Unconstrained compound expansion joint with equivalent displacement and pipeline system

Abstract

The invention relates to an equal-displacement unconstrained compound expansion joint and a pipeline system, and belongs to the technical field of metal corrugated pipes, the equal-displacement unconstrained compound expansion joint comprises an unconstrained compound expansion joint, and further comprises two symmetrically-arranged equal-displacement mechanisms, each equal-displacement mechanism comprises a connecting limiting rod, a first rack rod, a second rack rod and a follow-up gear box, and the connecting limiting rod, the first rack rod and the second rack rod are parallel to the axial direction of the unconstrained compound expansion joint. The rear end pipe, the middle pipe and the front end pipe are provided with a first pin shaft, a second pin shaft and a third pin shaft respectively, and the connecting limiting rod is movably connected with the three. The shaft distance between the first pin shaft and the second pin shaft is equal to the shaft distance between the second pin shaft and the third pin shaft. And the follow-up gear box is movably connected with the second pin shaft. Two ends of the first rack rod are respectively connected with the first pin shaft and the gear; the two ends of the second rack rod are connected with the third pin shaft and the gear correspondingly. The problems existing in the prior art are solved, high-precision transmission can be achieved, the number of transmission parts is small, the structure is compact, and rigidity is large.

Description

Technical Field

[0001] The invention relates to the technical field of metal bellows, in particular to an unconstrained compound expansion joint with axial and lateral compensation and equal displacement of the lateral deformation limited to a single plane. Background Art

[0002] Expansion joints with metal bellows as flexible elements are mainly used to compensate for changes in the size of pipelines or equipment due to installation or thermal expansion and contraction, and are widely used in various industries.

[0003] The core content of the expansion joint design is the design of the bellows. Generally speaking, the bellows used in pipelines are served under pressure. The resulting pressure thrust is calculated according to the formula (Where: ; ) calculation. Once the pressure thrust is too large, it will cause damage to the bellows itself or the equipment nozzle. The pressure thrust is mostly borne by the main fixed pipe rack at a certain position of the pipeline, and sometimes it may be borne by the equipment connected to the pipeline. When the pressure thrust is borne, the problem of damage to the bellows itself or the equipment nozzle is well solved, that is, an unconstrained expansion joint can be used. In order to increase the compensation amount, two bellows are sometimes used on a single expansion joint, that is, an unconstrained compound expansion joint. When there are two bellows, how to coordinate the deformation of the two bellows is a key issue to consider when designing the expansion joint, especially when the compound expansion joint requires both axial and lateral compensation, it is quite difficult to coordinate the deformation of the two bellows. The current solution to this problem is usually the proportional connecting rod compound free expansion joint of GB / T 12777-2019. Its shortcomings are that there are many moving parts, the structure is not compact, the rigidity is poor, and the transmission accuracy is not high.

[0004] Therefore, there is an urgent need for a technology that can overcome the above-mentioned design deficiencies and achieve bidirectional (axial and lateral) compensation. Summary of the invention

[0005] Technical issues to be solved: In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides an equal displacement unconstrained compound expansion joint and piping system, which solves the technical problems of the prior art such as many moving parts, loose structure, poor rigidity and low transmission accuracy.

[0006] Technical solution: In order to achieve the above object, the main technical solutions adopted by the present invention include: In a first aspect, the present invention provides an equal displacement unconstrained compound expansion joint, comprising a front end pipe, an intermediate pipe and a rear end pipe. The two ends of the intermediate pipe are connected to the front end pipe and the rear end pipe through a bellows to form an unconstrained compound expansion joint, and also comprises two equal displacement mechanisms, which are symmetrically arranged on both sides of the outer wall of the unconstrained compound expansion joint. ; The equal displacement mechanism comprises a connecting limit rod and a transmission assembly located on one side of the connecting limit rod, and the connecting limit rod and the transmission assembly are both parallel to the axial direction of the unconstrained compound expansion joint; The connection limit rod and the transmission assembly are installed on the front end tube, the middle tube and the rear end tube through a pin assembly.

[0007] Optionally, the transmission assembly includes a first rack bar, a second rack bar and a follower gear box; The first pin, the second pin and the third pin are respectively arranged on the rear end tube, the middle tube and the front end tube, and the pin assembly consists of the first pin, the second pin and the third pin; the axial spacing between the first pin and the second pin is equal to the axial spacing between the second pin and the third pin; the connecting limit rod connects the first pin, the second pin and the third pin and can rotate around the first pin, the second pin and the third pin; both ends of the connecting limit rod are provided with strip holes for the first pin and the third pin to move; The follower gear box is connected to the second pin shaft and can rotate around it; One end of the first rack rod is connected to the first pin shaft and can rotate around it, and the other end of the first rack rod is meshed with the gear in the follower gear box through the first rack part; one end of the second rack rod is connected to the third pin shaft and can rotate around it, and the other end of the second rack rod is meshed with the gear in the follower gear box through the second rack part.

[0008] Optionally, the follower gear box includes a box body and a gear disposed in the box body. The first rack portion of the first rack rod and the second rack portion of the second rack rod both extend into the box body to engage the gear, and the first rack portion and the second rack portion both slide in cooperation with the inner side wall of the box body.

[0009] Optionally, a first support, a second support and a third support are respectively provided on the rear end tube, the middle tube and the front end tube, and are used to install a first pin, a second pin and a third pin respectively.

[0010] Optionally, the first rack rod, the second rack rod and the follower gear box are all arranged on the outside of the connection limit rod.

[0011] Optionally, a third shaft sleeve is sleeved on the third pin shaft, and the third shaft sleeve is arranged between the connection limit rod and the second rack rod. A first shaft sleeve is sleeved on the first pin shaft, and the first shaft sleeve is arranged between the connection limit rod and the first rack rod.

[0012] Optionally, the third support is a double-layer door-shaped structure, which includes an inner door-shaped structure and an outer door-shaped structure. The inner door-shaped structure includes an inner vertical plate and an inner horizontal plate, the inner horizontal plate is connected to the outer ends of the two inner vertical plates, and the inner ends of the inner vertical plates are installed on the outer wall of the front end tube. The outer door-shaped structure includes two outer vertical plates and an outer horizontal plate, the outer horizontal plate is installed at the outer ends of the two outer vertical plates, and the inner ends of the outer vertical plates are installed on the inner horizontal plate. The third shaft sleeve and the connecting limit rod are both located between the inner horizontal plate and the outer horizontal plate, and the two ends of the third shaft sleeve abut against the outer horizontal plate and the connecting limit rod respectively. The second rack rod is located at the outer end of the outer horizontal plate and is supported by the outer horizontal plate.

[0013] Optionally, the first rack rod, the second rack rod and the follower gear box are all arranged on the inner side of the connection limit rod.

[0014] Optionally, the first support is a double-layer door-shaped structure, which includes a first door-shaped structure and a second door-shaped structure. The first door-shaped structure includes a first vertical plate and a first horizontal plate, the first horizontal plate is connected to the outer ends of the two first vertical plates, and the inner ends of the two first vertical plates are installed on the outer wall of the rear end tube. The outer layer door-shaped structure includes two second vertical plates and a second horizontal plate, the second horizontal plate is installed at the outer ends of the two second vertical plates, and is used to support the connection limit rod, and the inner end of the second vertical plate is installed on the first horizontal plate. The first pin shaft is sleeved with a first shaft sleeve, the first rack rod and the first shaft sleeve are both arranged between the first horizontal plate and the second horizontal plate, and the two ends of the first shaft sleeve respectively abut the first rack rod and the second horizontal plate.

[0015] In a second aspect, the present invention further provides a piping system, which comprises an equal displacement unconstrained compound expansion joint as described above.

[0016] Beneficial effects: The beneficial effects of the present invention are as follows: an equal displacement unconstrained compound expansion joint and piping system of the present invention adopts two equal displacement mechanisms symmetrically arranged on the outer wall of the unconstrained compound expansion joint to achieve the limit of the deformation of the two bellows of the unconstrained compound expansion joint in a consistent manner, especially it can accurately limit the axial compensation and the lateral compensation. The equal displacement mechanism mainly includes a connecting limit rod, a first rack rod, a second rack rod and a follower gear box. The entire equal displacement mechanism has few moving parts, and during use, the connecting limit rod, the first rack rod and the second rack rod always maintain a parallel relationship with each other, and there is no structure that expands radially outward along the unconstrained compound expansion joint, making its structure more compact.

[0017] Furthermore, the first pin, the second pin and the third pin are respectively provided on the rear end tube, the middle tube and the front end tube of the unconstrained compound expansion joint, and the axial spacing between the first pin and the second pin is equal to the axial spacing between the second pin and the third pin, so as to facilitate the subsequent precise control of the deformation of the bellows. The connecting limit rod is sleeved on the first pin, the second pin and the third pin and can rotate around the first pin, the second pin and the third pin, and both ends of the connecting limit rod are provided with strip holes for the first pin and the third pin to move, so that the connecting limit rod can be used to uniformly constrain the rear end tube, the middle tube and the front end tube without affecting the deformation of the unconstrained compound expansion joint. The connecting limit rod also enhances the stiffness of the equal displacement mechanism and the entire unconstrained compound expansion joint, and is also conducive to subsequent precise limiting. On this basis, one end of the first rack bar can rotate around the first pin shaft, and the other end of the first rack bar is meshed with the gear in the follower gear box through the first rack part, while one end of the second rack bar can rotate around the third pin shaft, and the other end of the second rack bar is meshed with the gear in the follower gear box through the second rack part. When the unconstrained compound expansion joint performs displacement compensation, the meshing gear rotates through the movement of the first rack bar and the second rack bar. At the same time, since the first rack part and the second rack part are equal to the gear module, the movement distances of the first rack bar and the second rack bar are equal and opposite in direction. That is to say, whether the middle tube is stationary or the end tube (such as the front end tube or the rear end tube) at one end is stationary, the compensation amount of the two bellows of the unconstrained compound expansion joint can be evenly divided, both of which are 1 / 2 of the total compensation amount, thereby achieving the purpose of equal compensation. In addition, the transmission accuracy of the gear and rack structure is high, thereby achieving the improvement of compensation constraint accuracy.

[0018] Furthermore, the follower gear box includes a box body and a gear disposed in the box body. The first rack portion of the first rack rod and the second rack portion of the second rack rod both extend into the box body to engage with the gear, and both rack portions are slidably matched with the inner side wall of the box body, and the movement trajectory of the first rack rod and the second rack rod is limited by the inner side wall of the box body to ensure that the first rack rod and the second rack rod can be parallel to the connection limit rod, so as to further ensure the accuracy of transmission and limit.

[0019] Furthermore, the first rack rod, the second rack rod and the follower gear box can all be arranged on the outside of the connecting limit rod, so that the connecting limit rod is closer to the outer wall of the unconstrained compound expansion joint, thereby increasing the stability and rigidity of the equal displacement mechanism and the entire unconstrained compound expansion joint, and further ensuring the transmission accuracy of the equal displacement mechanism.

[0020] In summary, compared with the prior art, the present invention solves the technical problems existing in the prior art and has a unique high-precision transmission advantage, which enables the two bellows of the unconstrained compound expansion joint to completely achieve equal displacement. In addition, the present invention has fewer main transmission parts, a compact structure, high rigidity, and good manufacturing processability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of a form of an equal displacement unconstrained compound expansion joint of the present invention; Figure 2 yes Figure 1 C-direction view; Figure 3 yes Figure 1 AA partial cross-sectional view; Figure 4 yes Figure 1 BB partial cross-sectional view; Figure 5 yes Figure 1 The deformation diagram of an unconstrained compound expansion joint with equal displacement when performing lateral compensation is shown; Figure 6 It is a structural schematic diagram of another form of an equal displacement unconstrained compound expansion joint of the present invention; Figure 7 It is a structural schematic diagram of another form of an equal displacement unconstrained compound expansion joint of the present invention; Figure 8 It is a partial schematic diagram of connecting the limit rod; Fig. 9 for Figure 1 A schematic diagram of the three-dimensional structure of the third support shown in ; Fig.10 for Figure 7 Schematic diagram of the three-dimensional structure of the first support shown in FIG.

[0022] Description of Reference Numerals 1. front tube, 2. first bellows, 3. middle tube, 4. second bellows, 5. rear tube, 6. connecting limit rod, 61. strip hole, 7. first support, 701. first vertical plate, 702. first horizontal plate, 703. second vertical plate, 704. second horizontal plate, 8. first pin, 9. first nut, 10. first sleeve, 101. second limit cap, 11. first rack rod, 12. second rack rod, 13. follower gear Box, 131. Box body, 14. Gear shaft, 15. Positioning sleeve, 16. Gear shaft positioning nut, 17. Gear, 18. Second pin shaft, 19. Second nut, 20. Second support, 21. Third support, 22. Third sleeve, 221. First limiting cap, 23. Third pin shaft, 24. Third nut, 25, support column, 26. Inner vertical plate, 27. Inner horizontal plate, 28. Outer vertical plate, 29. Outer horizontal plate, 30. Transition sleeve. DETAILED DESCRIPTION

[0023] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below with reference to the accompanying drawings and through specific embodiments. Figure 1 The orientation is used as a reference.

[0024] The embodiment of the present invention proposes an equal displacement unconstrained compound expansion joint, comprising a front end tube, an intermediate tube and a rear end tube, wherein the two ends of the intermediate tube are connected to the front end tube and the rear end tube by a bellows to form an unconstrained compound expansion joint. It also comprises two equal displacement mechanisms, which are symmetrically arranged on both sides of the outer wall of the unconstrained compound expansion joint. The equal displacement mechanism comprises a connecting limit rod and a transmission assembly located on one side of the connecting limit rod, wherein the connecting limit rod and the transmission assembly are both parallel to the axial direction of the unconstrained compound expansion joint. The connecting limit rod and the transmission assembly are installed on the front end tube, the intermediate tube and the rear end tube through a pin assembly. The transmission assembly comprises a first rack rod, a second rack rod and a follower gear box. The rear end tube, the intermediate tube and the front end tube are respectively provided with a first pin, a second pin and a third pin, and the pin assembly consists of a first pin, a second pin and a third pin. The axial spacing between the first pin and the second pin is equal to the axial spacing between the second pin and the third pin. The connecting limit rod is sleeved on the first pin shaft, the second pin shaft and the third pin shaft and can rotate around the first pin shaft, the second pin shaft and the third pin shaft. Both ends of the connecting limit rod are provided with strip holes for the first pin shaft and the third pin shaft to move. The follower gear box is connected to the second pin shaft and can rotate around it. One end of the first rack rod is connected to the first pin shaft and can rotate around it, and the other end of the first rack rod is meshed with the gear in the follower gear box through the first rack part. One end of the second rack rod is connected to the third pin shaft and can rotate around it, and the other end of the second rack rod is meshed with the gear in the follower gear box through the second rack part. Compared with the prior art, the present invention solves the problems existing in the prior art well and has a unique high-precision transmission advantage, which enables the two bellows to fully achieve equal displacement. In addition, the present invention has fewer main transmission components, a compact structure, high rigidity, and good manufacturing processability.

[0025] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0026] Embodiment 1: Reference Figure 1 and Figure 2 The present invention provides an equal displacement unconstrained compound expansion joint, comprising a front end pipe 1, an intermediate pipe 3 and a rear end pipe 5, wherein both ends of the intermediate pipe 3 are connected to the front end pipe 1 and the rear end pipe 5 through a bellows. Specifically, the front end of the intermediate pipe 3, i.e. Figure 1 The left end of the intermediate tube 3 shown in FIG. 1 is connected to the front end tube 1 through the first corrugated tube 2, while the rear end of the intermediate tube 3, i.e. Figure 1The right end of the intermediate pipe 3 shown in the figure is connected to the rear end pipe 5 through the second bellows 4. The front end pipe 1, the first bellows 2, the intermediate pipe 3, the second bellows 4 and the rear end pipe 5 form an unconstrained compound expansion joint. For the sake of convenience, the "unconstrained compound expansion joint" is referred to as the "expansion joint" below. When the "expansion joint" is in a normal state, that is, when no compensation action is required, the front end pipe 1, the first bellows 2, the intermediate pipe 3, the second bellows 4 and the rear end pipe 5 are coaxial to prevent the transmission components (such as: the equal displacement mechanism in the present invention, etc.) from having additional torque, thereby increasing the transmission friction and shortening the life of the transmission components.

[0027] The present invention also includes two equal displacement mechanisms. The two equal displacement mechanisms have the same structure, and the two equal displacement mechanisms are symmetrically arranged on both sides of the outer wall of the "expansion joint", that is, the two equal displacement mechanisms are arranged in a Figure 2 The OX-OY plane shown is a reference symmetrical arrangement, and the axis of the "expansion joint" is located on the coordinate axis OX. The equal displacement mechanism mainly includes a connecting limit rod 6, a first rack rod 11, a second rack rod 12 and a follower gear box 13, and the connecting limit rod 6, the first rack rod 11 and the second rack rod 12 are parallel to each other, and the connecting limit rod 6, the first rack rod 11 and the second rack rod 12 are all parallel to the axis of the "expansion joint", or in other words, they are parallel to the axis of the "expansion joint". Figure 2 The OX-OY planes shown are parallel. The "parallel" mentioned here means that when the "expansion joint" is in the normal state, the compensation process state and the final state of compensation, the connecting limit rod 6, the first rack rod 11 and the second rack rod 12 are always parallel to the axis of the "expansion joint".

[0028] The transmission assembly includes a first rack bar 11, a second rack bar 12 and a follower gear box 13. The first pin 8, the second pin 18 and the third pin 23 are respectively arranged on the rear end tube 5, the middle tube 3 and the front end tube 1. The pin assembly consists of the first pin 8, the second pin 18 and the third pin 23; the axial spacing between the first pin 8 and the second pin 18 is equal to the axial spacing between the second pin 18 and the third pin 23. The first pin 8, the second pin 18 and the third pin 23 can be selected to have equal diameters. Figure 1 , the axes of the first pin 8, the second pin 18 and the third pin 23 are all located in the OX-OZ plane. The connecting limit rod 6, the first rack rod 11, the second rack rod 12 and other components themselves can also be understood as a symmetrical structure based on the OX-OZ plane. The "symmetrical structure" mentioned here is explained by taking the connecting limit rod 6 as an example: Figure 2 The plane perpendicular to the OX axis is the OX-OZ plane, and the OX-OZ plane passes through the center line Z connecting the limit rod 6.

[0029] Furthermore, a first support 7, a second support 20 and a third support 21 may be respectively provided on the rear end tube 5, the middle tube 3 and the front end tube 1, and the first support 7, the second support 20 and the third support 21 are respectively used to install the first pin 8, the second pin 18 and the third pin 23. The first support 7, the second support 20 and the third support 21 can be respectively installed on the rear end tube 5, the middle tube 3 and the front end tube 1 by welding. The first pin 8, the second pin 18 and the third pin 23 can be installed more conveniently by setting the first support 7, the second support 20 and the third support 21. Compared with the form in which the first pin 8, the second pin 18 and the third pin 23 are respectively welded to the outer wall of the rear end tube 5, the outer wall of the middle tube 3 and the outer wall of the front end tube 1, with the existence of the first support 7, the second support 20 and the third support 21, the first pin 8, the second pin 18 and the third pin 23 can be detachably arranged on the first support 7, the second support 20 and the third support 21 to facilitate the maintenance and replacement of the first pin 8, the second pin 18 and the third pin 23. For example, the first pin 8, the second pin 18 and the third pin 23 can be Figure 1 The first nut 9, the second nut 19 and the third nut 24 shown in the figure are respectively installed on the first support 7, the second support 20 and the third support 21, thereby realizing a detachable installation. The specific installation method is as follows Figure 1 As shown, it belongs to the prior art and will not be described here. Of course, this is not an exhaustive list, and any other known prior art can also be used. When installing, the first support 7, the second support 20 and the third support 21 are arranged according to the Figure 1 and Figure 2 The positions shown are welded at the middle positions of the outer walls of the rear end tube 5, the middle tube 3 and the front end tube 1, respectively. The "middle position" mentioned here means that the first support 7 is welded at the middle position of the rear end tube 5 in the axial direction, the second support 20 is welded at the middle position of the middle tube 3 in the axial direction, and the third support 21 is welded at the middle position of the front end tube 1 in the axial direction. Pin holes are provided on the first support 7, the second support 20 and the third support 21 for installing the first pin 8, the second pin 18 and the third pin 23 respectively. At the same time, it is necessary to ensure that the axial spacing between the first pin 8 and the second pin 18 is equal to the axial spacing between the second pin 18 and the third pin 23, so as to further ensure that the subsequent compensation process can be accurately controlled. It is also necessary to ensure that: the axis of the first pin 8 is located in the middle position of the axial direction of the rear end tube 5, the second pin 18 is located in the middle position of the axial direction of the middle tube 3, and the third pin 23 is located in the middle position of the axial direction of the front end tube 1. The axes of the first pin 8, the second pin 18 and the third pin 23 are all perpendicular to the OX-OY plane.

[0030] In addition, when the first rack rod 11, the second rack rod 12 and the follower gear box 13 are arranged on the outside of the connecting limit rod 6, it is also necessary to ensure that the planes in which the first support 7, the second support 20 and the third support 21 contact the connecting limit rod 6, that is, the "contact surface" are in the same plane, and the "contact surface" is parallel to the OX-OY plane, and it is necessary to ensure that the "contact surfaces" in the two equal displacement mechanisms are symmetrical with each other based on the OX-OY plane.

[0031] The connection limit rod 6 is sleeved on the first pin 8, the second pin 18 and the third pin 23, or the first pin 8, the second pin 18 and the third pin 23 are all arranged through the connection limit rod 6. The connection limit rod 6 can rotate around the first pin 8, the second pin 18 and the third pin 23, that is, when the "expansion joint" occurs as Figure 5 In the compensation situation shown, the first pin 8, the second pin 18 and the third pin 23 can rotate relative to the connection limit rod 6 to ensure that the compensation action of the "expansion joint" is not hindered. Further, in order to ensure smooth relative rotation between the connection limit rod 6 and the second pin 18, a bearing can be optionally provided between the connection limit rod 6 and the second pin 18.

[0032] Both ends of the connection limit rod 6 are provided with strip holes 61, and the first pin shaft 8 and the third pin shaft 23 extend into the two strip holes 61 respectively, and the first pin shaft 8 and the third pin shaft 23 can slide along the corresponding strip holes 61, that is, the first pin shaft 8 and the third pin shaft 23 can not only rotate relative to the connection limit rod 6, but also slide along the strip holes 61. Further, the first pin shaft 8 and the side wall of the corresponding strip hole 61 are in contact and sliding fit, and the third pin shaft 23 and the side wall of the corresponding strip hole 61 are also in contact and sliding fit, so as to maintain the transmission accuracy.

[0033] The follower gearbox 13 is connected to the second pin shaft 18 and can rotate around the second pin shaft 18, or the follower gearbox 13 can rotate with the second pin shaft 18 as the axis. In order to facilitate the rotation of the follower gearbox 13, a bearing can be selected to be provided at the position where the follower gearbox 13 is connected to the second pin shaft 18. It can also be further understood that the follower gearbox 13 can rotate relative to the second support 20, that is, the follower gearbox 13 is installed on the second support 20 through the second pin shaft 18, so that the follower gearbox 13 can rotate relative to the second support 20. Similarly, the connection limit rod 6 is also connected to the second support 20 through the second pin shaft 18, so that the connection limit rod 6 can also rotate relative to the second support 20.

[0034] Further, see Figure 3The follower gear box 13 includes a box body 131 and a gear 17 arranged at the center of the box body 131. Specifically, a gear shaft 14 is connected to the box body 131, and the gear 17 is arranged on the gear shaft 14. The gear 17 can be positioned by the gear shaft 14, the positioning sleeve 15, the gear shaft positioning nut 16, etc. The specific installation method is the existing technology and is for reference only and will not be repeated here. The gear 17 can rotate around the gear shaft 14, and the gear shaft 14 is parallel to the OX-OY plane and perpendicular to the OX-OZ plane. The box body 131, the gear 17, etc. are all symmetrical structures based on the OX-OZ plane, that is, taking the gear 17 as an example: refer to Figure 3 , Figure 3 The surface perpendicular to the OZ axis is the OX-OZ surface. Figure 3 The gear 17 is a symmetrical structure based on the OX-OZ plane.

[0035] One end of the first rack rod 11 is connected to the first pin 8 and can rotate around the first pin 8, that is, one end of the first rack rod 11 is connected to the first support 7 through the first pin 8, etc., and is positioned by the first sleeve 10, so that the first rack rod 11 is kept parallel to the OX-OY plane and is ensured to be parallel to the connecting limit rod 6, and the other end of the first rack rod 11 is provided with a rack portion. For the sake of convenience, the rack portion is referred to as the "first rack portion", which extends into the meshing gear 17 in the box body 131, and the "first rack portion" slides with the inner wall of the box body 131.

[0036] One end of the second rack rod 12 is connected to the third pin shaft 23 and can rotate around the third pin shaft 23, that is, one end of the second rack rod 12 is connected to the third support 21 through the third pin shaft 23. The other end of the second rack rod 12 is also provided with a rack portion, which is referred to as a "second rack portion" for ease of description. The "second rack portion" also extends into the box body 131 to engage with the gear 17, and the "second rack portion" is slidably matched with the inner wall of the box body 131.

[0037] The first rack bar 11 and the second rack bar 12 are respectively arranged on the inner and outer sides of the gear 17. The "inner and outer" mentioned here refers to the inner and outer sides of the gear 17. Figure 1 and Figure 3 For reference, the side close to the "expansion joint" is the inner side, and the side away from the "expansion joint" is the outer side. In this embodiment, the first rack bar 11 is located on the inner side of the gear 17, and the second rack bar 12 is located on the outer side of the gear 17.

[0038] Furthermore, in this embodiment, the positional relationship between the first rack rod 11, the second rack rod 12, the follower gear box 13 and the connection limit rod 6 can be selected as follows: Option 1: The first rack rod 11, the second rack rod 12 and the follower gear box 13 are arranged on the outside of the connection limit rod 6. The "outside" mentioned here refers to Figure 1 For reference, the connection limit rod 6 is used as a reference, the side close to the "expansion joint" is the inner side, and the side away from the "expansion joint" is the outer side. This method can make the connection limit rod 6 closer to the "expansion joint", further ensuring the stability and rigidity of the entire "expansion joint" and the entire equal displacement mechanism, and further ensuring the transmission accuracy of the equal displacement mechanism.

[0039] Furthermore, the third pin shaft 23 is sleeved with a third shaft sleeve 22, which is arranged between the connection limit rod 6 and the second rack rod 12, and is used to limit one end of the connection limit rod 6, and at the same time, the second rack rod 12 and the connection limit rod 6 can be parallel to the OX-OY plane. The first pin shaft 8 is sleeved with a first shaft sleeve 10, which is arranged between the connection limit rod 6 and the first rack rod 11, and is used to limit the other end of the connection limit rod 6, and can ensure that the first rack rod 11, the OX-OY plane and the connection limit rod 6 are parallel. On the second pin shaft 18, the connection limit rod 6 is limited by the box body 131 of the follower gear box 13, that is, referring to Figure 3 As shown, the housing 131 of the gear box 13 abuts against the connecting limit rod 6. The entire connecting limit rod 6 is positioned by the first sleeve 10, the follower gear box 13 and the third sleeve 22, so that the connecting limit rod 6 can slide along the plane parallel to the OX-OY plane. Figure 8 , the diameters L of the third sleeve 22 and the first sleeve 10 are both greater than the width H of the strip hole 61 .

[0040] Option 2: You can also choose to set the first rack rod 11, the second rack rod 12 and the follower gear box 13 on the inner side of the connecting limit rod 6, that is, refer to Figure 6As shown, at this time, the first rack rod 11, the second rack rod 12, the follower gear box 13, etc. are all arranged between the connection limit rod 6 and the "expansion joint". The third pin shaft 23 is sleeved with a third shaft sleeve 22, and the third shaft sleeve 22 is arranged between the connection limit rod 6 and the second rack rod 12. The outer side of the connection limit rod 6 is provided with a first limit cap 221, and the first limit cap 221 is connected to the third pin shaft 23. The first limit cap 221 and the third shaft sleeve 22 limit the connection limit rod 6, and the diameters of the first limit cap 221 and the third shaft sleeve 22 are both larger than the width H of the strip hole 61. The first pin shaft 8 is sleeved with a first sleeve 10, which is arranged between the connection limit rod 6 and the first rack rod 11. The first pin shaft 8 is connected to the second limit cap 101, which is also arranged outside the connection limit rod 6. The second limit cap 101 and the first sleeve 10 limit the connection limit rod 6, and the diameters of the second limit cap 101 and the first sleeve 10 are greater than the width H of the strip hole 61. At the same time, the connection limit rod 6 is connected to the follower gear box 13 through the support column 25, and the connection limit rod 6 is fixedly connected to the support column 25, and the support column 25 is fixedly connected to the follower gear box 13. At this time, it is equivalent to that the connection limit rod 6 is indirectly connected to the second pin shaft 18 through the support column 25 and the follower gear box 13, and the connection limit rod 6 and the follower gear box 13 can rotate synchronously around the second pin shaft 18, or can rotate with the second pin shaft 18 as the axis. In this method, a transition sleeve 30 can be optionally provided between the first rack rod 11 and the first support 7. Of course, the first rack rod 11 can also be directly in contact with the first support 7. In short, no matter which case is adopted, it is necessary to ensure that the first rack rod 11 is parallel to the OX-OY plane.

[0041] Of course, the above-mentioned “Option 1” and “Option 2” are not exhaustive, and do not exclude the use of other structures that are the same as the concept of the present invention and can achieve the purpose of the present invention.

[0042] Further, see Figure 4 and Fig. 9For the above-mentioned "option one" method, the third support 21 can be set as a double-layer door-shaped structure, that is, including an "inner door-shaped structure" and an "outer door-shaped structure". The inner door-shaped structure includes an inner vertical plate 26 and an inner horizontal plate 27. The inner horizontal plate 27 is connected to the outer ends of the two inner vertical plates 26. The "outer end" mentioned here is the end away from the front end tube 1. The inner end of the inner vertical plate 26 is installed on the outer wall of the front end tube 1. The outer door-shaped structure includes two outer vertical plates 28 and an outer horizontal plate 29. The outer horizontal plate 29 is installed at the outer ends of the two outer vertical plates 28, that is, the end away from the front end tube 1, and the inner end of the outer vertical plate 28 is installed on the inner horizontal plate 27. The surface of the outer vertical plate 28 is parallel to the surface of the inner vertical plate 26. Preferably, when the "expansion joint" is in a normal state, the surface of the outer vertical plate 28 is parallel to the connection limit rod 6. At this time, the third sleeve 22 and the connection limit rod 6 are both located between the inner transverse plate 27 and the outer transverse plate 29, the connection limit rod 6 is located between the third sleeve 22 and the inner transverse plate 27, and the two ends of the third sleeve 22 abut against the outer transverse plate 29 and the connection limit rod 6 respectively. The second rack rod 12 is located on the outside of the outer transverse plate 29 and is supported by the outer transverse plate 29 so that it remains parallel to the connection limit rod 6, the first rack rod 11 and the OX-OY plane. The spacing between the two outer vertical plates 28 in the same third support 21 should preferably meet the requirement of "not hindering the connection limit rod 6 from rotating around the third pin 23". The use of a double-layer door-shaped structure as a double-layer positioning mode can improve the rigidity and positioning accuracy of the third support 21.

[0043] In addition, for the above-mentioned “Option 1”, the first support 7 and the second support 20 can adopt the same structure as the above-mentioned “inner door-shaped structure”, which will not be repeated here.

[0044] In addition, for the above-mentioned "option 2", the first support 7 can also adopt a double-layer door-shaped structure, referring to Figure 7 and Fig.10The first support 7 includes a first door-shaped structure and a second door-shaped structure. The first door-shaped structure includes a first vertical plate 701 and a first horizontal plate 702. The first horizontal plate 702 is connected to the outer ends of the two first vertical plates 701, that is, the end away from the rear end tube 5, and the inner ends of the two first vertical plates 701 are installed on the outer wall of the rear end tube 5. The second door-shaped structure includes two second vertical plates 703 and a second horizontal plate 704. The second horizontal plate 704 is installed at the outer ends of the two second vertical plates 703, that is, the end away from the rear end tube 5. The second horizontal plate 704 is used to support and connect the limit rod 6. The inner end of the second vertical plate 703 is installed on the first horizontal plate 702. Preferably, the surface where the second vertical plate 703 is located is parallel to the surface where the first vertical plate 701 is located. The first rack rod 11 and the first sleeve 10 are both arranged between the first transverse plate 702 and the second transverse plate 704. The first rack rod 11 is arranged between the first sleeve 10 and the first transverse plate 702, and the two ends of the first sleeve 10 abut the second transverse plate 704 and the first rack rod 11. Furthermore, in this form, a transition sleeve 30 can be optionally arranged between the first rack rod 11 and the first transverse plate 702, or the first rack rod 11 can be directly made to contact the first transverse plate 702, as long as the first rack rod 11 is parallel to the OX-OY plane. At this time, the spacing between the two second vertical plates 703 in the same first support 7 should preferably satisfy the requirement of "not hindering the first rack rod 11 from rotating around the first pin 8". In this way, the third support 21 can only adopt the same structure as the above-mentioned "inner door-shaped structure", that is, referring to Figure 7 As shown, at this time, the second rack rod 12 contacts the third support 21, and a third sleeve 22 is arranged between the second rack rod 12 and the connection limit rod 6, which will not be described in detail here.

[0045] The front and rear ends of the first bellows 2 of the present invention can be connected to the front end tube 1 and the middle tube 3 by welding, and the front and rear ends of the second bellows 4 can be connected to the middle tube 3 and the rear end tube 5 by welding. However, other connection forms that conform to the principles of the present invention should also be within the scope of protection. The tooth profiles of the gear 17, the first rack portion, and the second rack portion are not limited to involute tooth profiles, and components such as gear shafts and bearings are also exemplary examples.

[0046] The working principle of the present invention is as follows Figure 1 As shown, when the bellows pressure thrust is borne by the main fixed pipe support of the pipeline or the equipment connected to it, refer to Figure 2 The axial compensation of the "expansion joint" of the present invention is limited to the ±X axis direction, and the lateral compensation is limited to the ±Y axis direction.

[0047] The invention solves the disadvantages of common proportional connecting rod type compound expansion joints, such as multiple movable parts and poor precision, and can realize accurate equal distribution of displacement.

[0048] Embodiment 2: The present invention also provides a pipeline system, which includes the aforementioned "expansion joint". The pipeline system has the beneficial effects brought by the aforementioned "expansion joint".

[0049] Further explanation: See below Figure 1 — Fig.10 , the structure, principle, use process, etc. of the present invention are further sorted out in the form of examples. This description is only to combine the above-mentioned multiple preferred methods in an illustrative manner to facilitate a comprehensive description, but this description is not a limitation on the implementation methods of the present application. The description is as follows: The connection limit rod 6 is arranged in the form of the above-mentioned "option 1", that is, Figure 1 The form shown in .

[0050] Axial limit: like Figure 1 , Figure 2 As shown in FIG. 1 , when the "expansion joint" is in a normal state, the connecting limit rod 6 is in a neutral position. At this time, the first bellows 2 and the second bellows 4 are neither compressed nor stretched, and the first pin 8 and the third pin 23 are located in the middle of the long circular holes at both ends of the connecting limit rod 6, that is, the strip hole 61. When the first bellows 2 and the second bellows 4 are in an axially compressed state, the first pin 8 and the third pin 23 gradually move toward the inner edge of the strip hole 61, that is, refer to FIG. Figure 1 and Figure 8 , the first pin 8 moves to the left end of the corresponding strip hole 61, and the third pin 23 moves to the right end of the corresponding strip hole 61, and finally reaches the maximum limit position, that is, refer to Figure 8 , and stops at the arc end of the inner edge of the strip hole 61, realizing the limit of the maximum compression position. When the first bellows 2 and the second bellows 4 are in the axially stretched state, refer to Figure 1 and Figure 8 As shown, the first pin 8 moves to the right end of the corresponding strip hole 61, and the third pin 23 moves to the left end of the corresponding strip hole 61, and finally reaches the maximum limit position of the connection limit rod 6. Similarly, the maximum tensile displacement limit can be achieved.

[0051] In order to ensure that the first rack rod 11 and the second rack rod 12 can maintain a meshing state with the gear 17 when they move to the limit position of the connection limit rod 6, the first rack portion of the first rack rod 11 and the second rack portion of the second rack rod 12 must be reserved with sufficient length. For example, when the first rack rod 11 and the second rack rod 12 move to the limit position of the connection limit rod 6, the first rack portion of the first rack rod 11 and the second rack portion of the second rack rod 12 can reserve a distance of more than 20 mm. Figure 1To be specific: when the "expansion joint" is stretched to the limit position, the first rack portion of the first rack rod 11 extends 20 mm to the left from the position meshing with the gear 17, leaving enough space to prevent the first rack rod 11 from being disengaged from the gear 17, and at this time, the second rack portion of the second rack rod 12 extends 20 mm to the right from the position meshing with the gear 17. Similarly, when the "expansion joint" is compressed to the limit position, the first rack portion of the first rack rod 11 extends 20 mm to the right from the position meshing with the gear 17, and at this time, the second rack portion of the second rack rod 12 extends 20 mm to the left from the position meshing with the gear 17. Of course, the 20 mm mentioned here is only an optional number and is not a limitation of the present invention. The specific reserved length can be set as needed.

[0052] The equivalent axial displacement is described as follows: When the intermediate pipe 3 does not move: When the "expansion joint" performs displacement compensation, if the middle tube 3 does not move, the first pin shaft 8 and the third pin shaft 23 move in the strip hole 61, and the first pin shaft 8 and the third pin shaft 23 move toward each other or away from each other. Specifically, the first support 7 fixed on the rear end tube 5 drives the first rack rod 11 to move through the first pin shaft 8. Since the first rack portion of the first rack rod 11 is in meshing state with the gear 17, it will cause the gear 17 to rotate. At the same time, the third support 21 fixed on the front end tube 1 drives the second rack rod 12 to move through the third pin shaft 23. Since the second rack portion of the second rack rod 12 is in meshing state with the gear 17, it will also cause the gear 17 to rotate synchronously. That is, at this time, the first rack rod 11 and the second rack rod 12 The synchronous meshing gear 17 rotates, and the front end tube 1 and the rear end tube 5 move relative to the middle tube 3 at the same time. Since the first rack portion of the first rack bar 11, the second rack portion of the second rack bar 12 and the gear 17 have the same module, the moving distance of the first rack bar 11 is necessarily equal to the moving distance of the second rack bar 12, and the moving directions are opposite, that is, if the gear 17 is used as a reference, the moving distances of the first rack bar 11 and the second rack bar 12 are equal and opposite, therefore, the expansion or extension distances of the second bellows 4 corresponding to the first rack bar 11 and the first bellows 2 corresponding to the second rack bar 12 are also equal, thereby realizing that the compensation amount of the two bellows of the "expansion joint" is evenly divided, both of which are 1 / 2 of the total compensation amount, thereby achieving the purpose of equal compensation.

[0053] When the front end tube 1 does not move: The first support 7 on the rear end tube 5 drives the first rack rod 11 to move through the first pin shaft 8. At the same time, the first pin shaft 8 moves in the strip hole 61. Since the first rack portion of the first rack rod 11 is in meshing state with the gear 17, the gear 17 will inevitably rotate. After the gear 17 rotates, a relative movement between the second rack rod 12 will be formed. That is, when the front end tube 1 is stationary, the gear 17 will roll on the stationary second rack rod 12, driving the middle tube 3 and the moving rear end tube 5 to move in the same direction. That is to say, at this time, the middle tube 3 will also move relative to the front end tube 1. According to the principle of relativity of motion, it is also equivalent to the movement of the front end tube 1 relative to the middle tube 3 by an equal distance. At the same time, due to the first rack The rod 11 also meshes with the gear 17 to rotate, and the rear end tube 5 moves relative to the front end tube 1 and the middle tube 3 at the same time. That is to say, at this time, it is equivalent to that both the front end tube 1 and the rear end tube 5 move relative to the middle tube 3. Since the first rack portion of the first rack rod 11, the second rack portion of the second rack rod 12 and the gear 17 have the same module, it is inevitable that the distance moved by the first rack rod 11 relative to the middle tube 3 is equal to the distance moved by the second rack rod 12 relative to the middle tube 3, or in other words, the distance moved by the rear end tube 5 relative to the middle tube 3 (the distance the second bellows 4 is compressed or stretched) is equal to the distance the middle tube 3 moves relative to the front end tube 1 (the distance the first bellows 2 is stretched or stretched). Therefore, the distances of the second bellows 4 corresponding to the first rack rod 11 and the first bellows 2 corresponding to the second rack rod 12 are equal, so that the compensation amount of the two bellows of the "expansion joint" is evenly divided, and both are 1 / 2 of the total compensation amount, thereby achieving the purpose of equal compensation.

[0054] When the rear end pipe 5 does not move: The third support 21 on the front end tube 1 drives the second rack rod 12 to move through the third pin shaft 23. At the same time, the third pin shaft 23 moves in the strip hole 61. Since the second rack portion of the second rack rod 12 is in meshing state with the gear 17, the gear 17 will inevitably rotate. After the gear 17 rotates, a relative movement between the gear 17 and the first rack rod 11 will be formed. That is, when the rear end tube 5 is stationary, the gear 17 will roll on the stationary first rack rod 11, driving the middle tube 3 and the moving front end tube 1 to move in the same direction. That is to say, at this time, the middle tube 3 will also move relative to the rear end tube 5. According to the principle of relativity of motion, it is also equivalent to the movement of the rear end tube 5 relative to the middle tube 3 by an equal distance. At the same time, due to the second gear The bar 12 also meshes with the gear 17 to rotate, and the front end tube 1 moves relative to the rear end tube 5 and the middle tube 3 at the same time. That is to say, at this time, it is equivalent to that both the front end tube 1 and the rear end tube 5 move relative to the middle tube 3. Since the first rack portion of the first rack bar 11, the second rack portion of the second rack bar 12 and the gear 17 have the same module, it is inevitable that the distance moved by the first rack bar 11 relative to the middle tube 3 is equal to the distance moved by the second rack bar 12 relative to the middle tube 3, or in other words, the distance moved by the front end tube 1 relative to the middle tube 3 (the distance the first bellows 2 is stretched or stretched) is equal to the distance moved by the middle tube 3 relative to the rear end tube 5 (the distance the second bellows 4 is stretched or stretched). Therefore, the distance the first bellows 2 is stretched or stretched corresponding to the second rack bar 12 is equal to the distance the second bellows 4 is stretched or stretched corresponding to the first rack bar 11, thereby realizing that the compensation amount of the two bellows of the "expansion joint" is evenly divided, and both are 1 / 2 of the total compensation amount, thereby achieving the purpose of equal compensation.

[0055] The lateral equivalent displacement is described as follows: When the "expansion joint" performs lateral equal displacement compensation, see Figure 5 . For example, the rear end tube 5 is displaced a distance d along the Y-axis direction. At this time, the first support 7 fixed on the rear end tube 5 drives the connecting limit rod 6 to move through the first pin 8. Since the connecting limit rod 6 is respectively connected to the first pin 8 on the first support 7, the second pin 18 on the second support 20 and the third pin 23 on the third support 21, the rear end tube 5, the middle tube 3 and the front end tube 1 drive the second bellows 4 and the first bellows 2 to deform in a coordinated manner. Since the follower gear box 13 can rotate relative to the second support 20, the rotation angles of the first rack rod 11 and the second rack rod 12 are guaranteed to be consistent with the rotation angle of the connecting limit rod 6. The axial spacing between the first pin 8 and the second pin 18 is equal to the axial spacing between the second pin 18 and the third pin 23, that is, refer to Figure 5 Therefore, through plane geometry and trigonometric functions, it can be proved that the distance between the two oblique lines corresponding to the two a is Figure 5The distances between the two b in the figure are also equal, and the value of the diagonal line of each b is equal to , whose increment relative to a is , and the increments of the two b are equal. The two bellows of the "expansion joint", namely the first bellows 2 and the second bellows 4, are stretched according to the above increments to achieve the purpose of equal compensation. Figure 5 , the first bellows 2 and the second bellows 4 are non-uniformly deformed, but the first bellows 2 and the second bellows 4 are correspondingly deformed along the axis of the connecting limit rod 6, that is, Figure 5 For reference, when the upper side of the first bellows 2 is compressed, the lower side of the second bellows 4 undergoes the same deformation, and when the lower side of the first bellows 2 is stretched, the upper side of the second bellows 4 undergoes the same deformation.

[0056] In summary, the present invention solves the disadvantages of the common proportional connecting rod type compound expansion joint, such as many moving parts and poor precision. It has a unique high-precision transmission advantage, which can achieve accurate equal displacement distribution. This allows the two bellows to completely achieve equal displacement. In addition, the present invention has fewer main transmission parts, a compact structure, high rigidity, and good manufacturing processability.

[0057] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0058] In the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection", "fixing" and the like should be understood in a broad sense. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0059] In the description of this specification, the description of the terms "embodiment", "further description", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0060] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An equal displacement unconstrained compound expansion joint, comprising a front end pipe (1), an intermediate pipe (3) and a rear end pipe (5); the two ends of the intermediate pipe (3) are connected to the front end pipe (1) and the rear end pipe (5) through a bellows to form an unconstrained compound expansion joint, characterized in that: It also includes two equal displacement mechanisms; the two equal displacement mechanisms are symmetrically arranged on both sides of the outer wall of the unconstrained compound expansion joint; The equal displacement mechanism comprises a connecting limit rod (6) and a transmission assembly located on one side of the connecting limit rod (6), wherein the connecting limit rod (6) and the transmission assembly are both parallel to the axial direction of the unconstrained compound expansion joint; The connection limit rod (6) and the transmission assembly are mounted on the front end tube (1), the middle tube (3) and the rear end tube (5) via a pin assembly.

2. An equal displacement unconstrained compound expansion joint as claimed in claim 1, characterized in that: The transmission assembly comprises a first rack rod (11), a second rack rod (12) and a follower gear box (13); The rear end tube (5), the middle tube (3) and the front end tube (1) are respectively provided with a first pin shaft (8), a second pin shaft (18) and a third pin shaft (23); the pin shaft assembly is composed of the first pin shaft (8), the second pin shaft (18) and the third pin shaft (23); the axial distance between the first pin shaft (8) and the second pin shaft (18) is equal to the axial distance between the second pin shaft (18) and the third pin shaft (23); the connecting limit rod (6) connects the first pin shaft (8), the second pin shaft (18) and the third pin shaft (23) and can rotate around the first pin shaft (8), the second pin shaft (18) and the third pin shaft (23); both ends of the connecting limit rod (6) are provided with strip holes (61) for the first pin shaft (8) and the third pin shaft (23) to move; The follower gear box (13) is connected to the second pin shaft (18) and is capable of rotating around the second pin shaft; One end of the first rack rod (11) is connected to a first pin shaft (8) and is rotatable about the first pin shaft (8), and the other end of the first rack rod (11) is meshed with a gear (17) in a follower gear box (13) through a first rack portion; one end of the second rack rod (12) is connected to a third pin shaft (23) and is rotatable about the third pin shaft (23), and the other end of the second rack rod (12) is meshed with a gear (17) in a follower gear box (13) through a second rack portion.

3. The equal displacement unconstrained compound expansion joint according to claim 1, characterized in that: The follower gear box (13) comprises a box body (131) and a gear (17) arranged in the box body (131); The first rack portion of the first rack rod (11) and the second rack portion of the second rack rod (12) both extend into the box body (131) to mesh with the gear (17), and the first rack portion and the second rack portion both slide in cooperation with the inner side wall of the box body (131).

4. An equal displacement unconstrained compound expansion joint as claimed in claim 2, characterized in that: The rear end tube (5), the middle tube (3) and the front end tube (1) are respectively provided with a first support (7), a second support (20) and a third support (21), which are respectively used to mount the first pin shaft (8), the second pin shaft (18) and the third pin shaft (23).

5. An equal displacement unconstrained compound expansion joint as claimed in claim 4, characterized in that: The first rack rod (11), the second rack rod (12) and the follower gear box (13) are all arranged outside the connection limit rod (6).

6. An equal displacement unconstrained compound expansion joint as claimed in claim 5, characterized in that: A third shaft sleeve (22) is sleeved on the third pin shaft (23), and the third shaft sleeve (22) is arranged between the connection limit rod (6) and the second rack rod (12); a first shaft sleeve (10) is sleeved on the first pin shaft (8), and the first shaft sleeve (10) is arranged between the connection limit rod (6) and the first rack rod (11).

7. An equal displacement unconstrained compound expansion joint as claimed in claim 6, characterized in that: The third support (21) is a double-layer door-shaped structure, which includes an inner door-shaped structure and an outer door-shaped structure; the inner door-shaped structure includes an inner vertical plate (26) and an inner horizontal plate (27), the inner horizontal plate (27) is connected to the outer ends of the two inner vertical plates (26), and the inner ends of the inner vertical plates (26) are mounted on the outer wall of the front end tube (1); the outer door-shaped structure includes two outer vertical plates (28) and an outer horizontal plate (29), the outer horizontal plate (29) is mounted on the outer ends of the two outer vertical plates (28), and the inner ends of the outer vertical plates (28) are mounted on the inner horizontal plate (27); the third shaft sleeve (22) and the connecting limit rod (6) are both located between the inner horizontal plate (27) and the outer horizontal plate (29), and the two ends of the third shaft sleeve (22) are respectively abutted against the outer horizontal plate (29) and the connecting limit rod (6); the second rack rod (12) is located at the outer end of the outer horizontal plate (29) and is supported by the outer horizontal plate (29).

8. An equal displacement unconstrained compound expansion joint as claimed in claim 4, characterized in that: The first rack rod (11), the second rack rod (12) and the follower gear box (13) are all arranged on the inner side of the connection limit rod (6).

9. An equal displacement unconstrained compound expansion joint as claimed in claim 8, characterized in that: The first support (7) is a double-layer door-shaped structure, which includes a first door-shaped structure and a second door-shaped structure; the first door-shaped structure includes a first vertical plate (701) and a first horizontal plate (702), the first horizontal plate (702) is connected to the outer ends of the two first vertical plates (701), and the inner ends of the two first vertical plates (701) are installed on the outer wall of the rear end tube (5); the outer door-shaped structure includes two second vertical plates (703) and a second horizontal plate (704), and the second horizontal plate (704) The first shaft sleeve (10) is mounted on the outer ends of the two second vertical plates (703) and is used to support the connection limit rod (6). The inner end of the second vertical plate (703) is mounted on the first horizontal plate (702). The first pin shaft (8) is sleeved with a first shaft sleeve (10). The first rack rod (11) and the first shaft sleeve (10) are both arranged between the first horizontal plate (702) and the second horizontal plate (704). The two ends of the first shaft sleeve (10) are respectively in contact with the first rack rod (11) and the second horizontal plate (704).

10. A piping system, characterized in that: The piping system comprises an equal displacement unconstrained compound expansion joint as described in any one of claims 1-9.

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