US3822039A

US3822039A - Gas combustion control device

Info

Publication number: US3822039A
Application number: US00272650A
Authority: US
Inventors: Keijiro Mori; Keiichi Mori
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1972-07-17
Filing date: 1972-07-17
Publication date: 1974-07-02
Anticipated expiration: 1991-07-02

Abstract

For a device of the type in which the amount of fuel gas to be supplied to a gas burner is controlled by a proportional position type solenoid valve, there are provided a first control circuit which controls the exciting current to be applied to the solenoid of the valve in response to the temperature change of a medium heated by said gas burner, thereby controlling the supply of gas fuel to the gas burner, and a second control circuit which detects the magnitude of the exciting current and causes the abrupt change in output current of the first control circuit after the gas burner is ignited and when gas burner is extinguished, thereby causing the abrupt change in gas supply to the gas burner.

Description

United States Patent [191 Mori et al.

[111 3,822,039 [451 July 2,1974

[ GAS COMBUSTION CONTROL DEVICE [75] Inventors: Keijiro Mori, Nara; Keiichi Mori,

Osaka, both of Japan 22 Filed: Ju1y17, 1972 211 Appl. No.: 272,650

[52] US. Cl. 236/75, 236/78 D, 237/8 R,

317/153, 251/131 [51] Int. Cl. H0lh 47/26 I [56] References Cited UNITED STATES PATENTS 3,486,693 12/1969 Stang, Jr. et a1 236/78 X Primary Examiner--William E. Wayner ABSTRACT For a device of the type in which the amount of fuel gas to be supplied to a gas burner is controlled by a proportional position type solenoid valve, there are provided a first control circuit which controls the exciting current to be applied to the solenoid of the valve in response to the temperature change of a me dium heated by said gas burner, thereby controlling the supply of gas fuel to the gas burner, and a second control circuit which detects the magnitude of the exciting current and causes the abrupt change in output current of the first control circuit after the gas burner is ignited and when gas burner is extinguished, thereby causing the abrupt change in gas supply to the gas burner.

9 Claims, 9 Drawing Figures PATENIEIJJuL 21914 3.822.039

sum 2 BF 3 EXClTlNG CURRENT TEMPERATURE PATENTEDJIJL 2 m4 mamas GAS COMBUSTION CONTROL DEVICE BACKGROUND OF THE INVENTION The present invention relates to a gas combustion control device of the type for controlling the combustion rate of a gas burner in proportion to the variation in load.

In the conventional gas-combustion apparatus such as gas-combustion water heater for hot water heating, there have been provided a device for opening and closing a solenoid valve inserted in a gas supply pipe line in response to the temperature variation of circulating hot water or a device for controlling a proportional position type solenoid valve inserted in a gas supply pipe line in response to the variation in resistance of a temperature-variable resistor disposed in a hot water supply main for detecting the temperature variation of circulating hot water due to the load variation in order to control the gas combustion rate in response to the load variation. In the case of the control device for controlling the ON-OFF of the solenoid valve, the combustion is interrupted when the temperature of circulating. hot water rises above a predetermined level and the combustion is started again when the temperature falls below the predetermined level. Therefore there arise the disadvantages that the temperature of circulating hot water is always subject to variation and that the solenoid valve is easily susceptible to damage because its ON-OFF operations are very frequently cycled.

In the latter control device of the type utilizing the proportional position type solenoid valve, the gas supply to the gas burner is controlled in response to the variation in loadso that the above problems of the temperature variation and of the damages to the electromagnet valve may be overcome. However, new problems have arisen due to the combustion characteristics of the gas burner and the construction of the proportional position type solenoid valve. In general,v gas issues from the gas nozzle into the air-gas mixture controller so that the primary-air is sucked into the air-gas mixture controller under the ejector action of gas and mixed with gas. No problem arises when gas is supplied in relatively large amounts, but when the gas supply is gradually decreased in response to the decrease in load, the kinetic energy of gas issuing from the gas nozzle is decreased so that the amount of primary air sucked into the air-gas mixture controller is decreased, thus resulting in backfire. The occurrence of backfire is generally dependent upon the capacity of the gas burner, and is caused when the amount of gas is reduced to one-half to one-third of the maximum amount of gas supply.

In the control device of the type utilizing the proportional position type-solenoid valve, the plunger supporting means presents a problem. In the conventional solenoid valve, the plunger is generally supported by a bearing member so that friction is caused between the plunger and the bearing member. In the proportional position type solenoid valve, the plunger is caused to move by controlling the exciting current applied to the solenoid in response to the variation in load so that the spacing between a valve seat and a valve may be suitably adjusted. The spacing between the valve and the valve seat is generally of the order of 3 5 mm so that even a small variation in spacing causes a great change in gas flow rate, that is the amount of gas supply to the gas burner. Therefore, the frictional force exerted on the plunger causes the error in controlling the spacing between the valve and the valve seat, thus resulting in the poor control of gas flow rate in response to the variation in load.

I SUMMARY OF THE INVENTION The present invention has succeeded in overcoming the above and other problems encountered in the prior art control devices of the type described by electronically interrupting the exciting current applied to the solenoid of the proportional position type solenoid valve and by supporting the plunger by leaf springs.

One of the objects of the present invention is therefore to overcome the problems of backfire and of gas leakage by detecting the temperature of circulating fluid heated-by a gas burner by a temperature-variable resistor such as a thermistor and by controlling the exciting current to be applied to the proportional position type solenoid valve in response to the variation in resistance of the temperature-variable resistor in such a manner that the exciting current may be interrupted when it decreases to less than a predetermined level.

Another object of the present invention is to provide an electronic gas combustion control device which will not supply gas in large quantity when the gas burner is ignited again but will gradually increase the gas supply from zero for a short time, thereby preventing the explosion noise when the gas burner is ignited.

Another object of the present invention is to provide an improved proportional position type solenoid valve in which a plunger fitted into a solenoid or coil is supported by a pair of leaf springs, thereby eliminating the frictional force exerted to the plunger in order to attain the precise control of gas flow rate.

Another object of the present invention is to provide an improved proportional position type solenoid valve in-which a plunger is supported by a pair of leaf springs in such a manner that the solenoid valve may be prevented from becoming large in size and the displacement of the leaf springs about their fixed ends may be increased, thereby preventing the lateral displacement of the plunger off the axis of its vertical movement.

Another object of the present invention is to provide an improved proportional position type solenoid valve in which a plunger is supported by a leaf spring or springs extending from the free end of a leaf spring toward the other end thereof which is fixed to a stationary member, thereby preventing more positively the lateral displacement of the plunger off the axis of the vertical movement thereof.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a gas-combustion water heater for hot water heating to which is applied a gas combustion control device in accordance with the present invention;

FIG. 2 is a sectional view of a proportional position type solenoid valve incorporated in the gas combustion control device of the present invention;

FIG. 3 is a perspective view illustrating the plunger supporting means;

FIG. 4 is a perspective view illustrating avariation of the plunger supporting means in accordance with the present invention;

FIG. 5 is a sectional view taken along the line V-V of FIG. 4; 7

FIG. 6 is a perspective view illustrating still another variation of the plunger supporting means in accordance with the present invention;

FIG. 7 is a sectional view taken alongthe line VII- VII of FIG. 6;

FIG. 8 is a circuit diagram of an electronic control unit of the gas combustion control device in accordance with the present invention; and

FIG. 9 is a graph illustrating the relation between the temperature of hot water detected by a temperaturevariable resistor and the exciting current supplied to the solenoid of the proportional position type electromagnet valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1, 2 and 3, a heat exchanger 3 is communicated with a radiator not shown) through a main hot water pipe line 1, through which hot water is circulated by a circulation pump 4. Hot water at a low temperature is returned through a return main la, heated by the heat exchanger 3 and is supplied through a supply main lb. A gas nozzle 5 is disposed adjacent to one end 2b of a gas-air mixture controller 2a of a gas burner 2 in such a manner so that when gas issues from the nozzle 5, the primary air may be sucked into the gas-air mixture controller 20 under the ejector action of the gas. The gas and the primary airare mixed in a predetermined ratio in the controller 2a and the gas-air mixture issues from the nozzles, of the gas burner 2 for combustion. A gas governer 7 and a solenoid valve of the proportional position type are inserted into a gas pipe 6 communicating the gas nozzle 5 with a gas supply source (not shown).

The construction of the solenoid valve 8 is illustrated in detail in FIG. 2. A bobbin 10 carrying a coil .9 is disposed between upper and lower yokes 1,1 and 11a with spacers 12 and 12a interposed therebetween. Supporting members 13 and 13a are struck out of the yoke members 11 and 11a respectively as best shown in FIG. 3. A plunger 14 having a projection 15 which is made of a nonmagnetic material and a diameter smaller than that of the plunger 14, is slidably fitted into a hole of the bobbin 10. The bobbin 10 and its associated component parts are all enclosed in a casing 16. The base of a U-shaped leaf spring 17 is securely fixed to the supporting member 13 struck out of the yoke 11 and the leading ends of the leg portions of the U-shaped leaf spring 17 are pivoted with pivot pins 14a to the plunger 14 at the upper portion thereof. The leading ends of the leg portion of a U-shaped leaf spring 17a are also pivoted to the projection 15 of the plunger 14 with pivot pins 14b, but the base of the leaf spring 17a is fixed to the free end of an adjusting plate 18 whose other end v is securely fixed to the supporting member 13a struck out of the lower yoke lla. Therefore, the plunger 14 is supported by the pair of upper and lower

U-shaped leaf springs

17 and 17a so that the friction between the plunger 14 and the bobbin 10 may be prevented, and the forces of the

leaf springs

17 and 17a may be used as the retarding forces exerted on the plunger 14 when the coil 9 is energized.

' An adjusting plate 18 is provided in order to adjust the force of the leaf spring 170. More particularly, an adjusting screw 19 at the free end of the adjusting plate 18 may be loosened or tightened so as to cause the free end of the adjusting plate 18 to move toward or away from the yoke 11a, thereby changing the initial bending of the leaf spring and hence its reaction force. The spring force adjusting plate 18 serves to absorb the influencesv of uneven quality of the

leaf springs

17 and 17a due to the dimensional errors, and other factors of the

leaf springs

17 and 17a and of the coil 9 which will adversely affect the smooth motion of the plunger 14.

A partition disk or cover 20 covers the upper opening of the casing 16, and the upper portion of the plunger 14 extending through the center hole of the partition disk 20 is sealed with diaphragm 21. A joint 22 has

connections

23 and 24 for connection with the gas pipe line 6, and in a passage 25 between the

connections

23 and 24 is formed a valve seat 26 upon which seats a valve 27 fixed to the top end of the plunger 14. A packing 28 is interposed between the cover 20 and the joint 22. Leads 29 are extended from the coil 9 through the casing 16.

Referring back to FIG. 1, a thermistor 30 encapsuled in a protective tube 31 is inserted in the supply main lb, and is coupled to the coil 9 through an electrical control unit 32.

Next the mode of operation will be described hereinafter. First the circulation pump 4 is started to circulate hot water, but the temperature of hot water flowing through the supply main 1b is low because the hot water is not sufficiently heated by the heat exchanger 3. Hence the resistance of the thermistor 30 is high so that the control unit 32 is so actuated as to flow the maximum current through the coil 9 in the electromagnet valve 8 based upon the principle of the present invention to be described in more detail hereinafter. As a result, the plunger is moved (downwardly in FIG. 2) over the maximum distance against the

leaf springs

17 and 17a until the plunger moving force is in equilibrium with the forces of the

leaf springs

17 and 17a so that the valve 27 is moved away from the valve seat 26. Therefore, the maximum gas-air mixture is supplied to the gas burner 2 for the maximum combustion. This maximum combustion may be maintained so long as the heating load is equal to or higher than the heat generated by the maximum combustion.

When the load is decreased, hot water flowing through the supply main has a high temperature so that the resistance of the thermistor 30 is reduced. As a result, the control unit 32 causes the electric current flowing through the coil or solenoid 9 to decrease accordingly. Therefore the plunger 14 is caused to move upwardly in FIG. 2 under the force of the

springs

17 and 17a so that the valve 27 is now located closer to the valve seat 26. The gas passage 25 is now throttled so that the amount of gas supplied to the gas burner 2 is decreased accordingly.

From the foregoing description, it is seen that the supply of gas to the gas burner 2 is controlled by the solenoid valve 8 in proportion to the variation in load so that the temperature of the hot water flowing through the supply main lb may be maintained at the same level independently of the load variation. According to one of the novel feature of the present invention, when the combustion rate is reduced to less than a predetermined level or when the gas supply is throttled or reduced to less than a predetermined level,.the electro magnetic valve 8 is so actuated as to close the gas passage 25, thereby preventing backfire. Furthermore, when the gas burner 2 is ignited again, the supply of gas is gradually increased for a short time in order to prevent the undesired combustion or iginition noise as will be described in more detail hereinafter.

The most important mechanical component parts of the valve 8 are means for supporting the plunger 14 so that the supporting means will be described in more detail hereinafter. The supporting means or leaf springs 17 and 170 support the plunger 14 in such a manner that the latter will not make contact with the bobbin 10. As a result, no friction occurs between the plunger 14 and the bobbin 10. Furthermore, the delicate adjustment of the spacing between the valve seat 26 and the valve 27 may be accomplished in a simple, but very reliable manner. Since the retarding force may be applied to the plunger 14 by the

leaf springs

17 and 17a, other spring or the like may not be needed. This is one of the advantages in mechanical design of the present invention.

It is preferable that the lengths of the

leaf springs

17 and 17a are longer because of the following reason. It is apparent that the leading ends of the

U-shaped leaf springs

17 and 17a follow not only the axial movement of the plunger 14 but also the lateral movement thereof. The longer the

leaf springs

17 and 17a, the lesser the lateral displacement becomes so that the variation in spacing between the bobbin l0 and the plunger 14 may be minimized. As a consequence, the uniform magnetic force distribution may be attained so that the plunger 14 may be displaced in a more reliable and accurate manner.

However, when the length of the

leaf springs

17 and 17a becomes too long, the solenoid valve 8 becomes inevitably large in size. The present invention further provides means to overcome this problem.

Referring to FIGS. 4 and 5, a U-shaped leaf spring 33 similar to the leaf spring 17 in FIG; 3 is used. The plunger 14 is interposed between the

leg portions

33a and 33b of the leaf spring 33, and a pin 34 extends between the free ends of the

leg portions

33a and 33b. The plunger 14 consists of upper and lower sections, and the root of an arm 36 is interposed between the upper and lower sections of the plunger 14 and is securely fixed to the lower section with a screw 35 as best shown in FIG. 5. The leading end of the arm 36 is pivoted to the pin 34. Thus the plunger 14 is indirectly supported by the leaf spring 33 at the free ends of its leg portions 33a and 33h. Opposed to the leaf spring 17 shown in FIG. 3, supporting the plunger 14 at the free ends of its leg portions, the plunger 14 is interposed between the

leg portions

33a and 33b of the U-shaped leaf spring 33 so that the length of the leaf springs may be increased without increasing the size of the electromagnetic valve 8. When the leaf spring 33 is used for supporting the plunger l4, the lateral displacement thereof may be further minimized so that the deviation of the axis of the plunger 14 from that of the center hole of the bobbin may be minimized.

Next referring to FIGS. 6 and 7, still another plunger supporting means in accordance with the present invention will be described. In the instant embodiment,

spring is used, and the plunger 14 extends through the opening of the leaf spring 37 as best shown in FIG. 6. A U-shaped leaf spring 38, the second leaf spring, is struck out of the leaf spring 37 from one side thereof, and the free ends of the leg portions of the U-shaped leaf spring 38 are pivoted to the plunger 14 with pins 39 extending therefrom. The other side opposed to said one side from which the U-shaped leaf spring 38 extends, is securely fixed to the supporting member so that the leaf spring 37 swings in the direction indicated by the arrow a in FIG. 7 when the plunger 14 moves vertically whereas the U-shaped spring 38 swings in the direction indicated by the arrow b. In other words, the

leaf springs

37 and 38 swing in the opposite directions so that the lateral displacement of the leaf spring 38 may be cancelled by the lateral displacement of the leaf spring 37. Therefore, the plunger 14 may be moved vertically coaxially of the center hole of the bobbin 10.

Next referring to FTG. 8, the control unit 32 will be described in more detail hereinafter. A power source 40 and a switch 41 are connected in series to the primary winding of a transformer 42. The secondary winding of the transformer 42 is connected to the a-c input terminals of a diode bridge 43. One end of a resistor 44 is connected to the minus or negative output terminal of the diode bridge 43 whereas the other end is connected to one end of a capacitor 45 whose the other end is connected to a positive output terminal of the diode bridge 43. A series circuit consisting of a resistor 46, a Zener diode 47 is connected in parallel with the capacitor 45. A series circuit consisting of

resistors

48, 49 and 50 is connected in parallel with the Zener diode 47. In like manner, two series circuits, one consisting of a resistor 51, a variable resistor 52 and the thermistor 30 and the other consisting of

resistors

53 and 54 are connected in parallel with the Zener diode 47. The emitter of a transistor 55, a second active element, is connected to the junction between the

resistors

48 and 49, and the base of the transistor 55 is connected to a sliding arm of the variable resistor 52. The collector of the transistor 55 is connected to the junction between the base of a transistor 56, a first active element, and a resistor 5'7. The other end of the resistor 57 and one end of a resistor 58 are connected to the junction between the resistor 44 and the capacitor 45. The other end of the resistor 58 is connected to the emitter of the transistor 56. The collector of the transistor 56 is connected to one junction of a parallel circuit consisting of a diode 59, the solenoid or coil 9 of the electromagnetic valve 8, and two

series resistor

60 and 61, the other junction of the parallel circuit being connected to the positive output terminal of the diode bridge 43. The resistor 60 is a variable resistor whose sliding arm is connected to the base of a transistor 63, a third active element, through a resistor 62. A capacitor 64 is inserted between the base of the transistor 63 and the positive output terminal of the diode bridge 43. The emitter of the transistor 63 is connected to the junction between the

resistors

53 and 54, and the collector is connected to the junction between the

resistors

49 and 50 through a resistor 65. The circuit portion surrounded by the dotted line X indicates the first control circuit and that surrounded by the dotted line Y indicates the second control circuit.

Next the mode of operation will be described. When the switch 41 is closed so that commercial voltage is impressed across the primary winding of the trans- 7 former 42, a low voltage is induced across the secondary winding. The ac induced voltage is rectified by the diode bridge 43 so that a d-c voltage is applied across the capacitor 45. The resistor 44 serves to limit the rush current when the switch 41 is closed so that the diode bridge '43 may be prevented from being damaged. The current flows through the Zener diode 47 and the resistor 46. In this case, it should be noted that even when the current flowing through the resistor 46 varies, the voltage impressed across the three series circuits, first consisting of the

resistors

53 and 54, the second consisting of the

resistors

48, 49 and 50, the third consisting of the resistor 51, the variable resistor 52 and the thermistor 30, remains unchanged because of the Zener diode 47. Even when the commercial voltage varies, the voltage impressed across the three series circuits remains unchanged. The

resistors

48, 49 and 50, the resistor 51, the variable resistor 52 and the thermistor 30 form the arms of a bridge in which the emitter and the base of the transistor 55 are connected to the junctions between the arms of the bridge.

At the starting of the hot water boiler, cold water is flowing through the main 1 so that the resistanceof the thermistor 30 inserted into the main 1 is high. As a result, the base potential of the transistor 55 is lower than the emitter potential so that the transistor 55 conducts. The current flows from the collector of the transistor 55 to the base of the transistor 56 and the resistor 57 Therefore, the transistor 56 conducts so that the current flows throgh the resistor 58, the emitter and collector of the transistor 56 to the coil 9. In this case, the current flowing through the coil 9 is maximum so that the solenoid valve 8 is fully widely opened. As a result, the combustion rate of the gas burner 2 becomes maximum.

When the load is reduced so that the temperature of the hot water rises, the resistance of the thermistor 30 is gradually decreased. When the base potential of the transistor 55 becomes equal to the emitter potential, the transistor 55 is shifted from the saturation region to the active region so that the collector current is gradually decreased. As the collector current of the transistor 55 is decreased, the transistor 56 is shifted from the saturation region into the active region so that the current flowing through the coil 9 is decreased. As the current flowing through the coil 9 is decreased, the opening of the solenoid valve 8 is reduced so that the gas supply is controlled until the combustion rate attains equilibrium with the reduced load. The temperature of the hot water is dependent upon the voltage at which the emitter potential of the transistor 55 substantially equals the base potential. However, since the emitter potential is almost constant, the temperature of hot water is dependent upon the position of the sliding arm of the variable resistor 52. More particularly when the sliding arm of the variable resistor 52 is in a position above the position shown in FIG. 8, the temperature of hot water is relatively high, but when the sliding arm is in a position lower than the position shown in FIG. 8, the temperature isrelatively low. Thus, the temperature of hot water may be arbitrarily selected. It should be noted that the uneven quality of the thermistor 30 may be compensated by the variable resistor 52.

When the load is small, the gas supply is so controlled as to maintain a suitable combustion rate in the gas burner 2. However, the flow rate of gas cannot'be re duced to less than a predetermined level because backfire occurs when the flow rate is reduced to from onehalf to one-third of the maximum gas flow rate. Therefore in the hot water boiler of the type whose combustion rate is controlled in response to the variation in load, the supply of gas must be interrupted when the flow rate of gas becomes less than a predetermined level. In the control unit shown in FIG. 8, the gas flow rate may be detected by the current flowing through the coil 9.

When the load is reduced, the temperature of hot water rises so that the gas supply is controlled in a manner described above. When the gas flow rate becomes. for example, one half of the maximum flow rate, the voltage between the points a and b in FIG. 8 is lowered and the voltage at the points a and c become equal so that the transistor 63 conducts. The current flows through the resistor 65 and the resistor which forms one arm of the temperature detecting bridge. Therefore, the transistor is reverse biased so that the collector current of the transistor 55 is reduced. Hence the collector current of the transistor 56 which is the exciting current of the coil 9 is reduced accordingly. The reduction in collector current of the transistor 56 is felt by the

transistors

63 and 55 so that the current flowing through the coil 9 is immediately interrupted. At the safe combustion rate of the gas burner 2, the transistor 63 is reverse biased so that the variation in current flowing through the coil 9 will not influence the temperature detecting bridge circuit. The resistor 62 is inserted in order to limit the current and the capacitor 64 is'inserted in order to prevent the parasitic oscillation.

When the solenoid valve 8 is completely closed so that the combustion is interrupted, the temperature of hot water is gradually lowered so that the resistance of the thermistor 30 is gradually increased. Therefore, the transistor 55 is gradually forward biased, and so is the transistor 56. As a consequence, the transistor 63 is reverse biased. This is felt by the transistor 55 so that the latter conducts abruptly whereas the transistor 63 is cut off. Thus the solenoid valve 8 is widely opened so that the combustion is started again. As the temperature of hot water is raised, the solenoid valve 8 is actuated in the manner described above to control the optimum gas flow rate.

FIG. 9 illustrates the relation between the temperature of hot water and the current flowing through the coil 9. At the point A the combustion rate becomes one half of the maximum rate so that the solenoid valve 8 is closed. At the point B the current flowing through the coil 9 rises abruptly so that the solenoid valve 8 opens wide.

Referring back to FIG. 8, the adverse effect of the conducting transistor 63 upon the nonconducting transistor 55 for causing the same to conduct may be eliminated when the resistance of the resistor 62 is increased and the resistance of the resistor 50 is smaller than that of the resistor 49. In this case, the point B in FIG. 9 is in a relatively upper position. However, under the reversed conditions, the point B will be found in a lower position.

When the point B is so selected as to be above the point at which the solenoid valve 8 is opened, the gas is gradually increased from zero when the gas burner is ignited again. This setting is advantageous in that the gas burner may be ignited when the gas flow rate is still low and then the flow rate may be rapidly increased. By

9. this so-called slow ignition, the ignition may be started very quietly without causing any explosion noise.

The time during which the gas flow rate changes is a function of the rate of temperature change and of an amplification factor of the control circuit.

When the control unit so far described with reference to FIG. 8 is used, backfire may be prevented and the ignition'may be started very quietly.

So'far the present invention has been described as being applied to the gas-combustion water heater for hot water heating, but it will be understood that the present invention may be also applied to a gas furnace.

What is claimed is:

1. In a device of the type'in which the amount of fuel gas to be supplied to a gas burner is controlled by a proportional position type solenoid valve,

a gas combustion control device comprising a. a first control circuit including a bridge circuit having a temperature-variable resistor for detecting a medium heated by said gas burner as one arm thereof, said control circuit controlling the exciting current flowing through the solenoid of said electromagnet valve so as to control the amount of gas fuel to be supplied to said gas burner in response to the variation in resistance of said temperaturevariable resistor;

and g a second control circuit for detecting the magnitude of said current flowing through the solenoid of said solenoid valve in such a manner that when said current decreases less than a predetermined level the output current from said bridge circuit is so controlled as to interrupt said current flowing through the solenoid of said electromagnet valve.

2. A device as set forth in claim 1 wherein an output circuit of said second control circuit for controlling said output current of said bridge circuit is conneced'to one arm of said bridge circuit in such a manner that when said current flowing through the solenoid of said solenoid valve the unbalanced condition of said bridge circuit may be varied by said output current, thereby causing the abrupt change in the output of said bridge circuit.

3. A device as set forth in claim 1 wherein said first and second control circuits are so coupled to each other that said current flowing through the solenoid of said solenoid valve may be gradually increased in response to the temperature drop of said heated medium due to the interruption of the gas combustion in said gas burner and that when said current reaches to said predetermined level said current may be abruptly increased; and

the ignition of said gas burner is made prior to said abrupt increase of said current.

4. A device as set forth in claim 1 wherein said first and second control circuits are so coupled to each other that said current may be gradually decreased in response to the temperature rise of said heated medium and that said current may be abruptly decreased when said current reaches said predetermined level.

5. A device as set forth in claim ll wherein said first control circuit for controlling the exciting current comprises 7 said bridge circuit and a first active element which is controlled by asecond active element forming the output circuit of said bridge circuit, the output circuit of said first active element being connected in series to the solenoid of said solenoid valve; and

said second control circuit comprises a detector circuit for detecting the voltage applied across the solenoid of said solenoid valve, and

a third active element which is controlled in response to said detected voltage,

the output of said third active element being so connected to one arm of said bridge circuit that the variation in output current of said output circuit may cause the variation in bias voltage applied to said second active element in said bridge circuit.

6. A device as set forth in claim 1 wherein said proportional action type solenoid valve comprises said solenoid, a plunger and spring means for supporting said plunger.

7. A device as set forth in claim 6 wherein said spring means comprise leaf springs,

one end of each of said leaf springs being securely fixed to a stationary member of said device whereas the other end is bifurcated,

the bifurcated portions of said leaf spring being extended laterally of said plunger away from said one fixed end,

the leading ends of said bifurcated portions of said leaf spring supporting a rigid arm extending from said plunger.

8. A device as set forth in claim 6 wherein said spring means comprises first leaf springs,

one end of each of said leaf springs being securely fixed to a stationary member of said device,

the other end of said leaf spring being bifurcated,

the bifurcated portions of said leaf spring being extended laterally of said plunger away from said fixed one end,

second leaf springs being fixed to the leading ends of said bifurcated portions and extended toward said fixed one end of said first leaf spring,

the leading ends of said second leaf springs supporting said plunger.

9. A device as set forth in claim 6 wherein said spring means having adjusting means of reaction force thereof.

i t it: it a

Claims

1. In a device of the type in which the amount of fuel gas to be supplied to a gas burner is controlled by a proportional position type solenoid valve, a gas combustion control device comprising a. a first control circuit including a bridge circuit having a temperature-variable resistor for detecting a medium heated by said gas burner as one arm thereof, said control circuit controlling the exciting current flowing through the solenoid of said electromagnet valve so as to control the amount of gas fuel to be supplied to said gas burner in response to the variation in resistance of said temperature-variable resistor; and a second control circuit for detecting the magnitude of said current flowing through the solenoid of said solenoid valve in such a manner that when said current decreases less than a predetermined level the output current from said bridge circuit is so controlled as to interrupt said current flowing through the solenoid of said electromagnet valve.

2. A DEVICE AS SET FORTH IN CLAIM - WHEREIN AN OUTPUT CIRCUIT OF SAID SECOND CONTROL CIRCUIT FOR CONTROLLING SAID OUTPUT CURRENT OF SAID BRIDGE CIRCUIT IS CONNECTED TO ONE ARM OF SAID BRIDGE CIRCUIT IN SUCH A MANNER THAT WHEN SAID CURRENT FLOWING THROUGH THE SOLENOID OF SAID SOLENOID VALVE THE UNBALANCED CONDITION OF SAID BRIDGE CIRCUIT MAY BE VARIED BY SAID OUTPUT CURRENT, THERBY CAUSING THE ABRUPT CHANGE IN THE OUTPUT OF SAID BRIDGE CIRCUIT. -. A DEVICE AS SET FORTH IN CLAIM - WHEREIN SAID FIRST AND SECOND CONTROL CIRCUITS ARE SO COUPLED TO EACH OTHER THAT SAID CURRENT FLOWING THROUGH THE SOLENOID OF SAID SOLENOID VALVE MAY BE GRADUALLY INCREASED IN RESPONSE TO THE TEMPERATURE DROP OF SAID HEATED MEDIUM DUE TO THE INTERRUPTION OF THE GAS COMBUSTION IN SAID GAS BURNER AND THAT WHEN SAID CURRENT REACHES TO SAID PREDETERMINED LEVEL SAID CURRENT MAY BE ABRUPTLY INCREASED: AND THE IGNITION OF SAID GAS BURNER IS MADE PRIOR TO SAID ABRUPT INCREASE OF SAID CURRENT. $. A device as set forth in claim 1 wherein said first and second control circuits are so coupled to each other that said current may be gradually decreased in response to the temperature rise of said heated medium and thAt said current may be abruptly decreased when said current reaches said predetermined level.

5. A DEVICE AS SET FORTH IN CLAIM - WHEREIN SAID FIRST CONTROL CIRCUIT FOR CONTROLLING THE EXCITING CURRENT COMPRISES SAID BRIDGE CIRCUIT AND A FIRST ACTIVE ELEMENT WHICH IS CONTROLLED BY A SECOND ACTIVE ELEMENT FORMING THE OUTPUT CIRCUIT OF SAID BRIDGE CIRCUIT, THE OUTPUT CIRCUIT OF SAID FIRST ACTIVE ELEMENT BEING CONNECTED IN SERIES TO THE SOLENOID OF SAID SOLENOID VALVE: AND SAID SECOND CONTROL CIRCUIT COMPRISES A DETECTOR CIRCUIT FOR DETECTING THE VOLTAGE APPLIED ACROSS THE SOLENOID OF SAID SOLENOID VALVE, AND A THIRD ACTIVE ELEMENT WHICH IS CONTROLLED IN RESPONSE TO SAID DETECTED VOLTAGE, THE OUTPUT OF SAID THIRD ACTIVE ELEMENT BEING SOCONNECTED TO ONE ARM OF SAID BRIDGE CIRCUIT THAT THE VARIATION IN OUTPUT CURRENT OF SAID OUTPUT CIRCUIT MAY CAUSE THE VARIATION IN BIAS VOLTAGE APPLIES TO SAID SECOND ACTIVE ELEMENT IN SAID BRIDGE CIRCUIT. ". A device as set forth in claim 1 wherein said proportional action type solenoid valve comprises said solenoid, a plunger and spring means for supporting said plunger.

7. A device as set forth in claim 6 wherein said spring means comprise leaf springs, one end of each of said leaf springs being securely fixed to a stationary member of said device whereas the other end is bifurcated, the bifurcated portions of said leaf spring being extended laterally of said plunger away from said one fixed end, p1 the leading ends of said bifurcated portions of said leaf spring supporting a rigid arm extending from said plunger.

8. A device as set forth in claim 6 wherein said spring means comrises first leaf springs, one end of each of said leaf springs being securely fixed to a stationary member of said device, the other end of said leaf spring being bifurcated, the bifurcated portions of said leaf spring being extended laterally of said plunger away fromsaid fixed one end, second leaf springs being fixed to the leading ends of said bifurcated portions and extended toward said fixed one end of said first leaf spring, the leading ends of said second leaf springs supporting said plunger.