US3017478A - Thermally responsive switch - Google Patents

Description

Jan 16, 1962 c. GRlMsHAw 3,017,478

THERMALLY RESPONSIVE SWITCH Alfter/7 Jan. 16, 1962 c. GRlMsHAW THERMALLY RESPONSIVE SWITCH 2 Sheets-Sheet 2 Filed June 3. 1960 Unite States Patent 3,017,47 8 THERMALLY RESPONSIVE SWITCH Charles Grimshaw, Fulton, Ill., assigner to General Electric Company, a corporation of New York Filed .lune 3, 1960, Ser. No. 33,760 10 Claims. (Cl. Zilli-138) My invention relates to thermally responsive switches, and more particularly to such switches having two pairs of switch contacts actuated upon temperature change in opposite directions, with overtravel in temperature per mitted in both directions. Switches of this type are particularly suitable for use as llame detectors in fluid fuel burning systems, and the like.

To provide the desired overtravel in temperature, in flame detecting switches of the prior art which have hot contacts and cold contacts selectively engaged by a movable contact, various types of friction clutch arrangements have been utilized. These clutch arrangements are important to the function of such a switch, since they permit the switch to operate on temperature change rather than absolute temperature. In llame detecting switches such as these, the friction clutch often slips when the switch environment cools down below normal room temperature, or when the switch has been severely Vjarred. Examples of this are where the llame detector switches are stored in a cold warehouse, or where they are severely jarred or shaken during shipment. After the switch has been subjected to such colder temperatures or severe vibrations, when the switch is then brought into a warm room, the thermally responsive element warms up and the movable contact leaves the cold Contact, in the same manner as it does when the thermally responsive element feels the heat of combustion. The master control or main control is so arranged that it will not start the burner unless the llame detector switch is making contact on its cold side. In order to properly start the burner, it has thus then been necessary for the person who is installing the llame detector switch or starting the burner to connect a temporary jumper wire in the master control to short out certain terminals thereof so that the switch contacts will be in the proper starting position, or on the cold side. In order to eliminate the need of shorting out the terminals of the mastercontrol before starting the furnace, it has been found desirable to provide a means for maintaining the movable bimetal contact in engagement with the cold contact under normal ambient conditions so that the switch contacts of the detector switch will always be in the proper starting position even though the switch has been shaken in shipment or subjected to very low ambient temperatures. It has also been found desirable to incorporate this selfstarting feature in an improved ame detecting switch which is simple in construction and relatively inexpensive to manufacture.

Accordingly, it is the general object of my invention to provide a new and improved thermally responsive switch.

Another object of my invention is to provide an improved flame detecting switch of the type having hot and cold contacts, where the cold contacts will be normally maintained in a closed position.

A further object of my invention is to provide an improved flame detecting switch which is simple in construction and relatively inexpensive to manufacture.

In carrying out my invention, in one form thereof, I apply it to a thermally responsive switch which is used in a burner control circuit to detect the presence of flame, via radiation, and/or temperature change. This switch essentially includes a bimetallic arm with a movable contact mounted on its free end, a frictional clutch arrange- Patented Jan. 16, 1962 ment for rotatably supporting the other end of the arm, and a pair of fixed contacts which selectively cooperate with the movable contact in response toflexure of the bimetallic arm. The two fixed contacts are the cold and hot side contacts for the control circuit. To assure that the switch will normally maintain its movable contact in engagement with the cold contact for properly starting the burner, a biasing rod is connected to the supported end of the bimetallic arm. This rod serves as a rigid support for the bimetallic arm at all ambient temperatures below a certain predetermined temperature. When the ambient temperature is above this predetermined value, the biasing rod no longer has any significant operational effect upon the bimetallic contact arm. By using such a biasing rod in my llame detecting switch, an expeditious and inexpensive means for normally maintaining the switch contacts on the cold side for starting the burner has thus been obtained.

By further aspects of my invention, additional desirable features may be included in the switch, and the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that I regard as my invention. The invention, however, as to organization and method of operation, together with further objects and advantages thereof, may best be understood with reference to the following description when taken in conjunction with the accompanying drawings, in which: j

FIG. 1 is a plan view of an improved thermally responsive switch embodying my invention, in one form thereof, partially broken away to show the internal parts of the switch more clearly;

FIG. 2 is a cross-sectional view taken substantially along the line A-A of FIG. l;

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

FIG. 4 is an exploded view showing the various parts of the switch of FIG. 1, with the insulating base partially broken away and the transparent cover removed;

FIG. 5 is a rear perspective view of the switch of FIG. 1, showing the terminals and a mounting bracket assembly, with leads affixed to the terminals; and

FIG. 6 is a view similar to FIG. l, with the transparent cover attached to the base.

Referring now in detail to the drawings, and in particular to FIGS. l and 2, there is shown a thermally responsive ame detecting switch 1 wherein my invention has been advantageously employed. The switch housing 3 includes hollow insulating base 5 and glass window or cover 7. Window 7 is fastened to the open side of base 5 and also sealed thereto by some suitable sealant material such as silicone rubber to provide a transparent cover for the switch 1. To make the manufacturing operation simple, base 5 of my switch is of rectangular configuration, and it is manufactured from some suitable insulating material such as the ceramic steatite. Within hollow portion 9 of the base are sealed the operating components of my flame detecting switch 1.

To keep the cost of my switch 1 to a minimum, and also to provide a switch which is very small in over-all size, as shown in FIGS. 2 and 4, the operating components of my switch 1 are very simple in construction. More particularly, in bottom wall 11 of base 5 (as shown in FIG. 4), I have formed slots 13, 15, and 17. Slot 13 is for receiving bearing terminal 21, and it extends through bottom wall 11 near end wall 19, being generally parallel to wall 19 and midway between the side walls. Terminal 21, as seen in FIGS. 2, 4, and 5, includes tab 23 which extends outwardly through slot 13 for electrical connection to a lead wire. Rectangularly shaped boss 25 is extended inwardly from bottom wall 11 of base 5. Side 25a of boss 25 is generally coplanar to the side of slot 13 farthest away from end wall 19 and it serves to furnish additional support for terminal 21 within cavity 9 by engaging intermediate portion 29 of the terminal (see FIG. 4). Intermediate portion 29 of terminal 21 has a pair of shoulders 27 which are coplanar with tab 23 for supporting the terminal within the base. After tab 23 of the terminal 21 has been extended through slot 13 and fastened in position on the outside (as shown in FIG. by some suitable sealant such as the aforementioned silicone rubber, shoulders 2.7 are each held in secure engagement with the inner surface of bottom wall 11.

For rotatably supporting thermally responsive arm 31 within base 5, bearing terminal 21 is bent over transversely along line 33, as shown in FIG. 4, and it includes a pair of curved bearing fingers 35 at its inner end. By bending terminal 21 along line 33, the engagement of the associated upper edge 251? of boss 25 (as viewed in FIG. 4) with the line of bending of the terminal provides additional securement for bearing terminal 21 within base 5. The manner of rotatably mounting my thermally responsive arm 31 within base 5 of the liame detecting switch shall be described in detail hereinafter.

For an element which expands and contracts in response to thermal change and thus detects the presence of an oil burner :llame via radiation and/or temperature change, in my switch 1 I have chosen the particular construction of bimetallic arm 31 (as seen in FIG. 4). More particularly, arm 31 is made from a at strip of suitable thin bimetallic material which is bent angularly intermediate its ends along line 30 so that the high expansion side 31a has an intermediate angle in the order of 163. In order to provide clearance for terminal 62 and also to increase the bimetal energy output per weight of bimetallic material used, the side edges 37 of bimetal 31 are convergent toward its free end 39 so that the transverse width of the bimetal at its free end is less than the overall widths near and at its supported or pivoting end 41. Bimetal arm 31 has an appropriate aperture formed in its free end 39 for receiving a riveted silver contact 43. Contact 43 extends outwardly from both sides of the biymetal to provide single pole double throw action in the well-known manner.

To rotatably support arm 31 within base 5, supported end 41 of the arm is stepped inwardly from side edges 37 and fastened to a smooth rotatable cylindrical member or pin 45 (see FIG. 4). To be more specific, bimetal end 41 is welded tangentially to pin 45 and spaced equidistant from the ends of the pin. Portions of the smooth pin 45 adjacent its ends then extend outwardly in a transverse manner from underneath the stepped sides of the bimetal to t into or underneath the curved bearing fingers 35 of the terminal 21 (sce FIGS. 1 and 4).

To continuously bias bearing pin 45 into engagement with the curved fingers 35 and thus furnish the desired clutching action for my flame detecting switch 1, I have provided a U-shaped clutch spring 51 (see FIG. 4). Spring 51 includes a generally flat supporting portion 53 and a pair of spaced spring arms 55 extending therefrom. Near the end edge 61 of the supporting portion 53, I have formed a slot 57 with an inwardly and angularly turned tongue 59 extending toward end lwall 19. For securing spring 51 on the bottom wall 11 of bese 5, slot 57 is first slipped around boss 25 of the base. Then tab 23 of terminal 21 is pushed through base slot 13 from the inside of hollow portion 9. Tab 23 engages the outer transverse side 57a of slot 57 of spring 51 (as shown in FIG. 4) and it Wedges the spring into a secure position when the terminal 21 is sealed outside of base 5 (see also FIG. 2). The free end of tongue 59 then frictionally engages wall 25C of boss V25 due to the wedging effect of terminal tab 23 upon spring 51, to restrain the spring supporting portion 53 from any longitudinal movement within base 5. Shoulders 27 of terminal 21 bracket the side edges of spring 51 and engage wall 11 to restrain the spring support from any lateral slippage. End edge 61 of spring 51 is also turned upwardly to engage the inner surface of side wall 19 of the base and thus furnish further securement for the spring within the switch housing.

With clutch spring 51 securely mounted in position on bottom wall 11 of base 5 (as shown in FIG. 2), resilient arms 55 each tangentially engage the underside of pin 45 near its respective ends to bias the pin into frictional engagement with bearing fingers 35 of terminal 21. A very simplied slip-type clutching arrangement for rotatably supporting movable contact 43 within base 5 has thus been achieved. Such a clutching arrangement, as shall hereinafter be described in detail, provides overtravel or slip-clutching action upon continuous tlexure of the bimetal in the same direction after movable contact 43 has already engaged the hot or cold side contacts 44 and 46.

The hot and cold side contacts 44 and 46, respectively, represent the fixed contacts of my switch 1. As shown in FIG. 3, hot side contact 44 is attached to L-shaped terminal 60 at contact supporting section 60a inside of base 5. Tab 601 of terminal 60 is extended through the longitudinally extending slot 17 of base wall 11 and bent outwardly, being sealed to the outer surface of wall 11 by the aforementioned sealant, silicone rubber. Hot side contact 4dthus faces upwardly (as seen in FIG. 3) for engaging movable contact 43 upon down- -ward movement thereof. Cold side contact 46 is attached to the elongated L shaped terminal 62 at contact supporting section 62a. Tab 62h of terminal 62 is extended through longitudinally extending slot 15 and bent outwardly, being sealed to the outer surface of wall 11 in the same manner as terminal 60. Cold side contact 46 thus faces downwardly to engage movable contact 43 upon upward movement thereof. As shown on terminal 62 in FIGS. 3 and 4, side tab 62C has been angularly lanced from the flat surface of the intermediate area of cold contact terminal 62 to help control the tolerances during assembly of the switch parts by engagement with an adjacent wall protrusion of the switch base 5.

Turning now to a very important aspect of my invention which provides an improved built-in self-starting feature for my llame detecting switch, it will be noted that underneath rotatable pin 415 on the side thereof diametrically opposite to the side fastened to end 41 of the bimetal, I have welded one 4end of a J-shaped biasing or positioning rod 63. As shown in FIG. l, elongated portion 64 of rod 63 extends longitudinally underneath the bimetallic arm 31 and is centrally ldisposed so that it has freedom .to rotate with pin 45 between the spaced arms 55 of clutch spring 51 (see also FIG. 2). The other end of rod 63 is bent perpendicularly from the elongated portion 64 -to form connecting section 65 `and then it is bent perpendicularly back in the general direction of but slightly away from pin 45 to form biasing support section 67. As shown in FIGS. 2 and 4, elongated portion 64 and connecting section `65 are in a plane angularly related to bottom wall 11. Section 67 is disposed at an `acute angle with respect to this plane (as shown in FIG. 2), and it is generally parallel to wall 11 when the temperature is lless than F.

Pin 45 of my switch, with bimetallic arm 31 and biasing rod 63 attached thereto, as shown in FIG. 4, provide a switch sub-assembly. When this sub-assembly is mounted in the assembly switch 1, as shall be further described hereinafter, when the temperature of the switch is under 100 F., biasing section 67 engages the inner surface of bottom wall 11 of base 5 to bias bimetallic arm 31 to its uppermost position (as shown in FIG. 2). Movyable contact 43 is Ithus normally biased into engagement with cold side xed contact 46. The angular relationship between biasing section 67 of rod 63 rand the plane described by portion 64 and section 65 thereof, may be varied lto alter the upward biasing force exerted upon movable contact 43 during closure against cold contact 46, 'and thus adjust the predetermined temperature beneath which arm 31 will be biased by rod 63.

Turning now to an explanation of the operation of my improved flame detector switch 1, window 7 provides a transparent medium for the entry of radiant heat into hollow portion 9 of base 5. Bimetallic arm 31 will thus respond to the presence of a burner flame via radiation -and/or temperature change. When the temperature is under 100 F. or any other predetermined selected temperature, rod 63 is in the position shown in full in FIG. 2. Biasing section 67 of rod 63 engages base wall 11 and serves as -a rigid support for rotatable bimetal arm 31 to normally maintain movable contact 43 in engagement with cold side contact 46 (as shown in full in FIG. 2). In this manner, after switch 1 has been stored in a cold warehouse, or when it has been severely jarred or shaken during shipment, biasing rod 63 will always assure that movable contact 43 is in engagemen-t with the cold side fixed contact 46 when the flame detector switch is placed 1n operation. As an example, if my ame detector switch is cooled to -40 F. and then brought back to room temperature, movable contact d3 will remain in continuous engagement with the cold side fixed contact 46 until the ambient temperature has reached 100 F.

When my switch 1 has been connected in a master furnace controlling circuit for controlling a burner, it will then immediately start the burner because the cold side contacts are engaged. As the burner starts, the bimetal 31 will then flex downwardly to the dotted position 31h shown in FIG. 2. Movable Contact 43 will thus move from the cold side to the hot side fixed contact, its position then being represented by the dotted contact 43a of FIG. 2. This action signals the condition of the flame to a prima-ry relay of the master control circuit in the well-known manner. The burner will then, of course, gradually heat up the bimetal. As the temperature increases, with the movable con-tact d3 engaging the hot side con-tact 44, bimetal 31 tends to straighten itself out and open the angle between its ends. More specifically, since the bimetal is fixed at the movable contact end by closure with the hot side contact 4d, bimetal 31 exes to position 31e of FIG. 2, and bent portion 30 of bimetal 31 moves to position 30a. With an increase of temperature of about 30 F., bimetal 31, will then turn rotatable pin i5 in a counterclockwise direction (as seen in FIG. 2) to slip the frictional clutch provided by the engagement of pin 45 with the curved fingers 35. The biasing force provided by clutch spring 51 requires about a 30 F. rise in temperature to slip the clutch and rotate the pin 45. When this clutch slippage occurs, Ibiasing rod 63 moves upwardly to the position 63a (as shown in FIG. 2) to free supporting section 67 from the bottom wall 11 of the base. Rod 63 then no longer has any biasing effect upon bimetal 31.

In the event that the flame which is being `detected by my switch 1 should fail, the bimetal contact 43 moves from the hot side `contact toward the co-ld side contact. As soon as the movable contact 43 leaves the hot side contact, this immediately shuts off the fuel supply. The frictional clutch is -arranged to prevent slippage of the pin d5 of the rotatable bimetal until at least a 30 F. temperature drop is affected and the movable contact 43 has moved from the hot side contact and touches the cold side contact. Another 30 F. temperature `drop wipes the movable contact into the cold side contact, building up a torque equal to, and opposite to the clutch torque. With further cooling the clutch then slips and the biasing rod 63 is thus returned to its original biasing position (with -supporting section 67 in engagement with bottom wall 11 of the case).

It will thus be seen that by means of my J-shaped biasing rod, I have provided a very efficient and simple means for maintaining the cold side contacts of my flame detector switch in continuous engagement when the ambient temperature is under F.

In essence, I have thus pro-vided a fiame detector switch with an improved built-in self-starting arrangement. With this arrangement, my ame detector switch in its preferred embodiment has a slip clutch which operates on temperature difference above 100 F. but operates as if the `bimetal were fastened to a rigid support at all temperature below 100 F. It will be understood by those skilled in the art that the predetermined temperature at which my flame detector biasing rod is to cease its biasing effect upon bimetallic arm 31 'may be varied in accordance with the operational requirements for the particular switch application.

My improved ame detecting switch 1 has been designed principally for mounting in the blast tube of a domestic gun-type oil burner. For this purpose, I have illustrated it with one form of a mounting bracket assembly 69. This assembly (as shown in FIGS. 5 and 6) includes a U-shaped clip 71 which surrounds three sides of base 5 and partial-ly brackets the fourth side. Clamp 7 3 is welded to a flanged portion of clip 71 and includes a threaded clamp screw 75 for attaching the assembly to a suitable support within the blast tube of a burner. Various other types of supporting bracket assemblies can, of cou-rse, be utilized for my improved flame `detector switch, in accordance with the requirements of the application.

It will thus be understood that my new and improved ame detecting switch such as herein illustrated provides a simple and efficient means for detecting the presence of flame via radiation and/or temperature change, while also providing an improved means for assuring that the movable contact of the switch will always start on the cold contact side of the switch. It is thus no longer necessary to short out the terminals for starting the furnace, because my improved tiame detecting switch includes a simplified and expeditious means for biasing the movable contact to the preferred starting position. It should be realized that certain aspects of my invention may be incorporated efficiently and beneficially in other various types of thermally responsive switches.

While in accordance with the patent statutes, I have d-escribed what at present is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from my invention, and I, therefore, aim in the following claims to cover all such equivalent variations as fall within the true spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A thermally responsive device comprising an expansible and contractable member, clutch means for rotatably supporting one end of said member, movable contact means on the other end `of said member, a pair of fixed contacts arranged to selectively cooperate with said movable `Contact means in response to the expansion and contraction of said member thereby to control an electrical circuit, and a positioning means associated with the supported end of said member and acting upon said member to maintain said movable contact means in engagement with a cer-tain one of said fixed contacts when the ambient temperature of said device is less than a predetermined temperature value, thereby to assure that said device may be started with its movable contact means in engagement with said certain fix-ed contact when said device is connected in an electrical circuit and the ambient temperature of said device is less than said predetermined value.

2. A thermally responsive switch comprising a thermally responsive member, clutch means for rotatably supporting one end of said member, a movable contact positioned on the other end of said member, a pair of spaced fixed contacts arranged on opposite sides of said movable contact and selectively cooperable therewith in 7' response to the thermally responsive movement of said member thereby to control an electrical circuit, and a positioning means linked to the supported end of said member and acting thereupon to maintain Said movable contact in engagement with one of said iixed contacts when the ambient temperature of said switch is less than a predetermined temperature value, thereby to assure that said switch may be started with its mo-vable contact in engagement with said one of said fixed contacts when the switch is connected in an electrical circuit and the ambient temperature of said switch is less than said predetermined value.

3. A thermally responsive switch comprising a casing, said casing including a hollow cavity in which the mechanism of said switch is mounted and a transparent wall portion for admitting radiant heat into said cavity, a bimetallic contact arm positioned within said cavity, clutch means disposed Within said cavity for rotatably supporting one end of said arm, a movable contact supported by the other end of said arm, a pair of iixed contacts supported within said cavity and arranged on opposite sides of said movable contact to selectively cooperate therewith in response to the thermal expansion and contraction of said bimetallic arm thereby to con-trol an electrical circuit, and a positioning means connected to the supported end of said arm and acting thereupon to mair1 tain said movable contact in engagement with one of said fixed contacts when the ambient temperature of said switch is less than a predetermined temperature value, thereby to assure that said switch will be started with its movable contact in engagement with said one of said fixed contacts when the switch is connected in an electrical circuit and the ambient temperature of said switch is less than said predetermined value.

4. A thermally responsive ame detecting switch cornprising a casing, said casing including a hollow cavity in which the mechanism of said switch is mounted and a transparent wall portion for admitting radiant heat into said cavity, a bimetallic contact arm positioned within said cavity, a cylindrical member tangentially aiiixed to one end of said arm, a first terminal extending into said cavity, inner extension means on said first terminal for receiving said cylindrical member, a spring positioned adjacent said iirst terminal within said cavity and urging said cylindrical member into frictional engagement with said inner extension means thereby to provide a clutch means for controlling the rotatable movement of said arm, a movable contact supported by the other end of said arm, second and third terminals extending into said cavity, hot and cold side iixed contacts affixed to and supported by said second and third terminals respectively, said ixed contacts arranged on opposite sides of said movable contact to selectively cooperate therewith in response to the thermal expansion and contraction of said bimetallic arm thereby to control an electrical apparatus, and a positioning rod attached to said cylindrical member and arranged to act upon said arm to maintain said movable contact in engagement with the cold side ixed contact when the ambient temperature of said switch is less than a predetermined temperature value, thereby to assure that said iiame detecting switch will be started with its movable contact engaging the cold side contact when the switch is connected in an electrical circuit and 8 the ambient temperature of said switch is less than said predetermined value.

5. The switch defined in claim 4 wherein the positioning rod extends between the cylindrical member to which it is attached and an inner wall of said casing to normally engage said casing.

6. The switch as defined in claim 4 wherein the bi* metallic Contact arm comprises an elongated strip of bimetallic material having side edges convergent toward the end of the arm which supports the movable contact and stepped inwardly near the end of the arm affixed to the cylindrical member.

7. The switch as defined in claim 4 wherein the bimetallic contact arm comprises an elongated strip of bimetallic material having side edges convergent toward the end ot the arm which supports the movable contact and stepped inwardly adjacent the end of the arm affixed to the cylindrical member, said arm being bent angularly intermediate its ends.

8. The switch as dened in claim 4 wherein the spring which urges the cylindrical member into frictional engagement with the extension means of the iirst terminal is of generally U-shaped configuration and includes a spring biasing portion engaging said cylindrical member to continuously bias said member against said extension means, and a supported portion with a slot therein for receiving an inner boss of the casing and thereby positioning said spring within the casing.

9. The switch as defined in claim 4 wherein said iirst, second and third terminals are supported by and extend inwardly through a wall of the casing opposite to the transparent wall portion, and an inwardly extending rectangular boss is formed in said wall adjacent said rst terminal, said spring having a generally U-shaped coniiguration and a slot therein for receiving said. boss, said first terminal extending through said slot after said boss has been received by said slot thereby to wedge said spring into secure engagement with said wall.

l0. A thermally responsive switch comprising a bimetallic contact arm, clutch means for rotatably supporting one end of said arm, a movable contact positioned on the other end of said arm, a pair of spaced ixed contacts arranged on opposite sides of said movable contact and selectively cooperable therewith in response to the thermally responsive movement of said bimetallic Varm thereby to control an electrical circuit, iixed supporting means, and a positioning rod linked to the supported end of said arm and arranged to engage said supporting means to act upon said arm and maintain said movable contact in engagement with one of said rixed contacts when the ambient temperature of said switch is less than a predetermined temperature value, thereby to assure that said switch may be started with its movable contact in engagement with said one of said iixed contacts when the switch is connected in an electrical circuit and the ambient temperature of said switch is less than said predetermined value. l

References Cite-d in the tile of this patent UNITED STATES PATENTS 2,503,259 Hall Apr. 11, 1950 2,660,645 Deubel Nov. 24, 1953 2,882,371 Bishofberger Apr. 14, 1959 2,979,585 Werr Apr. il, 1961

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