Low Temperature Performance of Novel Electric Vehicle Motor Lubricating Greases

In this study the main focus is on the low temperature behavior and mobility of lubricating greases; a characteristic that has always been challenging for grease formulators. A series of lab-scale polyurea grease samples are prepared, with three different types of low viscosity synthetic base oils (ISO VG 32), and are examined in terms of their low temperature behavior as potential lubricants for electric motor bearings of electric vehicles (EVs) and hybrid electric vehicles (HEVs). The cold flow properties are analyzed by utilizing a Low Temperature Flow Tester following the DIN 51805-2 (Determination of flow pressure of lubricating greases according to Kesternich method) standard. The test matrix includes the cold flow pressure assessment at various temperatures ranging from -0^oC to -40^oC, whereas those measurements are also repeated after various relaxation periods - at selected temperatures - from 4h up to 8h before the actual determination. By employing this modified technique, the effect of an extended temperature control time on the relatively low temperature properties of the grease can be compared to the corresponding behavior at the standard test conditions. The comparative assessment of the results gives valuable information on the cold flow performance of upcoming advanced greases that can be utilized in electric vehicle motors.