Patent ID: 7160162

Claim:
An outboard motor for a watercraft, the outboard motor comprising: an internal combustion engine; a drive unit being configured to be supported by a hull of the watercraft and having an exhaust guide that forms an upper portion of the drive unit, the exhaust guide having an upper surface and a lower surface, the upper surface supporting the engine; an oil pan attached to the lower surface of the exhaust guide; and an exhaust system disposed within the drive unit and being comprised of: an exhaust passage configured to lead exhaust gas from the upper portion of the drive unit to a discharge end, the discharge end being disposed on the outboard motor so as to expel the exhaust gas into a body of water on which the watercraft is operated under at least some operating conditions of the outboard motor; and a branch passage extending from the exhaust passage at an intermediate portion thereof, the intermediate portion being disposed between the upper portion of the drive unit and the discharge end, the branch passage being configured to discharge the exhaust gas inside the exhaust passage to the ambient air, the branch passage being formed with an expansion chamber, the expansion chamber being at least partially defined between a portion of the exhaust guide and a portion of the oil pan; and wherein the branch passage further comprises an exhaust pipe, an upstream end of the exhaust pipe being located in a lower region of the expansion chamber, the exhaust pipe passing through an upper region of the expansion chamber and having a downstream end opening outside the expansion chamber.