US Patent 7320637 Filter window adapter unit

A filter window adapter unit adapted for use with a main split-sash window of school buses is provided. The adapter unit includes a mounting frame adapted to be installed over the main split-sash window of the school buses. An inner sash is disposed fixedly in a lower position in an inner track portion and carries a pane of glass. An outer sash is disposed movably in an outer track portion and carries an air filter. The outer sash is raised upwardly so as to cover a main window opening when the main split-sash is opened. As a result, the air filter prevents diesel fumes from the school buses from entering into the interior thereof.