Influence of additives blended with motor base oils on the braking torque under an auxiliary external DC electric field

The paper presents the results of experiments upon the influence of tribocharging of PAO and PAG synthetic motor base oils blended with different additives—friction modifiers (FM) and antiwear agents (AW)—and the effect of an external DC electric field on the braking torque. The experiments are carried out in a rotating shaft–oil–lip seal system which represents a specially built experimental facility to be a simplified model of an engine crankcase in the interior of which a metal shaft rotates. The research is especially aimed at the braking torque of a rotating shaft sealed with a lip seal and a possibility of reduction in the torque under external DC electric fields. DC voltage is applied between the stiffening ring of lip seal and a rotating, earthed shaft. The braking torque of rotating shaft is measured as a function of the oil–additive blend's temperature, the shaft's angular velocity, and the absolute value of the external DC voltage. In general, it is found that an external DC electric field causes the braking torque to change with the increasing DC voltage. The change depends on the additives and base oils used in their blends which in turn causes the torque to increase in the case of the PAO–additive blends or to decrease for the PAG–additive blends.