Lubricating system for chain saw

Claim 1

In a chain saw the combination comprising a frame including a motor and providing an oil reservoir, a sprocket drive shaft coupled to the motor at one end and having a sprocket at the other and normally rotating in the range of 3,000-5,000 r.p.m., a blade secured to the frame in the plane of the sprocket, a saw chain trained about the sprocket and blade, the frame presenting between the motor and the sprocket an arcuate inwardly facing wall approximately centered on the axis of the drive shaft, a circular single-lobed cam on the drive shaft adjacent the sprocket, an anti-friction bearing having an inner race mounted on the circular cam and having an outer race which defines with said wall a C-shaped recess, a length of flexible tubing nested in the recess, the tubing having an inlet connected to the reservoir and having an outlet passage communicating with chain for feeding of oil thereto, the outlet passage having an adjustable restriction and a by-pass leading back to the reservoir, the eccentricity of the cam being approximately equal to the radially measured inner diameter of the tubing in nested position, the tubing extending about the drive shaft substantially less than a full revolution so that the tubing is progressively closed with peristalic action during only a portion of each revolution of the drive shaft and open during the remaining portion of the revolution for impositive pumping of oil, the restriction being located downstream of the by-pass passage but ahead of the chain, and the by-pass passage being located adjacent the cam and being substantially unobstructed to prevent build up of any substantial pressure in the outlet passage so that almost all of the pumped oil is immediately bypassed back to the reservoir with only a minor percentage on the order of a few ounces per hour being fed to the chain for continuous lubrication of the latter.