GB2164207A - Bimetallic thermal switch to control electric circuits - Google Patents

Abstract

The bimetallic thermal switch is provided with two bimetallic convex discs (26, 28) contained in a metal cap (42) of a tight container (10) made of insulating material, the bottom wall (12) of which retains sets of contacts (18-19, 18'-19') connected to related terminals (14-15). Each of the movable contacts (19, 19') co-operates, by means of a link (24, 25), with the respective bimetallic disc (26, 28). The operating connection between contacts (18-19, 18'-19') and their respective bimetallic discs (26, 28) is effected by push rods (24, 25) each of which is provided with appendixes (24a, 24b, 25a, 25b) which are off-set with respect to each other so that the top ones (24a, 25a) engage the substantially central zones of said bimetallic discs where appendix 25a freely crosses a hole (27) in the bimetallic disc (26) contiguous to the sets of contacts (18-19) and (18'-19'). An elastic rubber sealing member (40) is retained in an annular channel. <IMAGE>

Description

SPECIFICATIONS Bimetallic thermal switch to control electric circuits This invention relates to a bimetallic thermal switch to control electric circuits and which is most conveniently applied in the sector of electrical appliances, internal combustion engines, especially automobile engines, and, in general, any other type of application contemplating the use of a fluid container in which the temperature must be sensed and controlled.

The thermal switch according to this invention consists of a container made of insulating material, housing the bimetallic type temperature sensing components, as well as the electrical control elements for the thermal source; said container can be installed conveniently, for example, in the drum of a washing machine or on the radiator of a motor vehicle to detect, check and control the temperature of the liquid contents. The following description refers, in particular, to laundry washing machines but it is obvious that the thermal switch can be applied for other uses as well.

The thermal switches presently in use, specifically but not exclusively for temperature control in washing machines, dishwashers and similar appliances, have the following drawbacks: -difficulty in providing a hermetically sealed, reliable thermal switch which can be rapidly produced at reasonably low cost; -fitting of the thermal switch on a moving body, such as the drum of a household appliance often necessitates excessive installation time.

Consequently, one purpose of this invention is to provide a thermal switch with the required safety and hermetic features, which may be produced economically and which may be assembled and installed quickly and reliably.

The thermal switch according to this invention consists of a body or housing made of plastic material, the bottom wall of which is used to retain and support on its outer part the terminals of the electric control elements for the heat source, whilst on its inner part are fitted the supports for the switching elements, influenced by springs adapted to ensure both the correct positioning of the contracts when same are closed and which also ensure electric continuity between the fixed and moveable contracts, as well as the operating connection between said moveable contacts and the bimetallic sensing element or elements.

The open end of the container of plastic material retains a bottom head, also of plastic material, provided with guiding means for pressure rods interposed between the heat sensing elements and the movable contacts; said bottom head also serves as a stiffening and reinforcing means for the container or housing.

The operating and pressure rods run in guide holes on the bottom head retained by the container, while the shape of the holes for said push rods may be elliptical to allow adequate seating of said rods of the thermal switch.

At least one or both ends of the push rod have terminal tracts which allow engagement, in operation, on the one side with the convex discs forming the heat sensing elements, and on the other side with the moving parts of the sets of contacts, thereby to actuate, in offset positions, the supports of said moveable contacts, along different axes parallel to each other. Forthis purpose, each terminal end of the push rods is eccentric as to the guided tract, while the axes of said eccentric terminal tracts may be parallel.

This eccentricity of the terminal tract (s) with respect to the guided tract (s) of the push rods is a particular preferred feature of this invention.

The bimetallic convex discs are retained in the relevant housings provided in the metal (preferably stainless steel) cap which enables transmission of the heat of the liquid, air, or gas to be detected and controlled by the thermal switch.

Preferably, the peripheral surfaces of the plastic material container and of the bottom guide head for the push rods are provided with at least one groove to house an annular sealing gasket made or rubber; this may consist for example of an O-ring or similar, which provides hermetic tight sealing of the thermal switch, possibly with the aid of adhesive cement applied at the outlet of the electric contact terminals.

A further object of the invention is to provide a thermal switch comprising at least one snap action type bimetallic sensing element, a push rod associated with said to transmit the trigger action to a spring blade which retains a moveable make-or break contact, co-operating with associated fixed counter contracts; said moveable and fixed contacts are provided with terminals that may be electrically connected with suitable external contacts; the thermal switch is provided with either a heat conductive sealing cap to house said heat sensing elements or with a guide element partially housed in said metallic cap and its body is also provided with housings to retain and guide slideably and axially each one of said push rods; while the bottom wall of said body houses contacts and arms for electrical terminals and is provided on its outer part with seats to house said terminals; at least one annular groove or channel to retain an annular elastic gasket is provided between the surfaces in contact with said insulating guide element and a crown ring housed near the opening of said insulating body, said annular gasket being tightened and deformed against the wails of said annular groove and the annular internal wall of the heat conductive metal cap, so as to form a fluid tight closure for the components housed in the insulating container, if necessary with the aid of a sealing-hardening type compound applied, for example, on the terminal outlets.

According to a further object of the invention, the thermal switch is provided with a number of overlapped snap-action type bimetallic sensing discs, suitably spaced and arranged at one end of the insulating container of the thermal switch; the other end, or bottom of said container retains the contacts and terminals; the aperture of the insulating container retains a guide element provided with one or more channels for the longitudinally moveable push rods and which transmit the movement of the bimetallic sensing discs to the contacts; the bimetallic disc closest to the contacts is perforated to permit passage of the push rod associated with the other bimetallic disc; the ends of the push rods are shaped eccentrically with respect to the cylindrical body of said rods, so as to convert the thrust on the axis of one of the rods along a different axis parallel to the first.

The outletterminalsfrom one of the ends of the plastic material insulating container may have different characteristics depending on end use requirements; for example, they may consist of tongues elastically engageable with related sheaths and having different shapes and dimensions.

Generally speaking, such terminals may be secured and grouped on a single insulating support to provide a connectorforfacilitating quick and reliable electrical connections between the thermal switch and the electrical devices controlled by it.

Embodiments of the invention are described in detail below, by example only, with reference to the accompanying drawings, wherein: Fig. 1 is a front elevation, partially in cross section, of the application of a thermal switch according to the invention to the wall of a container for liquids; Fig. 2 is the axial section, on a larger scale, of the thermal switch of Fig. 1; and Fig. 3 is a bottom to top view of Fig. 2, showing a variant of the arrangement of the electric terminals.

With reference to Fig. 1 the thermal switch is identified by letter A.

The thermal switch is moveably secured to the metal structure of the apparatus on which the temperature is to be controlled.

In the case shown, the thermal switch is applied to the bottom wall of a vessel B containing a fluid, for example water, the temperature of which is to be detected.

Specifically, thermal switch A is retained on the bottom of vessel B buy a bayonet fitting C, consisting, in the case shown of two brackets C, secured to said bottom, the ends C2 of which being folded at right angles so as to be inserted freely in angularly offset notches C3 on the periphery of a flange C4 secured to the body of said thermal switch A. An elastic gasket D is fitted between flange C4 and the edge of the hole on the bottom of said vessel B.

In this way, tight sealing between the interior and exterior of vessel B is obtained, in addition to the bayonet connection, in fact when thermal switch A is applied to the bottom of said vessel, gasket D is compressed.

Obviously, the connection between thermal switch A and the vessel in which the temperature is to be detected may be constructed differently; for example the bottom of vessel B may be provided, at the through-hole for the thermal switch, with an annular ledge, the inner wall of which has a groove with angularly displaced notches through which the opposite fins in flange C may be introduced in order to provide a bayonet connection.

With reference in particular to Fig. 2, the thermal switch shown is provided with a container 10 made of electrically insulating material, the bottom wall 12 of which retains a plurality of metallic appendices 14 in suitably orientated positions, depending on final requirements.

The ends 15 of the appendices project suitably from bottom wall 12 of insulating container 10 and are suitably designed to form the connecting means with the related metal sleeves which elastically engage the plates 15 and are linked to the electric circuit by the relevant conductors.

The other end of metal appendices 14 project inside the container 10 and each is metallically connected, for example by riveting or welding, with the elements of pairs of blades 1617 and 1617' which retain at their ends two fixed contacts 18--19 and 18'-1 9'. In the case illustrated blades 16 and 16', together with contacts 18 and 18', form the fixed contacts which co-operate with moveable contacts 19-19' which govern respective electric circuits.

Moveable blades 17 and 17' are urged against related fixed contacts 1616' by coil springs 20 which supply the required pressure to provide metal to metal continuity between contacts 1 & 9 and 1 8'-1 9', so as to ensure make-and-break operations as a function of the electric load of the circuit controlled by said contacts without causing damage.

One end of a push rod 24 and 25 engages on the opposite face of moveable blade 17-17' urged by springs 20.

The push rods 24--25 transmit the inflection movements of convex bimetallic sensing discs 26, 28. The thermal switch shown in figures 1 and 2 is provided with two pairs of contacts 18, 19 and 18', 19' the moveable blades 17-17'ofwhich are influenced by the deformations of bimetallic discs 26, 28 through associated push rods 24 and 25. The mid parts of both push rods 24 and 25 are slideably guided in the holes 30 and 32 of guide means 34 made of electrically insulating material.

The upper ends 24a and 25a of rods 24 and 25 orientated toward their respective sensors 26 and 28 are eccentric or staggered as to the centre line of said rods. Likewise, the opposite ends 24b and 25b engaging with blades 17 and 17' of moveable contacts 19, 19', depending on the arrangement of elements of the pairs 1617 and 16-17', engage directly the moveable blades 17-17'. Alternatively the ends 24b and 25b pass, with suitable play, through holes provided in blades 16 and 16' or fixed contacts 18 and 18'.

Consequently, the force of bimetallic sensors 26 and 28 is applied to the associated movable contacts 19 and 19' by means of push rods 24 and 25.

In the case of rod 24 the relevant force is exerted along the longitudinal axis x-x of terminal tract 24a and is transmitted to the movable arm along a different axis y-y, parallel to the first and passing through terminal tract 24b. The mid tract, guided by push rod 24, may lie on a different axis with respect to both axes x-x and y-y previously mentioned, as illustrated in Fig. 2.

The same arrangement applies to push rod 25 where the transmission of forceps of bimetallic sensor 28 to moveable blade 17' takes place along parallel axes x'-x' and y'-y'. Push rods 24 and 25 are guided in parallel by guide holes 30 and 32 provided in block 34 which is made of plastic material and is housed with its lower part inside plastic container 10, to stiffen and reinforce the latter.

The block 34 terminates, in its top part, with a flange 36, opposite but similar to flange 38 which defines the aperture of plastic material container 10; a groove is provided between the two flanges to house an elastic sealing ring 40, made for example or rubber, in order to ensure hermetic sealing of the thermal switch.

Bimetallic discs 26 and 28 are maintained in their operating positions by coaxial annular ledges inside metal cap 42, which is made preferably of stainless steel as it comes into contact with the fluid the temperature of which it detects.

The cap terminates with a folded-over edge 43 which may itself constitute or retain flange C3 shown in Fig. 1. Disc 26, the larger in diameter of the two bimetallic discs 26 and 28, is provided with a central hole 27 for the passage, with suitable play, of the previously considered appendix 25a of push rod 25.

Consequently, with reference to Fig. 2, the thermal switch shown detects the temperature prevailing in vessel B of Fig. 1, through stainless steel cap 42. When the temperature considered increases up to a given value, bimetallic discs 26 and 28 deflect and vary their concavity and trip sequentially.

Push rods 24 and 25 shift to actuate moveable blades 17 and 17' springs 20, acting on the blades, will be compressed and when contacts 18--19 and 18-19' are open the action of said springs urges moveable blades 17 and 17' into the closed position of said contacts; on the other hand; when bimetallic discs 26 and 28 return to their initial position due to lowering of the temperature of the fluid, the contact pairs are open. Bimetallic discs 26 and 28 may be mounted with their concavity in engagement with ends 24a and 25a of push rods 24 and 25; in this case, pairs of contacts 1 & 9 and 18'-19' are normally closed.However, bimetallic discs 26 and 28 can be arranged with their concavities in opposite directions with respect to each other so that one of the pairs of contacts will be open and the other closed, as shown in Fig. 2. In any case, this arrangement can be varied to meet specific applications. The electric circuits controlled by contact pairs 1 1 9 and 1 8'-1 9' can form four poles, which may be separated and isolated from each other, otherwise they can have one common pole (three poles). That is, instead of having pairs of contacts, the switch can have three contact sets wherein the second contact forms a pole for the opening and closing of the circuit.

Moreover, at least one of said contact pairs may consist of a system of changeover contacts, in which the moveable blades 17 and 17' are operated by means of push rods 24 and 25 with bimetallic discs 26 and 28 to control in a commutative way the respective electrical circuits.

Fig. 3 illustrates one advantageous arrangement of the terminals of the thermal switch A.

Specifically the bottom head 12 of body 10 is provided with shaped seats 50, each designed to retain radially a plate 52 and each connected mechanically and electrically with the corresponding metal appendices 14 which project from the bottom 12 as shown in Fig. 2.

Plates 52 are coupied in the known manner forceably and yieldably with their related sheaths (not shown as already considered) which are in turn connected to the electric circuit to be controlled.

Each of the external ends of appendices 14 (which form, in the case of figures 1 and 2, the tongues 15), is provided in its mid part with a longitudinal slot 55 thus forming an elastic fork (see fig. 3).

This fork shaped appendix engages in a related slot 56 provided toward one of the ends of each plate 52 and these parts are secured and tightened to each other by bending apart the arms of appendices 14to provide a satisfactory mechanical and electrical connection.

Other arrangements of the connecting terminals may be considered to meet specific uses of the thermal switch.

Similarly other solutions may be adopted for securing thermal switch A moveablyto vessel B containing the fluid the temperature of which is to be detected.

The number and arrangement of fork-shaped appendices 14 and of terminals 52 in the bottom wall 12 of the thermal switch A, may vary as is necessary to meet end-use requirements.

Moreover, the outer wall of housing 10 may be designed such that the user can handle the thermal switch more easily when inserting and removing thermal switch A from container B.

The insertion or removal of thermal switch A into or from the wall of container B is effected by applying a pressure on container 10 in the direction shown by the arrow in Fig. 1 and imparting at the same time a rotation to disengage or engage the elements of the bayonet connection, in the usual manner.

The bayonet connection is a preferred and advantageous solution for moveable connection of thermal switch A two container B since the sealing action between the inside and outside of the latter is ensured by sealing gasket D which is elastically deformable.

In particular, sealing at the position of terminal plates 14 can be assured also by suitable cements F applied in the bottom wall.12 of body 10 on the through passages to the exterioroffork-shaped appendices 14.

Obviously tabs 15 or appendices 14 may be secured to said bottom wall 12 also in the stamping phase of container 10.

Claims (4)

1. A Bimetallic thermal switch which operates by tripping in the presence of one or more temperatures and the electric circuit of which is independent from another electric circuit, or said circuits have a pole in common, wherein said thermal switch comprises a plastic insulating material housing, with a metal cover in contact, metal to metal, with the heat sensitive bimetallic element or elements and which container supports and retains electric contacts, and a second complementary part also made of plastic material and provided with guiding means for push rods which operatively connect the bimetallic heat sensitive elements with the moveable contact or contacts of at least one group of electric contacts, while at least one annular channel retains an elastic rubber sealing member which ensures hermetic sealing of the thermal switch.

2. A switch according to claim 1 wherein the annular channel for the sealing member is provided on the mating surfaces of the two plastic material parts in order to simplify the provision of said channel.

3. A switch according to claim 1 or 2, wherein the sealing member is a sealing ring of circular crosssection.

4. A switch according to any preceding claim, wherein the metal cover of the insulating housing is provided on its bottom with at least one annular ledges which retain the edges of bimetallic discs, the central parts of which engage with one of the ends of a push rod operatively secured to an elastic blade of the moveable contact pertaining to the group of contacts considered.

4. A switch according to any preceding claim, wherein the metal cover of the insulating housing is provided on its bottom with at least one annular ledge which retains the edge of a bimetallic disc, the central part of which engages with one of the ends of a push rod operatively secured to an elastic blade of the moveable contact pertaining to the group of contacts considered.

5. A switch according to any preceding claim, wherein blades of the group or groups of contacts terminate with appendices projecting from the bottom wall of the container to receive the electrical connections for said contact groups.

6. A switch according to claim 5, wherein the bottom wall of the container is provided on its outer surface with slotted appendices, for retaining connecting means with electrical conductors.

7. A switch according to any preceding claim, one comprising two superposed by-metallic discs arranged coaxially and retained in a housing provided in the metal cover and co-operating with associated push rods retained and guided in parallel in related holes provided in the complementary wall of housing, while the ends of said push rod cooperate operatively in part with the substantially central part of the related bimetallic discs and the remaining parts with the related moveable contacts of the relevant groups of contacts.

8. A switch according to claim 7, wherein each push rod terminates on at least one of its end with eccentric appendices which ensure on the one hand parallelism between said push rods and on the other hand the engagement of said ends with the substantially centre zones of the two bimetallic discs and with moveable contacts of the two groups of contacts.

9. A switch according to claim 7 or 8, comprising two deformable superposed bi-metallic discs providing trigger action, and which are coupled with related ajacent and parallel push rods to transmit the trigger action of said bimetallic discs to contacts, one for closing and the other for opening, pertaining to two groups of contacts provided with terminals for electric conductors joined to said contact groups, while an electrically insulating container houses and retains said electric contact groups and on its aperture is provided with a flange co-operating with the mating flange of a complementary part of said insulating container and said flanges retain in seal tight relation a metal cover provided with co-axial spaced ledges to retain the edges of two bimetallic discs the push rods of which are guided slideably in the parallel holes provided in said complementary part to guide push rod slideably and thus actuate the moveable contacts of the contact groups, whilst a groove is provided on the contact surfaces of said flange and mating flange, said groove being capable of containing an elastic annular gasketwhich is deformed and pressed either between said surfaces or between the latter and the inner wall of said metal cover in order to ensure tight sealing for the thermal switch, and which action can be enhanced, if necessary, by the application of sealing cement of flexible self-hardening type on the outlet of the connecting terminals.

10. A switch according to any of claims 7 to 9, wherein the trigger action sensing discs are superposed and suitably spaced from each other inside the metallic cover, the disc closest to the contact groups is provided with a central aperture to allow the free passage of the push rod associated with the other bi-metallic disc whilst the ends of said push rods terminate with appendices which are eccentric with respect to their own periphery so as to convert the thrust received along one axis into a thrust along a different parallel axis.

11. A switch according to any of claims 1 to 10, wherein the bottom part container is provided, on its outer surface, with shaped seats to house and retain in the desired position contact blades connected metal-to-metal with the slotted appendices projecting from said bottom wall.

12. A bimetallic thermal switch substantially as herein described and as illustrated in the accompanying drawings.

New claims or amendments to claims filed on 3 May 1985.

Superseded claims 1,4.

New or amended claims:

1. A Bimetallic thermal switch which operates by tripping in the presence of two or more temperatures and the electric circuit of which is independent from another electric circuit, or said circuits have a pole in common, wherein said thermal switch comprises a plastic insulating material housing, with a metal cover in contact, metal to metal, with the heat sensitive bimetallic elements and which container supports and retains electric contacts, and a second complementary part also made of plastic material and provided with guiding means for push rods which operatively connect the bimetallic heat sensitive elements with the moveable contact or contacts of at least one group of electric contacts, while at least one annular channel retains an elastic rubber sealing member which ensures hermetic sealing of the thermal switch.