| Based on Newton’s law of viscosity, Hydro-viscous drive, HVD for short, uses viscous fluid as its working medium, relying on fluid shear force between multiple sets of rotating friction disks to transfer power. It is a new type of fluid power transmission. HVD shows remarkable energy-saving effect when it is used in the soft-start of high-power water pumps, fans or belt conveyors. A vast literature for relative research shows shat fluctuation of output torque for HVD is the key factor which influences the stability of power transmission. The transmission of output torque is closely related to shear capacity about the oil film between the disks and contact characteristics of micro convex body from the disks themselves. The thesis focuses on researching the friction disks and the oil film between the disks. Based on the theory of fluid mechanics, heat transfer and elasto-plastic mechanics, the effect of some factors on the influence mechanism of power transmission is analyzed using methods of theoretical calculation, numerical simulation and experiment. The research also highlights thermal deformation of the disks and the disturbed fluid dynamic distribution of the oil film between the disks. Then the main research contents are put forward.Based on the theory of shear-film and squeeze-film considering the fluid-inertia item and the contact model of rough surface in which asperity contact properties is described, the oil film thickness rate and the relative angular velocity rate of the soft-startis deduced by means of the principle of bearing capacity balance and torque balance. And then the calculation model of total output torque and viscous torque of HVD during the soft-start is also derived. The effect of some factors, including boundary conditions, the ratio of real contact area and unit nominal area, material properties, kinematic parameters and structure parameters on power transmission are analyzed by numerical calculation.Based on the principle of pressure distribution of multidisk friction pairs, heat flux model about frictional heat during the soft-start is deduced. And then the FEMs (finite element method) of 2D temperature field and 3D temperature field of the disks are set up based on ANSYS. Transient 2D and 3D temperature distribution of multidisk friction pairs and Transient 3D temperature distribution of a set of friction pairs are calculated. Finally, the effect of fluid-inertia item and some factors on temperature distribution of the disks is investigated.Based on thermo-elasto-plastic constitutive equations and the FEM of non-linear equations, the coupled thermo-mechanical analysis model of the disks is developed. Based on the results of temperature distribution, thermo-elasto-plastic deformation law of the disks during the soft-start is investigated. The influence of four radial displacement constraints, including the disks without constraints, the disks with double constraints in which one is constrained from the outer radius of the separator disk and the other is constrained from the inner radius of the friction disk, single constraint from the outer radius of the separator disk and the inner radius of the friction disk respectively, on displacement field and stress field of the disks is detailedly researched. And then different kinds of saucer-warping deformation and wave-warping deformation can be seen from displacement distribution of the disks.On the basis of the oil film between one set of deformed disks, the mathematical model about the flow field of oil film is established. Analytical results related to the flow such as pressure, velocities and viscous torque of the oil film between axial deformed disks and radial deformed disks are obtained respectively. And then the effect of two kinds of deformation values on power transmission is researched. Numerical investigation is conducted on the fluid dynamic distribution of the oil film between three saucer-warping deformed disks by FLUENT. Then the effects of four working conditions, including constant inlet pressure, constant inlet flow, different jet inclined angles, nonisothermal interfaces on transmission performance are discussed.The special test bench of HVD is developed. The experimental studies of torque transfer characteristics of the oil film between parallel disks and deformed disks are carried out respectively. The influence of inlet flow rate, film thickness, inlet oil temperature, velocity difference and different structure of the disks on temperature distribution of the surface of the disks is analyzed. Furthermore, temperature field and pressure field of the oil film between the disks is researched. The effect of two kinds of deformation values on the stability of torque transfer is also investigated experimentally. The experimental results reflect the dynamic transmission law, which indirectly confirm the previous analysis results. |
PDF Full Text Request