Almost all electric motors have bearings that are lubricated by grease. The bearings introduce friction into the system, some of which is caused by the grease itself. If we can understand how overall bearing friction is affected by the grease, we will be able to develop greases to reduce that friction, contributing to the overall efficiency of the motor, Daegling explained.

Even a small improvement can be significant considering the huge number of electric motors in use, he noted. For a typical 11-kilowatt industrial motor, the purchase price represents only about 4 percent of the total cost, while maintenance (including lubricant) is about 1 percent. The other 95 percent is the cost of the energy to run it.

The most efficient motors available today can achieve efficiencies of around 97 percent. Smaller motors are less efficient but, while it might seem more fruitful to attack these motors with lubricant technology … a small percentage saving from a large energy bill can be higher than a larger percent from a small bill, Daegling explained. It makes sense to attack friction losses in all motors, but especially in larger ones.

Bearing energy losses are complex, and the accuracy and precision of existing bearing tests are not high enough to detect small but important differences in efficiency. Therefore, Shell worked with the University of Magdeburg to develop a new, more sensitive test rig to measure bearing friction more accurately.

Daegling said, Existing theories suggest that bearing torque increases slowly as rotating speed increases. Results from the new test rig showed this occurs only in the lower part of the speed range, and at levels lower than predicted. Above a certain speed, characteristic of each grease, torque increases steeply, almost linearly, to much higher values than predicted by current models.

To investigate the validity of the new test, Shell teamed with the University of Ghent to study the long-term efficiency of electric motors with grease-lubricated bearings. The results [of this test] agreed and showed a significant difference, greater than 40 percent, between the most efficient and least efficient greases, Daegling reported.

Existing models would not have predicted such a difference, he said, concluding that the new test rig paves the way to select greases that [save] energy in electric motors [and] provides a good basis to develop even more efficient greases.