US 2785252 A
Description (OCR text may contain errors)
March 12, 1957 E. L. PARR THERMOSTATIC swncn FOR ammo HEATERS Filed April 4, 1955 BY mam HZTURNE),
United States Patent THERR IOSTATIC SWITCH FOR ELECTRIC HEATERS Edward L. Parr, Burbank, Calif.
Application April 4, 1955, Serial No. 498,929
Claims. (Cl. 200-138) This invention relates to a thermostatic switch primarily for use in electric heaters having air circulating fans therein.
It is the object of the invention to provide a switch of the type referred to which is so small and compact that it may be placed Within the very limited space of small heaters and ventilators, such as commonly placed in automobiles to maintain comfortable room temperature within the car while the motor is inactive. Another object is to provide a switch composed of very few rigidly combined parts which may be depended upon to give perfect service during the life of the heater.
The invention accordingly comprises novel combinations of parts which are hereinafter fully described and a preferred form of the invention is illustrated in the accompanying drawing of which:
Fig. 1 is a cross-sectional view through the center of a switch embodying the invention;
Fig. 2 is a substantially corresponding plan view of the switch with a portion thereof partly broken away for the sake of clearness;
Fig. 3 shows one of the contact elements of the switch as it appears before mounted in position therein;
Fig. 4 is an edge view of this element; and
Fig. 5 is a bottom view of the switch housing.
The particular embodiment of the invention illustrated in the drawings comprises a cylindrical tray 1, the bottom of which is perforated to receive therein a smaller, somewhat similarly shaped switch base or housing 2. This housing is composed of suitable insulating material, a ceramic composition having been found very convenient and inexpensive. in two diametrically opposed openings in the base of the housing are mounted conductive terminal posts 3, 4 and T-shaped terminal plates 5, 6 are fastened to the outer ends of the posts.
A passage 7 is cut axially through the center of the housing base and a circular boss rises from the base in axial alinernent with the passage. This boss forms a seat for circular contact element 9. A circular curved bimetallic member 11 is coaxially seated on the bolt above the contact element 9 and a sleeve 12 is seated on the bolt between this member and the contact element 9 to maintain the parts in properly spaced relation to each other on the bolt. The bimetallic member 11 normally exerts sufficient pressure against the contact element 9 to insure perfect contact with the terminal posts 3, 4. A threaded nut 13 is applied to the bolt firmly to lock the parts in position thereon. This nut is in the drawings shown conically shaped to provide secure clamping of the parts when the bolt is operated to draw the nut into the seat 7 which is shaped fittingly to receive the nut.
Snap switches including terminal posts, a disk for contact with the posts and a bimetallic member urging the disk into contact with the posts have been produced. The objection to this type of arrangement is the difficulty of correctly alining the parts on the ceramic base surface to obtain perfect contact with the posts when the bimetallic member snaps into closing position. It has also been found that heat generated due to imperfect contact may cause the disk to warp and so to exaggerate this condition to such an extent no contact is made or that an arc may form between the disk and one of the contact posts. This will destroy the utility of the switch. Another disadvantage of this type of switch is that a spring must be placed behind the disk to force the disk away from the posts when the member snaps back.
All of this is entirely overcome by shaping the contact element 9 as indicated in Figs. 3 and 4 of the drawings. The element is composed of resilient, current conducting material and a spiral-shaped slit 15 is cut through the element. This slit extends from a point a distance from the central perforation 16 of the element nearly to the outer periphery thereof. The element is not flat but somewhat helically shaped, substantially as indicated in Fig. 4, and the outer rim 17 is unbroken to assure con tact with the posts in any circumferential position the element may assume when the parts are assembled. The portion 18 of the surface between the perforation 16 and the inner winding 19 of the slit must be wide enough to assure firm anchoring on the bolt and the width of the surface between the convolutions of the slit may gradually decrease until, at the outer end of the slit, the rim is merely wide enough to provide complete contact with the end of one of the posts. When so shaped and when the element is of the proper thickness and resilience, it is found that every portion of the slitted element is free to yield to assure perfect contact with the posts. The bimetallic element will when a certain degree of heat is reached pop upwardly and so release the contact element for return to its normal helical shape. In the drawings two contact posts are shown, but additional posts may, if desired, be employed.
The provision of the spirally slitted helically shaped contact element has the further advantage that fewer parts are required than found in any thermostatic snap switch that has come to my notice and that all of these parts are firmly locked in position. But while the particular arrangements and shapes above outlined have been found satisfactory, it is to be understood that modifications, within the scope of the claims hereto appended, may be embodied therein without departing from the spirit of the invention.
1. A thermostatic switch comprising, a dielectric base, contact posts seated on said base, a bolt in the center of the base rising from the surface thereof, a circular bimetallic member mounted on the bolt, a contact element on the bolt below the member in position to contact said posts, and means for locking the member and element in position on the bolt in correct relation to the contact posts, the element having therein a spirally shaped slit uniformly arranged above the center thereof and extending nearly to the outer edge of the element.
2. A thermostatic switch comprising, a support having a circular perforation therethrough, a cylindrical housing having a shoulder at the bottom thereof seated in the perforation of the support, contact posts rising from the sur face of the housing, a bolt seated in and rising from the center thereof, a circular bimetallic member on the bolt, and a resilient spirally slitted contact element mounted on the bolt between the member and the contact posts.
3. A thermostatic switch comprising, a support having a circular perforation therethrough, a cylindrical dielectric housing having a shoulder at the bottom edge thereof seated in the perforation of the support, contact posts rising from the bottom of the housing, a bolt seated in and rising from the center thereof, a circular bimetallic member mounted on the bolt, a resilient circular contact element on the bolt between the member and the posts, the element having therein a spirally formed slit uniformly placed about the center of the element, the inner end of the slit being spaced a distance away from the center of the element, the distance between the convolutions or" the slit gradually and uniformly decreasing toward the outer end of the slit, the slitted element being helically shaped.
4. In a thermostatic switch, a circular contact element having a central perforation and a. spirally shaped slit therethrough, the inner end of the slit being spaced a distance away from the center perforation and extending nearly to the periphery of the element, the distance between the convolutions of the slit decreasing uniformly from the inner to the outer end thereof, the element being helically shaped.
5. A thermostatic switch comprising, a support having a circular perforation therethrough, a cylindrical dielectric housing having a shoulder at the bottom edge thereof seated in the perforation of the support and a central conical passage therethrough, contact posts rising from the bottom of the housing, a bolt seated in and rising through said passage, a circular resilient contact element seated on the bolt between the member and the posts, the element having a spirally shaped slit therein, the element rising helically from the base, and a nut fittingly seated in said conical passage to engage the bolt firmly to clamp the member and the element in position on the base.
References Cited in the file of this patent UNITED STATES PATENTS 5l2,672 Egan Jan. 9, 1894 887,166 Wilhelm May 12, 1908 2,l99,638 Lee May 7, 1940