Hydraulic cylinder sealing structure and method for combined sealing of multiple sealing rings

Abstract

The hydraulic cylinder sealing structure comprises a plunger, the two ends of the plunger are sleeved with a left cylinder body and a right cylinder body respectively, a first oil cavity is formed between the plunger and the left cylinder body, and a second oil cavity is formed between the plunger and the right cylinder body. A first oil duct and a second oil duct which are communicated with the first oil cavity and the second oil cavity are respectively arranged in the plunger; a first combined sealing structure and a second combined sealing structure are correspondingly arranged at the positions, matched with the small end and the large end of the plunger, of the left cylinder body respectively; a third combined sealing structure and a fourth combined sealing structure are correspondingly arranged at the positions, matched with the small end and the large end of the plunger, of the right cylinder body respectively. The sealing structure can be well suitable for reliable sealing of the two-way oil cylinder, can well adapt to the high-pressure environment while guaranteeing the sealing performance requirement of the two-way oil cylinder, and guarantees reliable sealing under the high-pressure condition.

Description

Technical Field

[0001] The present invention relates to the technical field of bidirectional oil cylinder sealing, and in particular to a hydraulic cylinder sealing structure and method for combined sealing of multiple sealing rings. Background Art

[0002] Innovation in hydraulic cylinder sealing technology is crucial to improving the overall performance of hydraulic systems. As industrial equipment develops towards high pressure, precision and long life, the limitations of traditional seals are becoming increasingly prominent. A bidirectional hydraulic cylinder used in ship lock lifts currently has new requirements for its structural performance, considering the safety of its application area. It needs to ensure the following performance: (1) System stability: High-efficiency sealing can maintain constant pressure in the hydraulic chamber, ensure accurate actuator movement, and avoid system jitter or failure due to leakage; (2) Energy consumption and environment: Reducing leakage can reduce oil loss and environmental pollution, in line with the trend of green manufacturing; (3) Adaptability to extreme working conditions: Under high temperature, high pressure or frequent start-stop conditions, the sealing structure must have elastic compensation, wear resistance and self-cleaning capabilities to cope with complex dynamic loads.

[0003] Existing traditional sealing technologies mostly use a single sealing structure, such as O-rings and V-type combination seals. Although they can achieve basic sealing, they have significant shortcomings: (1) Insufficient sealing adaptability: A single seal is difficult to take into account both high and low pressure working conditions; (2) Lack of oil scraping ability: The traditional sealing structure has limited effect on scraping the oil film on the piston rod surface, and oil adhesion can easily cause external contamination; (3) Weak combination synergy: Although some solutions adopt multi-stage sealing combinations, the mechanical coordination between the seals is insufficient, resulting in uneven pressure distribution. The redundant seals fail to effectively form a multi-layer barrier, but instead aggravate friction loss.

[0004] Therefore, a hydraulic cylinder combined sealing solution with integrated multi-stage sealing synergy, adaptive oil scraping function and compact structure is needed to break through the existing technical bottleneck and meet the application requirements of high reliability, long life and complex working conditions. Summary of the Invention

[0005] The purpose of the present invention is to provide a hydraulic cylinder sealing structure and method with a combination of multiple sealing rings to address the above problems. This sealing structure can be well applied to the reliable sealing of bidirectional oil cylinders. While ensuring its sealing performance requirements, it can adapt well to high-pressure environments and ensure reliable sealing under high-pressure conditions. Moreover, it can scrape oil during use and effectively prevent external environmental pollution caused by oil leakage.

[0006] To achieve the above technical features, the present invention achieves the following objectives: a hydraulic cylinder sealing structure for sealing with a combination of multiple sealing rings, comprising a plunger, with a left cylinder body and a right cylinder body respectively fitted on both ends of the plunger, a first oil chamber formed between the plunger and the left cylinder body, a second oil chamber formed between the plunger and the right cylinder body, and a first oil passage and a second oil passage respectively provided inside the plunger to communicate with the first oil chamber and the second oil chamber; The positions where the left cylinder body cooperates with the small end and the large end of the plunger are respectively provided with a first combined sealing structure and a second combined sealing structure; The positions where the right cylinder body cooperates with the small end and the large end of the plunger are respectively provided with a third combined sealing structure and a fourth combined sealing structure.

[0007] Preferably, the first oil passage adopts a U-shaped oil passage structure, and the second oil passage adopts a Z-shaped oil passage structure.

[0008] Preferably, the first combined sealing structure, the second combined sealing structure, the third combined sealing structure and the fourth combined sealing structure all adopt the same structure; Wherein, the first combined sealing structure and the third combined sealing structure are arranged symmetrically; The second combined sealing structure and the fourth combined sealing structure are arranged symmetrically; The opening directions of the first combined sealing structure and the second combined sealing structure are opposite; The opening directions of the third combined sealing structure and the fourth combined sealing structure are opposite. Preferably, the second combined sealing structure comprises a first concave sealing ring, a first special-shaped thermoplastic sealing ring, a baffle, a second concave sealing ring, a second special-shaped thermoplastic sealing ring, a third concave sealing ring, a bidirectional special-shaped thermoplastic sealing ring and a sealing scraper ring positioned sequentially on the inner wall of the left cylinder body; The first special-shaped thermoplastic sealing ring is provided with a first inner support ring, the second special-shaped thermoplastic sealing ring is provided with a second inner support ring, and the bidirectional special-shaped thermoplastic sealing ring is provided with a third inner support ring.

[0009] Preferably, the first concave sealing ring, the second concave sealing ring and the third concave sealing ring are respectively made of carbon fiber powder-polytetrafluoroethylene material, are axially fixed by the boss on the cylinder body, and are transitionally fitted with the plunger.

[0010] Preferably, the first special-shaped thermoplastic sealing ring and the second special-shaped thermoplastic sealing ring are both special-shaped thermoplastic polyurethane sealing rings, with the opening direction facing the high-pressure side, and a clearance fit is adopted between the first special-shaped thermoplastic sealing ring and the second special-shaped thermoplastic sealing ring under normal working conditions; The bidirectional special-shaped thermoplastic sealing ring is a thermoplastic polyurethane sealing ring.

[0011] Preferably, the first inner support ring, the second inner support ring and the third inner support ring are all made of polytetrafluoroethylene.

[0012] Preferably, the baffle is mounted on the low-pressure side of the first special-shaped thermoplastic sealing ring; The first inner support ring has a notch at the joint with the baffle, so that the pressure of the oil is transmitted to the first special-shaped thermoplastic sealing ring, so that the first special-shaped thermoplastic sealing ring and the baffle are tightly fitted; The first special-shaped thermoplastic sealing ring, the second special-shaped thermoplastic sealing ring and the bidirectional special-shaped thermoplastic sealing ring are each provided with a stepped structure inside, so as to closely fit the plunger and the corresponding inner wall of the cylinder under the action of oil pressure; The first special-shaped thermoplastic sealing ring and the second special-shaped thermoplastic sealing ring are provided with a lip structure on the high-pressure side, and the two sides of the bidirectional special-shaped thermoplastic sealing ring are provided with a lip structure. The inclination angle of the lip structure matches the direction of movement of the plunger and ensures that it can still be fully expanded under low pressure or no load, actively scraping off the residual oil film on the surface of the plunger.

[0013] Preferably, the sealing scraper ring is a polyurethane sealing scraper ring, and a forward-extending scraper ring structure is provided on the outer side. The forward-extending scraper ring structure protrudes from the end face of the cylinder body and elastically fits with the surface of the plunger.

[0014] In another aspect, the present invention provides a method for sealing a hydraulic cylinder using a combination of multiple sealing rings, comprising the following steps: Step 1: High-pressure oil introduction: High-pressure oil is introduced into the first oil chamber and the second oil chamber through the first oil passage and the second oil passage respectively, and the high-pressure oil flows along the surface of the plunger; Step 2: Extrusion sealing of the first concave sealing ring: When high-pressure oil enters the end face of the first concave sealing ring, it squeezes the first concave sealing ring to cause radial expansion and deformation, thus achieving a sealing effect; Step 3: Extrusion sealing of the first special-shaped thermoplastic sealing ring: When the high-pressure oil enters the end face of the first special-shaped thermoplastic sealing ring, it squeezes the first special-shaped thermoplastic sealing ring and makes its inner and outer sides close to the plunger and the inner wall of the corresponding cylinder at the same time, so as to achieve an annular seal, and the baffle is used to axially block and limit the first special-shaped thermoplastic sealing ring; Step 4, tandem sealing: Afterwards, the hydraulic oil passes through the second concave sealing ring, the second special-shaped thermoplastic sealing ring and the third concave sealing ring in sequence for multiple composite sealing; Step 5: Extrusion sealing of bidirectional special-shaped thermoplastic sealing ring: After the oil enters the nested body composed of the bidirectional special-shaped thermoplastic sealing ring and the third inner support ring, the double-sided lip structure of the bidirectional special-shaped thermoplastic sealing ring resists the eccentric load and balances the radial pressure distribution; Step 6, seal scraper oil removal: One end of the sealing scraper ring protruding from the cylinder body is in contact with the surface of the plunger to prevent various impurities in a harsh environment from entering the matching structure of the sealing ring.

[0015] The present invention has the following beneficial effects: 1. This invention utilizes a multi-level seal design: combining single-lip, double-lip, concave-concave, and stepped-concave seals, nested and arranged in parallel, to form a multi-level pressure barrier, significantly reducing the risk of leakage. The nesting of two seals enhances the sealing performance of individual seals, while the lip structure reduces wear.

[0016] 2. The front extension of the sealing scraper ring of the present invention prevents foreign matter from entering the working environment to damage the sealing structure and affect the sealing performance.

[0017] 3. The present invention integrates adaptive oil scraping and sealing: the lip-shaped sealing ring is elastically expanded under the pressure of the oil to scrape off the oil film, and fits tightly, thus having the functions of oil scraping and sealing.

[0018] 4. Composite optimization of materials and shapes in the present invention: The lip shape adopts thermoplastic polyurethane to improve wear resistance and oil scraping response; The concave shape adopts carbon fiber powder-polytetrafluoroethylene material composite to improve extrusion resistance: The concave structure can effectively resist the extrusion deformation of the sealing ring caused by high-pressure oil, especially under high-pressure working conditions to prevent the sealing ring from being squeezed into the gap and causing failure.

[0019] 5. The concave trapezoidal shape of this invention utilizes carbon fiber powder-PTFE material, making the concave trapezoidal structure resistant to extrusion. Carbon fiber reinforcement significantly improves compressive strength and reduces deformation under high pressure. Carbon fiber provides self-lubrication, lowering the coefficient of friction and reducing wear. PTFE is resistant to acid and alkali corrosion and high temperatures, while carbon fiber prevents swelling, making it suitable for environments containing impurities and oil. Through material innovation, the carbon fiber powder-PTFE sealing ring significantly improves the sealing performance of hydraulic cylinders under complex operating conditions such as high pressure, high temperature, and oil-free conditions, combining the advantages of anti-extrusion, wear resistance, and self-lubrication. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below with reference to the accompanying drawings and examples.

[0021] Figure 1 It is a cross-sectional view of the overall structure of the present invention.

[0022] Figure 2 This is a partial enlarged view of the second combined sealing structure of the present invention.

[0023] In the figure: first concave sealing ring 1, first special-shaped thermoplastic sealing ring 2, first inner support ring 3, baffle 4, second concave sealing ring 5, second special-shaped thermoplastic sealing ring 6, second inner support ring 7, third concave sealing ring 8, bidirectional special-shaped thermoplastic sealing ring 9, third inner support ring 10, sealing scraper ring 11, plunger 12, left cylinder body 13, first oil channel 14, second oil channel 15, right cylinder body 16, first combined sealing structure 17, first oil chamber 18, fourth combined sealing structure 19, second oil chamber 20, third combined sealing structure 21, second combined sealing structure 22. DETAILED DESCRIPTION

[0024] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] Example 1: See also Figure 1-2 A hydraulic cylinder sealing structure with a combination of multiple sealing rings includes a plunger 12, with a left cylinder body 13 and a right cylinder body 16 respectively mounted on both ends of the plunger 12, a first oil chamber 18 formed between the plunger 12 and the left cylinder body 13, and a second oil chamber 20 formed between the plunger 12 and the right cylinder body 16, and a first oil passage 14 and a second oil passage 15 communicating with the first oil chamber 18 and the second oil chamber 20 are respectively provided inside the plunger 12; a first combined sealing structure 17 and a second combined sealing structure 22 are respectively provided at positions where the left cylinder body 13 cooperates with the small end and the large end of the plunger 12; a third combined sealing structure 21 and a fourth combined sealing structure 19 are respectively provided at positions where the right cylinder body 16 cooperates with the small end and the large end of the plunger 12. By adopting the above-mentioned sealing structure, when the system is filled with oil, the plunger 12 remains unchanged, and the left cylinder 13 and the right cylinder 16 move to the left and right respectively, and the cylinder body extends; when the oil chamber is unloaded, the left cylinder 13 and the right cylinder 16 retract under the external load condition. In order to prevent the high-pressure oil from leaking from the oil chamber, a first combined sealing structure 17, a second combined sealing structure 22, a third combined sealing structure 21 and a fourth combined sealing structure 19 are set at four positions of the cylinder body, wherein the first combined sealing structure 17 and the third combined sealing structure 21 are symmetrical in structure, and the second combined sealing structure 22 and the fourth combined sealing structure 19 are symmetrical in structure; except for the different diameters, the first combined sealing structure 17 and the third combined sealing structure 21, the second combined sealing structure 22 and the fourth combined sealing structure 19 have the same combination method and opening direction; in Figure 1 In the embodiment, the first combined sealing structure 17 and the third combined sealing structure 21 prevent oil from leaking to the left, and the second combined sealing structure 22 and the fourth combined sealing structure 19 prevent oil from leaking to the right.

[0026] Furthermore, the first oil passage 14 adopts a U-shaped oil passage structure, and the second oil passage 15 adopts a Z-shaped oil passage structure. By adopting the above different forms of oil passages, the corresponding first oil chamber 18 and second oil chamber 20 can be effectively supplied with oil, thereby achieving the purpose of driving the cylinder body.

[0027] Furthermore, the first combined sealing structure 17, the second combined sealing structure 22, the third combined sealing structure 21, and the fourth combined sealing structure 19 all have the same structure; wherein the first combined sealing structure 17 and the third combined sealing structure 21 are symmetrically arranged; the second combined sealing structure 22 and the fourth combined sealing structure 19 are symmetrically arranged; the first combined sealing structure 17 and the second combined sealing structure 22 have opposite opening directions; and the third combined sealing structure 21 and the fourth combined sealing structure 19 have opposite opening directions. The above-mentioned combined sealing structure can achieve a good sealing effect.

[0028] Furthermore, the second combined sealing structure 22 includes a first concave sealing ring 1, a first special-shaped thermoplastic sealing ring 2, a baffle 4, a second concave sealing ring 5, a second special-shaped thermoplastic sealing ring 6, a third concave sealing ring 8, a bidirectional special-shaped thermoplastic sealing ring 9 and a sealing scraper ring 11, which are positioned in sequence on the inner wall of the left cylinder body 13; through the above-mentioned comprehensive sealing structure, it effectively combines single-lip, double-lip, concave-concave and terraced sealing rings, and forms a multi-stage pressure barrier through nesting and parallel cooperation, which significantly reduces the risk of leakage.

[0029] The first special-shaped thermoplastic sealing ring 2 is provided with a first inner support ring 3, the second special-shaped thermoplastic sealing ring 6 is provided with a second inner support ring 7, and the bidirectional special-shaped thermoplastic sealing ring 9 is provided with a third inner support ring 10. The above inner support rings can provide good internal support for the special-shaped thermoplastic sealing ring, thereby greatly enhancing its anti-deformation effect.

[0030] Furthermore, the first concave sealing ring 1, the second concave sealing ring 5 and the third concave sealing ring 8 are respectively made of carbon fiber powder-polytetrafluoroethylene material, axially fixed by the boss on the cylinder body, and a transition fit is adopted between the plunger 12. Due to its relatively large elastic modulus, poor compression performance, and good friction performance, it forms a transition fit with the plunger, which can achieve a good sealing and self-lubricating effect. Carbon fiber reinforcement significantly improves the compressive strength and reduces the deformation under high pressure; carbon fiber provides self-lubrication, reduces the friction coefficient, and reduces the wear rate; polytetrafluoroethylene is resistant to acid and alkali corrosion and high temperature, and carbon fiber avoids swelling and is adapted to the environment of impurities in oil; carbon fiber powder-polytetrafluoroethylene sealing rings have significantly improved the sealing performance of hydraulic cylinders under complex working conditions such as high pressure, high temperature, and oil-free conditions through material innovation, and have the advantages of anti-extrusion, wear resistance, and self-lubrication.

[0031] Furthermore, the first special-shaped thermoplastic sealing ring 2 and the second special-shaped thermoplastic sealing ring 6 are both special-shaped thermoplastic polyurethane sealing rings, and the opening direction is toward the high-pressure side. Under normal working conditions, a clearance fit is adopted between them and the plunger 12; the bidirectional special-shaped thermoplastic sealing ring 9 is a thermoplastic polyurethane sealing ring.

[0032] Furthermore, the first inner support ring 3, the second inner support ring 7 and the third inner support ring 10 are all made of polytetrafluoroethylene. Polytetrafluoroethylene is resistant to acid and alkali corrosion and high temperature, and carbon fiber does not swell, and is suitable for an environment containing impurities and oil.

[0033] Furthermore, the baffle 4 is installed on the low-pressure side of the first special-shaped thermoplastic sealing ring 2 to prevent the first special-shaped thermoplastic sealing ring 2 from being squeezed into the gap by high-pressure oil and damaged.

[0034] Furthermore, there is a gap at the fitting point between the first inner support ring 3 and the baffle 4, and the pressure of the oil is transmitted to the first special-shaped thermoplastic sealing ring 2, so that the first special-shaped thermoplastic sealing ring 2 and the baffle 4 fit tightly, thereby achieving a good sealing effect.

[0035] Furthermore, the first special-shaped thermoplastic sealing ring 2, the second special-shaped thermoplastic sealing ring 6 and the bidirectional special-shaped thermoplastic sealing ring 9 are respectively provided with a step structure inside, so that they can fit tightly with the plunger 12 and the corresponding inner wall of the cylinder under the action of oil pressure, thereby achieving a good sealing effect.

[0036] Furthermore, the first special-shaped thermoplastic sealing ring 2 and the second special-shaped thermoplastic sealing ring 6 are provided with a lip structure on the high-pressure side, and the two sides of the bidirectional special-shaped thermoplastic sealing ring 9 are provided with a lip structure. The inclination angle of the lip structure matches the movement direction of the plunger 12, and ensures that it can still be fully expanded under low pressure or no load, and actively scrapes off the residual oil film on the surface of the plunger 12.

[0037] Furthermore, the sealing scraper ring 11 is a polyurethane sealing scraper ring, and is provided with a forward extension scraper ring structure on the outside. The forward extension of the scraper ring structure protrudes from the end face of the cylinder body and elastically fits with the surface of the plunger 12. This can prevent various impurities in harsh environments from entering the mating structure of the sealing ring and damaging the surface of the sealing ring.

[0038] Example 2: A method for sealing a hydraulic cylinder using a combination of multiple sealing rings comprises the following steps: Step 1: High-pressure oil introduction: High-pressure oil is introduced into the first oil chamber 18 and the second oil chamber 20 through the first oil passage 14 and the second oil passage 15 respectively, and the high-pressure oil flows along the surface of the plunger 12; Step 2: Extrusion sealing of the first concave sealing ring 1: When the high-pressure oil enters the end face of the first concave sealing ring 1, it will squeeze the first concave sealing ring 1 to cause radial expansion and deformation, thus achieving a sealing effect; Step 3: Extrusion sealing of the first special-shaped thermoplastic sealing ring 2: When the high-pressure oil enters the end face of the first special-shaped thermoplastic sealing ring 2, it squeezes the first special-shaped thermoplastic sealing ring 2 and makes its inner and outer sides close to the plunger 12 and the inner wall of the corresponding cylinder to achieve an annular seal, and the baffle 4 blocks and limits the axial position of the first special-shaped thermoplastic sealing ring 2; Step 4, tandem sealing: Afterwards, the hydraulic oil passes through the second concave sealing ring 5, the second special-shaped thermoplastic sealing ring 6 and the third concave sealing ring 8 in sequence for multiple composite sealing; Step 5: Extrusion sealing of the bidirectional special-shaped thermoplastic sealing ring 9: After the oil enters the nested body composed of the bidirectional special-shaped thermoplastic sealing ring 9 and the third inner support ring 10, the double-sided lip structure of the bidirectional special-shaped thermoplastic sealing ring 9 resists the eccentric load and balances the radial pressure distribution; Step 6, sealing and scraping oil of the sealing scraper ring 11: One end of the sealing scraper ring 11 protruding from the cylinder body is in contact with the surface of the plunger 12 to prevent various impurities in a harsh environment from entering the matching structure of the sealing ring.

[0039] The specific working process and principle of the present invention: When oil enters the oil port, the oil flows along the surface of the plunger 12 and first passes through the first concave sealing ring 1, which is a concave terraced sealing ring that is nested in the groove of the left cylinder body 13. The concave terraced structure of the concave terraced sealing ring can effectively resist the extrusion and deformation of the sealing ring by high-pressure oil, especially to prevent the sealing ring from being squeezed out and causing failure under high-pressure conditions. Moreover, for this concave terraced sealing ring, the oil pressure change can drive the sealing ring to expand radially, automatically compensating for the wear gap. In addition, the first concave sealing ring 1 has carbon fiber to provide self-lubrication, reduce the friction coefficient, and reduce the wear rate. After passing through the first concave sealing ring 1, the oil reaches the nested sealing ring of the first special-shaped thermoplastic sealing ring 2 and the first inner support ring 3. The terraced structure of the first special-shaped thermoplastic sealing ring 2 can have a larger oil contact area, which can make the sealing ring subject to greater pressure so that the first special-shaped thermoplastic sealing ring 2 fits more closely to the inner wall of the left cylinder body 13 and the surface of the plunger 12. The first special-shaped thermoplastic sealing ring 2 and the baffle 4 are matched with a small gap, which can better transmit the pressure of the oil to the sealing ring, making the first special-shaped thermoplastic sealing ring 2 and the baffle 4 fit more closely and improving the sealing performance.

[0040] At the same time, the composite single-sided lip of the first shaped thermoplastic sealing ring 2 and the first inner support ring 3 has a trapezoidal cross-section. The lip's inclination angle matches the direction of piston rod movement, allowing it to fully expand even under low pressure or no load, actively scraping away residual oil film on the piston rod surface. This composite trapezoidal cross-section of the first shaped thermoplastic sealing ring 2 and the first inner support ring 3 reduces the contact area with the piston rod, lowering frictional temperature rise and minimizing losses. After passing through the composite seal of the first shaped thermoplastic sealing ring 2 and the first inner support ring 3, the oil will pass through baffle 4. The presence of baffle 4 increases the hydraulic oil flow surface, reducing the fluidity of the hydraulic oil and thereby improving sealing performance.

[0041] The hydraulic oil then passes through a similar second concave seal ring 5, a second special-shaped thermoplastic seal ring 6, and a third concave seal ring 8. The cascaded sealing of these seals further enhances self-cleaning, oil scraping, and sealing performance. The oil then passes through a nested structure of a bidirectional special-shaped thermoplastic seal ring 9 and a third inner support ring 10. This combined seal ring exhibits a double-lip structure, which, while retaining the advantages of the single lip of the first special-shaped thermoplastic seal ring 2 and the first inner support ring 3, also prevents oil backflow. Furthermore, the nested double-lip structure of the bidirectional special-shaped thermoplastic seal ring 9 and the third inner support ring 10 offers resistance to unbalanced loads: the symmetry of the double-lip structure balances radial pressure distribution and reduces localized wear caused by piston rod deflection. Finally, there is a forward-extended seal scraper ring 11. This forward extension of the seal ring protrudes beyond the end face of the left cylinder block 13 and mates with the surface of the plunger 12, preventing impurities from entering the seal ring's mating structure and damaging the seal ring's surface in harsh environments.

Claims

1. A hydraulic cylinder sealing structure with a combination of multiple sealing rings, characterized in that: The plunger (12) comprises a plunger (12), wherein both ends of the plunger (12) are respectively fitted with a left cylinder body (13) and a right cylinder body (16), a first oil chamber (18) is formed between the plunger (12) and the left cylinder body (13), a second oil chamber (20) is formed between the plunger (12) and the right cylinder body (16), and a first oil passage (14) and a second oil passage (15) are respectively provided inside the plunger (12) for communicating with the first oil chamber (18) and the second oil chamber (20); A first combined sealing structure (17) and a second combined sealing structure (22) are respectively provided at positions where the left cylinder (13) cooperates with the small end and the large end of the plunger (12); A third combined sealing structure (21) and a fourth combined sealing structure (19) are respectively provided at positions where the right cylinder (16) cooperates with the small end and the large end of the plunger (12).

2. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 1, characterized in that: The first oil passage (14) adopts a U-shaped oil passage structure, and the second oil passage (15) adopts a Z-shaped oil passage structure.

3. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 1, characterized in that: The first combined sealing structure (17), the second combined sealing structure (22), the third combined sealing structure (21) and the fourth combined sealing structure (19) all adopt the same structure; Wherein, the first combined sealing structure (17) and the third combined sealing structure (21) are arranged symmetrically; The second combined sealing structure (22) and the fourth combined sealing structure (19) are arranged symmetrically; The first combined sealing structure (17) and the second combined sealing structure (22) have opening directions opposite to each other; The opening directions of the third combined sealing structure (21) and the fourth combined sealing structure (19) are opposite.

4. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 3, characterized in that: The second combined sealing structure (22) comprises a first concave sealing ring (1), a first special-shaped thermoplastic sealing ring (2), a baffle (4), a second concave sealing ring (5), a second special-shaped thermoplastic sealing ring (6), a third concave sealing ring (8), a bidirectional special-shaped thermoplastic sealing ring (9) and a sealing scraper ring (11), which are positioned sequentially on the inner wall of the left cylinder body (13); The first special-shaped thermoplastic sealing ring (2) is provided with a first inner support ring (3), the second special-shaped thermoplastic sealing ring (6) is provided with a second inner support ring (7), and the bidirectional special-shaped thermoplastic sealing ring (9) is provided with a third inner support ring (10).

5. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 4, characterized in that: The first concave sealing ring (1), the second concave sealing ring (5) and the third concave sealing ring (8) are respectively made of carbon fiber powder-polytetrafluoroethylene material, are axially fixed by the boss on the cylinder body, and are transitionally matched with the plunger (12).

6. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 4, characterized in that: The first special-shaped thermoplastic sealing ring (2) and the second special-shaped thermoplastic sealing ring (6) are both special-shaped thermoplastic polyurethane sealing rings, and the opening direction is toward the high-pressure side, and under normal working conditions, a clearance fit is adopted between them and the plunger (12); The bidirectional special-shaped thermoplastic sealing ring (9) is a thermoplastic polyurethane sealing ring.

7. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 4, characterized in that: The first inner support ring (3), the second inner support ring (7) and the third inner support ring (10) are all made of polytetrafluoroethylene.

8. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 4, characterized in that: The baffle (4) is installed on the low-pressure side of the first special-shaped thermoplastic sealing ring (2); A notch is provided at the fitting position between the first inner support ring (3) and the baffle (4), and the pressure of the oil is transmitted to the first special-shaped thermoplastic sealing ring (2), so that the first special-shaped thermoplastic sealing ring (2) and the baffle (4) are tightly fitted; The first special-shaped thermoplastic sealing ring (2), the second special-shaped thermoplastic sealing ring (6) and the bidirectional special-shaped thermoplastic sealing ring (9) are each provided with a step structure inside, so that they can fit tightly against the plunger (12) and the corresponding inner wall of the cylinder under the action of oil pressure; The first special-shaped thermoplastic sealing ring (2) and the second special-shaped thermoplastic sealing ring (6) are provided with lip structures on the high-pressure side, and the two sides of the bidirectional special-shaped thermoplastic sealing ring (9) are provided with lip structures. The inclination angle of the lip structure matches the movement direction of the plunger (12) and ensures that it can still be fully expanded under low pressure or no load, and actively scrapes off the residual oil film on the surface of the plunger (12).

9. The hydraulic cylinder sealing structure with multiple sealing rings combined for sealing according to claim 4, characterized in that: The sealing scraper ring (11) is a polyurethane sealing scraper ring, and a forward-extending scraper ring structure is provided on the outside. The forward-extending scraper ring structure protrudes from the end surface of the cylinder body and elastically fits with the surface of the plunger (12).

10. A method for sealing a hydraulic cylinder using a combination of multiple sealing rings, characterized in that: The sealing method is implemented by using the hydraulic cylinder sealing structure according to any one of claims 4 to 9, comprising the following steps: Step 1: High-pressure oil introduction: High-pressure oil is introduced into the first oil chamber (18) and the second oil chamber (20) through the first oil passage (14) and the second oil passage (15), respectively, and the high-pressure oil flows along the surface of the plunger (12); Step 2, extrusion sealing of the first concave sealing ring (1): When the high-pressure oil enters the end face of the first concave sealing ring (1), it squeezes the first concave sealing ring (1) to cause radial expansion and deformation, thereby achieving a sealing effect; Step 3, extrusion sealing of the first special-shaped thermoplastic sealing ring (2): When the high-pressure oil enters the end face of the first special-shaped thermoplastic sealing ring (2), it squeezes the first special-shaped thermoplastic sealing ring (2) and makes its inner and outer sides close to the plunger (12) and the inner wall of the corresponding cylinder at the same time, so as to achieve an annular seal, and the first special-shaped thermoplastic sealing ring (2) is axially blocked and limited by the baffle (4); Step 4, tandem sealing: The hydraulic oil then passes through the second concave sealing ring (5), the second special-shaped thermoplastic sealing ring (6), and the third concave sealing ring (8) in sequence to perform multiple composite sealing. Step 5, extrusion sealing of the bidirectional special-shaped thermoplastic sealing ring (9): After the oil enters the nested body composed of the bidirectional special-shaped thermoplastic sealing ring (9) and the third inner support ring (10), the double-sided lip structure of the bidirectional special-shaped thermoplastic sealing ring (9) resists the eccentric load and balances the radial pressure distribution; Step 6, sealing scraper (11) oil scraping: One end of the sealing scraper ring (11) protruding from the cylinder body is fitted onto the surface of the plunger (12) to prevent various impurities in a harsh environment from entering the matching structure of the sealing ring.

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