Patent ID: 8499750

Claim:
An oil mist separator for an internal combustion engine that separates an oil component in a gas, which is introduced from a crankcase of the internal combustion engine, from the gas, the oil mist separator comprising: a porous filter that separates, from the gas, the oil component in the gas, the porous filter being provided in a passage, through which the gas passes, wherein the porous filter is coated with a counteragent for neutralizing an acid substance; a plurality of gas passages that are separate from each other, each of the plurality of gas passages is provided with the porous filter that is coated with the counteragent; a switching device that selects one of the plurality of gas passages through which the gas is allowed to pass; a controller that estimates a degree of decrease in an amount of the counteragent, based on information concerning the degree of decrease, and that, when the degree of decrease exceeds a predetermined degree, controls the switching device so as to change the gas passage through which the gas is allowed to pass.