US2387904A - Heat coil operated thermal switch - Google Patents

Description

R. HETHERINGTON m wm;

HEAT COIL OPERATED THERMAL SWITCH Oct. 30, 1945.

Filed 001;. 17, 1942 1&1.

Patented Oct. 30, 1945 2,387,904 HEAT con. OPERATED THERMAL 'swrron Robert Hetherington, Sharon Hill, Pa., assiznor to Robert Hetherington & Son, Inc., Wilmington, Del., a corporation of Delaware Application October 17, 1942, Serial No. 462,350

17 Claims.

' My invention relates to snap switches of the type in which a bimetallic body is pushed past the center to throw the switch and is returned in part by reason of heat developed in a circuit shunted across from the main circuit when the main circuit is closed.

One of the purposes of the invention is to use a clicker switch in the thermally effected opening of a switch, forming with it a bimetallic pair and heat operating the bimetallic pair either by a mere overload to the pair or a sudden short circuit through the bimetallic pair, to generate the effective heat directly into the pair or by heating the pair by increasing the temperature surrounding the pair.

A further purpose is to interpose a time element into the operation of a plunger-operated switch, so that the switch will be retracted after expiration of the time interval. The range of timeinterval is within the control of the designer but within the designed range is capable of adjustment by altering the strength of reverse pressure against the clicker disc when thrown.

A further purpose is to shunt a heater circuit to ground through a clicker switch when the clicker switch has been thrown.

A further purpose is-to provide a heater coil shunted across part of the circuit, whereby the temperature within the switch is raised to a predetermined point where a bimetallic clicker disc will be operated.

A further purpose is to provide a bimetallic clicker switch which can be thrown past its critical position by a plunger and will stay in that position except as thermally operated, preferably making" adjustable the pressure opposing that throw and, therefore, the time before resetting.

A further purpose is to provide a bimetallic clicker disc and contacts thrown by it, the disc being capable of being thrown beyond its critical position and staying there except as thermally reset and in connection with this to assist the re setting by a spring which is adjustable to vary the resetting urge of the spring.

Further purposes will appear in the specifications and in the claims.

Figure 1 is a central longitudinal section of the preferred form of my switch in its normally open position.

Figure 1 is a fragmentary section corresponding to Figure 1 but with the parts in closed position. v

Figure 2 is a section of Figure 1 taken upon line 2-2.

Figure 3 is a fragmentary elevation of the bimetallic disc and its contact arms.

The switch is encased within a cylindrical metallic shell 6, open at the rear end. The front end of the shell is reduced in diameter at 7, forming an internal flange 8. Exteriorly the shell presents a threaded boss 9 which can be mounted within a threaded opening in any suitable grounded board, or mount, not shown.

The internally flanged shell is counterbored at it and apertured to form a shoulder M and oylindrical internal guide wall it.

Within the guide wall l2 slides an operating button it in plunger form whose flange it engages shoulder H. The casing and plunger are electrically conducting and are grounded. The plunger is rearwardly bored at iii to receive a plug l 6 which screws into the bore i5 or is roughened to add to its frictional engagement within that bore.

The plug is through-bored at the front at l! and counterbored from the front rearwardly at l8, producing an internal forwardly-facing shoulder l9.

Within the bore lies a bolt H which passes through the center of the disc of a bimetallic clicker 22, which operates effectively as a spring because of its radial compression of the material up to a certain point after which the radial expansion snaps it over. The clicker 22 is therefore treated herein as a clicker spring.

The head 23 of the bolt has play within the counterbore of the plug so that the disc 25 will be free to jump rearwardl by the heater coil form as later explained. The nut 24 afiords front abutment for the forward end 26 of a spiral spring 21.

The central disc bimetallic clicker spring 22 is shown best in Figures 1 and 3 and includes two dissimilar metals bonded together, namely a disc 28 united to a central clicker disc portion 29. The clicker disc 29 is "full at the middle so as to snap from a normal position at which it convexes toward the operating plunger, through a position where its central portion is approximately in the plane of its edges, to the other side of this plane where it convexes away from the op-' issuing November 10, 1942, as Patent No. 2,301,874.

The rear part 28 of the thickness of the switch disc shown in Figure 1 is made of material which differs in its co-efflcient of expansion from the co-efficient of expansion of the chcker disc part of the complete disc. If the bimetallic disc, therefore, be pushed by the operating plunger so as to snap beyond the central plane and convex the composite disc to the left in Figure 1, the disc will continue to act as a clicker disc alone unless and until there be such a change in the temperature within the casing as will cause relatively excessive expansion of the thermally responsive material. The composite diaphragm will then snap back to the initial position.

The composite diaphragm terminates at its perimeter in holding sections 38 of larger diameter than the part relied upon for clicker functions. The diaphragm carries contact-supporting arms 3i and 32.

Both theholding sections at the perimeter and the arms 36 and 32 at or near bends 33 are rigidly attached to the disc and the arms are in good electrical contact with the diaphragm.

The clicker spring is gripped directly at its Perimeter between the front end section 35 of insulation within the casing or shell and the axially projecting flange 35 of the cylindrical insulation 36. The complete insulation of the body of the casing includes also a rear insulation disc 3i. Within the rear disc are carried binding posts 38 and. 39 and the fixed contacts 50 and (ii which are have the clicker disc remain in closed position I (Figure 1') until operated upon by a force additional to that of the spiral spring.

With the parts in open position in Figure 1, the arms 3! and 32 lie generally as seen, with their contact discs 69 and 50 out of engagement with fixed contacts do and M. However, when the composite clicker disc is reversed in position from that seen in Figure l, i. e., as in Figure 1.

. the contact discs 69 and 56 close the circuit from the binding posts through the arms and the composite clicker disc.

The present invention contemplates closing a shunt circuit 5! through a resistance coil within tion seen in Figure 1. The structure by which rigidly mounted upon the posts 38 and 39 and are usually welded to them.

Mounting the composite clicker body rigidly by its perimetrical extensions leaves the intermedi ate central part of the composite clicker body free to move and to be moved axially with respect to the plunger and with respect to the plane of the clicker disc. Its movement in a rearward direction (that is'toward the left of Figure 1) is produced by pressure upon the plunger communicated directly to the disc, and is counter to the pressure of the spring through the nut.

The rear end of the spiral spring abuts against the flange of a collar 62. For centralizing purposes the spring surrounds a guide or core 63 forming part of the collar.

The collar is rigid with a bolt id which as disclosed is threaded within a metallic spool and within the central part of insulation disc 37. Its longitudinal position along the axis or the thread can therefore be set for adjustment purposes by a screw driver inserted from the end atll and fitting within a screw slot as shown.

The composite clicker disc, as so far described constitutes a thermal pair of which the disc described as thermally responsive merely has a different co-efficient of heat expansion from that of the choker disc, so selected as progressively to increase pressure from the left against the choker switch as the temperature within the chamber increases. The disc is limited in its movement to the left in Figure 1 by engagement with the end of the coil form 55.

If the spiral spring be strong enough, obviously the choker disc will not remain in its position at the left when clicked, but as soon as pressure upon the plunger is removed immediately will spring back to the position of Figure 1. However, the spiral spring may be made hght enough in its pressure so that the clicker disc will remain in its position in Figure 1 as moved to the left from that shown in Figure 1. That is, the condition inthe present case where it is desired to this is accomphshed is as follows:

Th preferably metallic spool 65 supports a shunt winding in the form of a resistance coil 58 I which at one end 52 is electrically connected to the spool. The other end 58 of this winding is connected with the casing or shell.

As a result, when the main circuit is closed as seen in Figure 1 the main circuit passes across from one fixed contact to the other fixed contact plate or strip through the contact discs 419, iii, the arms iii, 32 and the composite clicker disc, and at the same time current leaks to ground (casing or shell) from the composite disc through nut 26, spiral spring 2?, collar 52, bolt 65, spool 65, resistance coil Si and the grounded shell.

Since one side of the main circuit closed is grounded a shunt flow passes through the resistance coil at all times when the main circuit is closed. There is also, of course, a slight heating effect within the chamber due to flow of the main current through the resistance of the arms and composite disc.

In operation the plunger is pushed in, throwing the clicker to closed switch position seen in Figure 1 The clicker stays in this closed position until suficient heat has been developed to cause resetting of the switch to open position, introducing a time element within the circuit and making it possible to predetermine the range of time claps.-= ing before the switch current is interrupted, as by the type and hence range of clicker (composite) discs used, the number of turns, strength centered and at the same time is rigidly mounted upon the rear disc insulation by providing a projection 56 at the rear of the spool to fit into a recess -55 in the rear disc insulation and by holding the parts upon the insulation by the screw 66. To considerable advantage this screw may be threaded into both of the adjoining parts.

The invention recognizes that much more nearly exact adjustment of the time element can be made when the heat developed is used to opthe other part forming with it a thermal pair, and arms controlled by the diaphragm, adapted to close the switch through the diaphragm with movement of the diaphragm from normally open position convex toward the front to closing Position convex toward the rear, 9. spring tending to open the switch, a casing forming a closed chamber about the pair, a heating coil within the chamber connected through the spring as a shunt across a part of the circuit through the diaphragm, and means for operating the diaphragm whereby when the circuit is closed, current passes through the diaphragm and through the heating coil.

7. A pair of normally open fixed circuit contacts, a snap switch having a bimetallic diaphragm, one part of which is of clicker type and the other part forms with it a thermal pair, and arms controlled by the diaphragm adapted to close the switch through the diaphragm between the fixed circuit contacts with movement of the diaphragm from normally convex open position to concave closing position, a casing forming a closed chamber about the pair, a heating coil within the chamber connected as a shunt across a part of the circuit through the diaphragm, a metallic spool for the coil, through which form the shunt current passes, and means for operating the diaphragm, whereby when the circuit is closed, current passes through the diaphragm and through the heating coil.

8. A clicker switch having a clicker disc and a second disc forming. a thermally responsive pair, contact closing arms closing a circuit through the switch when the clicker disc is thrown, a spiral spring opposing the throw of the clicker switch, a resistance shunted across the path of the circuit closed when the clicker is thrown, tending to operate the thermally responsive switch and to open the circuit, and thus introducing a time element, and means through part of which the shunt current passes for adjusting the pressure of the spiral spring, to alter the time element introduced by the shunt.

9. In a snap switch, a bimetallic diaphragm presenting a thermal pair, normally convexed, means for holding the outer edges of the bimetallic diaphragm, binding posts for the circuit to be closed, fixed contact strips connected to the binding posts, contacts connected with the outer part of the diaphragm thrown by reversal of the convexity of the diaphragm and adapted to close the switch circuit through the contact strips, contact arms and bimetallic diaphragm, a heater coil shunted across the circuit, an electrically conducting mount for the coil through which mount part of the heater coil current passes and a plunger capable of throwing the diaphragm.

10. A switch mechanism comprising a grounded casing, insulation forming a switch chamber within the casing, binding posts and corresponding contacts for a switch circuit, a clicker switch diaphragm, forming a part oi a thermal pair, when heated opposing closing throw oi the diaphragm and fastened between parts of the insulation within the casing, contact arms connected with the radially outer part of the diaphragm, movable contacts carried by the arms and adapted to engage the fixed contacts when the diaphragm is clicked, a spring tending to press the diaphragm toward open switch position, means for clicking the diaphragm against the pressure of the spring, a heater coil within the chamber shunted between the diaphragm and the ground in closed diaphragm position and an electrically conducting spool upon which the heater coil is mounted and which limits the stroke or the diaphragm from open position to closed position.

11. A switch mechanism including a grounded casing, insulation forming. a switch chamber within the casing, binding posts and corresponding fixed contacts for a switch circuit, a thermal pair in the form of a composite diaphragm including a choker diaphragm fastened within the 0. arms connected with the outer part of the clicker diaphragm, movable contacts carried by the and adapted to engage the fixed contacts when the composite diaphragm is choked, a spring tending to hold the composite diaphragm in open switch position, means for clicking the diaphragm against the pressure of the spring, an electrically conducting spool for a heater coil and a heater coil within the chamber shunted between the diaphragm and the ground through the coil and spool in closed switch position 12. A switch mechanism including a grounded casing, insulation forming a switch chamber within the casing, binding posts and corresponding fixed contacts for a switch circuit, a thermal pair in the form of a composite diaphragm including a clicker diaphragm fastened within the casing, plunger means for throwing the diaphragm from normal open convex position to concave position, grounding means for the diaphragm, a spring tending normally to press the diaphragm into normal open position and insumcient in strength to reverse the diaphragm when the switch is closed, a spool within the chamber, a heating coil grounded through the casing at one end, connections between the other end of the heater coil and the diaphragm through the spool and means for altering the abutment against which the spring presses at the end farther from the diaphragm whereby the amount of heat required to be developed by the heater coil to reverse the diaphragm may be adjusted and the time of switch reversal may be changed.

13. A casing, insulation within the casing, a composite thermal pair clicker disc within the insulation, a plunger operating the disc, contact arms carried by the composite disc, fixed contacts engaged by the movable contacts to close a switch circuit through the disc, an electrically conducting spool within the casing, a heat coil mounted upon the spool, grounded at one end and connected to the spool at the other, thrown across the main circuit as a shunt when the switch is closed, connections from the spool to the composite disc and means for adjustably pressing the disc toward open position.

14. A thermally opened clicker time switch, comprising a casing, a plunger within the casing, a composite clicker disc including a thermally operated disc, held within the casing, a shunt resistance circuit, connections between the plunger and the composite disc, means having lost motion axially of the composite disc and limiting the throw of the disc, fixed contacts within the casing, arms carriedby the disc closthe spiral spring,

15. A thermally operated time switch including a casing, a composite disc providing a' thermal pair and embodying a clicker portion, contact arms carried by the disc,vmovable' contacts on the arms, insulation at the end and also near the circumference of the casing, holding the perimeter of the disc between them, fixed contacts within the casing engaged by the movable contacts, a plunger, insulation carried by the plunger, a bolt movable longitudinally within the insulation to give play to the composite disc, permitting it to jump beyond its center to close the contacts, a nut carried by the bolt resting against the composite disc on the side away from the plunger, a spiral spring pushing at one end to hold the disc in open switch position, an abutment for the other end of the spring, means for adjusting the abutment to tighten or slacken the spring, a spool about the spring and a heat coil about the spool electrically connected at one end through the spool to the composite disc and connected at the other end to the casing.

16. A switch mechanism including a grounded casing, insulation forming a switch chamber within the casing, binding posts and corresponding fixed contacts for a switch circuit, a thermal pair in the form of a composite diaphragm including a choker diaphragm fastened within the casing, plunger means for throwing the diaphragm from normal open convex position to concave position, a spring tending normally to press the diaphragm into normal open position and insufllcient in strength to reverse the diaphragm when the switch is closed, a coil mount, a heating coil within the chamber grounded through the casing at one coil end, connections between the other end of the heater coil and the diaphragm passing through the coil mount and means for adjusting the strength of the spring, whereby the amount of thermal action required to reverse the diaphragmand open the switch may be adjusted.

17. In a time switch, acasing, disc insulation in the front of the casing, cylindrical insulation within the casing, a composite thermal pair clicker disc having contact arms, held at its perimeter between the front insulation and the cylindrical insulation, rear disc insulation, movable contacts operated by the choker disc, a spool supported at one end within the rear insulation, a heater coil carried by the spool, connected at one end to the spool and at the other end to the casing, a spiral spring inside the spool normally pressing the composite disc toward open position, fixed contacts engaged by the movable contacts when the clicker disc is thrown, an abutment for the rear end of the spring adjustably mounted within the casing and connections between the spool and clicker switch through the pring.

ROBERT HE'IHERING'ION.

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