US2243753A - Furnace damper control system - Google Patents

Description

May 27, 1941. w. H. GILLE 2,

FURNACE DAMPER CONTROL SYSTEM Filed Sept. 15. 1957 v llllllillllllll Fig.1 i

INVENTOR Q Willis H. (iille ATTORN EY Patented May 27, 194i FURNACE DAMPER C'GN TROL SYSTEM Willis H. Giiie, St. Paul, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application September 15, 1937, Serial No. 164,006

8 Claims,

The present invention relates to a furnace damper control system and more particularly to one in which a manually operable basement firing switch is provided for causing the damper motor to move the dampers to firing position.

It is highly desirable where a damper motor controlled in accordance with some desirable controlling condition is used to operate the dampers of, a furnace, to provide a basement manually operable control which makes it possible for the dampers to be moved to a firing position. The need for this arises by the fact that when it is desired to fire the furnace, the dampers may be in draft retarding position, and if an attempt is made to fire the furnace when the dampers are in this position the result will be that fumes are liable to issue out of the firing door. The difiiculty which has frequently been encountered, however, with the provision of some basement controller, which usually takes the form in the case of an electric motor of a basement switch, is that the operator is apt to forget to move the switch back to the position in which the damper motor is automatically controlled. Since the firing position is usually one in which there is an appreciable amount of draft, the continued maintenance of the dampers in firing position is apt to lead to a dangerous condition wherein the furnace, and possibly the building, is excessively overheated. In order to overcome this disadvantage, various complicated arrangements have been provided for automatically returning the basement switch to its normal position after a predetermined period of time.

An object of the present invention is to provide a damper motor control system having a basement switch in which the condition responsive element of the limit control is effective to reset the basement switch to its normal position when the condition to which the limit control is responsive reaches a predetermined value.

A further object of the present invention is to provide a limit control for use in the control of a damper motor in which the limit control is provided with a basement switch which is automatically reset by the condition responsive element of the limit control when the limiting condition exceeds a predetermined value.

Further objects of the present invention will be apparent from a consideration of the accompanying specification, claims and drawing, in which Figure 1 is a schematic view of the improved furnace damper control system, and in which rotor 36 having-associated Figure 2 is a View showing a portion of the limit switch employed in connection therewith with the parts in the position assumed when the dampers are in a firing position.

Referring to the drawing for a more detailed understanding of the present invention, a furnace is generally indicated by the reference numeral it. This furnace is provided with a stack pipe H and with a draft'damper l2 and check damper it. Stops it and it are provided to limit the opening of the draft and check dampers, respectively. A firing door it is provided for the purpose of introducing fuel into the furnace when it is desired to fire the same. Extending upward from the furnace is a warm air duct I? which is provided with branch ducts 58 leading to various rooms. Only a single one of these branch ducts is shown, this particular branch duct leading to the space it.

A motor, generally designated by the reference numeral 29, is used to drive a shaft 25 which is provided at its opposite ends with cranks 22 and 23. Cranks 22 and 23 are connected to dampers l2 and It, respectively, by chains 24. and 25, or other similar devices. The chains 24 and 25 are guided by pulleys 25. The shaft 2i is biased by means of a spring 28 to the position shown in which the dampers are in their draft retarding position. The motor 26! is efiective when energized to rotate the shaft against the spring 23 until the draft damper i2 engages the stop It, at which time the check damper l3 will be closed. The motor 26 consists of a therewith a holding field winding 3! and a lifting field winding 32. The rotor 353 is connected through a reduction gear train 33 with the shaft 2i. When both the field windings 3| and 32 are energized, the torque exerted by rotor 33 is suflicient to move the dampers towards open position against the action of spring 28. When only the holding field winding 3! is energized, the motor is incapable of positively moving the dampers but is capable of holding them against the action of spring 28; The apparatus is operated so that the lifting winding is disconnected from the circuit when the dampers approach their draft open position. This disconnection of the lifting winding is accomplished by a switching mechanism consisting of a cam 3 t which is secured to the shaft 2!, a movable switch blade 35 cooperating with the cam, and a contact 36 which is adapted to be engaged by the switch blade 35. 35 is provided with a projecting toe portion 31, which toe portion is designed to engage the The cam sists of a blade 35 and move the same out of engagement with the contact 35 when the shaft 2| is rotated to a point where the dampers are in draft open position.

Located in the space H? is a room thermostat 45. This thermostat may be of any conventional construction and is shown as comprising a bimetallic element 4| to which is secured a contact arm 42 adapted to engage a fixed contact 43. Cooperating with the contact arm 42 1s a magnet 44. This magnet is adapted to exert a tendency to hold arm 42 in engagement with contact 43 when so moved. In this manner, it is necessary for a temperature change to occur after the contact arm 42 has moved into engagement with the contact 43 in order for this arm to separate from contact 43. By reason of the magnet 45, it is thus necessary for there to be a temperature differential between opening and closing of the thermostatic switch, and accordingly any tendency towards a chattering operation thereof is avoided. The thermostatic switch 45 is the primary control for the damper motor 25, as will be more obvious from the subsequent description.

A limit control is generally designated by the reference numeral 55. This limit control conbimetallic element and is designed to operate a switch associated therewith. In order to more clearly illustrate the construction of the limit control, the end face thereof is shown enlarged and revolved through an angle of 90, whereby certain features thereof are more clearly shown. Secured to the bimetallic element 5| is a rod 52 which is rotated thereby as the temperature is changed. Secured to the inner end of rod 52 is a cam 53 which isprovided with a projecting portion 54 and a second pro ectmg portion 55. Cooperating with the pro ectin-g portion 54 is a switch blade 56 which, in turn, 18 adapted to be normally in engagement with a second switch blade 51. The cam 53 is rotated in a counter-clockwise direction upon temperature rise, as indicated by the arrow thereon. When the temperature rise has continued sufficiently far, blade 56 is engaged by promotion 54 and moved out of contact making engagement with switch blade 51. The switch consisting of blades 55 and 51 constitutes a limit switch proper. Also located in the limit switch casing is a pair of switch blades '50 and BI. These switch blades 68 and 5| are-biased to an open position. Cooperating with the switch blade 60 is an arm 52 which is pivotally secured to a pin 63. A spring 64 biases the arm 62 against a stop 65. Cooperating with arm 62 is a second arm 51 which is provided with a slot 58 through which extends a pin 59 secured to arm 62. The arm 6'! is keyed to the pin 63. Also secured r gidly to the pin 63 is an operating knob WhlCh is not shown in the drawing but whose position is indicated therein by dotted lines, and which will be referred to hereinafter by that reference numeral. A leaf spring member 13 is rigidly mounted to a block 14. This leaf spring member '13 is normally in a flexed position by reason of its engagement with the end of arm 62. When, however, it is desired to move the basement switch to closed position, knob H is rotated in a counter-clockwise direction, rotating arm 61 and through the pin 69 and slot 68 the arm 52, and the end of spring T3 moves into a recessed portion 76, as indicated in Figure 2.

A step-down transformer 79 is employed for supplying power to the system. This step-down transformer 19 consists of a line voltage primary 8!] and a low voltage secondary 8|. The line voltage primary is connected to line wires 82 and 83 which lead to a suitable source of power (not shown).

Operation The various elements of the system are shown in Figure l in the position they occupy when the room temperature is satisfied, when the basement firing switch is in its normal position and in which the dampers are closed. Let it be assumed now that the temperature in the space l9 decreases below the value for which thermostat 40 is set. As soon as this takes place, contact arm 42 is moved into engagement with contact 53. The engagement of contact arm'42 with contact 43 results in the establishment of the following energizing circuit to the field winding 3| of motor 20: from the lower terminal of secondary 8| through conductor 85, limit switch blades 55 and 51-, conductors 85 and 81, bimetallic element 4|, contact arm 42, contact 43, conductors 88 and 89, field winding 3|, and conductor 95 to the other terminal of secondary 5|. At the same time, due to the fact that switch 35 is in engagement with contact 36, the following circuit will also be established to the lifting field winding 32: from the lower terminal of secondary 8| through conductor 85, limit switch blades 55 and 51, conductors 86 and 81, bimetallic element 4|, contact arm 42, contact 43, conductors 88, 9| and 92, contact 36, switch arm 35, conductor 94, lifting field winding 32, and conductor 90 to the terminal of secondary 8|. The establishment of these two circuits results in the energization of both field windings of motor 25 so that the motor is energized sufiiciently to rotate shaft 2| against the action of the biasing spring 28. The rotation of shaft 2| effects an opening of draft damper I2 and a closing of draft damper I3. This motion is limited, as previously explained, by the stop M which cooperates with the draft damper I2. Shortly before the draft damper l2 engages stop l4, however, the toe portion 31 of cam 34 engages the cam follower of switch 35, moving the same out of engagement with contact 36. When this occurs, the previously traced circuit through the lifting field winding 32 is interrupted with the result that this field winding is now deenergized, leaving only the holding winding 3| energized. The holding winding 3|, however, is able to hold the dampers in open position against the action of spring 28. In view of the fact that t holding winding 3| takes considerable less power than the lifting winding 32, the damper motor can be maintained continuously energized to hold the dampers in their draft open position without undue consumption of power.

With the dampers in their draft open position, the temperature of the furnace will be rapidly increased with the result that heated air will be delivered to the space l9. In the normal course of events, the temperature adjacent thermostat 40 will very quickly rise to the point at which it is set causing the arm 42 to move out of engagement with contact 43 against the resistance of magnet 44. When this occurs, the holding winding 3| is deenergized and the spring 2 8 operates to rotate shaft 2| back to the position shown in the drawing, again returning the dampers to their draft closed position. The same result follows if before the space temperature becomes sufficiently high the temperature in the bonnet of the furnace surrounding thermostatic element rises to an excessively high value. When this takes place, the cam 53 is rotated in a counter-clockwise direction sufiicien-tly to cause the projection 55 to move switch blade 55 out of contact making engagement with switch blade 51. It will be recalled that the switch blades 58 and 5'! were in circuit with both the field windings 3i and 32 so that as soon as these switch blades are separated the motor is completely deenergized.

Let it be assumed now that the dampers are in their draft closed position and it is desired to move them to a firing position, which in the illustrated embodiment of the invention is their normal draft open position. The knob ii is rotated in a counter-clockwise direction causing movement of arm t1 and consequently arm 62, as previously indicated. The movement of arm 62 causes switch blade til to be moved into engagement with switch blade 6i. Shortly after the engagement of switch blades 68 and 85 is effected, the spring i3 snaps into the shoulder portion it of arm 52 thus latching the contacts 68 and Si in closed position.

As soon as contacts to and 5! are closed, a circuit is established to the holding winding 35 as follows: from the lower terminal of secondary 8! through conductor 85, limit switch blades 56 and 5?, conductors 8t and 95, switch blades Eli and 5! conductors 9t, 9! and 89, holding winding 3| and conductor St? to the other terminal of secondary 8i A circuit is aiso established to the lifting winding as follows: from lower terminal of secondary 8! through conductor 35, switch blades 56 and 5?, conductors 86 and 95, basement switch blades 6i and S6, conductors 95 and 92, contact 36, switch blade 35, conductor 9d, lifting field winding 32, and conductor 83 to the other terminal of secondary Si. The establishment of these two circuits causes the damper motor to move to draft open position in which the furnace can be fired .rit mut any difficulties as to the issuance of fun; through the firing door. As soon as the firing is completed, the operator is supposed to turn the knob ii in a clockwise direction with the result that arm 2'5 is rotated in the same direction. It will be obvious that the movement of arm ii? initially has no effect upon arm 62 inasmuch as the bottom of slot fidmust engage the pin t9 before any movement will be im parted to $2. The initial movement of arm El, however, results in this aim engaging the leaf spring member E3 and moving the same off of the shoulder portion it. As soon as this takes place, the spr ng is immediately effective to move the arm 82 back to its original position against slight retarding action of leaf spring '53. In thi manner, the basement switch can readily be restored to its normal open position by actuation of the knob ii. 7

If, however, the operator forgets to move knob ii back to its original position, an unsafe condition will not resul as in many previous types of systems. As previously explained, the heatup of the air in the bonnet causes bimetallic element 5i to rotate the rod 52 and consequently the cam 53 in a counter-clockwise direction. This movement of cam 53, also as previously explained, has one eifect the separation of switch blades and 57, which deenergizes the motor 25 so that spring 23 moves the dampers to their draft closed position. Before the portion 5% of cam 53 is moved into engagement with limit switch blade 56, however, the raised portion 55 of cam 53 is moved into engagement with the leaf spring '13 to move the leaf spring from off of the shoulder it so that the arm 62 may be returned by means of spring 6 to its position indicated in Figure 1 wherein the arm 62 is resting against the stop 65. Such movement of arm 62 causes blades 56 and 6! to separate, so that the motor is again placed under the control of the thermostat it] and the limit switch 513.

It will be seen from the foregoing description that provision is made in the present invention whereby the basement switch is automatically reset directly by the temperature sensitive element of the limit switch. It is to be understood, of course, that this invention is applicable to any type of heating system employing a furnace having dampers. In the case of a steam heating system, the element 5! would be responsive to the pressure of the steam, and in a hot water heating system to the temperature of the hot water. It will further be seen that'the present invention provides for the provision of the basement switch in an extremely convenient location. The limit switch is almost invariably located at a convenient level whereas the damper motor, upon which the basement switch is usually located, is often at a relatively high level. By reason of th present invention, the condition responsive element of the limit control is employed to provide two functions; one, to shut down the burner and the other to open the basement switch so as to return the damper motor to the control of the room thermostat.

While a specific form of the invention has been shown for purposes of illustration, it is to be understood that the invention is to be limited only by the scop of the appended claims.

I claim as my invention:

1. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, motor means for operating said damper means, a main control means including a device responsive to a condition indicative of the demand for heat controlling said motor means, limit control means including a device responsive to a desired limiting condition also controlling said motor means and operative to cause said motor means to move said damper means to draft retarding position whenever said limiting condition assumes a first predetermined value, manually controlled means directly associated with said previously named means and movable between a normal first position in which both said main control means and said limit control means are in control and a second position, connections between said manually controlled means and said motor means operative upon said manually controlled means being moved to said second position to cause said motor means to move said damper means to a fire increasing position, and connections between said device responsiv to the limiting condition and said manually'operative means operative independently of said motor means upon said limiting condition assuming a second lower predetermined value to cause said manually operative means to move to said first position.

2. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, an electric motor operatively connected to said damper means for operating the same, a thermostatic switch having its temperature responsive element located in the space being heated, a limit switch including a thermostatic element responsive to the temperature of the air adjacent said furnace, a source of power, connections between said motor, said thermostatic and limit switches and said source of power whereby the position of the motor and consequently said dampers is determined by said switches, a manual firing switch mounted adjacent said limit switch movable between a first normal position in which said connections are effective to cause said thermostatic and limit switches to control said motor and a second position in which said motor moves said damper means to a fire increasing position regardless of the temperature in the space being heated, means biasing said firing switch to said first position, a latch for holding said switch in said second position when so moved, and a cam member actuated by the thermostatic element of said limit switch operative upon the temperar ture of the air adjacent said furnace reaching a predetermined value to release said latch.

3. In combination, heating means, control apparatus for said heating means comprising mechanism for increasing and decreasing heating, means responsive to a condition indicative of the demand for heat normally controlling said mechanism, manual means for controlling said mechanism to increase heating and for simultaneously terminating control by said condition responsive means, a device responsive to a desired limiting condition also controlling said mechanism and operative to cause said mechanism to decrease heating whenever the limiting condition assumes a first predetermined value, LL

and connections between said device and said manual means operative to restore control to said condition responsive means whenever the limiting condition assumes a second predetermined value.

4. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, an electric motor op eratively connected to said damper means for operating the same, a thermostatic switch havl ing its temperature responsive element located in the space being heated, a source of power, a limit switch, connections between said motor, said switches and said source of power whereby the position of the motor and consequently of the damper are determined by said switches, said limit switch including a thermostatic element responsive to the temperature of the air adjacent said furnace and operative upon said temperature reaching a first predetermined value to cause said motor to move said damper to draft retarding position, a firing switch located adjacent said limit switch and manually movable between a first normal position in which said connections are effective to cause said thermostatic and limit switches to control said motor, and a second position in which said motor moves said damper means to a fire increasing position regardless of the temperature in the space being heated, and mechanical connections between said thermostatic element of said limit switch and said firing switch operative upon the temperature of the air adjacent said furnace reaching a second predetermined value to cause said firing switch to be moved to its first position.

5. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, an electric motor op-- eratively connected to said damper means for operating the same, a thermostatic switch having its temperature responsive element located in the space being heated, a source of power, a thermostatic element responsive to the temperature of the air adjacent said furnace, a cam attached to said element to be operated thereby in accordance with said temperature, a limit switch having a member extending into the path of said cam so as to be engaged thereby for operating said switch when said temperature assumes a predetermined value, connections between said motor, said switches and said source of power whereby the motor position and consequently the damper position are determined by said switches, a firing switch located adjacent said limit switch and biased to a first position in which said connections are effective to cause said thermostatic and limit switches to control said motor, said basement switch being manually movable between said first position and a second position in which said motor moves said damper to a fire increasing position regardless of the temperature in the space being heated, and latch means for holding said firing switch in said second position, said latch means extending into the path of said cam so as to be released thereby when said temperature assumes a second predetermined value.

6. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, a damper motor for operating said damper means, a thermostatic switch having its temperature responsive element located in the space being heated, a limit switch including a thermostatic element responsive to the temperature within said furnace, a source of power, electrical connections between said motor, said thermostatic and limit switches and said source of power whereby the position of the motor and consequently said damper is determined by said switches, a firing switch located closely adjacent said limit switch and manually movable between a first normal position in which said connections are effective to cause said thermostatic and limit switches to control said motor and a second position in which said motor moves said damper means to a fire increasing position regardless of the condition of said thermostatic switch, and means independent of said electrical connections forming a mechanical connection between the thermostatic element of said limit switch and said firing switch whereby said thermostatic element causes said firing switch to be moved to its first position.

7. In combination, a furnace, damper means therefor movable between draft producing and draft retarding positions, a damper motor for operating said damper means, a thermostatic switch having its temperature responsive element located in the space being heated, a limit switch including a thermostatic element responsive to the temperature within said furnace, a source of power, electrical connections between said motor, said thermostatic and limit switches and said source of power whereby the position of the motor and consequently said damper is determined by said switches, a housing for said limit switch, a firing switch mounted on said housing manually movable between a first normal position in which said connections are effective to cause said thermostatic and limit switches to control said motor and a second position in which said motor moves said damper said mechanism to increase heating and for simultaneously terminating control by said condition responsive means, a device responsive to a limiting temperature also controlling said mechanism and operative to cause said mechanism to decrease heating when said limiting temperature assumes a predetermined safe limit, and connections between said device and said manua1 means operable to restore control to said condition responsive means upon a rise in said limiting temperature to a value within said safe limit.

WILLIS H- GILLE.

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