US2210084A

US2210084A - Thermally actuated switch

Info

Publication number: US2210084A
Application number: US196616A
Authority: US
Inventors: Clarence W Kuhn; Allan P Charbonneau
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1938-03-18
Filing date: 1938-03-18
Publication date: 1940-08-06
Anticipated expiration: 1957-08-06

Description

Aug. 6, 1940. c;. w. KUHN El AL 2,210,084

THERMALLY ACTUATED SWITCH Filed March 18, 1938 Patented Aug. 6, 1940 UNITED STATES THERMALLY ACTUATED SWITCH Clarence W. Kuhn and Allan P. Charbonneau, Wauwatosa, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application March 18,

8 Claims.

This invention relates to thermally actuated switches for protecting electric translating apparatus such as electric motors.

An object of the invention is to provide a simpie, compact and reliable thermally actuated switch unit for protecting an electric motor or other translating device under overload conditions.

Another object is to provide a protective switch of the aforesaid character which is responsive to abnormal current conditions in the motor circuit and which may also be associated with the motor in such a manner as to be influenced by heat conditions within the motor.

15 Another object is to provide a cycling overload switch for electric motors in which a single spring serves to effect snap operation of the switch and to also eifect resetting thereof.

Another object is to provide a switch of the aforesaid type which can readily be modified to provide for manual resetting.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates certain embodiments of the invention which will now be described, it being understood that various modifications may be made in the embodiments illustrated without departing from the spirit and scope of the appended claims.

In the drawing,

Figure 1 is a vertical sectional view of a switch unit embodying the invention;

Fig. 2 is a top view taken substantially on line 2-4 of Fig. 1;

Fig. 3 is a perspective view of one end of a cover shown in Fig. 1;

Fig. 4 is a view illustrating an electric motor having a switch unit embodying the invention mounted thereon;

Fig. 5 is a fragmentary side view partly in section illustrating a modification of the switch unit shown in Fig. 1;

Fig. 6 is a sectional view on line 6-6 of Fig. 5;

Fig. '7 is a sectional view similar to Fig. 5 illustrating another modification of the switch unit shown in Fig. 1, and

F g. 8 is a fragmentary sectional view on line 8-8 of Fig. '7.

Referring to Figs. 1 and 2, the same illustrate a switch unit including a snap switch mechanism I having electrothermal actuating means associated therewith comprising a thermally responsive bimetallic strip 2 and an electric heater 3. Said snap switch mechanism is carried by an elongated insulating base 4 formed of molded material and is mounted within a narrow recess 5 in the upper face of said base.

The snap switch mechanism i is made up of stamped sheet metal parts comprising a bracket 6, an operating lever I, a contact lever 8 and a 1938, Serial No. 196,616

stationary contact 9. Said mechanism also includes an over-center spring Ill for effecting snap movement of contact lever i into and out of engagement with the stationary contact 9 and for being located adjacent the right hand end of recess 5, and operating lever l is arranged within an opening IS in projection I4 and is pivotally mounted upon projection l3. As shown in dotted lines in Fig. 2, the right hand end of operating lever 1 is formed to provide a tongue l6, and projection I2 is provided with an opening for receiving said tongue and is notched on opposite sides of said opening as shown at ll to receive knife edged end portions on said operating lever. The upper and lower edges of opening IS in projection l4 act as stops to limit pivotal movement of operating lever l in opposite directions, and the free end of said operating lever is provided with an upwardly extending forked projection I8- which is located to the left of projection l4. Contact lever 8 is bifurcated to provide spaced arms |9l9 and the side portions of forked projection I8 are notched as shown at 20 to receive knife edges on the extremities of said arms Stationary contact 9 1s arranged below the free end of contact lever 8 and said contact lever is movable in opposite directions between said sta tionary contact and a stop projection 2| formed on the left hand end of recess 5. The over-center spring III is arranged between the arms l9l9 of contact lever 8 and has one end connected to the free end of said contact lever, and its opposite end connected to the upper end of projection l4 on bracket 6. Contact lever 8 is also connected to bracket 6 by a flexible connection 22 having one end soldered to the free end of said contact lever and its opposite end soldered to projection l3.

As'is apparent from Fig. 1, spring i0 acts to hold contact lever 8 in engagement with the forked projection l8 on operating lever l and also acts to hold said operating lever in engagement with projection l3 on bracket 8. Also as is .apparent from Fig. 1, spring l0 acts to bias operating lever l upwardly to normally hold the same in engagement with the top edge of the recess in projection I4. With operating lever i in normal position the pivot of contact lever B is located above the axis of spring Ill and the free end of said contact member is thus normally held in engagement with stationary contact 9. 'During downward movement of operating lever l or lower the left hand end of strip 2.

into the dotted line position shown in Fig. 1 the pivot of contact lever B is moved into a position below the axis of spring i 0 and said contact member is then moved with a snap action under the action of said spring out of engagement with stationary contact 9 and into engagement with the stop projection 2|. When operating lever 1 is released the same returns to normal position under the action of spring l0 and the pivot of contact lever 8 is moved into a position above the axis of spring Hi to thereby effect snap movement of said contact lever into engagement withstationary contact 9. As shown in Fig. 1, an adjusting screw 23 is associated with the left hand end of bracket 6, said screw being threaded into an opening in the bottom wall of casing 3. As is apparent, screw 23 may be adjusted to spring the left hand end of bracket 6 with respect to the right hand end thereof to vary the normal angular position of contact lever 8 with respect to spring in and thereby vary the pressure of said contact lever on stationary contact 9.

The bi-metallic strip 2 extends between opposite ends of recess 5 and is arranged to engage the upper end of forked projection it on operating lever i. The right hand end of strip 2 is supported within an opening in projection I3 on bracket 6 and the left hand end thereof is slotted to receive a grooved adjusting screw 23. Screw 26 is threaded within an opening in the left hand end of insulating base ii and is adjustable to raise Heater 3 is arranged above the bi-metallic strip 2 in spaced relation with respect thereto and is provided with end terminal portions which are secured to hollow

terminal rivets

25 and 23 passing through openings on opposite ends of base 3. As shown in Fig. 1, stationary contact 9 is secured within a recess in the under side of base l by the rivet 26, and said contact is provided with an opening for rendering screw 24$ accessible for adjustment. The right hand' end of heater 3 is provided with a terminal element 2! which is held in place by the terminal rivet 25 and said heater is enclosed by a removable cover 28. Cover 28 is U-shapedin cross-section, and as shown in Fig. 3 the opposite ends thereof are cut away as shown at 29 to clear the terminal portions of heater 3. Also as shown in Fig. 3 the end portions of cover 28 are provided with opposed projections 30 and as shown in Fig. 2 said projections engage shoulders 35 formed on opposite ends of base 3 to releasably hold said cover in position upon said base.

Referring now to Fig. 4, the same illustrates an electric motor 32 having a terminal housing 33 which is provided with a removable cover plate 33. The above described switch unit may be mounted within the terminal housing 33 and when so mounted the same is wrapped in a suitable insulating cover and connected in the motor circuit so that the current supplied to the motor passes through heater 3. As is apparent, when the switch mechanism is in closed position circuit is established from terminal 21 through the heater 3 to stationary contact 9, and thence through the snap switch mechanism l to terminal l2. The bi-metallic strip 2 is heated by heater 3 and upon given overload conditions said strip overcomes the biasing action of spring ID on operating lever 1 and moves said lever downwardly into circuit opening position. The motor circuit is thus interrupted, and upon cooling of bimetallic strip 2' operating lever I returns to normal position to reestablish the motor circuit. In

the embodiment shown in Fig. 3 the operation of the switch is influenced to some extent by heat generated within the motor. By adjusting screw 24 the position of the bi-metallic strip 2 with respect to heater 3 can be varied to vary the current value at which the switch is moved into open position.

The switch shown in Fig. 1 may be modified as shown in Figs. 5 and 6 to provide for manual resetting thereof. As shown in Fig. 5 the stop 2| (Fig. 1) is cut away to clear the free end of contact lever 8 and a resetting element 35 comprising a flat insulating bar is slidably mounted within recesses in the side walls of easing 4. Element 35 is held within said recesses by the cover member 28 and as shown in Fig. 6 said element has a push button 36 fixed to the right hand end thereof and is biased to move toward the right by a spring 31 held under compression between said push button and a washer 38 which bears against the right hand side of insulating base 5. Also as shown in Fig. 6 element 35 has a shoulder 39 on the left hand end thereof for engaging the left hand side of insulating base 4 to normally hold said element in the position shown in the drawing against the action of spring 31. The under side of element 35 is provided with a stop surface 50 and cam surface 6|. The stop surface 30 normally engages contact lever 3 upon opening thereof and said stop surface acts to permit movement of said contact lever into a position wherein the axis of spring I0 is maintained abovethe pivot of said contact lever upon return of operating lever i to normal position. Contact lever 8 is therefore normally maintained in open position upon return of operating lever i to circuit closing position. However, upon depression of push button 36 the cam portion M on element 35 acts to move contact lever 8 downwardly and with operating lever l in normal position the axis 40 of spring it is located below the pivot of contact lever 8 to provide for return of said contact lever to circuit closing position.

In Figs. 7 and 8 resetting of the switch is effected by means of a pivoted resetting element 53 comprising a flat insulating bar mounted within recesses in the side walls of base 6. As shown in Fig. 8 resetting element i3 has its left hand end pivoted as shown at it upon the left hand side wall of base 6 and the opposite end thereof is provided with an operating handle '55. Element 33 is biased upwardly by a bow spring 53 held within a recess in the right hand side wall of casing i, and is normally held in the position shown in the drawing against the action of said spring by cover 21. The resetting element 63 normally permits opening movement of contact lever B-into a position wherein the axis of spring l0 is-maintained above the pivot of contact lever 8 upon return of operating lever i to normal position. Contact lever 8 is therefore normally maintained in open position upon return of operating lever 1 to circuit closing position. However, upon downward movement of resetting element 63 contact lever 8 is moved downwardly, and with operating lever l in normal position the axis of spring l0 assumes a position below the pivot of said contact lever to provide for reclosure thereof.

What we claim as new and desire to secure by Letters Patent is:

1. In an overload protective device, in combination, a fixed support, a switch operating member movable in opposite directions between extreme circuit closing and circuit opening positions and having one end pivoted upon said support, a

contact element having one end pivoted upon the free end of saidoperating member, an over-center spring having one end connected to said contact element and its opposite end connected to said support, the pivot of said contact element being movable by said operating member relative to said spring to efiect snap movement of said contact element between circuit opening and circuit closing positions, and a thermally-actuable member for controlling said switch operating member.

2. In an overload protective device, in combination, a fixed support, a switch operating member movable in opposite directions between extreme circuit closing and circuit opening positions and having one end pivoted upon said support, a contact element having one end pivoted upon the free end of said operating member, an elongated over-centcr spring having one end connected to said contact member and its opposite end connected to said fixed support, the pivot of said contact element being movable by said operating member relative to said spring to eiiect snap movement of said contact element between circuit opening and circuit closing positions, said spring being also arranged to constantly urge said switch operating member toward circuit closing position, and means for controlling said switch operating member including a thermally-actuable member.

3. In an overload protective device, in combination, an elongated operating member having one end movable about a fixed axis, a thermal element responsive when heated to move said operating member ,out of a given normal position, a contact member pivoted upon the free end of said operating member, an elongated over center spring having one end secured to said contact member, a fixed support for the opposite end of said spring, the pivot of said contact member being normally located to one side of the axis of said spring and being movable into a position on the oppositeside of said axis by movement of said operating member out of normal position, and said operating member when moved out of normal position being biased to return to such position under the action of said spring, and means for adjusting said stationary support to vary the normal angular relation of said spring and said contact member.

4. In an overload protective device, the combination with a snap switch including an operating member movable in opposite directions between circuit opening and circuit closing positions and biased to move toward the latter position, an electric heater connected in series with said switch, an elongated bi-metal element arranged in heat receiving relation to said heater and supported at opposite ends, said bi-metal element tendingwhen heated to bow away from said heater, and being responsive upon a given current value in said heater to move said operating member into circuit opening position, and means for adjusting said bi-metal element with respect to said heater to vary the current value at which said bi-metal element responds to effect opening of said switch.

5. In an overload protective device, in combination, an elongated insulating base, a snap switch mounted within an elongated opening in one side of said base and having an operating part movable in opposite directions between extreme circuit opening and circuit closing positions, said operating part being biased toward circuit closing position, an elongated electric heater having its opposite ends secured to said base and connected in series with said switch,

an elongated bi-metal element mounted upon said base and arranged in heat receiving relation .to said heater, said bi-metal element being responsive upon a given current condition in said heater to move said operating member into circuit opening position, and means carried by said base for adjusting said bi-metal element with respect to said heater to vary the current condition at which said bi-metal element responds to effect opening of said switch.

6. In an overload protective device, in combination, a pivoted switch member movable in opposite directions between extreme circuit opening and circuit closing positions, a thermally actuated operating member therefor, an overcenter spring operatively connecting said switch member and said operating member to move said switch member out of circuit closing position with a snap action upon movement of said operating member out of agiven normal position, said spring being ineffective to return said switch member from circuit opening position to circuit closing position upon return of said operating member to normal position, and manual resetting means for rendering said overcenter spring effective to'return said switch member to circuit closing position but only upon return of said operating member to normal position.

'7. In an overload protective device, in combination, a pivoted switch member movable in opposite directions between given extreme circuit opening and circuit closing positions, a thermally actuated operating member therefor, a spring for effecting snap movement of said switch member out of circuit closing position upon movement of said operating member in one direction out of a given normal position, saidoperating member being constantly biased toward normal position under the action of said spring, and said spring being ineifective to return said switch member to circuit closing position upon return of said operating member to normal position, and manual means for resetting said switch member in circuit closing position through the medium of said spring, but only upon return of said operating member to normal position.

8. The combination with a switch having a circuit controlling member movable in opposite directions between given extreme circuit opening and circuit closing positions, an electric heater connected in series with said switch, a switch operating member having thermal actuating means associated therewith subjected to control by said heater, a spring for effecting snap movement of said contact member out of circuit closing position upon movement of said operating member in one direction out of a given normal position under the action of said thermal operating means. said operating member being constantly biased toward normal position under the action of said spring, and said spring being ineffective to return said contact member to circuit closing position upon return movement of said operating member to normal position, and manual means for resetting said contact member in circuit closing position through the medium of said spring but only upon return of said operating member to normal position.

ALLAN P. CHARBONNEAU.

CLARENCE W. KUHN.