US3418618A - Thermoresponsive device - Google Patents

Description

Dec. 24, 1968 H. A. MUDD 3,418,618

THERMORESPONS IVE DEVICE Filed Sept. 1, 1966 2 Sheets-Sheet 1 3/ .L 1 5 5 aelouueeoc ggdew eol INVENTOR.

z/mvzr 4, M02] n r aiwkp Dec. 24, H. A. MUDD THERMORESPONSIVE DEVICE Filed Sept. 1, 1966 2 Sheets-Sheet 2 United States Patent 3,418,618 THERMORESPONSIVE DEVICE Harry A. Mudd, Ciayton, M0., assignor to McQuay-Norris Manufacturing Company, St. Louis, Mo., a corporation of Delaware Filed Sept. 1, 1966, Ser. No. 576,671 7 Claims. (Cl. 337-387) ABSTRACT OF THE DISCLOSURE Thermosensitive switch operator wherein a tubular probe is composed of longitudinally complete semitubes connected together by a joint which has poor heat conductivity, and a straight stiff blade is anchored to the tubular probe at one end, but free to move radially relative to the tubular probe at the other end in response to one semitube being at a higher temperature than the other semitube; and such radial movement operates an electrical switch.

This invention relates to imporvements in a thermoresponsive device which is adapted to actuate a switch in response to changes in temperature.

In heating systems employing fuel burners, it is important to assure that the fuel burner is properly burning, otherwise accumulation of fuel and air may produce an explosive mixture that could subsequently be ignited, thereby causing extensive damage to the furnace, including damage to the area surrounding the furnace. Should the burner be extinguished after initial ignition while the fuel valve remains on, as may occur due to flame-out or fuel flow stoppage, it is advantageous to have a reliable means that senses this condition so as to provide prompt reignition of the burner, assuming that the furnace is designed with an automatic ignition system. It is further desirable sometimes to sound an alarm warning personnel of the malfunction of the burner. One of the most important components of such a burner system is a thermosensing device which monitors the burner. Such a device must remain reliable over a long period of usage, be simple in construction, and be inexpensive to manufacture. It is also important for such a thermosensing device to have a suitable response rate, and to be compact in size.

It is therefore an object of this invention to provide a thermosensing device having the above desirable features, and wherein the thermosensing device is adapted for a number of uses in addition to flame sensing.

Another object of this invention is to provide a thermoresponsive device that is rugged in construction, small in size, simple in design, and inexpensive to manufacture.

Another object of this invention is to provide a thermoresponsive device having a support means fabricated from a single piece of metal so as to attain a unitized structure that is especially adapted to hold a probe of the type described herein.

Another object of this invention is the provision of a thermo-sensing device of bimetal construction having a probe thereon which is sensitive to changes in ambient temperatures.

Another object of this invention is the provision of a thermoresponsive device that requires a minimum number of different components for the manufacture thereof.

Another object of this invention is the provision of a thermoresponsive device which produces a strong force at its thermoactuated or deflecting part which is especially suitable to the turning on and off of a microswitch.

A still further object of this invention is the provision of a thermosensing device that is adapted to actuate a microswitch at a predetermined temperature level, and which gives reliable and reproducible controlled results.

These objects are attained in accordance with the invention by the provision of a unitized support made from a single stamped out piece of metal that is especially suited to form a mount for the probe of the present invention. The probe is comprised of two similar elongated members fabricated from stamped-out pieces of metal that are joined together along their longitudinal edges to provide a hollow elongated tubular structure. A cantilever arm is rigidly afiixed at one end of the probe and extends longitudinally through the hollow structure so that differences in thermal expansion of one elongated member relative to the second adjacent elongated member produces a deflection in the fixed end of the cantilever arm, which in turn magnifies the deflection with respect to the mount means.

Other objects and features of this invention will be more readily appreciated from a consideration of the following detailed description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a perspective view showing the preferred embodiment of the invention;

FIGURE 2 is a top plan view of the device of FIG- URE 1;

FIGURE 3 is a side elevational view of the device seen in FIGURES 1 and 2 with part broken away to expose the arrangement of typical switch contacts;

FIGURE 4 is an exploded view, in perspective, showing the various components of the device as seen in FIG- URES 1 through 3, with some parts broken away and other parts not shown in order to more clearly illustrate the details of the invention;

FIGURE 5 is a sectional view taken along line 5-5 of FIGURE 2, with some parts not shown;

FIGURE 6 is a sectonal view identical to FIGURE 5, but with the device at a different temperature;

FIGURE 7 is a sectional view taken along line 77 of FIGURE 3;

FIGURE 8 is a sectional view taken along line 88 of FIGURE 3;

FIGURE 9 is a top plan view of a flat stamped metal blank from which one of the components of the device may be formed;

FIGURE 10 is an elevational side view of an alternative form of the invention, with some parts broken away and shown in section to show internal parts;

FIGURE 11 is a sectional view taken along line 1111 of FIGURE 10; and

FIGURE 12 is a sectional view taken along line 12.12 of FIGURE 10.

In the embodiment of the invention illustrated in FIG- URES 1 through 9, the thermosensitive device is illustrated generally by the numeral 12. The thermosensitive device includes a tubular casing forming a probe 13, one end of which is rigidly attached to a support 14, and the other end of which is secured to a cantilever arm 15. The support houses a switch 16, which may be an ordinary light-weight single or double pole, single or double throw switch, but preferably is a small, sensitive, microswitch that is adapted to be actuated by small distortion of the probe .13. In the form shown, the switch has a leaf spring contact 18 normally biased away from contact with a fixed contact 19, but arranged to be held in contact with the fixed contact by the free end 20 of the cantilever arm 15 when the probe 13 is at a uniform temperature throughout.

The support means 14 is formed from a single sheet of metal having sides 21 which are sloped at the forward extremity thereof. Apertures 22 are provided in one side of the support for the purpose of attaching the thermoresponsve' device to other existing structure by means of screws or the like, as desired. The support includes, a vertical forward partition or firewall 24 that separates the portion forming the bifurcated mount 25, 25' (FIG- URE 9) from the remaining support structure. A vertical rear firewall 26 is arranged in spaced parallel relation to the first-mentioned firewall. As seen in FIGURE 4 in conjunction with FIGURE 9, the wall 28 is shorter in length than the opposite wall 21 in order to accommodate the outwardly extending terminals of the switch 16. The short wall 28 is, in effect, extended by a dielectric sheet 30, which may be fish paper, plastic, or any other suitable insulation material. The terminals 32, 34 which project from the switch 16 extend a convenient distance through the insulator 30, and are arranged to be electrically connected to conductors in the circuit to be controlled by the thermosensitive device.

The movable end 20 of the cantilever arm is suitably apertured and provided with a keeper nut 36 that receives a screw 38, of plastic or other dielectric material, which in turn is positioned directly over the free end of spring contact .18 so as to form an adjustable forcetransmitting means between the end and the spring contact 18.

In the preferred form, the probe 13 is comprised of two geometrically identical stamped out sheet metal parts 40 and 41, each of which is an elongated semicylindrical top member. While the members 40 and 41 are geometrically identical, it must be understood that they can be, but are not necessarily, made of the same metal. The upper semicylindrical member 40 is provided with a longitudinally extending flange 46 on each side thereof, and a mating longitudinally extending flange 48 is likewise provided on opposite sides of the lower semicylindrical member 41. The flanges provide means by which the members 40 and 41 may be spotwelded, as at spots 3f, or otherwise mechanically joined together to form a tubular structure having longitudinal fins on opposite sides thereof, but it is preferable that the joint between flanges 46 and 48 not be continuous or hermetic in order to retard heat conductivity between the members 40 and 41.

At one end of the tubular probe 13, between the upper semcylindrical member 40 and the lower one 41, the cantilever arm 15 is rigidly attached by sandwiching the fixed end 42 thereof between opposite flanges 46 and 48, as shown in FIGURE 7. The cantilever arm 15 is shown in FIGURE 4 with the free end 20 thereof broken away, for clarity. The arm 15 is preferably deformed by a longitudinal flute 43, or other means for making it stifi. The cantilever arm 15 is reduced in width at 44, and this reduction in width is maintained out to the free end 20 of the arm 15 so as to enable the reduced portion 44 to have a substantial amplitude of movement within the hollow probe 13, free of the walls, in a manner as illustrated in FIGURES 5, 6, and 8. This assembly of parts leaves the reduced portion 44 of the cantilever arm 15 free to be moved or deflected in a vertical direction as illustrated in FIGURE 8; and, when the tubular casing or probe 13 is assembled with the support 14, the free end 20 of arm 15 projects into the support as shown in FIGURE 1.

FIGURE 9 illustrates a blank which has been die cut from a suitable sheet of metal, such as 24 gage 310 stainless steel, and from which the support 14 is formed. The blank is provided with apertures 50 through which a screw may be inserted to rigidly hold the switch 16 to the support and in proper operative relationship with respect to the cantilever arm 15. The blank is also provided with an aperture 51 which, in the completed assembly is to be substantially aligned with the end of the probe 13 (opposite the end at which arm .15 is secured between flanges 46 and 48). This permits the free end 20 of the cantilever arm 15 to extend through aperture 51 in a manner as best seen in FIGURE 1. The blank of FIGURE 9, when properly folded along the dashed lines of FIGURE 9 by simple bends, results in the unitary support 14 of FIGURES 1 through 4, which is secured in fixed relation, as by welding to probe 13 at the end of the latter, opposite the wider portion 42 ofarm 15.

Referring now to FIGURES 10, 11 and 12, a second embodiment of the invention is illustrated. In this embodiment, a probe comprised of a V-shaped upper member and a lower inverted V-shaped member 141 are joined together to form a tubular casing with a cantilever arm 144 rigidly affixed between the free ends or outward extremity of the V-shaped members as best seen in FIG- URE 11. Between the reduced portion 144 of the cantilever arm and the fixed enlarged end 142, the cantilever arm is twisted ninety degrees so as to permit the free end of the cantilever arm to move within the tubular structure formed by the two V-shaped members 140 and 141, in a manner as best illustrated in FIGURE 10 in conjunction with FIGURE 12. The V-shaped members are provided with flanges, 146 and 148, depending outwardly therefrom, that may be rigidly joined together as by spotwelding, although the members may alternatively be brazed or silver soldered. It is also possible to join the members by turning one flange down over the other in a manner that will rigidly hold the members together, although spotwelding has been found to be the more dependable and desirable means of attachment. At the fixed end of the probe, the flanges 146 and 148 are preferably spotwelded to the mount 25, 25 of the before-described support means 14 as illustrated in FIGURES 1 through 4.

As should now be evident to those skilled in the art, the thermosresponsive device of the instant invention is comprised essentially of three parts, two of which are identical in configuration. These parts are the cantilever arm, and the upper and lower members forming the tubular casing or probe. The cantilever arm is stamped from a single piece of metal. The upper and lower members that form the hollow casing or probe may be made in the same stamping machine by the same die, although in some instances it may be desirable to fabricate the upper and lower components of the casing from different metals to thereby provide a bimetal rather than a monometal thermoresponsive device. Accordingly, the number of manufacturing tools and operations is minimized.

With reference to FIGURE 4, the device is preferably assembled by first spotwelding the enlarged end 42 of the cantilever arm to the lower semicylindrical member 41. The upper semicylindrical member 40 is next superimposed in proper aligned relationship upon the mated lower member 41 and arm 44, where it is rigidly affixed thereto by spaced apart spotwelds placed along the adjacently faced together flange members 46- and 48 in a manner seen at 31 in FIGURE 2. The probe assembly is now complete, and may be subsequently spotwelded to the support .14 by additional spaced apart spotwelds joining the flange area of the probe to the bifurcated end of the support forming the depending mounts 25, 25'. The thermoresponsive device is equipped with the switch 16 and adjusting means 36, 38. The device may then be properly calibrated by subjecting the probe to the particular desired operational temperature level contemplated to be encountered when it is installed, and positioning the set screw of the adjusting means so as to actuate the switch within a desired temperature range.

Where the casing of the probe is comprised wholly of the same metal, the thermoresponsive device must be positioned near the burner where flame can directly impinge upon either one of the upper or lower parts which form the casing, and hence its use would be generally limited to that of a flame monitoring device wherein the flame directly impinges upon one only of the unflanged surfaces of the probe; orat least the probe must be positioned in a manner that allows the thermoexpansion of one of the members to be greater than the other member so as to produce a difference in thermal expansion of the respective parts of the tubular probe, which in turn provides a suitable amount of deflection in the free end of the cantilever arm with respect to the support structure. Where the respective parts of the tubular probe are made of metals of different composition, the flame which it is intended to monitor is preferably made to impinge on both halves of the tubular probe, or the whole may be exposed to ambient temperature and accordingly will respond to environmental temperature changes, since the difference in the coefficient of expansion of the upper and lower casing members will provide sufficient deflection of the free end of the cantilever arm to actuate the switch.

In operation, the thermoresponsive device illustrated in either FIGURE 1 or is placed in a suitable environment that will cause either one of the upper or lower members of the casing to expand a different amount in length when subjected to a temperature change. Since the cantilever arm is rigidly affixed to the free end of the probe, and the other end of the probe is rigidly aflixed to the support, a differential in expansion between the two opposite member forming the casing will produce a deflection in the probe, in a manner best illustrated by comparing FIGURE 5 with FIGURE 6, wherein FIGURE 5 represent-s the normal or standby condition, and FIG- URE v6 is an exaggerated showing of the actuated position of the thermoresponsive device when a flame has played on the upper part 40. A predetermined rise in temperature of part 40 above the temperature of part 41 bends the probe. This bending of the probe is amplified by the cantilever arm 44 in a manner that a slight motion as measured at the free end of the probe will produce a much larger motion at the free end of the cantilever arm. This motion of the cantilever arm is utilized to actuate an electrical switch.

The thermoresponsive device of the instant invention is adapted for use in a number of different applications since the probe thereof may be fabricated from either similar or dissimilar metals. The support and probe may be made in accordance with the teachings of either of the embodiments of the invention to thereby provide a thermoresponsive device that is simple in design, easy to manufacture, suitable in response rate, and low in cost.

While there is illustrated and described herein more than one embodiment of the invention, it is to be understood that such embodiments are merely illustrative and not restrictive, and that variations and modifications may be made therein without departing from the spirit and scope of the invention. Accordingly, the intellectual property that falls Within the preview of this invention is defined in the following annexed claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. A thermoresponsive device including two longitudinally aligned radially complemental members each having continuous sides, means rigidly joining said sides together in poor heat conducting relationship with each other to form a heat probe in the form of an elongated tube, said members each having substantially the same coeficient of thermal expansion, said probe having a fixed end and a free end, support means rigidly attached to the fixed end of said probe, an elongated monometallic actuating arm extending through said .probe having one end projecting through and beyond the fixed end of said probe, and the other end secured in cantilever relationship to said probe at the free end of said probe, whereby said free end of said cantilever arm will be deflected with respect to said support means when the temperature of one of said longitudinally aligned members is greater than that of the other.

2. The device of claim 1 wherein each said member is made from a piece of the same metal in the form of a semicylinder having outturned flanges along the longitudinal marginal edges thereof, with said flanges of each member being aligned in faced together relationship and rigidly joined together to provide the before-mentioned probe with the form of an externally flanged tube, said probe being joined to said support means by said flange.

3. The device of claim 1 wherein each said member is made from an elongated piece of metal stamped out in the form of an elongated angle and having a flange coextensive with and depending from each longitudinal marginal edge thereof, said fixed end of said cantilevered arm being located between said flanges at the free end of said probe, with the free end of said arm extending longitudinally through said enclosure and terminating adjacent said support means. r

4. The thermoresponsive device of claim 3 wherein said cantilever arm is twisted between the free end and the fixed end thereof so as to stiffen said arm in the direction perpendicular to a common plane defined by the longitudinally extending flanges.

5. The thermoresponsive device of claim 1 wherein said members are semicylindrical pieces of metal having a flange arranged alongside the longitudinal marginal edge thereof, whereby the recited joining of the two said members occurs along the said flanges to thereby provide a tube having pairs of adjacently joined flanges spaced substantially one hundred and eighty degrees apart.

6. The thermoresponsive device of claim 1 wherein said arm is cross-sectionally contoured to stiffen it against bending about axes which are substantially perpendicular to its length and thickness.

7. A thermosensing device comprising a support, an elongated hollow tube composed of cross-sectionally complemental parts, oppositely disposed heat-transfer-retarding joints extending axially of said tube and connecting said parts together, said joints including means for reinforcing said tube more against lengthwise bending about axes lying in planes perpendicular to a plane including opposite joints than about axes parallel to said plane, means rigidly mounting one end of said tube upon said support with the other end of said tube substantially remote from said support, an elongated strip secured in said joints at said other end of said tube, said strip extending through and beyond said one end of said tube with substantial clearance for movement relative to the interior of said tube at all increments thereof save the locus of securement in said joints, means for stiffening said strip against longitudinal bending within said tube, and electrical switch disposed for actuation by movement of the end of said strip beyond said one end of said tube when one of said complemental parts has undergone greater thermal expansion than the other of said parts.

References Cited UNITED STATES PATENTS 2,266,721 12/ 1941 Christiansen 200-137 2,392,065 1/1946 Rodgers 200l37 2,721,951 10/1955 Huntley 200l37 2,793,270 5/1957 Burch et al 200-137 3,132,805 5/1964 Tramontini et al. 236-102 3,213,244 10/1965 McCarrick 200-137 1,992,765 2/1935 Petersen 200138 BERNARD A. GILHEANY, Primary Examiner. R. COHRS, Assistant Examiner.

U.S. Cl. X.R. 337394, 398

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