Filter device for a vehicle

A measurement unit (13) is electrically-connected with the blower (12) and the air inlet duct (10). This computes a time integral of the airflow through the air filter (11) as a function of the air flow paths (A, B, C) set, and the blower voltage. It determines the degree of contamination of the air filter as a function of this total quantity, and visualizes it in a display (14).