Analysis And Design Of Magneto-rheological Automotive Fan Clutch

Magnetorheological (MR) fluids are suspensions of micron-sized, magnetizable particles in a carrier fluid such as synthetic oil and silicone oil, which are regarded as the intelligent materials that respond to an applied magnetic field with a change in their rheological properties. In the absence of an applied magnetic field, MR fluids exhibit Newtonian-fluid-like behavior. Upon application of a magnetic field, the polarization between two induced dipoles causes the suspended particles in the MR fluids to form a chain-like microstructure aligned with the direction of the applied magnetic field. The magnetic chain structure restricts the movement of the MR fluids, thereby changing the rheological properties of the suspension. These fluids exhibit a Bingham plastic behavior with the yield stress dependent upon strength of applied magnetic field. Thus MR fluids are viscoplastic fluids because they have the properties of both viscosity and plasticity. These fluids can be used in MR devices, the mechanical properties of which are controlled by the applied magnetic field,such as MR clutches and dampers.Automobile fan MR clutch is the device that transmit the torque by the shear stress of the MR fluids upon the applied magnetic flied. In order to establish the design method of the MR clutch, in this dissertation, the MR fluids materials and their applications have been analyzed. Based on the properties that the yield stress of MR fluids can be controlled by applied magnetic field, the flow of MR fluid between two circular plates in the MR clutch is investigated. The equation for the transmitting torque in the MR clutch has been derived. The geometrical design method is put forward to provide the theoretical foundation for the design of the MR clutch.The main work and conclusions in this dissertation are as follows:(1) The constitute and the main performance of MR fluids are introduced. Bingham model is used to describe the constitutive characteristics of MR fluids for direct-shear flow mode.(2) The mechanism that MR fluids result in MR effect has been analyzed. Based on the chain-like mode, equation for the yield stress of MR fluids is derived to provide the theoretical foundation for the parameters optimization design of the MR fluids.(3) Based on Bingham model and Navior-Stokes equation, the flows of the MR fluids in the automobile fan MR clutch is investigated. The equation for the torque developed by the MR clutch is derived. The results indicate that with the increase of the applied magnetic field strength the torque developed by the MR fluid goes up rapidly.(4) The torque transmitted by the automobile fan MR clutch can been divided into the viscous component with no magnetic field applied and the yield stress component with magnetically saturated. In order to provide the calculations of the key dimension parameters in the MR clutch, the active fluid volume that MR fluids result in MR effect is introduced. The relationship between the parameters of the key dimension and the parameters of the MR fluids material, speed, mechanical power and magnetic field strength is established. The results indicate that the MR fluid material parameters can be chosen when the mechanical power, speed and anticipated performance of the MR clutch, and the gap between two circular plates and the radius of circular plate in the MR clutch can been calculated.(5) ANSYS software is used to analyze the imitation optimization of magnetic back track and the MR clutch performance. It has been shown that the values of the torque calculated by the model agree with the imitation data.In this dissertation the contributions are summarized as follows:(1) The equation for the torque transmitted by the automobile fan MR clutch is established. The mechanism for transmitting force of the MR clutch is revealed.(2) The expression for the gap between two circular plates in automobile fan MR clutch is proposed to provide the theoretical foundation for the design of the MR clutch.