Research On Flow Field Characteristics Between Friction Plates Based On CFD Of Wet Clutch And Its Optimized Design

The requirements of large tractor on the stability of its transmission system,fuel economy,driver’s comfort and service life are increasingly under the working environment of high speed,heavy load and frequent engagement.The wet clutch is the core component of the tractor transmission system,and its performance directly affects the overall performance of the gearbox.The wet clutch transmits power through the friction torque of the main and follower plates during the engagement process.During this process,heat will be generated to increase the temperature of the friction plate.When the temperature is too high,the friction plate will be permanently invalid.In addition,temperature changes will affect the friction coefficient,causing the friction pair to produce impact during engagement,which may have a bad effect on the comfort of the driver.Therefore,studying the flow field performance of the cooling oil in the friction lining is essential to reduce the thermal failure of the friction plate and maintain good friction performance of the wet clutch.At present,there are few researches on the flow performance and convection heat transfer performance of the cooling oil between the friction plate by using computational fluid dynamics(CFD)technology.The existing research simplifies the oil film flow field to a large extent,ignoring the influence of the oil groove structure on the flow field.Based on this,the main research contents of this paper are as follows:1.Combined with the performance indicators and design requirements of the wet clutch,the suitable friction pair materials,reserve coefficients and sealing devices were selected and the design and calculation of the key components of the wet clutch were completed,Besides,the Creo software was used to establish a three-dimensional solid model of the wet clutch.2.The cylinder block and piston were lightened by topology optimization method.The volume and mass of the cylinder block were reduced by 49.97% and 50.28% respectively,and the volume and mass of the piston were reduced by 31.24% and 31.25% respectively.3.Based on CFD basic control theory and flow field numerical calculation method,the Fluent module in ANSYS Workbench was adopted to simulate and analyze the flow field performance between square oil grooves,radial oil grooves,arc rhombic oil grooves,and composite oil groove friction plate.Meanwhile the effects of oil groove structure,inlet oil flow rate and speed difference on the thermal characteristics of friction plate were studied.The research results showed that the flow state of the cooling lubricating oil in different oil tank structures was also different.Under the structure size designed in this paper,the highest temperature distribution on the friction plate surface can be obtained as follows:Tmax-No>Tmax-Square>Tmax-Radial>Tmax-Arc rhombus>Tmax-Complex.In addition,the inlet oil flow rate and the rotational speed difference both had effects on the temperature of the friction plate during engagement.The greater the inlet oil flow,the lower the temperature of the friction plate;and the greater the rotational speed difference,the higher the temperature of the friction plate.4.The response surface optimization method was used to optimize the structure of the square oil groove friction plate.Through the analysis of sensitivity and response surface,the influence of the interaction of oil groove width,oil groove depth and friction plate thickness on the maximum temperature of friction plate surface and the maximum flow rate of lubricating oil was obtained.After optimization,the maximum temperature of the friction lining surface was reduced by 3.05 K,and the maximum flow rate was increased by0.22%.The response surface optimization method was used to optimize the cylinder block and piston,and the influence of dimension parameters on the maximum deformation and equivalent stress of cylinder block and piston was studied.After optimization,the maximum deformation value and maximum equivalent stress value of the cylinder block and piston were both reduced.In summary,this article focused on the internal flow field characteristics of the friction plate of the wet clutch with different oil groove structures,explored the influence of different factors on the surface temperature of the friction plate during the engagement process,and optimized the structure of the square oil groove friction plate,cylinder and piston of the wet clutch.The research can provide a basis for the simulation analysis of the flow field performance of the wet clutch friction plate using CFD technology,provide a reference for the optimization design and selection of the friction plate oil groove structure,and provide a research idea for the independent design and development of new wet clutch structure in China.The research on the subject will be beneficial to prolong the service life of wet clutches and can help to improve the overall performance of the large tractor transmission system,which is of great significance to the stable and safe operation of tractor.