Three-phase three-wire electronic molded case circuit breaker

Abstract

This invention discloses a three-phase three-wire electronic molded case circuit breaker, including a base and a middle cover assembly. A transition assembly and an arc-extinguishing assembly are mounted on the base and connected to it via the middle cover assembly. The base also contains a tripping assembly and an armature assembly. The tripping assembly includes a frame with a lever mounted on it and a handle on the lever. A traction rod is located on one side of the frame, and an arc-shaped surface is located on one side of the traction rod. The armature assembly includes a fixed seat, one side of which is rotatably connected to a support frame. An extension rod is located on the side of the support frame away from the fixed seat. When it is necessary to reduce the distance between the contact block and the facing surface of the traction rod, the extension rod can be directly pulled upwards from the outside of the traction rod. When it is necessary to increase the distance between the contact block and the facing surface of the traction rod, the extension rod can be pulled downwards. Because the extension rod is extended, it is easier to deform, thus facilitating the adjustment of the distance between the traction rod and the contact block.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment technology, specifically to a three-phase three-wire electronic molded case circuit breaker. Background Technology

[0002] In molded case circuit breakers, the armature is a key moving component in the tripping mechanism. Its main function is to respond to changes in electromagnetic force and trigger the free tripping mechanism to achieve rapid circuit disconnection. Since the armature's contact portion drives the traction rod, the distance between the armature's contact portion and the traction rod needs to be manually fine-tuned in practical applications to ensure that the armature can effectively and reliably trigger the traction rod. However, in existing products, the armature is placed inside the traction rod, which makes armature adjustment cumbersome and even difficult. Summary of the Invention

[0003] The purpose of this invention is to provide a three-phase three-wire electronic molded case circuit breaker to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a three-phase three-wire electronic molded case circuit breaker, comprising a base and a middle cover assembly, wherein a transition assembly and an arc-extinguishing assembly are mounted on the base, and the middle cover assembly is connected to the base so that the electrical components of the transition assembly are connected to the electrical components within the middle cover assembly; the base also contains a tripping assembly and an armature assembly; the tripping assembly includes a frame, a lever is mounted on the frame, and a handle is provided on the lever; a traction rod is provided on one side of the frame, and an arc surface is provided on one side of the traction rod, through which space is released to facilitate the movement of the handle; the armature assembly includes a fixed seat, one side of the fixed seat is rotatably connected to a support frame, and an extension rod is provided on the side of the support frame away from the fixed seat, through which an abutment block provided on the extension rod extends to below the traction rod.

[0005] As a preferred technical solution of the present invention: the arc extinguishing component is installed in the arc extinguishing cavity provided on the base, and the side wall of the arc extinguishing cavity is also provided with an inclined surface, and the inclined surface is used to guide the arc extinguishing component to be assembled into the arc extinguishing cavity.

[0006] As a preferred technical solution of the present invention: the base is provided with a mounting seat, and a wiring terminal is provided in the mounting seat; wherein, the wiring terminal includes a conductive element; the conductive element includes a connecting plate, the connecting plate is provided with a groove, and the connecting plate is divided into a first mounting part and a second mounting part through the groove; both the first mounting part and the second mounting part are provided with a first clamping part and a second clamping part, and a wire clamp is fitted on the outside of the first clamping part and the second clamping part, and the wire clamp is moved on the corresponding clamping part by the provided bolts to clamp the wire.

[0007] As a preferred technical solution of the present invention: the mounting base is further provided with a slot, and is connected to the slot by a partition to prevent the wiring terminal from contacting the components inside the base.

[0008] As a preferred embodiment of the present invention: the distance between the first clamping part and the connecting plate is smaller than the distance between the second clamping part and the connecting plate, and both the first clamping part and the second clamping part are parallel to the connecting plate.

[0009] As a preferred embodiment of the present invention, the terminal block further includes a protective cover, which is fitted over the conductive element so that the wire clamp located on the first clamping part and the wire clamp located on the second clamping part are staggered.

[0010] As a preferred embodiment of the present invention: the protective cover is further provided with a first isolation plate and a second isolation plate; and one end of the first isolation plate and the second isolation plate are both inserted into the slot; the bottom surface of the protective cover is also provided with a wire inlet hole, and the number of the wire inlet holes is equal to the number of the wire clamps; the outer side surface of the protective cover is also provided with a round hole, and the number of the round holes is equal to the number of the wire clamps.

[0011] As a preferred technical solution of the present invention: the adapter assembly includes a bracket, on which an electronic trip unit and a circuit board are integrated; the middle cover assembly includes a middle cover, and a metering module and a communication module are provided on the side of the middle cover away from the adapter assembly; the communication module and the metering module are both connected to the circuit board in a board-to-board relationship.

[0012] As a preferred technical solution of the present invention: the electronic trip unit and the circuit board are connected in a board-to-wire relationship; the bracket is provided with a first mounting cavity and the electronic trip unit is provided in the first mounting cavity; a second mounting cavity is also provided below the first mounting cavity, and the circuit board is installed through the second mounting cavity.

[0013] As a preferred technical solution of the present invention: one side of the bracket is provided with a plug plate, and the plug plate is adapted to be connected to a slot provided on the base; the second mounting cavity is also provided with a socket, and the battery module installed on the circuit board is accommodated through the socket; the bottom of the middle cover is hinged to the provided cover plate.

[0014] The beneficial effects of the present invention by adopting the above technical solution are as follows: 1. Due to the setting of the extension rod, the contact block is close to the outside of the traction rod. When it is necessary to reduce the distance between the contact block and the facing surface of the traction rod, the extension rod can be directly pulled upward from the outside of the traction rod; when it is necessary to increase the distance between the contact block and the facing surface of the traction rod, the extension rod can be pulled downward; since the length of the extension rod itself is extended, it is easy to deform, thereby facilitating the adjustment of the distance between the traction rod and the contact block. 2. Because the traction rod has an arc surface, the arc surface is used to release space so that the handle is not interfered with by the traction rod when it is rotated; that is, when the handle arc pushes the release component to move, the handle will have a deformation amount, so the traction rod needs to provide space for the movement of the handle so that the handle will not come into contact with the traction rod when the arc deformation occurs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of one side of the main structure of the present invention after disassembly; Figure 2 for Figure 1 A magnified view of a portion of point A in the middle; Figure 3 This is a side view of the exploded internal structure of the base of the present invention; Figure 4 This is a schematic diagram of the other side of the internal structure of the base of the present invention after disassembly; Figure 5 This is a partial cross-sectional structural diagram of the base of the present invention; Figure 6 for Figure 5 A magnified view of a portion of point B in the middle; Figure 7 for Figure 5 A magnified view of a portion of point C in the middle; Figure 8 This is a side view of the tripping assembly of the present invention; Figure 9 This is a schematic diagram of the main structure of the armature assembly of the present invention; Figure 10 This is an exploded structural diagram of the cover assembly in this invention; Figure 11 This is a schematic diagram of one side of the structure after the transfer assembly is decomposed according to the present invention; Figure 12 This is a schematic diagram of the back structure of the support frame of the present invention; Figure 13 This is a schematic diagram of one side of the disassembled terminal block of the present invention; Figure 14 This is a schematic diagram of the other side of the disassembled terminal block of the present invention; Figure 15 This is a cross-sectional structural diagram of the protective cover of the present invention; Figure 16 This is a schematic diagram of the main structure of the conductive component of the present invention.

[0016] In the diagram: 1. Base; 2. Middle cover assembly; 20. Middle cover; 21. Cover plate; 22. Metering module; 23. Communication module; 3. Wiring terminal; 31. Protective cover; 310. First isolation plate; 311. Second isolation plate; 312. Cable inlet; 313. Round hole; 32. Conductive component; 320. Connecting plate; 321. First mounting part; 322. Second mounting part; 323. First clamping part; 324. Second clamping part; 325. Groove; 326. Connecting seat; 33. Wire clamp; 34. Bolt; 4. Adapter assembly; 40. Bracket; 41. 42. First mounting cavity; 43. Socket; 44. Electronic trip unit; 45. Circuit board; 46. Second mounting cavity; 47. Battery module; 5. Armature assembly; 50. Fixing base; 51. Support frame; 52. Extension rod; 53. Abutment block; 6. Tripping assembly; 60. Handle; 61. Frame; 62. Traction rod; 63. Arc surface; 64. Lever; 7. Arc extinguishing assembly; 8. Screw; 9. Terminal block; 10. Nut; 11. Partition; 12. Mounting base; 13. Arc extinguishing cavity; 14. Angled surface; 15. Slot; 16. Plug slot. Detailed Implementation

[0017] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "upper surface," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

[0018] One embodiment of the present invention: a three-phase three-wire electronic molded case circuit breaker, such as... Figure 1As shown, it includes a base 1 and a middle cover assembly 2. A transition assembly 4 and an arc-extinguishing component 7 are mounted on the base 1, and the middle cover assembly 2 connects to the base 1, allowing the electrical components of the transition assembly 4 to connect with the electrical components within the middle cover assembly 2. The base 1 also contains a tripping assembly 6 and an armature assembly 5. The tripping assembly 6 includes a frame 61, on which a lever 64 is mounted, and a handle 60 is provided on the lever 64. A traction rod 62 is provided on one side of the frame 61, and an arc surface 63 is provided on one side of the traction rod 62, through which space is released to facilitate the movement of the handle 60. Specifically, as shown... Figure 8 As shown, since the traction rod 62 is provided with an arc surface 63, the arc surface 63 is used to release space so that the handle 60 is not interfered with by the traction rod 62 when it rotates; that is, when the handle 60 pushes the release assembly 6 to move in an arc, the handle 60 will have a deformation amount, so the traction rod 62 needs to provide a space for the movement of the handle 60 so that the handle 60 will not abut against the traction rod 62 when it undergoes arc deformation.

[0019] Furthermore, the armature assembly 5 includes a fixed base 50, one side of which is rotatably connected to a support frame 51. The side of the support frame 51 away from the fixed base 50 is also provided with an extension rod 52, and the abutment block 53 provided on the extension rod 52 extends to the bottom of the traction rod 62 through the extension rod 52.

[0020] like Figure 9 As shown, due to the arrangement of the extension rod 52, the contact block 53 is close to the outside of the traction rod 62. When it is necessary to reduce the distance between the contact block 53 and the facing surfaces of the traction rod 62, the extension rod 52 can be directly pulled upward from the outside of the traction rod 62. When it is necessary to increase the distance between the contact block 53 and the facing surfaces of the traction rod 62, the extension rod 52 can be pulled downward. Since the extension rod 52 is extended in length, it is easy to deform, which makes it easier to adjust the distance between the traction rod 62 and the contact block 53.

[0021] like Figure 3 , Figure 4 The arc extinguishing assembly 7 is equipped with an arc extinguishing pressure booster. The setting of the arc extinguishing pressure booster increases the overall height of the arc extinguishing assembly 7, which makes it easy for the arc extinguishing assembly 7 to be blocked by the handle 60 during installation into the arc extinguishing chamber 13, thus affecting the installation efficiency of the arc extinguishing assembly 7. like Figure 5 and Figure 6As shown, to facilitate the assembly efficiency of the arc-extinguishing component 7, the arc-extinguishing component 7 is installed in the arc-extinguishing cavity 13 provided on the base 1, and the side wall of the arc-extinguishing cavity 13 is also provided with an inclined surface 14, which guides the arc-extinguishing component 7 into the arc-extinguishing cavity 13. Because the inclined surface 14 allows the arc-extinguishing component 7 to be inserted obliquely into the arc-extinguishing cavity 13, the assembly efficiency of the arc-extinguishing component 7 is improved within a limited space.

[0022] Existing terminal blocks are usually designed to fix only one wire. However, in some special cases, when terminal blocks need to fix multiple wires, existing terminal blocks cannot meet the user's needs, which brings inconvenience to the wiring of electrical appliances.

[0023] like Figure 13 , Figure 14 As shown, the base 1 is provided with a mounting seat 12, and a terminal block 3 is provided in the mounting seat 12; wherein, the terminal block 3 includes a conductive element 32; the conductive element 32 includes a connecting plate 320, the connecting plate 320 is provided with a slot 325, and the connecting plate 320 is divided into a first mounting part 321 and a second mounting part 322 through the slot 325; both the first mounting part 321 and the second mounting part 322 are provided with a first clamping part 323 and a second clamping part 324, and a wire clamp 33 is fitted on the outside of the first clamping part 323 and the second clamping part 324, and the wire clamp 33 is moved on the corresponding clamping part by a bolt 34 to clamp the wire.

[0024] In summary, since the connecting plate 320 of the conductive component 32 forms two mounting portions under the division of the slot 325, and each mounting portion has two clamping portions, and a wire clamp 33 is installed on each clamping portion, the terminal 3 can connect multiple wires at the same time, and each wire can be independently fixed.

[0025] See Figure 16 Since the distance between the first clamping part 323 and the connecting plate 320 is smaller than the distance between the second clamping part 324 and the connecting plate 320, and both the first clamping part 323 and the second clamping part 324 are parallel to the connecting plate 320, the wire clamps 33 installed on the first clamping part 323 and the second clamping part 324 can be distributed in a stepped manner on the conductive member 32. This allows the wire clamps 33 on the first clamping part 323 and the second clamping part 324 to be staggered, facilitating the insertion of wires into the wire clamps 33 and the conductive member 32.

[0026] Combination Figure 13 , Figure 14 and Figure 15Since the terminal block 3 also includes a protective cover 31, and the protective cover 31 is fitted over the conductive element 32, the wire clamps 33 located on the first clamping part 323 and the wire clamps 33 located on the second clamping part 324 are staggered. Therefore, the protective cover 31 can be used to protect the conductive element 32, and at the same time, the protective cover 31 can reduce the problem of connection between the conductive element 32 and the internal parts of the circuit breaker. For example, Figure 4 As shown, the screw 8 passes through the nut 10 inside the mounting base 12 and then through the terminal block 9 to engage with the connector 326 on the conductive element 32, thereby fixing the terminal 3 inside the mounting base 12.

[0027] like Figure 3 and Figure 7 As shown, the mounting base 12 is also provided with a slot 15, and is connected to the slot 15 by a partition 11 to prevent the terminal block 3 from contacting the components inside the base 1. Therefore, by utilizing the combined action of the partition 11 and the protective cover 31, the terminal block 3 can be stably and reliably located inside the mounting base 12, while also effectively preventing the terminal block 3 from contacting other components inside the circuit breaker.

[0028] To improve the stability of each wire clamp 33 after installation, the protective cover 31 is also provided with a first isolation plate 310 and a second isolation plate 311. One end of both the first isolation plate 310 and the second isolation plate 311 is inserted into the slot 325. Since both isolation plates are inserted into the slot 325, the two wire clamps 33 on the first clamping part 323 and the two wire clamps 33 on the second clamping part 324 are separated, and this separation also prevents the wire clamps 33 from rotating with the bolt 34.

[0029] Because the bottom surface of the protective cover 31 is also provided with inlet holes 312, and the number of inlet holes 312 is equal to the number of wire clamps 33; the outer side surface of the protective cover 31 is also provided with circular holes 313, and the number of circular holes 313 is equal to the number of wire clamps 33. Therefore, the wires entering the wire clamps 33 will not be confused, and the wires can be guided smoothly into the corresponding wire clamps 33. In addition, the independent design of the circular holes 313 allows each wire clamp 33 to be tightened independently, and there will be no problem of mutual interference during the tightening process.

[0030] Based on the three-phase three-wire electronic molded case circuit breaker, a communication module and power metering function have been added. Since the original internal space of the three-phase three-wire electronic molded case circuit breaker is very compact, it is more difficult to add a communication module and power metering function. Moreover, it is necessary to ensure the ease of assembly of the measuring circuit breaker. Ideally, the communication module and power metering function should be modularly designed.

[0031] like Figure 11 and Figure 12 As shown, the adapter assembly 4 includes a bracket 40, on which an electronic trip unit 44 and a circuit board 45 are integrated; see also Figure 10 The middle cover assembly 2 includes a middle cover 20, and the side of the middle cover 20 away from the adapter assembly 4 is provided with a metering module 22 and a communication module 23; the communication module 23 and the metering module 22 are both connected to the circuit board 45 in a board-to-board relationship.

[0032] In summary, by integrating the circuit board 45 and the electronic trip unit 44 onto the bracket 40, and then connecting the bracket 40 to the base 1, and finally connecting the metering module 22 and the communication module 23 to the circuit board 45, modular installation of the communication module 23, metering module 22, and electronic trip unit 44 with the bracket 40 is achieved. Furthermore, modular assembly of the adapter assembly 4, base 1, and middle cover assembly 2 is also possible. Moreover, through this technical solution, the device achieves a higher degree of modularity, facilitating assembly and subsequent maintenance.

[0033] Specifically, the bracket 40 is provided with a first mounting cavity 42 and an electronic trip unit 44 is provided in the first mounting cavity 42. Therefore, the electronic trip unit 44 has a reliable mounting position, which ensures the stability of the electronic trip unit 44 during operation and makes the assembly during production and disassembly later simpler and more convenient.

[0034] Similarly, a second mounting cavity 46 is provided below the first mounting cavity 42, and the circuit board 45 is mounted through the second mounting cavity 46. Specifically, bolts are used to connect the bracket 40 to the second mounting cavity 46, thus ensuring a reliable connection between the adapter assembly 4 and the base 1. At the same time, the bolts can be removed to facilitate the installation and replacement of the adapter assembly 4, further enhancing the modularity of the base 1, the adapter assembly 4, and the middle cover assembly 2.

[0035] like Figure 1 and Figure 2 As shown, one side of the bracket 40 is provided with a plug plate 41, and the plug plate 41 is adapted to connect with the plug slot 16 provided on the base 1. Therefore, before installation, the adapter assembly 4 is guided to be smoothly installed into the base 1 by the docking of the plug plate 41 and the plug slot 16. After installation, the joint action of the plug plate 41 and the plug slot 16 makes the stability of the adapter assembly 4 and the base 1 stronger, so as to ensure that the adapter assembly 4 will not be displaced during use, thereby ensuring the smooth assembly and disassembly of the metering module 22 and the communication module 23.

[0036] like Figure 11As shown, the second mounting cavity 46 is also provided with a socket 43, and the battery module 47 installed on the circuit board 45 is accommodated through the socket 43, thus making the battery module 47 have reliable stability after installation.

[0037] like Figure 10 As shown, the bottom of the middle cover 20 is hinged to the cover plate 21, that is, a pin hole is provided at the bottom of the middle cover 20, and a pin rod is provided on the cover plate 21 that matches the pin hole. The hinge connection between the cover plate 21 and the middle cover 20 is achieved by matching the pin rod with the pin hole.

[0038] Based on this, after the cover plate 21 is closed, the metering module 22 and the communication module 23 can be covered inside the middle cover 20. After the cover plate 21 is opened, one end of the cover plate 21 always rotates downwards to completely expose the installation area of ​​the middle cover 20, so as to facilitate the disassembly and assembly of the communication module 23 and the metering module 22 without interfering with the disassembly and assembly of the metering module 22 and the communication module 23.

[0039] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A three-phase three-wire electronic molded case circuit breaker, characterized in that: Includes a base (1) and a middle cover assembly (2), on which a transition assembly (4) and an arc extinguishing component (7) are mounted, and the middle cover assembly (2) is connected to the base (1) so that the electrical components of the transition assembly (4) are connected to the electrical components in the middle cover assembly (2); The base (1) is also provided with a release assembly (6) and an armature assembly (5); the release assembly (6) includes a frame (61), a lever (64) is mounted on the frame (61), and a handle (60) is provided on the lever (64). The frame (61) is provided with a traction rod (62) on one side, and a circular arc surface (63) is provided on one side of the traction rod (62), and the space is released through the circular arc surface (63) so that the handle (60) can move. The armature assembly (5) includes a fixed base (50), one side of which is rotatably connected to a support frame (51). The side of the support frame (51) away from the fixed base (50) is also provided with an extension rod (52), and the abutment block (53) provided on the extension rod (52) is extended to the underside of the traction rod (62) through the extension rod (52).

2. A three-phase three-wire electronic molded case circuit breaker according to claim 1, characterized in that: The arc extinguishing component (7) is installed in the arc extinguishing cavity (13) provided on the base (1), and the side wall of the arc extinguishing cavity (13) is also provided with an inclined surface (14), and the inclined surface (14) is used to guide the arc extinguishing component (7) to be assembled into the arc extinguishing cavity (13).

3. A three-phase three-wire electronic molded case circuit breaker according to claim 1, characterized in that: The base (1) is provided with a mounting seat (12), and a terminal block (3) is provided in the mounting seat (12); wherein, the terminal block (3) includes a conductive element (32); the conductive element (32) includes a connecting plate (320), the connecting plate (320) is provided with a slot (325), and the connecting plate (320) is divided into a first mounting part (321) and a second mounting part (322) through the slot (325); both the first mounting part (321) and the second mounting part (322) are provided with a first clamping part (323) and a second clamping part (324), and a wire clamp (33) is fitted on the outside of the first clamping part (323) and the second clamping part (324), and the wire clamp (33) is moved on the corresponding clamping part by a bolt (34) to clamp the wire.

4. A three-phase three-wire electronic molded case circuit breaker according to claim 3, characterized in that: The mounting base (12) is also provided with a slot (15), and is connected to the slot (15) by a partition (11) to prevent the terminal block (3) from contacting the components inside the base (1).

5. A three-phase three-wire electronic molded case circuit breaker according to claim 3, characterized in that: The distance between the first clamping part (323) and the connecting plate (320) is smaller than the distance between the second clamping part (324) and the connecting plate (320), and both the first clamping part (323) and the second clamping part (324) are parallel to the connecting plate (320).

6. A three-phase three-wire electronic molded case circuit breaker according to claim 3, characterized in that: The terminal block (3) also includes a protective cover (31), which is fitted over the conductive member (32) so that the wire clamp (33) on the first clamping part (323) and the wire clamp (33) on the second clamping part (324) are staggered.

7. A three-phase three-wire electronic molded case circuit breaker according to claim 6, characterized in that: The protective cover (31) is also provided with a first isolation plate (310) and a second isolation plate (311); and one end of the first isolation plate (310) and the second isolation plate (311) are inserted into the slot (325); the bottom surface of the protective cover (31) is also provided with a wire inlet hole (312), and the number of the wire inlet holes (312) is equal to the number of the wire clamps (33); the outer side of the protective cover (31) is also provided with a round hole (313), and the number of the round holes (313) is equal to the number of the wire clamps (33).

8. A three-phase three-wire electronic molded case circuit breaker according to claim 1, characterized in that: The adapter assembly (4) includes a bracket (40), on which an electronic trip unit (44) and a circuit board (45) are integrated; the middle cover assembly (2) includes a middle cover (20), and a metering module (22) and a communication module (23) are provided on the side of the middle cover (20) away from the adapter assembly (4); the communication module (23) and the metering module (22) are both connected to the circuit board (45) in a board-to-board relationship.

9. A three-phase three-wire electronic molded case circuit breaker according to claim 8, characterized in that: The electronic trip unit (44) and the circuit board (45) are connected in a board-to-wire relationship; the bracket (40) is provided with a first mounting cavity (42) and the electronic trip unit (44) is provided in the first mounting cavity (42); a second mounting cavity (46) is also provided below the first mounting cavity (42), and the circuit board (45) is installed through the second mounting cavity (46).

10. A three-phase three-wire electronic molded case circuit breaker according to claim 8, characterized in that: The bracket (40) has a plug plate (41) on one side, and the plug plate (41) is adapted to be connected to the slot (4) provided on the base (1); the second mounting cavity (46) is also provided with a socket (43), and the battery module (47) installed on the circuit board (45) is accommodated through the socket (43); the bottom of the middle cover (20) is hinged to the cover plate (21).

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