Sealing performance evaluation method for aviation heavy load and long stroke actuator

Abstract

The present invention relates to a sealing performance evaluation method for an aviation large-load long-stroke actuator. The method divides the actuator stroke into three stages. The first stage obtains the state of the rubber ring being compressed and squeezed in during assembly. The second stage obtains the state of the rubber ring contacting the fluoroplastic ring when the piston rod moves axially. The third stage obtains the deformation state of the rubber ring and the fluoroplastic ring after the oil pressure is increased. In each stage, simulation is performed using the finite element method, and the grid model of the simulation result is mapped and calculated to reduce or eliminate the grid distortion, which is used as the starting grid model of the next stage. The present invention effectively avoids the grid distortion problem caused by large elastic deformation of the seal, saves time cost, obtains the optimal structural parameters of the actuator, and thus effectively prevents the failure of the sealing ring in the large-load long-stroke actuator, and improves the sealing performance and reliability.

Description

Technical Field

[0001] The invention relates to a sealing performance evaluation method for an aviation large-load and long-stroke actuator, and belongs to the technical field of actuator sealing. Background Art

[0002] The landing gear retracting actuator is an important part of the aircraft landing gear. It is used to retract the main and front landing gears and the wheel hub, and lock the landing gear in a fixed position when the landing gear is fully lowered. Usually, the weight of the landing gear plus the wheel hub will exceed 300Kg, and the wind resistance will be greater when the aircraft takes off and lands; in addition, the ratio of the length and diameter of the landing gear retracting actuator piston rod is usually greater than 10, so the landing gear retracting actuator is a large-load long-stroke actuator.

[0003] The actuator is a hydraulic actuator and needs to be equipped with a sealing structure. Figure 1 As shown, it includes a piston rod 1, a sleeve 2 and a seal. The sleeve 2 is sleeved on the outside of the piston rod 1. A sealing groove 5 is provided at the position of the sleeve 2 facing the piston rod 1. The sealing groove 5 is filled with medium oil. The seal includes a rubber ring 3 and two fluoroplastic rings 4 arranged in the sealing groove 5. When there are two fluoroplastic rings 4, the two fluoroplastic rings 4 are respectively located on both sides of the rubber ring 3 and abut against the side walls of the sealing groove 5. When the actuator is performing an action, the piston rod 1 squeezes the rubber ring 3 and the fluoroplastic ring 4 so that the rubber ring 3 and the fluoroplastic ring 4 abut against each other to form a seal.

[0004] For heavy-load and long-stroke actuators, the seal structure bears a large load and a long movement stroke during the reciprocating process. As a result, the seal is prone to twisting, peeling, or falling off when the actuator moves, and then fails, resulting in medium oil leakage. In other words, compared with ordinary actuators, heavy-load and long-stroke actuators are more prone to leakage failures, and the leakage location mostly occurs at the matching part between the piston rod and the sleeve, that is, the seal location. This not only affects the flight safety and attendance rate of the aircraft, but also greatly increases the maintenance cost.

[0005] According to the applicant's understanding, some people have evaluated the sealing performance of seals by calculating the deformation of seals through finite element simulation methods. The fluid penetration method is used to simulate the fluid pressure during the simulation. However, the applicant's experiments show that when the fluid penetration method is used to simulate the fluid pressure in the finite element calculation, the large deformation of the seal will lead to a large compression rate, and the seal is very difficult to assemble under a large compression rate state. It is difficult to eliminate the grid distortion caused by the superelasticity of the seal. Therefore, the finite element calculation process is difficult to converge. At this time, the deformation of the seal cannot be obtained, and it is impossible to make an accurate evaluation of the sealing performance of the large-load and long-stroke actuator.

[0006] Therefore, how to effectively evaluate the sealing performance of large-load and long-stroke actuators to improve aircraft flight safety and reduce maintenance costs has become an urgent problem to be solved. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a more efficient method for evaluating the sealing performance of an aviation large-load and long-stroke actuator, which can effectively evaluate the reliability of the actuator sealing structure and avoid leakage failures caused by failure of the actuator sealing structure.

[0008] In order to solve the above technical problems, the technical solution proposed by the present invention is: a method for evaluating the sealing performance of an aviation large-load long-stroke actuator, wherein an annular sealing groove is provided on the inner side of the sleeve of the actuator, and two fluoroplastic rings and a rubber ring are installed in the sealing groove, and the fluoroplastic ring and the rubber ring are both sleeved on the piston rod, and the two fluoroplastic rings are separated on both sides of the rubber ring and located at the end of the sealing groove; the piston rod, the sleeve, the fluoroplastic ring and the rubber ring constitute a sealing structure; the evaluation method comprises the following steps:

[0009] Step 1: The sleeve and the piston rod are completely fixed to simulate the state in which the rubber ring is compressed and squeezed into the sealing groove during assembly, and a model of the sealing structure is established and meshed to obtain a first mesh model;

[0010] According to the material properties and contact properties of the sealing structure, a mesh model of the fluoroplastic ring and the rubber ring after deformation in the first mesh model is obtained, and a mapping calculation is performed to obtain a second mesh model;

[0011] Step 2: The constraint sleeve of the second grid model is completely fixed to constrain the piston rod to move only in the axial direction, so as to simulate the contact state between the rubber ring and the fluoroplastic ring when the piston rod moves axially;

[0012] The piston rod is axially displaced by a preset distance, and a mesh model of the fluoroplastic ring and the rubber ring after deformation in the second model is obtained according to the material properties and contact properties of the sealing structure, and a third mesh model is obtained by performing mapping calculation;

[0013] Step 3: Constrain the piston rod and the sleeve of the third grid model to be completely fixed, and apply a preset surface pressure to the non-contacting parts of the rubber ring, the piston rod, and the inner side of the sealing groove to simulate the state of the rubber ring and the fluoroplastic ring after the medium oil pressure is increased;

[0014] According to the material properties and contact properties of the sealing structure, a mesh model of the fluoroplastic ring and the rubber ring after deformation in the third mesh model is obtained;

[0015] The sealing performance of the actuator is evaluated based on the stress and strain data recorded at each node in the third grid model;

[0016] Among them, the method for mapping calculation of grid model A is: establish a model with the same outer contour as grid model A and perform grid division to obtain grid model B. For any node C in grid model B, if there is a node D corresponding to the position of node C in grid model A, the stress and strain data of node D are assigned to node C. Otherwise, find the grid unit E corresponding to the position of node C in grid model A, interpolate the stress and strain data of each node in grid unit E and assign them to node C.

[0017] The present invention divides the movement process of the actuator into three stages and calculates the deformation process of the rubber ring and the fluoroplastic ring by the finite element method. After the calculation of each stage is completed, the grid unit of the grid model will be distorted. The present invention uses a mapping method to map the calculation results of the previous stage to the grid model that has not been distorted, and uses the mapped grid model as the initial model of the finite element calculation of the next stage, thereby avoiding large distortion of the grid calculation in each stage, and avoiding the problem of grid distortion caused by the superelastic deformation of the seal in the prior art, which leads to the calculation failure. Therefore, the calculation efficiency is improved, the continuity of the calculation of each stage is guaranteed, and the reliability of the sealing structure of the actuator can be effectively evaluated. In this way, the present invention can analyze the reliability of multiple groups of pre-designed sealing structures, select the better solution, effectively avoid leakage failures caused by the failure of the sealing structure of the actuator, and improve reliability; the present invention can also quickly verify the reliability of the existing designed sealing structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the sealing structure.

[0019] Figure 2 Schematic diagram of the first model in an embodiment of the present invention.

[0020] Figure 3 Schematic diagram of the comparison of the mesh model before and after mapping.

[0021] Figure 4 This is a schematic diagram of the stress of the rubber ring and the fluoroplastic ring after the three stages.

[0022] Figure numerals: 1, piston rod; 2, sleeve; 3, rubber ring; 4, fluoroplastic ring; 5, sealing groove. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] like Figure 1As shown, an annular sealing groove 5 is provided on the inner side of the sleeve 2 of the actuator cylinder, and two fluoroplastic rings 4 and a rubber ring 3 are installed in the sealing groove 5. The fluoroplastic ring 4 and the rubber ring 3 are both sleeved on the piston rod 1, and the two fluoroplastic rings 4 are separated on both sides of the rubber ring 3 and located at the end of the sealing groove 5; the piston rod 1, the sleeve 2, the fluoroplastic ring 4 and the rubber ring 5 form a sealing structure.

[0025] The purpose of this embodiment is to evaluate the sealing performance of multiple different sealing structures, and its goal is to find a sealing structure with better sealing performance. Generally speaking, the rubber ring 3 has corresponding specifications, and the depth of the sealing groove 5 has corresponding specifications, which can be determined according to the size of the piston rod and the sleeve (this is the prior art and will not be repeated). The radial thickness of the fluoroplastic ring 4 is consistent with the depth of the sealing groove 5, so the only parameters that can be adjusted are the width of the sealing groove and the width of the fluoroplastic ring 4.

[0026] It should be noted that the width direction mentioned in this embodiment refers to the direction extending along the axial direction of the piston rod, and the thickness direction or depth direction refers to the direction extending along the radial direction of the piston rod.

[0027] The sealing performance evaluation method of the aviation large-load long-stroke actuator of this embodiment includes the following steps:

[0028] Step 1: The sleeve and the piston rod are completely fixed to simulate the state in which the rubber ring is compressed and squeezed into the sealing groove during assembly, and a model of the sealing structure is established and meshed to obtain a first mesh model. The mesh unit can be a common triangular unit or a quadrilateral unit.

[0029] According to the material properties and contact properties of the sealing structure, the mesh model of the deformed fluoroplastic ring and the rubber ring in the first mesh model is obtained (the rubber ring is squeezed into the sealing groove due to its elasticity, and the two sides contact the piston rod and the inner side of the end cover to generate contact stress, which is the prior art), and mapping calculation is performed to obtain the second mesh model.

[0030] Because the two-dimensional axisymmetric model of the sealing structure has the symmetry of the structure, in order to improve the calculation efficiency, when establishing the model of the sealing structure, only the two-dimensional axisymmetric model of the sealing structure section can be established. At this time, only the fluoroplastic ring needs to be installed on one side of the sealing groove. Figure 2 The figure shows the state of the rubber ring before deformation, and the overlapping part between the rubber ring and the piston rod is an interference fit.

[0031] Step 2: The constraint sleeve of the second grid model is completely fixed to constrain the piston rod to move only in the axial direction, so as to simulate the contact state between the rubber ring and the fluoroplastic ring when the piston rod moves axially;

[0032] The piston rod is axially displaced by a preset distance (this distance is set according to actual conditions, and is the prior art. In this embodiment, the moving distance is about 7 meters), and a mesh model of the fluoroplastic ring and the rubber ring after deformation in the second model is obtained according to the material properties and contact properties of the sealing structure, and a mapping calculation is performed to obtain a third mesh model;

[0033] Step 3: Constrain the piston rod and sleeve to be completely fixed in the third grid model, and apply a preset surface pressure to the non-contact part of the rubber ring, piston rod, and inner side of the sealing groove to simulate the state of the rubber ring and fluoroplastic ring after increasing the medium oil pressure.

[0034] According to the material properties and contact properties of the sealing structure, a mesh model of the fluoroplastic ring and the rubber ring after deformation in the third mesh model is obtained;

[0035] The sealing performance of the actuator is evaluated based on the stress and strain data recorded at each node in the third grid model. The sealing performance is usually judged based on the maximum contact stress criterion and the shear stress criterion.

[0036] Among them, the method for mapping calculation of grid model A is: establish a model with the same outer contour as grid model A and perform grid division to obtain grid model B. For any node C in grid model B, if there is a node D corresponding to the position of node C in grid model A, the stress and strain data of node D are assigned to node C. Otherwise, find the grid unit E corresponding to the position of node C in grid model A, interpolate the stress and strain data of each node in grid unit E and assign them to node C.

[0037] After each stage of calculation is completed, the grid units of the grid model will be distorted. The present invention adopts a mapping method to map the calculation results of the previous stage to the grid model that has not been distorted, and uses the mapped grid model as the initial model for the finite element calculation in the next stage, thereby avoiding large distortions in the grid calculations at each stage, making the calculations easier to converge, improving the calculation efficiency, and ensuring the continuity of the calculations at each stage. Figure 3 It is a schematic diagram of the mesh model before and after mapping in a calculation process. The left figure is the first mesh model after deformation, and the right figure is the second mesh model obtained after mapping calculation of the deformed first mesh model. It can be seen that the upper left corner of the left figure is obviously distorted, and the second mesh model corrects it. In this way, under the premise of retaining the stress and strain results in the calculation process, the problem of non-convergence of calculation caused by large distortion in the prior art is solved.

[0038] This embodiment takes a certain actuator as an example for comparative test. According to the size of the piston rod and the sleeve, the depth of the sealing groove is 4 mm, the thickness of the fluoroplastic ring is also 4 mm, the radius of the rubber ring is 2.3 mm, the fluoroplastic ring material is polytetrafluoroethylene, and the density of the fluoroplastic ring material is ρ=2.18×10 -3 g / mm 3 , Young's modulus E = 140MPa, Poisson's ratio μ = 0.4, the rubber ring is an O-shaped rubber ring made of nitrile rubber 5180F, the sealing groove is filled with medium oil, and a pressure of 28MPa is formed on the rubber ring. The friction coefficient of each contact surface is 0.25. The material of the rubber ring is described by the second-order polynomial form of Mooney-Rivlin (that is, the material parameters of the rubber ring are described by the constitutive relationship), and its constitutive model is:

[0039]

[0040] where U is the strain energy per unit reference volume, C ij and D i is a temperature-dependent material parameter, and are the first and second deviatoric strain tensor invariants; C 10 =1.214MPa, C 01 =0.2767MPa, C 20 =5.279MPa, C 11 =-10.068MPa, C 02 =5.146MPa, D 1 =D 2 =0.

[0041] This embodiment is based on finite element analysis to calculate and analyze the sealing performance at room temperature and constant pressure. In order to ensure the mesh quality of the rubber ring, geometric cutting is required. CAX4RH mesh units are used with a mesh size of 0.03mm. The fluoroplastic ring, sleeve, and piston rod use CAX4R mesh units. The mesh size of the fluoroplastic ring is 0.05mm, the mesh size of the sleeve is 0.2mm, and the mesh size of the piston rod is 0.5mm.

[0042] The width of the fluoroplastic ring is 1mm, and the width of the sealing groove is 6.0mm, 7.8mm, 8.0mm, and 9.2mm. The test is carried out to determine that the sealing performance is best when the sealing groove width is 9.2mm. Among them, when the sealing groove width is 9.2mm, the stress-strain of the three stages is as follows Figure 4As shown in the figure, the first stage results include the stress and strain of the mesh model after the rubber ring is deformed, the second stage results include the stress and strain of the mesh model after the fluoroplastic ring and the rubber ring are deformed, and the third stage results include the stress and strain of the mesh model after the fluoroplastic ring and the rubber ring are deformed; the calculation results of the sealing performance are shown in the following table:

[0043]

[0044] In addition, comparative tests were conducted with the sealing groove width of 9.2mm and the fluoroplastic ring widths of 0.8mm, 1.0mm, and 1.2mm, respectively, and it was determined that the sealing performance was best when the fluoroplastic ring width was 1mm.

[0045] Of course, the width of the sealing groove and the width of the fluoroplastic ring can also be adjusted at the same time to determine the sealing structure with the best sealing performance. Generally speaking, as the width of the fluoroplastic ring increases, the contact stress will decrease, which can prevent the fluoroplastic ring from excessive deformation. However, if the width of the fluoroplastic ring is too thick, the width left for the rubber ring in the sealing groove will be too small, which is also a factor that needs to be considered.

Claims

1. A method for evaluating the sealing performance of an aviation large-load long-stroke actuator, wherein an annular sealing groove is provided on the inner side of a sleeve of the actuator, and two fluoroplastic rings and a rubber ring are installed in the sealing groove, and the fluoroplastic ring and the rubber ring are both sleeved on a piston rod, and the two fluoroplastic rings are located on both sides of the rubber ring and at the end of the sealing groove; the piston rod, the sleeve, the fluoroplastic ring and the rubber ring constitute a sealing structure; the evaluation method comprises the following steps: Step 1: The sleeve and the piston rod are completely fixed to simulate the state in which the rubber ring is compressed and squeezed into the sealing groove during assembly, and a model of the sealing structure is established and meshed to obtain a first mesh model; According to the material properties and contact properties of the sealing structure, a mesh model of the fluoroplastic ring and the rubber ring after deformation in the first mesh model is obtained, and a mapping calculation is performed to obtain a second mesh model; Step 2: The constraint sleeve of the second grid model is completely fixed to constrain the piston rod to move only in the axial direction, so as to simulate the contact state between the rubber ring and the fluoroplastic ring when the piston rod moves axially; The piston rod is axially displaced by a preset distance, and a mesh model of the fluoroplastic ring and the rubber ring after deformation in the second model is obtained according to the material properties and contact properties of the sealing structure, and a third mesh model is obtained by performing mapping calculation; Step 3: Constrain the piston rod and the sleeve of the third grid model to be completely fixed, and apply a preset surface pressure to the non-contacting parts of the rubber ring, the piston rod, and the inner side of the sealing groove to simulate the state of the rubber ring and the fluoroplastic ring after the medium oil pressure is increased; According to the material properties and contact properties of the sealing structure, a mesh model of the fluoroplastic ring and the rubber ring after deformation in the third mesh model is obtained; The sealing performance of the actuator is evaluated based on the stress and strain data recorded at each node in the third grid model; Among them, the method for mapping calculation of grid model A is: establish a model with the same outer contour as grid model A and perform grid division to obtain grid model B. For any node C in grid model B, if there is a node D corresponding to the position of node C in grid model A, the stress and strain data of node D are assigned to node C. Otherwise, find the grid unit E corresponding to the position of node C in grid model A, interpolate the stress and strain data of each node in grid unit E and assign them to node C.

2. The sealing performance evaluation method of an aviation large-load long-stroke actuator according to claim 1 is characterized in that: When establishing the model of the sealing structure in step 1, only a two-dimensional axisymmetric model of the sealing structure cross section is established.

3. The sealing performance evaluation method of an aviation large-load long-stroke actuator according to claim 1 is characterized in that: In step three, the sealing performance of the actuator is evaluated based on the maximum contact stress criterion and the shear stress criterion.

4. The sealing performance evaluation method of an aviation heavy-load long-stroke actuator according to claim 1 is characterized in that: The fluoroplastic ring is made of polytetrafluoroethylene, and the rubber ring is made of nitrile rubber.

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