Variable-amplitude oil cylinder with buffering function

Abstract

The invention relates to a variable-amplitude oil cylinder with a buffering function, and belongs to the technical field of hydraulic oil cylinders, the variable-amplitude oil cylinder comprises a cylinder body, a piston rod and a cylinder cover, a hollow ring is slidably arranged between the cylinder body and the piston rod, a partition plate is arranged in the hollow ring, and the interior of the hollow ring is divided into a liquid storage cavity a and a liquid storage cavity b by the partition plate; a displacement sensor used for monitoring the displacement distance of the piston rod in real time is arranged at the tail end of the cylinder body, a piston is arranged at the tail end of the piston rod, the front end of the piston is connected with a plurality of connecting rods, the front ends of the connecting rods are connected with annular push plates arranged in the liquid storage cavity a in a sliding mode, and when the piston rod stretches out forwards, the annular push plates push liquid in the liquid storage cavity a into the liquid storage cavity b. Reverse thrust of liquid abuts against thrust of hydraulic oil pushing the piston rod, so that the piston rod is buffered, and the piston rod can extend out gently in the starting stage. The problem that when the oil cylinder is started, the piston rod rapidly stretches out to generate shaking and instant impulsive force, and consequently precision mechanical equipment borne by the piston rod is potentially damaged is solved.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic cylinders, and in particular to a variable-luff cylinder with a buffering function. Background Art

[0002] The luffing cylinder is a type of hydraulic cylinder, mainly used in various construction machinery and equipment, especially in lifting machinery, excavators and other equipment that need to adjust the working radius or height. Its main function is to change the length of the equipment's working arm by telescoping, thereby achieving a change in the working range, i.e. "luffing".

[0003] The working principle of the luffing cylinder is to use the pressure of the hydraulic oil to generate thrust on the piston, push the piston rod to extend or retract, and then drive the connected mechanical structure to extend or rotate to achieve luffing action.

[0004] When the prior art variable-luffing oil cylinder is opened, the piston rod will inevitably vibrate due to the rapid extension, and the instantaneous impact force will cause potential damage to the precision mechanical equipment carried.

[0005] A Chinese invention patent with the announcement number CN105422545A discloses an upper variable-length oil cylinder. The present invention discloses an upper variable-length oil cylinder, comprising a cylinder body and a piston rod, one end of the cylinder body is connected to a cylinder head through a pin shaft, a piston rod is arranged in the cylinder body, one end of the piston rod is connected to a rod head through a pin shaft, and an annular clamp retaining groove is arranged on the outer wall of the sliding sleeve, and the annular clamp retaining groove can prevent the piston rod from falling off from the inside of the cylinder body. The beneficial effects of the present invention are: improving the appearance quality of the oil cylinder, improving the wear resistance of the oil cylinder bearing, and at the same time, the pin shaft is effectively lubricated and protected, extending the life of the pin shaft, improving work efficiency, reducing production costs, and being able to well prevent the piston rod from falling off from the inside of the cylinder body.

[0006] However, there is still the problem that the piston rod will generate vibration and impact when it is extended, causing potential damage to the precision machinery it carries. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies in the prior art and to provide a variable-length oil cylinder with a buffering function, comprising a cylinder body and a piston rod slidably arranged in the cylinder body, a cylinder cover is arranged between the cylinder body and the piston rod, a hollow ring is slidably arranged between the cylinder body and the piston rod, a partition plate is fixedly arranged inside the hollow ring, the partition plate divides the interior of the hollow ring into a liquid storage chamber a and a liquid storage chamber b, a displacement sensor for real-time monitoring of the displacement distance of the piston rod is arranged at the rear end of the cylinder body, a piston is arranged at the rear end of the piston rod, a plurality of connecting rods are fixedly connected to the front end of the piston, and an annular push plate slidably arranged in the liquid storage chamber a is fixedly connected to the front end of the connecting rod, thereby solving the problem of the variable-length oil cylinder in the prior art that the piston rod will inevitably shake due to rapid extension when opened and the instantaneous impact will cause potential damage to the precision mechanical equipment carried.

[0008] The technical solutions of the present invention are as follows: A variable-length oil cylinder with a buffering function comprises a cylinder body and a piston rod slidably arranged in the cylinder body, a cylinder cover is arranged between the cylinder body and the piston rod, a hollow ring is slidably arranged between the cylinder body and the piston rod, a partition plate is fixedly arranged inside the hollow ring, and the partition plate divides the inside of the hollow ring into a liquid storage chamber a and a liquid storage chamber b, a displacement sensor for real-time monitoring of the displacement distance of the piston rod is arranged at the rear end of the cylinder body, a piston is arranged at the rear end of the piston rod, a plurality of connecting rods are fixedly connected to the front end of the piston, and an annular push plate slidably arranged in the liquid storage chamber a is fixedly connected to the front end of the connecting rod, and when the piston rod is extended forward, the annular push plate pushes the liquid in the liquid storage chamber a into the liquid storage chamber b to buffer the piston rod.

[0009] As a preferred embodiment, a through hole a is provided on the partition plate, an annular groove a is provided on one side of the partition plate, a plurality of mounting holes a are provided at the bottom of the annular groove a, a baffle a is slidably arranged in the annular groove a, a spring a is fixedly connected to the rear end of the baffle a, and the other end of the spring a is connected to the mounting hole a.

[0010] As a preferred embodiment, a through hole b is provided on the baffle a, an annular groove b is provided on one side of the baffle a, a plurality of mounting holes b are provided at the bottom of the annular groove b, a baffle b is slidably arranged in the annular groove b, a spring b is fixedly connected to the rear end of the baffle b, and the other end of the spring b is connected to the mounting hole b.

[0011] As a preferred embodiment, a through hole c is formed at the rear end of the hollow ring, an annular groove c is formed at the front end of the hollow ring, and a rubber damping strip is embedded in the annular groove c.

[0012] As a preferred embodiment, an oil inlet and an oil return port are arranged at the rear end of the cylinder body, a high-pressure steel pipe is arranged at the top of the cylinder body, and a balancing valve is arranged on the high-pressure steel pipe.

[0013] As a preferred embodiment, a support ring a, a sealing ring a, a baffle a, a Gly ring and an O-ring a are arranged between the cylinder body and the piston.

[0014] As a preferred embodiment, the front end of the piston rod is fixedly provided with a rod head, the rod head is provided with a straight-through pressure-injection oil cup, a steel-back bearing is provided inside the rod head, and the tail end of the piston rod is provided with a magnetic isolation washer, an elastic retaining ring, a wave spring washer and a magnetic ring.

[0015] As another preferred embodiment, a support ring b, an O-ring b, a baffle b, a step seal, a sealing ring b, a baffle c, an O-ring c and a dust ring are arranged between the cylinder cover and the piston rod.

[0016] The beneficial effects of the present invention are as follows.

[0017] The present invention is provided with a hollow ring, and the interior of the hollow ring is divided into a liquid storage chamber a and a liquid storage chamber b by a partition plate. When the piston rod is extended, the connecting rod fixedly connected to the front end of the piston moves forward, and the liquid in the liquid storage chamber a is pushed into the liquid storage chamber b through the annular push plate fixedly connected to the front end of the connecting rod. The reverse thrust of the liquid and the thrust of the hydraulic oil pushing the piston rod are offset, which can play a buffering role on the piston rod, so that the piston rod can be extended more smoothly during the starting stage instead of extending rapidly, thereby avoiding the inevitable shaking of the piston rod due to the rapid extension when the oil cylinder is started, and avoiding the instantaneous impact that will cause potential damage to the precision mechanical equipment carried.

[0018] A baffle a is slidably provided in the annular groove a opened on one side of the partition plate, and a baffle b is slidably provided in the annular groove b opened on one side of the baffle a. When the piston rod is extended, the piston drives the annular push plate forward to squeeze the liquid in the liquid storage chamber a. At this time, the baffle a slides outward along the annular groove a driven by the liquid, and the obstruction of the through hole a is released, so that the liquid in the liquid storage chamber a can be smoothly pushed into the liquid storage chamber b. When the piston rod is retracted, the piston drives the annular push plate to move backward. At this time, the annular push plate drives the baffle b to slide outward along the annular groove b, and the obstruction of the through hole b is released, so that the through hole a and the through hole b are connected, so that the liquid in the liquid storage chamber b is drawn back into the liquid storage chamber a. The structure is ingenious and the linkage effect is good.

[0019] The present invention is provided with a displacement sensor, through which the displacement distance of the piston rod can be monitored in real time, the telescopic displacement can be accurately fed back, and adjustments can be made in time according to needs.

[0020] In summary, the present invention has the advantages of being able to start the buffering effect on the piston rod, real-time monitoring of the displacement distance of the piston rod, good linkage effect, and ingenious structure, and is suitable for the technical field of hydraulic cylinders. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings: Figure 1It is a structural schematic diagram of the luffing oil cylinder with buffering function; Figure 2 It is a schematic diagram of the structure of the luffing cylinder with buffering function from a top view; Figure 3 for Figure 1 A magnified schematic diagram of point A; Figure 4 for Figure 1 An enlarged schematic diagram of point B; Figure 5 Schematic diagram of the position structure of the hollow ring; Figure 6 for Figure 5 An enlarged schematic diagram of point C; Figure 7 It is a schematic diagram of the state when the annular push plate pushes the liquid in the liquid storage chamber a into the liquid storage chamber b; Figure 8 for Figure 7 An enlarged schematic diagram of point D; Fig. 9 It is a schematic diagram of the state when the annular push plate is reset to draw the liquid in the liquid storage chamber b back to the liquid storage chamber a; Fig.10 for Fig. 9 An enlarged schematic diagram of point E; Fig.11 for Fig. 9 Enlarged schematic diagram of point F.

[0022] In the figure: cylinder body 1, piston rod 2, cylinder head 3, hollow ring 4, displacement sensor 5, oil inlet 11, oil return port 12, high-pressure steel pipe 13, balance valve 14, support ring a15, sealing ring a16, baffle a17, Gley ring 18, O-ring a19, piston 21, connecting rod 22, annular push plate 23, rod head 24, straight-through pressure injection cup 25, steel back bearing 26, magnetic isolation washer 27, elastic retaining ring 28, wave spring washer 29, magnetic ring 210, support ring b 31, O-ring b32, baffle b33, step seal 34, sealing ring b35, baffle c36, O-ring c37, dust ring 38, partition plate 41, liquid storage chamber a42, liquid storage chamber b43, through hole a44, annular groove a45, mounting hole a46, baffle a47, spring a48, through hole b49, annular groove b410, mounting hole b411, baffle b412, spring b413, through hole c414, annular groove c415, rubber damping strip 416. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings.

[0024] Embodiment 1

[0025] like Figures 1 to 11As shown, a variable-length oil cylinder with a buffering function comprises a cylinder body 1 and a piston rod 2 slidably arranged in the cylinder body 1, a cylinder cover 3 is arranged between the cylinder body 1 and the piston rod 2, a hollow ring 4 is slidably arranged between the cylinder body 1 and the piston rod 2, a partition plate 41 is fixedly arranged inside the hollow ring 4, and the partition plate 41 divides the inside of the hollow ring 4 into a liquid storage chamber a42 and a liquid storage chamber b43, a displacement sensor 5 for real-time monitoring of the displacement distance of the piston rod 2 is arranged at the rear end of the cylinder body 1, a piston 21 is arranged at the rear end of the piston rod 2, a plurality of connecting rods 22 are fixedly connected to the front end of the piston 21, and an annular push plate 23 slidably arranged in the liquid storage chamber a42 is fixedly connected to the front end of the connecting rod 22, and when the piston rod 2 is extended forward, the annular push plate 23 pushes the liquid in the liquid storage chamber a42 into the liquid storage chamber b43 to buffer the piston rod 2. The hollow ring 4 is divided into a liquid storage chamber a42 and a liquid storage chamber b43 by a partition plate 41. When the piston rod 2 is extended, the connecting rod 22 fixedly connected to the front end of the piston 21 moves forward, and the liquid in the liquid storage chamber a42 is pushed into the liquid storage chamber b43 by the annular push plate 23 fixedly connected to the front end of the connecting rod 22. The reverse thrust of the liquid offsets the thrust of the hydraulic oil pushing the piston rod 21, which can play a buffering role on the piston rod 2, so that the piston rod 2 can be extended more slowly during the starting stage instead of extending rapidly. When the oil cylinder is started, the piston rod 2 is prevented from shaking inevitably due to the rapid extension, and the instantaneous impact will cause potential damage to the precision mechanical equipment carried by it; the width of the liquid storage chamber b43 is smaller than the liquid storage chamber a42, and the annular push plate 23 will not push all the liquid in the liquid storage chamber a42 into the liquid storage chamber b43 when the piston 21 moves forward. While playing a buffering role when the piston rod 2 is extended, it will not affect the annular push plate 23 from being able to draw the liquid in the liquid storage chamber b43 back into the liquid storage chamber a42 when the piston rod 2 is reset.

[0026] like Figure 6 , 8 and Fig.10As shown, a through hole a44 is provided on the partition plate 41, an annular groove a45 is provided on one side of the partition plate 41, a plurality of mounting holes a46 are provided at the bottom of the annular groove a45, a baffle a47 is slidably provided in the annular groove a45, a spring a48 is fixedly connected to the rear end of the baffle a47, and the other end of the spring a48 is connected to the mounting hole a46. A baffle a47 is slidably provided in the annular groove a45 provided on one side of the partition plate 41, and a baffle b412 is slidably provided in the annular groove b410 provided on one side of the baffle a47. When the piston rod 2 is extended, the piston 21 drives the annular push plate 23 to move forward to squeeze the liquid in the liquid storage chamber a42. At this time, the baffle a47 slides outward along the annular groove a45 driven by the liquid, and the through hole a44 is removed, so that the liquid in the liquid storage chamber a42 can be smoothly pushed into the liquid storage chamber b43. When the liquid in the liquid storage chamber a42 is filled with liquid, the liquid in the liquid storage chamber a42 is pushed into the liquid storage chamber b43. Behind the liquid storage chamber b43, the hydraulic oil can drive the piston rod 2 and the piston 21 to move normally at a normal speed; when the piston rod 2 is retracted, the piston 21 drives the annular push plate 23 to move backward, at this time, the baffle a47 is reset under the action of the spring a48, and the annular push plate 23 drives the baffle b412 to slide outward along the annular groove b410, removing the obstruction of the through hole b49, so that the through hole a44 and the through hole b49 are connected, so that the liquid in the liquid storage chamber b43 is drawn back into the liquid storage chamber a42, the structure is ingenious, and the linkage effect is good.

[0027] like Figure 6 , Figure 8 and Fig.10As shown, a through hole b49 is provided on the baffle a47, an annular groove b410 is provided on one side of the baffle a47, a plurality of mounting holes b411 are provided at the bottom of the annular groove b410, a baffle b412 is slidably arranged in the annular groove b410, a spring b413 is fixedly connected to the rear end of the baffle b412, and the other end of the spring b413 is connected to the mounting hole b411. A baffle a47 is slidably disposed in the annular groove a45 opened on one side of the partition plate 41, and a baffle b412 is slidably disposed in the annular groove b410 opened on one side of the baffle a47. When the piston rod 2 is extended, the piston 21 drives the annular push plate 23 to move forward to squeeze the liquid in the liquid storage chamber a42. At this time, the baffle a47 slides outward along the annular groove a45 driven by the liquid, and the through hole a44 is removed to allow the liquid in the liquid storage chamber a42 to be smoothly pushed into the liquid storage chamber b43. When the liquid in the liquid storage chamber a42 fills the liquid storage chamber b43, the hydraulic oil can drive the piston rod 2 to move forward. The plug rod 2 and the piston 21 move normally at a normal speed; when the piston rod 2 is retracted, the piston 21 drives the annular push plate 23 to move backward, at this time, the baffle a47 is reset under the action of the spring a48, and the annular push plate 23 drives the baffle b412 to slide outward along the annular groove b410, removing the obstruction of the through hole b49, so that the through hole a44 and the through hole b49 are connected, so that the liquid in the liquid storage chamber b43 is drawn back into the liquid storage chamber a42, and when the annular push plate 23 is reset, the baffle b412 is reset under the action of the spring b413. The structure is ingenious and the linkage effect is good.

[0028] like Figure 5 ,and Fig.11 As shown, a through hole c414 is provided at the rear end of the hollow ring 4, and an annular groove c415 is provided at the front end of the hollow ring 4, and a rubber damping strip 416 is embedded in the annular groove c415. The aperture of the through hole c414 matches the connecting rod 22, and the connecting rod 22 is slidably arranged in the through hole c414 and can move forward and backward smoothly; the rubber damping strip 416 contacts the inner wall of the cylinder body 1 to generate a certain friction force, so as to prevent the hollow ring 4 from moving synchronously with the annular push plate 23 under the action of the thrust in the process of the piston 21 driving the annular push plate 23 to move forward and push the liquid in the liquid storage chamber a42 into the liquid storage chamber b43, resulting in the annular push plate 23 being unable to effectively push the liquid in the liquid storage chamber a42 into the liquid storage chamber b43, resulting in the buffering effect being affected.

[0029] like Figure 1 and Figure 2 As shown, the tail end of the cylinder body 1 is provided with an oil inlet 11 and an oil return port 12, and the top of the cylinder body 1 is provided with a high-pressure steel pipe 13, and a balance valve 14 is provided on the high-pressure steel pipe 13. The balance valve 14 can be used to control the flow to lock the piston rod 2. When the balance valve 14 is closed, the pressure in the circuit will rise to the set valve pressure value of the balance valve 14 and remain at this pressure, and the piston rod 2 will be locked in the desired position. The balance valve 14 is an existing mature technology and will not be elaborated on in detail here.

[0030] like Figure 3 As shown, a support ring a15, a sealing ring a16, a baffle a17, a Gly ring 18 and an O-ring a19 are arranged between the cylinder body 1 and the piston 21. The baffle a is also made of polytetrafluoroethylene, which plays a buffering role for the sealing ring a when the sealing ring a is under pressure. The O-ring a cooperates with the sealing ring a and the baffle a to further enhance the sealing effect. Compared with simply relying on the sealing ring a for sealing, the sealing effect is better.

[0031] like Figure 1 As shown, a rod head 24 is fixedly provided at the front end of the piston rod 2, a straight-through pressure injection oil cup 25 is provided on the rod head 24, a steel back bearing 26 is provided in the rod head 24, and a magnetic isolation washer 27, a spring ring 28, a wave spring washer 29 and a magnetic ring 210 are provided at the rear end of the piston rod 2. The oil cylinder can be lubricated by the straight-through pressure injection oil cup 25.

[0032] like Figure 4 As shown, a support ring b31, an O-ring b32, a baffle b33, a step seal 34, a sealing ring b35, a baffle c36, an O-ring c37 and a dust ring 38 are arranged between the cylinder cover 3 and the piston rod 2. The baffle b is made of polytetrafluoroethylene, which plays a buffering role for the sealing ring b when the sealing ring b is under pressure. The O-ring b32, the sealing ring b and the baffle b can play a good sealing role. Compared with simply relying on the sealing ring b for sealing, the sealing effect is better; the dust ring 38 can play a good dustproof effect.

[0033] The working process is as follows.

[0034] When the hydraulic oil in the oil inlet 11 drives the piston rod 2 to extend, the piston 21 drives the annular push plate 23 to move forward and squeeze the liquid in the liquid storage chamber a42. At this time, the baffle a47 slides outward along the annular groove a45 driven by the liquid, and the through hole a44 is removed, so that the liquid in the liquid storage chamber a42 can be smoothly pushed into the liquid storage chamber b43. The reverse thrust of the liquid and the thrust of the hydraulic oil pushing the piston rod 21 are offset, which can play a buffering role on the piston rod 2, so that the piston rod 2 can be extended more smoothly during the starting stage. After the liquid in 42 fills the liquid storage chamber b43, the piston rod 2 can move at a normal speed driven by the hydraulic oil. When the piston rod 2 is retracted, the piston 21 drives the annular push plate 23 to move backward. At this time, the baffle a47 is reset under the action of the spring a48, and the annular push plate 23 drives the baffle b412 to slide outward along the annular groove b410, removing the obstruction of the through hole b49, so that the through hole a44 and the through hole b49 are connected, so that the liquid in the liquid storage chamber b43 is drawn back into the liquid storage chamber a42 to prepare for the next extension of the piston rod 2.

[0035] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "front and back", "left and right", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the invention.

[0036] Of course, in the present technical solution, those skilled in the art should understand that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0037] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art under the technical guidance of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A variable-luff cylinder with a buffering function, comprising a cylinder body (1) and a piston rod (2) slidably arranged in the cylinder body (1), a cylinder cover (3) being arranged between the cylinder body (1) and the piston rod (2), characterized in that: A hollow ring (4) is slidably arranged between the cylinder body (1) and the piston rod (2), a partition plate (41) is fixedly arranged inside the hollow ring (4), and the partition plate (41) divides the inside of the hollow ring (4) into a liquid storage chamber a (42) and a liquid storage chamber b (43). A displacement sensor (5) for real-time monitoring of the displacement distance of the piston rod (2) is arranged at the rear end of the cylinder body (1), a piston (21) is arranged at the rear end of the piston rod (2), a plurality of connecting rods (22) are fixedly connected to the front end of the piston (21), and an annular push plate (23) slidably arranged in the liquid storage chamber a (42) is fixedly connected to the front end of the connecting rod (22), and when the piston rod (2) extends forward, the annular push plate (23) pushes the liquid in the liquid storage chamber a (42) into the liquid storage chamber b (43) to buffer the piston rod (2).

2. The luffing cylinder with buffering function according to claim 1, characterized in that: The partition plate (41) is provided with a through hole a (44), one side of the partition plate (41) is provided with an annular groove a (45), a bottom of the annular groove a (45) is provided with a plurality of mounting holes a (46), a baffle a (47) is slidably arranged in the annular groove a (45), a spring a (48) is fixedly connected to the rear end of the baffle a (47), and the other end of the spring a (48) is connected to the mounting hole a (46).

3. The luffing cylinder with buffering function according to claim 2, characterized in that: The baffle a (47) is provided with a through hole b (49), one side of the baffle a (47) is provided with an annular groove b (410), a bottom of the annular groove b (410) is provided with a plurality of mounting holes b (411), a baffle b (412) is slidably arranged in the annular groove b (410), a spring b (413) is fixedly connected to the rear end of the baffle b (412), and the other end of the spring b (413) is connected to the mounting hole b (411).

4. The luffing cylinder with buffering function according to claim 3, characterized in that: A through hole c (414) is provided at the rear end of the hollow ring (4), an annular groove c (415) is provided at the front end of the hollow ring (4), and a rubber damping strip (416) is embedded in the annular groove c (415).

5. The luffing cylinder with buffering function according to claim 4, characterized in that: The rear end of the cylinder body (1) is provided with an oil inlet (11) and an oil return port (12); the top of the cylinder body (1) is provided with a high-pressure steel pipe (13); and a balancing valve (14) is provided on the high-pressure steel pipe (13).

6. The luffing cylinder with buffering function according to claim 5, characterized in that: A support ring a (15), a sealing ring a (16), a baffle a (17), a Gly ring (18) and an O-ring a (19) are provided between the cylinder body (1) and the piston (21).

7. The luffing cylinder with buffering function according to claim 6, characterized in that: A rod head (24) is fixedly provided at the front end of the piston rod (2), a straight-through pressure injection oil cup (25) is provided on the rod head (24), a steel back bearing (26) is provided inside the rod head (24), and a magnetic isolation washer (27), an elastic retaining ring (28), a wave spring washer (29) and a magnetic ring (210) are provided at the rear end of the piston rod (2).

8. The luffing cylinder with buffering function according to claim 7, characterized in that: A support ring b (31), an O-ring b (32), a baffle b (33), a step seal (34), a sealing ring b (35), a baffle c (36), an O-ring c (37) and a dust ring (38) are provided between the cylinder cover (3) and the piston rod (2).

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