Outboard motor

摘要

An outboard motor (1) includes an exhaust emission control system which is arranged rationally and neatly in the housing of an outboard motor body, irrespective of various limitations on the outside shape of the housing. An oil pan (100) disposed below an engine (11) of the outboard motor (1) has an oil holding portion (101), and an exhaust pipe (110) is disposed vertically along a vertical wall portion of the oil holding portion A catalytic converter (120) is disposed in an intermediate portion of the exhaust pipe (110) in confronted relation to the vertical wall portion. The catalytic converter (120) has a particular shape in horizontal section which is greater in side in a first direction than in a second direction perpendicular to the first direction. A fresh-air delivery passage (20) is provided for introducing fresh air into an exhaust passage disposed upstream of the exhaust pipe (110). The fresh-air delivery passage (20) is connected at one end to the top plate of an intake box (25) and includes a check valve (21) disposed at an intermediate portion of the fresh-air passage. The check valve (21) is adapted to open only when the pressure in the exhaust passage is less than the atmospheric pressure. The exhaust system is perfectly protected against a possible entry of water, and an engine combustion failure and corrosion of the exhaust system resulting therefrom.