US3858139A

US3858139A - Time-delay relay and method of assembling same

Info

Publication number: US3858139A
Application number: US00383937A
Authority: US
Inventors: E Hunter
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1973-07-30
Filing date: 1973-07-30
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31
Also published as: DE2436116B2; FR2239752A1; JPS5851369B2; FR2239752B1; DE2436116A1; IT1016980B; JPS5043452A; DE2436116C3

Abstract

A time-delay relay comprising a housing having a chamber in which are mounted a thermally responsive switch assembly and a heater in heat-transfer relation with the switch assembly for heating the latter to effect actuation of the contacts thereof. A pair of heater terminals are positioned in terminal receiving slots in the housing, the terminals being locked into position in the slots upon insertion therein and having terminal contact portions extending into the chamber for conductive electrical contact with the heater. The thermostatic switch is positively held in its installed position within the chamber by means of a retainer on the exterior of the housing. Also disclosed is a method of assembling a time-delay relay in which the various components are inserted into respective openings and chambers in the housing and in which various components are secured together by means of a retainer on the exterior of the switch housing.

Description

United States Patent Hunter TIME-DELAY RELAY AND METHOD OF ASSEMBLING SAME [75] Inventor: Eugene A. Hunter, Dallas, Tex.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 30, 1973 [21] Appl. No.: 383,937

[52] US. Cl 337/88, 337/102, 337/112, 337/327, 337/354, 337/377 [51] Int. Cl. H01h 61/00 [58] Field of Search 337/88, 102, 107, 112, 337/113, 327, 341, 354, 377; 29/623; 174/52 [56] References Cited UNITED STATES PATENTS 3/1966 Huffman 337/102 X l/1968 Cardin 337/107 X 3,489,976 l/1970 Marcoux 337/102 3,518,601 6/1970 Tyler et al. 337/327 3,537,052 10/1970 Snider 337/354 Dec. 31, 1974 Primary Examiner-James D. Trammell Assistant Examiner-Fred E. Bell Attorney, Agent, or Firm-John A. Haug; James P. McAndrews; Edward J. Connors [5 7 ABSTRACT A time-delay relay comprising a housing having a chamber in which are mounted a thermally responsive switch assembly and a heater in heat-transfer relation with the switch assembly for heating the latter to effect actuation of the contacts thereof. A pair of heater terminals are positioned in terminal receiving slots in the housing, the terminals being locked into position in the slots upon insertion therein and having terminal contact portions extending into the chamber for conductive electrical contact with the heater. The thermostatic switch is positively held in its installed position within the chamber by means of a retainer on the exterior of the housing. Also disclosed is a method of assembling a time-delay relay in which the various components are inserted into respective openings and chambers in the housing and in which various components are secured together by means of a retainer on the exterior of the switch housing.

17 Claims, 11 Drawing Figures Pmtmm m 3,858,139

SHEET 10F 3 FIG.I

Pmmw ml 3,858,139

SHEET 30F 3 FIG.6

FIG. IO

TIME-DELAY RELAY AND METHOD OF ASSEMBLING SAME BACKGROUND OF THE INVENTION This invention relates to thermostatic electrical switches, and is particularly concerned with a timedelay relay (TDR) utilizing a thermostatic switch assembly for opening and closing an electrical circuit.

More particularly, this invention is concerned with a TDR in which a thermostatic switch assembly is held in position within a housing by means of a retainer, and with a simple and fast method of assembling a TDR in which electrical terminals may be inserted into openings in the housing whereupon they become locked in position in the housing. In prior art TDRs, the thermostatic switch assembly is adhesive-bonded into position in the housing and the electrical terminals for the thermostat heater are riveted to the housing. The adhesive bonding procedure required that the adhesive be cured, and this curing cycle increased the assembly time of the unit. Both the application of the adhesive and the installation of the rivets involved separate manufacturing steps which increased production time and costs. Known prior art assembly procedures have re- SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of a TDR which may be assembled without the use of rivets or adhesives; the provision of such a TDR in which all parts may be brought together along one axis or plane (e.g., a vertical one) thereby to simplify assembly; the provision of such a TDR in which terminals may readily be installed in the housing without the use of rivets, and the terminals and the thermostatic switch assembly may be snapped into the housing; the provision of a TDR in which many of the components perform multiple functions; the provision of such a TDR which has no dead metal parts for holding the unit together; the provision of such a TDR which, once assembled, substantially precludes tampering; the provision of such a TDR which is of rugged construction and is reliable in operation; and the provision of a method of assembly of such TDR's which results in a simpler, faster and more economical production. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

Briefly, a time-delay relay of this invention comprises a housing having a chamber with openings in its sidewalls, and a thermally responsive switch assembly having contacts and a thermostatic element. The contacts of this switch assembly are movable into and out of engagement with one another in response to actuation of the thermostatic element when the latter is subjected to predetermined temperature conditions thereby to make or break a first circuit. The time-delay relay further includes a heater for heating the thermostatic element, the heater being energized by a second circuit. The switch assembly has at least a portion thereof adapted for reception and mounting within the chamber in an operating position in which the switch assembly is in heat-transfer relation with the heater. A retainer is provided on the outside of the housing having portions thereof extending through the openings in the sides of the housing for gripping engagement with the switch assembly so as to hold the latter in its operating position.

This invention also encompasses a method of assembling a time-delay relay comprising a housing with a chamber having openings for reception of terminals, a thermostatic switch assembly, a heater for heating the switch assembly, a pair of terminal members for supplying electrical power to the heater and a clip for holding the switch assembly relative to the housing. The method comprises an initial step of inserting the terminal members into the openings in the housing, the terminals being adapted to snap into place when inserted in the openings thereby to secure them in the housing with portions of the terminals extending into said chamber. Next the heater and the switch assembly are inserted into the chamber with the heater in electrical contact with the portions of the terminals and in heattransfer relation with the switch assembly. Finally, the clip is snapped into openings in the sides of the housing for engagement with portions of the switch assembly thereby to positively secure the switch assembly in an assembled position relative to the housing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a timedelay relay of this invention illustrating a clip for locking a thermostatic switch assembly into a housing and also illustrating terminals inserted into openings in the housing with the terminals locked in position relative to the housing;

FIG. 2 is a side elevation of a time-delay relay of this invention as it appears assembled;

FIG. 3 is a plan view of the housing with the thermostatic switch assembly removed illustrating a chamber for reception of the thermostatic switch assembly and openings in the housing for receiving the terminals;

FIG. 4 is a bottom view of the housing with the clip and terminals removed;

FIG. 5 is a vertical section taken on line 5-5 of FIG. 3 with the switch assembly installed therein;

FIG. 6 is a vertical section taken on line 6-6 of FIG. 2 illustrating gripping engagement of the clip with the thermostatic switch assembly so as to secure the thermostatic switch assembly in an operating position in the housing;

FIG. 7 is a perspective view of the clip;

FIG. 8 is an enlarged plan view of one of the terminals;

FIG. 9 is a side elevation of the terminal shown in FIG. 8;

FIG. 10 is a plan view of another of the terminals; and

FIG. 11 is a side elevational view of the terminal shown in FIG. 10.

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

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, a time-delay relay (TDR) of this invention is generally indicated at 1. As best shown in FIG. 1, the TDR comprises a housing 3 having a chamber 5 therein, a thermostatic switch assembly 7 inserted in the chamber and an additional optional switch assembly 9 stacked on top of switch assembly 7 and'actuable concommitantly therewith.

More particularly, thermostatic switch assembly 7 includes a switch body 11 having a cylindric lower portion 13 adapted for reception and mounting in chamber of housing 3. Two switches indicated generally at l5a,l5b, are mounted within switch body 11. A snapacting composite thermostatic bimetallic disk or element 17, such as disclosed in US. Pat. No. 1,448,240, is mounted at the bottom of the lower portion 13 of switch body 11. Because of its nondevelopable or dished shape this bimetallic disk will snap from one curvature position to an opposite one in response to a change of temperature so as to provide mechanical power to make and break the contacts of switches l5a,15b. Bimetallic element 17 is mounted on the bottom of lower portion 130f switch body 11 by means of a cup 19 having good electrical and thermal conductivity, this cup, for example, being made of copper. The periphery of disk 17 is supported on an internal shoulder 21 within the cup. At temperatures below the selected snap-over temperature condition, the disk is dish-shaped with its convex side facing up. Upon being heated to a predetermined elevated temperature, the disk snaps over center so that its top face is concave. Upon cooling belowa second predetermined temperature, the disk will return to its original curvature.

As previously mentioned, a second switch assembly 9 may be stacked onto the top of the thermostatic switch assembly 7, the second assembly having two pairs of switches 27a,27b actuable in response to movement of the bimetallic disk 17 as the latter snaps over center. This second switch assembly includes an auxiliary switch body 29 within which switches 27a,27b are mounted and a cover 31 for enclosing them. Switches l5a,l5b and 27a,27b may control separate independent or related electrical circuits. These switches are essentially identical and each includes quick-

connect terminals

33a,33b secured, as by riveting, to either switch body 11 or 29. A flexible contact arm 35 carrying a contact 37 on its free end is secured to each terminal 33a and a contact 39 is mounted on each terminal 33b within switch body 11 and 29. Each movable arm 35 biases its contact 37 into engagement with a respective mating contact 39 to maintain the contacts normally closed during the heated mode. For ceratin applications, double-throw switch arrangements utilizing switch contacts 41 may be provided in cover 31, these double-throw contacts being engageable by back contacts 43 carried by switch arms 35 of switches 27a,27b. Terminals 44 are provided for connection of a separate or related electrical circuits to double-throw contacts 41. it will be understood that any one or more of these switches may be inverted and their switch arms biased away from a contact-closed mode whereby they are normally open switches, and that the arrangement of disk and switches may be such that contact arms may be lifted or permitted to move downwardly on a rise of temperature.

As generally indicated at 45, means are provided for actuating flexible contact arms 35 in response to bimetallic disk 17 snapping over center. This means is shown to comprise a yoke or bridge 47 bearing against the upper face of disk 17 and having outwardly extending

arms

49a,49b. Bores 5la.5lb and bores 53a,53b are provided in switch bodies 11 and 29, respectively, and

holes 55a,55b are provided in the flexible arms 35 of switches 15a,l5b. Tubes 57a and 57b are slidably received in respective bores 51a,51b the bottom end of each of these tubes bearing on a

respective arm

49a,49b of bridge 47 and the upper end of the tube being spaced slightly from the undersurface of its respective flexible arm 35 of switches 15a,l5b. Rods 59a,59b are received in

respective bores

53a,53b in switch body 29, and these rods extend through holes 55a,55b in flexible arms 35 of contacts 15a,15b and into tubes 57a,57b. Rods 59a,59b extend through tubes 57a,57b and bear on a

respective arm

49a,49b of bridge 47. With disk 17 in its heated (concave upwardly) position, the ends of rods 59a,59b are spaced slightly below the undersurface of flexible contact arms 35 of switches 27a,27b a distance similar to the distance the upper end of tubes 57a,57b are spaced from their respective flexible contact arms. With the upper ends of tubes 57a,57b and rods 59a,59b spaced from their respective flexible arms, as above described, they remain clear of the flexible arms during any creep of the bimetallic disk before it snaps over center from its concave position.

A heater 61 for heating bimetallic element 17 to a predetermined elevated temperature is mounted in heat-transfer relation with switch assembly 7, this heater being adhesive-bonded to the bottom face of cup 19. This heater is pill-shaped and has a characteristic resistivity-temperature curve having a steep-slope positive temperature coefficient (PTC) and is more particularly described in coassigned US. Pat. No. 3,489,976.

As shown in FIG. 7, clip 65 is a generally U-shaped member having a base portion 67 and upstanding legs 69 at the ends of the base portion. An inwardly extending ear 71 is provided at the top of each leg 69 and central lateral extensions 73 project outwardly from each side of base portion 67 for purposes as will appear. Openings 75 (FIG. 3) are provided in opposite sidewalls of housing 3, these openings extending into chamber 5. The cylindric lower portion 13 of switch housing 11 has a pair of vertical grooves 77 therein on opposite sides of the cylindric portion. Each groove 77 is closed at its lower end and provides a gripping surface or shoulder 79. Clip 65 is made of flexible resilient material (which is also preferably electrically insulative), such as anatural polysulphone. As shown in FIG. 4, housing 3 has a cruciform recess constituted by crossing grooves 81 in its bottom face for reception of base portion 67 and extensions 73 of clip 65, and also has vertically disposed recesses 83 in its opposite sidewalls extending down from opening 75 for reception of legs 69 of the clip. With the clip inserted in

recesses

81 and 83 and with cars 71 extending into openings 75, and into grooves 77 in switch body 11, the ears grippingly engage shoulders 79 thereby to hold the switch body in its operating position and to prevent removal of the switch body from the housing. The clip, when properly seated in housing 3, is flush with respect to the exterior of the housing. As indicated at 85, a flexible finger is provided at the upper end of each leg 69 for engagement with a portion of housing 3 adjacent openings 75, this portion being indicated at 87, so as to positively lock the clip in its installed position in the housing and to prevent disassembly of the TDR assembly. With clip 65 made of flexible resilient material, fingers 85 are forcibly bent in as ears 71 are pushed into openings 75.

As the ears assume their locking position in engagement with shoulder 79 of switch body 11, fingers 85 spring back and engage housing portions 87. As shown in FIG. 1, legs 69 may be sprung outwardly to permit installation of the clip in the housing 3. Alignment ribs 88 are provided on the sidewalls of chamber 5 for cooperation with alignment grooves (not shown) in the sides of lower portion 13 of switch body 11 to insure correct rotational positioning of switch assembly 7 relative to housing 3.

In accordance with this invention, terminals 630,63b are adapted to be snapped into position in housing 3. As indicated generally at 89, terminal openings are provided in housing 3. As best shown in FlGS. l, 3 and 5, terminal openings 89 are parallel to the centerline of chamber 5 and are open at the top of the housing. Each terminal has a shank or mounting portion 91 and a contact portion 93a,93b. The mounting portion of each terminal 63a, 63b is essentially the same so that only one mounting portion need be discussed in detail. As shown in FIGS. 9 and 11, the shank portion has a quick-connect terminal 95 disposed to extend horizontally outwardly of hosuing 3 when the terminal is installed therein, and thus at right angles to shank portion 91. Tabs or barbs 99 are struck from the shank at the upper end thereof to project angularly therefrom, and the contact portion 93 extends from the lower end of the shank. As shown in FIG. 5, the contact portion 93a of terminal portion 63a is adapted to reach into chamber 5 and to be in direct electrical contact with the undersurface of heater 61. The contact portion 93b of terminal 63b is configured to be in indirect electrical contact with heater pill 61 by contacting cup 19 adjacent the chamber wall, thereby to provide an electrical circuit for energizing the heater. Thus, the terminal portions 93a, 93b, whether directly or indirectly contacting heater 61, are in conductive electrical contact therewith. Terminals 63a, 63b are made of resilient metallic material so as to resiliently engage the heater and the cup thereby to maintain good electrical contact therewith.

Terminal openings 89 for each terminal 6311,6312 are identical and each has a shank-receiving slot 101 and a contact portion slot 103. Terminal openings 89 are open at the bottom of housing 3 (see FIG. 4) but are covered by extensions 73 of clip 65 when the clip is in place, thereby blocking access to the lower portions of terminals 630 and 63b. The contact slot portions 103 of terminal openings 89 open into chamber 5 thereby to permit the contact portions of 93a,93b of terminals 63a,63b to extend into the chamber for conductive electrical contact with heater 61. In HO. 5, it can be seen that the upper ends of terminal openings 89 open into chamber 5 and with an internal shoulder 105 provided in the shank receiving slots at the upper ends thereof. Upon installation of the terminals 63a,63b into respective terminal openings 89, shank portions 91 are received in the shank-receiving slots 101 and the lower contact portions 93a,93b of the terminal are received in corresponding contact-receiving slots 103 of the terminal openings 89 with the contact-receiving slots opening into chamber 5. Upon further insertion into the openings 89, tabs 99 are forced substantially back into alignment with shank portions 97 and upon full insertion of the terminals into the terminal openings, the tabs spring out and engage shoulder 105 (see FIG. 5)

thereby firmly to secure the terminals in installed positions within housing 3.

In further accordance with this invention, a method of assembling a time-delay relay, includes first inserting terminals 63a,63b into terminal openings 89 in housing 3 as above described thereby securely locking them in position as barbs 99 spring outwardly and engage the undersurfaces of shoulders 105. The thermostatic switch assembly 7 is then installed by inserting the lower portion 13 of switch body 11 into chamber 5 so that heater 61 is in electrical contact with the contact portion 93a of terminal 630 and cup 19 is in electrical contact with contact portion 93b of terminal 63/). Clip 65 is then moved into position to have its base portion 67 seat in cruciform recess 81 as its legs 69 slide into side recesses 83 of housing 3. Ears 71 of the clip then snap into openings 75 in the housing so as to engage respective shoulders 79 on switch body 11 thereby to hold the switch body in position relative to the housing. Upon ears 71 being inserted into openings 75 in housing 3 and into grooves 77 in switch body 11, fingers spring out and engage the portions 87 of housing 3 thereby to lock the clip thereto and prevent removal of the clip from the housing.

With clip 65 properly seated in

recesses

81 and 83 in housing 3, the clip is substantially flush with the exterior of the housing. It will be understood that various configurations of clip 65 could be used, including a clip extending around the sides of the housing rather than across the bottom. When a clip is used, such as that herein shown which extends across the bottom of the housing, all parts of the timedelay relay assembly may be brought into position for assembly along a single axis or in a single vertical plane thus enabling simpler and faster assembly procedures. Also, with the top of housing 3 clear of the clip, add-on switches such as indicated at 25, may be stacked on top of switch assembly 7 without interference from the clip.

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

As various changes could be made in the above constructions and methods 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.

What is claimed is:

1. A time-delay relay comprising:

a housing having a chamber therein and openings in its sidewalls;

a thermally responsive switch assembly having contacts and a thermostatic element, said contacts being movable into and out of engagement with one another in response to actuation of the thermostatic element when the latter is subjected to predetermined temperature conditions thereby to make and break a first circuit;

a heater for heating said thermostatic element, said heater being energized by a second circuit, said switch assembly having at least a portion thereof adapted for reception and mounting within said chamber in an operating position in which said switch assembly is in heat-transfer relation with said heater; and

a retainer on the outside of said housing having portions thereof extending through said openings in the sides of the housing for gripping engagement with said switch assembly so as to hold the latter in its said operating position.

2. A time-delay relay as set forth in claim 1 wherein said retainer has locking portions engageable with said housing thereby to prevent removal of the retainer from the housing.

3. A time-delay relay as set forth in claim 2 wherein said housing has a blind hole in one face thereof constituting the top of the housing with said hole constituting said chamber, and wherein said retainer is a clip having a portion thereof extending from one side of the housing to the other at the bottom of the housing.

4. A time-delay relay as set forth in claim 3 wherein said openings in said housing sidewalls are adapted to receive the gripping portions of said clip, each said gripping portion extending into said chamber via its respective said opening for engagement with said switch assembly.

5. A time-delay relay as set forth in claim 4 wherein said clip is a generally U-shaped member having a base portion adapted to span the bottom of the housing and upstanding legs extending along opposite sides of the housing, said legs each carrying said gripping portion and said locking portion on the upper end thereof.

6. A time-delay relay as set forth in claim 5 wherein said housing has a second face constituting the bottom of the housing, a recess in the bottom of the housing for reception of said base portion of the clip and recesses in said sidewalls for reception of the leg'portions of the clip, said clip being generally flush with the exterior of the housing.

7. A time-delay relay as set forth in claim 5 wherein said housing has openings in its bottom, and said base portion of said clip has portions extending therefrom for covering said openings in the bottom of the housing.

8. A time-delay relay as set forth in claim 5 wherein said switch assembly portion adapted for reception in said chamber has an upwardly facing surface, said gripping portions of said clip extending inwardly into the chamber for engagement with a respective said upwardly facing surface thereby to prevent removal of the switchassembly from the housing.

9. A time-delay relay as set forth in claim 8 wherein portions of said housing are engageable with said switch assembly when the latter is in its assembled operating position thereby forming a seat for the switch assembly in said housing.

10. A time-delay relay as set forth in claim 8 wherein said locking portion of said clip comprises a flexible fmger engageable with said housing when said gripping portion is in engagement with said surface thereby to prevent removal of the clip from its installed position.

11. A time-delay relay as set forth in claim 1 further comprising a pair of terminals adapted for conductive electrical contact with said heater, said terminals constituting a portion of said second circuit, said housing having terminal openings therein for reception of said terminals, each terminal having means engageable with said housing upon installation of the terminal in its respective terminal opening thereby to secure it in the housing.

12. A time-delay relay as set forth in claim 11 wherein each of said terminal openings extends from one face of said housing constituting its top face into the housing generally parallel to said chamber, each terminal opening being at least partially open to said chamber, each terminal member being insertable into its respective terminal opening thereby to assume an installed position within said housing in which a portion thereof constituting a contact portion extends into said chamber for conductive electrical contact with the heater, said terminal engagement means comprising a barb angularly projecting from said terminal, said housing having a portion adjacent each of said terminal openings adapted for engagement by said barb thereby to secure each of the terminal members in its installed position within the housing.

13. A time-delay relay as set forth in claim 12 wherein said housing has a blind hole in said top face, said blind hole constituting said chamber, each said opening comprising a slot extending from the top face into the housing generally parallel to the longitudinal axis of the chamber and having a first portion spaced outwardly of the chamber and a second portion opening from the first portion into the chamber.

14. A time-delay relay as set forth in claim 13 wherein said terminal member comprises a terminal portion adapted to extend from said housing when said terminal member is in its installed position, a shank portion adapted to be received by said first portion of said slot and a contact portion adapted to extend from said shank portion into said second portion of the slot and into the chamber for conductive electrical contact with the heater, said shank portion having said barb extending therefrom for engagement with said housing thereby to prevent removal of the terminal from said slot.

15. A time-delay relay as set forth in claim 14 wherein said terminal members are made of a resilient, electrically conductive material, and the contact portion of each terminal is adapted for resilient electrically conductive engagement with said heater so as to constitute portions of said second circuit.

16. A method of assembling a time-delay relay, said relay comprising a housing with a chamber and with openings for reception of terminals, 3 thermostatic switch assembly, a heater for heating said switch assembly, a pair of terminal members for supplying electrical power to the heater and a clip for holding the switch assembly relative to the housing, said method comprising the steps of:

inserting said terminal members into said openings in the housing, said terminals being adapted when inserted in said openings to be secured to said housing, portions of said terminals extending into said chamber;

inserting the heater and the switch assembly into said chamber with the heater in conductive electrical contact with said portions of the terminals and in heat-transfer relation with the switch assembly; and

snapping said clip into openings in the sides of said housing for engagement with portions of said switch assembly thereby to positively secure the switch assembly in an assembled position relative to the housing. 17. A method as set forth in claim 16 in which the step of snapping said clip into said openings also locks the clip to the housing.

Claims

1. A time-delay relay comprising: a housing having a chamber therein and openings in its sidewalls; a thermally responsive switch assembly having contacts and a thermostatic element, said contacts being movable into and out of engagement with one another in response to actuation of the thermostatic element when the latter is subjected to predetermined temperature conditions thereby to make and break a first circuit; a heater for heating said thermostatic element, said heater being energized by a second circuit, said switch assembly having at least a portion thereof adapted for reception and mounting within said chamber in an operating position in which said switch assembly is in heat-transfer relation with said heater; and a retainer on the outside of said housing having portions thereof extending through said openings in the sides of the housing for gripping engagement with said switch assembly so as to hold the latter in its said operating position.

6. A time-delay relay as set forth in claim 5 wherein said housing has a second face constituting the bottom of the housing, a recess in the bottom of the housing for reception of said base portion of the clip and recesses in said sidewalls for reception of the leg portions of the clip, said clip being generally flush with the exterior of the houSing.

8. A time-delay relay as set forth in claim 5 wherein said switch assembly portion adapted for reception in said chamber has an upwardly facing surface, said gripping portions of said clip extending inwardly into the chamber for engagement with a respective said upwardly facing surface thereby to prevent removal of the switch assembly from the housing.

10. A time-delay relay as set forth in claim 8 wherein said locking portion of said clip comprises a flexible finger engageable with said housing when said gripping portion is in engagement with said surface thereby to prevent removal of the clip from its installed position.

16. A method of assembling a time-delay relay, said relay comprising a housing with a chamber and with openings for reception of terminals, a thermostatic switch assembly, a heater for heating said switch assembly, a pair of terminal members for supplying electrical power to the heater and a clip for holding the switch asseMbly relative to the housing, said method comprising the steps of: inserting said terminal members into said openings in the housing, said terminals being adapted when inserted in said openings to be secured to said housing, portions of said terminals extending into said chamber; inserting the heater and the switch assembly into said chamber with the heater in conductive electrical contact with said portions of the terminals and in heat-transfer relation with the switch assembly; and snapping said clip into openings in the sides of said housing for engagement with portions of said switch assembly thereby to positively secure the switch assembly in an assembled position relative to the housing.

17. A method as set forth in claim 16 in which the step of snapping said clip into said openings also locks the clip to the housing.