Hydraulic system of a pusher centrifuge that uses the cylinder stroke to control the cylinder's direction change

Abstract

The invention discloses a hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder to change direction. The feature is that within the effective stroke of the pusher shaft, the main oil circuit where the piston in the oil cylinder works is led to the outside of the oil cylinder and a reversing valve is set. At the same time, taking the piston as a reference, the axial movement of the piston is output to the stroke reversing mechanism along the reverse direction of the pusher shaft; the reversing valve and the stroke reversing mechanism are connected through a reversing oil circuit, and there is an oil discharge negative pressure working position and a working position that forms an oil circuit with the reversing valve in the stroke reversing mechanism; the reversing valve obtains the reversing pressure through the area difference at both ends of the valve core in the equal-pressure oil circuit. By using the self-owned hydraulic circuit of the oil cylinder, a reversing control mechanism is set, the dynamic information of the piston is directly transmitted to the control system, and the oil circuit is redirected through the artificially set pressure difference. The structure is simple and reliable, and the pusher stroke is stable.

Description

Technical Field

[0001] The present invention relates to the technology of centrifuge manufacturing, in particular to a hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder to reverse. Background Art

[0002] The reversal of the pusher shaft of a traditional piston pusher centrifuge is realized by using a solenoid valve. For example, the patent publication number is CN208512819U, a piston pusher centrifuge reversing pusher mechanism, including a proximity switch, an oil cylinder, a piston, a pusher device, an electro-hydraulic reversing valve, a metering pump, and an oil tank. There is a piston in the oil cylinder. One side of the piston is fixed with a guide rod, and the other side is connected with a pusher device. An induction device is provided at one end of the guide rod located outside the oil cylinder, and two proximity switches are provided at a certain distance below the guide rod; the oil cylinder is connected with an electro-hydraulic reversing valve through an oil inlet and an oil return port. The oil inlet interface of the electro-hydraulic reversing valve is connected with the oil tank through a metering pump and an oil pipeline, and the oil outlet interface of the electro-hydraulic reversing valve is connected with the oil tank through a pipeline. These most common and general solenoid valve reversing structures control the solenoid valve to reverse through an electric signal. Not only are the solenoid valves prone to damage when operating at high frequencies, but also the noise is large and the energy consumption is high. In addition, in practical applications, there is also an internal design of the cylinder body that uses the stroke of the oil cylinder to switch the oil circuit to control the reversing valve to reverse. However, these existing structures have obvious defects: for example, when the guiding plunger and the front and rear piston discs have too large a gap due to wear, during operation, due to the fast running speed of the piston, the guiding plunger is impacted, causing the control oil passage to be connected to the end of the oil cylinder cavity in advance, resulting in the reverse sleeve reversing in advance, causing the pusher stroke to be shortened. In addition, these structures require high manufacturing precision, are complex in structure, and are very difficult to judge when a failure occurs. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems, and provide a hydraulic reversing mechanism for a piston pusher centrifuge. Through the design of an internal controller for the pusher stroke, it controls the reversing valve to reverse the oil cylinder, getting rid of the traditional application of solenoid valves, and having the characteristics of stable pusher stroke, simple structure, and convenient maintenance.

[0004] The above technical problems of the present invention are mainly solved by the following technical solutions: A hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder to reverse, characterized in that: within the effective stroke of the pusher shaft, the main oil passage where the piston in the oil cylinder works is led to the outside of the oil cylinder and a reversing valve is set, and at the same time, taking the piston as a reference, the axial movement of the piston is output to the stroke reversing mechanism along the reverse direction of the pusher shaft; the reversing valve and the stroke reversing mechanism are connected through a reversing oil passage, and there is a drain negative pressure working position and a working position that forms an oil circuit with the reversing valve in the stroke reversing mechanism; the reversing valve obtains the reversing pressure through the area difference at both ends of the valve core in the equal-pressure oil passage.

[0005] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the effective stroke of the pusher shaft is the distance between the fully retracted starting point of the pusher shaft and the fully extended extreme position.

[0006] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the pusher shaft is positioned within the stroke control frame through a stroke control sleeve. The pusher shaft and the stroke control sleeve perform relative axial movement. The stroke control sleeve and the stroke control frame provide an oil drain negative pressure oil passage and an oil passage that forms an oil circuit with the commutation valve.

[0007] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the commutation valve includes a commutation valve body. On both ends of the valve core within the commutation valve body, a left chamber and a right chamber of the commutation valve are respectively formed. And there is a section of internal oil passage in the axial center of the valve core, and several sections of oil through grooves are provided on the outer diameter of the valve core. On the commutation valve body, there are inlet and outlet oil passages that cooperate with the main oil passage of the piston's work.

[0008] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the oil cylinder, the stroke commutation mechanism, and the commutation valve are fixedly connected.

[0009] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the oil cylinder makes a rotational movement relative to the stroke commutation mechanism and the commutation valve.

[0010] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, the part of the stroke control sleeve located within the stroke control frame is positioned through a bearing. One end of the stroke control sleeve extending out of the stroke control frame is connected to the oil cylinder. The oil cylinder is positioned on the intermediate body through a bearing, and the commutation valve is fixed to the intermediate body.

[0011] In the above-mentioned hydraulic system of a pusher centrifuge that uses the stroke of an oil cylinder to control the oil cylinder's commutation, preferably, a guide rod of the piston is provided inside the oil cylinder.

[0012] This technical solution takes the effective stroke action elements of the pressure oil cylinder of the pusher centrifuge as the research object, and designs a control circuit that is connected to the main oil passage of the piston's work outside the oil cylinder. The action of this control circuit is combined with the action of the piston. When the piston is at the two extreme positions of the oil cylinder, the control circuit responds correspondingly and changes the walking direction of the main oil passage of the piston's work. This system does not require external power for commutation and is purely determined by the stroke points and dynamic processes during the operation of the oil cylinder itself.

[0013] This control loop system mainly consists of two parts: one is to utilize the reciprocating points during the operation of the piston to transmit signals to the reversing valve, enabling the reversing valve to immediately perform the main oil circuit diversion action. This information is completed through the direct "responsible body" - the piston to ensure the timeliness of the reversing of the pusher shaft. That is, one end of the pusher shaft extends out of the oil cylinder and is designed as a stroke control shaft, and a stroke reversing mechanism is composed of the stroke control shaft and related components. The stroke reversing mechanism has a two-way oil circuit control position: namely, a negative pressure oil discharge state position and a state position that forms a connected oil circuit with the reversing valve. Then, the oil circuit connected to the reversing valve cooperates with the reversing valve to perform the reversing action of changing the main oil circuit: that is, when the piston is in the retracted state, the main oil circuit supplies oil to the side of the pusher shaft, and when the piston needs to push the pusher shaft to work, the main oil circuit supplies oil to the side of the piston's stroke control shaft.

[0014] Since the pressures at both ends of the valve core in the reversing valve are equal, in this solution, the areas at both ends of the valve core are designed with a difference to form a pressure difference at both ends of the valve core, thereby obtaining an immediate action. That is, during the oil inlet process, if one end is in the oil discharge working position, the valve core moves towards the other end after the oil inlet. If the other end is in the circuit working position, a reversing force is obtained through the area difference at both ends of the valve core in the equal-pressure oil circuit, and the valve core moves towards one end.

[0015] Since both the stroke control shaft and the valve core are shaft structures, by taking advantage of their outer diameter and the arbitrary length of the central hole, the conditions for the pusher shaft to obtain reversing at two extreme positions can be fully met.

[0016] In this system, the main oil circuit for the active movement of the pusher shaft can be connected to the reversing valve body through an intermediate body arranged outside the pressure oil cylinder, making the reversing valve form an independent external control component. This avoids phenomena such as changes in the switching oil circuit time and resulting changes in the stroke caused by different feeding amounts and pressure changes in the hydraulic system. Of course, it also eliminates problems such as premature reversing caused by the traditional reverse sleeve structure.

[0017] This solution can meet the pusher operation of fixed oil cylinders and rotary oil cylinders.

[0018] Compared with the prior art, the beneficial effects of the present invention are: by utilizing the self-owned hydraulic circuit of the oil cylinder, a reversing control mechanism is arranged outside the oil cylinder, the dynamic information of the piston is directly transmitted to the control system, and the oil circuit diversion is obtained through a manually set pressure difference, getting rid of the defects existing in the traditional application of solenoid valves, solving problems such as unequal stroke changes and premature reversing caused by using a reverse sleeve reversing structure inside, with a simple and reliable structure, not affected by the system pressure, and a stable pusher stroke. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the present invention.

[0020] Figure 2 、Figure 3 These are schematic diagrams of two operating states of the present invention.

[0021] Figure 4 This is a schematic diagram of the structure of an embodiment of a rotary oil cylinder of the present invention.

[0022] Figure 5 is Figure 4 A partially enlarged structural schematic diagram of the stroke control frame part.

[0023] Figure 6 is Figure 4 A partially enlarged structural schematic diagram of the reversing valve part.

[0024] Figure 7 is Figure 4 A partially enlarged structural schematic diagram of a part of the oil cylinder push rod of...

[0025] Figure 8 is Figure 4 A schematic diagram of a reversing position state of an embodiment.

[0026] In the figure: 1. Piston, 2. Oil cylinder, 3. Push rod, 4. Hollow shaft, 5. Reversing valve body, 6. Spool, 7. Right reversing oil pipe, 8. Left reversing oil pipe, 9. Stroke control frame, 10. Stroke control sleeve, 11. Stroke control shaft, 12. Sealing cover, 13. Support gland, 14. Right oil hole for stroke control, 15. Middle oil hole for stroke control, 16. Left oil hole for stroke control, 17. First oil return port, 18. Right cover of reversing valve, 19. Left cover of reversing valve, 20. Right cavity of reversing valve, 21. Left cavity of reversing valve, 22. Right oil return port of reversing valve, 23. Oil inlet hole, 24. Inner oil circuit, 25. Left oil return port of reversing valve, 26. First reversing oil circuit, 27. Second reversing oil circuit, 28. Centrifuge bearing seat, 29. Sealing bush, 30. End cover, 31. Guide rod, 32. Cylinder head, 33. Propulsion cavity, 34. Return cavity. Specific embodiments

[0027] The following will further specifically describe the technical solution of the present invention through embodiments and in conjunction with the accompanying drawings.

[0028] In this embodiment, a hydraulic system for a pusher centrifuge that uses the stroke of an oil cylinder to control the reversing of the oil cylinder is as Figures 1 to 3As shown in the figure, within the effective stroke of the pusher shaft 3 of the pusher centrifuge, the main oil circuit where the piston 1 in the oil cylinder 2 works is led outside the oil cylinder 2 and a reversing valve is provided. At the same time, with the piston as the reference, the axial movement of the piston 1 is output to the stroke reversing mechanism in the reverse direction along the pusher shaft 3. The reversing valve and the stroke reversing mechanism are connected through a reversing oil circuit, and there is an oil discharge negative pressure station and a station forming an oil circuit with the reversing valve in the stroke reversing mechanism. The reversing valve obtains the reversing pressure through the area difference at both ends of the valve core 6 in the equal-pressure oil circuit. The effective stroke of the pusher shaft 3 refers to the distance between the pusher shaft 3 being fully retracted to the starting point and being fully extended to the limit position.

[0029] During the oil inlet process, when one end of the reversing valve is in the oil discharge station, the valve core moves towards the other end after the oil inlet; when the other end of the reversing valve is in the circuit station, the reversing force is obtained through the area difference at both ends of the valve core in the equal-pressure oil circuit, and the valve core moves towards one end of the reversing valve.

[0030] The pusher shaft 3 is positioned in the stroke control frame 9 through the stroke control sleeve 12. The pusher shaft 3 and the stroke control sleeve 10 perform relative axial movement. The stroke control sleeve 10 and the stroke control frame 9 jointly provide an oil discharge negative pressure oil passage and an oil passage forming an oil circuit with the reversing valve.

[0031] The reversing valve includes a reversing valve body 5. Inside the reversing valve body 5, the two ends of the valve core 6 respectively form a left reversing valve chamber 21 and a right reversing valve chamber 20, and there is a section of internal oil passage 24 at the axial center of the valve core 6. There are three oil passing grooves on the outer diameter of the valve core 6. And an oil inlet and an oil outlet matching the main oil circuit where the piston 1 works are provided on the reversing valve body 5. A guide rod 31 of the piston 1 is provided inside the oil cylinder 2.

[0032] Embodiment 1: The oil cylinder 2, the stroke reversing mechanism, and the reversing valve are all connected in a fixed manner relative to each other. In order to smoothly connect the main oil circuit where the piston 1 works with the reversing valve body 5, they are connected through an intermediate body between the two.

[0033] Embodiment 2: The oil cylinder 2 rotates relative to the stroke reversing mechanism and the reversing valve. Refer to Figure 4 , the part of the stroke control sleeve 10 located inside the stroke control frame 9 is positioned through a bearing. One end of the stroke control sleeve 10 extending out of the stroke control frame 9 is connected to the oil cylinder 2; the oil cylinder 2 is positioned on the centrifuge bearing seat 28 (intermediate body) through a bearing, and the reversing valve is fixed to the centrifuge bearing seat 28.

[0034] For the specific structure, refer to Figures 5 to 7, the piston 1 forms a left propulsion chamber 33 and a right return chamber 34 within the oil cylinder 2. At one end of the piston 1 opposite to the pusher shaft 3, a stroke control shaft 11 is connected and extends out of the oil cylinder 2. An oil passage hole is provided in the center of the pusher shaft 3, and two-position oil grooves are provided on the outer diameter of the pusher shaft 3. One of the oil grooves is connected to the propulsion chamber 33 through the central oil passage hole, and the other oil groove is connected to the return chamber 34. The two-position oil grooves are respectively connected to a reversing valve body 5 outside the oil cylinder 2 through a first reversing oil passage 26 and a second reversing oil passage 27. Both ends of the valve core 6 are respectively communicated with two-way oil passage control positions within the stroke control frame 9.

[0035] The part of the stroke control sleeve 10 located within the stroke control frame 9 is positioned by bearings at both ends. Sealing covers 12 and support gland covers 13 are respectively provided at the outer ends of the bearings and fixed to the stroke control frame 9. One end of the stroke control sleeve 10 extending outside the stroke control frame 9 is connected to the oil cylinder 2.

[0036] An oil passage groove is provided on the stroke control shaft 11, and three-position oil passage holes corresponding to the oil passage groove are provided in the stroke control sleeve 10. The distances between the three-position oil passage holes are equal, and the distance between two adjacent oil passage holes among them corresponds to the oil passage groove. The three-position oil passage holes are respectively a stroke control right oil hole 14, a stroke control middle oil hole 15, and a stroke control left oil hole 16. Two of the three-position oil passage holes (the stroke control right oil hole 14 and the stroke control middle oil hole 15) are connected to both ends of the valve core 6 in the reversing valve body 5 through the stroke control frame 9. A first oil return port 17 is provided in the stroke control frame 9, and the first oil return port 17 corresponds to the position of the stroke control left oil hole 16. The oil return passage in the stroke control frame 9 is communicated with the bearing part.

[0037] In the reversing valve, both ends where the valve core 6 and the reversing valve body 5 cooperate respectively form a reversing valve left chamber 21 and a reversing valve right chamber 20. The area of one end of the valve core 6 facing the reversing valve right chamber 20 is larger than that of the other end, and the inner oil passage 24 at the axial center of the valve core 6 leads from the oil inlet hole in the middle part of the valve core 6 to the reversing valve left chamber 21. The oil inlet hole in the middle part of the valve core 6 is aligned with the oil inlet hole 23 on the reversing valve body 5 when the valve core 6 is at the right end position. Three oil passage grooves are provided on the outer diameter of the valve core 6, and the lengths of the three oil passage grooves correspond to the oil inlet hole 23, the reversing valve left oil return port 25, and the reversing valve right oil return port 22 on the reversing valve body 5. At the same time, oil holes corresponding to the main oil passages (the first reversing oil passage 26 and the second reversing oil passage 27) of the pusher shaft 3 are provided on the reversing valve body 5.

[0038] The reversing valve body 5 and the stroke control frame 9 are connected through a left reversing oil pipe 8 and a right reversing oil pipe 7. Reversing valve left covers 19 and reversing valve right covers 18 that cooperate with the left reversing oil pipe 8 and the right reversing oil pipe 7 are respectively provided at both ends of the reversing valve body 5. Among them, the left reversing oil pipe 8 is connected to the reversing valve left chamber 21, and the right reversing oil pipe 7 is connected to the reversing valve right chamber 20.

[0039] One end of the oil cylinder 2 facing the stroke control frame 9 is provided with a cylinder head 32. The stroke control shaft 11 passes through the cylinder head 32 to the stroke control frame 9, and one end of the stroke control sleeve 10 extending outside the stroke control frame 9 is fixed on the cylinder head 32. Two oil grooves are provided on the outer diameter of the pusher shaft 3, and an oil passage is provided in the center of the pusher shaft 3. One of the oil grooves corresponds to the second reversing oil passage 27 and communicates with the central oil passage to the propulsion chamber 33 on the left side of the piston 1, and the other oil passage corresponds to the first reversing oil passage 26 and communicates with the return chamber 34 on the right side of the piston 1.

[0040] The pusher shaft 3 is located inside the hollow shaft 4. The hollow shaft 4 is positioned in the centrifuge bearing seat 28 through bearings. A sealing connection is provided between the hollow shaft 4 and the centrifuge bearing seat 28 through a sealing bushing 29. An end cover 30 is provided on the centrifuge bearing seat 28 at the outer end of the bearing. The hollow shaft 4, the sealing bushing 29, and the centrifuge bearing seat 28 are all provided with corresponding oil passages communicating with the first reversing oil passage 26 and the second reversing oil passage 27.

[0041] The following takes Embodiment 2 in which the oil cylinder 2 rotates relative to the stroke reversing mechanism and the reversing valve to illustrate the action process of the reversing shaft.

[0042] Action 1: Referring again to the appendix Figures 4 to 7 , the pressure oil enters the left chamber 21 of the reversing valve through the internal oil passage 24 inside the valve core 6 via the oil inlet hole 23. At this time, the stroke control right oil hole 14 is in a closed state (i.e., the stroke control right oil hole 14 and the stroke control middle oil hole 15 are disconnected), and the stroke control left oil hole 16 and the stroke control middle oil hole 15 are connected. The hydraulic oil in the right chamber 20 of the reversing valve passes through the right reversing oil pipe 7, is connected through the stroke control left oil hole 16 and the stroke control middle oil hole 15, and returns to the fuel tank from the first oil return port 17. The hydraulic oil pushes the valve core 6 to move to the right. At this time, the oil inlet hole 23 and the second reversing oil passage 27 are connected, and the first reversing oil passage 26 and the left oil return port 25 of the reversing valve are connected. The pressure oil enters the propulsion chamber 33 of the oil cylinder through the second reversing oil passage 27 from the oil inlet hole 23, pushing the piston 1 to move to the right. At this time, the hydraulic oil in the return chamber 34 of the oil cylinder returns to the fuel tank through the first reversing oil passage 26 via the left oil return port 25 of the reversing valve.

[0043] Action 2: Refer to Figure 8, the piston 1 moves to the right. When the stroke control right oil hole 14 is connected to the stroke control middle oil hole 15 (the stroke control left oil hole 16 and the stroke control middle oil hole 15 have been disconnected), the hydraulic oil passes through the oil inlet hole 23 to the oil passage 24 in the valve core 6, the left reversing oil pipe 8, the stroke control right oil hole 14, and the stroke control middle oil hole 15 and enters the right chamber 20 of the reversing valve through the right reversing oil pipe 7. At this time, although the pressures of the hydraulic oil in the left chamber 21 and the right chamber 20 of the reversing valve are the same, since the cross-sectional area of the right chamber 20 of the reversing valve is larger than that of the left chamber 21 of the reversing valve, the acting force of the right chamber 20 of the reversing valve on the valve core 6 is greater than the acting force of the left chamber 21 of the reversing valve on the valve core 6, and the valve core 6 moves to the left. At this time, the oil inlet hole 23 is connected to the first reversing oil passage 26, and the right oil return port 22 of the reversing valve is connected to the second reversing oil passage 27. The pressure oil enters the return chamber 34 of the oil cylinder from the oil inlet hole 23 through the first reversing oil passage 26 to push the piston 1 to move to the left. At this time, the hydraulic oil in the advancing chamber 33 of the oil cylinder returns to the fuel tank through the second reversing oil passage 27 and the right oil return port 22 of the reversing valve.

[0044] The above embodiments are illustrative of the present invention, not restrictive of the present invention. Any simple transformation of the process, method, structure, etc. of the present invention belongs to the protection scope of the present invention.

Claims

1. A hydraulic system for a pusher centrifuge that controls the reversal of an oil cylinder using the stroke of the oil cylinder, Characterized in that: Within the effective stroke of the pusher shaft (3), the main oil circuit in which the piston (1) in the oil cylinder (2) operates is led outside the oil cylinder and a reversing valve is provided. At the same time, based on the piston, the axial movement of the piston is output to the stroke reversing mechanism in the reverse direction of the pusher shaft; the reversing valve and the stroke reversing mechanism are connected through a reversing oil circuit, and there is an oil discharge negative pressure working position and a working position that forms an oil circuit with the reversing valve in the stroke reversing mechanism; the reversing valve obtains the reversing pressure through the area difference at both ends of the valve core (6) in the equal-pressure oil circuit; The pusher shaft is positioned within the stroke control frame (9) through the stroke control sleeve (10); the oil cylinder rotates relative to the stroke reversing mechanism and the reversing valve; the part of the stroke control sleeve located within the stroke control frame is positioned through a bearing, and one end of the stroke control sleeve extending outside the stroke control frame is connected to the oil cylinder; the oil cylinder is positioned on the intermediate body through a bearing, and the reversing valve is fixed to the intermediate body; A oil passage is provided in the center of the pusher shaft, and two oil grooves are provided on the outer diameter of the pusher shaft. One of the oil grooves is connected to the propulsion chamber (33) through the central oil passage, and the other oil groove is connected to the return chamber (34); the two oil grooves are respectively connected to the reversing valve body (5) outside the oil cylinder through the first reversing oil circuit (26) and the second reversing oil circuit (27), and both ends of the valve core are respectively connected to the two-way oil circuit control positions within the stroke control frame.

2. The hydraulic system for a pusher centrifuge that controls the reversal of an oil cylinder using the stroke of the oil cylinder according to claim 1, Characterized in that, The effective stroke of the pusher shaft (3) is the distance between the pusher shaft being fully retracted to the starting point and being fully extended to the limit position.

3. The hydraulic system for a pusher centrifuge that controls the reversal of an oil cylinder using the stroke of the oil cylinder according to claim 1 or 2, Characterized in that, The pusher shaft and the stroke control sleeve perform relative axial movement, and the stroke control sleeve and the stroke control frame provide an oil discharge negative pressure oil passage and an oil passage that forms an oil circuit with the reversing valve.

4. The hydraulic system for a pusher centrifuge that controls the reversal of an oil cylinder using the stroke of the oil cylinder according to claim 1 or 2, Characterized in that, The reversing valve includes a reversing valve body (5). On both ends of the valve core (6) within the reversing valve body, a left reversing valve chamber (21) and a right reversing valve chamber (20) are respectively formed, and a section of internal oil passage (24) is provided at the axial center of the valve core. Several sections of oil passing grooves are provided on the outer diameter of the valve core; on the reversing valve body, an oil inlet and an oil outlet that cooperate with the main oil circuit of the piston (1) are provided.

5. The hydraulic system for a pusher centrifuge that controls the reversal of an oil cylinder using the stroke of the oil cylinder according to claim 1, Characterized in that, A guide rod (31) of the piston (1) is provided within the oil cylinder (2).

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