Four-stroke-cycle engine

A four-stroke-cycle engine equipped with an exhaust gas cleaning device for supplying secondary air to exhaust gases for re-combustion of the exhaust gases, comprising:

• a basic component for said four-stroke-cycle engine, which includes a piston reciprocatably inserted in a cylinder and connected by a connecting rod to a rotatable crankshaft, a combustion chamber hermetically positioning the head of said piston, a valve mechanism for driving an intake valve and an exhaust valve which respectively open and close an intake port and an exhaust port communicating with said combustion chamber, a fuel feed device which produces an air-fuel mixture by mixing fuel with the air drawn into said combustion chamber through the intake port, an ignition device for igniting to explode the air-fuel mixture that has been drawn in and compressed in said combustion chamber, and a lubricating system for supplying lubricating oil to each of the moving parts, so that said valve mechanism, said fuel feed device, and said ignition device will be operated at a specific timing to thereby continuously cause a series of intake of the mixture, compression, power and exhaust strokes in said combustion chamber, thus transmitting the reciprocation of said piston produced by a series of the strokes as a rotational motion to said crankshaft through the connecting rod;
• an exhaust gas discharge section including the exhaust port;
• a hermetically closed crank chamber for housing the crankshaft;
• an intake passage connecting said crank chamber to the atmosphere;
• a first valve disposed within said intake passage and designed to open by the reciprocation of said piston when a negative pressure has been built up in said crank chamber;
• a guide passage connecting said crank chamber and said exhaust gas discharge section to guide the air as the secondary air from said crank chamber to said exhaust gas discharge section;
• a second valve disposed within said guide passage and designed to open by the reciprocation of said piston when a positive pressure is built up in said crank chamber;
• and
• an exhaust gas cleaning section for re-combustion of exhaust gases discharged to said exhaust gas discharge section and mixed with the secondary air.