Spark igniter system for gas appliance pilot ignition

Abstract

A spark igniter operative from a low voltage DC source for a gas or vaporous fuel pilot including a simplified ringing-choke DC-to-DC converter and a relaxation oscillator/pulser for producing the ignition spark. An inhibit circuit utilizing a flame rod and the flame rectification phenomenon disables the relaxation oscillator/pulser when the pilot flame is extant.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to igniters for gas or vaporous fuel heating appliances generally, and more particularly, to spark igniter devices for igniting a gas fueled pilot, which in turn, may ignite a main burner.

2. Description of the Prior Art

In the prior art, heating appliances, such as furnaces, hot water heaters, cooking devices, etc., operating from gaseous or vaporous fuels, are extremely well known. A variety of fuels are commonly used by such appliances including natural gas, propane, butane and other similar fuels. It has been common practice for a pilot to be left burning continuously at a relatively low gas consumption rate, in order that the appliance can (manually or automatically) be placed into full operation conveniently and without significant delay.

Recently, attention has been focused on measures for the conservation of fuels however, and this has tended to spawn various new hardware for starting of such gas appliances without the need for a continuous burning pilot.

Among these devices are those which provide for ignition of the appliance main burner by means of an electrically heated element, or by means of a spark gap. Spark gaps have the advantage of not requiring a heat-up time, and they are relatively economical of electrical energy. For the sake of reliability however, some recent devices of the type have provided for electrical ignition, by spark gap for example, of a gas fired pilot, the said gas-fired pilot in turn operating to ignite the main burner or burners of the appliance. The art concerning gas fired pilots is developed to the point where main burner ignition is very reliably effected. Direct spark ignition of a main burner has been undertaken in this art, but may introduce some problems such as excessive gas collection before ignition.

At least one prior art device is known which involves the use of spark ignition of a gas fired pilot. Such a device is described in U.S. Pat. No. 3,662,185, entitled "Spark Generator and Components Therefor." That device makes use of the so-called flame rod (known in these arts per se) which may act as one spark electrode and also as an electrode providing flame rectification or conduction as the pilot flame plays on the flame rod. The fact that such conduction occurs and is unipolar has given rise to the term "flame rectification." The resistance of the flame path is on the order of several megohms, and that resistance is employed as an element in a circuit for disabling the self-recycling spark voltage generator while the pilot is lighted. The indicated prior art device makes use of a voltage trippler as a power source for a relaxation oscillator employing an element such as a neon tube. Such gas discharge devices normally require somewhat higher operating voltages than are provided by the low voltage direct current power sources common in recreational vehicles and the like. That reference derives the necessary higher direct current source voltage by a relatively expensive method. The manner in which the present invention builds upon this reference to provide a unique and significantly more efficient and cost effective igniting system, will be evident as this description proceeds.

Another reference of interest is entitled "Ignition System and Components Thereof," U.S. Pat. application Ser. No. 447,889 filed on Mar. 4, 1974 (assigned to the present assignee).

SUMMARY OF THE INVENTION

The present invention makes use of a simplified low-cost ringing-choke DC-to-DC converter in combination with a relaxation oscillator and pulsing circuit for the spark gap, the latter elements resembling those of U.S. Pat. No. 3,662,185, aforementioned.

The converter circuit of the present combination includes an auto-transformer or tapped inductor which is energized from the low voltage source (typically 12 volts). A solid state device (transistor) is employed in a unique self-recycling oscillatory pulse generator. The primary current path passes through the upper part of the tapped inductor or auto-transformer (as illustrated) and the other part of the coil acts as a secondary, feeding regenerative and degenerative signal on a transient basis to the base electrode of the solid state device. The oscillatory pulse is in the nature of a damped wave in which the first swing (or half-cycle) contains the most energy. Another diode poled to pass this first half-cycle charges a filter capacitor. The converted DC appears across the said filter capacitor, thereby providing a power source for the relaxation oscillator/spark gap pulser combination.

The levels of power involved in the device provide relatively good safety.

The details of the device according to the invention will be understood from the description hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

A single FIGURE comprising an electrical schematic depicts the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, the structure and operation of the device of the invention will be described.

The invention is particularly useful, efficient, and economical in connection with electrical power sources as represented by the block E.sub.o, such as are typically used in recreational vehicles. Although the invention is not so limited, a typical embodiment designed for operation from the 12 volt storage battery system of a recreational vehicle will be described.

On the drawing, the circuitry to the right of C1 (the filter/storage capacitor) requires a direct current voltage on the order of approximately 90 to 100 volts for satisfactory operation. The circuitry to the left of C1 (and including C1 itself) is devoted to the development of this higher direct current voltage from the 12 volt source.

The aforementioned U.S. Pat. No. 3,662,185, shows and describes the relaxation oscillator/pulser circuit for operating the spark igniter across the gap between the flame rod FR and the pilot light grounded enclosure PL. Basically, this circuit operates to charge up a capacitor C2, through a large value resistor R4, to the firing voltage of neon lamp L1, which is typically on the order of 60 to 75 volts. The firing of L1 essentially connects C2 across R6, the latter being a relatively low value resistor, through a current limiting resistor R5 and diode D3 which acts as a current "check-valve." Thus, a pulse is provided to the gate electrode of the silicon controlled rectifier CR1, bringing that device into conduction. That conduction and the resultant current pulse occurs around a loop including C1, the primary or pulse transformer T1, and the CR1 anode/cathode main current path. The impedance or internal resistance of the ringing-choke converter, is such that it could not supply or sustain such a current, consequently the said current pulse is sustained substantially only until the charge of capacitor C1 is appreciably decreased. At that time, both the effective voltage across the anode cathode circuit of CR1 and the CR1 gate electrode triggering pulse from the neon lamp relaxation oscillator will have both greatly decreased. Extinguishment of L1 through the "dumping" of C2 charge, starts a new cycle of recharing of C2 through R4. The diode D3 prevents the flow of any back current from the CR1 gate electrode during transient conditions accompanying the spark discharge between FR and PL. Transformer T1, which has a relatively large step-up ratio, is capable of producing a secondary voltage on the order of 16 Kilovolts to produce the spark discharge.

It will be noted that, as is known, the flame rod FR, acts as an anode of a high resistance diode in cooperation with the flame itself and the grounded housing of the pilot PL. Since the relaxation oscillator/sparking pulser circuitry (i.e., that to the right of C1) is to be inhibited, or disabled, once the pilot flame is actually established, use is made of the so-called flame rectification characteristic just described. The forward resistance of this "flame diode" is in the megohm range and, in order to serve the purpose of inhibiting the relaxation oscillator/pulser, must be supplied with current poled at a positive potential with respect to ground as applied to FR.

In the circuit of the drawing, the junction of C2, L1 and R4 also provides a return for the secondary of the pulse transformer T1. Between spark cycles, the flame diode (assuming the pilot flame is extant) permits some current through R4 and the said secondary of T1 to pass through the said flame diode. The value of R4 is chosen so that the flame conduction resistance and the said R4 act as a divider, reducing the potential at the said junction of L1, C2 and R4 to a value below the minimum firing potential of L1.

From the foregoing information, it will be seen that the source constituted by the DC-to-DC converter (ringing-choke oscillator) to the left of C1, must be positive at the upper end of R4. While there are many ways that this can be accomplished with a DC-to-DC converter, it is essential that it be accomplished in an efficient, low cost manner.

Since, as already indicated, a grounded negative storage battery source (E.sub.o) of 12 volts, for example, is also an initial constraint, the DC-to-DC must handle this situation without resorting to multi-winding transformers, or other more expensive expedients.

Before describing the ringing-choke converter of the present invention in detail, it may be useful to point out that prior art ringing-choke converter circuits for general application, are commonly more complex. See, for example, the text entitled "RCA Silicon Power Circuits Manual" (a publication of Radio Corporation of America as part of their technical series SP-51, dated 1969). Page 168 describes a typical prior art ringing-choke inverter (or converter) circuit.

The ringing-choke oscillator circuit of the present invention includes only a tapped tank coil or auto transformer T2, a single PNP transistor, a pair of diodes, a filter/storage capacitor and three resistors.

It will be apparent to those skilled in the electronic circuit arts that a PNP transistor Q1 is appropriate for the polarities indicated and aforementioned. In an initial condition, current from the positive pole of the source E.sub.o passes through diode D1 through T2. Most of this current follows the tap through the emitter of Q1 and passes through the emitter/collector current path of the said Q1 to the negative E.sub.o terminal (i.e., ground). The resistors R1 and R2 constitute a base biasing arrangement for Q1, such that, in the quiescent condition, Q1 is biased into a conducting condition substantially below saturation. The growth of current through the upper portion of T2, i.e., from D1 to the tap, induces a signal into the lower half of T2 which is regenerative in polarity as it reaches the base of Q1. That is, this regenerative condition is extant until Q1 begins to saturate, at which time the rate of current growth in the upper portion of T2 falls off. As is well understood in electromagnetic circuit theory, the induced regenerative signal aforementioned in the lower portion of T2 then quickly reverses and becomes degenerative, hastening the cutoff of Q1 until that portion of the cycle runs its course. Subsequently the reconduction of Q1 starts the cycle over again. Thus, the junction of R2 and R3 provides an alternating signal which is rectified by D2 through current limiting resistor R3 in order to charge capacitor C1.

Although the flame conduction referred to hereinbefore is effective to inhibit the further function of the relaxation oscillator/pulser by reducing the voltage at the junction of R4 and C2, the ringing-choke oscillator continues to operate and maintain the fully charged condition of filter/storage capacitor C1.

Typical circuit values for the embodiment of the FIGURE are given in Table I below. A typical operating frequency for the said ringing-choke oscillator is 20KHz.

TABLE OF TYPICAL COMPONENT TYPES AND VALUES ______________________________________ D1, D2 and D3 IN4002 Q1 MPSD 51 (Motorola) R1 4.7K.OMEGA. R2 470.OMEGA. R3 150.OMEGA. R4 22 Megohms R5 1K.OMEGA. R6 1K.OMEGA. CRI SCR C1 2.2 .mu. fd C2 0.001.mu. fd ______________________________________

Certain modifications and variations will suggest themselves to those skilled in these arts. Accordingly, it is not intended that the scope of the invention should be limited by the drawing or this description.

Claims

What is claimed is:

1. A spark pilot ingiter for gaseous and vaporous fuel systems including a fuel operated pilot, said igniter including a spark gap adjacent to said pilot, said igniter being operative from a low voltage first direct current power source, comprising:

a ringing choke oscillator connected to said first direct current power source for producing a second direct current voltage source higher than said power source;

charging means including a first capacitor and a series resistance, said first capacitor being connected to charge from said second direct current voltage source;

a first solid state switch device having main current carrying electrodes including an anode and a cathode and a control electrode capable of controlling the effective resistance between said anode and cathode from a relatively low to a relatively high value;

a high ratio step-up transformer having primary and secondary windings, said primary winding being connected in series with said main current carrying electrodes of said first solid state switch device and said second direct current voltage source, said secondary winding being operatively connected to said spark gap;

a relaxation oscillator connected to said second voltage source for producing periodic output voltage pulses, said voltage pulses being connected to said first solid state switching device control electrode to cause said resistance between said anode and cathode to assume said low effective resistance value momentarily, thereby to produce a pulse of current in said transformer primary and a corresponding stepped-up voltage applied to said spark gap contemporaneously with the occurrence of said relaxation oscillator output pulses thereby to effect ignition of said pilot;

means including a flame rod extending at least partially into the flame of said pilot, said flame rod being connected to provide a flame current path through said flame from a terminal of said transformer secondary;

and a return current path for the other terminal of said transformer secondary connected to a point in the circuit of said relaxation oscillator such that said flame current reduces the effective supply voltage to said relaxation oscillator below the point of operability of said relaxation oscillator.

2. Apparatus according to claim 1 in which said ringing choke oscillator comprises a first series current path having in order, a forward poled diode, an inductor, first and second resistors, all in series across said first power source, said diode connecting to a first terminal of said first power source and the second of said resistors connecting to a second terminal of said first power source;

and including means comprising a tap along the winding of said inductor and a second solid state device having an emitter-collector current path and a base electrode, said emitter-collector current path being connected from said inductor tap to said second terminal of said first power source, and said base electrode being connected to the junction of said resistors, thereby to produce oscillatory pulses of relatively high peak voltage at the junction of said inductor and the first of said resistors with respect to said first power source second terminal.

3. Apparatus according to claim 2 further including a third resistor and second forward poled diode in series, connected to said oscillatory pulses, and a second capacitor connected on one terminal through said series third resistor and second diode to said oscillatory pulses and on the other terminal to said first power source second terminal, thereby to produce said second voltage source available across said second capacitor.

4. Apparatus according to claim 3 in which said first and second resistors are selected to provide a base electrode bias for said second solid state device to produce a normally conducting condition of said emitter-collector current path.

5. Apparatus according to claim 2 in which said first and second resistors are selected to provide a base electrode bias for said second solid state device to produce a normally conducting condition of said emitter-collector current path.

6. Apparatus according to claim 3 in which said inductor tap is located such that, so long as said second solid state device emitter-collector current is increasing a regenerative signal is induced in the portion of said inductor not in series with said emitter-collector current path, and so that, upon saturation of said second solid state device, a degenerative signal is induced in said portion of said inductor not in series with said emitter-collector current path.

7. Apparatus according to claim 6 in which said first direct current power source first terminal is the positive terminal and said second terminal thereof is the negative terminal.

8. Apparatus according to claim 7 in which said second solid state device is a PNP transistor the collector electrode of which is the grounded terminal of said first and second power sources.