Liquid filter, in particular an oil filter

An oil filter for purifying lubricating oil for an internal combustion engine of a motor vehicle, comprising:

• a filter housing having a receiving space and a ring filter element having a longitudinal axis arranged in the receiving space of the filter housing for filtering a liquid,
• the filter housing including an inlet for raw liquid and an outlet for cleaned liquid,
• a no-load duct, which is opened when the ring filter element is taken out, a pin being integrally formed on a lower end disc of the ring filter element, which pin projects parallel to the longitudinal axis and eccentrically, and which penetrates an opening of the no-load duct in a sealing manner when the ring filter element is inserted into the filter housing,
• a ramp disposed on a bottom of the receiving space, wherein the ramp extends circumferentially about the longitudinal axis from the bottom with a lower end at the opening of the no-load duct and rises axially with increasing ramp length into the interior of the receiving space,
• wherein the ramp and the pin are matched to each other in such a manner that when the ring filter element is inserted into the filter housing the pin as long as it has not yet penetrated the opening of the no-load duct engages on the ramp and slides towards the bottom when the ring filter element is rotated about the longitudinal axis and penetrates the opening of the no-load duct at the lower end of the ramp, and
• at least one structure arranged adjacent to the ramp in the receiving space, the at least one structure preventing insertion of the ring filter element into the receiving space unless the pin of the ring filter element engages and slides along the ramp until the pin penetrates the opening of the no-load duct at the lower end of the ramp,
• wherein the at least one structure includes at least one rib, and wherein the at least one rib extends in a radial direction transversely to the ramp with respect to the longitudinal axis, and
• wherein the at least one structure further includes a plurality of positioning ribs, wherein the plurality of positioning ribs are arranged on an inner wall of the filter housing facing the ring filter element and extend in an axial direction and bear against the ring filter element when the ring filter element is arranged in the receiving space of the filter housing.