Oct. 8, 1946. 2,408,873 c. M. OSTERHELD SNAP ACTING THERMOST‘ATIC SWITCH Filed March' 20, 1944 2/7 w-J 727-5 . . BIME r111. ~ 8/) —6 B/MET‘IL 0 f/ —7 J91 3.; 77f” ‘9.9 1s(4 ‘99 93 BYLAR0W)? /V allél’ENTOR. i'rman 6 C 713-10 n23 k . 2,408,873 Patented Oct. 8, 1946 UNITED STATES PATENT OFFICE _, - 2,408,873 _ smr some. THERMOSTATIC swrrcn Clark M. Osterh'e'ld, Stoughton, Wis., assignor to McGraw Electric Company, Elgin, Ill., a cor poration of Delaware Application March 20, 1944, Serial No. 528,549 9 Claims. (Cl. 200-138) 1 My invention relates to switches and particu larly to snap acting thermostatic switches. An object of my invention is to provide a 2 site‘ sides of the bar to form a socket of channel shape, or secured thereto at its free end socket members 28 and 29, which are of channel shape relatively simple, compact and inexpensive snap acting thermostatic switch assembly. and are secured as by welding or brazing to op shall increase the contact pressure until the in may use a bimetal bar 3|, the thickness of which posite sides of the bar 25. The shape of the bottom wall of the socket members may be ?at Another object of my invention is to provide or have a special form, as will be referred to a relatively simple snap acting thermostatic hereinafter. , switch in which there shall be pressure between I provide a second or auxiliary bimetal/bar 3|, the contacts until theinstant of separation. Another object of my invention is to provide 10 which is preferably, although not necessarily, relatively thinner than the bimetal bar 25. I means in a snap acting thermostatic switch that is on the order of .015", although this particular dimension is noted for illustrative purposes only. Other objects of my invention will either be apparent from a description of several different 15 The inner end of the second bimetal bar 3| is provided with a knife edge, and the outer end forms of devices embodying my invention or will thereof has secured thereto a contact member be pointed out during such description and set stant of separation. 33. The knife edge end of bimeta1 bar 3| is adapted to be located in the members of chan Figure 1 is a view, in side elevation; of a snap 20 nel shape formed or provided at the free end of the ?rst bimetal bar 25. I wish to point out that acting thermostatic switch embodying my in the high expansion element is on the same side vention, of the assembly in this form of device as well as Fig. 2 is a View in front elevation thereof, in all of the other forms using two bimetal Fig. 3 is a top plan view thereof, Fig. 4 is an enlarged view, in end elevation, 25 members. The supporting block or base 2| has mounted of the free end of one member of the switch,v _ thereon a contact member 35 adapted to engage Fig. 5 is a top plan view of another form em with and be disengaged from the contact mem bodying my invention, ber 33 on the second bimetal bar 3|. A stop Fig. 6 is an exploded top plan view of the two means for the free end of the second bimetal bar toggle members embodied in the form shown in 3| comprises a bar 31, of substantially Z-shape, Fig. 5, having one end portion thereof secured against Fig. 7 is a view, in side elevation, of the parts the upper surface of base 2| as by a machine shown in Fig. 6, screw 39. The other end portion of the bracket Fig. 8 is a view, in side elevation, of another 31 has secured therein an adjustable stop screw form of device embodying my invention, 35 4| which may be held in any desired adjusted po Fig. 9 is a fragmentary view, in side elevation, sition by a lock nut 43. of a modi?cation embodying my invention, and, The bimetal bar 25 has a medial longitudinally Fig. 10 is a view, in side 9 vation, of another extending slot 45 therein starting at the free end ‘modi?cation embodying my invention. Referring ?rst of all to Figs. 1 to 4 inclusive, ' 40 and extending thereinto over about one-half of its length. The second bimetal bar 3| has a I have there shown a base 2|, of electric-insulat— similar elongated central slot 41 therein starting ing material on which the parts of the switch at the knife edge end thereof and an over-center particularly constituting my invention are mount spring 49 is located in the two slots and has the ed. I provide a small block 23, of electric-insulat ing material, secured to base 2| adjacent one of 45 ends thereof secured to the respective interme diate portions of the two bimetal bars 25 and 3|. the ends thereof. I provide a ?rst or main bi The combination of the two bimeta1 bars 25 and metal bar 25 having one of its ends secured to 3| and the over-center spring constitute a toggle base 23 as by one or more machine screws 21. and, upon change of temperature, the second bi For illustrative purposes only I may here state that the thickness of-the bimetal bar 25 may be 50 metal bar 3| will move from one limiting posi tion to an opposite limiting position with a snap on the order of .025” or .030", although I do action. not desire to be limited thereto. The free end A brief description of the opera-tion of the de of bar 25 has either formed therein a socket vice shown in Figs. 1 to 4 is as follows: Fig. 1 member, which is of channel shape in lateral sec tion, as by bending integral portions out on oppo 55 shows the general positions of the parts when forth in the appended claims. In the drawing, . 3,408,878 3 the temperature of the air is at a relatively low value so that the two contact members it and ll are in circuit-closing position, that is if the switch controls an electric heater, the said heater / ll. This results in greater pressure between the contacts a and I! Just before disengagement thereof. Referring now to Figs." 5 to 'l inclusive of the will be energized. The position of the knife edge end of the second bar 3! will be substantially that ‘ drawing, ' I have there shown a modi?cation em shown in Fig. 1 of the drawing, that is the knife edge end will be in engagement with the upper _ ,insulating material has mounted thereon adia bodying my invention. A base II, of electric corners of the socket members of channel shape.‘ ' , ‘ 1 cent toone end thereof a small block I: also of electric-insulating material against which is se The spring 40 is under tension and causes . the‘ knife edge end to be held tightLv in engagement ‘ . ‘with the inner wall of the socket member and also causes a contact pressure to existbetween the contact members it and SI. ‘ ‘ V ycured one end of a‘bimetal bar It as by machine screws 51. The bimetal bar II is of substantially the shape shownin Fig. 6, having cut out side , portions I58 adjacent the free end thereof and having ‘an extended slot 8| extending inwardly Upon increase of the temperature of .the am-. 15 from the free end, centrally of the bar 55. bient air. the ?rst bimetal bar 25 will ?ex in a A second bimetal bar BI, which is relatively clockwise direction around its ?xed end, while shorter than bimetal bar. iiphasside portions the second bimetal bar II will tend to ?ex inia ll removed. therefrom at thatv end adapted to counter-clockwise direction around the ?xed con engage socket members “formed in or secured to tact member 35. It may be here pointed out that 20 the free end of bar“. Bar 83 has slot 89 there the lateral width of the socket member of chan in extending substantially longitudinally central nel shape is such that the bimetal bar 3| will not ly thereof from itsinner end., An over-center engage the outside ends of the lower siderpore spring ‘II is adapted to be positioned in the alined tions of the socket members when the parts are in the positions shown in Fig. l of the drawing 25 slots 6i and ll and to have its ends connected with the intermediate portions of the two bars or in the opposite positions as shown by the bro SI and 63. The inner ends ‘I! of the second bi ken lines in Fig. 1. The tension of spring 49 will metal bars 83 are of rounded shape adapted to cause a certain pressure between, the knife edge fit into the socket members I‘! provided at the end of bar SI and the socket member, the result being that the parts comprising‘ particularly the 30 free end of bimetal bar II. In this form of the device the second bimetal bar 63 may be thinner adjacent engaged end portions of the two bimetal than the ?rst bimetal bar 86. bars will have a certain amount of frictional re The second' bimetal bar 83 has a contact mem sistance to any lateral movement of the knife ber 15 provided at the outer, i’ree, movable end edge end of bar II in the socket members. This thereof which is adapted to engage with and be has the result that there will be a predetermined 35 disengaged from a ?xed contact member 11 amount of pressure between the two contact mounted on the base II. I provide a stop mem members 33 and SI. thereby reducing the voltage ber for the free end of the second bimetal bar BI comprising a bracket 19 01' L-shape, having one end thereof secured to block 5| as by a machine gagement of contact member 33 from the ?xed 40 screw ii, an adjustable stop screw 83 being pro contact member 3!, the knife edge end of bar ll vided in the other end thereof adapted to be will have moved laterally in the socket member engaged by the movable end of bimetal bar 63. to a position intermediate the side walls thereof A pair of leaf springs 85 have one end thereof in case the bottom wall is ?at, and immediately secured against an intermediate portion after, if not substantially coincident with the 45 ?xedly of bimetal bar 55 at the sides thereof and extend snap acting movement of bimetal bar ll to the over the cut out portions 59, the length of these opposite position, the knife edge end of bar ll springs being such as to extend to and slightly will move into the ‘lower comer of the socket overlap the side portions 81 on bimetal bar 63, the member. overlap of the leaf springs 85 over the portions The longitudinal distance between the contact 50 81 being on the order of a few thousandths of an member 33 and the holding screw 21 is less, in inch only. It is evident that the two springs the positions of the parts shown in Fig. 1, than 85, having one end secured to the ?rst or main it will be when the two bars 25 and ll are in sub bimetal bar 55 and having the second end there stantially longitudinally alined positions, which of overlapping and engaging with an intermediate latter positions they will occupy an instant be portion of the second or auxiliary bar 63, will fore the above described snap acting movement cause a lateral pressure against bar 63, the result of the second bar ii, with the attendant result being that the contact member 15 will be sub that during the change of positions from those ject to an increased pressure against the ?xed shown in Fig. 1 to when they are in substantial contact member 11. This contact pressure is alinement with each other, the contact member II will have a sliding movement on contact mem 60 additive to that produced by the inner end of the second bimetal bar moving in the socket members ber II with the result that a self-cleaning pair 61 provided at the free ends of the ?rst bimetal of contacts is obtained. ‘bar 55. It is evident that the springs 85, the I may increase the frictional resistance to movement of the inner end of bar 3| by making 65 ends of which engage one side of bimetal bar it, will have those ends move past the ends of the the bottom‘ wall of other than ?at shape. I portions 81 of the second bimetal bar when snap have shown a preferred shape in Figs. 1 and 4, acting movement of the second bar occurs, so that this shape including a raised central portion and then the leaf springs 85 will exert a lateral pres two lowered side portions. The longitudinal dis tance between‘the contact member 33 and the 70 sure on the second bimetal bar 63, this pressure now being in the opposite direction to that ex holding screw 21 will be momentarily increased erted by the'leaf springs 85 in the ?rst place. during the time of snap-over action by the move Referring now to Fig. 8 of the drawing, I have ment of the knife edge end of bar 3| from one there shown a modi?cation of the device shown side portion to the other side portion with the result of greater tension in the over-center spring 75 in Figs. 5 to 7 inclusive, comprising a base SI, of electric-insulating material having a small drop of the current ?owing through. and con trolled by the switch. Just prior to the disen 3,408,878 - . 5 6 block 99 also of electric-insulating material se the ?xed contact member. This will be evident cured thereagainst. A ?rst bimetal bar 95 has one end thereof secured against block 93 as by one or more machine screws 91. The free end of the bar 95 has mounted thereon a socket member com prising a pair of leaf springs 99 which provide a socket member of substantially channel shape in from a consideration-of the'e?ect of the over center tension spring provided ineach of the various modi?cations, a component part of the tension of the over-center spring being active to cause the engaging contact pressure between the engaged contact members. Further, it is evident that the ?exing of the main bimetal bar, as in lateral section, the main portions of the members a clockwise direction toward the ?xed contact 99 being resilient and of arcuate shape, the length of these portions being such as to extend over the 10 member (as seen in Fig. 1) causes inherently a pressure of one contact member against the other. knife edge end of a second bimetal bar Ilil, it which contact pressure is absent in many other being understood that the bottom face of the forms of snap acting switches. socket member provided by the spring members ' The provision of a knife edge end of the second 99 is ?at and even to receive the knife edge end of the second bimetal bar llll. Here again I may 15 bar held in relatively tight frictional engagement in a socket member further causes increased con make the thickness of the second bimetal bar tact pressure between the contact members. The HH less than that of the ?rst or main bimetal bar 95. further provision of spring ‘means, of leaf shape, ‘ having one end thereof secured to the ?rst bimetal I provide a contact member I03 on the outer end of bimetal bar "H, which contact member is 20 bar and extending over the junction of the two adapted to be engaged with and disengaged from a ?xed contact member I05 secured to the other end of base 9|. I provide further a stop for the free end of bimetal bar I?l, this stop compris ing a bracket ll", of Z-shape, having one end thereof secured against base 9| and having an adjustable stop screw I09 engaged with the other end thereof. It is evident that the same com ments with regard to the wiping action of con tact I93 on contact I05 made hereinbefore in connection with the form shown in Figs. 1 to 4 in clusive, will apply here also. Further, the effect of the leaf springs 99 will be substantially the bars to engage the second bar, laterally thereof, intermediate its ends further provides additional contact pressure between the engaged contacts. The provision of two bimetal toggle arms also ensures that the temperature differential of oper ation of my improved thermostatic switch, that is, the change of temperature necessary to cause movement of the second arm from one to the other of its positions, will be relatively small. Making the thickness of the second bimetal bar less than that of the ?rst bimetal bar also tends to reduce the temperature differential of operation and when combined with the leaf springs results in a snap acting thermal switch, in which the en same, as regards the increase of pressure be tween the engaged contact members, as herein 35 gaged contacts are held with an appreciably .large or heavy contact pressure up to the instant before set forth in connection with the form of disengagement. shown in Figs. 5 to '7 inclusive, it being understood Various modi?cations may be made without de that the lateral distance between the outer ends parting from the spirit and scope of my inven of the arcuate portions of leaf springs 99 is such that one such leaf will engage the second bimetal 40 tion, and all such modi?cations clearly covered by the appended claims shall be considered as bar IIH before substantial straight alinement of part of my invention. the two bars occurs, preparatory to snap-over movement of the second bar. . I claim as my invention: 1. A snap acting thermostatic switch assembly I have shown another modi?cation in Fig. 9 comprising a ?rst bimetal bar, a second bimetal in which there is interposed, between the two bar having one end pivotally engaging one end of main arms HI and H3 of bimetal, a third short the ?rst bar, the high expansion component of arm H5 having ends of channel shape in lateral the two bars being on the same side of the as sections. The ends of the bimetal bars Ill and sembly and an over—center spring having its ends I I3 will be positioned in the upper corners of the respective sockets when the bars are in the posi 60 connected to the intermediate portions of said bars. tions shown in Fig. 9 and will occupy the lower 2. A snap acting thermostatic switch assembly corners of the sockets when the contact members comprising a ?rst and a second bimetal bar hav - ing ends pivotally connected with each other to there shown a further modification comprising a 65 form a toggle, an elongated slot at the adjacent - are out of engagement with each other. Referring now to Fig. 10 of the drawing, I have ?rst bimetal bar H‘l having socket members H9 at its free end. I provide a second arm IZI made of a single metal and having a rounded end portions of each of said bars, anover-center spring positioned in said slot and having its ends connected to intermediate portions of said bars to cause snap acting movement of the other end end adapted to be positioned in the socket mem ber I I9, while a contact member I23 is secured 60 of said second bar between two opposite limiting positions, a ?xed support for the other end of to the other free end of the single metal bar l2l. said ?rst bar, a contact member on the other end It is to be understood that the device shown in of said second bar, a ?xed contact member and a Fig. 10 of the drawing is adapted to be mounted stop member de?ning said limiting positions, the on a suitable base, and to be provided with an over-center spring substantially as shown in Fig. 65 high expansion component of said two bars be ing on the same side of the assembly to cause 1 of the drawing, but‘since the only di?erence be ?exing of both bars in the same direction around tween the device shown in Figs. 1 to 4 inclusive the fixed support and the ?xed vcontact member and that shown in Fig. 10 is that the second bi and stop upon change of ambient temperature. metal‘ bar of Fig. 1 is replaced by a single metal 3. A snap acting thermostatic switch assembly bar, it is thought unnecessary to show the addi 70 tional parts in Fig. 10 0f the drawing. 1’ The device particularly embodying my inven ' comprising a ?rst bimetal bar having one end thereof ?xed and having a laterally enlarged re cessed end portion at its other end, a second bi tion and shown in various forms provides a struc metal bar having one .end positioned in said en~ ture which inherently causes an appreciable con tact pressure of the movable contact member on 75 larged recessed end portion of said ?rst bar and 2,408,873 7 . movable laterally therein. an overcenter spring having its ends connected to said ?rst and second bar and bridging the engaged ends thereof, a ?xed contact member and ‘a contact member on the other end oi'the second bar adapted to engage with and be vdisengaaecl from said ?xed contact member with a snap action by the coincident ?ex ure in the same direction oi’ both bimetal bars around the ?xed and contact members respec tively. . 4. A thermostatic switch assembly comprising a ?rst bimetal bar having one end thereof ?xed, a second bimetal bar having one end pivotally engaging the other end of the ?rst bar, an over center spring having its ends connected to inter mediate portions or the respective‘ bars, a ?xed contact member, a contact member on the other end of the second bar adapted to be moved into 8 the side of the latter bar'intermediate its ends as the two bars move into longitudinal alinement with each other to cause a substantial pressure 01’ the contact on said auxiliary bar against the ?xed contact. 7. A thermostatic switch assembly comprising a ?rst bimetal bar having one end thereof ?xed and having laterally enlarged recessed portions at its ‘other end, a second bimetal bar having a 10 knife edge end portion at one of its ends engag ing said end portion or channel shape or the ?rst bar and movable laterally therein, an over-center spring bridging the engaging end portions of the two bars and having its ends connected to the re spective bars intermediate their ends, the high expansion component 01' both bars being on the same side of the assembly and cooperating with engagement with and be disengaged from said , said over-center spring to cause the other end oi’ ?xed contact member with a snap action and 20 the second bar to move from one limiting posi tion to another with a snap action under‘rela spring means on said ?rst bar at its other end tively small changes or temperature. and extending therebeyond over the second bar to engage the latter at one side thereof as the two bars move into alinement with each other to cause a substantial pressure oi.’ the contact mem ber on the second bar against the ?xed contact member just prior to disengagement of said two contact members. 5. A thermostatic switch assembly comprising a ?rst bimetal bar having one end thereof ?xed. a second bimetal bar having one end pivotally engaging the other end of the ?rst bar, an over center spring having its ends connected to inter mediate portions 01' the respective bars and bridg ing the engaged ends thereof, a ?xed contact member, a, contact member on the other end oi’ the second bar adapted to be moved into engage ment with and be disengaged from said ?xed con tact member with a snap action and leaf spring . means on said ?rst bar at its other end and ex tending therebeyond over the second bar to en sale the sides of the second bar intermediate its ends to cause a substantial pressure of the con 8. A snap acting thermostatic switch mecha nism comprising a pair of toggle arms. at least one of which is a bimetal bar, one of said toggle arms having one end ?xed and having socket members of channel shape in lateral section at its other end, the bottom wall of said socket mem bers having a raised central portion and two low er side portions, said second arm having one end in said socket members and movable laterally therein, an over-center spring having its ends connected to the intermediate portions of said toggle arms to cause snap acting movement of the second arm upon change of ambient tempera ture, the tension of said spring being increased by said raised central portion to cause increased contact pressure upon said lateral movement of said second arm, a ?xed contact and a contact on the other end of said second arm adapted to be engaged with and disengaged from said ?xed con tact with a snap action. 9. A snap acting thermostatic switch assembly comprising a ?rst bimetal bar having one end tact member on said second bar on said ?xed ?xed and having a socket member 01' channel contact member just prior to disengagement or I ' shape in lateral section at its other end, a sec the two contact members. 6. A thermostatic switch‘assembly comprising a main and an auxiliary bimetal bar pivotally connected‘ with each other in end-to-end relation, ond bimetal bar 01' lesser thickness than said ?rst bar having an end positioned in said socket mem her, the high expansion component of both bars the high expansion component or both bars being 50 being on the same side 01' the assembly, said bars having elongated slots in their adjacent end por on the same side of the assembly, an over-center tions, an over-center spring in said slots having spring connected with the two bars intermediate its ends connected with the respective bars ad their ends, a ?xed contact, a contact on the free Jacent to the ends of the slots, at ?xed contact end oi’ said auxiliary bar adapted to engage with and be disengaged from the ?xed contact with -55 and a contact on the other end of said second bar adapted to engage with and be disengaged from a snap action and leaf spring means on that end said ?xed contact with a snap action under rela or the main bar pivotally engaged by the auxiliary tively small changes of temperature. bar extending over the auxiliary bar to engage CLARK M. OSTERHELD.