Thermal effects on the torque characteristics of a magnetorheological clutch

The temperature dependence of the properties of magnetorheological fluids has been already considered in the literature, but such an aspect related to MR clutches/brakes has not yet been analysed, though thermal effects on torque proved to be significant. In this paper the torque characteristic of a permanent magnet magnetorheological clutch is investigated focusing on the influence of temperature. An experimental campaign was carried out on a test bench equipped with a caulk heating up to 80o C. The torque characteristics were measured and both the fluid and the clutch case temperature were monitored at the beginning and at the end of each test. Torque data were processed and well fitted by a formula where the temperature dependence is expressed by Arrhenius law, taking into account the temperature variation during the test. In particular a loss of transmitted torque for increasing temperature was found. The dependence of the gap average shear stress on temperature was also approximately estimated on the basis of finite element magnetic analyses and simplifying assumptions which could be used to estimate torque-temperature dependence on similar devices.