Effects of engine base oil type and ZDDP on the electrical double layer in the rotating shaft-oil-lip seal system with and without an external DC electric field

The paper presents the results of experiments on tribo-charging of a blend of mineral base oil and different zinc dialkylditophosphate (ZDDP) contents. Experiments were carried out on the specially built experimental facility to be a simplified model of an engine crankcase in whose interior an earthed metal shaft rotated at given angular velocities. The potential of a stiffening ring of a lip seal was measured directly with an electrometer. The experimental results are presented in the form of some characteristics that are relationships of the potential induced on the stiffening ring to the oil temperature for different angular shaft velocities and the ZDDP contents. Also the effects of an external DC electric field on the braking torque of the steel shaft were examined for a range of oil temperatures, angular velocities, and ZDDP contents. An analysis of the research results obtained permitted one to show how the ZDDP content in a blend with the base oil tested, angular velocity, and oil temperature could affect charging in the interface system: rotating shaft-oil and oil-lip seal, as well as the whole oil film in between and both electrical double layers (EDL) at the surfaces of the shaft and of the lip of a lip seal.