Filter system for the lubricant of an internal combustion engine

A filter system for a lubricating oil circuit, said filter system comprising a series of at least two filter elements which can be successively connected to the oil circuit, and a three-way detented differential pressure operated piston changeover valve for directing oil in the lubricating oil circuit to one of the filter elements, said changeover valve comprising a housing having an inlet for raw oil and a series of at least two outlets each respectively connected to a raw oil side of a respective filter element of said series of filter elements and a control piston axially movably positioned within a connecting bore disposed in the housing between said inlet and said series of at least two outlets, a spring biasing said control piston toward an initial position, one end of said piston being in communication with the raw oil side of the one filter element such that said piston is urged in response to pressure of the raw oil away from said initial position and the opposite end of said piston being in communication with a clean oil side of the one filter element such that said piston is urged in response to Pressure of the clean oil toward said initial position, and wherein three detent pistons are arranged to control the position of the control piston within the housing, said control piston of said changeover valve being moved to a next successive position when a first threshold pressure difference is reached between the raw oil side and the clean oil side of the one filter element to switch the oil flow through one of said outlets in the changeover valve to a next successive one of the outlets in the changeover valve for directing raw oil to one of the other filter elements in the filter series.