Study On Fluid-structure Coupled Vibration And Stability Of High Speed Multi-plates Open Wet Clutches

Wet clutch is widely used in various transmissions as a core component for its high thermal capacity,excellent shifting performance.The shear stress of the lubrication oil causes drag torque inevitably when the wet clutch has speed differential between the input and the output.The drag torque leads to power loss.The decrease of drag torque is one of most effective measurements of improving transmission efficiency.The experimental results reveal that the impact vibration will happen between the ffrictional plates when the rotating speed is up to 70m/s,which leads to sharp increase of the drag torque and the power loss.The impact vibration will,in addition,cause thermal damage of frictional plates.The preliminary analysis concludes that flow-structure interaction induces the impact vibration.The aeration of oil at high speed range reduces the flow stiffness and damping,which causes the vibration easily.Impact vibration is induced when the energy generated by flow is more than that absorbed by damping at high speed.A transverse vibration dynamic model of flexible rotating plate is built considering the centrifugal stress.Model simulation shows that the critical speed of rotating frictional plate is much more than the working speed at which impact vibration happens.The impact vibration is not induced by the flutter of rotating frictional plate.It is necessary to make the flow-structure coupled analyses to reveal the impact vibration mechanism.A homogeneous flow model and a flow-structure coupled dynamic model are developed against the impact vibration of wet clutch.Flow stiffness and damping are introduced to couple the plates' impact vibration.A FEM algorithm is presented to numerically solve the zero-order lubrication equation and first-order lubricaation equation.Nine stiffness coefficients and nine damping coefficients are deduced by numerical integral.The axial motion and the wobble motion are not coupled in case of alignment,but they are coupled in case of misalignment.However,the influences on axial stiffness,axial damping,direct stiffness,cross-coupled stiffness,direct damping and cross-coupled damping can be ignored.A model of axial vibration is built to analysis the axial stability.Self-excited vibration will induce by negative damping coefficient in spiral groove when the clearance is small,and speed number is larger than critical value.The reason is that the spiral groove is able to obtain high hydrodynamic pressure.A model are also developed to analysis the wobble stability and wobble self-excited vibration.Spiral groove can improve dimensionless equivalent stiffness coefficient,so it has high wobble stability.The damping generated by two phase flow is small,because the dimensionless equivalent stiffness coefficient is close to direct stiffness coefficient.The only improvement of wobbly stability is to increase the critical disturbance frequency and provide extra damping.Like the half frequency whirling is the inherent characteristics of journal bearing,the critical frequency ratio is about 0.5.The test results confirm that the condition of wobble self-excited vibration is much easily satisfied than that of axial self-excited vibration.Thus,the impact vibration is mainly characterized by the wobble vibration.The analysis on effects of stability and the groove optimization are completed.The characteristics of stiffness and damping for T groove and herringbone groove are presented.The wobble stable working zones of classical groove are calculated according to flow-structure coupled model.Convergence clearance favors the improvement of axial damping and dimensionless equivalent stiffness coefficient,so it improves the stability of axial self-excited vibration and wobble self-excited vibration.The feasibility of improving wobble vibration through extra stiffness and damping material is also studies.The impact model of the rotating frictional plates is built,and the analysis of nonlinear characteristics of wobbles vibration is presented.Phase angle of impact ranges from-180°~180° after wobble instability,which means the nutation of the rotating plates.The wobble vibration with periodic characteristic is determined by the fluid stiffness,damping and the inertia of plate.But it already has the nonlinear characteristics and the non-coincident phase trajectory.High speed drag torque model considering impact and friction is built and validated by experimental results.The research findings on flow-structure coupled vibration can support the instability analyses of high speed wet clutch,and propose the solving measures to reduce the impact vibration,which is of important theoretical significance and practical value.