Advanced science.  Applied technology.


Modification of Bruker Universal Testing Machine to Evaluate Tribology Properties of Electric Vehicle Driveline Lubricants in an Electrified Environment, 08-R6241

Principal Investigators
Carlos Sanchez
Andrew Velasquez
Peter Lee
Inclusive Dates 
01/01/22 to 01/05/23


Electrification has continued to permeate through the automotive market, with future projections showing an exponential growth in market share for both light and heavy-duty applications. Existing tribological test machines for the automotive industry were originally developed to model internal combustion engine propelled operation and are now less representative. One such machine, the Bruker Universal Mechanical Tester, is used to evaluate friction and wear on modeled surfaces simulating in-vehicle operation. However, there are no provisions to evaluate friction and wear performance in the presence of an electric field. The Tribology section of the Fuels and Lubricants Division modified the Universal Mechanical Tester to evaluate how the wear performance of driveline lubricants changes in an electrified environment.


The methodology needed to electrify the UMT test rig in a way that simulates in-vehicle conditions is to isolate the rotating component from other potential paths to ground and apply a voltage to it. Electrical isolation can be achieved by replacing paths to ground around the rotating component with a material that exceeds the dielectric strength of the lubricant, likely PTFE or similar plastic. The goal is to ensure that the weakest path to ground is through the lubricant. On the other side of the lubricant, a metal component will have a free path to ground to complete the circuit.

Once the test stand is electrified, in-vehicle conditions can be simulated on the UMT. The Tribology team can take a speed and load operating point and model it by scaling the geometry of the test hardware to fit the UMT’s capability. For example, the front motor bearing inside a Tesla Model S may see 18,000 RPM shaft speed and 1 GPa contact pressure. While the UMT cannot spin at 18,000 RPM, the ball bearing geometry in the test rig can be decreased to change the effective sliding speed to match that of the real bearing while staying inside the operating envelope of the test machine. The same methodology can be applied to real contract pressure and UMT applied load.


Following modification of the test rig to accept an applied voltage, a study varying rotational speed, applied load, lubricant temperature, voltage type, voltage waveform, and AC frequency was completed. Three test lubricants were used: an ultra-low viscosity automatic transmission fluid (ATF) formulated to Ford’s MERCON specification, an ATF formulated to General Motor’s DEXRON VI specification, and a J2360 automotive gear oil used in differential applications. Statistical analysis was completed on the results to compare different variables and the relative impact of each. With some combinations, an increase of up to 20% wear scar width was observed with voltage applied. A presentation summarizing the results will be given at the Society of Tribology and Lubrication Engineers (STLE) conference in May this year.