This article presents considerations regarding materials used to fabricate a hydraulic clutch with an ER fluid operating in non-standard working conditions. The hydraulic clutch was a subassembly of the device used for exerting a controlled force on the stationary object. This clutch was driven by an electric motor. The force was controlled by changing the shear stresses in the ER fluid. Shear stresses were changed in two ways: by changing the angular velocity of the electric motor and by changing the high voltage applied to the electrodes located on the driving part and the driven part of the clutch. The increase in these stresses caused an increase in the torque transmitted and an increase in the pressure force. In order to construct the clutch, mathematical models based on the Bingham model were developed, which took into account the influence of temperature and humidity on the shear stress in the ER fluid, allowing calculation of the clutch performance. In addition, numerical calculations of the temperature distribution inside the clutch were carried out using the ANSYS program because of the intense heat generation during the clutch operation. The developed mathematical models were used to optimize the clutch. The aim of the optimization was to obtain a high transmitted torque with small dimensions of the clutch, taking into account the thermal capacity of the clutch. Based on the optimization results, a prototype of a hydraulic clutch with an ER fluid was designed and made, assuming that for metal materials their anti-corrosion properties are the most important, since the presence of conductive metal oxides causes electrical breakdowns. The plastics used in the clutch prototype were mainly evaluated for insulating properties and high temperature resistance. When choosing the ER fluid, its sensitivity to temperature and humidity as well as durability were taken into account. The clutch prototype has been tested on a specially built test rig. The test results confirmed the proper selection of both construction materials and ER fluids. Based on the results of these tests, guidelines for the construction of clutches with ER fluids were formulated.
The article describes design optimization of a viscous disc clutch with an electrorheological (ER) fluid. The design optimization is conducted based on mathematical models of ER fluid and clutch geometry. As important issues for the optimal design, the assumed values are: the torque transferred by the clutch, the dimensions of the clutch and the steady-state operating temperature of the clutch. The assumed design variables are: the angular velocity of the input shaft, the number of working gaps of the clutch and the selected dimensions of the clutch. The aim of the design optimization is to search for design variables such as the angular velocity of the input shaft, the number of working gaps of the clutch and the selected dimensions of the clutch, for which the clutch transfers the highest possible torque, while the dimensions of the clutch are small and the steady-state operating temperature is low. The design optimization is conducted searching at least two different objective functions created taking into account the volume, the transferred torque and the steady-state operating temperature of the clutch. Two numerical methods are used: the Monte Carlo method and the Genetic Algorithm method. The optimization calculations are performed for two sets of design variables, consisting of 3 and 8 elements, and a final prototype designed via the optimization is depicted with the pricipal design parameters.
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The article introduces a new flow rheometer of a simple structure, designed to determine the blocking stress in valves with electrorheological (ER) and magnetorheological (MR) fluids. It combines the advantages of rotary and flow rheometers. In this rheometer, a flow of a small ER/MR fluid sample placed in a revolving channel, is forced by the centrifugal force. The designed rheometer has a characteristically simple structure due to the lack of components such as pistons or pumps used to induce the flow of ER/MR fluid, and it does not have the basic disadvantage of flow rheometers, which is the necessity to analyse a large sample of fluid. The results of measurements conducted with the new rheometer were compared with results from two standard rheometers: a flow rheometer and a rotary rheometer. In order to adjust the measurement results from the new rheometer to these obtained from standard rheometers, the research featured a method of selecting numerical coefficients occurring in formulas used to calculate shear stress. The method is based on optimization method and it minimizes the differences between measurements for the same values of electric or magnetic field strength.
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