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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.

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.

This paper describes the magnetic design of an innovative fail-safe clutch based on magnetorheological fluid (MRF). A cylindrical arrangement of permanent magnets (PMs) is used to excite the fluid. The suitable distribution of magnetic field inside the MRF and the transmissible torque is obtained by moving the PMs along the axial direction. The device is designed using a magneto/mechanical FEM model, developed on purpose and based on a three-dimensional (3-D) finite-element code, which takes into account the B-H and τ -H functions of the nonlinear materials (e.g., MRF, PM, and ferromagnetic materials). The flux density maps and the shear stress maps inside the fluid are carefully analyzed. Furthermore, in order to validate the FEM model, some preliminary experimental measurements are performed on a prototype. Finally, the magnetic axial force acting on the PM system is investigated.Index Terms-FEM analysis, magnetorheological clutch, permanent magnets.

In this article the torque characteristic of a permanent magnet magnetorheological (MR) clutch is investigated focusing on the\ud influence of temperature. An experimental campaign was carried out on a test bench equipped with a caulk oxen, heating up to 80◦C.\ud The torque characteristic was measured monitoring both fluid and clutch case temperature. Torque data were processed and well\ud fitted by a formula where the temperature dependence is expressed by Arrhenius law. In particular, a loss of transmitted torque for\ud increasing temperature was found. An approximate dependence of MR fluid shear stress on temperature, useful for similar devices,\ud was also obtained