US1891441A - Piston - Google Patents

Description

Dec. 20, 1,932.

A. B. NORTON PISTON Filed March 15. 1929 INVENTOR ALL/5W B 1701270117 dam ATTORNEY Patented Dec. 20, 1932 UNITED STATES PATENT OFFICE ALIEN B. nonron, or crlnvnmrm, 01:10, assiexon, BY MESNE ASSIGNMENTS, TO

THE CLEVELAND TRUST COMPANY, OF CLEVEIAND, OHIO, A CORPORATION OF OHIO, AS TRUSTEE PISTON Application filed March 15, 1929. Serial No. 3467,228-

This invention relates to pistons and is particularly applicable to pistons of aluminum, its alloys and the like, or other materials such as magnesium and its alloys having a relatively hi h coeflicient of expansion and which are uset l in cylinders of cast iron or other materials which have a lower coeflicient of expansion.

The desirability of aluminum and similar materials for use in pistons of internal combustion engines is well known as such materials possess light weight, high heat conductivity, and so forth, while the disadvantages arising from the high coeflicient of expansion of these materials is also well known. Due to this high coefiicient of expansion, pistons of such materials must be fitted with a large clearance in order that they will not stick within the cylinders in which they operate when hot, andwhen so provided with a large clearance the pistons may fit too loosely within the cylinders when cold and slap while the engine is becoming warmed up. Various means have been proposed to restrain the expansion of the aluminum pistons and make their expansion conform more nearly that of the cylinders in which they operate, and, while some of these attempts have been tolerably satisfactory in the results obtained in operation, they vhave necessitated elaborate and expensive apparatus for and operations in the production of the pistons.

It is an object of this invention to produce a simple piston which may be fitted with rela: tively large clearance, so thatit may be composed of aluminum or like material of high coeflicient of expansion, within a cylinder of lower coeflicient of expansion and which piston is provided with means for preventing slapping during the period while the engine is warming up,

Other objects hereinafter appear. As the time required to warm a cylinder and its piston to their operating temperature is relatively short, it is not nearly so essential that large bearing surfaces be provided during this period as it is while the motor is operating at its normal operating temperature. The invention will be better understood from the description of one practical emiron and other materials.

bodiment thereof, illustrated in the accompanying drawing, in which Figure 1 is a central longitudinal sectiona view of a piston embodying the invention;

Figure 2 is a transverse section thereof taken on the line 11-11 of Figure 1 and showing the parts in their relation when cold; and

. Fi re 3 is a view similar to Figure 2 but showing the partsin their relationship when the ist'on is heated to operating temperature.

The piston comprises a head 1 from which depends a cylindrical trunk or skirt 2 having glidin surfaces and provided adjacent the head wlth the usual piston ring grooves 3.

surface of'the skirt intermediate its length. The parts thus far described are similar to those of the ordinary trunk type piston,'as it has heretofore been constructed of cast Two circumferentially extending grooves 5 and 6 are formed in the exterior surface of the skirt, and within these grooves rings or bearing means 7 and 8 of iron, steel, or other material which expands at a rate lower than that of the aluminum, preferably near that of the cylinder in which the piston is to operate, are positioned,

These rings are of a size to be flush with or slightly below the cylindrical surface'of the skirt when the piston 1s heated to its operating temperature. The rings are secured at diametrically opposite points, in the vertical plane of the wr1st pin axis, to the sides of the skirt as by bolts 9 passing through the skirt and having nuts 10 bearing upon washers 11 of hard brass or the like seated on the inner surface of the skirta These washers are preferably of brass which has substantially the same coeflicient of expansion as the aluminum of the skirt and are conveniently positioned by being cast into the same. Their function is to distribute the pressures exerted upon the v formed by these pressures. c

As the rings are of a material of lower coeflicient of expansion than the skirt, and as they fit within the grooves when the piston is heated to operating temperature, it is obvious that as the piston cools below this temperature this skirt will shrink at a greater rate than the rings, and that the rings being constrained to remain tightly against the portions of the skirt in the plane of the wrist pin axis, the parts of the rings intermediate these points will be forced to bulge outwardly as shown at 12. The diameter across the exterior of the ring in a plane normal to the wrist pin axis, that is, across the thrust faces of the piston, therefore decreases at even a less rate than would the diameter of the rings if free to contract uninfluenced by the contraction of the piston skirt. The bulging portions of these rings therefore act as skids, or extended bearings, upon the cylinder walls so that when the engine is cold no excessive clearance in the direction normal to the wrist pin axis exists between these rings and the cylinder walls, and slapping of the piston is therefore eliminated.

Obviously as the piston is heated up to its operating temperature the skirt expands at a rate greater than the rings, and, moving the points of connection between the rings and skirt outwardly, causes the rings to approach and finally assume a circular form seated in the bottom of the grooves in the skirt. When this condition is reached the entire bearing faces of the skirt contact with the cylinder walls and the piston functions as it would if the entire skirt were one integral piece.

From the above it will be seen that the skirt may be fitted with suflicient clearance that it may expand and contract freely with changes in temperature, while. even though it contracts to a considerable distance from the cylinder walls, the rings bearing thereon prevent all slapping or cocking out of line.

While I have described the illustrated embodiment of my invention in some particularity, obviously many variations and modifications thereof will readily occur to those skilled in the art to which it appertains, and I do not, therefore, limit myself to precise details shown and described, but claim as my invention all embodiments coming within the scope of the appended claims.

I claim:

1. In a piston of aluminum or magnesium or an alloy of either, a circumferentially continuous skirt provided with a groove in the exterior thereof, a bearing ring of material of lower coefficient of expansion than aluminum within said groove and having its exterior surface substantially flush with that of the skirt when the piston is raised to its highest operating temperature, and securing means between said ring and skirt intermediate the bearing faces of the piston, said ring being free from the skirt except at the point of the securing means.

2. In a piston of aluminum or magnesium or an alloy of either, a circumferentially continuous skirt provided with grooves in the exterior thereof, two bearing rings of material of lower coefiicient of expansion than aluminum within said grooves and having their exterior surfaces substantially flush with that of the skirt when the piston is raised to its highest operating temperature, said rings and skirt having portions relatively movable incident to temperature changes and securing means. between said rings and skirt intermediate the bearing faces of the piston, one of the rings being above and one 4. In a piston of aluminum or magnesium or an alloy of either, a circumferentially con-.

tinuous skirt provided with a groove in the exterior thereof, a bearing ring of material of lower coefficient of expansion than aluminum within said groove and having its exterior surface substantially flush with that of the skirt when the piston is raised to its highest operating temperature, and securing bolts passing through the ring and skirt between said ring and skirt intermediate the bearin faces of the piston, and bearing members 0 hard material in, the interior of said skirt and between the skirt and said securing bolts.

5. In a piston of aluminum or magnesium or an alloy of either and having gliding surfaces, bearing means associated therewith composed of a material having a different co-efiicient of expansion presenting when cold a larger diameter normal to a vertical plane through the wrist pin axis than do the piston gliding surfaces adjacent thebearin member or members and a diameter in t e vertical plane through the wrist pin axis not larger than the diameter of the piston, and presenting when hot a diameter at least as small as the diameter of the gliding surfaces at all points on the gliding surfaces.

6. In a'piston of a light metal alloy having a relatively high co-efiicient of e ansion, a skirt having wrist pin bosses and g ding surfaces intermediate the Wrist pin bosses, a member composed of a material having a relatively low co-efiicient of expansion secured to said piston against radial movement with respect thereto at opposite points substantially on a diameter parallel to the axis of the wrist pin bosses and including a portion passing around one of said gliding surfaces, said portion being free from the iston for radial movement relative to said g iding surface and being of such size as to lie substantially flush with said gliding surface when the piston is raised to normal operating temperature.

a In testimony whereof I hereunto afiix my signature this 5th day of March, 1929.

ALLEN B. NORTON.

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