US2954447A

US2954447A - Thermostatic switch

Info

Publication number: US2954447A
Application number: US781266A
Authority: US
Inventors: John D Bolesky; Edward G Them; Rupert F Cox
Original assignee: Therm O Disc Inc
Current assignee: Therm O Disc Inc
Priority date: 1958-12-18
Filing date: 1958-12-18
Publication date: 1960-09-27
Anticipated expiration: 1977-09-27

Description

Sept. 27, 1960 J. D. BOLESKY ETAL 2,954,447

THERMOSTATIC SWITCH Filed Dec. 18, 1958 33 FIG. 2

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INVENTORS. JOHN D. BOLESKY. EDWARD G THEM 8 RUPERT F COX ATTORNEY atent Patented Sept. 27, 1360 THERMOSTATIC SWITCH John D. Bolesky, Edward G. Them, and Rupert F. Cox,

Mansfield, Ohio, assignors, by direct and mesne assignments, to Therm-O-Disc, Incorporated, Mansfield, Ohio, a corporation of Ohio Filed Dec. 18, 1958, Ser. No. 781,266

8 Claims. (Cl. 200138) This invention relates to an electrical switch, and more particularly to a thermostatically controlled switch. The present invention is described and illustrated herein as embodied in a thermostatically-actuated switch of the type which is used to interrupt electric circuits on the exceeding of a predetermined temperature to which the switch may be subjected.

Among the disadvantages associated with previously proposed switches of this general type has been the complexity and relatively high cost of such switches. Also such previously proposed switches were found to be susceptible to arcing when the switch contacts are closed or opened. Such arcing may result in defective operation of the electrical circuit being controlled by the switch. Moreover, if the tendency toward arcing continues over a period of time, the switch contacts are likely to become burned so that the switch ultimately becomes completely defective.

The present invention is directed to a novel switch construction which avoids these disadvantages.

It is among the objects of the present invention to provide a novel and improved thermostatically controlled electrical switch.

It is also an object of the present invention to provide a novel switch which has an improved coaction between the switch contacts when the latter are opened or closed which inhibits arcing between the switch contacts at this time.

It is another object of this invention to provide a novel switch in which the mobile switch contact has a rocking or wiping movement on the fixed switch contact when these contacts are either closed or opened, such rocking or wiping movement tending to prevent the arcing between these switch contacts resulting in the burning thereof.

Another object of this invention is to provide a novel and improved switch which is particularly well-adapted for use in conjunction with a snap-acting thermostatic element.

Another object of this invention is to provide a novel switch in which the required movement of the contactcarrying arm in the switch is reduced.

Another object of this invention is to provide a novel thermostatically operated switch of simplified construction which is less costly than previous switches of this general type.

Other objects and advantageous features of the invention not at this time more particularly pointed out will become more apparent as the nature of the invention is better understood from the following detailed description, taken in conjunction with the accompanying drawing.

- In the drawing:

Figure l is a sectional view taken centrally through the present switch with the snap-acting thermostatic element in its normal position; taken on line 11 of Figures and 6;

Figure 2 is a similar view showing the switch when the thermostatic element is in its opposite extreme position;

Figure 3 is a sectional view taken centrally through the switch along the line 33 of Figures 1, 5 and 6;

Figure 4 is a top view of the switch, partly in plan and partly in section, taken along the line 44 of Figure 1;

Figure 5 is a sectional view taken along the line 5-5 of Figure 1;

Figure 6 is a bottom plan view of the switch shown in Figure l; and

Figure 7 is a perspective view of the contact-carrying arm of the present switch.

Referring to the drawing, the thermostatic switch of the present invention includes a bottom housing member 10 of suitable insulation material. This bottom housing member has an upstanding annular side wall 11 having three circumferentially spaced, radially outwardly protruding portions 11a, 11b and (Figure 6) which extend up from its lowerend. These'outwardly protruding portions terminate about half-way up the housing side wall 11. Between these protruding portions at their upper ends, the housing side wall presents three circumferentially spaced, downwardly facing shoulders 13. Above these shoulders 13 and the upper ends of the protruding portions 11a, 11b and 116 the housing side wall has an integral radially outwardly offset upper end 12. A bottom wall 14 extends across the lower end of the bottom housing member 10, being joined integrally to the lower end of the side wall 11.

The switch housing also includes a top cover 15 of the same insulation material. The top edge of the bottom housing member 10 is formed with an annular groove 16 at its periphery which receives a complementary annular peripheral portion 17 of the top cover 15. Also, the top cover just inward radially from its peripheral portion 17, presents a rabbet 18 which receives a complementary annular protrusion 19 on the top edge surface of the lower housing member 19. Just inward radially from the rabbet 18 the top cover 15 presents a downwardly protruding annular portion 15a which is received snugly in a complementary annular recess 20, which is formed in the bottom housing member 10 and is open at the latters upper end. With this arrangement, the top cover 15 has a snug fit with the bottom housing member 10 when these parts are assembled together. The top cover 15 extends across the upper end of the bottom housing member and substantially closes the same.

A two-piece metal holder is provided for mounting the switch. This holder includes a flat plate member 21 which engages beneath the downwardly-facing shoulders 13 on the bottom housing member 10. The plate member 21 is formed with a central opening 22 which is shaped complementary to the lower portion of the side wall 11 of the bottom housing member 10 so as to slidably receive the same. The holder also includes an upper member which presents a substantially cylindrical upstanding side wall 23 which extends snugly around the enlarged upper portion 12 of the side wall 11 of the bottom housing member 10 and around the periphery of the top cover 15. This cylindrical side wall portion 23 is joined at its lower end to a flat transverse flange 24 which lies flush with the top of the plate member 21. These members are formed with aligned mounting holes 25 for receiving suitable mounting means, such as the screws shown in dotted lines in Figure l. The flange 24 at its periphery has four tabs 24a-24d (Figure 6) which are turned under the plate member 21 to secure the two holder members together. At its upper end the cylindrical side wall 23 of the upper holder member terminates in a radially inturned flange 26 which extends snugly across the top of the top cover 15 just inward from the latters periphery. This flange 26 at its radially inward edge is joined to an upstanding cylindrical portion 27 which at its upper end terminates in a radially in-turned lip 28.

A bimetal disk 29, which has a snap action when subjected to suitable temperature changes, is slidably engaged between the lip 28 on the holder and the annular top edge 30 on the housing cover 15. This bimetal disk, when subjected to heat, is capable of reversing the direction of its concavity with a snap action from the condition shown in Figure 1, where it is bowed upwardly, to the condition shown in Figure 2, where it is bowed downwardly.

The housing cover is formed with a centrally disposed circular opening 31 through which a plunger 01' bumper 32 of suitable insulation material extends slidably. At its upper end the bumper prments a rounded face 33 which is positioned to be engaged by the middle of the bimetal disk 29. At its lower end the bumper presents a rounded end face 34 which is positioned to engage and operate the switch mechanism inside the housing.

In the embodiment shown in the drawing, the switch is of the single pole, double throw type, having a pair of separate fixed contacts which are positioned to be engaged alternatively by corresponding mobile contacts. However, it is to be understood that this invention also may be embodied in a single pole, single throw switch in which one of the fixed contacts and the corresponding mobile contact are omitted.

Referring particularly to Figures 1 and 2, the switch includes a lower fixed contact 40 of suitable electrically conductive material. This contact member overlies the top face 14a of the housing bottom wall An integral leg 4-1 extends from the contact proper down through the bottom wall 14 of the housing for connection to a terminal 4-2 which extends just below the housing bottom wall 14.

. he upper fixed contact member 43 extends in spaced relationship above the top face 14a of the-housing bottom wall 14. This contact member has an integral transverse extension 44 which extends down through the housing bottom wall 14 for connection to a terminal .5, which is located just below the housing bottom wall 14.

From Figures 1 and 2 it will be apparent that the respective lower and upper fixed

contacts

40 and 43 are spaced laterally from one another, being located on opposite sides of the axis of movement of the plunger 32. Also, it will be apparent from these figures that the upper fixed contact 43 presents a downwardly-facing contact surface which is positioned at a higher level than the upwardly-facing contact surface on the lower fixed contact 4t In accordance with the present invention, there is provided a novel cantilever-mounted contact-carrying arm 46 or blade which is positioned to be actuated by the plunger 32 and which carries a pair of mobile contacts for engagement respectively with the upper fixed contact 43 and the lower fixed contact itl. In one practical embodiment this arm is made of beryllium copper. It is of thin material presenting a rather broad surface area, and is flexible and resilient.

Referring to Figure 3, the cantilever support for the contact-carrying arm 46 is provided by a bushing 47 which extends up from the housing bottom wall M. In one practical embodiment, this bushing is rectangular in cross section and is seated at its lower end in a complementary upwardly-facing recess 48 formed in the housing bottom wall 14. The bushing presents a fiat substantially horizontal upper face 49 on which the flat back end 46a of the contact-carrying arm 46 rests. A rivet 50 extends down through aligned

openings

51, 52, and 53 formed respectively in the contact-carrying arm 46, the bushing 47 and the housing bottom wall 14. At its lower end this rivet is secured to a contact terminal 54 disposed just below the housing bottom wall 14. At its upper end the rivet presents an enlarged transverse head 55 which overlies the top face of the contact-carrying arm 46 around the hole 51 therein. With. this arrangement the contact-carrying arm is securely mounted in cantilever fashion.

As best seen in Figure 7, the contact-carrying arm 46 is formed with a pronounced bend 56, which extends along a line laterally inward from one side edge and terminates short of the longitudinal centerline of the arm. This bend is located just beyond the forward edge of the cantilever support bushing 47. Because of this bend, the outer free end 57 of the contact-carrying arm is inclined upwardly rom the level of the top of the cantilever support bushing $7.

The free end 57 of the contact-carrying arm 46 carries a pair of laterally spaced

contacts

58, 59 for engagement selectively with the upper and lower fixed contact 0 43 and 4 h. One of these mobile contacts 58 presents an upwardly facing contact surface for engagement with the bottom surface of the upper fixed contact 43. At the opposite side, the free end 57 of the contact-carrying arm 46 carries a mobile contact 59 which presents a downwardly-facing contact surface for engagement with the upwardly-facing contact surface on the lower fixed contact ltl. Both of the

mobile contacts

58, 59 and the corresponding fixed contacts are ofiset laterally from the longitudinal centerline of the contact-carrying arm 46, on opposite sides of such centerline. Because of the flexible nature of the contact-carrying arm 46 and the laterally offset disposition of the

mobile contacts

58, 59 with respect to the longitudinal centerline of the arm, the arm is capable of flexing laterally (i.e. about its longitudinal centerline) In the normal condition of the switch, shown in Figure 1, the free end of the contact-carrying arm 4-6 is inclined from side to side at an acute angle to the plane of its fiat mounting portion 4611. This is partly due to the fact that the bend line 56 is formed in the arm 46 only at the side of the arm where the mobile contact 59 is located. This non-symmetrical disposition of the bend line 56 would of itself tend to cause the free end of the arm to be tilted or inclined from side to side, with the side where the mobile contact 59 is located being higher; In addition, the upper fixed contact 43 is positioned at a level slightly lower than the level which the corresponding mobile contact 58 on the contact-carrying arm 46 would assume if the outer end of this arm were free to extend up the full amount determined by the bend 56 inthis arm. That is, the upper fixed contact 43 holds this side of the free end of the arm down, imposing a stress on the free end of the arm and tilting it an even greater amount from side to side.

Thus, the free end of the contact-carrying arm is stressed in its normal (Figure 1) position and it resiliently biases its mobile contact 53 upward into engagement with the upper fixed contact 43.

When the birnetal disk 29 is subjected to a temperaturechange which causes it to snap down to the inwardly bowed condition shown in Figure 2, it forces the plunger 32 downwardly and the rounded lower end 34 on the plunger transmits this force to the contact-carrying arm 4-6 at a point thereon which is located slightly to the right of its longitudinal centerline as viewed in Figure 5 midway between its ends. Thus the free end of the contact-carrying arm is moved downwardly in such a manner as to insure that its mobile contact 58 is first moved out of engagement with the upper fixed contact 43 and then to move its mobile contact 59 into engagement with the lower fixed contact 40.

An extremely important aspect of the present invention plunger force is applied. Because of this, as the plunger force first applied, it exerts a lateral torque on the contact-carrying arm which tends to cause the mobile contact 58 to rock on the upper fixed contact 43 as it is separating therefrom. Rather than moving directly down away from the upper fixed contact 43, the mobile contact 58 is progressively peeled away from the upper fixed contact. Because of this novel interaction between the fixed and mobile contacts, the tendency for an arc to form between them as they are being separated, is greatly reduced. I

in like manner, the point of application of the plunger force is offset laterally to one side of a straight line 62 (Figure 7), joining the other mobile contact 59 on the contact-carrying arm and the mounting hole 51 for this arm. Because of this, after the mobile contact 59 first engages the lower fixed contact 4!} and as the plunger 32 continues to move downwardly, the mobile contact 59 rocks on the lower fixed contact 4%}. Due to this rocking action, the tendency for an arc to form between these contacts at this time is greatly reduced.

When the plunger 32 moves downward, as described, the lateral torque which it exerts on the contact-carrying arm 46 tends to increase the side-to-side inclination of the free end of this arm.

Thus, in both of its extreme positions the contactcarrying arm 46 has positive forces exerted thereon which tend to maintain its free end inclined from side to side. In its normal (Figure 1) position this force is due to the laterally offset location of the bend line 5a in this arm and the position of the upper fixed contact 43. In its actuated (Figure 2) position this force is provided by the plunger, which is offset to one side of the lower fixed contact 40 which is engaged at this time. In both cases, such side to side inclination of the free end of the contact-carrying arm 46 enhances the above-described rocking action of the engaged contacts.

In addition, because of such inclination, the mobile contact which is disengaged from the corresponding fixed contact is spaced farther apart from that fixed contact than it would be in the absence of such inclination. Thus, the present switch provides adequate spacing between the disengaged contacts with reduced movement of the free end of the contact-carrying arm 46 when the switch is operated.

As shown in the drawings, both the upper fixed contact 43 and the lower fixed contact 40 present convex contact surfaces which are rounded in the direction of the justdescribed rocking actions, so as to facilitate such rocking actions. As shown, the mobile contacts 58- and 59 also present convex contact surfaces. However, it is to be understood that the respective contact surfaces can be substantially flat and still obtain greatly improved operation of the switch from the arc-prevention standpoint, as compared with previous switches for this same purpose.

Having thus described our invention so that those persons skilled in the art may understand and practice the same, what we desire to obtain by Letters Patent is covered in the appended claims.

We claim:

1. A thermostatic control device comprising a support, a flexible contact-carrying arm mounted on said support and having -a movable portion disposed outwardly from said support, one side of said arm having a bend therein to position the outer free end of the arm at an acute angle laterally to the portion thereof engaging said support, a mobile contact mounted on the outer end of said movable portion of the contact-carrying arm, a fixed contact positioned tobe engaged by said mobile contact, and means including a bimetallic disc for applying a force to said contact-carrying arm on the center line thereof between said support and said mobile contact so as to move the mobile contact with respect to the fixed contact and rock said mobile contact on said fixed contact when in engagement therewith.

2. The device of claim 1 wherein said mobile contact normally engages said fixed contact, and said forceapplying means separates the contacts by rocking the mobile contact on the fixed contact and then moving the mobile contact away from the fixed contact.

3. The device of claim 1 wherein said mobile contact normally is spaced from engagement with said fixed contact, and said force-applying means moves the mobile contact into engagement with the fixed contact and then rocks the mobile contact on the fixed contact.

4. A thermostatic control device comprising a support, a flexible, resilient contact-carrying arm mounted at one end in cantilever fashion on said support and having a movable free end extending outward from said support, a pair of laterally spaced mobile contacts on the outer free end of the contact-carrying arm, fixed contacts positioned in the path of movement of said mobile contacts to be engaged thereby, and means including a bimetallic disc and a reciprocating member for applying a force to said contact-carrying arm at a location thereon between its mounted end and its free end and intermediate a pair of straight lines between said support and said mobile contacts so as to move said mobile contacts with respect to said fixed contacts and rock a mobile contact on its adjacent fixed contact when in engagement therewith.

5. The device of claim 4 wherein said contact-carrying arm has a bend therein between said support and one of said mobile contacts, said bend being formed along a line which extends laterally inward from one side edge of the arm and terminatm short of the opposite side edge of the arm, and said free end of the contact-carrying arm when adjacent contacts engage each other lies in a plane extending laterally of the arm at an acute angle to the mounted end of the arm.

6. In a thermostatic control device, the combination of a resilient flexible contact-carrying leaf arm mounted at one end in cantilever fashion and having a movable free end beyond its mounted end, a pair of separate mobile contacts mounted on opposite faces of and adjacent to the free end of said arm at locations thereon which are offset laterally from the longitudinal centerline of the arm on opposite sides of said centerline, and a pair of oppositely facing fixed contacts positioned respectively to be engaged by said mobile contacts in the alternate positions of the free end of the arm, said arm having a bend formed along a line which extends laterally inward from one side edge thereof and terminates short of the center line of the arm whereby when one set of contacts are so engaged said free end of the arm is tilted from side to side increasing the gap between the other of said set of contacts.

7. The combination of claim 6 wherein there is provided means for exerting a force on said arm substantially on its longitudinal centerline at a location thereon between its mounted end and the mobile contacts to move the free end of the arm away from one of said fixed contacts and toward the other fixed contact.

8. The combination of claim 6 wherein there is provided means for exerting a force on said arm intermediate the extremities thereof at a point between a pair of lines extending from the point where the arm is secured on the support to the mobile contacts carried on said arm.

References Cited in the file of this patent UNITED STATES PATENTS 1,853,964 Dorgeloh et al. Apr. 12, 1932 2,705,602 Muhmer Apr. 5, 1955 2,717,297 Walker Sept. 6, 1955 2,814,685 Flight et a1. Nov. 26, 1957 2,861,143 Grover Nov. 18, 1958 2,873,328 Hajny Feb. 10, 1959