US2290399A - Thermal safety switch - Google Patents

Description

July 21, 1942. J, M. WILSON THERMAL SAFETY SWITCH Filed D90. 26, 1940 IIIIIIIIII INVENTOR v 'J @1mm M.W115oy\. BY

^ ATTORNEY Patented July 21, 1942 2,290,399

THERMAL SAFETY SWITCH John M. Wilson, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application December 26, 1940, Serial No. 371,619

15 Claims. (Cl. 20o-116) The present invention is directed broadly to a thermally actuated switch, and more particu-` larly to a switch which is biased open but normally latched closed and which is tripped open by a thermal element.

The primary object 'of the invention is to proin construction, inexpensive to manufacture, and yet durable and reliable in operation. A further y vide a switch of the above type which is simple at 20 and is located between the leg I9 and the lefthand side of casing I0, as shown in Figure 1 of the drawing. The bracket;l I8 supports a pair of spaced insulating sheets 2| between which is mounted the coils of an electric resistance heater 22. One end of this heater is connected by means of wire 24 to a terminal 25. The other end of the heater is connected bywire 26 to 'the terminal 21.

object is to provide a switch having a minimum l0 The threaded stem of a screw 29 is inserted number of parts. through an oversize hole in the side of the casing Another object is to provide a thermal safety l and screw-threadedly engages an opening in switch in which the latch is mounted on one the leg I9 of the bracket II. The leg I9 is tenblade and is latch'ed on the free end ,of a secsioned for movement toward the right as seen ond blade, the two blades compensating each in Figure 1, and, therefore, holds the head of other for changes in ambient temperature, and the screw 29 against the outer face of the casing the switch being carried by the latch. I0. Rotation of the screw 29 will th'erefore ad- Still another object is to provide the switch just the position of the leg I9 and hence shift the with a manual reset member which may be position of the free ends ofl the two bimetallic moved a certain distance to reset the switch, and elements I3 and I4. Theupurpose of this ada greater distance to latch itself and maintain justment will be described-later the switch in open position. The cover for the A third bracket 39 is connected to the base of switch may cooperate-with the reset member to the casing I0 by some suitable means such`r as prevent it from being moved far enough to latch the screw 3|. A second pair of bimetallic eleitself opensc long as-the cover is in place. ments 32 and 33 are connected at their lower These and other objects will readily become ends to the bracket 30 by any suitable connectapparent as the following specification is read ing means. The upper ends of the elements 32 in the light of 'the accompanying drawing in and 33 are pivotally connected with a metallic which plate 35 which in turn carries an insulating Figure l is a side view of the switch with part 30 member 36. The insulating member 39 supports of the casing being Shown in section. the stationary electrical contact 31 which coop- Figure 2 is a section taken along the line 2-2 erates with a, movable contact 38. The movable 0f Figure 1, looking in the direction of the arcontact 39 is carried on the free end of a flexrOWS, and ible blade 39 which is connected to the insulating Figure 3 iS a detail View Showing the manual 35 member 36 as shown at 40. The lefthand end reset member in its latched position. of the member 39 extends out beyond the insu- Referring to the drawing, the reference nulating member 3B and normally engages over the meral I0 indicates a casing for the switch mechfree end of the bimetallic element I3. A tenanism. Actually, the casing is open only at the sion spring 42 is looped 'at its upper end over top but the side is shown as cut away in Figure 40 the members 39 and 36, and at its lower end is 1 inorder to provide a clear view of the switch looped under the horizontal leg of the bracket Operating mechanism. An L-shaped bracket Il II, a portion of the base of the casing I0 being is connected to the bottom of th'e casing by any cut away to accommodate this looped portion of suitable means, such as 'the screw as shown Iat I2. F the spring 42. The effect of this spring is to hold A pair of bimetallic elements I3 and I4 are 4" the lfthand end of the member 39 in engagement mounted at the lower ends to the bracket II and l with the free end'of the bimetallic member I3. are separated therefrom by means of the metallic The members 35, 36 and 39 together form in efblock I5. The element I4 is provided with a fect a pivoted latch member 58 and will be re- PlOjeCiOn l5 Which bears against the element ferred to as such in the remainder of the speci- I3. These elements are adapted to warp in the cation.

same direction on heating and two elements are The terminal 25 may be connected by vmeans of used instead of one in order that more power -a wire 44 to the upper end of leg I9 of the brackbe available for operating the switch. et II as shown in Figure 1, or the leg I9 may be A second smaller bracket I8 is connected to made a separateV terminal to provide a separate the vertical leg I9 of the bracket II as shown 55 circuit through the switch. The circuit to the switch formed by the contacts 3l and 38 may therefore be traced from the terminal 25, through wire 44, bracket II, metallic block I5, bimetallic element I3 and ilexible switch blade 39 to the movable Contact 38. A parallel circuit extends directly from the bracket II through the tension spring 42 and to the switch blade 38. The stationary contact 3l is connected by a conductor 45 directly to the bracket 30 which carries at its upper end the terminal 4E. The switch therefore controls the circuit connections between terminals 25 and 48.

A manual reset device in the form of an inn sulating member 48 extends through an opening 49 in the horizontal portion of bracket 30. The reset member is provided with a pair of shoulders 58 which prevents its upper end from passing downwardly through the opening 9. The up,- per end of the reset member 48 is relatively narrow and isinserted through an opening in the members 35 and 38 and terminates slightly below the switch blade 33 as seen in Figure i.

As stated above, the two vbimetallic elements I3 and I4 warp in the same direction on heating and therefore provide a greater force than a single element fora given temperature change, although the deflection is about the same. The bimetallic elements 32 and 33 also warp in the same direction and here again two elements'are used instead of one in order to increase the available force. Moreover, the elements 32 and 33 Warp in the same direction as the elements i3 and I4, and as the upper ends of the elements 32 and 33 carry the latch 58, it can be seen that on variations in ambient temperature the relative position of the upper end of the bimetallic element I3 and the lethand end of the latch 58 will remain unchanged. v

When the circuit is closed through the electrical heater 22, it will become heated and'will gradually raise the temperature of the brackets I8 and II on which it is mounted, as well as the metallic block I and will, after a predetermined interval of time, raise the rtemperature of the bimetallic elements I3 and I4 suciently to cause the upper end of the element I3 to nove out from under the lefthand end of the latch 58. The time necessary for the element I3 to trip the latch 58 depen-ds upon the distance the free end of element I3 must travel. This in turn depends upon the position of the free end of element I3 with respect to the lefthand end of the latch 58 when the parts are cold. This relative position, and hence the timing of the switch, are adjustable by rotating the screw 29. After it is tripped, the latch will be pulled downwardly by the spring 42 at which time the latch will pivot freely about the upper ends of the bimetallic elements 32 and 33. Movement of the latch will be stopped by the vengagement of member 35 with the shoulders 58 on the reset member 48, and at this .time the upper end 43 will engage the flexible contact blade 39 and cause the movable contact 38 to separate from the stationary contact 31, there by opening the circuit through the switch. .At this time it will be seen that the switch is effectively locked in open position and can be reclosed only by a manual operation.

The resetting operation is effected by manually moving the reset member 48 in an upwardly direction by pushing on the lower end 5I. This causes the shoulders 58 to again pivot the latch 58 about the upper ends of the members 32 and 33, and if `the members I3 and I4 have cooled, the latch may be relatched on the upper end of the member I3. 'It will be noted that during this operation and as long as the shoulders 58 on reset member 48 are in engagement with the latch 58 that the upper end 43 of the reset mem ber is maintaining the movable contact out of engagement with the stationary Contact. In other words, these contacts cannot be closed by the-reset member 48 other than by relatching the latch 5B on the bimetallic element I3 and then releasing the member 48 at which time the ilexible blade 39 is free to cause engagement of the contacts 31 an-d 38. In other words, this switch is provided with what is known as a ltripfree reset. l

The manual reset member 48 is provided with a latch which is shown at 53. After the manual reset member is raised sufliciently far and then moved to the left, the bottom of the latch 53 may be made to engage with the foot 54 of the bracket Il, thereby maintaining the reset member 48 in its raised position, at which time it will be holding the contacts 3l and 38 separated. This ,feature provides for a positive manual oil position for the switch. Inorder to release the switch for movement to closed .position again, it is necessary only to move thehandle 5I of the reset member 48 to the right, at which time the spring 42 will return the parts' to the position shown in Figure '1.

One of theA principal `uses of aswitch of this type is as a safety switch in connection with automatic oil burner control equipment. In such a case, the switch will be mounted on a panel along with other devices, such as relays vand transformer. This panel is usually provided with a cover enclosing all of the parts, such as is indicated in part in'Figure 1 by the reference numeral 54. It is intended that the cover 54 bear such a relation to the reset member-48 that with the cover in position,.the member 48 may bey pushed upwardly far enough to relatch the latch 58 lon the free end of the bimetallic element I3 after it has been tripped, but not far enough to cause the latch 53 -to seat on the foot of the bracket i I. The purpose of this is so that when the safety switch is opened for some reason, the house owner may reset the switch by pushing the member 48 upwardly without danger of latching the switch in open position. However, when the service man comes to repair the oil burner, he may remove the cover and then latch the switch in open position to facilitate repairs. Thusthere is no danger under the normal use of this switch of ever latching it in open position and thus preventing operation of the oil burner, but yet a simple manual off position is provided for the service man when he comes to make repairs.

Various changes and modifications of the above device will undoubtedly occur to those who are skilled in the art, and it is therefore to be understoodthat I am to be limited only by the scope ofv the appended claims and not by the specific embodiment of the invention which I have chosen to-disclose.

I claim as myinvention:

1. A thermostatic switch comprising in combination, rst and second bimetallic blades xved at one-end and free at the other, a latch pivotally carried by'the free end of said rst blade and normally latching on the free end of said second blade, means for causing movement of one of said blades away from the other whereby said latch isreleased, a normally closed switch moved to open position by said latch upon its release, and manual reset means for said latch, said last named means including means for maintaining saidswitch open until after saidlatch has been relatched on the free end of said second blade.

2. A thermostat-tic switch comprising in combination, first and second bimetallic blades `fixed at one-,end and free at the other, a latch pivotally carriedby the free end of said rst blade .and normally latching on the free end of said second blade, means for'causingmovement of one of said blades away Afrom the other whereby said latch is released, a normally closed switch carried by said latch, and means for causing. opening of said switch upon release of ysaid latch, said means acting also as a reset means for said latch and maintaining said switch open during the resetting operation. l

ILA-thermostatic switch comprising in combination, rst and secondy bimetallic blades xed at one end and free at the other, a latch pivotally carried bythe free end of said first blade and normally latching on the free end ofl said second blade, means for causing movement of one of ,said` blades away from the other whereby said latch is released, a stationary contact mounted on said latch, a movable contact mounted on said latch and biased into engagement with said stationary Contact, a manual reset member having a iirst portion engageable with said movable 'contact for separating said contacts upon release of said latch, and a second portion on saidreset member for vresetting said latch, said rst portion maintaining said contacts separated during the resetting operation,

4. A thermostatic switch comprising in combination, rst and second bimetallic blades xed at one end andfree at the other, a latch pivotally carried by the free end of said first blade and normally latching on the free end of said second blade, means for causing movement of one of said blades away from the other whereby said latch isv released, a stationary contact mounted on said latch, a movable contact mounted on said latch and biased into engagement with said stationary contact, means engaging said movable Contact for moving it out of engagement with said stationary contact upon release of said latch, and means for manually resetting said latch.

5. A thermostatic time switch comprising ln combinaticn, a rst bimetallic blade xed at one end to a rst support and free at the other end, a second bimetallic blade fixed at one end to a second'support and free at the other end, said blades being so arranged that their free ends move in the same direction on temperature variations, a latch pivotally carried by said rst blade and normally latched on the free end of said second blade, an electric heater for one of said blades causing it to warp in a direction to release said latch, a nromally closed switch moved to open position by said latch upon its release, and manual reset means including means for maintaining said switch open during the resetting operation. i

6. A thermostatic timev switch comprising in combination, a first bimetallic blade lixed at one end to a first support and free at the other end, a second bimetallic blade fixed at one end to a second support and free at the other end, said blades being so arranged that their free ends movein the same direction on temperature variations, a latch pivotally carried by said first blade and normally latched on the free end of said second blade, an electric heater for one of said blades causing it to warp in a direction to release said latch, a normally closed switch moved to open position by said latch upon its release, and

manual reset means including means for maintaining said switch open during the resetting operation, and means for adjusting one of saidk supports for varying the time necessary for said one blade to release said latch.

7. A thermostatic switch comprising in combination, aV bimetallic blade xed at one end and free at the other, a movably mounted latch biasedfor movement in one direction, said latch including an insulating member, a xed contact mounted on said member, a resilient blade xed to said insulating member and carrying a movable contact at a free end, said resilient blade biasing said movable contact into engagement with said stationary contact, said resilient blade having a portion which extends slightly beyond 'sai'i insulating member and which is normally latched on the free end of said bimetallic blade, means for heating said blade to cause it to warp in a direction to release said latch, and means acting in conjunction with said latch for separating sai-d contacts upon release of said latch 8. A thermostatic switch comprising in combination, a bimetallic blade xed at one end and free at the other, a movably mounted latch biased for movement in one direction, said latch including an insulating member, a lixed contact mounted on said member, a resilient blade xed to lsaid insulating member and carrying a movable contact at a freeend, Vsaid resilient blade `biasing said movable contact into engagement with said` Istationary contact, said resilient blade having "a portion which extends slightly beyond said insulating member and which is normally latched on the 'free-end of said bimetallic blade, means for heating said blade to cause it to warp inr a directionto release said latch, means for conducting electric current through said thermostatic switch, said last named means including said bimetallic bladev and extending portion of said resilient blade, and means acting 1n conjunction with said latchl for separating said contacts upon release of said latch,

9. A thermostatic switch comprising in combination, a bimetallic blade xed at one end to a metallic support and free at the other, a movably mounted latch, said latch including an insulating member, a xed contact mounted on said member, a resilient blade fixed to said insulating member and carrying a movable contact at a free end, said resilient blade biasing said movable contact into engagement with said stationary contact, said resilient blade having a portion which extends slightly beyond said insulatingmember and which is normally latched on the free end of said bimetallic blade, means for heating said blade to cause it to warp in a direction to release said latch, a spring connected between said resilient blade and said metallic support for biasing said latch into engagement with the free end of said bimetallic blade, means for conducting electric current through said thermostatic switch, said last named means including said metallic support, bimetallic blade, and resilient blade forming one path, and :said metallic support, spring, and resilient blade forming a parallel path, and means actingl` in conjunction with said latch for separating said contacts upon release of said latch.

10. A thermal safety switch comprising in combination, a bimetallic blade xed at one end and free at the other, a biased latch having a metallic portion normally latched on the free end o1' said blade, an electric heater for said bimetallic blade for causing it to warp in a direction to release said latch, a normally closed switch carried by said latch and electrically con-- nected to said metallic portion, means acting in conjunction with said latch for opening said switch upon release of said latch, and means for passing current, through said switch including the vlatched portions of the bimetallic blade and latch.

1l. A thermal safety switch comprising in combination, a bimetallic blade xed at one end and free at the other, a movably mounted latch having a metallic portion, a spring biasing said metallic portion into engagement with the free end of said bimetallic blade, an electric heater for said bimetallic blade for causing it to warp in a direction to release said latch, a normally closed switch carried by said latch and electrically connected to said metallic portion, means acting in conjunction with said latch for opening said switch upon release of said latch, and means for passing current through said switch including the latched portions of the bimetallic blade and latch forming a rst path, said spring forming a parallel path.

12Ay In a'thermal safety device comprising a biased open switch, a thermal element normally latching said switch in closed position, and an electric heater for heating said element to cause it to warp and release said switch, the combination of a manual reset member which is biased to a rst position, said member being movable to a second position in which it operates to relatch said switch on said element following a release, said member being movable to a third position beyond said second position in which it maintains said switch in open position, and means for retaining said member'in said position.

13. In a thermal safety device comprising a biased open switch, a thermal element normally latching said switch in closed position, and an electric heater for heating said element to cause yit to warp and release said switch, the combina tion of amanual reset member which is biased to a first position, said member being movable to a second position in which it operates to relatch saidv switch on said element following a release, said member being movable to a third position beyond said second position in which it maintains said switch in open position, lmeans Afor retaining said member in said position, and

cover means preventing said manual reset member from being moved to its third position, but permitting movement to its second position.

14. In a thermal safety switch comprising nrst and second bimetallic bladesv xed at one end and free at the other, and a releasable bridging member pivotally secured upon the free end of one of said blades and releasably latched upon the free end of the other of said blades, the combination of, a xed contact carried by said bridging member, a movable contact also mounted thereon, and reset means for resetting said bridging member after it has been released by the action of said bimetallic blades, said reset means including means for holding said movable contact lout of engagement with said xed contact when said bridging member is released and during the resetting operation.

15. In a thermal safety switch comprising iirst and second bimetallic blades xed at one end and free at the other, and a releasable bridging member pivotally secured upon the free end of one of said blades and releasably latched upon the free end of the other of said blades, the combination of, switch means carried by said bridging member, and reset means for resetting said bridging member after it has been released bythe action of said bimetallic blades, said reset means including means for disabling said switch means when said bridging member is released and during the resetting operation.

JOHN M. WILSON.

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