EP0182487A2

EP0182487A2 - Thermostat

Info

Publication number: EP0182487A2
Application number: EP85307253A
Authority: EP
Inventors: Pietro De Filippis; Ciro Calenda; Giuseppe Notaro; Henry Boulanger
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1984-10-24
Filing date: 1985-10-10
Publication date: 1986-05-28
Anticipated expiration: 2005-10-10
Also published as: DE3587064D1; EP0182487B1; EP0182487A3; DE3587064T2

Abstract

A thermostat equipped with a bimetallic element sensitive to a given temperature comprises a monolithic base open at one end in which two terminals connectable to an electric circuit are inserted and precisely located, each having one end bent at a right angle and each carrying a stationary contact, an element carrying movable contacts for connecting the stationary contacts with one another, a spring housed in a seat on said base biasing the movable contact element to engage the stationary contacts, a sliding element for moving and guiding said movable contact-carrying element, a bimetallic element suitably spaced from the said sliding element for initiating movement of the sliding element in response to temperature change, and a lid which fastens the said bimetallic element to the said base with said spacing from the sliding element.

Description

Background of the Invention

The present invention relates to a single-temperature .thermostat, provided with a bimetallic element sensitive to a given intervening and restoring temperature.
Various types of thermostats with bimetallic elements are already known from the prior art. These thermostats are, however, of complex structure and thus expensive, and tend to have space requirements that often pose mounting problems.
Thus, for example, from German Patent Publication 2 45 1327 a thermostat is known wherein a bimetallic disc operates a shaft that acts on an elastic strip secured at one end so as to raise the second end and interrupt the electric circuit. This structure is complex and cumbersome, and requires a special configuration for the terminal carrying the stationary contact and for the elastic strip carrying a movable contact.

Brief Summary of the Invention

Object of the present invention is therefore to provide a one-temperature thermostat with a bimetallic element having a simple structure and able to assure optimal reliability.
According to the invention, the above object is achieved by providing a monolithic cylindrical base, open at one end, wherein two terminals connectable to an electric circuit are inserted, having one of their ends bent 90⁰ and carrying a stationary contact, an element carrying a movable contact that connects the said two stationary contacts by the action of a spring, and a sliding element able to raise the said movable contact by the effect of a bimetallic element fastened in the said open end of the base by means of a lid.
This structure of a thermostat is arranged in a novel way so . that, aside from being very simple, it also offers the advantage that the entire thermostat can be easily and rapidly assembled, reducing besides the cost of production.
It should be noted that the terminals have the double function, namely or external connection and fixed contact holder. In addition, the shape of the base and of the terminals themselves allows bending the terminals at any angle desired so as to satisfy the various interconnect requirements of the trade.
The said lid is made in form of a bowl that is suitably shaped in a novel way around on the outside so as to allow it application on the base of the thermostat by means of a simple cylindrical die which fitted onto the said lid folds in the outward bent rim on a lower projection of the base of the thermostat, thus avoiding a rolling, folding or the like and speeding up the fastening operation of the lid.
In addition, the said lid is shaped so as to pass all vertical stresses onto the said rim of the base, thus preventing any interferences on the disc on the part of the lid in consequence of blows or deformations accidentally suffered by the latter.

Description of the Drawings

Other advantages and features of the present invention will become evident from the description of the two embodiments thereof, as illustrated by way of example in the attached drawings, wherein:

Fig. 1 shows a longitudinal view in cross section of a first embodiment of the thermostat;
Fig. 2 shows an enlarged partial cross section view as shown in Fig. 1 illustrating a terminal fastened in the base of the thermostat;
Fig. 3 shows a front view of a terminal similar to that shown in Fig. 2 illustrating an alternate embodiment of the invention;
Fig. 4 shows another alternate embodiment of the thermostat;
Fig. 5 shows a top view of the thermostat of Fig. 4 with the lid removed;
Fig. 6 is a diagrammatic view which shows a method for assembling the bimetallic disc and the lid into the thermostat;
Fig. 7a shows a front view of one embodiment of the lid;
Fig. 7b shows a crosssectional view along line A-A of Fig. 7a;
Figs. 8a and 8b diagrammatically show another alternate method for mounting the terminals by ultrasound;
Figs. 9a, 9b and 9c show a method for calibrating the thermostat with a movable notched plate;
Fig. 10a shows a front view of the sliding guide plate for the movable contact as used in the thermostat of Figs. 4 and 5;
Fig. 10b shows a crosssectional view along line B-B of Fig. 10a; and
Fig. 11 shows a view in perspective of the monolithic base of the thermostat diagrammatically illustrating mounting of the thermostat.
Fig. 12 is a section view along the principal axis of an alternate embodiment of the thermostat of the invention;
Fig. 13 is a plan view of the base used in the device of Fig. 12;
Fig. 14 is a section view along line 14-14 of Fig. 13;
Fig. 15 is a partial section view to enlarged scale along line 15-15 of Fig. 12; and
Fig. 16 is a partial section view along line 16-16 of Fig. 12 diagrammatically illustrating a step in the assembly of the device of Fig. 12.

Description of the Preferred Embodiments

Fig. 1 shows a first embodiment of a thermostat according to the invention. The said thermostat consists of a cylindrical base or body 1 of plastic material having a lower cavity 18. In diagrammatically opposite positions, two slits 17 are provided which pass from the lower cavity to the outside through the upper closed wall of body 1. In the upper part of the said body a cylindrical seat 19 is provided in which a helical spring 6 is mounted whose upper end is supported on the bottom of said seat 19. Into the said slits 17 of rectangular configuration terminals 7 and 8 are inserted whose lower ends are bent at right angles and each carrying a contact 9. In spring 6 a rod 4 of ceramic material is inserted on which, with a force fit, a contact plate 5 of steel or other magnetic material is slipped which supports itself on the said two contacts 9 of terminals 7 and 8 so the plate 5 and rod 4 are fixed together and movement of the rod is guided in the seat 19.
The union between rod 4 and contact plate 5 is calibrated so that the lower end of the said rod 4 is slightly above a t conventional thermally responsive, snap-acting bimetallic disc 3 whose rim is captured between a shoulder 1.1 at the mouth of cavity 18 and the upward bent rim of a lid 2. Preferably ends of the plate 5 are guided in a groove 5.1 in the body.
To assemble bimetallic disc 3 and lid 2, a magnetic field is applied to the contact plate 5 by poles N and S so as to attract it toward the base, with compressing of spring 6, as shown schematically in Fig. 6. In this way, also rod 4 is caused to retreat, thus creating a free space for easy insertion of disc 3 and mounting of the lid 2. Subsequently, the magnetic field is removed and the said contact plate 5, by the action of spring 6, returns to its normal position.
Thanks to this calibration of shaft 4, at the moment of reversal of bimetallic disc 3 in consequence of a temperature increase, the latter abruptly strikes shaft 4 thus causing an interruption of the electric current by the lifting of said contact plate 5 from contacts 9 of terminals 7 and 8, against the action of spring 6. In this way, the period of arcing between the contacts is reduced to a minimum.
The same applies to the closing phase of the contacts, that is, the return of the bimetallic disc to its starting position on cooling of the disc.
Thus to assure this abrupt opening and closing of the contact it is necessary to provide, during the assembly phase of the various components of the thermostat, and initial creep-action play between the bimetallic disc and the rod of ceramic material. It should moreover be made sure that this play is kept as small as possible on account of a much larger abrupt or snap acting movement portion than a gradual portion existing in the travel of the said bimetallic disc.
The said lid 2 is shaped cylindrically around on the outside with a flared rim 2.1 so as to allow its application on the base by way of a simple forced insertion of lid 2 resting on the edge 1.2 of base 1 in a simple die of circular configuration. This manner of fastening the said lid is much faster and much more effective than rolling or folding as presently used.
The said lid 2 is shaped so as to unload vertical stresses, caused by possible deformations of the lid when in operation, onto the rim 1.2 of base 1, thus absolutely preventing any deformations or stresses of the lid from being transmitted to the bimetallic disc and thus altering its characteristics.
In fact, the lid 2 has a circular projection 23 which closely follows the internal flange or shoulder 1.1 of base 1, the said bimetallic disc 3 being wedged between said circular projection 23 and said internal flange of base 1.
Figs. 7a and 7b show another design of lid wherein the circular projection 23 is replaced by four projecting sectors 33 uniformly distributed over a circular circumference, which equally function as support of the disc and assist in calibration of the thermostat.
The terminals 7 and 8, made in one piece, preferably have a tongue 20 as shown in Figs. 1 and 2 which during mounting enmeshes itself in the terminal inside the base until a terminal shoulder 7.1, 8.1 engages the base but which is then dislodged into narrow slot 1.3 in the base for wedging it against a corresponding shoulder 16 on the outside of the said base. The terminals 7, 8 can be bent against above tongue 20 around a shoulder 22 along side the narrow slot 1.3 without their strong fixation inside the base being impaired thanks to the combined action of tongue 20 and shoulder 16 and 22 which act in unison toward improving the said fixation. In an alternate embodiment the terminals have small teeth 21 which engage, during mounting, in corresponding cutouts of said base 1, as shown in Fig. 3.
The insertion of the terminals in the base can be effected by ultrasonic energy. As illustrated schematically in another alternate embodiment in Figs. 8a and 8b, a terminal 7 has three sectors 7, 7' and 7" of decreasing widths which are joined laterally by marginal grooves 30 and 31 of equal radiuses.
Under the action of ultrasonic vibrations, the said terminal 7 penetrates in base 1 while heating up, the so developed heat superficially melting a thin layer of the material of the base which after completion of the insertion (Fig. 8b) will have filled up again the said cavities 30 and 31, thus assuring a perfect fixation and sealing of terminal 7 in base 1.
Figs. 4 and 5 show a second embodiment of the invention, which differs from that shown in Fig. 1 in that the rod 4 of ceramic material is replaced by a motion transfer guide plate 13 preferably of insulating material such as plastic, ceramic or similar material, _ which is guided into diametrically opposed grooves 15, made in the cavity 18. On the outer end of spring 6 a contact plate 14 carrying movable contacts is fastened, in the manner similar to plate 5 of the first embodiment. A guide plate 13 preferably has raised edges 13.1 and a central depression 13.2 and the contact plate has grooves 14.1 fitted around parts of the raised edges 13.1 of the guide plate . in this case, the guide plate 13 and contact-holding plate 14 also moved together but the movement is guided by the grooves 15 and not by the seat 19 as in the version of Fig. 1.
The said plate 13 has a lug 21 whose distance from bimetallic disc 3 is suitably chosen, in accordance with the type of bimetal used to provide a desired calibration of the thermostat.
Another kind of calibration is shown schematically in Figs. 9a and 9b. Here, the movable contact plate 14 has a V-shaped notch 35 at its center which facilitates bending of the said plate by a force 35.1 as indicated in Fig. 9a to an extent desired and thus permit the calibration of the distance of the guide plate 13 from the said bimetallic disc. The said notch prevents, moreover, an application of larger bending forces that could damage the rim of the base on which the movable contact plate 14 supports itself.
The guided plate 13 preferably has two lateral projections 34, as shown in Fig. 10, which serve to pose a substantially longer resistance path to the passage of creep surface currents that could otherwise travel from the plate 14 along the insulator 13 and unload onto the bimetallic element and thus on the lid.
The said lid 2 has a circular projection 23 that closely follows the inner flange of base 1, the said bimetallic element being fastened to said inner flange of the base by said circular projection 23 of the lid when the latter is fastened on base 1.
This embodiment of Figs. 4 and 5 is particularly suited for more elevated temperatures, above 200⁰c. for example, to which the contact plate 5 of Fig. 1 could rise causing local fusions in the groove 5.1 of plastic in which it is guided. In this case, instead, thanks to the guided sliding of plate 13 in the grooves 15 of the base, the said drawback is avoided. In fact, the plate 13, being thermally insulated from the contact plate 14, never reaches temperatures that are dangerous for the plastic of the base in which it is guided.
It should finally be noted that the monolithic base, as shown schematically in perspective view in Fig. 11, has a useful surface 36 for the application of a clip 36.1 for mounting the thermostat on the based to be thermostated, this being made possible by virtue of the fact that terminals 7, 8 are separated from the ring by two barriers 37 formed in the monolithic base itself.
In an alternative embodiment, 100 in Fig.12 indicates the novel and improved thermostat of this invention which is shown to include a generally cylindrical cup-shaped base 102 of a generally rigid, ultrasonically fusible, electrically insulating organic material or the like having a cavity 104 open at one end, having a pair of terminal slits 106 extending through the bottom 108 of the base, having a pair of locating shoulders 110 on the base at each side of the respective terminal slits 106 inside the base cavity (see Figs. 13 - 14 ) having a pair of locating shoulders 112 on the outside of the base adjacent the respective terminal slits 106, having a shoulder 114 extending around the base adjacent the open end of the base cavity, and having a flange part 116 extending around the outer rim of the open base end. A seat 118 is formed in the bottom of the base cavity between the terminal slits 106, and a pair of grooves 120 are provided in the wall of the base cavity at opposite sides of the seat 118.
In accordance with this invention a pair of L-shaped strip terminals 122 are each provided with a plurality of portions 122.1, 122.2 and 122.3 of progressively narrower width in the longer leg 122.4 of the terminal and have scallops or notches 122.5 formed in the edges of that terminal leg. The shorter leg 122.6 of the terminal has a stationary electrical contact 124 secured thereto, preferably by riveting or the like as shown, and, if desired, an opening 122.7 is provided in each terminal to facilitate precise bending of the terminal at the junction of the legs.
As shown in Fig. 16 each terminal 122 has its longer leg inserted into a terminal slit 106 and pressed into the slit as indicated in Fig. 16 by the arrow 122a while ultrasonic energy is applied to the slit area of the base in any conventional manner (not shown) so that the relatively wider strip portions 122.1, 122.2 and 122.3 of the terminal are progressively pushed into a slit 106 and are embedded in the lateral walls of the base adjacent the slit, while the scallops are filed with the ultrasonically fusible base material as will be understood, until respective lateral edges of the shorter base leg 122.6 engage respective locating shoulders 110 on the base, thereby to locate the terminals 122 in the base for precisely positioning the stationary contact 124 as shown in Fig. 12 The distal ends of the longer terminal legs 122.4 are then bent as shown in Fig.12 to bear against corresponding locating shoulders 114 on the outer side of the base. In that arrangement, pushing of quick connect connectors or the like onto the terminal ends as is diagrammatically illustrated by the broken lines 125 in Fig. 12 in making electrical connection to the terminals does not tend to displace the terminals 122 from their desired assembled position ultrasonically sealed in the slits 106 as will be understood. Preferably the distal terminal ends extend from the thermosat 100 in the direction shown but it will be understood that the terminal ends may be bent in any direction to make desired electrical connection without tending to disturb the seating of the terminals in the base. r
In accordance with this invention, a helical coil compression spring 127 is disposed in the base seat 118.
A flat metal movable contact element 128, preferably of a steel or other magnetic, electrically conductive metal material has a pair of movable contacts 30 secured thereto, preferably be riveting or the like, in spaced relation to each other to engage the stationary contacts 124 and a slit 128.1 is provided in the movable contact element. In that configuration the movable contact element 128 is adapted to be readily blanked from a strip material in a low cost manufacturing procedure. A flat metal motion transfer element 132 is also adapted to be inexpensively blanked from a strip material with a configuration as shown generally in Fig.15 wherein a tab _'132.1 is located at one edge of the strip- adapted to be inserted into the movable contact element slit 128.1 and to be riveted or expanded therein for securing the motion transfer element in the movable contact element together as is diagrammatically illustrated in Fig.'15. Lateral edges 132.2 of the motion transfer element are proportioned to be slidably received in the respective grooves 120 in the base and an opposite edge of the motion transfer element has an extending portion 132.3. The movable contact element with the attached motion transfer element is then disposed on the spring 127 so that the spring biases the movable contact element into electrical engagement with the stationary contacts 124 for interconnecting the stationary contacts and for disposing the extending portion 132.3 of the motion transfer element at a selected location adjacent the open end of the base 102.
A conventional dished, thermostat metal disc element 134 is disposed with its perimeter 134.1 resting on the base shoulder 114 and a thin pliable film 136 of an electrically insulating material such as a polyimide material or the like sold under the name Kapton is disposed over the thermostat element as shown in Fig. 1. Preferable a magnet is positioned to draw the movable contact element 128 and motion transfer element 132 down into the base cavity 104 against the bias of the spring 118 as shown in the noted copending patent application to facilitate assembly of the disc and film in the thermostat 100. A cup-shaped metal lid 138 is then disposed over the open base end and has its rim 138.1 swaged or otherwise formed over the base flange 116 for securing the lid to the base, the base having an annular ridge 138.2 formed therein to be positioned adjacent the rim 134.1 of the thermostat element, thereby to cooperate with the base shoulder 114 in precisely locating the thermostat element 134 with a selected spacing relative to the extending portion 132.3 of the motion transfer element.
In that arrangement, the thermostat element 134 is adapted to move to an inverted dished configuration with snap action in conventional manner when the thermostat element is heated to a selected actuating temperature, thereby to engage the extending portion 132.3 of the motion transfer element as will be understood for moving the movable contact element 128 against the bias of the spring 118 to disengage the stationary contacts 124 and open the circuit between the device terminals 122. Then, upon subsequent cooling down to a relatively lower reset temperature, the thermostat element is adapted to return to its original dished configuration as shown in Fig,12 with snap action for permitting the bias of the spring 118 to reengage the movable contact element with the stationary contacts for reclosing the device circuit. As will be understood, the lid 138 is thermally conductive for readily transmitting heat to the thermosat element 134 from a temperature zone being monitored by the thermostat 100.
In accordance with this invention, the motion transfer element 132 preferably has a slit 132.4 therein located between the tab 132.1 and the extending portion 132.3 of the element, whereby, when the transfer element is secured together with the movable contact element 128 by pressing in the direction diagrammatically illustrated by the arrows 140 in Fig.15 the motion transfer element is adapted to be selectively compressed as is diagrammatically illustrated at 132.5 for providing a precise spacing between the movable contact 128 and the extending portion 132.3 of the transfer element. In that arrangement the extending portion 132.3 of the motion transfer element is adapted to be easily and precisely located so it is accurately spaced relative to the thermostat element 134 to permit initial creep action of the thermosat element without causing opening of the thermostat contacts but is then adapted to provide sharp snap acting movement of the movable contact element when the thermostat circuit is to be opened in response to the selected temperature change. In that way, the thermostat 100 is characterized by utilizing low cost, easily manufactured and assembled components and is also characterized by accurate thermal response characteristics as assembled, each thermostat component being individually characterized by low cost manufacture and by ease of assembly and the thermostat as a whole being characterized by reliable and accurate assembly.
It should be understood that although particular embodiments of the thermostat of this invention have been described by way of illustrating the invention, this invention includes all modifications and equivalents of the disclosed embodiments falling within the scope of the appended claims.

Claims

1. A thermostat having thermally responsive bimetallic means, said thermostat being characterised in that it consists of a monolithic base open at one end, in which two terminals connectable to an electric circuit are inserted, each terminal having one end bent at right angles and carrying a stationary contact, a movable contact element for connecting the said stationary contacts with one another, a spring mounted in a seat of the base biasing the movable contact element between open and closed circuit positions relative to the stationary contacts, a sliding element operatively joined with the said movable contact-carrying element and having a portion extending therefrom, a thermally responsive bimetallic element suitably spaced from the extending portion of said sliding element, and a lid which fastens the said bimetallic element to the said base.

2. Thermostat as set forth in claim 1, being further characterised in that the said sliding element consists of a rod joined by means of a force fit with said movable contact element, the said joint being calibrated with great accuracy thanks to the absence of hard-to-control effects such as elastic return and the like so that the end of rod is exactly at the required distance from the said bimetallic element.

3. Thermostat as set forth in claim 1, being further characterized in that said sliding element has lateral edges thereof slidable in grooves in the base, in that said sliding element has a
Claim 3 continued
circular lug thereon of a radius and center not greater than the part guided between said grooves so as to allow the said sliding element possible movements and/or adjustments inside said grooves with a minimum of friction and without altering the calibration distance between said lug and said disk, and in that the sliding element 13 has two lateral projections to oppose a substantial creep surface resistance to the passage of creep surface currents from the movable contact plate to prevent unloading of the same onto a unit formed by the said disc and lid.

4. Thermostat as set forth in claim l, being further characterized in that said terminals are each made in one piece and fixated in the base by means of a tongue 20 made in the terminal itself.

5. Thermostat as set forth in claim 4, being further characterized in that said terminals are adapted to be bent at any angle desired above said tongue 20 around a shoulder 22 on base I, said shoulder making it possible to absorb both programmed an accidental deformations of said terminals so as to maintain, and even improve, the fixation of the said tongue against the flange of said base.

6. Thermostat as set forth in claim 1, being further characterized in that said lid has a circular projection that closely follows an internal flange of said base 1, said bimetallic element being captured between said internal flange of the base and said circular projection of the lid so as not to suffer vertical deformations or stresses to which the lid may be subjected.

7. Thermostat as set forth in claims 3, being further characterized in that said lid has projections equidistant from one another, disposed on a common circumference, said projections functioning as supports for the disc so that after determination of the actual point in which lug of said guide plate finds itself with the contacts in the closed position further calibration of the thermostat is adapted to be made by squeezing the said projections by an amount such as to obtain a more precise predetermined play between disc and lug, the accuracy of the calibration being assured by the fact that the said projections are of a configuration as to exclude any error whatsoever due to elastic return.

8. Thermostat as set forth in claim 1, being further characterized in that the said movable contact element has a V-shaped notch at its center to facilitate calibration of the thermostat by application of a slight bending force to the movable contact element.

9. Thermostat as set forth in claim 1, being further characterized in that said terminals each have three sectors of Claim 9 continued
decreasing width which are laterally jointed by marginal grooves and of selected radiuses for mounting the said terminals in the monolithic base by means of ultrasound.

10. Thermostat as set forth in claim 1 being further characterized in that said monolithic base has a useful surface for application of a clip for mounting the thermostat on the surface to be thermostated, said clip being able in this particular case to consist also of metal by virtue of the fact that said surface is separated from the said terminals by two barriers the presence of which being made possible by the particular form of realization of the said terminals, said barriers ensuring the necessary distances both spatially and superficially between the said terminals and said clip thus providing the electrical insulation from the ground.

11. Thermostat as set forth in claim 1, further characterized in that said lid is mounted on said monolithic base by means of a cylindrical die which bends the rim of said lid inwards and around an appropriate seat of said monolithic base.

12. A thermostat according to claim 1 having a cup-shaped insulating base with a bottom and with a cavity open at one end, a pair of terminals mounted on the base bottom locating respective stationary contacts inside the cavity and having portions extending from the base outside the base bottom, a movable contact element movable between positions engaging and disengaging the stationary contacts for closing and opening an electrical circuit between the terminals, a dished thermostat metal element mounted on the base at the open base end to be movable with snap action in response to selected temperature change, a lid secured to the base over the open base end for locating .the thermostat element, spring means biasing the movable contact element to one of said circuit positions, and a motion transfer element secured to the movable contact element to be movable with the thermostat metal element for moving the movable contact element to the other circuit position against the spring bias, characterized in that the movable contact element comprises a flat metal sheet element having a slit therein, the motion transfer element comprises a flat metal element having a tab at one edge secured within said slit for securing the motion transfer element to the movable contact element and having an opposite edge portion extending from the element to be engaged by the thermostat metal element, the motion transfer element having lateral edge parts slidably engaged with the base for guiding movement of the movable contact element between said open and closed circuit positions.

13 A thermostat as set forth in claim 12further characterized in that the motion transfer element has a slit therein between said tab and said extending portion thereof, the motion transfer element being compressible relative to the slit for precisely positioning the extending portion thereof relative to the movable contact element secured thereto by the tab.

14 A thermostat as set forth in claim 13 further characterized in that a thin electrically insulating film is secured over the thermostat metal element between the thermostat metal element and the lid for electrically isolating the thermostat metal contacts from the lid.

15 A thermostat as set forth in claim 14 further characterized in that the base has grooves therein at respective opposite sides of the base cavity and the motion transfer element has lateral edges thereof slidable in said respective grooves for guiding movement of the movable contact element between said open and closed circuit positions.

16 A thermostat as set forth in claim12 further characterized in that the base has a pair of slits in the base bottom, has locating shoulder means inside the base adjacent respective terminal slits and has locating shoulder means on the outside of the base adjacent the respective terminal slits, each terminal comprises an L-shaped terminal member having a longer leg and a shorter leg, having a stationary contact secured to the shorter leg, and having a plurality of sections of the longer leg _'of progressively narrower Claim 16 continued
width scalloped along lateral edges thereof, and the longer terminals legs are inserted into and ultrasonically sealed in the respective terminal slits in the base bottom with the shorter terminal legs abuted with locating shoulder means inside the base cavity, the longer terminal legs being further bent outside the base into engagement with said respected locating shoulder means outside the base, thereby to positively receive the terminals in the desired position in the base bottom and to retain the terminals therein even when subjected to axially applied forces while interconnecting the terminals in an electrical circuit.