CN219853098U - Ultra-thin double-acting hydraulic stretcher - Google Patents

Abstract

The utility model belongs to the technical field of bolt fastening in the construction or installation process of large equipment and facilities, and discloses an ultrathin double-acting hydraulic stretcher, which comprises an oil cylinder, a piston and a stretching sleeve, wherein the stretching sleeve is arranged in the piston; the lower end of the oil cylinder is provided with a stretcher base, and the diameter of the stretcher base is smaller than the diameters of the lower part and the upper part of the cylinder body. The double-acting hydraulic stretcher can be suitable for application scenes with relatively narrow use space.

Description

Ultra-thin double-acting hydraulic stretcher

Technical Field

The utility model belongs to the technical field of bolt fastening in the construction or installation process of large equipment and facilities, relates to a hydraulic stretcher for pre-tightening bolts, and particularly relates to a double-acting hydraulic stretcher.

Background

The hydraulic stretcher is a special bolt pre-tightening tool, and the bolt pre-tightening force can be simply understood as the clamping force of the bolt on the connected piece along the axial direction of the bolt, and the bolt pre-tightening force is generated by stretching the screw rod in the elastic range. When the bolts are used for fastening and connecting the parts, the pretightening force is too small, and the fastening and connecting strength is insufficient. The bolts may be broken due to excessive pre-tightening force, or the connecting member may be crushed, bitten, twisted, deformed or broken, or the thread may be damaged due to excessive shearing force. The magnitude of the pretightening force is an important factor affecting the reliability of the fastening connection of the bolts.

At present, two modes of controlling the pretightening force of the bolt are mainly adopted: one is to control the torque applied to the nut by a torque wrench and achieve the purpose of controlling the pretightening force; the other is that the purpose of controlling the pretightening force is achieved by applying the pulling force of the target pretightening force to the screw rod by the hydraulic stretcher before the screw bolt is screwed. Compared with torque wrench, the hydraulic stretcher is mainly applied to construction and installation engineering of large-scale equipment and facilities such as wind power, bridges and the like with higher requirements on bolt firmness based on safety factors.

In some situations where hydraulic stretchers are required, there may be situations where the hydraulic stretchers are used in a small space, which may cause the hydraulic stretchers to be inconvenient to operate or even unusable. For example, in wind turbines, a locking disc is typically used to connect the wind turbine main shaft with the gearbox low-band shaft, but in some wind turbines (such as the wind turbine shown in fig. 1 of the patent application publication No. CN111075661 a), the main shaft bearing is very close to the locking disc, resulting in an existing hydraulic tensioner, especially a double-acting hydraulic tensioner, which cannot be used between the main shaft bearing and the locking disc because of the tensioner thickness problem, or which, although it can be placed, is not operable or inconvenient because of the limited remaining operating space.

In view of the above, how to improve the structure of a hydraulic stretcher, in particular to a double-acting hydraulic stretcher, so as to reduce the thickness of the stretcher, and further to be suitable for the situation that the use space is relatively narrow is a problem to be solved in the prior art.

Disclosure of Invention

The utility model aims to solve the technical problem of how to improve the structure of the hydraulic stretcher to reduce the thickness of the stretcher. A double acting hydraulic tensioner of relatively lower thickness is proposed.

In order to achieve the aim, the utility model provides an ultrathin double-acting hydraulic stretcher, which comprises an oil cylinder, a piston and a stretching sleeve, wherein the oil cylinder is of a hollow structure which is penetrated up and down, an oil cavity is arranged in the middle of the oil cylinder, the piston is assembled in the oil cylinder in a sliding way, the piston consists of an upper guide section, a middle stress section and a lower guide section, and the middle stress section slides in the oil cavity; the piston is of a hollow structure which is penetrated up and down, a stretching sleeve is placed in the piston, the main body part of the stretching sleeve is a columnar body, the upper end is provided with an end cap, the lower end is provided with a threaded hole used for being connected with the upper end of a pre-tightening screw, the upper part of an inner cavity of the piston is a stretching sleeve end cap accommodating cavity used for accommodating the stretching sleeve end cap, and the middle lower part is a stretching sleeve main body part mounting hole; the height of the stretching sleeve end cap is smaller than the depth of the stretching sleeve end cap cavity, a spanner connecting hole is formed in the upper end of the stretching sleeve end cap, and the top of the oil cylinder is lower than or flush with the top of the piston in a reset state. The front side wall of the cylinder body is provided with a reset oil inlet and an extension oil inlet corresponding to the top and the bottom of the oil cavity respectively.

According to the technical scheme, through the structural arrangement that the top of the oil cylinder is lower than or at least flush with the upper end of the piston in a reset state, the movement space needed by the upper end of the piston is overlapped with the spanner operation space, the thickness of the oil cylinder is compressed to be the lowest, and then the spanner connecting part of the stretching sleeve, the stretching sleeve end cap and the upper guide section of the piston are overlapped in the transverse direction through arranging the stretching sleeve end cap accommodating cavity with the depth larger than the stretching sleeve end cap height on the upper part of the piston and arranging the spanner connecting hole on the upper end of the stretching sleeve end cap, so that the thickness of the stretcher is effectively compressed, and the hydraulic stretcher is lighter and thinner as a whole. So that the stretcher is suitable for application scenes with narrow use spaces.

In addition, skillfully utilizes the characteristic of small reset pressure of the stretcher, realizes the structural arrangement that the diameter of the upper guide section is larger than that of the lower guide section on the premise of not increasing the diameter of the stressed section in the middle of the piston, creates conditions for arranging a stretching sleeve end cap containing cavity on the upper part of the piston (the diameter of the stretching sleeve end cap is larger than that of the stretching sleeve main body), further achieves the technical effect of effectively compressing the thickness of the stretcher and simultaneously not increasing the width of the stretcher so as to ensure that the stretcher can be suitable for application scenes with same limited transverse space.

Further, the hydro-cylinder includes the cylinder body and sets up the cylinder cap in the cylinder body upper end, the cylinder cap center establishes the mounting hole on the piston, the upper portion guide section lateral wall sliding fit of piston goes up the mounting hole inner wall and the piston, through sealing washer sliding seal between the two, the oil pocket is established on cylinder body upper portion, the middle part atress section lateral wall sliding fit of oil pocket inner wall and piston, through sealing washer sliding seal between the two, the piston lower assembly hole is established to the cylinder body lower part, the lower mounting hole inner wall and the lower part guide section lateral wall sliding fit of piston are established to the piston, through sealing washer sliding seal between the two, the cylinder body lower extreme is the stretcher base, the screw rod through-hole is established at stretcher base center.

Further, the cylinder cover is arranged in an L-shaped step groove at the inner side of the upper end of the cylinder body, the cylinder cover is connected with the cylinder body through threads, the cylinder cover is sealed through a sealing ring, and the top of the cylinder cover is flush with the top of the cylinder body. The structure can ensure that the thickness of the stretcher is not additionally increased due to the arrangement of the cylinder cover on one hand, and a step groove is formed at the upper end of the cylinder body on the other hand, so that an L-shaped corner structure with the same shape and the same orientation as the bottom of the oil cavity is formed, and conditions are provided for arranging the oil inlet and the oil outlet of the same structure.

Further, a sealing ring mounting groove is formed in the lower end of the side wall of the middle stress section of the piston, the sealing ring is assembled in the sealing ring mounting groove, and a gap is formed between the lower edge of the sealing ring mounting groove and the inner wall of the oil cavity. When the pressure in the oil cavity is increased, the pressure formed by the oil pressure on the seal is increased, so that the seal ring is further pressed against the upper edge of the seal ring mounting groove and the inner wall of the oil cavity. Further, the greater the oil pressure, the better the sealing effect.

Further, the lower extreme of piston is equipped with the binding off structure, the inboard of binding off structure forms the anticreep inclined plane, the position top of tensile cover lower extreme to the anticreep inclined plane is equipped with a spacing inclined plane that diameter shrink formed. The stretcher is prevented from being separated from the stretching screw when the stretching sleeve breaks.

Further, in order to be suitable for the application scene that wind-powered electricity generation locking dish circumference bolt is intensive relatively, as the improvement, the diameter of stretcher base is less than the diameter of cylinder body lower part and upper portion.

The diameter of the base part for supporting the lower end of the cylinder is smaller than the diameter of the middle upper part of the cylinder, so that the lower end of the stretcher forms a space for avoiding the nut of the firm bolt of the locking disc and the sleeve of the sleeve spanner. So that the hydraulic stretcher is simultaneously suitable for application scenes with narrow intervals of bolts at the periphery of the locking disc.

Further, the stretcher base has a left-right width that is less than the diameter of the stretcher base. Smaller left-right widths may be suitable for the case of smaller lock disk fastening bolt spacing, but while maintaining the diameter of the tensioner base from being too small to ensure that the base has sufficient support capability.

The beneficial effects of the utility model are as follows: according to the utility model, through improving the structures of the oil cylinder, the piston and the stretching sleeve and the structural relation among the oil cylinder, the piston and the stretching sleeve, the thickness of the double-acting hydraulic stretcher is effectively reduced, so that the hydraulic stretcher can be better suitable for application scenes with relatively narrow use space.

Drawings

FIG. 1 is a schematic illustration of an example application of the double acting tensioner of the present utility model for wind power lock disk installation.

Fig. 2 is a schematic view showing the positional relationship between the lock disk and the spindle bearing in the example shown in fig. 1.

Fig. 3 is a schematic view of a piping connection structure of the example shown in fig. 1.

Fig. 4 is a schematic diagram showing a front view of the hydraulic stretcher according to the example shown in fig. 1.

Fig. 5 is a schematic view showing the positional relationship between the hydraulic stretcher and the fastening nut and the socket wrench in the example shown in fig. 1.

Fig. 6 is a schematic diagram showing a side cross-sectional structure of the hydraulic stretcher in the example shown in fig. 1.

Fig. 7 is a schematic diagram showing a front cross-sectional structure of the hydraulic stretcher in the example shown in fig. 1.

Fig. 8 is a schematic diagram of the piston structure of the hydraulic stretcher in the example shown in fig. 1.

Fig. 9 is a schematic diagram of the hydraulic tensioner cylinder in the example shown in fig. 1.

FIG. 10 is a schematic diagram of another example application of the double acting tensioner of the present utility model for wind power lock disk installation.

Fig. 11 is a schematic view of a piping connection structure of the example shown in fig. 10.

Fig. 12 is a schematic view showing a front cross-sectional structure of the hydraulic stretcher in the example shown in fig. 10.

FIG. 13 is a schematic view of the cross-sectional structure of A-A in FIG. 12.

Fig. 14 is a schematic view showing the relationship between the hydraulic stretcher and the fastening nut and the socket wrench in the example shown in fig. 10.

Detailed Description

The structural features of the hydraulic tensioner of the present utility model will be further described below with reference to the accompanying drawings, taking installation of a wind power locking disc as an example.

Example 1.

Referring to FIGS. 1-5, an example of an application of a 30 hole wind lock disk using the double action tensioner of the present utility model is shown. In the example, the locking disc 3 is used for connecting the wind power main shaft 301 and the gearbox low-speed shaft 303, the distance between the side surface of the locking disc 3 and the main shaft bearing 302 is 176mm, namely the mounting space of the stretcher is 176mm in height, the diameter of a fastening circle of the locking disc 788mm, 30M 33 bolts are uniformly distributed along the fastening circle, and the center distance of the bolts is 82mm. 15 of the 30M 33 bolts are fastening bolts 33, and the other 15 are double-headed pre-tightening screws 34. 15 ultrathin double-acting hydraulic stretchers provided by the utility model are configured in a system. The maximum radius of the upper end of the stretcher 2 (shown in fig. 4) is 64mm, the radius of the middle main body part is 57.5mm, the radius of the lower end is 45mm, the radius of the circumscribing circle of the nut of the fastening bolt is 25mm, and the outer diameter of the hexagonal sleeve for screwing the fastening nut is 64mm. The hydraulic stretcher has the thickness of 138mm and reserves the space for screwing the wrench of 38 mm.

The system is provided with a double-output hydraulic pump, and the hydraulic pump 1 comprises a high-pressure working oil port 102 and a low-pressure working oil port 101. The stretching oil inlet and outlet and the resetting oil inlet of the 15 hydraulic stretcher are respectively connected in parallel to the high-pressure working oil inlet and the low-pressure working oil inlet of the hydraulic pump according to the oil circuit schematic diagram shown in fig. 3, and the actual structure diagram is shown in fig. 1. Referring to fig. 4, each hydraulic tensioner is configured with two connector modules, a low pressure connector module 251 and a high pressure connector module 252, respectively, each comprising three interconnected interface ends. The first interface end of the high-pressure joint module is connected with a stretching oil inlet and outlet of the hydraulic stretcher, the second interface end and the third interface end are connected with an oil pipe, the first interface end of the high-pressure joint module is connected with a resetting oil inlet and outlet of the hydraulic stretcher, and the second interface end and the third interface end are connected with the oil pipe.

The 15 hydraulic stretchers are numbered 1# -15 along the circumference in sequence, a high-pressure working oil port of the hydraulic pump is connected with a second interface end of a high-pressure joint module of the 1# hydraulic stretchers through a first section of long oil pipe, and a low-pressure working oil port of the hydraulic pump is connected with a second interface end of a low-pressure joint module of the 1# hydraulic stretchers through a second section of long oil pipe. The third interface end of the high-pressure interface module of the 1# hydraulic stretcher is connected with the second interface end of the high-pressure interface module of the 2# hydraulic stretcher through a first section of short oil pipe, and the third interface end of the low-pressure interface module of the 1# hydraulic stretcher is connected with the second interface end of the low-pressure interface module of the 2# hydraulic stretcher through a second section of short oil pipe. The third interface end of the high-pressure joint module of the 2# hydraulic stretcher is connected with the second interface end of the high-pressure joint module of the 3# hydraulic stretcher through a third section of short oil pipe, and the fourth interface end of the low-pressure joint module of the 2# hydraulic stretcher is connected with the second interface end of the low-pressure joint module of the 3# hydraulic stretcher through a second section of short oil pipe. And by analogy, the third interface end of the high-pressure joint module of the 14# hydraulic stretcher is connected with the second interface end of the high-pressure joint module of the 15# hydraulic stretcher through a twenty-seventh section of short oil pipe, and the third interface end of the low-pressure joint module of the 14# hydraulic stretcher is connected with the second interface end of the low-pressure joint module of the 15# hydraulic stretcher through a twenty-eighth section of short oil pipe. The third interface end of the high-pressure interface module and the third interface end of the high-pressure interface module of the 15# hydraulic stretcher are respectively sealed by plugging screws.

Referring to fig. 6-9, the hydraulic stretcher in this example includes an oil cylinder 21, a piston 22, and a stretching sleeve 23, where the oil cylinder 21 is a hollow structure penetrating up and down, the piston 22 is slidably assembled in the cylinder 21, the piston 22 is also a hollow structure penetrating up and down, the stretching sleeve 23 is placed in the piston 22, the main body of the stretching sleeve 23 is a cylindrical body, the upper end is provided with an end cap 231, and the lower end is provided with a threaded hole 232 for connecting with the upper end of the pre-tightening screw. The upper part of the inner cavity of the piston 22 is a stretching sleeve end cap accommodating cavity 221 for accommodating the stretching sleeve end cap 231, the lower part is a stretching sleeve main body part mounting hole 225, and the height of the stretching sleeve end cap 231 is smaller than the depth of the stretching sleeve end cap accommodating cavity 221. The upper end of the end cap of the stretching sleeve is provided with a wrench connecting hole 233. The lower extreme of piston is equipped with the binding off structure, the inboard of binding off structure forms anticreep inclined plane 226, the tensile cover lower extreme is equipped with a spacing inclined plane 234 that diameter shrink formed to the position top of anticreep inclined plane.

The piston is composed of an upper guide section 222, a middle stress section 223 and a lower guide section 224, wherein the diameter of the upper guide section 222 is larger than that of the lower guide section 224, and the diameter of the middle stress section 223 is larger than that of the upper guide section 222.

The oil cylinder 21 comprises a cylinder body 211 and a cylinder cover 212 arranged at the upper end of the cylinder body 211, wherein the cylinder cover is arranged in an L-shaped step groove at the inner side of the upper end of the cylinder body, and the cylinder cover is connected with the cylinder body through threads and is sealed through a sealing ring. The cylinder cover 211 is provided with an upper piston assembly hole 217, the inner wall of the upper piston assembly hole 217 is in sliding fit with the side wall of the upper guide section 222 of the piston, and the upper piston assembly hole 217 and the side wall of the upper guide section 222 of the piston are in sliding seal through a sealing ring. The top of the cylinder head 212 is flush with the top of the cylinder 211 and the top of the piston in the reset state.

The upper portion of cylinder 211 is equipped with oil cavity 213, the inner wall of oil cavity 213 is in sliding fit with the side wall of middle stress section 223 of piston 22, the lower end of middle stress section 223 of piston 22 is equipped with a sealing ring installation groove, sealing ring 2231 is equipped in the sealing ring installation groove, and gap 2131 is equipped between the lower edge of the sealing ring installation groove and the inner wall of oil cavity.

The lower part of the cylinder body 211 is provided with a lower piston assembly hole 214, the inner wall of the lower piston assembly hole 213 is in sliding fit with the side wall of the lower guide section 224 of the piston, and the lower piston assembly hole and the side wall of the lower guide section 224 of the piston are in sliding seal through a sealing ring. The lower end of the cylinder body is used as a stretcher base for supporting the stretcher, and a screw through hole is arranged in the center of the stretcher base.

A reset oil inlet and outlet 215 and a stretching oil inlet and outlet 216 are respectively arranged on the side wall of the cylinder body corresponding to the top and bottom of the oil cavity 213. The reset oil inlet and outlet 215 and the stretching oil inlet and outlet 216 are composed of an inner port, an outer port and an oil liquid channel connected with the inner port and the outer port, the inner port of the reset oil inlet and outlet 215 is arranged on a step surface used for installing a cylinder cover on the inner side of the upper end of the cylinder body, a gap is arranged between the bottom of the cylinder cover and the step surface used for installing the cylinder cover, and a low-pressure oil inlet buffer space is formed. The outer port of the return oil inlet/outlet 215 is disposed on the outer side surface of the cylinder body, and the oil channel connecting the inner port and the outer port of the return oil inlet/outlet 215 extends vertically downward from the inner port and then extends horizontally outward to the outer port.

The inner end of the stretching oil inlet and outlet 216 is arranged on a step surface forming the bottom surface of the oil cavity on the inner side of the middle part of the cylinder body, and a gap is arranged between the bottom of the middle stress section of the piston and the step surface forming the bottom surface of the oil cavity, so that a high-pressure oil inlet buffer space is formed. The outer port of the stretching oil inlet/outlet 216 is disposed on the outer side surface of the cylinder body, and the oil liquid channel connecting the inner port and the outer port of the stretching oil inlet/outlet 216 extends vertically downwards from the inner port and then extends horizontally outwards to the outer port.

The reset oil inlet and outlet 215 and the stretch oil inlet and outlet 216 have the following structural advantages: the two oil inlet and outlet ports are all arranged on the cylinder body, and compared with the two oil inlet and outlet ports respectively arranged on the cylinder body and the cylinder cover, the two oil inlet and outlet ports are machined on one part. And the structures of the reset oil inlet and outlet 215 and the stretching oil inlet and outlet 216 are completely the same from the inner port to the oil liquid channel and from the inner port to the outer port, and the two oil inlet and outlet comprise three forming processing steps including processing of the inner port and the vertical extending part channel, processing of the transverse extending part channel and processing of the outer port, which can be synchronously completed by adopting double cutters.

Example 2.

Referring to fig. 10-14, a modified version of example 1 is shown, the application scenario is the same as that of example 1, the installation space of the stretcher is 176mm high, the fastening circle diameter of the locking disc is 788mm, the hydraulic structure and main dimensions are the same as those of example 1 (as shown in fig. 4), the maximum radius of the upper end is 64mm, the radius of the middle main body part is 57.5mm, the radius of the lower end is 45mm, the radius of the nut circumscribing circle of the fastening bolt is 25mm, and the outer diameter of the hexagonal sleeve for screwing the fastening nut is 64mm. The hydraulic stretcher has the thickness of 138mm and reserves the space for screwing the wrench of 38 mm. Each hydraulic tensioner is configured with two connector modules, a low pressure connector module 251 and a high pressure connector module 252, respectively, each connector module including three interconnected interface ends. The first interface end of the high-pressure joint module is connected with a stretching oil inlet and outlet of the hydraulic stretcher, the second interface end and the third interface end are connected with an oil pipe, the first interface end of the high-pressure joint module is connected with a resetting oil inlet and outlet of the hydraulic stretcher, and the second interface end and the third interface end are connected with the oil pipe.

One of the improvements over embodiment 1 is that 32M 33 bolts are uniformly distributed along the tightening circle of the locking plate, so that the pretightening force of the locking plate is more uniform. But the increased number of 2 bolts also resulted in a reduction of the bolt center-to-center distance to 77mm. For this reason, in the stretcher described in example 1, the left and right sides of the lower end of the cylinder body of the cylinder were each removed by a width of 9mm, and the left and right widths of the stretcher bases were made smaller than the front and rear widths, so that a sufficient space was left between two adjacent stretchers to lock the nuts of the disc-fastening bolts and the socket of the socket wrench, as shown in fig. 14.

The second improvement is that: four hydraulic pumps with working oil ports are used, and the pipeline connection method of the hydraulic stretcher is improved. The hydraulic pump includes two low-pressure working ports 1011, 1012 and two high-pressure working ports 1021, 1022.

The 16 hydraulic stretchers are numbered 1# -16# along the circumference in sequence, one high-pressure working oil port 1022 of the hydraulic pump is connected with the second interface end of the high-pressure joint module of the 1# hydraulic stretcher through a first section of long oil pipe, and one low-pressure working oil port 1012 of the hydraulic pump is connected with the second interface end of the low-pressure joint module of the 1# hydraulic stretcher through a second section of long oil pipe. The third interface end of the high-pressure interface module of the 1# hydraulic stretcher is connected with the second interface end of the high-pressure interface module of the 2# hydraulic stretcher through a first section of short oil pipe, and the third interface end of the low-pressure interface module of the 1# hydraulic stretcher is connected with the second interface end of the low-pressure interface module of the 2# hydraulic stretcher through a second section of short oil pipe. The third interface end of the high-pressure joint module of the 2# hydraulic stretcher is connected with the second interface end of the high-pressure joint module of the 3# hydraulic stretcher through a third section of short oil pipe, and the fourth interface end of the low-pressure joint module of the 2# hydraulic stretcher is connected with the second interface end of the low-pressure joint module of the 3# hydraulic stretcher through a second section of short oil pipe. And by analogy, the third interface end of the high-pressure joint module of the 15# hydraulic stretcher is connected with the second interface end of the high-pressure joint module of the 16# hydraulic stretcher through a twenty-seventh section of short oil pipe, and the third interface end of the low-pressure joint module of the 15# hydraulic stretcher is connected with the second interface end of the low-pressure joint module of the 16# hydraulic stretcher through a twenty-eighth section of short oil pipe. The third interface end of the high-pressure joint module of the 16# hydraulic stretcher is connected with the other high-pressure working oil port 1021 of the hydraulic pump through a third long oil pipe, and the third interface end of the low-pressure joint module of the 16# hydraulic stretcher is connected with the other low-pressure working oil port 1011 of the hydraulic pump through a fourth long oil pipe. Meanwhile, two oil pipe joints respectively used for connecting the low-pressure working oil port 1012 and the high-pressure working oil port 1022 of the hydraulic pump adopt oil pipe joints with built-in check valves. The unidirectional circulating oil way design can effectively improve the oil return efficiency.

Claims (8)

1. The ultrathin double-acting hydraulic stretcher comprises an oil cylinder, a piston and a stretching sleeve, wherein the oil cylinder is of a hollow structure which is penetrated up and down, an oil cavity is arranged in the middle of the oil cylinder, the piston is assembled in the oil cylinder in a sliding manner, the piston consists of an upper guide section, a middle stress section and a lower guide section, and the middle stress section slides in the oil cavity; the piston is of a hollow structure which is penetrated up and down, a stretching sleeve is placed in the piston, the main body part of the stretching sleeve is a columnar body, the upper end is provided with an end cap, the lower end is provided with a threaded hole used for being connected with the upper end of a pre-tightening screw, the upper part of an inner cavity of the piston is a stretching sleeve end cap accommodating cavity used for accommodating the stretching sleeve end cap, and the middle lower part is a stretching sleeve main body part mounting hole; the height of the stretching sleeve end cap is smaller than the depth of the stretching sleeve end cap cavity, a spanner connecting hole is formed in the upper end of the stretching sleeve end cap, and the top of the oil cylinder is lower than or flush with the top of the piston in a reset state; the front side wall of the cylinder body is provided with a reset oil inlet and an extension oil inlet corresponding to the top and the bottom of the oil cavity respectively.

2. The ultra-thin double-acting hydraulic tensioner of claim 1, wherein the oil cylinder comprises a cylinder body and a cylinder cover arranged at the upper end of the cylinder body, an upper piston assembly hole is formed in the center of the cylinder cover, the inner wall of the upper piston assembly hole is in sliding fit with the side wall of the upper guide section of the piston, an oil cavity is formed in the upper part of the cylinder body, the inner wall of the oil cavity is in sliding fit with the side wall of the middle stress section of the piston, the inner wall of the oil cavity is in sliding fit with the side wall of the lower guide section of the piston, a lower piston assembly hole is formed in the lower part of the cylinder body, the inner wall of the lower piston assembly hole is in sliding fit with the side wall of the lower guide section of the piston, a tensioner base is arranged at the lower end of the cylinder body, and a screw through hole is formed in the center of the tensioner base.

3. The ultra-thin double-acting hydraulic tensioner of claim 2, wherein the cylinder cover is arranged in an L-shaped step groove at the inner side of the upper end of the cylinder body, the cylinder cover is connected with the cylinder body through threads and is sealed through a sealing ring, and the top of the cylinder cover is flush with the top of the cylinder body.

4. The ultra-thin double-acting hydraulic tensioner according to claim 3, wherein the reset oil inlet and outlet and the stretching oil inlet and outlet are composed of an inner port, an outer port and an oil channel connecting the inner port and the outer port, the inner port of the reset oil inlet and outlet is arranged on a step surface for installing a cylinder cover on the inner side of the upper end of the cylinder body, a gap is arranged between the bottom of the cylinder cover and the step surface for installing the cylinder cover to form a low-pressure oil inlet buffer space, the outer port of the reset oil inlet and outlet is arranged on the outer side surface of the cylinder body, and the oil channel connecting the inner port and the outer port of the reset oil inlet and outlet extends vertically downwards from the inner port and then horizontally outwards to the outer port;

the inner port of the stretching oil inlet and outlet is arranged on a step surface forming the bottom surface of the oil cavity on the inner side of the middle part of the cylinder body, a gap is formed between the bottom of the middle stress section of the piston and the step surface forming the bottom surface of the oil cavity, a high-pressure oil inlet buffer space is formed, the outer port of the stretching oil inlet and outlet is arranged on the outer side surface of the cylinder body, and an oil liquid channel connected with the inner port and the outer port of the stretching oil inlet and outlet extends vertically downwards from the inner port and then extends horizontally outwards to the outer port.

5. The ultra-thin double-acting hydraulic tensioner of claim 1, wherein a seal ring mounting groove is formed in the lower end of the side wall of the middle stress section of the piston, the seal ring is assembled in the seal ring mounting groove, and a gap is formed between the lower edge of the seal ring mounting groove and the inner wall of the oil cavity.

6. The ultrathin double-acting hydraulic tensioner as in claim 1, wherein the lower end of the piston is provided with a closing-in structure, an anti-drop inclined plane is formed on the inner side of the closing-in structure, and a limiting inclined plane formed by diameter shrinkage is arranged above the position of the lower end of the tensioning sleeve opposite to the anti-drop inclined plane.

7. An ultra thin double acting hydraulic tensioner according to claim 2, wherein the diameter of the tensioner base is smaller than the diameter of the lower and upper portions of the cylinder.

8. The ultra-thin double acting hydraulic tensioner of claim 7, wherein the tensioner base has a side-to-side width that is less than the diameter of the tensioner base.