US3711810A

US3711810A - Temperature responsive control apparatus for furnaces and the like

Info

Publication number: US3711810A
Application number: US00846409A
Authority: US
Inventors: J Stafford; R Brooks
Original assignee: Ranco Inc
Current assignee: Ranco Inc of Delaware; Robertshaw US Holding Corp
Priority date: 1969-07-31
Filing date: 1969-07-31
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16

Abstract

Two snap switches are actuated individually by longitudinal movements of two wires anchored at one end to a common leg, which has a greater coefficient of expansion than the wires, and attached at their other ends to switch operating levers spring biased to tension the wires. One switch controls an electrically operated fuel valve for a hot air furnace and closes the valve circuit during normal operating temperatures of the furnace. When the furnace temperature exceeds a desired maximum, the wire is moved by the leg to open the switch. The switch is also opened by the spring force in the event the operating wire for the switch is broken. The other switch controls operation of a fan motor for circulating air through the bonnet of the furnace and is actuated by its operating wire to close the fan circuit when the temperature of the furnace rises to a given temperature and to open the circuit when the temperature falls to a given degree. The spring force tensioning the operating wire actuates the switch to closed circuit position in the event the wire breaks.

Description

United States Patent 1 91 Stafford et'al.

[54] TEMPERATURE RESPONSIVE CONTROL APPARATUS FOR FURNACES AND THE LIKE [75] lnventors: Joseph H. Stafford, Columbus; Robert E. Brooks, Worthington,

[58] Field of Search ..200/l60; 337/384, 388, 392, 337/394, 395

[56] References Cited UNITED STATES PATENTS 3,204,070 8/1965 Marano ..200/ l 60 3,072,769 l/l963 Roeser 2,83l,093 4/l958 Trussell....

2,651,690 9/l953 Raney ..200/67 D FOREIGN PATENTS OR APPLICATIONS l,020,l92 2/1966 Great Britain ..337/388 5] Jan. 16, 1973 Primary Examiner-Bernard A. Gilheany Att0rneyWatts, Hoffmann, Fisher & Heinke [57] ABSTRACT Two snap switches are actuated individually by longitudinal movements of two wires anchored at one end to a common leg, which has a greater coefficient of expansion than the wires, and attached at their other ends to switch operating levers spring biased to tension the wires.

One switch controls an electrically operated fuel valve for a hot air furnace and closes the valve circuit during normal operating temperatures of the furnace. When the furnace temperature exceeds a desired maximum, the wire is moved by the leg to open the switch. The switch is also opened by the spring force in the event the operating wire for the switch is broken. The other switch controls operation of a fan motor for circulating air through the bonnet of the furnace and is actuated by its operating wire to close the fan circuit when the temperature of the furnace rises to a given temperature and to open the circuit when the temperature falls to a given degree. The spring force tensioning the operating wire actuates the switch to closed circuit position in the event the wire breaks.

3 Claims, 10 Drawing Figures PATENTEDJAH 1 6 197a SHEET 1 OF 2 INVENTORS ROBE/P 7' E. BROOKS ATTORNEYS PATENIEBJMI 16 ms SHEET 2 BF 2 INVENTORS ROBERT E moo/(5 JOSEPH H. 574 FFORD A TTORNEYS TEMPERATURE RESPONSIVE CONTROL APPARATUS FOR FURNACES AND THE LIKE I BACKGROUND OF THE INVENTION It has been proposed heretofore to provide a thermostatically operated switch apparatus comprising a snap acting switch actuated by an operating member biased in one direction and having one end of a wire attached thereto for moving the operating member in the op,- 1

posite direction, the other end of which wire is attached to a leg or rod supported on the base on which the switch is mounted and having a different coefficient of expansion than that of the wire so that the wire is THE PRESENT INVENTION The present invention provides an improvement over the control apparatus just described in that the electric switch is not only actuated to one position when the wire is moved by expansion of the leg to indicate a temperature limit, for example, but is also actuated to the same position when the switch operating member is relieved of the restraint imposed by the wire. Thus, should the wire break or become separated from the leg, the switch may be operated to a position to prevent unsafe operation of heating equipment controlled thereby. For example, if the switch is utilized to limit the temperature of the furnace by controlling an electrically operated fuel valve, should the wire break, the switch will open and close down the furnace. If the switch is used to control operation of an air circulating fan, should the wire break, the fan control switch will close and maintain air circulation to prevent overheating of the furnace.

Another feature of the present invention is the provision of a thermostatically operated switching apparatus comprising a frame which may be attached to the exterior of a hot air furnace, for example, and which supports an elongated thermally responsive member inside the furnace. The frame encloses a switch housing in which one or more switches are supported, each switch being actuated by a switch operating member comprising a first lever pivoted on a second range lever supported on the frame, the first lever having one end of a wire attached thereto, the other end of the wire being attached to the remote end of the thermally responsive member, the first lever being spring biased to apply tension to the wire and to pivot about the point of connection with the wire so as to bias the range lever about its pivot and against an adjustable stop carried by the housing. This construction facilitates the manufacture, assembly and calibration of the components of the switching apparatus and provides a durable and accurately operating control device.

Other objects and advantages of the invention will be apparent from the following description of a preferred form thereof, reference being made to the accompanying drawings wherein:

FIG. 1 is a wiring diagram of a fuel valve and electric motor fan for a hot air heating system;

FIG. 2" is a perspective'view of a combination fan control and limit switch mechanism for controlling the operation of an air circulating fan and a fuel valve in a hot air furnace;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a top plan view of the switch mechanism shown in FIG. 2 showing certain parts broken away;

FIG. 5 is a sectional view taken substantially along line 55 of FIG. 7 and on a reduced scale;

FIG. 6 is a sectional view taken substantially along line 6-6 of FIG. 7;

FIGS. 7, 8 and 9 are fragmentary sectional views taken substantially along line 77 of FIG. 4 and on a larger scale showing certain parts of a switch mechanism in different positions; and

FIG.. 10 is a fragmentary sectional view taken substantially along line 10-10 of FIG. 4.

Referring to the drawings, a control apparatus C is shown which is adapted to control an electric solenoid operated fuel valve V of a hot air furnace and an electric fan motor F for circulating air from the space to be heated by the furnace, through the bonnet of the furnace and back to the space. For sake of brevity, the furnace and air circulating ducts are not shown as they form no part of the invention. Such furnaces are conventional and include an outer shell which forms the hot air bonnet in which air is heated and forced to the space to be heated by the fan.

The energizing circuit for the fan motor F and valve V is shown in part in FIG. 1 and includes power lines L1,L2 which may be connected with a suitable source of current through a conventional thermostatic switch, not shown. As is well understood in the art, the lines L1,L2 are connected and disconnected with the power source in accordance with the requirement for heat in the space served by the hot air heating system.

The control apparatus C comprises a sheet metal frame 11 having a rectangular wall 12 and

integral end walls

13,14 and two side walls 15,16 formed by turning portions of the sheet metal. The side walls 15,16 are somewhat shorter than the end walls. The open sides of the frame 11 are adapted to be closed by a U-shaped cover 18 having flanges 19 at opposite ends which slide along the outer edges of the

end walls

13,14. Only one of the flanges 19 appears in the drawings. Preferably, the

end walls

13,14 have knock-out portions to form electric conduit entrances.

One end of a leg 17 is welded to the outside of the wall 12. The leg comprises a strip of stainless steel formed in the shape of a channel having its walls tapering towards its extremity remote from the frame 11.

The wall 12 has openings 11a, 11b through which bolts may extend to attach the frame to the exterior of the wall of the hot air bonnet of a furnace. When the frame is attached to a furnace, the leg 17 extends into the bonnet and its temperature follows that of the air in the bonnet.

Two

electric snap switches

20,21 are mounted in a housing 22, which is preferably formed of molded insulating material and is secured between the side walls 15,16 of the frame 11. The

switches

20,21 are adapted to be connected in series circuit with the solenoid circuit for the fuel valve and the fan motor, respectively. The switch 20 is actuated by thermally responsive means comprising the leg 17 and a wire 23, and the switch 21 is adapted to be actuated by thermally responsive means comprising the leg 17 and a wire 24. One end of each of the

wires

23,24 is attached to the outer end of the leg 17 and the other ends of the wires are attached to switch actuating members described more fully hereinafter, and which maintain tension on the wires and multiply movements of the wires for actuating the respective switches. The

wires

23,24 are formed of a material such as lnvar, having a lesser coefficient of expansion than the material forming the leg 17 so that when the temperature of the leg increases the leg will elongate and move the wires longitudinally and outwardly from the frame 11. When the temperawalls 15,16 of the frame 11 with the open side facing the bottom wall 12 and the outer edges of the

end walls

26,27 engaging the bottom wall. The housing 22 is secured to the frame 11 by four lugs formed at the sides thereof and which are received in notches in the edges of the side walls 15,16. The lugs 30 are secured in the notches by mashing the material at the upper corners of the notches over portions of the lugs.

Referring more particularly to the construction of switch 20, two L-shape

blade type terminals

31,32 extend from the top wall 25 of the switch housing, as viewed in FIG. 7, for example, and provide spade-type terminals for connecting the switch in the fuel valve circuit. The foot of the terminal 31 is attached to the housing wall 25 by a rivet 33 which also secures a conductor bar 34 against the inside surface of the top wall. The rivet 33 also forms an electrical connection between the terminal and conductor bar. The conductor bar 34 supports one end of a flexible leaf spring type contact arm 35, which is secured to the conductor bar by a rivet 36. The other end of the contact arm 35 has a contact member 37 attached thereto which is adapted to engage a fixed contact member 40 when the contact arm is flexed towards the fixed contact. The fixed contact 40 is attached to a foot portion 41 of a conductor bar 42, which bar is secured to the inner surface of the top wall of the housing by a rivet 43 which also secures the foot portion of the terminal member 32 to the exterior of the insulator block 22. The foot 41 extends from a leg portion 44 projecting from the bar 42. Movement of the contact arm 35 from the contact 40 is limited by a screw 45 which is threaded in an opening through the top housing wall 25. Preferably, the outer end of the screw 45 is inset in a recess in the insulator and the recess is filled with a solidified plastic insulating material at the factory to prevent unauthorized adjustment of the screw in the field and to insulate the screw from electrical contacts.

The contact arm 35 is flexed between contact 40 and stop screw 45 with a snap movement by a U-shaped toggle link 46 which is pivoted to the arm adjacent its free end and which link is snap actuated about its pivot by a toggle spring 47. The contact arm 35 has a central rectangular opening therethrough, the edges of which opening are offset to provide two knife edge pivots for receiving notches in the end edges of the legs of the toggle link 46, which link is disposed in the opening through the contact arm. The toggle link 46 has flanges 48,49 projecting from opposite sides and engage a tongue 50 which projects from a bracket '51 into the space between the flanges at the yoke end of the toggle link. The bracket 51 is secured to the conductor bar 34 by the rivet 33. The toggle spring 47 is a tension spring, one end of which is attached to the yoke portion of the toggle link 46 and the opposite end of which is attached to a finger forming the outer end of an actuator lever 52.

The actuator lever52 is formed of a D-shape sheet 7 metal member having two parallel lugs or flanges 53 54 turned from opposite sides and which are notched to receive pivot edges of two

ears

55,56 formed on the bracket 51. The actuator lever 52 is adapted to swing about the pivot formed by

ears

55,56 and cause the toggle spring 47 to shift from one side to the other of a dead centerposition lying on a line extending through the pivot for the toggle link 46 and the point of connection of the toggle spring with the link. As the toggle spring 47 is shifted in one position through the dead center position it causes the toggle link 46 to swing about its pivot in the same direction and across the center line of the contact arm 35 to the stop tongue 50. This shift in position of the toggle link causes the tension of the spring 47 on the link toforce the contact arm in the opposite direction to either open or close contacts 37 and 40, as the case may be. The snap switch described is more fully disclosed in US. Pat. No. 2,651,690.

The axis of the pivot for the actuating lever 52 is above the center line of force of the toggle spring 47, as viewed in FIG. 7 for example, so that the tension of the toggle spring constantly urges the lever clockwise about its pivot. The swinging end of actuator lever 52 rests on a switch operating member in the form of a lever 57 and its movement is controlled by the movement of the latter. The lever 57 is pivoted on a range adjusting lever 60 and is urged counterclockwise by a coil spring 61 resting on the wall 12 and engaging the underside of the lever. counterclockwise movement of the lever 57 by the force of the spring 61 is limited by the wire 23 which is attached to the lever and the lever applies a tension on the wire.

The lever 57 comprises a channel-shaped sheet metal member having

side flanges

62,63, each of which has a wedge-shaped pivot point 64 which nests in V-shaped notches 65 formed in

side flanges

66,67 of the lever 60. A button 68 of insulating material is attached to the lever 57 and is engaged by a dimple formed in the finger of the lever 52 to provide a rolling contact between the levers.

The lever 60 is comprised of a channel-shaped sheet metal member having the

side flanges

66,67 and is pivoted on a pin 69 supported by opposite side walls- 15,16 and engaged in notches 70 formed in the edges of the side flanges.

The wire 23 extends through an opening in the bottom wall 12 of the frame, between the side flanges of the

levers

60 and 57 and through an opening in the lever 57. The end of the wire 23 projecting through the opening in the lever 57 is upset or otherwise enlarged to prevent withdrawal of the wire through the opening.

It will be seen that the force of spring 61 causes the lever 57 to fulcrum about the end of wire 23 and press downwardly against the lever 60 and urge the latter counterclockwise about its pivot. Counterclockwise movement of the lever 60 is limited by a screw 71 which is threaded through an opening in the wall of the recess 25 and which has an end portion engaged by the outer end of the lever 60.

It will be understood that when the control mechanism is installed on a hot air furnace with the leg 17 extending into the hot air bonnet, an increase in temperature causes the leg to elongate which moves the wire 23 outwardly and rotates the lever 57 clockwise about its pivot as viewed in FIG. 7. The actuator lever 52 moves clockwise with the lever 57 and shifts the toggle spring 47 downwardly through its dead center position relative to the toggle link 46 which causes the toggle link 46 to snap counterclockwise about its pivot and shift the toggle spring to a position in which it urges the link to force the contact arm 35 against the stop screw 43 as seen in FIG. 8, thus breaking the circuit through contacts 37,40. The function of the switch is to open the fuel valve circuit and shut down the burner in the event the temperature in the furnace bonnet becomes excessive for some reason or other. The temperature at which the switch 20 opens can be regulated by positioning the lever 60 about its pivot by adjustment of the screw 71. This adjustment shifts the position of the pivot for the lever 57 longitudinally of the wire 23 so that the lever 57 will cause the switch 20 to be opened in response or more or less longitudinal movement of the wire.

Contraction of the leg 17 due to cooling thereof permits the spring 61 to move the

levers

52,57 counterclockwise and whenthe toggle spring 47 is raised above its dead center position relative to the toggle link 46, the link shifts and flexes the contact arm 35 to the position shown in FIG. 7 to close the switch contacts.

it will be appreciated that the point at which movement of the wire 23 downwardly causes opening of the switch 20 will depend upon the position of lever 60 as determined by the screw 71. The point at which movement of the wire 23 upwardly causes reclosing of the switch depends upon the position of stop 45. The

screws

71 and 45 are adjusted so that the switch 20 will close at somewhat above normal ambient temperatures and will open at a temperature above normal operating temperatures in the furnace bonnet so as to provide a safety cutout of the furnace operation.

ln the event that the wire 23 breaks or separates from the leg 17 the force of spring 61 then urges the lever 57 upwardly, as viewed in FIGS. 7-9 and shifts the actuator lever 52 upwardly beyond the switch closing position. This causes the forward portion 73 of the lever 52 to engage the toggle link 46 adjacent its pivot and move the contact arm 35 upwardly against the stop .45, as seen in FIG. 9. Thus, in the event the wire 23 fails for any reason, the switch 20 will open to prevent further operation of the furnace.

The switch 21 is of similar construction as switch 20, and for sake of brevity, it is shown in FIG. 10, but is not described in detail. Suffice to say, spade type terminals 75,76 correspond to

terminals

30,31 and a circuit therebetween is established by a contact arm 77 which corresponds to arm 35. The arm 77 has a contact member 78 on the free end which is shifted between a fixed contact 79 and a stop 82, spaced from the fixed contact, by a toggle link 81 which is in turn shifted from one side of a dead center position to the other by an actuator lever 80. The stop 82 is formed by a bridge integral with the housing 22. The contact 79 is on a screw 83 which is similar to the stop screw 45. By this arrangement the switch 21 opens the fan motor circuit as the temperature of the leg 17 cools and closes the circuit when the temperature of the leg rises to a predetermined degree. The lever rests on a lever 85 which is similar to the lever 57, and is urged from the frame wall 12 by a coil spring 86, which corresponds to spring 61. The lever 85 is pivoted on a lever which is similar to the lever 60 and is pivoted on the pin 69. The wire 24 is attached to the lever 85 in the same manner as the wire 23 is attached to the lever 57. The force of the spring 86 acting on lever 85 pivots the latter about the wire 24 and urges the lever 90 against a screw 91 threaded in an opening in the wall of housing 25. The screw 91 may be adjusted to change the temperature range at which the switch 20 is operated in a similar manner to that described relative to the screw 71.

The

screws

83 and 91 of the switch 21 are adjusted so that when the air temperature in the bonnet of the furnace is below F., for example, the switch is open. When the temperature in the bonnet rises to 140 F., the leg 17 lengthens and moves the wire 24 longitudinally to cause closing of the switch 21. By this arrangement, the fan motor F is operated to circulate the air to be heated by the furnace only when the temperature of the bonnet is sufficient to provide adequate heating to the space served by the hot airfurnace.

Should the wire 24 break or become separated from the leg 17 or the lever 85, the force of the spring 86 will move the lever 82 against the contact arm 77 and move it to engage the contact 79 and close the fan motor circuit. Thus, the fan will operate continuously and maintain air flow through the furnace bonnet and prevent overheating of the furnace.

We claim:

1. Control apparatus comprising a frame, an electric switch mechanism supported on said frame and having contacts movable to open and closed circuit positions, an operating member movable in opposite directions between first and second switch operating positions for actuating said switch mechanism to said open and closed circuit positions, respectively, said operating member having a range of movement in one direction beyond said second position, means biasing said operating member continually in said one direction, thermally responsive means including an element attached to said operating member and normally restraining movement of said'operating member in said one direction beyond said second position, and means responsive to movement of said operating member in said one direction beyond said switch closing position to open said switch contacts.

2. Control apparatus as defined in claim 1 further characterized by said switch mechanism including a shiftable contact arm carrying a contact member at the movable end thereof, an over center toggle mechanism for shifting said contact arm between said switch open and closed circuit positions and including a lever having a portion extending generally parallel to and normally spaced from said contact arm, said lever being biased to engage and follow movement of said'operat-.

ing member when said operating member moves between said first and second positions a toggle spring and toggle link interconnecting said lever and contact arm and operative to shift said contact arm from a contact closing position to a contact opening position and vice versa when said lever moves from and towards said contact arm respectively, said lever adapted to move toward said contact. arm and transmit its movement directly to said contact arm when said operating member moves beyond said second position.

3. Control apparatus comprising, a frame having a wall, a leg projecting from one side of said wall and forming one element of a thermally responsive power means, a first lever pivotally supported on the other side of said wall with said pivot relatively close to one end thereof, a second lever pivoted at one end to said first lever intermediate the pivot of said first lever and said one end thereof, a wire having one end attached to the extremity of said leg and one end attached to said second lever, a compression spring on said wall urging said second lever from said wall, said wire attached to said second lever between the pivot for said second lever and the point of thrust of said spring on said second lever whereby said second lever tends to pivot about the end of said wire attached thereto and urge said one end of said first lever towards said wall, a switch housing on said frame, a switch mechanism in said housing and including a switch actuator adapted to engage said second lever for movement thereby, an abutment supported on'said housing and engaged by the other end of said first lever, and means to adjustably shift said abutment from said wall.

Claims

1. Control apparatus comprising a frame, an electric switch mechanism supported on said frame and having contacts movable to open and closed circuit positions, an operating member movable in opposite directions between first and second switch operating positions for actuating said switch mechanism to said open and closed circuit positions, respectively, said operating member having a range of movement in one direction beyond said second position, means biasing said operating member continually in said one direction, thermally responsive means including an element attached to said operating member and normally restraining movement of said operating member in said one direction beyond said second position, and means responsive to movement of said operating member in said one direction beyond said switch closing position to open said switch contacts.

2. Control apparatus as defined in claim 1 further characterized by said switch mechanism including a shiftable contact arm carrying a contact member at the movable end thereof, an over center toggle mechanism for shifting said contact arm between said switch open and closed circuit positions and including a lever having a portion extending generally parallel to and normally spaced from said contact arm, said lever being biased to engage and follow movement of said operating member when said operating member moves between said first and second positions, a toggle spring and toggle link interconnecting said lever and contact arm and operative to shift said contact arm from a contact closing position to a contact opening position and vice versa when said lever moves from and towards said contact arm respectively, said lever adapted to move toward said contact arm and transmit its movement directly to said contact arm when said operating member moves beyond said second position.

3. Control apparatus comprising, a frame having a wall, a leg projecting from one side of said wall and forming one element of a thermally responsive power means, a first lever pivotally supported on the other side of said wall with said pivot relatively close to one end thereof, a second lever pivoted at one end to said first lever intermediate the pivot of said first lever and said one end thereof, a wire having one end attached to the extremity of said leg and one end attached to said second lever, a compression spring on said wall urging said second lever from said wall, said wire attached to said second lever between the pivot for said second lever and the point of thrust of said spring on said second lever whereby said second lever tends to pivot about the end of said wire attached thereto and urge said one end of said first lever towards said wall, a switch housing on said frame, a switch mechanism in said housing and including a switch actuator adapted to engage said second lever for movement thereby, an abutment supported on said housing and engaged by the other end of said first lever, and means to adjustably shift said abutment from said wall.