A new unified theory for flow analysis of magneto-rheological (MR) fluids and application of MR fluids in a high-torque clutch.

摘要

The focus of this study is to develop a new unified approach for the flow analysis of magneto-rheological (MR) fluids through channels without using the concept of shear yield stress property of MR fluids. For engineering analysis of MR fluid flow, it is customary to assume a constitutive model, such as, Bingham Plastic or Herschel-Bulkley model which depends on definition of a unique shear yield stress. At macroscopic level, the shear yield stress experimental data traditionally is obtained for MR fluid flow over a steel surface. However, preliminary studies showed that if the material and geometric characteristic of the wall surface change, different shear yield stress values are obtained.;In the present study it is attempted to demonstrate that a unique shear yield stress does not exist and that shear yield stress is not a material property. An extensive experimental study is conducted to investigate the relationship between the pressure drop (directly proportional to the shear stress) of a MR fluid as a function of the applied magnetic field strength, volumetric flow rate, and surface roughness, without utilizing the concept of shear yield stress. A unified method is developed in order to determine the non-dimensional friction factor, which is defined as normalized shear stress, in terms of dimensionless Mason number and dimensionless surface morphology parameters. It is demonstrated that, for a given surface morphology, the proposed unified method can estimate the friction factor of MR fluid flow with a single curve for all flow rates and magnetic fields that are considered in this study, without using a shear yield stress.;The current study has also focused on a practical application of a MR fluid in an automotive limited slip (LSD) differential clutch. The design, development, performance characterization and heating analysis of a MR fluid LSD is presented in the second part of this dissertation. The controllability of MR fluids provides a controlled torque transmission and slippage for an LSD application. Three-dimensional electromagnetic finite element analyses (FEA) are performed to optimize the magnetic circuit and clutch design. Based on the results obtained from the FEA, the theoretical torque transfer capacity of the clutch is predicted utilizing Bingham-Plastic constitutive model of the MR fluid, based on the findings of the first part of this dissertation. Theoretical studies on heating of the MR fluid LSD clutch are also presented. A lumped parameter system approach is assumed for theoretical heating analysis.;The clutch is characterized at different velocities and electromagnet input currents. The torque transfer capacity, the response time of the clutch and effects of the electric power input and slippage on temperature rise of the clutch are examined. The effect of temperature rise on the torque performance of the clutch is also examined. It is demonstrated that the proposed MR fluid LSD clutch is capable of transferring controllable high torques with a fast response time. The effect of temperature increase on the torque performance of the clutch is also examined. The results showed that the transferred torque is insensitive to clutch temperature increase. For all cases, theoretical and experimental results are in excellent agreement.