US3566328A - Electrical circuit overload protector of the thermally responsive bimetal element type - Google Patents

Abstract

AN ELECTRICAL CIRCUIT OVERLOAD PROTECTIVE DEVICE OF THE THERMALLY RESPONSIVE BIMETAL TYPE WHICH CAN BE SELECTIVELY SET FOR EITHER AUTOMATIC OR MANUAL RESET MODES OF OPERATION. OVERLOAD RESPONSIVE UNITS, FOR ONE OR MORE CIRCUIT BRANCHES EMPLOYING STACKS OF BIMETAL DISCS AS THERMALLY RESPONSIVE ELEMENTS, AND ARE MOUNTED WITHIN A HOUSING ON A COMMON BASE. EACH OVERLOAD UNIT HAS AN INDIVIDUAL SNAP ACTING SWITCH WHICH OPENS IN RESPONSE TO AN OVERLOAD CONDITION AS DETECTED BY THE HEAT DEVELOPED IN A HEATER COIL CONNECTED IN THE BRANCH CIRCUIT WHICH SURROUNDS IT THERMALLY RESPONSIVE ELEMENT. THE SWITCHES OF THE OVERLOAD UNITS ARE ALL CONNECTED IN A SINGLE SERIES CIRCUIT BETWEEN TERMINALS PROVIDED FOR CONNECTION TO A CIRCUIT TO BE CONTROLLED. IN A MANUAL TRIP-FREE MODE OF OPERATION A PUSHBUTTON LEVER UPON SUBSIDENCE OF ALL OVERLOAD CONDITIONS IS DEPRESSED INWARDLY OF THE HOUSING TO AFFORD MANUAL RESET OF THE MOVABLE CONTACT MEMBERS OF ANY SWITCH TRIPPED OPEN BY OVERLOAD RESPONSE. ALTERNATELY THE RESET LEVER MAY BE LATCHED IN SUCH DEPRESSED POSITION WHEREIN THE CONTACT OPENING MOVEMENT OF THE MOVABLE SWITCH CONTACT MEMBERS IS SO LIMITED THAT THEY WILL IN DIVIDUALLY AUTOMATICALLY RESET UPON SUBSIDENCE OF THE OVERLOAD CONDITION IN THEIR RESPECTIVE BRANCH CIRCUITS. A MODIFIED FORM OF AMBIENT TEMPERATURE COMPENSATED BIMETALLIC DISC TYPE OF OVERLOAD RESPONSIVE UNIT IS PROVIDED FOR USE WHEREIN THE DEVICE WILL BE SUBJECTED TO HIGH OR WIDELY VARYING AMBIENT TEMPERATURE CONDITIONS.

Description

Feb. 23, 1971 u. F. CARTER ETAL v 3,566,328

. ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE Filed May 13. 1968 4 Sheets-Sheet 2 ain Igfg M2 74 Ill 7ig.5f

Fab. 23, 1 971 u. F. CARTER E TAL 3,566,328 I ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE Filed ma 13, 1968 4 Sheets-Sheet s v 44, 1 7 70 70b 9 255 H 86 a q C 765 94 94a 96 98 Low txe Mam (mm) 5% Feb. 23,1971 g, AR E ETAL 3,566,328

ELECTRICAL CIRCUIT ,OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE 7 Filed May 13, 1968 Y Y "4 Sheets-Sheet 4 4'0! 7 Y I I United States Patent US. Cl. 337-335 3 Claims ABSTRACT OF THE DISCLOSURE An electrical circuit overload protective device of the thermally responsive bimetal type which can be selectively set for either automatic or manual reset modes of operation. Overload responsive units, for one or more circuit branches employing stacks of bimetal discs as thermally responsive elements, and are mounted within a housing on a common base. Each overload unit has an individual snap acting switch which opens in response to an overload condition as detected by the heat developed in a heater coil connected in the branch circuit which surrounds its thermally responsive element. The switches of the overload units are all connected in a single series circuit between terminals provided for connection to a circuit to be controlled. In a manual trip-free mode of operation a pushbutton lever upon subsidence of all overload conditions is depressed inwardly of the housing to afford manual reset of the movable contact members of any switch tripped open by overload response. Alternately the reset lever may be latched in such depressed position wherein the contact opening movement of the movable switch contact members is so limited that they will individually automatically reset upon subsidence of the overload condition in their respective branch circuits. A modified form of ambient temperature compensated bimetallic disc type of overload responsive unit is provided for use wherein the device will be subjected to high or widely varying ambient temperature conditions.

Features of the invention described in this application are disclosed and claimed in the copending Uriel F. Carter, Arthur F. Kolb and Edward A. Mallonen application Ser. No. 729,879, filed May 13, 1968 and assigned to the assignee of this application.

This invention relates to an improved overload protective device of the thermally responsive, bimetal element type.

A primary object of the invention is to provide a protective device of the aforementioned type employing bimetal discs in a special stacked relation as the thermally responsive element in each of one or more overload units.

Another object is to provide in each overload unit a separate snap-action electric switch for individualized control by its associated thermally responsive element of the aforementioned type.

A further object is to provide a protective device of the foregoing type where the aforementioned switches of the individual overload units are electrically connected in a single series circuit so that the latter will be interrupted 3,566,328 Patented Feb. 23, 1971 upon opening of any switch unit in response to an overload condition to which its associated thermally responsive element may be subjected.

Still another object is to provide an overload protective device of the aforementioned type which can be selectively set so that reset of tripped switches of the overload unit will automatically reset, or alternatively require manual operation of a reset lever to effect reset of the switches upon subsidence of the overload conditions in protected circuit branches.

An additional object aiforded by the overload device is trip-free action of the switches of the respective overload elements in the event the overload condition has not subsided when the reset lever is manually operated.

A still further object is to provide a modified form of ambient temperature compensated overload responsive element of the aforementioned bimetal disc type which can be used interchangeably for the overload device for those aforementioned.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate preferred embodiments of the invention which will now be described in detail it being understood that the embodiments disclosed are susceptible of modification in respect of details Without departing from the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of an overload circuit protector switch incorporating the invention;

FIG. 2 is a front elevational view of the switch;

FIG. 3 is a left end elevational view of the switch with portions of the housing broken away;

FIG. 4 is a view similar to FIG. 3 but showing the switch in another operating mode;

FIG. 5 is a top plan view of the inside of the housing base showing the overload responsive switch mechanism;

FIG. 6 is a fragmentary cross sectional view taken generally along the line 6-6 of FIG. 1 showing an overload responsive element;

FIG. 7 is a view similar to FIG. 6 but showing a modified form of overload responsive element;

FIG. 8 is a view in cross section to greatly enlarged scale of a portion of a stack of bimetal disc elements shown in FIGS. 6 and 7;

FIG. 9 is a more or less schematic representation of the overload element depicted in FIG. 6;

FIG. 10 is a view like FIG. 9, but showing the overload device in another operating condition;

FIG. 11 is a view like FIG. 5 but with the overload responsive and switch elements removed; and

FIG. 12 is an isometric view of a switch drive lever and movable member shown in FIGS. 5, 6 and 7.

DETAILED DESCRIPTION Referring to FIGS. 1 to 3, they show a circuit protector switch having a metal mounting plate 10, a unitary insulating housing 12 to which plate 10 is attached, and an insulating bottom cover and base member 14. The switch has a reset button 16 mounted on the end portion of a metal lever 18 which is reciprocably movable in a guide passage 12a formed in housing 12.

The top opening recesses 20 are provided on housing 12. Intermediate partition portions 22, 24, 26 and righthand end wall 28 of housing 12 provide electrical barriers between the recesses. Spaced apart pairs of combination wire terminal and overload heater mounting plates 30 are secured in place in each of the recesses by screws 32 which take into threaded recesses. One of each pair of plates 30 located at the rear is mounted at a higher level than the plate at the front. The center recess between partitions 24 and 26 is at a higher elevation to provide increased electrical and heat clearance between each adjacent sets of recesses and to provide for clearance for the interfit of a terminal mounting member 98. i As thus far described, the housing 12 and elements mounted thereon are exactly the same as a counterpart housing shown and described in the Carter et al. application, Ser. No. 699,270, filed Jan. 19, 1968, now Patent No. 3,478,292, and assigned to the assignee of the present application. Housing 12 was designed to be interchangeably used in both types of overload protector switches. Each of the aforementioned top opening recesses in housing 12 has mounted therein between the spaced plates 30, a plate 34 to which is fastened a metal cylindrical tube 36 whcih has an anodized insulating exterior surface. The plates '34 are secured in place by screws 38. As will hereinafter be more fully explained, bimetal disc overload elements are centered without appreciable peripheral clearance in each of the tubes 36, and as shown in the left-hand recess between partitions 22 and 24, a helical heater coil 40 is positioned around and in contact with each of the tubes 36 and secured to the upper and lower terminal plates by screws 42.

The terminal plates 30 have outward and slightly downwardly projecting tabs 30a to which are secured wire retaining members 44 by screws 46. In actual service, the other two recesses would also be fitted with heater coils 40, the same having been omitted in FIGS. 1 and 2 to clarify construction details of the plates 34 and tubes 36. With each pair of terminals 30 wired in series in branches of a three-phase A.C. circuit it will be apparent that the heater coils 40 will be subjected to the load current in their respective branches. Heat generated by such current flow will transfer by conduction to the tubes 36, and as will hereinafter be explained, causes movement of the bimetal discs of the overload elements.

As shown in FIGS. 5, 6 and 11, the overload responsive elements and switches controlled thereby for each of the three branches are mounted on the inside of base 14. As best seen in FIGS. and 6, each overload responsive element comprises a support bracket 48, a rectilinear movable rod 50, a stack of bimetal discs or washers 52, a loading spring 54, a spring gland 56, an adjusting pin 58 and adjusting screw 60. A flanged cylindrical insulating member 62 seats against the flanged end portion 50a of rod 50 and provides a spindle on which the stack of discs 52 are mounted. A cylindrical insulating spacer 64 abuts at its upper end against the lowermost bimetallic washer and has the lower end portion of spindle 62 projecting into its bore.

' The lower end ofspacer 64 seats against the upper end of adjusting screw 60 which is centrally bored to accommodate rod 50, and exteriorly threaded to be adjustable in the complementally threaded insert 66 molded in place in the upper arm 48a of bracket 48. Adjusting screw 60 has a laterally and upwardly extending arm 60a which extends through an arcuate slot 34a formed in cover plate 34. As will hereinafter be explained, lever 60a within the limits of slot 34a affords a certain range of adjustment for controlling the compressor loading of the stack of discs 52.

Adjusting pin 58 has a cylindrical flanged end portion 58a, an intermediate portion 58b which is rectangular in transverse cross section and an upper cylindrical end por tion 580 of reduced diameter. The upper end portion 580 is internally threaded and the lower end portion of rod 50 is threadedly engaged therein. Also the upper end portion 580 projects into an opening 56a which extends from the 4 lower end of gland 56- to the bottom of the spring receiving recess 56b that opens to the upper end of the gland. Loading spring 54 is of the coiled compression type and seats at its upper end in a shallow recess 48b formed in the lower surface of arm 48a of bracket 48 and at its lower end against the bottom of recess 56b in gland 56.

As shown in greatly enlarged cross section in FIG. 8, the bimetal discs 52 comprise two metal layers; layer 52a having a relatively high coeflicient of thermal expansion and the other 52b having a relatively low coefficient of thermal expansion. In plan view the disc 52 are annular, and as shown in FIG. 8, they are convexly warped in transverse cross sectional form similar to that found in Belleville washers. They are stacked on the spindle portion of the guide 62 in the arrangement shown in FIG. 8 with one pair abutting along respective concaved edges, and an adjacent pair abutting on respective opposed convexed surfaces, etc., in a repeating alternate series. At ambient or room temperature the distance between bottoms of concaved surfaces on alternate pairs will be some distance X.

As the temperature of the discs 52 increase they will individually flatten and each of the distances X will decrease with increasing temperature. Consequently, the total height of the stack of discs 52 will decrease as a function of the sum of the individual decrease in X, between alternate pairs of discs in the stack. If the temperature of the discs 52 thereafter decreases the individual distance X increases as the individual discs in the stack return to their ambient temperature warped or dished shape in cross section depicted in FIG. 8.

The foregoing arrangement of the discs 52, in affording decrease in individual warpage with increase in temperature is an advantage. As the stresses between the discs decreases with rise in temperature, subjection to thermal shock temperature rises which can occur during high electrical overload conditions will prevent the elastic limit of the discs from being exceeded. Accordingly, repeatability of change in total stack height and hence the force developed by the discs 52 for a given temperature change is considerably enhanced.

The lower end of gland 56 bears against arcuate protrusions 68a formed on each of the arms 68b of a switch drive lever 68. Drive lever 68 is provided with a central rectangular opening 680 which accommodates the rectangular portion 58a of adjusting pin 58. The arms 68b which are disposed on opposite sides of opening 680 also have arcuate protrusions 680! which bear against the upper surface of the end portion 58a of pin 58. Drive lever 68 has upstanding end portions 68:; and 68f which are provided with V-shaped notches 68g and 68h, respectively. Portion 68e engages within its notch 68g the inner edge of an opening of a movable, flat leaf switch member 70 which carries a contact 72 (see FIGS. 6 and 12). A C-shaped snap spring 74 seats along one edge in the notch 68h of lever 68 and has attachment within a slot 74a thereof with outer arms 70a and 70b and intermediate contact carrying portion 700 of member 70.

The opposite end portion 70d of member 70 is sandwrched together with portion 76a of current conductor 76 between an upstanding boss 14b formed on the inside surface of boss 14 and the lower surface of the mounting pad 48a: of bracket 48. As best shown in FIG. 5, screws 78 whlch penetrate alined openings in pad 48c, portion 70d of member 70 and portion 766! of conductor 76 secure the member 70 and conductor 76 in electrical contact in place on base 14.

As best shown in FIGS. 6 and 11, contact 72 through movement of member 70 is adapted to engage with a stationary contact 80 secured to the portion'82a of a current conductor 82which is in turn secured to a boss on base 14 by a screw 84.

Switch member 70 together with snap spring 74 and drive lever provide a snap action type of electrical switch such as that disclosed and claimed in Patent No. 3,-

207,868. Reference should be made to that patent for detailed information on the formation and arrangement by switch member 70 and snap spring 74.

Reference will now be made to FIGS. 9 and 10, to provide an understanding how each of the overload responsive devices and snap switches function under normal and overload electrical conditions. The representations in FIGS. 9 and 10 are simplified showings with certain parts of the overload devices hereinbefore described deleted. Numerals of like parts have been designated with additional prime postscripts. The overload device and switch as shown in FIG. 9 are in positions assumed under non-overload conditions. The bimetal discs 52' are enlarged and shown with exaggerated curvature for purposes of illustration. wardly against switch drive lever 68' and tends to cause the left end of snap spring 74' to move downward, and hence tends to toggle member 70' upwardly to disengage contact 72' from contact 80. However, a balancing upward force exerted on drive lever 68 by adjusting pin 58' due to the counter force action of the bimetal discs 52' acting through rod 50, holds the snap switch in the contact engaged position depicted in FIG. 9.

Now assume that a current overload condition occurs and persists. Thus the heat transferred by conduction from the current carrying coil 40' to the discs 52' will cause them to flatten in a direction decreasing the degree of their individual convexed curvature. Thus the distance Y in FIG. 9 between the upper flanged end of rod 50' and spacer 64' will decrease to the distance depicted in FIG. 10 and rod 50' consequently moves downwardly. The force exerted by spring 54' then causes gland 56 to move downwardly and hence move drive lever 68' downwardly. When the left end of snap spring 74 is moved across the plane of leaf member 70, snap action toggling of the latter member in the upward direction occurs to disengage contact 72' from stationary contact 80' as depicted in FIG. 10. Drive lever 68' during such snap movement pivotally moves by virtue of its protrusions 68a and 68d rocking on the upper surface of portion 58a and the lower end of the spring gland 56'. In the first position member 70' bears against a stopreset bar 86'.

It may be assumed that when the overload condition has subsided, discs 52' will cool and hence assume their normal or ambient temperature curvature condition. Thus the distance Z depicted in FIG. 10 will increase and rod 50 will be moved upwardly to correspondingly move drive lever 68' upward. With stop-reset bar 86' set in the rotary position depicted in FIGS. 9 and 10, the apex r of notch 68h will not move upwardly beyond the plane of member 70 by the time rod 50' and drive lever 68' reach their respective normal, or non-overload position depicted in FIG. 9. In other words, the overload responsive switch will not automatically reset upon subsidence of the overload condition, and member 70' must then be manually reset (moved downwardly across the apex of notch 68h) to return it to the circuit closed position of FIG. 9. This 'will hereinafter be more fully explained in conjunction with FIGS. 4 and 5.

If stop-reset bar 86' is instead set at the rotary position depicted for bar 86 in FIG. 6 when the aforedescribed overload condition occurs, member 70' upon snap upward movement will assume a switch-open position intermediate those depicted in FIGS. 9 and 10. Hence, upon subsequent subsidence of the overload condition the apex of notch 68h will move across the plane of member 70' to cause snap toggling of the latter to the circuit closed position shown in FIG. 9. In other words, the switch will automatically reset upon return of the overload responsive device to normal or non-overload conditions. This action will also be more fully described in conjunction with FIGS. 4 and 5.

Now referring to FIG. 11, it will be seen that conductor 82 has an integral portion 82b like portion 76a of conductor 76. A second conductor 82 is also secured on boss 14:: on base 14 to the right of the first mentioned conductor 82. A third conductor 88 is secured to boss 14c by a screw 90 and has a stationary contact 92 secured thereto. Conductor 76 has an integral L-shaped portion 7612 which seats within a complementally formed recess 14d in member 14 and a portion 76c which extends upwardly at a right angle to afford electrical connection between portion 76b and a terminal end portion 76d. Conductor 88 has a portion 88a lying in a shallow recess is base member 14 that connects with a portion 88b which is bent upward at right angles and then laterally toward the left as viewed in FIG. 11. Portion 88b connects with a terminal end portion 880 like portion 760 of conductor 76.

As best shown in FIGS. 2, 5 and 11, terminal members 94 and 96 are secured together with terminal portions 76d and 88c, respectively, to a lower surface of side boss portions 98a and 98b of an insulating terminal mounting member 98 which has an intermediate barrier portion 980. As best seen in FIGS. 2 and 5, terminals 94 and 96 have outwardly and slightly downwardly depending tabs 94a and 96a to which are secured by screws 100, wire retaining members 102 of a form similar to the aforementioned members 44.

Now referring to FIGS. 5 and 11, it will be seen that the overload switch device comprises three overload switch devices. With their respective switches closed, it will be apparent that current will be completed from terminal member 94 to 96. Thus with terminals 94 and 96 appropriately connected in the energizing circuit of an electromagnetic contactor or relay (not shown) such circuit will be maintained when no overload condition exists in any of the branches of the polyphase circuit in which the heater coils 40 associated with the respective overload devices are connected.

In the event an overload occurs in any such branch circuit suificient to cause opening of its associated overload responsive switch the circuit will, of course, be opened between terminals 94 and 96, thereby opening the circuit to any electromagnet or other circuit that may be connected thereto.

Referring to FIGS. 3, 4 and 5, it will be seen that stop-reset bar 86 is journaled for rotation on cylindrical end portions 86a in the bearing brackets 14 and 14g formed integrally with member 14. Immediately adjacent bearing 14 in FIG. 5, rod 86 is provided with an arm 86b, and between the latter and its opposite end portion 86a it has a portion 860 with the cross sectional form best shown in FIGS. 6, 9 and 10.

The arm 86b of rod 86 is disposed within the opening 104a of an insulating member 104 which is molded about and is an extension of reset lever 18. A coiled compression spring 106 seats at one end within a recess 14h formed in base 14 and at its other end fits about a short cylindrical boss 104b formed on member 104. Spring 106 biases member 104 and lever 18 upwardly to normally assume the position depicted in FIG. 4. In moving to that position the lower lip portion 1040 at the entrance of opening 104a in member 104 engages arm 86b and rotates it clockwise to the position depicted in FIG. 4. In this latter position the portion 86c will be rotated to assume the position depicted for rod 86' in FIGS. 9 and 10.

If reset lever 18 is moved inwardly of housing 12 to the position depicted in FIG. 3, the upper lip portion 104d of member 104 engages arm 86b of rod 86 and rotates the latter to the position depicted in FIG. 3 wherein the portion 860 then assumes the rotary position depicted in FIG. 6. It will be seen that in this last mentioned rotary position for the portion 860 the clearance distance between the free ends of the movable switch member 70 is considerably less than in positions depicted for rod 86' in FIGS. 9 and 10.

; :If with the rod 86 in the rotary position depicted in FIG. 6, an overload occurs, the free end of any switch member 70 which moves to contact disengaging position will engage the rod 86 and thereby limit its movement. With the contact opening movement of any member 70 so limited, any tripped switch will automatically reset upon subsidence of the overload condition as aforedescribed. It will also be understood that after responding to an overload condition, a switch member 70 is moved to an open position depicted for member 70 in FIG. 10 that subsequent rotation of rod 86 to the position shown in FIG. 6 following subsidence of the overload condition will cause it to engage the end of the member 70' and move it downwardly sufliciently so that snap spring 74 will then toggle the same to the contact engaged position shown in FIGS. 6 and 9.

When lever 18 is moved to its inward extreme position shown in FIG. 3, it can be retained latched in that position by moving a lever 108 into engagement in a notch 18a formed in lever 18. Thus rod 86 will be retained in the rotary position wherein its portion 860 assumes the position depicted in FIG. 6. Accordingly, the overload device will be set in its automatic reset mode, and upon subsidence of overload in all branches circuit completion between terminals 94 and 96 will be automatically restored.

Lever 108 is provided with an elongated opening and a screw 110 penetrates such opening and takes into a threaded recess a housing 12. When lever 108 is engaged within the notch 18a of lever 18 tightening of screw 110 insures retention of reset lever in the automatic reset mode. Of course, when lever 108 is out of engagement with lever 18 it can also be held in that position by tightening of screw 110.

The temperature trip point of any of the aforedescribed overload responsive switches is determined by the adjustment of adjusting pin 58 on the threaded end of rod 50. Turning pin 58 further on to rod 50 will, through its bearing on drive lever 68, move the latter upwardly a corresponding amount. Drive lever 68 because it bears against the lower end of gland 56- will move the latter upwardly and spring 54 will be correspondingly compressed. Spring 54 then exerts increased force downwardly on gland 56, drives lever 68, pin -8 and rod 50. Thus discs 52 will be caused to be compressed, and their stack height reduced. Accordingly, the upward force exerted on rod 50 by the stack of discs will then counterbalance the inward force of spring 5-9 acting downwardly on drive lever 68 at its new upper position.

It will be apparent that with drive lever 68 moved upwardly that the apex of its notch 68h will be moved upwardly a corresponding amount above the plane of movable contact member 70. Hence lever 68 will have to be moved downwardly a greater distance before the apex of notch 68h passes the plane of member 70 at which point snap-action toggling of the latter to contact opening position occurs. Accordingly, the aforedescribed change in adjustment of pin 58 results in an increase of the trip point temperature. It will be apparent from the foregoing that if adjusting pin 58 is backed farther down from an initial position on rod 50, that the trip point temperature will be decreased.

Screw 60 aflords another more limited adjustment of the trip point temperature of each overload device. If lever 60a is turned counterclockwise in slot 34a in plate 34, as viewed in FIG. 1, screw 60 will advance upwardly in insert 66 thereby moving spacers 62 and 64 upwardly which results in increased compression and hence decrease in the height of the stack of discs 52. -As a consequence of this drive lever 68 is moved upwardly to a new ambient temperature position. Conversely, if lever 60a is rotated clockwise in slot 34a the height of the stack of discs 52 will decrease resulting in a corresponding lowering of the ambient temperature position of drive lever 68. The arcuate length of the slot 34a determines 8 the range of change in trip point temperature that can be effected by adjustment of the screw 60.

Normally the basic trip point temperature is determined after assembly of the overload device by adjustments of pin 58 to afiord a trip point temperature which is some specified value above normal ambient temperature. Then with selection of a heater coil most appropriate for the particular load conditions, screw 60 permits a limited range change to partially compensate for the fixed increments existing between a heater coil of a given rating and those available which are immediately above or below it in rating tables.

FIG. 7 shows a modified form of ambient temperature compensated overload responsive switch unit which can be used in place of those aforedescribed. In this modified form the loading spring 54 is deleted and a stack of bimetal discs 112 together with a spacer 114 inserted in its place. The discs 1'12 are the same in form as the discs 52, but somewhat greater in outer diameters, and warped depth at the same ambient temperatures. They are also stacked in the same arrangement as shown for discs 52 in FIG. 8.

It will be apparent that if the modified overload responsive switch units are subjected to ambient temperature conditions which vary relatively widely, that change in forces developed by the discs 52 with temperature will be offset by a corresponding change in forces developed by the discs 112. Consequently,, the distance of the notch 68h of drive lever 68 above the plane member 70 (in contact closed position) will not change appreciably as the ambient temperature varies. Thus the trip point temperature of the compensated overload devices will not be appreciably afiected by ambient temperature changes that may be encountered in certain conditions of mounting and housing of the overload devices.

The use of the ambient temperatures compensated overload responsive units is desirable when the overload protection switches are inside of enclosures which are subject to internal generation of heat by other equipment mounted therein, or to external heat such as by the sun or other heat radiating sources.

What is claimed is:

1. A thermally responsive overload switch comprising, in combination:

electric switch means having a pivoted operating lever movable in opposite directions to effect opening and reclosing of switch contacts, and

a thermally responsive switch operating mechanism comprising:

spring means biasing said operating lever for movement in the contact opening direction, means including a reciprocally movable member having engagement with said switch operating lever, and a plurality of dished, annular bimetal discs disposed about said reciprocally movable member in stacked relation, said discs under ambient temperature conditions biasing said reciprocally movable member in a direction opposing movement of said operating lever by said spring means in said contact opening direction,

and said discs under overload temperature conditions transversely flattening to decrease the bias exerted by said reciprocally movable member on said operating lever so that the latter can move to contact opg ning position.

2. A thermally responsive overload switch according to claim 1 wherein said spring means biasing said operating lever in the contact opening direction comprises a coil compression spring engaging a fixed abutment at one end and at its other end with a hollow member which in turn engages said switch operating lever, and which, with said spring is concentrically disposed about said reciprocally moveable member, and wherein said recip- 9 rocally moveable member has a portion engaging said operating lever on a side opposite that engaged by said hollow member.

3. A thermally responsive overload switch according to claim 2 wherein said switch means additionally comprises a leaf spring moveable contact member on which said operating lever is pivoted and a C-shaped toggle spring engaging in a slot therein adjacent one end with said contact member and pivoted at its opposite end on said operating lever, and wherein said last mentioned end of said toggle spring when moved in either direction across the plane of said contact member causing snap action movement of said contact member in the direction opposite thereto.

References Cited UNITED STATES PATENTS 3/1965 Roeser 20067(D) 7/1962 Shivers 73363.5(X) 2/1941 Van Almelo 337335 1/1933 Appelberg 337-354(X) 10/ 1965 Schwartz 200-67 (D) 4/1956 Lauder et al. 200153(.19)

10 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner U.S. Cl. X.R.

T52 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.565.328 Dated April 26, 1971 lnventofls) Uriel F. Carter and Edward A. Mallonen It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C0lumn 5, line 15, the sentence --It will be seen that spring 54' urges gland 56' down-- is omitted.

Column 6, line 12; "is" should read in--.

Signed and sealed this 13th day of July 1971 (SEAL) Attest:

EDWARD M.FLETCIER,JR. WILLIAM E. SGHUYLER, JR Attesting Officer Commissioner of Patents

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