Multi-stage central sleeve hydraulic cylinder structure capable of extending and retracting step by step

Abstract

The invention belongs to the technical field of hydraulic mechanisms, in particular to a multi-stage central sleeve hydraulic cylinder structure capable of extending and retracting step by step, and provides the following scheme that the multi-stage central sleeve hydraulic cylinder structure comprises a base, a cylinder sleeve, a piston column and a lower piston, the lower piston is slidably connected to the interior of the cylinder sleeve, and the piston column is fixedly connected to the top of the lower piston. The on-off and oil inlet quantity of the middle-section oil inlet pipe and the upper-section oil inlet pipe are adjusted through the three-way metering valve, sequential quantitative stretching and retracting of the inner sleeve and the outer sleeve are achieved, when the outer sleeve rises, the distance between the upper piston and the middle piston is increased, the spiral hose can adaptively extend, and flexible connection of the middle-section oil inlet pipe during stretching and retracting is ensured; an oil way is adjusted through the two-way metering valve and the three-way metering valve, so that the displacement process of the lower piston, the upper piston and the middle piston can be independently controlled, synchronous or sequential action of the outer sleeve, the inner sleeve and the piston column is achieved, the movement precision is improved, the control flexibility is improved, and the differential requirements of engineering machinery for thrust and speed are met.

Description

Technical Field

[0001] This invention relates to the field of hydraulic mechanism technology, and in particular to a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages. Background Technology

[0002] Multistage hydraulic cylinders, as the core actuators of hydraulic transmission systems, are widely used in fields such as engineering machinery, aerospace, and special vehicles. They achieve a balance between long stroke and compact space through a nested sleeve structure. Traditional multistage hydraulic cylinders adopt a multi-piston series design, in which hydraulic oil drives the pistons of each stage to extend and retract sequentially.

[0003] A search revealed that Chinese patent application CN112762053B discloses a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, including a cylinder body, multiple intermediate cylinders, and a piston rod. Each stage of the intermediate cylinder and piston rod can extend or retract in stages, solving the problem of disordered piston order.

[0004] The above-mentioned hydraulic cylinder structure still has certain problems in application. It cannot achieve independent control of each stage of cylinder and piston rod, and has defects such as large pressure loss and slow response. There is an urgent need to design a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages to solve the above problems. Summary of the Invention

[0005] To address the technical problem that existing technologies cannot achieve independent control of each stage of the cylinder and piston rod, this invention proposes a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages.

[0006] This invention proposes a multi-stage center sleeve hydraulic cylinder structure with progressively extending and retracting sleeves, comprising a base, a cylinder liner, a piston rod, and a lower piston. The lower piston is slidably connected to the inside of the cylinder liner. The piston rod is fixedly connected to the top of the lower piston. An inner sleeve is fitted onto the top of the piston rod. A middle piston is fixedly connected to the bottom of the inner sleeve. An outer sleeve is fitted onto the top of the inner sleeve. The top of the outer sleeve extends above the cylinder liner. An upper piston is fixedly connected to the bottom of the outer sleeve. Both the middle and upper pistons are slidably connected to the inside of the cylinder liner. A lifting platform is fixedly connected to the top of the outer sleeve. A bottom section oil inlet pipe is fixedly connected to the bottom of one side of the cylinder liner. A two-way metering valve is installed in the middle. The piston bodies of the middle piston and the upper piston are connected to the same middle section oil inlet pipe. The bottom end of the middle section oil inlet pipe is connected to the space between the middle piston and the lower piston. The middle section oil inlet pipe is set as a spiral hose in the part between the middle piston and the lower piston. The top end of the middle section oil inlet pipe extends to the outside of the top of the cylinder liner. The piston body of the upper piston is connected to the upper section oil inlet pipe. The bottom end of the upper section oil inlet pipe is connected to the space between the upper piston and the middle piston. The top end of the upper section oil inlet pipe extends to the outside of the top of the cylinder liner. The top ends of the middle section oil inlet pipe and the top ends of the upper section oil inlet pipe are fixedly connected to the same three-way metering valve.

[0007] Preferably, a limiting ring is fixedly connected to the inner circumference of the bottom of the cylinder liner, and the bottom of the lower piston contacts the top of the limiting ring.

[0008] Preferably, a sealing ring is embedded in the middle of the lower piston, and the outer diameter of the sealing ring corresponds to the inner diameter of the cylinder liner.

[0009] Preferably, the outer diameter of the middle piston corresponds to the inner diameter of the cylinder liner, and the outer diameter of the upper piston corresponds to the inner diameter of the cylinder liner.

[0010] Preferably, the bottom of the inner sleeve is provided with a first storage groove, the piston rod is inserted into the inside of the first storage groove, and the two sides of the piston rod are fixedly connected with first guide rails. The inner walls of the two sides of the first storage groove are provided with first limiting grooves, and the two first guide rails are slidably connected to the inside of the two first limiting grooves respectively.

[0011] Preferably, the bottom of the outer sleeve is provided with a second storage groove, the inner sleeve is inserted into the inside of the second storage groove, the outer walls on both sides of the inner sleeve are fixedly connected with second guide rails, the inner walls on both sides of the second storage groove are provided with second limiting grooves, and the two second guide rails are slidably connected to the inside of the two second limiting grooves respectively.

[0012] Preferably, a pipe clamp is fixedly connected to the top outer wall of the cylinder liner, and the upper section of the oil inlet pipe extending outside the cylinder liner is fixedly connected to the inside of the pipe clamp.

[0013] Preferably, the upper oil inlet pipe and the middle oil inlet pipe are connected to the same connecting buckle at the end near the three-way metering valve.

[0014] Preferably, a conical groove is provided at the middle position of the bottom of the lifting platform, a through groove is provided at the middle of one side of the conical groove, and a sliding groove is provided at the middle of the through groove. The inner diameter of the sliding groove is larger than the inner diameter of the through groove. A trigger cone is fixedly connected at the middle position of the top of the inner sleeve, and an insertion hole adapted to the trigger cone is provided at the middle position of the top of the outer sleeve. The trigger cone is inserted into the inside of the conical groove. A push rod is inserted into the end of the through groove near the trigger cone. An arc-shaped trigger plate is fixedly connected to the end of the push rod inside the conical groove. The arc-shaped trigger plate is attached to the outer wall of the trigger cone. A sliding plate is fixedly connected to the end of the push rod inside the sliding groove. The sliding plate is slidably connected to the inside of the sliding groove. A push plate is slidably connected inside the through groove. The same spring is fixedly connected between the push plate and the sliding plate. The spring is in a compressed state. A detachable and fixed pressure sensor is inserted into the end of the through groove away from the trigger cone. One side of the push plate is attached to the pressure sensing end of the pressure sensor.

[0015] Preferably, an external mounting component is fixedly connected to one side of the lifting platform, one end of the pressure sensor extends to the side of the external mounting component away from the lifting platform, a hanging rod is fixedly connected to the side of the external mounting component away from the lifting platform, a limit buckle is fixedly connected to the end of the hanging rod away from the external mounting component, and a rotating hook adapted to the hanging rod is rotatably connected to the outer wall of the pressure sensor.

[0016] Compared with the prior art, the present invention provides a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, which has the following beneficial effects: 1. This multi-stage central sleeve hydraulic cylinder structure, capable of sequential extension and retraction, utilizes a three-way metering valve, a middle section oil inlet pipe, an upper section oil inlet pipe, and a spiral hose. The three-way metering valve regulates the on / off state and oil flow of the middle and upper section oil inlets, enabling sequential quantitative extension and retraction of the inner and outer sleeves. When the outer sleeve rises, the distance between the upper and middle pistons increases, allowing the spiral hose to extend adaptively, ensuring flexible connection of the middle section oil inlet pipe during extension and retraction. The oil circuit is regulated by a two-way and a three-way metering valve, allowing independent control of the displacement of the lower, upper, and middle pistons. This enables synchronous or sequential movement of the outer sleeve, inner sleeve, and piston rod, improving motion accuracy, enhancing operational flexibility, and meeting the diverse thrust and speed requirements of engineering machinery.

[0017] 2. This multi-stage central sleeve hydraulic cylinder structure, capable of extending and retracting in stages, incorporates a conical groove, a trigger cone, a spring, and a pressure sensor. The conical groove fits against the arc-shaped trigger plate, compressing the spring via a push rod and a sliding plate. The spring then transmits the thrust to the push plate and the pressure sensing end of the pressure sensor. When the pressure changes, the controller reduces the hydraulic oil flow. When the pressure reaches its initial maximum value, the controller disconnects the oil supply from the upper inlet pipe via a three-way metering valve. The pressure sensor provides real-time feedback on the force level, and the controller dynamically adjusts the oil volume to achieve automatic deceleration and precise stopping of the outer sleeve's extension and retraction speed, avoiding overtravel impact. Simultaneously, the conical design of the trigger cone reverses the direction of the trigger force, causing the pressure sensor to bear lateral force, avoiding the problem of easy damage when the pressure sensor directly bears axial load. Furthermore, the inclined surface effect of the conical surface can be used to amplify the detection sensitivity of minute displacements.

[0018] 3. This multi-stage central sleeve hydraulic cylinder structure, which can extend and retract in stages, is equipped with a rotating hook, a hanging rod, and a limit buckle. Rotating the rotating hook causes it to hook onto the hanging rod. The limit buckle and the side of the external mounting part together limit the rotating hook, preventing the pressure sensor from being pulled out of the through slot, thus fixing the pressure sensor. When the pressure sensor needs to be removed for maintenance or calibration, rotating the rotating hook again causes it to disengage from the hanging rod and separate from the side of the limit buckle and the external mounting part, allowing the pressure sensor to be pulled out of the through slot. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention. Figure 2 This is a cross-sectional view of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention. Figure 3 for Figure 2 Enlarged view of point A in the image; Figure 4 This invention provides a trigger cone and external mounting component for a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages. Figure 5 This is a schematic diagram of the internal structure of a cylinder liner of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention. Figure 6 This is a schematic diagram of the middle section oil inlet pipe and the upper section oil inlet pipe structure of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention. Figure 7 This is a schematic diagram of the assembly of the outer sleeve, inner sleeve, and piston column of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention. Figure 8 This is a top view of a multi-stage central sleeve hydraulic cylinder structure that can extend and retract in stages, as proposed in this invention.

[0020] In the diagram: 1. Base; 2. Cylinder liner; 3. Outer sleeve; 4. Lifting platform; 5. Bottom section oil inlet pipe; 6. Two-way metering valve; 7. Middle section oil inlet pipe; 8. Upper section oil inlet pipe; 9. Pipe clamp; 10. Connecting buckle; 11. Three-way metering valve; 12. Inner sleeve; 13. Middle piston; 14. Piston column; 15. Upper piston; 16. Lower piston; 17. Sealing ring; 18. Limiting ring; 19. Spiral hose; 20. Conical groove; 21. Trigger cone; 22. Through groove; 23. Pressure sensor; 24. Push plate; 25. Slide groove; 26. Spring; 27. Slide plate; 28. Push rod; 29. ​​Arc-shaped trigger plate; 30. External mounting component; 31. Rotary hook; 32. Hanging rod; 33. Limiting buckle; 34. First guide rail; 35. Second guide rail; 36. First storage slot; 37. Second storage slot. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Reference Figure 1-8A multi-stage center sleeve hydraulic cylinder structure with progressively extending and retracting sleeves includes a base 1, a cylinder liner 2, a piston rod 14, and a lower piston 16. The lower piston 16 is slidably connected to the inside of the cylinder liner 2. The piston rod 14 is fixedly connected to the top of the lower piston 16. An inner sleeve 12 is fitted onto the top of the piston rod 14. A middle piston 13 is fixedly connected to the bottom of the inner sleeve 12. An outer sleeve 3 is fitted onto the top of the inner sleeve 12. The top of the outer sleeve 3 extends above the cylinder liner 2. An upper piston 15 is fixedly connected to the bottom of the outer sleeve 3. Both the middle piston 13 and the upper piston 15 are slidably connected to the inside of the cylinder liner 2. A lifting platform 4 is fixedly connected to the top of the outer sleeve 3. A bottom section oil inlet pipe 5 is fixedly connected to the bottom of one side of the cylinder liner 2. A two-way metering valve 6 is provided in the middle. The plugs of the middle piston 13 and the upper piston 15 are connected to the same middle section oil inlet pipe 7. The bottom end of the middle section oil inlet pipe 7 is connected to the space between the middle piston 13 and the lower piston 16. The part of the middle section oil inlet pipe 7 located between the middle piston 13 and the lower piston 16 is set as a spiral hose 19. The top end of the middle section oil inlet pipe 7 extends to the outside of the top of the cylinder liner 2. The plug of the upper piston 15 is connected to the upper section oil inlet pipe 8. The bottom end of the upper section oil inlet pipe 8 is connected to the space between the upper piston 15 and the middle piston 13. The top end of the upper section oil inlet pipe 8 extends to the outside of the top of the cylinder liner 2. The top ends of the middle section oil inlet pipe 7 and the top ends of the upper section oil inlet pipe 8 are fixedly connected to the same three-way metering valve 11.

[0023] In use, the workpiece requiring telescopic control is connected externally via the lifting platform 4, and the base 1 provides overall support for the device. Hydraulic oil enters the cylinder liner 2 through the bottom inlet pipe 5, pushing the lower piston 16 upward, which in turn drives the piston rod 14 and the inner sleeve 12 to rise. The oil inlet volume is adjusted by the double-way metering valve 6 to achieve quantitative telescopic control of the lower piston 16. The middle inlet pipe 7 and the upper inlet pipe 8 control the movement of the middle piston 13 and the upper piston 15, respectively. The on / off state and oil inlet volume of the middle inlet pipe 7 and the upper inlet pipe 8 are adjusted by the three-way metering valve 11 to achieve the telescopic control of the inner sleeve 12. 2. The outer sleeve 3 extends and retracts in sequence. When the outer sleeve 3 rises, the distance between the upper piston 15 and the middle piston 13 increases, and the spiral hose 19 can extend adaptively to ensure the flexible connection of the middle section oil inlet pipe 7 during extension and retraction. The oil circuit is regulated by the double-way metering valve 6 and the three-way metering valve 11, so that the displacement process of the lower piston, upper piston 15, and middle piston 13 can be controlled independently. This enables the outer sleeve 3, inner sleeve 12, and piston rod 14 to move synchronously or sequentially, improving motion accuracy, enhancing operational flexibility, and meeting the differentiated thrust and speed requirements of engineering machinery.

[0024] In this invention, a limiting ring 18 is fixedly connected to the inner wall circumference of the bottom of the cylinder liner 2. The bottom of the lower piston 16 contacts the top of the limiting ring 18. The limiting ring 18 is fixed to the bottom of the cylinder liner, restricting the downward position of the lower piston 16 and preventing excessive retraction. This avoids the bottom of the lower piston 16 impacting the cylinder liner 2, which could lead to sealing failure or structural collision. It also ensures that the lower piston 16 is in the same position when it resets, thus improving the repeatability accuracy.

[0025] In this invention, a sealing ring 17 is embedded in the middle of the lower piston 16. The outer diameter of the sealing ring 17 corresponds to the inner diameter of the cylinder liner 2. The sealing ring 17 fits tightly against the inner wall of the cylinder liner 2 to prevent hydraulic oil leakage and maintain oil pressure, thus maintaining sealing performance under high pressure.

[0026] In this invention, the outer diameter of the middle piston 13 corresponds to the inner diameter of the cylinder liner 2, and the outer diameter of the upper piston 15 corresponds to the inner diameter of the cylinder liner 2, ensuring that the hydraulic oil does not leak and is evenly stressed when the middle piston 13 and the upper piston 15 slide, thus dispersing the load pressure and adapting to heavy-load conditions.

[0027] In this invention, the bottom of the inner sleeve 12 is provided with a first storage groove 36, the piston rod 14 is inserted into the inside of the first storage groove 36, and the two sides of the piston rod 14 are fixedly connected with first guide rails 34. The inner walls of the two sides of the first storage groove 36 are provided with first limiting grooves, and the two first guide rails 34 are slidably connected to the inside of the two first limiting grooves respectively. The inner sleeve 12 slides in the first storage groove 36, and the first guide rails 34 and the first limiting grooves are correspondingly engaged.

[0028] In this invention, the bottom of the outer sleeve 3 is provided with a second storage groove 37, and the inner sleeve 12 is inserted into the interior of the second storage groove 37. The outer walls on both sides of the inner sleeve 12 are fixedly connected with second guide rails 35. The inner walls on both sides of the second storage groove 37 are provided with second limiting grooves. The two second guide rails 35 are slidably connected to the interior of the two second limiting grooves respectively. The outer sleeve 3 slides in the second storage groove 37. The second guide rails 35 and the second limiting grooves cooperate accordingly. The radial offset of the sliding process is restricted by the first guide rail 34 and the second guide rail 35, ensuring linear movement and preventing the inner sleeve 12 and the outer sleeve 3 from bending or jamming when they extend or retract.

[0029] In this invention, a pipe clamp 9 is fixedly connected to the top outer wall of the cylinder liner 2. The upper section of the oil inlet pipe 8 extending outside the cylinder liner 2 is fixedly connected to the inside of the pipe clamp 9. The pipe clamp 9 fixes the upper section of the oil inlet pipe 8 to the top outer wall of the cylinder liner 2 to prevent the upper section of the oil inlet pipe 8 from shaking or loosening, reduce pipe wear caused by vibration, and prevent leakage.

[0030] In this invention, the upper section oil inlet pipe 8 and the middle section oil inlet pipe 7 are fitted with the same connecting buckle 10 at the end near the three-way metering valve 11. The connecting buckle 10 constrains the middle section oil inlet pipe 7 and the upper section oil inlet pipe 8, simplifying the pipeline layout and facilitating the connection of the three-way metering valve 11.

[0031] In this invention, a conical groove 20 is provided at the middle position of the bottom of the lifting platform 4, and a through groove 22 is provided at the middle of one side of the conical groove 20. The middle part of the through groove 22 is set as a sliding groove 25, and the inner diameter of the sliding groove 25 is larger than the inner diameter of the through groove 22. A trigger cone 21 is fixedly connected to the middle position of the top of the inner sleeve 12. An insertion hole adapted to the trigger cone 21 is provided at the middle position of the top of the outer sleeve 3. The trigger cone 21 is inserted into the inside of the conical groove 20. A push rod 28 is inserted into one end of the through groove 22 near the trigger cone 21. An arc-shaped trigger piece 29 is fixedly connected to one end of the push rod 28 located inside the conical groove 20. The arc-shaped trigger piece 29 fits against the outer wall of the trigger cone 21. One end of the push rod 28 located inside the slide groove 25 is fixedly connected to a slide plate 27. The slide plate 27 is slidably connected to the inside of the slide groove 25. A push plate 24 is slidably connected inside the through groove 22. The same spring 26 is fixedly connected between the push plate 24 and the slide plate 27. The spring 26 is in a compressed state. A detachable pressure sensor 23 is inserted into the end of the through groove 22 away from the trigger cone 21. One side of the push plate 24 is attached to the pressure sensing end of the pressure sensor 23. The pressure sensor 23 is connected to a controller via a signal line. When oil is supplied between the upward piston 15 and the middle piston 13, the outer sleeve 3 rises independently, and the trigger cone 21 gradually moves from the conical groove 20. As the bottom of the piston detaches, spring 26 gradually returns to its original position. The pressure from spring 26 decreases on push plate 24 and the sensing end of pressure sensor 23. Pressure sensor 23 simultaneously feeds a signal back to the controller. The controller controls the hydraulic oil flow rate in inlet pipe 8 to decrease through three-way metering valve 11, slowing down the extension speed of outer sleeve 3. When trigger cone 21 completely leaves the bottom of conical groove 20, spring 26 fully returns to its original position, the pressure detected by pressure sensor 23 disappears, and the controller disconnects the oil supply to upper section inlet pipe 8 through three-way metering valve 11, causing outer sleeve 3 to stop rising. When hydraulic oil between upper piston 15 and middle piston 13 is drawn out, trigger cone 21... 21 gradually enters the conical groove 20. The conical groove 20 fits against the arc-shaped trigger plate 29 and compresses the spring 26 through the push rod 28 and the slide plate 27. The spring 26 then transmits the thrust to the push plate 24 and the pressure sensing end of the pressure sensor 23. When the pressure changes, the controller controls the hydraulic oil flow to decrease. When the pressure reaches the initial maximum value, the controller disconnects the oil supply of the upper section oil inlet pipe 8 again through the three-way metering valve 11. The slide plate 27 slides inside the slide groove 25. On the one hand, it limits the extension and retraction stroke of the spring 26 to prevent deviation. On the other hand, the slide plate 27 isolates the two ends of the through groove 22 to prevent dust or foreign objects from entering the inside of the conical groove 20.

[0032] In this invention, an external mounting component 30 is fixedly connected to one side of the lifting platform 4. One end of the pressure sensor 23 extends to the side of the external mounting component 30 away from the lifting platform 4. A hanging rod 32 is fixedly connected to the side of the external mounting component 30 away from the lifting platform 4. A limit buckle 33 is fixedly connected to the end of the hanging rod 32 away from the external mounting component 30. A rotating hook 31 adapted to the hanging rod 32 is rotatably connected to the outer wall of the pressure sensor 23. Rotating the rotating hook 31 causes it to hook onto the hanging rod 32. The limit buckle 33 and the side of the external mounting component 30 together limit the rotating hook 31, preventing the pressure sensor 23 from being pulled out of the through slot 22, thus fixing the pressure sensor 23. When the pressure sensor 23 needs to be removed for maintenance or calibration, the rotating hook 31 is rotated again to disengage from the hanging rod 32 and separate from the side of the limit buckle 33 and the external mounting component 30, allowing the pressure sensor 23 to be pulled out of the through slot 22.

[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting, comprising a base (1), a cylinder liner (2), a piston rod (14), and a lower piston (16), wherein the lower piston (16) is slidably connected to the interior of the cylinder liner (2), and the piston rod (14) is fixedly connected to the top of the lower piston (16), characterized in that, The piston rod (14) is fitted with an inner sleeve (12) at the top. The bottom of the inner sleeve (12) is fixedly connected to a middle piston (13). The top of the inner sleeve (12) is fitted with an outer sleeve (3). The top of the outer sleeve (3) extends to the top of the cylinder liner (2). The bottom of the outer sleeve (3) is fixedly connected to an upper piston (15). The middle piston (13) and the upper piston (15) are both slidably connected to the inside of the cylinder liner (2). The top of the outer sleeve (3) is fixedly connected to a lifting platform (4). The bottom section oil inlet pipe (5) is fixedly connected to the bottom of one side of the cylinder liner (2). A double-way metering valve (6) is provided in the middle of the bottom section oil inlet pipe (5). The plugs of the middle piston (13) and the upper piston (15) are inserted into the same middle section oil inlet pipe. 7) The bottom end of the middle section oil inlet pipe (7) is connected to the space between the middle piston (13) and the lower piston (16). The middle section oil inlet pipe (7) located between the middle piston (13) and the lower piston (16) is set as a spiral hose (19). The top end of the middle section oil inlet pipe (7) extends to the outside of the top of the cylinder liner (2). The upper piston (15) is plugged with the upper section oil inlet pipe (8). The bottom end of the upper section oil inlet pipe (8) is connected to the space between the upper piston (15) and the middle piston (13). The top end of the upper section oil inlet pipe (8) extends to the outside of the top of the cylinder liner (2). The top end of the middle section oil inlet pipe (7) and the top end of the upper section oil inlet pipe (8) are fixedly connected to the same three-way metering valve (11).

2. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, A limiting ring (18) is fixedly connected to the inner wall of the bottom of the cylinder liner (2), and the bottom of the lower piston (16) contacts the top of the limiting ring (18).

3. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, A sealing ring (17) is embedded in the middle of the lower piston (16), and the outer diameter of the sealing ring (17) corresponds to the inner diameter of the cylinder liner (2).

4. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, The outer diameter of the middle piston (13) is matched with the inner diameter of the cylinder liner (2), and the outer diameter of the upper piston (15) is matched with the inner diameter of the cylinder liner (2).

5. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, The bottom of the inner sleeve (12) is provided with a first storage groove (36), the piston rod (14) is inserted into the inside of the first storage groove (36), and the two sides of the piston rod (14) are fixedly connected with first guide rails (34). The inner walls of the two sides of the first storage groove (36) are provided with first limiting grooves, and the two first guide rails (34) are slidably connected to the inside of the two first limiting grooves respectively.

6. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, The bottom of the outer sleeve (3) is provided with a second storage groove (37), the inner sleeve (12) is inserted into the inside of the second storage groove (37), the outer walls on both sides of the inner sleeve (12) are fixedly connected with second guide rails (35), the inner walls on both sides of the second storage groove (37) are provided with second limiting grooves, and the two second guide rails (35) are slidably connected to the inside of the two second limiting grooves respectively.

7. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, The top outer wall of the cylinder liner (2) is fixedly connected to a pipe clamp (9), and the upper oil inlet pipe (8) extending outside the cylinder liner (2) is fixedly connected to the inside of the pipe clamp (9).

8. The multi-stage central sleeve hydraulic cylinder structure with progressively extending and retracting sleeves according to claim 1, characterized in that, The upper section oil inlet pipe (8) and the middle section oil inlet pipe (7) are connected to the same connecting buckle (10) at the end near the three-way metering valve (11).

9. The multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 1, characterized in that, A conical groove (20) is provided at the middle of the bottom of the lifting platform (4). A through groove (22) is provided at the middle of one side of the conical groove (20). A sliding groove (25) is provided at the middle of the through groove (22). The inner diameter of the sliding groove (25) is larger than the inner diameter of the through groove (22). A trigger cone (21) is fixedly connected at the middle of the top of the inner sleeve (12). An insertion hole adapted to the trigger cone (21) is provided at the middle of the top of the outer sleeve (3). The trigger cone (21) is inserted into the inside of the conical groove (20). A push rod (28) is inserted into one end of the through groove (22) near the trigger cone (21). One end of the push rod (28) located inside the conical groove (20) is fixedly connected to... An arc-shaped trigger piece (29) is attached to the outer wall of the trigger cone (21). The push rod (28) is fixedly connected to a slide plate (27) at one end inside the slide groove (25). The slide plate (27) is slidably connected to the inside of the slide groove (25). A push plate (24) is slidably connected inside the through groove (22). The same spring (26) is fixedly connected between the push plate (24) and the slide plate (27). The spring (26) is in a compressed state. A detachable fixed pressure sensor (23) is inserted into one end of the through groove (22) away from the trigger cone (21). One side of the push plate (24) is attached to the pressure sensing end of the pressure sensor (23).

10. A multi-stage central sleeve hydraulic cylinder structure capable of progressively extending and retracting according to claim 9, characterized in that, An external mounting component (30) is fixedly connected to one side of the lifting platform (4). One end of the pressure sensor (23) extends to the side of the external mounting component (30) away from the lifting platform (4). A hanging rod (32) is fixedly connected to the side of the external mounting component (30) away from the lifting platform (4). A limit buckle (33) is fixedly connected to the end of the hanging rod (32) away from the external mounting component (30). A rotating hook (31) adapted to the hanging rod (32) is rotatably connected to the outer wall of the pressure sensor (23).

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