Bearings for eApplications - Wälzlagerlösungen für elektrifizierte Antriebssysteme

Abstract

The use of a converter in variable-speed drives leads to parasitic effects like additional losses or electrical bearing currents. Damages due to fluting or WEC formation or a bad electromagnetic compatibility of the drive can be the result of too high currents. Various remedies are presented which lead to a reduction of the bearing currents. A good protection against circular currents is the use of insulating layers or a rolling bearing with ceramic rolling elements. In the case of high production volumes, a bearing with special plastic overmolded ring can be a more economical solution.

However, insulation is not a good protection against EDM currents and can even increase the risk of these currents in drives with gearboxes. Effective countermeasures are brushes or carbon fiber rings. To avoid additional components the integration in the bearing is of interest. Therefore, Schaeffler developed a so-called shunt bearing that combines an electrically conductive element with a high-speed ball bearing to save space. Another integrated remedy is the use of a conductive grease. However, in e-mobility such greases are faced to high demands. Extensive testing of such grease candidates together with a rolling bearing manufacturer is advisable, also due to the lack of long-term experience.

The creation of a design process against bearing-current-related damages is a basic prerequisite for an assessment of the necessity and effectiveness of remedies. The presented validation concept explains the steps required for this.