| The viscous coupling is composed of housing,hub,inner plates alternated with outer plates and working fluid-viscous silicone oil.Spacers may be added between erery two inner plates or outer plates in some viscous couplings.It has two working states sheering silicone oil and self-induced torque amplication (STA).Silicone oil is sheered by thin plates to transmitted torque,as is described as Newton Inner Friction Law.While rotating elements of the coupling is experencing grate relative rotating speed for along time,inners plates are drived to associated with outer plates by such reasons as higher temperature,aggrandized pressure and so on.This rigid coulomb friction between plates amplifies transmitted torque in double times or more.So the rotating elements realize equal speed.Silicone oil,as working medium,has large scale concocted viscidity,excellent anti-sheering stability and anti heating stability and anti oxidation stability.This ensures that the viscous coupling works effectively and steadily.Applying the viscous coupling to automobile is a new technology to improve the performance.That being an axis-axis differential is the same as a whell-whell differential can effectively better the utilization between the tyre and the ground.Take a wheel-whell differential for example, silicone is sheering by not big relative rotating speed between left wheel and right wheel.The result is torque can be transmitted between them and assigned variably.Once big relative rotating speed happens longly,STA causes rotating elements in the same speed .The torque is transmitted to an extreme extent and auto acquires strong drag force.In case of axis-axis differential,two-wheel drive changes to four-wheel drive.It can be arranged to be all-time drive orshort-time drive,which also transmits torque variably.With the viscous coupling,the auto improves its portrait accelerating ability,driving security,fuel using potential.The viscous coupling is a research hotspot in both china and overseas.In sheering silicone state,the mathematical and simulative model of torque transmitted and heat transmitted is clearly known.Whereas the theory of STA is not explained convincingly.Most experiments just measure the value of torque transmitted.So is the time when STA occers.The design of coupling is based on semiexperence and smeitheory.At present,the flow field and temperature field in the coupling is under research.They are simulated in this paper.We believe it is good to the understanding of coupling and can help in the design and life-span calculation.In order to simulate the flowing law,the following steps is put in practice.(1) Building the parts and assemble them in CATIA in accordance with its real model.It is the basis of the predigested flow region.In the cooperated simulating setting ANSYS Workbench,the predigested flow region is established,involving an inner plate and an outer plate.The hump phenomenon model is also established,containing two outer plates and a inner plates.(2) Two methods-ICEM CFD and CFX Mehs are adopted to generate the mesh of geometry model of predigested flow region.The gird qulity has great significance to post computational time,convergence,accuracy,the accomplishment of iterativeness.After comparing the two meshes,the simply manipulated and easily controlled quality CFX Mesh is imported to CFX Pre.(3) In ANSYS CFX Pre,at first,the computational flow region is established.In this region,specifics applied are narrated as follows.Multiphase flow is modeled as two fluids exist in thecoupling.Interpahse mass transferring indicates the dissolution andevaporation between the two fluids.Moving grid shows the movement of inner plate due to sicone expandness,augmented pressure etc.MUSIG model indicates the dispersed air's agglomeration and breakup behavior.Sheer stress transport truly depicted that sheering silicone's flow.Total energy equation takes into account the influence of friction and pressure to temperature varying.Use CFX expressional language to programme the density-temperature characteristic,viscidity-temperature and sheering rate characteristic,mass transfer between silicone and air,moving rule of inner plate.The time step and simulational total time is expressed in CEL variables.So they can be changed easily.(4) The simulation results under one working situation are given as many as possible.Most of them are in graph.The results include transmitted torque magnitude,the velocity distribution of silicone,the dispersing distribution of air,pressure distribution on plates,pressure grads on plates and so on.These results are provided to expose the flow disciplinarian.The transmitted torques under different rotating velocities are protracted.The figure indicates that the torque grows more and more slowly accompanied with growing rotating velocity.(5) About STP,several explainal learned standpoints are Introduced and comparison are drawed.The process of STA is simulated.The results shows that after a stable working time.the banlance is broken.The inner plate begins to move and the transmitted torque are amplified.The velocity field and the temperature field under STA are given in graph.The pressure distribution,the air bubble distribution,the shape of plates etc are the induced factors to trigger STA.(6) The plates expand owing to friction with silicone oil and heat.It brings stresses and strain.These not only influence the design of plates,but also influence the flow field.Make use of both ANSYS and ANSYS CFX to simulate this fluid-solid coupling fields.InANSYS Workbench the simulation project is built,including solid plates and its surrounding flow field.The solid plate is in solid structure mesh and the surrounding flow field is in CFX mesh.Define the solid plate as a flexible dynamics body.The next step is to write the ANSYS input file.Then followed by simulation in ANSYS CFX.The total stresses field,main stresses field,structure and heat strain about plates are given.The results indicate that the magnitude isnot large.It verifies that coulomb friction between plates are the main factor of wearing.From researches above,it is believed that the knowing about viscous coupling is added.But there are still very much work to do to comprehend it deeply.Hope that in a short while we can understand it in every detail.
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