vplil 7, 1959 M E BOURNS 2,881,294

TEMPERATURE RESPONSIVE RESISTOR Filed March 30, 1955 Jim. 2

fifa. ./0.

"nu, 45,/ l 4 if# INVENTOR.

4 56 46 25 4Z g-E x 14/ BY United States Patent 2,881,294 TEMPERATURE RESPONSIVE RESISTOR Marlaii E. Bourns, Riverside, Calif. Application March 30, 1955, Serial No. 497,877 1 Claim. (Cl. 201-48) The present inventionv relates to new and improved temperature responsive variable resistors and like devices such as, for example, potentiometers.

It is frequently desired to vary an electrical value in accordance with temperature. A wide variety of different devices have been developed for the purpose in the Ipast. Perhaps the most common of these devices are thermistors of one sort .and another. All thermistors operate by virtue of a change in the electrical resistance of a resistance element with temperature. Usually thermistors employ various semi-conductive systems having irregular temperature-conductive characteristics for the resistance element itself. Such semi-conductive systems tend to be very sensitive to variation in manufacturing conditions and in many cases to various atmospheric conditions.

It is an object of this invention to provide a new and improved type of temperature responsive resistor; more specifically, it is an object of this invention to provide a variable resistor in which the change of resistance is directly proportional to the change in temperature of the resistor. Related objects of the invention are to provide devices of the class described which are exceedingly accurate; which give a substantially uniform variation in resistance value over a comparatively wide range of temperatures; and which are easily and cheaply manufactured and assembled. Further objects of this invention as well as many advantages of it are more fully explained in the remainder of this description, the appended claim and the accompanying drawings in which:

Fig. 1 is an end view of the temperature responsive variable resistor of the invention;

Fig. 2 is a cross-sectional view taken at line 2-2 of Fig. l;

Fig. 3 is a cross-sectional view taken at line 3-3 of Fig. 2;

Fig. 4 is a cross-sectional view similar to Fig. 2 of a modified resistor of the instant invention;

Fig. 5 is a cross-sectional view similar to Fig. 3 of a second modified resistor of the invention;

Fig. 6 is a cross-sectional view taken at line 6 6 of Fig. 5;

Fig. 7 is a cross-sectional view taken at line 7-7 of Fig. 5;

Fig. 8 is a cross-sectional view similar to Fig. 2 of the drawings taken at line 8-8 of Fig. 9 showing the third modilied resistor of the invention;

Fig. 9 is a cross-sectional view taken on line 9 9 of Fig. 8; and

Fig. 10 is a detailed view showing a contact construction employed with the invention.

In the various figures of the drawings like numerals have been used to designate like parts wherever convenient for purposes of illustration and explanation. It yis to be understood that the instant invention is not to be 7 considered as being limited to variable resistors constructed as precisely illustrated in the drawings inasmuch either heated or cooled the arm as the sizes and shapes of many of the parts shown have been altered from their normal proportional sizes so as to simplify the explanation and illustration of the invention.

In Figs. l, 2, and 3 of the drawings there is shown a temperature responsive variable resistor 10 of the invention which is formed with terminals so as to be capable of being used as a potentiometer. The resistor 10 includes a non-conductive base 12 formed of an appropriate resinous material such as, for example, a lled phenolic resin to which there is attached by means of suitable adhesive such as an adhesive based upon an epoxy resin a lid 14. This lid 14 is formed of the same materials as the base 12. Held between the lid 14 and the base 12 is an L-shaped end 16 of a bimetallic movable element 18. This L-shaped end 16 is prevented from moving by contact with three upstanding projections 20 formed integrally with the base 12. Thus, with this construction the end 16 is securely held against a printed circuit layer 22 formed of conductive material such as for example a silver paint so as to be in electrical contact with this layer. If desired, the end 16 may be soldered or otherwise contacted to the layer 22 although this is not considered necessary.

The movable element 18 includes a long bimetallic arm 24 which is attached to the end 16 so as to project therefrom to immediately above a printed circuit resistance layer 26 formed of any appropriate printed circuit composition of a type known to the art. This layer 26 is preferably of arcuate shape so that if the resistor 10 is 24 will bend moving a small contact 28 attached to this arm immediately above the layer 26 with respect to the layer 26. Preferably this contact is formed as shown in Fig. 10 of the drawings so as to include a curved extremity 30, which resiliently bears against the layer 26 so as to be in electrical contact therewith. The contact 28 may be attached to the arm 24 by any convenient means such as, for example, welding, or the like.

The ends of the layer 26 are covered by layers 32 by the same material as the layer 22 so as to be in electrical communication with the layer 26. The layers 32 are formed so as to project along the base 12 outwardly from the lid so as to terminate upon a projecting end 34 of the base 12. The layer 22 is also brought out from under the lid 14 so as to terminate upon the same end. Thus with this construction various electrical connections may be made to the three layers 22 and 32.

Those skilled in the art will realize from the aforegoing description that the resistor 10 forms a very simple compact device which may be used for the purpose intended. When the resistor 10 is heated or cooled the arm 24 bends moving the contact 28 along the layer 26 so as to accomplish the intended variation in electrical resistance. It is possible to modify the construction shown in Figs. 1, 2, and 3 of the drawings so as to produce a modified resistor 36 such as is shown in Fig. 4 of the drawings. This modified resistor diiers from the resistor 10 primarily in that two movable elements 18 are held by projections 20 in such a manner that these movable elements 18 point toward one another so that contacts 28 disposed upon them move with respect to two separate resistance layers 26 of the same shape and construction previously described. Two adjacent ends of these two resistance layers 26 shown in Fig. 4 are vconnected together through the use of a short electrically conductive layer 38 of the same type as the layer 22. The other ends of the two layers 26 are shown in Fig. 4 of the drawings as connected to layers 32 as previously described.

Thus with the construction shown in Fig. 4 two movable. members. are. provided., in such., a manner that both of these movable membersv move with respect to what, in eifect, is a single resistance layer created from two levers 2.6 SQasto provide editable temperature variation.

inmenv. missile andlother applisatqnsfinwhich @Single movable element 18 as ydescribed in connection with'the resistor. 10..: does.. Het. provide. Suientmoton withVA res-pect to the resistancelayer.26soias to produce an` elec-y tricalv signal variationofa desired amountor in which a uniquecurrent dividing action is desired. Obviously the endsofjthelayers 32 and 22 show-nin both Figs. 2 andA needl notbe all connected into an electrical circuit.

In Figs. 5,6,- and 7.of the drawings apsecondrnodiiied-l resistorf40of the inverrtionisl shown which includesVv a',

base 1.2,anda lidflft as .previously described. Upon this.

blass V12.l fhsrelefe. mounted. parallel elongated nroiectiens.. 42 between which there. issdisppssd af wpundresistane element 44 of the. type well known to the art. Preferably this. resistance element is held in position through the use of 7 an. epoxy resin adhesive.v The` ends of this` resistance. elementare connected through wiresY 46 to bolts. 48 projecting through the base 12` so that appropriateelectrical connection maybe .made to this resistance i element.

In the construction shown in` FigsI 5, v 6, and 7 the lid 14 is held with respect to tliebase 121`byV means of bolti 50 which projects through. bothl the. base 12 andthe lid 14.. Movementof the. lid 14 ,or ofthebase 12 about this bolt is prevented b yedge lugs -52- formed integrally with;

thebase` 12 engaging the interior of the adjacent portions of the lid 14. Aboutv the boltl 510 thereisv positioned a metallic .'slee've. 54ttheendsfofwhich bear against both`A thebase 12fand the. lidvr14." Y This sleeve is` preferably .ofA such Ydimension thatitfitsltightly against the..bolt 50 so. asftolbe'inv electrical contact therewith. Secured to ,thev sleeve54 asfbyV weldingjor the like aretwobowed metal. lic arms 56 the. endsof whichremote'iromthe.sleeve 54.l

projections 42 and the projections 6i). so as to placethis` contact in electrical c omnrunicationl with. differentI portions of the resistanceelement .414," Thus,- withthis construction1 the projections'42iandthe projections 60act as guides preventing undesired movement of the contact 28. The use of such guidesV is tenceedingly` advantageous when theresistor40` is u ed under conditions'wher'e it is apt to ously designed:to lbef'sfed. as fone. terminal ofVv this .resis torf40.

vIn Figs. 8, and .9 of the drawingsa third modied resistor 62 ofthe invention is illustrated which is foi-med' of two identical"nonfconductive housing sections 64. and 66 formed of materials such. as. previously indicated. Within both of these sections there are provided integrally formed projections 68 so as to dene arcuate grooves 4. 7.0.v The twoseetions`64and 66. are 'held together. by means of a bolt 50 of the class previously described around which there is disposed between the two sections a sleeve 54, also as previously indicated. In this case the sleeve is held between the sections 64 and 66 so as to :be secure against rotation. Various means preventing rotation of this sleeve 5 4 canbe employed if desired. Attached to this sleeve is a bimetal helical or spiral movable elementL 72: to the end of which there is secured a contact 28 of the type illustrated in Figs. 5 6, and 7 of the drawings in such a manner that the curved extremity 30 of this. contact28 is in electrical engagement with a resistance layer 2 6k disposed betweenfthe projections 68. The upper end 58 of this contact 28is located Within the groove opposite the resistance layer 26 so as to serve as an additional guide means tending to prevent undesirable movement of the contact 28. The projections 68 on the sections 6.4;alsoserve to preventtsuch'undesirablc movement of the.4 contact 28; The ends of the resistance :layer are contacted by, small bolts 48 passing through one of the sections 64#` so that these boltsY may. be used as end terminals lfor the layer 26 with the resistorV 62; The

bolt S0 is also designed to be used as a terminal of thiscategory.

The operation of` the resistor 62 isessentially similarto the operation of the other resistors previously de.

scribed, If the `temperature of the resistor 62feither-in-- creases o r decreases-the movable kelement 72 will either tend to unwinduor-.windabout the rbolt 50 moving the contact member 28..along the grooves 70 so asto place this contact in electrical'communication with different portions ofthe layer 256.

Those skilled in the art will realize that a number-sof'.k

different variablej resistor-constructions may be designed embodying the essential features of this invention, For

this .reason thepresent invention isto be considered aslv being limitedl only by the appended claim.

I claim:

A temperatureresponswe variable resistor which com-A prises: av base formed of la non-conductive material, saidY base including three upstanding projectionsformedfintegrally therewithl so as to extend from one. sidey of said base; a bimetallicpfternperature responsiveelement having an Ll-shapedfend and a movable end `positioned with respect to said base .with said L-shaped lend held in a xed position by said upstanding projections; a resilient contact attached to said movable end of said temperaturesaid lid holding samp-.temperature responsive( element in` place against v.said base incontactv with one ror' said terminal means.

References Cited in the file of this patent UNITED STATES PATENTS 2,248,672 Holmes July 8, 1941 2,258,989 Liner V oet.l 14, 1941 2,264,487 Smulski -7---- Dec. 2, 1941l