| Sealing performance is one of the most important indicators for assessing engine performance and quality during engine manufacturing and assembly.Poor sealing performance of the engine can cause water leakage,oil leakage and air leakage,which will not only cause engine power loss,service life decreasing,but also lead to environmental pollution and energy waste.One of the main reasons for poor engine sealing is that the sealing performance of the matched surface between cylinder head and cylinder body is poor.The sealing performance of this matched surface is the result combining of the manufacturing precision of the matched surface,the manufacturing precision of the gasket,the tightening order of the cylinder head bolt,consistency of the preload force and the material characteristics of each component.The surface topography of this engine matched surface is the first link to have an effect.If the surface morphology of the matched surface does not meet the sealing requirements,subsequent inspection and assembly will become meaningless.Therefore,it has a great significance to explore the sealing of the matched surface between cylinder body and head from the perspective of surface topography.The laser holographic interferometry technology has the characteristics of non-contact,high speed,large field of view and high precision.It can quickly and accurately obtain the highprecision surface topography of the matched surface,and provide a method for studying the sealing performance of the matched surface between cylinder head and body.In this paper,based on laser holographic interferometry measurement,the sealing performance of matched surface between cylinder body and head is studied.The main research work is as follows:(1)Analysis of the sealing principle of the matched surfaceThe process and mechanism of the sealing surface between the cylinder body and cylinder head,the form of the gasket sealing and the root cause of leakage were explored.Based on the finite element model of the flange gasket sealing,the compression and rebound characteristics of the gasket during the sealing process were analyzed.Then based on the fractal theory of the metal gasket leakage model,the effects of the characteristics of the sealed medium,surface roughness,and bolt pre-tension on the leakage were analyzed.(2)Model establishment for the relationship between microscopic surface topography parameters and leakage amountMicroscopic topography model and point cloud data of the matched surface were obtained based on laser holographic interferometry measurement.The point cloud data is processed,and the required surface topography parameters are extracted and calculated.Through the data processing,the relationship between the surface micro-topography parameters and the leakage amount of the machined surface was obtained,and the characteristics of the surface topography parameters of the machined surface to ensure the sealing performance of the matched surface were obtained.Based on the relational model,the sealing performance of the sealing path was evaluated and the locations where leaks could occur were identified.(3)Model establishment of the matched surfaceBased on the high-precision data measured by laser holographic interferometry and 3D model of the surface morphology of the matched surface,the sample area on the matched surface is selected to establish the contact model and perform the finite element analysis of the sealing matched surface.Based on the contact analysis,the corresponding leakage channel was extracted and the CFD simulation was performed,then the leakage rate of the sample area was obtained.(4)Evaluation of sealing performance for the matched surfaceBased on the measurement data,the sample area most likely to leak on the matched surface of the cylinder head is selected for finite element sealing contact analysis and CFD simulation analysis of the leakage channel,and the leakage rate is calculated.Combined with the relative contact area in the static sealing contact theory to calculate the threshold of the leakage rate,the sealing performance of the two sets of cylinder head matched surfaces was evaluated and the cylinder head where leakage could occur were identified.Based on the high-precision measurement data of the matched surface between cylinder body and cylinder head,the sealing mechanism of the matched surface is explored,and the relationship between the surface topography parameters and the leakage rate is obtained.Based on the measured data,a finite element contact analysis model of the true rough surface morphology of the matched surface was performed.The leakage channel was extracted and the fluid dynamic simulation analysis was performed on the leakage channel.The leakage rate threshold was calculated and the sealing performance of the matched surfaces of the two groups of cylinder heads was evaluated.The matched surfaces of the cylinder heads which is most likely to leak were found. |
