1. Field of the Invention
The present invention generally relates to piston rings for internal combustion engines. In particular, the present invention relates to a lubricant control piston ring for two-stroke engines.
2. Description of Related Art
Internal combustion engines operate on alternating compression and expansion cycles, which cycles reflect a state of operation within a combustion chamber. During the compression cycle, the compression of a mixture of air and fuel typically precedes an ignition of the mixture. The ignition of the mixture results in combustion of the mixture, which causes an accompanying expansion within the combustion chamber.
The compression and expansion of the combustion chamber volume is generally enabled by a piston that reciprocates within a cylinder bore. Because the diameters of the piston and the receiving cylinder bore differ, a sealing arrangement is needed. Accordingly, one or more circumferential grooves are provided within an upper end of the piston. To provide a seal, resilient rings are installed in these grooves, which rings have a slightly larger outer diameter than the piston. The rings generally bear directly against the cylinder wall and create a seal between the sides of the piston ring groove and the cylinder wall. The degree to which these components contact one another can vary significantly due to disparate thermal expansions and thermal deformations.
With reference now to FIG. 1, a portion of a piston 20 is shown in cross-section. The piston 20 reciprocates within a cylinder bore 22 that is formed in a cylinder body 24. The diameter of the piston 20 must be less than the diameter of the cylinder bore 22 such that the piston 20 can reciprocate relatively freely therein.
To create a substantially sealed combustion chamber 26, the piston 20 carries a plurality of piston rings. The upper piston ring is a compression ring 28 while the lower piston ring is a lubricant scraping ring 30. The compression ring 28 is designed to substantially seal against fluid migration between the combustion chamber and a crankcase (not shown). The lubricant scraping ring 30 scrapes oil or other lubricant from the cylinder wall during movement of the piston 20. Each of the rings 28, 30 is designed to provide a small ring gap between the outermost surface of the ring and the cylinder wall. Typically, the ring gap is adequate to avoid substantial interference under the most severe operation conditions (i.e., a high temperature/high load operation of the engine).
In the past, the scraping ring 30 was sized to allow lubricant to pass into the area defined between the scraping ring 30 and the sealing ring 28 under predetermined operating conditions. For instance, the outer profile was tapered to alter the wiping characteristics of the ring. Such a design, however, decreased the degree to which the scraping ring 30 contacted the cylinder bore wall. In addition, the lubricant scraping ring 30 blocked a substantial portion of the oil splashed upward from the crankcase chamber side of the piston ring 30. Because of prior scraping ring designs, too much oil was blocked by the scraping ring 30 and adequate oil was not supplied to the top compression ring 28. Such a lack of oil was especially prevalent during high temperature operation due to relative thermal expansion and deformation of engine components. As a result, the top compression ring 28 wore quickly or the cylinder bore 22 was scored by dry running the piston rings 28 within the cylinder bore 22.
Accordingly, an improved oil control ring is desired that will encourage proper lubrication of the top compression ring under all running speeds.
One aspect of the present invention involves a piston ring for use on a piston of an internal combustion engine. The piston ring comprises an outer surface and a central axis. A peripheral portion of the outer surface generally is defined at a first distance from the central axis and defines a maximum distance from the central axis. A plurality of recesses are positioned along the outer surface. At least a portion of the recesses are disposed at a second distance from the central axis. The first distance is greater than the second distance and the recesses extend through the peripheral portion of the outer surface.
Another aspect of the present invention involves a piston ring for use on a piston of an internal combustion engine. The piston ring comprises a top surface, a bottom surface, an inside surface connecting the top surface to the bottom surface and an outside surface connecting the top surface to the bottom surface. A plurality of recesses are formed in the outer surface.
Yet another aspect of the present invention involves an engine comprising a cylinder body. A cylinder bore extends through at least a portion of the cylinder body. A piston is reciprocally mounted within the cylinder bore and an annular cavity is defined between the piston and the cylinder wall. At least one piston ring is positioned substantially about a portion of the piston and extends into the annular cavity. The piston ring comprises an outer surface that is positioned substantially adjacent the cylinder wall with the outer surface comprising a plurality of recesses that define a corresponding plurality of channels extending between a first portion of the annular cavity and a second portion of the annular cavity. The first portion is separated from the second portion by the piston ring.
A further aspect of the present invention involves an engine comprising a cylinder body. A cylinder bore is formed within the cylinder body and defines a cylinder. A piston is positioned within the cylinder and is capable of reciprocating within the cylinder. A compression ring is disposed about a portion of the piston. The piston is connected to a crankshaft. The crankshaft is journaled within a crankcase chamber that is at least partially defined by a crankcase cover and a combustion chamber is defined at least in part by the cylinder bore and the piston. A scavenge passage is formed within the cylinder body such that it selectively connects the combustion chamber and the crankcase chamber. Means for controlling the lubrication of said compression ring are disposed within the cylinder body.