Lubrication system for four-stroke engine

A single-cylinder, four-stroke cycle, spark ignition internal combustion engine for mounting on a power tool comprising:

• a cylinder (81);
• a piston (15) slidably disposed in the cylinder (81);
• a crankcase (10) disposed below the cylinder (81);
• an oil reservoir (30) disposed below the crankcase (10);
• a cam actuation section (40) comprising a lower camshaft case (41), an upper space (431), a plurality of pushing rods (43) passing through the upper space (431), a plurality of passageways (432) disposed on the top of the camshaft case (41) with the pushing rods (43) passing through, a camshaft (44) with a cam (441) and a reduction gear (442), a camshaft follower (45) engaged with the camshaft (44), a lower gear (46) secured to the crankshaft (13) and being in mesh with the reduction gear (442), and a gaseous oil tube (42) extending to a position above the oil level of the oil reservoir (30);
• an upper rocker arm case (50) disposed above the cam actuation section (40) and being in fluid communication therewith, the rocker arm case (50) comprising a rocker arm (511) and a valve (512) on the top of the cylinder (81) wherein the rocker arm (511) is adapted to operate by actuating the camshaft follower (45) and the pushing rods (43) by rotating the cam (441);
• a check valve case (20) disposed below the crankcase (10) and being in fluid communication with the crankcase (10) and the oil reservoir (30), the check valve case (20) having an oil mist return tube (22) extending into the oil reservoir (30), and a check valve (21);
• a first branch tube (60) being in fluid communication with the check valve case (20) and the gaseous oil tube (42), the first branch tube (60) having a diameter larger than that of the oil mist return tube (22);
• a first venturi (61) disposed in the gaseous oil tube (42) externally of the oil reservoir (30);
• a second branch tube (70) interconnecting the crankcase (10) and the cam actuation section (40) and being in fluid communication therewith;
• a second venturi (71) disposed in the second branch tube (70);
• a flexible oil tube (73) having a weight (731) at one end immersed in the oil reservoir (30);
• a tubing member (72) connected to the flexible oil tube (73);
• a crankshaft (13) rotatably disposed in the crankcase (10);
• a connecting rod (14) interconnecting the crankshaft (13) and the piston (15);
• an oil return section (83) disposed on the top of the rocker arm case (50), the oil return section (83) comprising a plurality of oil return reservoirs (831) being in fluid communication with each other, and a plurality of channels (832) interconnecting the oil return section (83) and the rocker arm case (50);
• an oil return line (84) interconnecting the oil return section (83) and the crankcase (10);
• and
• a liquid oil and gaseous oil separation chamber (85) disposed between the oil return section (83) and the rocker arm case (50), the liquid oil and gaseous oil separation chamber (85) being in fluid communication with the rocker arm case (50) and including a top porous plate (851) for absorbing lubricating oil;
• wherein irrespective of the posture of the internal combustion engine in response to moving the piston (15) in a first direction to decrease the volume of the crankcase (10), oil mist in the crankcase (10) enters the check valve case (20) a first portion of the oil mist flows to the oil reservoir (30) via the oil mist return tube (22), a second portion of the oil mist being smaller than the first portion thereof in volume flows to the first branch tube (60), liquid oil in the oil mist is formed in the oil mist return tube (22) and flows into the oil reservoir (30), gaseous oil in the oil mist is accumulated on the oil level of the oil reservoir (30) and flows to the gaseous oil tube (42), the oil mist also branches from the check valve case (20) to flow to the first venturi (61) via the first branch tube (60), and the oil mist is mixed with the gaseous oil from the gaseous oil tube (42) at the first venturi (61) to form a nebulized mixture which is sent to the cam actuation section (40) and the rocker arm case (50) in sequence for lubrication;
• and
• wherein irrespective of the posture of the internal combustion engine in response to moving the piston (15) in a second direction to increase the volume of the crankcase (10), excess oil mist and liquid oil in the crankcase (40) are inhaled into the second branch tube (70), lubricating oil in the oil reservoir (30) is sucked into the flexible oil tube (73) and flows to the second branch tube (70) via the tubing member (72), the lubricating oil is nebulized in the second venturi (71) and flows to the crankcase (10), oil mist and liquid oil in the rocker arm case (50) enter the oil return reservoirs (831) via the channels (832), a portion of oil mist enters the liquid oil and gaseous oil separation chamber (85) with liquid oil contained therein being absorbed by the porous plate (851), the absorbed liquid oil is sent to the oil return section (83) via the channels (832), the oil mist and the liquid oil contained in the oil return section (83) are inhaled into the oil return line (84) prior to entering the crankcase (10), and the oil mist and the liquid oil in the oil return line (84) and the second branch tube (70) flow from the crankcase (10) to the check valve case (20).