Patent ID: 6047678
Filing Date: 2000-04-11
Classification: F01M,F02B,F02F,F05C

Abstract:
A motor driven power tool comprising:a frame to be carried by an operator;a rotary driven implement supported by the frame; anda four-cycle internal combustion engine mounted to the frame providing a rotary power source for the rotary driven implement, the engine having:a lightweight engine block forming a cylindrical bore, an enclosed crankcase in communication with the cylindrical bore, an enclosed cam case and a bearing journal extending between the crank case and the cam case;a piston reciprocally cooperating within a cylindrical bore;a connecting rod assembly having a first bearing for pivotally cooperating with the piston, an elongated central region and a second bearing spaced from the first bearing;a crankshaft having a crankpin cooperating with the connecting rod second bearing, an elongated axial shaft pivotally mounted upon the engine block bearing journal and provided with a driven end, an output end and an internal axial passageway having two axially spaced apart inlet/outlet ports, and a web-counterweight cooperating with the crankpin and the axial shaft maintaining the crankpin and axial shaft in spaced-apart parallel relation, the web-counterweight having a radially extending internal passageway having a first end in communication with one of the inlet/outlet ports in the axial shaft and a second end in communication with the crank case, the other of the inlet/outlet ports of the axial shaft being in communication with the cam case to thereby interconnect the cam case and crank case;a cylinder head assembly attached to the engine block to define a combustion chamber in cooperation with the cylinder bore and the piston, said cylinder head assembly having overhead intake and exhaust ports, a spark plug hole extending into the combustion chamber and an intake valve, an exhaust valve and a spark plug respectively cooperating with the intake and exhaust ports and spark plug hole;a cam shaft including cams for sequentially activating the intake and exhaust valves, a cam shaft drive means drivably connecting said crankshaft and said cam shaft for driving said cam shaft at 1/2 engine speed; anda valve cover attached to the cylinder head to define a valve chamber whereby an oil mist formed by lubricating oil which partially fills the crankcase is free to pass through the passageway in the crankshaft while the engine is running as large oil droplets are precluded from entering the rotating radially extending passageway in the crankshaft web-counterweight as a result of centrifugal force thereby resulting in the engine being operable in a number of orientations without having liquid oil flowing into the valve chamber.