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-on disc (6) and a bimetallic disc (7) are arranged in superimposed fashion. The cover (4) and the spring snap-on disc (6) of the outer container (2) respectively carry a fixed contact (10) and at least one movable contact (11, 16) in one piece. The outer container (2) is covered with a protective cover (15) over-molded from an insulating material.

Description

TECHNICAL FIELD

[0001] The present invention relates to a temperature limiting device for protecting electrical equipment and the like, and a method for implementing the device. BACKGROUND

[0002] In the technical field of production of temperature limiters suitable for guaranteeing thermal protection of electrical equipment or of components of equipment such as electric motors, the overheat protection temperature limiters currently known in use are based on the use of a bimetallic disc adapted to switch the configuration of a spring snap-in disc, thus causing the corresponding closure or opening of the circuit of the equipment to be protected. In the specific field, such temperature limiting devices are also known as bimetallic thermal switches.

[0003] In particular, the bimetallic disc is able to switch from a low temperature position to a high temperature position, at which it causes the opening of the circuit by acting on the spring snap-in disc, thus interrupting the heating.

[0004] For example, such a temperature limiting device is shown in European patent EP 0 678 891.

[0005] The temperature limiter comprises an outer container which defines a cup-shaped housing closed by a lid, inside which a bimetallic disc and a spring snap-in disc are arranged in superimposed form. The lid carries the fixed contact of the switch, while the spring snap-in disc carries the movable contact. In normal operating conditions, i.e. at low temperatures, the movable contact is pressed against the fixed contact by the spring snap-in disc, thus causing the closure of the circuit, allowing the passage of the current. On the other hand, when the temperature exceeds a preset threshold, the position of the bimetallic disc is reversed, causing the displacement of the spring snap-in disc. In this case, the movable contact is separated from the fixed contact, the circuit is opened, thus interrupting the passage of the current and the heating.

[0006] In use, the bimetallic thermal switch is usually inserted inside the stator winding of an electric motor during the production of the motor, so that the thermal switch is directly thermally coupled with the winding.

[0007] However, it is important to note that, in order to ensure mechanical stability and fixing on the winding, it is often necessary to use chemical substances such as solvent-based paints, water-based paints, resins, etc. to impregnate the stator of the electric machine. Therefore, in this production step, there is a high risk that the chemicals used to impregnate the stator will penetrate into the bimetallic thermal switch, causing malfunctions in the switch itself. To prevent this risk, the bimetallic thermal switch is usually protected by a resin cover applied in a dosed or cast manner. Once the resin cover has solidified, it coats the parts of the switch that are at risk of being penetrated, thus ensuring safe use of the switch even in the event of impregnation with the aforementioned chemical substances. Essentially, the cover is made by applying drops of resin on the device by means of a drop dispenser.

[0008] The existing documents WO 2023 / 286102, WO 2023 / 286103, DE 10 2004 015 394 and DE 102013 102 006 show respectively a bimetallic thermal switch having a resin cover applied on the top by dosed or cast manner.

[0009] For this purpose, resins that polymerize as a function of temperature, such as one-component epoxy resins or two-component epoxy resins, silicon resins, etc., are currently used for the surface treatment of bimetallic thermal switches. However, these resins have significant limitations in terms of production process and final product quality.

[0010] In terms of production process, the resins used require the use of a furnace to complete polymerization, or long maturation times at room temperature. This therefore causes the production flow to be interrupted to complete this thermal treatment, whether at room temperature or at high temperature. Since it is not possible to achieve a continuous production flow, the production process is affected by this interruption.

[0011] In addition, due to the temperature itself, this type of resin is usually highly susceptible to room temperature, with a high variation in viscosity. This characteristic requires the temperature of the work area to be regulated, avoiding the same resin being almost liquid during the hot periods of the year and very viscous during the cold periods, thus bringing significant complexity to dosing and process steps.

[0012] In this specific field, there is another problem that arises with the type of product used and the process implemented in the prior art, known as the "capillary phenomenon". In fact, it is found that, when this process is implemented on a bimetallic thermal switch, the resin in liquid form penetrates into the gaps present between the parts, in particular between the cover and the outer container, in the part where it is riveted, or between the cover and the rivet that is the electrical contact.

[0013] The higher the liquid degree of the resin, the longer the time of the first polymerization, so-called "gel time", and the more evident this phenomenon. If the resin penetrates inside the bimetallic thermal switch, it prevents it from working properly, thus seriously compromising the safety of the equipment in which it is installed.

[0014] Another problem found in practice is that, before impregnation, the heads of the windings are subjected to strong pressures to be finally shaped, which can cause damage to the temperature limiting device, thus causing its failure. SUMMARY

[0015] The task of the present invention is to solve the above-mentioned problems by designing a temperature limiting device having a coating of the outer container which is able to provide the best protection against external agents.

[0016] Within the scope of this task, another object of the present invention is to provide a temperature limiting device provided with a coating which is able to prevent the entry of chemicals and other liquid substances inside the casing containing the operating components of the device.

[0017] Another object of the present invention is to provide a temperature limiting device which is simple in structure and function concept, absolutely reliable in function, widely usable and relatively low in cost.

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

[0019] The temperature limiting device comprises an outer container which defines a cup-shaped casing closed by a lid, inside which a spring-clip disc and a bimetallic disc are arranged in superimposed form.

[0020] Preferably, the outer container is made of an electrically conductive material.

[0021] Preferably, the lid is made of an insulating material.

[0022] Alternatively, the lid is made of a combination of materials, isolated with respect to the outer container.

[0023] The bimetallic disc is axially associated with the spring-clip disc.

[0024] The temperature limiting device comprises at least one fixed contact, integral with the lid of the outer container and partly protruding above the lid, and at least one movable contact, integral with the spring-clip disc.

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

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

[0027] According to the present application, the temperature limitation device is externally coated by a protective cover formed by overmoulding of an insulating material.

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

[0029] Preferably, the insulating material is an engineering polymer.

[0030] Preferably, the insulating material is a thermoplastic material of the polyphenylene sulfide (PPS) type or the like.

[0031] Preferably, said protective cover at least partially incorporates the connection cable of the temperature limitation device.

[0032] According to an embodiment of the present application, said movable contact comprises a movable bridge which is integral with the spring snap disc and with the bimetallic disc by axial fixing means, so as to be clamped in a bundle-like manner.

[0033] Preferably, the movable bridge has a circular shape and is adapted to abut against the pair of fixed contacts.

[0034] The present application also relates to a method for implementing a temperature limitation device, which envisages: a. providing a temperature limitation device comprising: an outer container made of an electrically conductive material, which defines a cup-shaped casing closed by a lid, inside which there is a spring snap disc and a bimetallic disc associated with the spring snap disc, arranged in superimposed form; at least one fixed contact integral with the lid of the outer container and protruding in part above said lid; at least one movable contact integral with the spring snap disc; b. associating said temperature limitation device with a pair of electric connection cables; c. overmoulding on said outer container of said temperature limitation device a protective cover made of an insulating material.

[0035] In particular, the step c. of overmoulding a protective cover made of an insulating material provides the following: c1. inserting the device to be covered into a specific mould positioned below the injection moulding machine; c2. converting the insulating material to be injected into a liquid state; c3. injecting the insulating material in a liquid state into the cavity of the mould; c4. solidifying the insulating material injected into the mould until the final shape is obtained.

[0036] Advantageously, the overmoulding step c. of the protective cover made of insulating material envisages a complete overmoulding of the outer container of the temperature limiting device.

[0037] Advantageously, the method involved provides for overmoulding the protective cover by means of an engineering polymer of the polyphenylene sulphide (PPS) type or the like. BRIEF DESCRIPTION OF DRAWINGS

[0038] The details of the application will be more evident from the detailed description of a preferred embodiment of the temperature limiting device, illustrated by way of example in the accompanying drawings, in which: Figure 1 a schematic axial section view of a temperature limiting device according to the present application is shown; Figure 2 schematic axial section views of different embodiments of a temperature limiting device according to the present application are shown. DETAILED DESCRIPTION

[0039] With reference first of all to Figure 1 , the temperature limiting device according to the present application is indicated as a whole with 1.

[0040] The temperature limiting device comprises an outer container 2 which defines a cup-shaped casing 3. The casing 3 of the outer container 2 is closed at the top by a lid 4 which is fixed by a peripheral folded edge 5 of the outer container 2. The outer container 2 is made of an electrically conductive material, for example brass. The lid 4 is made of an insulating material, for example a ceramic material or the like, or alternatively of a combination of materials, even of metal, but which is insulating with respect to the outer container 2.

[0041] Inside the casing 3 of the outer container 2, a spring snap disc 6 and a bimetallic disc 7 are arranged in superimposed form. In the normal operating condition, the spring snap disc 6 has a slightly arched shape and rests perimetrically on the bottom of the casing 3 of the outer container 2; the bimetallic disc 7 has a more arched shape and rests perimetrically on the edge of the spring snap disc 6.

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

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

[0044] The lid 4 carries in a known manner a fixed contact 10 of an axially inserted thermal switch; the spring-clip disc 6 in turn carries a movable contact 11 of an axially inserted thermal switch. The fixed contact 10 projects below the lid 4; the movable contact 11 projects above the bimetallic disc 7 through an axial hole formed in said bimetallic disc 7.

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

[0046] Under normal operating conditions, i.e. at low temperatures, the movable contact 11 is elastically pushed against the fixed contact 10 by the spring-clip disc 6, thus closing the electrical circuit and allowing the passage of current, as described below.

[0047] The temperature limiting device preferably comprises a separation ring 12 made of a metallic material, which is arranged above the bimetallic disc 7 and is adapted to engage with the 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 spacer 8. On the other hand, in the absence of the annular spacer 8, the separation ring 12 is clamped directly between the bimetallic disc 7 and the lid 4.

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

[0050] According to the present application, the outer container 2 is externally covered with a protective cover 15 made by overmoulding of a suitable insulating material. In particular, said insulating material is suitably an engineering polymer of the polyphenylene sulfide (PPS) type. PPS is a thermoplastic material with excellent mechanical properties, heat resistance and chemical resistance.

[0051] In particular, the overmoulding of the insulating material is carried out by inserting the device to be covered into a specific mould located below an injection moulding machine, while liquefying the polymer and subsequently injecting it into the mould cavity, and solidifying the polymer in the cavity to obtain the final shape.

[0052] In the case illustrated, the protective cover 15 advantageously extends so as to completely cover the outer container 2, also sheathing the cables 13, 14 connected to the outer container 2 and to the fixed contact 10, respectively. However, it is also possible to provide that the protective cover 15 extends so as to only partially cover the outer container 2, in particular at least covering the lid 4, the folded edge 5 of the outer container 2, the portion of the fixed contact 10 projecting above the lid 4 and the cables 13, 14 connected to the outer container 2 and to the fixed contact 10.

[0053] From the above description, the operation of the temperature limiting device of the present application is easily understood.

[0054] In normal operating conditions, the spring snap disc 6 and the bimetallic disc 7 are located between the bottom of the housing 3 defined by the outer container 2 made of electrically conductive material and the lid 4 integrated with the fixed contact 10 and are locked.

[0055] The spring snap disc 6 constitutes an element through which the electric current passes and supports the movable contact 11 so as to keep it pressed against the fixed contact 10 under constant pressure.

[0056] The bimetallic disc 7 is supported by the movable contact 11, which passes through it, and is able to react to any variation in the temperature of the device to be protected. When a predetermined switching temperature is reached, the bimetallic disc 7 snaps rapidly to the opposite position, concave downwards, thus pushing the spring snap disc 6 downwards.

[0057] In this way, the contact between the fixed contact 10 and the movable contact 11 is momentarily interrupted, thus interrupting the increase in the temperature of the device to be protected. Conversely, when the temperature decreases and reaches the normal value of the preset operation, the bimetallic disc 7 snaps back to the initial position again and the contact is closed.

[0058] Figure 2 Different embodiments of the temperature limiting device are shown, in which the lid 4 of the outer container 2 carries a pair of fixed contacts, indicated with 10a and 10b for clarity. The fixed contacts 10a and 10b pass through the lid 4 in a position parallel to each other and portions of the fixed contacts 10a and 10b project from the lid 4 itself.

[0059] The fixed contacts 10a and 10b are associated with the electric connection cables 13, 14 of the device, respectively. Preferably, the cables 13, 14 are formed in one piece with the fixed contacts 10a and 10b by means of suitable welding elements 19.

[0060] Inside the housing 3 defined by the outer container 2, a movable bridge 16 is arranged in a circular shape, adapted to abut against the fixed contacts 10a and 10b. The movable bridge 16 is formed in one piece with the spring snap disc 6 and the bimetallic disc 7 by means of an axial rivet 17, so as to be clamped in a bundle-like manner. Essentially, the function of the movable bridge 16 is the same as that performed by the movable contact 11 in the previously described solution.

[0061] Preferably, the movable bridge 15 is made of brass, bronze or similar material, coupled with a noble metal or alloy thereof, such as silver or similar, with or without a noble metal coating.

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

[0063] As in the previous case, if the temperature of the device to be protected varies, exceeding the predetermined switching temperature, the bimetallic disc 7 snaps quickly to the opposite position, concave downwards, thus pushing the spring snap disc 6 downwards, causing the contact between the movable bridge 16 and the fixed contacts 10a and 10b to be broken.

[0064] In the solution described above, the outer container 2 of the device is completely or partially covered externally by a protective cover 15 made by overmoulding of an engineering polymer of the polyphenylene sulfide (PPS) type or the like.

[0065] The temperature limiting device according to the present application achieves the purpose of ensuring protection of the device from the effects of liquid or dust penetration and from mechanical stresses.

[0066] This result is achieved by the inventive concept of obtaining the protective cover of the device by overmoulding of an insulating material, preferably consisting of an engineering polymer of the polyphenylene sulfide (PPS) type or the like, thus forming a hermetic and highly resistant shell around the outer container and the electrical connection cable.

[0067] In particular, the use of a suitable engineering polymer, such as PPS, allows a higher temperature range of use compared to the resins traditionally used.

[0068] The production process by overmoulding in a specific mould is therefore very different from the traditional process of applying the resin on a limited portion of the bimetallic thermal switch by dosing or pouring.

[0069] According to an advantageous aspect of the present application, the production process by overmoulding does not require the use of a furnace to complete the polymerisation at high temperature, nor does it require the pauses due to the polymerisation at room temperature; rather, it allows to obtain the finished product in a time span of a few seconds using an injection moulding machine and a suitable mould.

[0070] The temperature limiting device described by way of example can be modified and varied in many different ways according to different requirements.

[0071] In the practical use of the application the materials used, as well as the shapes and dimensions, can be any according to requirements.

[0072] In the event that the technical features mentioned in each claim are accompanied by reference signs, the sole purpose of these reference signs is to improve the understanding of the claims, and therefore they do not have any limiting effect on the scope of each element illustrated by means of these reference signs.

Claims

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

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

3. The apparatus of claim 1 or 2, wherein, - the insulating material is an engineering polymer.

4. The apparatus of claim 3, wherein, - the insulating material is a thermoplastic material of the polyphenylene sulfide (PPS) type.

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

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

7. The device of any of the preceding claims, wherein, - the device comprises a separation ring (12) made of a metal material, arranged above the bimetallic disc (7) and adapted to engage with a peripheral portion of the bimetallic disc (7) itself.

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

9. The apparatus of claim 7, wherein, - the movable bridge (16) is adapted to abut against a pair of fixed contacts (10a, 10b) passing through the lid (4) and of which a portion protrudes from the lid (4) itself.

10. A method for manufacturing a temperature limiting device, characterized by, - the method provides for performing the following operations: a. providing a temperature limiting device (1) comprising: an outer container (2) made of electrically conductive material, defining a cup-shaped housing (3) closed by a lid (4), inside which there are arranged in superimposed form: a spring snap disc (6); a bimetallic disc (7) associated with the spring snap disc (6); at least one fixed contact (10) integral with the lid (4) of the outer container (2) and of which a portion protrudes above the lid (4); at least one movable contact (11, 15) integral with the spring snap disc (6); b. associating the temperature limiting device (1) with a pair of electrical connection cables (13, 14); c. overmoulding the outer container (2) in insulating material so as to form a protective cover (15) that completely covers the outer container (2) of the temperature limiting device (1). c. Overmoulding a protective cover (15) made of insulating material on the outer container (2) of the temperature limiting device (1).

11. The method of claim 10, wherein, The step c. of overmoulding a protective cover (15) made of insulating material provides a complete overmoulding of the outer container (2) of the temperature limiting device (1).

12. The method of claim 10 or 11, wherein, The method provides for overmoulding the protective cover (15) by means of an engineering polymer of the polyphenylene sulfide (PPS) type or the like.

13. The method of any one of claims 10 to 12, wherein, The step c. of overmoulding a protective cover (15) made of insulating material provides: c1. inserting the device to be covered into a specific mould located below an injection moulding machine; c2. converting the insulating material to be injected into a liquid state; c3. injecting the insulating material in a liquid state into the cavity of the mould; c4. solidifying the insulating material injected into the mould until the final shape is obtained.

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