US3711237A

US3711237A - Ignition and control devices for fuel burners

Info

Publication number: US3711237A
Application number: US00168292A
Authority: US
Inventors: E Jaulmes
Original assignee: Ateliers de la Motobecane SA
Current assignee: MBK Industrie SA
Priority date: 1971-03-09
Filing date: 1971-08-02
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16
Also published as: CA981356A; ES393321A1; DE2136556A1; NL7111128A; JPS5310293B1; FR2128949A5

Abstract

The subject matter of the disclosure relates to a control device which is an improvement on French Pat. No. 1,598,786 wherein the ignition and detection of the presence or absence of a flame are both effected at a relatively low frequency (less than 1 Hz) whereas according to the improvement, means are provided to effect the ignition at a relatively higher frequency and the detection at a relatively low frequency. Additional safety means may be included.

Description

United States Patent 1191 Jaulmes 1 1 Jan. 16, 1973 54 IGNITION AND CONTROL DEVICES 3,614,280 10 1971 Yamaguchi ..431 /266 FOR FUEL BURNERS 3,377,125 4/1968 Zielinski ..431/74 [75] e to Eric Jau France 3,384,440 5/1968 Mayer ..431/66 [73] Assignee: Ateliers De La Motobecane, Pantin, Primary ExaminerEdward G. Favors France Attorney-Orville N. Greene et a1.

22 F'led: Au 2 1971 1 g 57 ABSTRACT [21] Appl. No.: 168,292

The sub ect matter of the d1sclosure relates to a control device which is an improvement on French Pat. [30] Forelgn Appl'catlon Pnonty Data No. 1,598,786 wherein the ignition and detection of March 9, 1971 France ..7108138 the Preseme or absence Of a flame are both effected at a relatively low frequency (less than 1 Hz) Whereas [52] US. Cl ..43l/69, 431/266 according to the improvement, means are provided to [51] Int. Cl ..F23n 5/12 effect the ignition at a relatively higher frequency and [58] Field of Search.........43l/25, 27, 69, 266, 66, 74 the detection at a relatively low frequency. Additional safety means may be included. [56] References Cited 18 Claims, 17 Drawing Figures UNITED STATES PATENTS 3,405,998 10/1968 Walbridge ..43l/25 PATENTEUJAH 16 I975 SHEET 1 UF 4 HEM, Y o W V 2:2:

Eric Joulmes ATTORNEYS PATENTEDJAH 16 I973 3.711.237

sum 2 or 4 I I 'II [EVENT 1R.

Eric Jaulmes BY C ,W

ATTORNEY PATENTEUJMI 16 I973 3.711.237

sum 3 or 4 Fric Jau/mcs ATTORNEY PATENTEDJAN 1B 1975 3.711.237

SHEET u 0F 4 INVENTOR.

En'cJaulmcs ATTORNEY IGNITION AND CONTROL DEVICES FOR FUEL BURNERS In French Pat. application No. 1,598,786, the applicant has described an ignition and safety device for burners which consume hydrocarbons or other combustible fluids in which the ignition and the detecting of the presence or absence of a flame are effected using a single electrode, by a spark repeated at a very low frequency, below 1H2. The ignition is obtained by discharging a condensor in the primary of the ignition transformer.

The principle on which the detection is based is the difference, in conditions of ionization and non-ionization, in the value of the damping coefficient, in a transient mode, of a very small third coil which, with a condenser connected in parallel, forms a damped oscillating circuit.

However, in this device the repetition of the sparks used for ignition at the very low frequency, below lI-Iz, has certain disadvantages with certain types of gas, and with imperfect gas mixtures and also when large flow burners are employed. In particular sparks of this kind are unsuitable for the proper ignition of heavy hydrocarbons.

A serious disadvantage of other devices which use a single electrode for ignition and detection and which produce a permanent supply of sparks at the frequency of the supply circuit, is their noisy operation. They also generate interference which affects radio and television reception to such an extent that it could lead to their being prohibited.

In a device embodying the present invention, a pulse generating means is operable to deliver to the single electrode a succession of spark-producing pulse trains, the pulse trains being separated from one another by intervals which are longer than the duration of each train, a detector means detects the presence or absence of a flame when a spark appears across the said gap, and there are means whereby, when ignition takes place, the pulse generating means changes over automatically to cause the production of sparks at a frequency substantially lower than the frequency of the pulses in the trains. Thus, the frequency of the pulses in the pulse trains may be that of the main supply and the frequency of the sparks produced for detection purposes, once ignition has taken place, may not be greater than lI-Iz. The interval between successive pulse trains when ignition is attempted, allows the unburnt mixture to disperse in the atmosphere, to reduce risk of explosion.

In the preferred form of apparatus, if the flame is extinguished re-ignition at the low frequency is attempted and then, if this is unsuccessful, several successive trains of pulses at the higher frequency are supplied before the device finally resets itself to a safety condition such that manual intervention is required before further attempts can be made.

The invention is also applicable to temperature regu- Iation, for example in heating systems, and it can also be applied in safety systems, in particular those which operate:

a. if the flame is accidentally extinguished (for example if it flows out) for a short period, to attempt reignition, first at low frequency, and then by successive trains of sparks;

b. if the flame remains extinguished, to close and lock electrically the shut-off member for the combustible fluid so that a manual operation is required to restore the supply;

0. in the case of a general failure of the gas or electricity supply, to provide the possibility of automatic re-ignition of the burner as soon as the supply is restored, this being effected by means of an additional contact controlled by pressureresponsive device;

. in the case of an ignition failure, to lock the shutoff member electrically, so that manual reactivation is required, as in case (b);

e. in the case of a short circuit of the ignition electrode, to take action as described for case (b); f. in the case of an abnormally high burner temperature, to take action as described for case (b).

In order that the invention may be better understood, an example of apparatus embodying the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates diagrammatically the operation of currently employed devices;

FIG. 2 illustrates diagrammatically the operation of the device described in the above-mentioned patent;

FIG. 3 illustrates diagrammatically the operation of a device embodying the present invention;

FIG. 4 shows a circuit similar to that shown in the above-mentioned patent;

FIGS. 5 to 12 show oscillograms illustrating the method of functioning of this device;

FIG. 13 is the overall circuit of a device embodying the present invention.

FIG. 14 is a circuit for a variant intended particularly for igniting heavy hydrocarbons;

FIG. 15 shows the synchronization signal used in the latter;

FIG. 16 shows the pilot signal; and

FIG. 17 shows the interruptions of the inductive current.

From the earlier application French Pat. No. 1,598,786, it will be remembered that the circuit shown in FIG. 4 functions as follows. The damped oscillatory discharge in the principal discharge circuit constituted by a condenser C and the primary winding N of an ignition coil, supplies across the secondary winding N the sparks required for ignition and for detection. At each detection spark, the oscillating circuit N C is excited, and produces a damped osciallation at approximately 200 KHZ (see FIG. 5). The negative part of this oscillation is detected by a condenser C and by the base-emitter junction of a transistor T (see FIG. 6). A negative potential is therefore applied to the base of T, during the entire oscillation period, which blocks it and produces on its collector a rectangular signal whose duration is proportional to the oscillation period t (see FIG. 7). This signal allows the condenser C to be charged through two resistances R and R according to the time constant (R R, C If there is no flame, and consequently t is greater than this time constant, the voltage across the terminals of the condenser C, reaches the threshold of a junction transistor T triggering this transistor (see FIG. 8), and producing a positive pulse across the terminals of a resistance R In contrast to this, FIGS. 9 to 12, which correspond respectively to FIGS. 5 to 8, shows that if the flame is burning, the damping is very small, the detected signal is also weak, and consequently the rectangular signal is also weak and its duration t becomes less than 2,. Thus, the threshold of the unijunction transistor T is not reached, and consequently no pulse appears across the resistance R According to the present invention, as represented in the part A of FIG. 13, the frequency of the series of sparks, which is the supply frequency, is attained by means of a disc whose response threshold is reached when the two condensers C and C which are connected in series, are charged up to a voltage corresponding to this threshold. The condenser C is charged by a rectifying diode D, and discharged by a thyristor T As shown in FIG. 3 a very satisfactory frequency for ignition is 50 Hz but other frequencies significantly greater than I I-lz may be applied.

The switching to the detection frequency is obtained by short circuiting the condenser C which is very small compared to the condenser C by means of an NPN transistor T This transistor T is saturated when the condenser C, reaches the saturation threshold. This period is determined by the time constant R C, It is necessary to provide a voltage divider consisting of resistances R and R, such that the voltage across the condenser C, is prevented from reaching excessively high values.

The inductive train of sparks used for igniting heavy fuel products is obtained, as shown in FIG. 14, by derivin g a comparatively heavy current with the help of a resistance R This current is passed, by means of a power transistor T in the primary coil N 1 of the ignition transformer. As shown in FIG. 15, the synchronization signal of this transistor is derived by means of a zener diode Zn and applied to the monostable integrated circuit CM. This circuit acts through a transistor Ta to cause the power transistor T to become conductive at the beginning of a half sinewave of the supply voltage (this is the pilot signal shown in FIG. 16) and to block the power transistor T when the inductive current reaches its maximum (see FIG. 17). The integrated circuit CM is locked when the condenser C is charged and the transistor T, is saturated.

In this device, the detection sparks can be obtained at low frequency over the circuit R C diac. The pulses used for attempted reignition can also be obtained at the terminals of the circuit N C There will not be described the means used for detection, for safety locking and for integrating the pulses produced in the absence of a flame (shown in part B of FIG. 13).

During the ignition phase, which can be long or short in duration, the detection circuit naturally indicates absence of flame. It is therefore necessary to lock the safety system during the ignition period. This is obtained by short circuiting the condenser C by means of a PNP transistor T as soon as the voltage is applied and by causing the transistor T to be unblocked progressively before the end of the ignition period. To obtain this, a diode D is interposed in series with the base of the transistor T the anode-cathode path of the diode D being conductive as soon as voltage is applied. As soon as the potential across the condenser C is sufficient to block the diode D this blocks the transistor T allowing the condenser C to charge up.

In order to close the fuel supply member, (for example an electrovalve EV), and to cause the repeated attempts to re-ignite, in the case where the flame goes out either for a short period or finally, the pulses indicating absence of flame, derived from the terminals of the resistance R are integrated through the diode D in a condenser C When this condenser C is charged, the transistor T saturates opening a relay RL (in part D of FIG. 13) having two contacts C RL and C RL. This interrupts the control sparks and the condenser C discharges slowly, until the transistor T becomes blocked again, whereupon the relay RL closes, producing a fresh sequence of sparks at the ignition electrode A1. If the fuel fails to ignite or is absent, and assuming that the detection system (part B of FIG. 13) is unlocked, pulses appear over the terminals of the resistance R These pulses, integrated again in the condenser C reopen the relay RL. The process is repeated until a flame appears.

To allow the system to be put into a state of safety at the end of a certain number of attempts to reignite, the number of attempts is counted by the circuit represented in the part E of FIG. 13. This circuit will now be described.

The counting circuit comprises a non-locked detection circuit consisting of a transistor T and a unijunction transistor T During the ignition phase the circuit produces a sequence of pulses across a resistance R The pulses are integrated in a condenser C by way of a diode D3. A transistor T connected in series with a resistance R becomes saturated, charging the condenser C Each time the relay RL closes and a fresh sequence of sparks occurs, the condenser C charges up step by step until the threshold of the uni-junction transistor T is reached.

As soon as this threshold is reached, the transistor T is triggered. A pulse appears on the terminals of the resistance R The thyristor T is triggered, short circuiting the relay RL and so ensuring that it remains open. Consequently, the device can be returned to zero only by an intervention by the operator. If the fuel ignites at the first attempt, or at the second attempt, the control spark occurs in an ionized medium, and consequently no pulse appears across the resistances R and R and the process of reignition does not take place.

There will now be described the safety device which comes into operation when an electrode short circuits, or when there is an ignition failure (part C of FIG. 13). The detection signal derived from the terminals of the circuit N;,, C is also applied, over a condenser C to a further detection circuit which is essentially similar to the circuit shown in part B of FIG. 13, except that the means for locking during the ignition phase are omitted. In this circuit, the time constant is chosen such that in the case of an ionized medium, the uni-junction transistor T delivers a pulse to the terminals of a resistance R As soon as the relay RL is closed, the condenser C charges up over the resistance R A transistor T connected in parallel, partially discharges this condenser at each detection spark. When an electrode short circuits, the damping is very weak and consequently no pulse occurs across the resistance R The partial discharges of the condenser C and therefore interrupted and this allows the response threshold of the uni-junction transistor T to be reached. Consequently, this transistor conducts and a positive pulse appears across the resistance R This pulse triggers the thyristor T finally closing the shut-off member. In this circuit there can, if desired, be provided a positive-temperaturecoefficient resistance CTP, connected in parallel with the resistance R and selected on the basis of the highest temperature to be detected. When the temperature rises abnormally the value of the positive-temperature-coefficient resistance increases and consequently the value of the combination of this resistance with R This increases the time constant and consequently no further pulses appear across resistance R This brings the system into a condition corresponding to a short circuited electrode, or to an ignition failure.

The temperature control which will now be described (see part D of FIG. 13) is carried out by means of a relaxation oscillator comprising a uni-junction transistor T The high frequency pulses appearing across a resistance R are integrated in the condenser C by way of a diode D When the voltage on this condenser reaches the threshold of a zener diode Z the transistor T becomes saturated, closing the main relay RL and opening the electrovalve EV for the fuel. When the temperature rises, after being previously set by means of a potentiometer R a negative temperature coefficient resistance CTN decreases in value until the saturation current of the transistor T is attained, whereupon the circuit ceases to oscillate and consequently the transistor T becomes blocked, opening the relay RL.

FIG. 13 shows a pressure controlled contact P,, which interrupts the general feed to the system as soon as the gas pressure drops. When the pressure returns to normal, the entire system is restarted automatically by the pressure controlled contacts The low voltage required by the system is provided by a circuit (the part F of FIG. 13) which has no input transformer, the isolation from the supply circuit being provided by the ignition transformer. The circuit has a condenser C connected in series with a diode bridge D The filtering is done by a condenser C A resistance R limits the short circuit current when the system is in the safety condition.

I claim:

1. An ignition and safety device for burners consuming hydrocarbon fuels or other combustible fluid fuels, comprising: a single electrode for igniting the fuel positioned to form a spark gap between itself and the burner; pulse-generating means operable to deliver to the electrode a succession of spark-producing pulse trains, the pulse trains being separated from one another by intervals which are longer than the duration of each train; detector means for detecting the presence of absence of a flame when a spark occurs across the said gap; and means whereby when ignition takes place the pulse-generating means changes over automatically to cause the production of sparks at a frequency substantially lower than the frequency of the pulses in the said first mentioned trains.

2. A device in accordance with claim 1, in which the frequency of the pulses in the said pulse trains is that of the main supply, and in which the frequency of the sparks produced once ignition has taken place is not greater than 1 Hz.

3. A device in accordance with claim 2 in which the detector means includes means responsive to the extinction of the flame to cause a number of attempts to re-ignite the flame by sparks at the said lower frequency and, if this is unsuccessful, to cause the application to the electrode of a number of the said high-frequency pulse trains.

4. A device in accordance with claim 3 in which the detector means includes means responsive to a predetermined number of the said pulse trains without ignition taking place to close and block a fuel valve in such a manner that manual intervention is required to reopen it.

5. A device in accordance with claim 3 for igniting light hydrocarbons, in which the ignition means are of the capacitive discharge type.

6. A device in accordance with claim 3 for igniting heavy hydrocarbons, in which the ignition means are of the inductive type.

7. A device in accordance with claim 1 including a pressure-controlled device responsive to a failure of the fuel supply to cut the electrical supply to the circuit and operative to re-establish the electrical supply automatically when the fuel supply is re-established.

8. A device in accordance with claim 3 in which the detector means includes means responsive to a shortcircuit condition between the electrode and the burner to close a fuel valve in such a manner that manual intervention is required to re-open it.

9. A device in accordance with claim 3 in which the detector means includes means responsive to an abnormally high burner temperature to close a fuel valve in such a manner that manual intervention is required to open it.

10. A device in accordance with claim 1 for controlling temperature in heat exchanges, in which the temperature control is maintained by successive ignition and extinction periods, the device including a relaxation oscillator controlled by variations in the resistance of a thermistor.

l 1. A device in accordance with claim 1 in which the pulses of the said higher frequency are interrupted to form pulse trains by a relay operated by pulses produced in the absence of a flame.

12. A device in accordance with claim 1 in which the individual sparks in the said trains of sparks are generated at the frequency of the alternating current supply by means of a circuit including a threshold diode connected in series with the gate of a discharge thyristor.

13. A device in accordance with claim 1 in which the pulses for producing the sparks at the said lower frequency are obtained by means of two series-connected capacitors connected in a charging circuit and a transistor arranged to short-circuit one of the said capacitors when it is driven into conduction by the periodic charging of a further capacitor.

14. A device in accordance with claim 6, including a power transistor connected to interrupt the current flowing through the primary coil of an ignition transformer and thereby to produce an inductive spark having a duration of at least 1,500 microseconds, the power transistor being biased by a monostable circuit.

15. A device in accordance with claim 4 including means to count the attempts to re-ignite the fuel comprising an integrating capacitor which is charged, one step at a time, with each train of pulses, and a transistor operative when this capacitor is charged to its threshold level to energize a relay which closes a fuel valve.

16. A device in accordance with claim 7 including a circuit having a capacitor which is charged over a resistor, the capacitor being partially discharged with each low-frequency detection spark when the burner is functioning normally, and a transistor responsive to the charge on the said capacitor and operable when the detection spark fails to take place or when there is a short circuit in the electrode circuit, to close the said fuel valve.

17. A device in accordance with claim 8 including a circuit having a capacitor which is charged over a resistor, the capacitor being partially discharged with each low-frequency detection spark when the burner is functioning normally, and a transistor responsive to the charge on the said capacitor and operable when the detection spark fails to take place or when there is a short circuit in the electrode circuit, to close the said fuel valve.

18. A device in accordance with claim 10 including means for detecting an abnormal increase in the burner temperature comprising a resistance having a positive temperature coefficient, in a resistance-capacitance circuit such that in the case of an abnormal increase in temperature the voltage across a capacitance fails to reach the threshold of a transistor to the control electrode of which the capacitor is connected.

Claims

1. An ignition and safety device for burners consuming hydrocarbon fuels or other combustible fluid fuels, comprising: a single electrode for igniting the fuel positioned to form a spark gap between itself and the burner; pulse-generating means operable to deliver to the electrode a succession of sparkproducing pulse trains, the pulse trains being separated from one another by intervals which are longer than the duration of each train; detector means for detecting the presence of absence of a flame when a spark occurs across the said gap; and means whereby when ignition takes place the pulse-generating means changes over automatically to cause the production of sparks at a frequency substantially lower than the frequency of the pulses in the said first mentioned trains.

8. A device in accordance with claim 3 in which the detector means includes means responsive to a short-circuit condition between the electrode and the burner to close a fUel valve in such a manner that manual intervention is required to re-open it.

11. A device in accordance with claim 1 in which the pulses of the said higher frequency are interrupted to form pulse trains by a relay operated by pulses produced in the absence of a flame.