Patent ID: 6705263
Filing Date: 2004-03-16
Classification: F01L,F01M,F02B,F02F

Abstract:
A handheld type four-cycle engine, comprising:an engine main body, the engine main body including a crankcases having a crank chamber, a cylinder block having a cylinder bore, and a cylinder head having an intake port and an exhaust port; a crankshaft supported in the crankcase and housed inside the crank chamber; a piston fitted inside the cylinder bore and connected to the crankshaft; an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and the exhaust valve being mounted in the cylinder head; a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and the exhaust valve; and a power output mechanism provided on one end of the crankshaft projecting out of the engine main body; wherein the valve operation mechanism includes a camshaft rotatably supported in the cylinder head so as to open and close the intake valve and the exhaust valve; and a timing transmission placed outside the engine main body on the side opposite to the power output mechanism and operates for providing association between the crankshaft and the camshaft, wherein the valve operation mechanism includes the timing transmission which has a rotating drive member linked to the crankshaft, and a cam system for transmitting the rotational force of a rotating driven member of the timing transmission to the intake valve and exhaust valve for opening and closing forces; a first valve operation chamber and an oil tank are provided on one side of the engine main body, the first valve operation chamber housing the timing transmission, the oil tank including oil mist generation means for generating an oil mist from stored oil, and the lower end of the first valve operation chamber opening inside the oil tank; a second valve operation chamber housing the cam system is provided in the upper part of the engine main body so as to be in line with the first valve operation chamber; a first lubrication system includes first and second oil passages placed alongside each other and providing communication between the oil tank and the crank chamber and first oil feed means for circulating the oil mist generated inside the oil tank from the oil tank via the first oil passage, the crank chamber, and the second oil passage, back to the oil tank; and a second lubrication system includes a third oil passage providing communication between the first valve operation chamber and the second valve operation chamber, a fourth oil passage providing communication between the second valve operation chamber and the crank chamber, the second oil passage, and second oil feed means for circulating the oil mist generated inside the oil tank from the oil tank via the first valve operation chamber, the third oil passage, the second valve operation chamber, the fourth oil passage, the crank chamber, and the second oil passage, back to the oil tank.