US3311157A

US3311157A - Mertler etal. thermal probe and pilot burner

Info

Publication number: US3311157A
Authority: US
Publication date: 1967-03-28
Anticipated expiration: 1984-03-28

Description

March 1967 C.$.MERTLER ETAL 3,311,157

THERMAL PROBE AND PILOT BURNER 2 Sheets-Sheet 1 Filed July 9, 1964 p w E E M M W M m m 0 3 N? r 4 W in r fi mi ,0 a 7 4 M/ x M m M344 5 March 28, 1967 c, 5, ER ETAL 3,311,157

THERMAL PROBE AND PILOT BURNER 2 Sheets-Sheet 2 Filed July 9, 1964 s m; w m; W W i 2% 5 w A W;

United States Patent 3,311,157 THERMAL PROBE AND PILOT BURNER Charles S. Mertler and Truman H. Cline, both of Mansfield, Ohio, assignors to Stevens Manufacturing Company, Inc., a corporation of Ohio Filed July 9, 1964, Ser. No. 381,419 4 Claims. (Cl. 158-125) This invention relates to a burner ignition unit for gas appliances.

Commonly, in various gas appliances, such as in the oven of a range, a main burner is arranged to be lighted by a pilot burner which is provided with a flarme switch whose purpose is to detect whether the pilot burner is on or off. This flame switch controls a valve in the gas supply line to the main burner, so that the gas supply to the main burner will be cut off if the pilot burner is off. The flame switch has a thermal probe which, when heated by the pilot burner, expands to operate the switch. For proper operation, the thermal probe must be properly positioned with respect to the pilot burner flame, so that it will operate in accordance with the performance characteristics for which it has been calibrated. For example, if the pilot flame is not close enough to the thermal probe or is not properly directed with respect to the thermal probe, the -probe will not heat fast enough nor properly to operate the switch in the manner intended.

Prior to the present invention, conventional arrangements of this type have had separate mountings for the pilot burner and the associated thermal probe. This required the gas appliance manufacturer to carefully mount the pilot burner both with respect to the main burner and with respect to the thermal probe of the flame switch. In addition, separate mounting brackets were required for the pilot burner and the flame switch, adding to the cost and physical size of the pilot burner and flame switch installation.

Where automatic electric ignition of the pilot burner was provided for, the prior arrangements commonly did not provide for operation of the pilot burner ignition coil, the flame switch, and the electrically-operated main burner valve controlled by the flame switch from a single low voltage source.

The present invention is directed to a novel pilot burner and flame switch unit which avoids these and other disadvantages inherent in prior arrangements for the same general purpose.

In accordance with the present invention the pilot burner and the flame switch, including the thermal probe, are constructed as a rigid, compact unit whose component parts are accurately positioned with respect to one another to provide the calibrated performance characteristics, and only a single mounting is required for the entire unit. The gas appliance manufacturer is required only to mount the unit so as to position the pilot burner properly with respect to the main burner in the appliance.

The proper positioning of the pilot burner with respect to the thermal probe is assured by the unitary, rigid construction of the pilot burner and flame switch unit.

Preferably, also, the present ignition unit includes an electric ignition coil firmly supported in igniting relationship to the pilot burner and electrically connected to the flame switch to light the pilot burner automatically when the usual pilot burner ignition control is operated by the user of the appliance. Both the ignition coil and the flame switch may be connected to a single low voltage source of electricity, as is the electrically-operated main burner valve which is controlled by the flame switch, thereby simplifying the electrical power supply requirements for the ignition system embodying the present ignition unit.

It is a principal object of this invention to provide a novel and improved burner ignition unit for gas appliances.

Another object of this invention is to provide such an ignition unit which is compact, readily mounted, and requires no calibration adjustment when being installed in the appliance.

Another object of this invention is to provide such an ignition unit in which the pilotburner and the flame switch are embodied in a unitary structure which insures proper positioning of the pilot burner and the thermal probe of the flame switch with respect to one another.

Another object of this invention is to provide a novel and improved electric ignition unit which simplifies the power supply connections for the complete ignition system in which it is embodied.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a top plan view of the presently-preferred embodiment of the pilot burner and flame switch unit according to the present invention;

FIGURE 2 is a longitudinal view, partly in elevation and partly in section, of the FIGURE 1 unit;

FIGURE 3 is an end elevational view of the unit, taken from the left end of FIGURE 2;

FIGURE 4 is an enlarged cross-section taken along the line 4-4 in FIGURE 2;

FIGURE 5 is a fragmentary longitudinal section taken along the line 55 in FIGURE 4 on a more enlarged scale;

FIGURE 6 is an enlarged fragmentary perspective view of the switch in the present unit; and,

FIGURE 7 is a simplified schematic diagram of a burner ignition circuit in which the present pilot burner and flame switch unit is embodied.

Referring first to FIGURES 1 and 2, the ignition unit of the present invention comprises a rigid housing 10, an elongated pilot burner tube 11 fixedly mounted on the housing and projecting therefrom and presenting flame ports 12 in spaced relation to the housing, an elongated thermal probe 13 supported by housing 10 and projecting therefrom generally parallel to the pilot burner tube to be heated by the pilot flame at the latters flame ports 12, and a single pole, double throw switch 14 (FIGURE 2) positioned inside housing .10 to be operated by thermal probe 13. A glow coil or ignition coil 15 is rigidly supported from housing 10 in a position to light the pilot burner. This glow coil is electrically connected to switch 14 so that the glow coil may be energized first to light the pilot burner, after which the thermal probe becomes heated by the pilot burner and operates the switch to deenergize the glow coil.

The switch housing 10 comprises a rigid metal front plate 16, a heat-resistant insulating body 17 such as a ceramic body, and a thin layer 18 of insulation (such as mica) sandwiched between them. A pair of screws 19 (FIGURE 3) hold the housing parts assembled together. The ceramic body 17 is formed with a recess 20 of approximately rectangular outline, as shown in FIGURE 4,

in which the switch 14 is located. An opening 21 (FIG- URE 2) extends through the front plate 16 and the insulation layer 18 into this recess. This opening loosely receives the inner end of the thermal probe 13.

The front plate 16 of the housing has a depending portion 16a which projects below the bottom edge of the housing body 17, as shown in FIGURES 2 and 3. The pilot burner tube 11 extends through this portion of plate 16 and is welded at 22 to the front face of the latter. From this location, the pilot burner tube 11 extends away tend perpendicular to one another.

from the front of the switch housing horizontally and then upward at an acute angle and then horizontally perpendicularly away from the housing. At the lastmentioned horizontal portion away from the switch housing, the pilot burner tube presents the longitudinally spaced, upwardly directed flame ports 12 and presents at its underside an ignition port 23. The right end or outboard end of the pilot burner tube 11 is closed by a rigid metal end plate or support member 24. The outboard end of tube 11 carries the thermal probe 13, and this is conveniently accomplished by carrying it in the end plate 24, which in turn is fastened to the outer end of the burner tube 11, as by welding at 25.

At the back side of the front plate 16 the pilot burner 11 extends horizontally in back of the switch housing and is rigidly attached to an externally screw threaded, annular inlet fitting 26. In use, fitting 26 is connected to a gas line, which supplies fuel that flows through the pilot burner tube 11 and issues from the latter at the ignition port '23 and the flame ports 12. The gas line may also support the entire assembly.

The pilot burner tube 11 is made of a suitable metal, such as a stainless steel, which preferably has a low thermal coeificient of expansion.

The thermal probe 13 is an elongated tubular push rod of a suitable metal, such as another type of stainless steel,

, which has a substantially different thermal coeflicient of expansion from that of the pilot burner, preferably a higher rate. As already mentioned, the left end of push rod 13 is loosely received in the opening 21 leading into the recess 20 in the housing body 17. This end of the push rod 13 is crimped over a rigid switch-operating pin 27 of ceramic or other suitable electrical insulation material, which projects into the recess 20 in the switch housing. The opposite (right) end of push rod 13 is slidably received in a hollow adjusting screw 28, which is threadedly mounted in the end plate 24. A ball 29 is engaged between this end of push rod 13 and the inner end of the conical recess 60 in the adjusting screw. The ball 29 seating against the conical recess 60 permits a degree of freedom of the end of push rod 13 in the adjusting screw 28 for self-aligning purposes. Alternatively, the push rod 13 may be fixed to the adjusting screw 28, if desired.

The switch 14 in the switch housing recess 20 comprises an electrically conductive carrier or leaf spring 30 (FIG- URE 6) having a flat mounting portion 31, which is seated against the bottom wall 32 of the recess by an electrically. conductive rivet 33, as shown in FIGURE 5. Rivet 33 extends through the back wall of the housing body 17 and at the back face of the latter it is attached to a rigid first terminal 33a (FIGURE 3). The leaf spring 30"presentsan elongated, flexible and resilient, normally flat leaf 34, which is attached to the mounting portion-31 by an integral U-shaped portion 35, which provides a cantilever support for leaf 34. The switchoperating pin 27 extends perpendicular to leaf 34 and is positioned to engage the latter a short distance away from the U-shaped portion 35, as shown in FIGURE 6. The leaf 34 has an opening 34' close to where it is engaged by the operating pin 27 for the purpose of access to the rivet 33. At its opposite free end the leaf 34 carries movable contact means in the form of first and secnd wire

movable contact members

36 and 37 on its opposite faces. The leaf spring 30 constitutes a movable, electrically conductive carrier for the

movable contacts

36 and 37.

The first movable contact member 36 is positioned in confronting relationship to a first fixed wire contact member 38, which is attached to a rigid, stationary, electrically conductive switch arm 39 carried by an electrically conductive rivet 40. The

switch contact members

36 and 38 ex- Rivet 40 extends through a spacer 40c and through the back wall of the I housing body 17 and at the back face of the latter it is "connected to'a rigid second terminal 40a (FIGURE 3),

which projects down beyond the switch housing. As shown in FIGURE 2, terminal 46a presents a rigid, forwardly extending, horizontal leg 40b at one side of the pilot burner tube 11.

The second movable contact member 37 carried by leaf 34 is positioned in confronting relationship to a second fixed wire contact member 41, which is attached to an electrically conductive rivet 42.

Switch contact members

37 and 41 extend perpendicular to one another. Rivet 42 extends through the back wall of the housing body 17 and at the latters back face it is connected to a third terminal 42a, which projects to one side of the switch housing, as shown in FIGURE 3.

The leaf spring 30 has an inherent bias such that cantilever leaf 34 normally positions the first movable contact 36 to engage the first fixed contact 38 and positions the second movable contact 37 out of engagement with the second fixed contact 41. When the operating pin 27 moves to the left in FIGURES 2, 5 and 6, it displaces the leaf 34 against the spring bias to move the first movable contact 36 out of engagement with the first fixed contact 38 and to move the second movable contact 37 into engagement with the second fixed contact 41.

A rivet 43 mounts a fourth terminal 43a on the back of the housing body 17. This terminal has a forwardly projecting rigid leg 43b (FIGURES l and 3) which extends at the opposite side of the pilot burner tube 11 from the terminal leg 40b.

The ignition coil 15 is electrically fastened at its opposite ends to the free ends of the terminal legs 40b and 43b. With this arrangement, the ignition coil is supported by the terminal legs 40b and 43b in close proximity to the ignition port 23 of the pilot burner tube 11 and is connected electrically between the second and

fourth terminals

40a and 43a.

A shield plate 44 is fastened, as by welding, to the burner tube 11 and projects rearwardly horizontally below the terminal legs 40b and 43b and the glow coil 15 to protect these parts. This shield helps to prevent drafts from striking the pilot flame which might blow it out. Also a lanced tongue 62 in the shield 44 carries an insulating tube 63 which supports the center of the ignition coil 15 against sagging.

With this construction of the pilot burner and flame switch unit, the pilot burner 11 and the thermal probe 13 are properly positioned with respect to one another by virtue of the rigid mounting of the pilot burner on the switch housing 10 and the sliding fit of the thermal probe in the same switch housing. There is no possibility that they may become misaligned by careless or rough handling by the personnel installing them on the gas appliance. Only a single mounting bracket is required for the complete unit, and when installing the unit the only matter of concern to the installer is to position the pilot burner properly with respect to the main burner of the appliance. This enables a more exact mounting of the pilot burner with respect to the main burner; Also, the present ignition unit, due to its unitary construction, is extremely compact and may much more readily be used with small sized main burners and in compact heaters. The ignition coil, pilot burner and flame switch of the present ignition unit are all properly positioned with respect to each other by the novel unitary, rigid construction described hereinbefore.

The flame switch can be readily calibrated simply by adjusting the screw 28, whose position determines the position of the thermal probe 13 and the switch operating pin 27 at normal ambient temperatures.

When the pilot burner 11 is lighted, its flame at ports 12 heats the thermal probe 13. Both the pilot burner and the thermal probe are heated, but the probe 13 expands at a much faster rate when heated. Since the right end of the thermal probe 13 is supported by the end plate 24, the thermal probe will move to the left relative to the pilot burner tube 11 and the operating pin 27 carried by the thermal probe will displace the switch leaf 34 against its spring bias to open the normally-closed

first contacts

36, 28 and to close the normally-open

second contacts

37, 41.

An alternative arrangement is to have the burner tube 11 and probe 13 of the same material. This provides complete ambient temperature compensation. Since the probe 13 is in the pilot flame and the burner tube 11 is not, there is a temperature differential between these two parts, and hence a differential expansion to actuate the switch. In either case the thermal expansion of the probe 13 is greater because of the higher temperature of this probe.

FIGURE 7 shows the foregoing ignition unit schematically in an oven burner ignition circuit.

The first terminal 330 of the present ignition unit is connected to the lower end of a secondary winding 45 of a step-down transformer 46, whose primary winding 47 is connected through a switch 48 across a conventional 110120 volt A.C. house current source 49. In one practical embodiment, the secondary voltage of the transformer is 12 volts.

The upper end' of the transformer secondary winding 45 is connected through a clock switch 50, an oven thermostat switch 51 and a conductor 59 to the fourth terminal 43a of the present ignition unit.

Also, conductor 59 is connected to the third terminal 42a of the present ignition unit through an operating coil 52 for a valve 53 connected in the gas supply line to a main burner 54 (either the bake burner or the broil burner) in the oven. A manually operable main shutoff valve 55 is connected between the gas inlet manifold 56 and the electrically-operated main burner valve 53.

The switch 48 is under the control of a manually operable control knob 57. The control knob also is arranged to operate a pilot burner valve 58 connected to control the flow of gas from the outlet side of the main shutofr" valve 55 to the pilot burner 11.

Initially, with the pilot burner unlit, the temperature of the thermal probe 13 will be such that the

first switch contacts

36 and 38 will be closed and the

second switch contacts

37 and 41 will be open, as shown in FIGURES 5 and 7.

Assuming that the clock switch and the oven therlowing takes place:

Gas is supplied to the pilot burner 11 and escapes from the ignition port 23 and the flame ports 12 of the latter.

The ignition coil 15 is energized from the transformer 46 by way of the first terminal 33a, the

first switch contacts

36 and 38, the second terminal 40a, through the ignition coil 15 and thence to fourth switch terminal 43a. The ignition coil ignites the gas at the ignition port 23 and the resulting flame at the pilot burner flame ports 12 heats the thermal probe 13.

Due to their different rates of heat expansion, the thermal probe 13 expands lengthwise with respect to the pilot burner tube 11, and consequently, the thermal probe moves to the left in FIGURE 2, forcing the switch-operating pin 27 inward against the spring leaf 34 to open the normally-closed

first switch contacts

36 and 38 and to close the normally-open

second switch contacts

37 and 41.

The opening of the

first switch contacts

36 and 38 disconnects the energization circuit for the ignition coil 15.

The closing of the

second switch contacts

37 and 41 completes an energization circuit for the valve-operating coil 52 from transformer 46 by way of the first switch terminal 33a, the

second switch contacts

37, 41 and the third terminal 42a. The energization of coil 52 through this circuit opens valve 53, which permits gas to flow to 6 the main burner 54 where it will be ignited by thepilot burner 11.

If the pilot burner goes out, the thermal probe 13 will contract in length as it cools and will retract the switchoperating pin 27 to permit the

second switch contacts

37 and 41 to open and the

first switch contacts

36 and 38 to close. This will shut off the main burner 54 and will energize the ignition coil 15 again to relight the pilot burner 11, after which the

second switch contacts

37 and 41 will close again to re-open the main burner valve 53.

The present arrangement of the switch contacts, the terminals and the ignition coil is advantageous in that it enables a single low voltage power source to provide the power supply for the complete ignition system.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A burner ignition unit comprising a housing having a recess therein and an opening leading into said recess,

an elongated pilot burner attached to said housing and projecting therefrom,

an ignition coil positioned to ignite the pilot burner,

terminals attached to said housing and rigidly supporting said ignition coil and providing electrical connections thereto,

a support member attached to the end of said pilot burner away from said housing,

an adjusting screw threaded in said support member and having a recess,

a thermal probe supported at one end in said adjusting screw recess and extending therefrom toward said housing and having a free end slidably disposed in said opening in the housing, said thermal probe being positioned to be heated by the pilot burner and having a thermal expansion substantially greater than that of said pilot burner,

and a switch in said housing recess positioned to be operated by said thermal probe as the latter expands longitudinally relative to said pilot burner.

2. A burner ignition unit comprising a housing having a recess therein and an opening leading into said recess, an elongated pilot burner attached to said housing and pro ecting therefrom,

a thermal probe supported at one end by said support member and extending therefrom toward said housing and having a free end slidably disposed in said opening in the housing, said thermal probe being positioned to be heated by the pilot burner and having a thermal expansion substantially greater than that of said pilot burner,

a switch in said housing recess comprising an electrically conductive flexible and resilient leaf spring having a movable free end, first and second movable contacts on the opposite faces of said leaf spring adjacent its free end, first and second fixed contacts on opposite sides of said leaf spring adjacent its free end for engagement respectively by said movable contacts, said leaf spring having an inherent bias toward said opening in the housing to position said first movable contact engaging said first fixed contact and to position said second movable contact out of engagement with said second fixed contact,

separate terminals mounted on said housing and connected respectively to said leaf spring, said first fixed contact, and said second fixed contact,

and a switch operator of electrical insulation material between the free end of said thermal probe and said leaf spring to move the latter against its bias to disengage said first movable contact from said first fixed contact and to position said second movable contact in engagement with said second fixed contact in response to expansion of the thermal probe by heat from the pilot burner and from the ambient tern perature.

3. A burner ignition unit comprising, a housing having 50 side thereof and 18 attached to one end of said ignition coil, a third terminal rigidly mounted on said opposite side of said housing and connected to said second fixed contact,

a fourth terminal rigidly mounted on said opposite side of said housing, said fourth terminal having a leg which extends from the housing along the pilot burner at the opposite side thereof and is attached to the opposite end of said ignition coil,

and a switch operator of electrical insulation material connected to the free end of said thermal probe and engageable with said leaf spring to move the latter against its bias to disengage said first movable cona pair of opposite sides and a recess between said sides tact from said first fixed contact and to move said and an opening in one of said sides leading into said resecond movable contact into engagement with said cess, second switch contact in response to lengthwise exan elongated tubular pilot burner attached to said pansion of the thermal probe by heat from the pilot housing and extending away from said housing at burner. said one side thereof, said pilot burner presenting l5 *5. A burner ignition unit comprising a housing having ignition and flame port means spaced from said an opening, h i an elongated pilot burner attached to said housing and an ignition coil extending in igniting relation to the projecting therefrom,

il t b 21 support member attached to the end of said pilot an end plate attached to the end of said pilot burner 2t} burner y from Said housing,

away f id h i a thermal probe supported at one end by said support an l t d th l probe Supported t one d by member and extend-ing therefrom toward said houssaid end plate and extending therefrom toward said ing and having a tffie 6nd ly isposed in Said housing and having a free end slidably disposed in p g in the housing, Said thermal Probe hsihg said opening in the housing, said thermal probe positioned to be heated by the pilot burner and havbeing positioned to be heated by flame at said fiame g a thermal expansion substantially greater than port means of the pilot burner and having a therthat Of Said Pilot burner, mal coefficient of expansion substantially greater 3 double throw Switch Said housing Comprising 3 h h f id il b resilient leaf spring having a movable free end coa switch in said housing recess comprising a cantilever- Operahlh alternatively with first and nd fiX d mounted, flexible and resilient leaf spring of elec- Contacts, trically conductive material having a movable free Said leaf Spring having an inherent s ward said end, first and second movable contacts on the op- Opening in th@ housing to Position Said leaf Spring posite faces of said leaf at its free end, first and g engaging Said first fixed Contact, second fi d contacts on opposite id of id l f and a switch operator of electrical insulation material Spring at its fr e and i f ti mlationship between the free end of said thermal probe and said respectively to said first and second movable contacts teat Spring to move the latter against its bias to for engagement by the latter, said leaf spring havengage said leaf spring from said first fixed contact ing a bias toward said opening in the housing to 40 h to position Said leaf p g in ahgtlgemeht With i i id fi t bl Contact engaging id said second fixed contact in response to longitudinal first fixed contact and to position said second mov- Xpahsioh of the thermal Probe y twat m th able contact away from engagement with said second Pilot burner and from the ambient temPeratul'efixed contact, ;a first terminal rigidly mounted on the opposite side 45 References Cited b the Examiml of said housing and connected to said leaf spring, UNITED STATES PA :a second terminal rigidly mounted on said opposite side of said housing and connected to said first fixed 2:13 1 2 contact, said second terminal having a leg which ex- 3183959 5/1965 Romanelfi 158 128 X tends from the housing along the pilot burner at one FREDERICK L. MATTESON, 111., Primary Examiner. E. G. FAVORS, Assistant Examiner.

Claims

1. A BURNER IGNITION UNIT COMPRISING A HOUSING HAVING A RECESS THEREIN AND AN OPENING LEADING INTO SAID RECESS, AN ELONGATED PILOT BURNER ATTACHED TO SAID HOUSING AND PROJECTING THEREFROM, AN IGNITION COIL POSITIONED TO IGNITE THE PILOT BURNER, TERMINALS ATTACHED TO SAID HOUSING AND RIGIDLY SUPPORTING SAID IGNITION COIL AND PROVIDING ELECTRICAL CONNECTIONS THERETO, A SUPPORT MEMBER ATTACHED TO THE END OF SAID PILOT BURNER AWAY FROM SAID HOUSING, AN ADJUSTING SCREW THREADED IN SAID SUPPORT MEMBER AND HAVING A RECESS,