US2165199A - Rheostat switch - Google Patents

Description

y 1939. H. w. BATCHELLER RHEOSTAT SWITCH Filed April 8, 1936 Patented July 11, 1939 UNITED STATES PATENT OFFICE to Standard Mfg. (70.,

VtVorcester, Mass, a corporation of Massachuse ts Application April 8, 1936, Serial No. 73,218

7 Claims.

This invention relates to rheostat switches and more particularly to switches which are designed for use in controlling currents of low voltage and low amperage such as are employed for the operation of small motors. The embodiments of the invention hereinafter described are designed for controlling current for motors in automobile heating units. It is an object of the invention to provide a rheostat switch which is capable of withstanding considerable overloading withoutr injury from the resulting heat. It is a further object of the invention to provide a switch of the type described characterized by parts which are simple and easy to manufacture and to assemble.

Various other advantageous features of structure will be apparent to one skilled in the art from the disclosure of the invention in the description which follows and on the drawing of which- Figure 1 is a sectional view of a rheostat switch embodying the invention.

Figure 2 is an exploded perspective view of most of the parts of the switch illustrated in Figure 1.

Figure 3 is a perspective ber of the switch shown in Figure 1.

Figure 4 is a section on the line 4-4 of Figure 3.

Figure 5 is a perspective view of a resistance element employed in the rheostat.

Figure 6 is a section similar to Figure 4, but including the resistance element.

Figure 7 is a side elevation of a modified form of the invention, portions being broken away to show in section.

For the control of small electric motors, a

rheostat switch is often desired so that the speed of the motor can be suitably regulated. To this end, rheostat switches have heretofore been made with a resistance element on which a contact element or shoe is adapted to slide, these elements being connectible into a circuit so that a larger or smaller amount of the resistance element can be cut into the circuit. Some of these rheostat switches may include a tell-tale light which is so connected as to light when the switch is turned on and to be extinguished when the switch is turned off. The lamp may be so connected as to burn at full voltage for any adjustment of the rheostat, or to be in series with the resistance element so that it is dimmed as the resistance is cut into the circuit. Customarily one end of the resistance element is connected to a switch terminal, the contact shoe being connected to the other terminal so that the current can pass into view of the base mem the resistance element through the connected end, and out through the shoe. It is evident that the portion of the resistance element adjacent to the connected end undergoes more severe treatment than the portions further removed from the connected end since relatively large currents flow through the adjacent portion when only that portion is cut into the circuit. When more of the resistance element is cut into the circuit, the current is correspondingly reduced so that the heating effect on the portion of the resistance element included in the circuit is not so severe. It is an object of the present invention to mount the resistance element in such a manner as to avoid overheating and resultant failure of the portion thereof adjacent to the connected end. To this end, I mount the resistance element on a base consisting of a slab of refractory material such as unglazed porcelain, the slab being provided with an arcuate channel to receive the 20 bedded in the refractory cement which preferably 25 covers the major portion thereof, leaving the tops of the coils exposed for contact with the contact shoe. Furthermore, according to the invention, several of the coils of resistance wire adjacent to the connected end thereof are entirely covered by the cement so that all of the coils thus covered are simultaneously cut into the circuit when the contact shoe engages the first exposed portion of the resistance element. Thus the portion of the resistance element adjacent to the connected end, which receives the most severe usage, is protected in two ways: first, by being completely embedded in refractory cement adapted to conduct heat rapidly away from the coils, and, second, by insulating from the contact shoe the several coils of the resistance element adjacent to the connected end so that a sufficient length of resistance wire is initially cut into the circuit to prevent excessive over- I heating of the portion adjacent to the connected end.

The rheostat switch structures, hereinafter described in detail as embodiments of the invention, also include other advantageous features of structure by which the switches may be easily constructed and assembled so that a considerable saving in expense of manufacture is made possible.

Referring to Figure 1, the switch structure may include a base III of refractory material such as unglazed porcelain, this base, as indicated in Figures 2 and 3, being in the form of a slab or block having an arcuate channel I 2 in the front face thereof. Within and concentric with this channel is a central recess I4. The base I0 is also preferably formed with peripheral notches I6 adapted to receive tabs I8 on a cup-shaped metal housing member 20 which, with the slab I0, encloses the working parts of the switch. Opposite the base I0, the housing member 20 opens into a sleeve 22 which projects therefrom and is secured to or integral with the housing. This sleeve is preferably screw-threaded to receive a pair of nuts 24 by which the entire switch may conveniently be mounted on a dash-board 26 or other suitable support.

A resistance element 30 is disposed in the new ate channel I2, this element being preferably in the form of a helical coil of wire of suitable material. The coil is of such size that the tops of the individual coils project above the surface of the slab I0 when the coil is placed in the channel I2. An end portion of the coil, however, is disposed in a portion 32 of the channel l2 which is deeper than the rest of the channel, so that this portion of the coil is completely below the face of the slab I0, as indicated in Figure 6. Prior to the insertion of the resistance unit 30 in the channel I2, a suitable quantity of plastic refractory cement is laid therein. When the element 30 is then pressed into the channel, the major portion of 'each convolution becomes embedded in this cement, the convolutions in the deep portion 32 of the channel being entirely covered by the cement. A shallow groove 34 may be formed in the face of the slab I0 leading from the deep end of the channel I2 so as to receive the end portion 38 of the resistance element 30 adjacent to the coils which are in the deep portion 32 of the channel. The depth of the groove 34 is less than the diameter of the resistance wire so that the portion 36 of the wire projects laterally above the face of the slab ID for permanent engagement by a contact element 40, which, as indicated in Figure 2, is in the form of a metal plate overlying the end portion 36 of the resistance wire and the convolutions of resistance wire which are buried in the cement in the deep portion 32 of the channel. The contact element 40 is thus insulated from the resistance element except where it is in direct contact with the end portion 36 thereof. This contact element may be secured in place as by a binding post 42 which extends through an aperture 44 in the block I0,

the binding post being internally threaded to receive a screw 46 by which a wire can be readily attached to connect the switch into a circuit.

A second contact element 50 is illustrated in Figure 2. This element, as shown, has an annular portion 52 which is arranged to surround the central depression I4 in the slab I0, this annular portion having a central flange 54 projecting into the recess I4 so as to hold the contact portion 52 centered with respect to the resistance element 30 which partially surrounds it and is arranged concentrically therewith. This contact element is also provided with a radially extending portion 56 which is integral with the annular portion and which is secured by a binding post 42 projecting through an aperture 44 in the slab I0 in the manner described. The contact elements 40 and 50 are preferably secured permanently to the base I0, the ends of the corresponding binding posts 42 being preferably swaged to secure these contact elements tightly against the face of the base I0.

A movable contact member 60 is mounted on a stem 62 and is arranged to rotate so as to cause a shoe portion 64 of the member 60 to slide in a circular arc from an off position upon the radial portion 56 of the contact element 50 to an on position on the contact element 40-. Further rotation of the member 60 causes the shoe 84 to slide from the member 40 into contact with successive exposed portions of the resistance element 30. When the shoe 64 first comes in contact with a portion of the element 30, all of the convolutions of this element which are buried in cement below the contact member 40 are simultaneously cut into the circuit. Further rotation of the member 60 results in the inclusion of more and more of the resistance element 30 in the circuit. In order to provide a convenient stop for the shoe 64, an ear I0 is bent up from one side of the radial portion 56 of the contact member 50. One side of this ear is engaged by the shoe 64 when the switch is in the off position. The

other side of the ear is engaged by the shoe 64 when the maximum amount of the resistance element 30 has been cut into the circuit. It is desirable that yielding detent means be provided for indicating, through the sense of touch, when the switch is in its on" and off positions. To this end, a lug I2 is formed on the member 60. This may be readily provided by indenting the upper surface of the member 60 so as to cause a projecting bulge in the lower surface thereof. This bulge is adapted to enter successively a pair of depressions such as notches ,I4 and I6 in the member 50. The member 60 is resiliently pressed toward the base I0 as by a suitable spring I8 so that the shoe 64 is thereby continuously pressed against whatever element it is in contact with, and the lug I2 is pressed against the marginal portion of the annular element 52 so that it snaps into the notches 14 and I6 as it moves into registry therewith. These notches are so related with reference to the elements 56 and 40 as to receive the lug I2 when the shoe 64 is in contact respectively with said elements.

The contact member 60 is loosely slidable on the stem 62, the latter having one or two flat sides as at 80 to prevent relative rotation between the stem and the contact member. The stem 62 projects through a central aperture 82 in a disk 84 of insulating material having a greater diameter than that of the sleeve 22, the aperture 82 being shaped similarly to the cross section of the stem 62 so as to prevent relative rotation between these parts. When the entire switch is assembled, as illustrated in Figure 1, the stem 62 projects through the central aperture in the annular element 52 and enters the recess l4. As the contact member 60 is loose on the stem 62, a spring I8 presses it resiliently against thebase I0. Secured to the insulating disk 84 is a suitable lamp socket which may consist of two metal members 90 and 92. The inner member 90 is in the form of a hollow cylinder having an end flange 94 which is notched as at 96 to receive a pair of tongues 98 on the member 92. These tongues are adapted to extend through slots I00 in the disk 84 and to be bent against the further face of the disk so as to hold the member 90 and 92 permanently against the upper or forward face of the disk. The member 90 is provided with a pair of bayonet slots I04 to receive the customary lateral pins I06 on the base I08 of a lamp H0. The pins I06 are resiliently held in the bayonet slots by the pressure of a spring II2 within the stem 62, pressing against a plunger II4 which engages the tip I I5 of the lamp base. As indicated in Figure 1, the flange 94 of the member 90 is of sufficient diameter to bear against the inner end of the sleeve 22. The spring 18 presses this flange against the end of the sleeve so that a good electrical contact is maintained between the member 90 and the sleeve 22, the latter being grounded preferably through the dash-board 26. The spring I I2, which presses the plunger II4 against the tip I I6 of the lamp, maintains a good contact between the member 90 and the shell I08 of the lamp base, as well as maintaining a good connection between the plunger H4 and the tip H6 of the lamp. Thus the shell I08 of the lamp is constantly connected to ground and the tip H6 is constantly connected to the contact shoe 64.

An operating member is provided consisting of a finger knob I20 of translucent material, preferably molded about the end portiofiiof. a tube I22. This tube is adapted to nest within the sleeve 22 and to fit over the member 92. The tube I22 and the member 92 may be keyed for rotation togather by means of a lug I24 struck up from the wall of the member 92 and engaging in a notch I26 in the tube I22. The outer end portion of the tube is preferably perforated as at I30 to permit rays of light from the lamp IIO to shine through the translucent finger knob I20. Rotation of the knob I20 results in rotation 'of the member 92 which is keyed thereto and which is secured to the disk 84 by means of the lugs 98. Rotation of the disk results in rotation of the stem 62 and the contact member 60, thus causing the contact shoe I54 to swing in an arc for sliding engagement successively with the contact member 40 and successive exposed portions of the resistance element 30. In connecting a rheostat switch as herein described, into a circuit, the contact member 40 is preferably connected to the wire leading directly to the battery or other source of voltage, the contact member 50 being connected to the fan motor or to any other device to be controlled by the switch.

If a tell-tale light is not desired, the operating member may be of simpler construction as indicated in Figure '7. As therein shown, a solid stem I40 is employed in the place of the hollow stem 62, this stem being preferably embedded in the end of an operating member I42 which is molded in a generally cylindrical form and is of sufficient length to project through the sleeve 22 and beyond the end thereof so as to provide a finger portion I46. The inner end of the member I42 is flanged as at I50, this enlarged end portion thus being equivalent to the insulating disk 84. The base I0 and members mounted thereon are preferably as hereinbefore described.

It is evident that various modifications and changes may be made in details of the structure herein shown and described without departing from the spirit or scope of the invention as defined in the following claims.

I claim:

I. As a new article of manufacture, a slab of refractory material having an arcuate groove in a face thereof, said groove having a portion at one end thereof deeper than the remainder of the groove, a helical coil of resistance wire disposed in said groove so that several convolutions at one end thereof are in the deeper portion and do not project above the face of the slab but a portion of each convolution in the remainder of the groove projects above said surface, refractory cement substantially filling said groove and entirely covering the convolutions in the deeper portion thereof, and a contact element connected to said coil at said end thereof adjacent to the covered convolutions for engagement by a contact shoe.

2. As a new article of manufacture, a slab of refractory material having an arcuate groove in a face thereof, said groove having a portion at one end thereof deeper than the remainder of the groove, a helical coil of resistance wire disposed in said groove so that the convolutions thereof which are in the deeper portion do not project above the face of the slab but a portion of each convolution in the remainder of the groove projects above said surface, refractory cement substantially filling said groove and entirely covering the convolutions in the deeper portion thereof, and a contact member mounted on said slab to overlie the covered convolutions, said contact member being in direct electrical connection with the end only of said wire adjacent to the covered convolutions.

3. In a rheostat, a slab of refractory material, a helical coil of resistance wire having a number of convolutions adjacent to one end thereof entirely embedded in said refractory material and having the remainder of the convolutions partially embedded in said material, a terminal element connected to said end only of said coil, a contact shoe slidable across the exposed portions of the partially embedded convolutions and said terminal, and a second terminal constantly connected to said shoe.

4. In a rheostat switch, a member of refractory material, a helical coil of resistance wire having a number of convolutions adjacent to one end thereof entirely embedded in said refractory material and having the remainder of the convolutions partially embeded in said material, a fixed contact element connected to the end only of the resistance wire adjacent to the fully embedded convolutions, and a movable element slidable over the fixed element and the exposed portions of the partially embedded convolutions whereby said fully embedded coils represent the minimum portion of the resistance coil which can be included in the circuit.

5. In a rheostat switch, a member of refractory material having a channel therein, a coiled resistance element disposed in said channel, a fixed contact element mounted on said member and electrically connected to one end of said resistance element, refractory cement covering and insulating from said fixed contact element a number of the convolutions of said resistance element adjacent to said end, and a movable contact element slidable upon said fixed contact element and the remaining convolutions.

6. In a rheostat switch, a member of refractory material having a channel therein, a coiled resistance element disposed in said channel, a fixed contact element mounted on said member and electrically connected to one end of said recoil of resistance wire disposed in said groove, and

a pair of stationary contact elements mounted on said slab, one said element having a circular portion within and concentric with the circle defined by said groove and another portion extending radially beyond said circle between the ends of said groove, the other said element being connected to an end of said resistance wire and being arranged to overlie and be insulated from several turns of the wire adjacent to said end, the

first said element having an upstandingv ear at anedge of the radially extending portion thereof to act as a stop for a rotatable contact shoe and a pair of recesses in the circular portions thereof to act as yielding detents for said shoe when said shoe is respectively in contact with said ear and in contact with said other contact element.

HUGH W; BATCHELLER.

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