Patent ID: 6726512
Filing Date: 2004-04-27
Classification: F02B

Abstract:
An outboard motor for a watercraft comprising:an engine body defining at least one cylinder bore in which a piston reciprocates; a cylinder head affixed to one end of said engine body for closing said cylinder bore and defining with said piston and said cylinder bore a combustion chamber; an intake passage in fluid communication with said combustion chamber and configured to provide air for an air/fuel mixture to said combustion chamber; a throttle body in fluid communication with said intake passage and having a throttle plate configured to control an air flow in said intake passageway; a throttle position sensor configured to determine a position of said throttle plate; an intake air pressure sensor in fluid communication with said intake passage, being positioned between said throttle valve and said combustion chamber and being configured to determine air pressure in said intake passage; a fuel injector configured to deliver fuel to said combustion chamber for said air/fuel mixture; an engine speed detector configured to determine an engine speed; and an engine control unit configured to control said fuel injector based upon feedback from at least one of said throttle position sensor, said engine speed detector, and said intake air pressure sensor, wherein between a closed state of said throttle plate and a first predetermined air pressure, a constant air/fuel ratio is maintained, from said first predetermined air pressure to a second predetermined air pressure, said air/fuel ratio is steadily increased as a function of a change in air pressure to approximately a lean limit ratio, said second predetermined air pressure being less than a maximum intake air pressure, said maximum intake air pressure occurring when said air pressure in said intake passage becomes approximately constant, from said second predetermined intake air pressure to said maximum intake air pressure, said air/fuel ratio is maintained at approximately said lean limit ratio, and from said maximum intake air pressure to a maximum throttle opening, said air/fuel ratio is decreased in accordance with feedback from said throttle position sensor and said engine speed detector.