Four-stroke internal combustion engine lubrication device

Abstract

There is provided a four-stroke internal combustion engine lubrication device that is capable of appropriately lubricating various parts regardless of engine orientation, of improving the capability for collecting excess oil within a valve chamber or the like and the capability for supplying oil to the various parts, and of reliably preventing oil leakage from a breather port provided in the valve chamber. It comprises: a reed valve ( 40 ) that allows oil flow from an oil chamber ( 17 ) into a crankcase ( 15 ) but prevents oil flow from the crankcase ( 15 ) to the oil chamber ( 17 ); an oil supply passage ( 35 ) for supplying oil from the crankcase ( 15 ) to a valve chamber ( 18 ); and a plurality of independent oil collection passages ( 51, 52 ) with differing inlet/outlet positions and for collecting in the oil chamber ( 17 ) the excess oil in the valve chamber ( 18 ). The dimensions of the various parts are so designed as to constantly maintain the oil chamber ( 17 ) under negative pressure during operation. The excess oil within the crankcase ( 15 ) is returned to the oil chamber ( 17 ) utilizing the negative pressure of the oil chamber ( 17 ).

1 . A four-stroke internal combustion engine comprising:
 a cylinder portion into which a piston is inserted;   a valve chamber formed above the cylinder portion;   a crankcase formed below the cylinder portion;   an oil chamber formed at the outer circumference of the crankcase, the oil chamber being configured to cause oil therein to flow into the crankcase in mist form utilizing an up/down motion of the piston;   a one-way valve configured to allow oil flow from the oil chamber into the crankcase, but prevent oil flow from the crankcase to the oil chamber;   an oil supply passage configured to supply oil from the crankcase to the valve chamber; and   a plurality of independent oil collection passages with differing inlet/outlet positions, the oil collection passages configured to collect in the oil chamber excess oil in the valve chamber, wherein   dimensions of the engine are configured such that the oil chamber would be constantly maintained under negative pressure during operation, and   excess oil within the crankcase is returned to the oil chamber utilizing the negative pressure of the oil chamber.   
     
     
         2 . The four-stroke internal combustion engine according to  claim 1  wherein the one-way valve is a reed valve. 
     
     
         3 . The four-stroke internal combustion engine according to  claim 1 , wherein the oil chamber is disposed adjacent to the crankcase in such a manner as to surround the crankcase with a baffle in-between, and
 a predetermined number of fine holes are formed in the baffle in order to return the excess oil within the crankcase to the oil chamber utilizing the negative pressure of the oil chamber.   
     
     
         4 . The four-stroke internal combustion engine according to  claim 1  wherein, in order to improve capability for sucking oil into the oil chamber and to prevent backflow, an effective passage sectional area of the narrowest portion of each of the oil collection passages is set to or below a predetermined value. 
     
     
         5 . The four-stroke internal combustion engine according to  claim 1  wherein an oil mist within the crankcase is supplied to the valve chamber via an L-shaped passage portion formed within a crankshaft, a gas-liquid separation chamber provided at the outer circumference thereof, and the oil supply passage. 
     
     
         6 . The four-stroke internal combustion engine according to  claim 2  wherein
 a valve opening in the reed valve is disposed at a position that is set apart from the engine centerline by a predetermined distance in a predetermined direction below the crankshaft, and 
 in conjunction therewith, the shape of the oil chamber that surrounds the crankcase is so configured as to comprise, so that the valve opening in the reed valve would assume a position above the level of the oil within the oil chamber regardless of engine orientation, an expansive bulging portion configured to protrude further outward, as compared to other sides, on a side below the crankshaft and where the valve opening in the reed valve is located relative to the engine centerline. 
 
     
     
         7 . The four-stroke internal combustion engine according to  claim 2 , wherein the oil chamber is disposed adjacent to the crankcase in such a manner as to surround the crankcase with a baffle in-between, and
 a predetermined number of fine holes are formed in the baffle in order to return the excess oil within the crankcase to the oil chamber utilizing the negative pressure of the oil chamber.