Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1997-08-25
2001-03-13
DePumpo, Daniel G. (Department: 3611)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S467000, C277S482000
Reexamination Certificate
active
06199868
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to piston and piston ring assemblies for internal combustion engines, and more particularly to an improved piston assembly including a piston ring with a compressible support and sealing member for enhancing engine efficiency and reducing piston to cylinder wall wear.
BACKGROUND OF THE INVENTION
In a typical internal combustion engine, including a piston and ring assembly reciprocable within an associated cylinder bore, the majority of the cylinder wall wear occurs at the upper portion of the cylinder bore. This is the area of the bore where the face of the one or more piston rings frictionally engages the bore with a scraping action against the cylinder bore surface. In contrast, the lower end of the cylinder bore wall is more lightly loaded, with the piston skirt causing measurably less wear in this lower wall area. As a consequence of these discrepancies in cylinder wear, a cylinder bore tends to become gradually tapered, i.e., exhibiting a relatively larger diameter at the top than at the bottom.
The bore of the cylinder also exhibits considerably more wear in a direction “across” the engine, that is, at those portions oriented 90 degrees to the piston pin, than in a direction along the length of the engine (i.e., in alignment with the piston pin). This phenomenon results from the significantly higher loads exerted by the piston in the direction across the engine as the piston reciprocates within the cylinder bore due to the angularity of the connecting rod with respect to the piston pin. During the power stroke of the engine, the total force pushing down on the piston (due to combustion gas pressure) may often be of a magnitude of many tons of pressure. This extreme force acts against the piston to jam the piston with a side load against the cylinder wall. There is relatively little side loading in the lengthwise direction of the engine (parallel to the piston pins and crank shaft journals) because the connecting rod is straight (i.e., non-angular) at all times with respect to those portions of the cylinder bore. Additional side loads are created by inertia forces of the piston, which forces increase significantly with higher piston weights.
The above-described piston side loads result in the cylinder bore exhibiting wear in an oval shape. Since the heaviest side loads occur during the power stroke, the side of the bore which is loaded during this period of the four-stroke cycle exhibits the most wear. This portion of the cylinder bore is normally referred to as the major thrust side of the bore, with the opposite upper surface of the bore being referred to as the minor thrust side. In the majority of engines currently built and which rotate counterclockwise (as viewed from the rear), the major thrust side is located at the right side of the bore (when viewed from the rear).
In addition to the two above-described normal types of wear (which simultaneously cause the cylinder bore to become tapered, as well as out-of-round), the cylinder bore will often deviate from a true cylinder because of strains caused by unevenly torqued cylinder head fasteners. Distortion can also be caused by abnormal engine temperatures due to general overheating of the engine cooling system, or localized overheating caused by restrictive or clogged cooling passages. These uncontrolled heat effects may cause “low” and “high” spots in the cylinder bore, and may result in the bore wearing to a “wavy” surface (along the axis of the bore) instead of a relatively even taper.
The one or more piston rings of a piston and ring assembly should ideally exert sufficient pressure against the cylinder bore to form a tight seal, thereby preventing leakage of combustion gasses downwardly, and preventing movement of oil upwardly. When a piston ring exerts more pressure than is required to create an effective seal, the result is an undesirable increase in piston ring and cylinder wall wear, and increased engine friction which reduces power, increases engine heat, and raises fuel consumption.
The sides of the piston rings (i.e., the top and bottom surfaces), and the piston ring lands of the piston (which contain the rings) also exhibit wear. While the pistons of an engine move the rings upwardly and downwardly with respect to the cylinder walls, the rings are in constant sideways motion (radially of the piston) to accommodate their reaction to irregularities on the surface of the cylinder wall, and to accommodate movement of the pistons due to side loads. When the top of the piston moves toward the cylinder wall (from side loading) the ring will be forced back into the piston ring groove. There must be sufficient clearance available, in a radial direction behind the ring, so that the ring face may be forced inwardly to become flush with the edge of the piston, without the piston ring “bottoming-out” (in the radial direction) against the back wall of the ring groove. If the piston ring does bottom-out, the impact of the combustion and inertia forces acting upon the piston will be transmitted to the ring, and the ring will eventually break. In order to assure that bottoming-out is avoided, all piston ring lands are machined so that there is normally between 0.005 inches and 0.015 inches clearance radially behind the ring, when the ring face is flush with the outer radial surface of the piston. The space that is established behind the ring is normally referred to as the “back wall area”, or the “back wall clearance”.
The back wall area also functions to increase the sealing pressure of the ring face on the cylinder bore wall during the combustion stroke, when the normal top and bottom piston ring clearance (i.e., its axial clearance) is all at the top of the ring due to combustion forces pushing the ring tightly against the bottom of the ring groove. The combustion gasses pass though this axial clearance, and raise the gas pressure in the back wall area, thereby forcing the piston ring outwardly to seal more tightly against the cylinder bore wall. To enhance this effect, the back or inside surface of the top piston ring of a piston and ring assembly is typically cut with a chamfer, thereby decreasing the time required for creating sealing pressure in the back wall area, and increasing the pressure therein. When such a chamfer is made in the upper edge of the ring, the combustion gas will flow more readily into the back wall area because the sharp edge of the ring has been removed, thereby reducing turbulence and “squeeze” of the combustion gas. The ring-to-cylinder wall pressure will also be increased because the effective surface area acted upon by the combustion gas is relatively increased.
One of the problems exhibited by all current piston designs is that when the ring bounces, or flutters, within the cylinder bore, the seal at the ring face to the cylinder wall is momentarily lost, and combustion gas leaks past the ring face. This results in a drop in pressure in the back wall area, further reducing the ability of the ring to seal tightly against the cylinder bore wall. Such ring bounce is most often caused by irregularities on the cylinder wall surface (i.e., such as “waviness” described above) or by rapid shifts in the piston from the major thrust side to the minor thrust side of the cylinder bore. Both of these phenomenons occur at higher engine (and piston) speeds. Ring flutter is usually caused by combustion pre-detonation or pre-ignition, which can cause high speed shock waves in the cylinder, and which vibrate the ring causing it to lift off of the cylinder wall.
On the compression stroke of the engine, the compression (i.e., intake charge) pressure pushes down on the piston while the connecting rod resists this pressure by its connection to the piston pin. The combined action of these two forces, in all reciprocating piston engines, pushes or thrusts the piston against that side of the cylinder bore toward which the connecting rod is angled from its connection to the associated crankshaft.
In contrast, during the power stroke, the connecting rod slop
DePumpo Daniel G.
Evans Engineering Company, Inc.
Fitch Even Tabin & Flannery
LandOfFree
Piston assembly with piston ring support and sealing member does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piston assembly with piston ring support and sealing member, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piston assembly with piston ring support and sealing member will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2447786