A circuit protection element

Abstract

This invention discloses a circuit protection element, comprising a housing, an elastic arm, a fixed arm, and a PTC fuse. One end of the elastic arm has a movable contact that extends into the housing; one end of the fixed arm extends into the housing and has a fixed contact, which contacts the movable contact. The PTC fuse comprises, from top to bottom, a first shape memory alloy layer, a PTC thermistor layer, and a second shape memory alloy layer. The first shape memory alloy layer is attached to the elastic arm, and the second shape memory alloy layer is attached to the fixed arm. When the temperature of the first and second shape memory alloy layers rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch, generating a mechanical thrust to push the elastic arm upward, thus separating the movable contact from the fixed contact. This circuit protection element can withstand high current operation, has dual overcurrent and overtemperature protection functions, an automatic reset function, and can maintain a small current under abnormal conditions.

Description

Technical Field

[0001] This invention belongs to the field of circuit protection technology, and particularly relates to a circuit protection element. Background Technology

[0002] In modern electrical and electronic systems, circuit protection is an indispensable part of ensuring the safe and reliable operation of equipment. With the development of technology and the expansion of applications, the requirements for circuit protection components are also increasing. Currently, there are three main types of widely used circuit protection components: positive temperature coefficient (PTC) thermistors, fuses, and circuit breakers. For PTC thermistors, the impedance is low at room temperature, but when the temperature exceeds the Curie temperature, the impedance increases sharply, effectively reducing the current and protecting the circuit. Fuses have a built-in alloy fusible element; when the circuit current increases sharply, the alloy fusible element melts at high temperature, thus cutting off the circuit. Circuit breakers, when the temperature reaches a set point, use the mechanical action of built-in metal fittings to separate the movable contacts from the fixed contacts, thereby cutting off the circuit.

[0003] However, all of the aforementioned circuit protection components have their own drawbacks. For example, a PTC thermistor is a protection element based on the positive temperature coefficient effect of materials. Its characteristic is that it exhibits low impedance under normal operating conditions, allowing current to flow smoothly. However, when the ambient or internal temperature rises to a certain threshold, namely the Curie point, its impedance increases rapidly, effectively limiting the current flowing through it and preventing overcurrent damage to the circuit. Furthermore, the PTC thermistor can automatically return to its low-resistance state after the temperature returns to normal. However, in high-current applications, its relatively high impedance may lead to significant power loss, affecting system efficiency. Fuses, on the other hand, are disposable products. After the alloy molten element melts, a new component must be replaced, resulting in resource waste and increased operating costs. For circuit breakers, when they operate, the current is completely cut off, and the circuit completely stops working. However, for some devices, such as battery management systems, it is desirable for circuit protection components to provide a small current after implementing their protection function to maintain the device's basic functions. In summary, while existing circuit protection components each have their own advantages, they also have some limitations, especially in dealing with high current loads, reducing resource consumption, and meeting the needs of special application scenarios.

[0004] Therefore, there is an urgent need for a circuit protection element to address the shortcomings of existing technologies. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a circuit protection element that can not only withstand high current operation, but also integrates a dual protection mechanism for overcurrent and overtemperature, and has an automatic reset function to reduce resource consumption; in addition, it can maintain a small current in abnormal conditions to prevent complete power failure; these characteristics make the circuit protection element particularly suitable for special application scenarios and in line with the development trend of miniaturization and micro-miniaturization of electronic components.

[0006] To achieve the above objectives, the present invention provides a circuit protection element, including a housing; an elastic arm, one end of which has a movable contact extending into the housing, and the other end extending out from one side of the housing; a fixed arm, one end of which extends into the housing, and the other end extending out from the other side of the housing, the fixed arm having a fixed contact, the movable contact and the fixed contact being in contact; the elastic arm and the fixed arm are each independently made of a copper-based alloy or a nickel-based alloy, and the movable contact and the fixed contact are both made of conductive noble metals; and a PTC fuse, the PTC fuse being located at... Inside the housing, the PTC fuse comprises, from top to bottom, a first shape memory alloy layer, a PTC thermistor layer, and a second shape memory alloy layer. The PTC thermistor layer has a flexible structure. The first shape memory alloy layer is attached to the elastic arm, and the second shape memory alloy layer is attached to the fixed arm. When the temperature of the first and second shape memory alloy layers rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch, generating a mechanical thrust to push the elastic arm upward, thereby separating the movable contact from the fixed contact.

[0007] Compared with the prior art, the circuit protection element of the present invention has the following beneficial effects:

[0008] 1. The flexible arm and fixed arm of this application are made of highly conductive copper-based alloy or nickel-based alloy, and the movable contact and fixed contact are made of conductive noble metal. This ensures that under normal working conditions, most of the current flows through the flexible arm, movable contact, fixed contact and fixed arm, while only a very small amount of current flows through the PTC fuse. At the same time, because these alloys have low resistance characteristics, they can provide efficient current conduction under high current conditions and reduce heat generation caused by resistance, thereby meeting the requirements of high current operation.

[0009] 2. The PTC fuse structure of the present invention comprises, from top to bottom, a first shape memory alloy layer, a PTC thermistor layer, and a second shape memory alloy layer. The first shape memory alloy layer is attached to the elastic arm, while the second shape memory alloy layer is attached to the fixed arm. Under normal operating conditions, since the elastic arm, movable contact, fixed contact, and fixed arm are all good conductors of heat and are integrated and located within the housing, the temperature of these components remains consistent. However, when the circuit encounters abnormal conditions such as overheating or overcurrent, the temperature of each metal component rises rapidly, causing the temperature of the first and second shape memory alloy layers attached to them to rise accordingly. Once the temperature reaches the transformation temperature of the shape memory alloy, the first and second shape memory alloy layers undergo a phase transition, driving the PTC fuse to change from a flat shape to an arc shape with a notch, thereby generating a mechanical thrust to lift the elastic arm upward, thus separating the movable contact from the fixed contact. At this time, the current is guided to the PTC fuse, thereby activating the secondary protection mechanism. If the current continues to increase, causing the internal temperature of the fuse to rise to the Curie point, the internal resistance of the PTC thermistor layer increases sharply, resulting in a significant decrease in current, but still maintaining a small level to prevent a complete power outage and ensure the basic operation of the device. During this process, the PTC fuse continues to be energized and heats up, which helps maintain the specific shape of the first and second shape memory alloy layers at high temperatures. This also provides technicians with ample time for troubleshooting and repair, avoiding the inconvenience caused by a complete power outage. Therefore, the circuit protection element of this invention can meet the needs of special application scenarios. After the circuit fault is cleared, as the current returns to normal, the internal temperature of the device gradually decreases. When the temperature drops below the transformation temperature of the shape memory alloy, the PTC fuse deforms again, causing the elastic arm to reset and the movable contact to re-contact the fixed contact, restoring the circuit to normal operation. This automatic reset characteristic reduces the need to replace the fuse, thus reducing resource consumption.

[0010] 3. The PTC fuse has a flat shape at low temperatures, which allows it to fit more effectively with the elastic and fixed arms, forming good contact and improving heat conduction efficiency, thereby increasing the sensitivity of temperature response. Specifically, if the ambient temperature rises abnormally, causing the internal temperature of the circuit protection element to rise, it will also trigger the PTC fuse to deform, causing the movable contact to separate from the fixed contact. At this time, the current is directed to the PTC fuse, thereby activating the secondary protection mechanism to prevent the equipment from being damaged by high temperature. When the ambient temperature returns to the normal range, the PTC fuse automatically resets, and the circuit resumes normal operation. Therefore, the circuit protection element of this invention not only has overcurrent protection function but also overtemperature protection function. That is, the circuit protection element of this invention realizes the integrated design of temperature control metal element and PTC thermistor. Its integrated design can effectively save space and meet the current development needs of miniaturization and micro-miniaturization of electronic components.

[0011] Preferably, when the temperature of the first shape memory alloy layer and the second shape memory alloy layer rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch facing the fixed arm, so that the two ends of the PTC fuse contact the fixed arm and the middle section of the PTC fuse contact the elastic arm, thereby separating the movable contact from the fixed contact.

[0012] Preferably, when the temperature of the first shape memory alloy layer and the second shape memory alloy layer rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch facing the elastic arm, so that the two ends of the PTC fuse contact the elastic arm and the middle section of the PTC fuse contact the fixed arm, thereby separating the movable contact from the fixed contact.

[0013] Preferably, the thickness of the flexible arm and the fixed arm are each independently 50 to 500 μm.

[0014] Preferably, the thickness of the first shape memory alloy layer and the second shape memory alloy layer are each independently 50 to 300 μm.

[0015] Preferably, the raw materials for preparing the PTC thermistor layer, by mass parts, include 50-110 parts of a polymer, 20-40 parts of a conductive filler, 0.1-1 parts of a coupling agent, 0.1-3 parts of a dispersant, and 1-3 parts of a flame retardant. The polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butene-styrene copolymer, polydimethylsiloxane, polyethylene terephthalate, ethylene-propylene rubber, butadiene-acrylonitrile copolymer, silicone rubber, nitrile rubber, natural rubber, high-density polyethylene, low-density polyethylene, polypropylene, polyvinylidene fluoride, polystyrene, polytetrafluoroethylene, chloroprene rubber, and polycarbonate.

[0016] Preferably, the materials of the first shape memory alloy layer and the second shape memory alloy layer are each independently selected from at least one of nickel-titanium alloys, copper alloys and iron alloys.

[0017] Preferably, the materials of the flexible arm and the fixed arm are each independently selected from Cu-Ni-Si-Mg alloys, Cu-Ni-Si-P alloys, Cu-Ni-Sn-P alloys, Cu-Ni-Co-Si alloys, Cu-Ni-Si alloys, Cu-Zr alloys, Cu-Be alloys, Cu-Ni-Be alloys, Cu-Sn alloys, Cu-Mg-P alloys, Cu-Zn-Sn alloys, Cu-Fe-P alloys, Cu-Fe-Mg-P alloys, or Ni-Be alloys.

[0018] Preferably, the movable contact and the fixed contact are each made of at least one of gold, silver, and a gold-silver alloy.

[0019] Preferably, the PTC fuse comprises, from top to bottom, a first shape memory alloy layer, a first connection layer, a first metal foil layer, a PTC thermistor layer, a second metal foil layer, a second connection layer, and a second shape memory alloy layer.

[0020] Preferably, the materials of the first metal foil layer and the second metal foil layer are each independently selected from at least one of Cu, Ni, Al, Au and Ag; the thicknesses of the first metal foil layer and the second metal foil layer are each independently 5 to 35 μm. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the circuit protection element of the present invention under normal operating conditions.

[0022] Figure 2 for Figure 1 The circuit diagram of the circuit protection element under normal operating conditions.

[0023] Figure 3 This is a schematic diagram of the circuit protection element of the present invention under abnormal operating conditions.

[0024] Figure 4 for Figure 3 Circuit diagram of circuit protection components under abnormal operating conditions.

[0025] Figure 5 This refers to the martensitic phase of the first shape memory alloy layer of the present invention at low temperature.

[0026] Figure 6 This refers to the austenitic phase of the first shape memory alloy layer of the present invention at high temperature.

[0027] Figure 7 This is another schematic diagram of the circuit protection element of the present invention under abnormal operating conditions.

[0028] Figure 8 This is another schematic diagram of the circuit protection element of the present invention under abnormal operating conditions.

[0029] Figure 9 This is another schematic diagram of the circuit protection element of the present invention under abnormal operating conditions.

[0030] Figure 10 This is a schematic diagram of the structure of the PTC fuse of the present invention.

[0031] Figure 11 This is another structural schematic diagram of the PTC fuse of the present invention. Detailed Implementation

[0032] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0033] To address the limitations of existing circuit protection components in handling high-current loads, reducing resource consumption, and meeting the needs of special application scenarios, please refer to... Figures 1-4This invention provides a circuit protection element 100, which can be used as a circuit protection component in portable electronic products such as mobile communication devices and laptops. The circuit protection element 100 includes an elastic arm 11, a fixed arm 12, a PTC fuse 13, and a housing 14. One end of the elastic arm 11 is provided with a movable contact 111 and extends into the housing 14, while the other end of the elastic arm 11 extends out from one side of the housing 14. One end of the fixed arm 12 extends into the housing 14, while the other end of the fixed arm 12 extends out from the other side of the housing 14. The fixed arm 12 is provided with a fixed contact 121, and the movable contact 111 and the fixed contact 121 are in contact. The flexible arm 11 and the fixed arm 12 are each made of copper-based alloy or nickel-based alloy, while the movable contact 111 and the fixed contact 121 are both made of conductive noble metal. That is, the flexible arm 11, the fixed arm 12, the movable contact, and the fixed contact 121 are all made of highly conductive metal. This ensures that under normal working conditions, most of the current flows through the flexible arm 11, the movable contact 111, the fixed contact 121, and the fixed arm 12, while only a very small amount of current flows through the PTC fuse 13. At the same time, since the materials used to make the flexible arm 11, the fixed arm 12, the movable contact 111, and the fixed contact 121 have low resistance characteristics, they can provide efficient current conduction under high current conditions and reduce heat generation caused by resistance, thereby meeting the requirements of high current operation. In addition, the PTC fuse 13 is located inside the housing 14. The PTC fuse 13 includes a first shape memory alloy layer 132, a PTC thermistor layer 131, and a second shape memory alloy layer 133 from top to bottom. The PTC thermistor layer 131 has a flexible structure. The first shape memory alloy layer 132 is attached to the elastic arm 11, and the second shape memory alloy layer 133 is attached to the fixed arm 12. Under normal working conditions, since the elastic arm 11, the movable contact 111, the fixed contact 121, and the fixed arm 12 are all good conductors of heat and are connected as one unit and located inside the housing 14, the temperature of these components remains consistent. When the circuit encounters abnormal conditions such as overheating or overcurrent, the temperature of each metal component rises rapidly, causing the temperature of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 that are attached to it to rise accordingly. Once the temperature reaches the transformation temperature of the shape memory alloy, the first shape memory alloy layer 132 and the second shape memory alloy layer 133 will undergo a phase change, driving the PTC fuse 13 to change from a flat shape to an arc shape with a notch, thereby generating a mechanical thrust to push the elastic arm 11 upward, thereby separating the movable contact 111 from the fixed contact 121. At this time, the current is guided to the PTC fuse 13 to activate the secondary protection mechanism.If the current continues to increase, causing the internal temperature of the PTC fuse 13 to rise to the Curie point, the internal resistance of the PTC thermistor layer 131 increases sharply, resulting in a significant decrease in current, but still maintaining a small level to avoid a complete power outage and ensure the basic operation of the device. During this process, the PTC fuse 13 continues to be energized and heats up, which helps maintain the specific shape of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 at high temperatures. This also provides technicians with sufficient time for troubleshooting and repair, avoiding the inconvenience caused by a complete power outage. Therefore, the circuit protection element 100 of the present invention can meet the needs of special application scenarios. After the circuit fault is cleared, as the current returns to normal, the internal temperature of the device gradually decreases. When the temperature drops below the transformation temperature of the shape memory alloy, the PTC fuse 13 deforms again, causing the elastic arm 11 to reset, so that the movable contact 111 re-contacts the fixed contact 121, and the circuit returns to normal operation. This automatic reset feature reduces the need to replace the fuse, so the circuit protection element 100 of the present invention can reduce resource consumption.

[0034] Furthermore, the fixed arm 12 containing the fixed contact 121, the PTC fuse 13, and the elastic arm 11 containing the movable contact 111 are arranged as follows: Figure 1The structures shown are stacked from bottom to top and fixed and encapsulated using a housing 14, thereby obtaining the circuit protection element 100 of the present invention. The materials of the elastic arm 11 and the fixed arm 12 are each independently selected from Cu-Ni-Si-Mg alloys, Cu-Ni-Si-P alloys, Cu-Ni-Sn-P alloys, Cu-Ni-Co-Si alloys, Cu-Ni-Si alloys, Cu-Zr alloys, Cu-Be alloys, Cu-Ni-Be alloys, Cu-Sn alloys, Cu-Mg-P alloys, Cu-Zn-Sn alloys, Cu-Fe-P alloys, Cu-Fe-Mg-P alloys, or Ni-Be alloys; preferably, the materials of both the elastic arm 11 and the fixed arm 12 are Cu-Ni-Si-Mg alloys, and the chemical composition of the Cu-Ni-Si-Mg alloy, calculated by mass percentage, includes: 3.0% Ni, 0.65% Si, 0.15% Mg, and the balance being Cu. Meanwhile, the thickness of the elastic arm 11 and the fixed arm 12 are each independently 50-500 μm, and both the elastic arm 11 and the fixed arm 12 are prepared using cutting and stamping techniques well known in the art. The movable contact 111 and the fixed contact 121 are each made of at least one of gold, silver, and a gold-silver alloy; both the movable contact 111 and the fixed contact 121 are prepared using conventional electroplating or chemical plating techniques. The housing 14 is a plastic housing 14, which can be prepared using conventional integrated injection molding technology, or by first preparing different parts of the housing 14 separately using conventional injection molding methods, and then combining the various parts of the housing 14 into a whole using conventional adhesive methods or ultrasonic welding methods; the injection molding, adhesive, and ultrasonic welding methods used are all methods well known to those skilled in the art.

[0035] Please continue reading. Figure 1 The PTC fuse 13 is flat at low temperatures, allowing it to more effectively fit with the elastic arm 11 and the fixed arm 12, forming good contact and improving heat conduction efficiency, thereby increasing the sensitivity of temperature response. Specifically, if the ambient temperature rises abnormally, causing the internal temperature of the circuit protection element 100 to rise, the PTC fuse 13 will also be triggered to deform, causing the movable contact 111 to separate from the fixed contact 121. At this time, the current is directed to the PTC fuse 13, thereby activating the secondary protection mechanism to prevent the equipment from being damaged due to high temperature. When the ambient temperature drops back to the normal range, the PTC fuse 13 automatically resets, and the circuit resumes normal operation. Therefore, the circuit protection element 100 of the present invention not only has overcurrent protection function but also overtemperature protection function. That is, the circuit protection element 100 of the present invention realizes the integrated design of temperature control metal element and PTC thermistor. Its integrated design can effectively save space and meet the current development needs of miniaturization and micro-miniaturization of electronic components.

[0036] Specifically, the first shape memory alloy layer 132 of the present invention has a double-layer shape memory effect, and correspondingly, the second shape memory alloy layer 133 also has a double-layer shape memory effect. More specifically, when the temperature rises to a specific transition temperature, the shape memory alloy layer will change from... Figure 5 The martensitic phase transformation shown at low temperature Figure 6 The austenitic phase is shown at high temperatures; conversely, when the temperature drops below the transformation temperature, the shape memory alloy layer can revert from the austenitic phase back to the original martensite phase. This bidirectional phase transformation characteristic allows the first shape memory alloy layer 132 and the second shape memory alloy layer 133 to reversibly change their shape with temperature changes. Simultaneously, the PTC thermistor layer 131 of this invention has a flexible structure, and the materials of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 also possess high elasticity. This gives the PTC fuse 13 flexible and bendable characteristics, allowing the phase transformation of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 to drive the PTC fuse 13 from a flat shape to an arc shape with a notch.

[0037] Please see Figure 7 When the temperatures of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 rise to their respective deformation temperatures, the PTC fuse 13 changes from a flat state to an arc shape with a notch facing the fixed arm 12. This causes both ends of the PTC fuse 13 to contact the fixed arm 12 and the middle section of the PTC fuse 13 to contact the elastic arm 11, resulting in the movable contact 111 separating from the fixed contact 121. Alternatively, it is also possible to... Figure 7 The placement direction of the PTC fuse 13 is reversed. When the temperature of the two shape memory alloy layers reaches their respective deformation temperatures, the PTC fuse 13 will change from a flat state to a shape resembling... Figure 3 As shown, the notch faces the elastic arm 11 in an arc shape. In this case, both ends of the PTC fuse 13 are in contact with the elastic arm 11, while the middle section of the PTC fuse 13 is in contact with the fixed arm 12. This will also cause the movable contact 111 to separate from the fixed contact 121. Therefore, whether the flat PTC fuse 13 is transformed into an arc shape with the notch facing the fixed arm 12 or an arc shape with the notch facing the elastic arm 11, the circuit can be safely disconnected.

[0038] To ensure that the PTC fuse 13 can effectively contact the fixed arm 12 and the elastic arm 11 at high temperatures, the shape of the PTC fuse 13 can be trained using a shape memory alloy. This allows the PTC fuse 13 to flatten at low temperatures, while its ends transform into a shape that changes as the temperature rises. Figure 8The first plane 15 shown is tightly fitted to the fixing arm 12 to ensure good heat conduction and electrical connection. Meanwhile, the middle portion of the PTC fuse 13 not only maintains an arc-shaped design, but the middle section of this arc also forms a [missing information - likely a shape or feature] at high temperatures. Figure 9 The second plane 16 shown will contact and fit with the elastic arm 11; this ensures that the PTC fuse 13 can maintain the effectiveness and stability of the circuit protection function in a high-temperature environment by both making a firm contact with the fixed arm 12 through the first plane 15 at both ends and making good contact with the elastic arm 11 through the second plane 16 in the middle part.

[0039] Specifically, the transverse structure of the PTC fuse 13 of the present invention can be selected in different geometric shapes according to specific application requirements, such as rectangular, elliptical, or circular shapes; the longitudinal structure of the PTC fuse 13 is composed of multiple layers with different functions, and the layers are tightly fitted together. Depending on the number of layers, the PTC fuse 13 can be divided into two types, namely as follows: Figure 10 Structure A shown and as Figure 11 Structure B is shown. Depending on its specific number of layers and functional configuration, each type of PTC fuse 13 can be applied to different application scenarios.

[0040] Specifically, such as Figure 10 As shown, the PTC fuse 13 of structure A has a seven-layer structure, namely a first shape memory alloy layer 132, a first connecting layer 134, a first metal foil layer 136, a PTC thermistor layer 131, a second metal foil layer 137, a second connecting layer 135, and a second shape memory alloy layer 133, with each layer bonded to the others. The first connecting layer 134 connects the first metal foil layer 136 and the first shape memory alloy layer 132, and the second connecting layer 135 connects the second metal foil layer 137 and the second shape memory alloy layer 133. Simultaneously, the first metal foil layer 136 and the second metal foil layer 137 not only provide physical support, ensuring that the PTC thermistor layer 131 can maintain its predetermined shape and position, but also enhance the mechanical stability of the PTC fuse 13. That is, by sandwiching the PTC thermistor layer 131 between the first metal foil layer 136 and the second metal foil layer 137, deformation or displacement of the PTC fuse 13 during use can be effectively prevented. Accordingly, the PTC fuse 13 of structure B has a three-layer structure, consisting of a first shape memory alloy layer 132, a PTC thermistor layer 131, and a second shape memory alloy layer 133 from top to bottom, with each layer bonded to the other. Of course, for the PTC fuse 13 of structure B, the first shape memory alloy layer 132 and the second shape memory alloy layer 133 also ensure that the PTC thermistor layer 131 can maintain its predetermined shape and position.

[0041] Specifically, the thickness of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 is independently 50-300 μm; the material of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 is independently selected from at least one of nickel-titanium alloys, copper alloys and iron alloys; more specifically, the material of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 is independently selected from at least one of Ni-Ti alloys, Ni-Ti-Cu alloys, Ni-Ti-Co alloys, Ni-Ti-Fe alloys, Ni-Ti-Nb alloys, Cu-Zn alloys, Cu-Zn-Al alloys, Cu-Zn-Sn alloys, Cu-Zn-Si alloys, Cu-Zn-Ga alloys, Cu-Sn alloys, Fe-Pt alloys, Fe-Mn-Si alloys, Fe-Ni-Co-Ti alloys, Fe-Mn-Al-Ni alloys, and Fe-C-Mn-Si-Cr-Ni alloys. Furthermore, the materials of the first metal foil layer 136 and the second metal foil layer 137 are each independently selected from at least one of Cu, Ni, Al, Au and Ag; and the thicknesses of the first metal foil layer and the second metal foil layer are each independently 5 to 35 μm.

[0042] Specifically, the raw materials for preparing the PTC thermistor layer 131 include, by mass parts, 50 to 110 parts of polymer, 20 to 40 parts of conductive filler, 0.1 to 1 part of coupling agent, 0.1 to 3 parts of dispersant and 1 to 3 parts of flame retardant. More specifically, the content of the polymer may be, but is not limited to, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, or 110 parts; the content of the conductive filler may be, but is not limited to, 20 parts, 25 parts, 30 parts, 35 parts, 38 parts, or 40 parts; the content of the coupling agent may be, but is not limited to, 0.1 parts, 0.2 parts, 0.3 parts, 0.5 parts, 0.6 parts, 0.8 parts, or 1 part; the content of the dispersant may be, but is not limited to, 0.1 parts, 0.5 parts, 0.8 parts, 1 part, 1.6 parts, 2.0 parts, 2.5 parts, or 3 parts; and the content of the flame retardant may be, but is not limited to, 1 part, 1.5 parts, 1.8 parts, 2 parts, 2.3 parts, 2.6 parts, 2.8 parts, or 3 parts.

[0043] Furthermore, the polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butene-styrene copolymer, polydimethylsiloxane, polyethylene terephthalate, ethylene-propylene rubber, butadiene-acrylonitrile copolymer, silicone rubber, nitrile rubber, natural rubber, high-density polyethylene, low-density polyethylene, polypropylene, polyvinylidene fluoride, polystyrene, polytetrafluoroethylene, chloroprene rubber, and polycarbonate. The conductive filler is at least one of carbon black, carbon fiber, carbon nanotubes, graphite, graphene, metal powder, metal fiber, and metal-ceramic powder. The coupling agent is at least one selected from γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH560), γ-(methacryloyloxy)propyltrimethoxysilane (KH-570), anilinemethyltriethoxysilane (Sj-42), vinyltrimethoxysilane (A-171), bis(dioctyloxypyrophosphate)ethylene titanate (GR-311), triisostearoyl titanate isopropyl (TTS), isopropoxytris(dioctylpyrophosphate)titanate (GR-201), and isopropyl dioleoyloxy(dioctylphosphate)titanate (GR-101). The dispersant is at least one selected from fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyethylene glycol, polyvinylpyrrolidone, ethylene bis-stearamide, and sorbitan fatty acid ester polyoxyethylene ether. The flame retardant is at least one of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), zinc borate (2ZnO·3B2O3·3.5H2O), decabromodiphenyl ether (DBDPO), decabromodiphenyl ethane (DBDPE), octabromoether (TBBPA-OPE), tricresyl phosphate (TCP), triphenyl phosphate (TPP), ammonium polyphosphate (APP), melamine cyanurate (MEL), melamine (MEL), tetrabromobisphenol A (TBBPA), chlorinated paraffin (CP), tricresyl phosphate (TCP), and dimethyl methylphosphonate (DMMP).

[0044] Further, the preparation method of the PTC fuse 13 of structure A includes: (1) mixing the formulated amount of polymer, conductive filler, coupling agent, dispersant and flame retardant by melt blending to obtain a block composite material with PTC effect, wherein the melt blending temperature is 100~300℃ and the blending time is 5min~2h; (2) granulating the block composite material by using a single screw or twin screw extruder to obtain a granular composite material; (3) gradually mixing and melting the granular composite material by a single screw or twin screw extruder, extruding it into a thin sheet PTC thermistor layer 131, passing it through upper and lower rollers, automatically coating it, and bonding a layer of metal foil on the upper and lower sides to obtain a three-layer PTC chip body; (4) using conductive adhesive bonding technology or welding method to tightly bond the two shape memory alloy sheets to the upper and lower surfaces of the PTC chip body, thereby obtaining the PTC fuse 13 of structure A. More specifically, step (1) involves mixing 20-40 parts of high-density polyethylene (Merck, USA), 20-40 parts of low-density polyethylene (Merck, USA), 10-30 parts of ethylene-octene copolymer (Dow Chemical Company, USA), 20-40 parts of carbon black powder (Guangdong Meilian New Materials Co., Ltd.), 0.1-1 parts of γ-aminopropyltriethoxysilane (KH-550) (Hubei Fangde New Materials Co., Ltd.), 0.1-3 parts of fatty alcohol polyoxyethylene ether (Chengdu Huaxia Chemical Reagent Co., Ltd.), and 1-3 parts of Al(OH)3 (Wuhan Jixin Yibang Biotechnology Co., Ltd.) in a mixer for 10-30 minutes at a temperature of 110-150°C and a rotation speed of 50-100 rpm to obtain a block composite material.

[0045] Further, the preparation method of the structure B type PTC fuse 13 includes: (1) mixing the formulated amount of polymer, conductive filler, coupling agent, dispersant and flame retardant by melt blending to obtain a block composite material with PTC effect, wherein the melt blending temperature is 100-300℃ and the blending time is 5min-2h; (2) granulating the block composite material using a single screw or twin screw extruder to obtain a granular composite material; (3) hot pressing the granular composite material at 120-200℃ for 3-20min using a tablet press, and then cold pressing for 1-15min to obtain a sheet; (4) placing the sheet between two shape memory alloy sheets, hot pressing at 50-90℃ for 3-15min, and then cold pressing for 5-20min to obtain the structure B type PTC fuse 13.

[0046] It should be noted that the methods involved in the preparation of PTC fuses 13 of structure A and structure B, such as single-screw extrusion granulation, twin-screw extrusion granulation, tableting and coating, as well as conductive adhesive bonding, welding, and tableting by a tablet press, are conventional methods in this field and will not be described in detail here.

[0047] Please continue reading. Figures 1-4 The entire working process of the circuit protection element 100 of the present invention is as follows: Under normal working conditions, the movable contact 111 on the elastic arm 11 contacts the fixed contact 121 on the fixed arm 12, forming the main current path. The current flows in through the external port T1, mainly through the elastic arm 11, the movable contact 111, the fixed contact 121, and the fixed arm 12, and flows out through the other port T2 (or in the opposite direction). At this time, only a small amount of current flows through the PTC fuse 13 for monitoring. Since the elastic arm 11, the fixed contact 121, the movable contact 111, and the fixed arm 12 are all made of thermally conductive material and are integrated, they are encapsulated in a sealed housing 14, so that these components can maintain almost the same temperature during operation. The upper and lower surfaces of the PTC fuse 13 are respectively attached to the elastic arm 11 and the fixed arm 12, which allows it to monitor the internal temperature changes of the device in real time. When an abnormal increase in current through the circuit protection element 100 causes a rapid rise in the temperature of the metal components, the shape memory alloy layer in the PTC fuse 13 also heats up. Once the temperature reaches the transformation temperature of the shape memory alloy, the alloy drives the PTC fuse 13 to deform, generating a mechanical force that pushes the elastic arm 11 upward, forcing the movable contact 111 to disengage from the fixed contact 121. This action redirects the current to the PTC fuse 13, activating the secondary protection mechanism. If the current continues to rise, the temperature inside the PTC fuse 13 will further increase until it reaches its Curie point. At this point, the internal resistance of the PTC fuse 13 increases sharply, rapidly limiting the current and protecting the circuit and equipment from damage. When the circuit fault is cleared and the current returns to a safe level, as the internal temperature gradually decreases, when it falls below the transformation temperature of the shape memory alloy, the fuse deforms again, causing the elastic arm 11 to return to its original position. The movable contact 111 then re-engages with the fixed contact 121, and the circuit resumes normal operation. Furthermore, the circuit protection element 100 also features ambient temperature protection; if the external temperature rises abnormally, the PTC fuse 13 will respond and take action to protect the circuit and equipment even without overcurrent. Once the ambient temperature returns to normal, the fuse will automatically reset, ensuring the circuit can resume normal operation. This design not only improves the safety of the electrical system but also enhances its ability to respond to unexpected situations.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A circuit protection element, characterized in that, include: case; An elastic arm, one end of which has a movable contact and extends into the housing, and the other end extends out from one side of the housing; A fixed arm, one end of which extends into the housing and the other end extends out from the other side of the housing, is provided with a fixed contact, and a movable contact is in contact with the fixed contact. The elastic arm and the fixed arm are each made of copper-based alloy or nickel-based alloy, and the movable contact and the fixed contact are both made of conductive precious metal. The PTC fuse is located inside the housing. From top to bottom, the PTC fuse includes a first shape memory alloy layer, a PTC thermistor layer, and a second shape memory alloy layer. The PTC thermistor layer has a flexible structure. The first shape memory alloy layer is attached to the elastic arm, and the second shape memory alloy layer is attached to the fixed arm. When the temperature of the first shape memory alloy layer and the second shape memory alloy layer rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch, thereby generating a mechanical thrust to push the elastic arm upward, causing the movable contact to separate from the fixed contact.

2. The circuit protection element as described in claim 1, characterized in that, When the temperature of the first shape memory alloy layer and the second shape memory alloy layer rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch facing the fixed arm, so that the two ends of the PTC fuse contact the fixed arm and the middle section of the PTC fuse contact the elastic arm, thereby separating the movable contact from the fixed contact.

3. The circuit protection element as described in claim 1, characterized in that, When the temperature of the first shape memory alloy layer and the second shape memory alloy layer rises to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch facing the elastic arm, so that the two ends of the PTC fuse contact the elastic arm and the middle section of the PTC fuse contact the fixed arm, thereby separating the movable contact from the fixed contact.

4. The circuit protection element as described in claim 1, characterized in that, The thickness of the elastic arm and the fixed arm are each independently 50 to 500 μm.

5. The circuit protection element as described in claim 1, characterized in that, The thicknesses of the first shape memory alloy layer and the second shape memory alloy layer are each independently 50–300 μm.

6. The circuit protection element as described in claim 1, characterized in that, The raw materials for preparing the PTC thermistor layer, by mass parts, include 50-110 parts of polymer, 20-40 parts of conductive filler, 0.1-1 parts of coupling agent, 0.1-3 parts of dispersant, and 1-3 parts of flame retardant. The polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butene-styrene copolymer, polydimethylsiloxane, polyethylene terephthalate, ethylene-propylene rubber, butadiene-acrylonitrile copolymer, silicone rubber, nitrile rubber, natural rubber, high-density polyethylene, low-density polyethylene, polypropylene, polyvinylidene fluoride, polystyrene, polytetrafluoroethylene, chloroprene rubber, and polycarbonate.

7. The circuit protection element as described in claim 1, characterized in that, The materials of the first shape memory alloy layer and the second shape memory alloy layer are each independently selected from at least one of nickel-titanium alloys, copper alloys and iron alloys.

8. The circuit protection element as described in claim 1, characterized in that, The materials of the elastic arm and the fixed arm are each independently selected from Cu-Ni-Si-Mg alloys, Cu-Ni-Si-P alloys, Cu-Ni-Sn-P alloys, Cu-Ni-Co-Si alloys, Cu-Ni-Si alloys, Cu-Zr alloys, Cu-Be alloys, Cu-Ni-Be alloys, Cu-Sn alloys, Cu-Mg-P alloys, Cu-Zn-Sn alloys, Cu-Fe-P alloys, Cu-Fe-Mg-P alloys, or Ni-Be alloys; the materials of the movable contact and the fixed contact are each independently selected from at least one of gold, silver, and gold-silver alloys.

9. The circuit protection element as described in claim 1, characterized in that, The PTC fuse comprises, from top to bottom, a first shape memory alloy layer, a first connection layer, a first metal foil layer, a PTC thermistor layer, a second metal foil layer, a second connection layer, and a second shape memory alloy layer.

10. The circuit protection element as described in claim 9, characterized in that, The materials of the first metal foil layer and the second metal foil layer are each independently selected from at least one of Cu, Ni, Al, Au and Ag; the thickness of the first metal foil layer and the second metal foil layer is each independently 5 to 35 μm.

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