Patent Grant
7104240
The present invention relates to internal combustion engines, and, more particularly, to lubrication of combustion cylinders in such engines.
In an internal combustion (IC) engine, when a piston reciprocally moves in sliding contact within the cylinder, friction and wear are most severe at top dead center (TDC) and bottom dead center (BDC) of the stroke positions of the piston. At these exact points where the piston changes direction, a condition of zero velocity occurs causing a reduction in hydrodynamic oil film thickness which can lead to metal-to-metal contact. This condition is most severe at TDC because lubricating oil on the surface is exposed to combustion temperatures which may cause unfavorable changes in its viscosity. This condition renders it more difficult to retain oil in the pores of the metal surfaces, accelerating the oil film diminishment rate subsequent to when the liner is wiped clean by the oil wipe rings situated beneath the combustion rings of the piston.
It is known to hone the inside surface of a combustion cylinder to produce scratches that retain lubricant oil. For example, a commonly used plateau honing operation provides deep scratches extending entirely around the inside surface of the combustion cylinder that retain lubricant oil. A second honing operation provides a smooth finish for the piston ring and piston to ride on. The deep scratches are not well controlled and are not conducive to the build up of a good squeeze film or hydrodynamic oil film.
What is needed in the art is an internal combustion engine providing improved oil lubrication of the combustion cylinders and reduced oil consumption.
The present invention provides an internal combustion engine including a combustion cylinder having an inside surfaces which is ablated to have discrete pock marks which vary in density distribution along the length of the combustion cylinder.
The invention comprises, in one form thereof, an internal combustion engine including at least one cylinder block having at least one combustion cylinder. A number of cylinder liners are respectively associated with each combustion cylinder. Each cylinder liner defines a corresponding cylinder inside surface. Each cylinder liner includes a plurality of discrete oil retaining indentations in a predefined pattern on the cylinder inside surface. The plurality of oil retaining indentations are bounded in both peripheral and longitudinal directions of the corresponding cylinder liner.
An advantage of the present invention is that the discrete indentations formed as pock marks better hold oil than conventional scratches formed in the inside surface of a combustion cylinder.
Another advantage is that the discrete indentations decrease radiation and convection heat transfer, thereby reducing volotization and pyrolysis.
Yet another advantage is that the discrete indentations provide lower oil consumption, longer particulate trap life and better performance.
A still further advantage is that the discrete indentations provide lower friction and wear resulting in longer engine life and better fuel economy.
A still further advantage is that multiple ablation manufacturing methods may be used to form the discrete indentations in the inside surface of the cylinder liner.
A further advantage is that the discrete indentations may be formed with precise uniformity and spacing.
Another advantage is that the improved oil lubrication using discrete indentations provides very low emissions levels and reduces contamination of after treatment devices.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Piston 16 is reciprocally movable within cylinder liner 14 between a TDC position and a BDC position, indicated generally in
At the TDC position and the BDC position, piston 16 reverses reciprocating movement within cylinder liner 14, and thus reaches a piston speed of zero at the TDC and BDC positions. When moving from the TDC position to the BDC position, or vice versa, piston 16 is accelerated and reaches a maximum piston speed approximately at the center of the piston stroke.
From an oil lubrication perspective, the worst case position of piston 16 during a piston stroke is at the TDC position, whereat piston 16 is at a zero traveling speed and the operating temperate is the highest as a result of combustion at or near the TDC position. High combustion gas pressures at TDC apply high loads to the piston rings, decreasing the oil film thickness. The traveling speed of piston 16 as a result of the piston position within cylinder liner 14 is graphically illustrated in
Cylinder liner 14 includes an inside surface 22 against which piston rings 18 slide. As described above, inside surface 22 is conventionally formed with a plurality of generally annularly extending deep scratches which retain oil for lubrication of piston 16 and rings 18. Since the scratches are typically formed with a specified honing operation, the scratches extend around the entire periphery of inside surface 22. Control of the exact position of the scratches is not easily accomplished, since the exact positioning of the scratches depends upon the rotational speed, axial feed rate and characteristics of the honing tool.
In contrast, the present invention forms a plurality of discrete oil retaining indentations at inside surface 22 of cylinder liner 14, which are preferably in the form of pock marks. Rather than extending around the entire periphery of inside surface 22 as is the case with annularly extending scratches, pock marks 24 are bounded in both peripheral and longitudinal directions of cylinder liner 14.
According to another aspect of the present invention, the distribution density of pock marks 24 is dependent upon a longitudinal position on cylinder liner 14. Since the oil lubrication needs are greater at the TDC and BDC positions, pock marks 24 have a distribution density which is greater at the longitudinal ends of cylinder liner 14 and less at the longitudinal middle of cylinder liner 14. In other words, the distribution density of pock marks 24 is greater at the TDC and BDC positions. A distribution density which is greater at the TDC and BDC positions and less at the middle position of cylinder liner 14 is shown in
In the embodiment shown in
Pock marks 24 have a generally dot shape as shown in
Cylinder liner 14 may be formed from any suitable liner material allowing formation of pock marks 24, such as iron, steel, etc. Liners formed from iron are typically much more common than liners formed from steel, since iron includes graphite pockets which retain oil for lubrication. With the present invention, steel liners can also be used since pock marks 24 likewise retain oil for lubrication. Steel liners have the advantage of being much stronger than iron liners.
In another embodiment illustrated in
During manufacture, cylinder liner 14 is formed with pock marks 24 as described above, prior to being pressed within cylinder block 12. In one embodiment, pock marks 24 are formed on inside surface 22 using a photolithography ablation process, similar to a photolithography ablation process used on ceramics in the micro-electronics industry. In general, a photosensitive layer is placed on inside surface 22 and exposed to light to remove portions of the photosensitive layer. The light preferably is produced by a laser which is targeted at selected locations on inside surface 22 where the pock marks are desired to be formed. The laser can be controllably movable to aim the laser at the selected pock mark locations. Alternatively, cylinder liner 14 can be rotated and moved in a longitudinal direction relative to a stationary laser which is then actuated at selected locations to remove portions of the photosensitive layer. The cylinder liner is then exposed to an etching agent, such as an acid, to remove material from inside surface 22 at selected pock mark locations. The dot shaped pock mark shown in
In another embodiment, pock marks 24 may be formed using a laser ablation process in which the laser is configured to actually remove material from inside surface 22 of cylinder liner 14. This type of ablation process may be more suitable for forming the custom shaped pock marks as shown in
In the embodiment shown and described above, oil retaining indentations are formed in the inside surface of a cylinder in an IC engine. However, it should be understood that such oil retaining indentations may be formed in other reciprocating piston and cylinder arrangements, such as a fluid compressor (e.g., air compressor).
Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.
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