Dynamic design of electric turbo-compound

Electric turbo-compounding is gaining popularity among hybrid vehicles. This device is composed of an electric machine - mounted on the shaft between the turbine and the compressor - that can operate both as a motor and as a generator. This allows recovering part of the thermal energy that otherwise would be discharged at the exhaust. In this way, the drivability and fuel consumption are improved. In this context, the Research Unit High Efficiency Hybrid Powertrain has been founded to develop new components to increase the efficiency of hybrid vehicles. Politecnico di Torino has been involved to study and design a prototype of a high-speed hysteresis machine for an electric turbo-compound. In the mechanical design of a high-speed electric machine different aspects must be considered: the machine works at 150000 rpm, and at this speed issues like vibration linked with rotordynamic and rotor failure because of high centrifugal forces may arise. To address these aspects, the present thesis deals with the mechanical design and dynamic investigation of the electric machine rotor to prevent the aforementioned problems. In the first part, tensile tests are conducted to identify the mechanical properties of different semi-hard magnetic materials. This step allowed the selection the material suitable for the realization of the rotor. From this analysis, the CROVAC results to be the best for this application. Subsequently, a finite element analysis is carried out to study the dynamics of the rotor. The comparison between experimental data and analytical models of the free-free rotor is proposed: this allows tuning the parameters to have an accurate finite element model. Finally, an appropriate analysis of the O-Rings used to support the shaft is carried out so that the critical speeds and unbalance response can be computed. The satisfying numerical results of the supported rotor allow moving on the experimental tests at a high rotational speed. These tests are successfully conducted, and they have confirmed the proper functioning of the rotor and the goodness of the design and assemble. Thus, these analyses have allowed to obtain an experimentally validated finite element model for the free-free rotor, and from the high-speed experimental test the waterfall diagram is got: the first critical speed is very close to the predicted one.