US2257990A - Switch - Google Patents

Description

Oct. 7, 1941.

W. J. TURENNE SWITCH Filed Jan. 29 1940 Patented Oct. 7, 1941 UNITED STATES? PATENT OFFICE swrrcn Wilfred J. Tnrenne, Fayville, Mass. Application January 29, 1940, Serial No. 316,069

This invention, which is an improvement on the apparatus disclosed in United States Letters Patent No. 2,090,407, August 17, 1937, and No. 2,185,433, January 2, 1940, relates to thermostatic switches, and the object thereof, generally stated, is to improve the switches shown in said Letters Patent in the manner hereinafter more fully set forth.

Experience has shown that there is sometimes a tendency to distortion of the circuit-controlling metal strips when the switch, after a period of use to maintain a relatively high temperature (such as 400 F.) is cooled to a much lower temperature. This is due to the fact that both ends of the circuit-controlling member are rigidly connected to its supports in the switches disclosed in said patents and in other prior patents. The diificulty is overcome by rigidly securing the circuit-controlling member at one end only and connecting it at the other end slidably to an abutment member, the arrangement being such that by manually operable adjusting means in co-operative engagement with said circuit-controlling member and the casing or other means whereby the circuit-controlling member is supported, there is effected relative movement between the abutment member and, the circuitcontrolling member as a whole. It has been found also that the means for guiding that head of the circuit-controlling member to which the switch adjusting means is attached is not at times wholly satisfactory, for the reason that the relative movement between said head and the casing is not always rectilinear. The means disclosed in the later of the two patents aforesaid are a pair of oppositely disposed V-shaped ribs formed in the inner wall of the casing and taking into correspondingly shaped notches formed in one of the heads of the circuit-controlling member. This difllculty is overcome by making the ribs and notches substantially rectangular, whereby the axial movement of the notched head with respect to the casing is always a straight line movement whereby the axis of the circuitcontrolling member is maintained at all times coincident with the axis of the casing.

The means for adjusting the switch for opening or closing the circuit controlledat a predeterminecl temperature heretofore comprised two members threaded, respectively, interiorly and exteriorly, and the arrangement was such that only a portion of the threads of the interiorly threaded member, which having been cut with a tap are accurate, engaged the threads of the out with a die, were not consistent throughout their entire length. This sometimes made it 'diincult accurately to adjust the switch to function at preselected temperatures. This difflculty has been overcome by threading the interiorly threaded member throughout its length, and theexteriorly threaded member only a portion of its length, so that the threads of the interiorly threaded member or sleeve engage all of the threads of the exteriorly threaded member or stud for every adjustment of the circuit-controlling member throughout the range of operation of the switch.

. In the accompanying drawing, Figure 1 is a longitudinal section of a thermostatic switch embodying the present invention.

Figs. 2 and 3 are elevations on an enlarged In the particular drawing selected for illus-- trating the principle underlying the invention, such drawing being illustrative only and not restrictive. I0 is a casing, herein shown as tubular, formed of a material having a relatively high coeflicient of expansion such, for example, as brass, in which is disposed the circuit-controlling member ii, herein shown as a pair of bowed metallic leaf springs i2 formed of a metal having a relatively low coefficient of expansion, such for example, as invar, or other suitable metal whose coefllcient of expansion is practically nil. While the spring members l2, l2, are shown in the present instance as bowed inwardly, it is to be understood, of course, that they may be bowed outwardly with their concave sides opposed, as shown in Patent No. 2,185,433. In either case, each spring is provided with a suitable electric contact l3 secured thereto at the central portion thereof and insulated therefrom by insulating material indicated at H.

The circuit controlling members l2, it, are provided with heads l5, ",rigidly secured thereto at the respective ends thereof. The head i! comprises the flanged disc lid, two opposing sides of which are cut away or slotted to receive the cxteriorly threaded member, which, having been spring members i2 i2, and the clamping disc llb between which two discs, the bent over ends of said spring members, are disposed. The head it consists of the flanged disc "a. and clamping disc lib between which the other ends of the spring members are placed. It is to be understood, however, that any suitable means, such as those shown in either of the prior patents aforesaid, may be used for the heads of the circuitcontrolling member and that they may be rigidly secured thereto by welding or in any other suitable manner. a

For adjusting the switch, a variety of means may be employed. In the embodiment of the invention shown in Fig. i, such means comprises the stud l'l rigidly connected at its inner end to the head It and threaded at its outer end, the threaded end preferably being slit, as shown at It, to increase the resiliency thereof and strengthen the grip of its threads on those of its co-operating member which consists of an interiorly and exteriorly threaded sleeve II, the interior threads whereof are in engagement with those of said stud and the exterior threads with those of the threaded bore through the disc II which forms one of the end closures of the casing. It will be understood, of course, that the threads of the stud have a higher pitch than the exterior threads of the sleeve.

Surrounding the stud and secured to the end closure 20 is a tubular shield 2|, shown in the present instance as having one end disposed within the counterbored part of the threaded bore passing through said end closure and its inner end spaced away from the flanged disc Ii.

Rigidly secured as by welding or soldering to the end closure 22 of the casing is a rod 23 passing through and loosely engaging the head I, said rod having a flange 24 at its inner end and provided with flns 25 spaced away from the outer end of the head aforesaid when the inner end thereof abuts said flange.

The flanged rod 23 constitutes an abutment member for transmitting to the circuit-controllingmember the stress created by the expansion of the casing.

Insulated conductors 26, 28, from the heating unit or other device to be controlled, enter the switch through the closure 20 and are electrically connected to the electric contact members II, il, in any suitable manner, as indicated at 21, 21. Preferably, each of said conductors is wrapped once or twice around the shield II to anchor them in position. v

A portion of the inner wall of the casing intermediate its ends preferably is covered with insulating material, as indicated at 28, and insulating discs 28' may be placed in the end of the casing to which the rod 23 is attached.

Means are provided to prevent relative. rotational movement between the head I! and the casing during the adjustment of the switch. The means shown in the drawing for attaining this result consist in a pair of oppositely disposed substantially rectangular ribs 29 formed in the wall of the casing and taking into a pair of correformed, which were V-shaped, however, were not wall thereof for but a limited distance on account of the bulk of the insulated conductors. For this reason the ribs must be of substantial width. A ribformed on the inner wall of a tubular member of soft metal, such as brass, by a blow from a tool applied to the outer wall will, in general, be curvilinear and not rectangular and would therefore be useless for the double purpose of preventing relative rotational move ment between the head II and the casing during the adiustment of the switch and insuring a straight line movement of the circuit-controlling member longitudinally of the casing during such adjustment whereby the axis of said member is maintained at'all times coincident with the axis of the casing.

After much experimentation it was found that a substantially rectangular rib could be produced in the following manner:

A square ended tool ii is placed radially against the outer face of the casing and sufficient force applied to produce an inwardly extending rib which, as aforesaid, will have rounded corners, as indicated in dotted lines at 32a, 32b, the general conformation of the groove so formed in the outer wall of the casing being indicated in dotted lines at Ila, 83b. The casing is then rotated a few degrees in a clockwise direction substantially about the axis 84 of said groove and the tool placed substantially in the position indicated in dotted lines at Ila against the inner wall of said groove, indicated at Ila, and then upon the application of suitable force'thereto, the rounded corner, {to is forced inwardly so that said corner becomes substantially square. The casing is then rotated in few degrees in a counterclockwise direction about said axis 34 and the tool placed in the position flb against the wall 33b of the groove, whereupon by the application of suitable force the curved corner 32b is pushed inwardly and becomes substantially square.

The operation of the improved switch herein described will be readily understood by those skilled in the art by the disclosures of the above mentioned patents.

When the switch is maintaining any temperature within its range for which it has been adjusted, the head I is, as shown in Fig. i, in engagement with the flange 24, the latter having been drawn thereagainst by the expansion of the casing. when the adjustment is for a relatively high temperature, the longitudinal expansion of the casing required to separate the contacts II, II, is of course greater than when the switch is adjusted for a substantially lower temperature. Should the switch, after having been used to maintain such relatively high temperature, be brought, within a comparatively short period of time, to a much lower temperature, as frequently occurs in practice, the stress to which the leaf springs would be subjected were both ends of the circuit-controlling member rigidly secured to its supports, as in the case of the prior patents, would distort said springs so that thereafter the switch would not function properly. In the case of the present invention, however, the sliding connection between the head II and abutment member I8 will permit the latter to ass'mao move inwardly without exerting any longitudinal member will be separated before the sleeve has engaged more than three or four of the threads of said closure, and this possibility would be enhanced if the lower head were ri idly secured to the rod 28. With the present invention, however, it suflices. in such situation, to back the sleevesuiilcientlyto disengage the exterior threads thereof with those of the closure II and then give it, say, one additional turn. so that the inner end thereof ispositioned a short distance outwardly of the outer face of said closure. Therein engagement with the interior threads of the sleeve, the user can then push the sleeve and stud and the circuit-controlling member-inwardly, the head I being slidably connected with the rod 23, until the exterior threads of said sleeve are in position to engage the threads of the closure II, whereupon it will be possible to give the sleeve a number of turns before the electrical contacts separate.

\ upon, the threaded end of the stud II, being still 7 There is a third advantage in the sliding con- I nection of one of the heads of the circuit-controlling member with its circuit, v'ls.,-inthe switch of Patent No. 2,090,407, the lower head of. which is rigidly secured to its support. it is somewhat difficult to engage the threads of the adjusting screw with those of the cylinder head and with those of the circuit-controlling member head and have a sumcient number of threads in engagement to permit of the adjustment of the switch for all temperatures within its range. In that switch the threads of the adjusting screw were first engaged with those of the head of the circuit-controlling member and then the upper threaded end of said screw engaged with the threads of the cylinder head. As will be obvious, it would be necessary at times to exert undue pressure on the circuit-controlling member and distort the springs thereof in order to engage the threads on the upper end of the adjusting screw with the threads of the cylinder head, and it was frequently found that even after exerting such pressure on the circuit-controlling member, an insufficient number of the threads on menuper end of the adjusting screw were in engagement with the threads of the cylinder head to enable all adjustments within the temperature range of the switch to be obtained.

In the present invention, as will be manifest, the loose connection of the head It with the rod 23 eliminates any necessity for exerting pressure on the leaf springs in order to engage the threaded sleeve sumciently for any required temperature adjustment. It will be obvious that the foregoing advantages apply equally well to the switch shown in Patent No. 2,185,433, aforesaid.

As above noted, another feature of the present invention which eliminates any possibility of distortion of the leaf springs is the substantially rectangular rib and notch arrangement above described and such arrangement, although it may be used with advantage in the structures disclosed in either of the prior patents aforesaid, is particularl advantageous-in the case of the present invention for the reason that by virtue of the sliding'connection of the head It with its supporting member, the relative movement between the circuit-controlling member and the casing necessarily is greater than in the structures of said patents.

A feature found by practice to be of great importance in the.present case is the arrangement whereby the interior threads of the sleeve II are in engagement with all of the threads of the stud for every adjustment of the circuit-controlling member throughout the range of operation of the switch. 'It is to be understood. of course, that the pitch of the exterior threads of the sleeve is somewhat lower-than that of the interior threads thereof in order to obtain the necessary differential action for accurate adjustment. The interior threads of the sleeve having been tap-cut and therefore accurate throughout their entire length. are for every adjustment of theoircuit-controlling member in engagement with all of the threads of the stud which,-being die-cut, can never be absolutely accurate throughout the length of the threaded portion of said stud. Thus, such inequality or irregularity in the exterior threads of the stud II is equalized Nor compensated for and thereby the accuracy of adjustment is greatly enhanced in sharp contradistinction to the arrangement of the prior art, referring to Patent No. 2,185,433, for example, wherein the accurately cut interior threads of the sleeve are in engagement with only a relatively small number'of the'necessarilysomewhat inaccurately cut exterior threads of the stud. which results in unequal longitudinal movement of the stud per turn of the sleeve, such movement varying with the location on the stud of the threads thereof which are in engagement with the threads of the sleeve. -It is not necessary in order to effect the improvements above recited that the head It should be in loose engagement with its supporting member, for said head may be rigidly secured to the rod It and, as shown in Fig. '7, the head it arranged for limited sliding movement over the unthreaded end of the stud II.

In the present instance this is done by notching the sleeve portion of the disc Ila. as indicated at 38, and driving a pin 38 through a hole in said stud, such pin passing through said notch and aflording a means for restraining relative rotational movement between the stud and head and also constituting an abutment member for transmitting to the circuit-controlling member I i the stress created by the expansion of the eas- 'ing is. m Fig. '1 the bottom of the notch isshown out of contact with said, pin. but it will be understood, of course, that when the switch is maintaining any given temperature for which it has been adjusted, the pin=is in engagement with thebottomofsaid notch,iustasinthecase of the switch shown in Fig. l, the sleeve, which is integral with the disc lid, is always in engagement with the flange 2 when the switch is maintaining any temperature for which it is in a justment.

The rod 23 preferably is formed of invar, or any other substantially non-expansible alloy, and if desired, the stud il may be formed of such material for extreme accuracy.

Having thus described illustrative embodiments ofmy invention without, however, limiting the same thereto, what I claim and desire to secure by Letters Patent is: Y

l. A thermostatic switchoomprising a casing of material having a relatively high coefllcient of expansion, said casing having a threaded bore at one end and an abutment member rigidly secured to and extending inwardly oi the other end thereof, a circuit-controlling member of material ly secured to the other end 01' said circuit-controlling member and slidably connected to said abutment member.

2. A thermostatic switch comprising a casing of material having a relatively high coemcient oi expansion, said casing having a threaded bore at one end and an abutment member rigidly secured to and extending inwardly oi the other end thereof, a circuit-controlling member ofmaterial having a relatively low coefllcient of expansion disposed within said casing, a head secured to one end of said circuit-controlling member, means for adjusting the longitudinal position of said circuit-controlling member, said means having a threaded stud secured to said head, and an interiorly and exteriorly threaded sleeve, the interior threads whereof are in engagement with all of the threads of said stud for every adjustment oi said circuit-controlling member throughout the range of said switch, and the exterior threads whereof are in engagement with the threads 01' said bore, and a second head rigidly secured to the other end or said circuit-controlling member and slidably connected to said abutment member.

3. A thermostatic switch comprising a casing of material having a relatively high coeiilcient of expansion, 0. circuit-controlling member of material having a relatively low coemcient or expansion disposed therein, heads rigidly secured to the respective ends or said circuit-controlling member, and means for adjusting said circuitcontrolling member to maintain any temperature within the range of the switch, one or said heads being provided with two oppositely disposed substantially rectangular notches and the inner wall of said casing having two substantially rectangular ribs co-operating, respectively, with said notches.

4. A thermostatic switch comprising a casing, a circuit-controlling member enclosed therein, means for adjusting said circuit-controlling member to maintain any temperature within the range or the switch, heads rigidly secured to the respective ends of said circuit-controlling member and abutment means loosely engaging one oi said heads, said abutment means being movable with respect to such head for transmitting to said circuit-controlling member the stress created by the expansion oi said casing and being independent oi! said adjusting means.

5. A' thermostatic switch comprising a casing of material having a relatively high coeiilcient of expansion, a circuit-controlling member of material having a relatively low coemcient of expansion disposed in said casing, heads rigidly secured to the respective ends of said circuit-controlling member, a threaded stud passing through and having loose engagement with one of said heads, means rigidly connected to said stud and having relative longitudinal movement with respect to the head through which said stud passes for restraining relative rotational'movement between said stud and such head, said means constituting an abutment member {or transmitting to said circuit-controlling member the stress created by the expansion or said casing, and manually operable means in co-operative engagement with said casing and said stud for eilectlng relative movement between said stud and said circuit-controlling member.

WILFRED J. TURENNE.

Images