Piston

This invention relates to anti-friction pistons and is an improvement over the piston disclosed in U.S. Pat. No. 3,398,653 issued to the same inventor on Aug. 27, 1968. The pistons of both the earlier patent and instant invention include roller bearings each bearing including multiple rollers 30a mounted on an axle in the piston skirt so that friction may be reduced between the piston and a cylinder in which it reciprocates.

The present invention provides the advantages of the piston of U.S. Pat. No. 3,398,653 and further permits a reduction of piston cost and piston weight and an attendant reduction of energy expenditure to drive the piston in a cylinder. The foregoing improvements over the piston of U.S. Pat. No. 3,398,653 are accomplished by the reduction of the required number of roller bearings and the triangular arrangement of the bearings in openings in the piston skirt.

In addition, the provision of a reduced diameter skirt which is lighter and stronger permits the utilization of lighter connecting rods and wrist pins. An additional feature of the improved piston is the provision of lubricating openings aligned over the roller bearings in the oil ring groove to distribute oil in the path of travel of the roller bearings.

A further significant advantage of the invention is a simplified mounting of the roller bearings on their respective axles in grooves made in the piston skirt by numerically controlled ball end mills. The use of a milling machine eliminates expensive drill jigs and problems of drill "walk" on the cylindrical piston skirt which heretofore had been encountered in providing the drilled axle holes. It also eliminates the need of a different jig for each piston size. By setting up the new piston in an indexing head of a milling machine, the ball end mill tool produces extremely accurate grooves in the piston skirt, each perpendicular to a radius of the piston and opening radially outwardly. A cavity or opening is cut or otherwise provided intermediate the length of each of said grooves in communication therewith to receive a roller bearing. The axles of the bearings rest in the accurately milled outwardly open grooves, the ends of which may be staked to secure the roller bearings in place for ease of assembly of the piston in a cylinder.

Three point stability of the piston in a cylinder is provided by triangular areas formed by two upper roller bearings and one lower roller bearing equidistant from each of said two upper bearings. Two triangular areas are provided in symmetrical arrangement opposite each other in the piston skirt equidistant from the piston's wrist pin openings with the upper bearings above the centerline of the wrist pin and the lower bearings below the centerline of the wrist pin.

FIG. 1 is a front elevational view of the piston of the invention.

FIG. 2 is a schematic bottom plan view of the piston of FIG. 1 with portions of the skirt broken away for illustrative purposes.

FIG. 3 is a schematic elevational view of the piston of FIGS. 1 and 2 with portions broken away and portions cut of angular position for illustrative purposes.

FIG. 4 is an enlarged schematic portion of FIG. 2 illustrating pertinent detail of the roller bearing mounting in a milled groove.

Throughout the drawings, like parts are provided like reference numerals.

The numeral 10 generally designates the novel anti-friction piston of the invention. The piston 10 includes a head 12 of circular cross-section and a skirt 14 of a diameter less than the diameter of head 12. Adjacent the top of the piston 10 is a groove 16 for a compression ring 18, and below that, a groove 20 for an oil ring 22. The skirt 14 has wrist pin openings 24 located on opposite sides thereof which pass through bosses 26 on the inside of skirt 14.

On the piston skirt 14, six roller bearings 30 having multiple rollers 30a of the type described in U.S. Pat. No. 3,398,653 are arranged to form two areas of three point stability symmetrically oriented equidistant from wrist pin openings 24. The triangular areas are each formed of two upper roller bearings 30 and one lower roller bearing 32 equidistant from each of the two upper bearings 30 with which it is associated.

The roller bearings 30 and 32 are rotationally mounted on axles 34 which, in turn, rest in milled grooves 36. Intermediate the ends of grooves 36 are openings or cavities 40 in the skirt 14 to accommodate the rollers 30 and 32. The ends 42 of grooves 36 may be staked against the axles 34 to secure the roller bearings in place for ease of assembly of the piston in a cylinder. The cylinder may be in an internal combustion engine, a compressor or the like.

The three point stability of the piston is provided in the illustrated embodiment by means of the four upper roller bearings 32 being located 30.degree. on either side of a perpendicular bisector of the wrist pin opening center line and the lower roller bearings being in a vertical plane including the perpendicular bisector of the wrist pin opening center line. The center line lies vertically between the upper and lower roller bearings.

The position of the roller bearings 30 and 32 in the piston skirt 14 as shown in FIG. 2 is accurate but in FIG. 3 the roller bearings 30 and 32 are shown schematically and are out of position for illustrative purposes.

The oil ring groove 20 has pairs of lubricating openings 35, through which lubricating oil may flow, communicating the groove 20 with the interior of the piston. The pairs of openings 35 are aligned over the roller bearings 30 and 32 to distribute oil in the path of travel of the roller bearings.

The above description should not limit the scope of protection of this invention. The claims below set forth the bounds of the invention.