US3364971A - Ignition system for fuel burners - Google Patents

Description

Jan. 23,1968

. HAYES IGNITION SYSTEM FOR FUEL BURNERS Filed June 28, 1966 TRS fLz

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- ATTORNEY United States Patent O 3,364,971 IGNITIN SYSTEM FOR FUEL BURNERS Thomas E. Hayes, Goshen, Ind., assigner to Penn Controis, Inc., Wheaton, lll., a corporation of Delaware Filed June 28, 1966, Ser. No. 561,198 9 Claims. (Cl. 15S- 28) ABSTRACT F THE DISCLOSURE In a control for fuel burners the time required to charge a capacitor limits the attempt to ignite the fuel. Should the attempt be unsuccessful, the supply of fuel to the burners is terminated. Fail-safe features are provided for misoperation of the llame detector, causing the timing capacitor to remain fully charged preventing further attempts to ignite the fuel. Mechanism is Vprovided for discharging the capacitor for new attempts -to ignite the fuel, which dischanging mechanism differentiates between normal circuit interruption, as for example through thermostatic action, and between failure to ignite or flame out of the burner.

This invention relates to an ignition system for fuel burners and more particularly with respect to such systems which utilize a capacitor to time the igniting operation of the burner.

Attempts have been made in the prior art to provide such systems with capacitor timed igniting operations, termed trial for ignition, as for example the U.S. patent to Earl I. Weber, 3,174,534, issued Mar. 23, 1965. It is desirable that such ignition systems be of simple construction for reasons of economy in manufacturing and operation and yet provide reliable operation. Since the failure of ignition systems to operate properly may cause considerable damage it is desirable that failure of the control results in its being operated to avcondition which stops the feeding of fuel to the burner. Such operation of an ignition control may be termed fail-safe operation.

It is, therefore, an object of the invention to provide an improved ignition control system which is of simple, economical construction and yet provides reliable operation.

It is another object to provide such ya control which responds -to malfunctions of its own components by placing the burner in a safe condition and yet utilize only one control relay.

In carrying out the invention, according to a preferred embodiment, upon a call for heat, a first circuit is established for the energizing coil of a control relay through a timing capacitor; the initial charging current ow through the capacitor providing sufficient energization for operation of the relay. Operation of the relay energizes fuel delivery means to provide fuel for ignition simultaneously with energization of the igniter means for igniting such fuel. The capacitor charging -rate is used to time the igniting operation, providing a time contest between the capacitor attaining its charged condition and the fuel igniting means igniting the fuel. Under conditions where the fuel is ignited, the burner flame is detected 4by a photoconductive cell which establishes a holding circuit for the control relay, bypassing the timing capacitor lbut subject to lthe contacts of a demand switch, such as a thermostat.

In the absence of the photocell detecting a flame, the relay releases as the capacitor arrives at its charged value, completing the trial for ignition and ceasing delivery of fuel to the burner.

As part of the fail-safe feature of the control in the event that the photocell becomes shorted, a second charging circuit for the timing capacitor is provided. This circuit maintains the capacitor in charged condition, preventing energization of the control relay.

The timing capacitor is also maintained in its charged condition, preventing energization of the control relay, under conditions where the photocell is inadvertently excited during a shutdown period.

Under conditions where the photoconductive cell becomes open circuited, the holding circuit for the control relay cannot be established and the system locks out in a safe condition.

A fuse in the relay circuit is selected of the type to open the circuit, if the charging capacitor or a diode in series therewith shorts producing a steady state current through the coil, but to remain closed when subjected to the normal charging current pulse during a trial for ignition. This fuse may be termed a slow blow fuse.

A relatively low impedance is provided for shunting connection with the timing capacitor by a pair of rel-ay contacts which are normally opened for both the operated and unoperated condition of the control relay. These contacts are designed so as to place the low impedance in shunting relation with the timing capacitor to quickly discharge the timing capacitor only under conditions where the control relay releases due to the relay circuit being interrupted by the thermostat contacts or a temporary interruption of the applied line voltage. This quick discharge of the timing capacitor allows immediate restarting of the fuel burner control. However, should the relay release be due to a failure to ignite, reenergization of the control relay for another trial for ignition cannot be undertaken until the timing capacitor has been discharged, providing a desired lockout These contacts, therefore, distinguish whether a control relay release is due to normal thermostat action or momentary line voltage interruption or to a flame-out or failure to ignite.

Features and advantages of the invention will be seen from the above, from the following description when considered in conjunction with the drawing, and from the appended claims.

In the drawings:

FIG. 1 is a schematic line ldiagram of the ignition control circuits, embodying the invention, with the circuits arranged in across-the-line form;

FIG. 2 is a simplified diagrammatic representation of a portion of a furnace showing the fuel feeding means, burner, igniter and photocell for the subject control;

FIG. 3 is a simplified diagrammatic elevational view of a control relay utilized in the circuits of FIG. 1 and including contacts which distinguish between different releases of the rel-ay; and

FIG. 4 is a sectional view taken along the line 4 4 of FIG. 3.

For convenience, the invention will be described as applied to an ignition system for a liquid fuel burner utilizing a lburner motor and an igniter operated from the secondary of a transformer, it being understood, nevertheless, that the invention is as applicable to other ignition systems including gas burner types.

Referring to FIGS. 1 and 2, L1, L2 designate supply lines connected to any conventional alternating current power source (not shown) for supplying power to the circuit components. M designates a split phase burner motor for propelling fuel 8 to a burner B in a furnace 9, for ignition, while IGN indicates an igniter for igniting such fuel, the igniter being mounted on furnace 9 in any convenient manner in igniting relation to the fuel burner and being energized by an ignition transformer designated TRS. RL designates a control relay, while C1 designates the ignition timing capacitor. PC designates a photoconductive photocell which is mounted on furnace 9 to detect the ame of the burning fuel 8 at the burner B.

Resistors are generally designated R, while rectifiers are generally designated CR, sufx letters being added to distinguish the resistors and rectiers from like components. F designates a fuse of the slow blow type which is selected to conduct ignition timing pulses during charging of capacitor C1 but to open the charging circuit under conditions where a steady state current of a certain magnitude flows through it. T designates contacts of a snapaction type thermostat located in a space to be heated.

Contacts of relay RL bear the same letter designation as the relay with numeral suflixes added to distinguish one pair of contacts from the other, all contacts being shown for the released condition of the relay. Contacts RL4 of the relay are constructed to distinguish vbetween a release of relay RL under conditions due to power interruption or opening of thermostat contacts T and a release due to failf ure to ignite or llame-out. When relay RL releases due to power interruption or the snap opening of thermostat contacts T, contacts RL4 vibrate between closed and opened position for a certain time and then remain open.

The relay construction to eiect this will now be described with reference to FIGS. 3 and 4, wherein the relay is shown as a pile-up type comprising a coil RL mounted on a magnetic frame, generally designated 10. Frame includes an armature 12 hinged at 13 for magnetic coaction with pole face 14A of a pole piece 14 when coil RL is energized. A spring 16 biases armature 12 upward against the magnetic attraction of pole piece 14. An actuating bar 17 mounted for movement with armature 12 actuates leaf-type spring contacts cantilevered to co-act with associated stationary contacts, the contact pairs being designated RL1, RL2 and RLS in accordance with their designations in the FIG. l circuitry.

The contact pair RL4 of FIG. l is shown in FIGS. 3 and 4 as a movable contact RL4a mounted for movement with armature 12 to co-act with a stationary contact RL4b mounted on U-shaped bracket 19. RIAa is positioned near the free end 1Sa of a leaf spring member 18 which is attached at its other end to armature 12 for movement therewith, Mounted on the free end 18a of spring member 18 is a certain mass 20. Mass 20 and spring member 18 are selected to provide a spring-mass which will vibrate at a certain frequency and amplitude under conditions where the power through coil RL of the pile-up relay is interrupted abruptly, as for example by the snap separation of thermostat contacts T of FIG. 1 or a power interruption to the circuitry.

Under conditions where the holding voltage through coil RL is interrupted abruptly, such as by power interruption to the circuits of FIG. 1 or by the snap opening of thermostatic contact T, armature 12 (FIGS. 3 and 4) under the influence of its biasing spring 16, releases with a snap, as is characteristic of all but specially designed relays. Such a snap causes oscillation of springmass 18-20 at an amplitude sufficient to vibrate movable contact RL4a into successive engagement with stationary contact RL4b, thereby, repeatedly connecting low impedance shunt R4 (FIG. l) in shunting relationship with timing capacitor C1. The duration of the oscillation under such snap release of armature 12 (FIGS. 3 and 4) is calculated to discharge capacitor C1 (FIG. 1) sufficiently to enable relay RL to be re-energized immediately should power be reapplied to its energizing coil.

However, under conditions where the holding voltage of relay RL is passed through slowly in a decreasing direction, as for example, under conditions where capacitor C1 charges at a decreasing rate, to its cutout value, armature 12 (FIGS. 3 and 4) releases without enough snap to cause contact RL/-la to vibrate to engage contact RL4b suiciently to discharge capacitor C1. Contacts RL4 (FIG. l) of the relay, thus, distinguish between a snap type release of armature 12 (FIGS. 3 and 4) and a slower release. This characteristic is used to provide safe ignition operation of the burner, as will be described next.

In one tested embodiment of the invention which operated satisfactorily the following circuit components were utilized.

Resistors Capacitor Rectifiers R1, R2 (100 kilo-ohms). R3 (I mega-ohm). R4 (500 ohms).

C1 (50 microfarads).

CRI, CRS (IN4005).

CB2 (IN4003).

In operation, assume that thermostat contacts T (FIG.y

motor M, causing it to propel fuel to the lburner for ignition by the igniter IGN which is simultaneously energized through transformer TRS by the closing of contacts RL1.

Relay RL also separates its contacts RL2 and closes its contacts RLS, preparing a holding circuit for relay coil RL through thermostat contacts T and photoconductive cell PC. Resistor R2 is selected of such value as to limit current through this holding circuit to a value insuicient to operate relay RL but suicient to maintain the relay, if already operated, in operated condition provided that the resistance of photoconductive cell PC is reduced through its excitation by the burner flame.

Next assume that the fuel is ignited, exciting photocell PC to reduce its resistance sutliciently to provide a holding current through coil RL. Under such conditions, relay RL remains operated through its holding circuit, con- -tinuing operation of the fuel burner subject to satisfac-V tion of the demand for heat as indicated by thermostat contacts T.

Now assume instead in the above case that the fuel fails to be ignited. Under such conditions, as capacitor C1 charges to its cut-off value, current flowing .through it and coil RL falls to a value insufficient to maintain the relay energized. It may, also, be noted that since photoconductive cell PC is not excited by a llame, a holding circuit for coil RL is not established. Relay RL releases, reseparating its contacts its contacts RL1, RLS andreclosing contacts RL2, restoring the circuit to its initial condition. This completes the trial for ignition, the duration of which is timed by the R-C value of the above described ignition circuit through capacitor C1. Reclosing of contacts RL2 is without effect, since the resistance of photoconductive cell PC under its unexcited condition is sufficiently high so as to electrically isolate capacitor C1 and coil RL from supply line L1.

The charged condition of capacitor C1 prevents a second trial for ignition -until thermostat contacts T are reopened and capacitor C1 discharges sufficiently through resistor R3, thus, providing a safety period after a trial for ignition which resulted in a failure to ignite the fuel..

Other provisions for fail-safe and reliable operation are included in the above circuitry. For example, since the only holding circuit which may be established for coil RL is through thermostat contacts T, shorting of photocell PC while the fuel burner is in operation causes relay RL to continue operation of the burner only so long as the thermostat contacts T remain engaged calling for heat. Assuming that such a short circuit occurs and continues after the heat requirement is satisfied, thermostat contacts T reopen, causing relay RL to release, as was described above. Relay RL'in releasing, recloses its contacts RL2, causing a trickle of current to ow through shorted photoconductive cell PC, resistor R1 and diode CR2 slowly charging capacitor C1 to fully charged condition. The resistance of resistor R1 is selected to prevent such current iiow from being of sufficient magnitude to cause relay RL to reoperate. Under such conditions, on the next demand for heat, as thermostat contacts T close, capacitor C1 is already charged sufticiently to prevent the flow of current through relay coil RL in sufiicient magnitude to cause reoperation of the relay. The ignition system is thus safely locked out.

The system also locks out in this manner under conditions of photocell PC being inadvertently excited during periods of no demand by thermostat contacts T, as for example, by ambient light or an undesired flame at the burner.

Next assume that photocell PC becomes open-circuited. Under such conditions relay RL is operated by the initial charging current through thermostat contacts T and capacitor C1, as was previously described. However, at the end of the trial for ignition, that is, when capacitor C1 charges to its cut-off value, relay RL releases, since the holding circuit through photocell PC cannot be established.

Next assume that either rectifier CR1 or capacitor C1 becomes short-circuited, producing a relatively high steady state current through coil RL. Under such conditions, slow blow fuse F opens, interrupting the circuit for coil RL, causing the ignition system to operate to a safe condition. As was previously explained, fuse F is such as to remain conducting under conditions Where the normal charging pulse to capacitor C1 ows through it, but to open the circuit under conditions Where a steady current of sufficient magnitude to operate relay RL flows through it.

After an unsuccessful trial for ignition or ame out of the burner, capacitor C1 must discharge through its discharge circuit provided by resistor R3 before another trial for ignition may be attempted. This prevents accumulation of fuel in the burner and provides safe operation. This waiting period, however, is not necessary for safety and is undesirable under conditions where an interruption of energizing power to coil RL is due to a momentary power interruption which quickly stops the burner motor M or one due to normal thermostat control. Under Such conditions, it is desirable to immediately restart burner operation. Under conditions of power interruption or snap opening of thermostat contacts T, the current flowing through coil RL is stopped abruptly causing a snap-action release of the relay armature 12 (FIG. 2). Such snap action release, as was previously described, causes armature 12 to snap upward with sufficient force to cause contact RL4a (FIGS. 3 and 4) to vibrate and repeatedly engage contacts RL4b. Such momentary repeated closing of contacts RIA (FIG. 1) connects resistor R4 in shunting relationship across timing capacitor C1 immediately discharging capacitor C1. The oscillations of spring-mass 1820 (FIGS. 3 and 4) quickly dampen to place contacts RL4a and RL4b in their normally open position. This places the ignition control circuit in condition for immediate restarting of the fuel burner without the aforementioned capacitor discharge waiting period and lock out.

It may be noted that the low impedance shunt for quickly discharging capacitor C1 need not be a resistor but may instead be a second capacitor (not shown) for capacitor C1 to discharge into.

It is, thus, seen that the subject ignition control is of simple and economical design, yields reliable operation and automatically responds to malfunctions of its own circuit components for operating to a safe condition, thereby, maximizing its ability to control ignition of burners safety.

As changes can be made in the above described construction and many more apparently different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter 6 contained in the above descripition or shown on the accompanying drawing be interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. A control for a fuel burner including means for feeding fuel to a burner and an electric igniter energizable and positioned for igniting at said burner said fuel, said control comprising;

a source of A.C. power,

a control relay including actuating coil and diode means constructed and arranged to enable operation of said relay from said A.C. power source,

a capacitor,

fuel demand means including switch means for electrically connecting said power source and said capacitor into energizing electrical relation with said control relay coil and diode means for actuating said control relay,

flame detecting means having a normally high resistance which decreases to a relatively low resistance when it detects flame, said flame detecting means being positioned to detect the dame vof fuel burning at said burner,

a first current limiting resistor interconnecting said flame detecting means in series circuit with said control relay coil and diode means, said first resistor being of such value as to limit current flow through said relay coil and diode means under said low resistance conditions of said flame detecting means to below the pull in value but above the hold in value of said relay,

a diode and a second current limiting resistor electrically connecting said ame detecting means in a charging circuit for said capacitor, said second resistor being selected of such value as to limit current to said capacitor to less than the pull in value of said control relay for charging said capacitor under conditions where said flame detecting means is of negligible resistance,

and circuit transfer means controlled by said relay for,

upon operation of said control relay, electrically disconnecting said charging circuit of said capacitor and instead connecting said flame detecting means-resistor series circuit through said demand switch to said power source to establish a holding circuit for said relay, and for reconnecting said detecting means-resistor series circuit to said power source by shunting said demand switch upon release of said relay.

2. A control as set forth in claim 1 wherein said ame detecting means is a photoconductive cell.

3. Control apparatus as set forth in claim 1 wherein said demand means is a thermostat positioned in a space heated by heat generated by said fuel burner.

4. Control apparatus as set forth in claim 1 wherein said transfer means comprises switching contacts of said control relay.

5. Control apparatus as set forth in claim 1 wherein said control relay includes contacts for controlling energization from said power source of said fuel feeding means and said igniter means.

6. Control apparatus as set forth in claim 1 wherein there is also provided a low impedance shunt connectable in shunting relation to said capacitor,

and wherein there is provided circuit interrupting means subject to release of said control relay for connecting said shunt across said capacitor,

said circuit interrupting means comprising contact means normally open for both the operated and released condition of said relay but constructed to differentiate between a relatively snap type release of said relay and a slower release by vibrating into successive closed momentary engagement only under conditions of said snap release.

7. Control apparatus as set forth in claim 1 wherein there is, also, provided a discharge circuit of substantially negligible resistance for said capacitor,

and wherein there is provided means for selectively connecting said discharge circuit into shunting relation with said capacitor, said connecting means including a spring mass actuatable by the release of said relay, a movable contact mounted on said spring mass for movement therewith, a stationary contact mounted for coaction with said movable contact, said spring mass being selected for causing successive momentary engagement or" said movable contact with said stationary contact under conditions Where said spring mass is actuated by a snap type release of said relay but to avoid such momentary engagement under conditions of a relatively slower release of said relay. S, Control apparatus as set said relay includes an armature,

and wherein said vibrating contact means include an elongated spring member cantilevered from said armature for movement therewith, and a movable contact positioned near the free end of said cantilevered spring member,

forth in claim 6 wherein a predetermined mass attached to said free end, and

a second Contact stationarily positioned in relation to said movable contact for coaction therewith under conditions where a snap release of said armature causes suicient oscillation of said spring member, mass and movable contact to vibrate said movable contact into successive momentary engagement with said stationary contact.

9. Control apparatus as set forth in claim 1 wherein there is provided current sensitive circuit interrupting means in series with said control relay coil, said current sensitive means being selected to conduct the normal coil energizing current pulse flowing through said capacitor and said control relay coil but to interrupt current flow through said coil under conditions of steady state en' ergizing current ilow.

References Cited UNITED STATES PATENTS 3,042,107 7/1967 Burckhardt 158-28 3,174,528 3/1965 Staring 158-28 3,304,989 2/1967 Alexander et al. 15S- 28 JAMES W. WESTHAVER, Primary Examiner.

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