Patent ID: 8206480

Claim:
Air filter unit ( 10 ′) comprising at least one main air filter ( 1 ) and an auxiliary air filter that is connected by means of an air conduit ( 4 ) to the main filter ( 1 ) and comprises at least one auxiliary filter element, the at least one auxiliary filter element ( 2 ′) arranged inside a filtered air conduit ( 4 ), wherein the auxiliary filter element is formed by an at least partially porous wall of an auxiliary air conduit ( 2 ′) closed off at an end such that airflow entering an interior of the auxiliary air conduit ( 2 ′) can only flow through the at least partially porous wall to exit the auxiliary air conduit ( 2 ′), said auxiliary air conduit arranged at a filtered air side of the main air filter ( 1 ) within the air conduit ( 4 ) connected to the main air filter ( 1 ), wherein filtered airflow exiting the main filter ( 1 ), passes in an interior of the auxiliary filter ( 2 ′) formed by the at least partially porous wall of the auxiliary air conduit ( 2 ′), flows though pores in the at least partially porous wall, reaches a gap ( 5 ) between the auxiliary air filter ( 2 ′) and the filtered air conduit ( 4 ), then flows along the gap ( 5 ) to exit the air filter unit ( 10 ′).