Oiling system for piston of internal combustion engine

A piston is provided with a boss having a radial bore for reception of a piston pin. The upper portion of this bore receives lubricating oil through an oiling hole extending from a depression on the outer surface of the piston, the depression being open at the bottom and extending downward on opposite sides of the boss. Downward facing inclined walls form the upper limits of the depression and serve to cause flow of lubricating oil into the oiling holes.

This invention relates to systems for internal combustion engines and is 
particularly directed to improvements for lubricating the aligned bores in 
bosses formed on the piston, the bores receiving the piston pin that 
connects the piston to the connecting rod. 
In the past, as a means for oiling the piston pin bores, oiling holes have 
been provided in the pin bosses along the direction of piston movement, so 
that lubricating oil under the piston is caused to enter the oiling holes 
during descending movement of the piston. However, when loading of the 
piston is very heavy during the power stroke, the conventional oiling 
means is unable to perform sufficient oiling function, and the lubrication 
between the piston pin bore and the piston pin may be insufficient in some 
cases. 
Accordingly, the general object of this invention is to provide an improved 
oiling system for the piston pin of an internal combustion engine. More 
particularly, the invention relates to supplying lubricating oil to the 
upper interior portion of the bores which receive the piston pin. 
Other objects and advantages will appear hereinafter.

Referring to the drawings, the piston P is provided with two piston ring 
grooves 1 and one oil ring groove 2, all of conventional form. The oil 
ring groove 2 has a plurality of radial oil holes 3. Pin bosses 4 are 
located below the oil ring groove 2 and each is provided with a radial 
bore 5 to receive the piston pin, not shown. Near the outer end of each 
bore 5 a groove 6 is provided for reception of a retaining ring, not 
shown. The piston pin is positioned inwardly of the retaining ring such 
that the effective length of the bore requiring lubrication is the portion 
inwardly of the groove 6. A depression 7 is formed on the outer surface of 
the skirt of the piston P extending circumferentially on either side of 
each boss 4. Each depression 7 is in the form of a cavity opening 
downward. The upper walls 8 of each depression 7 are inclined upward 
toward the upper portion of the boss 4. Oiling holes 9 are provided in the 
upper part of the outer end of each boss 4, the oiling holes 9 preferably 
being inclined in the same direction as the upper walls of the depression 
7 and inclined inward along the axial direction of each boss 4. The inner 
end of the oiling hole communicates with the upper part of the piston pin 
bore 5 in each boss 4. The angle of inclination .alpha. of the oiling hole 
9 in reference to a horizontal plane is from 0.degree. to 30.degree., and 
the angle of inclination .beta. of the upper wall 8 in reference to the 
horizontal plane is 0.degree. to 15.degree.. Assuming that the length of 
the upper, effective portion of the bore 5 is labeled "b" and the distance 
between the inner end of the oiling hole 9 and the groove 6 in the bore 5 
is labeled "a" both as shown in FIG. 2, then the ratio of these lengths 
may desirably be determined by the following formula: 
EQU b/a=2 
In operation, when the piston P moves down in the cylinder bore, 
lubricating oil under the piston P enters the depression 7 as shown by 
arrows in FIG. 1. The lubricating oil in the depression 7 is checked and 
gathered by the upper walls 8 and is automatically introduced into the 
oiling holes 9 near the walls 8. The lubricating oil then flows through 
the oiling hole 9 into the piston pin bore 5 in the piston boss 4 for 
lubrication of the internal periphery of the bore 5. 
When an excessive load is applied to the piston, as in the case where the 
piston is so large in diameter that the load applied to the piston during 
the power stroke is far greater than the load caused by inertia, the 
oiling system of the present invention makes it possible to provide good 
lubrication on the upper portion of the piston pin bore. The seizure 
resistance is remarkably improved. Furthermore, forced introduction of 
lubricating oil into the oiling hole 9 from oil flowing into the 
depression 7 also serves to reduce the amount of lubricating oil which 
reaches the combustion chamber. 
Having fully described my invention, it is to be understood that I am not 
to be limited to the details herein set forth but that my invention is of 
the full scope of the appended claims.