US3183329A

US3183329A - Pressure operated switch with lever which rocks freely about its transverse axis through two points of engagement

Info

Publication number: US3183329A
Application number: US104900A
Authority: US
Inventors: John V S Dahlgren
Original assignee: Wilcolator Co
Current assignee: Wilcolator Co
Priority date: 1961-04-24
Filing date: 1961-04-24
Publication date: 1965-05-11
Anticipated expiration: 1982-05-11
Also published as: GB958319A; DE1192294B

Description

y 1965 J. v. s. DAHLGREN 3,183,329

PRESSURE OPERATED SWITCH WITH LEVER WHICH ROCKS FREELY ABOUT ITS TRANSVERSE AXIS THROUGH TWO POINTS OF ENGAGEMENT Filed April 24. 1961 4 Sheets-Sheet 1 ll' 1 n 7 MHIrTN 1 n L .w b a a w m 4 I h #6 Y8m4q 3 M 84 Q 44 b u 4 0 22 6 b 3 4 30 ll. M I 7 4 5 n, 3. fl v u 5 I HL 9 7 3 A 0 0M 4 2 3 4 G 3 k 4 5 0 III n... a r Wire r a Uh INVENTOR JOHN V. S. DAHLGREN ATTO EY May 11, 196 J. v. s. DAHLGREN 3,183,

PRESSURE OPERATED SWITCH WITH LEVER WHICH ROCKS FREELY ABOUT ITS TRANSVERSE AXIS THROUGH TWO POINTS OF ENGAGEMENT Flled Aprll 24. 1961 4 Sheets-Sheet 5 Fig. 5

as as 37 4o '2 INVENTOR JOHN v.5. DAHLGREN zig. 6 1, 7 8 g ATTORNEY y 11, 1955 s. DAHLGREN 3 183,329

J. V. PRESSURE OPERATED SWITCH WITH LEVER WHICH ROCKS FREELY ABOUT ITS TRANSVERSE AXIS THROUGH TWO POINTS OF ENGAGEMENT Filed April 24, 1961 4 Sheets-Sheet 4 mam Ila 49 45 JOHN V.S. DAHLGREN Fig. 7

ATTORNEY United States Patent PRESSURE OPERATED SWITCH WITH LEVER WHICH ROCKS FREELY ABOUT ITS TRANS- VERSE AXIS THROUGH TWO POINTS OF ENGAGEMENT John V. S. Dahlgren, Fair Haven,

Wilcolator Company, New Jersey Filed Apr. 24, 1961, Ser. No. 104,900 2 Claims. (Cl. 200-140) This invention relates to pressure operated switch mechanisms, especially useful in controlling energization of electric heaters and the like in response to pressure variations in a power element such as an expansible bellows containing a fluid which changes in volume or pressure according to changes in temperature thereof. More particularly, the invention is directed to improvements in switch mechanisms of that type having slow opening and closing contacts, operated directly in accordance with pressure fluctuations, as distinguished from switch mechanisms having fast or snap acting contact means.

Because such slow acting type switches are opened and closed by minute changes in volume of the expansible elements operating them, it may be said that they have a Zero temperature differential which is particularly desirable for accurately controlling electrically operated means for maintaining a temperature within close tolerances such as is required in photographic developing baths and the like. Due to the minute movements of the power elements required to operate the switches, small changes in the physical arrangement of the switch mechanisms, such as result from misalignment and wear of parts, pitting or roughening of the contacts, ambient temperature changes, and the like, result in relatively wide variations from the desired predetermined operating temperature.

The improvements of the present invention are concerned with the provision of a slow acting switch embodying such constructions and arrangements of parts as to maintain proper positioning of the contacts, to minimize the likelihood of wear and of misalignment of parts, and to thereby provide a switch mechanism which is highly reliable and constant in operation over long periods of time and under adverse conditions. In the practice of this invention there is provided an adjustable switch mechanism comprising two spaced stationary contacts and a relatively movable bridging contact carried by a lever for movement into and out of engagement with the stationary contacts for making and breaking an electric circuit therethrough, the lever being movable about an adjustable pivot member in one direction by a power element, such as an expansible bellows, and being biased in the other direction by spring means opposing the bellows, the pivot member, power element and spring means each acting on the lever along a center-line defining the long axis of the lever so that the lever is free of off-center forces which would tend to rock the lever about its long axis and thereby misalign the bridging contact with respect to the spaced stationary contacts, the connection of the pivot and bellows to the lever along the center-line thereof being such as to frictionally resist rocking of the lever about its long axis when the contacts are open yet permitting the bridging contact to level itself against the stationary contacts upon each closing of the contacts.

It is another object of this invention to provide a pressure operated switch mechanism of the above mentioned character in which the lever is formed of molded insulating material and the connections therewith by the adjustable pivot member and the bellows means are effected by providing the lever with a tapered or V-shaped first socket N.J., assignor to The Elizabeth, NJ., a corporation of in which a rounded point of the adjustable pivot member is received and a conical second socket in which the rounded point of a post forming part of the bellows means is received, whereby the alignment of the points of application of forces on the lever is determined by the fixed positions of the sockets in the lever, which sockets are permanently and accurately positioned in the process of molding the lever, thereby assuring a minimum of offcenter forces and a maximum of stability in the operating characteristics of the switch over long periods of time.

Still another object of this invention is the provision of a pressure operated switch mechanism having an adjustable pivot means in the form of a rotatable threaded shaft extending through a threaded sleeve in which the shaft may be advanced or retracted by rotation thereof for changing the operating characteristics of the switch, the sleeve being slotted to provide spring fingers for resiliently gripping the shaft so that a predetermined torque is required for turning thereof, the sleeve having an internal annular undercut area whereby only the end portions of fingers grip the shaft, the turning torque thereby being substantially independent of the pitch of the threads and dependent upon the gripping force of the fingers.

The invention may be further described as residing in other constructions and arrangements of parts, the objects and advantages of which will become apparent from the following detailed description of a presently preferred embodiment of the invention and from the accompanying sheets of drawings, in which:

FIG. 1 is a perspective view of a pressure operated switch mechanism embodying the invention;

FIG. 2 is a sectional view of the mechanism of FIG. 1 taken substantially along line 22 thereof and on an enlarged scale;

FIG. 3 is a sectional view of the switch mechanism taken substantially along line 3-3 of FIG. 2;

FIG. 4 is a sectional view of the switch mechanism taken substantially along line 44 of FIG. 2;

FIG. 5 is a sectional view taken substantially along line 55 of FIG. 2;

'FIG. 6 is a sectional view taken substantially along line 6-6 of FIG. *2;

FIG. 7 is a sectional view taken substantially along line 7-7 of FIG. 2;

FIG. 8 is a fragmentary view taken along line 88 of FIG. 2, and

FIG. 9 is a sectional view similar to FIG. 2 but with parts shown in different positions.

In the form of the invention illustrated in the drawings and described hereinafter, there is provided a switch mechanism or control device, generally indicated at 10, which is operated in response to temperature changes and is adjustable to select a predetermined temperature at which the contacts thereof will open and close, and which device is particularly useful in controlling the energization of non-inductive loads or other low current drawing loads such as electric heaters, although it will be understood that the device is susceptible of other uses.

The device 10 comprises a box like casing 11 provided with a cover 12 and a terminal block 14 of insulating material mounted in One end of the casing between the cover and bottom of the casing and secured therein by bolts 16. The bolts 16 together with a screw 17 serve to hold cover 12 in place as shown, and the cover is conveniently provided with raised embossments 12a which have threaded openings 12b for receiving screws for mounting the device against a panel.

A pair of laterally spaced

stationary contacts

20 and 21 are secured by rivet portions 20a and 21a thereof to the inner ends of a pair of

terminal members

22 and 23 and to an inwardly directed flange 14a of insulator block 14. The terminal members extend through block 14 and the outer ends 22a and 23a of the terminal members serve to connect the device in a circuit to be controlled thereby. An elongated bridging contact 25 is secured, as by a rivet 26, to one end of a lever 27 formed of Bakelite or other suitable rigid insulating material, and is carried thereby for movement into and out of bridging engagement with the

contacts

20 and 21 for making and breaking an electrical circuit therethrough.

Lever 27 is provided near the central portion thereof with a tapered or V-shaped depression or socket 28 having flat sloping side walls 28a and in which is received the generally pointed but rounded off end 30a of an adjustable control shaft 39 so as to form a universal pivotal connection between the lever 27 and the shaft 3% This pivotal connection, best illustrated in FIGS. 2 and 4, comprises a point of contact with each side wall 28a of socket 28 thereby providing a substantially friction free pivot for lever 27 in its movement during opening and closing of the contacts, the movement being in effect about the center of radius 31 of shaft point 3tla. The V-shape of socket 28 accommodates slight manufacturing variations in the positioning of shaft 30 with respect to the length of the lever.

Control shaft 30, which has one end portion 34b projecting outwardly of cover 12 for reception of a control knob, extends through a threaded sleeve 32 in which the shaft may be advanced or retracted by rotation of the outer end portion 30b for selection of the temperature at which the contacts will be opened and closed by lever 27, the operation of which will become apparent as the description proceeds. Sleeve 32 has the inner end thereof cross-slotted to provide four resilient fingers 32a as is best shown in FIGS. 2 and 4, and these fingers are squeezed inwardly during manufacture so as to have a slight inward set so that control shaft 30 is gripped thereby and a predetermined torque is required to turn the shaft. An annular internal groove 32b is formed in sleeve 32, as by undercutting to remove a portion of the sleeve threads, so that the threaded control shaft Bil is resiliently gripped by only the end portions of fingers 32a, whereby the required turning torque is substantially independent of the pitch of the screw threads.

Sleeve 32 is provided with a flange 320 which is acted on by clamping bar or bracket 34 which serves to clamp the flange and one end of a flexible leaf spring 35 to the cover 12. Clamping bar 34 is conveniently secured by a pair of screws 36 extending through cover 12, and through an apertured plate 37 overlying cover 12 and through which shaft end portion 30b extends. A flat washer member 40, having a projecting lug 40a, is disposed between fiat plate 37 and cover 12 in surrounding relation to shaft end portion 30b and is secured for rotation therewith by cooperation with a flat side 300 of shaft end portion 30b. The projection 40a cooperates with a dOWn turned lug 37a formed on plate 37 and serves to limit the rotation of shaft 30 during adjustment of the device.

Leaf spring 35 has a central opening 35b through which shaft 30 extends and has its free end 350 in engagement with a rounded projection 4-2 formed at the end of lever 27 remote from the bridging contact 25. Spring 35 acts to resiliently bias lever 27 in a clockwise direction as viewed in FIG. 2 about pivot point 30a and thereby tends to move bridging contact 25 to its closed position against spaced contacts 2%) and 21.

A power element in the form of an expansible bellows is mounted on the bottom wall 11a of the casing and has an axially extending post 46 having a generally pointed but rounded off end 46a received in a conical depression or socket 47 formed in lever 27 between socket 28 and projection 42 and on the side of lever 27 opposite thereto. Post end 46a and socket 47 form a pivotal connection between post 46 and lever 27 with the center of movement located substant al y at the center of radius 48 of post end 46a. Bellows 45 has a base 45a having a reduced portion extending through a slot 4% in casing wall 11a and receiving a nut 50 securing the bellows to the casing wall. A tubular member 51, which extends from base 45a and is in communication with the interior of bellows 45, terminates in a bulb portion 52. Bulb 52, tube 51 and bellows 45 contain a fluid which expands and contracts with increases and decreases in temperature, thereby causing the bellows to expand and contract resulting in axial movement of post 46 in accordance with temperature changes experienced by the bulb 52 and in a manner well known in the art to which the invention pertains.

Axial movement of post 46 upon expansion of bellows 45 rotates lever 27 in a counter-clockwise direction about pivot point 30a in opposition to the biasing effect of spring 35 and so as to move bridging contact 25 to an open position. It will be recognized that advancing or retracting of control shaft 3t} so as to move point 30a thereof will serve to respectively decrease or increase the temperature at which the contacts will be separated by a rise in temperature at the bulb 52. It will also be recognized that the movements of lever 27 and contact 25 will tend to be directly in accordance with fluctuations in temperature, and that the temperature at which the contacts will open upon rise in temperature will be substantially the same as the temperature at which the contacts will close on a decrease in temperature. In other words, there is a zero differential between the opening and closing temperatures. These direct action and zero differential characteristics of the switch mechanism make it particularly suitable for maintaining a predetermined temperature within close tolerances.

The

sockets

28 and 47 in lever 27, and projection 42 thereon are so located that the forces acting on lever 27 through control shaft 30, post 46 and spring 35 all act on a center-line L of the lever, which line lies in a plane passing through the centers of

radius

31 and 48, through the point of contact of spring 35 against projection 42, and through the working surfaces of bridging contact 25. Lever 27 is therefore free of off-center forces which would tend to rock the lever about its long axis and disturb the alignment of bridging contact 25 with respect to spaced

contacts

20 and 21 during opening and closing of the contacts.

Sockets

28 and 47, and projection 42, are permanently and accurately positioned by the process of molding lever 27, thereby assuring a minimum of off-center forces acting on the lever and a maximum of stability in the operating characteristics of the switch over long periods of time.

Inasmuch as the rounded end 30a of the control shaft engages the opposite side walls 28a of socket 28, rocking movement of lever 27 about its own long axis, as defined by the center-line L through centers of

radius

31 and 48, will be frictionally resisted. Such frictional resistance serves to inhibit rocking or tilting of the bridging contact as the result of vibration, jarring or the like to which the device may be subjected when the contacts are open, and yet permits the bridging contact to level itself, if necessary, against the spaced contacts as it is moved thereagainst by the influence of spring 35 on lever 27.

From the foregoing detailed description of a switch mechanism embodying the present invention it will be appreciated that there has been provided thereby an improved switch mechanism of the slow opening type which may be accurately set to operate at a predetermined pressure or temperature and which will maintain its accuracy over long periods of use.

Although the invention has been described with reference to a specific embodiment of switch mechanism and to a specific use thereof, it will be understood that the invention is not limited thereto, but rather the invention includes all those changes, modifications, and uses as are reasonably embraced by the scope of the claims hereof.

Having described my invention, I claim:

1. A switch mechanism comprising a support structure, a pair of spaced fixed contacts on said structure, a lever carrying a contact bar extending transversely thereof and movable by said lever into and out of engagement with said contacts, pivot means for said lever comprising a recess in said lever intermediate the ends thereof and having two opposed plane sides extending parallel to the longitudinal axis of said lever and inclined toward one another inwardly from one side of said lever and a shaft carried on said support structure and having a rounded end engaging said opposed plane sides by point contacts, a spring supported on said structure and engaging said lever to urge said lever in one direction about said pivot means, means forming a rolling point contact between said spring and lever, condition responsive means for moving said lever in one direction about said pivot means, and means forming a rolling point contact between said condition responsive means and said lever, said rolling point contacts lying in a common plane which extends longitudinally of said lever and through the center of said rounded end of said shaft.

2. A switch mechanism according to the preceding claim and wherein said lever has a spherical embossment at the end remote from said contact bar, and said spring comprises a leaf spring member attached at one end to said support structure and having a fiat portion of the other end bearing against said embossment to form a rolling point contact with said lever.

References Cited by the Examiner UNITED STATES PATENTS 2,739,204 3/56 Garner et a1 200-140 2,930,876 3/60 Siri 200-440 BERNARD A. GILHEANY, Primary Examiner. MAX L. LEVY, Examiner.

Claims

1. A SWITCH MECHANISM COMPRISING A SUPPORT STRUCTURE, A PAIR OF SPACED FIXED CONTACTS ON SAID STRUCTURE, A LEVER CARRYING A CONTACT BAR EXTENDING TRANSVERSELY THEREOF AND MOVABLE BY SAID LEVER INTO AND OUT OF ENGAGEMENT WITH SAID CONTACTS, PIVOT MEANS FOR SAID LEVER COMPRISING A RECESS IN SAID LEVER INTERMEDIATE THE ENDS THEREOF AND HAVING TWO OPPOSED PLANE SIDES EXTENDING PARALLEL TO THE LONGITUDINAL AXIS OF SAID LEVER AND INCLINED TOWARD ONE ANOTHER INWARDLY FROM ONE SIDE OF SAID LEVER AND A SHAFT CARRIED ON SAID SUPPORT STRUCTURE AND HAVING A ROUNDED END ENGAGING SAID OPPOSED PLANE SIDES BY POINT CONTACTS, A SPRING SUPPORTED ON SAID STRUCTURE AND ENGAGING SAID LEVER TO URGE SAID LEVER IN ONE DIRECTION ABOUT SAID PIVOT MEANS, MEANS FORMING A ROLLING POINT CONTACT BETWEEN SAID SPRING AND LEVER, CONDITION ABOUT SAID PIVOT MEANS, AND MEANS LEVER IN ONE DIRECTION ABOUT SAID PIVOT MEANS, AND MEANS FORMING A ROLLING POINT CONTACT BETWEEN SAID CONDITION RESPONSIVE MEANS AND SAID LEVER, SAID ROLLING POINT CONTACTS LYING IN A COMMON PLANE WHICH EXTENDS LONGITUDINALLY OF SAID LEVER AND THROUGH THE CENTER OF SAID ROUNDED END OF SAID SHAFT.