GB2092384A - Thermostats - Google Patents

Abstract

In a thermostatic switch wherein the switch contacts 20,26 are opened or closed pursuant to actuation of a bimetallic disc 38, a main housing 12 contains all of the switch components except the bimetallic disc 38, and a secondary housing 14 mounted on one end of the main housing 12 contains the bimetallic disc 38, the secondary housing 14 having a substantially greater peripheral dimension than the main housing 12 whereby a relatively large bimetallic disc 38 may be used to actuate a relatively small switch. <IMAGE>

Description

SPECIFICATION Thermostatic switch assembly The instant invention relates to thermostatic switches. More particularly the instant invention relates to a thermostatic switch assembly primarily for use in small appliances or other electrical devices utilizing circuitry which must be opened or closed in response to a predetermined temperature change.

Thermostatic switch assemblies employing bime tallic discs which exert flexing action in response to predetermined temperature changes are well-known in the art and have found wide use where the electrical continuity of a circuit or a portion thereof must be interruptable as a result of such a temperature change. Thermostatic switch assemblies employing bimetallic discs which cooperate with other elements within a main housing to effect or interrupt electrical continuity have been made in a number of configurations for various applications and in this regard particular attention is drawn to the applicant's prior U. S. patents No. 3,258,567 and 3,496,511 as well as U.S. patents to Mertler, No. 2,753,421; Cox, No.3,081,388; Kirchhubel, No. 3,164,701; Ruckriegel petal, No.3,164,702; Vargas, No.3,614,702; and Bucheister, No. 4,039,991, said patents representing the closest prior art of which the applicant is aware.

One of the primary constraints which must be considered when designing thermostatic switch assemblies is the size of the bimetallic disc. The bimetallic disc is designed to flex at a predetermined temperature as a result of differences in the expansion characteristics of the two dissimilar metals used in the construction thereof. Unfortunately, the smaller the disc the less accurate it becomes in exerting flexing action at a predetermined temperature; and, as a result, the size of the bimetallic disc is often the determining factor for the size of the entirethermo- static switch assembly. In many cases, particularly where low current circuitry is involved, the size of the switch portion of the assembly could be much smaller and still function equally well.Traditionally, however, thermostatic switch assemblies have been constructed with the size of the entire assembly being dictated primarily by the required size of the bimetallic disc. Unfortunately, switch assemblies designed in this manner have two main drawbacks.

Often times, the main housings of the assemblies are made of relatively expensive non-conductive materials such as Mycalex and therefore any unnecessary oversizing thereof results in unnecessary cost increases for the finished product. Furthermore with recent tendencies toward the use of microcircuitry, increased significance has been given to the size of electrical components, and therefore it is often advantageous to make switch assemblies as small as possible. Unfortunately, this also isn't always possible with traditional design techniques.

The thermostatic switch assembly of the instant invention overcomes drawbacks heretofore encountered in previously known assemblies by providing an assembly using a main housing of substantially smaller peripheral dimension than the bimetallic disc. The switching apparatus of the assembly is designed for the current loads anticipated in the particular circuit whereas the bimetallic disc is designed for the particular tolerances and temperature differential anticipated. As a result, the thermostatic switch assembly disclosed in the instant invention can frequently result in substantial savings in material costs over previously known assemblies while providing an efficient and accurate thermostatic switching device of substantially smaller size.

The instant invention relates to a thermostatic switch assembly having a main housing with an open cavity formed therein. A secondary housing of substantially greater peripheral dimension is attached to the main housing and contains a bimetallic disc which exerts a flexing action in response to a predetermined temperature change. While it is understood that various means are available for interrupting an electrical circuit in response to said flexing action, preferably, such interruption is effected with a contact arm and a fixed contact which are engageable and are mounted within the cavity in the main housing of the assembly, the contact arm being biased to engagement with the fixed contact but being disengageable therefrom.The fixed contact and the contact arm are electrically connected to terminals mounted exteriorly on the main housing and accordingly when the arm is in engagement with the fixed contact, electrical continuity is effected between the two external terminals. A transfer is provided extending between the bimetallic disc and the contact arm providing communication therebetween to thereby effect the engagement or disengagement of the arm with the fixed contact in response to flexing action of the disc and in this manner electrical continuity between the two external terminals is correspondingly effected between the two external terminals is correspondingly effected or interrupted in response to a predetermined temperature change.To further facilitate the communication between the disc and the arm, a guide is positioned within the main housing, the guide having a central bore extending therethrough with the transfer pin extending through the bore to guide the movement of the pin within the main housing.

The accuracy of a thermostatic switch assembly for effecting or interrupting current flow in response to a predetermined temperature change depends primarily on the accuracy of the bimetallic disc in exerting a flexing action within a particular temperature differential. It is known that the predictability of the flexing action of a bimetallic disc is increased as the size of the disc is increased. Furthermore, it is known that the stability of a disc in accurately providing a flexing action in response to a temperature change over a required disc life time is also increased as the size of the disc is increased.

Accordingly, in order to maintain tight tolerances in disc operation, particularly when the disc is required to flex within a narrow temperature differential, enlargement of the disc size is often the only solution. The instant invention therefore provides a thermostatic switch assembly which may be used where close tolerances and narrow temperature differentials are required. In addition since the main housing of the assembly of the instant invention is of substantially small peripheral dimension than the secondary housing containing the bimetallic disc, the entire assembly is smaller resulting in substantial savings in material costs as well as adding versatility to the unit by making it more suitable for use in confined areas.Furthermore, aside from the obvious substantial savings in material costs, other production advantages may often be realized when thermostatic switch assemblies are manufactured in accordance with the instant invention. Since most thermostatic switch assemblies are used in low current applications, the main housing portion of the assembly containing the contact arm and the fixed contact may often be manufactured as a standarized unit with one size being suitable for use in various applications. Thermostatic discs of various sizes may then be used in connection with the standarized main housing as needed to suit tolerance requirements, simplifying both production and inventory proceedures.

Accordingly, it is an object of the instant invention to provide a thermostatic switch assembly having a main housing containing a switching mechanism and a secondary housing of substantially greater peripheral dimension containing a bimetallic disc also of substantially greater peripheral dimension than said main housing which exerts a flexing action in response to a temperature change, the disc communicating with the switch assembly to accurately effect or disrupt the continuity of an electrical circuit in response to said temperature change.

Another object of the instant invention is to provide a thermostatic switch assembly of reduced size capable of operating with precision in narrow temperature differentials.

A still further object of the instant invention is to provide an economical thermostatic switch assem bly which can operate at close tolerances in narrow temperature ranges.

Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing.

In the drawing which illustrates the best mode presently contemplated for carrying out the present invention: Figure 1 is a perspective view of the thermostatic switch assembly of the instant invention; Figure 2 is a top plan view thereof; Figure 3 is an elevational side sectional view thereof taken along line 3-3 in Figure 2; and Figure 4 is a similar side sectional view thereof with the bimetallic disc flexed upwardly causing the switch to open.

Referring now to the drawing, the thermostatic switch assembly of the instant invention is shown in Figures 1 through 4 generally indicated at 10. As will be noted, the switch assembly 10 has a substantially cylindrical main housing 12 with a secondary hous ing generally indicated at 14 attached to the bottom end thereof. The main housing is constructed of a non-conductive material such as Mycalex and as may be noted, particularly from Figures 3 and 4, has an open cavity 16 also of substantially cylindrical configuration formed in the interior thereof.

Mounted within the cavity 16 are a moveable contact arm 18 and a fixed contact 20, the arm 18 being constructed of a suitable resilient conducting material such as copper and as may be noted particularly from Figures 3 and 4 is attached to the top of the main housing 12 at 22 with any suitable means such as a rivet 24 as shown. As will be further noted, the arm 18 extends outwardly from the mounting point 22 doubling back on itself and terminating adjacent to the contact 20 with a contact 26 provided on the end of the arm 18 to improve the electrical contact between said arm and said fixed contact. As a result of the configuration of the contact arm 18, it has somewhat of a spring like tendency causing the end thereof and the contact 26 to be biased to engagement with the fixed contact 20.A pair of electrical terminals 28 and 30 are provided on the top of the housing 12 being attached thereto by conventional means such as rivets 24 and 32 as shown. As will be noted, the terminals 28 is electrically connected to the contact 20 by means of the rivet 32 which extends through the housing and is connected to the contact 20. As a result, electrical continuity is provided between the terminals 28 and 30 when the arm 18 with the contact 26 is in engagement with the fixed contact 20.

Covering the opening of the cavity 16 at the bottom of the main housing 12 is a guide 34, which, as will be noted, is formed as a plug extending a distance into the cavities 16 with a bore 36 provided centrally therethrough. The secondary housing 14, as will be noted from Figures 1 and 2 is of substantially circular configuration and is attached to the main housing 12 at the bottom end thereof, the housing 14 being of substantially greater peripheral dimension than the housing 12 and containing a substantially circular bimetallic disc 38 also of substantially greater peripheral dimension than said main housing. The secondary housing 14 is preferably made of aluminum although any suitable formable material may be used and consists of a flange ring 40 and a cap 42.As will be noted, the flange ring 40 has a neck portion 44 which is attached to the outer lower portion of the main housing 12 and extends to a distance downwardly therefrom terminating with an outwardly extending flange portion 46. A spacer ring 48 with a central opening 49 therethrough is provided beneath the flange portion 46, the peripheral edges of the cap 42 being curled around the ring 48 and the flange portion 46 to securely attach the cap 42 to the flange ring 40. As may be noted, the cap 42 is formed with a shelf 50 providing support for the disc 38 around the periphery thereof while allowing clearance for flex ing movement of the disc 38 within the secondary housing 14. As may be noted from Figures 3 and 4, a transfer pin 52 is provided extending through the bore 36 and the guide 34 from the disc 38 to the contact arm 18, the transfer pin 52 being made of a suitable non-conductive material such as a ceramic.

The disc 38 is a conventional thermostatic bimetal lic disc constructed of two dissimilar metals having substantially different thermal expansion character istics. As a result, the disc 38 is capable of exerting a slight flexing action when subjected to a predetermined temperature change.

As will be noted, in the position shown in Figure 3, the disc 38 is curved slightly downwardly with the transfer pin 52 resting thereon, the top portion of said pin being spaced slightly from the air 18. As will be further noted with the disc 38 and the pin 52 in these positions, the contact 26 on the arm 18 engages the fixed contact 20 providing electrical continuity between the terminals 28 and 30. When the bimetallic disc 38 is subjected to a predetermined temperature change the configuration thereof changes, i.e., slightly flexes upwardly to the position illustrated in Figure 4. As a result, the transfer pin 52 engages the contact arm 18 causing the end thereof and the contact point 26 to be disengaged from the tab 20 thereby interrupting electrical continuity between the terminals 28 and 30.

As is well known, various elements of the thermostatic switch assembly described may be manufactured from various different suitable construction materials, the main housing 12, the transfer pin 52 and the guide 34 of necessity being of nonconductive materials. In certain applications where moisture-proof thermostatic switch assemblies are desirable, the housing 12 and the guide 34 will preferably be made from materials such as Mycalex which will not decompose with contact arcing and will provide a suitable moisture-proof assembly.

Unfortunately, many of the housing materials available such as Mycalex are relatively expensive and thereby substantially increase the cost of the entire assembly particularly when the main housing of the assembly is oversized to match the dimensions of the disc. However, when thermostatic switch assemblies are constructed according to the instant invention and current requirements don't mandate the use of an enlarged contact arm and fixed contact to effect the switching function, substantial savings can be realized as a result of reduced material costs.

As seen, therefore, the instant invention combines benefits of an enlarged bimetallic disc for greater thermostatic precision with the cost reduction benefits and other size advantages associated with a smaller main housing to provide a substantial improvement over previously known thermostatic switch assemblies.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

Claims (7)

1. A thermostatic switch assembly comprising: a. main housing made of a non-conductive material having an open cavity formed therein; b. first electrical terminal means mounted on the exterior of said housing; c. second electrical terminal means mounted on the exterior of said housing; d. a secondary housing having an open cavity therein attached to said main housing said secondary housing being of substantially greater peripheral dimension than said main housing; e. a bimetallic disc located within said cavity in said secondary housing, said disc also being of substantially greater peripheral dimension than said main housing and being responsive to a predetermined temperature change for exerting a flexing action; and f. means for effecting and interrupting electrical continuity between said first and second terminal means in response to said flexing action.

2. In the thermostatic switch assembly of claim 1, said means for effecting and interrupting electrical continuity comprising: a. a fixed contact mounted within said cavity in said main housing, said contact being electrically connected to said first terminal means; b. a resilient contact arm mounted within said cavity in said main housing, electrically connected to said second electrical terminal means and engageable with said tab to thereby provide electrical continuity between said first and second terminal means, said arm being normally biased to engage mentwith said fixed contact but being moveable between positions of engagement and spaced disen gagementtherewith to correspondingly effect or interrupt said continuity;; c. a transfer pin extending between said disc and said arm to cause disengagement of said arm from said fixed contact in response to said flexing movement; and d. guide means located within said main housing for guiding, said pin between said arm and said pin.

3. In the thermostatic switch assembly of claim 2, said main housing being substantially cylindrical in shape said secondary housing further comprising: a. a substantially circular ring having a neck portion which is attached to said main housing and a flange portion which extends substantially radially outwardly from said neck portion; and b. a substantially circular cap attached to said flange portion, said cap having an open cavity formed therein for containing said disc.

4. In the thermostatic switch assembly of claim 3, said cavity in said cap having a shelf formed therein for positioning said disc.

5. In the thermostatic switch assembly of claim 3, said guide means comprising a substantially circular plug with a bore therethrough which is in alignment between said arm and said disc, said pin extending through said bore and thereby being guided between said arm and said disc.

6. In the thermostatic switch assembly of claims 1 or 2 said main housing being made of Mycalex.

7. A thermostatic switch assembly substantially as hereinbefore described with reference to and as shown in the accompanying drawings.