Piston ring with improved lubrication delivery

A piston ring has a body member for sitting in a ring groove of a piston. The body member has an inner periphery, upper wall, lower wall and an outer periphery. The outer periphery has a concavity therein for storing lubricant therein. The upper wall has an outer section proximate to the outer periphery is constructed to be resiliently flexible between a flexed and unflexed position such during a portion of a power stroke, the volume of the concavity to store the lubricant is decreased by the flexing of the upper wall to the flexed position for expelling lubricant therefrom to a wall of the cylinder. The wall resiliently returns to the unflexed position during other times to allow excess lubricant from the wall of the cylinder to pass into the concavity.

TECHNICAL FIELD

This invention relates to a piston ring and more particularly to a split piston ring for a piston in an internal combustion engine.

BACKGROUND OF THE INVENTION

Pistons in internal combustion engines have long incorporated piston rings to improve performance. Piston rings reduce blow-by of gases during the compression and power strokes and allow lubricating oil or other lubricant to coat the cylinder wall but prevent excessive lubricating oil from entering the combustion chamber.

Many types of piston rings have been developed having differently contoured outer peripheries. For example, piston rings may have a taper face, a barrel face, or a plain face. The piston ring, commonly made from iron, may also have a porous coating, film, outer layer or surface to pick up oil for forming a lubricant film as it glides against the engine cylinder wall.

The piston ring construction may have the ring being substantially planar or it may incorporate a negative or positive twist in its relaxed position. The shape or twist of the piston ring, during operation of the piston ring, may change during the down strokes and the upward strokes for providing wiping of the lubricant during the down stroke and bypassing the lubricant film during the upstroke.

Lubrication regimes always balance the need to provide as low a viscosity of the lubricant as possible to decrease the inherent friction of the lubricant but also provide the needed high viscosity near the top dead center position of the power stroke to reduce mixed/boundary lubrication regimes. Not only is it recognized that the lubricant film thickness may vary and different lubrication requirements may be needed during different crank angles of the engine, but different circumferential positions around the piston may have different lubrication requirements particularly if there is a distorted cylinder bore, the piston has a tilt, or the piston and piston ring are not truly cylindrical.

What is need is an improved piston ring that provides for a cavity that absorbs and stores lubricant when excess lubricant is on the engine cylinder wall and can provide additional lubricant during the power stroke when more lubrication is needed.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a piston ring for a piston of an engine cylinder; includes a body member for sitting in a ring groove of the piston. The body member has an inner periphery, upper wall, lower wall and an outer periphery. The outer periphery has a concavity therein for storing lubricant therein. The upper wall has an outer section proximate to the outer periphery and is constructed to be resiliently flexible between a flexed and unflexed position such during a portion of a power stroke, the volume of the concavity to store the lubricant is decreased by the flexing of the upper wall to the flexed position in order to expel lubricant therefrom to a wall of the cylinder. The upper wall resiliently returns to the unflexed position at other times to allow excess lubricant from the wall of the cylinder to pass into the concavity.

Preferably, an insert member is housed in the concavity. The insert member is porous to absorb lubricant and compressible to release the lubricant.

In one embodiment, the insert member is a woven carbon fiber. The piston ring preferably has a positive stop member for limiting the flexing of the upper wall and the compression of the insert member. In one embodiment, the stop member may be a plurality of teeth at the outer periphery. Preferably, the upper wall has its outer section tapered to the outer periphery. In one embodiment, the concavity is asymmetrically positioned closer to the upper wall than the lower wall.

In accordance with another aspect of the invention, a piston for an engine cylinder of an internal combustion engine has a piston head having a side wall with at least one annular groove for seating a piston ring. The piston ring has a body member for sitting in a top ring groove of the piston. The body member has an inner periphery, upper wall, lower wall and an outer periphery. The outer periphery has a concavity therein for storing lubricant therein. The upper wall has an outer section proximate to the outer periphery and is constructed to be resiliently flexible between a flexed and unflexed position such during a portion of the power stroke, the volume of the concavity to store the lubricant is decreased by the flexing of the upper wall to the flexed position for expelling lubricant therefrom to a wall of the cylinder. The wall resiliently returns to the unflexed position during other times to allow excess lubricant from the wall of the cylinder to pass into the concavity.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now toFIG. 1, an internal combustion engine10has a cylinder12with a cylinder wall14. A piston16is constructed for receiprocating motion within the cylinder. The piston has three circumferentially placed grooves18axially spaced along the piston. The three grooves18seat a compression piston ring20, a wiper ring22, and an oil ring24respectively.

The compression ring20as more clearly shown inFIGS. 2 and 3has a main circular shaped body member26. The compression ring20has an inner peripheral wall28, an upper wall30and a lower wall32. An outer peripheral section34has a concavity or recess36extending around the ring20and open to the outer periphery through passage section41. An insert member38that is porous and compressible is fitted in the concavity36. For example, one material suitable for this insert is woven carbon fiber formed in a matrix. Other materials are possible if they are compressible, heat resistant, porous and lubricant absorbent.

The upper wall30has an outer section40above the concavity36that is tapered in a direction that narrows or thins out toward the outer peripheral section34. The taper allows the upper wall30to flex during a portion of the power stroke when extreme gas pressure from the combustion is exerted on the upper wall as illustrated inFIG. 3.

The ring may also have an uneven split such that the upper wall30may have a thinner dimension than the lower wall32. This uneven split can be provided by asymmetrical placement of the concavity36closer to the upper wall than the bottom wall or a different shape or different taper to the upper wall than the lower wall to provide for more flexibility of the upper wall section40. For example, the upper wall30may be more severely tapered than lower wall32. As shown inFIG. 3, the tapered wall30and lower wall32form a generally trapezoidal shaped concavity in cross-section and the insert38may have a generally corresponding trapezoidal shape in cross-section. The trapezoidal shaped concavity and insert (in cross-section) are oriented such that the concavity and insert has a corresponding larger axial dimension at its outer periphery than at its inner periphery or radial midsection.

This flexing in effect decreases the volume of the concavity36and compresses the insert38such that any oil or other lubricant used for the lubrication of the engine that is absorbed in the insert member38is squeezed out and pushed out of concavity36to the cylinder wall14during the boundary/mixed lubrication regime only. It has been found that the upper wall30can flex with respect to the lower wall32during mixed/boundary lubrication regime when upwardly directed frictional forces exerted on the lower wall section32are much greater than the upwardly directed frictional forces exerted on the upper wall section30. The mixed boundary lubrication regime occurs most often during the top dead center position of the power stroke when the speed of the piston head with the respect to the cylinder is slowest and the combustion process is commenced in the cylinder, producing heat build-up that is transferred to the piston and cylinder. The condition can produce undesireable metal to metal contact with no or insufficient lubricant film between the piston ring and cylinder. This mixed boundary regime that provides metal to metal contact can produce micro-welds which can result in less efficiency, more wear on the engine and seizing of the engine if left uncontrolled.

This great discrepancy in frictional forces between the upper wall and lower wall during the mixed/boundary lubrication regime provides for a moment to be applied on the upper wall outer section40which flexes the upper wall outer section downward closer to the lower wall32, compressing the insert38by the gas pressure decreasing the size of concavity36and thereby expelling lubricant from the concavity through passage41and onto the cylinder wall14. Thus, increased lubricant film is applied during the time that lubrication is most needed to reduce or eliminate the metal to metal contact.

After the mixed lubrication regime is over and hydrodynamic lubrication regime occurs, the upwardly directed forces applied on the respective upper walls30becomes greater than the forces on the lower wall32and the upper wall outer section40resiliently biases back to the position shown inFIG. 2. The insert member38can then absorb excess oil or lubricant by contact from the wall of the cylinder during the hydrodynamic lubrication regime when oil or other lubricant film between the cylinder wall and piston ring is too thick. Any excess lubricant film during the hydrodynamic lubrication regime that would otherwise provide for increased frictional forces can be absorbed into the porous media of the insert38before the cycle is repeated.

A positive stop42may be provided at the outer periphery34of the ring to prevent the upper wall from overly flexing and overly compressing the insert beyond its elastic limits. The positive stop42may be in the form of circumferentially placed teeth downwardly extending from the upper wall30and constructed to abut the lower wall32before permanent deformation of the porous insert occurs. Other positive stops may be devised such as an internal posts and web formed in the insert which can abut the lower and upper walls when the walls come to a predetermined minimum distance.

The ring has a conventional radial split44for allowing conventional installation about the piston and for reducing blow-by gases.

It should be recognized that the flexure of the upper wall need not be circumferentially uniform. The mixed boundary regime may not be uniform about the piston ring and the greater forces may not occur simultaneously about the entire ring. Only the circumferential section of the upper wall that undergoes mixed boundary lubrication regime may flex to compress the respective circumferential section of the insert38in its proximity which expels the needed lubrication out of the passage31to the needed circumferentially located position in the cylinder. In this fashion, lubricant is squeezed onto the specific spots around the piston ring that need extra lubrication.

In certain applications, it may be acceptable to only have the concavity and have no porous compressible insert for applying the lubricant during the mixed/boundary lubrication regime and storing excess lubricant during the hydrodynamic lubrication regime. The decrease of size of the concavity forces stored lubrication therein out to the cylinder during the mixed boundary lubrication regime. The increase in size of the concavity during the hydrodynamic lubrication regime allows for entry of excess lubricant.

While this invention is best used and has the most benefit for use with the top compression ring, it may also be applied to the wiper ring. Furthermore, there is a possibility of eliminating the bottom oil ring in certain applications.

In this fashion, the invention provides for improved lubrication delivery by providing more specific lubrication at specific locations precisely when needed. The improved lubrication allows for a reduction in hydrodynamic lubrication drag related losses in two ways. It eliminates excess lubricant and also allows the use of lower viscosity lubricants. The use of lower viscosity lubricants also reduce the oil pump volume and pump associated losses. The use of lower viscosity lubricant still provides adequate hardware protection by specifically directing more lubricant at the required moments during localized mixed/boundary lubrication regimes. The use of lower viscosity lubricants also reduces the minimum torque to start an engine at low temperature and allows for battery size reduction needed for start requirements. The invention also may reduce NOx concentration at low temperature for emission benefits.

Other variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.