Tribologisch und elektrisch induzierte Effekte im Kommutator-Bürste-Kontakt im permanent erregten Gleichstrommotor

Ausschlaggebend für die Lebensdauer eines Gleichstrommotors ist der Verschleiß des tribologischen Systems Kohlebürste-Kommutator. Für eine längere Lebensdauer sollen in dieser Arbeit gezielte Modifikationen im Tribosystem durchgeführt werden, um dessen Verschleißbeständigkeit zu erhöhen. In dieser Dissertation wurde der Einfluss der Materialausrichtung der Kohlebürste auf den Kommutator-Bürste-Kontakt untersucht. Dazu wurden Kohlebürsten mit axialer, radialer und tangentialer Pressrichtung in einem Prüfstand untersucht. Reibungs- und Verschleißwerte differierten zwischen den einzelnen Varianten bei stromlosen und bestromten Versuchen. Weiterhin wurde der Einfluss eines leitenden Schmieröls auf den Reibkontakt charakterisiert. Bei bestromten Prüfstandsversuchen kamen schlecht leitende, sowie ein gut leitender Schmierstoff zum Einsatz. Durch die Zugabe einer ionischen Flüssigkeit bei der gut leitenden Variante konnte der hohe Verschleiß von geschmierten Systemen reduziert werden.

The wear of the tribolgic system carbon brush and commutator of a DC motor is decisive for its lifetime. For a longer lifetime of the device, specific modifications are requested to achieve better wear resistance of the tribosystem. Detailed literature research illustrated the absence of knowledge about the effects of a distinct orientation of brush materials, the morphological characteristics of the brush and the influence of a lubricating film on the tribolgic system. Since these subjects are believed to imply a potential for optimization of the motor performance, these three topics present the matter of the presented work. In the first part the influence of the brush materials direction on the contact behaviour of the DC motor was investigated. For this aim, brushes with axial, radial and tangential material orientation were analyzed on a test rig. In non-conducting mode, friction and wear values differed between the individual variants. The results showed that the lowest brush wear was determined at the axial and radial variant. By analyzing the system, different friction processes were observed during the currentless experiments. With the application of current, the brush wear increased and showed no more obvious differs. At the same time a inhomogeneous wear pattern could be observed on the commutator lamellae. To optimize this effect, a method for increasing the strength of the commutator copper content on the surface has been applied. As a result, the wear of the commutator segments could be lowered and homogenized. In the second part of the thesis, the influence of a lubricant film on the frictional contact is characterized. The applicability of a conductive as well as a nonconductive oil type was analyzed. By adding an ionic liquid to the lubricant oil the high wear rate of the system could be reduced. In the third part, the influence of the sintering temperature during the manufacturing process on the tribological behaviour was investigated. Within the analysis, brushes with high and low resistivity were detected. Through chemical analysis of fracture surfaces accumulation of foreign elements at the grain boundaries could be observed. It could be proved by means of a sampling test that the sinter process parameters with respect to the temperature control have a parent influence on the development of low resistive brushes. The finding is based on the better conjunction of copper particles in the brush, resulting in an increase of conductivity.