Motors and generators of all sizes depend on bearings that must be carefully designed, produced within tolerance, optimally selected, and maintained within limits to guarantee the expected lifetime. Consumer equipment often uses plain bearings or small ball bearings. Small to medium industrial equipment uses rolling bearings of various forms. Utility-scale generators use large sliding bearings with forced lubrication to accommodate misalignment and thermal expansion. As with tribology in general, the bearings used in electrical machines often have a determining effect on the efficiency, durability and compactness of the machine in question. Small changes to lubrication, duty cycle, loading or environmental conditions can have a dramatic effect on bearing lifetime.
Industrial developments are driving the use of electric motors in novel applications, for example ancillary drives in aeroplanes, ship propulsion and displacing hydraulic drives in numerous industrial applications. Rare-earth permanent magnet motors offer improvements in torque density and efficiency. Electronic inverter controls offer cost-effective speed control, braking and regeneration, and may be mounted remotely from the electrical machine or integrated into it. Compact drivetrains often integrate electrical machines with gears, clutches and brakes.
The driving influences on the trend for wider application of sophisticated electrical drive systems are a combination of "push" and "pull" factors: the demand for cost-effective improvement to overall system efficiency, the possibility to increase control complexity and interconnectedness, and the shift in the industrial and end-user skills base away from "basic" mechanical engineering.
Tribologists have a key part to play in supporting the needs of industry, acting as a "bridge" between the electrical machine designer or systems engineer, and the critical mechanical domain that can often be overlooked by these higher-profile professionals. The optimal design, validation and maintenance of bearing solutions for electrical machines is filled with complex challenges. All indications are that this domain will become more interesting and intense in the coming years.