Low stress piston device and hydraulic cylinder

Abstract

The utility model discloses a low stress piston device and hydraulic cylinder, piston device includes piston rod and piston, and the threaded section and the guide section are equipped in sequence in the axial direction to the piston rod end, is equipped with at least two tool withdrawal grooves on the guide section, is threaded tool withdrawal groove and extrusion surface tool withdrawal groove respectively, and the two tool withdrawal grooves are smoothly connected through linear transition section, and the threaded section and the guide section are equipped in sequence in the axial direction to the piston inner hole wall, and the stress release groove is equipped between both, and threaded tool withdrawal groove and extrusion surface tool withdrawal groove and stress release groove jointly constitute the low stress bearing structure of double stress release, and the hydraulic cylinder has low stress piston device. Through above -mentioned mode, the utility model compact structure, cost reduction can effectively reduce the stress concentration on piston rod, reduces the stress and stress amplitude of piston and piston rod connection, improves piston rod life.

Description

Technical Field

[0001] This utility model relates to the field of hydraulic cylinder technology, and in particular to a low-stress piston device and hydraulic cylinder. Background Technology

[0002] With the rapid development of industrial technology, mechanical equipment has permeated various fields, and many devices rely on hydraulic cylinders to complete various actions. Hydraulic cylinders, with their simple structure, large output force, ability to serve as high-power power components, high working efficiency, stable and reliable performance, and convenient use and maintenance, are widely used in various mechanical fields. Among the components of a hydraulic cylinder, the reliability of the piston rod and piston connection plays a crucial role in the cylinder's performance and service life. Currently, most hydraulic cylinders, for the sake of parts interchangeability, design the piston rod and piston as separate structures, using threaded connections to meet operational requirements. This threaded connection is also a common method for connecting pistons and piston rods in hydraulic cylinders. In this case, the strength of the piston rod and piston connection becomes a critical consideration, as its strength often directly determines the overall performance and service life of the piston rod. If the piston rod and piston connection breaks, it will not only cause numerous losses but may even lead to safety accidents. Currently, the most common piston structures are integral and split types, such as... Figure 1-2 As shown.

[0003] A split piston typically consists of two parts: a piston section for mounting a guide ring, providing guidance and support; and a nut for locking the piston section. This combined structure often requires significant assembly space, making it difficult to rationally arrange for compact hydraulic cylinder designs. Furthermore, this design typically exhibits substantial deformation during use, increasing the risk of nut pull-out under heavy loads. The increased material usage and parts management also contribute to the relatively higher cost of this design.

[0004] An integral piston is typically a single component, integrating guiding, support, and locking functions. This piston design allows for a very short piston, occupying minimal assembly space, making it suitable for hydraulic cylinders with high compactness requirements. Furthermore, it uses less material, simplifying material management and resulting in better economic efficiency. Moreover, the integral piston structure has obvious shortcomings: when using threaded connection and applying oil pressure, the stress in the relief groove of the connecting step and the first two teeth of the thread engagement is high and the stress amplitude is large, which often leads to breakage in the relief groove or the first tooth of the thread engagement.

[0005] After the integral piston and piston rod are connected, significant stress is often generated. Under frequent impacts and alternating loads, after a certain period of operation, fatigue cracks are prone to develop at the piston rod connection point, especially at the stepped area where the piston rod connects to the piston. This is because under the long-term action of frequent impacts and alternating loads, high-frequency fatigue cracks will be generated in this area due to alternating stress. As the crack initiation continues to expand and deepen, it eventually leads to instantaneous fracture of the piston rod step. Since the piston rod and cylinder body are the two core components of a hydraulic cylinder, a piston rod fracture can render the entire hydraulic cylinder unusable, and in severe cases, can easily cause safety accidents.

[0006] The conventional solution to this problem is to replace the material with a higher-performance one or to use heat treatment to improve the material properties, thereby reducing the probability of high-frequency fracture and extending the service life of the piston rod. However, these traditional methods often increase the number of processing steps and manufacturing processes, thus significantly increasing the production cost of the piston rod.

[0007] Therefore, there is an urgent need to provide a piston and piston rod connection structure that is compact, reliable in load bearing, has excellent fatigue resistance, and does not require additional high-cost materials or complex heat treatment, so as to achieve long service life and high safety operation of hydraulic cylinders under heavy load and high-frequency impact conditions. Utility Model Content

[0008] The main technical problem solved by this utility model is to provide a low-stress piston device and hydraulic cylinder, which has a compact structure, reduced cost, and can effectively reduce stress concentration on the piston rod, reduce the connection stress and stress amplitude between the piston and piston rod, and improve the service life of the piston rod.

[0009] To solve the above-mentioned technical problems, the present invention provides a low-stress piston device, comprising: a piston rod, the end of which is provided with a threaded section and a guide section in sequence along the axial direction; the guide section is provided with at least two relief grooves, namely a thread relief groove and a pressing surface relief groove, which are smoothly connected by a straight transition section; a piston, the inner wall of which is provided with a threaded mating section and a guide mating section in sequence along the axial direction, and a stress relief groove is provided between the two; the thread relief groove and the pressing surface relief groove together with the stress relief groove constitute a low-stress load-bearing structure with dual stress relief.

[0010] In a preferred embodiment of the present invention, one end of the bottom of the thread relief groove transitions to the first inclined surface through a first rounded chamfer, and the other end of the first inclined surface is connected to the root of the thread segment. The bottom of the threaded relief groove is transitioned to the second inclined surface through a second rounded chamfer, and the second inclined surface is connected to the extrusion surface relief groove through a straight transition section.

[0011] In a preferred embodiment of the present invention, the tilt angle of the first inclined surface is 20~40°, and the tilt angle of the second inclined surface is 35~60°.

[0012] In a preferred embodiment of the present invention, the extrusion surface relief groove includes an arc surface. One end of the arc surface smoothly transitions to the straight transition section through a third arc chamfer, and the other end of the arc surface extends radially after transitioning through a fourth arc chamfer. The axial length of the straight transition section is 4.5~6mm.

[0013] In a preferred embodiment of this utility model, the piston rod diameter D1 corresponding to the bottom of the thread relief groove is equal to the nominal thread diameter M - 1.3 * pitch p - 0.5, and the piston rod diameter D3 corresponding to the bottom of the extrusion surface relief groove is 3-5 mm smaller than the piston rod diameter D2 corresponding to the straight transition section.

[0014] In a preferred embodiment of this utility model, the radius of the third rounded chamfer is 8~10mm, and the radius of the fourth rounded chamfer is 2~3mm.

[0015] In a preferred embodiment of the present invention, one end of the bottom of the stress relief groove extends radially to connect with the threaded mating section after transitioning through a fifth rounded chamfer, and the other end of the bottom of the stress relief groove transitions to the third inclined surface through a sixth rounded chamfer, and the other end of the third inclined surface connects with the guide mating section.

[0016] In a preferred embodiment of this utility model, the piston rod diameter D4 at the bottom of the stress relief groove is at least 5 mm larger than the piston rod diameter D5 at the guide mating section, and the piston rod diameter D5 at the guide mating section is at least 0.5 mm larger than the piston rod diameter at the threaded mating section.

[0017] In a preferred embodiment of this utility model, the bottom width of the stress relief groove is at least 4 mm.

[0018] To solve the above-mentioned technical problems, the present invention provides a hydraulic cylinder, including a cylinder body and the low-stress piston device.

[0019] The beneficial effects of this utility model are: by optimizing the extrusion surface relief groove and thread relief groove on the piston rod, as well as the stress relief groove on the piston, the stress concentration, connection stress and stress amplitude of the piston rod are reduced, fatigue damage is reduced, fracture is avoided, and the working performance and service life are significantly improved. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic diagram of a traditional split piston and piston rod assembly in the background art; Figure 2 This is a schematic diagram of the structure of a conventional integral piston and piston rod assembly in the background art; Figure 3 This is a schematic diagram of a preferred embodiment of the low-stress piston device of this utility model; Figure 4 This is a schematic diagram of a preferred embodiment of the piston rod of this utility model; Figure 5 This is a schematic diagram of a preferred embodiment of the piston of this utility model; Figure 6 yes Figure 4 A magnified view of a section at point A in the middle; Figure 7 yes Figure 5 A magnified view of a section at point B in the middle; The components in the attached diagram are labeled as follows: 1. Piston rod; 11. Threaded section; 12. Guide section; 2. Piston; 21. Threaded mating section; 22. Guide mating section; 3. Threaded relief groove; 31. First inclined section; 32. Second inclined section; 4. Extrusion surface relief groove; 41. Arc surface; 5. Straight transition section; 6. Stress relief groove; 61. Third inclined section. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] This utility model relates to a preferred embodiment of a low-stress piston device.

[0024] Please see Figure 3 The low-stress piston device includes a piston rod 1 and a piston 2. The piston rod 1 has a threaded section 11 and a guide section 12 arranged sequentially along the axial direction at its end. The guide section 12 has a threaded relief groove 3 and a pressing surface relief groove 4. The inner wall of the piston 2 has a threaded mating section 21 and a guide mating section 22 arranged sequentially along the axial direction, with a stress relief groove 6 between them.

[0025] The piston rod 1 and piston 2 are connected by an axial thread and guided to transmit power. The threaded relief groove 3 and the extrusion surface relief groove 4 work together with the stress relief groove 6 to form a low-stress load-bearing structure with double stress relief, which reduces the stress concentration problem that traditional piston devices are prone to in high-frequency reciprocating motion.

[0026] In detail, the first is the thread relief groove 3, such as... Figure 4 and Figure 6 As shown, the thread relief groove 3 serves as the core for dispersing stress at the connection between the threaded section 11 and the guide section 12 on the piston rod 1. The axial length L of the groove bottom is set as large as possible to extend the stress transmission path, avoid stress superposition in local areas, and provide sufficient space for the gradual release of stress.

[0027] From a structural transition perspective, one end of the bottom of the thread relief groove 3 transitions to the first inclined surface 31 through the first rounded chamfer R1, and the other end of the first inclined surface 31 connects to the root of the thread section 11; the other end of the bottom of the groove transitions to the second inclined surface 32 through the second rounded chamfer R2, and the second inclined surface 32 is then connected to the extrusion surface relief groove 4 through the straight transition section 5. This multi-segment transition structure ensures that the force transmission path is continuous and without abrupt changes.

[0028] The first beveled section 31 has an inclination angle of 20-40°, preferably 30°; the second beveled section 32 has an inclination angle of 35-60°, preferably 45°. This minimizes stress concentration at the root of the threaded section 11 while ensuring the structural strength of the piston rod 1. Simultaneously, both the first and second rounded chamfers R1 and R2 use the largest possible radii to further reduce stress concentration in the transition area and make the stress distribution more uniform.

[0029] Meanwhile, the axial length of the straight transition section 5 is controlled at 4.5~6mm, preferably 5mm, which can ensure sufficient stress attenuation while avoiding excessive reduction in the effective bearing area of ​​the piston rod 1 due to an excessively long transition section.

[0030] Furthermore, regarding the piston rod diameter D1 corresponding to the bottom of the thread relief groove 3, D1 = nominal thread diameter M - 1.3 * pitch p - 0.5, ensuring the compatibility of D1 with the thread segment size, meeting the processing requirements of the thread relief groove, and avoiding abnormal stress caused by dimensional deviations.

[0031] Secondly, there is the extrusion surface relief groove 4, such as Figure 4 and Figure 6 As shown, it includes an arc surface 41, one end of which smoothly transitions to the straight transition segment 5 via a third arc chamfer R3, and the other end extends radially after transitioning via a fourth arc chamfer R4. The third arc chamfer R3 and the fourth arc chamfer R4 employ a double-R transition to achieve a smooth connection and optimize the stress transfer path.

[0032] Specifically, the radius of the third rounded chamfer R3 is 8~10mm, which can effectively disperse the stress at the junction of the straight transition section and the rounded surface; the radius of the fourth rounded chamfer R3 is 2~3mm, and the smaller radius is suitable for the size requirements of the radial extension section, avoiding structural interference caused by an excessively large transition radius.

[0033] In terms of size matching, the piston rod diameter D3 corresponding to the bottom of the extrusion surface relief groove 4 is 3~5mm smaller than the piston rod diameter D2 corresponding to the straight transition section 5. This forms a stress buffer zone in the area of ​​the extrusion surface relief groove 4, which can quickly release the residual stress generated by the piston rod 1 during high-frequency extrusion motion, while avoiding rigid friction between this area and the inner wall of the piston.

[0034] Furthermore, there is the stress relief groove 6, such as Figure 5 and Figure 7 As shown, one end of the groove bottom extends radially after transitioning through the fifth rounded chamfer R5 and connects with the threaded mating section 21. The other end of the groove bottom of the stress relief groove 6 transitions to the third inclined section 61 through the sixth rounded chamfer R6. The other end of the third inclined section 61 connects with the guide mating section 22.

[0035] Among them, the fifth rounded chamfer R5 is designed to be as large as possible according to the size of the stress relief groove, so as to minimize stress concentration by increasing the radius of the rounded chamfer; the radius of the sixth rounded chamfer R6 is preferably more than 2mm, which not only meets the processing requirements, but also reduces stress accumulation to a certain extent.

[0036] In terms of size matching, the piston rod diameter D4 at the bottom of the stress relief groove 6 is at least 5mm larger than the piston rod diameter D5 at the guide mating section 22, which can provide sufficient space for stress release and effectively release stress; the piston rod diameter D5 corresponding to the guide mating section 22 is at least 0.5mm larger than the piston rod diameter corresponding to the threaded mating section 21, which can not only ensure the accuracy of the guide mating, but also reduce the collision between the threaded mating section and the guide mating section through the size difference.

[0037] Meanwhile, the bottom width L1 of the stress relief groove 6 is at least 4mm, providing ample space for stress relief and avoiding secondary stress concentration caused by the groove being too narrow.

[0038] By setting the thread relief groove 3, the extrusion surface relief groove 4 and the stress relief groove 6 as described above, the various stresses borne by the piston rod 1 and piston 2 during the movement can be effectively dispersed, ensuring low stress in the entire piston device.

[0039] Provided the piston and piston rod materials have sufficient strength, the piston and piston rod should be connected using the largest possible torque during installation. A high-torque connection offers multiple benefits: To effectively prevent piston loosening, avoid connection loosening caused by vibration during long-term high-frequency operation of hydraulic cylinder, and ensure the stability of the overall structure; It can generate sufficient compressive stress on the piston and piston rod extrusion surfaces, so that a sealing effect can be achieved directly between the piston bore and piston rod without the need for a sealing ring; Under high torque, when the hydraulic cylinder is in a working condition where the pressure in the large and small chambers changes alternately, the connection part generates a smaller stress amplitude, thereby effectively reducing fatigue damage and improving the fatigue life of the connection part.

[0040] Based on the above structure, this utility model also relates to a hydraulic cylinder, including a cylinder body and the aforementioned low-stress piston device.

[0041] Specifically, during the operation of a hydraulic cylinder, when oil pressure is applied alternately to the large and small chambers: On the one hand, by optimizing the extrusion surface relief groove, thread relief groove, and stress relief groove, the stress concentration concentrated in the extrusion surface relief groove, thread relief groove, and the first two threads can be significantly reduced. These parts are high-incidence areas of stress concentration in traditional structures and common starting points for fracture failures. By effectively dispersing the stress in these critical parts, fractures in the relief groove or the first two threads can be fundamentally avoided, significantly improving the working performance and service life of the piston rod. On the other hand, it can effectively reduce the stress amplitude generated during the alternating operation of the large and small cavities: Under alternating pressure conditions in hydraulic cylinders, the connection between the piston rod and the piston experiences periodic load changes, and the magnitude of the stress amplitude directly affects the rate of fatigue damage accumulation. This design, through optimization of the preload force brought about by the high-torque connection and stress buffering by various relief grooves and stress relief grooves, significantly reduces the stress fluctuation amplitude of the connection under alternating loads, delays the propagation of fatigue cracks, and further improves the service life of the piston rod and piston connection.

[0042] The beneficial effects of this low-stress piston device are: With its compact structure and reduced cost, the optimized extrusion surface relief groove, thread relief groove, and stress relief groove can effectively reduce stress concentration on the piston rod. At the same time, it can reduce the stress and stress amplitude of the piston and piston rod connection during the alternating operation of the large and small chambers, thereby reducing fatigue damage, avoiding breakage of the relief groove or the first two threads, and significantly improving the working performance and service life of the piston rod.

[0043] The above description is merely an embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made using the content of this utility model specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.

Claims

1. A low-stress piston device, characterized in that, include: The piston rod has a threaded section and a guide section arranged sequentially along the axial direction at its end. The guide section has at least two relief grooves, namely a thread relief groove and a pressing surface relief groove. The two relief grooves are smoothly connected by a straight transition section. The piston has a threaded section and a guide section arranged sequentially along the axial direction on its inner bore wall, with a stress relief groove between the two sections. The thread relief groove and the extrusion surface relief groove together with the stress relief groove constitute a low-stress load-bearing structure with dual stress relief.

2. The low-stress piston device according to claim 1, characterized in that, One end of the bottom of the thread relief groove transitions to the first inclined surface through a first rounded chamfer, and the other end of the first inclined surface connects to the root of the thread segment. The bottom of the threaded relief groove is transitioned to the second inclined surface through a second rounded chamfer, and the second inclined surface is connected to the extrusion surface relief groove through a straight transition section.

3. The low-stress piston device according to claim 2, characterized in that, The tilt angle of the first inclined surface is 20~40°, and the tilt angle of the second inclined surface is 35~60°.

4. The low-stress piston device according to claim 2, characterized in that, The extrusion surface relief groove includes an arc surface. One end of the arc surface smoothly transitions to the straight transition section through a third arc chamfer, and the other end of the arc surface extends radially after transitioning through a fourth arc chamfer. The axial length of the straight transition section is 4.5~6mm.

5. The low-stress piston device according to claim 4, characterized in that, The piston rod diameter D1 at the bottom of the thread relief groove is equal to the nominal thread diameter M - 1.3 * pitch p - 0.

5. The piston rod diameter D3 at the bottom of the extrusion surface relief groove is 3-5 mm smaller than the piston rod diameter D2 at the straight transition section.

6. The low-stress piston device according to claim 4, characterized in that, The radius of the third rounded chamfer is 8~10mm, and the radius of the fourth rounded chamfer is 2~3mm.

7. The low-stress piston device according to claim 1, characterized in that, One end of the stress relief groove extends radially to connect with the threaded section after transitioning through the fifth rounded chamfer. The other end of the stress relief groove transitions to the third inclined section through the sixth rounded chamfer, and the other end of the third inclined section connects with the guide section.

8. The low-stress piston device according to claim 7, characterized in that, The piston rod diameter D4 at the bottom of the stress relief groove is at least 5 mm larger than the piston rod diameter D5 at the guide mating section, and the piston rod diameter D5 at the guide mating section is at least 0.5 mm larger than the piston rod diameter at the threaded mating section.

9. The low-stress piston device according to claim 7, characterized in that, The bottom width of the stress relief groove is at least 4 mm.

10. A hydraulic cylinder, characterized in that, Includes a cylinder block and a low-stress piston assembly as described in any one of claims 1-9.

Images