Circuit protection element

Abstract

The invention discloses a circuit protection element, which comprises a shell, an elastic arm, a fixed arm and a PTC (Positive Temperature Coefficient) fuse, and is characterized in that one end of the elastic arm is provided with a movable contact and extends into the shell; one end of the fixed arm extends into the shell, a fixed contact is arranged on the fixed arm, and the movable contact is in contact with the fixed contact; the PTC fuse comprises a first shape memory alloy layer, a PTC thermistor layer and a second shape memory alloy layer from top to bottom, 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 temperature of the second shape memory alloy layer rise to the respective deformation temperature, the PTC fuse is driven to change from a flat shape to an arc shape with a notch to generate mechanical thrust to jack up the elastic arm, so that the movable contact is separated from the fixed contact. The circuit protection element can bear large current work, has an over-current and over-temperature dual protection function and an automatic reset function, and can maintain small current under abnormal conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit protection, and in particular relates to a circuit protection element. Background Art

[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 science and technology and the expansion of the scope of application, the requirements for circuit protection components are also increasing. There are three main types of circuit protection components currently in widespread use: positive temperature coefficient (PTC) thermistors, fuses and circuit breakers. For PTC thermistors, the impedance is low at room temperature, but when the temperature is higher than the Curie temperature, the impedance value increases sharply, thereby effectively reducing the current and protecting the circuit; fuses have built-in alloy melts, and when the circuit current increases sharply, the alloy melts at high temperature, thereby cutting off the circuit; circuit breakers, when the temperature reaches the set temperature, use the mechanical action of the built-in metal accessories to push the movable contact and the fixed contact to separate, thereby cutting off the circuit.

[0003] However, the above-mentioned circuit protection components all have their own shortcomings. For example, the PTC thermistor is a protection element based on the positive temperature coefficient effect of the material. Its characteristic is that it exhibits low impedance characteristics under normal working conditions, allowing current to pass smoothly. However, when the ambient or its own temperature rises to a specific threshold, namely the Curie point, the impedance will increase rapidly, thereby effectively limiting the current flowing through it, preventing overcurrent from damaging the circuit, and the PTC thermistor can automatically restore its low resistance state after the temperature drops to normal levels; however, in high current application scenarios, due to its relatively high impedance, it may cause large power loss and affect the efficiency of the system. Fuses are disposable products. After the alloy melt melts, new components need to be replaced, resulting in waste of resources and increased use costs. For a circuit breaker, when it is activated, the current is completely cut off and the circuit stops working completely, but for some devices, such as battery management systems, it is more hoped that the circuit protection components can provide a small current to maintain the basic functions of the device after implementing the protection function. In summary, although existing circuit protection components each have certain 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, a circuit protection element is urgently needed to solve the deficiencies of the prior art. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a circuit protection element, which can not only withstand large current operation, but also integrates dual protection mechanisms of overcurrent and overtemperature, and has an automatic reset function to reduce resource consumption; in addition, it can also maintain a small current under abnormal circumstances 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 miniaturization of electronic components.

[0006] To achieve the above objectives, the present invention provides a circuit protection element, comprising a housing; an elastic arm, one end of which is provided with a movable contact and extends into the housing, and the other end extends from one side of the housing; a fixed arm, one end of which extends into the housing, and the other end extends from the other side of the housing, a fixed contact is provided on the fixed arm, the movable contact and the fixed contact are in contact, the elastic arm and the fixed arm are independently made of a copper-based alloy or a nickel-based alloy, and the movable contact and the fixed contact are both made of a conductive precious metal; a PTC fuse, the PTC fuse is located Inside the shell, the PTC fuse includes a first shape memory alloy layer, a PTC thermistor layer, and a second shape memory alloy layer from top to bottom. The PTC thermistor layer has a flexible structure, the first shape memory alloy layer is in contact with the elastic arm, and the second shape memory alloy layer is in contact with the fixed arm. When the temperatures of the first shape memory alloy layer and the second shape memory alloy layer rise to their respective deformation temperatures, the PTC fuse is driven from a flat shape to an arc shape with a notch, thereby generating a mechanical thrust to push up the elastic arm, so that the movable contact is separated 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 elastic arm and fixed arm of the present application are made of highly conductive copper-based alloy or nickel-based alloy, and the movable contact and fixed contact are made of conductive precious metal, which ensures that under normal working conditions, most of the current flows through the elastic arm, movable contact, fixed contact and fixed arm, and only a very small amount of current passes through the PTC fuse; at the same time, since 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 needs of high current operation.

[0009] 2. The PTC fuse structure of the present invention includes a first shape memory alloy layer, a PTC thermistor layer and a second shape memory alloy layer from top to bottom. The first shape memory alloy layer is bonded to the elastic arm, and the second shape memory alloy layer is bonded to the fixed arm. Under normal working conditions, since the elastic arm, the movable contact, the fixed contact and the fixed arm are also good thermal conductors, and are connected as a whole and located in the housing, the temperature between these components is kept 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 and the second shape memory alloy layer bonded thereto to rise accordingly. Once the temperature reaches the transition temperature of the shape memory alloy, the first shape memory alloy layer and the second shape memory alloy layer will undergo a phase change, driving the PTC fuse from a flat shape to an arc shape with a notch, thereby generating a mechanical thrust to lift the elastic arm upward, thereby separating the movable contact from the fixed contact. At this time, the current is directed to the PTC fuse to activate 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, causing the current to drop significantly but still maintain a small level, avoiding complete power failure, which is sufficient to ensure the basic function of the equipment; in this process, the PTC fuse continues to be powered on and heated, which helps to maintain the specific shape of the first shape memory alloy layer and the second shape memory alloy layer in a high temperature state, which also provides technicians with sufficient time to conduct troubleshooting and maintenance, avoiding the inconvenience caused by complete power failure, so the circuit protection element of the present invention can meet the needs of special application scenarios. When the circuit fault is eliminated, as the current returns to normal levels, the internal temperature of the device gradually decreases. When the temperature drops below the transition temperature of the shape memory alloy, the PTC fuse deforms again, prompting the elastic arm to reset, so that the movable contact and the fixed contact are re-contacted, and the circuit returns to normal working state. This automatic reset feature reduces the need to replace the fuse, so the circuit protection element of the present invention can reduce resource consumption.

[0010] 3. The PTC fuse is flat at low temperatures, and can more effectively fit with the elastic arm and the fixed arm to form good contact, thereby improving the efficiency of heat conduction and further improving 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 and separate the movable contact from the fixed contact. At this time, the current is directed to the PTC fuse to activate the secondary protection mechanism to prevent the equipment from being damaged by high temperature; and when the ambient temperature falls back to the normal range, the PTC fuse automatically resets and the circuit resumes normal operation. Therefore, the circuit protection element of the present invention not only has an overcurrent protection function, but also has an overtemperature protection function, that is, the circuit protection element of the present invention realizes the integrated design of the temperature-controlled metal element and the PTC thermistor. Its integrated design can effectively save space and meets the current development needs of miniaturization and microminiaturization 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 toward the fixed arm, so that both ends of the PTC fuse are in contact with the fixed arm and the middle section of the PTC fuse is in contact with the elastic arm, so that the movable contact is separated 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 the notch facing the elastic arm, so that the two ends of the PTC fuse are in contact with the elastic arm and the middle section of the PTC fuse is in contact with the fixed arm, so that the movable contact is separated from the fixed contact.

[0013] Preferably, the thickness of the elastic arm and the fixed arm is independently 50-500 μm.

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

[0015] Preferably, the raw materials for preparing the PTC thermistor layer include, by mass, 50 to 110 parts of a high molecular polymer, 20 to 40 parts of a conductive filler, 0.1 to 1 parts of a coupling agent, 0.1 to 3 parts of a dispersant and 1 to 3 parts of a flame retardant, wherein the high molecular polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butylene-styrene copolymer, polydimethylsiloxane matrix, 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 independently selected from at least one of nickel-titanium alloy, copper alloy and iron alloy.

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

[0018] Preferably, the material of the movable contact and the fixed contact is independently 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 connecting layer, a first metal foil layer, a PTC thermistor layer, a second metal foil layer, a second connecting layer, and a second shape memory alloy layer.

[0020] Preferably, the material of the first metal foil layer and the second metal foil layer is 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 independently 5 to 35 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the circuit protection element of the present invention under normal working state.

[0022] Figure 2 for Figure 1 Circuit diagram of the circuit protection component in normal working condition.

[0023] Figure 3 It is a schematic diagram of the structure of the circuit protection element of the present invention in an abnormal working state.

[0024] Figure 4 for Figure 3 Circuit diagram of the circuit protection element in abnormal working state.

[0025] Figure 5 It is the martensite phase of the first shape memory alloy layer of the present invention at a low temperature.

[0026] Figure 6 It is the austenite phase of the first shape memory alloy layer of the present invention at a high temperature.

[0027] Figure 7 It is another structural schematic diagram of the circuit protection element of the present invention in an abnormal working state.

[0028] Figure 8 It is another structural schematic diagram of the circuit protection element of the present invention in an abnormal working state.

[0029] Fig. 9 It is another structural schematic diagram of the circuit protection element of the present invention in an abnormal working state.

[0030] Fig.10 It is a structural schematic diagram of the PTC fuse of the present invention.

[0031] Fig.11 Another structural schematic diagram of the PTC fuse of the present invention. DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0033] To address the limitations of existing circuit protection components in dealing with high current loads, reducing resource consumption, and meeting the needs of special application scenarios, please refer to Figure 1 to Figure 4The present 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 laptop computers. The circuit protection element 100 includes an elastic arm 11, a fixed arm 12, a PTC fuse 13, and a housing 14, wherein one end of the elastic arm 11 is provided with a movable contact 111 and extends into the housing 14, and the other end of the elastic arm 11 extends from one side of the housing 14; one end of the fixed arm 12 extends into the housing 14, and the other end of the fixed arm 12 extends from the other side of the housing 14, and a fixed contact 121 is provided on the fixed arm 12, and the movable contact 111 and the fixed contact 121 are in contact. Among them, the materials of the elastic arm 11 and the fixed arm 12 are independently copper-based alloy or nickel-based alloy, and the materials of the movable contact 111 and the fixed contact 121 are all conductive precious metals, that is, the elastic arm 11, the fixed arm 12, the movable contact and the fixed contact 121 are all made of highly conductive metals, which ensures that under normal working conditions, most of the current flows through the elastic arm 11, the movable contact 111, the fixed contact 121 and the fixed arm 12, and only a very small amount of current passes through the PTC fuse 13; at the same time, because the materials used to prepare the elastic 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 the heat generation caused by resistance, thereby meeting the needs of high current operation. In addition, the PTC fuse 13 is located inside the shell 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 in contact with the elastic arm 11, and the second shape memory alloy layer 133 is in contact with 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 also good thermal conductors, and are connected as a whole and located in the shell 14, the temperatures of these components remain consistent. When the circuit encounters abnormal conditions such as overheating or overcurrent, the metal components heat up rapidly, causing the temperature of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 bonded thereto 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 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 directed to the PTC fuse 13, thereby starting the secondary protection mechanism.If the current continues to increase, so that the internal temperature of the PTC fuse 13 rises to the Curie point, the internal resistance of the PTC thermistor layer 131 increases sharply, resulting in a significant drop in current but still maintained at a small level, avoiding complete power failure, which is sufficient to ensure the basic function of the device; in this process, the PTC fuse 13 is continuously powered on and heated, which helps to maintain the first shape memory alloy layer 132 and the second shape memory alloy layer 133 in a specific shape at high temperature, which also provides technicians with sufficient time to troubleshoot and repair, avoiding the inconvenience caused by complete power failure, so the circuit protection element 100 of the present invention can meet the needs of special application scenarios. When the circuit fault is eliminated, as the current returns to normal levels, the internal temperature of the device gradually decreases. When the temperature drops below the transition temperature of the shape memory alloy, the PTC fuse 13 deforms again, prompting the elastic arm 11 to reset, so that the movable contact 111 re-contacts with the fixed contact 121, and the circuit returns to normal working state. 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] Further, the fixed arm 12 including the fixed contact 121, the PTC fuse 13 and the elastic arm 11 including the movable contact 111 are pressed Figure 1The structure shown is stacked from bottom to top, and fixed and packaged by a housing 14, thereby obtaining the circuit protection element 100 of the present invention. The elastic arm 11 and the fixed arm 12 are made of materials independently selected from Cu-Ni-Si-Mg alloy, Cu-Ni-Si-P alloy, Cu-Ni-Sn-P alloy, Cu-Ni-Co-Si alloy, Cu-Ni-Si alloy, Cu-Zr alloy, Cu-Be alloy, Cu-Ni-Be alloy, Cu-Sn alloy, Cu-Mg-P alloy, Cu-Zn-Sn alloy, Cu-Fe-P alloy, Cu-Fe-Mg-P alloy or Ni-Be alloy; preferably, the elastic arm 11 and the fixed arm 12 are made of Cu-Ni-Si-Mg alloy, and the chemical composition of the Cu-Ni-Si-Mg alloy is calculated by mass percentage: 3.0% Ni, 0.65% Si, 0.15% Mg, and the balance is Cu. At the same time, the thickness of the elastic arm 11 and the fixed arm 12 is independently 50 to 500 μm, and the elastic arm 11 and the fixed arm 12 are both prepared by cutting and stamping techniques well known in the art. Among them, the material of the movable contact 111 and the fixed contact 121 is independently at least one of gold, silver and gold-silver alloy; at the same time, the movable contact 111 and the fixed contact 121 are prepared by conventional electroplating or chemical plating technology. Among them, the shell 14 is a plastic shell 14, which can be prepared by conventional integrated injection molding technology, or different parts of the shell 14 can be prepared separately by conventional injection molding methods, and then the various parts of the shell 14 are combined into a whole by conventional gluing methods or ultrasonic welding methods; the injection molding, gluing and ultrasonic welding methods used are all methods well known to those skilled in the art.

[0035] Please continue to see Figure 1 , the PTC fuse 13 is flat at low temperatures, and can more effectively fit with the elastic arm 11 and the fixed arm 12 to form a good contact, thereby improving the heat conduction efficiency and further improving the sensitivity of the temperature response. Specifically, if the ambient temperature rises abnormally, causing the internal temperature of the circuit protection element 100 to rise, it will also trigger the PTC fuse 13 to deform and separate the movable contact 111 from the fixed contact 121. At this time, the current is directed to the PTC fuse 13 to start the secondary protection mechanism to prevent the equipment from being damaged by high temperature; and when the ambient temperature falls 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 an overcurrent protection function, but also has an overtemperature protection function, that is, the circuit protection element 100 of the present invention realizes the integrated design of the temperature-controlled metal element and the PTC thermistor, and its integrated design can effectively save space, which meets the current development needs of miniaturization and microminiaturization 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 martensite phase at low temperature is transformed into Figure 6 The austenite phase in the high temperature state shown; on the contrary, when the temperature drops below the transition temperature, the shape memory alloy layer can recover from the austenite phase to the original martensite phase. This bidirectional phase change characteristic enables the first shape memory alloy layer 132 and the second shape memory alloy layer 133 to reversibly change their shapes when the temperature changes. At the same time, the PTC thermistor layer 131 of the present 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 have high elasticity, which makes the PTC fuse 13 flexible and bendable, and then the PTC fuse 13 can be driven by the phase change of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 from a flat shape to an arc shape with a notch.

[0037] Please see Figure 7 When the temperature of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 rises to their respective deformation temperatures, the PTC fuse 13 changes from a flat state to an arc shape with the notch facing the fixed arm 12, so that both ends of the PTC fuse 13 contact the fixed arm 12 and the middle section of the PTC fuse 13 contacts the elastic arm 11, which causes the movable contact 111 to separate from the fixed contact 121. Figure 7 The placement direction of the PTC fuse 13 in the shape memory alloy is reversed. When the temperatures of the two shape memory alloy layers reach their respective deformation temperatures, the PTC fuse 13 changes from a flat state to a Figure 3 The notch is in an arc shape facing the elastic arm 11. 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, which also causes 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 the arc shape with the notch facing the elastic arm 11, the circuit can be safely disconnected.

[0038] In order to ensure that the PTC fuse 13 can effectively contact the fixed arm 12 and the elastic arm 11 under high temperature, the shape of the memory alloy can be trained to make the PTC fuse 13 flat at low temperature, and when the temperature rises, the two ends of the PTC fuse 13 will be transformed into Figure 8The first planes 15 shown in the figure are both closely fitted with the fixed arm 12 to ensure good heat conduction and electrical connection. At the same time, the middle part of the PTC fuse 13 not only maintains the arc design, but also forms a middle section of the arc at high temperature. Fig. 9 The second plane 16 shown in the figure will contact and fit with the elastic arm 11; this ensures that the PTC fuse 13 can be firmly in contact with the fixed arm 12 through the first planes 15 at both ends and in good contact with the elastic arm 11 through the second plane 16 in the middle part in a high temperature environment, thereby maintaining the effectiveness and stability of the circuit protection function.

[0039] Specifically, the transverse structure of the PTC fuse 13 of the present invention can be selected into different geometric shapes according to specific application requirements, such as rectangular, elliptical or circular; the longitudinal structure of the PTC fuse 13 is composed of multiple layers with different functions, and each layer is tightly fitted. According to the number of layers, the PTC fuse 13 can be divided into two types, namely Fig.10 The structure A shown and Fig.11 The structure shown is B. According to its specific number of layers and functional configuration, each type of PTC fuse 13 can be suitable for different application scenarios.

[0040] Specifically, Fig.10 As shown, the PTC fuse 13 of structure A type has a seven-layer structure, namely, a first shape memory alloy layer 132, a first connection layer 134, a first metal foil layer 136, a PTC thermistor layer 131, a second metal foil layer 137, a second connection layer 135, and a second shape memory alloy layer 133, and each layer is bonded to each other; wherein the first connection layer 134 serves to connect the first metal foil layer 136 with the first shape memory alloy layer 132, and the second connection layer 135 serves to connect the second metal foil layer 137 with the second shape memory alloy layer 133. At the same time, the first metal foil layer 136 and the second metal foil layer 137 not only provide physical support to ensure 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, the PTC fuse 13 can be effectively prevented from deformation or displacement during use. Accordingly, the PTC fuse 13 of structure B has a three-layer structure, which is a first shape memory alloy layer 132, a PTC thermistor layer 131, and a second shape memory alloy layer 133 from top to bottom, and each layer is bonded to each 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 can 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 are each independently 50 to 300 μm; the material of the first shape memory alloy layer 132 and the second shape memory alloy layer 133 are each 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 are each 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. In addition, the materials of the first metal foil layer 136 and the second metal foil layer 137 are 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 independently 5 to 35 μm.

[0042] Specifically, the raw materials for preparing the PTC thermistor layer 131 include, by mass, 50 to 110 parts of high molecular 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 high molecular polymer may be but is not limited to 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, and 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, and 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, and 1 part; the content of the dispersant may be but is not limited to 0.1 parts, 0.5 parts, 0.8 parts, 1 parts, 1.6 parts, 2.0 parts, 2.5 parts, and 3 parts; 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, and 3 parts.

[0043] Further, the high molecular polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butylene-styrene copolymer, polydimethylsiloxane matrix, 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 nanotube, graphite, graphene, metal powder, metal fiber, and metal ceramic powder. The coupling agent is at least one of γ-aminopropyl triethoxysilane (KH-550), γ-glycidyloxypropyl trimethoxysilane (KH560), γ-(methacryloyloxy)propyl trimethoxysilane (KH-570), aniline methyl triethoxysilane (Sj-42), vinyl trimethoxysilane (A-171), bis(dioctyl pyrophosphate) ethylene titanate (GR-311), triisostearoyl titanate isopropyl (TTS), isopropoxy tri(dioctyl pyrophosphate) titanate (GR-201), isopropyl dioleyl (dioctyl phosphate) titanate (GR-101). The dispersant is at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyethylene glycol, polyvinyl pyrrolidone, ethylene bis stearic acid amide, 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] Furthermore, the preparation method of the PTC fuse 13 of structure A type includes: (1) mixing a formulated amount of high molecular 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°C and the mixing time is 5min-2h; (2) granulating the block composite material by 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 through upper and lower rollers, automatically laminating, and compounding a layer of metal foil on the upper and lower surfaces to obtain a three-layer structure PTC chip body; (4) using a conductive adhesive bonding technology or a welding method, the two shape memory alloy sheets are tightly attached to the upper and lower surfaces of the PTC chip body, respectively, thereby obtaining the PTC fuse 13 of structure A type. More specifically, step (1) comprises placing 20 to 40 parts of high-density polyethylene (Merck, USA), 20 to 40 parts of low-density polyethylene (Merck, USA), 10 to 30 parts of ethylene-octene copolymer (Dow Chemical Company, USA), 20 to 40 parts of carbon black powder (Guangdong Meilian New Materials Co., Ltd.), 0.1 to 1 part of γ-aminopropyltriethoxysilane (KH-550) (Hubei Fangde New Materials Co., Ltd.), 0.1 to 3 parts of fatty alcohol polyoxyethylene ether (Chengdu Huaxia Chemical Reagent Co., Ltd.) and 1 to 3 parts of Al(OH)3 (Wuhan Jixin Yibang Biotechnology Co., Ltd.) in an internal mixer for mixing, the mixing time is 10 to 30 minutes, the temperature is 110 to 150°C, and the rotation speed is 50 to 100 rpm, thereby obtaining a block composite material.

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

[0046] It is necessary to explain that the single-screw extrusion granulation, twin-screw extrusion granulation, tableting and coating, as well as conductive adhesive bonding, welding, tablet pressing and other methods involved in the preparation method of the structure A type PTC fuse 13 and the structure B type PTC fuse 13 are conventional methods in the field and will not be described in detail here.

[0047] Please continue to see Figure 1 to Figure 4 The entire working process of the circuit protection element 100 of the present invention is specifically 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 to form a main current path, and the current flows in through the external port T1, mainly flows through the elastic arm 11, the movable contact 111, the fixed contact 121 and the fixed arm 12, and flows out from the other port T2 (or in the opposite direction); at this time, only a trace 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 good conductor materials and are connected as a whole, 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 enables it to monitor the temperature changes inside the device in real time. When the abnormal increase of current passing through the circuit protection element 100 causes the metal parts to heat up rapidly, the shape memory alloy layer in the PTC fuse 13 will also heat up accordingly. Once the temperature reaches the transformation temperature of the shape memory alloy, the shape memory alloy will drive the PTC fuse 13 to deform, generating a mechanical thrust to push up the elastic arm 11, forcing the movable contact 111 to disengage from the fixed contact 121. This action turns the current to the PTC fuse 13, and activates 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 time, the internal resistance of the PTC fuse 13 increases sharply, thereby quickly limiting the current and protecting the circuit and equipment from damage. When the circuit fault is eliminated, the current falls back to a safe level. As the internal temperature gradually decreases, when it drops below the transformation temperature of the shape memory alloy, the fuse deforms again, causing the elastic arm 11 to return to its original position, and the movable contact 111 re-contacts with the fixed contact 121, and the circuit resumes normal operation. In addition, the circuit protection element 100 also has an ambient temperature protection function; if the external temperature rises abnormally, even if there is no overcurrent, the PTC fuse 13 will respond and take action to protect the circuit and equipment. Once the ambient temperature returns to the normal range, the fuse will automatically reset to ensure that the circuit can return to normal working state. This design not only improves the safety of the electrical system, but also enhances the ability to respond to unexpected situations.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A circuit protection element, characterized in that: include: case; An elastic arm, one end of which is provided with a movable contact and extends into the shell, and the other end of which extends out from one side of the shell; A fixed arm, one end of which extends into the interior of the housing, and the other end of which extends from the other side of the housing, a fixed contact is provided on the fixed arm, the movable contact is in contact with the fixed contact, the elastic arm and the fixed arm are 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 precious metals; A PTC fuse, the PTC fuse is located 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 is a flexible structure, the first shape memory alloy layer is in contact with the elastic arm, and the second shape memory alloy layer is in contact with 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 up the elastic arm, so that the movable contact is separated from the fixed contact.

2. The circuit protection element according to claim 1, wherein: When the temperatures of the first shape memory alloy layer and the second shape memory alloy layer rise to their respective deformation temperatures, the PTC fuse is driven to change from a flat shape to an arc shape with a notch toward the fixed arm, so that the two ends of the PTC fuse are in contact with the fixed arm and the middle section of the PTC fuse is in contact with the elastic arm, so that the movable contact is separated from the fixed contact.

3. The circuit protection element according to claim 1, wherein: When the temperatures of the first shape memory alloy layer and the second shape memory alloy layer rise 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 are in contact with the elastic arm and the middle section of the PTC fuse is in contact with the fixed arm, so that the movable contact is separated from the fixed contact.

4. The circuit protection element according to claim 1, wherein: The thickness of the elastic arm and the fixed arm is independently 50 to 500 μm.

5. The circuit protection element according to claim 1, wherein: The thickness of the first shape memory alloy layer and the second shape memory alloy layer are independently 50 to 300 μm.

6. The circuit protection element according to claim 1, wherein: The raw materials for preparing the PTC thermistor layer include, by weight, 50 to 110 parts of a high molecular polymer, 20 to 40 parts of a conductive filler, 0.1 to 1 part of a coupling agent, 0.1 to 3 parts of a dispersant and 1 to 3 parts of a flame retardant, wherein the high molecular polymer is selected from at least one of polyurethane, ethylene-octene copolymer, polyamide, polyacrylamide, styrene-ethylene-butylene-styrene copolymer, polydimethylsiloxane matrix, 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 according to claim 1, wherein: The materials of the first shape memory alloy layer and the second shape memory alloy layer are independently selected from at least one of nickel-titanium alloy, copper alloy and iron alloy.

8. The circuit protection element according to claim 1, wherein: The materials of the elastic arm and the fixed arm are independently selected from Cu-Ni-Si-Mg alloy, Cu-Ni-Si-P alloy, Cu-Ni-Sn-P alloy, Cu-Ni-Co-Si alloy, Cu-Ni-Si alloy, Cu-Zr alloy, Cu-Be alloy, Cu-Ni-Be alloy, Cu-Sn alloy, Cu-Mg-P alloy, Cu-Zn-Sn alloy, Cu-Fe-P alloy, Cu-Fe-Mg-P alloy or Ni-Be alloy; the materials of the movable contact and the fixed contact are independently at least one of gold, silver and gold-silver alloy.

9. The circuit protection element according to claim 1, wherein: The PTC fuse comprises, from top to bottom, a first shape memory alloy layer, a first connecting layer, a first metal foil layer, a PTC thermistor layer, a second metal foil layer, a second connecting layer, and a second shape memory alloy layer.

10. The circuit protection element according to claim 9, wherein: The materials of the first metal foil layer and the second metal foil layer are 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 independently 5 to 35 μm.

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