A high-efficiency mechanical pressing device for new energy battery packaging

Abstract

The present invention belongs to the field of battery manufacturing technology, and discloses a high-efficiency mechanical pressing device for new energy battery packaging, including a supporting component; a horizontal positioning component; a longitudinal positioning component; a moving component; a driving component and a pressing component. Through the Z-shaped pressing component, the four third hydraulic rods increase the stroke at the same time, the Z-shaped plate moves vertically downward, and the top shell and the bottom shell are pressed in the vertical direction. After being lifted and downward again, the stroke of the two third hydraulic rods on the right side is longer than that on the left side, so that the Z-shaped plate can press the top cover in a left-slanting manner. The right-slanting pressing is the opposite operation. During the pressing process, the Z-shaped plate rotates around the axis of the two second rotating shafts and the third rotating shaft, and compresses the multiple third springs therein, which solves the problem that the existing pressing device only uses a single top-down longitudinal pressing method for one-time pressing, which may cause the corresponding edge pressing gaps between the top cover and the bottom shell to be inconsistent.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery manufacturing, and in particular relates to a high-efficiency mechanical pressing device for packaging new energy batteries. Background Art

[0002] New energy battery packaging is a crucial step in the power battery manufacturing process, directly affecting battery performance, safety, lifespan, and cost. Prismatic batteries are widely used by domestic automakers due to their customizable size, compact arrangement, higher energy density than cylindrical batteries, simpler production process, thinner size, and better heat dissipation. The packaging process involves not only physical protection but also multiple factors such as electrical connection, thermal management, and mechanical stability.

[0003] The battery pack mainly covers battery cells, shell structural parts and management system, among which the shell structural parts play the role of placement and protection. Generally, the upper and lower covers are adopted. After the battery cells and other circuit boards in the bottom shell are placed, the upper cover is locked with bolts. However, in the actual production process, there are production tolerances between the upper cover and the bottom shell. Generally, they need to be mechanically pressed before they can be bolted. However, the existing pressing device only uses a single top-down longitudinal pressing method for one-time pressing, which may cause the corresponding edge pressing gaps between the upper cover and the bottom shell to be inconsistent, resulting in inconsistent stress of the bolts in the next bolt locking process, thereby causing deformation of the upper cover. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-efficiency mechanical pressing device for new energy battery packaging to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned object, the present invention provides the following technical solution: an efficient mechanical pressing device for new energy battery packaging, comprising a supporting assembly, wherein both the front and rear sides of the supporting assembly are fixedly mounted with lateral positioning assemblies, and further comprising a linkage pressing structure, which comprises two longitudinal positioning assemblies, wherein both the longitudinal positioning assemblies are fixedly mounted on the left and right sides of the supporting assembly, and a moving assembly is fixedly mounted on the inner sides of the two longitudinal positioning assemblies, and the inner movable card of the moving assembly is connected to the driving assembly;

[0006] A pressing assembly, wherein the pressing assembly is movably hinged at the bottom of the driving assembly, and the pressing assembly includes a Z-shaped plate, which can be divided into three parts: a top plate, an inclined plate and a bottom plate from top to bottom, and the connecting parts are all hinged. Two groups of U-shaped rods are fixedly installed on the top of the Z-shaped plate, and the upper left side of the Z-shaped plate is movably hinged with a second rotating shaft, and the lower right side of the Z-shaped plate is movably hinged with a third rotating shaft. The upper and lower sides of the inclined plate of the Z-shaped plate are elastically connected to multiple third springs, and a rotating balance is rotatably installed in the middle position of the inclined plate of the Z-shaped plate.

[0007] Preferably, the top end of the third spring on the left side is elastically connected to the top plate of the Z-shaped plate, and the top end of the third spring on the right side is elastically connected to the bottom plate of the Z-shaped plate.

[0008] Preferably, the supporting assembly includes a base, and a plurality of rollers are rotatably installed in the middle position of the base, the front rotating ends of the plurality of rollers are fixedly connected to pulleys, the outer edges of the plurality of pulleys are movably sleeved with belts, the rotating shaft of the pulley on the right side is fixedly connected to a motor, and the bottom of the motor is fixedly connected to the base.

[0009] Preferably, the two lateral positioning assemblies include a fixed plate, which is fixedly mounted on the front and rear sides of the base, and two first hydraulic rods are fixedly mounted on the top of the fixed plate, and the telescopic ends of the two first hydraulic rods are fixedly connected to a Y-shaped rod, and the front ends of the two Y-shaped rods are rotatably mounted with two rubber wheels.

[0010] Preferably, the two longitudinal positioning assemblies include two groups of support seats, and the two groups of support seats are respectively fixedly installed on the left and right sides of the base, and a second hydraulic rod is obliquely installed on the top of the support seat, and the telescopic end of the second hydraulic rod is fixedly connected to the trapezoidal block, and a first rotating shaft is rotatably installed on the right side of the middle part of the trapezoidal block, the outer edge of the first rotating shaft is elastically connected to a first spring, and the other end of the first spring is fixedly connected to a fixed shaft, and the fixed shaft is fixedly installed on the top of the support seat.

[0011] Preferably, the moving assembly includes four longitudinal rods, which are fixedly mounted on the top of the base, and two screw rods are fixedly mounted on the top of the four longitudinal rods. The outer edges of the two screw rods are threadedly connected to the stepper motors, and the outer edges of the two stepper motors are fixedly mounted with rectangular frames, and the inner sides of the two long sides of the rectangular frame are provided with tracks.

[0012] Preferably, the driving assembly includes four electric wheels, and the four electric wheels are movably clamped in the two tracks. The central axes of the four electric wheels are fixedly connected with L-shaped blocks, and the bottoms of the four L-shaped blocks are fixedly connected with a third hydraulic rod. The outer edges of the telescopic ends of the four third hydraulic rods are movably sleeved with a second spring, and the telescopic ends of the four third hydraulic rods are movably hinged to the four U-shaped rods.

[0013] The beneficial effects of the present invention are as follows:

[0014] 1. The present invention is equipped with a Z-shaped pressing assembly. The four third hydraulic rods increase their stroke at the same time. The Z-shaped plate moves vertically downward, and the top shell and the bottom shell are pressed in the vertical direction. After being lifted downward again, the stroke of the two third hydraulic rods on the right is longer than that on the left, so that the Z-shaped plate can press the top cover in a left-slanting manner. The right-slanting pressing is performed in the opposite direction. During the pressing process, the Z-shaped plate rotates around the two second rotating shafts and the axis where the third rotating shaft is located, rotates toward the position of the inclined plate between the bottom plate and the top plate, and compresses the multiple third springs therein, thereby solving the problem that the existing pressing device only uses a single top-down longitudinal pressing method for one-time pressing, which may cause inconsistent pressing gaps between the corresponding edges of the top cover and the bottom shell.

[0015] 2. The present invention is equipped with a newly designed longitudinal positioning assembly. When the roller drives the bottom shell to move to the middle position of the supporting assembly, the two longitudinal positioning assemblies are started, and the second hydraulic rod increases the stroke, obliquely pushing the trapezoidal blocks to the left and right sides of the bottom shell. During the movement of the trapezoidal blocks, the first rotating shaft will rotate and displace, pulling the first spring on the fixed shaft to complete the elastic deformation. When the four trapezoidal blocks complete the clamping of the bottom shell, the bottom shell is at the longitudinal center of the supporting assembly. The contact part of the trapezoidal blocks and the bottom shell will have a certain displacement clearance through the first spring to prevent the hydraulic pressure from damaging the bottom shell.

[0016] 3. The present invention is equipped with a displacement mechanism that cooperates with a moving component and a driving component. The stepping motor drives the rectangular frame to move longitudinally on the screw rod, moves the driving component and the pressing component to a position close to the battery bottom shell and the top cover, and then starts the four electric wheels. The four electric wheels move within the track and position the pressing component to the longitudinal position of the bottom shell again. Through the moving and positioning action of the moving component and the driving component, it is ensured that the pressing component is directly above the top shell, thereby improving the accuracy of the pressing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0018] Figure 2 This is a schematic diagram of the supporting assembly structure of the present invention;

[0019] Figure 3 For the present invention Figure 2 A schematic diagram of the structure at center A;

[0020] Figure 4 For the present invention Figure 2 A magnified schematic diagram of the structure at point B in the middle;

[0021] Figure 5 This is a schematic diagram of the structure of the mobile component of the present invention;

[0022] Figure 6 For the present invention Figure 5 A magnified schematic diagram of the structure at point C in the middle;

[0023] Figure 7 It is a schematic diagram of the structure of the press-fit assembly of the present invention.

[0024] In the figure: 1. Support assembly; 2. Horizontal positioning assembly; 3. Longitudinal positioning assembly; 4. Moving assembly; 5. Driving assembly; 6. Pressing assembly; 11. Base; 12. Roller; 13. Pulley; 14. Belt; 15. Motor; 21. Fixed plate; 22. First hydraulic rod; 23. Y-shaped rod; 24. Rubber wheel; 31. Support seat; 32. Second hydraulic rod; 33. Trapezoidal block; 34. First rotating shaft; 35. First spring; 36. Fixed shaft; 41. Longitudinal rod; 42. Screw rod; 43. Rectangular frame; 44. Stepping motor; 45. Track; 51. Electric wheel; 52. L-shaped block; 53. Third hydraulic rod; 54. Second spring; 61. Z-shaped plate; 62. U-shaped rod; 63. Second rotating shaft; 64. Third rotating shaft; 65. Third spring; 66. Rotary balancing. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] like Figures 1 to 7 As shown, an embodiment of the present invention provides an efficient mechanical pressing device for new energy battery packaging, comprising a supporting assembly 1, with lateral positioning assemblies 2 fixedly mounted on both the front and rear sides of the supporting assembly 1, and further comprising:

[0027] The linkage pressing structure includes two longitudinal positioning components 3, which are fixedly installed on the left and right sides of the supporting component 1. The inner sides of the two longitudinal positioning components 3 are fixedly installed with a moving component 4, and the inner movable card of the moving component 4 is connected to the driving component 5;

[0028] The pressing assembly 6 is movably hinged at the bottom of the driving assembly 5. The pressing assembly 6 includes a Z-shaped plate 61. The Z-shaped plate 61 can be divided into three parts: a top plate, an inclined plate and a bottom plate from top to bottom. The connecting parts are all hinged. Two sets of U-shaped rods 62 are fixedly installed on the top of the Z-shaped plate 61. The upper left side of the Z-shaped plate 61 is movably hinged with a second rotating shaft 63, and the lower right side of the Z-shaped plate 61 is movably hinged with a third rotating shaft 64. The upper and lower sides of the inclined plate of the Z-shaped plate 61 are elastically connected to multiple third springs 65. A rotating balance 66 is rotatably installed in the middle position of the inclined plate of the Z-shaped plate 61; the top end of the left third spring 65 is elastically connected to the top plate of the Z-shaped plate 61, and the top end of the right third spring 65 is elastically connected to the bottom plate of the Z-shaped plate 61;

[0029] The four third hydraulic rods 53 on the left and right increase their strokes at the same time, and the Z-shaped plate 61 hinged thereto will move vertically downward, pressing the top shell and the bottom shell together in the vertical direction. At this time, the four third hydraulic rods 53 shorten their strokes again to drive the Z-shaped plate 61 to lift once, and then move downward again. This time, the strokes of the two third hydraulic rods 53 on the right are longer than those on the left, so that the Z-shaped plate 61 can press the top cover in a left-slanting manner. The right-slanting pressing is done in the opposite way. During the pressing process, the Z-shaped plate 61 rotates around the axis of the two second rotating shafts 63 and the third rotating shaft 64, and rotates between the bottom plate and the top plate toward the inclined plate position, and compresses the multiple third springs 65 therein. When pressing left or right, a motor is installed in the rotary balancing 66, which automatically rotates to the opposite position of the pressing to complete the balancing, thereby solving the problem that the existing pressing device only uses a single top-down longitudinal pressing method for one-time pressing, which may cause the corresponding edge pressing gaps between the top cover and the bottom shell to be inconsistent.

[0030] The supporting assembly 1 includes a base 11, a plurality of rollers 12 are rotatably mounted in the middle of the base 11, the front rotating ends of the plurality of rollers 12 are fixedly connected to pulleys 13, the outer edges of the plurality of pulleys 13 are movably sleeved with belts 14, the rotating shaft of the right pulley 13 is fixedly connected to a motor 15, and the bottom of the motor 15 is fixedly connected to the base 11;

[0031] Start the motor 15, the motor 15 rotates clockwise, and drives the multiple motors 15 to rotate clockwise through the belt 14 and the pulley 13, so that the multiple rollers 12 can convey the battery bottom shell from left to right;

[0032] The two lateral positioning assemblies 2 include fixed plates 21, which are fixedly mounted on the front and rear sides of the base 11. Two first hydraulic rods 22 are fixedly mounted on the top of the fixed plates 21. The telescopic ends of the two first hydraulic rods 22 are fixedly connected to Y-shaped rods 23. The front ends of the two Y-shaped rods 23 are rotatably mounted with two rubber wheels 24.

[0033] During the transportation of the bottom shell, the front and rear lateral positioning assemblies 2 are activated, the first hydraulic rod 22 increases its stroke, and the four sets of rubber wheels 24 are driven by the Y-shaped rod 23 to approach the bottom shell, slowly positioning the bottom shell so that it can be in the lateral center of the supporting assembly 1;

[0034] Among them, the two longitudinal positioning components 3 include two groups of support seats 31, which are fixedly installed on the left and right sides of the base 11 respectively. A second hydraulic rod 32 is obliquely installed on the top of the support seat 31. The telescopic end of the second hydraulic rod 32 is fixedly connected to a trapezoidal block 33. A first rotating shaft 34 is rotatably installed on the right side of the middle part of the trapezoidal block 33. The outer edge of the first rotating shaft 34 is elastically connected to a first spring 35. The other end of the first spring 35 is fixedly connected to a fixed shaft 36, and the fixed shaft 36 is fixedly installed on the top of the support seat 31;

[0035] When the roller 12 drives the bottom shell to move to the middle position of the supporting assembly 1, the two longitudinal positioning assemblies 3 are activated, and the second hydraulic rod 32 increases its stroke, obliquely pushing the trapezoidal block 33 to the left and right sides of the bottom shell. During the movement of the trapezoidal block 33, the first rotating shaft 34 rotates and moves, pulling the first spring 35 on the fixed shaft 36 to complete elastic deformation, so that the contact part between the trapezoidal block 33 and the bottom shell will have a certain displacement clearance to prevent the hydraulic pressure from damaging the bottom shell. When the four trapezoidal blocks 33 complete the clamping of the bottom shell, the bottom shell is at the longitudinal center of the supporting assembly 1.

[0036] The moving assembly 4 includes four longitudinal rods 41, which are fixedly mounted on the top of the base 11. Two screw rods 42 are fixedly mounted on the top of the four longitudinal rods 41. The outer edges of the two screw rods 42 are threadedly connected to stepper motors 44. The outer edges of the two stepper motors 44 are fixedly mounted with rectangular frames 43. The inner sides of the two long sides of the rectangular frame 43 are each provided with a track 45.

[0037] The stepper motor 44 drives the rectangular frame 43 to move longitudinally on the screw rod 42, moving the driving assembly 5 and the pressing assembly 6 to a position close to the battery bottom shell and the top cover. Then, the four electric wheels 51 are started, and the four electric wheels 51 move within the track 45, positioning the pressing assembly 6 in the longitudinal position of the bottom shell again. Through the movement and positioning of the moving assembly 4 and the driving assembly 5, it is ensured that the pressing assembly 6 is directly above the top shell.

[0038] The drive assembly 5 includes four electric wheels 51, each of which is movably engaged in the two tracks 45. An L-shaped block 52 is fixedly connected to the central axis of each of the four electric wheels 51. The bottoms of each of the four L-shaped blocks 52 are fixedly connected to a third hydraulic rod 53. The outer edges of the telescopic ends of the four third hydraulic rods 53 are movably sleeved with a second spring 54. The telescopic ends of the four third hydraulic rods 53 are movably hinged to four U-shaped rods 62.

[0039] The four electric wheels 51 move in the track 45 and position the pressing assembly 6 to the longitudinal position of the bottom shell again. Through the moving and positioning action of the moving assembly 4 and the driving assembly 5, it is ensured that the pressing assembly 6 is directly above the top shell.

[0040] Working principle:

[0041] When using the present invention, first place the battery bottom shell and upper cover to be pressed together on the supporting assembly 1, start the motor 15, and the motor 15 rotates clockwise, driving the multiple motors 15 to rotate clockwise through the belt 14 and the pulley 13, so that the multiple rollers 12 can convey the battery bottom shell from left to right;

[0042] During the transportation of the bottom shell, the front and rear lateral positioning assemblies 2 are activated, the first hydraulic rod 22 increases its stroke, and the four sets of rubber wheels 24 are driven by the Y-shaped rod 23 to approach the bottom shell, slowly positioning the bottom shell so that it can be in the lateral center of the supporting assembly 1;

[0043] When the roller 12 drives the bottom shell to move to the middle position of the supporting assembly 1, the two longitudinal positioning assemblies 3 are activated, and the second hydraulic rod 32 increases its stroke, obliquely pushing the trapezoidal block 33 to the left and right sides of the bottom shell. During the movement of the trapezoidal block 33, the first rotating shaft 34 rotates and moves, pulling the first spring 35 on the fixed shaft 36 to complete elastic deformation, so that the contact part between the trapezoidal block 33 and the bottom shell will have a certain displacement clearance to prevent the hydraulic pressure from damaging the bottom shell. When the four trapezoidal blocks 33 complete the clamping of the bottom shell, the bottom shell is at the longitudinal center of the supporting assembly 1.

[0044] The battery shell is displaced to the exact center of the supporting assembly 1, and the moving assembly 4 is started. The stepping motor 44 drives the rectangular frame 43 to move longitudinally on the screw rod 42, and the driving assembly 5 and the pressing assembly 6 are moved to a position close to the battery bottom shell and the top cover. Then, the four electric wheels 51 are started. The four electric wheels 51 move within the track 45 and position the pressing assembly 6 again in the longitudinal position of the bottom shell. Through the movement and positioning of the moving assembly 4 and the driving assembly 5, it is ensured that the pressing assembly 6 is directly above the top shell;

[0045] At this time, the stroke of the four third hydraulic rods 53 on the left and right are increased at the same time, and the Z-type plate 61 hinged thereto will move vertically downward, pressing the top shell and the bottom shell in the vertical direction. At this time, the four third hydraulic rods 53 shorten their stroke again to drive the Z-type plate 61 to lift once, and then move downward again. This time, the stroke of the two third hydraulic rods 53 on the right is longer than that on the left, so that the Z-type plate 61 can press the top cover obliquely in a left-slanted manner, and the right-slanted pressing is the opposite operation. During the pressing process, the Z-type plate 61 rotates around the axis of the two second rotating shafts 63 and the third rotating shaft 64, rotates toward the oblique plate position between the bottom plate and the top plate, and compresses the multiple third springs 65 therein. When pressing left and right, a motor is installed in the rotary balancing 66, which automatically rotates to the opposite position of the pressing to complete the balancing, and the workflow ends here.

[0046] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0047] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high-efficiency mechanical pressing device for new energy battery packaging, comprising a supporting assembly (1), characterized in that: The supporting assembly (1) comprises a base (11), and lateral positioning assemblies (2) are fixedly mounted on both the front and rear sides of the supporting assembly (1), and further comprises: A linkage pressing structure, comprising two longitudinal positioning assemblies (3), the two longitudinal positioning assemblies (3) being fixedly mounted on the left and right sides of the supporting assembly (1), a moving assembly (4) being fixedly mounted on the inner sides of the two longitudinal positioning assemblies (3), and a driving assembly (5) being movably connected to the inner side of the moving assembly (4); A pressing assembly (6), wherein the pressing assembly (6) is movably hinged at the bottom of the driving assembly (5), and the pressing assembly (6) comprises a Z-shaped plate (61), wherein the Z-shaped plate (61) can be divided into three parts, namely, a top part, an inclined plate and a bottom plate from top to bottom, and the connecting parts thereof are all hinged, and two groups of U-shaped rods (62) are fixedly installed on the top of the Z-shaped plate (61), and the upper left side of the Z-shaped plate (61) is movably hinged with a second rotating shaft (63), and the lower right side of the Z-shaped plate (61) is movably hinged with a third rotating shaft (64), and the upper and lower sides of the inclined plate of the Z-shaped plate (61) are elastically connected to a plurality of third springs (65), and a rotating balance (66) is rotatably installed at the middle position of the inclined plate of the Z-shaped plate (61); The two longitudinal positioning assemblies (3) include two groups of support seats (31), which are fixedly mounted on the left and right sides of the base (11), respectively. A second hydraulic rod (32) is obliquely mounted on the top of the support seat (31), and the telescopic end of the second hydraulic rod (32) is fixedly connected to the trapezoidal block (33). A first rotating shaft (34) is rotatably mounted on the right side of the middle of the trapezoidal block (33). The outer edge of the first rotating shaft (34) is elastically connected to a first spring (35), and the other end of the first spring (35) is fixedly connected to a fixed shaft (36). The fixed shaft (36) is fixedly mounted on the top of the support seat (31).

2. The high-efficiency mechanical pressing device for new energy battery packaging according to claim 1 is characterized in that: The top end of the third spring (65) on the left side is elastically connected to the top plate of the Z-shaped plate (61), and the top end of the third spring (65) on the right side is elastically connected to the bottom plate of the Z-shaped plate (61).

3. The high-efficiency mechanical pressing device for new energy battery packaging according to claim 2 is characterized in that: A plurality of rollers (12) are rotatably mounted at the middle of the base (11), the front rotating ends of the plurality of rollers (12) are fixedly connected to pulleys (13), the outer edges of the plurality of pulleys (13) are movably sleeved with belts (14), the rotating shaft of the right pulley (13) is fixedly connected to a motor (15), and the bottom of the motor (15) is fixedly connected to the base (11).

4. The high-efficiency mechanical pressing device for new energy battery packaging according to claim 3 is characterized in that: The two lateral positioning assemblies (2) include fixed plates (21), the two fixed plates (21) are fixedly mounted on the front and rear sides of the base (11), two first hydraulic rods (22) are fixedly mounted on the top of the fixed plates (21), the telescopic ends of the two first hydraulic rods (22) are fixedly connected to Y-shaped rods (23), and the front ends of the two Y-shaped rods (23) are rotatably mounted with two rubber wheels (24).

5. The high-efficiency mechanical pressing device for new energy battery packaging according to claim 3 is characterized in that: The moving assembly (4) includes four longitudinal rods (41), the four longitudinal rods (41) are fixedly mounted on the top of the base (11), two screw rods (42) are fixedly mounted on the top of the four longitudinal rods (41), the outer edges of the two screw rods (42) are threadedly connected to the stepping motor (44), and the outer edges of the two stepping motors (44) are fixedly mounted with a rectangular frame (43), and the inner sides of the two long sides of the rectangular frame (43) are provided with a track (45).

6. The high-efficiency mechanical pressing device for new energy battery packaging according to claim 5, characterized in that: The driving assembly (5) comprises four electric wheels (51), each of the four electric wheels (51) being movably engaged in the two rails (45), each of the central axes of the four electric wheels (51) being fixedly connected to an L-shaped block (52), each of the bottoms of the four L-shaped blocks (52) being fixedly connected to a third hydraulic rod (53), each of the outer edges of the telescopic ends of the four third hydraulic rods (53) being movably sleeved with a second spring (54), and each of the telescopic ends of the four third hydraulic rods (53) being movably hinged to the four U-shaped rods (62).

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