US Patent 7367174 Rotary lawn mower with pivotal mulch door

A rotary walk behind lawn mower has a wheeled cutting deck with a downwardly facing cutting chamber. A rotatable cutting blade is contained inside the cutting chamber above a lower edge of a peripheral sidewall and beneath a central hub, an annular channel being formed between the sidewall and the hub of the cutting chamber for receiving grass clippings from the cutting blade. A portion of the peripheral sidewall of the cutting chamber above the level of the cutting blade and a portion of a top wall of the cutting chamber form a pivotal mulch door for opening and closing the annular channel in which the grass clippings are moving.