US3023350A

US3023350A - Electrical switch means

Info

Publication number: US3023350A
Application number: US803282A
Authority: US
Inventors: William A Broadley; Edward P Jastram Jr
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1959-03-31
Filing date: 1959-03-31
Publication date: 1962-02-27
Anticipated expiration: 1979-02-27
Also published as: GB952330A; FR1252490A; NL249998A

Description

Feb. 27, 1962 w. A. BROADLEY ETAL 3,023,350

ELECTRICAL SWITCH MEANS Filed March 51, 1959 5 Sheets-$heet 1 172067250715: M'Zlziarrz A. Bmadley,

Edzard f? Jas tramJi A yo Feb. 27, 1962 w. A. BROADLEY ETAL 3,023,350

ELECTRICAL SWITCH MEANS Filed March 31, 1959 5 Sheets-Sheet 4 lNSl/LA T/ON [72 @972 60 715 William A .15 raadley,

Feb. 27, 1962 w. A. BROADLEY ETAL 3,023,350

ELECTRICAL SWITCH MEANS Filed March 31, 1959 5 Sheets-Sheet 5 306 Inventor's.-

William A,Braad 2qy, Edward I. Jas train];

United States Patent 3,023,350 ELECTRICAL SWITCH MEANS William A. Broadley, East Walpole, and Edward P.

Jastram, Jr., Rehoboth, Mass., assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Mar. 31, 1959, Ser. No. 803,282 16 Claims. (Cl. 318-221) This invention relates to the protection of electric motors, and more particularly, to means providing protection against overheating of electric motors which are subject to the heat-transfer influence of the convective flow of a fluid medium and electric motors in environments wherein ambient temperature conditions vary widely.

In protecting electric motors against overheating, it has been the practice to provide a thermally responsive device operatively connected to disconnect the motor electrically under fault conditions before the latter overheats. One problem that arises due to factors, for example, such as heat-transfer characteristics, etc., is that of subjecting the thermally responsive device to a rate of heating substantially proportional to that of the motor under all conditions so as neither unduly to overprotect nor unduly to underprotect the motor.

In attempting to effect heating of the thermally responsive device at a rate substantially proportional to that of the motor, electric heaters have been provided for adding heat to the thermally responsive device in addition to any heat transferred from the motor itself and/or generated in the thermally responsive device due to its internal electrical resistance. One diificulty that often presents itself is that the motor (or more pertinently, the winding or windings thereof) is exposed to or is otherwise rapidly responsive to changes in the heat-transfer influence of the convective flow of a fluid medium while, for one reason or another, the thermally responsive device is sealed and therefore is not responsive or is at least not as quickly responsive to such changes in the heat-transfer influence. This difliculty is magnified in those environments where the heat-transferring capacity of the convective flow varies due to variable temperatures of the fluid medium and/or variable rates of convective flow. Merely by way of example, a refrigeration compressor unit is one of the environments wherein this problem may be manifested.

Accordingly, it is an object of this invention to provide new and improved means for counteracting these difliculties.

A further object of the invention is the provision of an improved, sealed, thermally responsive protective device which is adapted to be responsive to changes in the heat-transfer influence of the convective flow of a fluid medium at substantially a. rate of response proportional to that of the means to be protected which is exposed to said convective flow.

A further object of the invention is the provision of such an improved sealed, thermally-responsive device which is relatively compact and inexpensive.

A further object of the invention is to provide an improved combination including at least one motor Winding exposed to the heat-transfer influence of the convective flow of a fluid medium and protected by a sealed, thermally responsive device which is adapted to be responsive to said influence at a rate substantially the same as that at which said motor winding is responsive.

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 following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated by way of example:

FIG. 1 is a schematic view of an electrical circuit having portions disposed within a compressor unit, all according to a first embodiment of the invention;

FIG. 2 is an elevational view in section of a thermally responsive device sealed Within a casing and having a heater wire wrapped about the outside of the casing, corresponding parts being included schematically in FIG. 1;

FIG. 3 is a sectional view taken along line 33 in FIG. 2;

FIG. 4 is a bottom plan view of the structure shown in FIG. 3;

FIG. 5 is a schematic view of an electrical circuit according to a second embodiment of the invention;

FIG. 6 is an elevational view with parts broken away of a thermally responsive switch having three electric heaters wrapped about the outside of the casing thereof, corresponding parts being included schematically in FIG. 5;

FIG. 7 is a schematic view of an electrical circuit according to a third embodiment of the invention;

FIG. 8 is an elevational view in section of a thermally responsive device sealed within a casing and having a heater wire wrapped about the outside of the casing, corresponding parts being included schematically in FIG. 7;

FIG. 9 is a sectional view taken along line 9-9 in FIG. 8;

FIG. 10 is a sectional view taken along line 10-10 in FIG. 8;

FIG. 11 is a schematic view of an electrical circuit according to a fourth embodiment of the invention;

FIG. 12 is a top plan view of a thermally responsive switch, corresponding parts being included schematically in FIG. 11;

FIG. 13 is an elevational view thereof;

FIG. 14 is a sectional view taken along line 1414 in FIG. 13; and

FIGS. 15 and 16 are sectional views taken along lines 1515 and 1616, respectively, in FIG. 14.

In protecting the winding or windings of an electric motor by means of a sealed thermally responsive device which is heated by an electric heater to aid in eflecting heating of the thermally responsive device at a rate substantially proportional to that at which the motor heats, the situation whereby the motor winding or windings are subject to the heat-transfer influence of the convective flow of a fluid medium arises not infrequently in a number of different installations. Depending upon the particular installation, the fluid medium may be at a higher or lower temperature than the winding or windings of the motor when under quiescent conditions and may even fluctuate between such higher and lower temperatures. The convective flow of the fluid medium may result directly or indirectly from operation of the motor or may be totally independent of operation of the motor. The instant invention is applicable in all of these cases. The term sealed as employed throughout the specification is intended to include sealing against entry of at least one or more of the following, individually or in combination: moisture, refrigerant fluids, impregnating media such as varnishes, resins or the like and their vapors, lubricants and fuels and their vapors and other deleterious substances.

Referring to FIG. 1, in which an arrangement according to a first embodiment of the invention is shown, the two sides of a single-phase, electrical current supply source are indicated by the

reference numerals

20 and 22. The circuitry of FIG. 1 includes an on-off switch 24 and a contactor which may take the form of an electromagnetic relay generally indicated by the reference numeral 26. Contacts 28 and coil 30 of relay 26 are electrically connected in parallel circuit arrangement with respect to each other and in series circuit relation to switch 24. When relay 26 is energized, bridging member 32 thereof movesinto engagement with and electrically connects contacts 28. One terminal 34 of an electric heater 36 is connected in series with contacts 28 of the relay, and the other terminal 38 of heater 36 is electrically connected in series with each of

windings

40 and 42 of an electric motor 43. Motor 43 may be of the split-phase type, winding 40 being the main winding and winding 42 being the auxiliary or start winding. It will be understood that a displacement of the phase angle between

windings

40 and 42 can be effected in any desired manner such as by the use of capacitors, inductors, etc. Start winding 42 is disposed in series with a start winding switch means 44 which may be in the form of a centrifugal switch or a starting relay to de-energize the start winding 42 as the motor comes up to speed. Motor winding 40 is connected to the other side 22 of the current supply source as is start winding 42 through switch means 44.

The circuit shown in FIG. 1 includes a normally closed, thermally responsive switch generally indicated by the reference numeral 46. Thermally responsive switch 46 includes a thermally responsive device 48 operatively connected through a motion-transfer member 50 to effect opening and closing of a switch 52. In a manner to be described below with respect to FIGS. 2-4, electric heater 36 is disposed in heat-transfer relation to thermally responsive device 48. Thermally responsive switch 46 includes a pair of

terminals

54 and 56, the former being connected to side 20 of the current source through relay coil 30 and switch 24 and the latter being connected to side 22 of the current source.

Referring to FIGS. 2-4, thermally responsive switch 46 includes a cup-shaped casing member 58 formed of a material having a comparatively high heat conductivity such as, for example, copper or steel. Cup-shaped casing member 58 is provided with an internal, inwardly-directed shoulder 60 about its inner periphery. Thermally responsive device 48 of the thermally responsive switch 46 takes the form of a conventional thermostatic disc. Disc 48 is formed in a well-known manner with at least two layers or components, one having a higher coefiicient of thermal expansion than the other so that upon heating thereof the disc snaps from one position of stability to another. Upon cooling thereof, the disc will snap back to the opposite position of stability. The high expansion layer or component of disc 48 as viewed in FIG. 2 is uppermost whereupon the disc snaps from the full-line position shown in FIG. 2 to the broken-line position upon heating to a predetermined temperature and snaps back to said full-line position upon cooling to a predetermined temperature. Another cup-shaped member 62 is disposed within cup-shaped member 58 and is snugly fitted therein so as to prevent relative movement therebetween. Cupshaped member 62 is formed of one of the conventional, electrically insulating plastics. The outer peripheral surface portion of cup-shaped member 62 adjacent shoulder 60 of cup-shaped member 58 is spaced from this shoulder for the reception of the radially outer marginal portions of disc 48. Cup-shaped member 62 is provided with an aperture 64 through which transfer pin 50 extends. Transfer pin 50 includes a reduced-diameter portion 66 which extends through an aperture 68 in a movable contact-carrying arm 70 of the switch generally indicated by the reference numeral 52. Transfer pin 50 interfits sufiiciently loosely with

apertures

64 and 68 to prevent jamming of the transfer pin in either of these apertures. Contact-carrying member 70 is supported at one end in cantilever fashion by a member 72 having a distal or outer end terminating in an electrical terminal 56. Member 70 carries a movable contact 76 for engagement with a stationary contact 78 supported by a member 80 which terminates at its distal or outer end with an electrical terminal 54. Contact-carrying member 70 is inherently resiliently biased to the contacts-open position shown in broken lines in FIG. 2 so that

contacts

76 and 78 are open when thermally responsive device 48 is in the broken-line position of FIG. 2 and the latter holds

contacts

76 and 78 closed when in the full-line position of FIG. 2. Thermally responsive switch 46 further includes a header or casing cover member 82. A section of glass 84 is bonded to the mutually adjacent portions of header member 82 and to each of

members

72 and 80 thereby to support

members

72 and 80 within

apertures

86 and 88, respectively, of header member 82 with a conventional glass-to-metal seal. Header member 82 provides an internal shoulder 90 about its inner periphery for the seating of the adjacent or open end of cup-shaped

members

58 and 62. The mutually engaged portions of cup-shaped member 58 and header member 82 are sealed to each other by soldering, brazing or welding or the like to provide a sealed casing including cupshaped member 58, header member 82 and glass sections 84. The casing of thermally responsive switch 46 may include a thin layer of electrical insulating material 92 such as fish paper or Mylar (the latter being a registered trademark for a film of polyethylene terephthalate resin) wrapped about and in engagement with the exterior surface of cup-shaped member 58 and portions of header member 82; this insulating layer being of a relatively small thickness so as to offer as little resistance to the flow of heat therethrough as conveniently possible.

The electric heater 36 as shown in FIGS. 2-4 may, as one example, take the form of a coil of electrical insulation coated wire having a significant electrical resistivity so as to be heated upon the passage of electrical current therethrough. The

terminals

34 and 38 of electric heater 36 as well as

terminals

54 and 56 of thermally responsive switch 46 as shown in FIGS. 2 and 4 are adapted for electrical connection as shown in the diagrammatic circuit of FIG. 1. Heater 36 is disposed in thermally conductive juxtaposition against the casing of thermally responsive switch 46 such as, for example, wrapped thereahout so as to he in heat-transfer relation to thermally responsive device 48. That is, thermally responsive device 48 is in heat-transfer relation with the casing 58 of thermally responsive switch 46 and the latter is in heat-transfer relation with heater 36. Accordingly, upon heating of heater 36, heat will be transferred therefrom through the layer of electrical insulating material 92, through and along cup-shaped member 58, to thermally responsive device 48. As another example, the heater for this, as well as each of the other embodiments disclosed herein, could be in the form of a length of insulation coated electrically conductive foil wrapped about or otherwise disposed in thermally conductive juxtaposition against the outside of the casing of the thermally responsive switch in heat-transfer relation to the thermally responsive device.

For the purposes of mounting thermally responsive switch 46, cup-shaped member 58 can be soldered, brazed, welded or the like to a supporting strap or plate 94 within an interfitting aperture 96 therein. It will be understood that thermally responsive switch 46 may be mounted against

windings

40 and 42 of the motor or otherwise in good heat-transfer relation therewith such as, for example, by being mounted against the end bell of the motor.

Referring back to FIG. I, it will be seen that thermally responsive switch 46, heater 36 and motor 43, along with a pump 100, are disposed within the housing 162 of a compressor unit generally designated by the reference numeral 184. Oftentimes start winding switch 44 will be located outside housing 102 rather than inside as shown in FIG. 1, but this feature does not form a part of and has no bearing on the instant invention. The electric motor is operatively connected for driving pump 100 to effect the flow of a fluid medium which may take the form of a refrigerant from an inlet 106 in housing 102 through the housing and past an outlet 168 in the housing.

Motor windings

40 and 42 are exposed to and lie in the path of the refrigerant flow through the housing. The refrigerant, being generally at a substantially lower temperature than the motor windings, takes heat from the windings and by convection carries this heat out of the housing. This arrangement significantly increases the allowable current rating of the motor as compared with the corresponding allowable current rating of the motor when it is not so cooled by the convective flow of refrigerant.

Thermally responsive device 48, which along with switch 52, is disposed within a casing which is sealed to prevent the entry of moisture, refrigerant, etc., and is therefore not exposed to this convective flow. Consequently, thermally responsive device 43 is cooled very slowly by the convective flow of refrigerant through the housing. Thermally responsive device 48 is heated, in large part at least, by electric heater 36 and since this heater lies in the path of and is exposed to said convective flow of refrigerant, the cooling effect on the heater is reflected substantially as rapidly on the heater and in turn on the thermally responsive device as on the motor windings. This is not to imply, of course, that thermally responsive device 48 must heat or cool at the same rate as one or more of the motor windings. Rather, with this invention, changes in the heat-transfer effect of the convective flow will be reflected substantially as rapidly on the thermally responsive device as on one or more of the motor windings so that the thermally responsive device and the motor windings heat and cool at rates proportional to each other under all conditions, this even though the thermally responsive device is sealed within a casing while the motor windings are exposed to the convective flow.

In operation, switch 52 being normally closed, relay coil 30 will be electrically energised upon closing of switch 24. Relay 26, when electrically energized, closes contacts 28 whereby heater 36 and

motor windings

40 and 42 are electrically energized, As the motor comes up to speed, start winding 42 will be de-energized by opening of switch means 44, The motor drives pump 100 causing the refrigerant to be Pumped from inlet 106, through housing 102 in convective heat-transfer relation to heater 36 and windings 4t) and 42, and past outlet 108. Accordingly, upon

motor windings

40 and 42 approaching the condition of the overheating due to a fault, thermally responsive device 48 will be heated to its tripping temperature whereupon the latter trips to the broken-line position shown in FIG, 2 thereby to open

contacts

76, 78 which in turn de-energize relay winding 30 to effect dropout of relay 26 and de-energization of

windings

40 and 42 along with heater 36. It will be apparent that with heater 36 in series with start winding 42 of the motor as well as with main winding 40, the heat-transfer effect of the convective flow on the start winding as well as on the main winding will be reflected upon the rate at which the heater 36 heats thermally responsive device 48 during starting of the motor as well as during a locked rotor condition or upon failure of switch 44 to open when the motor comes up to speed. However, if for some reason it were desired, heater 36 could be electrically connected in parallel circuit relation with start winding 42 (while still in series with main winding 40) so as not to carry the start winding current.

A compressor unit 104 as set forth herein is adapted for operative connection in a cooling system including a condensor and an evaporator (along with other accouterment) in a number of different installations such, for example, as refrigerators, freezers, air conditioners, etc. With an installation such as a heat pump, the cooling effect of the convective flow of refrigerant on the motor windings would, ordinarily at least, be substantially less during operation as a heating apparatus than during operation as a cooling apparatus due, for the most part, to the lower rate of flow and higher temperature of the refrigerant. The invention is equally applicable to this condition because a change in the heat-transfer effect of the convective fiow is reflected on the thermally responsive device substantially as fast as it is on the motor windings whether the change is due to reversal of the refriger ating cycle or otherwise. Some examples of other conditions which would result in changes in the heat-transfer effect of the convective flow would be an increase or de crease in the temperature of the convective flow and an increase or decrease in the quantitative rate of the flow (including stoppage of the convective flow) Referring to the exemplary embodiment shown in .FIGS. 5 and 6,

reference numerals

110, 112 and 114,

respectively, designate the three lines of a three-phase, electrical current supply source. Coil 116 of an electromagnetic relay generally indicated by the reference numeral 118, on-off switch 120 and thermally responsive switch 122 are electrically connected in series circuit relationship with each other across lines 110 and 114. Thermally responsive switch 122 includes a thermally responsive device 124 operatively connected through a motiontransfer member 126 to open and close a switch 128. Thermally responsive switch 122 is or may be substantially identical with thermally responsive switch 46 of the embodiment of FIGS. 1-4 described above. Refer ring to FIG. 6, thermally responsive switch 122 may be mounted on a supporting member 130 in a manner similar to that described with respect to the preceding embodiment. Three

electrical heaters

132, 134 and 136 are provided, each of which if desired, can be covered with a coating of electrical insulation and each of which is disposed in heat-transfer relation to the thermally responsive device 124 of the thermally responsive switch 122. Referring to FIG. 6 in this regard, each of

heaters

132, 134 and 136 is disposed in thermally conductive juxtaposition against the sealed casing of the thermally responsive switch 122 such as, for example, wrapped thereabout so as to transfer heat to thermally responsive device 124 in the manner described above with respect to the embodiment of FIGS. l-4. From a common connection, heater 132 is connected in series circuit relation with a first three-phase motor winding 138 and spaced contacts 140 of relay 118 to line 110; heater 134 is connected in series with motor winding 142 and spaced contacts 144 of relay 118 to line 112 and heater 136 is connected in series with motor winding 146 through spaced contacts 148 of relay 118 to line 114.

The three-phase motor 149 which includes

windings

138, 142 and 146 is operatively connected to drive pump 150 for pumping a convective How of refrigerant from inlet 152 of the housing 154 of a compressor unit generally designated by the reference numeral 156, through the housing in heat-transfer relation to

motor windings

138, 142 and 146 as well as to

heaters

132, 134 and 136, and out of housing 154 through outlet 158 therein. Since thermally responsive device 124 is heated, in large part at least, by

heaters

132, 134 and 136, with the latter exposed to and lying in the path of the same convective flow as

motor windings

138, 142 and 146, changes in the heat-transfer effect of the convective fiow will be reflected on the thermally responsive device substantially as rapidly as on the motor windings. By suitable adjustment of parameters, heating and cooling of the thermally responsive device 124 take place at a rate substantially proportional to that which heating and cooling of the motor windings take place.

Thermally responsive switch 122, as well as each of the thermally responsive switches of each of the other embodiments, may be disposed in heat-transfer relation with the motor windings of the associated motor so as to transfer a significant amount of heat from the motor windings to the thermally responsive device 124.

It will be apparent that so long as no fourth wire is utilized leading from the common connection of each of

heaters

132, 134 and 136 to ground, any one of these heaters could be eliminated at least in some installations since a current overload through winding 138, for example, if heater 132 were eliminated, would be reflected by corresponding additional heating of

heaters

134 and 136.

No electric current is carried by the thermally

responsive elements

48 and 124, respectively, of the thermally

responsive switches

46 and 122, respectively, according to the two embodiments previously described. The thermally responsive switches of the two embodiments subsequently to be described differ in that the respect ve thermally responsive device carries the current flowing through the motor winding or windings with which it and one or more respective heaters are respectively connected in series circuit relation.

Referring to the schematic arrangement shown in FIG. 7,

reference numerals

160 and 162 designate the two sides of a single-phase electrical current supply source. A terminal 164 of a thermally responsive switch generally designated by the reference numeral 166 is connected through an on-ofi switch 168 to side 162 of the current supply source. The other terminal 170 of thermally responsive switch 166 is connected to an electric heater 172, the latter being disposed in heat-transfer relation to a thermally responsive device 174 of thermally responsive switch 166 as will later be described more in detail with respect to FIGS. 8-10.

Heater 172 is electrically connected in series circuit relationship with each of main winding 175 and auxiliary or start winding 176 of a split-phase electric motor 177;

windings

175 and 176 being connected in parallel relationship with each other. A start-winding switch means 178 is connected in series with start winding 176 for deenergizing the latter as the motor comes up to speed. Main winding 175 is connected to the other side 160 of the current supply line as is start winding 176 through switch means 178.

Referring to FIGS. 8-10, thermally responsive switch 166 includes a generally rectangular, cup-shaped casing member 180 formed of a material having a high heat conductivity such as, for example, copper or steel. The open end of casing member 180 is closed by a header or cover member 182,

flanges

184 and 186 provide respectively by these casing members being sealed together as by welding to provide a sealed casing. A section of glass 188 is bonded to the mutually adjacent portions of header member 182 and each of terminals 164 and 170 thereby to support these terminals within

apertures

190 and 192, respectively, of header member 182 with a conventional glass-to-metal seal.

; A cup-shaped member 194 formed of a conventional material such as moldable, electrically insulating material is disposed within the casing of thermally responsive switch 166. A pair of headed studs 196 and 198 extend through interfitting apertures in cup-shaped member 194. Stud 196 is welded at one end to a strap 200 and stud 198 is welded at one end to a strap 202.

Straps

200 and 202 are welded to terminals 164 and 170, respectively, thereby to support cup-shaped member 194 and the parts fixed with respect thereto within the casing of thermally responsive switch 166 and electrically to connect each of studs 196 and 198 to a respective terminal 164 and 170. At the distal end of each of studs 196 and 198 is a stationary contact 204 and 206, respectively. Threadedly engaged with a tapped hole 209 in cup-shaped member 194 is a post 208 which is secured in adjusted relation to cup-shaped member 194 by means of a lock nut 210. Post 208 includes a reduced-diameter portion 212 extending loosely through an aperture 214 in thermally responsive device 174. Thermally responsive device 174 is loosely confined between a flange 216 and a headed over portion 218 provided by thepost 208. The thermally responsive device 174 is formed in a conventional manner of two or more layers or components having respectively different coefficients of thermal expansion so as to be snappable from a first position of stability to a second position of stability upon being heated to a predetermined temperature and snappable back to said first condition upon being cooled to a predetermined temperature. Thermally responsive device 174 carries a pair of

movable contacts

220 and 222, these movable contacts being engaged with stationary contacts 204 and 206 when the thermally responsive device is in said first condition in the solid line position in FIG. 10 and being spaced from and electrically disconnected from contacts 204 and 206, respectively, when in said second condition as shown by the dashed-line position in FIG. 10. Thermally responsive device 174 includes opposed

ears

221 and 223 as clearly shown in FIG. 8, respectively, which interfit loosely with

grooves

225 and 227 provided by member 194 thereby preventing substantial rotation of the thermally responsive device about post 208.

The outer surface of cup-shaped member 180 as in the species of FIGS. l-4 may be wrapped with or may otherwise have disposed thereabout a layer of electrical insulating material 224 such as fish paper or Mylar which is of a minimum thickness so as to offer as little resistance to the flow of heat therethrough as is conveniently possible. Electric heater 172 is coated with a thin layer of electrical insulation and is disposed in heat-transfer relation to thermally responsive device 174 through the casing such as, for example, by wrapping the electric heater about and disposing it in engagement with the outer surface of the casing.

The layers or components of which thermally responsive device 174 is formed can be and most often are of a significant electrical resistance so as to be heated in part by the flow of current therethrough.

Referring to FIG. 7, electric motor 177 is operatively connected to drive a pump 226 for pumping the refrigerant of a refrigerating system from an inlet 228, through the housing 230 of a compressor unit generally designated by the reference numeral 232, and past an outlet 234 in the housing. Windings and 176 as well as heater 172 lie in the path of and are exposed to the flow of refrigerant through the housing. As with each of the other embodiments, the heat transfer effect of the convective flow of refrigerant will be reflected upon heater 172 substantially as rapidly as upon

windings

175 and 176 so as to have a proportional cooling effect on the thermally responsive device 174.

In operation switch 168 is closed to energize main winding 175 and start winding 176, it being noted that both the main and start winding currents flow through heater 172 and thermally responsive device 174. The thermally responsive device will be heated, in part, to

the extent determined by the electrical resistance thereof (for a given value of current flow therethrough) and, in large part at least, by heat transferred from heater 172, in addition to any heat transferred thereto from the motor windings. Upon either or both of

windings

175 and 176 approaching the condition of overheating, thermally responsive device 174 will snap from the contacts-closed position to the contacts-open position electrically to

deenergize windings

175 and 176 as well as heater 172, which snap-action will take place regardless of changes in the heat-transfer effect of the convective flow of refrigerant. As with the embodiment of FIGS. l-4, heater 172 could be disposed so as to be in parallel circuit relation with start winding 176 (while still in series with main winding 175), if desired. In addition to the above-mentioned beneficial advantages and results, the provision of the external heater or heaters wrapped around and in heat-transfer relation to the casing of the sealed thermally responsive switching means 46 and 122, 166 described above additionally has the advantage of enabling production of a protective sealed device which is smaller, more compact and less expensive than that which would be possible with a sealed protective device having such heaters sealed internally therein.

Referring to the schematic arrangement shown in FIG. 11, the three lines of a three-phase, electrical current supply are designated by the

numerals

236, 238 and 240. A three-phase on-off switch generally designated by the reference numeral 241 includes three pairs of mutually spaced

contacts

242, 244 and 246, respectively. A first terminal 248 of a thermally responsive switch generally designated by the reference numeral 250 is disposed in series circuit relation with an electric heater 252 and a three-phase motor winding 254 through contacts 244 to line 238. Another terminal 256 of thermally responsive switch 250 is electrically connected in series circuit relationship with an electric heater 258 and a three-phase motor winding 260 through contacts 246 to line 240. A third terminal 262 of thermally responsive switch 250 is electrically connected in series circuit relationship with a third three-phase motor winding 264 through contacts 242 to line 236. No electric heater is included in the current flow path between terminal 262 and contacts 242 for the reasons described above with respect to the embodiment shown in FIGS. and 6. Such a third electric heater could be added if a neutral, fourth wire to ground were added or if otherwise desired. This embodiment demonstrates that the thermally responsive switch according to the invention may be provided with internal heating means and may include one or more internal heaters sealed within the casing along with the thermally responsive device. Thermally responsive switch 250 as schematically shown in FIG. 11, includes three

internal heaters

266, 268 and 270, each electrically connected to a stationary

electrical contact

272, 274 and 276, respectively. Thermally responsive switch 250 further includes a thermally responsive device 312 carrying three

movable contacts

273, 275 and 277, for engagement respectively with

stationary contacts

272, 274 and 276.

Referring to FIGS. 12-16, thermally responsive switch 250 includes a cup-shaped casing member 280 formed of a material having a comparatively high thermal conductivity. Casing member 280 provides an internal shoulder 282 for the reception of a radially outer marginal portion of a header or casing cover member 284. The mutually contiguous portions of cup-shaped member 280 and header 284 are sealed to each other such as by welding. A section of glass 286 is bonded to the mutually adjacent portions of header member 284 and each of

terminals

248, 256 and 262 thereby to support these terminals within

apertures

288, 290 and 292, respectively, of the header member with a conventional glass-to-metal seal. I

Disposed within the casing provided by casing member 280 and header 284 is a generally cup-shaped member designated by the reference numeral 294. Cup-shaped member 294 is formed of a conventional moldable electrical insulating material and is provided with a plurality of

apertures

295, 297, 299 and adjacent shoulders 295a, 297a, 299a. Each set of apertures and shoulders 295, 295a; 297, 297a; and 299, 299a, respectively, co-operatively interfits with and fixedly mounts an electrically

conductive member

296, 298 and 300, respectively.

Members

296, 298 and 300 are in turn respectively connected to, as by welding or the like, and supported by

terminals

248, 256 and 262. Cup-shaped member 294 is provided with another set of

apertures

301, 303 and 305 and shoulders 301a, 303a and 305a alternately spaced between said

apertures

295, 297, 299 and shoulders 295a, 297a and 299a and at a lower elevation as seen in FIG. 14. Each set of apertures and shoulders 301, 301a; 303, 3031:; and 305, 305a interfits with and receives respectively contact providing

members

302, 304 and 306. Each of

members

302, 304 and 306 includes a turnedover portion providing respectively

contacts

272, 274 and 276. In a suitable manner, as by welding or the like, internal electric heater 266 electrically connects contact 272 with member 296, internal electric heater 268 electrically connects contact 274 with member 298, and internal electric heater 270 electrically connects contact 276 with member 300.

As best seen in FIG. 14, a post 308 is fixedly secured in threaded engagement with cup-shaped member 294 by means of a lock nut 310. Thermally responsive device 312 provides a substantially centrally located aperture 314 within which is disposed a reduced diameter portion 316 of the post 308. Thermally responsive device 312 is loosely confined between an adjacent shoulder 318 and a headed end 320 provided by the post. Substantial rotation of thermally responsive device 312 about the axis of post 308 is prevented by a plurality of ears 322 projecting radially outwardly from the disc and loosely interfitting with mating recesses 324 provided by cup-shaped member 294 as best seen in FIG. 15. Thermally responsive device 312 is similar to the thermally responsive device of each of the preceding embodiments, and is formed of a plurality of layers or components having mutually different coefiicients of thermal expansion whereby the thermally responsive device snaps from the contacts-closed position as shown in full lines in FIG. 14 to the contacts-open position shown in broken lines in this figure upon being heated to a predetermined temperature, and snaps back to the full-line, contacts-closed position upon being subsequently cooled to a predetermined temperature. As in the embodiment of FIGS. 7-10, thermally responsive device 312 may, and most often does, have sufficient electrical resistance to cause heating thereof due to the flow of motor winding current therethrough. The open end of cup-shaped member 294 is further provided with a shoulder 326 as seen in FIG. 14 for the reception of a circular member 328 formed of electrical insulating material and cemented in place about its periphery to shoulder 326.

A thin film 330 of electrical insulating material such as fish paper or Mylar may be wrapped about the outer surface of cup-shaped member 280.

External heaters

252 and 258 are covered with a thin layer of electrical insulation and are disposed in thermally conductive juxtaposition against the exterior of the casing of thermally responsive switch 250, such as by wrapping said heaters thereabout so as to dispose said heaters in heat-transfer relation to the thermally responsive device 312 through the casing. I

Referring back to FIG. 11, three-phase electric motor 331 which includes

windings

254, 260 and 264 is operatively connected to drive a pump 332 for pumping the refrigerant of the refrigerating system from an inlet 334 of the housing 336 of a compressor unit generally designated by the reference numeral 338, through the housing 336 and past the outlet 340 of housing 336, the latter also forming the outlet of pump 332 Motor windings 254,

260 and 264 and

external heaters

252 and 258 lie in the path of and are disposed to the heat-transfer effect of the convective fiow through housing 336. Thermally responsive device 312 is enclosed within a sealed casing and is therefore not as rapidly cooled by the convective flow as are the motor windings or

heaters

252 and 258. However, since

heaters

252 and 258 are in heat-transfer relation with the thermally responsive device, changes in the heat-transfer efiect of the convective flow will be reflected on the thermally responsive device 312 substantially as rapidly as upon the motor windings.

In operation, closing of three-phase switch 241 effects energization of

motor windings

254, 260 and 264 whereby three-phase motor 331 comes up to speed and drives pump 332 for pumping the convective flow of refrigerant in heat-transfer relation to the motor windings and the external electric heaters. Upon any one or more of the motor windings approaching the condition of overheating due to a fault, thermally responsive device 312 will snap to the contacts-open position thereby electrically de-energizing the motor windings and all of the heaters.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

Dimensions of certain of the parts as shown in the drawing have been modified for the purposes of clarity of illustration.

As many changes could be made in the above construe tions 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.

We claim:

1. In combination; an electric motor having at least one winding; said winding lying in the path of and being exposed to the convective flow of a fluid medium; electric heater means; an electric switch; said motor winding, heater means and switch being electrically connected in series circuit relation with each other; a thermally responsive device operatively connected for opening said switch upon reaching a predetermined temperature; and a sealed casing encompassing said thermally responsive device; said heater means being associated with said casing in heattransfer relation to said thermally responsive device and lying in the path of and being exposed to the convective flow of said fluid medium.

2. The combination as set forth in claim 1 wherein said heater means disposed in thermally conductive juxtaposition is against an outer surface of said casing,

3. In combination; an electric motor having at least one winding, said winding lying in the path of and being exposed to the convective flow of a fluid medium; an electric heater electrically connected in the same electrical circuit as said winding, a thermally responsive device operatively connected for opening said electrical circuit upon reaching a predetermined temperature, and a sealed casmg encompassing said thermally responsive device, said heater being associated with said casing in heat-transfer relation to said thermally responsive device and lying in the path of and being exposed to the convective flow of said fluid medium.

4. The combination as set forth in claim 3 wherein said heater is disposed in thermally conductive juxtaposition against an outer surface of said casing.

5. In a compressor unit for pumping the refrigerant of a refrigerating system; an electric motor having at least one Winding lying in the path of refrigerant flow through said unit; an electric heater and an electric switch electrically connected in series circuit arrangement with each other and with said winding; a thermally responsive device operatively connected for opening said switch upon reaching a predetermined temperature; and a sealed 12 casing encompassing said thermally responsive device, said heater being associated with said casing in heat transfer relation to said thermally responsive device and lying in said path of and being exposed to said refrigerant flow through said unit.

6. The combination as set forth in claim 5 wherein said heater is disposed in thermally conductive juxtaposition against an outer surface of said casing.

7. In a compressor unit for pumping the refrigerant of a refrigerating system comprising an electric motor having at least one winding lying in the path of and being exposed to the convective flow of a fluid medium; electrical heater means; electric switch means; said motor winding; heater means and switch means being electrically connected in series circuit relation with each other; a thermally responsive device for opening and closing said switch means at predetermined temperature conditions, said thermally responsive device being enclosed within a sealed casing, said heater means being associated with said casing in heat-transfer relation to said thermally responsive device and lying in the path of and being exposed to the convective flow of a fluid medium.

8. The combination as set forth in claim 7 and wherein said heater means is disposed in thermally conductive juxtaposition against an outer surface of said casing.

9. In a protective device for an electric motor having at least one winding electric heater means, said means and said winding; lying in the path of and being exposed to the convective flow of a fluid medium; electric switch means; said motor winding, heater means and switch means being electrically connected together in series circuit relation, said protective device including thermally responsive means for opening said switch means at predetermined temperature conditions, sealed casing means enclosing said thermally responsive means, said heater means being operatively associated with said casing means in heat-transfer relation to said thermally responsive means.

10. The protective device as set forth in claim 9 and wherein said heater means in operative association with said casing is disposed in thermally conductive juxtaposition against an outer surface of said casing means.

11. The structure as set forth in claim 8 and wherein said motor comprises a main winding and a starting winding electrically connected in series circuit with each other and with said heater means and said switch means.

12. The structure as set forth in claim 8 and wherein said electric motor comprises a main winding and start winding electrically connected to each other in parallel circuit relationship and in series circuit relationship with said heater means and said switch means.

13. The structure as set forth in claim 8 and wherein said motor comprises a plurality of windings and said heater means comprises at least two heater elements each electrically connected in series circuit relationship with a respective one of said plurality of windings.

14. The structure as set forth in claim 13 and wherein said thermally responsive device comprises a plurality of internal heaters enclosed with said thermally responsive device in said sealed casing.

15. A protective device adapted to be connected to an electric motor having at least one winding lying in the path of and being exposed to the convective flow of a fluid medium; said protective device comprising electric switch means; heater means for said switch means; said heater means, switch means and motor winding being electrically connectable together in series circuit relation; thermally responsive means associated with said protective device for opening said switch means at predetermined conditions; sealed thermally conductive casing means enclosing said thermally responsive means; said heater means being operatively associated with said casing means externally thereof and in heat-transfer relation to said thermally responsive means and exposed to the said convective flow of a fluid medium when elec- 13 trically connected in series circuit relation with said motor Winding.

16. A protective device adapted to be connected to an electric motor having at least one winding lying in the path of and being exposed to the convective flow of a fluid medium; said protective device comprising a thermally responsive means operative to control an electrical circuit for Said motor at predetermined conditions; said means being disposed within a switch housing; heater means for said thermally responsive means; said heater means, thermally responsive means and motor winding being electrically connectable together in series circuit relation; and said heater means being proximally disposed adjacent said switch housing externally thereof in heat-transfer relation to said thermally responsive means and directly exposed to the said convective flow of a fluid medium when electrically con- 5 nected in series circuit relation with said motor winding.

References Cited in the file of this patent UNITED STATES PATENTS 2,169,989 Pearce Aug, 15, 1939 2,354,529 Ludwick July 25, 1944