US2308401A - Thermal and electromagnetic switch opening mechanism - Google Patents

Description

Jan. 12, 1943.: E TAYLOR 2,308,401

THERMAL AND ELECTROMAGNETIC SWITCH OPENING MECHANISM Filed April 27, 193

w-A. 711851K 51....

Patented Jan. 12, 1943 THERMAL AND ELECTROMAGNETIC SWITCH OPENING MECHANISM Elmer H. Taylor, Newburyport, Mass., assignor to The Chase-Shawmut Company, Newburyport,

Mass., a corporation of Massachusetts Application A pril 27, 1939, Serialv No. 270,306

Claims.

'I'his invention relates to electric switches and to current responsive trippingfmeans therefor, and especially to tripping means having a thermally actuated element responsive after a delayed period of ltime to effect the opening of the switchA on moderate overloads and to independently acting electromagnetic means to effect the instant opening of the switch upon high overloads or short circuits.

'I'here is a type of'switch, especially adapted for motor control, employing a latch member or the equivalent to maintain the co-acting switch members or contacts releasably in closed position wherein a bimetallic strip responsive to the current passing through the contacts is utilized to maintain the latch releasably in switch closed position, the bimetallic strip normally support- .ing the latch against the pressure exerted thereon as by the engaged contacts, the strip being heated` by the current passing through the switch to warp away from holding engagement with the latch to permit the contacts to separate. Usually the bimetal strip is so arranged that the latch exerts pressure on the strip in the direction of its length and the strip acts as a strut. The endwise pressure of the latch thereon tends to cause the strip to buckle and hence the strip has to be made sufllciently heavy to prevent the buckling. When the strip is internally heated, that is to say, when the strip carries the switch current and is heated by reason of its resistance to the ilow of such current, the buckling pressure of the latch on the strip is of no particular consequence since the strip has to be thick in order to make its resistance low enough to give reasonably satisfactory perfomance. With such an internally heated strip it has been proposed to flex the strip electro-magnetically to obtain the release the latch instantly upon heavy current.

In my copending application Serial No. 172,412, filed November 2. 1937, I have shown that if the bimetal strip is heated'externally, as by a current traversed resistor or heating element disposed in heat imparting relation to the bimetal strip, the strip could be made thinner and thus the electro-magnetic means could be made smaller and also that a better performance of the switch under all current conditions could be obtained. With an externally heated bimetal strip the buckling pressure. of the latch on the strip becomes important and limits thethinness of the K strip and the operating characteristics of the switch that are determined by the thickness of the strip. If the tendency of the strip to buckle under the latch engaging pressure were reduced or eliminated a still better performance of the switch under overloads could be obtained and the electromagnetic means could be made still smaller, which latter is desirable not only for reasons of economy but also because the tripping means rordinarily has to be located in a very confined space, especially in this type of switch.

Hence an object of the present invention is a 4 construction whereby the latch is held releasably in switch closed position by a member, as a strut member, that receives the entire latch pressure and can be made to have any desired characteristics and wherein the bimetal strip is freed from the latch pressure and can be of such structural dimensions as are desired to obtain the desired circuit opening characteristics of the switch upon overload, the only limiting feature of the bimetal strip being that it rmust have sufiicient power to overcome the frictional engagement between the strut member and the latch so as to eiiect disengagement of the two under the desired conditions of time delay and overload. The bimetal strip thus can be made thinner than with the construction set forth in my above copending application and the electromagnetic means associated therewith can be made correspondingly smaller.

yA further object of the invention is generally to improve upon electric switches and circuit breakers and combined thermal and magnetic opening means therefor.

Fig. l is a sectional elevation through an electric switch or circuit breaker embodying the present invention.

Fig. 2 is a perspective detail of the strut of Fig. 1.

Fig. 3 is a perspective detail of the strut fulcrum of Fig. 1.

Fig. 4 is a section along line 4-4 of Fig. 1.

The switch herein illustrated as embodying the present invention is constructed generally as i1- lustrated in my copending application Serial No. 233,006, led October 3, 1938.

The switch comprises a supporting block i0 of insulating material that houses and carries the various switch elements. The stationary contact i2 of the switch is connected to a terminal strut Il to which a circuit conductor can be connected by the screw I6. The movable switch contact i8 is carried by a movable switch member or strip 20 having a resilient S bend 22 intermediate its ends and a depending end part 2| clamped to a depending ear 26 by suitable means as the rivet 2B, the ear depending from a horizontal bracket plate 30 fixed to the supporting block i0. v

Said plate 38 has a pair of upstanding arms 32 which carry between them a pivot 34. A switch operating member 38, which operates as a latch, as will later become apparent, has a slot 38 through which said pin is loosely extended, said operating member having a cam projection 40 which bears upon the movable switch member 20 and a horizontally extended latch projection 42 the end of which bears releasably against the top end face of a strut member 44.

The operating member is moved vertically about the strut member as a pivot by an actuating member 46 pivoted on the pin 34 and having a manually engageable operating knob or projection 48. The actuating vmember has a cam surface 50 which engages a cooperating cam surface 52 of the operating member to effect vertical pivotal movements of the operating member about the strut member in response to swinging of the actuating member in opposite directions to effect the manual opening and closing of the switch. The arrangement is such that when the strut member 44 is moved out from under the latch projection 42 the inherent resiliency of the movable switch member causes the operating member to be rotated in a clockwise direction to effect the automatic opening of the switch,

The construction and operation of the switch mechanism as thus described will not be explained in further detail as it is unnecessary and the mechanism herein illustrated is only one form of mechanism that can be used in connection with the present invention.

In accordance with the present invention said strut member 44 can be formed of a relatively rigid and inflexible strip sufficiently inflexible to resist the downward pressure of the latch 42 thereon without buckling or if the strip does buckle somewhat under the latch pressure such buckling is of no importance providing, of course, that the buckling is not sufficiently great to move the parts associated therewith out of operative relation with each other. 4

The important feature of the strut member with respect to the present invention is that it should support the latch member against its pressure and be capable of movement out from under the latch by the thermal and electromagnetic tripping means, hereinafter to be explained, to permit the latch to move into switch open position.

In order that the thermal and magnetic tripping means shall have as little work as possible to do, and hence need have mainly the power necessary to overcome the frictional engagement between the latch and the strut, the strut member is made rigid and the lower end thereof is pivotally supported on a fulcrum offering but slight frictional resistance to the short movement of the strut. To this end the bracket plate 30 on opposite sides of the depending ear 28 is provided with forwardly extending fulcrum ears 54 which have aligned V-shaped fulcrum grooves 58 in their upper faces. The lower end part of the strut 44 is provided with opposed spaced depending legs 58 which have V-shaped lower edge parts 80 located in the grooves 58. The arrangement thus gives a knife edged fulcrum support for the strut which permits it to be moved easily out from under the latch.

The thermal tripping means comprises a straight bimetal strip 82 composed of two metals of dissimilar coefficients of expansion secured together back to back. Said strip is disposed in relatively close confronting parallel relation with the strut member and is secured to .the bracket ear 28 by the aforesaid rivet 28, being maintained in spaced relation with the strut member by an interposed washer 84. A plate 88 on said rivet is disposed between the legs Il of the strut member to prevent undue edgewise movement of the strut member on its fulcrum support.

A cylindrical armature 18 is secured to the upper end part of the strut and extends laterally therefrom on the side opposite the latch 42. The armature is provided with an annular groove 12 therein in which the upper end part of the bimetal strip 82 is located loosely. The armature .thus forms a connection between the bimetal strip and the strut member by which the strip on warping toward the right can move the strut out from under the latch and when cooled oi! and re- V turning to straightened or unwarped position can restore the strut member to its normal latch holding position. The resetting movement of the latch can also move the strut member toward the right, the bimetal strip serving as a spring to restore the strut member into its normal position under the latch. Preferably the width of the groove l2 is slightly greater than the thickness of the bimetal strip.

'I'he bimetal strip is heated by a, preferably selfsupporting external heating element 14 consisting of a conductor of suitable electrical resistance bent into grid form and disposed in sumciently close proximity to the front face of the strip ,to impart heat thereto. One end of the conductor is connected to the rivet 2l and thus is in series with the separable switch members i2 and I8. I'he other end of the heating conductor is connected by means of a bolt 1I with one end of a solenoid 80. Said solenoid, as here shown, consists of a few turns, two turns being sufficient for some switches, of a low resistance conductor. The other end of the conductor is connected by a screw l2 to a terminal plate I4 to which a circuit terminal may be secured by suitable means as the screw 82. l

As thus arranged a moderate overload current traversing the heating element 14 is arranged to heat the bimetal strip and ultimately after a suitable period of time delay cause the strip to warp sumciently to remove the strut member 44 out from under the latch whereupon the switch mechanism effects downward displacement of the latch member and the separation of the switch contacts. For moderate overload currents the solenoid is designed to be ineective so .that it does not exert any substantial pull on the strut member. When, however, the switch is traversed by heavy overloads, say upwards of 400 or 500 percent of full load current, the magnetic effect of the current traversing the solenoid is sufficient to act instantly to move the strut member out from holding engagement with the latch, thereby to effect instant tripping or opening of the switch upon the occurrence of such heavy current.

With this construction the bimetal strip can be made thinner than heretofore. Thus the operating characteristics of the bimetal strip are not restricted by necessary strength requirements heretofore imposed upon the strip and the strip may be given any reasonable characteristics desired. For instance. the time delay of operation of the switch upon moderate currents may be made much less than heretofore and a much faster operating switch on moderate overloads can be obtained with this construction while at the same time getting the desirable instant operation upon higher overloads. By being able to make the strip thin the electromagnet can be made smaller and cheaper since it is not required to flex a stiff bimetal strip.

I claim:

1. Ina switch tripping device, a. switch operating member normally biased for movement in a direction to effect an operation of the switch, a swingable strut positioned and arranged normally to engage and hold said switch operating member from such movement, and electromagnetic means operative to move said strut out of holding relation, a warpable blmetal strip having a connection with said strut and said electromagnetic means to maintain said strut yieldably in the aforesaid holding relation, said bimetal strip constituting also a spring to restore said strut to said holding relation when it has been moved electromagnetically away therefrom, said bimetal strip warping when heated and moving said strut away from said holding relation, an electric heater disposed adjacent said bimetal strip effective to heat and warp it under predetermined conditions, and supporting means holding the aforesaid parts in the aforesaid relation.

2. In a switch tripping device, a switch operating member biased for movement in a predetermined direction, a holding strut releasably engaged with v'said switch operating member and supporting it against the bias thereon, and a warpable bimetal strip in close side by sldeparallei relation with said strut arranged when warped to disengage said strut from said switch operating member, electromagnetic means acting independently of said bimetai strip upon said strut in a direction to move it toward disengaging position. and supporting means holding the aforesaid parts in the aforesaid relation.

3, In a switch tripping devicel a switch operating member normally biased for movement in a direction to enect an operation of the switch, a swingable strut normally arranged to engage and hold said switch operating member from said movement, a bimetal strip having a connection with said strut to maintain it yieldably in the aforesaid holding relation and to restore said strut to said holding relation when it is moved temporarily away therefrom and to warp when heated and to move said strut away from said holding relation, an electric heater disposed adjacent said bimetal strip effective to heat and warp it under predetermined conditions, and electromagnetic means operative tc warp said bimetal strip mechanically to move said strut out of holding relation, and supporting means holding the aforesaid parts in the aforesaid relation.

4. In a switch tripping device, the combination as in claim 1 in which the said electromagnetic vmeans has an armature connected to said strut,

and the said connection of the bimetal strip to the strut and the electromagnetic means is through the said armature.

5. In a, switch tripping device, a switch operating normally biased for movement in a direction to effect an operation of the switch. holding mechanism positioned and arranged normally to engage and hold said switch operating member from such movement comprising a pair of swinging plates connected to swing together, one plate being a strut arranged normally to engage and hold said switch operating member from the aforesaid movement and the other plate being of bimetal warpable when heated to swing the strut away from its aforesaid holding position and to release saidswitch operating member, electrical means for heating said bim'etal plate, electromagneticemeans for swinging said holding mechanism, and supporting. means holding the aforesaid parts in the aforesaid relation.

suma n. TAYLOR.

Certificate of Correction Patent No. 2,308,401 January 12, 1943 ELMER H. TAYLOR It is hereby eertied that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 3, second column, line 26, before the Word normally insert member;

and that the said Letters Patent should be read as corrected above, so that the sam may conform to the record of the ease in the Patent Office.

Signed and sealed this 5th day of December, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certiiicate of Correction Patent No. 2,308,401 January 12, 1943 ELMER H. TAYLOR It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 3, second column, line 26, before the Word normally insert member;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the ease in the Patent Ofee. Signed and sealed this 5th day of December, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommzssz'onar of Patents.

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