A new type of wear-resistant rubber bearing bushing assembly

Abstract

The application discloses a novel wear-resistant rubber trunnion bushing assembly and relates to the technical field of vehicle bushing damping, which comprises a rubber bushing and a trunnion body, the trunnion body is arranged in the inner hole of the rubber bushing, and a trace gap is arranged between the trunnion body and the rubber bushing, and the trunnion body and the rubber bushing can slide in the circumferential direction during work. The trace gap with a size of 0.01-0.05 mm fundamentally changes the stress transmission path of the traditional trunnion bushing, converts the rubber torsional deformation into low-friction sliding friction, and effectively solves the technical problems of rubber fatigue cracking and degumming failure. The structure is compact, the process is mature, the cost is controllable, and the novel wear-resistant rubber trunnion bushing assembly is suitable for heavy-load damping occasions such as commercial vehicle suspension systems and cab suspension systems, and has significant technical progress and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of vehicle bushing vibration reduction technology, specifically a novel wear-resistant rubber trunnion bushing assembly. Background Technology

[0002] Trunnion bushings are important vibration damping components in commercial vehicle suspension systems, cab mounting systems, and chassis transmission systems. Their main function is to absorb vibration and impact through the elastic deformation of the rubber body, while allowing a certain degree of relative rotation between the inner and outer sleeves to adapt to various operating conditions during vehicle operation.

[0003] Traditional trunnion bushings are typically made of an inner sleeve, an outer sleeve, and a vulcanized rubber body. In practical use, they present the following problems: First, the shrinkage of the rubber after vulcanization generates internal stress, making the rubber body prone to fatigue cracks under alternating loads, thus reducing the bushing's fatigue life. Second, the rubber layer thickness is often poorly designed; either the stiffness is too low to withstand large loads, or the stiffness is too high, resulting in poor vibration damping, making it difficult to balance high stiffness and vibration damping performance. Third, the relative rotation between the inner and outer sleeves relies entirely on the torsional deformation of the rubber body. Long-term operation leads to significant stress inside the rubber body and at the metal bonding surface, easily causing rubber cracking and bonding surface delamination. Fourth, frictional wear exists between the bushing end face and adjacent components, causing axial positioning failure of the bushing. Fifth, the metal sleeve has insufficient rust resistance, making it prone to corrosion in humid or corrosive environments, affecting the product's appearance and service life.

[0004] Therefore, it is necessary to design a new type of trunnion bushing structure with high fatigue life, high radial stiffness, good wear resistance, and strong rust prevention to solve the above-mentioned problems in the existing technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a novel wear-resistant rubber trunnion bushing assembly. This assembly improves fatigue performance by eliminating internal stress during rubber vulcanization through a diameter reduction process, achieves high radial stiffness to meet heavy load conditions through a thin rubber layer design, reduces rubber body stress by achieving relative sliding friction through a small gap between the PTFE wear-resistant bushing and the trunnion, enhances end-face wear resistance through a UPE wear-resistant gasket, and strengthens rust prevention through black zinc plating. These improvements significantly enhance the service life and NVH performance of the bushing assembly.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a novel wear-resistant rubber trunnion bushing assembly, comprising a rubber bushing and a trunnion body, wherein the trunnion body is inserted into the inner hole of the rubber bushing, and a small gap is pre-set between the trunnion body and the rubber bushing, so that the trunnion body and the rubber bushing can slide relative to each other in the circumferential direction during operation.

[0007] Based on the above technical solution, the micro-gap is 0.01-0.05mm. This radial gap of 0.01-0.05mm provides the necessary physical space for the trunnion to slide circumferentially relative to the wear-resistant bushing. When a relative angular displacement occurs between the trunnion and the outer sleeve, the trunnion no longer forces the rubber body to undergo torsional deformation, but can instead slide slightly circumferentially along the inner surface of the wear-resistant bushing within the gap range. This gap value is rationally designed—the lower limit of 0.01mm is sufficient to ensure sliding freedom and avoid jamming due to processing errors or thermal expansion; the upper limit of 0.05mm is controlled within a reasonable range to prevent excessive gap from causing impact loads and vibration noise, while ensuring that the overall structural rigidity and positioning accuracy of the bushing are not affected.

[0008] Based on the above technical solution, the rubber bushing includes a concentric inner sleeve and an outer sleeve, with a rubber body vulcanized between the inner and outer sleeves. Preferably, the rubber layer thickness of the rubber bushing is 4-6 mm. The thinner rubber layer thickness gives the bushing higher radial stiffness, meeting the requirements of high-load working conditions. Simultaneously, due to the vibration damping characteristics of rubber, it can reduce impact and damage to the system, improving the overall NVH performance of the vehicle. The thin rubber layer design achieves a balance between high stiffness and vibration damping performance. Preferably, the inner and outer sleeves of the rubber bushing, as well as the trunnion, are all treated with black zinc plating. Black zinc plating has excellent rust prevention capabilities, effectively protecting metal parts from corrosion, extending product service life, and also providing a more aesthetically pleasing black appearance. Preferably, the rubber body material is natural rubber with a Shore hardness range of Shore A65 to A75. Natural rubber has good elasticity, fatigue resistance, and damping characteristics. The selection of the hardness range can be optimized according to different stiffness requirements to adapt to different application conditions, while also possessing good processing performance.

[0009] Based on the above technical solution, the outer diameter of the rubber bushing is reduced after vulcanization to eliminate the internal stress caused by the shrinkage of the rubber after vulcanization. Preferably, after the rubber bushing is reduced in diameter, the outer diameter is ground to improve the dimensional accuracy of the outer diameter, ensuring it meets the assembly requirements of the entire assembly. Grinding after diameter reduction not only guarantees the dimensional accuracy and surface quality of the outer diameter but also ensures the fit accuracy between the bushing and the mounting hole, improving assembly quality and reliability.

[0010] Based on the above technical solution, a wear-resistant bushing is interference-fitted into the inner hole of the inner sleeve.

[0011] Based on the above technical solution, the wear-resistant bushing is made of copper-plated steel sheet, and the inner wall of the wear-resistant bushing is coated with PTFE. Preferably, the copper-plated steel sheet is No. 20 copper-plated steel sheet, and the thickness of the PTFE coating is 0.2-0.3 mm. No. 20 steel has good plasticity and strength, making it suitable for rolling and forming processes; the copper plating provides excellent rust protection; the 0.2-0.3 mm PTFE coating thickness ensures sufficient wear resistance without affecting the overall size and rigidity of the bushing due to excessive thickness.

[0012] Based on the above technical solution, wear-resistant pads fitted onto the trunnion body are respectively provided on both ends of the rubber bushing.

[0013] Based on the above technical solution, the wear-resistant gasket is made of stainless steel, and both the inner wall of the wear-resistant gasket and the side that abuts against the rubber bushing are provided with a UPE wear-resistant material layer. The stainless steel substrate has good strength and corrosion resistance; the UPE (ultra-high molecular weight polyethylene) material has extremely high wear resistance, which can effectively improve the wear resistance between the gasket and the trunnion and the end face of the rubber bushing, reduce end face wear, and ensure the axial positioning accuracy of the bushing.

[0014] Based on the above technical solution, a retaining spring is provided on the outer side of the wear-resistant pad and sleeved on the trunnion body for axial positioning of the rubber bushing and the wear-resistant pad.

[0015] Based on the above technical solution, the two ends of the trunnion body are respectively provided with limiting grooves for installing retaining rings.

[0016] The beneficial effects of this invention are as follows: (1) The present invention adopts a diameter reduction process, which reduces the outer diameter of the outer sleeve after the rubber bushing is vulcanized, effectively eliminating the internal stress caused by the shrinkage of the rubber after vulcanization, significantly improving the fatigue performance and durability of the rubber bushing, and extending the service life of the product.

[0017] (2) The present invention adopts a 4-6mm thin rubber layer design, which makes the bushing have high radial stiffness and can meet the working conditions of large load; at the same time, the vibration reduction characteristics of rubber are used to reduce the impact and damage to the system, thus achieving a balance between high stiffness and good vibration reduction performance, and effectively improving the NVH performance of the whole vehicle.

[0018] (3) The core inventive point of this invention lies in the relative sliding design between the wear-resistant bushing and the trunnion. By pre-setting a micro-gap of 0.01-0.05mm between the trunnion and the wear-resistant bushing, combined with the low-friction characteristics of the PTFE coating, the trunnion can slide relative to the wear-resistant bushing in the circumferential direction. This design transforms the relative motion borne by the torsional deformation of the rubber body in the traditional structure into low-friction sliding friction, fundamentally changing the stress transmission path, significantly reducing the working stress inside the rubber body and the metal bonding surface, effectively avoiding failure problems such as rubber cracking and bonding surface delamination, and significantly extending the service life of the assembly. Experimental data show that within the gap range of 0.01-0.05mm, the rotational torque decreases with the increase of the gap (from 150N•m to 70N•m), verifying the effectiveness of the gap design in reducing the stress load on the rubber body.

[0019] (4) The wear-resistant bushing of the present invention adopts a composite structure of No. 20 steel copper-plated steel plate + PTFE coating. The PTFE coating thickness is 0.2-0.3mm, which has excellent wear resistance and low friction coefficient; the copper plating layer has excellent anti-rust effect; the rolling forming process is simple and the manufacturing cost is low.

[0020] (5) The present invention uses UPE wear-resistant gaskets with stainless steel as the base material. One side of the surface and the inner hole are covered with high wear-resistant UPE material, which significantly improves the wear resistance between the gasket and the end face of the trunnion and the rubber bushing, reduces end face wear, and ensures the axial positioning accuracy and service life of the bushing.

[0021] (6) The inner and outer rubber bushings and trunnions of the present invention are all treated with black zinc plating, which has excellent rust prevention ability, can adapt to various complex working environments, and extend the service life of the product.

[0022] (7) The present invention has a compact structure, is easy to assemble and has reliable performance. It is applicable to commercial vehicle suspension systems, cab suspension systems and other occasions, and has good engineering application value and market prospects. Attached Figure Description

[0023] Figure 1 This is a perspective view of the novel wear-resistant rubber trunnion bushing assembly of the present invention; Figure 2 This is a front view of the novel wear-resistant rubber trunnion bushing assembly of the present invention; Figure 3 This is a side view of the novel wear-resistant rubber trunnion bushing assembly of the present invention; Figure 4 This is a cross-sectional view of the novel wear-resistant rubber trunnion bushing assembly of the present invention; Figure 5 This is a cross-sectional view of the rubber bushing of the present invention; Figure 6 This is a cross-sectional view of the wear-resistant bushing of the present invention; Figure 7 This is a perspective view of the trunnion body of the present invention; Figure 8 This is a cross-sectional view of the wear-resistant pad of the present invention.

[0024] Figure label: 1-Rubber bushing; 11-Outer sleeve; 12-Inner sleeve; 13-Rubber body; 14-Wear-resistant bushing; 15-PTFE coating; 2-Ternary shaft body; 21-Limiting groove; 22-Snap ring; 3-Abrasion-resistant gasket; 31-UPE abrasion-resistant material layer. Detailed Implementation

[0025] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0026] In the description of this invention, it should be noted that the directional terms such as "center", "lateral (X)", "longitudinal (Y)", "vertical (Z)", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0027] The following description, in conjunction with the accompanying drawings, further illustrates specific embodiments of the present invention, making the technical solution and its beneficial effects clearer and more explicit. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the invention.

[0028] See Figures 1-4 As shown, this embodiment of the invention provides a novel wear-resistant rubber trunnion bushing assembly, including a rubber bushing 1 and a trunnion body 2. The trunnion body 2 passes through the inner hole of the rubber bushing 1, and a small gap is pre-set between the trunnion body 2 and the rubber bushing 1, allowing the trunnion body 2 and the rubber bushing 1 to slide relative to each other in the circumferential direction during operation. Specifically, the small gap is 0.01-0.05mm.

[0029] See Figure 5As shown, the rubber bushing 1 includes an inner sleeve 12 and an outer sleeve 11 arranged concentrically, with a rubber body 13 vulcanized between the inner sleeve 12 and the outer sleeve 11. Both the inner sleeve and the outer sleeve are made of high-quality steel pipes and have a black zinc plating treatment, providing excellent rust resistance. The rubber body is made of natural rubber material with a Shore hardness of 70, exhibiting good elasticity and fatigue resistance. The rubber layer thickness of the rubber bushing is 5mm. This relatively thin rubber layer thickness gives the bushing high radial stiffness, meeting the requirements of high-load working conditions. Simultaneously, due to the vibration damping characteristics of rubber, it can reduce the impact and damage to the system, improving the overall NVH performance of the vehicle. Specifically, after vulcanization, the outer diameter of the outer sleeve 11 of the rubber bushing 1 is reduced to eliminate the internal stress caused by the shrinkage of the rubber after vulcanization. The reduction process involves slightly compressing the outer diameter of the outer sleeve using specialized equipment, causing a certain degree of plastic deformation in the outer sleeve, thereby eliminating the internal stress generated by the shrinkage of the rubber during the vulcanization and cooling process. After the diameter reduction process, the residual stress inside the rubber body is effectively released, and the rubber body is in a more uniform stress state, which significantly improves the fatigue durability of the rubber bushing. After the diameter reduction, the outer diameter of the outer sleeve is ground to improve the dimensional accuracy and surface finish of the outer diameter, so as to meet the assembly requirements of the entire assembly component and ensure the fitting accuracy between the bushing and the mounting hole.

[0030] See Figure 6 As shown, a wear-resistant bushing 14 is interference-fitted into the inner hole of the inner sleeve 12. Specifically, the wear-resistant bushing 14 is made of copper-plated steel plate, and the inner wall of the wear-resistant bushing 14 is provided with a PTFE coating 15. In this embodiment, the copper-plated steel plate is No. 20 steel plate with copper plating treatment, which has excellent rust prevention effect. The PTFE coating is applied to the inner surface of the copper-plated steel plate, and the PTFE coating thickness is 0.25mm, which has excellent wear resistance and an extremely low coefficient of friction. The manufacturing process of the wear-resistant bushing is as follows: first, the copper-plated steel plate is cut to a predetermined size, then the PTFE coating is applied to its inner surface, and finally the plate is rolled into a cylindrical shape using special equipment. The rolled wear-resistant bushing has a longitudinal seam. Due to the interference fit into the inner hole of the rubber bushing, the wear-resistant bushing is subjected to radial pressure, and the seam can fit tightly without affecting the performance.

[0031] The wear-resistant bushing is pressed into the inner hole of the rubber bushing with an interference fit, forming a single unit with the rubber bushing. The interference fit ensures a firm and reliable connection between the wear-resistant bushing and the rubber bushing, preventing relative rotation or axial movement during operation.

[0032] See Figure 8As shown, wear-resistant gaskets 3, fitted onto the trunnion body 2, are respectively provided on both ends of the rubber bushing 1. Specifically, the wear-resistant gaskets 3 are made of stainless steel, and a UPE wear-resistant material layer 31 is provided on the inner wall of the wear-resistant gasket 3 and on the side that abuts against the rubber bushing 1. In this embodiment, 304 stainless steel is used, which has good mechanical strength and corrosion resistance. UPE (ultra-high molecular weight polyethylene) material has extremely high wear resistance, several times that of ordinary steel. The wear-resistant gaskets are provided on the end faces of the rubber bushing, located between the rubber bushing and the flange of the trunnion, which can effectively improve the wear resistance between the gaskets and the trunnion and the end face of the rubber bushing, reduce end face wear, and ensure the axial positioning accuracy of the bushing.

[0033] See Figure 7 As shown, a retaining ring 22 is provided on the outer side of the wear-resistant pad 3 and sleeved on the trunnion body 2. The retaining ring is an elastic retaining ring used to axially limit the rubber bushing 1 and the wear-resistant pad 3, preventing the bushing from axially moving during operation. Specifically, each end of the trunnion body 2 is provided with a limiting groove 21 for installing the retaining ring 22.

[0034] The assembly process of this invention is as follows: First, the inner and outer sleeves are vulcanized with the rubber body to form a rubber bushing blank. Then, the outer diameter of the outer sleeve is reduced to eliminate the internal stress of rubber vulcanization. After the diameter reduction, the outer diameter of the outer sleeve is ground to ensure the dimensional accuracy of the outer diameter. Next, the copper-plated PTFE coated steel sheet is cut and rolled into a wear-resistant bushing. The wear-resistant bushing is then press-fitted into the inner hole of the rubber bushing. Then, the wear-resistant gasket is fitted onto the trunnion, and the trunnion is inserted into the inner hole of the wear-resistant bushing (ensuring a radial clearance of 0.01-0.05mm). Finally, a retaining ring is installed for axial positioning, completing the assembly of the entire bushing assembly.

[0035] The working principle of this invention is as follows: In traditional trunnion bushing designs, the trunnion and bushing inner bore are fitted with an interference fit or a very small clearance, and the relative rotation between the inner and outer sleeves is entirely absorbed by the torsional deformation of the rubber body. Under long-term alternating loads, the interior of the rubber body and the metal-rubber bonding surface are subjected to large shear stresses, which can easily lead to rubber fatigue cracking and delamination of the bonding surface. This is the most common failure mode of traditional trunnion bushings.

[0036] This invention fundamentally changes the transmission method of relative motion by pre-setting a micro-gap of 0.01-0.05mm between the trunnion and the wear-resistant bushing. When a relative angular displacement occurs between the trunnion and the outer sleeve, the trunnion no longer forces the rubber body to undergo large-scale torsional deformation, but instead slides slightly in a circumferential direction along the PTFE coating on the inner surface of the wear-resistant bushing within the 0.01-0.05mm gap range. The theoretical basis for this design is: First, the radial clearance of 0.01-0.05mm provides the necessary physical space for relative sliding. The lower limit of 0.01mm is sufficient to ensure that the sliding freedom is maintained under machining tolerances and thermal deformation conditions, avoiding jamming; the upper limit of 0.05mm ensures that the clearance is not too large, preventing impact loads and vibration noise, while maintaining the overall structural rigidity and axial positioning accuracy of the bushing.

[0037] Secondly, the PTFE coating on the inner surface of the wear-resistant bushing 3 has an extremely low coefficient of friction (μ≈0.05-0.10). With the sliding space provided by the gap, the relative movement between the trunnion and the wear-resistant bushing is achieved in the form of low-friction sliding friction. The self-lubricating properties of the PTFE coating ensure the smoothness of the sliding process and long-term durability.

[0038] Third, the stress transmission path has been fundamentally changed. In traditional designs, the load transmission path is "outer sleeve → rubber body → inner sleeve", with the rubber body bearing all the torsional deformation stress. In this invention, the path becomes "outer sleeve → rubber body (minor elastic deformation) → wear-resistant bushing → PTFE-coated sliding surface → trunnion". The rubber body only needs to bear minor elastic deformation, and most of the relative motion is borne by the PTFE sliding surface. The shear stress inside the rubber body and at the metal-rubber bonding surface is significantly reduced.

[0039] To verify the above theoretical mechanism, this invention conducted torque tests under different clearance values, and the experimental data are shown in the table below: Table 1. Torque Test under Different Clearance Values Example 1 0.01 150 Example 2 0.02 140 Example 3 0.03 110 Example 4 0.04 80 Example 5 0.05 70 As shown in Table 1, as the radial clearance increases from 0.01 mm to 0.05 mm, the torque decreases from 150 N·m to 70 N·m, a reduction of 53%. This decrease in torque indicates that as the clearance increases, the torsional stiffness contribution of the rubber body decreases, and more relative motion is borne by the sliding friction of the PTFE, resulting in a corresponding reduction in the stress on the rubber body. The clearance range of 0.01-0.05 mm achieves a good engineering balance between sliding freedom and structural stiffness, ensuring both relative sliding and maintaining the necessary radial load-bearing capacity of the bushing.

[0040] Meanwhile, due to the extremely low coefficient of friction and excellent wear resistance of the PTFE coating, the wear caused by sliding friction is minimal, further ensuring the long-term reliable operation of the bushing.

[0041] This invention achieves a balance of high radial stiffness, low torsional stress, excellent wear resistance, and good rust prevention by organically combining several technologies, including a diameter reduction process, a thin rubber layer design, a micro-clear gap between the PTFE wear-resistant bushing and the trunnion, a UPE wear-resistant gasket, and black zinc plating for rust prevention. This significantly improves the service life and NVH performance of the trunnion bushing assembly. The core invention is the micro-clear gap between the wear-resistant bushing and the trunnion. Through the synergistic effect of the 0.01-0.05mm micro-clear gap and the PTFE low-friction coating, it fundamentally changes the stress transmission path of traditional trunnion bushings, transforming rubber torsional deformation into low-friction sliding friction. This effectively solves the technical problems of rubber fatigue cracking and delamination failure. The structure is compact, the process is mature, and the cost is controllable. It is suitable for heavy-duty vibration damping applications such as commercial vehicle suspension systems and cab mounting systems, demonstrating significant technological advancements and promising application prospects.

[0042] In the description of this specification, references to terms such as "an embodiment," "preferred," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. Illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0043] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A novel wear-resistant rubber trunnion bushing assembly, comprising a rubber bushing (1) and a trunnion body (2), characterized in that: The trunnion body (2) is inserted into the inner hole of the rubber bushing (1), and there is a small gap between the trunnion body (2) and the rubber bushing (1) during operation. The trunnion body (2) and the rubber bushing (1) can slide relative to each other in the circumferential direction.

2. The novel wear-resistant rubber trunnion bushing assembly as described in claim 1, characterized in that: The micro-gap is 0.01-0.05 mm.

3. The novel wear-resistant rubber trunnion bushing assembly as described in claim 1, characterized in that: The rubber bushing (1) includes an inner sleeve (12) and an outer sleeve (11) arranged concentrically, and a rubber body (13) is vulcanized between the inner sleeve (12) and the outer sleeve (11).

4. The novel wear-resistant rubber trunnion bushing assembly as described in claim 3, characterized in that: After vulcanization, the outer diameter of the outer sleeve (11) is reduced to eliminate the internal stress caused by the shrinkage of the rubber after vulcanization.

5. The novel wear-resistant rubber trunnion bushing assembly as described in claim 3, characterized in that: The inner hole of the inner sleeve (12) is fitted with a wear-resistant bushing (14) by interference fit.

6. The novel wear-resistant rubber trunnion bushing assembly as described in claim 5, characterized in that: The wear-resistant bushing (14) is made of copper-plated steel plate, and the inner wall of the wear-resistant bushing (14) is provided with a PTFE coating (15).

7. The novel wear-resistant rubber trunnion bushing assembly as described in claim 1, characterized in that: The rubber bushing (1) is provided with wear-resistant pads (3) that are fitted onto the trunnion body (2) at both ends.

8. The novel wear-resistant rubber trunnion bushing assembly as described in claim 7, characterized in that: The wear-resistant pad (3) is made of stainless steel, and the inner wall of the wear-resistant pad (3) and the side that abuts against the rubber bushing (1) are provided with a UPE wear-resistant material layer (31).

9. The novel wear-resistant rubber trunnion bushing assembly as described in claim 7, characterized in that: The wear-resistant pad (3) is provided with a retaining ring (22) sleeved on the trunnion body (2) for axial positioning of the rubber bushing (1) and the wear-resistant pad (3).

10. The novel wear-resistant rubber trunnion bushing assembly as described in claim 9, characterized in that: The two ends of the trunnion body (2) are respectively provided with limiting grooves (21) for installing snap rings (22).

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