US2815417A - Thermostat - Google Patents

Description

De@ 3e 1957 I M. LENoxR 2,815,417

v THERMOSTAT Filed Feb. 19, 1957 2 sheets-sheet 1 l' yy I INVENT OR E /yic/w/ Lenoir fat/pcg, ggge" ahlen j 'I/IORNEYS Dec. 3, 1957 M. LENQIR 2,815,417

l THERMOSTAT Filed Feb. 19, 1957 '2 sheets-sheet 2 INVENTOR ATTORNEYS auf e 2,815,4l? Patented Dec. 3, 1957 THERMOSTAT Michel Lenoir, Lyon, France, assignor to Petercam, Societe Anonyme, Paris, France Application February 19, 1957, Serial No. ftlnll Claims priority, application France March 1S, 1956 7 Claims. (Cl. 20h- 138) This invention relates to electrical switches of the bimetallic control type and in particular to an improved construction for a switch of very small dimensions known as a miniature switch and which can be placed in normally quite inaccessible places where it may be left permanently to control the temperature there such as, for example, within an electrical coil or winding on a motor, or on the inside of a pipe of small diameter, etc.

The principal object of the invention is to provide a miniature sized bimetallic type of a reverser switch which has a small time constant, a means of adjustment or regulation to adjust the temperature at which the switch operates, and which is provided with a pair of stationary contact members between which a movable contact member operates, the movable contact member being controlled in accordance with the displacement of a bimetallic strip member as the temperature on the latter changes.

More particularly, the invention is characterized by a very thin gauge elongated, metallic, electrically conductive casing and which also has a good heat conductive characteristic, and into which is slidable an assembly comprising a metallic support plate which carries a pair of spaced stationary contact members and an elongated elastic strip pressed endwise to take a curved form constituting a movable contact member which is placed between the stationary contact members. One end of the elastic strip is attached to a support which is adjustable longitudinally along the support plate in order to adjust the compression on the elastic strip and the opposite end of the elastic strip is attached to the movable end of a generally U-shaped bimetallic member thus causing the curved strip to press its convexly curved surface against one or the other of said stationary contact members depending upon the amount of heat applied to the bimetallic member. The elastic strip is caused to iiex rapidly from one convex position across dead center to another convex position even though the movement of the bimetallic member has no snap acting characteristic, and one leg of the bimetallic member over a greater part of its length lies adjacent, and bears constantly against, the inner face of the wall of the casing which surrounds the assembly thus providing accurate and fast heat transfer through the casing to the bimetallic member in response to a change in temperature of the device being monitored.

The foregoing objects and advantages of the invention will become more apparent from the following detailed description of one practical embodiment of the invention and from the accompanying drawings which illustrate the same. These drawings are greatly enlarged in order that all detailed structure shall be entirely clear. However, it is to be understood that the switch is of the so-called miniature type and its overall length, as depicted in the large scale drawings, actually will be of the order of one inch or less.

In the drawings:

Fig. l is a side view in elevation of the improved bimetallic switch in accordance with my invention;

Fig. 2 is a top plan View of the switch shown in Fig. l;

Fig. 3 is a central vertical longitudinal sectional view taken on line Ill- III of Fig. 2;

Fig. 4 is a vertical transverse section taken on line V-IV of Fig. 3;

Figs. 5 and 6 are fragmentary views of the interconnecting end portions of two components of the switch;

Fig. 7 is a diagrammatic view showing the forces involved in operation of the switch components; and

Fig. 8 is a side View in elevation of the improved switch shown in Fig. 1 and with the ends thereof sealed.

With reference now to the drawings and to Fig. 3 in particular, the bimetallic switch in accordance with the linvention comprises a structural sub-assembly which includes a primary support member in the form of a generally rectangular elongated metallic plane plate 1 made of relatively thin gauge material and which preferably is electrically conductive. The normal attitude of the plate is vertical and the upper and lower edge portions are bent inwardly at right angles to the plane of the plate so as to form horizontally extending lower and upper flanges 1a, 1b. Near the left end of plate 1, a tongue 1c is struck out from the plate, and which lies in parallel spaced relation to the upper flange 1b, and a conductor 2 with an insulation covering 3 is held tightly in the space between flange 1b and tongue 1c. As is evident from Fig. 3, the inner end of conductor 2 is bent into a curved shape and forms one stationary contact member 2a of the switch.

Toward the middle of the plate 1, another tongue portion 1d is struck out to lie in parallel spaced relation to the bottom flange 1a, and a second conductor 4 with an insulating cover 5 is held tightly in the space between ange la and tongue 1d. The inner end of conductor d is likewise bent into a curved shape and forms a second stationary contact member 4a of the switch and which is located vertically below and spaced from and confronts contact member 2a. In order to insulate the contact members 2a, 4a from the support plate 1 a thin mica sheet 6 is inserted therebetween.

The opposite end portions of the plate 1 are also bent inwardly to lie at right angles thereto and form vertical end iianges 1e and 1f. The upper edge of the left hand flange 1e is spaced from flange 1b to permit passage of conductor 2 and its insulating cover 3, and the lower edge of the right hand flange 1f is spaced from ange la to permit passage of conductor 4 and its insulation cover 5.

Seated upon the lower flange 1a is the flat base portion 7a of a generally U-shaped support member 7 made of relatively thin gauge, electrically conductive metallic material, and which is adjustable longitudinally along the liange la by means of a pair of vertically spaced adjustment screws 8 which are threaded through the end flange le and engage the left upstanding leg 7b of the member 7. The upper portion of the right upstanding leg 7c of member 7 terminates in an outwardly pointing V-shaped notch 7d and which is apertured at 7e at its apex as indicated in Fig. 5. The latter view also shows the bending axes x-x and y-y of. this V-shaped end portion.

Arranged for operation between the stationary contact members 2a and 4a is an elastic, elongated, electrically conductive metallic strip 9 and the latter forms the movable contact members of the switch. The left end of strip 9 is provided with a tongue portion 9a shown in Fig. 6 and which is adapted to be received in the aperture '7e of support member 7 for oscillation about an axis y-y' normal to the plane of the plate 1. The opposite end of the strip 9 is supported by the movable leg portion 10a of a generally U-shaped bimetallic strip member 10. The lower` leg portion 10a which is free to move as the temperature changes terminates in a V-shaped notch 10b and which is apertured at 10c its apex to receive the opposite tongued end 9b of the elastic strip 9. The notched portion b is similar to the notched portion 7d of the support member 7 and contains a similar axis y-y for oscillation of the corresponding end of the strip 9 as the bimetallic strip 10 shifts, when heated, from one position to another in a manner to be described in more detail later on. The upper leg portion ltld of the bimetallic strip 10, and which is longer than lower leg portion ltla, is secured against movement by virtue of the fact that it is pressed tightly between the upper surface of tlange lb and the inner surface of the top wall of a casing 1li which is also made of relatively thin gauge, electrically conductive and heat conductive material, the top wall of the rectangularly configured casing 11 sliding in close engagement with the top face of bimetallic strip portion ltlrl, and the lower wall of casing 11 sliding in close engagement with the underface of the bottom flange 1a of the support plate 1. To prevent any relative longitudinal displacement between the upper leg portion 10d of the bimetallic strip and the flange 1b, the latter is provided with a centrally located pair of parallel spaced, transversely extending slots 1k into which an offset central portion ltle of the bimetallic leg portion 10d is entered, the said central, offset portion 10e thus underlying the ange lb for the distance therealong between the slots lk. In order that the curved portion 10f of the bimetallic strip l@ can be deformed when its temperature is changed, it will be noted that the lange 1b is spaced from the end liange 1f so as to enable the bimetallic strip to pass freely therebetween. The amplitude of the movement of the under leg 19a of the bimetallic strip 10 is limited by the space between two tongues 1g and 1h also struck out from the back plate 1 and which lie on opposite sides of the bimetallic leg 10a in parallel spaced relation and parallel to the upper and lower flanges 1a and 1b,

In order that the stationary contact members 2n and 4a may be insulated from the corresponding side of the outer casing 11, it will be seen from Fig. 4 that a thin mica plate 12 is inserted therebetween. A conductor 13, soldered to the casing 11 is electrically connected to the left end of the elastic metallic strip 9 by virtue of the fact that the casing 11, plate 1 and support member 7 are all made from electrically conductive material, Thus, depending upon the position of strip member 9, which is controlled by the bimetallic strip 1d, a circuit will be completed between conductor 13 and conductor 4 or between conductor 13 and conductor 2 to thus form a reversing or inverter type of switch.

Reference is now made to Fig. 7 which indicates the operating principles which are involved. In this tigure, z-z indicates the horizontal median plane between the stationary contact members 2a and au, m is the component, in such plane, of the compression or end force applied by the support member 7 to the end of the elastic strip 9 and n and p are the components, normal to said plane, of the force exercised by the bimetallic strip ltl on the strip 9.

As indicated in Fig. 7, the strip 9 is compressed between its opposite end supports into a longitudinally curved Shape. When the bimetallic strip l@ is colcL the curvature of strip 9 is along the line through the points owl and the central portion of the same is curved convexly into engagement with stationary contact member 2a. When the bimetallic strip 1t) becomes heated, such as by the heat given ott from an electrical coil carrying a current overload and with which it lies in good heat transfer relation through the casinfy 11, the end of the strip 9 which was at the position z, under the action of upward force n transmitted by the end Mib of bimetallic strip 1li, shifts with the latter and comes to the position u. The strip 9 is then aligned with points owu. As said end 10b of the bimetallic strip lt) continues its upward movement to the position indicated in 3, the strip 9 will be caused to abruptly disengage itself from stationary contact member 2a, and undergo a reversal of curvature so l as to bring it into quick engagement with the oppositely located stationary contact member 4a. The strip 9 is then positioned along the line through the points ovr. The distance tr corresponds to a course of travel of the movable end 10b of bimetallic strip 1t) and which is limited by the stop tongues 1g and lili.

Upon cooling of the bimetallic strip 10, under the action of the downward force p resulting from distortion of strip 10, the strip 9 will rst be guided into a flat position defined by the line through points ovs. The movable end of strip lil continuing its movement, strip 9 will abruptly disengage itself from stationary contact member 4a and, reversing its curvature, becomes engaged with the oppositely located stationary Contact member Za and again lies on the line through points owt.

ln both cases, it is evident that the abrupt exing movement of the strip 9 from engagement with one of the stationary contact members to engagement with the other stationary contact member takes place regardless of the speed of displacement of the movable end of the bimetallic strip 10. The temperature at which the strip 9 is caused to flex from one terminal position to the other is, of course, determined by the amount of pressure applied to it via support 7 and screws 3. It will also be noted that during these ditferent movements, the end of strip 9 at its support on member 7 effects a small amount of movement to and fro along axis z-z as represented by the distance between points o and o. Because of this small longitudinal movement there results a corresponding, advantageous longitudinal, rubbing movement of the surface of the strip 9 over the stationary contact members Za and 4a which serves to keep the contact members clean.

As indicated in Fig. 8, it is possible to seal the casing 11 by making the same longer than the elongated support member i to establish end cavities iff;- and l5 at the opposite ends of the casing, and lling such cavities with a heat resistant solid material 16 such as an artificial resin known under the trade name Araldite The resin at the left end of the casing is seen to cover the slotted heads of the adjustment screws S and hence eliminate the possibility of the switch from changing its initial characteristic after it has once been set.

In conclusion, while I have described and illustrated one practical embodiment for my invention it is to be understood that various minor departures therefrom may be made without, however, departing from the spirit and scope of the inventive concept as defined in the appended claims.

I claim:

l. In a miniature thermostatic switch of the bimetallic type, an assembly comprising an elongated metallic support strip, a pair of stationary contact members mounted on said suppont strip -in spaced confronting relation, a lmovable contact member in the form of an elastic strip member disposed between said stationary Contact members, a longitudinally yieldable support member to which one end of said elastic strip is pivotally secured for oscillation about the pivot axis which is normal to the longitudinal axis of said elastic strip and a bimetallic strip mounted on said support strip, the opposite end of said elastic strip member being pivotally secured to an outer end of said bimetallic strip member for oscillation about the pivot axis which is parallel to the pivot axis of oscillation at the opposite end of said elastic strip member, said elastic strip member being held in a longitudinally curved attitude between the pivotal supports at the opposite ends thereof so as to engage one of said stationary Contact members, said outer end of said bimetallic strip being free to deflect in the plane of said elastic strip member with changes in temperature thereof so as to effect a like movement of the corresponding end of said elastic strip member causing the latter to reverse its curvature and move into engagement with the other stationary contact member; and a metallic casing for receiving and into which said assembly is slid longitudinally for encasing the latter.

2. A thermostatic switch as defined in claim 1 and which further includes means for adjusting the end pressure .applied to said elastic strip member.

3. A thermostatic switch as defined in claim 1 wherein said pressure adjusting means comprises a screw adapted to bear against said support member.

4. A thermostatic switch as defined in claim 3 and which further includes means sealing in said adjusting 10 6. A thermostatic switch as defined in claim 1 wherein 15 said elongated support strip is channel shaped in crosssection having upper and lower anges and said casing is of rectangular configuration in cross-section and slides in Contact with one flange of said support strip.

7. A thermostatic switch as defined in claim l wherein said bimetallic strip is U-shaped having one short leg and one long leg, said long leg being pressed against said casing for the greatest part of its length and said short leg being pivotally connected at the outer end thereof to the corresponding end of said elastic strip member.

References Cited in the le of this patent UNITED STATES PATENTS 1,797,886 Thomas Mar. 24, 1931 2,240,625 FitzMaurice May 6, 1941 2,643,311 Giuirida et al. June 23, 1953 2,767,284 Moksu Oct. 16, 1956

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