A piston assembly

Abstract: A piston body (12) has added thereto in interlayered fashion, separate piston-ring lands (26), and spacers (28). In one embodiment, a pair of rider rings (22, 24) are coupled to the piston body (12), in spaced apart locations, to guide the piston assembly (10) in reciprocation, and to space the piston-ring lands (26) away from the surface of an enclosing cylinder, the lands (26) having a diameter which is slightly less than that of the rider rings (22, 24). The lands (26) are formed of a ceramic material to offer, thereby, a substantially wear-resistant surface to the piston rings (30) which are set between pairs of the lands, and about the spacers (28). The body (12) is centrally bored and tapped, and the lands (26) and spacers (28) are centrally apertured; a headed bolt (20) has the shank (18) thereof passing through the lands, spacers and rider rings, and threadedly engaged with the tapped bore (18), to secure the assembly together.

Description: This invention pertains to reciprocating-component machinery, such as reciprocating-piston engines, pumps, and gas compressors, and in particular to a novel piston assembly for reciprocation within a cylinder. Reciprocating, ringed pistons are susceptible to high wear rates, notably in the piston ring lands or carriers, principally due to the spinning action of the piston rings during compression strokes of the piston. It is an object of this invention to devise a piston assembly which provides wear-resistant piston ring seating surfaces. FR-A-1,446,110 discloses a piston for use in high pressure compressors or pumps which are made up of several elements on a shank. US-A-3,149,543 discloses the use of non-metallic elements to seat wear and seal rings. The present invention is as claimed in the claims. The invention provides a piston assembly for reciprocation within a cylinder, comprising a piston body having a reciprocation axis; piston-ring lands coupled to, and arranged lengthwise of said body; and means coupled to said body for (a) guiding said body in reciprocation within an enclosing cylinder, and (b) spacing said lands from confronting surfaces of such an enclosing cylinder; wherein said lands are formed of a non-metallic mineral to define wear-resistant, piston ring seating surfaces thereof. Further objects of this invention, as well as novel features thereof, will become more apparent by reference to the following description, which is given by way of example only, taken in conjunction with the accompanying figures, in which: Figure 1 is an axial, cross-sectional view of a preferred embodiment of the invention; and Figure 2 is a view similar to Figure 1, of an alternative embodiment of the invention. As shown in Figure 1, the novel piston assembly 10 comprises a piston body 12 having a longitudinal, reciprocating axis 14. The body 12 has an axial, threaded bore 16 formed therein which receives the threaded shank 18 of a headed bolt 20. Set against an uppermost, annular end of the body 12 is an apertured, lower, rider ring 22. Underlying the head of the bolt 20 is an apertured, upper, rider ring 24. Stacked between the rider rings 22 and 24, in interlayered fashion, are separate piston-ring lands 26, and separate piston spacers 28. Between pairs of adjacent lands 26, one spacer 28 is interposed. The rider rings 22 and 24, together with the bolt 20, comprise means for guiding the piston body 12 in its reciprocation within a cylinder (not shown), and for spacing the lands 26 from the confronting surface of such a cylinder. The rider rings 22 and 24 have a greatest diameter which causes them to effect a slidable interface with such confronting surface of a cylinder, and piston rings 30, which are set within adjacent lands 26, and about the spacers 28, sealingly close onto the cylinder wall. The lands 26, however, have a common diameter which is smaller than that of the rings 22 and 24. Consequently, they do not contact the cylinder surface. To present a significantly wear-resistant surface to the piston rings 30, the lands 26 are formed of a non-metallic e.g. ceramic material. An alternative embodiment of the inventive piston assembly 10a is similar in most respects to the embodiment 10 of Figure 1. This second embodiment 10a, however, dispenses with the separate rider rings. Rather, the piston body 12a has an uppermost, annular end which is radially expanded to define, thereat, a first guiding surface 22a. Body 12a is also axially bored and threaded at 16a to receive the threaded shank 18a of a headed bolt 20a. The head of the bolt defines a second, reciprocation-guiding surface 24a. Again, stacked between the bolt head and the uppermost, annular end of the body 12a are interlayered lands 26, of ceramic material, and piston spacers 28, arranged to receive the piston rings 30 between the ceramic lands 26. In this embodiment also, the diameter of the ceramic lands 26 is slightly less than the diameter of surfaces 22a and 24a. While we have described the invention in connection with specific embodiments thereof, it is to be clearly understood that this is done only by way of example, and not as a limitation to the scope of the invention as claimed. For example, given numbers of spacers 28 and lands 26 are depicted, but the numbers of each are not limiting. Too, in each of the embodiments, headed bolts are employed; this is arbitrary, as the threaded bores 16 and 16a could receive a threaded stud which, in turn, would receive a topmost, threaded nut for closure onto the stack of lands 26 and spacers 28. These, and all such modifications and/or alterations of the disclosure are deemed to be within the ambit of the invention and embraced by the following claims.

Claims: A piston assembly (10, 10a) for reciprocation within a cylinder, comprising: a piston body (12) having a reciprocation axis (14); piston-ring lands (26) coupled to, and arranged lengthwise of said body (12); and means 22, 24; 22a, 24a coupled to said body (12) for (a) guiding said body in reciprocation within an enclosing cylinder, and (b) spacing said lands (26) from surfaces of the enclosing cylinder; wherein said lands (26) are formed of a nonmetallic mineral and (a) define seating surfaces for piston rings (30), (b) confine piston rings (30) therebetween, and (c) are resistant to wear of said seating surfaces, by such piston rings, seated upon said surfaces and between said lands, due to spinning movement of such piston rings. A piston assembly (10, 10a) as claimed in claim 1, comprising: separate piston-ring lands (26), and separate spacers (28), interlayered along a length of said body (12, 12a); means (18, 24: 18a, 24a) coupled to said body to hold said lands (26) and spacers (28) in position on said body; said body-guidance means (22, 24, 22a, 24a) has one greatest diameter; and said lands (26) have one, common, diameter which is less than said greatest diameter. A piston assembly, according to claim 2, wherein: said guiding and spacing means (22a, 24a) comprises means for effecting a slidable interface with such confronting surfaces of an enclosing cylinder. A piston assembly, according to claim 2 or claim 3, wherein: said body (12) is axially bored (16, 16a); and said guiding and spacing means comprises a headed bolt (20a); wherein the shank (18a) of said bolt (20a) is set in said bore (16a), and the head (22a) of said bolt (20a) comprises means for effecting a slidable interface with such confronting surfaces of such an enclosing cylinder. A piston assembly, according to claim 4, wherein: said axial bore (16a) in said body (12) is threaded; said lands (26) are centrally apertured; said shank (18a) of said bolt (20a) penetrates said lands (26) and threadedly engages said axial bore (18a) to secure said lands to said body. A piston assembly, according to claim 2, wherein: pairs of adjacent lands (26) are spaced apart, axially, by intervening spacers (28). A piston assembly, according to claim 2, wherein: said guiding and spacing means comprises (a) a headed bolt (20), and (b) a centrally-apertured rider ring (24). A piston assembly, according to claim 7, wherein: said body (12) has an axially-extending, threaded bore (16) formed therein; and the shank (18) of said bolt (20) penetrates said rider ring and threadedly engages said threaded bore. A piston assembly, according to claim 2, wherein: said guiding and spacing means comprises (a) a headed bolt (20), and (b) a pair of centrally-apertured, and axially spaced apart rider rings (22, 24). A piston assembly, according to claim 9, wherein: said body (12) has an axially-extending, threaded bore (16) formed therein; said lands (26) are centrally apertured and interposed between said rider rings (22, 24); the shank (18) of said bolt (20) penetrates said rings (22,24) and lands (26), and threadedly engages said axial bore (16) to secure said rings (22, 24) and lands (26) to said body.

Inventors: WEHBER WAYNE F, WEHBER, WAYNE F.
Applicants: DRESSER RAND CO, DRESSER-RAND COMPANY
Application year: 1991
Main classification: F16J9
IPC codes: F16J9, F04B53