Piston ring

April 8, 1952

R. H. COLVIN

2,591,920

PISTON

RING

24, 1947

Filed Nov.

n45‘

FCT/O NS r .070x45’

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ZPi-Q.e

INVENTOR.

Τζο/Χι/ £/.

BY

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XXXVxXXXxXXXW^W

ATTYS.

Patented Apr. 8, 1952

2,591,920

UNITED STATES PATENT OFFICE

This invention relates to piston rings and more particularly to split piston rings of the type in which the twisting or torsion of the ring is controlled in a predetermined manner when the latter is compressed to fit in a cylinder bore.

In general, split piston rings are formed from out-of-round castings or the like. This out-ofround shape of the blank ring in the free or uncompressed condition is required so that when the ring is compressed in an operating condition in a cylinder bore, pressure will be exerted by the ring against the cylinder walls. Although this ring pressure is frequently referred to as being uniformly distributed about its periphery when in the compressed state, it is to be understood that this is not exactly true. The ring pressure actually varies as much as 1½ to 1 or 2 to 1 and even more at different points about the ring periphery. Due to the many variables in piston ring manufacturing it is practically impossible to obtain rings that will have a perfectly uniform pressure distribution. Accordingly, manufacturers design the rings for a predetermined pressure distribution pattern which through experience has been found to be satisfactory. This pressure pattern varies from manufacturer to manufacturer. Thus, some manufacturers use a pressure distribution pattern that is cardioid shaped, others use a pressure distribution pattern that is pear shaped, and others use still different shaped pressure patterns.

The aforegoing is best understood when it is considered that the ring is normally of an outof-round shape in the unstressed condition, and in compressing the ring to a true circle to fit the cylinder bore, portions of the ring are not stressed exactly the same. For example, when an elongated bar having a square section such as a steel bar is bent into a circle, the inside edge of the section will tend to become thicker due to compression and the outside edge of the section will become smaller due to stretching. When materials such as cast iron and similar materials having relatively non-compressible and nonelastic characteristics, such as are used in piston rings, are used under the above conditions, the formed section is distorted by twisting. Thus, no matter how flat and parallel the top and bottom sides of a piston ring, formed from maaterial having a generally rectangular shape, are when in the free state, when the ring is compressed to the cylinder diameter, they are no longer flat and parallel.

In finishing piston rings, that is, in fashioning the rings to the correct outside diameter, a group

2,591,920

PISTON RING

Robert H. Colvin, Delavan, Wis., assignor to Burd Piston Ring Co., Rockford, Ill., a corporation of Illinois

Application November 24, 1947, Serial No. 787,641

Claims.

(Cl. 309—44) of ring blanks are compressed to the approximate outside diameter and are then placed in side by side relation and compressed as by an arbor. The rings are then ground, polished, or honed and the like to the correct diameter. It is readily apparent that when this operation is completed that the rings will have been compressed to diameter and flattened by the endwise pressure. Thus, the rings in the finished form are inherently under twisting or torsional forces as described above.

Because of this twisting, the outer peripheral surface is not truly at right angles to the sides of the ring. Such a ring when it is compressed to diameter in a ring groove in a piston having side clearances and reciprocable in a cylinder bore will not present a ring surface that is a true cylindrical surface. At some portions around the ring the top edge thereof will bear on the cylinder walls, at other points the bottom edge will bear on the cylinder walls, and in some cases an intermediate portion will bear on the cylinder walls. In some instances it is desirable to form the ring so that only one edge for example the bottom edge of the ring will engage the walls of the cylinder, particularly in the case where the ring is used for the purpose of sealing compression and controlling oil usage. In such cases, however, it is desired that this edge engage the cylinder walls at all points around the entire periphery of the ring. Where there is torsion and twisting in the ring when it is compressed as above described this is not always possible.

An object of my invention is the provision of a piston ring wherein the twisting and torsion of the ring is controlled in a predetermined manner so that a predetermined surface on the ring, throughout its periphery, is brought to bear against the cylinder walls.

Another object of the invention is to provide a piston ring of the above character in which wear on the cylinder bore is held to a minimum, which is rugged and simple in construction, and which is easy and inexpensive to manufacture.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which—

Figure 1 is a sectional view of a ring embodying my invention disposed in a cylinder bore;

Fig. 2 is a plan view of the ring;

Fig. 3 shows a plurality of cross-sectional views of the ring in Fig. 2 taken at sections A—A, B—B, C—C, D—D, and E—E, respectively;

3,691,920

Fig. 4 is a sectional view of the ring taken along the line 4—4 of Fig. 2;

Fig. 5 is a plan view of another piston ring embodying a modification of the invention;

Fig. 6 is a sectional view taken through line 6—6 of Fig. 5;

Fig. 7 is an elevational view of another piston ring embodying another modification of the invention, and

Fig. 8 is a view taken substantially along the line 8—8 of Fig. 7.

Referring now to the drawings, the invention is shown embodied in a piston ring 11 of the type adapted for use with a conventional piston 12 arranged to reciprocate in a cylinder bore 13 of an engine, compressor or the like. In general, the ring is formed from an out-of-round annular member having a shape such as that shown in Figs. 2, 5 and 7. Preferably, it has a generally rectangular shaped cross-section and has a gap 14 formed at one position along the periphery to provide opposed faces 16 and il on the ring. The length of the gap 14 is such that the ring 11 can be compressed to fit in the cylinder bore 13.

The invention is concerned with a ring construction which controls the elastic deformation of the ring in a predetermined manner in the compressed state so that a desired peripheral surface 18 of the ring is positively brought to bear on the cylinder walls 19 and the pressure about the periphery of the ring at the point of contact with the cylinder bore is distributed in accordance with a predetermined pressure distribution pattern. For this purpose the ring is formed with an unbalanced cross-section that varies in a prescribed manner around the periphery of the ring 11. As shown in the embodiment in Fig. 2 this is accomplished by forming a bevel 21 on one inside edge of the ring 11. The dimensions of the bevel 21 vary for each particular cross-section along the periphery of the ring as shown by the sectional views in Fig. 3. The dimensions of the bevel are such that there is proportionally more bevel at the points of least bend of the ring when it is compressed to diameter. The amonut of bevel for any section or portion of the ring is inversely proportional to the amount of bend that the particular section will undergo in compressing it to cylinder bore diameter and is directly proportional to the amount of twist desired in the ring section.

The aforegoing can best be seen by referring to Figs. 2, 3 and 4. As previously pointed out the piston ring 11 is made from an annular out-ofround blank of generally rectangular cross-section, the manufacture and design of which is carefully controlled in order to assure that the pressure around the ring when it is restrained in the cylinder bore is distributed in accordance with a predetermined pattern. When the ring is restrained in the bore, the internal stresses in the ring produce an elastic deformation of the ring such that the sides 22 and 23 of the piston ring 11 are no longer exactly parallel and the peripheral face 24 is not an exact cylindrical surface so does not have full contact surface with the walls 19 of the cylinder 13. The twist normally varies throughout the periphery of the ring. Thus, the section 180 degrees from a mid-point between the end faces 16 and 17, due to higher internal stresses, is usually deformed or twisted the most while the portions adjacent the respective faces 16 and 17 are twisted least because of the proportionately small internal stresses in the ring at this portion of the ring.

It is difficult, if not impossible, to determine by mathematics alone the amount of bevel that should be formed on the ring 11 for any crosssection. Although it is theoretically true that when a ring is formed from an annular member having a generally rectangular cross-sectional shape in the free state, any cross-section thereof should be symmetrical when the ring is compressed, tests show that this is not true and that deformation apparently does not follow a true mathematical formula since the respective crosssections are not symmetrical on either side of a transaxial plane passing through the center of the ring. This may be due to non-uniformity or variations of material or imperfections in manufacturing at various points about the ring. Because of these discrepancies in the manufacture of a ring it is difficult to develop accurate mathematical formulas by which the amount of bevel 21 for any given section can be readily determined. As a consequence, I have found it neces,ary as a practical matter to determine the amount of bevel required to obtain the proper twist for any given group of ring sizes by experiment, that is, by fitting a sample ring 11 in a bore of predetermined dimensions and using bluing to determine the fit. Thus, for the finished ring, size 4 inches by A inches, shown in Fig. 2, which is by way of illustration only, I have found that the bevel for the section A—A taken adjacent the face 16 should be a .090 inch by 45 degrees bevel, which means that the chamfer commences on the top surface 23, .090 inch from an inner edge 20 measured along an extension of the top surface 23 and commences on the inner edge 20, .090 inch from the top surface 23 measured along an extension of the inner edge 20. At section B—B on a radius approximately 45 degrees from the face 16, the dimensions of the bevel should be approximately .070 inch by 45 degrees. At section C—C taken on a radius approximately 90 degrees from ‘the face 16 the dimensions of the bevel should be .055 inch by 45 degrees. At section D—D taken on a radius approximately 135 degrees from the face 16 the dimensions of the bevel 21 should measure .045 inch by 45 degrees. At section E—E on a radius approximately 180 degrees from the face ίβ the dimensions of the bevel should be .040 inch by 45 degrees. Due to the symmetry of the ring shown in Fig. 2 the cross-sections on the right hand side of the ring as shown in Fig. 2 are the same as the corresponding cross-sections for the left hand side of the ring. Thus, it is seen that the dimensions of the bevel 21 from faces 16 and 17 get smaller as the position approximately 180 degrees away is approached. It is to be understood that the bevel 21 can be formed during the casting of the annular blank from which the ring 11 is formed or can be machined on a pre-cast ring. In casting the bevel 21, the dimensions of the bevel on the original casting are somewhat larger than indicated above for the finished ring to allow for machining the casting. The allowance for machining in any case will depend on the practice of each individual manufacturer.

Although i have illustrated my invention by employing a non-uniform bevel 2 i along one edge of the ring II it is to be understood that the unbalancing of any section can be effected by notching, grooving or the like. In Figs. 5 and 6 there is shown an embodiment of the invention in which a plurality of annularly spaced stepped

0,801,620

5.......

notches 26 are formed along the inner edge of the ring 11, serving the same purpose as the bevel 21, i. e., to unbalance any given section of the ring

11. It is io be understood that although I have shown the unbalance of the section at one edge only of the ring, it is evident that any edge or any other portion of the ring may be unbalanced to produce the desired control of the twisting. Thus, in Figs. 7 and 8 there is shown still another embodiment of the invention. In this construction a groove 27 is formed on the interior of the ring II to provide an unbalanced cross-section. The dimensions of the groove 27 vary at different cross-sections of the ring in accordance with the foregoing principles. The groove, how- 15 ever, is located at one side of the centerline of the section as shown in Hg. 8 so as to obtain an unbalanced cross-section.

The ring construction hereinbefore described is advantageous in that it provides for a positive 20 resilient seal between the ring 11 and the piston .

12, thereby assuring a finer degree of control, relative to pumping of oil, than heretofore possible. The dimensions of the groove 28 on the piston 12 are of necessity somewhat larger 25 than the thickness of the ring 11 in order to permit assembly. Due to the controlled twist-: ing of the ring 11 as herein described an upper edge 29 of the ring, about its periphery engages: the upper wall of the groove 28 as seen in Hg. 3 ^;!0and a lower edge 31 of the ring engages the lower wall of the groove. Because of the pre-controlled twisting of the ring positive engagement of the walls of the groove and the edges of the ring is assured. This positive engagement between the ring and the walls of the piston groove results in a construction that controls the pumping of oil to a finer degree than in prior constructions. u _n