Miniature thermal protector applied to three-phase motor

Abstract

The invention relates to the technical field of thermal protectors, in particular to a small thermal protector applied to a three-phase motor, which comprises a shell and a bottom plate arranged in the shell, a bimetallic strip and a spring piece controlled by a bimetallic strip deformation circuit are sequentially arranged at one end of the bottom plate, and the bimetallic strip comprises an arc-shaped connecting area connected with the bottom plate. A U-shaped transition area is arranged at one end of the arc-shaped connection area, and a wave working area is arranged on one side of the U-shaped transition area in a pressing and embedding mode and used for improving the structural stability of the bimetallic strip. The wave working area comprises a wave active layer, an adhesion layer and a wave passive layer which are arranged in a stacked mode, and the wave active layer is arranged close to the spring piece and used for weakening deformation stress of the bimetallic strip and improving durability of the thermal protector. Structures of the bimetallic strip and the spring piece in the small thermal protector are improved, thermal protection deformation stress of the bimetallic strip is weakened, the service life of the thermal protector is prolonged, and sensitivity is improved.

Description

Technical Field

[0001] This invention relates to the technical field of thermal protectors, specifically a small thermal protector for three-phase motors. Background Technology

[0002] The working principle of small thermal protectors is mainly based on a dual protection mechanism of temperature sensing and current sensing. By monitoring changes in the motor's temperature or current, it promptly cuts off the circuit when an abnormality occurs, preventing damage to the motor due to overheating or overload. The bimetallic strip thermal protector is the most common type, its core consisting of a bimetallic strip made of two metals with different coefficients of thermal expansion (such as copper and iron) pressed together. When the motor is overloaded or heat dissipation is poor, causing the temperature to rise, the bimetallic strip bends due to the different expansion rates of the two metals, pushing the contacts to disconnect the circuit and cut off the motor power. When the temperature drops to a safe range, the bimetallic strip returns to its original shape, and the contacts close again (automatic reset type), or manual reset is required.

[0003] In the design of thermal protectors, two parallel moving contacts are riveted to one end of the bimetallic strip to connect to the external circuit. A lead extends from one end of the base plate to connect to the electrical wire. The thermal protector is soldered into the three-phase motor through the connection of the moving contacts and the lead to the external circuit wires. However, bimetallic thermal protectors rely on mechanical mechanisms for operation. After prolonged use, the operating mechanism may experience mechanical fatigue, aging, or deformation, causing the operating threshold to deviate from the set value, resulting in poor thermal protection performance. Therefore, it is necessary to design a small thermal protector with a simple structure, long service life, and sensitive protection for three-phase motors. Summary of the Invention

[0004] The purpose of this invention is to provide a small thermal protector for three-phase motors to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A small thermal protector for a three-phase motor includes a housing and a base plate disposed in the housing. A bimetallic strip and a spring sheet controlled by a bimetallic strip deformation circuit are sequentially disposed at one end of the base plate. The bimetallic strip includes an arc-shaped connecting area connected to the base plate. One end of the arc-shaped connecting area is configured as a U-shaped transition area. A wave working area is pressed into one side of the U-shaped transition area to increase the structural stability of the bimetallic strip. The wave working area includes a wave active layer, an adhesive layer and a wave passive layer stacked together. The wave active layer is located close to the spring sheet to reduce the deformation stress of the bimetallic sheet and increase the durability of the thermal protector.

[0006] Preferably, a counteracting component is provided on the side of the housing near the spring sheet to counteract excess deformation of the bimetallic sheet and reduce losses. The offsetting component has an arc-shaped portion in the middle, and an offsetting portion is provided at one end of the arc-shaped portion near the spring sheet. The offsetting portion is inclined toward the spring sheet, and a moving gap is provided between the offsetting portion and the spring sheet.

[0007] Preferably, the offsetting component is made of an elastic insulating material, the offsetting component has a C-shaped structure, an elastic strip is provided in the middle of the offsetting component, and the distance between the offsetting part and the spring sheet is 0.2-1mm greater than the distance between the bimetallic strip and the spring sheet.

[0008] Preferably, the damping component includes a connecting piece connected to the arcuate portion, the connecting piece being connected to the housing, and the inner wall of the housing being provided with a damping pad for protecting the thermal protector from vibration and impact.

[0009] Preferably, the base plate is provided with a riveting end that penetrates the bimetallic strip and the spring sheet, the bimetallic strip is inclinedly disposed in the housing, and a gap is provided between the bimetallic strip and the spring sheet.

[0010] Preferably, the spring sheet is provided with an actuating contact that contacts the bimetallic strip when deformed, and a control contact that fits against the base plate on the side near the bimetallic strip. Both the actuating contact and the control contact are in the shape of an eagle's beak arc.

[0011] Preferably, both the actuating contact and the control contact are provided with elastic sheets on their outer sides, and the inner thickness of the elastic sheets is smaller than the outer thickness, which is used to disperse stress and buffer.

[0012] Preferably, a protective component is provided on the side of the bimetallic strip away from the spring sheet, a resistance wire is provided on the outside of the protective component, an adhesive layer connected to the bimetallic strip is provided on the outside of the resistance wire, and a connecting wire connected to the base plate is provided at the end of the resistance wire for early warning protection of the thermal protector.

[0013] Preferably, an indicator light connected to the base plate is provided on the outer side of the housing, the indicator light is provided with a lighting threshold, and a spring part is provided at one end of the connecting wire near the bimetallic strip.

[0014] Preferably, the wave active layer is made of copper-nickel-manganese alloy, the adhesive layer is made of nickel-cobalt alloy, and the wave passive layer is made of iron-nickel-chromium alloy.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, by setting up a multi-regional collaborative structure of arc-shaped connection area, U-shaped transition area and wave-shaped working area on the bimetallic sheet, the problem of stress concentration at the fixed end of the traditional planar bimetallic sheet can be changed. The installation stress is dispersed by the arc-shaped curved surface, the deformation tension is reduced by the wave-shaped structure, the connection stability between the multiple regions of the bimetallic sheet is increased by the U-shaped transition area, and the deformation end of the bimetallic sheet can be optimized by the adhesive layer through the improvement of the materials of the wave active layer and wave passive layer in the bimetallic sheet, thereby extending the fatigue resistance of the bimetallic sheet and increasing the service life of the thermal protector. 2. In this invention, the design of the offsetting component between the spring sheet and the base plate can be used to precisely match the distance between the offsetting part and the spring sheet. This allows the deformation of the bimetallic strip after the spring sheet is pushed open to disconnect the circuit when the temperature of the bimetallic strip changes to bend in the opposite direction to the deformation of the offsetting part, thereby offsetting the deformation of the offsetting part. The elastic tension of the offsetting part is used to limit the maximum deformation of the bimetallic strip, avoiding excessive wear of the bimetallic strip and improving the temperature protection sensitivity of the thermal protector. 3. In this invention, by using a resistance wire in the protective component, the temperature change on the surface of the bimetallic strip can be sensed in real time. The resistance fluctuation of the resistance wire can be used to transmit the resistance signal to the indicator light on the outside of the housing through the connecting wire. When the resistance reaches the threshold, the indicator light will illuminate as a warning. This allows for sensitive detection of the operating environment of the thermal protector, facilitating rapid shutdown and maintenance of the three-phase motor. It also avoids serious faults such as coil burnout caused by prolonged motor overload, reduces motor maintenance costs, and improves the effectiveness of the thermal protector. Attached Figure Description

[0016] Figure 1 This is a partial structural cross-sectional view of the thermal protector in this invention; Figure 2 This is an exploded view of a partial structure of the thermal protector in this invention; Figure 3 This is a schematic diagram of the structure of the base plate and the spring sheet in this invention; Figure 4 This is an exploded view of the spring sheet structure in this invention; Figure 5 This is a schematic diagram of the bimetallic sheet in this invention; Figure 6 This is an exploded view of the bimetallic sheet structure in this invention; Figure 7 This is a partial structural diagram of the protective component in this invention; Figure 8 This is an exploded view of the structure of the components and levers introduced in this invention.

[0017] In the diagram: 1. Outer shell; 2. Base plate; 3. Bimetallic strip; 4. Spring sheet; 5. Arc-shaped connection area; 6. U-shaped transition area; 7. Wave working area; 8. Wave active layer; 9. Adhesive layer; 10. Wave passive layer; 11. Protective component; 12. Resistance wire; 13. Adhesive layer; 14. Spring part; 15. Connecting wire; 16. Pushing contact; 17. Control contact; 18. Elastic sheet; 19. Riveted end; 20. Counteracting component; 21. Connecting piece; 22. Arc-shaped part; 23. Counteracting part; 24. Movement gap; 25. Damping pad; 26. Indicator light. Detailed Implementation

[0018] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] Please see Figure 1-8 The present invention provides a technical solution: A small thermal protector for three-phase motors is disclosed. Current thermal protectors using a bimetallic strip 3 for circuit protection involve attaching a housing 1 to the outside of the three-phase motor. A base plate 2 is located inside the housing 1 and connected to the external circuitry. A bimetallic strip 3 and a spring plate 4 are located on one side of the base plate 2, with one end of the spring plate 4 in contact with the circuitry on the base plate 2. Utilizing the different heat resistance coefficients of the two metals on the bimetallic strip 3, the bimetallic strip 3 deforms towards the spring plate 4 when exposed to high temperatures, causing the spring plate to separate from the base plate 2 and disconnecting the three-phase motor circuit for thermal protection. To improve the lifespan of the bimetallic strip in the thermal protector and enhance its protection sensitivity and accuracy, the bimetallic strip 3 is modified. First, the part connecting the bimetallic strip 3 and the base plate 2 is set as an arc-shaped connection area 5 (bending radius of 2-4mm). The stress at the connection end between the bimetallic strip 3 and the base plate 2 is weakened. A U-shaped transition area 6 is set at one end of the arc-shaped connection area 5. A wave working area 7 (wave height of 1-3mm and wavelength of 5-8mm) is pressed into one side of the U-shaped transition area 6 to increase the structural stability of the bimetallic strip 3. The structural characteristics between the U-shaped transition area 6 and the wave-shaped bimetallic strip 3 are used to increase the connection between the two areas. The wave-shaped structure of the wave working area 7 is used to weaken the deformation tension generated when the bimetallic strip 3 deforms, and to avoid cracking at the connection end of the two areas due to frequent deformation. The three-dimensional structure of the wave-shaped working area can evenly distribute the deformation stress to the wave peaks and valleys, reduce the local stress fluctuation during bending deformation, and fully adapt to the high-frequency operation scenarios during the start-up, operation and shutdown of the three-phase motor, greatly reducing the risk of structural fatigue. Next, wave active layer 8, adhesive layer 9 and wave passive layer 10 are stacked in wave working area 7. Wave active layer 8 is placed close to spring plate 4. By utilizing the wave-shaped structure of the two sides, the deformation stress of bimetallic sheet 3 is weakened, and the durability of thermal protector is increased.

[0020] To avoid excessive deformation of the bimetallic strip 3 after heat protection, such as Figure 2 and 3 As shown, in some embodiments, a counteracting component 20 may be provided in the housing 1 on the side near the spring sheet 4. The middle part of the counteracting component 20 is an arc-shaped part 22, and the end of the arc-shaped part 22 near the spring sheet 4 is a counteracting part 23. The outer side of the counteracting part 23 is inclined towards the spring sheet 4. A moving gap 24 is provided between the counteracting part 23 and the spring sheet 4 to disconnect the circuit of the spring sheet 4. When the bimetallic strip 3 deforms and drives the spring sheet 4 to separate from the base plate 2 and disconnect the circuit, it can back against the spring sheet 4 in the opposite direction, thereby counteracting the excessive deformation of the bimetallic strip 3, preventing excessive deformation of the bimetallic strip 3, and reducing the wear of the bimetallic strip 3.

[0021] In some embodiments, the offsetting component 20 can be made of elastic insulating material and configured in a C-shape to facilitate the offsetting component 20 to utilize its own deformation and increase deformation stability through the central arc structure. Then, an elastic strip is provided in the middle of the offsetting component 20 to improve structural stability. Next, the distance between the offsetting part 23 and the spring sheet 4 is greater than the distance between the bimetallic strip 3 and the spring sheet 4 by 0.2-1 mm, providing favorable conditions for offsetting the excess deformation of the bimetallic strip 3.

[0022] When the offset component 20 is installed, a connecting piece 21 is set on the offset component 20. The connecting piece 21 is connected to the arc-shaped part 22. When the connecting piece 21 is installed, the connecting piece 21 is connected to the outer shell 1 by riveting. In order to increase the connection between the offset component 20 and the outer shell, a damping pad 25 (thickness of 0.5mm-2mm) can be set on the inner wall of the outer shell 1, located between the outer shell 1 and the connecting piece 21, to protect the thermal protector from vibration and impact.

[0023] At the same time, such as Figure 1 and 2 As shown, the bimetallic strip 3 and the spring plate 4 are fixed to one end of the base plate 2 by riveting end 19, and the bimetallic strip 3 is inclinedly set in the housing 1. A gap is provided between the bimetallic strip 3 and the spring plate 4 to allow the bimetallic strip 3 to move during the heat deformation process. The spring plate 4 can provide favorable conditions for the circuit disconnection of the thermal protector.

[0024] To reduce wear caused by the bimetallic strip 3 pushing open the spring plate 4, a protective structure will be added to the contact end of the two structures, and the contact end between the spring plate 4 and the base plate 2 will also be protected. Figure 2 , 3As shown in Figure 4, in some embodiments, an actuating contact 16 is provided on the side of the spring sheet 4 near the bimetallic strip 3 to protect the contact end between the bimetallic strip 3 and the spring sheet 4 when deformed. A control contact 17 is provided at the contact point between the spring sheet 4 and the base plate 2 to protect the lifting and lowering of the spring sheet 4. Furthermore, both the actuating contact 16 and the control contact 17 can be shaped into an eagle beak arc structure. An elastic sheet 18 is provided on the outer side of both the actuating contact 16 and the control contact 17. The inner thickness of the elastic sheet 18 is smaller than its outer thickness. The structural deformation of the elastic sheet 18 is used to disperse stress for buffering and increase durability.

[0025] In some embodiments, to improve the accuracy of bimetallic strip 3 heat detection and quickly display high-temperature environments, such as... Figure 2 and 7 As shown, a protective component 11 can be provided on the side of the bimetallic strip 3 away from the spring plate 4. A resistance wire 12 is used on the outside of the protective component 11. The resistance wire 12 is used to detect the different resistance states generated by temperature changes, so that the thermal protector can use the resistance wire 12 as a sensor to detect the temperature of the motor with high precision. Then, an adhesive layer 13 is provided on the outside of the resistance wire 12 to connect it to the bimetallic strip 3. The end of the resistance wire 12 is connected to the base plate 2 through a connecting wire 15. The end of the connecting wire 15 near the bimetallic strip 3 is set as a spring part 14 to facilitate the shape change of the bimetallic strip 3. The detection data is transmitted to the circuit control terminal on the base plate 2 of the thermal protector to provide temperature warning protection for the thermal protector.

[0026] In the use of the protective component 11, an indicator light 26 can be installed on the outside of the housing 1. The indicator light 26 is connected to the base plate 2 to facilitate the transmission of the resistance value of the resistance wire 12 to the indicator light 26, control the switch of the indicator light 26, and then set a lighting threshold in the indicator light 26. After the resistance wire 12 detects a change in motor temperature, its own resistance value changes accordingly. This resistance signal is transmitted to the circuit control module on the base plate 2 through the connecting line 15. The circuit control module compares the received resistance signal with the preset threshold. When the resistance value exceeds the preset threshold, the temperature warning mechanism is immediately triggered, and the indicator light 26 is controlled to light up, providing an early warning of the high temperature state of the motor, so that external personnel can shut down the motor in time and extend the service life of the thermal protector.

[0027] To increase the fatigue strength of the bimetallic strip 3 in the thermal protector, in some embodiments, the active wave layer 8 can be made of copper-nickel-manganese alloy, the adhesive layer 9 of nickel-cobalt alloy, and the passive wave layer 10 of iron-nickel-chromium alloy. The active wave layer 8 and the passive wave layer 10 are bonded to the adhesive layer 9 by vacuum diffusion welding to achieve atomic-level bonding at the interface, eliminating the interface stress concentration in traditional composite processes. After "low-temperature aging + gradient annealing" treatment (low-temperature aging refers to heating and holding the material at a lower temperature (300℃→200℃→100℃) to eliminate internal stress, stabilize the structure and properties; gradient annealing is to gradually reduce the heating temperature according to the temperature gradient, holding for 1 hour at each stage to further optimize the internal structure of the material and reduce residual stress), the residual stress inside the material is reduced, increasing the service life of the thermal protector.

[0028] Working principle of this invention: The small thermal protector for three-phase motors operates through a process of "temperature detection - deformation triggering - circuit protection - early warning," achieving thermal protection for the three-phase motor through the coordinated action of various components. The specific steps are as follows: Step 1: During the use of the thermal protector housing 1 against the outside of the three-phase motor, the heat generated by the motor during operation is transferred to the inside of the housing. The resistance wire 12 in the protection component 11 senses the temperature change in real time, and its resistance value changes accordingly. The resistance signal detects the temperature inside the housing, and the detected data is transmitted to the circuit control module on the base plate 2 via the connecting wire 15 (the end near the bimetallic strip is the spring part 14, which is adapted to deformation). When the resistance value exceeds the lighting threshold of the indicator light 26, the circuit control module triggers an alarm, illuminating the indicator light 26 on the outside of the housing 1, prompting the operator that the motor is in a high-temperature state, allowing for timely shutdown and maintenance, and providing rapid and sensitive protection for the three-phase motor to prevent the fault from escalating.

[0029] Step two: As the motor surface temperature continues to rise, the bimetallic strip 3 deforms towards the spring plate 4 due to the difference in thermal expansion coefficients between the two metals (the active wave layer 8 is a copper-nickel-manganese alloy, and the passive wave layer 10 is an iron-nickel-chromium alloy). The bimetallic strip 3 bends towards the spring plate 4, and the deformed bimetallic strip 3 pushes the actuating contact 16 on the spring plate 4, causing the control contact 17 on the spring plate 4 to separate from the circuit on the base plate 2, disconnecting the power supply circuit of the three-phase motor and preventing the motor from being damaged due to high temperature overload. During this process, the actuating contact 16 (eagle-beak-shaped arc) on the spring plate 4 contacts the bimetallic strip 3, the control contact 17 adheres to the base plate 2, and the outer elastic sheet 18 (thin on the inner side and thick on the outer side) disperses the contact stress, reduces wear, and extends the component life. The arc-shaped connection area 5 on the bimetallic sheet 3 weakens the stress at the connection end with the base plate 2, the U-shaped transition area 6 ensures structural stability, and the wave working area 7 disperses deformation tension through the wave structure, avoiding cracking of the bimetallic sheet 3 due to frequent deformation and increasing the structural stability of the bimetallic sheet 3.

[0030] Step 3: After the spring plate 4 separates from the base plate 2, the bimetallic strip 3 may continue to deform. At this time, the offsetting component 20 inside the housing 1 comes into play. The offsetting component 20 is an elastically insulating C-shaped structure. Its offsetting part 23 is inclined towards the spring plate 4, and the distance between it and the spring plate 4 is 0.2-1mm larger than the distance between the bimetallic strip 3 and the spring plate 4. The excess deformation of the bimetallic strip 3 pushes the spring plate 4 towards the offsetting part 23. The offsetting part 23, through its own elastic deformation, resists the spring plate 4 in the opposite direction, limiting the maximum deformation of the bimetallic strip 3, avoiding excessive wear, ensuring the accuracy of subsequent reset, extending the service life of the bimetallic strip, and thus improving the performance of the thermal protector and providing sensitive protection for the three-phase motor.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. The present invention is not limited to the above embodiments; the embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A small thermal protector for a three-phase motor, comprising a housing (1) and a base plate (2) disposed within the housing (1), wherein a bimetallic strip (3) and a spring plate (4) controlled by a deformation circuit of the bimetallic strip (3) are sequentially disposed at one end of the base plate (2), characterized in that: The bimetallic sheet (3) includes an arc-shaped connecting area (5) connected to the base plate (2). One end of the arc-shaped connecting area (5) is set as a U-shaped transition area (6). A wave working area (7) is pressed into one side of the U-shaped transition area (6) to increase the structural stability of the bimetallic sheet (3). The wave working area (7) includes a wave active layer (8), an adhesive layer (9) and a wave passive layer (10) stacked together. The wave active layer (8) is located close to the spring sheet (4) to reduce the deformation stress of the bimetallic sheet (3) and increase the durability of the thermal protector.

2. A small thermal protector for a three-phase motor according to claim 1, characterized in that: A counteracting component (20) is provided on the side of the outer shell (1) near the spring sheet (4) to counteract the excess deformation of the bimetallic sheet (3) and reduce losses; The offset component (20) has an arc-shaped part (22) in the middle, and an offset part (23) is provided at one end of the arc-shaped part (22) near the spring sheet (4). The offset part (23) is inclined toward the spring sheet (4), and a moving gap (24) is provided between the offset part (23) and the spring sheet (4).

3. A small thermal protector for a three-phase motor according to claim 2, characterized in that: The offset component (20) is an elastic insulating material. The offset component (20) has a C-shaped structure. An elastic strip is provided in the middle of the offset component (20). The distance between the offset part (23) and the spring sheet (4) is greater than the distance between the bimetallic strip (3) and the spring sheet (4) by 0.2-1mm.

4. A small thermal protector for a three-phase motor according to claim 3, characterized in that: The offsetting component (20) includes a connecting piece (21) connected to the arc-shaped portion (22), the connecting piece (21) being connected to the outer shell (1), and the inner wall of the outer shell (1) being provided with a damping pad (25) for protection against vibration and impact on the thermal protector.

5. A small thermal protector for a three-phase motor according to claim 1, characterized in that: The base plate (2) is provided with a riveting end (19) that penetrates the bimetallic strip (3) and the spring sheet (4). The bimetallic strip (3) is inclinedly disposed in the outer shell (1), and a gap is provided between the bimetallic strip (3) and the spring sheet (4).

6. A small thermal protector for a three-phase motor according to claim 1, characterized in that: The spring sheet (4) is provided with an actuating contact (16) that is in contact with the deformation of the bimetallic sheet (3) and a control contact (17) that is attached to the base plate (2) on the side near the bimetallic sheet (3). The actuating contact (16) and the control contact (17) are both in the shape of an eagle's beak arc.

7. A small thermal protector for a three-phase motor according to claim 6, characterized in that: Both the actuating contact (16) and the control contact (17) are provided with elastic sheets (18) on their outer sides. The inner thickness of the elastic sheet (18) is smaller than its outer thickness, which is used to disperse stress and buffer.

8. A small thermal protector for a three-phase motor according to claim 1, characterized in that: A protective component (11) is provided on the side of the bimetallic strip (3) away from the spring sheet (4). A resistance wire (12) is provided on the outside of the protective component (11). An adhesive layer (13) connected to the bimetallic strip (3) is provided on the outside of the resistance wire (12). A connecting wire (15) connected to the base plate (2) is provided at the end of the resistance wire (12) for early warning protection of the thermal protector.

9. A small thermal protector for a three-phase motor according to claim 8, characterized in that: An indicator light (26) connected to the base plate (2) is provided on the outer side of the outer casing (1). The indicator light (26) is provided with a lighting threshold. A spring part (14) is provided at one end of the connecting line (15) near the bimetallic strip (3).

10. A small thermal protector for a three-phase motor according to claim 9, characterized in that: The active wave layer (8) is made of copper-nickel-manganese alloy, the adhesive layer (9) is made of nickel-cobalt alloy, and the passive wave layer (10) is made of iron-nickel-chromium alloy.

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