US3264437A - Automatically resettable thermal actuated switch - Google Patents

Description

1. M. MILLER 3,264,437

Aug. 2, 1966 FIG. 1

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Inna flll-liffili 2 3 22 2. J22 l-I i I flm gm lLUlIII l IIIIHI I 3o 5- l-"llV/l v 30) L40 l7 23 a ('8 I X 12' 25' l5 f I' Il 9. f I l4 2| I 24 40' INVENTOR. IMRICH M. MILLER United States Patent 3,264,437 AUTUMATICALLY RESETTABLE THERMAL ACTUATED SWITCH Imrich M. Miller, 72 E. 35th St, Paterson, NJ. Filed Sept. 6, 1963, Ser. No. 307,092 7 Uaims. (Cl. 200-414) This invention relates to a thermally actuated switch and more particularly to a thermal actuated switch which is automatically resettable.

One form of switch which is currently in use is the so called temperature sensitive or thermally actuated switch which operates to open or close a pair of contacts or other similar devices, upon sensing a predetermined critical environmental temperature. A common use for such a switch is an electrical circuit breaker in which the sensing of the elevated temperatures produced by an overload of current in the electrical circuit causes the switch to open, thereby opening the electrical circuit.

As is known, temperature sensitive switches generally use either a bimetallic heat sensitive member or a meltable metallic alloy as the temperature sensitive element to control the actuation of the switch. In many applications where a bimetallic member is used, such member usually being two pieces of dissimilar metal which are joined together, the temperature at which the switch is actuated by the bimetallic member cannot be controlled precisely enough. This is due to variations in the two metals forming the bimetallic member, variations in the lengths of the two pieces of metal, junction variations, etc. Therefore, in applications where the switch must be actuated at a precise temperature, a bimetallic member might not be accurate enough to operate the switch at the correct time. This creates a potential hazard because damages might occur to the circuit in which the switch is located if the critical temperature is exceeded before the switch opens. Where a meltable alloy is used as the temperature sensitive element, the melting point of the alloy is more precisely controllable so that the temperature at which the switch is actuated can be controlled more accurately. However, the use of such an alloy presents difiiculties in the construction of the switch, and particularly where the switch is to be automatically resettable.

The present invention relates to a thermal switch which uses both a bimetallic member and an alloy as temperature sensitive elements to actuate the switch. The alloy is used as the principal temperature sensitive element to control the actuation of the switch at a desired critical temperature. In accordance with the invention, the bimetallic element and other elements arranged in a predetermined manner control the opening or closing of the switch in a manner so that the switch automatically resets to its initial position when the environmental temperature has dropped below the critical temperature.

It is therefore an object of this invention to provide an automatically resettable thermally actuated switch.

A further object of this invention is to provide a temperature sensitive switch which utilizes both a bimetallic member and an alloy to control the actuation of the switch at a predetermined temperature.

Yet a further object of the invention is to provide an automatically resettable thermal sensitive switch which uses an alloy as the temperature sensitive element.

Another object of the invention is to provide an automatically resettable thermal switch which is opened and closed upon each rise and fall of the environmental temperature above and below a critical temperature.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which:

FIGURE 1 is a side elevational view of one embodiment of the switch made according to the present invention;

FIGURE 2 is a view, taken partially in section, of one type of alloy junction for use with the switch;

FIGURE 3 is a plan view of the switch as used for driving a gear train;

FIGURE 4 is an elevational view of another embodi ment of the invention; and

FIGURE 5 shows another embodiment of the invention using a double-pole switch.

Referring first to FIGURES 1 and 2, the automatically resettable switch of the present invention is formed by respective upper and lower contact arms and 12 having the electrical contacts 11 and 13 affixed thereto. The upper contact arm 10 is illustratively shown as being held in a relatively fixed position by a block 16 of insulating material which is connected to a switch housing, switch-frame, or other type base member 17. A pair of leads 14, are electrically connected to the respective contact arms 10, 12 at any desired position thereof. These leads connect the switch into an electrical circuit (not shown) which forms no part of the present invention.

The lower arm 12 has a shaft 18 at its end remote from contact 13. Shaft 18 is held within an alloy junction 20 which is held on a ratchet Wheel 22. The ratchet wheel is pivotally mounted to the frame at 36. A pawl 21, which is pivotally mounted at 23, holds the ratchet wheel 22 in a fixed position and prevents clockwise rotation of the wheel. One end of a thermal sensitive member 24 is connected to the lower contact arm 12 by a pusher piece 25 of electrically insulating material. This pusher piece is preferably mounted for limited pivotal movement, as shown, to permit free motion of the arm 12. The other end of member 24 is fixedly mounted to the switch frame or housing by an electrically insulating member 26. The thermal sensitive member 24 is preferably a piece of a suitable type of bimetallic material whose shape changes from one form to another upon sensing a predetermined temperature. Many suitable bimetallic materials of this type are well known in the art and no further description is needed therefor. A spring type catch 27 electrically insulated from the frame by member 28 is also provided to hold the arm 12 in the position shown in FIGURE 1.

The alloy junction 20 includes a cup-shaped member 32 which is fastened to the ratchet 22 and holds an amount of an alloy 34 therein. The alloy 34 is a composition which will melt and become liquified at a certain predetermined critical temperature. Many suitable alloys are known which can perform this function, for example, compositions of various proportions of tin, lead, copper, etc. While the term alloy connotes that at least two materials are combined, it is intended that a single material for example lead, can be used at the junction if desired. The alloy material 34 in the joint solidifies below the critical temperature and fixedlyholds the shaft to prevent rotation of the wheel relative thereto. When the critical temperature is exceeded, the alloy melts and the switch operates in a manner to be described.

As shown in FIGURE 2, the cup 32 has a cover 35 so that the switch may be utilized with the ratchet wheel 22 in a vertical position. The cover prevents the alloy from running out of the cup when it is in a liquid state. In this arrangement the shaft 18 is provided with a hub 19 which extends through an opening in the cover to provide more surface area for alloy 34 to become effective in engaging and holding the shaft 18.

It should be understood that there are many possible mounting variations for attaching the alloy holder cup 32 to the wheel and for immersing the shaft 18 in the alloy. For example, the cup 32 may be mounted in an opening in the wheel 22 and either the wheel or the cup pivotally mounted to the frame. Also, the hub 19 on the shaft may be omitted so that a smaller surface area contact is made between the shaft and the alloy. This may be desirable in some light contact quick opening switch applications. It should also be clear that the cover 35 may be omitted from the cup if the switch is to be used in a horizontal position.

The critical temperature at which the switch is to be actuated is selected and the composition of the alloy 34 is chosen to melt at this particular temperature. The bimetallic member 24 is constructed to be flexed in the direction shown in FIGURE 1 when the environmental temperature is in a safe operating range somewhat below the selected critical temperature so that it urges the arm 12 toward arm 10. The materials for the member 24 are chosen so that the member flexes in the opposite direction to tend to pull the arms 11 and 12 apart when the environmental temperature is in a range of predetermined number of degrees below the critical temperature at which the alloy melts. The temperature at which member 24 flexes in the direction opposite from that shown in FIGURE 1 is preferably selected to be several degrees, for example 10 F., below the melting temperature of the alloy. Of course, any suitable temperature differential between the flexure temperature of member 24 and the melting point of the alloy 34 may be selected.

Considering the operation of the switch, when the device with which the switch is used is running normally, the environmental temperature will be below both the fiexure temperature of member 24 and the critical temperature of the alloy. Under these conditions the bimetallic member 24 pushes the two contacts 11 and 13 into engagement. During this time, the alloy 34 in the joint 20 is solidified and it firmly holds the shaft 18 to prevent it from rotating in the joint. Since the bimetallic element 24 limits the upward travel of arm 12 to the position shown, the ratchet wheel 22 is prevented from rotating over the pawl in the counterclockwise direction. At the same time, the pawl 21 prevents the ratchet 22 from turning in a clockwise direction.

When the temperature rises to the point where the bimetallic member 24 is to flex in a direction to pull the two arms 10, 12 away from each other, this temperature being below the melting (critical) temperature of the alloy, movement or flexation of the member 24 is still prevented at this time. This is so because the shaft 18 cannot move in the solidified alloy in joint 20 and the pawl 21 prevents the ratchet wheel from moving clockwise. When the temperature increases further to the critical temperature, the alloy 34 in the joint 20 melts and the shaft 18 is free to move relative to the joint. After the alloy melts, the bimetallic member 24 flexes in the direction opposite to that shown and the contact arm 12 is pulled away from arm with the shaft 18 rotating in the joint 20. The movement of arm 12 breaks the electrical contact between elements 11 and 13. It should be understood that when arm 12 moves downwardly there is still no movement of the ratchet wheel 22, since this is prevented by the pawl 21.

As described above, the switch contacts are automatically opened when the operating temperature exceeds the critical temperature. The automatic closing of the switch contacts when the operating conditions are safe again, for example when a circuit overload has been removed, is described below.

As the temperature decreases and goes below the critical temperature, the first thing that happens is that the alloy in the joint 20 freezes. This holds the shaft 18 of arm 12 fixed against rotation in the joint while contact 13 is still spaced out of engagement with contact 11. At this time, the temperature has not dropped sufliciently to permit bimetallic element 24 to flex back to its original position and push the arm 12 toward arm 10. However, as the temperature decreases further, the bimetallic arm flexes back to its original position and the arm 12 is pushed in the direction to engage contacts 11-13. Since rotation of the shaft 18 in the joint cannot occur at this time, the movement of arm 12 turns the ratchet wheel 22 in the counterclockwise direction and the wheel is advanced one notch before the pawl is engaged again. Thus, the switch is automatically reset with an advance of one step of the ratchet wheel.

As can be seen, the switch of FIGURES 1 and 2 opens its contacts upon the alloy sensing the predetermined critical temperature and automatically resets and closes its contacts when the temperature drops a predetermined number of degrees below the critical temperature. Since the melting point of the alloy can be precisely selected, actuation of the switch at the critical temperature is assured with considerably more accuracy than could normally be obtained by using only a bimetallic member. Also, the automatic resetting of the switch is advantageous since it eliminates the need for an operator to perform this task manually.

FIGURE 4 shows a switch for closing a circuit upon sensing the critical temperature, rather than opening the circuit as shown in FIGURE 1. In FIGURE 4, the arm 10' is spaced below the arm 12'. Therefore, at temperatures below the critical temperature the bimetallic element 24 flexes upwardly and holds arm 12 and contact 13' away from arm 10' and contact 11. As the temperature increases to the flexation point of member 24, the member 24 tries to flex downwardly but is prevented from doing so since the contact arm 12 is frozen in the joint 20 and the ratchet wheel 22 is held against clockwise rotation by the pawl 21. As the temperature increases still further, the alloy in the joint melts and the shaft 18 is free to rotate. Therefore, bimetallic member 24 flexes downwardly and pulls arm 12 down so that the contact members 11 and 13 engage and close the circuit.

When the temperature starts to decrease, the switch of FIGURE 4 is automatically reset to the open circuit condition in the following manner. First, the alloy in the joint 20 freezes the shaft 18 of arm 12'. As the temperature goes still lower, the bimetallic member 24 flexes back to its original condition and pushes arm 12 away from arm 10' to break contact between elements 11 and 13. As arm 12 moves, the ratchet wheel 22 is advanced one notch in the counter-clockwise direction.

Either of the switches of FIGURES l or 4 can be converted into a double throw switch by providing another stationary switch arm 50 and contact 51 in the manner shown in FIGURE 5. For example, using the switch of FIGURE 1, the movable contact arm 12 is provided with contact members 13 on both sides thereof. When the temperature is below the critical temperature, there is a circuit connection between the contact 13 on arm 12 and the contact 11 on stationary arm 10. Now, however, when the critical temperature is exceeded and arm 12 is pulled downwardly, contact 13 makes electrical connection with the contact 51 and completes another circuit. This circuit, for example, could be an alarm circuit to give an indication that the critical temperature has been exceeded and the main circuit through contacts 11 and 13 opened. Therefore, the switch of FIGURE 5 can be used to control two electrical circuits with the addition of arm 50.

A similar arrangement to control two circuits can be provided for the switch of FIGURE 4 by placing the arm 50 above the arm 12. Here the second circuit formed by the contact 51 would be closed at temperatures below the critical temperature.

It should be recognized that the thermal sensitive switch of the present invention has many uses. For example, it can be utilized as a circuit breaker to open a circuit and as a thermal sensitive switch to close a circuit in any electrical circuit applications. The switch also can be used in mechanical or electro-mechanical applications.

For example, an electrically operated counter can be energized by a pulse of energy each time the switch is opened or closed. If it is desired to provide a thermal sensitive mechanical counter to sense the number of times the critical temperature is exceeded, a gear 40 or other suitable drive member may be affixed to the ratchet wheel 22 of either of the switches of FIGURES l or 4. This is shown in FIGURE 3. The gear 40 drives a suitable mechanical counter and the counter is advanced one count for each rise and fall of the temperature through the critical temperature. Such a device may be useful, for example, where it is desired to count the number of times that a particular device such as an oil burner goes on in any given period. Also, a counter or other suitable device may be driven by the gear 49 and the electrical switching operation still be provided in the manner previously described. As still another use for the switch, a contact arm (not shown) may be carried by wheel 22 or affixed to :the drive member 40 and the advancement of the wheel one notch for each rise and fall of the temperature through the critical point used to operate the contact arm as the movable element of a stepping switch. Here, the stepping switch would be temperature sensitive.

Therefore it can be seen that a novel thermal sensitive switch has been provided which is automatically resettable. The switch of the present invention is actuated precisely at a given temperature since it is primarily dependent for its temperature sensing function upon an alloy whose melting point can be relatively precisely controlled. Also, since the switch is automatically resettable, it can be used in many applications where it is desired not to employ the services of an operator. While the switch has been illustratively shown as moving only a single contact or contact arm it should be understood that a plurality of such arms can be moved at one time and/or each arm may carry a plurality of contacts.

While I have described preferred embodiments of my invention it will be understood that many other modifications may be made without deviating from the principles thereof; therefore I wish to be limited not by the foregoing description, but solely by the claims granted to me.

What is claimed is:

1. An automatically resettable thermostat type switch which is operative in response to ambient temperature to change from a first to a second operative position comprising:

a movable contact arm,

a first thermal sensitive means connected to said contact arm for positioning said contact arm at said first operative position in response to sensing temperatures below a critical temperature and to said second operative position in response to sensing temperatures above said critical temperature,

a second thermal sensitive means connected to said contact arm for restraining the positioning of the contact arm from said first to said second operative position by said first thermal sensitive means until a first temperature above said predetermined critical temperature is sensed by said second thermal sensitive means and for preventing said first thermal sensitive means from moving said contact arm from said second to said first operative position until said first thermal means senses a temperature equal to or less than said critical temperature, and means for holding said second thermal sensitive means at a predetermined position during the time the temperature rises from said critical temperature to said first temperature and falls from said first temperature to said critical temperature.

2. An automatically resettable thermostat type switch as set forth in claim 1 wherein said second thermal sensitive means comprises an alloy which melts at said first temperature above said predetermined critical temperature and which solidifies at a temperature between said first temperature and said critical temperature.

3. A thermostat type switch responsive to ambient temperat-ure changes comprising:

a movable contact arm,

a first bi-directional movable thermal sensitive means connected to said contact arm for positioning it between first and second operative positions in response to ambient temperatures respectively above and below a critical temperature,

a joint including a material which melts at a first temperature above said critical temperature and solidifies in response to ambient temperatures below said first temperature,

first means connected to said arm and having a portion :thereof in contact with the meltable material of said joint to permit the movement of said armby said first thermal sensitive means to said first position when the ambient temperature reaches said first temperature and to said second position only after the material has solidified and said critical temperature has been reached, and means in contact with said first means for holding said contact arm at said second position until said first temperature is reached and said material melts.

4. A thermostat type switch as set forth in claim 3 wherein said holding means is a ratchet and pawl.

5. A thermostat type switch as set forth in claim 4 wherein said joint is mounted in said ratchet wheel and said wheel is moved by the contact arm going from said second to said first position when said meltable material is solidified.

6. A thermostat switch as set forth in claim 3 wherein said meltable material is located in a holder forming part of said joint, and said holder is connected to said holding means.

7. A thermostat switch as set forth in claim 6 wherein said holding means is a ratchet and pawl which moves one step for each cycling of the temperature from said critical temperature to said first temperature and back to said critical temperature again.

References Cited by the Examiner UNITED STATES PATENTS Re 17,650 4/1930 Kendig 200 124 1,659,862 2/1928 Dodge 200 124 1,678,878 7/1928 Sandin 200 124 1,844,492 2/1932 Wilms 200 124 FOREIGN PATENTS 422,902 4/1933 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. AN AUTOMATICALLY RESETTABLE THERMOSTAT TYPE SWITCH WHICH IS OPERATIVE IN RESPONSE TO AMBIENT TEMPERATURE TO CHANGE FROM A FIRST TO A SECOND OPERATIVE POSITION COMPRISING: A MOVABLE CONTACT ARM, A FIRST THERMAL SENSITIVE MEANS CONNECTED TO SAID CONTACT ARM FOR POSITIONING SAID CONTACT ARM AT SAID FIRST OPERATIVE POSITION IN RESPONSE TO SENSING TEMPERATURES BELOW A CRITICAL TEMPERATURE AND TO SAID SECOND OPERATIVE POSITION IN RESPONSE TO SENSING TEMPERATURES ABOVE SAID CRITICAL TEMPERATURE, A SECOND THERMAL SENSITIVE MEANS CONNECTED TO SAID CONTACT ARM FOR RESTRAINING THE POSITIONING OF THE CONTACT ARM FROM SAID FIRST TO SAID SECOND OPERATIVE POSITION BY SAID FIRST THERMAL SENSITIVE MEANS UNTIL A FIRST TEMPERATURE ABOVE SAID PREDETERMINED CRITICAL TEMPERATURE IS SENSED BY SAID SECOND THERMAL SENSITIVE MEANS AND FOR PREVENTING SAID FIRST THERMAL SENSITIVE MEANS FROM MOVING SAID CONTACT ARM FROM SAID SECOND TO SAID FIRST OPERATIVE POSITION UNTIL SAID FIRST THERMAL MEANS SENSES A TEMPERATURE EQUAL TO OR LESS THAN SAID CRITICAL TEMPERATURE, AND MEANS FOR HOLDING SAID SECOND THERMAL SENSITIVE MEANS AT A PREDETERMINED POSITION DURING THE TIME THE TEMPERATURE RISES FROM SAID CRITICAL TEMPERATURE TO SAID FIRST TEMPERATURE AND FALLS FROM SAID FIRST TEMPERATURE TO SAID CRITICAL TEMPERATURE.

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