A normally open thermoswitch

Abstract

The normally open thermal switch of the present invention includes a housing, in which a first conductor and a second conductor are inserted through a cavity, and the first and second conductors inside the housing are insulated from each other. One end of the first conductor inside the housing is cantilevered, and an expansion bladder is disposed between the cantilevered first conductor and the housing. A limit indicator and one end of the second conductor inside the housing are respectively located on the displacement path of the cantilevered first conductor. One end of the limit indicator is inserted through and limited to the housing wall, and the other end is disposed on the first conductor. When the temperature of the expansion bladder reaches a set temperature threshold, the expansion bladder expands towards the first conductor, driving the first conductor to displace and make conductive contact with the second conductor, so that the first and second conductors are directly connected. At the same time, the limit indicator is driven to extend out of the housing. The normally open thermal switch of the present invention has a simple structure and can quickly connect heat dissipation components to the circuit to achieve protection of power devices.

Description

Technical Field

[0001] This invention relates to the fields of power control and electric vehicles, and in particular to protective devices for power devices in the event of fault current. Background Technology

[0002] Power devices are a crucial component of modern power electronic systems. They primarily refer to electronic components designed to handle high voltage and high current, achieving power conversion and control, such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), IGBTs (Insulated-Gate Bipolar Transistors), and power diodes. These devices feature high efficiency, low loss, and excellent switching characteristics, and are widely used in motor control, solar photovoltaics, and new energy vehicles. However, in practical applications, these devices may face faults such as overcurrent, overvoltage, and short circuits, causing excessively high temperatures. This can lead to serious consequences such as performance degradation, reduced lifespan, or even damage. Therefore, the heat dissipation design of power devices is of paramount importance.

[0003] When the aforementioned faults occur, the heat dissipation requirements of power devices will be higher, necessitating more effective heat dissipation methods, such as using cooling fans, heat sinks, or cooling systems. While power devices themselves can dissipate heat sufficiently during normal operation, prolonged use of cooling fans, heat sinks, or cooling systems in the circuit can lead to unnecessary power loss. Therefore, to avoid power-consuming components like cooling fans, heat sinks, or cooling systems in the circuit during normal operation, the cooling fan, heat sink, or cooling system should be switched on promptly when the temperature reaches a certain threshold range.

[0004] However, the current single-switch function cannot achieve the above-mentioned temperature-based access function. It requires the control switch to be combined with temperature monitoring instruments and control circuits, resulting in a complex circuit structure and high space occupancy.

[0005] To address the aforementioned operating conditions, a novel thermal switch has been invented. This switch is a sealed, integrated device, directly connected in series or parallel to a branch near the power device. When a circuit fault occurs, the heat generated by the power device causes the liquid, gas, or solid with a high coefficient of thermal expansion within the sealed capsule, which is in direct contact with one of the conductors, to rapidly expand. The expanding capsule pushes one conductor to make contact with the other conductor, thereby conducting the circuit. When a fault occurs in the operating circuit containing the power device, the thermal switch promptly activates, connecting the heat dissipation branch of the power device to cool it down. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to set a normally open thermal switch, which is connected in series with the branch where the cooling fan, radiator or cooling system is located, and then connected in parallel with the circuit near the power device, so that the thermal switch is placed close to the power device; when the temperature of the power device reaches the designed warning threshold range, the thermal switch closes, conducts the branch where the cooling fan, radiator or cooling system is located, and the cooling fan, radiator or cooling system works to protect the power device from heat dissipation.

[0007] To solve the above-mentioned technical problems, the present invention provides a normally open thermal switch, comprising a housing with a cavity, in which a first conductor and a second conductor are disposed. One end of the first conductor and the second conductor located outside the housing respectively serve as the connection end of the normally open thermal switch, and the first conductor and the second conductor located inside the housing are insulated from each other. One end of the first conductor located inside the housing is cantilevered, and an expansion bladder is disposed between the cantilevered first conductor and the housing. A limit indicator and one end of the second conductor located inside the housing are respectively located on the displacement path of the cantilevered first conductor. One end of the limit indicator is inserted through and limited on the housing wall, and the other end is disposed on the first conductor. When the temperature of the expansion bladder reaches a set temperature threshold, the expansion bladder expands toward the first conductor, driving the first conductor to displace and make conductive contact with the second conductor, so that the first conductor and the second conductor are directly connected. At the same time, the limit indicator is driven to extend out of the housing.

[0008] Preferably, a receiving space is provided in the housing, the opening end of the receiving space faces the first conductor which is cantilevered, the expansion bladder is located in the receiving space, and the receiving space limits the expansion bladder to expand only in the direction of the opening end of the receiving space, the first conductor cantilevered across the opening end of the receiving space, is located on the expansion direction path of the expansion bladder and contacts the expansion bladder; the limiting indicator is located outside the receiving space.

[0009] Preferably, a raised rib is provided on one side of the accommodating space, and the first conductor is laid on the raised rib.

[0010] Preferably, a positioning groove is provided on the rib, and the first conductor is placed in the positioning groove.

[0011] Preferably, a heating resistor is also provided in the cavity of the housing as a current limiting device, and the expansion bladder is disposed on the heating resistor; the two ends of the heating resistor are electrically connected to the first conductor and the second conductor in the housing to form a current limiting circuit; when the first conductor and the second conductor are in direct conductive contact, the current flows through the series circuit formed by the first conductor and the second conductor connected in series.

[0012] Preferably, the limiting indicator is engaged with the first conductor to restrict the initial position of the first conductor. Preferably, a limiting member is provided on the outer peripheral surface of the limiting indicator located inside the housing, and a limiting hole is formed in the first conductor. One end of the limiting indicator located inside the housing is inserted into the limiting hole, and the limiting member presses against the first conductor to limit the initial position of the first conductor.

[0013] Preferably, the limiting member is a horizontal bar-shaped structure disposed on the two opposite outer sides of the limiting indicator, and the side of the limiting member facing the first conductor is set as an inclined surface. In the initial position and the final position, the first conductor remains in contact with the limiting member.

[0014] Preferably, a through-hole is provided in the shell wall of the housing, and the limit indicator is installed in the through-hole.

[0015] Preferably, the limiting indicator is positioned by a limiting structure, wherein the limiting structure is: an elastic barb structure is provided on the outer periphery of the limiting indicator, the barb structure elastically abutting against the mounting hole to form the limiting structure; or, the limiting indicator is assembled in the mounting hole in an interference fit to form the limiting structure; or, a limiting spring is provided between the limiting member and the outer periphery of the housing wall of the mounting hole to form the limiting structure.

[0016] Preferably, one end of the first and second conductors located outside the housing is disposed outside the housing as a connection terminal of the thermal switch in a patch type, a bent flat type, or a straight quick-connect type.

[0017] Preferably, the expansion bladder includes an elastic bag and a gas, liquid, or solid with a high coefficient of thermal expansion filled in the bag. When the solid with a high coefficient of thermal expansion is an integral structure and remains an integral structure after expansion, the expansion bladder is composed of a solid with a high coefficient of thermal expansion. Alternatively, the expansion bladder includes a stretchable bag and a gas, liquid, or solid with a high coefficient of thermal expansion filled in the bag. When the expansion bladder is not inflated, it is in a compressed state. When the expansion bladder inflates, the expansion energy can deform from a compressed state to a stretched state.

[0018] Preferably, the outer periphery of the expansion bladder, perpendicular to the direction of the force exerted by the expansion bladder on the first conductor, is configured as a retractable serrated structure.

[0019] Preferably, one end of the first conductor located inside the housing is configured as an arc-shaped structure protruding toward the second conductor.

[0020] Preferably, the housing includes a cover and a base, the base being located at the open end of the cover and closing the open end; a rib is provided on the base, the inner surface of the base, the rib and the side wall of the cover cooperate to form an accommodating space, the first conductor cantilevered over the accommodating space, and the expansion bladder is disposed in the accommodating space and contacts the first conductor.

[0021] Preferably, the cover and the base are connected and fixed by a snap-fit ​​mechanism.

[0022] This invention employs an expansion bladder that can expand under heating. The driving force generated when the expansion bladder expands causes the first and second conductors of the normally open thermal switch to make conductive contact, thereby closing the thermal switch. The response is rapid. Furthermore, the normally open thermal switch is a simple single device with a simple structure, which does not require the design of complex circuits to realize the conduction connection of the branch where the cooling fan and cooling system are located.

[0023] Therefore, the normally open thermal switch of the present invention is low in cost, can effectively protect power devices, and improve the service life of power devices. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of a normally open thermal switch in its initial state.

[0025] Figure 2 yes Figure 1 A side view structural diagram.

[0026] Figure 3 yes Figure 1 A schematic diagram of the structure after the action.

[0027] Figure 4 This is a schematic diagram of a normally open thermal switch with a serrated structure in the initial state.

[0028] Figure 5 yes Figure 4 A schematic diagram of the structure after the action.

[0029] Figure 6 This is a cross-sectional view of a normally open thermal switch in its initial state, equipped with a heating resistor.

[0030] Figure 7 yes Figure 6The structural diagram after the action.

[0031] Figure 8 This is a schematic diagram of a normally open thermal switch with a bent, flat connection end.

[0032] Figure 9 This is a schematic diagram of a normally open thermal switch with a straight-out quick-connect structure.

[0033] Figure label:

[0034] 1. Cover body; 2. Base; 3. First conductor; 31. One end of the first conductor located outside the shell; 32. One end of the first conductor located inside the shell; 4. Second conductor; 41. One end of the second conductor located outside the shell; 42. One end of the second conductor located inside the shell; 5. Rib; 6. Expansion bladder; 6a. Expansion bladder; 61. Serrated structure; 7. Limit indicator; 71. Limiting element; 8. Heating resistor. Detailed Implementation

[0035] The normally open thermal switch of the present invention includes a housing with a cavity. A first conductor and a second conductor are disposed in the cavity of the housing. One end of the first conductor and the second conductor located outside the housing respectively serve as the connection end of the normally open thermal switch. The first conductor and the second conductor located inside the housing are insulated from each other. One end of the first conductor located inside the housing is cantilevered. An expansion bladder is disposed between the cantilevered first conductor and the housing. A limit indicator and one end of the second conductor located inside the housing are respectively located on the displacement path of the cantilevered first conductor. One end of the limit indicator is disposed on the housing wall and the other end is disposed on the first conductor. When the temperature of the expansion bladder reaches a set temperature threshold, the expansion bladder expands toward the first conductor, driving the first conductor to displace and make conductive contact with the second conductor, so that the first conductor and the second conductor are directly connected. At the same time, the limit indicator is driven to extend out of the housing.

[0036] The following describes preferred embodiments in detail with reference to the accompanying drawings. The directional terms used are for reference only and do not constitute a limitation on the technical solution of this invention.

[0037] See Figures 1 to 3A normally open thermal switch mainly includes a housing, a first conductor, a second conductor, and an expansion chamber. The housing is made of insulating material and includes a cover 1 and a base 2. The cover 1 is a cap-like structure with one open end and one closed end. The base 2 is positioned at the open end of the cover 1 and closes the open end, forming a relatively sealed housing with a cavity inside. The side walls of the base 2 and the cover 1 are equipped with snap-fit ​​structures. The base 2 is connected and fixed to the cover 1 by snap-fit. For example, a protruding snap-fit ​​protrusion is provided on the side wall of the base 2 that mates with the cover 1, and a snap-fit ​​hole is provided on the corresponding side wall of the cover 1. During assembly, the snap-fit ​​protrusion of the base 2 is located in the cover 1 and the snap-fit ​​hole, forming a fixed connection. The cover 1 and the base 2 can also be connected and fixed by bolts, rivets, laser welding, or adhesive bonding.

[0038] The first conductor 3 and the second conductor 4 pass between the contact surfaces of the cover 1 and the base 2 on opposite sides of the housing, respectively, with one end of the first conductor 3 and the second conductor 4 located in the cavity inside the housing, and the other ends (31, 41) located outside the housing and bent and attached to the outer surface of the base 2 in a patch manner. One end of the second conductor 4 is fixed to the top of the cover 1, which is opposite to the base 2 inside the housing, and is horizontally fixed to the inner surface of the top of the cover 1. The first conductor 3, located inside the housing, is partially attached to the inner wall of the cover 1 and bent away from the base at a certain distance, so that the first conductor 3 inside the housing is cantilevered within the housing. One end of the first conductor 3 inside the housing is away from the end of the second conductor 4 located at the top of the cover 1 and close to the inner surface of the base 2, so that the first conductor 3 and the second conductor 4 are mutually insulated. The cantilevered portion of the first conductor 3 inside the housing has a certain degree of elasticity. One end (32) of the first conductor 3 located inside the housing is configured as an arc-shaped structure protruding towards one end of the second conductor 4. When one end of the first conductor 3 is displaced towards the second conductor 4, the arc-shaped structure at the end of the first conductor 3 can make conductive contact with the second conductor 4 immediately, thus shortening the response time of the conductive contact between the first conductor 3 and the second conductor 4.

[0039] The structure of the connection terminals of a normally open thermal switch, such as Figure 1 As shown, the first conductor 3 and the second conductor 4 are located outside the housing, and one end (31, 41) of the connection terminal of the normally open thermal switch is set as a surface mount structure. In other embodiments, other structures can also be used, such as... Figure 8 As shown, the ends of the first conductor 3 and the second conductor 4 located outside the housing are bent outwards at the opening end face of the cover 1 on opposite sides, respectively, so that the connection end of the normally open thermal switch has a bent, flat-out structure. A connection hole is provided on the connection end of the bent, flat-out structure to facilitate the connection of the normally open thermal switch to the circuit via bolts. For example... Figure 9As shown, the first conductor 3 and the second conductor 4 do not need to be bent at one end outside the housing. They extend directly from between the cover and the base outside the housing in a straight-out quick-plug structure on the same side outside the housing. The connection end of the normally open thermal switch with this structure is convenient for quick plug-in installation with the external mounting base.

[0040] A raised rib 5 is provided on the inner surface of the inner wall of the cover 1 near where the base 2 passes through the first conductor 3. The raised rib 5, the inner surface of the base 2, and the side wall of the cover 1 form an accommodating space with one open end. The accommodating space is located on one side of the housing where the first conductor 3 is bent. The first conductor 3, after being bent inside the housing, is cantilevered and spans above the open end of the accommodating space and the raised rib 5. That is, the open end of the accommodating space faces the direction of the cantilevered first conductor, and one end of the first conductor 3 faces the direction of the base 2. A positioning groove (not shown) can also be provided on the top of the raised rib 5 facing the top of the cover, and the first conductor 3 is located in the positioning groove on the raised rib 5.

[0041] The expansion bladder 6 is disposed in the accommodating space between the first conductor 3 and the base 2. The accommodating space restricts the expansion direction of the expansion bladder, allowing it to expand only in the direction from the base 2 toward the top of the cover 1, that is, only toward the opening end of the accommodating space. This structure ensures that when the temperature rises to the designed threshold range, the expansion of the expansion bladder 6 can drive the cantilevered portion of the first conductor 3 to displace toward one end of the second conductor 4, making one end of the first conductor 3 and one end of the second conductor 4 make conductive contact, closing the normally open thermal switch and turning on the circuit where the thermal switch is located.

[0042] In this design, the expansion bladder is confined within the housing. Preferably, it is confined to have only one free end, thus limiting the expansion direction of the bladder. This allows it to expand in the direction that pushes the first conductor, located within the housing, away from its initial position when the bladder reaches a temperature threshold, thereby bringing the first conductor into contact with the second conductor. Different confining methods can be employed. For example, the bladder's material, combined with the internal structure of the housing, can be used to achieve confining the bladder to only one free end. Alternatively, the internal structure of the housing can be configured to allow the bladder to expand or extend in only one direction within the accommodating space. When the bladder has only one free end, its expansion direction is determined during expansion, resulting in a more reliable product and more efficient energy utilization.

[0043] The expansion bladder 6 comprises an elastic bladder and a filler with a high coefficient of expansion within the bladder. The filler can be a gas, liquid, or solid with a high coefficient of expansion. Liquids include kerosene, for example. When a solid with a high coefficient of expansion is used as the filler, if the solid is a monolithic structure and maintains its monolithic structure after expansion, the bladder can be omitted, and the solid can be used directly as the expansion bladder. Generally, the outer periphery of the expansion bladder is a regular shape, such as a smooth columnar structure. When the bladder is elastic, the expansion bladder 6 is in a contracted state when not inflated. When the expansion bladder 6 inflates, the bladder of the expansion bladder 6 undergoes elastic deformation under the expansion of the filler, expanding towards the opening end of the accommodating space under the constraint of the accommodating space.

[0044] The bladder 6 can also be a non-elastic bladder, or a non-elastic, stretchable bladder. When the bladder is not inflated, the bladder is in a compressed state. When the bladder inflates, the expanding filler drives the bladder to deform from a compressed state to a stretched state. For example, the bladder could be a columnar steel structure with a wavy or serrated outer circumferential surface, allowing the bladder to be compressed and stretched. When the filler inside the bladder is not inflated, i.e., at the initial position of the bladder 6, it is in a compressed state. When it inflates, the high expansion coefficient of the filler expands, driving the bladder 6 to change from a compressed state to a stretched state, thereby driving the displacement of the first conductor.

[0045] for example Figure 4 and Figure 5 The serrated expansion bladder 6a shown has a serrated outer circumferential surface 61 perpendicular to the direction of expansion from the base 2 toward the top of the cover 1. When the expansion bladder 6 is not inflated, see [reference needed]. Figure 4 The inflatable bladder 6 is in a compressed state. When the inflatable bladder 6 inflates, see... Figure 5 The high expansion coefficient of the filler expands, driving the expansion bladder 6 to change from a compressed state to a stretched state towards the opening of the accommodating cavity. Figure 4 and Figure 5 The stretchable and non-elastic bladder shown has its expansion bladder expanding only in the direction of the opening of the accommodating space, which can further constrain the expansion direction of the expansion bladder 6.

[0046] The limiting indicator 7 is located on one side of the rib 5, i.e., outside the accommodating space where the expansion bladder is located. A mounting hole is provided on the top of the cover 1 corresponding to the position of the first conductor 3, and the limiting indicator 7 is installed in the mounting hole. One end of the limiting indicator 7 passes through the mounting hole on the top of the cover 1, and the other end is located in the cavity of the housing. A limiting member 71 is provided on the outer periphery of the limiting indicator 7 located in the housing. A limiting hole is provided on the first conductor 3, and one end of the limiting indicator 7 located in the housing is inserted into the limiting hole of the first conductor 3. The limiting member 71 is positioned above the first conductor 3, pressing it against the first conductor 3. The limiting member 71 is a horizontal bar structure that is vertically set on the two opposite outer surfaces of the limiting indicator 7. The surfaces of the limiting members 71 on both sides of the limiting indicator 7 facing the first conductor 3 are provided with inclined surfaces. The inclined surface of the limiting member 71 on one side of the limiting indicator 7 is in contact with the surface of the first conductor 3 in the initial position, and the inclined surface of the limiting member 71 on the other side of the limiting indicator 7 is in contact with the surface of the first conductor 3 in the final position. This ensures that the limiting member 71 and the first conductor remain in contact during the displacement of the limiting indicator 7 driven by the first conductor 3.

[0047] To further define the initial position of the limit indicator 7, a limiting structure is provided on the limit indicator 7. A flexible barbed structure (not shown) is provided on the outer periphery of the end of the limit indicator 7 located at the mounting hole as a limiting structure. The flexible barbed structure and the mounting hole are interference-fitted to define the initial position of the limit indicator 7. When the expansion bladder 6 drives the first conductor 3 to move, the first conductor 3 abuts against the limiting member 71, driving the limit indicator 7 to move towards the outside of the housing. The limit indicator 7 overcomes the limitation of the barbed structure, and the end of the limit indicator 7 facing outwards protrudes from the outer surface of the housing wall, indicating to the operator that the normally open thermal switch has been activated and that the circuit containing the power device has malfunctioned. After the limit indicator 7 is activated, the flexible barbed structure moves to the outside of the housing, forming a termination position, preventing the limit indicator 7 from re-entering the housing.

[0048] The initial position of the limit indicator can also be limited by the following methods: the limit indicator is assembled in the mounting hole with an interference fit to form a limit structure to limit the initial position of the limit indicator; or, a limit spring is set between the limit member of the limit indicator and the inner wall of the cover around the outer periphery of the mounting hole to form a limit structure to limit the initial position of the limit indicator.

[0049] The limit indicator 7 is located on the displacement path of the first conductor 3, which is cantilevered. When the expansion bladder expands, it drives the first conductor 3 to move at one end of the cantilevered position. The first conductor 3 then drives the limit indicator 7 to overcome the limitation of the initial position and move towards the outside of the shell to issue a warning.

[0050] Figures 1 to 3 Working principle:

[0051] A normally open thermal switch is connected in series in the circuit containing the cooling fan, heat sink, or cooling system, with the thermal switch placed close to the power device. Under normal operating conditions, the thermal switch is in the normally open state.

[0052] When a fault current occurs, the power device heats up. The heat generated by the power device, combined with the heat generated by the normally open thermal switch itself, causes the expansion bladder 6 to expand. When the temperature of the expansion bladder 6 reaches or exceeds the designed temperature threshold, the expansion bladder 6 expands, driving one end of the suspended first conductor 3 to move towards one end of the second conductor 4. This causes the convex side of the arc-shaped structure at one end of the first conductor 3 to make conductive contact with one end of the second conductor 4, thereby closing the normally open thermal switch. This connects the circuit containing the cooling fan, radiator, or cooling system, allowing the cooling fan, radiator, or cooling system to work and dissipate heat for the power device, thus achieving heat dissipation protection for the power device. At the same time, the first conductor 3 abuts against the limit element 71 on the limit indicator 7, driving the limit indicator 7 to move towards the outside of the housing. This causes the end of the limit indicator 7 facing outwards to extend beyond the outer surface of the housing wall, reminding the operator that the thermal switch has been activated and a circuit fault has occurred.

[0053] The advantage of the normally open thermal switch of the present invention is that it is a single device with a simple structure. It is only connected to a cooling fan, heat sink or cooling system when the device power cannot be dissipated normally by itself during fault circuit current, thereby reducing power loss.

[0054] In other embodiments, to improve the response speed of the normally open thermal switch, a heating resistor 8 is provided at the expansion bladder 6 as a current-limiting component. See also Figures 6 to 7 A heating resistor 8 is installed on the base 2 at the bottom of the accommodating space inside the housing. One end of the heating resistor 8 is electrically connected to the first conductor 3, which can be achieved through welding, conductive contact, or other conductive connection methods. The other end of the heating resistor 8 passes through the base 2 and is electrically connected to the end of the second conductor 4 located outside the housing. The heating resistor 8 forms a current-limiting circuit by conductively connecting the first conductor 3 and the second conductor 4. Because the resistance of the heating resistor 8 is much greater than the resistance of the first and second conductors, the current flowing through the heating resistor is very small. The small circuit flowing through the heating resistor cannot enable the cooling fan, radiator, or cooling system to work. In other words, under normal operating conditions, the circuit containing the cooling fan, radiator, or cooling system is not conductive.

[0055] Figures 6 to 7 Working principle:

[0056] Under normal operating conditions, the current in the current-limiting circuit with the heating resistor connected in series on the thermal switch is very small and can be ignored.

[0057] When a fault current occurs, the current flowing through the heating resistor increases, causing the resistor's temperature to rise and rapidly heating the expansion chamber. Combined with the heat generated by the power device, the expansion chamber expands rapidly, driving the first conductor 3 to displace and make conductive contact with the second conductor 4. Because the resistance of the first and second conductors is very small, almost all the current flows through them, and the current is almost normal. Therefore, the cooling fan, heat sink, or cooling system operates normally, dissipating heat for the power device and achieving thermal protection. Connecting a heating resistor can improve the response speed of the thermal switch; however, under normal operating conditions, the thermal switch experiences some power loss due to the presence of the heating resistor.

[0058] In the above embodiments, the limiting indicator is mounted on the first conductor to limit its initial position. However, when one end of the bent, cantilevered first conductor located within the housing has a certain rigidity, even without the limiting indicator, the first conductor will not displace towards the second conductor and make conductive contact with it due to its own rigidity. Therefore, when the bent first conductor within the housing has sufficient rigidity, even if one end of the cantilevered first conductor is vibrated, it will not make conductive contact with the second conductor. In this case, the limiting indicator only needs to be placed on the displacement path of the first conductor, without limiting its position. When the first conductor has sufficient rigidity, the driving force generated by the expansion of the expansion bladder should increase accordingly to overcome the rigidity of the first conductor, allowing the first conductor to displace and make conductive contact with the second conductor.

Claims

1. A normally open thermal switch, characterized in that, The device includes a housing with a cavity. A first conductor and a second conductor are disposed within the cavity of the housing. One end of the first conductor and the second conductor located outside the housing serves as the connection terminal of the normally open thermal switch, respectively. The first conductor and the second conductor located inside the housing are insulated from each other. One end of the first conductor located inside the housing is cantilevered. An expansion bladder is disposed between the cantilevered first conductor and the housing. A limit indicator and one end of the second conductor located inside the housing are respectively located on the displacement path of the cantilevered first conductor. One end of the limit indicator is inserted through and limited on the housing wall, and the other end is disposed on the first conductor. When the temperature of the expansion bladder reaches a set temperature threshold, the expansion bladder expands toward the first conductor, driving the first conductor to displace and make conductive contact with the second conductor, so that the first conductor and the second conductor are directly connected. At the same time, the limit indicator is driven to extend out of the housing.

2. The normally open thermal switch according to claim 1, characterized in that, An accommodating space is provided in the housing, the opening end of the accommodating space faces the first conductor which is cantilevered, the expansion bladder is located in the accommodating space, and the accommodating space limits the expansion bladder to expand only in the direction of the opening end of the accommodating space, the first conductor cantilevered across the opening end of the accommodating space, is located on the expansion direction path of the expansion bladder and is in contact with the expansion bladder; the limiting indicator is located outside the accommodating space.

3. The normally open thermal switch according to claim 2, characterized in that, A raised rib is provided on one side of the accommodating space, and the first conductor is laid on the raised rib.

4. The normally open thermal switch according to claim 3, characterized in that, A positioning groove is provided on the protruding rib, and the first conductor is placed in the positioning groove.

5. The normally open thermal switch according to claim 2, characterized in that, A heating resistor is also provided in the cavity of the housing as a current limiting device, and the expansion bladder is disposed on the heating resistor; the two ends of the heating resistor are electrically connected to the first conductor and the second conductor in the housing to form a current limiting circuit; when the first conductor and the second conductor are in direct conductive contact, the current flows through the series circuit formed by the first conductor and the second conductor connected in series.

6. The normally open thermal switch according to claim 1, characterized in that, The limit indicator is mounted on the first conductor to limit the initial position of the first conductor.

7. The normally open thermal switch according to claim 6, characterized in that, A limiting member is provided on the outer peripheral surface of the limiting indicator located inside the housing. A limiting hole is opened on the first conductor. One end of the limiting indicator located inside the housing is inserted into the limiting hole. The limiting member presses on the first conductor to limit the initial position of the first conductor.

8. The normally open thermal switch according to claim 7, characterized in that, The limiting member is a horizontal bar-shaped structure disposed on the two opposite outer sides of the limiting indicator. The side of the limiting member facing the first conductor is set as an inclined surface. In the initial position and the final position, the first conductor remains in contact with the limiting member.

9. The normally open thermal switch according to claim 7, characterized in that, A through-hole is provided in the shell wall of the housing, and the limit indicator is installed in the through-hole.

10. The normally open thermal switch according to claim 9, characterized in that, The limiting indicator is positioned by a limiting structure, which is: an elastic barb structure is provided on the outer periphery of the limiting indicator, and the barb structure elastically abuts against the mounting hole to form the limiting structure; or the limiting indicator is assembled in the mounting hole in an interference fit to form the limiting structure; or a limiting spring is provided between the limiting member and the outer periphery of the housing wall of the mounting hole to form the limiting structure.

11. The normally open thermal switch according to claim 1, characterized in that, One end of the first and second conductors located outside the housing is provided outside the housing as the connection terminal of the thermal switch in a patch type, a bent flat type, or a straight quick-connect type.

12. The normally open thermal switch according to claim 1, characterized in that, The expansion bladder includes an elastic bag and a gas, liquid, or solid with a high coefficient of thermal expansion filled in the bag. When the solid with a high coefficient of thermal expansion is an integral structure and remains an integral structure after expansion, the expansion bladder is composed of a solid with a high coefficient of thermal expansion. Alternatively, the expansion bladder includes a stretchable bag and a gas, liquid, or solid with a high coefficient of thermal expansion filled in the bag. When the expansion bladder is not expanded, it is in a compressed state. When the expansion bladder expands, the expansion energy can deform from a compressed state to a stretched state.

13. The normally open thermal switch according to claim 12, characterized in that, The outer periphery of the expansion bladder, perpendicular to the direction of the force exerted by the expansion bladder on the first conductor, is configured with a retractable serrated structure.

14. The normally open thermal switch according to claim 1, characterized in that, One end of the first conductor located inside the housing is configured as an arc-shaped structure protruding toward the second conductor.

15. The normally open thermal switch according to any one of claims 1 to 14, characterized in that, The housing includes a cover and a base. The base is located at the open end of the cover and closes the open end. A rib is provided on the base. The inner surface of the base, the rib and the side wall of the cover form an accommodating space. The first conductor cantilevered over the accommodating space. The expansion bladder is disposed in the accommodating space and contacts the first conductor.

16. The normally open thermal switch according to claim 15, characterized in that, The cover and the base are connected and fixed by a snap-fit ​​mechanism.

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