein,

other hooked end portion is similarly connected to a gen-.

The link 35 is pivotally carried by pivotal means comprising a movable contact frame 36, to the upper surface of which is riveted a brack-.

sharp V notches formed in spaced depending arms 39 of. thecontact frame 36 (best seen in FIGURE 4) thereby. link 35 and to provide the pivotal mounting between the the contact frame 36. The contact frame 36 isplvotably mounted on the frame 11 by an additional pair of depending arms 40 having respective able depressions (not shown) in a pair of spaced ears 41 As shown in FIGURES 2 and 3, the rear central portion of the contact frame 36 is shaped to provide a sub-. stantially square opening 44 through which the bight portion of the toggle link 35 projects. depending portion. provided with which overlies the square opening 44 and overhangs an end portion of the toggle link 35 opening 44 thereby to limit the amount of upward movement of the link 35 within the opening 44.

A pressure switch having a toggle mechanism similar to the one just described is disclosed in C. A. Schaefer Patent No. 2,741,678 which issued Apr. 10, 1956.

The bracket 38 has a an adjustable arm 46 respective openings through which extend generally T- shaped contact pins 47, respectively. Each pin 47 carries a contact bridge 48. formed of conductive material and is connected to, the operating lever to, and extends upwardly.-

tip portions pivoted in suit-.

extending through the v spective holes in the end portions of the pins 47, respectively, maintain the movable contact assemblies on the carrier 37. Each assemblage of the contact pin 47 in the carrier 37 thus comprises a lost-motion connection means connecting the contact bridge 48 to the carrier 37.

As shown in FIGURE 4, the post 25 is provided with a shoulder against which a cup washer 53 is normally biased by a spring 54. The spring 54 is compressed by a nut 56 bearing against :a second cup washer 55 which is positioned at the upper end of the spring 54. A cover 66 is provided to protect the operating mechanism and includes an aperture receiving the upper end portion of the post 24. A cover nut 67 is provided for cooperation with the threads of the post 24 to maintain the cover 66 in place.

A pressure plate 68 (FIGURE 4) has a pair of spaced upstanding arms extending through apertures provided in the embossed section 42 of the frame 11 which engage respective spaced notches 69 (FIGURE 3) formed in the operating lever 29. The pressure plate 68 is responsive to pressure of a fluid in a conduit 70.

For use, opposite sides of a power line (not shown) are connected to the outside pair of the terminal screws 21 as viewed in FIGURES 1 and 2, and conductors (not shown) leading to a load such as an electric motor or the like are connected to the respective inside pair of terminal screws 21. A load is therefore connected to the power line when the pairs of the movable contacts 49 engage their complementary pairs of the fixed cont-acts 22.

When the pressure in the conduit 70 is below a predetermined value, the switch is in the closed position because of the bias of the spring 26. When the pressure in the conduit 70 builds up, the pressure plate 68 presses against the operating lever pivotal mounting in the slots 31 against the bias of the spring 26, thereby to carry the end of spring 33 attached thereto upwardly until the operating lever 29 engages the undersurface of the cup washer 53. Continuation of this upward movement lifts the washer 53 from its seat whereby the bias of both of the springs 54 and 26 operate to oppose the upward movement of the lever 29. When the lever 29 has been raised to a predetermined position, the spring 33 passes overcenter and the bight portion of the toggle link 35 moves upwardly with a snap action thereby to rotate the contact frame 36 in a counterclockwise direction as viewed in FIGURE 4 about its pivot arms 40. As the toggle link 35 snaps upwardly, its bight portion strikes the undersurf-ace of the adjustable arm 46 thereby to impart a hammer blow to the contact =frame 36 so that the carrier 37 and the movable contacts 49 carried thereby are rapidly moved to an open circuit position breaking the electrical circuit through the switch. As will be seen from FIGURES 2 and 4, the open position of the contact frame 36 is limited by the interengagement between the extension 43 and the arm 14. The distance through which toggle link 35 travels during the opening of the switch is determined by the position of the arm 46 of the bracket 45. The arm 46 may be bent to provide adjustment.

Upon a decrease in pressure, the force exerted by the pressure plate 68 on the operating lever 29 decreases and the operating lever 29 then moves downwardly under the influence of springs 26 and 54 until the cup washer 53 again seats. Thereafter, the bias of spring 26 only acts upon the operating lever 29. Inasmuch as the bias of both of the springs 26 and 54 operate against the operating lever 29 at the instant the contacts separate, and only the bias of the spring 26 operates against the operating lever 29 at the time the contacts reclose, it will be seen that changes in the operating difierential of the switch may be accomplished by varying the bias of the spring 54. This is eifected, as previously described, by adjusting the position of the nut 56.

As the lever 29 continues to move in a downward direction with decreasing pressure in the conduit 70, the end 29 and rotates it about its continuity of operating spring 33 attached to the operating lever 29 center. The force exerted by the link 35 at the point of its pivot on the contact frame 36 causes the contact frame 36 to move to the closed circuit position with a snap action. The bight portion of the link 35 aids this closing movement by striking a hammer blow against the lower wall portion of the rectangular opening 44 in the frame 36. Without more, however, a problem of contact welding is frequently encountered in the closing operation, notwithstanding the hammer blow provided by the downwardly traveling toggle link 35 as it strikes the contact frame 36 at the lower wall of the opening 44. This is particularly true when relatively large currents are being controlled by the switch. Some of the effect of the link 35 striking the frame 36 is lost by the action of the resilient support springs 50 which absorb a significant amount of the force generated by the impact of the movable contacts 49 upon the respective fixed contacts 22.

The problem which may be encountered is depicted in FIGURES 5 and 6. FIGURE 5 shows the position of one pair of the contacts 49 and the contact carrier 37 in the open circuit position. The contact spring 50 holds the contact bridge in the fully extended position. During a closing operation as previously described, one or the other of the contacts 49 on the contact bridge 48 of FIGURES 5 and 6 may make contact with its complementary fixed contact 22 before the other, as shown in FIGURE 6. As previously stated, if the current being controlled is sufiiciently large, one of the contacts 49, after making initial physical con tact with the associated contact 22, may become welded thereto when the other contact 49 on the bridging member 48 either approaches close enough to its associated fixed contact 22 to establish an arc, or makes actual contact followed by a rebound with or without consequent arcing. Upon the cessation of the are at the next zero point in the current cycle, energization of the load is interrupted because the welding of one of the contacts 49 to its complementary fixed contact 22 holds the other movable contact 49 in a position out of electrical contact with its complementary fixed contact 22 as shown in FIGURE 6. For clarity, the space between the disengaged contacts 22 and 49 is shown exaggerated.

To correct this problem in accordance with the present invention, the stop 43 which, in previous pressure switches, limited movement of the contact carrier 37 in the closing direction to a vertical position such that the resilient contact springs 50 remained in partially compressed condition, is shaped to allow the contact carrier 37 to travel beyond the vertical position to the position shown in FIG- URE 4. In this position the resilient contact springs 50 are completely compressed and, during a closing operation, the contact carrier 37 strikes the cup washers 51 which bear against their respective bridging members 48. Thus, it is seen that if there is a tendency for a condition such as shown in FIGURE 6 to occur, the present invention provides an efiicient and reliable method of insuring electrical between both the movable contacts 49 and their respective fixed contacts 22. This is accomplished by the contact carrier 37 completely compressing the resilient support springs 50 and phyically striking the cup washers 51 as described above, thereby providing a second hammer blow to the bridging member 48 in the closing operation. The first hammer blow is provided by the downwardly traveling toggle link 35 striking the lower wall of the opening 44 in the contact frame 36, and the second hammer blow is provided by the contact carrier 37 striking the cup washers 51 which bear against their respective bridging members 48. Any tendency for either or both of the contact bridges 48 to remain in the welded position of FIGURE 6 is thereby eliminated.

What is claimed is:

1. A pressure switch comprising a base, a pair of stationary contacts supported on said base, a movable bridging means having contact portions at opposite ends thereof complementary to said stationary contacts, respectively, pivotal means pivotally supported on said base and movable between an open circuit position and a closed circuit position, a contact arm mounted on said pivotal means and movable therewith between said open and closed circuit positions mounting means mounting said bridging means on an end portion of said contact arm, said mounting means including a lost-motion connection means permitting restricted movement of said bridging means relative to said contact arm in a path toward and away from said contact arm and permitting restricted pivotal movement of said bridging means about an axis extending transversely of said bridging means between said contact portions and substantially normal to said path, a contact spring biasing said bridging means away from said contact arm and normally maintaining the bridging means spaced from the contact arm at a distance limited by said connection means, snap-acting toggle means causing said pivotal means to move in oposite directions, selectively, between said open and closed circuit positions with a snap action thereby to move said contact portions on said bridging means into and out of engagement with the respective stationary contacts, pressure responsive means for actuating said snap-acting toggle means, said snapacting toggle means being operative to move said contact arm in a direction toward said stationary contacts with suflicient force to compress said contact spring upon engagement of said contact portions with said stationary contacts, stop means on said pivotal means movable with said pivotal means between first and second positions which correspond, respectively, to said open and closed circuit positions of said pivotal means, said base having a portion engaged by said stop means in said first position so as to establish the open circuit position of said pivotal means, said stop means, in said second position, being in non-interfering relationship with all other components of said pressure switch and therefore being wholly inoperative to arrest the movement of said pivotal means during movement thereof to said closed circuit position, said bridging means being non-resiliently engaged by said contact arm to establish said second position of said step means and said closed circuit position wherein said contact portions are in engagement with their respective stationary contacts and said contact spring is compressed and ineffective to resiliently space said bridging means from said contact arm, whereby said bridging means receives a hammer blow after at least one of said contact portions engages its complementary stationary contact upon movement of said contact arm to said closed circuit position, and said mounting means being operative after initial movement of said contact arm toward said open circuit position from said closed circuit position to impart a hammer blow to said bridging means.

2. A pressure switch according to claim -1 including an operating lever pivotally mounted on said base, biasing means biasing said operating lever toward one position, and wherein said snap-acting toggle means includes a toggle link means pivotally mounted on said pivotal means and a toggle spring interconnecting said operating lever and said toggle link, said pressure responsive means elfects movement of said operating lever against and with the bias of said biasing means causing the line of action of said toggle spring to be moved alternately in opposite directions across the pivot point of said link on said pivotal means to effect a rapid overcenter snapping movement of said link in both directions and consequent rapid pivoting of said pivotal means and said contact arm, limiting means on said pivotal means determines the limit of travel of said toggle link in both directions of movement thereof, said toggle link imparting a hammer blow to said limiting means as said toggle link is snapped overcenter whereby a sudden and substantial force is imparted to said pivotal means and said contact arm to move said bridging means both into and out of engagement with said stationary contacts.

3. In a pressure switch, a base, a pair of fixed contacts supported on said base, movable contact means engageable with said fixed contacts, pivotal means pivotally mounted on said base for moving said contact means in opposite directions to respective open and closed circuit positions with respect to said fixed contacts, resilient mounting means including lost-motion connection means resiliently mounting said contact means on said pivotal means and resiliently spacing said contact means away from said pivotal means normally at a distance limited by said con nection means, a toggle link pivoted on said pivotal means, an operating lever pivoted on said base, a toggle spring interconnecting said toggle link and said operating lever, biasing means biasing said operating lever toward one po sition, pressure responsive means for moving said operating lever against said biasing means, the line of action of said toggle spring being movable across the pivot point of said toggle link by operating lever to effect an overcenter snapping movement of said toggle link, limiting means-on said pivotal means for determining the limit of travel of said toggle link in both directions of movement thereof, said toggle link imparting a hammer blow to said limiting means as said toggle link is snapped overcenter, whereby a sudden and substantial force is imparted to said pivotal means in moving said contact means both to open and closed circuit positions, stop means on said pivotal means movable with said pivotal means between first and second positions which correspond, respectively, to said open and closed circuit positions of said contact means, said base having a portion engaged by said stop means in said first position so as to establish the open circuit position of said contact means and said pivotal means, said stop means, in said second position, being in non-interfering relationship with all other components of said pressure switch and therefore being wholly inoperative to arrest the movement of said pivotal means during movement of said contact means to said closed circuit position, said toggle spring having sufiicient force to overcome the bias of said resilient mounting means and to render the resilient mounting means ineifective to resiliently space said contact means away from said pivotal means, whereby movement of said pivotal means in a circuit closing direction is arrested, consequent upon the engagement of said contact means with said fixed contacts, solely by the non-resilient engagement of said pivotal means with said contact means, and said mounting means engaging said contact means after initial movement of said pivotal means away from engagement with said contact means, thereby to impart a hammer blow to said contact means.

References Cited UNITED STATES PATENTS 1,287,491 12/ 191 8 Spaulding 20067 1,818,801 8/1931 Herden ZOO--67 2,347,874 5/1944 Bluemle 20077 2,741,678 4/ 6 Schaefer et al. 200-83 3,194,909 7/1965 Epstein 200*78 BERNARD A. GILHEANY, Primary Examiner. H, B, GILSON, G. MAIER, Assistant Examiners,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,340 ,372 September 5 1967 Carl A. Schaefer It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 61, for "phyically" read physically column 5, line 6, after "positions" insert a comma; line 19, for "oposite" read opposite same column 5 line 58 after "link" strike out "means"; column 6, line 25, before "operating" insert said Signed and sealed this 24th day of September 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. A PRESSURE SWITCH COMPRISING A BASE, A PAIR OF STATIONARY CONTACTS SUPPORTED ON SAID BASE, A MOVABLE BRIDGING MEANS HAVING CONTACT PORTIONS AT OPPOSITE ENDS THEREOF COMPLEMENTARY TO SAID STATIONARY CONTACTS, RESPECTIVELY, PIVOTAL MEANS PIVOTALLY SUPPORTED ON SAID BASE AND MOVABLE BETWEEN AN OPEN CIRCUIT POSITION AND A CLOSED CIRCUIT POSITION, A CONTACT ARM MOUNTED ON SAID PIVOTAL MEANS AND MOVABLE THEREWITH BETWEEN SAID OPEN AND CLOSED CIRCUIT POSITIONS MOUNTING MEANS MOUNTING SAID BRIDGING MEANS ON AN END PORTION OF SAID CONTACT ARM, SAID MOUNTING MEANS INCLUDING A LOST-MOTION CONNECTION MEANS PERMITTING RESTRICTED MOVEMENT OF SAID BRIDGING MEANS RELATIVE TO SAID CONTACT ARM IN A PATH TOWARD AND AWAY FROM SAID CONTACT ARM AND PERMITTING RESTRICTED PIVOTAL MOVEMENT OF SAID BRIDGING MEANS ABOUT AN AXIS EXTENDING TRANSVERSELY OF SAID BRIDGING MEANS BETWEEN SAID CONTACT PORTIONS AND SUBSTANTIALLY NORMAL TO SAID PATH, A CONTACT SPRING BIASING SAID BRIDGING MEANS AWAY FROM SAID CONTACT ARM AND NORMALLY MAINTAINING THE BRIDGING MEANS SPACED FROM THE CONTACT ARM AT A DISTANCE LIMITED BY SAID CONNECTION MEANS, SNAP-ACTING TOGGLE MEANS CAUSING SAID PIVOTAL MEANS TO MOVE IN OPOSITE DIRECTIONS, SELECTIVELY, BETWEEN SAID OPEN AND CLOSED CIRCUIT POSITIONS WITH A SNAP ACTION THEREBY A MOVE SAID CONTACT PORTIONS ON SAID BRIDGING MEANS INTO AND OUT OF ENGAGEMENT WITH THE RESPECTIVE STATIONARY CONTACTS, PRESSURE RESPONSIVE MEANS FOR ACTUATING SAID SNAP-ACTING TOGGLE MEANS, SAID SNAPACTING TOGGLE MEANS BEING OPERATIVE TO MOVE SAID CONTACT ARM IN A DIRECTION TOWARD SAID STATIONARY CONTACTS WITH SUFFICIENT FORCE TO COMPRESS SAID CONTACT SPRING UPON ENGAGEMENT OF SAID CONTACT PORTIONS WITH SAID STATIONARY CONTACTS, STOP MEANS ON SAID PIVOTAL MEANS MOVABLE WITH SAID PIVOTAL MEANS BETWEEN FIRST AND SECOND POSITIONS WHICH CORRESPOND, RESPECTIVELY, TO SAID OPEN AND CLOSED CIRCUIT POSITIONS OF SAID PIVOTAL MANS, SAID BASE HAVING A PORTION ENGAGED BY SAID STOP MEANS IN SAID FIRST POSITION SO AS TO ESTABLISH THE OPEN CIRCUIT POSITION OF SAID PIVOTAL MEANS, SAID STOP MEANS, IN SAID SECOND POSITION, BEING IN NON-INTERFERING RELATIONSHIP WITH ALL OTHER COMPONENTS OF SAID PRESSURE SWITCH AND THEREFORE BEING WHOLLY INOPERATIVE TO ARREST THE MOVEMENT OF SAID PIVOTAL MEANS DURING MOVEMENT THEREOF TO SAID CLOSED CIRCUIT POSITON, SAID BRIDGING MEANS BEING NON-RESILIENTLY ENGAGED BY SAID CONTACT ARM TO ESTABLISH SAID SECOND POSITION OF SAID STOP MEANS AND SAID CLOSED CIRCUIT POSITION WHEREIN SAID CONTACT PORTIONS ARE IN ENGAGEMENT WITH THEIR RESPECTIVE STATIONARY CONTACTS AND SAID CONTACT SPRING IS COMPRESSED AND INEFFECTIVE TO RESILIENTLY SPACE SAID BRIDGING MEANS FROM SAID CONTACT ARM, WHEREBY SAID BRIDGING MEANS RECEIVES A HAMMER BLOW AFTER AT LEAST ONE OF SAID CONTACT PORTIONS ENGAGES ITS COMPLEMENTARY STATIONARY CONTACT UPON MOVEMENT OF SAID CONTACT ARM TO SAID CLOSED CIRCUIT POSITION, AND SAID MOUNTING MEANS BEING OPERATIVE AFTER INITIAL MOVEMENT OF SAID CONTACT ARM TOWARD SAID OPEN CIRCUIT POSITION FROM SAID CLOSED CIRCUIT POSITION TO IMPART A HAMMER BLOW TO SAID BRIDGING MEANS.

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