CN112049838A

CN112049838A - Hydraulic cylinder capable of automatically controlling displacement and hoist

Info

Publication number: CN112049838A
Application number: CN202010837612.1A
Authority: CN
Inventors: 周一松; 万木春; 李恒
Original assignee: WUHAN LIDI HYDRAULIC EQUIPMENT CO Ltd
Current assignee: WUHAN LIDI HYDRAULIC EQUIPMENT CO Ltd
Priority date: 2020-08-19
Filing date: 2020-08-19
Publication date: 2020-12-08
Anticipated expiration: 2040-08-19
Also published as: CN112049838B

Abstract

The invention provides a hydraulic cylinder and a hoist capable of automatically controlling displacement, which comprises a cylinder body and a piston movably arranged in the cylinder body, wherein the piston is fixedly connected with a piston rod; the piston is also provided with a fixed rod, one end of the fixed rod is fixedly connected with the bottom of the rodless cavity of the cylinder body, the other end of the fixed rod is positioned in the hole, a magnetic ring is arranged at the end head of the fixed rod and is sleeved with a detection rod, and the relative displacement between the piston and the cylinder body is detected through the relative movement of the detection rod and the magnetic ring. In the hoist, a cylinder body of a hydraulic cylinder is fixedly connected with a gate, a frame is arranged above the gate, and a piston rod is connected with the frame; the end of a piston rod of the hydraulic cylinder is positioned at the top of the frame. The structure of the invention prevents the magnetic displacement sensor from being soaked in water for a long time, and is convenient for field maintenance and replacement.

Description

Hydraulic cylinder capable of automatically controlling displacement and hoist

Technical Field

The invention relates to the field of opening and closing machines, in particular to a hydraulic cylinder capable of automatically controlling displacement and an opening and closing machine.

Background

Along with the wide application of hydraulic hoist of domestic hydraulic and hydro-power engineering, the reverse hanging hydraulic hoist is often used for vertically opening and closing a working gate and an accident gate in urban river landscape engineering and lake drainage pumping stations. In order to detect the opening value of the opening and closing of the gate, a displacement sensor is required to be arranged for stroke detection, particularly, the double-lifting-point hydraulic hoist is required to obtain the piston displacement values of the two oil cylinders for synchronously controlling the deviation values of the two sides of the gate, and the gate is prevented from being blocked due to the fact that the two sides are asynchronous. The piston rod of the oil cylinder of the inverted hydraulic hoist is usually upward, and the top end of the piston rod is fixedly arranged on a hydraulic hoist frame above the gate slot. The inverted hydraulic hoist adopting the external displacement sensor has a plurality of use problems.

In the prior art, the following schemes are generally adopted for detecting the displacement of the hydraulic cylinder: 1. the external steel wire rope type displacement sensor has poor waterproof performance, and if the sensor is submerged in a flood level, the sensor is easily damaged, and if the sensor enters impurities, a rope winding mechanism is easily blocked or disorderly grooved. Once aquatic weeds or branches and miscellaneous trees exist in water, the aquatic weeds or branches and miscellaneous trees are extremely easy to wind on the steel wire rope, and the steel wire rope is abnormally wound, so that signal acquisition fails. 2. The built-in steel wire rope type displacement sensor has more mechanical parts, and the measurement precision is greatly influenced by the mechanical parts. And because the cylinder body of the inverted hydraulic hoist cylinder is fixedly connected with the gate, the top of the piston rod is fixed, and the gate is opened and closed along with the movement of the cylinder body, if the sensor is fixed at the bottom of the cylinder and the pull rope is fixed on the piston, more requirements can be put forward on the spatial position in the gate body, and the design and the manufacture of the gate are influenced. More importantly, even though the waterproof performance of the sensor in a closed space can meet the requirement and be normally used, the sensor is inconvenient to overhaul when in failure. In addition, the sensors must be connected to cables which must be secured for reliable retraction from the top of the gate, which also increases the difficulty of installation and deployment. 3. The laser displacement sensor can be arranged on the oil cylinder rack like an external steel wire rope type displacement sensor, and displacement at two ends of the gate is measured by directly irradiating a reflector arranged on the gate. The laser displacement sensor is susceptible to the influence of temperature drift on the accuracy of measurement precision and repetition precision. Particularly, when the hydraulic hoist is used in a reverse hanging type hydraulic hoist, the high water level can cause that the laser sensor can not detect any data from a moving gate or an oil cylinder body. 4. The ultrasonic displacement sensor is the same as the laser displacement sensor, and has the problems of precision and measurement accuracy. 5. The magnetostrictive displacement sensor is usually arranged on a rear end cover of the oil cylinder, a slender rod of the sensor extends into a slender hole preset on a piston rod, and a magnetic ring is arranged on the piston or the piston rod at the piston end. When the piston moves, the movement of the magnetic ring generates a displacement signal and transmits the displacement signal to the PLC for synchronous control. Referring to fig. 7, if the displacement sensor is installed on the inverted hydraulic hoist in this way, the same problems as those of the displacement sensor using a built-in wire rope will be encountered, and a great technical problem will be caused to the maintenance and operation. For example, chinese patent document CN 104595282 a describes a hydraulic cylinder with a built-in magnetostrictive displacement sensor. In order to solve the above problem, chinese patent document CN 104895862 a describes a hydraulic cylinder having a displacement sensor, in which a magnetostrictive displacement sensor is provided on a piston rod, and a magnetic ring is provided on an end cover of the cylinder. However, in the scheme, the magnetic ring and the sensor rod are blocked by the outer wall of the piston rod, and the measurement accuracy is affected.

Disclosure of Invention

The invention aims to solve the technical problem of providing a hydraulic cylinder and a hoist capable of automatically controlling displacement, which can facilitate the overhaul and the replacement of a displacement sensor, avoid the damage under the working condition of high water level and prolong the service life.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a hydraulic cylinder capable of automatically controlling displacement comprises a cylinder body and a piston movably arranged in the cylinder body, wherein the piston is fixedly connected with a piston rod, a magnetic displacement sensor is arranged at the end of the piston rod, a hole penetrating through the piston and communicated with a rodless cavity is formed in the piston rod, the magnetic displacement sensor is fixedly connected with a detection rod, and the detection rod is positioned in the hole;

the piston is also provided with a fixed rod, one end of the fixed rod is fixedly connected with the bottom of the rodless cavity of the cylinder body, the other end of the fixed rod is positioned in the hole, a magnetic ring is arranged at the end head of the fixed rod and is sleeved with a detection rod, and the relative displacement between the piston and the cylinder body is detected through the relative movement of the detection rod and the magnetic ring.

In the preferred scheme, the fixed rod is fixedly connected with a rodless cavity end cover of the cylinder body;

a gap is formed between the fixed rod and the inner wall of the hole to form a first oil duct, one end of the first oil duct is communicated with a first oil port close to the end of the piston rod, and the other end of the first oil duct is communicated with a rodless cavity of the cylinder body;

the piston rod is provided with a first oil port close to the end head, a first oil duct is arranged in the piston rod, the first oil duct and the second oil duct are sealed mutually, one end of the first oil duct is communicated with the first oil port, the other end of the first oil duct is communicated with the rod cavity, and the opening of the first oil duct is located at the position close to the end face of the rod cavity of the piston.

In a preferred scheme, an end surface groove is formed in the end surface, close to the rodless cavity, of the piston and used for allowing hydraulic oil to enter the rodless cavity.

In a preferred scheme, an end surface groove is formed in the end surface, close to the rod cavity, of the piston and used for allowing hydraulic oil to enter the rod cavity.

In the preferred scheme, a rod cavity end cover is also arranged on the cylinder body, and a buffer cavity is arranged on the rod cavity end cover;

and a buffer ring is arranged at the position of the piston rod close to the piston, and the buffer cavity is used for accommodating the buffer ring and forms a buffer structure at the upper limit stroke of the piston.

In a preferred scheme, a sealed cabin is further arranged at the top end of the piston rod, the magnetic displacement sensor is fixedly arranged in the sealed cabin, and a lead of the magnetic displacement sensor penetrates through the sealed cabin in a sealed structure.

In the preferred scheme, a rod cavity end cover is also arranged on the cylinder body and is in sealing connection with the piston rod;

the inner wall of the end cover with the rod cavity is provided with a step hole, a plurality of Y-shaped sealing rings are arranged in the step hole, Y-shaped openings of the Y-shaped sealing rings are attached to the outer wall of the piston rod, an extrusion block is further arranged on the outer edge of each Y-shaped sealing ring, the height of each extrusion block is higher than that of a base of the Y-shaped sealing ring, a gland is further arranged at the end of each step hole, the outer wall of the gland is provided with threads, the gland is in threaded connection with the step hole of the end cover with the rod cavity, the gland is in contact with the extrusion block and is used for deforming through extrusion of the extrusion block, the Y-shaped openings of the Y-shaped sealing rings are attached to the.

A cylinder body of the hydraulic cylinder is fixedly connected with a gate, a frame is arranged above the gate, and a piston rod is connected with the frame;

the number of the hydraulic cylinders is at least 1;

the end of a piston rod of the hydraulic cylinder is positioned at the top of the frame.

In the preferred scheme, a ball head is arranged on the outer wall of the piston rod close to the end head, a ball seat is arranged on the frame, and the ball head is positioned in the ball seat;

the ball head is positioned below the magnetic displacement sensor.

In the preferred scheme, a connecting seat is fixedly arranged at the position, close to the end cover of the rod cavity, of the cylinder body, the connecting seat is fixedly connected with the top end of the gate, and the cylinder body is embedded in the gate.

According to the hydraulic cylinder and the hoist capable of automatically controlling displacement, provided by the invention, the magnetic displacement sensor is arranged on the piston rod, and the fixed rod is arranged to install the magnetic ring to be matched with the detection rod of the magnetic displacement sensor, so that the magnetic displacement sensor can be prevented from being soaked in water for a long time, and the on-site maintenance and replacement are convenient. And the magnetic displacement sensor is sealed in the hydraulic cylinder, so that the magnetic displacement sensor cannot contact high-pressure hydraulic oil, and the service life and the measurement accuracy of the magnetic displacement sensor are greatly prolonged. In a preferable scheme, the hoist disclosed by the invention is installed by adopting a ball head structure, and the cylinder body is embedded into the gate, so that the installation space is saved, partial installation and operation errors can be compensated, and the hoist is convenient to install and maintain. The invention can greatly prolong the service life of the vulnerable equipment related to the magnetic displacement sensor and is convenient to maintain and replace.

Drawings

The invention is further illustrated by the following examples in conjunction with the accompanying drawings:

fig. 1 is a partial structural sectional view of a hydraulic cylinder of the present invention.

Fig. 2 is a schematic structural diagram of the hydraulic cylinder of the present invention.

Fig. 3 is another preferred structure of the hydraulic cylinder of the present invention.

Fig. 4 is a schematic view of the seal structure of the hydraulic cylinder of the present invention.

Fig. 5 is a schematic front view of the hoist according to the present invention.

Fig. 6 is a schematic top view of the hoist according to the present invention.

Fig. 7 is a schematic diagram of a prior art hydraulic cylinder with a magnetic displacement sensor.

In the figure: the hydraulic pressure sensor comprises a piston rod 1, a cylinder body 2, a gate 3, a frame 4, a magnetic ring 5, a magnetic displacement sensor 6, a ball head 7, a detection rod 8, a ball seat 9, a fixing rod 10, a first oil port 11, a second oil port 12, a piston 13, an end surface groove 14, a second oil passage 15, a first oil passage 16, a rodless cavity end cover 17, a rod cavity end cover 18, a gland 19, a Y-shaped sealing ring 20, an extrusion block 21, an elastic ring 22, a V-shaped sealing ring 23, a sealing cabin 24, a pressing ring 25, a hydraulic structure 26, a door groove 27, a connecting seat 28 and an end sealing gasket 29.

Detailed Description

Example 1:

as shown in fig. 1 to 3, a hydraulic cylinder for automatically controlling displacement comprises a cylinder body 2 and a piston 13 movably arranged in the cylinder body 2, wherein the piston 13 is fixedly connected with a piston rod 1, a magnetic displacement sensor 6 is arranged at the end of the piston rod 1, a hole 32 penetrating through the piston 13 and communicated with a rodless cavity is arranged in the piston rod 1, the magnetic displacement sensor 6 is fixedly connected with a detection rod 8, and the detection rod 8 is positioned in the hole 32;

the piston is further provided with a fixed rod 10, one end of the fixed rod 10 is fixedly connected with the bottom of the rodless cavity of the cylinder body 2, the other end of the fixed rod is located in the hole 32, a magnetic ring 5 is arranged at the end of the fixed rod 10, the magnetic ring 5 is sleeved with a detection rod 8, and relative displacement between the piston 13 and the cylinder body 2 is detected through relative movement of the detection rod 8 and the magnetic ring 5. By the structure, under the working condition of inversely hanging the hydraulic cylinder, the position of the magnetic displacement sensor 6 is prevented from being soaked in water for a long time, and the maintenance and the replacement from the top are facilitated. If the magnetic displacement sensor is damaged, the magnetic displacement sensor can be pulled out of the piston rod, so that the magnetic displacement sensor is convenient to overhaul or replace and is not influenced by the water level. Preferably, as shown in fig. 1 to 3, the detection rod 8 is sleeved in the fixing rod 10 to save space. With this structure, the displacement of the cylinder 2 is ensured to be kept synchronized.

In a preferred scheme, as shown in fig. 2, a fixed rod 10 is fixedly connected with a rodless cavity end cover 17 of a cylinder body 2;

a gap is formed between the fixed rod 10 and the inner wall of the hole 32 to form a first oil duct 16, one end of the first oil duct 16 is communicated with a first oil port 11 close to the end of the piston rod 1, and the other end of the first oil duct is communicated with a rodless cavity of the cylinder body 2; by the structure, the first oil port 11 can be located above the water surface, so that the joint of the oil way is prevented from being soaked in water, and the hydraulic oil pipe is convenient to assemble, disassemble and maintain.

According to a preferable scheme, as shown in fig. 2, a second oil port 12 is further formed in the position, close to the end, of the piston rod 1, a second oil passage 15 is further formed in the piston rod 1, the second oil passage 15 and a first oil passage 16 are sealed with each other, one end of the second oil passage 15 is communicated with the second oil port 12, the other end of the second oil passage 15 is communicated with the rod cavity, and an opening of the second oil passage 15 is located at a position, close to the end face of the rod cavity of the piston 13. By the structure, the second oil port 12 can be positioned above the water surface, so that the joint of the oil way is prevented from being soaked in water, and the hydraulic oil pipe is convenient to assemble, disassemble and maintain.

In a further preferred scheme, the piston rod 1 is made of two sleeved steel pipes, the sleeved steel pipes are positioned through welded rod pieces, and the steel pipes in the middle form a hole 32 for arranging the detection rod 8 and the fixing rod 10. The cavity between the two steel pipes forms a second oil duct 15, and the first oil port 11 is formed by the steel pipe penetrating through the two sleeved steel pipes. The structure is suitable for the hydraulic cylinder with larger volume. As another alternative, as shown in fig. 2, a pipe burying scheme may also be adopted, and an oil pipe as the second oil passage 15 is buried in the piston rod 1. The scheme is suitable for the hydraulic cylinder with small volume.

In a preferred embodiment, as shown in fig. 2, a face groove 14 is provided in the end face of the piston 13 adjacent to the rodless chamber for the hydraulic oil to enter the rodless chamber.

In a preferred embodiment, as shown in fig. 2 and 3, a face groove 14 is provided in the end face of the piston 13 adjacent to the rod chamber for the hydraulic oil to enter the rod chamber.

In a preferred scheme, as shown in fig. 3, a rod cavity end cover 18 is further arranged on the cylinder body 2, and the rod cavity end cover 18 is provided with a buffer cavity 31;

a cushion ring 30 is further provided at a position of the piston rod 1 close to the piston 13, and a cushion chamber 31 is used for accommodating the cushion ring 30 and forming a cushion structure at the upper limit stroke of the piston.

In a preferred embodiment, as shown in fig. 1, a sealed chamber 24 is further provided at the top end of the piston rod 1, the magnetic displacement sensor 6 is fixedly disposed in the sealed chamber 24, and the lead of the magnetic displacement sensor 6 passes through the sealed chamber 24 in a sealed structure.

In a preferable scheme, a rod cavity end cover 18 is further arranged on the cylinder body 2, and the rod cavity end cover 18 is connected with the piston rod 1 in a sealing mode;

as shown in fig. 4, a step hole is formed in the inner wall of the rod cavity end cover 18, a plurality of Y-shaped sealing rings 20 are arranged in the step hole, a Y-shaped opening of each Y-shaped sealing ring 20 is attached to the outer wall of the piston rod 1, two deformable wings are arranged on the Y-shaped opening, an extrusion block 21 is further arranged on the outer edge of each Y-shaped sealing ring 20, the height of each extrusion block 21 is higher than that of the base of the Y-shaped sealing ring 20, a gland 19 is further arranged at the end of each step hole, threads are arranged on the outer wall of the gland 19, the gland 19 is in threaded connection with the step hole of the rod cavity end cover 18, the gland 19 is in contact with the extrusion block 21 and is used for enabling the Y-shaped opening of the Y-shaped sealing ring 20 to be attached to the outer wall of the piston rod 1 by deforming the extrusion of the. By the structure, better sealing effect is realized, particularly, in addition to the sealing effect on hydraulic oil, better sealing effect on external water is also realized, and the structure of the arranged extrusion block 21 is matched with the adjustment of the gland 19, so that the abrasion of the Y-shaped sealing ring 20 can be compensated. More preferably, a pressing ring 25 is further provided between the Y-rings 20. The provision of the pressing rings 25 prevents interference due to deformation of the wings of the adjacent Y-rings 20. It is further preferred that the back of the Y-seal 20 is beveled, as shown in fig. 3, which shows the bevel, the actual Y-seal 20 is annular, and the back of the Y-seal 20 is beveled. The corresponding pressing block 21 also has a deformable slope, and the Y-shaped seal ring 20 is deformed by the deformation of the pressing block 21 and the slope pressing. Further preferably, a packing is also provided on the inner wall of the rod cavity end cover 18. The V-shaped sealing ring 23 is further arranged, a groove is formed in the top of the V-shaped sealing ring 23, an elastic ring 22 is arranged in the groove, and abrasion of the V-shaped sealing ring 23 is compensated through deformation of the elastic ring 22.

By adopting the scheme, the invention has the following technical advantages:

1. a sealed cabin 24 of the magnetic displacement sensor 6 is arranged at the top end of a piston rod, a detection rod 8 is arranged in the center of the piston rod, a magnetic ring is fixed on a fixed rod 10 arranged in a cylinder body, the fixed rod 10 is fixedly connected to a rodless cavity end cover 17, the magnetic ring 5 moves along with the movement of the cylinder body 2, and relative displacement signals of the piston rod can be collected by the detection rod 8 and transmitted to a PLC. If the sensor is damaged, the sensor can be pulled out of the piston rod of the oil cylinder, so that the sensor is convenient to overhaul or replace and is not influenced by the water level.

2. The sealed cabin 24 of the magnetic displacement sensor adopts a sealed waterproof structure, and the wire harness penetrates out of the sealed cabin in a waterproof structure, so that even if all equipment is submerged at a high water level, the damage of the magnetic displacement sensor caused by water inflow or accidents caused by electric leakage can be avoided.

3. There is no on-cylinder line outside the cylinder block 2. Hydraulic oil enters a rodless cavity and a rod cavity of the cylinder body 2 through an oil duct arranged in the piston rod, and the slender detection rod 8 of the magnetic displacement sensor 6 is designed in the center of the piston rod, so that the entering and the backflow of the hydraulic oil are not influenced.

4. The detection rod 8 and the pipeline part of the magnetic displacement sensor 6 are both arranged in the piston rod of the oil cylinder, so that the detection precision is high, the detection is not influenced by the external weather, the temperature and floating objects in water, and the signal detection is safe and reliable.

5. In order to enable the piston rod of the hydraulic hoist to be used in urban water environment for a long time, the surface of the piston rod is also provided with a coating which has better anti-corrosion performance than a chrome-plated piston rod, in the embodiment, the surface of the piston rod adopts a supersonic flame spraying tungsten carbide (WC) coating, and the coating thickness is 0.20 mm.

6. The piston rod seal of the invention adopts a plurality of layers of Y-shaped seal rings, which is equivalent to adding a special reverse waterproof seal, can effectively prevent water from directly permeating into the cylinder body 2 when the water level is high, and simultaneously prevent the water attached on the piston rod from being brought into the cylinder body 2 due to the 'backflow' phenomenon when the piston rod moves in a stretching way.

Example 2:

on the basis of embodiment 1, as shown in fig. 5 to 6, and the preferable scheme is as shown in fig. 4 and 5, a hoist using the hydraulic cylinder for automatically controlling displacement is provided, wherein a cylinder body 2 of the hydraulic cylinder is fixedly connected with a gate 3, a frame 4 is arranged above the gate 3, and a piston rod 1 is connected with the frame 4;

the number of the hydraulic cylinders is at least 1;

the end of the piston rod of the hydraulic cylinder is positioned at the top of the frame 4.

Preferably, the number of the hydraulic cylinders is 2, and the hydraulic cylinders are respectively positioned at positions close to two sides of the gate 3. In this example, a master-slave control mode is adopted, in which the displacement of one cylinder 2 is set as the master and the displacement of the other cylinder is set as the slave. The displacement of the slave cylinder 2 is controlled to follow the displacement of the master cylinder 2 as a reference.

In the preferred scheme, a ball head 7 is arranged on the outer wall of the piston rod 1 close to the end, a ball seat 9 is arranged on the frame 4, and the ball head 7 is positioned in the ball seat 9; with this structure, the installation and running errors of the hydraulic cylinder can be compensated.

The ball head 7 is located below the magnetic displacement sensor 6. With the structure, the maintenance of the magnetic displacement sensor 6 is not influenced by the installation of the ball head 7.

In a preferred scheme, as shown in fig. 4, a connecting seat 28 is fixedly arranged at a position of the cylinder body 2 close to the rod cavity end cover 18, the connecting seat 28 is fixedly connected with the top end of the gate 3, and the cylinder body 2 is embedded in the gate 3. With this structure, the cylinder 2 can be easily inserted into the gate 3, and the installation space can be saved.

The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and features in the embodiments and examples in the present application may be arbitrarily combined with each other without conflict. The protection scope of the present invention is defined by the claims, and includes equivalents of technical features of the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.

Claims

1. The utility model provides an automatic pneumatic cylinder of control displacement, it includes cylinder body (2), still includes piston (13) that the activity set up in cylinder body (2), piston (13) and piston rod (1) fixed connection, characterized by: the end of the piston rod (1) is provided with a magnetic displacement sensor (6), a hole (32) which penetrates through the piston (13) and is communicated with the rodless cavity is formed in the piston rod (1), the magnetic displacement sensor (6) is fixedly connected with a detection rod (8), and the detection rod (8) is positioned in the hole (32);

the piston is characterized by further comprising a fixing rod (10), one end of the fixing rod (10) is fixedly connected with the bottom of the rodless cavity of the cylinder body (2), the other end of the fixing rod is located in the hole (32), a magnetic ring (5) is arranged at the end of the fixing rod (10), the magnetic ring (5) is sleeved with a detection rod (8), and relative displacement between the piston (13) and the cylinder body (2) is detected through relative movement of the detection rod (8) and the magnetic ring (5).

2. An automatically controlled displacement hydraulic cylinder as defined in claim 1 wherein: the fixed rod (10) is fixedly connected with a rodless cavity end cover (17) of the cylinder body (2);

a gap is formed between the fixed rod (10) and the inner wall of the hole (32) to form a first oil duct (16), one end of the first oil duct (16) is communicated with a first oil port (11) close to the end of the piston rod (1), and the other end of the first oil duct is communicated with a rodless cavity of the cylinder body (2);

the position, close to the end, of the piston rod (1) is further provided with a second oil port (12), a second oil duct (15) is further arranged in the piston rod (1), the second oil duct (15) and the first oil duct (16) are sealed mutually, one end of the second oil duct (15) is communicated with the second oil port (12), the other end of the second oil duct (15) is communicated with the rod cavity, and the opening of the second oil duct (15) is located in the position, close to the piston (13), of the end face of the rod cavity.

3. An automatically controlled displacement hydraulic cylinder as defined in claim 2 wherein: an end surface groove (14) is arranged on the end surface of the piston (13) close to the rodless cavity and used for allowing hydraulic oil to enter the rodless cavity.

4. An automatically controlled displacement hydraulic cylinder as defined in claim 2 wherein: an end face groove (14) is arranged on the end face of the piston (13) close to the rod cavity and used for allowing hydraulic oil to enter the rod cavity.

5. An automatically controlled displacement hydraulic cylinder as defined in claim 2 wherein: the cylinder body (2) is also provided with a rod cavity end cover (18), and the rod cavity end cover (18) is provided with a buffer cavity (31);

a buffer ring (30) is further arranged at the position, close to the piston (13), of the piston rod (1), and the buffer cavity (31) is used for accommodating the buffer ring (30) and forms a buffer structure at the upper limit stroke of the piston.

6. An automatically controlled displacement hydraulic cylinder as defined in claim 1 wherein: the top end of the piston rod (1) is also provided with a sealed cabin (24), the magnetic displacement sensor (6) is fixedly arranged in the sealed cabin (24), and a lead of the magnetic displacement sensor (6) penetrates through the sealed cabin (24) in a sealed structure.

7. An automatically controlled displacement hydraulic cylinder as defined in claim 1 wherein: the cylinder body (2) is also provided with a rod cavity end cover (18), and the rod cavity end cover (18) is hermetically connected with the piston rod (1);

the inner wall of the end cover (18) with the rod cavity is provided with a step hole, a plurality of Y-shaped sealing rings (20) are arranged in the step hole, a Y-shaped opening of each Y-shaped sealing ring (20) is attached to the outer wall of the piston rod (1), an extrusion block (21) is further arranged on the outer edge of each Y-shaped sealing ring (20), the height of each extrusion block (21) is higher than that of the base of the Y-shaped sealing ring (20), a gland (19) is further arranged at the end of each step hole, threads are arranged on the outer wall of each gland (19), each gland (19) is in threaded connection with the step hole of the end cover (18) with the rod cavity, each gland (19) is in contact with each extrusion block (21) and used for enabling the Y-shaped opening of each Y-shaped sealing ring (20) to be attached to the outer wall of the piston rod (1) tightly by extruding the.

8. A hoist using the automatically controlled hydraulic cylinder according to any one of claims 1 to 7, characterized in that: a cylinder body (2) of the hydraulic cylinder is fixedly connected with a gate (3), a rack (4) is arranged above the gate (3), and a piston rod (1) is connected with the rack (4);

the number of the hydraulic cylinders is at least 1;

the end of a piston rod of the hydraulic cylinder is positioned at the top of the frame (4).

9. The hoist of claim 8, wherein the hoist comprises: a ball head (7) is arranged on the outer wall of the piston rod (1) close to the end, a ball seat (9) is arranged on the rack (4), and the ball head (7) is positioned in the ball seat (9);

the ball head (7) is positioned below the magnetic displacement sensor (6).

10. The hoist of an automatically controlled displacement hydraulic cylinder according to claim 9, characterized in that: the cylinder body (2) is close to the position of the rod cavity end cover (18), a connecting seat (28) is fixedly arranged, the connecting seat (28) is fixedly connected with the top end of the gate (3), and the cylinder body (2) is embedded in the gate (3).