Piston ring assembly

A piston ring assembly comprises a piston ring, a spring for providing an outward force on the ring, and a rail for engaging a cylinder wall. The piston ring is retained in a piston groove in a piston. During upward movement of the piston in a cylinder, oil above the ring face is forced between the first front surface and the top surface into the piston groove to an inner portion of the piston groove. During downward movement of the piston, the downward force urges cocking of the piston ring about the ring face to tilt the ring face away from the cylinder wall, leaving the lower front of the ring face in scraping abutment with the cylinder wall.

BACKGROUND OF THE INVENTION 
The present invention relates to piston rings for internal combustion 
engines and, more particularly, to an oil control ring to minimize the oil 
consumption of piston engines. 
The difference in diameter between a piston and the cylinder in which it 
operates necessitates the use of some type of a sealing arrangement. The 
sealing arrangement is necessary if any substantial amount of compression 
is to be developed, and if excessive movement of oil from the crankcase 
into the combustion chamber is to be prevented. It is conventional 
practice to provide one or more peripheral grooves on the piston, and to 
install resilient rings in these grooves which are the approximate form of 
an interrupted circle. It is the intention that the ring or rings should 
bear directly against the cylinder wall, and should affect a seal against 
the sides of the groove in which the ring is positioned. 
The inevitable difference between the width of the ring groove and the 
thickness of the ring creates a problem which has proven to be extremely 
difficult to solve. At least a few thousandths of an inch clearance is 
required between the ring and the groove in order to permit the ring to 
move and to position itself radially under its own resiliency. As the 
combined effect of inertia and/or gas pressure urges a ring against one 
particular wall of the groove, it is obvious that the gas pressure or oil 
can find its way in the clearance area between the ring and the opposite 
side of the groove. The periodic nature of both the inertia and the gas 
pressure forces is such that conventional ring installations exhibit a 
tendency to move back and forth in a periodic relationship in the groove. 
This movement causes a corresponding series of periods in which the ring 
permits the passage of oil or gas pressure around it. It is generally 
recognized that oil will tend to move around underneath and in back of a 
ring, and gradually work its way into the upper area of the cylinder where 
it is carbonized by the combustion heat. 
It is recognized, of course, that the oil ring should permit enough 
lubricant to remain on the cylinder wall to sufficiently lubricate the one 
or more compression rings. The essential function of an oil ring, then, is 
not to scrape all of the oil from the cylinder wall, but to meter 
lubricant to the compression rings by permitting a thin, uniform, 
consistent film of oil to be retained along the cylinder wall. 
Theoretically, it is easier to provide this consistency with a single rail 
oil ring design, rather than a double rail oil ring design, since it is 
much more difficult to manufacture a double rail wherein both rails 
provide consistent pressure against the cylinder wall. 
It is seen then that there exists a need for an oil control ring that 
provides a consistent amount of oil to the cylinders to properly lubricate 
the compression rings, without allowing excess oil which could impair 
engine performance or contaminate engine exhaust. 
SUMMARY OF THE INVENTION 
This need is met by the oil control ring according to the present 
invention, wherein the oil control ring has a reverse keystone angle on 
the top of the ring. In accordance with one aspect of the present 
invention, a piston ring assembly comprises a piston ring positioned in a 
piston groove, and having a top front extending downwardly along a top 
side of the piston groove and toward a cylinder wall at an angle of 
approximately three degrees, with respect to a horizontal to form a 
"reverse keystone" top side angle, and further having a bottom surface 
extending inwardly along a bottom side of the piston groove. The piston 
ring assembly further comprises a rail extending outwardly from the ring 
to form a ring face adapted to engage the cylinder wall. The rail has a 
first front surface extending outwardly and downwardly from the top 
surface of the piston ring toward an upper surface of the ring face at an 
angle of approximately thirty degrees surface with respect to a vertical, 
a second front surface extending downwardly and inwardly from a lower 
surface of the ring face at an angle of approximately fifteen degrees with 
respect to the horizontal, and a third front surface extending vertically 
downwardly from the second front surface toward the bottom side of the 
piston groove. Finally, the piston ring assembly comprises a spring for 
providing an outward force on the rail, causing the rail to scrape oil off 
of the cylinder wall during downward movement of the piston. Reciprocal 
movement of the piston causes cocking of the piston ring about the 
scraping corner of the ring face. 
This cocking movement of the piston ring about the scraping corner 
minimizes the oil consumption of the piston engine because the reverse 
keystone top side angle produces concentrated and high seal pressure 
around the top side of the ring and the ring face as the piston moves 
downward. On the upstroke, the ring face tends to slide over the oil film 
rather than scrape oil toward the combustion chamber. An advantage of the 
concentrated and high seal pressure is that it reduces the amount of oil 
allowed to pass both behind the piston ring and along the ring face, 
thereby reducing oil consumption. 
Other advantages and features of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, in FIGS. 1A and 1B there is illustrated a 
cutaway, cross-sectional view of a piston ring assembly 10. Although FIGS. 
1A and 1B illustrate an assembly adapted for heavy duty applications, the 
piston ring assembly 10 can be applied to light duty applications as well. 
The piston ring assembly 10 includes a piston ring, such as an oil control 
ring 12, positioned in a piston groove 14. The ring 12 may be formed of 
iron, steel, or other suitable materials, and is spring loaded with a 
"reverse keystone" top side angle along a top surface 16. The top surface 
16 extends downwardly along a top side 18 of the piston groove 14 and 
toward a cylinder wall 20 of cylinder 22 at a first angle of between one 
and ten degrees, and preferably approximately three degrees, with respect 
to the horizontal. A bottom surface 24 of the ring 12 extends inwardly 
along a bottom side 26 of the piston groove 14. 
Continuing with FIGS. 1A and 1B, the piston ring assembly 10 further 
includes a spring 28, which provides an outward force to push the ring 12 
toward the cylinder wall 20. A rail 30 protrudes outwardly from the ring 
12 such that when the spring 28 pushes the ring 12, the rail 30 extends 
toward the cylinder wall 20. The rail 30 defines a ring face 32 adapted to 
engage the cylinder wall 20. The oil ring face may be formed by any 
suitable method, including profile grinding, which offers low unit 
pressure variation and consistent performance. 
The rail 30 has a first front surface edge 34 which extends outwardly and 
downwardly from the top surface 16 of the ring 12 toward an upper corner 
36 of the ring face 32 at a second angle of between ten and thirty 
degrees, and preferably less than thirty degrees, with respect to the 
vertical. A second front surface 38 extends downwardly and inwardly from a 
lower corner 40 of the ring face 32 at a third angle of between three and 
fifteen degrees, and preferably less than fifteen degrees, with respect to 
the horizontal. Finally, a third front surface 42 extends substantially 
vertically downwardly from the second front surface 38 toward the bottom 
side 26 of the groove 14. 
Referring now to FIG. 1A, the ring 12 is retained in the groove 14 in a 
piston 44. During upward movement of the piston 44 in the cylinder 22, in 
the direction shown by arrow 46, oil 48 above the ring face 32 is forced 
between the first front surface 34 and the top surface 16 into the piston 
groove 14 to an inner portion of the piston groove 14. Conversely, during 
downward movement of the piston 44, as illustrated in FIG. 1B with the 
direction of piston movement shown by arrow 50, the downward force of the 
piston causes the ring 12 to cock about the lower ring face corner 40, in 
the direction of arrow 52. This causes the ring face 32 to tilt away from 
the cylinder wall 20, leaving the lower corner 40 of the ring face 32 in 
scraping abutment with the cylinder wall 20. 
The change in face 32 attitude plus the increase in unit pressure at the 
lower corner 40 of the ring face 32 improves oil control by providing a 
consistent, but not excessive, amount of oil to reach the engine 
cylinders. In addition, the seal between the top surface 16 of the ring 12 
and the top side 18 of the piston groove 14 prevents oil 48 in the back of 
the groove 14 from passing between the top surface 16 and the top side 18 
and reaching the combustion chamber of the engine. 
The lower corner 40 of the ring face 32 is situated on a horizontal line 
which passes through the center of the spring 28, as shown by cross-hairs 
41. Since the spring 28 is located in the approximate middle of the ring 
12, the lower corner 40 is also situated on a horizontal line which passes 
through the center of the ring 12, as shown by cross-hairs 43. Therefore 
during upward movement of the piston 44, the corner 40, and the 
cross-hairs 41 and 43, generally share a common horizontal line. Since the 
spring 28 is located at the approximate pivot point of the ring 12, the 
spring 28 does not affect the torsional movement of the ring 12. Hence, 
this design prevents the spring 28 pressure from inhibiting the rotational 
movement about the lower corner 40, so that the spring 28 provides only 
the radial force against the cylinder wall 20, which force the ring 12 
inherently lacks without the spring 28. 
In a preferred embodiment of the present invention, the lower corner 40 is 
on the horizontal center line 41 through the spring 28 whether the piston 
is in the sliding mode or the scraping mode. During downward movement of 
the piston 44, the downward force urges the ring 12 axially against the 
groove top side 18, causing cocking of the ring 12 about the lower corner 
40, and the spring 28 provides an outward force on the ring 12 to bring 
the rail 30 into scraping abutment with the cylinder wall 20. This leaves 
the lower corner 40 in scraping abutment with the cylinder wall 20. On the 
downstroke of the piston 44, then, the reverse keystone angle along the 
top surface 16 of the ring 12 produces concentrated and high seal pressure 
at the top side 16 of the ring 12 so oil 48 is scraped away from the 
cylinder wall 20. The oil 48 that is scraped away from the cylinder wall 
20 in FIG. 1B is guided to one or more oil ring drainage slots 54 which 
direct the oil to an interior of the piston 44, through a piston drainage 
slot 55, and, ultimately, toward an engine crankcase. On the upstroke of 
the piston 44, the piston does not exert a twisting moment on the ring 12. 
Hence, the ring face 32 tends to slide over the oil 48 which collects on 
the cylinder wall 20 rather than scrape oil toward a combustion chamber. 
Excess oil flows up over the top surface 16 as shown in FIG. 1A, to the 
piston groove drainage slot 55. 
Although FIGS. 1A and 1B illustrate a piston ring assembly 10 wherein the 
piston ring 12 has a single rail, the concept may be applied to a piston 
ring having a double rail. In the double rail configuration, a second ring 
face would extend from the substantially vertical third front surface 42 
below the oil drainage slots 54. The ring face of the second rail is, 
preferably, substantially identical to the ring face 32 illustrated in the 
single rail design of FIGS. 1A and 1B. In the double rail configuration, 
the top rail is moved away from the cylinder wall during the cocking 
movement of the ring around the spring. This causes a double pressure on 
the lower rail which remains in contact with the cylinder wall, providing 
an extremely strong scraping action during downward movement of the 
piston. 
Having described the invention in detail and by way of reference to the 
preferred embodiment thereof, it will be apparent that other modifications 
and variations are possible without departing from the scope of the 
invention defined in the appended claims.