An oil supply device for a crankcase of an internal combustion engine feeds oil from a reservoir to a main oil duct of the crankcase. A filter switching device allows a selection from a plurality of oil filter units in the flow path of the oil to be selectively connected into the oil flow path, to set a proportion of the oil filter units to active and a proportion of the oil filter units to passive. A switching unit switches between the active and passive states and opens up a pressurized oil flow path to the active oil filter unit(s) and also a drainage flow path between the passive oil filter unit(s) and a drainage duct. An evacuation device drains or evacuates oil from the drainage duct which has accumulated at the passive oil filter unit(s).