Experimental study of a magnetorheological clutch as a torque limiter for dog type automated manual transmission

Automated manual transmissions (AMTs) offer a cost-effective and energy-efficient solution for small vehicles such as urban micro-cars. However, achieving fast and smooth gear shifts is challenging when relying on conventional friction clutches, due to their limited responsiveness and controllability. To address these limitations, this study presents the development and experimental validation of a dog-type AMT prototype incorporating a programmable magnetorheological (MR) clutch designed to regulate torque transfer following gear engagements. The design rationale for the prototype is presented along with its implementation on an all-terrain vehicle (ATV) test platform representing an urban micro-car. An extensive experimental characterization is conducted using various open-loop torque control strategies to assess their impact on shift quality and ride comfort. In performance mode, results show best-in-class shift durations with averages of 24.5 ms and best-case shifts as quick as 9 ms. In comfort mode, analysis of system dynamics revealed strong correlations between torque modulation, shift smoothness, and comfort metrics, pointing to an optimal clutch slipping energy of about 150 J per shift. While comfort remains a subjective metric influenced by human factors, this study suggests that the high responsiveness of MR clutches can provide both optimal damping conditions for comfort and ultra-fast shifts for performance. A major limitation related to sedimentation in the MR clutch under certain operating conditions is also identified, highlighting the need for further investigation of this phenomenon.