Temperature limiting device

Abstract

The temperature limiting device comprises an outer container (2) defining a cup-shaped housing (3), closed by a lid (4), inside which a spring snap-in disc (6) and a bimetallic disc (7) are arranged in a stack. The lid (4) of the outer container (2) and the spring snap-in disc (6) bear integral a fixed contact (10) and at least one movable contact (11, 16), respectively. The outer container (2) is externally coated by a protective cover (15) made by overmoulding an insulating material.

Description

DescriptionTEMPERATURE LIMITING DEVICETechnical field

[0001] The present invention relates to a temperature limiting device for the protection of electrical equipment and the like, as well as a method for the realization of such a device.Prior art

[0002] In the technical field concerning the production of temperature limiters adapted to guarantee the thermal protection of electrical devices or components of equipment such as electric motors and the like, the use is currently known of anti-overheating temperature limiters based on the use of a bimetallic disc adapted to switch the configuration of a spring snap- in disc which correspondingly closes or opens an electrical circuit of the device to be protected. Such temperature limiting devices, in the specified field, are also referred to as bimetallic thermal switches.

[0003] In particular, the bimetallic disc is able to switch from a low temperature position to a high temperature position where it acts on the spring snap-in disc to open the electrical circuit and thereby interrupt the heating.

[0004] Such a temperature limiting device is illustrated for example in European patent EP 0 678 891.

[0005] This temperature limiter comprises an outer container defining a cup-shaped housing, closed by a lid, inside which a bimetallic disc and a spring snap-in disc are arranged in a stack. The lid carries the fixed contact of the switch, while the spring snap-in disc carries the movable contact. Under the normal operating condition, i.e. at low temperature, the movable contact is pressed by the spring snap-in disc against the fixed contact and thus closes the electrical circuit, allowing the current to pass. When, on the other hand, the temperature exceeds a predetermined threshold value, the bimetallic disc reverses its position, consequently displacing the spring snap-in disc. In this way, the movable contact detaches from the fixed contact and the electrical circuit is opened, interrupting the passage of current and heating.

[0006] In use, the bimetallic thermal switch is usually inserted inside the stator winding of the electric motor, during the motor production step, so that the thermal switch is in direct thermal coupling with the winding.

[0007] However, it should be noted that the need to ensure mechanical solidity and fixing to the winding often involves the need to impregnate the motor stator through chemicals, for example solvent paints, water-based paints, resins and the like. During this production step, there is therefore a high risk of penetration of the chemicals used for the impregnation of the stator into the bimetallic thermal switch, with consequent malfunction of the switch itself. To prevent this risk, bimetallic thermal switches are usually protected by a resin cover,applied by dosing or casting. This resin cover, once solidified, coats the parts of the switch potentially at risk of infiltration in order to ensure safe use, even in the case of impregnation with the aforementioned chemicals. In essence, the cover is made by applying a drop of resin on the device through a drop dispenser.

[0008] Prior documents WO 2023 / 286102, WO 2023 / 286103, DE 10 2004 015 394 and DE 10 2013 102 006 respectively illustrate a bimetallic thermal switch having at the top a resin cover applied by dosing or casting.

[0009] For this purpose, resins that polymerize due to the effect of temperature, for example mono- or bi-component epoxy resins, silicone resins and the like are currently used for finishing bimetallic thermal switches. However, these resins have obvious limitations both in terms of the production process and the quality of the final result.

[0010] As far as the production process is concerned, the used resins require the use of a furnace to complete polymerization, or long maturation times at room temperature. This involves a pause in the production flow, necessary for completing the heat treatment, whether at room temperature or at high temperature. The production process is affected by this pause, as a continuous production flow is not achieved.

[0011] Furthermore, resins of this type are often very susceptible to room temperature, with high viscosity variations, due to the variation of the temperature itself. This peculiarity entails the need to regulate the temperature of the working areas, in order to avoid that the same resin is almost liquid in the hot periods of the year and very viscous in the cold periods, with obvious complications in the dosing and process step.

[0012] Another problem complained of in the specified sector, in relation to the type of product and realization process used in the prior art, consists in the so-called "capillarity" phenomenon. In fact, it has been found that, once applied above the bimetallic thermal switch, the liquid resin infiltrates between the cracks present between one component and the other, in particular between the lid and the outer container, in the riveted portion thereof, or between the lid and the rivet that acts as electrical contact.

[0013] This phenomenon is all the more marked, the more liquid the resin is and the longer the first polymerization time, known as "gel-time". If the resin penetrates inside the bimetallic thermal switch, it can prevent its correct operation, with serious consequences for the safety of the equipment in which it is installed.

[0014] Another problem found is determined by the fact that the heads of the windings, before impregnation, are subjected to strong pressures to give them the final shape. These pressures can cause damage to the temperature limiting device, resulting in malfunction.Disclosure

[0015] The task of the present invention is to solve the aforementioned problems, by devising a temperature limiting device that has a coating of the outer container providing optimalprotection from external agents.

[0016] Within the scope of this task, a further object of the invention is to provide a temperature limiting device provided with a coating that prevents the entry of chemicals and other liquid substances into the housing containing the operating components of the same device.

[0017] A further object of the invention is to provide a temperature limiting device of simple constructional and functional conception, absolutely reliable in functioning, versatile in use and relatively inexpensive in cost.

[0018] Said objects are achieved, according to the present invention, by the temperature limiting device according to claim 1.

[0019] The temperature limiting device comprises an outer container defining a cup-shaped housing, closed by a lid, inside which a spring snap-in disc and a bimetallic disc are arranged in a stack.

[0020] Preferably said outer container is made of conductive material.

[0021] Preferably said lid is made of insulating material.

[0022] Alternatively, said lid is made by means of a combination of materials such as to be isolated with respect to said outer container.

[0023] The bimetallic disc is axially associated with said spring snap-in disc.

[0024] The temperature limiting device comprises at least one fixed contact integral with said lid of the outer container and protruding for a portion thereof above the same lid and at least one movable contact integral with said spring snap-in disc.

[0025] Preferably, the temperature limiting device comprises a separation ring of metallic material arranged above said bimetallic disc and adapted to engage a peripheral portion of the bimetallic disc itself.

[0026] Said separation ring is clamped between said bimetallic disc and said lid of the outer container or an annular-shaped spacer member arranged inside said cup-shaped housing.

[0027] According to the present invention, the temperature limiting device is externally coated with a protective cover made by overmoulding an insulating material.

[0028] Advantageously, said protective cover completely incorporates said outer container of the temperature limiting device.

[0029] Advantageously said insulating material is a technopolymer.

[0030] Advantageously said insulating material is a thermoplastic material of the polyphenylene sulfide (PPS) type and the like.

[0031] Preferably said protective cover at least partially incorporates the connection cables of the temperature limiting device.

[0032] According to an embodiment of the invention, said movable contact comprises a movable bridge integral, by means of axial fixing means, to said spring snap-in disc and to said bimetallic disc, clamped in a bundle-like manner.

[0033] Preferably said movable bridge has a circular shape and is adapted to be brought into abutment with a pair of fixed contacts.

[0034] The present invention also concerns a method for the realization of a temperature limiting device which envisages a. providing a temperature limiting device comprising an outer container of conductive material, defining a cup-shaped housing closed by a lid, inside which there are arranged in a stack a spring snap-in disc; a bimetallic disc associated with said spring snap-in disc; at least one fixed contact integral with said lid of the outer container and protruding for a portion thereof above the same lid; at least one movable contact integral with said spring snap-in disc; b. associating with said temperature limiting device a pair of electrical connection cables; c. overmoulding a protective cover of insulating material above said outer container of the temperature limiting device.

[0035] In particular, said step of c. overmoulding a protective cover of insulating material provides for c1. inserting the device to be covered into a special mould, positioned below an injection press; c2. bringing the insulating material to be injected to the liquid state; c3. Injecting the insulating material in the liquid state into the cavity of said mould; c4. allowing the insulation material injected into said mould to solidify until the final shape is acquired.

[0036] Advantageously said step of c. overmoulding a protective cover of insulating material envisages completely incorporating said outer container of the temperature limiting device.

[0037] Advantageously, the method in question provides for overmoulding said protective cover by means of a technopolymer of the polyphenylene sulfide (PPS) type and the like.Description of the drawings

[0038] The details of the invention will be more apparent from the detailed description of preferred embodiments of the temperature limiting device, illustrated by way of example in the accompanying drawings, in which: figure 1 shows an axial sectional view of the temperature limiting device according to the present invention; figure 2 shows a similar axial sectional view of a different embodiment of the temperature limiting device according to the present invention.Description of embodiments of the invention

[0039] With reference first to figure 1 , the temperature limiting device according to the present invention is indicated as a whole with 1 .

[0040] The temperature limiting device comprises an outer container 2 defining a cup-shaped housing 3. The housing 3 of the outer container 2 is closed at the top by a lid 4, retained by a peripheral folded edge 5 of the outer container 2. The outer container 2 is made of conductive material, for example brass. The lid 4 is made of insulating material, such as for example ceramic material and the like, or alternatively of a combination of materials, even metallic, but such as to be insulated with respect to the outer container 2.

[0041] Inside the housing 3 of the outer container 2, a spring snap-in disc 6 and a bimetallic disc 7 are arranged in a stack. Under the normal operating condition, the spring snap-in disc 6, having a slightly arched shape, rests peripherally on the bottom of the housing 3 of the outer container 2; the bimetallic disc 7, having a more arched shape, rests peripherally on the edge of the same spring snap-in disc 6.

[0042] The spring snap-in disc 6 is preferably made of stainless steel coated with precious material, for example silver; the bimetallic disc 7 preferably consists of a sheet made by coupling iron and copper.

[0043] The lid 4 is clamped against an annular-shaped spacer member 8, which in turn rests peripherally on an annular shoulder 9 formed internally by the outer container 2. In practice, the lid 4 and the spacer member 8 are clamped in a bundle-like manner against the annular shoulder 9 by the folded edge 5 of the outer container 2, suitably riveted. The spacer member 8 is for example made of brass or the like.

[0044] The lid 4 carries axially inserted, in a manner known per se, a fixed contact 10 of the thermal switch; the spring snap-in disc 6 in turn carries a movable contact 11 of the thermal switch that is inserted axially. The fixed contact 10 protrudes below the lid 4; the movable contact 11 protrudes above the bimetallic disc 7, through an axial hole made in the same bimetallic disc 7.

[0045] The contacts 10, 11 are preferably made of precious metal, for example silver, or an alloy thereof, or a composition of a precious metal with a conductive metal, for example the stem of copper and the head of silver.

[0046] Under the normal operating condition, i.e. at low temperature, the movable contact 11 is elastically pushed by the spring snap-in disc 6 against the fixed contact 10 and thus closes the electrical circuit, allowing the current to pass, as specified below.

[0047] Preferably, the temperature limiting device comprises a separation ring 12 of metallic material arranged above the bimetallic disc 7 and adapted to engage a peripheral portion of the bimetallic disc 7 itself.

[0048] The separation ring 12 is clamped between the bimetallic disc 7 and the lid 4 of the outer container 2. In particular, in the illustrated case, the separation ring 12 is clamped between the bimetallic disc 7 and the annular-shaped spacer member 8. If, on the other hand, this spacer member 8 is not present, the separation ring 12 is clamped directly between thebimetallic disc 7 and the lid 4.

[0049] The temperature limiting device is associated with the cables 13, 14 of connection to the outer container 2 and to the fixed contact 10, respectively.

[0050] According to the present invention, the outer container 2 is externally coated by a protective cover 15 made by overmoulding a suitable insulating material. In particular, said insulating material is suitably a technopolymer of the polyphenylene sulfide (PPS) type. PPS is a thermoplastic material with high mechanical properties and thermal and chemical resistance.

[0051] In particular, the overmoulding of the insulating material is carried out by inserting the device to be covered inside a special mould, positioned under an injection press, while the polymer is liquefied and subsequently injected into the mould cavity, where it then solidifies to acquire the final shape.

[0052] In the illustrated case, the protective cover 15 advantageously extends so to entirely cover the outer container 2, also incorporating the cables 13, 14 of connection to the outer container 2 and to the fixed contact 10, respectively. However, it is possible to provide that the protective cover 15 extends so as to only partially cover the outer container 2, specifically coating at least the lid 4, the folded edge 5 of the outer container 2, the portion of the fixed contact 10 protruding above the lid 4 and the cables 13, 14 of connection to the outer container 2 and to the same fixed contact 10.

[0053] The operation of the temperature limiting device according to the present invention is easily understandable from the foregoing description.

[0054] Under the normal operating condition, the spring snap-in disc 6 and the bimetallic disc 7 are centred and locked between the base of the housing 3 defined by the outer container 2 of conductive material and the lid 4 having the fixed contact 10 integrated therein.

[0055] The spring snap-in disc 6 constitutes the element through which the electric current passes and supports the movable contact 11 which is kept under constant pressure against the fixed contact 10.

[0056] The bimetallic disc 7, supported by the movable contact 11 that passes through it, is able to react to any variations in the temperature of the equipment to be protected. When a predetermined switching temperature is reached, the bimetallic disc 7 snaps into the reverse position, with the concavity facing downwards, and pushes the spring snap-in disc 6 downwards.

[0057] In this way, the contact between the fixed and movable contacts 10, 11 opens instantly and therefore the increase in temperature in the equipment to be protected is interrupted. When, conversely, the temperature drops and reaches the preset operating normal value, the bimetallic disc 7 snaps again to return into the initial position and the contact is closed.

[0058] Fig. 2 illustrates a different embodiment of the temperature limiting device in which the lid 4of the outer container 2 carries a pair of fixed contacts, for the sake of clarity indicated with 10a and 10b. The fixed contacts 10a and 10b pass through the lid 4 in mutually parallel positions and protrude for a portion thereof from the lid 4 itself.

[0059] The fixed contacts 10a and 10b are associated respectively with the electrical connection cables 13, 14 of the device. Preferably, the cables 13, 14 are made integral with the fixed contacts 10a and 10b by means of appropriate welding elements 19.

[0060] Inside the housing 3 defined by the outer container 2 there is arranged a movable bridge 16, of circular shape, adapted to be brought into abutment with the fixed contacts 10a and 10b. The movable bridge 16 is made integral, by means of an axial rivet 17, to the spring snap-in disc 6 and the bimetallic disc 7, clamped in a bundle-like manner. In essence, the movable bridge 16 performs the same function performed, in the previous solution, by the movable contact 11 .

[0061] The movable bridge 15 is preferably made of brass, bronze or the like, coupled to a precious metal or an alloy thereof such as for example silver or the like, with or without a precious metal coating.

[0062] The spring snap-in disc 6 is locked against a circular seat obtained inside the housing 3 by a spacer ring 18.

[0063] As in the previous case, if there is a variation in the temperature of the equipment to be protected, such that it exceeds a predetermined switching temperature, the bimetallic disc 7 snaps into the reverse position, with the concavity facing downwards, and pushes the spring snap-in disc 6 downwards, opening the contact between the movable bridge 16 and the fixed contacts 10a and 10b.

[0064] As in the solution described above, the outer container 2 of the device is externally coated, in part or entirely, by a protective cover 15 made by overmoulding a technopolymer of the polyphenylene sulfide (PPS) type and the like.

[0065] The temperature limiting device according to the present invention achieves the purpose of ensuring the protection of the same device from the risk of penetration of liquids or dust, as well as from mechanical pressure.

[0066] This result is obtained by the inventive idea of realizing a protective cover of the device obtained by an overmoulding process of insulating material preferably consisting of a technopolymer of the polyphenylene sulfide (PPS) type and the like, so as to create an airtight and highly resistant enclosure around the outer container and the electrical connection cables.

[0067] In particular, the use of a suitable technopolymer, such as for example PPS, allows to have a higher temperature range of use, compared to the conventionally used resins.

[0068] The overmoulding production process inside a special mould therefore advantageously differs from the traditional technique of applying a resin on a limited portion of the bimetallicthermal switch by dosing or casting.

[0069] According to an advantageous aspect of the invention, the overmoulding production process does not require the use of furnaces to complete the polymerization at high temperature or of pauses for the polymerization at room temperature; rather it is possible to use injection presses and appropriate moulds to obtain a finished product in a span of a few seconds.

[0070] The temperature limiting device described by way of example is susceptible to numerous modifications and variations according to different needs.

[0071] In the practical implementation of the invention, the materials employed, as well as the shape and sizes, may be any according to requirements.

[0072] Where technical features mentioned in each claim are followed by reference marks, such reference marks have been included for the sole purpose of increasing the understanding of the claims and consequently they do not have any limiting value on the scope of each element identified by way of example by such reference marks.

Claims

1 . A temperature limiting device, comprising an outer container (2) of conductive material, defining a cup-shaped housing (3) closed by a lid (4), inside which there are arranged in a stack a spring snap-in disc (6); a bimetallic disc (7) associated with said spring snap-in disc (6); at least one fixed contact (10) integral with said lid (4) of the outer container (2) and protruding for a portion thereof above the same lid (4); at least one movable contact (11 , 16) integral with said spring snap-in disc (6); characterized in that said outer container (2) is externally coated by a protective cover (15) made by overmoulding an insulating material.

2. The device of claim 1 , wherein said protective cover (15) completely incorporates said outer container (2) of the temperature limiting device (1 ).

3. The device of claim 1 or 2, wherein said insulating material is a technopolymer.

4. The device of claim 3, wherein said insulating material is a thermoplastic material of the polyphenylene sulfide (PPS) type and the like.

5. The device of any one of the preceding claims, wherein said protective cover (15) at least partially incorporates the electrical connection cables (13, 14) of the temperature limiting device.

6. The device of any one of the preceding claims, wherein said protective cover (15) extends so as to coat at least said lid (4), a folded edge (5) of said outer container (2), said portion of the fixed contact (10) protruding above the lid (4).

7. The device of any one of the preceding claims, wherein it comprises a separation ring (12) of metallic material arranged above said bimetallic disc (7) and adapted to engage a peripheral portion of the bimetallic disc (7) itself.

8. The device of claim 1 , wherein said movable contact comprises a movable bridge (16) integral, by means of axial fixing means (17), to said spring snap-in disc (6) and to said bimetallic disc (7), clamped in a bundle-like manner.

9. The device of claim 7, wherein said movable bridge (16) is adapted to be brought into abutment with a pair of fixed contacts (10a, 10b) that pass through said lid (4) and protrude for a portion thereof from the lid (4) itself.

10. A method for making a temperature limiting device, characterized in that it envisages a. providing a temperature limiting device (1 ) comprising an outer container (2) of conductive material, defining a cup-shaped housing (3) closed by a lid (4), inside which there are arranged in a stack a spring snap-in disc (6); a bimetallic disc (7) associated with said spring snap-in disc (6); at least one fixed contact (10) integral with said lid (4) of the outer container(2) and protruding for a portion thereof above the same lid (4); at least one movable contact (11 , 15) integral with said spring snap-in disc (6); b. associating with said temperature limiting device (1 ) a pair of electrical connection cables (13, 14); c. overmoulding a protective cover (15) of insulating material above said outer container (2) of the temperature limiting device (1 ).11 . The method of claim 10, wherein said step of c. overmoulding a protective cover (15) of insulating material provides for completely incorporating said outer container (2) of the temperature limiting device (1 ).

12. The method of claim 10 or 11 , wherein it provides for overmoulding said protective cover (15) by means of a technopolymer of the polyphenylene sulfide (PPS) type and the like.

13. The method of any one of claims 10 to 12, wherein said step of c. overmoulding a protective cover (15) of insulating material provides for c1. inserting the device to be covered into a special mould, positioned below an injection press; c2. bringing the insulating material to be injected to the liquid state; c3. Injecting the insulating material in the liquid state into the cavity of said mould; c4. allowing the insulation material injected into said mould to solidify until the final shape is acquired.

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