High-voltage cabinet with self-adaptive pressure relief channel

Abstract

The invention discloses a high-voltage cabinet with a self-adaptive pressure relief channel, and belongs to the technical field of high-voltage cabinets, and the high-voltage cabinet comprises a cabinet body which is provided with a pressure relief port; the pressure relief plate is adaptively mounted at the pressure relief opening and seals the pressure relief opening, one side of the pressure relief plate is detachably connected with the cabinet body through an insulating material fastener, and the breaking strength of the insulating material fastener is adaptive to a preset pressure relief threshold value of the cabinet body; the sliding block can be driven to slide in one direction along the limiting piece through the extrusion counter-acting force between the extrusion part and the cabinet body, so that the pressure relief plate and the surface of the cabinet body finally form a flow guide channel, and on one hand, sundries, small animals and the like in the outdoor environment can be effectively prevented from invading the interior of the cabinet body; and on the other hand, when residual high-temperature gas in the cabinet body is gradually cooled and shrunk, external normal-pressure gas can smoothly enter the cabinet body through the flow guide channel to balance air pressure inside and outside the cabinet body in real time, so that structural damages such as door plate sinking and frame deformation caused by negative pressure difference of the cabinet body are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage cabinets, in particular to a high-voltage cabinet with an adaptive pressure relief channel. BACKGROUND

[0002] The high-voltage cabinet usually contains busbars, circuit breakers, cable heads and other key components. During long-term operation, internal arc short-circuit faults may be caused by factors such as insulation aging, condensation creepage, foreign matter invasion, and poor contact of contacts. When a fault occurs, the arc will release a large amount of heat within milliseconds, causing the air in the cabinet to expand rapidly and the internal air pressure to rise sharply. If the pressure cannot be released in time and effectively, the cabinet body will be deformed, broken or even exploded.

[0003] To solve the above problems, the existing technology generally adopts a protection scheme of setting a pressure relief port and a pressure relief plate on the high-voltage cabinet body. The traditional pressure relief structure is that the pressure relief plate is connected to the cabinet body through metal screws and nylon screws on both sides. When the pressure in the cabinet reaches a preset threshold, the nylon screws break or fail, and the pressure relief plate opens to release the pressure.

[0004] However, in actual use, if the pressure relief plate is deformed and cannot be reset, the pressure relief port is always in an open state, so that foreign matter or rodents in the external environment can easily enter the cabinet body. If the pressure relief plate is reset and re-seals the pressure relief port, as the high-pressure gas in the cabinet cools and shrinks, the external air cannot be supplemented after the pressure relief port is sealed, resulting in a pressure difference between the inside and outside of the cabinet body. Since the high-voltage cabinet body is usually a metal sheet splicing structure with limited rigidity, the extrusion force of the external atmospheric pressure will cause the cabinet body to be damaged, such as door panel depression, frame deformation, and partition cracking.

[0005] Therefore, it is necessary to provide a high-voltage cabinet with an adaptive pressure relief channel to solve the above technical problems. SUMMARY

[0006] The purpose of the present application is to provide a high-voltage cabinet with an adaptive pressure relief channel to solve the technical problems raised in the background.

[0007] Based on the above idea, the present application provides the following technical scheme: a high-voltage cabinet with an adaptive pressure relief channel, comprising: a cabinet body, a pressure relief port is formed on the cabinet body; a pressure relief plate, which is adaptively installed at the pressure relief port and seals the pressure relief port, is detachably connected to the cabinet body on one side through an insulating material fastener, and the breaking strength of the insulating material fastener is adapted to the preset pressure relief threshold of the cabinet body; a protruding portion is provided on the other side of the pressure relief plate, the pressure relief plate is hingedly connected to the cabinet body through the protruding portion, and the hinged connection position has a one-way movement freedom degree towards the side away from the cabinet body. The protruding part is provided with a pressing part towards the bottom side of the cabinet, when the pressure relief plate is turned away from the cabinet under the action of the cabinet pressure, the pressing part is in extrusion contact with the surface of the cabinet and forms a guiding force, which drives the hinge position of the pressure relief plate and the cabinet to gradually move away from the cabinet, so as to maintain the effective opening area of the pressure relief port.

[0008] As a further scheme of the present application: the insulation material fastener is a nylon screw with a breaking strength that can adapt to a preset pressure relief threshold.

[0009] As a further scheme of the present application: the hinge cooperation is composed of a limiting piece fixed to the cabinet, a sliding block slidingly arranged in the limiting piece, and a rotating shaft fixed to the protruding part, the rotating shaft is arranged through the sliding block and rotatably cooperates with the sliding block, and the sliding block can only slide away from the cabinet relative to the limiting piece.

[0010] As a further scheme of the present application: the rotating shaft is elastically connected with the sliding block along the circumferential direction of the rotating shaft, so that the pressure relief plate can be reset and re-covered on the pressure relief port.

[0011] As a further scheme of the present application: one end of the rotating shaft arranged through the sliding block is fixedly provided with a gear, and a rack is engaged outside the gear, the rack is assembled on the cabinet and only has a one-way movement freedom degree away from the cabinet.

[0012] As a further scheme of the present application: a guide plate is fixedly installed on the cabinet, a positioning strip is fixedly installed on the rack, and the positioning strip slides in a guide groove on one side of the guide plate.

[0013] As a further scheme of the present application: the cross sections of the positioning strip and the guide groove are both T-shaped.

[0014] As a further scheme of the present application: a limiting assembly is arranged between the positioning strip and the guide plate, and between the sliding block and the limiting piece, so that the sliding block and the rack can only move away from the cabinet.

[0015] As a further scheme of the present application: the limiting assembly includes a clamping jaw and a pin shaft connected with the clamping jaw, the pin shaft is arranged through the clamping jaw and rotatably connected with the clamping jaw, and the clamping jaw is elastically connected with the pin shaft along the circumferential direction of the pin shaft, the inner wall of the limiting piece and the side surface of the guide plate close to the rack are both provided with a clamping groove matched with the clamping jaw. Compared with the prior art, the beneficial effects of the present application are that when the pressure relief plate is deflected away from the cabinet under the impact force of the high-pressure gas in the cabinet, the extrusion reaction force between the extrusion part and the cabinet drives the sliding block to slide unidirectionally along the limiting piece, so that the protruding part is away from the surface of the cabinet with the sliding block; after the pressure in the cabinet is released, the pressure relief plate reversely rotates under the force of the elastic force, and finally forms the flow guide channel as shown in Figure 3 . On the one hand, it can effectively block the invasion of sundries, small animals and the like in the outdoor environment into the cabinet; on the other hand, when the high-temperature gas remaining in the cabinet gradually cools and shrinks, the external normal-pressure gas can smoothly enter the cabinet through the flow guide channel, and the air pressure inside and outside the cabinet is balanced in real time, so that structural damage such as door plate depression and frame deformation of the cabinet due to negative pressure difference is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0016] The present application will be further described below in combination with the drawings and examples.

[0017] Figure 1 is a schematic diagram of the overall structure of the present application; Figure 2 is a schematic diagram of the pressure relief plate of the present application in an open state; Figure 3 is a schematic diagram of the flow guide channel structure of the present application; Figure 4 is a schematic diagram of the extrusion part structure of the present application; Figure 5 is a schematic diagram of the pressure relief plate mounting structure of the present application; Figure 6 is an enlarged structural schematic diagram of A of the present application; Figure 5 is a schematic diagram of the gear and rack cooperation of the present application; Figure 7 is an enlarged structural schematic diagram of B of the present application; Figure 8 Figure 7 is a schematic diagram of the rack and guide plate cooperation of the present application. Figure 9 is a schematic diagram of the rack and guide plate cooperation of the present application.

[0018] In the figure: 1, cabinet; 101, pressure relief port; 2, pressure relief plate; 201, protruding part; 202, extrusion part; 3, nylon screw; 4, limiting piece; 5, claw; 6, sliding block; 7, clamping groove; 8, rotating shaft; 9, pulley; 10, guide plate; 11, gear; 12, rack; 1201, positioning strip; 13, elastic piece; 14, pin shaft; 15, flow guide channel. DETAILED DESCRIPTION

[0019] As Figures 1-9 ​As shown, a high-voltage cabinet with an adaptive pressure relief channel mainly comprises a cabinet body 1 and a pressure relief port 101 arranged on the cabinet body 1, and the pressure relief port 101 is blocked by a pressure relief plate 2. When an arc fault occurs inside the cabinet body 1, the gas inside the cabinet body 1 will be rapidly heated and expand outward. Due to the increase of the gas pressure inside the cabinet body 1, the pressure relief plate 2 is separated from the cabinet body 1, so that the high-pressure gas can be discharged through the pressure relief port 101, thereby avoiding the problem of explosion of the cabinet body 1 caused by the failure of timely discharge of high-pressure gas.

[0020] In actual use, the pressure relief port 101 can be arranged at the top, bottom or back of the cabinet body 1. In this embodiment, the pressure relief port 101 is located at the top of the cabinet body 1. In embodiment one, the pressure relief plate 2 is assembled at the pressure relief port 101 of the cabinet body 1 by fasteners. Specifically, the two sides of the pressure relief plate 2 are detachably connected to the cabinet body 1 by metal screws and nylon screws 3. When the gas pressure inside the cabinet body 1 rises sharply to a preset threshold due to a fault (such as arc short circuit), the nylon screw 3 will break due to the tensile force exceeding its breaking strength, causing the connection between the pressure relief plate 2 and the cabinet body 1 to fail. At this time, the pressure relief plate 2 is flipped away from the cabinet body 1 under the impact of the high-pressure gas in the cabinet, and the pressure relief port 101 is opened synchronously, so that the high-pressure gas in the cabinet body 1 can be discharged in a directional manner.

[0021] However, in actual application, when the pressure relief plate 2 is flipped and deformed under high pressure, it is difficult to reset to the sealing position of the pressure relief port 101, resulting in that the pressure relief port 101 is in an open state for a long time. Debris or rodents in the external environment can easily enter the interior of the cabinet body 1, which may cause secondary faults.

[0022] In embodiment two, the mounting structure of the pressure relief plate 2 is optimized. Specifically, the side of the pressure relief plate 2 away from the nylon screw 3 is fixedly hinged to the cabinet body 1. When the gas pressure in the cabinet body 1 rises to a preset threshold and causes the nylon screw 3 to break, the pressure relief plate 2 can be deflected away from the cabinet body 1 to open by rotating in a directional manner, which can effectively avoid irreversible large deformation of the pressure relief plate 2 after being impacted compared with the structure of embodiment one.

[0023] However, this hinged structure still has deficiencies: after the pressure relief plate 2 is opened for pressure relief, if it reversely resets under the action of gravity or residual elastic force and covers the pressure relief port 101 again, at this time the fault arc in the cabinet body 1 has extinguished, and the remaining high-temperature gas will quickly cool and shrink, resulting in the air pressure in the cabinet body 1 further dropping from the normal pressure state after pressure relief to a negative pressure state lower than the external atmospheric pressure. After the reset, the pressure relief plate 2 and the pressure relief port 101 form a sealed structure, and external air cannot enter the cabinet body 1 in time to balance the pressure, resulting in an obvious pressure difference between the inside and outside of the cabinet body 1. Since the cabinet body 1 of the high-voltage cabinet is mostly a structure welded by thin plates or spliced by bolts, the continuous extrusion of the external atmospheric pressure is likely to cause structural damages such as concave door panels, warped frames, and deformed compartment partitions in the cabinet body 1.

[0024] Based on the above problems, this solution improves the second embodiment, specifically referring to Figures 1-9 as shown: A protruding portion 201 is provided on the side of the pressure relief plate 2 away from the nylon screw 3. The protruding portion 201 can be integrally formed or welded with the pressure relief plate 2, and the protruding portion 201 can be a block structure and distributed on the front and rear sides of the pressure relief plate 2 or directly a strip structure. A limiting member 4 with a "return" - shaped structure is provided at the end of the protruding portion 201, and the limiting member 4 is fixedly connected to the cabinet body 1. A slider 6 slides in the limiting member 4, and a rotating shaft 8 fixed to the protruding portion 201 passes through the slider 6 and is rotatably connected to the slider 6. When the gas in the cabinet body 1 expands rapidly due to a line fault, the nylon screw 3 breaks and the pressure relief plate 2 can rotate around the axis of the rotating shaft 8 to open the pressure relief port 101, so that the high - pressure gas in the cabinet body 1 can be discharged through the pressure relief port 101.

[0025] Furthermore, the rotating shaft 8 is elastically connected to the slider 6 along its circumferential direction. Through this structure, after the high - pressure gas in the cabinet body 1 is discharged through the pressure relief port 101, the pressure relief plate 2 can reset under the action of elastic force and cover the pressure relief port 101 again, thereby preventing sundries or rodents in the external environment from entering the cabinet body 1 through the pressure relief port 101.

[0026] The bottom of the protruding portion 201 is flush with the bottom of the pressure relief plate 2, and both are closely attached to the surface of the cabinet body 1 (for the specific structure, refer to Figure 4 ). Among them, the area of the bottom of the protruding portion 201 near the outer side edge is set as an extrusion portion 202. When a fault occurs in the cabinet body 1 and the pressure relief plate 2 rotates away from the cabinet body 1 around the axis of the rotating shaft 8 to open, the extrusion portion 202 will produce an extrusion effect with the surface of the cabinet body 1, thereby forming a guiding force along the extending direction of the limiting member 4, driving the slider 6 to slide away from the cabinet body 1 along the limiting member 4. It should be clear that in this solution, the slider 6 and the limiting member 4 adopt a one - way sliding fit design, only allowing the slider 6 to move away from the cabinet body 1 and unable to reverse and reset.

[0027] Based on the above structural design, in actual working conditions: when the pressure relief plate 2 is deflected away from the cabinet 1 under the impact force of the high-pressure gas in the cabinet 1, the extrusion reaction force between the extrusion part 202 and the cabinet 1 drives the sliding block 6 to slide along the limiting piece 4 in one direction, so that the protruding part 201 moves away from the surface of the cabinet 1 with the sliding block 6; after the pressure in the cabinet 1 is released, the pressure relief plate 2 reverses under the action of the elastic force, and finally forms a flow guide channel 15 with the surface of the cabinet 1 as shown. Figure 3 The flow guide channel 15 has the following technical effects: on the one hand, it can effectively block the invasion of sundries, small animals and the like in the outdoor environment into the inside of the cabinet 1; on the other hand, when the sensor detection unit (such as an arc light sensor, a temperature sensor, a pressure sensor, etc.) in the cabinet 1 detects a fault signal, it will transmit the signal to the relay protection device to trigger a trip instruction to quickly cut off the fault circuit. Subsequently, as the residual high-temperature gas in the cabinet 1 gradually cools and shrinks, the external normal pressure gas can smoothly enter the cabinet 1 through the flow guide channel 15, and the air pressure inside and outside the cabinet 1 is balanced in real time, thereby avoiding structural damage such as door panel depression and frame deformation of the cabinet 1 due to negative pressure difference.

[0028] It should be noted that the linkage control of the above-mentioned sensor detection unit and the relay protection device is a mature technical means in the electrical field, and the specific circuit connection and control logic will not be described here.

[0029] In order to adaptively control the area of the flow guide channel 15, further improvements are made on the basis of the above-mentioned scheme, as follows: The end of the rotating shaft 8 extending to the outside of the sliding block 6 is fixedly sleeved with a gear 11, and the outside of the gear 11 is engaged with a rack 12. During the sliding process of the sliding block 6 along the limiting piece 4, the gear 11 can engage with the rack 12. Further, a guide plate 10 is fixedly installed on the cabinet 1, and the rack 12 and the guide plate 10 slide in one direction, so that the rack 12 can only slide away from the cabinet 1. Through this structure, when the pressure relief plate 2 is deflected away from the cabinet 1 along the rotating shaft 8, the gear 11 engages with the rack 12 and drives the rack 12 to gradually move away from the cabinet 1. When the pressure relief plate 2 is reset, the rotating shaft 8 will drive the gear 11 to rotate in the opposite direction. Since the rack 12 cannot slide towards the cabinet 1, when the gear 11 and the rack 12 are engaged in the opposite direction, the reverse force of the rack 12 on the gear 11 can drive the sliding block 6 to continue to slide away from the cabinet 1 along the limiting piece 4, so as to increase the area of the flow guide channel 15.

[0030] In summary, the area of the flow guide channel 15 in the present scheme has the adaptive adjustment characteristic of adapting to the fault pressure in the cabinet 1: the higher the fault gas pressure in the cabinet 1, the stronger the impact force on the pressure relief plate 2, which promotes the deflection angle of the pressure relief plate 2 to be farther away from the cabinet 1. The deflection angle of the pressure relief plate 2 is directly related to the meshing stroke of the gear 11 and the rack 12. The greater the deflection angle, the wider the meshing area of the gear 11 and the rack 12, and then through the transmission action of the gear 11 and the rack 12, the slider 6 is driven to move a farther distance away from the cabinet 1.

[0031] The displacement amount of the slider 6 is positively related to the opening area of the flow guide channel 15, that is, the farther the slider 6 moves, the greater the area of the flow guide channel 15 formed between the pressure relief plate 2 and the surface of the cabinet 1 after the pressure relief plate 2 is reset. Because the higher the initial gas pressure in the cabinet 1, the more gas is discharged during the pressure relief process, and the absolute value of the negative pressure formed by the subsequent gas cooling and contraction is also greater, at this time, through the self-adaptive expansion of the flow guide channel 15, the inflow efficiency of the external normal pressure gas can be greatly improved, the internal and external gas pressures of the cabinet 1 are quickly balanced, thereby solving the problem of structural deformation of the cabinet 1 caused by excessive negative pressure difference under the high gas pressure fault scene.

[0032] The rack 12 is fixedly installed with a positioning strip 1201, and the positioning strip 1201 slides in a guide groove on one side of the guide plate 10. It should be noted that the cross sections of the positioning strip 1201 and the guide groove are both T-shaped, thereby facilitating the separation of the positioning strip 1201 and the guide plate 10.

[0033] A limiting assembly is arranged between the positioning strip 1201 and the guide plate 10, and between the slider 6 and the limiting piece 4, so that the slider 6 and the rack 12 can only move away from the cabinet 1.

[0034] Specifically, the limiting assembly includes a claw 5 and a pin shaft 14 connected with the claw 5, and the claw 5 is arranged on the limiting piece 4. Figures 7-9As shown, the pin shaft 14 passes through the pawl 5 and is rotationally connected with the pawl 5, and the pawl 5 is elastically matched with the pin shaft 14 in the circumferential direction of the pin shaft 14, the inner wall of the limiting piece 4 and the side of the guide plate 10 close to the rack 12 are both provided with a clamping groove 7 matched with the pawl 5, and the end of the pawl 5 away from the pin shaft 14 can be inserted into the clamping groove 7 to limit the movement of the rack 12 or the sliding block 6 towards the side close to the cabinet 1. It should be noted that the pin shaft 14 at the limiting assembly on one side of the sliding block 6 is fixed with the sliding block 6, and the pin shaft 14 at the limiting assembly on one side of the positioning strip 1201 is fixed with the positioning strip 1201. Similar to the structure of the ratchet and pawl, in actual use, the pawl 5 is always deflected to the side of the clamping groove 7 under the elastic force, and in the process of moving the sliding block 6 or the rack 12 away from the cabinet 1, the end of the pawl 5 away from the pin shaft 14 can be inserted into the clamping groove 7 to avoid the reverse reset of the sliding block 6 or the rack 12.

[0035] Of course, the above-mentioned cooperation structure based on the pawl 5, the pin shaft 14 and the clamping groove 7 is only one of the preferred schemes for realizing one-way linear limiting of the present application. In actual application, various mature and reliable mechanical structures can also be used to achieve the same one-way linear limiting function, for example, by cooperating the wedge block with the groove, specifically, the elastic wedge block (such as wedge-shaped protrusion with compression spring) is arranged on the side surface of the sliding block 6, and the wedge-shaped groove matched with the elastic wedge block is arranged on the inner wall of the limiting piece 4 in the sliding direction; when the sliding block 6 moves away from the cabinet 1, the elastic wedge block is extruded and contracted by the side wall of the groove; when the sliding block 6 tries to move reversely, the elastic wedge block pops out and is embedded in the groove under the action of the spring force, thereby preventing the sliding block 6 from returning.

[0036] As shown in Figure 6 The bracket is fixedly installed on the side surface of the sliding block 6 and passes through the strip-shaped groove on the side surface of the limiting piece 4 and can slide relative to the limiting piece 4, the pulley 9 is rotationally installed on the bracket, and the pulley 9 rolls and fits on the outer surface of the limiting piece 4, thereby facilitating the stable cooperation of the sliding block 6 with the limiting piece 4.

[0037] As shown in Figures 8-9 The ladder-shaped holes are arranged on the pawl 5 and the sliding block 6, thereby facilitating the installation of the pin shaft 14 and the rotating shaft 8, specifically, the elastic member 13 such as torsional spring or coil spring is sleeved on the outer side of the pin shaft 14 and the rotating shaft 8. The two ends of the elastic member 13 sleeved on the pin shaft 14 are connected with the pin shaft 14 and the pawl 5 respectively, and the two ends of the elastic member 13 sleeved on the rotating shaft 8 are connected with the rotating shaft 8 and the sliding block 6 respectively.

[0038] The above-described are only preferred examples of the present application, which are used to facilitate the understanding and implementation of the present application by those skilled in the art, but cannot be used to limit the scope of the present application. Therefore, equivalent changes made within the scope of the present application are still within the scope of the present application.

Claims

1. A high-voltage switchgear with an adaptive pressure relief channel, characterized in that, include: Cabinet (1), wherein a pressure relief port (101) is provided on the cabinet (1); Pressure relief plate (2) is adapted to be installed at the pressure relief port (101) and seals the pressure relief port (101). One side of the pressure relief plate (2) is detachably connected to the cabinet (1) by an insulating material fastener. The breaking strength of the insulating material fastener is adapted to the preset pressure relief threshold of the cabinet (1). A protrusion (201) is provided on the other side of the pressure relief plate (2). The pressure relief plate (2) is hinged to the cabinet (1) through the protrusion (201), and the hinged position has a unidirectional degree of freedom of movement relative to the cabinet (1) toward the side away from the cabinet (1). The protrusion (201) is provided with a pressing part (202) on the side facing the bottom of the cabinet (1). When the pressure relief plate (2) rotates away from the cabinet (1) under the pressure inside the cabinet, the pressing part (202) presses against the surface of the cabinet (1) and forms a guiding force, which drives the hinge position of the pressure relief plate (2) and the cabinet (1) to gradually move away from the cabinet (1) so as to maintain the effective opening area of ​​the pressure relief port (101).

2. A high-voltage switchgear with an adaptive pressure relief channel according to claim 1, characterized in that: The insulating material fastener is a nylon screw (3) with a fracture strength that can be adapted to a preset pressure relief threshold.

3. A high-voltage switchgear with an adaptive pressure relief channel according to claim 1, characterized in that: The hinged connection consists of a limiting member (4) fixed to the cabinet (1), a slider (6) slidably disposed in the limiting member (4), and a rotating shaft (8) fixed to the protrusion (201). The rotating shaft (8) passes through the slider (6) and is rotatably engaged with the slider (6). The slider (6) can only slide relative to the limiting member (4) in a direction away from the cabinet (1).

4. A high-voltage switchgear with an adaptive pressure relief channel according to claim 3, characterized in that: The rotating shaft (8) is elastically connected to the slider (6) along its own circumference, so that the pressure relief plate (2) can be reset and cover the pressure relief port (101) again.

5. A high-voltage switchgear with an adaptive pressure relief channel according to claim 4, characterized in that: The rotating shaft (8) passes through one end of the slider (6) and is fixedly fitted with a gear (11), and a rack (12) meshes with the outside of the gear (11). The rack (12) is mounted on the cabinet (1) and has only one degree of freedom of movement in one direction away from the cabinet (1).

6. A high-voltage switchgear with an adaptive pressure relief channel according to claim 5, characterized in that: A guide plate (10) is fixedly installed on the cabinet (1), and a positioning strip (1201) is fixedly installed on the rack (12). The positioning strip (1201) slides in the guide groove on one side of the guide plate (10).

7. A high-voltage switchgear with an adaptive pressure relief channel according to claim 6, characterized in that: The cross-sections of the positioning strip (1201) and the guide groove are both T-shaped.

8. A high-voltage switchgear with an adaptive pressure relief channel according to claim 6, characterized in that: Limiting components are provided between the positioning bar (1201) and the guide plate (10), and between the slider (6) and the limiting member (4), so that the slider (6) and the rack (12) can only move in the direction away from the cabinet (1).

9. A high-voltage switchgear with an adaptive pressure relief channel according to claim 8, characterized in that: The limiting component includes a pawl (5) and a pin (14) connected to the pawl (5). The pin (14) passes through the pawl (5) and is rotatably connected to the pawl (5). The pawl (5) is elastically engaged with the pin (14) along the circumferential direction of the pin (14). The inner wall of the limiting component (4) and the side of the guide plate (10) near the rack (12) are provided with a groove (7) that engages with the pawl (5).

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