US2255672A - Electrical control device - Google Patents

Description

Sept. 9, 1941. w. c. MASON ELECTRICAL CONTROL DEVICE Filed July 1, 1938 2 Sheets-Sheet l n mm W NM W E 0 W2 W Z Sept. '9, 1941. w. c. MASON ELECTRICAL CONTROL DEVICE] Filed July 1, 1958 2 Sheets-Sheet '2 fuel, smoking and Patented Sept. 9, 1941 UNITED STATES PATENT OFFICE 2 Claims.

My invention particularly relates to an electrical control which is primarily adapted for use with fluid fuel burners and which is characterized by its simplicity, low cost of manufacture and by the fact that it will completely control the operation of a fuel burner whereby to insure safety in its operation under all conditions.

In the control of fuel burners, for example, oil burners, it is necessary where they are arranged for automatic control to provide means which is operable to shut off the burner in the event that, during an operation thereof, the burner flame is extinguished for some reason or other, or, when the burner is initially placed in operation, following a shut-off period, ignition of the fuel fails to take place. Such means should not only be positive in operation but should also operate very rapidly so that the burner is shut off, in the event of a failure of burner operation, before a suflicient period of time has elapsed to permit a dangerous condition to be created such as the formation of explosive mixtures. Such rapid operation will also shut off the burner, in event of failure, before an appreciable quantity of liquid fuel is deposited in the combustion chamber, an occurrence which would produce uncleanliness and undesirable odor, and would cause smoking when the burner was next placed in operation.

It is therefore a first object of my invention to provide a control device, adapted to be used with a fluid fuel burner, which device, though simple in construction, will completely and positively control the operation of the burner and which device is characterized by its rapidity of operation in that it will shut off the burner in such-a short interval of time that all dangers due, for example, to the formation of explosive mixtures are entirely obviated. For example, a burner which is controlled by a control device of the character herein contemplated can be shut off in the event ignition fails to take place or for any other cause combustion fails or does not occur within a period of the order of a few seconds from the time of starting an operation of the burner or from the moment combustion ceases. Therefore, an appreciable amount of fuel will not be deposited in the combustion chamber thereby substantially eliminating any odor of the unclean burner conditions.

An important feature of my invention lies in the provision of a thermal-responsive element which will expand and contract rapidly under varying temperature conditions and, at the same time, exert sufficient force to operate a control switch associated therewith, said element being capable of being placed within a combustion chamber or where temperatures of high order exist under burner operating conditions whereby due to the thermal-responsive character of the element it will operate with extreme rapidity to effect a desired operation of the control elements with which it is associated. A further object, therefore, resides in providing a control device which comprises an element of the foregoing character.

Further objects of my invention reside in the provision of a control unit comprising an electrically controlled switch which, preferably, comprises a bimetallic element operable in response to heat generated by electrical means to close or open an electrical circuit. A switch construction of this character entails a low manufacturing cost and yet comparatively slow, predetermined speeds of operation of the switch may be effected so that where such a bimetallic element or a phi-- rality thereof are employed to open or close'a circuit through two or more pairs of contacts, as herein contemplated, one of a pair of contacts may be actuated in timed relation to a second movable contact to make or break an electrical circuit therethrough.

A still further object resides in providing, in a control device, a switch element of the above character which is so arranged that the degree to which the bimetallic element may be warped is limited, thereby preventing excessive strains being set up in the element after an electrical contact has been made thereby, which might otherwise produce deformation therein and impair the designed operation thereof with respect to timing.

Another object of my invention resides in the provision of a switch comprising a bimetallic element of the foregoing character which is so constructed that said bimetallic element will operate to close a circuit through a pair of cooperative contacts and exert a force substantially sufficient only to hold said contacts firmly in engagement so that said contacts will be substantially instantaneously parted when the circuit is open to the electrical heating means associated with said bimetallic element.

With these and other objects in view, my invention includes the novel elements and the combinations and arrangements thereof described below and illustrated in the accompanying drawings, in which- Fig. 1 is an elevation view of one form of my panel to the terminal 9.

control device with a portion of one element thereof broken away;

Fig. 2 is a sectional elevation view thereof taken in about the plane 2--2 of Fig. 1;

Fig. 3 is a wiring diagram illustrating the electrical interconnection of my control device with an electrical load;

Fig. 4 is a fragmentary view, partially in section, illustrating the switch element shown in Fig. 2 in an alternative position;

Fig. 5 illustrates one manner of associating the device of Fig. 1 with a thermal-responsive element.

Fig. 6 is a fragmetary plan view of a part of the control panel and illustrating two pairs of' contacts in relatively spaced position;

Figs. 7 and 8 are views similar to Fig. 6 but showing the contacts in the relativepositionsthey will assume according to the degree of actuation of a bimetallic element associated there'- with;

Fig. 9 is an elevation view of a modified form of control device;

Fig. 10 is a side elevation view thereof;

Fig. 11 is a fragmentary, side elevation view showing the switch arm in an alternative position;

Fig. 12 is a fragmentary plan View thereof, partially, in selection; and

Fig. 13 is a wiring diagram illustrating the control device of Fig. 9 electrically interconnected with an electrical load.

The control device illustrated in Figs. 1 to 8 inclusive comprises a panel I which may be formed of any suitable electrical, insulating material and upon which is mounted a first switch element indicated generally at 2 and a second switch element indicated generally at 3. The switch 2 comprises a bimetallic arm 4 which is preferably mounted upon and secured to an insulating block 5 on the panel I which serves predeterminately to space the contacts borne by the bimetallic element from those contacts which are mounted upon the panel in cooperative relation thereto. The arm 4 is, at least in part, sur-- rounded by an insulating sleeve 6 about which is wound a coil 1 of electrical resisting wire forming a heating element adapted when energized to actuate the arm 4 or cause it to warp. One end of the resistor I is electrically connected to the arm d as indicated at B and the other end thereof is electrically connected to a terminal 9 by means of a collar ill, a lead H, and conductor l2, which may be arranged to extend through the is provided on the underside thereof with a contact 13 (see Fig. 6) and panel I is provided with .a contact I4 arranged to be engaged by contact l3 when the arm 4, in response to heat generated by coil 1, is warped. Arm 4 is also provided with a laterally extending arm l5, preferably of resilient material, and bearing a contact is which is adapted to engage a contact i! mounted on the panel I when arm 4 is warped as above described.

The bimetallic arm 4; i

For a reason, which will hereinafter be apparent contacts l6 and I! are preferably somewhat more closely spaced than contacts 13 and 14 so that an electrical circuit will be closed through contacts i6 and I? before contacts 13 and I4 engage each other and the resilience of arm l5 permits this operation without producing appreciable torsional stresses in the bimetallic arm. The contact I4 is electrically connected through a conductor l8, which may be imbcdded in the panel I as il-- lustrated in dotted lines, t-O'tcrminal 9 and contact H is electrically connected through a conductor E9 to a terminal 28.

The various electrically operated parts of a fuel burner are herein referred to as the electrical load of the burner and, by way of example, illustrated as a motor and inductance in the wiring diagram of Fig. 3. One side of this load is adapted to be connected through conductor 2! to terminal 28 and the other side of said load through conductor 22 to terminal 23. Likewise, the primary of an ignition transformer 24 for said burner is adapted to be connected between the terminal 9 and a terminal 25. Hence, it will be seen, generally speaking, that the heating coil 1 is connected in the primary circuit of the trans former Hand contacts 66 and H are designed toc'ontrol the flow of current to the conductor 2! on one side of the load circuit.

The switch 3 is similar to switch 2 in that it comprises a bimetallic arm 26 surrounded by an insulating sleeve 21 which has wound thereabout a heating coil 28. One end of the heating coil is electrically connected to the arm 26 as indicated at 29 and the other end thereof is connected to terminal 25 through the medium of collar 38, lead 3| and conductor 32. Arm 26 is provided on the inner surface thereof with a contact 33 which is adapted to engage a contact 34 mounted in cooperative relation thereto on the panel I. Contact 34 is electrically connected with terminal 25 through conductor 35. Arm 26 is also provided with contact 36 which is mounted on the outer surface thereof and designed normally to lie in engagement with a contact 31 which is mounted upon, but electrically insulated from, a movable arm 33 which may be designed to overlie the bimetallic arm 26. Contact 3'! is electrically connected with terminal 23 by means of a flex lead 39 and conductor 46.

v From the foregoing, it should be apparent that the heating coil 28, like heating coil 1, is included in the primary circuit of the ignition transformer 24 and that contact 37 is connected to one sid I of the load circuit of the burner.

Assuming, therefore, that terminal 4! of switch 2 which is in electrical contact with the arm 4 thereof is connected through conductor 42, thatmostat 43 and conductor 44 to one side of a source of electrical energy 45, that the other side of said source is grounded and that terminal 48 of switch 3, in electrical contact with arm 26 thereof, is also grounded, it will be seen that, if the circuit through thermostat 43 is closed, a closed circuit will exist including in series heating coils 1 and 28 and the primary winding of the ignition transwhen the heating coil 1 thereof is energized it willwarp to close the circuit through contacts 6 and H before the bimetallic arm 26 of switch 3 is warped sufficiently to open the circuit between contacts 36 and 31 thereof and means are pro- Vided, as described in the following, which function-to prevent a separation of the contacts 36 an'd'31 in the event of proper burner operation but which will permit a separation thereof in the '75 event combustion fails to take place.

The free end of arm 38 may be provided with a slot and an opening adjacent thereto as illustrated in which one end of a rod 41 may be secured, the other end of rod 41 being secured, as illustrated in Fig. 5, to the arm 48 of a lever 49 which is pivotally mounted as at 50 in a bracket The other arm 52 of lever 49 has adjustably connected thereto by means of a nut 53 a thermal-responsive element or wire 54, the threaded end of which passes through an opening in the arm 52. Element 54 is adapted to be placed within the combustion chamber indicated generally at 55 or in those spaces where temperatures of high order exist during the operation of a burner. One end of wire 54 may be bent over as at 56 to secure it to one side of the combustion chamber so that the wire extends thereacross with its opposite end connected to arm 52 of lever 49. A spring 5! is preferably connected between the arm 48 of lever 49 and bracket 5| whereby normally to urge the contact 31 carried by arm 38 into engagement with contact 36 and the degree to which the arm 38 may be moved by spring 51 is dependent upon the thermal-responsive element 54. In the absence of combustion in the combustion chamber, element 54 will permit spring5'l to maintain contact 31 of arm 38 in engagement with contact 38 during a portion only of the movement of the bimetallic arm 26 when it warps under the influence of heat generated by the coil 28. That degree of movement of arm 38 which will maintain contacts 36 and 3'! together for a predetermined time interval during operation of the switch 3 may be adjusted by means of the adjusting nut 53. Hence, assuming that the burner is placed in operation and that the fuel fails to ignite, bimetallic arm 26 will warp and, after a predetermined interval of time, contacts 36 and 31 will part, as illustrated in Fig. 4, thereby opening the electrical circuit to the electrical load of the burner. However, should combustion take place, element 54 will instantly expand thereby permitting spring 51 to maintain the contacts 36 and 31 in engagement and the circuit to the electrical load wil be preserved.

The element 54', for example, may be formed of a 16-gauge wire, preferably nichrome wire, and of a length of about 9 or inches. When an element of this character is subjected, as herein contemplated, to temperatures of about 1400 to 1500 F., expansion thereof occurs with extreme rapidity and so quickly that switch 3 may be designed to break the circuit to the burner in the event combustion does not occur within a period of the order of 3 or 4 seconds after an operation of the burner has been initiated, or, assuming that the burner is operating, within a like period of time after combustion ceases. Furthermore, by employing a thermal-responsive element of the character above described it not only responds quickly to temperature changes, that is, to either an increase or decrease in temperature, but it is also capable of exerting sufiicient force to actuate the arm 38 associated with the switch 3.

Other thermal-responsive devices such as bimetallic elements cannot be subjected to temperatures of the high order herein contemplated without being practically destroyed and such elements when designed for quick operation can exert only a comparatively small force and one insufficient for practical purposes to effect a positive control or actuation of a switch element. On the other hand, if such elements were designed to exert the required degree of force, suflicient for positive and accurate control purposes, the speed of operation thereof would necessarily be extremely slow. Such thermal-responsive elements are, therefore, of practically no value in a control device where quick response and direct, positive control thereby are desired.

I have also provided means for limiting the degree to which the respective bimetallic elements of switches 2 and 3 may be warped while maintaining a circuit to the electrical load of the fuel burner. These means comprises electrical contacts which serve, when the bimetallic arms have been warped to a suflicient degree, to shunt the heating coils associated therewith. Upon shunting of the heating coils, the bimetallic arms immediately begin to cool and return to their normal position. However, in so doing, engagement between the contacts which serve to shunt the coils is broken and, the coils being again energized, will again cause the bimetallic arms to warp. The contacts I3 and I4 of switch 2 effect this intermittent energization of the heating coil 1 and the resilient arm l5 serves to maintain contacts l6 and I! in engagement during this operation. Likewise, contacts 33 and 34 of switch 3 serve to provide intermittent energization of coil 28. The electrical circuit of these contacts hereinbefore described, should be apparent from an examination of Fig. 3.

The intermittent operation of the heating coils I and 28 perform two functions. First, it prevents excessive strains or stresses being set up in the bimetallic elements due to prolonged heating thereof and, secondly, as, for example, in the case of switch 2, it serves to cause the bimetallic arm to move a distance sufficient only to hold the contact IS in engagement with contact I! so that the arm 4, when it starts to return to its normal position, will substantially immediately separate these contacts. For example, if the bimetallic arm were continuously subjected to heat from its heating coil during burner operations, it would require a much longer period to cool sufliciently to separate the contacts.

Fig. 6 illustrates switch 2 in open position;

Fig. 7 illustrates the arm 4 actuated to a position wherein contact between the respective pairs of contacts is made, thereby closing the circuit therethrough to the electrical load and shunting the heating coil 1, and Fig. 8 illustrates contacts l3 and i4 separated due to a shunting of the heating coil with arm l5 maintaining the contacts l6 and I! in engagement. The bimetallic arm of switch 3 functions in like manner intermittently to engage contacts 33 and 34 while the circuit through contacts 36 and 3'! is maintained.

In conjunction with the foregoing, the operation of the foregoing described embodiment of my invention should be apparent from the following brief description thereof with reference to the wiring diagram of Fig. 3. Bearing in mind that switch 2 is normally open and switch 3 normally closed and assuming that thermostat 43 closes, the heating coils of switches 2 and 3 are placed across the source of supply and in series with the primary of the ignition transformer. Both bimetallic elements of switches 2 and 3, therefore, commence to warp and it will be understood, in order to engage contacts 16 and I! of switch 2 before contacts 36 and 31 of switch 3 are opened, the arm 4 of switch 2 is preferably designed to warp more quickly than the arm 26 of switch 3. Of course, this result may be effected by properly arranging the spacing of the contacts of the respective switches and permitting the arms thereof to warp substantially at the same rate. When the circuit is closed through switch 2, the fuel burner coxnmences to operate and ignition of the combustible mixture is produced by the spark gap in the secondary circuit of the ignition transformer. If proper combustion occurs, contacts 36 and 31 of switch 3 will be maintained in engagement, as hereinabove described through the expansion of wire 54. However, assuming combustion fails to take place, contacts 36 and 31 of switch 3 will be parted thereby breaking the circuit to the electrical load. It will be understood that the operations of switches 2 and 3 may b so relatively timed, due to the extremely quick control action obtainable. with my device, that the circuit through switch 2 to the load may be effected for the brief period of about 3 or 4 seconds before switch 3 operates to open the circuit therethrough in the event combustion fails to occur.

It will be understood that if ignition fails due, for example, to an opened secondary of the transformer, insuflicient current will flow through the primary thereof to energize the heating coils sufficiently to effect warping of the bimetallic elements of the switches.

In the embodiment of my invention illustrated in Figs. 9 to 13, inclusive, I have illustrated a control device comprising asingle bimetallic arm which device functions positively to control a circuit to the electrical load of a fuel burner in substantially the same manner as the device hereinabove described. In this embodiment, the bimetallic arm 53 has associated therewith a heating coil 59, one end of which is connected through the collar 60, lead 6i and conductor 62 to one terminal 63 to which one leg of the primary winding of the ignition transformer is adapted to be connected. The bimetallic arm 58 carries a laterally extending, preferably resilient, arm 64 which is insulated therefrom by means of insulators 65 but electrically connected through a yoke 66 to a contact 61. A contact 68 on arm 64 is adapted to engage the contact 69 mounted on the panel la. Contact 69 is connected through conductor 10 to one terminal H to which one leg of the electrical load may be connected. A second terminal 12 is provided to which the other leg of the load circuit may be connected and conductor 13 from the thermostat 43 is also adapted to be connected to ter minal 12. A conductor 14 connects terminal 12 with terminal 15 to which the other leg of the primary of the ignition transformer may be connected.

Bimetallic arm 58 also carries a contact 76 which is adapted to engage contact 11 mounted on the panel la and contact 11 is connected through conductor 18 to terminal 63. These latter contacts serve intermittently to shunt the heating coil 59 in the manner hereinabove described and contacts 68 and 69 serve to close the circuit to the electrical load iii-the mannerv above described with respect to switch 2.

Contact 61 carried on the bimetallic element and electrically connected with contact 68, however, is designed normally to engage a contact 19 which is carried on a movable, preferably resilient, arm 80, one end of which is suitably secured to the insulating blocks 81 which serve to hold the respective'switch elements in proper relationship. A movable arm 82, generally similar to arm 38 of switch3 and operable substantially in like manner, is also secured at one end to the supporting blocks 81 and the free end thereof is designed to be connected with the element 41 associated with the thermal-responsive element 54. The arm 82, however, is provided with an opening 83 through which a threaded stud 84 is adapted to extend. The stud is preferably threaded through openings in the spaced, overbent end of the arm 88 and the head 85 thereof is somewhat larger than the opening 83 so that arm may be moved relative to arm 82 but the extent of such movement is adjustably limited by means of the stud 84. I

The fixed ends of bimetallic arm 58, resilient arm 80 and arm 82 are electrically connected together at the insulating blocks 81 and to the terminal 86 which may be connected to ground as in the case of switch 3.

In operation, assuming the thermostat 43 closes, the circuit through heating coil 59 is closed thereby causing arm 58 to warp toward the right, as viewed in Fig. 10. As this occurs, resilient arm 80 will follow arm 58 maintaining contacts 61 and 19 in engagement. The contacts are so arranged that contacts 68 and 69 will engage before arm 58 has moved a sufiicient distance to separate contacts 6'! and 19, assuming arm 82 is held stationary, and, of course, the extent of movement of arm 80 carrying contact '19 is limited by the engagement of the head of stud 84 with the arm 82. The resiliency of lateral arm 64 permits contacts 68 and 69 to be made before completion of the warping movement of arm 58 without producing appreciable strains therein. Hence, after contacts 68 and 69 are brought into engagement, arm 58 continues to warp and the contacts are so relatively arranged that, assuming arm 82 is held stationary, contacts 61 and 79 will be maintained for a pre determined interval of time, for example of the order of 3 or 4 seconds, after the engagement of contacts 68 and 69. Therefore, inasmuch as the circuit to the load is made through these contacts, the fuel burner will begin to operate. However, if combustion does not occur, arm 83 controlled by the thermal-responsive element 54 will not be actuated to maintain contacts 61 and 19 in engagement and, after the head of stud 84 engages arm 82, these contacts will be parted because continued warping of arm 58 will carry contact 67 away from contact 19. If combustion occurs, however, arm 82 will be moved, as by spring 51, to maintain contacts 6'! and 19 together and the circuit to the load will be continued. Fig. 11 illustrates the relative positions assumed by the various parts of the control device when the control device is operated to eiTect an operation of the fuel burner but combustion fails to occur.

It will be noted that contacts 16 and 11 produce an intermittent energization of the coil 59 thereby preventing excessive straining of arm 58 as would occur if the coil were continuously energized but, at the same time, arm 58 is maintained in a position wherein engagement between contacts 68 and 69 and 6'! and 19, respec tively, may occur.

From the foregoing, it is believed apparent that my control device is extremely simple in construction, may be manufactured at a very low cost, and serves positively and accurately to control the operation of a fuel burner. It should also be noted that, in the event combustion fails to take place for any reason whatsoever, the

control device will operate to shut off the burner in such a short interval of time that danger due to the production of explosive mixtures and also the production of odors and smoking due, for example, to the deposition of fuel in appreciable amounts within the combustion chamber is entirely obviated.

Furthermore, it will be seen that the dual switch feature of my control device positively prevents reoccurrence of attempted burner operations if, for example, combustion does not occur. In the absence of this feature, a control circuit would repeatedly function, assuming the thermostat associated therewith closes, to start the burner in operation and, if combustion fails,

to open the circuit and thereafter to close said circuit again. Obviously, under such control, the burner would intermittently deposit fuel in the combustion chamber thereby forming not only a very undesirable, odorous and unclean condition but also a dangerous one.

While I have described my invention in its preferred embodiments it is to be understood that the words which I have used are words of description rather than of limitation. Hence, changes within the purview of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects:

What I claim is:

1. In a control circuit for a liquid fuel burner comprising an electrical load and an ignition transformer, a source of electrical energy, a thermostat, a first, normally closed switch and a second, normally open switch connected in series with said thermostat and electrical load across said source of electrical energy, and electrical means, in series with said transformer and thermostat across said energy source, for effecting the opening of said first switch and the closing of said second switch, said first switch having associated therewith a thermal-responsive element acting, when thermally actuated, to prevent the opening of said first switch.

2. In a control circuit for a liquid fuel burner comprising an electrical load and an ignition transformer, a source of electrical energy, a thermostat, a first, normally closed switch and a second, normally open switch connected in series with said thermostat and electrical load across said source of electrical energy, said switches having thermal-responsive, switch-actuating elements, and electrical heating means associated with said switch-actuating elements and in series with the primary of said transformer and said thermostat across said energy source, said heating means being operable, when energized, to effect a closure of said second switch and an opening of said first switch, and said first switch having associated therewith a thermal responsive element, adapted to be placed within the combustion chamber of said burner, acting, when thermally actuated, to prevent the opening of said first switch.

WILLIAM C. MASON.

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