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As an appropriate material for automotive thermoelectric generators, which directly convert waste heat of exhaust gas into electricity, we have developed Mg2(Si1-xSnx) thermoelectric materials with high thermoelectric performance. The performance is evaluated with the dimensionless figure of merit (ZT), and the ZT has been improved through the development of the fabrication process and the investigation of the optimum composition and dopant element. A novel liquid-solid reaction synthesis method incorporating hotpressing for the sample fabrication was effective in reducing the thermal conductivity. The n-type Mg2(Si0.50Sn0.50) doped with Sb attained a high ZT of 1.1 at 620 K. The p-type Mg2(Si0.25Sn0.75) doped with Li and Ag simultaneously achieved a ZT of 0.3 at 600 K. The effective maximum power of n-type thermoelectric element and that of p-type were calculated with the thermoelectromotive force and the mean resistivity.

For DC brush motors directly driven by 42V vehicle battery, carbon brush deterioration due to high voltage arc is a major factor to determine motor life [1]. The brush deterioration is significant especially in multipolar motors with lap-wound armature because they allow a large circulating current to flow into their brushes and it decreases commutation performance [2], [3], [4]. In this report, we propose 1) a new brush material capable of preventing brush deterioration even under high-voltage conditions and 2) a new winding method to minimize circulating current under electromagnetic polarization and to suppress high-voltage arc. With each of these new technologies, DC brush motor driven by 42V battery can operate longer than that driven by 14V battery.