US3470514A

US3470514A - Electrical switch particularly adapted for use in pressurized areas

Info

Publication number: US3470514A
Application number: US571238A
Authority: US
Inventors: Walter Reeve Harper Jr
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1966-08-09
Filing date: 1966-08-09
Publication date: 1969-09-30
Anticipated expiration: 1986-09-30

Description

&pt. 30, 1969 w, R. HARPER, JR 3,

ELECTRICAL SWITCH PARTICULARLY ADAPTED FOR USE IN PRESSURIZED AREAS Filed Aug. 9, 1966 2 Sheets-$heet 1 0 BIMETAL 30 26 23 24 30 16' l I? ,7 y

r" I :2 I I 1 I 42\ 26- 22 4 I 40 44 ll 20 4o Q6 50 /9 I 46 lill Inn,

I I a3 18 2/ INVENTOR,

WALTER ,REEVE HARPER,

1 ATTY.

United States Patent O US. Cl. 337-89 12 Claims ABSTRACT OF DISCLOSURE An electrical switch especially useful as a motor protector in the three to five horsepower range in pressurized atmospheres comprising an elliptical shaped housing having a fistular stitf casing ring forming sidewalls and mounting stationary contacts and a stiff center post mounting a thermostatic element with movable contacts mounted thereon Relatively thin top and bottom covers seal the device. The spatial relationship between the thermostatic element and the contacts are unaifected in the event excessive ambient pressure collapses the covers. The covers are kept thin to confine the sections affected by collapsing to parts which will not affect the calibration of the device; to optimize heat flow from the motor to the thermal element in the switch and to facilitate original calibration of the switch.

The switch is calibrated by depressing one of the cover members while supports the casing ring.

Means are provided to limit the travel of the thermal element in the form of dimples in the cover members.

Eyelets having an attenuated Wall portion are provided to prevent excessive heat reaching and fracturing glass in the header and provide resiliency to .absorb mechanical This invention relates to thermally responsive electric switches, and more particularly to thermally responsive electric switches of a type including a dished snap-acting thermostatic disc as the thermostatic element thereof.

Among the several objects of the invention may be noted the provision of a construction particularly suitable for a hermetically sealed motor protector employed in a pressurized area.

Another object is the provision of a motor protector which is inexpensive yet reliable, one which is of a minimal size yet has a relatively high rating.

It is still another object to provide a switch which can readily be made in mass production, and which will have a low rejection rate.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the appended claims.

In the accompanying drawings, in which several of the various possible embodiments of the invention is illustrated:

FIG. 1 is a plan view of the device with the cover partly broken away;

FIG. 2 is a cross-section taken along the line 22 of FIG. 1;

Patented Sept. 30, 1969 FIG. 3 is a view similar to FIG. 1 but enlarged and partly in cross-section and with the cover removed;

' FIG. 4 is a perspective of a backup plate employed in a second embodiment of the instant invention;

FIG. 5 is a cross-section similar to FIG. 2 but including the backup plate of FIG. 4.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Dimensions of certain other parts as shown in the drawings have been modified and/or exaggerated for the purposes of clarity of illustration.

The protector of the instant invention is used to protect, although it is not limited to, motors of the three to five horsepower range and are designed to interrupt the current to the motor upon both current overloads and excessive generated heat. Additionally this protector is designed to be used in pressurized atmospheres of up to 600 p.s.i., as in refrigeration apparatus. Factors which must be considered in the design of such a protector include the following: the impedance to heat flow to the thermally responsive element from the motor must be kept to a minimum and the size and expense must also be minimized to make a competitively successful device yet the device must be reliable to fulfill its intended function.

Referring to the drawings, a thermostatic switch generally designated by numeral 10, constructed in accordance with this invention is shown as elliptic in cross section to achieve a minimum space package for the type of thermostatic element employed. Elliptical shaped housing comprising ring 14 which is comparatively thick to provide stiffness is joined to top and

bottom covers

16, 18 respectively as by welding at 17, 19. A stiff center post 20 extends between

covers

16, 18 and is attached thereto as by Welding at 21 and 23. Any strong material such as cold rolled steel may conveniently be used for casing 14 and post 20. Disc 24, an elliptical shaped snap-acting disc of a suitable bimetal is provided with a bore 26 for loosely and rotatively fitting disc 24 to center post 20 in groove 22 formed therein.

The instant design employs stiff mounting elements, casing member 14 and mounting post 20, explained supra. An inspection of the drawings will illustrate that these elements are made much thicker than the cover elements 16; 18. It has been found that to provide the necessary stiffness casing 14 formed of a suitable material such as cold rolled steel should be at least three times the thickness of the cover members. An example of the relative thickness actually used are: casing 14 thickness of 0.100; covers 16, 18 thickness of 0.032". The cover members are kept relatively thin to facilitate calibration of the device which is accomplished by depressing cover 16 while restraining the outer periphery of 'ring 14. It will be noted that heat flow from the motor to the thermosatic element will not be unduly impaired by reason of the relatively thin covers. Further, the amount of material used is kept to a minimum making a more economic device.

It will be seen that by mounting the movable and stationary contacts on the stiff elements the spatial relationship between the elements will not be affected in the advent of the covers collapsing due to excessive exterior pressure and hence the trip temperature of the device will not be deleteriously alfected.

Cover 16 is provided with two dimples 30, aligned with the major axis of the elliptic housing generally and contacts 34 on disc 24.

Dimples 30 are formed in cover 16 and located in respect to disc element 24 so as to limit the travel of the disc when the latter snaps from the contacts-closed position to the contacts-open position to restrict the overtravel of the disc and dampen the disc oscillation. Without the restraining dimples 30 the disc would travel beyond the stable at-rest contacts-open position due to inertia forces and momentum in the disc upon snapping. These dimples serve an analogous function to the abutment means 64 set forth in US. Patent No. 3,213,240 to which reference may be had for more information relating to its function.

Two ceramic barriers 36 are mounted on shoulder portions 38, formed in ring 14. Barriers 36 are formed with seat portion 40 including a recessed portion 42. Stationary contacts 44 are mounted on

elements

46, 48 respectively.

Elements

46, 48 are current carrying members and one or both may be employed as heating elements to provide heat anticipation if desired.

Supports

46, 48 are formed with tab portions 50 which fit into recesses 42 thereby locking barriers 36 into place against shoulder 38.

Elements

46, 48 are provided with connecting portions 52, 54 to which leads 56 are connected as by welding at 57. Leads 56 are inserted through apertures 58 in casing 14 and are provided with eyelets 60 comprising frame or rim 62 having an attenuated wall portion 64 depending from rim 62 and which fits into seat 66 formed in casing 14 and welded thereto. The eyelets 60 are formed with attenuated depending wall portion 64 which serves two functions. First, it provides a high electrical resistance to the welding current when covers 16, 18 are attached to casing 14 thereby preventing excessive heat from reaching and fracturing the glass in header 60 upon assembly of the device. Secondly, attenuated wall 64 is resilient and absorbs mechanical shock during the welding operation thereby protecting the fragile glass. Conductor 68 of a conventional type may be connected, as at 69, to lead 56 or alternatively, terminal member 70 can be used and may be attached in a conventional manner as at 71. Sleeve 72 of conventional electrical insulation is inserted over leads 56 and eyelet 60 and infilled with an electrical insulating material such as epoxy 74 and serves as a strain reliever.

Switch utilizes several means to increase its rating. One such way is by directing the current to and from the contacts immediately adjacent thereto in parallel and opposite directions, creating electromagnetic fields which produce forces which act upon the are formed between the contacts upon engaging and disengaging thereof and direct the arcs into barriers 36 formed of refractory material to minimize the vaporization and melting of the metallic elements of the switch. Further, it will be noted that in order to maintain electrical continuity as the thermostatic elements snaps to an open contacts position an arc would exist in two places, e.g. between the mating contacts. This would result in four areas of arc termination which would facilitate arc cooling and minimize deleterious effects due to the are.

A second embodiment of the invention is illustrated in FIGS. 4 and 5. As best seen in FIG. 4 backstop 80 is provided with welding projections '81 to facilitate connecting, as by welding, to post at 83. Post 20 fits through aperture 82 in backstop 80. Cutout portions 84 are provided in backstop 80 and are aligned with dimples 30.

Backstop 80 can be used to help maintain the reset temperature of the disc at a specific level even if cover 16 is deformed because it is not referenced to ring 14. In view of the above it will be seen that the several objects of the invention are achieved, and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense; and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

" I claim:

1. A hermetically sealed electric switch comprising:

a stiff fistular casing,

a stiff mounting post,

at least one stationary contact seat element of electrical insulation supported on the casing,

at least one stationary contact mounted on the seat element,

a thermostatic element mounted on the mounting post,

a movable contact located on a distal portion of the thermostatic element and adapted to move into and out of engagement with at least one stationary contact,

thereby closing and opening respectively in electric circuit, and

a top and bottom cover less stifi than the casing and the mounting past closing the fistular casing.

2. A switch according to claim 1 in which the casing in cross section and the thermostatic element is elliptic in shape; two movable contacts are mounted along the major axis of the thermostatic element on spaced distal portions thereof, and two stationary contacts are mounted on two stationary contact supports located on seat elements.

3. A switch according to claim 2 in which the seat elements are composed of ceramic-type material and are employed as are barriers, the stationary contact supports have portions which mount the stationary contacts and are located such that an electric current passing through the supports adjacent the stationary contacts pass the current in the thermostatic element in approximated parallel, opposite directions.

4. A switch according to claim 3 in which the casing is provided with shoulders which receive the seat elements; the seat elements are each formed with a recess, and each stationary contact support has a tab portion which is received in the recess of the respective seat element to lock the seat element in place.

5. A switch according to claim 2 in which the thermostatic element is formed with an aperture therein, the mounting post is received therethrough to rotatively mount the thermostatic element and the seat elements are provided with stop surfaces to limit the rotation of the thermostatic element.

6. A switch according to claim 2 in which at least one of the stationary contact support is a heater element.

7. A switch according to claim 1 in which the thermostatic elemcnt is a snap acting disc and dimples are formed in a cover and located to restrain movement of the disc beyond the at-rest stable contacts open position.

8. A switch according to claim 2 which is hermetically sealed by welding the covers to the casing and in which two apertures are provided in the casing,

a lead inserted through each aperture and is connected to a respective contact support,

each lead is provided with an eyelet having a rim portion with a bore therein through which the lead is inserted,

glass insulation material connects the lead to and electrically isolates the lead from the eyelet, and

an attenuated wall depending from the rim and welded to the casing.

9. A switch according to claim 2 in which a backstop element overlays the thermostatic element.

10. A switch according to claim 1 in which the casing member is substantially stiffer than the covers.

11. An electrical switch having a thermostatic element and two electric current path means bringing current to and from the element so that current passes from one current path means through the thermostatic element to the other current path means, at least one of the current path means comprising a movable contact mounted on the thermostatic element; a seat element composed of ceramic like material employed as an arc barrier mounted in the swith; a stationary contact; a support mounted on the seat element and mounting the stationary contact, the support extending from the stationary contact immediately adjacent thereto in a direction toward the other current path means and being intermediate the two current path means whereby an electric current passing through the support adjacent the stationary contact passes the current in the thermostatic element in approximately parallel, opposite directions.

12. A hermetically sealed switch having a casing and top and bottom covers which is hermetically sealed by welding the covers to the casing and in which two apertures are provided in the casing,

an attenuated wall depending from the rim and having a distal end remote from the glass material welded to the casing.

References Cited UNITED STATES PATENTS 2,806,109 9/1957 Sterling 200-144 2,950,371 8/1960 Stringfellow 200-444- 2,685,014 7/1954 Mang 200138 2,839,638 6/1958 Epstein 200-113 2,855,485 10/ 1958 Webking 200-438 3,242,292 3/1966 Malone 200-122 3,308,255 3/1967 Faggiano 20013 BERNARD A. GILHEANY, Primary Examiner R. COHRS, Assistant Examiner US. Cl. X.R. 337-110