A study of factors affecting torque transmission in permanent magnet-based magnetorheological fluid clutch

In this article, the study of several factors affecting the torque transmission capability of a permanent magnet-based, drum-type magnetorheological fluid (MRF) clutch is presented. These factors are: number of magnetic poles in the magnet assembly, material of the clutch, MRF layer thickness, and relative rotational velocity between the input and output stages of the clutch. For this purpose, a special single-MRF layer clutch was designed and fabricated, one which allows the convenient assembly and disassembly to reduce preparation time for testing. The average transmitted torque of this clutch under several combinations of the aforementioned factors was recorded and analyzed. Additionally, several magnetostatic simulations of the clutch were carried out, and both the magnetic flux density and transmittable torque calculated from the results of these simulation were compared against experimental measurements. It was found that magnet assemblies with lower number of magnetic poles resulted in higher torque outputs, however, the effectiveness of the utilized torque variation mechanism was reduced due to magnetic saturation of the components of the clutch. The material of the clutch was found to have a significant effect at low relative rotational velocities, resulting in a nonlinear relationship between transmitted torque and relative angular velocity. This nonlinear effect was more significant when aluminum was used in the components which interact directly with the MR fluid whereas the use of ferromagnetic components reduced this effect. Finally, the thickness of the MRF layer was found to have a significant effect on the transmitted torque of the MRF clutch, although not according to what magnetostatic simulations predict.