US3062933A

US3062933A - Limit control device

Info

Publication number: US3062933A
Application number: US60092A
Authority: US
Inventors: Chester P Burbey; Harold A Marble
Original assignee: TUCK AIRE FURNACE Co
Current assignee: TUCK AIRE FURNACE Co; TUCK-AIRE FURNACE Co
Priority date: 1960-10-03
Filing date: 1960-10-03
Publication date: 1962-11-06
Anticipated expiration: 1979-11-06

Description

Nov. 6, 1962 c. P. BURBEY ETAL 3,062,933

LIMIT CONTROL DEVICE 4 Sheets-Sheet 1 Filed Oct. 5. 1960 m H mHL 5 5 Y mMM F. m? M HEM m MR4 m d 3 &# VJ

LIMIT CONTROL DEVICE 4 Sheets-Sheet 2 Filed Oct. 3, 1960 v m I m- HEP $1 NM r &

Chas/er JOHFZOU IF z 3 INVENTORY P fiurbz/ BY ro/d A Mar-Me ATTORNEY! United States Patent Ofitice 3,062,933 Patented Nov. 6, 1962 3,062,933 LIMIT CUNTKUL DEVICE Chester P. Burb'ey, Palo Alto, and Harold A. Marble, Burlingame, Calif assiguors to Tuck-Aire Furnace Company, San Francisco, Calif, a corporation of California Filed Oct. 3, 1960, Ser. No. 60,092 19 Claims. c1. zoo-81.9

This invention relates to a limit control device and more particularly to a limit control device for use with furnaces.

This is a continuation-in-part of our application Serial No. 746,912, filed on July 7, 1958, now abandoned.

In the operation of gas furnaces, controls are provided to limit the operating temperature of the furnace to a safe predetermined temperature. In counter flow furnaces, often two or more controls are required to satisfy American Gas Association and Underwriters Laboratory requirements. Onewof the controls is mounted in the upper part of the furnace and is frequently called the upper limit control-and the other is mounted in the lower part of the furnace and is oftencalled the lower limit control. The upper limit control prevents overheating of the upper part of the furnace and turns off the gas supply. Overheating of this type occurs if a fan or blower motor becomes jammed. It also can occur if the fan belt breaks. The lower limit control prevents air discharged from the furnace from being overheated. Although the use of two such controls is satisfactory, there is a need for a single control device which will perform the functions of both of the conventional controls. Such a control device would appreciably reduce the initial cost and the cost of installation.

In general, it is an object of the present invention to provide a single limit control device which will perform the functions of two conventional limit controls.

Another object of the invention is to provide a limit control device of the above character which is responsive to a moving air stream.

Another object of the invention is to provide a limit control device of the above character which is also responsive to temperature changes.

Another object of the invention is to provide a limit control device of the above character in which the sensitivity can be controlled.

Another object of the invention is to provide a limit control device of the above character which hasa wind operated reset.

Another object of the invention is to provide a limit control device of the above character which can be manually reset.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawing:

FIGURE 1 is a plan view of a limit control device embodying our invention;

FIGURE 2 is a front elevational view of the limit control switch shown in FIGURE 1;

FIGURE 3 is a partial front elevational view similar to FIGURE 1 with a portion of the wind vane broken away;

FIGURE 4 is a cross-sectional view taken along the line 4-4 of FIGURE 1;

FIGURE 5 is a cross-sectional taken along the line 5--5 of FIGURE 4;

FIGURE 6 is a cross-sectional view similar to FIG- URE 4 but showing the limit control device with the switch in a closed position;

FIGURE 7 is an enlarged cross-sectional view taken along the line 7-,7of FIGURE 4;

FIGURE 8 is a cross-sectional line 88 of FIGURE 7;

FIGURE 9 is a wiring diagram showing our limit control device connected into a conventional furnace;

FIGURE 10 is a plan view showing another embodiment of our limit control device;

FIGURE 11 is a plan view similar to FIGURE 10 but showing a portion of the wind vane cut away;

FIGURE 12 is a side elevational view partly in crosssection of the limit control device shown in FIGURES 10 and 11;

FIGURE 13 is a cross-sectional side elevational view of still another embodiment of our limit control device; FIGURE 14 is a front elevational view of the same;

FIGURE 15 is a cross-sectional view taken along the line 15-15 of FIGURE 14;

FIGURE 16 is across-sectional view taken along the line 16-46 of FIGURE 15; and

FIGURE 17 is a partial line 1717 of FIGURE 13.

In general, the limit control device consists of a switch movable between two positions with temperature responsive means for moving the switch from one of the posi* tions to the other position. The device also includes view taken along the means responsive to airflow for moving said switch from' said other position to said one position to reset said switch.

The limit control device shown in FIGURES 19 of the drawing consists of a housing 11 of suitable insulating material such as Bakelite and a mounting plate 12 to which the housing is secured by suitable means such as screws 13. An elongate framework has its front end fixed to the mounting plate 12. As shown, the framework 14 is substantially U-shaped in cross-section and is tapered toward the rear. The framework is provided with openings 16 in its lower portion for a purpose hereinafter described.

A snap-acting switch 17 is mounted within the housing 11 and consists of stationary contacts 18 and a movable contact member 19 carrying a pair of contacts 21 which are adapted to contact or engage the stationary contacts 18. The contact member is provided with a pair of earlike portions 22 which are rockably seated on one end of a contact carrying member 23. The contact carrying member 23 is pivotally mounted between a pair of posts 24aftixed to the housing 11 by suitable means such as the screw '26. A spring 27 has one end secured to an extension 28 of the contact carrying member 23, and the other end is secured to a' link 29 which is secured to a post 31 afiixed to the housing 11.

From the construction described, it is readily apparent that as the end of the contact carrying member 23 to which the spring 27 is secured passes through center, the switch will be moved rapidly toward a closed position or an open position, depending upon the direction of movement of the member 23 to prevent excessive arcing of the contacts.

An operating arm 32 is mounted on the contact carrying member 23 and extends generally in the same direction as the contact carrying member. The operating arm 32 is adapted to be moved by a manual reset button 33. The manual reset button 33 is provided with a plunger 34 which is fixed to the extreme end of the operating arm 32. Thus, it is apparent when the reset button 33 is moved inwardly, the contacts of the switch are moved toward a closed position.

An adjusting screw 36 is threaded into the housing and is adapted to be positioned so that it will be engaged by the operating arm 32 for a purpose hereinafter described.

An additional operating arm 37 has one end mounted on the contact carrying member 23 at right angles to the operating arm 32 and extends rearwardly through a slot 38 in the mounting plate 12. The operating arm 37 explan view looking along the tends rearwardly for a substantial distance into the framework 14. The operating arm 37 is adapted to be engaged by temperature responsive means 39 and wind responsive means 41.

The temperature responsive means consists of a lever 43 which has one end pivotally connected to the framework 14 at 44. The other end of the lever is threadably engaged by a screw 46 by which the positioning of that end of the lever can be controlled relative to the framework 14. A coil spring 47 is mounted on the screw 46 and ensures that the screw firmly grips the lever 43. The lever 43 is provided with openings 43 for a purpose hereinafter described.

An operating lever 49 is pivotally mounted on the lever 43 at 51 and has a portion 52 which is adapted to engage the operating arm 37. The other end of the operating lever 49 is provided with a forked construction 53 in which upper forked

portions

53a and 53b are adapted to engage the upper surface of one end of a bimetallic element 54 and in which a lower forked portion 590 is adapted to engage the lower surface of the same end of the bimetallic element. The other end of the bimetallic element is affixed to the end of the lever 43 at 56.

The wind responsive means 41 consists of a wind vane 58 which has a substantially planar upper surface 59. Suitable means is provided for attaching the vane to the operating arm 37 and, as shown, consists of a portion 61 of the vane which is bent downwardly and which is provided with a slit 62 which is adapted to receive the operating arm 37. The portion 61 also seats in a notch 63 provided in the operating arm. The other end of the vane is also provided with a portion 64 which is bent downwardly and engages the operating arm 37 is a suitable manner. For example, as shown, the portion 64 can also be bent inwardly to engage a slit 65 in the operating arm 37.

A typical wiring diagram showing the use of one of our limit control devices is shown in FIGURE 9. As shown, the limit control device 67 is connected to line voltage in series with a room thermostat 68, a solenoid operated gas valve 69 and a safety pilot device 71.

Operation of our limit control device may now be briefly described as follows: Let it be assumed that our limit control device has been installed in a counter-flow furnace in the path of air flow and connected as shown in the wiring diagram in FIGURE 9. Let it also be assumed that the furnace is operating properly and that the snap-acting switch is in closed position as shown in FlGURE 6 of the drawing. Now let it be assumed that the outlet air from the furnace becomes overheated for some reason, such as all the outlet ducts from the furnace being closed. As the furnace heats up, the hot air will pass through the

openings

16 and 48 and over the bimetallic element 54 to cause it to heat up. As the bimetallic element heats up, the end of the bimetallic element engaging the forked portions of the operating lever 49 will be moved downwardly, as viewed in FIG- URE 6, to urge the other end of the lever 49 into engagement with the operating arm 37. When the predetermined temperature, for which the control device is set, is reached, the bimetallic element through the lever 49 will cause the operating arm 37 to be lifted which will cause opening of the contacts of the switch 17.

It will be noted that upward movement of the operating arm 37 carries with it the vane 58. As soon as the furnace starts cooling, the operating lever 49 moves out of engagement with the operating arm 37. The operating arm 49 cannot cause resetting of the switch 17 because it cannot engage the arm on downward travel. However, as soon as the lever 49 moves out of engagement with the operating arm 37, the pressure of the wind or air against the vane 58 will cause downward movement of the vane and the operating arm 37 to reset or close the contacts of the switch 17. Thus, it can be said that the vane 58 serves as air-operated reset means,

In the case of a power failure, there often is enough residual heat in the furnace to cause operation of the bimetallic element and opening of the contacts. Normally this would require that the switch be manually reset. However, with our switch, the switch will be reset automatically as soon as the blower starts operating. As is well known in many furnaces, the burner must be turned on and burn until a predetermined temperature is reached in the furnace before the fan or blower will be turned on.

If the temperature in the furnace rises for some other reason, such as, for example, if the fan belt breaks or the blower motor becomes jammed, the switch 17 will be opened in the same manner when the temperature within the furnace rises above a predetermined temperature. However, in this case, the switch 17 will not be automatically reset by the vane 53 because no air or Wind is passing through the furnace and over the vane 58.

Before the control device will automatically reset, the damage or malfunctioning component in the furnace must be repaired. The switch can, however, be manually reset by operating the manual reset button 33.

The temperature at which the bimetallic element 54 will cause opening of the contacts of the switch 17 is adjusted by the screw 46 by raising or lowering the lever 43.

The adjustment screw 36 is utilized to increase or decrease the pressure required on the wind vane 58 to reset the switch 17. Thus, as the screw 36 is moved inwardly to limit the amount of movement of the operating arm 32, the contact carrying member 23 will be moved closer to the point at which snap action occurs. For that reason, less pressure will be required on the operating arm 37 to move the switch to the closed position. The position of the screw as .does not affect the sensitivity or operation of the temperature responsive means 39.

Another embodiment of the invention is shown in FIG- URES 10, ll and 12. This embodiment of our invention is very similar to the embodiment hereinbefore described except for the differences in the operating arm 37 and the Wind responsive means 41. As shown, a relatively short operating arm 74 is provided which is adapted to be engaged by the portion 52 of the operating lever 49. The operating arm 74 is adapted to be engaged by wind responsive means 76 which consists of a wind vane 77 which has upwardly inclined side edges 78 and 79. The rear end of the vane is pivoted to the framework 14 at 81 and is provided with a downwardly turned portion 82 at its forward end which rests upon the operating arm 74. The operation of this embodiment is similar to that hereinbefore described. When the snap-acting switch 17 is opened by the temperature responsive means 39, the switch will be automatically reset by the wind or air acting upon the wind vane 77. Pressure on the wind vane will urge the operating arm downwardly to close the contacts of the switch.

Another embodiment of our invention is shown in FIGURES 13 through 17 As can be seen from the drawings, it is similar to the embodiments hereinbefore described. It consists of a Bakelite housing 86 secured to a metal plate 87 by screws 88. An elongated framework 89 very similar to the framework 14 has its front end secured to the metal plate 87. Openings 91 are provided to facilitate air flow through the limit control device as hereinafter described.

A snap-acting switch 92 is mounted within the housing 86 and consists of a pair of stationary contacts mounted in the housing and which are provided with screws 94 to facilitate attachment of leads or wires to the stationary contacts. A movable contact member 96 is movable into and out of engagement with the stationary contacts and when in engagement with the stationary contacts serves to form an electrical connection between the stationary contacts. The movable contact member 96 is provided with cars 97 which are loosely mounted in recesses 98 provided on opposite sides of a mounting member 99. A leaf spring member 101 is provided which has ears 102 which also extend into the recesses 98. The leaf spring member underlies the U-shaped mounting member 99 as shown particularly in FIGURE 16. The leaf spring member 101 is provided with an in-turned central portion 103 which seats in an indentation 104 provided in the contact member 96. The inturned portion 103 therefore serves to generally position the contact member 96. The U-shaped mounting member is provided with lugs which are pivotally mounted on a stationary member 107. The stationary member 107 has ears 108 which are fixed in slots provided in vertical posts 109.

The mounting member 99 is provided with an extension 1 11 which carries one end of a spring 112. The other end of the spring 112 is connected to a link 113 carried by a post 114. An arm 116 of suitable insulating material is fixed to the mounting member 99 by rivets 116 and extends upwardly in the same general direction as the mounting member. The free end of the arm 116 is provided with a member 117 which 118.

A reset pin 121 is loosely mounted in a collar-like member 122 to permit pivotal movement of the reset pin 121 for a purpose hereinfater described. An abutment member 123 is mounted on the reset pin and is provided with a shoulder 124 which is adapted to engage the flange "118 of the member 117 as shown particularly in FIGURE 15. And is also shown in FIGURE 15, the reset pin extends through an opening 126 provided in the plate 87 and overlies the framework 89 for a purpose hereinafter described.

An operating arm 128 of suitable insulating material is secured to one side of the mounting member by suitable means such as the rivets 129 and extends through an opening 131 in the plate 87. The operating arm 128 is adapted to be engaged by temperature responsive means 131 whereas the reset pin 121 is adapted to be engaged by wind responsive means 132.

The temperature responsive means 131 is substantially identical to the temperature responsive means 131 hereinbefore described, and consists of a lever 133 pivotally connected to the framework 89 at 134. The other end of the lever is threadably engaged by a screw 136 to permit vertical adjustment of the lever. A spring 137 maintains firm engagement between the screw 136 and the lever 133. Openings 138 are provided in the lever arm and are in general registration with the openings 91 in the framework 89. An operating lever 141 is pivotally connected to the framework 89 at 142 and has one end portion 143 which is disposed in a slot 144 provided in the operating arm 128. The other end of the operating lever 141 is provided with a forked portion 146 which forms a recess 147 which receives one end of a suitable temperature sensitive element 148 such as a bimetallic element. The other end of the bimetallic element is fixed to the lever 133 by suitable means such as rivets 151.

The wind responsive means 132 consists of a wind vane 156 providing a flat surface which lies generally in a horizontal plane when the switch is in its normal position as shown in FIGURE 13. The vane 156 is pivotally mounted to the framework 89 at 157. The vane is provided with two extending arm portions 158 which carry a cylindrical counterweight 159. One of the arms 158 carries an operating extension 161 which is adapted to engage the reset pin 121 as shown particularly in FIGURES 13 and 15. As will be noted particularly from FIGURE 17, the vane 156 has such a width that it is slightly less than the width of the U-shaped member 89. However, the vane 156 is provided with an end portion 163 of substantially greater width than the other portions of the vane so that the vane cannot drop below the upper edges of the U-shaped framework 89. This carries a flange 6 portion of increased area makes the device more sensitive because of the lever arm advantage.

Operation of this embodiment of our limit control device may now be briefly described as follows: Let it be assumed that the limit control switch has been installed in a counter-flow furnace so that it is mounted in a vertical position with the wind vane 136 being in a substantially horizontal position. When the furnace is operating properly, the switch 92 will be closed and the wind vane 156 will be in engagement with the U-shaped frame and will be lifting the inner end of the reset pin 121 upwardly. Now let it be assumed that for some reason, the outlet air from the furnace reaches a temperature above a predetermined safe temperature. When this occurs the air flowing through openings 91 and 138 will cause the bimetallic element 148 to heat up and will cause its free end to move downwardly to cause movement of the operating lever 141 and upward movement of the operating lever 128 to open the switch 92. As will be noted from FIGURE 13 this opening of the switch 92 is not effected by the Wind operated means 132. However, as soon as the switch 92 is opened, the furnace is shut down and the wind vane moves to the position shown in FIGURE 13 because of the weight of the counter-weight 159. The reset pin is therefore permitted to drop down so that the shoulder 124 comes into engagement with the flange 118 to hold the switch 92 in the open position as shown in FIGURES 15 and 16.

As soon as the furnace cools, the operating lever 141 will attempt to move downwardly. However, the switch 92 cannot be moved to the closed position until the reset pin 121 is actuated to release the flange 118.

If the control is such that the fan does not cease operating upon overheating of the furnace, the vane 156 will maintain the reset pin out of engagement out of the flange 118 and therefore the switch 92 can be closed as soon as the bimetallic element 148 cools below the predetermined safe temperature.

As the temperature in the furnace rises because something has happened to the blower and no air is passing through the furnace, the wind vane will move to the position shown in FIGURE 13 and will permit the reset pin to come into engagement with the flange 118 when the switch 92 is opened by the bimetallic element 148 because of overheating of the furnace.

As soon as the air flow is resumed through the furnace, the wind operated means 132 will release the reset pin 121 to permit the switch 92 to be moved to the closed position.

Our limit control device has been found to operate very satisfactorily because very little pressure is required to raise the inner end of the reset button to release the flange 118. The reset pin is mounted in the housing 86 in such a manner that the switch can be reset manually when desired. However, before the limit control device resets itself automatically there must be air flow through the furnace and the temperature of the air through the furnace must be below a predetermined safe temperature.

The arrangement of the switch 92 is such that snap action is obtained when the switch is moved between open and closed positions. The temperatures at which the bimetallic element 148 causes opening or closing of the switch 128 is adjustable by adjustment of the screw 136. The reset pin 121 is always in a position to engage the flange 118. The switch is mounted in such a manner that the inner end of the reset pin is pulled downwardly by the force of gravity about the pivot point provided by the collar 122. The pin is relatively small so that it can be raised readily by the wind op erated means to facilitate automatic resetting of the limit control device.

It is apparent from the foregoing that we have provided a new and improved limit control switch which is particularly adapted for use in counter-flow furnaces and which can be utilized to take the place of two or more conventional switches. The reset which is responsive to air flow is particularly advantageous in that it eliminates the use of an additional switch which is normally required to detect malfunctioning of the fan or blower. The limit control device is extremely sensitive to high rates of temperature change and is readily adjusted and installed.

It is also apparent from the foregoing that instead of a wind operated reset, that an air pressure operated reset can be utilized to accomplish the same purpose. The blower in the furnace by creating an air flow also creates a differential in pressure between the interior of the furnace and normal atmospheric pressure. This pressure diiierential can be used to operate a diaphragmlike device or similar device to reset the switch and thereby accomplish the same results as the wind operated reset.

We claim:

1. In a limit control device, a switch movable between two positions, an operating arm, manual reset means adapted to engage said operating arm to move said switch from an open to a closed position, an additional operating arm mounted on said switch, temperature responsive means including a bimetallic element adapted to engage said additional operating arm for moving said switch from a closed to an open position, and wind responsive means operatively connected to said operating arm to move said switch from an open to a closed position.

2. A limit control device as in claim 1, together with means for adjusting the amount of wind pressure required to cause movement of the switch from an open to a closed position, said adjustment means comprising means adapted to engage said first named operating arm to prevent movement of said operating arm beyond a predetermined position, and to increase the sensitivity of the operating arm to air movement.

3. In a limit control device, a housing, a switch mounted in said housing and movable between open and closed positions, an operating arm mounted on said switch and extending through said housing, a framework mounted On said housing, temperature responsive means including a bimetallic element carried by said framework and adapted to engage said operating arm to move said switch from a closed to an open position, and wind responsive means including a vane adapted to be engaged by the wind for controlling the movement of said switch from an open to a closed position.

4. A limit control device as in claim 3 wherein said vane is mounted solely on said operating arm.

5. A limit control device as in claim 3 wherein said vane has one end pivotally mounted on the framework and has the other end engaging the operating arm.

6. In a limit control device, a switch movable between open and closed positions, an operating arm secured to said switch for moving said switch from one of said positions to the other of said positions, temperature responsive means including a bimetallic element engaging said operating aim for operating said switch, and wind responsive means including a vane adapted to be engaged by the wind for controlling the movement of said operating arm.

7. In a limit control device, a housing, a switch mounted in said housing and movable between open and closed positions, an operating arm mounted on said switch and extending through said housing, a framework secured to the housing, an additional operating lever pivotally mounted in said framework and having one end engaging said operating arm, a bimetallic element having one end secured to said framework and having the other end engaging said operating lever, and wind responsive means including a vane adapted to be engaged by the wind for controlling the movement of said first named operating arm.

8. A limit control device as in claim 7 wherein said S additional operating arm and said bimetallic element are substantially in axial alignment.

9. In a limit control device, a housing, a switch mounted in said housing and movable between open and closed positions, an operating arm mounted on said switch and extending through said housing, a framework mounted on said housing, an operating lever pivotally mounted in said framework and having one end engaging said operating arm and adapted to move said first named operating arm to move said switch from a closed to an open position, a bimetallic element having one end secured to said framework and having the other end engaging said operating lever, and wind responsive means including a vane adapted to be engaged by the wind for controlling the movement of said switch from an open to a closed position.

10. In a limit control device, a switch movable between first and second positions, an operating arm secured to said switch, temperature responsive means including a bimetallic element engaging said operating arm for moving said switch from said first position to said second position, and wind responsive means controlling the movement of said switch from said second position to said first position.

11. In a limit control device, a housing, a switch mounted in said housing and movable between first and second positions, an operating arm mounted on said switch and extending through said housing, an additional operating lever pivotally mounted in said framework and having one end engaging said operating arm, a bimetallic element having one end secured to said framework and having the other end engaging said operating lever, said bimetallic element serving to move said switch between said first and second positions, and wind responsive means controlling the movement of said switch from said second position to said first position.

12. In a limit control device, a switch movable between first and second positions, an operating arm secured to said switch, temperature responsive means engaging said operating arm and moving said switch between said first and second positions, reset means adapted to lock said switch in one of said positions and wind responsive means for automatically releasing said reset means to permit the control of said switch to be returned to said temperature responsive means.

13. A limit control device as in claim 12 wherein said reset means includes a member continuously and yieldably urged into an engaging position.

14. A limit control device as in claim 13 wherein reset means can be operated manually to reset the switch.

15. In a limit control device, a housing, a switch mounted in said housing and movable between open and closed positions, an operating arm mounted on said switch for operating the same and extending through said housing, a frameword mounted on said housing, an operating lever pivotally mounted in said framework and having one end engaging said operating arm, a bimetallic element having one end secured to said framework and the other end engaging said operating lever for moving the switch between said first and second positions, reset means mounted in the housing and adapted to engage said switch to maintain said switch in one of said first and second positions, and wind responsive means for releasing said reset means.

16. A limit control device as in claim 15 wherein said reset means is provided with means to permit manual operation of the reset means to reset the switch.

17. A limit control device as in claim 15 wherein said wind responsive means is provided with a counter weight to normally maintain said wind responsive means out of engagement with the reset means when the wind is not impinging upon the wind responsive means.

18. A limit control device as in claim 16 wherein said reset means includes a pin pivotally mounted in said housing and means yieldably urging said pin into engagement with said switch.

1,9. A limit control device as in claim 16 wherein said References Cited in the file of this patent reset means includes an arm secured to said switch, a pin UNITED STATES PATENTS pivotally mounted in said housing and normally urged downwardly by gravity, and an abutment member carried 2,518,176 Powers 81 1950 by the pin and having a shoulder adapted to engage the 5 2,348,167 Matthflws 1958 arm carried by the switch. ,848,582 Booth Aug. 19, 1958