A numerical model to predict film torque of hydro-viscous clutch was developed.The model was established with computational fluid dynamics(CFD).The pressure distribution,velocity of flow and film torque were obtained based on vertical-horizontal grooved plate and radial grooved plate separately.The boundary conditions,such as the relative rotation,the fluid temperature and the oil feeding pressure,were also discussed.The results showed that the film torque of two kinds of grooved plate increased with increasing relative rotation.However,the film torque decreased with increasing fluid temperature and feeding pressure.Meanwhile,the film torque of radial grooved plate was less than vertical-horizontal grooved plate at the same condition.Our study showed that the model can efficiently calculate the film torque with complex geometry parameters and boundary conditions.
Rotational speed stability is an important evaluation indicator of the performance of a hydro-viscous clutch(HVC).To improve the rotational speed stability of HVCs in mixed lubrication and the running condition of the friction pairs,the speed stability of an HVC in mixed lubrication was studied.To this end,the friction coefficients of both copper-based and paper-based friction pairs were experimentally tested using an MM1000-III wet friction machine.Theoretically,a torsional vibration model of the system is presented.The phase plane analysis method is applied to evaluate the stability of the torsional vibration model,where a critical negative gradient(CNG)is defined.The results show that the friction coefficient in mixed lubrication is an important parameter for the stability of the rotational speed.The system will be unstable when the negative gradient of the friction coefficient-slip speed is larger than the CNG.According to the definition of the CNG,suggestions regarding choice of friction pairs are made to improve the rotational speed stability of an HVC in mixed lubrication.
The current design of hydro-viscous clutch(HVC)in tracked vehicle fan transmission mainly focuses on high-speed and high power.However,the fluid torque under the influence of fluid temperature can not be predicted accurately by conventional mathematical model or experimental research.In order to validate the fluid torque of HVC by taking the viscosity-temperature characteristic of fluid into account,the test rig is designed.The outlet oil temperature is measured and fitted with different rotation speed,oil film thickness,oil flow rate,and inlet oil temperature.Meanwhile,the film torque can be obtained.Based on Navier-Stokes equations and the continuity equation,the mathematical model of fluid torque is proposed in cylindrical coordinate.Iterative method is employed to solve the equations.The radial and tangential speed distribution,radial pressure distribution and theoretical flow rate are determined and analyzed.The models of equivalent radius and fluid torque of friction pairs are introduced.The experimental and theoretical results indicate that tangential speed distribution is mainly determined by the relative rotating speed between the friction plate and the separator disc.However,the radial speed distribution and pressure distribution are dominated by pressure difference at the lower rotating speed.The oil film fills the clearance and the film torque increases with increasing rotating speed.However,when the speed reaches a certain value,the centrifugal force will play an important role on the fluid distribution.The pressure is negative at the outer radius when inlet flow rate is less than theoretical flow,so the film starts to shrink which decreases the film torque sharply.The theoretical fluid torque has good agreement with the experimental data.This research proposes a new fluid torque mathematical model which may predict the film torque under the influence of temperature more accurately.
CUI HongweiYAO ShouwenYAN QingdongFENG ShanshanLIU Qian
