High-pressure axial flow fan for livestock farm

Abstract

The utility model discloses a high-pressure axial flow fan for a farm, which comprises a shell, a fan blade, a fan blade, a fan blade, a fan blade, a fan blade and a fan blade, and is characterized in that the shell comprises a barrel, a front baffle and a flange; a plurality of first reinforcing ribs are wound around the cylinder with the axis as the center line, second reinforcing ribs are arranged between the first reinforcing ribs, the first reinforcing ribs and the second reinforcing ribs are fixedly connected with the rear end face of the front baffle, a circle of third reinforcing ribs are wound around the cylinder with the axis as the center line, and the third reinforcing ribs are fixedly connected with the first reinforcing ribs. The motor is located in the shell and fixedly connected with the shell through a supporting assembly; the impeller is located in the shell and is in transmission connection with the motor. According to the utility model, the structural strength of the whole shell is enhanced, so that the shell is not easy to deform under the continuous high-pressure working condition; the motor is firmly installed, the position does not deviate under the high-pressure working condition, the working stability of the whole impeller is guaranteed, and therefore the continuous high-pressure working strength and stability of the whole high-pressure axial flow fan are guaranteed, and the ever-increasing performance requirement of a farm for the high pressure of the fan is met.

Description

Technical Field

[0001] The utility model belongs to the technical field of axial flow fans, and in particular relates to a high-pressure axial flow fan for a farm. Background Art

[0002] Currently, ventilation within farms is crucial for the healthy growth of animals within them. As land resources decrease, the aquaculture industry is increasingly intensive. As farms expand in scale and intensify, the pressure requirements for fan ventilation are increasing. Currently, the fan pressure for centralized ventilation within farms needs to reach 400 Pa or even higher. However, the performance of fans currently used in farms on the market is difficult to meet, and the fan structure is difficult to achieve the continuous high-pressure operating intensity required. Therefore, a high-pressure axial flow fan for farms was designed to address this issue.

[0003] It should be noted that the above technical background is merely for the purpose of providing a clear and complete description of the technical solutions of the present invention and to facilitate understanding by those skilled in the art. It should not be assumed that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present invention. Utility Model Content

[0004] In order to overcome the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a high-pressure axial flow fan for a farm.

[0005] In order to achieve the above purpose and other related purposes, the technical solution provided by the present invention is: a high-pressure axial flow fan for a farm, comprising:

[0006] The outer shell includes a cylindrical body and a front baffle and a flange respectively provided on the front and rear sides thereof; the cylindrical body is provided with a plurality of evenly distributed reinforcing ribs 1 around the axis as the centerline, and a reinforcing rib 2 is provided between each of the reinforcing ribs 1, and the reinforcing ribs 1 and 2 are both fixedly connected to the rear end surface of the front baffle; the cylindrical body is provided with a circle of reinforcing ribs 3 around the axis as the centerline, and the reinforcing ribs 3 are fixedly connected to the reinforcing ribs 1;

[0007] a motor, the motor being located inside the housing and fixedly connected to the housing via a support assembly;

[0008] The impeller is located inside the housing and is drivingly connected to the output shaft of the motor.

[0009] In this solution, by providing reinforcing ribs 1, 2 and 3 on the surface of the shell, the structural strength of the entire shell is enhanced, so that it is not easily deformed under continuous high-pressure working conditions.

[0010] Furthermore, the support assembly includes a fastening cover, a fastening strip and a fastening plate, and the fastening strips are provided in plurality and are evenly distributed on the outer surface of the fastening cover; the motor is fixedly connected to an organic disk at one end portion close to its output shaft, and the organic disk is fixedly connected to the fastening plate; the end of the fastening strip away from the fastening cover is fixedly connected to the inner wall of the cylinder.

[0011] The impeller includes a shaft disc, a lower hub, blades and an upper hub which are fixedly connected in sequence. The output shaft of the motor passes through a through hole 1 provided on the fastening disc and is fixedly connected to the shaft disc.

[0012] In this solution, the fastening cover, the fastening strip and the fastening disk are fixedly connected, the motor and the fastening disk are fixedly connected through the machine disk, the fastening strip is fixedly connected to the inner wall of the cylinder, so that the motor is fixed inside the shell, the concentricity between the fastening cover and the cylinder is set, the output shaft of the motor is at the center of the cylinder, the output shaft of the motor is fixedly connected to the shaft disk, driving the impeller to rotate, the shaft disk, the lower hub and the upper hub are fixedly connected together in sequence, and the blades are fixedly clamped between the lower hub and the upper hub to ensure the stability of the entire impeller. The position will not shift under high-pressure working conditions.

[0013] Furthermore, the shaft disc includes a first disc, a second disc, and a third disc fixedly connected in sequence. The first disc is fixedly connected to the end face of the lower hub, and the diameter of the second disc corresponds to the second through-hole defined at the center of the lower hub. In this embodiment, the shaft disc is configured as a stepped structure, so that the first disc contacts the back of the lower hub, and the second disc is positioned just inside the second through-hole, contacting the inner wall of the second through-hole. This increases the contact area between the shaft disc and the lower hub, making the fixation between the shaft disc and the lower hub more secure and the overall structure more compact.

[0014] Furthermore, the lower hub is fixedly connected to the upper hub, and corresponding positions of the lower hub and the upper hub are respectively provided with a lower semicircular groove and an upper semicircular groove. One end of the blade is fixedly connected to a connector, which is adapted to the lower semicircular groove and the upper semicircular groove, and is clamped between the lower semicircular groove and the upper semicircular groove. In this solution, the installation angle of the blade can be adjusted, thereby adjusting the air volume of the fan and improving the performance of the fan.

[0015] Furthermore, a hubcap is secured to the end of the upper hub away from the lower hub, and a cover plate connector is fixedly connected to the second disc. The cover plate connector sequentially passes through the second through-hole and the third through-hole in the upper hub and is fixedly connected to the hubcap. In this solution, the hubcap and the shaft disc are secured together by the cover plate connector, and the upper hub is sealed by the hubcap, resulting in a gently curved surface for the entire impeller, which better guides the airflow and enhances fan performance.

[0016] Furthermore, a protective net is fixedly mounted on the front baffle, and the protective net is in the same plane as the side of the front baffle away from the cylinder. In this solution, the front baffle has a flat mounting surface, which is convenient for installation. The protective net can prevent large foreign objects from being drawn into the impeller and can also cut and guide the airflow.

[0017] Furthermore, the distance between the end of the blade close to the cylinder and the inner wall of the cylinder is less than 2 mm. In this solution, the smaller gap distance can reduce the amount of air leakage and further improve the overall performance of the fan.

[0018] Furthermore, the cross-sections of the cylinder and the flange are circular, and the cross-section of the front baffle is square. In this solution, the combination of the square and the circular makes the installation of the entire axial flow fan more convenient.

[0019] Furthermore, a counterweight is provided on the upper hub. In this solution, the counterweight makes the entire working process of the fan more stable.

[0020] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0021] The high-pressure axial flow fan for farms designed by the utility model is characterized in that by arranging reinforcing ribs 1, 2 and 3 on the surface of the outer shell, the outer shell reinforcing ribs 1 and 2 are formed as one piece, thereby strengthening the structural strength of the entire outer shell and making it not easily deformed under continuous high-pressure working conditions. The fastening strips are curved and not easily bent, thereby strengthening the strength of the fastening strips. Since the twelve fastening strips are fixedly arranged, the motor is firmly installed and the position will not shift under high-pressure working conditions, thereby ensuring the stability of the operation of the entire impeller, thereby ensuring the strength and stability of the continuous high-pressure operation of the entire high-pressure axial flow fan, thereby meeting the farm's growing performance requirements for high-pressure fans. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the appearance structure of the utility model;

[0023] Figure 2 This is a schematic diagram of the support assembly and impeller structure of the utility model;

[0024] Figure 3 This is an exploded schematic diagram of the support assembly and impeller structure of the present invention;

[0025] Figure 4 This is a schematic diagram of the motor structure of the utility model;

[0026] Figure 5 This is a schematic diagram of the support assembly structure of the utility model;

[0027] Figure 6This is a schematic diagram of the shaft disc structure of the utility model;

[0028] Figure 7 This is a schematic diagram of the lower hub structure of the present utility model;

[0029] Figure 8 This is a schematic diagram of the blade structure of the utility model;

[0030] Figure 9 This is a schematic diagram of the upper hub structure of the present utility model;

[0031] Figure 10 This is a schematic structural diagram of the hub cover of the present utility model;

[0032] Figure 11 This is a structural diagram of the cover plate connector of the present invention.

[0033] In the above drawings, 1. outer shell; 11. cylinder; 12. front baffle; 13. flange; 2. protective net; 3. reinforcing rib one; 31. lifting hole; 4. reinforcing rib two; 5. reinforcing rib three; 6. motor; 61. machine disc; 7. support assembly; 71. fastening cover; 72. fastening strip; 721. mounting hole; 73. fastening disc; 731. through hole one; 8. impeller; 81. lower hub; 811. lower semicircular groove; 812. through hole two; 82. blade; 821. connector; 83. upper hub; 831. upper semicircular groove; 832. through hole three; 833. counterweight; 84. shaft disc; 841. disc one; 842. disc two; 843. disc three; 9. hub cover; 91. cover plate connector. DETAILED DESCRIPTION

[0034] The following describes the implementation of the present invention through specific embodiments. People familiar with this technology can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0035] It should be noted that in the description of the present utility model, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the utility model product is usually placed when in use. These are only for the convenience of describing the present utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", "third" and the like are only used to distinguish descriptions, and cannot be understood as indicating or implying relative importance. Terms such as "horizontal", "vertical", and "overhanging" do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0036] It should also be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections, direct connections, indirect connections via an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] In the description of this application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of this application; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0038] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0039] Example:

[0040] See attached Figure 1 , Attachment Figure 2 and attached Figure 3 As shown, this embodiment provides a high-pressure axial flow fan for a farm, comprising:

[0041] Housing 1 includes a cylinder 11 and a front baffle 12 and a flange 13 respectively provided on its front and rear sides. A plurality of evenly distributed reinforcing ribs 3 are disposed around the cylinder 11 with the axis as the centerline. Reinforcing ribs 4 are disposed between each of the reinforcing ribs 3. Reinforcing ribs 3 and ribs 2, 4 are fixedly connected to the rear end surface of the front baffle 12. A circle of reinforcing ribs 5 is disposed around the cylinder 11 with the axis as the centerline. Reinforcing ribs 3, 5 are fixedly connected to reinforcing ribs 3.

[0042] The motor 6 is located inside the housing 1 and is fixedly connected to the inner wall of the housing 1 through a support assembly 7;

[0043] The impeller 8 is located inside the housing 1 and is drivingly connected to the output shaft of the motor 6.

[0044] In this embodiment, by providing reinforcing ribs 1 3 , 2 4 and 3 5 on the surface of the housing 1 , the structural strength of the entire housing 1 is enhanced so that it is not easily deformed under continuous high-pressure working conditions.

[0045] In some other embodiments, four reinforcing ribs 3 are provided and are respectively located at the corners of the front baffle 12; eight reinforcing ribs 2 4 are provided and are evenly distributed between each reinforcing rib 1; the shell 1 and the reinforcing ribs 1 3, 2 4 and 3 5 are an integrally formed structure, further strengthening the structural strength of the entire shell 1.

[0046] In some other embodiments, the housing 1 can be made of PVC or stainless steel depending on the usage.

[0047] See attached Figure 4 and attached Figure 5 As shown, the support assembly 7 includes a fastening cover 71, a fastening strip 72 and a fastening disc 73. A plurality of fastening strips 72 are provided and are evenly distributed on the outer surface of the fastening cover 71. The end of the motor 6 close to its output shaft is fixedly connected to the organic disc 61, and the organic disc 61 is fixedly connected to the fastening disc 73. The end of the fastening strip 72 away from the fastening cover 71 is fixedly connected to the inner wall of the cylinder 11. See the attached Figure 3 As shown, the impeller 8 includes a shaft disc 84, a lower hub 81, blades 82 and an upper hub 83 fixedly connected in sequence, and the output shaft of the motor 6 passes through a through hole 731 opened on the fastening disc 73 and is fixedly connected to the shaft disc 84.

[0048] The motor 6 adopts a permanent magnet motor with high motor efficiency, which improves the fan performance. The fastening cover 71, the fastening strip 72 and the fastening disk 73 are fixedly connected. The motor 6 and the fastening disk 73 are fixedly connected through the machine disk 61. The fastening strip 72 is fixedly connected to the inner wall of the cylinder 11, so that the motor 6 is fixed inside the shell 1. The fastening cover 71 and the cylinder 11 are set concentrically. The output shaft of the motor 6 is at the center of the cylinder 11. The output shaft of the motor 6 is fixedly connected to the shaft disk 84 to drive the impeller 8 to rotate. Bolt holes are opened at the relative positions of the shaft disk 84, the lower hub 81 and the upper hub 83. The shaft disk 84, the lower hub 81 and the upper hub 83 are fixedly connected together in sequence by bolts and nuts. The blades 82 are fixedly clamped between the lower hub 81 and the upper hub 83 to ensure the stability of the entire impeller. The position will not shift under high-pressure working conditions.

[0049] In some other embodiments, the surface of the fastening strip 72 is designed to be a curved surface structure. The fastening strip 72 is curved and not easy to bend, thereby strengthening the strength of the fastening strip 72.

[0050] In other embodiments, twelve fastening strips 72 are provided, and the fastening cover 71 is integrally connected to the fastening plate 73. Since twelve fastening strips 72 are fixedly provided, the motor 6 is firmly mounted and does not shift in position under high-pressure operation, thereby ensuring the stability of the entire impeller operation.

[0051] See attached Figure 6 As shown, the shaft disc 84 includes disc one 841, disc two 842 and disc three 843 fixedly connected in sequence. Disc one 841 is fixedly connected to the end face of the lower hub 81, and the diameter of disc two 842 contacts the inner wall of through hole two 812 opened at the center of the lower hub 81. Disc 1 841, disc 2 842 and disc 3 843 are an integrated structure, and bolt holes are provided at positions corresponding to the shaft disc 84 and the lower hub 81. The shaft disc 84 and the lower hub 81 are fixed together by bolts and nuts. Multiple bolt holes are provided to ensure the concentricity between the shaft disc 84 and the lower hub 81. By setting the shaft disc 84 as a stepped structure, the disc 1 841 contacts the back of the lower hub 81, and the disc 2 842 is just inside the through hole 2 812 and contacts the inner wall of the through hole 2 812, thereby increasing the contact area between the shaft disc 84 and the lower hub 81, making the fixation between the shaft disc 84 and the lower hub 81 more firm and the overall structure more compact.

[0052] See attached Figure 7 , Attachment Figure 8 and attached Figure 9As shown, the lower hub 81 is fixedly connected to the upper hub 83, and a lower semicircular groove 811 and an upper semicircular groove 831 are respectively provided at corresponding positions of the lower hub 81 and the upper hub 83. One end of the blade 82 is fixedly connected to a connecting head 821, and the connecting head 821 is adapted to the lower semicircular groove 811 and the upper semicircular groove 831. The connecting head 821 is clamped at a position between the lower semicircular groove 811 and the upper semicircular groove 831. Bolt holes are provided at positions corresponding to the lower hub 81 and the upper hub 83. After the lower hub 81 and the upper hub 83 are locked by means of bolts and nuts, the lower semicircular groove 811 is just spliced ​​together with the upper semicircular groove 831. The connecting head 821 can be placed in the space where the lower semicircular groove 811 and the upper semicircular groove 831 are spliced ​​and stuck, unable to move. By loosening the bolts fixing between the lower hub 81 and the upper hub 83, the connecting head 821 can be rotated in the space where the lower semicircular groove 811 and the upper semicircular groove 831 are spliced, thereby adjusting the installation angle of the blades 82, thereby achieving the adjustment of the air volume of the fan and improving the performance of the fan.

[0053] See attached Figure 3 , Attachment Figure 10 and attached Figure 11 As shown, the hubcap 9 is secured to the end of the upper hub 83 away from the lower hub 81. A cover plate connector 91 is fixedly connected to the second disc 842. The cover plate connector 91 passes through the second through-hole 812 and the third through-hole 832 provided in the upper hub 83 and is fixedly connected to the hubcap 9. The cover plate connector 91 secures the hubcap 9 to the shaft disc 84, and the hubcap 9 seals the upper hub 83, giving the entire impeller 8 a gently curved surface. This improves the airflow diversion effect and enhances the performance of the fan.

[0054] See attached Figure 1 As shown, a protective net 2 is fixedly mounted on the front baffle 12, and the protective net 2 is flush with the side of the front baffle 12 away from the cylinder 11. A groove is provided on the mounting surface of the front baffle 12, and the protective net 2 is fixed to the front baffle 12 within the groove. The protective net 2 is fastened with screws to ensure that the protective net 2 and the front baffle 12 are flush with each other, making the mounting surface of the front baffle 12 smooth and easy to install. The protective net 2 can prevent large foreign objects from being drawn into the impeller and can also cut and guide the airflow.

[0055] See attached Figure 1 and attached Figure 3 As shown, the distance between the end of the blade 82 close to the cylinder 11 and the inner wall of the cylinder 11 is less than 2 mm. A smaller gap distance can reduce air leakage and further improve the overall performance of the fan.

[0056] See attached Figure 1 As shown, the cross-section of the cylinder 11 and the flange 13 is a circular structure, and the cross-section of the front baffle 12 is a square structure. By combining the square and the circular structure, the entire axial flow fan is more convenient to install.

[0057] See attached Figure 9 As shown, a counterweight 833 is provided on the upper hub 83, and the counterweight 833 is fixed to the upper hub 83 by rotating a thread. During the dynamic balancing test of the impeller 8, the counterweight 833 is increased or decreased by rotating, so that the impeller 8 reaches a relatively balanced state, making the entire working process of the fan more stable.

[0058] In some embodiments, see Appendix Figure 1 As shown, a hoisting hole 31 is provided on the reinforcement rib 3. By opening the hoisting hole 31 for hoisting, the fan is conveniently installed.

[0059] In some embodiments, see Appendix Figure 5 As shown, the end surface of the fastening strip 72 is provided with a mounting hole 721. Screws or rivets are driven through the barrel 11 into the mounting hole 721 to facilitate fixing the fastening strip 72 to the barrel 11.

[0060] The high-pressure axial flow fan for farms designed by this utility model strengthens the structural strength of the entire shell by improving the shell structure, making it not easy to deform under continuous high-pressure working conditions; and the motor is firmly installed and the position will not shift under high-pressure working conditions, thereby ensuring the stability of the entire impeller operation, thereby ensuring the strength and stability of the continuous high-pressure operation of the entire high-pressure axial flow fan, and meeting the farm's growing performance requirements for high-pressure fans.

[0061] The above implementation methods are only for illustrating the technical concept and features of the utility model. Its purpose is to enable people familiar with this technology to understand the content of the utility model and implement it. It cannot be used to limit the scope of protection of the utility model. Any equivalent changes or modifications made according to the spirit of the utility model should be included in the scope of protection of the utility model.

Claims

1. A high-pressure axial flow fan for a farm, characterized in that: include: A shell (1), the shell (1) includes a cylinder (11) and a front baffle (12) and a flange (13) respectively arranged on the front and rear sides thereof; the cylinder (11) is provided with a plurality of uniformly distributed reinforcing ribs (3) around the axis as the center line, and reinforcing ribs (4) are provided between each of the reinforcing ribs (3), and the reinforcing ribs (3) and (4) are both fixedly connected to the rear end face of the front baffle (12); the cylinder (11) is provided with a circle of reinforcing ribs (5) around the axis as the center line, and the reinforcing ribs (5) are fixedly connected to the reinforcing ribs (3); a motor (6), the motor (6) being located inside the housing (1) and fixedly connected to the housing (1) via a support assembly (7); An impeller (8), the impeller (8) is located inside the housing (1) and is drivingly connected to the output shaft of the motor (6).

2. The high-pressure axial flow fan for a farm according to claim 1, characterized in that: The support assembly (7) comprises a fastening cover (71), a fastening strip (72) and a fastening plate (73); a plurality of fastening strips (72) are provided and are evenly distributed on the outer surface of the fastening cover (71); The motor (6) is fixedly connected to an organic disk (61) at one end portion close to the output shaft thereof, and the organic disk (61) is fixedly connected to the fastening disk (73); One end of the fastening strip (72) away from the fastening cover (71) is fixedly connected to the inner wall of the cylinder (11).

3. The high-pressure axial flow fan for a farm according to claim 2, characterized in that: The impeller (8) comprises a shaft disc (84), a lower hub (81), blades (82) and an upper hub (83) which are fixedly connected in sequence, and the output shaft of the motor (6) passes through a through hole (731) provided on the fastening disc (73) and is fixedly connected to the shaft disc (84).

4. The high-pressure axial flow fan for a farm according to claim 3, characterized in that: The shaft disc (84) includes a disc one (841), a disc two (842) and a disc three (843) which are fixedly connected in sequence. The disc one (841) is fixedly connected to the end face of the lower hub (81). The diameter of the disc two (842) is corresponding to the through hole two (812) opened at the center of the lower hub (81).

5. The high-pressure axial flow fan for a farm according to claim 3, characterized in that: The lower hub (81) is fixedly connected to the upper hub (83); a lower semicircular groove (811) and an upper semicircular groove (831) are respectively provided at positions corresponding to each other on the lower hub (81) and the upper hub (83); one end of the blade (82) is fixedly connected to a connector (821); the connector (821) is adapted to the lower semicircular groove (811) and the upper semicircular groove (831); the connector (821) is clamped at a position between the lower semicircular groove (811) and the upper semicircular groove (831).

6. The high-pressure axial flow fan for a farm according to claim 4, characterized in that: The upper wheel hub (83) is clamped with a wheel hub cover (9) at one end away from the lower wheel hub (81), and the second disc (842) is fixedly connected with a cover plate connector (91). The cover plate connector (91) passes through the second through hole (812) and the third through hole (832) provided on the upper wheel hub (83) in sequence and is fixedly connected to the wheel hub cover (9).

7. The high-pressure axial flow fan for a farm according to claim 1, characterized in that: A protective net (2) is fixedly mounted on the front baffle (12), and the protective net (2) and a side of the front baffle (12) away from the cylinder (11) are in the same plane.

8. The high-pressure axial flow fan for a farm according to claim 3, characterized in that: The distance between one end of the blade (82) close to the cylinder (11) and the inner wall of the cylinder (11) is less than 2 mm.

9. The high-pressure axial flow fan for a farm according to claim 1, characterized in that: The cross-sections of the cylinder (11) and the flange (13) are circular structures, and the cross-section of the front baffle (12) is square structure.

10. The high-pressure axial flow fan for a farm according to claim 3, characterized in that: A counterweight (833) is provided on the upper hub (83).

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