US3369093A - Snap acting thermally responsive element with contacts at the periphery thereof in rocking and sliding engagement with corresponding fixed contacts during snap action - Google Patents

Description

Feb. 13, 1968 w. R. HARPER, JR 3,369,093

SNAP ACTING THERMALLY RESPONSIVE ELEMENT WITH CONTACTS AT THE PERIPHERY THEREOF IN ROCKING AND SLIDING ENGAGEMENT WITH CORRESPONDING FIXED CONTACTS DURING SNAP ACTION Filed Aug. 16, 1966 United States Patent 3,369,093 SNAP ACTING THERMALLY RESPONSIVE ELE- MENT WITH CONTACTS AT THE PERIPHERY THEREOF IN ROCKING AND SLIDING EN- GAGEMENT WITH CORRESPONDING FIXED CONTACTS DURING SNAP ACTION Walter Reeve Harper, Jr., Barriugton, R.I., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware- Filed Aug. 16, 1966, Ser. No. 572,702 3 Claims. (Cl. 200-122) ABSTRACT OF THE DISCLOSURE A bimetallic snap-acting plate marginally carries on one side two opposite curved-face contacts between which the plate centrally supports a movable insulated third contact. The curved faces of the marginal contacts with sliding action rockingly engage one of two fixed conductive line terminals in a main circuit. From each line terminal extends a conductive finger. These fingers engage the other side of the plate, one opposite each of the two contacts at the plate margin so as to bias them into free rocking engagement with the two conductive line terminals. When the plate snaps said two contacts move freely without restricting movements of the plate margins and without breaking the electrical connection in the main circuit. Thus the third contact is moved by the plate with efiicient snap-action to and from an adjustable part of a third line terminal which is in a control circuit. The assembly of said two line terminals, fingers, plate and third contact is carried in one housing. The third line terminal and its adjustable part are carried in a second housing. These housings are provided with a rotary bayonet type coupling means for convenient assembly prior to scaling, so as coaxially to relate the movable third contact to the adjustable part of the third line terminal.

Among the several objects of this invention may be noted the provision of an improved switch which will quickly snap open to break a relay circuit in response to heating resulting from current flow in a motor circuit or the like passing through the switch, without breaking the motor circuit, except through action of the relay circuit; and the provision of a snap-acting switch of the type described which is less complex, more reliable, lighter in weight and less expensive to construct and assemble than former relay switches of the same class. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the construction hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

FIG. 1 is a plan view of a switch made according to the invention;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1, parts being broken away;

FIG. 3 is a fragmentary cross section similar to FIG. 2 showing portions of the switch in a moved position;

FIG. 4 is a fragmentary cross section view taken along line 44 of FIG. 1; and

FIG. 5 is a fragmentary view looking along line 5-5 of FIG. 3.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring to the drawings, the switch comprises a casing 1 molded from a suitable electrical insulating material, such as a phenolic resin. Casing 1 has holes 3 which are adapted to receive bolts or other mounting members (not shown) for attaching the casing to a suitable support, such as a compressor housing. Casing 1 has a well 5 which includes a lower generally cylindrical portion 7 and a somewhat larger upper cylindrical portion 9. The well is surrounded by a wall 11. Three semicylindrical ribs 13 spaced 120 apart on wall 11 project radially inward into the upper cylindrical portion 9 of the well 5.

Well 5 receives the lower end portion of a head 15 which is made of a suitable electrical insulating material, such as a phenolic resin. The casing 1 and head 15 constitute the switch housing as a whole. Carried in the head 15 is a conventional heater wire 16 connected with a heater terminal 18. These parts 16 and 18 may be omitted, if desired. Head 15 has a generally cylindrical outer wall 17 which is enlarged at its lower margin to form a rim 19, the latter being substantially the same diameter as the cylindrical portion 9 of well 5. Rim 19 has three arcuate notches 21 spaced 120 apart. The notches extend the full height of the rim and are adapted to receive ribs 13 on the casing as the base is inserted into the well 5. The height of rim 19 is such that the upper end of the rim is just beneath the lower end of the ribs 13 when the base is fully inserted into well 5 with the lower end of the base engaging a shoulder 23 at the bottom of portion 9 of the well. This permits a bayonet type of connecting action, the head 15 being rotated within the well 5 to unalign the ribs and grooves and to align one of the notches 21 with a hole 25 (FIGS. 2 and 3) in the casing so that a locking pin 27 can be inserted into the hole 25 and the notch 21 to lock the casing and base in assembled relation. Then the space between the base wall 17 and the well is filled with a sealing material 29. The bayonet assembly arrangement facilitates assembly and reduces manufacturing cost.

A downwardly opening generally cylindrical chamber 31 in head 15 is partially closed by an annular baflle 33 seated against a shoulder in the lower end of wall 17. Slots 35 and 37 extend through head 15 from the top of the head to the chamber 31. These slots receive switch terminals 39 and 41. The inner ends of the terminals are bent over to form contacts designated 43 and 45. The other ends of the terminals project above the head 15 and may be attached to suitable terminal lead wires (not shown) of a primary circuit, such as the start winding circuit of a motor driving a refrigeration compressor. The circuit between contacts 43 and 45 is completed through a thermally responsive bimetal snapacting electrically conductive dished element 47 carrying contacts 49 and 51 mounted on marginal portions thereof, the latter engaging contacts 43 and 45, respectively. The element 47 is preferably a dished bimetallic disc having one layer of a low thermal coefficient of expansion and the other layer of a somewhat higher thermal coefficient of expansion so that upon heating and cooling of the member it snaps between the positions shown in FIGS. 2 and 3. Element 47 is normally heated as current is passed through it and in addition by the auxiliary heater, if used. The pairs of contacts 43, 49 and 45, 51 are held in rocking engagement at all times by a pair of retainers 53, 55 which pass through slots 35 and 37 and have fingers 57 and 59, respectively, at their lower ends..These fingers bear against the lower side of the disc 47 at about the centers of the contacts to hold the disc margin against vertical movement and thereby hold the contacts in rocking engagement. The other end portion of the retainers are curved into loops and bear against the top of head 15 to anchor the retainers in the slots 35 and 37.

A follower generally designated 61 is articulated with the center of disc 47 by a screw 63. The screw extends through a hole in the center of the disc and is threaded into a central dome-shaped portion of follower 61. The

underside of the screw head is inwardly beveled. This and the dome shape permit free movements ofarticulation. The follower 61 moves up and down with vertical movements of the center portion of the strip 47, as is apparent from a comparison of FIGS. 2 and 3.

The follower is made from an electrical insulating material. In the bottom of follower 61 there is a slot 67 (FIGS. 2, 3 and 5) defined by a pair of arcuate walls 69. A switch contact 71 has an end portion positioned in slot 67 which is cemented to the follower by an adhesive 73.'Contact 71 has an arm 75 projecting from the slot and through baffle 33 into the lower portion of well 5. A crimp connector 77 attached to a braided flexible (pigtail) electrical conductor 79 is welded to arm 75 of the switch contact 71. Another crimp connector 81 (FIGS. 4 and 5) is attached to the other end of conductor 79 and welded to the inner end of a terminal 83. Terminal 83 is generally Z-shaped as shown in FIG. 4 and passes through a slot 85 in casing 1. An end of terminal 83 projects from the casing as shown in FIGS. 1 and 4 so that an electrical conductor (not shown) for a motor circuit can be attached to the projecting end portion of the terminal.

A switch contact 89 is secured to an end of a screw 91, the latter being adjustable toward and away from contact 71 through a threaded hole 93- in casing 1. Walls 69 straddle contact 89 and guide contact 71 into engagement with contact 89 when the strip moves to its FIG. 2 closed position. A terminal 95 surrounds the other end portion of screw 91. Terminal 95 and screw 91 are held in place by a lock nut 97 on the screw. Terminal 95 constitutes another terminal for the secondary or pilot circuit controlled by operation of the switch.

By way of illustration, operation of the switch of the invention will be described in connection with protection of the start winding circuit of a motor driving a refrigeration compressor. This circuit is connected across terminals 39 and 41, or 39 and 18 if a heater is used, so that a permanent path for electric current is provided through contacts 43, 49, element 47, and contacts 51 and 45, to complete the circuit to the compressor winding. This circuit path through the switch remains closed at all times due to the provision of retainers 53 and 55 which hold the contacts 43, 49 and 45, 51 in rocking engagement. The start winding circuit normally includes a contactor (not shown) controlled by the relay circuit connected across terminals 83 and 95. The path through the switch for current in the relay circuit is from contact 83 through the flexible pigtail conductor 79 to contact 71, then through contact 89 and screw 91 to terminal 95. Screw 91 is 'adjusted so that contacts 71 and 89 are in engagement when the disc 47 is in the FIG. 2 position.

During normalstarting operation of the compressor, the current of its driving motor passes between terminals 39, 41 and along disc 47 which heats the disc 47. When the disc becomes heated to a predetermined critical temperature it snaps from the FIG. 2 to the FIG. 3 position. This does not directly interrupt the current path through the switch to the compressor start winding because the retainers 53 and 55 hold the contacts 43, 49 and 45, 51 in rocking engagement at all times. However, this movement of the center portion of the disc 47 elevates the follower 61 and the contact 71 secured to it. This separates contacts 71 and 89 to open the relay circuit. The relay circuit, when opened, deenergizes the contact-or in the motor circuit, thereby opening the motor circuit. After disc 47 has cooled to a predetermined low temperature, it snaps back from the FIG. 3 to the FIG. 2 position, thereby closing the secondary or pilot circuit path through the switch so'that the contactor and the motor can be energized again. The temperature at which the switch opens the contacts 71 and 89 in the pilot circuit is variable by adjusting screw 91 to vary the pressure exerted on the center of disc 47. This provides desirable adjustment of the temperature (and thus the current) at which the switch contacts 71, 89 are opened.

The switch is substantially smaller and less expensive than other relay control devices for compressor motors. This reduction in size and price results from the novel arrangement of the parts of the switch and from their joint operation. The rocking contacts maintained between contacts of the pairs 43, 49 and 45, 51 exert a wiping action which keeps them clean and of low contact resistance.

While snap-acting member 47 is shown as a dished disc, it may be of other appropriately dished forms for obtaining snap action.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing-from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermally responsive snap-acting switch comprising two spaced main line terminals, a conductive thermostatic plate having a snap-acting deformable portion, two contacts on one face of the plate disposed on opposite sides of said deformable portion, each contact shaped for sliding and rocking contact with one of said terminals, a conductive finger extending from each of said terminals into conductive engagement withthe opposite face of the plate adjacent one of said contacts to bias said contact against the adjacent line terminal when the contact is stationary and when it slides and rocks whereby the contacts slide and rock during snap action without separation from the line terminals, a movable third contact supported by said deformable portion of the plate, a third control line terminal having a conductive part positioned relative to said third contact for engagement and disengagement thereby when said deformable portion of the plate snap-acts in'response to temperature change.

2. A switch made according to claim' 1, wherein said two line terminals, fingers, plate and third contact are carried as an assembly in a first housing, said third line terminal and its adjustable conductive part are carried as another assembly in a second housing, said housings being provided with rotary bayonet type coupling means holding them together with said third contact and the conductive part of the third line terminal being coaxially related.

3. A switch made according to claim 2, wherein said plate is in the form of a bimetallic disk the central portion of which is deformable, said two contacts are located at opposite margins thereof and said third contact is centrally located on said central deformable portion, said fixed part of the third terminal being adjustable for calibration.

References Cited UNITED STATES PATENTS 2,127,575 8/1938 Thompson et al. 200122 2,694,121 11/1954 Van der Pyl 200138 3,244,848 4/1966 Chapin et al 200-67 3,297,845 1/1967 Mertler 200-138 BERNARD A. GILHEANY, Primary Examiner.

H. A. LEWITTER, Assistant Examiner.

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