CN117722474A - Asymmetric high damping ratio tensioner - Google Patents

Abstract

The invention discloses an asymmetric high damping ratio tensioner which comprises a rocker arm, a base, a rotating shaft, a belt pulley assembly, a radial damping mechanism and an axial damping mechanism, wherein the belt pulley seat and a rotating support are respectively arranged at two ends of the rocker arm; the rocker arm rotates around the rotating shaft to load or unload in a reverse direction, damping force is generated by friction between the radial damping mechanism and the inner side of the base along with the rotation of the rocker arm, and the damping force during loading is larger than that during unloading; the belt pulley assembly is rotatably arranged on the belt pulley seat, the outer side of the belt pulley assembly is pressed against the belt to tension the belt, the belt pulley assembly rotates along with the movement of the belt, and the relaxation change of the belt drives the rocker arm to rotate forward or reversely; the tensioner has higher loading damping than unloading damping, and asymmetric damping force.

Description

Asymmetric high damping ratio tensioner

Technical Field

The invention belongs to the technical field of tensioners of engine accessory systems, and particularly relates to an asymmetric tensioner with high damping ratio.

Background

Symmetrical damped tensioners are commonly used in current market applications, and this type of tensioner has the same damping in both loading and unloading directions. While asymmetric damped tensioners have high damping in the loading direction and low damping in the unloading direction, for commercial vehicles, because engine vibrations and accessory loads are high, if no engine accessory vibration isolation product is applied, symmetric damped tensioners with relatively high damping and high tension are often required, which is costly and can be improved by asymmetric damped tensioners. In addition, in the acceleration and deceleration processes, the symmetrical damping tensioner can possibly generate belt tooth jump or slipping, and the application of asymmetric damping can realize low damping rapid unloading during acceleration and high damping smooth loading during deceleration, so that the higher the damping ratio in a certain range is, the greater the improvement on the system is.

A tensioning wheel with an asymmetric damping mechanism is disclosed in chinese patent application number CN 201310344488.5. The damping principle of the tensioning wheel is as follows: the force F1 is the spring contact force caused by the contact of the end of the spring 60 with the contact post 39 on the swing arm 30 during the spring torsion, F2 is the force caused by the contact of the end of the spring with the receiving slot of the damping member 70, F3 is the normal reaction force acting on the first friction surface 75 of the damping member 70, F4 is the tangential friction force acting on the first friction surface 75, and F5 is the orthogonal reaction force acting on the damping bracket ramp 74 in contact with the contact ramp 303 of the third support 36 on the swing arm 30 and transferred to the damping member 70. The damping characteristic of the tensioner 10 is that the force F2 and the force F5 form a resultant force F3 via an angle β, thereby generating a frictional damping force F4. The asymmetric damping coefficient is generated by different friction forces caused by different rotation directions of the swing arm 30 during loading and unloading.

The above prior patent has the following disadvantages: 1) The torsion spring is stressed to bear the forward force in the torsion direction, and the tangential force generated by the contact point of the damping block and the swing arm is additionally increased besides the forward force in the torsion direction, so that the service life of the spring is shortened, and the durability is not facilitated; 2) The friction surface of the damping piece is too small, which is not beneficial to durability; 3) Since the friction force is not entirely converted by the torsion force of the spring, the variation of the friction force is small, resulting in a small damping ratio of loading and unloading; 4) The damping block and the damping ring are not beneficial to molding and assembly; the prior art is therefore unable to meet the high damping ratio and durability requirements of asymmetric damping tensioners.

Disclosure of Invention

Aiming at the problems and the technical requirements, the invention provides the asymmetric tensioner with high damping ratio, which can easily realize the asymmetric damping requirements of loading and unloading directions, and can adjust the damping ratio on the basis, thereby reaching the operation standard of high damping ratio.

The technical scheme of the invention is as follows: the utility model provides an asymmetric high damping ratio tensioning ware, includes rocking arm, base, pivot, band pulley subassembly, radial damping mechanism and axial damping mechanism, the rocking arm both ends are band pulley seat and swivel mount respectively, and the shaft hole of swivel mount core is used for installing the pivot, and swivel mount front is equipped with the annular step groove of many circles, and radial damping mechanism establishes in annular step groove, and swivel mount back is equipped with axial damping mechanism, and the base passes through the pivot to be connected in swivel mount front, and cylindric base is with radial damping mechanism cladding inside; under the condition that the base is kept in a mounting and fixing state, the rocker arm rotates around the rotating shaft to load or unload in a reverse direction, damping force is generated by friction between the radial damping mechanism and the inner side of the base along with the rotation of the rocker arm, and the damping force during loading is larger than that during unloading; the belt pulley assembly is rotatably arranged on the belt pulley seat, the outer side of the belt pulley assembly is pressed against the belt to tension the belt, the belt pulley assembly rotates along with the movement of the belt, and the relaxation change of the belt drives the rocker arm to rotate positively or reversely.

In the scheme, the acting force between the belt and the belt wheel assembly is the force for driving the rocker arm to rotate, the damping force for the rocker arm to rotate is from the radial damping mechanism and the axial damping mechanism, wherein the damping force of the axial damping mechanism is constant no matter the rocker arm rotates positively or negatively, and the damping force of the rocker arm in forward rotation loading is far greater than the damping force in reverse rotation unloading, so that the low-damping rapid unloading in acceleration and the high-damping stable loading in deceleration can be realized.

Further, radial damping mechanism includes torsional spring, damping ring, damping sleeve, ejector pad and holding tank, annular ladder groove and the coaxial setting of pivot, include from inside to outside highly decreasing first ladder, second ladder and third ladder, the torsional spring sets up on the second ladder, be equipped with the fan-shaped holding tank of undercut on the ladder face of first ladder and second ladder, the ejector pad corresponds the embedding holding tank in, the both ends face of ejector pad all points radially, the torsional spring is installed on the second ladder, torsional spring upper end fixed connection is in the base inner bottom surface, the torsional spring other end top is tightly on the ejector pad terminal surface, under torsional spring moment of torsion effect, ejector pad another terminal surface is tightly with the holding tank terminal surface top, the torsional spring outside is equipped with the damping ring, damping ring and damping sleeve all establish on the third ladder, the thrust of torsional spring to the ejector pad is FA, the thrust of ejector pad and holding tank terminal surface is FR, during rocking arm drive torsional spring loading, the radial outside top tight damping ring and damping sleeve of resultant force drive ejector pad that FA and FR formed, increase damping force. The end of the torsion spring keeps continuously propping up the push block, the push block keeps motionless in the circumferential direction, and because the shape of the push block is also fan-shaped, the extrusion forces FA and FR which are opposite to the two ends of the push block can form resultant force which pushes the fan-shaped push block outwards in the radial direction, and the push block applies the extrusion force in the damping ring and the damping sleeve.

Further, the end face of the accommodating groove is only partially propped against the end face of the pushing block, the part of the first ladder corresponding to the accommodating groove is propped against the pushing block, a clearance gap is arranged between the second ladder and the pushing block, and the second ladder is not contacted with the end face of the pushing block. The end face of the accommodating groove is tightly propped against the pushing block, so that the contact surface between the accommodating groove and the pushing block is reduced, friction force is reduced, the pushing block is prevented from being blocked when expanding outwards along the radial direction, the distance L from the axis to the end face propping-up stress point of the accommodating groove is an actual force arm of FR, and when the force arm L is smaller, the FR is correspondingly increased.

Further, the inner side surface of the push block is in an arc shape coaxial with the rotating shaft, the outer side surface of the push block is in an arc shape, the width of the push block is gradually reduced from one end to the other end, and the interval between the push block and the damping ring is continuously widened from the wide end to the narrow end of the push block. The shape of the push block is approximately wedge-shaped, when the push block expands outwards, the stress point at the outer side of the push block can be improved, compared with a uniform circular arc stress surface, the stress range is reduced, the pressure at the stress position is increased, and the damping force is adjusted more sensitively.

Further, the base is rotationally connected with the rotary support through the rotating shaft, an integrally formed piece is arranged between the rotating shaft and the base, two limiting blocks are arranged on the base shell, the outer edge of the rotary support is vertically tilted outwards to form a limiting handle, and the limiting handle can only move between the two limiting blocks, so that the limiting handle limits the rotating angle of the rocker arm.

Further, the damping sleeve is nested outside the damping ring, a plurality of positioning holes are formed in the damping ring, a plurality of positioning protrusions corresponding to the positioning holes one to one are formed in the inner side of the damping sleeve, positioning clamping strips are arranged at the bottom of the damping sleeve inwards, positioning grooves are formed in the middle of the pushing block, and the positioning clamping strips are correspondingly embedded into the positioning grooves.

Further, the damping ring bottom surface is equipped with the recess, is equipped with the fixture block on the second ladder global, unsmooth spacing chucking between recess and the fixture block, and the damping ring rotates along with rotatory support and synchronous rotation.

Furthermore, the damping ring is made of rigid materials, the damping sleeve is made of flexible elastic materials, and the outer side of the damping sleeve is attached to the inner wall of the base.

Further, the axial damping mechanism comprises a thrust washer and a fixed washer, a bushing is arranged on the outer side of the rotating shaft, the thrust washer is sleeved on the outer side of the bushing, the inner end face of the thrust washer abuts against the back face of the rotary support, the fixed washer is arranged on the outer end face of the thrust washer, the fixed washer tightly presses the thrust washer and the rotary support, and the torsion spring axially abuts against the thrust washer.

Further, the pulley assembly comprises a dust cover, a pulley bolt and a pulley, a bearing positioning seat is arranged on the pulley seat, the pulley is rotatably arranged on the bearing positioning seat, the pulley bolt penetrates through the pulley bearing from the outer side to be connected with the bearing positioning seat, and the dust cover is pressed on the outer side of the end of the pulley bolt.

The invention has the beneficial effects that: the tensioner is characterized in that a push block is embedded in a rotary support, two end faces of the push block are both directed radially, one end face of the push block receives acting force FA exerted by the end part of a torsion spring, the other end face of the push block is propped against the end face of a containing groove to generate reaction force FR, the push block can be extruded outwards along the radial direction under the combined action of the FA and the FR, and the outer side face of the push block tightly props up the damping ring, the damping sleeve and the inner wall of the base to generate damping force; the tensioner achieves the purpose of use only by the movable push block, has simple structure, does not need to increase manufacturing cost and has high economy.

Drawings

FIG. 1 is an overall exterior view of the tensioner of the present invention;

FIG. 2 is a diagram of the torsion spring versus push block in the tensioner;

FIG. 3 is an installation view of a damping ring and damping sleeve in a tensioner;

FIG. 4 is a positioning chart of a damping ring and an annular step groove in a tensioner;

FIG. 5 is an assembly view of an annular step groove and push block in a tensioner;

FIG. 6 is an internal structural view of the base;

FIG. 7 is an overall exploded view of the tensioner of the present invention;

FIG. 8 is an overall cross-sectional view of the tensioner;

FIG. 9 is a block diagram of the components inside the tensioner;

FIG. 10 is a force diagram of a pusher;

marked in the figure as: rocker arm 1, pulley seat 11, rotary support 12, shaft hole 13, annular step groove 14, first step 141, second step 142, fixture block 1421, clearance gap 1422, third step 143, accommodation groove 144, limit handle 15, base 2, limit block 21, spindle 22, radial damping mechanism 3, torsion spring 31, damping ring 32, positioning hole 321, groove 322, damping sleeve 33, positioning clip 331, push block 34, positioning groove 341, axial damping mechanism 4, bushing 41, thrust washer 42, fixed washer 43, pulley assembly 5, dust cover 51, pulley bolt 52, pulley 53, bearing positioning seat 54.

Detailed Description

The invention is further described below with reference to the drawings and examples.

The asymmetric high damping ratio tensioner comprises a rocker arm 1, a base 2, a rotating shaft 22, a belt pulley assembly 5, a radial damping mechanism 3 and an axial damping mechanism 4, wherein the belt pulley seat 11 and a rotary support 12 are respectively arranged at two ends of the rocker arm 1, a shaft hole 13 of a core part of the rotary support 12 is used for installing the rotating shaft 22, a plurality of circles of annular stepped grooves 14 are formed in the front surface of the rotary support 12, the radial damping mechanism 3 is arranged in the annular stepped grooves 14, and the axial damping mechanism 4 is arranged at the back surface of the rotary support 12. The base 2 and the rotary support 12 are rotationally connected through a rotary shaft 22, an integrally formed part is arranged between the rotary shaft 22 and the base 2, two limiting blocks 21 are arranged on the outer shell of the base 2, a limiting handle 15 is arranged on the outer edge of the rotary support 12 in an outward vertical warping mode, the limiting handle 15 can only move between the two limiting blocks 21, and the limiting handle 15 limits the rotating angle of the rocker arm 1.

The base 2 is connected to the front surface of the rotary support 12 through a rotating shaft 22, and the cylindrical base 2 covers the radial damping mechanism 3; in the state that the base 2 is kept stationary, the rocker arm 1 rotates around the rotating shaft 22 to load or unload in a reverse direction, damping force is generated by friction between the radial damping mechanism 3 and the inner side of the base 2 along with the rotation of the rocker arm 1, and the damping force during loading is larger than the damping force during unloading; specifically, radial damping mechanism 3 includes torsional spring 31, damping ring 32, damping sleeve 33, ejector pad 34 and holding tank 144, annular ladder groove 14 and the coaxial setting of pivot 22, including the first ladder 141 that highly decline from inside to outside, second ladder 142 and third ladder 143, torsional spring 31 sets up on second ladder 142, be equipped with the fan-shaped holding tank 144 of undercut on the ladder face of first ladder 141 and second ladder 142, ejector pad 34 corresponds the embedding in holding tank 144, the both ends face of ejector pad 34 all points radially, torsional spring 31 installs on second ladder 142, torsional spring 31 upper end fixed connection is in the base bottom surface, the other end top of torsional spring 31 is tightly on the ejector pad terminal surface, under torsional spring 31 moment of torsion effect, the other terminal surface of ejector pad 34 is tightly held with holding tank 144 terminal surface top, the torsional spring 31 outside is equipped with damping ring 32, damping ring 32 outside is equipped with damping sleeve 33, damping ring 32 and damping sleeve 33 all set up on third ladder 143, the thrust of torsional spring 31 to ejector pad 34 is FA, ejector pad 34 is FR with holding tank 144 terminal surface's top force, during 1 and FR 31, driving force and FR 31 form radial force and damping sleeve 32 top of driving force. The end of the torsion spring 31 keeps continuously pushing against the push block 34, the push block 34 is kept motionless in the circumferential direction, and the extrusion forces FA and FR opposite to the two ends of the push block 34 can form a resultant force pushing the fan-shaped push block 34 outwards in the radial direction because the push block is also fan-shaped, and the push block 34 applies the extrusion forces to the damping ring 32 and the damping sleeve 33, so that the damping force is increased.

In a preferred embodiment, the end surface of the accommodating groove 144 only partially abuts against the end surface of the push block 34, the portion of the first step 141 corresponding to the accommodating groove 144 abuts against the push block, a clearance gap 1422 is provided between the second step 142 and the push block 34, and the second step 142 is not contacted with the end surface of the push block. The inner side surface of the push block 34 is in a circular arc shape coaxial with the rotating shaft 22, the outer side surface of the push block 34 is in a circular arc shape, the width of the push block 34 gradually decreases from one end to the other end, and the interval between the push block 34 and the damping ring 32 continuously widens from the wide end to the narrow end of the push block.

In the above embodiment, the end surface of the accommodating groove 144 is tightly propped against the part of the push block 34, so that the contact surface between the accommodating groove 144 and the push block 34 is reduced, the friction force is reduced, the push block 34 is prevented from being blocked when expanding outwards in the radial direction, the distance L from the axle center to the tightly propping force point of the end surface of the accommodating groove 144 is actually the force arm of FR, and when the force arm L is smaller, the FR is correspondingly increased. The push block 34 is approximately wedge-shaped, and the end of the push block is wide and the end of the push block is narrow, so that when the push block 34 expands outwards, the stress point on the outer side of the push block can be improved, the stress range is reduced compared with a uniform arc stress surface, the pressure at the stress position is increased, and the damping force is adjusted more sensitively.

The pulley assembly 5 is rotatably arranged on the pulley seat 11, the outer side of the pulley assembly 5 is pressed against a belt to tension the belt, the pulley assembly 5 rotates along with the movement of the belt, and the relaxation change of the belt drives the rocker arm 1 to rotate forward or reversely. The pulley assembly 5 comprises a dust cover 51, a pulley bolt 52 and a pulley 53, wherein a bearing positioning seat 54 is arranged on the pulley seat 11, the pulley 53 is rotatably arranged on the bearing positioning seat 54, the pulley bolt 52 penetrates through the pulley core from the outside to be connected with the bearing positioning seat 54, and the dust cover 51 covers the pulley bolt 52.

The damping ring 32 is made of rigid materials, the damping sleeve 33 is made of flexible elastic materials, and the outer side of the damping sleeve 33 is attached to the inner wall of the base 2; the damping sleeve 33 is nested outside the damping ring 32, a plurality of positioning holes 321 are formed in the damping ring 32, a plurality of positioning protrusions corresponding to the positioning holes 321 one by one are formed in the inner side of the damping sleeve 33, positioning clamping strips 331 are inwards arranged at the bottom of the damping sleeve 33, positioning grooves 341 are formed in the middle of the pushing block 34, and the positioning clamping strips 331 are correspondingly embedded into the positioning grooves 341. The bottom end surface of the damping ring 32 is provided with a groove 322, the peripheral surface of the second step 142 is provided with a clamping block 1421, the concave-convex limiting clamping between the groove 322 and the clamping block 1421 is realized, and the damping ring 32 rotates synchronously along with the rotation of the rotary support 12.

The axial damping mechanism 4 comprises a thrust washer 42 and a fixed washer 43, a bushing 41 is arranged on the outer side of the rotating shaft 22, the thrust washer 42 is sleeved on the outer side of the bushing 41, the inner end face of the thrust washer 42 abuts against the back face of the rotary support 12, the fixed washer 43 is arranged on the outer end face of the thrust washer 42, the fixed washer 43 tightly presses the thrust washer 42 and the rotary support 12, and the torsion spring 31 axially abuts against the thrust washer 42.

The scheme of the invention is a double damping structure, the damping force of the rotation of the rocker arm 1 comes from the radial damping mechanism 3 and the axial damping mechanism 4 at the same time, wherein the damping force of the axial damping mechanism 4 is constant no matter the rocker arm 1 rotates positively or negatively, so that the asymmetric characteristic of damping is provided by the radial damping mechanism 3 only.

The operating principle of the tensioner of the present invention:

the rocker arm loading process comprises the following steps: the rocker arm 1 rotates positively to drive the rotary support 12 to rotate, the force of the torsion spring 31 against the push block is the reaction force of the end part of the FA containing groove 144 to the push block 34 is FR, the resultant force of FA and FR acts on the push block 34 in the radial direction to push the push block 34 outwards, the push block 34 presses the outer damping ring 32 and the damping sleeve 33 outwards, the damping ring 32, the damping sleeve 33 and the inner wall of the base 2 are compressed in the radial direction, and the damping force loaded by the rocker arm 1 is greatly improved.

Rocker unloading process: when the rocker arm 1 rotates, the torsion spring 31 is reset, the acting force of FA and FR on the pushing block is reduced, the extrusion force of the outer side of the pushing block on the damping ring 32, the damping sleeve 33 and the inner wall of the base 2 is reduced, the damping force is greatly reduced, and therefore the damping force is maintained in a lower state during unloading.

While the invention has been described with respect to several preferred embodiments, the scope of the invention is not limited thereto, and any changes and substitutions that would be apparent to one skilled in the art within the scope of the invention are intended to be included within the scope of the invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (10)

1. An asymmetric high damping ratio tensioner characterized by: the rotary support comprises a rocker arm, a base, a rotating shaft, a belt wheel assembly, a radial damping mechanism and an axial damping mechanism, wherein the belt wheel seat and a rotary support are respectively arranged at two ends of the rocker arm, a shaft hole of a core part of the rotary support is used for installing the rotating shaft, the front surface of the rotary support is provided with a plurality of rings of annular stepped grooves, the radial damping mechanism is arranged in the annular stepped grooves, the back surface of the rotary support is provided with the axial damping mechanism, the base is connected to the front surface of the rotary support through the rotating shaft, and the cylindrical base covers the radial damping mechanism; in the mounting and fixing state of the base, the rocker arms rotate around the rotating shafts to load or unload in a reverse direction, damping force is generated by friction between the radial damping mechanism and the inner side of the base along with the rotation of the rocker arms, and the damping force during loading is larger than that during unloading; the belt pulley assembly is rotatably arranged on the belt pulley seat, the outer side of the belt pulley assembly is pressed against the belt to tension the belt, the belt pulley assembly rotates along with the movement of the belt, and the relaxation change of the belt drives the rocker arm to rotate positively or reversely.

2. An asymmetric high damping ratio tensioner as claimed in claim 1, wherein: the radial damping mechanism comprises a torsion spring, a damping ring, a damping sleeve, a push block and a containing groove, wherein the annular stepped groove is coaxially arranged with the rotating shaft, the annular stepped groove comprises a first step, a second step and a third step which are gradually decreased from inside to outside, the torsion spring is arranged on the second step, the stepped surfaces of the first step and the second step are provided with sector containing grooves which are recessed downwards, the push block is correspondingly embedded into the containing groove, both end surfaces of the push block are all directed radially, the torsion spring is arranged on the second step, the upper end of the torsion spring is fixedly connected to the inner bottom surface of the base, the other end of the torsion spring is tightly propped against the end surface of the push block, the other end surface of the push block is tightly propped against the end surface of the containing groove under the action of torsion spring, the damping sleeve is arranged outside the torsion spring, the damping ring and the damping sleeve are both arranged on the third step, the thrust of the torsion spring to the push block is FA, the propping force of the push block and the end surface of the containing groove is FR, and the resultant force formed by FA and FR drives the push block to radially outwards prop against the damping ring and the damping sleeve when the rocker arm drives the torsion spring to load, so that the damping force is increased.

3. An asymmetric high damping ratio tensioner as claimed in claim 2, wherein: the end face of the accommodating groove is only partially propped against the end face of the pushing block, the part of the first ladder corresponding to the accommodating groove is propped against the pushing block, a clearance gap is arranged between the second ladder and the pushing block, and the second ladder is not contacted with the end face of the pushing block.

4. An asymmetric high damping ratio tensioner as claimed in claim 3, wherein: the inner side surface of the push block is arc-shaped coaxial with the rotating shaft, the outer side surface of the push block is arc-shaped, the width of the push block is gradually reduced from one end to the other end, and the interval between the push block and the damping ring is continuously widened from the wide end to the narrow end of the push block.

5. An asymmetric high damping ratio tensioner as claimed in claim 4, wherein: the base is connected with the rotary support in a rotating way through the rotating shaft, an integrally formed piece is arranged between the rotating shaft and the base, two limiting blocks are arranged on the base shell, the outer edge of the rotary support is vertically tilted outwards to form a limiting handle, and the limiting handle can only move between the two limiting blocks, so that the limiting handle limits the rotating angle of the rocker arm.

6. An asymmetric high damping ratio tensioner as claimed in claim 5, wherein: the damping sleeve is nested outside the damping ring, a plurality of positioning holes are formed in the damping ring, a plurality of positioning protrusions corresponding to the positioning holes one to one are formed in the inner side of the damping sleeve, positioning clamping strips are arranged at the bottom of the damping sleeve inwards, positioning grooves are formed in the middle of the pushing block, and the positioning clamping strips are correspondingly embedded into the positioning grooves.

7. An asymmetric high damping ratio tensioner as claimed in claim 6, wherein: the damping ring bottom end face is equipped with the recess, is equipped with the fixture block on the second ladder global, unsmooth spacing chucking between recess and the fixture block, and the damping ring rotates along with the swivel mount and rotates in step.

8. An asymmetric high damping ratio tensioner as claimed in claim 7, wherein: the damping ring is made of rigid materials, the damping sleeve is made of flexible elastic materials, and the outer side of the damping sleeve is attached to the inner wall of the base.

9. An asymmetric high damping ratio tensioner as claimed in claim 8, wherein: the axial damping mechanism comprises a thrust washer and a fixed washer, a bushing is arranged on the outer side of the rotating shaft, the thrust washer is sleeved on the outer side of the bushing, the inner end face of the thrust washer abuts against the back face of the rotary support, the fixed washer is arranged on the outer end face of the thrust washer, the fixed washer tightly presses the thrust washer and the rotary support, and the torsion spring axially pushes the thrust washer tightly.

10. An asymmetric high damping ratio tensioner as claimed in claim 9, wherein: the pulley assembly comprises a dust cover, a pulley bolt and a pulley, a bearing positioning seat is arranged on the pulley seat, the pulley is rotatably arranged on the bearing positioning seat, the pulley bolt penetrates through a pulley bearing from the outer side to be connected with the bearing positioning seat, and the dust cover is pressed on the outer side of the pulley bolt end.