# Active Electromagnetic Clutch for Crankshaft Decoupling from a Belt Drive System
## 6 Conclusions  
This work presents a novel electromagnetic clutch that decouples the crankshaft from the belt driven system. It provides the possibility for AC extension during the start-stop operation, avoiding the engine drag torque. The working principle of the clutch and its electromagnetic behavior are modeled. Experimental tests demonstrate the functionality of the proposed actuator. Two procedures to estimate the clutch state are described. The  
Figure 11: Coil current and microphone pressure when the clutch is (**a**) opening (clutch moving towards minimum air gap), and (**b**) closing (clutch moving towards maximum air gap). The coil current is clearly disturbed at the instant when the hub drastically stops moving due to mechanical contact. A microphone is used to determine the instant of the impact.  
Figure 10: Frequency response at different air gaps. Tests were conducted with average coil currents of (**a**) 1.0 A, (**b**) 1.4 A, and (**c**) 2.8 A. The inductance variation becomes smaller when the drive current increases. The evaluation of the clutch state from the inductance variation is difficult to achieve when the coil current is larger than 1.4 A due to magnetic saturation.  
first, focused on the inductance estimate, can potentially give a more precise estimate of the air gap but is severely hindered by saturation. The second one employs the current disturbance due to back-EMF to identify the clutch state. Although not particularly precise, this latter technique can identify the clutch state as binary information.  
The experimental test validated that the opening and closing phases required 50 and 25 ms, respectively. As a result, the time constraints of 100 ms for switching between operating modes in a vehicle were satisfied. Real-time deployment of these algorithms is carried out on a clutch control unit. The experimental test was undertaken with an active electromagnetic clutch paired with the control control unit, making it an effective choice for automotive applications. From a functional safety perspective, both strategies can be combined to provide a redundant state estimation scheme.  
Further developments of this project include the installation of the actuator in a vehicle and its use to implement and assess energy-saving strategies.  
Conceptualization, L.M.C.M., R.G., A.B., N.A., A.T. and W.V.; methodology, L.M.C.M., R.G., S.H., A.B. and W.V.; software, L.M.C.M.; validation, L.M.C.M.; formal analysis, L.M.C.M. and R.G.; investigation, L.M.C.M., R.G. and S.H.; resources, N.A., A.T. and W.V.; data curation, L.M.C.M. and R.G.; writing--original draft preparation, L.M.C.M. and R.G.; writing--review and editing, S.H., A.B., N.A., A.T. and W.V.; visualization, L.M.C.M. and R.G.; supervision, N.A., A.T. and W.V.; project administration, N.A., A.T. and W.V.; funding acquisition, N.A., A.T. and W.V. All authors have read and agreed to the published version of the manuscript.  
This study was carried out within the Ministerial Decree no. 1062/2021 and received funding from the FSE REACT-EU-PON Ricerca e Innovazione 2014-2020. This manuscript reflects only the authors' views and opinions, neither the European Union nor the European Commission can be considered responsible for them.  
Not applicable.  
The datasets presented in this article are not readily available because they are protected by a collaboration agreement between the interested parties.  
The authors declare no conflicts of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} AC & air conditioning \\ BDS & belt drive system \\ CAN & controller area network \\ CCU & clutch control unit \\ DIS & disable coupling with engine \\ EM & electric machine \\ EMF & electromotive force \\ EN & enable coupling with engine \\ FEAD & front-end accessory drive \\ ICE & internal combustion engine \\ PI & proportional--integral \\ \end{tabular}