US3367387A

US3367387A - Combustion control device for fuel burners

Info

Publication number: US3367387A
Application number: US541270A
Authority: US
Inventors: Sugiyama Iwao
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1965-04-13
Filing date: 1966-04-08
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06
Also published as: DK114365B

Description

Feb. 6, 1968 IWAO SUGIYAMA 3,367,387

COMBUSTION CONTROL DEVICE FOR FUEL BURNERS Filed April 8, 1966 INVENTOIG flung SLLGIVHMQ ATTORNEY United States Patent COMBUSTIGN CONTROL DEVICE FOR FUEL BURNERS lwao Sugiyama, Hitachi-511i, Japan, assignor to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Apr. 8, 1966, Ser. No. 541,270 Claims priority, application Japan, Apr. 13, 1965, 40/21,381 7 Claims. (Cl. 15828) ABSTRACT OF THE DISCLOSURE A combustion control device for fuel burners designed for automatic controlling of the fuel ignition, firing and flame extinguishment of oil or gas burners. The control is solid state with a three-terminal semiconductor controlling the energization of the ignition device relay coil. A thermistor circuit with a set voltage firing device controls the three-terminal, semiconductor element and a resistance heated temperature responsive safety switch will de-activate the device after a set period of time without ignition.

The object of the present invention is to provide a combustion control device of the character described which is capable of automatically, performing different functions such as igniting and extinguishing the burner, reigniting the burner when its flame has died out inadvertently, and interrupting the ignition operation whenever the fuel has failed to ignite, with rapidness and safety. With burners, it is important that ignition and especially reignition be elfected rapidly. In cases where the burner flame has extinguished during operation, unburned fuel may build up in the combustion chamber to such an extent as to incur the danger of explosion unless reignition is effected without delay.

To overcome this difiiculty, the combustion control device according to the present invention employs a lightsensitive element to sense the burner flame and a detec tion circuit which comprises essentially semiconductor elements and thus operable with an increased reliability to send a signal to the ignition device based upon the output of the light-sensitive element.

Another object of the present invention is to provide a device of the character described which functions to interrupt the igniting operation whenever ignition has not been completed in a predetermined length of time so that the attendant may correct any defects in the system. To attain this object, use is made of a safety device which comprises a thermo-relay operable to de-energize the ignition and fuel-feeding devices under heat of a heating element, which is held energized while the ignition is receiving a signal output of the detection circuit.

A further object of the present invention is to prevent any variation in time specified for the safety device to operate under the control of the thermo-relay when the ambient temperature or the source voltage varies to cause variation in rate in which heat is produced by the heating element, thereby to enable the device to interrupt the igniting process without fail. To serve this purpose, a thermistor circuit is incorporated, according to the present invention, in the detection circuit, which essentially comprises semiconductor devices.

A still further object of the present invention is to provide a combustion control device of the character described which includes a detection circuit the components of which can be fabricated at reduced costs and in sizes reduced to a minimum. This object can be attained according to the present invention by the use of a detection circuit com prising essentially semiconductor elements.

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The foregoing and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a combustion control device embodying the present invention; and

FIG. 2 is a graphical representation of the voltagecurrent characteristic of the N-P-N two-terminal AC control element employed in the detection circuit shown in FIG. 1.

Referring to the drawings and first to FIG. 1, the combustion control device illustrated therein includes a controlling switch 1 which is connected in series with a safety switch 2. Also connected in series are a silicon-controlled rectifier 3, a compensating resistor 4, a diode 5 and a relay coil 6 associated with an ignition device 17, to form together with the above switches 1 and 2 a series circuit between source terminals 7 and 8. In cases where the control device is employed with burners for space heating or like use, the controlling switch takes the form of a temperature switch. The safety switch 2 is actually a handrestoring thermo-relay, which is temperature-responsive. A smoothing capacitor 9 is connected in parallel with the relay coil 6 and an electric heater element 10 to serve the purpose of heating the safety device 2 is connected between one of the source terminal 8 and the cathode of siliconcontrolled rectifier 3, which will be referred to hereinafter as SCR. A self-holding relay has a coil 11 associated with a fuel feeding device 14 has one of its lead wires connected to the safety switch 2 by way of the self-holding contact 12 of the relay and has the other lead wire connected to source terminal 8. Another contact 13 of the relay is operable jointly with the self-holding contact 12 and serves to connect the fuel-feeding device 14 between the source terminals 7 and 8. The fuel-feeding device is of an appropriate structure including a solenoid valve, a fuel pump and a motor-driven blower. A relay contact 15 provided for the ignition device is connected in parallel to the self-holding contact 12 and operable with another contact 16, which operates to connect the ignition device 17 between the source terminals 7 and 8. The ignition device 17, comprising a step-up transformer and sparkforming electrodes, serves for spark ignition of the burner.

Reference numeral 18 indicates an indirectly-heated positive-characteristic thermistor which comprises a temperature-sensitive resistance element 19 and an electric heating element 20, the temperature-sensitive resistance element 19 characteristically having a resistance value increasing with rise in temperature. The heating element 20 of the thermistor 18 has one terminal connected to one of the source terminals 7 by way of safety and controlling switches 2 and 1 and the other terminal connected to the other source terminal 8 through an adjusting resistor 21. Another thermistor 22 also of positive characteristic is provided in the vicinity of the safety switch 2 so as to respond to the ambient temperature of the device, characteristically having a resistance value increasing with rise in temperature. A compensating resistor 23 and a capacitor 24 are series-connected to the thermistor 22, which is also series-connected to the temperature-sensitive resistance element 19. In this series circuit, the temperature-sensitive resistance element 19 has an outside terminal connected to the anode of the SCR 3 while the capacitor 24 has an outside terminal connected to the cathode of the SCR 3.

Reference numeral 25 indicates a two-terminal alternating-current controlling element including three semiconductor layers of N-P-N and which exhibits, as shown in FIG. 2, a bidirectional and symmetrical, negative resistance characteristic. Thus, the controlling element is rendered conducting when the terminal voltage reaches its breakover voltage V and thereafter remains conducting even if the terminal voltage is reduced. One terminal of this two-terminal alternating-current controlling element 25 is connected to the junction between the compensating resistor 23 and capacitor 24 and the other terminal is connected to the gate terminal 26 of SCR 3.

Reference numeral 27 indicates a lightsensitive element in the form of a cadmium sulfide (CdS) element, which is rendered conducting by the flame of the burner. Being connected in parallel to the capacitor 24, the lightsensitive element 27 shares the voltage between the anode and cathode of the SCR 3 to impress it across the terminals of capacitor 24.

With the above-described circuit arrangement, when the controlling switch 1 is closed, an AC source voltage is impressed across. the thus closed circuit including the source terminal 7, controlling switch 1, safety switch 2, SCR 3, compensating resistor 4, diode 5, relay coil 6 for the ignition device, and source terminal 8 in that order. In the case where no gate current is flowing through the gate terminal 26 of the SCR 3, the latter is in a nonconducting state, the source voltage appearing between the anode and cathode of the SCR 3. Thus, the series circuit parallel-connected between the anode and cathode of the SCR 3 and including temperature-sensitive resistance element 19, thermistor 22, compensating resistor 27 and capacitor 24 in that order is energized to charge the capacitor 24. In this manner, if the burner is not firing and thus the light-sensitive element 27 has a sufliciently large resistance value, the capacitor 24 is effectively charged by the source voltage to a fully high voltage value in each half-cycle. The voltage of the capacitor 24 is thus impressed through the medium of the cathode gate of the SCR 3 to the two-terminal alternating-current controlling element. Accordingly, when in the forward voltage region of the SCR 3 the charging voltage of capacitor 24 reaches the value of the breakover voltage V of the two-terminal alternating-current controlling element 25, the latter element is rendered conducting to cause a current to flow through the gate terminal 26 of SCR 3, thus rendering the SCR conducting. As a result, a current is caused to flow through the relay coil 6 for the ignition device, closing the contacts 15 and 16 to energize the relay coil 11 and the ignition device 17. Upon energization of the relay coil 11,

contacts

12 and 13 are closed so that the coil 11 self-hlds and a current is directed through the fuel-feeding device 14. In this manner, fuel is fed by the device 14 to the burner and ignited by means of the ignition device 17 to start combustion. Where the burner has thus assumed its normal firing state, the lightsensitive element 27, receiving light rays from the flame, is reduced in value of resistance and hence in voltage it shares. Since the voltage shared by the light-sensitive element 27 is the maximum voltage to which the capacitor 24 is chargeable, the two-terminal AC control element 25 can serve to render the SCR 3 nonconducting blocking any gate current thereof and to maintain the nonconducting state of the SCR 3 during the normal combustion as long as the voltage shared by the lightsensitive element is held below the 'breakover voltage V of the two-terminal alternatingcurrent controlling element 25. When the SCR 3 is rendered nonconducting and the relay coil 6 associated with the ignition device 17 is de-energized, contacts 15 and 16 are opened. Despite the opening of the contact 15, the relay coil 11 for the fuel-feeding device remains energized through the selfholding contact 12, which jointly with contact 13 remains closed. Opening of the contact 16 interrupts the current previously flowing through the ignition device 17 and thus the latter ceases to function.

Where the burner is used for space heating, the controlling switch 1 is opened when the room temperature reaches the specified level, and in this case the current flowing through the relay coil 11 for fuel feed is interrupted so that

contacts

12 and 13 open to de-energize the feeding device 14 to stop the oil supply to the burner and its flame is extinguished ready for the next ignition process.

In the event that the burner previously normally operating is accidentally rendered diflicult to maintain combustion and the flame is extinguished, the resistance value of the light-sensitive element 27 is abruptly increased because of the disappearance of the light rays previously impinging upon the element 27. As the result, the voltage shared by the light-sensitive element 27 increases so that the capacitor 24 is charged to the breakover voltage V of the two-terminal alternating-current controlling element 25. After the voltage of capacitor 24 has reached the breakover voltage V of the two-terminal alternating-current controlling element 25, the charged capacitor 24 acts through the controlling element 25 to cause a gate current flowing through the gate terminal 26 of the SCR 3 thus to render the latter conducting. The current flowing through the SCR 3 excites the relay coil 6, closing contacts 15 and 16 to energize the ignition device 17 for re-ignition.

When the reignition has normally been effected, the light rays from the flame formed impinge upon the lightsensitive element 27 to reduce its resistance value to such an extent that the ignition device is rendered inoperative and the burner assumes its normal firing state, as with the case of the first ignition described hereinbefore.

In cases of such inadvertent extinguishment of the burner flame, however, it is not infrequent that the reignition process cannot be duly completed. In such cases, the light-sensitive element 27 not receiving enough light exhibits a relatively high resistance value with the result that the charge voltage of the capacitor 24 reaches the value of breakover voltage V of the two-terminal alternating-current controlling element 25, causing a gate current through the SCR 3 to render the latter conducting. In the conducting state of the SCR 3, the heating element 10 is also energized to generate heat. In the case where the SCR 3 is held conducting only for a short period of time, i.e., where the igniting process is completed in a normal manner, the total amount of heat generated by the heating element 10 is limited and the safety switch 2 does not operate. On the other hand, if the ignition process continues for a longer period of time and the total amount of heat generated by the heating element 10 is so increased that the temperature of the safety switch 2 reaches its operating point, the switch 2 is opened to de-energize the ignition relay coil 6 and fuel feed relay coil 11 with the result that the

contacts

12, 13, 15 and 16 are opened to render both the fuel-feeding and ignition devices 14 and 17 inoperative. During the ignition process, fuel fed to the burner is released into the combustion chamber as a combustible. Therefore, if the ignition process be continued, unburned fuel would be built up in the combustion chamber to incur the danger of explosion. Such danger of explosion or the like accident can be effectively prevented by determining the rate of heat generation of the electric heater 10 and the operating temperature of the safety switch 20 so that the latter is operated as soon as the amount of unburned fuel released into the combustion chamber reaches a specified value. Moreover, after operation of the safety switch 20, the attendant can repair the defective parts of the system and then manually restore the safety switch 20 ready to start the reignition process.

The rate of heat generation of the heating element 10 generally tends to vary with the source voltage, but with the arrangement shown, it can be held constant irrespective of variations of the source voltage since the voltage variations are detected by the indirectly-heated positivecharacteristic thermistor 18 and are taken up as the phase angle at which the SCR 3 is rendered conducting is corrected. In other words, if the source voltage rises, the heating element 20 of the indirectly-heated thermistor 18 is increased in rate of heat generation to raise the temperature of the temperature-sensitive resistor 19 and hence its resistance value with the result that the time constant of the series circuit including the temperature-sensitive resistor 19, positive-characteristic thermistor 22, compensating resistor 23 and capacitor 24 is increased to reduce the charging rate of the capacitor 24. This in turn reduces the charge voltage of the capacitor 24 relative to the source voltage waveform and hence the time required for the capacitor voltage to reach the value of breakover voltage V of the two-terminal alternatingcurrent controlling element 25. Accordingly, the phase angle at which the SCR 3 starts to conduct current is delayed to cut off a larger portion of the voltage waveform. Thus, despite the rise of the source voltage, the power consumption of the heating element remains unchanged and its rate of heat generation is held constant.

On the other hand, in the event that the source voltage is reduced, the rate of heat generation of the heating element 20 of the positive-characteristic thermistor 18 is also reduced to lower the temperature of the temperaturesensitive resistance element 19 so that the time constant of the series circuit charging the capacitor 24 is decreased to increase the rate of charging the latter. This causes the phase angle at which the SCR 3 starts conducting current to advance and thus a smaller portion of the voltage Waveform is cut off. This increases the phase angle of the voltage applied to the heating element 10 and thus prevents reduction in rate of heat generation of the latter. After all, the heating element It} in the circuit shown is not affected by any variations in the source voltage.

Another problem to be considered is the effect of the ambient temperature of the safety device 2 upon the temperature rise thereof. It is to be noted at this point that the ambient temperature of the safety switch 2 is detected by the positive-characteristic thermistor 22 to adjust the phase angle at which the SCR 3 starts to conduct current so that the time required for operation of the safety switch 2 is held constant. In other words, if the ambient temperature of the safety switch 2 rises, the resistance value of the positive-characteristic thermistor 22 is increased so that the time constant of the series circuit including the temperature-sensitive resistance element 19, positive-characteristic thermistor 22, compensating resistor 23 and capacitor 24 is increased to reduce the rate at which the charge voltage of the capacitor 24 is raised. Accordingly, just as with the case where the source voltage rises, the phase angle at which the SCR 3 starts to conduct current is delayed to reduce the voltage applied to the heating element 10 and hence the rate of heat generation thereof whereby any premature operation of the safety switch 2 is effectively prevented. On the other hand, if the ambient temperature of the safety switch 2 falls, the resistance value of the positive-characteristic thermistor 22 and hence the time constant of the associated series circuit are reduced so that the phase angle at which the SCR 3 starts to conduct current is, in this case, advanced to increase the rate of heat generation of the heating element 10 thereby to enable the safety switch 2 to attain its operating temperature in a decided time. In this manner, it will be appreciated that the safety switch 2 can perform its intended function under the control of the thermo-relay with complete satisfaction.

It will be obvious that the SCR 3 may be replaced by any other three-terminal semiconductor-controlled element.

The invention is not restricted to the details set forth herein but may be varied in many ways within the scope of the invention as defined in the appendant claims.

What is claimed is:

1. A combustion control device for a fuel burner including ignition means and fuel feed means, comprising: a series circuit including a controlling switch, a heat responsive safety switch, a three-terminal semiconductor controlled element, and a first relay coil; first relay means, in-

cluding said first relay coil, for controlling the energization of said ignition means; a smoothing capacitor connected in parallel with said first relay coil; a diode and a compensating resistor connected in series with each other and with said first relay coil; electric heating means for heating said safety switch and being connected in parallel with said first relay coil, said diode and said compensating resistor; a self-holding second relay means for controlling the fuel feed means and having a relay coil connected in series with said controlling and safety switches; said first relay means having contact means for controlling current to said self-holding relay coil and the ignition means; said second relay means having self-holding contact means for providing current to its relay coil and for controlling current to the fuel feed means; and light-sensitive means for sensing the presence of the flame of the burner and for accordingly controlling said semiconductor-controlled element.

2. A combustion con-trol device for a fuel burner including ignition means and fuel feed means, comprising: a series circuit including a controlling switch, a heat responsive safety switch, a three-terminal semiconductor-controlled element, and a first relay coil; electric heating means for heating said safety switch and being connected in series with said three-terminal semiconductor-con trolled element and in parallel with said electric heating means; first relay means, including said first relay coil, for controlling the ignition means; self-holding second relay means for controlling the fuel feed means and having a second relay coil connected in series with Said controlling and safety switches; said first means having relay contact means for controlling current to said self-holding relay coil and the ignition means; said second relay means having selfholding contact means for controlling current to the fuel feed means; a capacitor and a compensating resistor con nected in circuit between the anode and cathode of said three-terminal semiconductor-controlled elements; twoterminal alternating current controlling means for being conductive only within a specific trigger voltage range and interconnecting the gate of said three-terminal semiconductor-controlled element and the junction between said capacitor and said compensating resistor; and light-sensitive means connected in parallel to said capacitor and having a resistance value decreasing with increasing received light rays from the burner flame.

3. The combustion control device of claim 2, including a positive-characteristic thermistor in series with said capacitor and compensating resistor; said positive-characteristic thermistor constituting means for detecting the ambient temperature of said safety switch; said capacitor having an outside terminal connected to the cathode of said three-terminal semiconductor-controlled element; said thermistor having an outside terminal connected to the anode of said three-terminal semiconductor-controlled element.

4. The combustion control device of claim 2, including an indirectly-heated positive-characteristic thermistor connected in circuit with said capacitor and having an electric heating element; a voltage source; said thermistor electric heating element, said controlling switch and said safety switch being connected in series across said voltage source; said capacitor having an outside terminal connected to the cathode of said three-terminal semiconductor-controlled element; said thermistor having an outside terminal connected to the anode of said three-terminal semiconductor-controlled element.

5. A combustion control device for a fuel burner having ignition means and fuel feed means, comprising: a voltage source; relay means for controlling the energization of the ignition means and having a relay coil; a threeterminal semiconductor means for controlling the energization of said relay coil by said voltage source; lightsensitive means having a resistance value changing in response to the light received from the burner flame; a capacitor connected in parallel with said light-sensitive means; a trigger means for conducting current only at a voltage substantially higher than a predetermined fixed trigger voltage and being connected in series with said parallel connection of said capacitor and light-sensitive means, between the gate and one of the terminals of said three-terminal semiconductor-controlled means.

6. The device according to claim 5, including temperature responsive safety switch means for de-energizing said three-terminal semiconductor means; thermistor means for changing in resistance value according to the ambient temperature of said safety switch means; self-heated thermistor means having a heating resistance across said voltage source and a second thermistor receiving heat from said heating element; said second thermistor, said first mentioned thermistor means and said trigger means being series connected between the gate and other terminal of said three-terminal semiconductor means.

7. A combustion control device for a fuel burner ineluding ignition means, comprising: a voltage source; relay means, having a relay coil, for controlling energization of the ignition means; three-terminal semi-conductor means for controlling the energization of said relay coil; temperature responsive safety switch means for controlling the connection of said three-terminal semiconductor means to said voltage source; means connected between the gate of said three-terminal semiconductor means and one of its remaining terminals for providing a control voltage suificient to allow passage of current through said threeterminal semiconductor means according to the reception of light from the burner flame; temperature compensating means connected in series between the gate and the other of said remaining terminals of said three-terminal semiconductor means; said temperature compensating means including first thermistor means for changing in resistance value according to the ambient temperature of said temtemperature responsive safety switch means and second thermistor means for changing in resistance value according to the voltage of said voltage source; said second thermistor means including a thermistor in series with said first thermistor means and a heating resistance across said voltage source and supplying heat directly to said second thermistor means thermistor.

References Cited UNITED STATES PATENTS 3,079,982 3/1963 Staring 15828 3,238,992 3/1966 Forbes 158-28 3,270,799 9/1966 Pinckaers 158-l28 3,276,507 10/1966 Eldridge et al. l58+28 JAMES W. WESTHAVER, Primary Examiner.