CN113124114A

CN113124114A - Treadmill drive belt automatic tensioning device with damping mechanism

Info

Publication number: CN113124114A
Application number: CN202110254974.2A
Authority: CN
Inventors: 吴子健; 何仁
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2021-03-09
Filing date: 2021-03-09
Publication date: 2021-07-16

Abstract

The invention discloses an automatic tensioning device of a treadmill transmission belt with a damping mechanism, which comprises: the base is fixed on the treadmill bracket; the tensioning arm comprises a connecting part hinged with the base and a tensioning part connected with the transmission belt, and the central axis of the connecting part is parallel to and does not coincide with the central axis of the tensioning part; the belt wheel is hinged with the tensioning part, the central shaft of the belt wheel is superposed with the central shaft of the tensioning part, and a transmission belt of the treadmill is arranged on the outer diameter of the belt wheel; the torsion spring is positioned between the tensioning arm and the base, and two ends of the torsion spring are respectively connected with the tensioning arm and the base; the damping device is arranged on the base and is positioned on the inner side of the torsion spring, and the inner diameter of the torsion spring contracts to be in contact with the damping device when the torsion spring is stressed. Has the advantages that: the invention has simple structure, is small and exquisite, is light and easy to install, saves the complicated driving wheel translation structure of the traditional transmission system and prolongs the service life.

Description

Treadmill drive belt automatic tensioning device with damping mechanism

Technical Field

The invention relates to an automatic tensioning mechanism for a treadmill, in particular to an automatic tensioning device for a treadmill transmission belt, which is provided with a damping mechanism and used for preventing the treadmill transmission belt from slipping, and belongs to the technical field of treadmill transmission.

Background

For the traditional electric running machine, the front end and the rear end of the running board are respectively provided with a roller, and the running belt is sleeved on the front roller and the rear roller. The general DC/AC motor is installed at the foremost end of the running machine, and drags the front roller to rotate through the poly-wedge belt, so as to drive the whole running belt to run, thereby realizing the running function.

In the transmission system of the conventional treadmill, in order to ensure that the transmission belt does not slip to lower the transmission efficiency, the preset tension of the transmission belt is high. Too high system tension both can influence the life-span of other band pulleys, causes the quick tensile wearing and tearing of drive belt itself again easily to system tension reduces, and the system problem of skidding appears. Slippage of the drive belt system not only creates NVH (noise, vibration and harshness) problems, but also causes sudden changes in the belt speed, with the potential risk of injury to the user.

The current primary solution to treadmill belt slip is to constantly check the belt tension. When the transmission belt is found to be loose, the horizontal distance between the transmission belt and the driven wheel on the roller is increased through the motor driving wheel capable of translating, and therefore the transmission belt is tensioned again. Such a process mainly suffers from several drawbacks: 1. the complexity of the transmission structure of the treadmill is increased; 2. the adjustment process is complicated, the adjustment range is small, the adjustment accuracy is completely judged by a user subjectively, and the tension cannot be accurately controlled; 3. the motor driving wheel adjusting method is mainly realized through structures such as sliding rails or reserved holes, certain gaps cannot be avoided in matching, and the NVH problem can be caused when the motor is accelerated and decelerated.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the defects in the prior art, further improve the efficiency and stability of a transmission system of the treadmill and ensure the safety of a user, the invention discloses an automatic tensioning device of a transmission belt of the treadmill, which is provided with a damping mechanism.

The technical scheme is as follows: an automatic treadmill belt tensioning device with a damping mechanism, comprising:

the base is fixed on the treadmill bracket;

the tensioning arm comprises a connecting part hinged with the base and a tensioning part connected with the transmission belt, and the central axis of the connecting part is parallel to and does not coincide with the central axis of the tensioning part; the tensioning arm and the base can rotate relatively by taking the central shaft of the connecting part as a center;

the belt wheel is hinged with the tensioning part, the central axis of the belt wheel is superposed with the central axis of the tensioning part, a transmission belt of the treadmill is arranged on the outer diameter of the belt wheel, and the belt wheel can freely rotate along with the transmission belt and can tension the transmission belt;

the torsion spring is positioned between the tensioning arm and the base, two ends of the torsion spring are respectively connected with the tensioning arm and the base, and the torsion spring drives the tensioning arm to swing to one side for realizing the tensioning of the transmission belt;

the damping device is arranged on the base and is positioned on the inner side of the torsion spring, and the inner diameter of the torsion spring contracts to contact with the damping device when the torsion spring is stressed so as to realize a damping effect.

The transmission system of the treadmill is further tensioned by installing the invention on the treadmill bracket; the torsion spring can provide stable tension for the transmission system. When the transmission belt is worn, the torsion spring can drive the tensioning arm to continuously tension the transmission belt, so that the complex process that the tightness of the transmission belt needs to be adjusted frequently in a transmission system of the traditional treadmill is avoided. In addition, the wrap angle of the driving wheel and the driven wheel is increased due to the design of the tensioning device, the transmission efficiency of the system is improved, and stable tension is provided for the system.

Preferably, in order to reduce the overall size of the invention, the base is provided with a convex connecting part along the central axis direction thereof, the bottom of the connecting part of the tensioning arm is provided with a concave cavity, and the structural size of the cavity is matched with that of the convex connecting part; and the protruding connecting part is positioned in a cavity at the bottom of the connecting part when the base and the tensioning arm are installed. The length of the invention is shortened by the convex connecting part in the cavity at the bottom of the connecting part, and the invention is more compact.

Preferably, in order to facilitate the connection between the treadmill bracket and the treadmill of the present invention, a pivot is disposed between the base and the connecting portion of the tensioning arm, the pivot is fixedly connected with the base, and the connecting portion of the tensioning arm is rotatably fixed on the pivot; the bottom of the pivot is provided with a central threaded hole which is matched with a connecting bolt connected with the treadmill support.

Preferably, in order to avoid abnormal wear caused by direct contact between two metal surfaces of the connecting part of the pivot shaft and the tensioning arm, a certain damping effect can be achieved to absorb part of vibration of the tensioner, and a bushing is arranged between the outer diameter of the pivot shaft and the inner diameter of the connecting part of the tensioning arm.

Preferably, in order to visually know the wear condition of the transmission belt, the connecting part of the tensioning arm is provided with at least three scale indicating parts along the circumferential direction, the base is provided with a pointer, and the position indicated by the pointer is located between the three scale indicating parts when the installation is completed. After the transmission belt is installed, if the pointer is between the first scale and the second scale, the tension provided by the tensioning device is proved to be accurate, the installation is correct, and after the transmission belt system works for a long time, when the pointer on the base exceeds the second scale and deviates to a third scale, the transmission belt is proved to be stretched to be incapable of providing stable tension, and the belt needs to be replaced.

Preferably, in order to avoid the unstable system or collision with surrounding structures caused by the over-large swing of the tensioning device, the rotation range of the tensioning arm is limited, the connecting part of the tensioning arm is provided with a fan-shaped limiting groove along the radial direction, the base is provided with a boss and a stop block, the stop block is positioned at the top end of the boss, and the stop block is positioned in the limiting groove during installation.

Preferably, for the installation of the drive belt, be equipped with the positioning hole who runs through the spacing groove upper surface on the spacing groove, be equipped with corresponding location counter bore on the bellying of stating the base, be equipped with the dowel pin in the drive belt installation, during the installation drive belt, the dowel pin passes positioning hole and inserts the location counter bore, extracts the dowel pin after the drive belt installation is accomplished. The positioning pin is mainly used for fixing the tensioning arm at the installation position, so that a user can conveniently install the transmission belt.

Preferably, in order to absorb the energy generated by the shaking of the transmission belt, the tension of the transmission belt is more stable, and the NVH performance of a transmission system is further improved; the damping device is of an elastic annular structure, and notches in the axial direction are formed in the circumference of the damping device. When the torsion spring is not tightened, a certain gap exists in the inner ring of the torsion spring, so that the torsion spring is prevented from scraping the damping device when not tightened; when the torsion spring is stressed and contracted, the torsion spring presses the damping device, the gap can compensate the deformation of the damping device, and the relative sliding friction between the damping device and the outer diameter of the connecting part of the tensioning arm generates damping to inhibit the swinging of the tensioning arm.

Preferably, in order to further realize the adaptation of the internal structure of the damping device to the deformation of the damping device, an elongated slot along the axial direction is arranged on the inner diameter of the damping device. When the damping device deforms, the long groove structure can avoid the influence of extrusion between the inner diameter structures on the service life.

Preferably, in order to further improve the service life of the invention, a bearing is arranged in the belt pulley, the belt pulley is connected with the tensioning part through the bearing, a connecting bolt is arranged in the axial direction of the bearing and the tensioning part, and the connecting bolt penetrates through the inner diameter of the bearing and is connected with a threaded hole in the center of the tensioning part; and a dustproof cover is arranged between the connecting bolt and the bearing and covers the end face of the outer side of the bearing.

Has the advantages that:

1. the transmission system of the treadmill is further tensioned by installing an automatic tensioning device on the treadmill support. And the torsion spring can provide stable tension to the system. When the transmission belt is worn, the torsion spring can drive the tensioning arm to continuously tension the transmission belt, so that the complex process that the tightness of the transmission belt needs to be adjusted frequently in a transmission system of the traditional treadmill is avoided. In addition, the wrap angle of the driving wheel and the driven wheel is increased due to the design of the tensioning device, the transmission efficiency of the system is improved, and stable tension is provided for the system.

2. By additionally arranging the damping device in the automatic tensioning device, abnormal abrasion caused by contact between the contracted torsion spring and the pivot is avoided, and part of energy generated by shaking of the transmission belt can be absorbed. Not only can the tension of the transmission belt be more stable, but also the NVH performance of the transmission system is further improved.

3. The upper and lower stops on the tensioner arm limit the range of oscillation of the tensioner. Such a design ensures that the tensioning device can provide a relatively stable tension to the drive belt within a certain range. And the swing amplitude of the tensioning device can be controlled to avoid collision with other parts of the treadmill. In addition, after the three pointers on the tensioning arm are matched with the pointers on the stop block, a user can accurately judge whether the tension of the tensioning device is in a specified safety range or not and whether a new transmission belt needs to be replaced or not.

4. The automatic tensioning device is simple in structure, small, exquisite, light and easy to install, a driving wheel translation structure with a complex traditional transmission system is omitted, and the service life is prolonged.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a cross-sectional view of an assembled structure of the present invention;

FIG. 2 is an exploded view of the present invention;

FIG. 3 is a three-dimensional view of the tensioner arm of the present invention;

FIG. 4 is a bottom view of the tensioner arm of the present invention;

FIG. 5 is a cross-sectional view of the tensioner arm of the present invention;

FIG. 6 is a three-dimensional view of the base of the present invention;

FIG. 7 is a three-dimensional view of the damping device of the present invention;

wherein, 1-a base; 2-a tensioning arm; 3-belt wheel; 4-a torsion spring; 5-a damping device; 6-a pivot; 7-a bushing; 8-positioning pins; 11-a bump connection; 12-a boss; 13-a stopper; 14-positioning the counter bore; 21-a connecting part; 22-a tensioning section; 23-a scale indication; 24-a limit groove; 25-positioning the through hole; 31-a bearing; 32-connecting bolts; 33-dust cover; 51-notch; 52-long groove; 61-central threaded hole.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

As shown in fig. 1 and 2, an automatic treadmill belt tensioner with a damping mechanism comprises:

the base 1 is fixed on the treadmill bracket;

the tensioning arm 2 comprises a connecting part 21 hinged with the base 1 and a tensioning part 22 connected with a transmission belt, and the central axis of the connecting part 21 is parallel to and does not coincide with the central axis of the tensioning part 22; the tensioning arm 2 and the base 1 can rotate relatively around the central shaft of the connecting part 21;

a pulley 3, wherein the pulley 3 is hinged with the tension part 22, the central axis of the pulley 3 is coincident with the central axis of the tension part 22, the transmission belt of the treadmill is installed on the outer diameter of the pulley 3, and the pulley 3 can freely rotate along with the transmission belt and can tension the transmission belt;

the torsion spring 4 is positioned between the tensioning arm 2 and the base 1, two ends of the torsion spring 4 are respectively connected with the tensioning arm 2 and the base 1, and the torsion spring 4 drives the tensioning arm 2 to swing to one side for realizing the tensioning of the transmission belt;

and the damping device 5 is installed on the base 1 and is positioned inside the torsion spring 4, and the inner diameter of the torsion spring 4 contracts to be in contact with the damping device 5 when the torsion spring is stressed.

The transmission system of the treadmill is further tensioned by installing the invention on the treadmill bracket; the torsion spring 4 can provide a stable tension to the transmission system. When the transmission belt is worn, the torsion spring 4 can drive the tensioning arm to continuously tension the transmission belt, so that the complex process that the tightness of the transmission belt needs to be adjusted frequently in a transmission system of the traditional treadmill is avoided. In addition, the wrap angle of the driving wheel and the driven wheel is increased due to the design of the tensioning device, the transmission efficiency of the system is improved, and stable tension is provided for the system.

As shown in fig. 1 and 5, in order to reduce the overall size of the present invention, a protruding connection portion 11 is provided on the base 1 along the central axis direction thereof, a concave cavity is provided at the bottom of the connection portion 21 of the tensioning arm 2, and the structural size of the cavity matches with the protruding connection portion 11; the convex connecting part 11 is positioned in a cavity at the bottom of the connecting part 21 when the base 1 and the tensioning arm 2 are installed. The length of the invention is shortened and the invention is more compact because the convex connecting part 11 is positioned in the cavity at the bottom of the connecting part 21.

As shown in fig. 1, in order to facilitate the connection of the present invention with the treadmill frame, a pivot 6 is disposed between the base 1 and the connecting portion 21 of the tensioning arm 2, the pivot 6 is fixedly connected with the base 1, and the connecting portion 21 of the tensioning arm 2 is rotatably fixed on the pivot 6; the bottom of the pivot 6 is provided with a central threaded hole 61, and the central threaded hole 61 is matched with a connecting bolt connected with the treadmill bracket.

As shown in figures 1 and 2, in order to avoid abnormal wear caused by direct contact between two metal surfaces of the connecting part of the pivot shaft and the tensioning arm and to play a certain damping role to absorb part of vibration of the tensioner, a bush 7 is arranged between the outer diameter of the pivot shaft 6 and the inner diameter of the connecting part 21 of the tensioning arm 2.

As shown in fig. 1 and 3, in order to visually understand the wear of the transmission belt, the connecting portion 21 of the tensioning arm 2 is provided with at least three scale indicating portions 23 along the circumferential direction, the base 1 is provided with a pointer, and the position indicated by the pointer when the installation is completed is located between the three scale indicating portions 23. After the transmission belt is installed, if the pointer is between the first scale and the second scale, the tension provided by the tensioning device is proved to be accurate, the installation is correct, and after the transmission belt system works for a long time, when the pointer on the base exceeds the second scale and deviates to a third scale, the transmission belt is proved to be stretched to be incapable of providing stable tension, and the belt needs to be replaced.

As shown in fig. 3, 4 and 6, in order to avoid the unstable system or collision with surrounding structures caused by too large swinging of the tensioning device, by limiting the rotation range of the tensioning arm 2, the connecting part 21 of the tensioning arm 2 is provided with a fan-shaped limiting groove 24 along the radial direction, the base 1 is provided with a boss 12 and a stop 13, the stop 13 is positioned at the top end of the boss 12, and the stop 13 is positioned in the limiting groove 24 during installation.

As shown in fig. 1, 3, 4 and 6, in order to facilitate installation of the transmission belt, a positioning through hole 25 penetrating through the upper surface of the limiting groove 24 is formed in the limiting groove 24, a corresponding positioning counter bore 14 is formed in the boss 12 of the base 1, a positioning pin 8 is arranged in the installation process of the transmission belt, when the transmission belt is installed, the positioning pin 8 penetrates through the positioning through hole 25 and is inserted into the positioning counter bore 14, and the positioning pin 8 is pulled out after the installation of the transmission belt is completed. The positioning pin 8 mainly fixes the tensioning arm 2 at the installation position, so that a user can conveniently install the transmission belt.

As shown in fig. 7, in order to absorb the energy generated by belt vibration, the tension of the belt is more stable, and the NVH performance of the transmission system is further improved; the damping device 5 is an elastic annular structure, and an axial gap 51 is formed in the circumference of the damping device 5. When the torsion spring 4 is not tightened, a certain gap exists in the inner ring of the torsion spring, so that the torsion spring 4 is prevented from scraping the damping device when not tightened; when the torsion spring 4 is stressed and contracted, the torsion spring 4 presses the damping device 5, the notch 51 can compensate the deformation of the damping device 5, and the relative sliding friction between the damping device 5 and the outer diameter of the connecting part 21 of the tensioning arm 2 generates damping to restrain the swinging of the tensioning arm 2.

In order to further adapt the internal structure of the damping device 5 to the deformation thereof, the damping device 5 is provided with an axially extending slot 52 on the inner diameter. When the damping device 5 deforms, the long groove 52 structure can prevent the extrusion between the inner diameter structures from influencing the service life.

As shown in fig. 1 and 2, in order to further improve the service life of the present invention, a bearing 31 is provided in the pulley 3, the pulley 3 is connected with the tension part 22 through the bearing 31, a connecting bolt 32 is provided on the bearing 31 and the tension part 22 in the axial direction, and the connecting bolt 32 passes through the inner diameter of the bearing 31 to be connected with a threaded hole in the center of the tension part 22; a dust cover 33 is arranged between the connecting bolt 32 and the bearing 31, and the dust cover 33 covers the outer end face of the bearing 31.

The working process of the invention is as follows:

when the motor driving wheel works, the driving belt is dragged to operate, the belt wheel 3 with the bearing is pushed, then the tension is transmitted to the torsion spring 4 through the tensioning part 22 and the connecting part 21 of the tensioning arm 2 in sequence, the torsion spring 4 contracts to provide pre-tightening force for the tensioning arm 2, and the treadmill driving belt is automatically tensioned through the operation of the belt wheel 3.

The core contraction part of the damping device 5 of the tensioning device is a plastic damping ring, the plastic damping ring is installed on the base 1, the damping ring is not in contact with the outer diameter of the connecting part 21 of the tensioning arm 2 in a free state, when the torsion spring 4 is stressed, the torsion spring 4 presses the plastic damping ring to be in contact with the plastic damping ring, the damping ring and the connecting part 21 of the tensioning arm 2 generate damping through sliding friction, and the swinging of the tensioning arm 2 is restrained.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An automatic treadmill belt tensioning device with a damping mechanism, comprising:

the base (1), the said base (1) is fixed on treadmill support;

the tensioning arm (2) comprises a connecting part (21) hinged with the base (1) and a tensioning part (22) connected with a transmission belt, and the central axis of the connecting part (21) is parallel to and does not coincide with the central axis of the tensioning part (22); the tensioning arm (2) and the base (1) can rotate relatively by taking the central shaft of the connecting part (21) as a center;

the belt wheel (3), the belt wheel (3) is hinged with the tensioning part (22), the central axis of the belt wheel (3) is coincident with the central axis of the tensioning part (22), the transmission belt of the treadmill is installed on the outer diameter of the belt wheel (3), and the belt wheel (3) can freely rotate along with the transmission belt and can tension the transmission belt;

the torsion spring (4) is positioned between the tensioning arm (2) and the base (1), two ends of the torsion spring (4) are respectively connected with the tensioning arm (2) and the base (1), and the torsion spring (4) drives the tensioning arm (2) to swing to one side for realizing tensioning of the transmission belt;

the damping device (5) is installed on the base (1) and located on the inner side of the torsion spring (4), and the inner diameter of the torsion spring (4) contracts to be in contact with the damping device (5) when the torsion spring is stressed.

2. The treadmill belt automatic tensioning device with damping mechanism of claim 1, wherein: the base (1) is provided with a convex connecting part (11) along the central axis direction, the bottom of the connecting part (21) of the tensioning arm (2) is provided with an inwards concave cavity, and the structural size of the cavity is matched with that of the convex connecting part (11); when the base (1) and the tensioning arm (2) are installed, the protruding connecting part (11) is located in a cavity at the bottom of the connecting part (21).

3. The treadmill belt automatic tensioning device with damping mechanism of claims 1 or 2, wherein: a pivot (6) is arranged between the base (1) and the connecting part (21) of the tensioning arm (2), the pivot (6) is fixedly connected with the base (1), and the connecting part (21) of the tensioning arm (2) is rotatably fixed on the pivot (6); the bottom of the pivot (6) is provided with a central threaded hole (61), and the central threaded hole (61) is matched with a connecting bolt connected with the treadmill support.

4. The treadmill belt automatic tensioning device with damping mechanism of claim 3, wherein: and a bushing (7) is arranged between the outer diameter of the pivot (6) and the inner diameter of the connecting part (21) of the tensioning arm (2).

5. The treadmill belt automatic tensioning device with damping mechanism of claim 1, wherein: connecting portion (21) of tensioning arm (2) are equipped with at least three scale indicating part (23) along the circumferencial direction, be equipped with the pointer on base (1), when the installation is accomplished the position that the pointer instructed is located between three scale indicating part (23).

6. The treadmill belt automatic tensioning device with damping mechanism of claim 1, wherein: the connecting part (21) of the tensioning arm (2) is provided with a fan-shaped limiting groove (24) along the radial direction, the base (1) is provided with a boss (12) and a stop block (13), the stop block (13) is positioned at the top end of the boss (12), and the stop block (13) is positioned in the limiting groove (24) during installation.

7. The treadmill belt automatic tensioning device with damping mechanism of claim 6, wherein: be equipped with on spacing groove (24) and run through locating hole (25) of spacing groove (24) upper surface, be equipped with corresponding location counter bore (14) on boss (12) of stating base (1), be equipped with stop pin (8) in the drive belt installation, during the installation drive belt, stop pin (8) pass stop hole (25) and insert location counter bore (14), extract stop pin (8) after the drive belt installation is accomplished.

8. The treadmill belt automatic tensioning device with damping mechanism of claim 1, wherein: the damping device (5) is of an elastic annular structure, and notches (51) in the axial direction are formed in the circumference of the damping device (5).

9. The treadmill belt automatic tensioning device with damping mechanism of claim 8, wherein: and the inner diameter of the damping device (5) is provided with a long groove (52) along the axial direction.

10. The treadmill belt automatic tensioning device with damping mechanism of claim 1, wherein: a bearing (31) is arranged in the belt wheel (3), the belt wheel (3) is connected with the tensioning part (22) through the bearing (31), a connecting bolt (32) is arranged in the axial direction of the bearing (31) and the tensioning part (22), and the connecting bolt (32) penetrates through the inner diameter of the bearing (31) and is connected with a threaded hole in the center of the tensioning part (22); be equipped with shield (33) between connecting bolt (32) and bearing (31), shield (33) cover bearing (31) outside terminal surface.