Gas supply regulating device for dual-fuel diesel engine

Abstract

The application discloses a kind of gas supply adjusting device of dual-fuel diesel engine in diesel engine gas supply technical field, including flow control valve, the flow control valve includes valve main body, respectively in the air inlet pipe and the air outlet pipe of valve main body two ends, and the valve stem of connecting valve core in valve main body, the gas supply adjusting device further includes pressure relief mechanism, the pressure relief mechanism includes the cylinder body inserted on air inlet pipe, eccentrically opened in the bottom of cylinder body and is communicated with the air inlet pipe and is opened, is arranged in the plate body for closing the mouth in cylinder body, and, one end is connected plate body, the other end is penetrated cylinder body and is rotated lever, the rotated lever and valve stem transmission connection are connected.This application is provided with pressure relief mechanism on air inlet pipe, when valve stem rotates and drives valve core to move to reduce gas flow, rotated lever is rotated with valve stem synchronously, and then drives plate body to move and makes the mouth gradually open, releases upstream pressure, effectively solves the problem that upstream pressure is accumulated when traditional flow valve is reduced opening.

Description

Technical Field

[0001] This invention relates to the field of diesel engine gas supply, and more specifically to a gas supply regulating device for a dual-fuel diesel engine. Background Technology

[0002] Currently, marine dual-fuel diesel engines typically operate in a natural gas / diesel dual-fuel mode. Because the engine's demand for gas flow varies significantly under different load conditions, high-pressure gas from the gas tank is usually delivered to the engine via gas pipelines. During the intake process, a gas supply regulating device precisely controls the natural gas flow. Currently, this is typically achieved by installing a flow control valve on the pipeline, connected to the gas tank outlet pipeline via a flange structure. While this achieves flow regulation, it has the following drawbacks: When the gas flow is reduced by the flow control valve, the reduced valve opening causes a contraction in the flow cross-section, leading to a temporary increase in upstream pressure. Over long-term use, this periodic pressure surge can easily cause seal failure at the upstream flange connection, resulting in gas leakage and seriously threatening the safety of ship operation. Therefore, we propose a gas supply regulating device for dual-fuel diesel engines. Summary of the Invention

[0003] The purpose of this invention is to provide a gas supply regulating device for a dual-fuel diesel engine, which solves the problem that when the gas supply is regulated by a flow control valve, the reduced valve core opening leads to a contraction of the flow cross section, which causes a temporary increase in the upstream pressure. This can easily cause the sealing of the upstream flange connection to fail, resulting in gas leakage and seriously threatening the safety of ship operation.

[0004] The present invention achieves the above objectives through the following technical solutions:

[0005] A gas supply regulating device for a dual-fuel diesel engine includes a flow control valve. The flow control valve includes a valve body, an inlet pipe and an outlet pipe respectively located at both ends of the valve body, and a valve stem connected to the valve core inside the valve body. The inlet pipe and the outlet pipe are respectively connected to the outlet pipe of the gas storage tank body and the gas flow pipe through flanges. The gas supply regulating device also includes a pressure reduction protection mechanism. The pressure reduction protection mechanism includes a cylinder inserted into the inlet pipe, an eccentrically located opening at the bottom of the cylinder and communicating with the inlet pipe, a plate on the bottom wall of the cylinder for closing the opening, and a rotating rod connected at one end to the plate and penetrating through the cylinder at the other end. The rotating rod and the valve stem are kinetically connected. When the valve stem drives the valve core to reduce the gas flow, the rotating rod synchronously drives the plate to rotate and adjust the opening area of ​​the opening.

[0006] A further improvement is that a matching movable plate is movably provided inside the cylinder, the movable plate is movably sleeved on the outside of the rotating rod, and the movable plate is connected to the inner wall of the cylinder through an elastic element.

[0007] A further improvement is that the flange includes two sets of detachably fixed flanges, a sealing ring is provided between the two sets of flanges, a guide seat is provided on one side of the cylinder, a connecting frame driven to rise and fall by a telescopic device is provided in the guide seat, two sets of limiting plates are symmetrically arranged on both sides of the connecting frame, the two sets of limiting plates are connected and fixed by a connecting piece, and the two sets of limiting plates are respectively located on both sides of the flange of the air inlet pipe and the air outlet pipe of the main body of the air storage tank;

[0008] When the telescopic device moves the connecting frame downwards, the connecting frame moves its two sets of limiting plates at its ends to clamp the outside of the flange at the air inlet pipe and the air outlet pipe of the main body of the air storage tank.

[0009] A further improvement is that a toothed ring is embedded on the side of the flange at the end of the air inlet pipe facing the main body of the gas storage tank. The toothed ring is coaxial with the flange and located outside the sealing ring. The toothed ring is provided with several sets of detection sensors for detecting gas, and also includes an alarm. The alarm will sound when the detection sensors detect gas.

[0010] A further improvement is that the toothed ring is connected to the connecting frame via a transmission component, which drives the toothed ring to rotate when the connecting frame is raised or lowered.

[0011] A further improvement is that the transmission component includes a drive gear that is embedded in the end of the air intake pipe, facing the main body of the air tank and meshing with a gear ring. The shaft of the drive gear passes through the flange and is rotatably connected to the guide seat through an elastic reset member. A connecting rope is wound around the shaft of the drive gear. One end of the connecting rope passes through the guide seat and is connected to the connecting frame. The connecting rope drives the drive gear to rotate when the connecting frame moves downward.

[0012] A further improvement is that an expansion bladder seal is provided on the side of the flange at the end of the air inlet pipe facing the main body of the air tank. The expansion bladder seal is located outside the toothed ring. The expansion bladder seal is connected to an air storage cylinder through an air pipe. The air storage cylinder is mounted on a connecting frame. A piston rod assembly is movably inserted into one end of the air storage cylinder, and a return spring is sleeved on the outer wall of the piston rod assembly. When the connecting frame moves downward, the piston rod assembly compresses the gas in the air storage cylinder into the expansion bladder seal, causing the expansion bladder seal to expand and seal the flange.

[0013] A further improvement is that the inner and outer sides of the inflatable airbag seal are provided with limiting protrusions, the axial length of which is less than the axial length of the sealing ring.

[0014] A further improvement is that a follower plate is sleeved on the outer wall of the rotating rod, and a detection element is provided on the follower plate. A contact element corresponding to the detection element is provided on the cylinder. When the detection element and the contact element are in the same position, the flow control valve is in an unadjusted flow state. When the valve rod drives the valve core to rotate and reduce the gas flow, the rotating rod drives the follower plate to separate the detection element from the contact element, thereby causing the telescopic device to drive the connecting frame to descend.

[0015] A further improvement is that each of the two sets of limiting plates has several sets of balls rotatably embedded on the opposite side for contacting the flange.

[0016] The beneficial effects of this invention are as follows: This invention is equipped with a pressure reduction protection mechanism on the air inlet pipe. When the valve stem rotates and drives the valve core to move to reduce the gas flow, the rotating rod rotates synchronously with the valve stem, thereby driving the plate to move and gradually opening the port. This allows the gas to enter the cylinder through the opened port, releasing the upstream pressure. This effectively solves the problem of upstream pressure accumulation when the opening of the traditional flow valve is reduced, and significantly reduces the probability of gas leakage caused by damage to the flanges at the upstream air inlet pipe and the gas outlet pipe of the main body of the gas storage tank due to periodic pressure impact. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the gas supply regulating device of the present invention;

[0018] Figure 2 For the present invention Figure 1 A schematic diagram of a local structure in the image;

[0019] Figure 3 This is a schematic cross-sectional view of the cylinder structure in the pressure reduction protection mechanism of the present invention;

[0020] Figure 4 This is a schematic diagram of the pressure reduction protection mechanism in the gas supply regulating device of the present invention;

[0021] Figure 5 This is a schematic diagram of the flange structure in the gas supply regulating device of the present invention.

[0022] In the diagram: 100, main body of the gas storage tank; 200, valve body; 201, valve stem; 300, gas flow pipeline; 400, flange; 500, sealing ring; 600, pressure reduction protection mechanism; 601, cylinder; 602, rotating rod; 603, connecting rope; 604, port; 605, plate; 606, movable plate; 607, elastic element; 608, guide seat; 609, connecting frame; 610, limiting plate; 611, ball bearing; 612, connecting piece; 613, telescopic device; 614, follower plate; 615, toothed ring; 616, expansion bladder seal; 617, limiting protrusion ring; 618, gas pipe; 619, gas storage tank; 620, detection sensor. Detailed Implementation

[0023] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0024] Example 1

[0025] Please see the appendix Figure 1-4 A gas supply regulating device for a dual-fuel diesel engine, comprising a flow control valve connecting the gas storage tank body 100 and the gas flow pipeline 300, wherein a gas filter, a gas mixer, etc. can be connected to the gas flow pipeline 300, and finally connected to the dual-fuel diesel engine, which will not be described in detail here.

[0026] The flow control valve includes a valve body 200, an inlet pipe and an outlet pipe respectively located at both ends of the valve body 200, and a valve stem 201 connected to the valve core inside the valve body 200. The flow control valve is a conventional structure in the art. Its valve stem 201 can be driven to rotate by electrical equipment such as a motor, or it can be manually adjusted by a handwheel. The flow control valve is a conventional structure in the art and is not limited to the above structures, so it will not be described in detail here.

[0027] The inlet pipe and outlet pipe are connected to the outlet pipe of the gas storage tank body 100 and the gas flow pipe 300 respectively via flanges. The flanges include two sets of detachable and fixed flanges 400, and a sealing ring 500 is provided between the two sets of flanges 400. Specifically, flanges 400 are provided at the ends of the inlet pipe, the end of the outlet pipe, the outlet pipe of the gas storage tank body 100, and the end of the gas flow pipe 300. For example, two sets of flanges 400 can be fixedly connected by bolts. The sealing ring 500 is embedded between two sets of flanges 400 to improve the sealing between the two sets of flanges 400. This method is a common flange connection method in pipelines in this field, and will not be described in detail here.

[0028] The gas supply regulating device also includes a pressure reduction protection mechanism 600. The pressure reduction protection mechanism 600 includes a cylinder 601 inserted into the air inlet pipe, an eccentrically located port 604 at the bottom of the cylinder 601 and connected to the air inlet pipe, preferably two sets of ports 604 respectively located on both sides of the bottom of the cylinder 601, a plate 605 located on the bottom wall of the cylinder 601 for sealing the ports 604, and a rotating rod 602 connected at one end to the plate 605 and the other end penetrating the cylinder 601. The rotating rod 602 is connected to the valve stem 201. The rotating rod 602 and the valve stem 201 can be connected by a sprocket drive assembly (including sprocket and chain). When the valve stem 201 drives the valve core to reduce the gas flow, the rotating rod 602 synchronously drives the plate 605 to rotate and adjust the opening area of ​​the port 604.

[0029] When the flow control valve does not adjust the gas supply flow, plate 605 closes port 604, preventing gas from entering cylinder 601 through port 604. When valve stem 201 rotates, causing valve core to move and reduce gas flow, rotating rod 602 rotates with valve stem 201. In turn, rotating rod 602 drives plate 605 to open port 604. The smaller the gas flow is adjusted, the larger the rotation angle of valve stem 201. Similarly, rotating rod 602 drives plate 605 to make the opening area of ​​port 604 larger. This method effectively solves the problem of upstream pressure accumulation when the traditional flow valve reduces the opening degree, and significantly reduces the probability of gas leakage caused by damage to flanges at the upstream inlet pipe and gas tank body 100 outlet pipe due to periodic pressure impact (bolt stress relaxation, seal ring 500 damage, etc.).

[0030] Preferably, in this embodiment, a matching movable plate 606 is movably provided inside the cylinder 601. The movable plate 606 is movably sleeved on the outside of the rotating rod 602, and the movable plate 606 is connected to the inner wall of the top of the cylinder 601 through an elastic member 607, such as a spring. When the opening 604 is open, some gas can enter the cylinder 601 through the opening 604, thereby driving the movable plate 606 to move upward and squeeze the elastic member 607 to release the upstream pressure. When the pressure returns to normal, the movable plate 606 is reset under the action of the elastic member 607, thereby allowing the gas in the cylinder 601 to return to the intake pipe.

[0031] Example 2

[0032] Please see the appendix Figure 1-5 Based on Embodiment 1, the cylinder 601 of this embodiment is provided with a guide seat 608 on one side. The guide seat 608 is a vertical frame structure. The guide seat 608 is provided with a connecting frame 609 driven to rise and fall by a telescopic device 613 (e.g., an electric telescopic rod). Two sets of limiting plates 610 are symmetrically arranged on both sides of the connecting frame 609. There are a total of four limiting plates 610, which are symmetrically arranged in pairs. The two sets of limiting plates 610 are connected and fixed by a connector 612. The connector 612 is, for example, an adjustable telescopic rod. The two sets of limiting plates 610 are located on both sides of the flange of the air inlet pipe and the air outlet pipe of the air storage tank body 100, respectively.

[0033] When the telescopic device 613 drives the connecting frame 609 downward, the connecting frame 609 drives the two sets of limiting plates 610 at its ends to clamp the outside of the flange at the air inlet pipe and the air outlet pipe of the air storage tank body 100. The limiting plates 610 can fix the two flanges 400 in the flange, so that the two flanges 400 are not easily moved or separated due to pressure when the flow control valve is adjusted, thus ensuring the connection stability of the two flanges 400 and making the bolt structure fixing the two flanges 400 less likely to loosen.

[0034] Preferably, in this embodiment, each of the two sets of limiting plates 610 is rotatably embedded with a number of sets of balls 611 for contacting the flange. These balls 611 can be rubber balls to reduce the damage to the flange 400 caused by contact with the flange, and at the same time facilitate the limiting plates 610 to clamp the flange and limit its movement.

[0035] Preferably, in this embodiment, the outer wall of the rotating rod 602 is fitted with a follower plate 614, the follower plate 614 is provided with a detection element, and the cylinder 601 is provided with a contact element corresponding to the detection element. The detection element is, for example, a Hall sensor, and the contact element is a permanent magnet. Alternatively, the detection element can be a photoelectric switch, and the contact element can be a reflective label. Of course, it is not limited to these structures.

[0036] When the detection element and the contact element are aligned, the flow control valve is in an unregulated flow state, i.e., the gas supply is at a normal flow rate. When the valve stem 201 drives the valve core to rotate and reduce the gas flow, the rotating rod 602 drives the follower plate 614 to separate the detection element and the contact element. Then, the telescopic device 613 drives the connecting frame 609 to descend. Both the detection element and the telescopic device 613 are electrically connected to an external controller. When the detection element and the contact element are separated, the detection element sends a signal to the external controller. The external controller controls the telescopic device 613 to drive the connecting frame 609 to descend. When the detection element and the contact element are aligned again, the external controller controls the telescopic device 613 to drive the connecting frame 609 to rise and reset.

[0037] Example 3

[0038] Please see the appendix Figure 3-5 Based on Embodiment 2, in this embodiment, a toothed ring 615 is embedded in the flange 400 at the end of the air inlet pipe facing the gas tank body 100. Specifically, an annular groove is formed on the side of the flange 400 at the end of the air inlet pipe facing the gas tank body 100. The toothed ring 615 is rotatably mounted in the annular groove through a bearing. The toothed ring 615 is coaxial with the flange 400 and is located outside the sealing ring 500. Several sets of detection sensors 620 for detecting gas are provided on the toothed ring 615. The detection sensors 620 are, for example, gas detection sensors. An alarm is also included. The alarm will sound when the detection sensors 620 detect gas. Specifically, the detection sensors 620 and the alarm are electrically connected to an external controller. When the detection sensors 620 detect gas, it indicates that there is a gas leak at the flange of the air inlet pipe and the gas outlet pipe of the gas tank body. The alarm will then send a signal to the external controller, which will control the alarm to alert the user.

[0039] Preferably, in this embodiment, the toothed ring 615 is connected to the connecting frame 609 via a transmission component, and the transmission component drives the toothed ring 615 to rotate when the connecting frame 609 is raised or lowered.

[0040] Preferably, the transmission component in this embodiment includes a drive gear that meshes with a gear ring 615 on the side of the flange 400 facing the gas tank body 100 embedded at the end of the air inlet pipe. The shaft of the drive gear passes through the flange 400 and is rotatably connected to the guide seat 608 through an elastic reset member (e.g., a torsion spring). A connecting rope 603 is wound around the shaft of the drive gear. One end of the connecting rope 603 passes through the guide seat 608 and is connected to the connecting frame 609. Specifically, the connecting rope 603 extends to the top of one side of the guide seat 608 and then passes through its outer wall and is connected to the connecting frame 609. When the connecting frame 609 moves downward, the connecting rope 603 drives the drive gear to rotate.

[0041] When the flow control valve is adjusted to reduce the gas flow, the telescopic device 613 will drive the connecting frame 609 to move downward, which in turn will pull the shaft of the drive gear to rotate via the connecting rope 603. The shaft will drive the drive gear, which in turn will drive the gear ring 615 to rotate. When the flow control valve is adjusted to reset to its initial state, the telescopic device 613 will drive the connecting frame 609 to move upward and reset. This will cause the elastic reset component to drive the shaft, which will drive the drive gear, which will then drive the gear ring 615 to rotate and reset. When the gear ring 615 rotates, it will drive the detection sensor 620, effectively improving the gas detection range of the detection sensor 620 for the flange.

[0042] Example 4

[0043] Please see the appendix Figure 3-5 Based on embodiment 3, in this embodiment, the flange 400 at the end of the air inlet pipe is further provided with an expansion airbag seal 616 on the side facing the air tank body 100. The expansion airbag seal 616 is, for example, a rubber airbag ring. The expansion airbag seal 616 is located outside the toothed ring 615. The expansion airbag seal 616 is connected to an air storage cylinder 619 through an air pipe 618. The air storage cylinder 619 stores gas. The air storage cylinder 619 is provided on the connecting frame 609. A piston rod assembly is movably inserted into one end of the air storage cylinder 619. The piston rod assembly includes a piston that is movably disposed in the air storage cylinder 619 and a piston rod connected to the piston. A return spring is sleeved on the outer wall of the piston rod assembly. Specifically, one end of the return spring is connected to the end of the piston rod, and the other end is connected to the outer wall of the air storage cylinder 619.

[0044] When the telescopic device 613 moves the connecting frame 609 downward, the piston rod assembly contacts the outer wall of the air inlet pipe (or the bottom wall of the guide seat 608). As the connecting frame 609 continues to move downward, the piston rod assembly compresses the air in the air storage cylinder 619, causing the air in the air storage cylinder 619 to enter the expansion bladder seal 616. The expansion bladder seal 616 expands and contacts another flange 400. The expansion bladder seal 616 forms a second auxiliary sealing structure on the outer side between the two adjacent flanges 400. On the one hand, this effectively prevents the sealing ring 500 from being damaged by pressure when the flow control valve is adjusted to reduce the gas flow, thus preventing the gas from leaking directly to the outside. On the other hand, after the expansion bladder seal 616 expands, the detection sensor 620 is located between the sealing ring 500 and the expansion bladder seal 616, making it easier for the detection sensor 620 to better detect whether there is a gas leak in the flange.

[0045] Preferably, the inner and outer sides of the inflatable airbag seal 616 in this embodiment are also provided with limiting protrusions 617. The thickness of the limiting protrusions 617 is less than the thickness of the sealing ring 500. The setting of the limiting protrusions restricts the expansion of the inflatable airbag seal 616 along its axial direction when gas enters the inflatable airbag seal 616.

[0046] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A gas supply regulating device for a dual-fuel diesel engine, comprising a flow control valve, the flow control valve comprising a valve body (200), an inlet pipe and an outlet pipe respectively disposed at both ends of the valve body (200), and a valve stem (201) connected to a valve core inside the valve body (200), the inlet pipe and the outlet pipe being respectively connected to the outlet pipe of the gas storage tank body (100) and the gas flow pipe (300) via flanges, characterized in that: The gas supply regulating device also includes a pressure reduction protection mechanism (600), which includes a cylinder (601) inserted into the air inlet pipe, an eccentrically located opening (604) at the bottom of the cylinder (601) and connected to the air inlet pipe, a plate (605) on the bottom wall of the cylinder (601) for sealing the opening (604), and a rotating rod (602) with one end connected to the plate (605) and the other end penetrating the cylinder (601). The rotating rod (602) is connected to the valve stem (201) in a transmission connection. When the valve stem (201) drives the valve core to reduce the gas flow, the rotating rod (602) synchronously drives the plate (605) to rotate and adjust the opening area of ​​the opening (604).

2. The gas supply regulating device according to claim 1, characterized in that: The cylinder (601) is movably provided with a matching movable plate (606), which is movably sleeved on the outside of the rotating rod (602), and the movable plate (606) is connected to the inner wall of the cylinder (601) through an elastic element (607).

3. The gas supply regulating device according to claim 1, characterized in that: The flange includes two sets of detachably fixed flanges (400), and a sealing ring (500) is provided between the two sets of flanges (400). A guide seat (608) is provided on one side of the cylinder (601). A connecting frame (609) driven to lift by a telescopic device (613) is provided inside the guide seat (608). Two sets of limiting plates (610) are symmetrically arranged on both sides of the connecting frame (609). The two sets of limiting plates (610) are connected and fixed by a connector (612). The two sets of limiting plates (610) are respectively located on both sides of the flange of the air inlet pipe and the air outlet pipe of the main body of the gas storage tank (100). When the telescopic device (613) drives the connecting frame (609) downward, the connecting frame (609) drives the two sets of limiting plates (610) at its end to clamp the outside of the flange at the air inlet pipe and the air outlet pipe of the main body of the air tank (100).

4. The gas supply regulating device according to claim 3, characterized in that: A toothed ring (615) is embedded on the side of the flange (400) at the end of the air inlet pipe facing the main body (100) of the gas storage tank. The toothed ring (615) is coaxial with the flange (400) and located outside the sealing ring (500). The toothed ring (615) is provided with several sets of detection sensors (620) for detecting gas, and also includes an alarm. The alarm will sound when the detection sensors (620) detect gas.

5. The gas supply regulating device according to claim 4, characterized in that: The toothed ring (615) is connected to the connecting frame (609) via a transmission component, which drives the toothed ring (615) to rotate when the connecting frame (609) is raised or lowered.

6. The gas supply regulating device according to claim 5, characterized in that: The transmission component includes a flange (400) embedded at the end of the air inlet pipe facing the air tank body (100) and a drive gear meshing with a gear ring (615). The shaft of the drive gear passes through the flange (400) and is rotatably connected to the guide seat (608) through an elastic reset member. A connecting rope (603) is wound around the shaft of the drive gear. One end of the connecting rope (603) passes through the guide seat (608) and is connected to the connecting frame (609). The connecting rope (603) drives the drive gear to rotate when the connecting frame (609) moves downward.

7. The gas supply regulating device according to claim 4, characterized in that: An expansion airbag seal (616) is provided on the side of the flange (400) at the end of the air inlet pipe facing the main body (100) of the air tank. The expansion airbag seal (616) is located outside the toothed ring (615). The expansion airbag seal (616) is connected to an air storage cylinder (619) through an air pipe (618). The air storage cylinder (619) is mounted on a connecting frame (609). A piston rod assembly is movably inserted at one end of the air storage cylinder (619), and a return spring is sleeved on the outer wall of the piston rod assembly. During the downward movement of the connecting frame (609), the piston rod assembly compresses the gas in the air storage cylinder (619) into the expansion airbag seal (616), causing the expansion airbag seal (616) to expand and seal the flange.

8. The gas supply regulating device according to claim 7, characterized in that: The inner and outer sides of the inflatable airbag seal (616) are also provided with limiting protrusions (617), and the axial length of the limiting protrusions (617) is less than the axial length of the sealing ring (500).

9. The gas supply regulating device according to claim 3, characterized in that: The outer wall of the rotating rod (602) is fitted with a follower plate (614), and the follower plate (614) is provided with a detection element. The cylinder (601) is provided with a contact element corresponding to the detection element. When the detection element and the contact element correspond, the flow control valve is in an unadjusted flow state. When the valve stem (201) drives the valve core to rotate and reduce the gas flow, the rotating rod (602) drives the follower plate (614) to separate the detection element from the contact element, and then the telescopic device (613) drives the connecting frame (609) to descend.

10. The gas supply regulating device according to claim 3, characterized in that: Both sets of limiting plates (610) are rotatably embedded on opposite sides with several sets of balls (611) for contacting the flange.

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