Piston skirt oil seal

Details Piston skirt oil seal Piston skirt oil seal

1999-11-04

2001-02-13

McMahon, Marguerite (Department: 3747)

Internal-combustion engines

Particular piston and enclosing cylinder construction

Piston

C123S572000

Reexamination Certificate

active

06186110

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improvements made to a piston of an internal combustion engine of which a piston skirt oil seal system separates an oil sump and a combustion chamber of the internal combustion engine through the use of an impervious boot.
BACKGROUND OF THE INVENTION
Piston rings are well known. They are usually received within an annular groove disposed about an outer periphery of a piston. The piston reciprocates within a cylinder chamber of an internal combustion engine, compressing fluids such as gases within the cylinder into a combustion chamber. These fluids are ignited and expand within the combustion chamber, forcing the piston away from the point of ignition.
The primary function of piston rings is to provide an effective seal of the gases, called “blow-by control”, and is accomplished by placing a first piston ring, called a compression seal, near the uppermost portion of the piston. The compression seal is designed to seal during an up-stroke of the piston to compress the gases within the chamber. A secondary function of piston rings is to prevent excess lubricating oil from entering the combustion chamber. To accomplish the secondary function, a second piston ring, called an oil seal, is placed below the compression seal to prevent oil from being carried up into the combustion chamber. Thus, the compression seal and the oil seal both cooperate to seal the combustion chamber from escaping gases or entering lubricating oil.
Generally, a piston reciprocating in a cylinder chamber creates a great deal of friction between the outer surface of the piston and the adjacent cylinder wall. Oil is used to lubricate the contacting surface between the piston and the cylinder wall. The oil used to lubricate tends to move up the cylinder wall from the oil sump, providing a smooth lubrication surface across which the piston may traverse. Commonly, excess oil from the oil sump migrates through the piston chamber and is allowed to move up the cylinder wall unrestrained. Inevitably, some oil passes the piston rings or seals designed to retard oil movement into the combustion chamber. Typically, the piston rings or seals wear through use causing the seals to fail and permitting unwanted oil to enter the combustion chamber. Additionally, piston rings also may not provide proper seals to contain oil because the rings tend not to effectively contact the cylinder wall due to pressure from blow-by gases that are created by explosions in the combustion chamber and the hydrodynamic influence of the oil on the cylinder wall. Blow-by gases tend to move out of the combustion chamber and down the cylinder wall. The pressure produced by the blow-by gases pushes the compression rings away from the cylinder wall. Consequently, oil on the cylinder walls may pass the rings and again enters the combustion chamber.
Once in the combustion chamber, the oil ignites. The burning of oil in the combustion chamber not only wastes oil, but it causes the internal combustion engine to emit unwanted excess noxious gases. Consequently, additional catalyst is required in the catalytic converter to treat the excess noxious gases prior to exhausting the gases into the environment.
To overcome these problems, pistons have been designed to encompass oil rings with openings used to drain oil. However, holes used to drain oil are typically susceptible to a problem called reverse oil pumping where oil flows from the interior of the piston through blow-by relief openings to the cylinder wall. This event may actually allow more oil to ultimately enter the combustion chamber. Accordingly, the problem of unwanted oil entering the combustion chamber from the piston chamber remains.
SUMMARY OF THE INVENTION
The invention is directed to a piston skirt oil seal system comprising a piston with a skirt operating in a cylinder chamber between an oil sump and a combustion chamber. A first O-shaped retainer is received into an annular groove circumscribed into a lower portion of the skirt, and a second O-shaped retainer is received into an annular groove circumscribed into a lower portion of a cylinder wall above the oil sump. A boot made of a flexible, impervious membrane with top and bottom edges is attached to the first and second O-shaped retainers, respectively, to separate the oil sump from the combustion chamber forming a barrier and essentially an oil free cylinder wall or an oil free zone. In an alternative embodiment, the boot comprises a series of concentric rings arranged between the first and second O-shaped retainers that telescope upwards and downwards with the reciprocation of the piston to serve as a barrier to oil migration.
The boot acts as a barrier to the migration of oil from the oil sump to the combustion chamber, reducing the amount of noxious gases and unburned hydrocarbons introduced to the catalyst for treatment in an internal combustion engine. Besides preserving the catalyst, the boot also saves oil that is otherwise wasted when it travels from the oil sump, through the cylinder chamber, and into the combustion chamber where it needlessly burns during the combustion process. The barrier also eliminates the problem of unwanted oil release into the combustion process. Ports provided in the cylinder wall below the piston ring travel and between the first and second O-shaped retainers in the oil-free zone remove blow-by gases generated during the combustion process. The absence of oil in the oil-free zone permits the ports to effectively remove the blow-by gases without concern that the ports will clog with oil, rendering the ports inoperable.
Without oil on the cylinder wall to lubricate the piston and rings, the piston and rings must be self-lubricating or gas lubricated. The self-lubricating piston and rings are provided of a carbon, graphite or similar coating to overcome friction generated from contact between the piston and cylinder wall as the piston reciprocates. Gas lubricated rings use gas present in the combustion chamber as its lubrication film source between the piston and cylinder wall as the piston reciprocates. The self-lubricating or gas lubricated piston and rings eliminate the need for oil to be present throughout the cylinder wall.


REFERENCES:
patent: 3847513 (1974-11-01), Foster
patent: 4381648 (1983-05-01), Balas
patent: 4773305 (1988-09-01), Nissels
patent: 4774874 (1988-10-01), Adahan

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