This paper investigates breakdown characteristics in the bearings of variable speed electric drive trains. The analyses reveal that breakdown phenomena previously known from high-voltage technology appear to also occur in the bearing contact, though at significantly lower voltages. By loading the bearing with AC voltage of different frequencies at various mechanical load points, five states, which range from partial discharge through arc discharge to a completely conductive channel, emerge. Consistent with the concept that the magnitude of the breakdown voltage depends on the lubricant film height, the contact force, and the frequency of the AC voltage, a thicker lubricant film results in a higher breakdown voltage, analogously to a capacitor with a larger plate spacing, which requires a higher potential difference to be punctured. Furthermore, the sinusoidal frequency of the AC load correlates with the breakdown voltage. The breakdown tends to occur earlier at low frequencies, which is illustrated by the fact that at low frequencies, capacitive behaviour can only be observed at higher speeds, i.e., at a larger lubrication gap, while no voltage can be built up over the bearing at lower speeds. An increase of the contact force for the same lubricant film height lowers the breakdown voltages. The reduction of the breakdown voltage by the contact force may result from an increase of the relative permittivity of the lubricant with higher pressure and likewise of the contact area; the increased area may also increase the number of surface-roughness peaks where an increase in the electric field occurs.

The effect of variable DC bearing current amplitude, bearing current polarity, mechanical force, rotation speed, bearing temperature, and number of the balls on the fluting in an axial ball bearing type 51208 is investigated under DC currents. The results are obtained from two different test setups with two different lubricants (mineral-oil-based grease and polyglycol oil). The speed varies between 100 rpm and 2000 rpm, the axial bearing force between 200 N and 2400 N, the DC current amplitude between 0.5 A and 20 A, the bearing temperature between 29 °C and 80 °C, the number of steel balls per bearing between 3 and 15, and the test duration between 6 h and 168 h. The results show that with a higher bearing current density and/or a higher bearing speed, a lower bearing force and/or a lower bearing temperature, a bigger number of roller elements, but also at a negative polarity of a DC electric bearing current, the occurring of fluting is more probable and occurs at an earlier stage of operation.

INTRODUCTIONIn the context of sustainability and energy transition, friction reduction is an important aspect (1). Therefore, rolling bearings are used in many applications in which components move...

This article describes a procedure to partition electrical capacitance measurements of a single-stage gearbox into its individual components: the capacitances of contact zone, inlet/outlet zone of the contact, trailing tooth flank, oil sump, and surrounding components, such as the housing. It is shown via a comparison of bearinx simulations with experimental measurements that the capacitance of a gear stage can be calculated sufficiently accurate by using experimentally determined correction factors. For the presented test rig, the correction factor kC amounted to 4.8, with a relative permittivity εr of 2.3. Furthermore, it is shown why both a high temporal resolution and the recording of at least one gear revolution are necessary to capture the capacitive behavior of a gearbox in an experimental investigation. It is also shown how speed, load, temperature, and a variation of the tooth width from 3 mm to 12 mm affect the capacitance and how the capacitance varies along the line of action.

Zusammenfassung: Im Rahmen dieses Beitrags werden Ergebnisse einer Untersuchung an feststoffgeschmierten Wälzlagern vorgestellt. Betrachtet werden dabei Lager, welche einen speziellen, modifizierten Käfig verwenden. Die Käfigtaschen des Käfigs dienen dabei, zusätzlich zu ihrer ursprünglichen Funktion, der Führung der Wälzkörper, als Schmierstoffdepot. Es werden zunächst Prüfaufbau und die Versuchsbedingungen erläutert und in diesem Zusammenhang wird gezeigt, dass der in diesem Beitrag verwendete Aufbau, verglichen mit dem Aufbau vorangegangener Arbeiten, eine deutlich reduzierte Streuung aufweist. Als eine nicht zu vernachlässigende Fehlerquelle bei der gravimetrischen Bestimmung des Käfigtaschenverschleißes wurde das hygroskopische Verhalten des Polymercompounds identifiziert. Einer Verfälschung dieser Messergebnisse durch die unkontrollierte Feuchtigkeitsaufnahme aus der Umgebung, muss durch einen zeitlich vorgelagerten Trocknungsprozess unter definierten Bedingungen vorgebeugt werden. Zudem wird gezeigt, dass die Käfigtaschen sowohl durch den Innenring des Lagers, als auch durch die Wälzkörper verschlissen werden. Hierbei wird eine Messmethode zur Ermittlung der, durch den Innenring verschlissenen, Materialmenge vorgestellt. Durch Oberflächenanalysen der Messingstruktur des Käfigs wird eine Reduzierung des Zinks nachgewiesen, sowie eine Änderung der Oberflächenstruktur festgestellt. Als Ursache wird ein Sublimieren des Zinks aufgrund der Versuchsbedingungen vermutet. Weiterhin wird gezeigt, dass die Prüftemperatur von 300 °C zu einem Schrumpfen der Lagerringe führt. Eine Vorwegnahme dieser Maßverringerung ist durch Temperierung bei 300 °C für 48 h möglich.

IntroductionFast switching frequency inverters are a key component in modern electric drive trains. They provide high efficiency in a wide speed range, which is why they are frequently used in vari...