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Magneto-rheological (MR) fluids react to magnetic fields undergoing changes in their mechanical characteristics, viscosity in particular. After an analytical and numerical study, an MR squeeze-film damper has been designed and set up on a reduced scale rotor test-rig. Numerical simulations were carried out in order to evaluate the dynamic behaviour of the damped rotor as a function of the current supplied to the adjustable device. A linear model that depicts the main characteristics of the system has been developed as a useful tool in damper and control design. By testing different fluids, an optimal fluid has been singled out. Tests conducted on the selected fluid show that it is possible to have the optimum conditions for each steady rotational speed.

This work was carried out in the framework of a funded project aimed at evaluating the feasibility of an ad hoc clutch for the disengagement an auxiliary device, i.e. the vacuum pump used with the powerbrake in diesel engine vehicles, when its operation is not required. In this way it is possible to improve the overall vehicle efficiency. Strict design specifications were defined with reference to available room, torque transmission, absence of axial loads and fail-safe operation. A magnetorheological clutch with permanent magnets was conceived to fulfil the technical requirements. Different clutch geometries were compared with particular reference to the fail-safe operation and torque capabilities. After an iterative procedure, in which both mechanical design and magnetic field analyses were considered, the most promising solution was defined and a prototype was built and tested. A four-pole sliding permanent magnet was adopted to generate the magnetic field. The experimental results validated the developed models and demonstrated the feasibility developed models and demonstrate the feasibility of the proposed solution. A principle for the automatic clutch actuation is also presented.

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This paper describes the design and testing of a novel Permanent Magnet (PM) clutch based on Magneto-Rheological Fluid (MRF). It was inspired by a prototype previously developed by the authors and contains a novel gap shape conceived to reduce the torque loss in the disengaged operating mode. Several geometries and material arrangements were investigated and the performance in terms of transmissible torque in different operating conditions were assessed by FE numerical models. The prototype was manufactured and some experimental tests were performed. The new prototype was rated on the basis of performance indices and the design effectiveness was proved by a higher value of efficiency in the disengaged operating mode.