A rotary pump may include a rotary cover and a rotary housing that may be engaged with one another during operation. A ring gear may be positioned within an internal portion of the rotary cover and rotary housing, and an inner gear may be positioned within a portion of the ring gear. The rotary pump may be configured with a pressure relief portion that may be in fluid communication with an outlet of the pump. The rotary pump may be configured such that pressurized fluid passing through the pressure relief portion is routed to an inlet of the rotary pump.

An oil separator includes a case, electrode plates, filters, and a power supply unit. The electrode plates are arranged in the case with a space in between such that any two adjacent electrode plates face each other. The filters are made of an electrically insulating material and each arranged between any two adjacent electrode plates. The power supply unit is connected to the electrode plates and applies voltage between any two adjacent electrode plates, thereby creating a potential difference between the adjacent electrode plates. The filling factor of each filter is in a range from 0.005 to 0.03. The voltage applied between any two adjacent electrode plates by the power supply unit is in a range from 0.5 to 5 kV. The distance between any two adjacent electrode plates is in a range from 3 to 20 mm.

An object of the present invention is to suppress a blockage caused by oil particles in an upstream side of a filter in an oil removal apparatus that collects oil particles in a filter disposed between an anode and a cathode. While an internal combustion engine is operative, application of a voltage to a bipolar electrode is controlled such that a voltage application period, in which the voltage is applied to the bipolar electrode, and a voltage application stoppage period, in which application of the voltage to the bipolar electrode is stopped, are repeated alternately at predetermined periodic intervals.