US2559490A - Fuel burner control system - Google Patents

Description

July 3, 1951 R. E. YATEs ET AL FUEL BURNER CONTRO;d SYSTEM Original Filed Nov. 12, 1947 met@ July s, 1951 F`UEL BURNER CONTROL SYSTEM Robert E. Yates, Joseph M. Engel, and William W. Riesche, Chicago, Ill., assignors to Drying Systems, Inc., Chicago, Ill., a corporation of Illinois Original application November 12, 1947, Serial No. 785,488.- Divided and this application September 16, 1948, Serial No. 49,484

7 Claims.

This application is a division of our copending application, Serial No. 785,488, led November 12, 1947, now matured into Patent 2,538,952 issued on January 23, 1951.

This invention relates to safety control means and particularly to such safety control means for use with gas burners.

Safety control mechanisms for gas burners and the like have been used quite extensively in industrial burner installations, but in recent years there has been a tendency to utilize gas burners in domestic appliances where the cost of the control system is an important factor. One instance in which the use of a safety control system is highly desirable is in domestic clothes dryers, but heretofore it has been considered that such safety systems have been too costly to justify their use in such devices. It is, however, apparent that where a gas burner is utilized in a domestic clothes dryer, the operation of such a burner should be rendered extremely safe, and it is, therefore, an important object of the present invention to afford control means for such burners so that such safe operation may be attained. A related object is to afford a control means operating on an electronic principle, and so constructed and arranged that it may be economically utilized in controlling the gas burner of a domestic clothes dryer or the like.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiment, and the principles thereof and what We now consider to be the best mode in which we have contemplated applying those principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

Fig. 1 is a schematic wiring diagram illustrating the control circuit of the present invention; and

Fig. 2 is a fragmentary wiring diagramshowing another form of ignition means.

For purposes of disclosure, the present invention is illustrated in Fig. 1 as associated with a burner 45 which is adapted to be supplied with fuel such as gas by a valve indicated diagrammatically at 90, and the fuel thus supplied is arranged to pass through a, metallic sensing ring R (Cl. 15S-117.1)

and into and through a re-igniter 85 in the form of a wire mesh, as described in detail in our aforesaid parent application. This llame F is lighted by means including a -spark plug 58, and is utilized as described in such parent application tol heat air that is forced through a clothes drier unit by a fan that is driven by the fan and drum motor 3|, shown in Fig. 1.

The operation of the fuel valve 90 is governed by a burner safety control system |20, Fig. 1, which includes an electron tube |2|, and the power for the control system |20 as well as for the .driving motor 3| is controlled by -a common thermostatic switch means which operates to stop the cycle of operation of the machine upon completion of the drying cycle. Thus, in Fig. 1, a

source of alternating current is afforded by wires LI and L2, the wire L2 being connected to one terminal of an overload switch |20. The other terminal of the overload switch |26 is connected by a wire |22 to one terminal of a combination starting and thermostatic cutout switch |28, the other terminal of which is connected to the wire L|. The combination starting and thermostatic switch |28 is of conventional construction and the thermostatic element thereof is mounted in association with the air outlet passage as described in our aforesaid parent application so as to open the switch |28 when the temperature of the outgoing air becomes unduly high due to completion of the drying action upon the clothes in the machine. Thus, when the machine is to be started, the switch |28 is closed so as to thereby start the motor 3|, and the control system |20 is arranged to be supplied with power only during the time when the switch |28 remains closed.

The control system |20 includes means for affording the necessary power and bias for the electron tube |2|, and in the present instance such means comprise an autotransformer |30 having sectional windings defined by terminals |3|, |32, |33 and |34. The terminals |3| and |32 are disposed at opposite ends of a section |30-I of the transformer winding, the terminals |32 and |33 are disposed at opposite ends of the winding section |30-2 while .the terminals |33 and |34 are disposed at opposite ends of a section |30-3 of the transformer winding, such sections of the transformer winding being in series so that the terminals |3| and |34 are at opposite ends of the complete winding. The terminal |3| is connected by a wire |36 at the junction between the wires |24 and |25, while wires |31, |38 and |39, in a series, connect the terminal 32 with 3 the line wire L2. Thus when the switch |28 is closed, the transformer winding is energized, and the line wires are connected so as to alford plate circuit power for the plate circuit of the electron tube |2|, as will now be described. This electron tube |2| may take the form of a type 2D21 Thyratron. and this tube has an anode |40, a cathode |4|, a shield grid |42, anda control grid |43. The tube also has a heater filament |44. 'I'he cathode |4| of the tube is connected by a wire |45 to the wire |31, while the anode or plate |40 is connected to Yone terminal of the operating coil ||5 of the valve 90, the other terminal of this coil being connected by a wire |46 to the terminal |3| of the transformer |30.v The operating coil ||5 of the fuel valve 80 is thus included in the plate circuit of the tube |2|, and the coil ||5 will be energized whenever plate current flows in the plate circuit of the tube l2 The energizing circuit for the filament |44 is afforded by connecting the same across the section ISL-120i the transformer, and for this purpose a wire |48 extends from the wire |31 to one terminal of the filament |44, while the other terminal thereof is connected by a wire |49 to the terminal |33.

The tube |2| is normally biased to a nonconductive state by bias voltage applied to the shield grid |42, and when the tube |2| is to be rendered conductive, an appropriate positive voltage is applied to the control grid |43 as will hereinafter be described. In affording the desired negative or blocking bias for the shield grid |42, a. wire |50, a resistance |5| and a wire |53 are extended in a series from the terminal |34 to the shield grid |42. Thus the negative voltage from the terminal |34 which is more negative at the critical time than the cathode voltage takenjrom the terminal |32, is applied to the shield grid |42 in what may be termed the positive cycles of the alternating current or, in other words, in those cycles when the plate |40 is positive with respect to the cathode |4|, and the magnitude of the negative bias that is thus afforded is such that in the absence of an appreciable positive potential on the control grid |43, the tube |2| will be non-conductive. Moreover, even when the tube |2| is conductive, the most common failure that may occur in the tube, which failure involves burning out of the filament |44, will cause the tube to become non-conductive so as to result in whatv is usually termed a. safe failure."

When the switch |28 is closed so as to thereby start the motor 3 the burner operation is not initiated or started until a separate starting switch means in the form of a starting button |60 is operated. The starting button |60 is arranged as will hereinafter be pointed out to cause the tube |2| to become conductive, so as to thereby open the vfuel valve 90 and also to cause the ignition means which include the spark plug 58 to be energized. The transformer |6| has a secondary coil |6|S and a primary coil |6IP. The secondary coil |6 IS has one terminal grounded at |62 while the other terminal thereof is connected by a wire |63 to the spark plug 58. The other I side of the spark plug 58 is, of course, grounded to the burner 46 and this ground connection is indicated in Fig. 1 at |64. The primary coil |6|P has one terminal thereof connected to the wire |38, while the other terminal thereof is connected to a stationary switch contact |65 of the switch |60. A cooperating stationary contact |66 of the switch |60 is connected by wires |61 and |68 to the wire |46, and a conducting cross arm |69 on the switch |60 may thus be engaged with the contacts |65 and |66 to energize the ignition transformer |6|. The switch |60 also has a second conducting cross bar |10 that may be engaged with stationary contacts |1| and |12 when the starting button |60 is pressed, and these contacts are effective, as will hereinafter be described, to ,apply positive voltageto the control grid |43/so as to thereby cause the fuel valve 90 to be opened. In attaining this action, the switch means aorded by the bar |10 and the contacts |1| and |12 completes a circuit which effectively simulates the presence of a flame at the burner 45. and for this reason the normal action of the control system will rst be described.

The flame sensing ring R. is arranged and asl sociated with the electron tube |2| in such a way that when a ame is present so as to extend between the burner and the name sensing ring R, a positive voltage will be applied to the control grid |43 so as to render the tube |2| conductive. In attaining this result, the burner 45 is connected to the line wire L2 by a resistance |15 and the wires |38 and |39. 'I'he flame sensing ring R in turn has a wire |16 extended therefrom to one end of a resistor |11, the other end of this resistor being connected to a resistor |18. The other end of the resistor |18 is connected to the control grid |43. At the juncture of the resistors |11 and |18, one terminal of a condenser |80 is connected at the juncture of the wires |61 and |68.

When a flame F extends between the burner 45 and the flame sensing ring R, a circuit is completed through the flame F and the resistance of the flame constitutes a circuit element of a circuit that extends from ground at |64, or cathode potential, to the wire |68 through the condenser |80. As will be hereinafter explained, this is effective during the 'forward or positive cycles to cause a positive voltage to be applied to the control grid |43.- Through the use of electrical values in the circuit of the order hereinafter set forth, this voltage on the control |43 may be made effective to cause the tube |2| to become conductive. In the starting operation, this action is attained through the switch bar |10, the contact |12 being connected by a wire |8I to the burner 45 while the contact |1| is connected through a resistor |82 to the wire |16. A stabilizing condenser |80A is connected between the grid |43 and the wire |31 so as to produce uniformity of operation.

In setting up the control thus described, the

following values for the various circuit elements have been found to be satisfactory:

Condenser 180A microfarads .00015 Condenser 180 do .0005 Resistance 151 ohms 50,000 Resistance 178 megohms 1.5 Resistance 177 .do 1.0 Resistance ohms 2,000. Resistance 182 -megohms-- 'I through the condenser |80 'and the resistor |18 from the side of the transformer winding that is connected to the anode. Under such circumstances there is no current flow through the condenser |80, for although one side of the condenser is connected to the same terminal of the transformer |30 as the anode |40, the other side of the condenser |80 may be said to be floating because all of the circuit branches from such other side of the condenser |80, are at this time in an open circuit relation. Thus the switch bar of the start switch is in an open relation. while the branch through the flame sensing ring R is open due to the lack of a flame F. The other branch circuit through the resistor |18 to the control grid |43 is also open, since the tube is blocked by the highly negative shield grid bias, so that there is no flow of cathode-control grid current. Moreover, the impedance of the stabilizing condenser |80A is high so that there is no current flow therethrough and the effect is the same as an open circuit at this point. Thus, although one side of the condenser |80 is connected so as to be positive in those half cycles when the anode or plate is positive, the lack of current flow, or the extremely small current flow across the condenser |80 in such forward half cycles, assures that positive grid bias will not he applied to the control grid at this time.

As a result of this circuit arrangement, the tube |20 remains non-conductive until such time as the start button |60 is actuated. This, of course, operates the ignition means so as to produce igniting action at the spark plug 58, and in addition, a circuit is closed from the ground side of the line through the resistors |81 and |11 and the condenser |80 to the hot side of the line. In this respect it may be noted that the value of the resistor |82 is such as to simulate the resistance of a flame between the burner 45 and the sensing ring R, and hence the effect on the bias of the control grid |43 is the same as when a flame is sensed. Thus the circuit that is established between the line wires L| and L2 includes the condenser |80, the resistance |11, and the amesimulating resistance |82, and this circuit acts as a voltage divider from which the control grid bias is tapped through the limiting resistor |18. The point at which the control grid is thus tapped is such that the grid |43 is rendered sufliciently positive to cause firing of the tube |2| throughout a substantial portion of each forward cycle so long as the resistance in the voltage dividing circuit is kept within a certain range.

When the firing of the tube |2| in response to operation of the start button |60 has caused opening of the fuel valve ||5, and the fuel fed to the burner 45 has been ignited, the presence of a flameF will be sensed by the sensing ring R. This completes a circuit that is in parallel with the resistor |82 and which includes the resistance of the flame F and at this time the start button |60 may be released so as to place the system under sole control of the flame sensing means. The flame resistancel has been found to Varyfrom about two to seventy megohms, and throughout this range, the voltage dividing network will be effective to maintain a firing bias on the control grid |43. If, however, the flame F is extinguished, or if the sensing ring R becomes grounded, the positive bias voltage on the control grid |43 will be reduced or changed in such a way as to enable the negative bias of the shield grid |42 to regain control and render the tube |2| nonconductive.

In the case of a grounding of the sensing ring', the resistance at the fiame gap is reduced to zero so that the effective position of the control grid tap will be so changed in an electrical sense as to reduce the control grid bias to such a. point that it is below the positive value required to re the tube, land hence the shield grid |42 will regain control in the next inverse cycle.

Flame failure will of course return the system to its original condition insofar as biasing voltage on the control grid |43 is concerned, and hence the shield grid will resume control, and the tube will become non-conductive. In either event, the valve I5 will be de-energized, and will close so as to shut olf the supply of fuel to the burner 45.

In Fig. 2 of ,the drawings an alternative form of ignition means have been illustrated whereby the use of a relatively expensive ignition transformer |61 may be avoided and in this embodiment of the invention a spark coil 26|v of substantially conventional construction is utilized. The spark coil 26| is auto-wound to afford a winding 262 having terminals 263, 264 and 265, and a contact 266 extended from the terminal 263 has a Vibrating armature contact 251 associated therewith to act in the usual manner as a periodic circult breaking means. The contacts 266 and 261 have a condenser 268 connected thereacross, and the contact261 is connected to the contact |65 of the start switch |60. The other contact |69, instead of being connected to the wire |61, is connected by a wire 269 to the wire |50, and another and separate winding section |30-4 that is afforded in the transformer |30 to afford the usual 6-volt source for the spark coil 26|. A wire 210 extends from the other end of the winding |30-4 to the tap 264 on the spark coil winding. The section ofthe spark coil winding between the taps 264 and 265 constitutes the secondary, and the tap 265 is connected by a wire 21| to the spark plug 58 While the tap 264 is grounded at 212. With the structure thus afforded, the required ignition means functions in a highly satisfactory manner, and yet may be provided at a reasonable cost.

The values specied hereinabove for the circuit elements are of course what we consider to be optimum values, but it will be recognized that such values may vary within certain limits While still producing safe operation of the burner. Thus' the condenser |80 may be varied between about .0003 and .0007 microfarad, while the condenser |A may be varied between about .000075 and .0002 microfarad. Similarly, the total value of the resistances |11 and |18 may be varied between one and ve megohms, and if desired, the resistance |18 and |11 may be combined and placed between the condenser |80 and the control grid |43. When this is done, the ame constitutes the sole resistance for cooperation in series with the condenser |80 in affording the voltage dividing network from which the control grid voltage is tapped.

From the foregoing description it willbe evident that the present invention enables a gas burner to be safely utilized in a rapidly moving current of air such as the air that is forced through a clothes dryer or the like, and this is accomplished through the use of structure that is extremely simple in character.

Thus, while we have illustrated and described the preferred embodiments of our invention, it is to be understood that this is capable of variation and modification, and we therefore do not wish to be limited to the precise detailsset forth, but desire to avail ourselves of such changes and alterationsv as fall within the purview of the following claims:

We claim:

1. In a burner safety control system, a gas filled electron tube having an anode. a cathode, a heater, a shield grid and a control grid, a gas burner, a normally closed power operated control valve for supplying gaseous fuel to said burner, an electrically operable device governing said control valve and having one terminal thereof connected to said anode, an autotransformer having a winding having first and second terminals defining the ends of a first section, a third terminal defining one end of a second section that is extended from said second terminal, and a fourth terminal defining the end of a third sec- ,il

tion that is extended from said third terminal, an alternating current power source having a hot lead connected to said first terminal of said transformer and to the other terminal of said device, and having a grounded lead connected to said second terminal and said cathode, means connecting said second and third terminals across said heater, means connectingl said fourth terminal to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current when said firstterminal is positive, means connecting said burner to ground. a flame sensing element disposed in position to be enveloped by a flame issuing from said burner, a resistance and a small capacity condenser connected in series between said sensing element and said hot lead with said resistance located electrically adjacent to said sensing element, and a relatively high resistance connected between said control grid and the juncture of said condenser and said first mentioned resistance.

2. In a burner safety control system, a gas filled electron tube having an anode, a cathode, a heater, a shield grid and a control grid. a gas burner, a normally closed power operated control valve for supplying gaseous fuel to said burner, an electricallyv operable device governing said control valve and having one terminal thereof connected to said anode, an autotransformer having a winding having first and second terminals defining the ends of a first section, a third terminal defining one end of a second section that is extended from said second terminal, and a fourth terminal defining the end of a third section that is extended from said third terminal, an alternating current power source having a hot lead connected to said first terminal of said transformer and to the other terminal of said device, and having a grounded lead connected to said second terminal and said cathode, means connecting said second and third terminals across said heater, means connecting said fourth terminal to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current when said first terminal is positive, means connecting said burner to ground, a flame sensing element disposed in position to be enveloped by a flame issuing from said burner, circuit means including a relatively large electrical resistance connected between said sensing element and said control grid, and a relatively small capacity condensecnnnected be- Y tween said hot lead and said circuit means at such a point as to locate at least a substantial portion of said resistance between said point and said control grid.

' 3. In a burner safety contr lsystem, a gas filledv electron tube having an anode, a cathode, a heater. a shield grid and a control grid, a gas burner, a normally closed power operated control valve for supplying gaseous fuel to said. burner, an electrically operable device governing said control valve and having one terminal thereof connected to said anode, an autotransformer having a winding having first and second terminals deflning the ends of a first section. a third terminal defining one end of a second section that is extended from said second terminal, and a fourth terminal defining the end of a third section that-is extended from said third terminal, an alternating current power source having a hot lead connected to said first terminal of said transformer and to the other terminal of said device, and having a grounded lead connected to said second terminal and said cathode, means connecting said second and third terminals across said heater, means connecting said fourth terminal to said shield grid to apply a blocking negative bias to said shield -grid in the forward cycles of the alternating current when said first terminal is positive. means connecting said burner to ground, a flame sensing ,element disposed in position to be enveloped by a flame issuing from said burner, a relatively high value resistance and a small capacity condenser connected in series between said control grid and said hot lead and circuit means connected between said control grid and the juncture of said condenser and said first mentioned resistance.

4. In a burner safety control system, a gas filled electron tube having an anode, a cathode, a heater, a shield grid and a control grid, a gas burner, a normally closed power operated control valve for supplying gaseous fuel to said burner, an electrically operable device governing said control valve and having one terminal thereof connected to said anode, an autotransformer having a winding having first and second lterminals defining the ends of a flrst section, a third terminal defining one end of a second section that extended from said second terminal, and a fourth terminal defining the end of a third section that is extended from said third terminal, an alternating current power source having a hot lead connected to said first terminal of said transformer and to the other terminal of said device, and having a grounded lead connected to said second terminal and said cathode, means connecting said second and third terminals across said heater,'means connecting said fourth terminal to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current when said first terminal is positive, means connecting said burner to ground, a flame sensing element disposed in'position to be enveloped by a fiame issuing from said burner, a resistance of between one `and flve megohms and a condenser of from .0003 to .0007 microfarad capacity connected in series between said hot lead and said control grid, and circuit means connected between said sensing element and the juncture of said condenser and said rst mentioned resistance.

5. In a burner safety control' system, a gas filled electron tube having an anode, a cathode, a shield grid and a control grid, an electrically operable control device having one terminal con-l nected to said anode, an alternating current power source having a grounded lead connected to said cathode and a hot lead connected to the other terminal of said device, means operatively associated with said power source and connected to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current during which said anode is positive, a small capacity condenser and a high value resistor connected in series between said hot lead and said control grid, a small capacity stabilizing condenser connected between said control grid and cathode, a burner electrically connected to ground and to which gaseous fuel may be supplied, a flame sensing element disposed in an insulated relation and in the path of a ame issuing from said burner, and means including a relatively high value resistor connecting said sensing element to the juncture of said first mentioned resistor and condenser.

6. In a burner safety control system, a gas filled electron tube having an anode, a cathode, a shield grid and a control grid, an electrically operable control device having one terminal con- 1 nected to said anode, an alternating current power source having a grounded lead connected to said cathode and a hot lead connected to the other terminal of said device, means operatively associated with said power source and connected to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current during which said anode is positive, a small capacity condenser and a high value resistor connected in series between said hot lead and said control grid, a burner electrically connected to ground and to which gaseous fuel may be supplied, a llame sensing element disposed in an insulated relation and in the path of a llame issuing from said burner, and means including a relatively high valve resistor connecting said sensing element to the juncture of said first mentioned resistor and condenser.

7. In a burner safety control system, a gas illled electron tube having an anode, a cathode,

a shield grid and a control grid, an electrically operable control device having one terminal connected to said anode, an alternating current power source having a grounded lead connected to said cathode and a hot lead connected to the other terminal of said device, means operatively associated with said power source and connected to said shield grid to apply a blocking negative bias to said shield grid in the forward cycles of the alternating current during which said anode is positive, a condenser having a capacity of from about .0003 microfarad to about .0007 microfarad and a resistor having a value of from one to ve megohms connected in series between said hot lead and said control grid, a stabilizing condenser having a capacity of from .00075 to .0002 microfarad connected between said control grid and cathode, a burner electrically connected to ground and to which gaseous fuel may be supplied, a flame sensing element disposed in an insulated relation and inthe path of a ame issuing from said burner, and means connecting said sensing element to the juncture of said resistor and said rst mentioned condenser.

ROBERT E. YATES.

JOSEPH M. ENGEL.

WILLIAM W. RIESCHE..

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,324,330 Smith July 13, 1943 2,379,871 Beam et al. July 10, 1945 2,431,158 Yates Nov. 18, 1947 2,455,350 Beam Dec. 7, 1948

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