Engine Lubrication Method

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

• a cylinder block having a cylinder, a cylinder head, a piston mounted for reciprocation in said cylinder, said cylinder head defining an air-fuel combustion chamber;
• a lower case mating with said cylinder block by a plane perpendicular to the cylinder bore axis;
• a crankshaft chamber formed by said cylinder block and said lower case;
• an air-fuel mixture intake port and an exhaust gas port in said cylinder head;
• a valve cover on said cylinder head defining a valve chamber;
• an intake valve and an exhaust valve mounted in said intake and exhaust port, respectively, for reciprocation between port-open and port-closed positions;
• a valve-actuating valve train in a valve chamber, said valve train including at least one rocker arm and at least one valve train push rod assembly extending therefrom within said valve chamber and engaging said rocker arm;
• a lubrication oil reservoir formed below the lower case;
• said oil reservoir is partitioned from the crankshaft chamber so as to avoid oil leakage in any slanted state;
• a crankshaft rotatably mounted by ball bearings in said crankshaft chamber, wherein said crankshaft includes a crank portion and at least one counterweight web and has an axis which is on the mating plane of said cylinder block and said lower case;
• a connecting rod having articulated connections at one end thereof to said piston and at an opposite end thereof to said crank portion, thereby forming a piston-connecting rod crankshaft assembly;
• and
• a cam chamber having at least one cam being drivably connected to said crankshaft, said at least one cam having a cam gear and being driven at one-half crankshaft speed, the opposite end of said push rod assembly being drivably connected to said cam whereby said push rod assembly is actuated with a reciprocating motion upon rotation of said at least one cam, said cam chamber having communication means to the oil reservoir and the valve chamber;
• an oil pump connected drivably to said cam gear-cam assembly, wherein said pump brings lubrication oil from said oil reservoir and valve chamber and splashes the oil in parallel into the cylinder and into the cam chamber to lubricate the engine parts inside the cylinder and the cam chamber and the valve chamber, wherein said lower case has a circular arc wall to separate said oil reservoir from said crankshaft chamber, said circular arc wall at least partially surrounding said web at a slight distance therefrom, and said circular arc wall having at least one drain hole and a valve to communicate between said crankshaft chamber and oil separating chamber;
• said oil separating chamber having communicating means between oil separating chamber and valve chamber or between said oil separating chamber and oil reservoir, wherein the opening of the valve is controlled by reciprocating motion of said piston, and wherein said valve opens when pressure in the crankshaft chamber is positive and closes when the pressure in the crankshaft chamber is negative, thereby the valve establishing a lubrication oil mist flow circuit from said crankshaft chamber to said oil separating chamber or from said oil separating chamber to said valve chamber or from said valve chamber to said cam chamber or from said cam chamber to said oil reservoir.

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

• a cylinder block having a cylinder, a cylinder head, a piston mounted for reciprocation in said cylinder, said cylinder head defining an air-fuel combustion chamber;
• a lower case mating with said cylinder block by a plane perpendicular to the cylinder bore axis;
• a crankshaft chamber formed by said cylinder block and said lower case;
• an air-fuel mixture intake port and an exhaust gas port in said cylinder head;
• a valve cover on said cylinder head defining a valve chamber;
• an intake valve and an exhaust valve mounted in said intake and exhaust port, respectively, for reciprocation between port-open and port-closed positions;
• a valve-actuating valve train in a valve chamber, said valve train including at least one rocker arm and at least one valve train push rod assembly extending therefrom within said valve chamber and engaging said rocker arm;
• a lubrication oil reservoir formed below the lower case;
• said oil reservoir is partitioned from the crankshaft chamber so as to avoid oil leakage in any slanted state;
• a crankshaft rotatably mounted by ball bearings in said crankshaft chamber, wherein said crankshaft includes a crank portion and at least one counterweight web and has an axis which is on the mating plane of said cylinder block and said lower case;
• a connecting rod having articulated connections at one end thereof to said piston and at an opposite end thereof to said crank portion, thereby forming a piston-connecting rod crankshaft assembly;
• and
• a cam chamber having at least one cam being drivably connected to said crankshaft, said at least one cam having a cam gear and being driven at one-half crankshaft speed, the opposite end of said push rod assembly being drivably connected to said cam whereby said push rod assembly is actuated with a reciprocating motion upon rotation of said at least one cam, said cam chamber having communication means to the oil reservoir and the valve chamber;
• a cam chamber cover connected to support said cam gear-cam assembly, wherein lubrication oil is inhaled through said cam chamber cover from said oil reservoir when the pressure in the crankshaft chamber is negative and a rotary valve provided between said cam shaft and said cam chamber cover opens and splashes the oil into the cylinder to lubricate the engine parts inside the cylinder, wherein said lower case has a circular arc wall to separate said oil reservoir from said crankshaft chamber, said circular arc wall at least partially surrounding said web at a slight distance therefrom, and said circular arc wall having at least one drain hole and a valve to communicate between said crankshaft chamber and oil separating chamber;
• said oil separating chamber having communicating means between oil separating chamber and valve chamber or between said oil separating chamber and oil reservoir, wherein the opening of the valve is controlled by reciprocating motion of said piston, and wherein said valve opens when pressure in the crankshaft chamber is positive and closes when the pressure in the crankshaft chamber is negative, thereby the valve establishing a lubrication oil mist flow circuit from said crankshaft chamber to said oil separating chamber or from said oil separating chamber to said valve chamber or from said valve chamber to said cam chamber or from said cam chamber to said oil reservoir.