US2897319A - Electric switch - Google Patents

Description

July 28, 1959 E, R. WOLFF 2,897,319

ELECTRIC SWITCH Filed June 26, 1958 w.- uni.

6O INSULATION INVENTOR. ERNST R. \A/OLFF United States Patent Q ELECTRIC swrrcn Ernst R. Wolff, Bloomington, 111., assignor to General Electric Company, a corporation of New York Application June 26, 1958, Serial No. 744,696

9 Claims. (Cl. 200-122) This invention relates to electric overload actuated devices and particularly to such devices adapted for use with electromagnetic contactors.

Overload actuated devices for use with electromagnetic contactors ordinarily utilize a bimetallic strip disposed to actuate a set of contacts, and a heater element energized by the circuit to be controlled, arranged alongside the bimetallic strip to cause heating and deflection thereof.

In prior art devices such bimetallic strips have been arranged so as to deflect in a direction away from the heater since movement toward the heater would eventually cause the bimetallic strip to contact the heater, causing damage. Such deflection away from the heater, however, detracts from the sensitivity and efliciency of the device.

It is an object of the present invention to provide an overload actuated device of improved sensitivity and efliciency and incorporating a bimetallic strip disposed to deflect toward a closely adjacent heater, and able to deflect its full amount without damage to itself or to the heater.

It is another object of the invention to provide an overload actuated device comprising a bimetallic strip and a movable switch member and means for directly connecting the strip to the switch member while permitting snap action of contacts carried by the switch member.

In accordance with the invention, an overload actuated device is provided including a bimetallic strip supported at one end and free to deflect at the other. An elongated heater is disposed closely adjacent the bimetallic strip. The bimetallic strip is arranged so that its free end deflects toward the heater. Means is provided, however, for limiting movement of thefree end of the strip toward the heater, and additional means is provided whereby continued deflection of the bimetallic strip produces movement of its normally stationary end so that the strip may deflect its full amount without damaging restraint.

The particular aspects of the invention considered to be novel are set forth in the appended claims. The construction of a particular embodiment of the invention, together with further objects and advantages thereof, will be easily understood, however, from the following detailed description taken in conjunction with the accompanying drawings in which:

Figure 1 is a perspective view of an overload protective device constructed in accordance with the invention;

Figure 2 is a side elevation of the device of Figure 1, the side cover being removed;

Figure 3 is a fragmentary side elevation View showing the bimetallic strip in a deflected condition;

Figure 4 is an exploded view of the parts of the device of Figure 1.

Referring now to Figures 1 and 2, the invention is shown as incorporated in an overload actuated device comprising an insulating housing 1 and a side cover 2 serving Patented July 28, 1959 to retain the parts in mounted condition. The device is adapted to be mounted by the engagement of appropriate screws with the threaded fastener 3 which is trapped in the bottom of housing 1 and to which access is provided through aperture 4. External operating members are provided including knob 5 (which cooperates with the molded projection 6 on housing 1 as a stop) and reset lever '7 which may be positioned for either manual or automatic operation through the positioning of spring 8 either in slot 9 for automatic operation or in slot 1% for manual reset operation. Terminals 11 and 12. are provided for connecting suitable conductors to resistance heater 13.

Referring now particularly to Figures 2 and 4, terminal members 11 and 12 are trapped in the molded housing 1 by the engagement of projections 14 with mating slots or deformities in the molded housing members 1 and 2. Each terminal member has a threaded opening 15 for establishing electrical connection from heater 13 to the external circuit. Threaded opening 16 in each terminal member is engaged by screw fasteners 17 which pass through apertures 18 in the flanges of the resistance heating element to establish mechanical and electrical connection between the resistance heating element 13 and terminal members 11 and 12 thereby positioning resistance heating element 13 within housing members 1 and 2.

A bimetallic strip 20 is rigidly affixed at one end to member 21 and is arranged so that its high expansion side is away from resistance heater 13 thereby causing the bimetallic strip to deflect toward resistance heater 1?) as its temperature increases.

Member '21 has two bent-up angular portions 22 which pivotally engage extensions 23 of support member 24. Support member 24 is fixedly positioned within housing 1 by the engagement of end 25 and tab 26 with mating slots in housing 1. Support member 24- also carries threaded spring fastener 27 which engages and supports screw 28 Whose head portion extends wtihin the housing and whose end portion is engaged by the knob 5. As shown in Figure 2, the member 21 has bent-up end tabs 29 and 31) which are trapped behind the head of the fastener 28 so as to compress the spring 31 which is trapped between the depression 32 in member 21 and depression 33 in support member 24. Thus the spring 31 urges the member 21 into engagement with the head of screw 28 at one end and into engagement with projections 23 at the other end.

Positioned near the free end of bimetallic element 29 and arranged for sliding movement perpendicular to the bottom of housing 1 is switch actuator 35 having projections 36 riding in slot 37 (see Figures 3 and 4) in housing member 1 and in a similar slot in cover member 2. The tab 38 is positioned to engage tongue 49 of switch arm 39.

As shown in Figure 4, switch arm 39 has two arms 41 and 42 which are rigidly fastened to support member 43 which in turn is positioned within the housing 1 by the engagement of shoulder members 44 and 45 with mating slots in the molded housing 1. Before the arms 41 and 42 are welded or otherwise fastened to the member 43, they are compressed in the direction of arrows 46 so as to stress the spring switch arm 39 thereby rendering it bistable. Such a bistable condition enables pressure on tongue 40 in the direction of arrow 47 to cause switch arm 39 to snap in the direction of the arrow 48.

Support member 50 carries contact 51 and is trapped by the engagement of projections 52 and 53 with mating slots in the molded housing 1. Switch arm 39 carries contact 54 near its movable end and the engagement of the contacts 51 and 54 serves to complete a circuit between the members 43 and 50.

With the mechanism thus far described, and with bimetal 20 and switch arm-39 in the solid position shown in Figure 2 it will be observed that heat radiated from the resistor 13 will cause bimetal element 20 to deflect into the position shown in dotted lines thereby moving switch actuator 35 against the tongue 40 of switch arm 39 causing the switch arm to snap from the position shown in solid lines to that shown in the dotted lines. This movement of switch arm 39 breaks the circuit between the contacts 51 and 54 and thus any circuit which may be connected between the support members 43 and 50. The molded housing also has internal ribs 70 and 71 which define a switching chamber to confine any contact arc.

Reset lever 7 is guided for sliding motion within housing 11. by tab 66 and shoulder 61 which slide within the slot shown generally as 62 in Figure 1. Spring 8 is held against the housing 1 by the fastener 63, this spring serving to hold the reset lever in the slot as well as to position it in the manual or automatic positions.

If reset lever 7 is in the manual position (shown in Figure l and in the solid line position of Figure 2), movement of the lever to the dotted position shown in Figure 2 will bring the molded projection 55 into engagement'with the bent over lip 56 on arm 39, thereby forcing the contact 54 and the switch arm 39 back into the stable circuit closing position. If, on the other hand, the reset lever 7 is in the automatic position, switch arm 39 will not be free to snap completely overcenter but rather the tab 56 will engage the projection 55 shortly after circuit opening movement so that when the bimetal element 20 cools so as to return to its normal position the stressed spring action of switch arm 39 will again close the con tacts.

The mounting of the bimetallic strip 24) enables the undefiected position of the free end of the bimetallic strip 20 to be varied relative to the resistance heater 13 as well as to the tongue 49 on switch arm 39 thereby adjusting the calibration of the device.- By rotating knob in the direction of arrow 58, screw 28 is advanced out of the switch housing thereby rotating support member 21 about the pivot points 22-23 and compressing the spring 31. This adjustment of the free end of bimetallic strip 20 enables the trip rating of the circuit breaker to be adjusted within limits. As an example, the limits 85% to 115% of nominal trip rating having been indicated on the knob to enable the user to make his own adjustment. This adjustment also enables the user to compensate for varying ambient temperatures in which the switching device operates so as to ensure that the heat which is added to the bimetallic element to operate the contacts is proportional only to the current in the resistance unit rather than to that current plus thetemperature of the ambient surroundings.

Referring to Figure 3, a stop 59 is provided integral with the housing 1 and disposed to be engaged by the end of bimetallic strip 20 to limit the movement of such end in a direction toward the heater 13'. Due to thermal inertia action however, the heater 13 may continue to radiate heat and to further increase the temperature of the bimetallic strip 29 even after this has occurred, thereby causing further bending of the bimetallic strip. Such further bending is permitted in accordance with the present invention by the fact that the support member is pivotally supported at 23 and that the ends 29 and 30 are movable away from the head of the screw 28 against the bias of the spring 3L Upon further heating of the bimetallic strip 29 beyond the point where its end engages stop 59, therefore, the support member .21 pivots about the projections 23 and its end 30 moves away from the head of screw 28, the parts then being. in a condition as shown in Figure 3. Such overheating therefore does not cause excessive stresses in the bimetallic 4 strip 20 such as would be likely to cause distortion thereof and alteration of the'calibration of the device.

Although I have described a particular embodiment of my invention, it is obvious that many modifications can be made. It is to be understood, therefore, that I intend by the appended claims to cover all such modifications that fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An overload protective device comprising an electric heater, a bimetallic strip member extending generally parallel to and closely spaced fromsaid heater, one end of said bimetallic strip being movable toward said heater upon an increase in temperature of said bimetallic strip, stop means limiting said movement of said movable end toward said heater, means supporting said bimetallic strip adjacent its other end, and means providing for movementof said supported end of said bimetallic strip after said movable end engages said stop means.

2. An electric overload protective device as set forth in claim 1 wherein said supporting means comprises means for pivotally supporting said bimetallic strip on an axis adjacent said other end.

3. An overload protective device comprising an electric heater, an elongated bimetallic strip member extending parallel to and closely spaced from said electric heater, means supporting said bimetallic strip adjacent one end thereof, the other end of said bimetallic strip being movable toward said electric heating means upon heating, stop means limiting movement of said movable end of said bimetallic strip toward said heating means, a pair of relatively movable contacts, means operated by said movable end of said bimetallic strip for actuating said movable contacts upon predetermined amount of movement of said bimetallic strip toward said electric heater, means pivotally supporting said bimetallic strip on an axis adjacent one end of said bimetallic strip, spring means biasing said bimetallic strip for rotation about said pivotal axis in the same direction as the movable end of said bimetallic strip moves when heated, and stop means limiting said pivotal movement of said bimetallic member.

4. An overload protective device as set forth in claim 3 wherein said stop means limiting said pivotal movement of said bimetallic strip is adjustable to' permit calibration of'said overload protective device.

5. An overload protective device comprising a relatively stationary electric heater, an elongated strip of bimetallic material supported closely adjacent said heater and'parallel thereto, said bimetallic strip being disposed and arranged to deflect when heated so that its movable portion moves toward said heater, means pivotally supporting'said bimetallic strip on an axis adjacent one end thereof, spring means biasing said bimetallic strip for rotation about said pivotal axis toward said electric-heater, relatively stationary stop means limiting said pivotal movement of said bimetallic member towardsaid heater, saidstop means comprising a first'portion and means for adjustably positioning said firstportion, and a second portion comprising a projection for limiting the amount of adjusting movement of said first portion.

6 An overload protective device comprising an elongated electric heater, an elongated bimetallic strip extending parallel to and closely spaced from said heaten'said bimetallic strip having its low expansion side adjacent said heater, supporting means supporting said bimetallic strip at one end thereof whereby the other end of said bimetallic strip deflects toward said electric heater upon an increase of temperature of said bimetallic strip, electric contact means, means actuated by said movable end of said bimetallic strip for actuating said contactmeans, said supporting means for said bimetallic strip comprising meanspivotally supporting said bimetallic, strip and comprisinga supporting; member mounted for pivotal movement on a-pivotal axis adjacent saidmounted end of said bimetallic strip, spring means urging said supporting member for rotation about said pivotal axis in a direction to move said bimetallic strip toward said heater, stop means limiting said rotational movement of said supporting member, said stop member being adjustable toward and away from said electric heater whereby to adjustably vary the amount of deflection of said movable end of said bimetallic strip toward said heater which is necessary to actuate said contacts.

7. An overload protective device comprising an insulating casing, an elongated electric heater supported on said insulating casing, an elongated bimetallic strip member extending closely adjacent to and parallel to said electric heater, said bimetallic strip having its low expansion side adjacent said electric heater, supporting means for supporting said bimetallic strip comprising a relatively rigid member having a mounting portion, means rigidly affixing one end of said bimetallic strip to said mounting portion of said mounting means, means pivotally supporting said supporting means for rotation in said casing for rotation about a pivotal axis adjacent said mounting portion, spring means urging said supporting means for rotation about said pivotal support in a direction to move said bimetallic member toward said electric heater, stop means carried by said insulating casing for rotational movement of said supporting means about said pivotal axis in said direction, said stop means including a first portion mounted for a substantial range of movement with respect to said insulating casing to initially calibrate said device and a second portion having a relatively small range of movement with respect to said insulating casing for permitting restricted adjusting movement of said stop member after setting of said initial calibration.

8. An electric switch comprising an insulating body, an elongated supporting member pivotally supported on said insulating body adjacent one end thereof, an elongated bimetallic strip rigidly afiixed to said supporting member adjacent said one end and extending generally parallel thereto, electric contact means carried by said insulating body, means connected to said movable end of said bimetallic strip for operating said movable contacts upon predetermined deflection of said bimetallic strip, spring means biasing said support member for rotation about said pivotal support in a first direction, adjustable stop means carried by said insulating body and including a portion engaging said supporting member adjacent the end opposite said one end, said stop member being adjustable with respect to said insulating body through a substantial distance to initially calibrate said device, an adjustment limiting member attached to said adjustable stop member, a projection carried by said insulating body and disposed and arranged to be engaged by said adjustment limiting member to restrict the movement thereof, whereby limited adjusting movement is permitted of said adjustable stop member after the assembly thereto of said adjustment limiting member.

9. An overload actuated mechanism comprising a housing, a first contact supported by said housing, a switch arm having one end supported by said housing, a second contact mounted on said switch arm and movable relative to said first contact, a bimetallic strip, means supporting said strip on said housing, said means permitting movement of one end of said strip toward said switch arm in response to increasing strip temperature, and a switch operator positioned intermediate said movable end of said strip and said switch arm and movable by said strip to operate said switch arm, said switch arm, switch operator and strip being relatively positioned within said housing to form a disconnected U thereby to define a central opening to receive a resistance heater, a stop within said housing positioned to limit move ment of said strip toward said switch arm, said means supporting said strip including means for absorbing the reaction forces created by engagement of said strip with said stop.

References Cited in the file of this patent UNITED STATES PATENTS 1,783,520 Pearce Dec. 2, 1930 1,996,720 Getchell Apr. 2, 1935 2,116,097 Carlson May 3, 1938 2,166,545 Getchell July 18, 1939 2,210,084 Kuhn et a1. Aug. 6, 1940 2,322,161 Schleicher June 5, 1943 2,359,124 Laidig Sept. 26, 1944 2,743,333 Epstein Apr. 24, 1956

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