Selection of Materials Used in Viscous Clutch With ER Fluid Working in Special Conditions

Artur Olszak,Grzegorz Mędrek,Jan Zwolak,Seung-Bok Choi,Andrzej Kęsy,Karol Osowski,Przemysław Motyl,Zbigniew Kęsy

doi:10.3389/fmats.2019.00139

Abstract

The paper presents considerations regarding materials used to fabrication 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, however, 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 tests 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.

Highlights

The most important factors that have recently contributed to mechanical devices’ better results and which have increased the devices’ reliability are the implementation of new materials and integration with digital electronics
It was assumed that radiuses r in the mathematical model of the viscous clutch with electrorheological fluids (ER) fluid are described by a proportional enlargement of the model clutch whose geometry was determined based on the analysis of already existing clutches and brakes with smart fluid (Papadopoulos, 1998; Kavlicoglu et al, 2002; Smith et al, 2007; Nguyen and Choi, 2010; Erol and Gurocak, 2011) using the magnification factor sk
The main goal of the optimization was to receive a viscous clutch with ER fluid with the smallest possible dimensions, transmitting the largest possible torque, but at the same time the amount of dissipated heat, dependent on the side surface of the clutch, ensured a possibly low temperature of the ER fluid during the constant work of the clutch

Summary

Introduction

The most important factors that have recently contributed to mechanical devices’ better results and which have increased the devices’ reliability are the implementation of new materials and integration with digital electronics. In viscous clutches and brakes, both of these factors are combined by using new construction materials and hydraulic working fluids of a new type, i.e., smart fluids which react to a physical field by altering their rheological properties. ER and MR fluids are divided into two groups, according to their composition: monophasic and biphasic. Viscous clutches consist of the driving part connected to input shaft and the driven part connected to the output shaft. Immobilizing the driven part causes the clutch to become a brake In these clutches the torque is transmitted as a result of friction caused by shear stress in the working fluid between the driving part and the driven part. Two main types of viscous clutches can be distinguished, according to the shape of driving and driven part: cylindrical and disc clutches

Results

Discussion

Conclusion