Simulation Analysis of Shock Absorber Lip Seal

Transcription

1 Simulation Analysis of Shock Absorber Lip Seal Dandan Zhao 1, Yonggang Lv 2, Qingue Zhang 3 1,2,3 College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qianwangang Road, Qingdao, Shandong, China Abstract Shock absorber lip seal is a key component to guarantee the normal work of the shock absorber. To further study on the sealing performance of the shock absorber lip seal, this study firstly analyzed the structure and sealing theory of the shock absorber lip seal for determining factors that affect the sealing performance of the shock absorber at the stage of initial assembly, inner and outer stroke. Then, the simulation analysis of the shock absorber lip seal was carried out at the stage of initial assembly, inner and outer stroke. The results show that the Von Mises stress of the shock absorber lip seal is mainly concentrated on the lip and waist at the stage of initial assembly, inner and outer stroke, the maimum stress of inner and outer stroke are greater than of initial assembly, and the maimum stress of inner stroke is greater than of outer stroke. Moreover, the contact pressure distribution of shock absorber lip seal in the stage of initial assembly, inner and outer stroke are similar to the triangle, the maimum contact pressure of the inner and outer stroke are essentially equal, but less than the maimum contact pressure of initial assembly. These results coincided with the actual working condition of the shock absorber lip seal. The conclusions show that not only has great significance to the research of the shock absorber lip seal but also has an important reference value for researching on sealing performance of reciprocating oil seal. Keywords shock absorber lip seal; contact pressure; Von Mises stress; initial assembly; insert outer stroke; inner stroke I. INTRODUCTION Shock absorber lip seal is an important part of the shock absorber, once the shock absorber lip seal failure can make shock absorber leakage and abnormal sound, and affect the vehicle comfort, stability and safety [1-3]. Many researchers have studied the sealing performance of the shock absorber lip seal. Müller HK et al. [4] and Suetsugu N et al. [5] investigated the sealing mechanism of the reciprocating oil seal, and proposed that lip seal volume was deformed and contact pressure occurred between the seal and the piston rod after the reciprocating oil seal was installed on the piston rod. Nikas GK [6] calculated the static contact pressure of the reciprocating rectangular oil seal for reducing the leakage and wear of oil seals. Prokop J et al. [7] and Mao JF et al. [8] analyzed the contact pressure of the PTEF oil seal and the combined oil seal using the finite element method respectively, whereas this method was not suitable for the lip seal. Salant RF et al. [9] built the numerical model of reciprocating piston rod lip seal and researched the contact condition of lip seal. Choi HJ et al. [10] achieved the optimum design of shock absorber lip seal structure by analyzing the contact area, stress and contact pressure distribution of the lip seal with the method of finite element analysis. By all accounts, the stress and contact pressure distribution of shock absorber lip seal have been studied, while the analysis of shock absorber lip seal is based on the initial assembly stage, and there is no study on the distribution of stress and contact pressure in different working process of shock absorber lip seal. To compensate for the lack of researches, this study analyzes the structure and sealing mechanism of the shock absorber lip seal, and the simulation analysis method of the lip seal is proposed in the stage of initial assembly, inner and outer stroke. The analysis results of initial assembly, inner and outer DOI : /IJRTER ZL99V 253

2 stroke stage are compared, which has great value to the design and the improvement of sealing performance of shock absorber lip seal. II. METHODOLOGY 2.1. Structure of the shock absorber lip seal The lip seal is widely used in the shock absorber because of its good sealing performance. As shown in Figure 1, the shock absorber lip seal is mainly composed of the main lip, dust lip, spring and skeleton. Piston rod Air Dust lip Skeleton B d' d β Spring b α Oil R Main lip Figure 1. Schematic diagram of shock absorber lip seal In Figure 1, B is the width of the shock absorber lip seal, D and d are outside and inside diameter of the shock absorber lip seal, α and β are oil and air side angle of the shock absorber lip seal, R is the distance between the lip and the center of the spring, d' is diameter of the piston rod and b is the width of the contact area between the seal and the piston rod. The static contact pressure is generated because of lip seal is installed on the piston rod by the interference fit. The maimum static contact pressure locates in the lip, and to decay along both sides of the static maimum contact pressure. The size of static contact pressure plays an important role in the sealing performance of lip seal. The static contact pressure too large which can cause the lip seal aging and generate abnormal sound, in contrast, the static contact pressure too small will make the lip seal leakage, and the shrink range δ affects the size of static contact pressure: d d δ= (1) 2 The static contact pressure distribution is asymmetric because of oil and air side angle of the shock absorber lip seal are unequal, and the maimum value near the oil side. In addition, the distance between the lip and the center of the spring also affects the static contact pressure distribution [11] The hydrodynamic theory of the shock absorber lip seal Friction is generated between the seal lip and the piston rod when the piston rod moves, and lip surface eposed micro rough teture which form microscopic hydrodynamic wedge, thus forming the hydrodynamic oil film to generate dynamic pressure and prevent oil leakage. The contact pressure between the seal lip and the piston rod is composed of the static contact pressure and oil film dynamic pressure, and oil film dynamic pressure does not effectively change the distribution of the static contact pressure because the oil film thickness is only a few tenths of microns, but oil film dynamic pressure can offset part of the static contact pressure, so it is assumed that the oil film pressure has the same distribution as the static contact pressure. A working cycle of the piston rod includes inner and outer stroke. In the outer stroke, most of the oil is scraped and only a thin layer of oil film is adsorbed on the surface of the piston rod, and adsorbed oil film is pumped back to the All Rights Reserved 254

3 cylinder in the inner stroke, thus the lip seal leakage is the difference between the two stroke leakages. The oil flow of the shock absorber lip seal can be regarded as one-dimensional flow because of the symmetry in the circumferential direction. Etending direction of the piston rod is the forward direction of ais, and the contact pressure and oil film distribution are shown in Figure 2. p ω A Oil A Shock absorber oil seal Air h 0 d' Piston rod (a) Oil film pressure and velocity distribution of the outer stroke u 0 p ω E Oil Shock absorber oil seal E h 1 h 0 Air u 1 Piston rod (b) Oil film pressure and velocity distribution of the inner stroke Figure 2. Oil film pressure and velocity distribution of shock absorber lip seal In Figure 2, p is oil film pressure, d' is diameter of the piston rod, u0 is the speed of the piston rod in the outer stroke, ωa is the maimum pressure gradient in the outer stroke, dp ω A = d, h 0 is the A residual oil film thickness in the outer stroke, ωe is the maimum pressure gradient in the inner stroke, dp ω E = d, u 1 is the speed of the piston rod in the inner stroke and h1 is the residual oil film E thickness in the inner stroke. According to the one-dimensional Reynolds equation, the leakage Q of a working cycle of the piston rod can be deduced [4]: 2μ u0 u 1 Q πdl 9 ωa ω (2) E In equation (2), L is stroke of the piston rod and μ is dynamic viscosity of oil. Can be deduced from the above, shock absorber lip seal leakage relates to piston rod diameter, stroke, oil dynamic viscosity, eternal stroke and speed of the piston rod, internal stroke and speed of the piston rod and the maimum oil film pressure gradient of the outer stroke and the inner stroke. However, the piston rod diameter, eternal speed and internal speed of the piston rod, oil dynamic viscosity and stroke are fied values for the specified type of shock absorber, so that the shock absorber lip seal leakage is only related to the maimum oil film pressure gradient of the outer stroke and the inner stroke. The maimum oil film pressure gradient of the outer stroke and the inner stroke can be obtained according to the static contact pressure distribution because of the oil film pressure has the same distribution as the static contact pressure. All Rights Reserved 255

4 III. SIMULATION ANALYSIS The shock absorber lip seal is simulated as shown in Table 1. The Von Mises stress and the contact pressure distribution are studied at the stage of initial assembly, inner and outer stroke according to the simulation results. Table 1. Parameters of shock absorber oil seal Parameters values D(mm) 32 d(mm) 16 B(mm) 8 R(mm) 0.4 δ(mm) 0.5 β α Because of forces of the shock absorber lip seal are the symmetry in the circumferential direction, so it only needs to carry out the finite element simulation analysis to the two-dimensional plane model of the shock absorber lip seal. The material of the lip seal is acrylonitrile-butadiene rubber, and it belongs to the super elastic material. The 2 parameter Mooney-Rivlin material model is adopted, in which C01=1.47, C10= The super elastic element hyper74 are used to mesh the lip seal, and the element Plane82 is used to divide the skeleton and spring into the grid. In addition, the elastic modulus of the skeleton is 2e5 Mpa, and the Poisson's ratio of the skeleton and the spring is 0.3. The finite element model of the shock absorber lip seal is shown in Figure o 45 o Figure 3. Finite element model of the shock absorber lip seal Contact pairs are built between the spring and the lip seal, the seal lip and the piston rod. The corresponding constraints and loads are applied to finite element model of the shock absorber lip seal, and simulated the shock absorber lip seal in the stage of initial assembly, inner and outer stroke. Among them, the speed of the outer stroke u0=3 m/s, the speed of the inner stroke u1=1 m/s and the stroke is 15 mm. The Von Mises stress of the shock absorber lip seal is shown in Figure 4. (a) Von Mises stress cloud picture of the Initial All Rights Reserved 256

5 (a) Von Mises stress cloud picture of the Initial assembly (c) Von Mises stress cloud picture of the inner stroke Figure 4. Von Mises stress cloud picture of the shock absorber lip seal In Figure 4, the Von Mises stress of the shock absorber lip seal is mainly concentrated on the lip and waist at the stage of initial assembly, inner and outer stroke, and the maimum stress of initial assembly, inner and outer stroke are 6.61Mpa, 6.52Mpa and 5.87Mpa. The maimum stress of inner stroke and outer stroke are greater than of initial assembly, and the maimum stress of inner stroke is greater than of outer stroke. It is consistent with the practical work condition of the shock absorber lip seal, because the piston rod in addition to has the surplus force also has the friction resistance, and due to oil side angle is great than air side angle which make friction resistance of inner stroke is larger than of outer stroke. Contact pressure cloud picture of the initial assembly, inner and outer stroke are shown in Figure 5. (a) Contact pressure distribution cloud picture of the Initial assembly (b) Contact pressure distribution cloud picture of the outer All Rights Reserved 257

6 (c) Contact pressure distribution cloud picture of the inner stroke Figure 5. Contact pressure distribution cloud picture of the shock absorber lip seal In Figure 5, the contact pressure distribution of shock absorber lip seal in the stage of initial assembly, inner and outer stroke are similar to the triangle, the maimum value near the oil side, and to decay along both sides of the maimum contact pressure. The maimum contact pressure of the inner stroke and outer stroke are essentially equal, but less than the maimum contact pressure of initial assembly. It is shown that the motion of the piston rod has no influence on the contact pressure distribution and size of the contact pressure, and is consistent with the hydrodynamic analysis results of the 2 section. IV. CONCLUSIONS In order to study the stress and contact pressure distribution of the specific working process of the shock absorber lip seal, the structure and fluid dynamic sealing mechanism of the shock absorber lip seal were analyzed, and simulated the shock absorber lip seal in the stage of initial assembly, inner and outer stroke. The conclusions were obtained: (1) The Von Mises stress of the shock absorber lip seal is mainly concentrated on the lip and waist at the stage of initial assembly, the maimum stress of inner stroke and outer stroke are greater than of initial assembly, and the maimum stress of inner stroke is greater than of outer stroke. (2) The contact pressure distribution of the shock absorber lip seal in the stage of initial assembly, inner and outer stroke are similar to the triangle, the maimum contact pressure of the inner stroke and outer stroke are essentially equal, but less than the maimum contact pressure of initial assembly. (3) The motion of the piston rod has no influence on the contact pressure distribution and size of the contact pressure, and the pressure gradient of the outer stroke is greater than of the inner stroke. In addition, the research on the sealing performance of the shock absorber lip seal should consider the stage of initial assembly, inner and outer stroke, can not simply analyze one stage. The present study is significant in finding an ideal way to research shock absorber lip seal for improving sealing performance. However, the method cannot be directly applied to other type reciprocating oil seals. ACKNOWLEDGEMENT This work was supported by the National Natural Science Foundation of China (Grant Nos and ), the Special Funds for Cultivation of Taishan Scholars, the Shandong Provincial Natural Science Foundation of China (Grant Nos. ZR2015EM017 and ZR2014EEM021), and the Science and Technology Development Program of Shandong Province (Grant No. 2014GGX103043). REFERENCES [1] J. C. Dion, The Shock Absorber Handbook, SAE International, J. Wiley, [2] S. B. Purohit, S. R. Lapalikar, and V. Jain, Effect of road profile and curves generated by wheel on the performance of a shock absorber of a motorcycle, Indian Journal of Science and Technology, vol. 4, no.5, pp , All Rights Reserved 258

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